Page 13

Chapter 1

INTRODUCTION

1.1 BACKGROUND

The demand for mining equipment with a longer life span has led to the development of

new, harder more wear resistant materials. New varieties of high chromium white cast

iron have been developed for use specifically in slurry pumps where the sand and

metallic particles effectively act as miniature cutting tools on the pumps inner surfaces.

Materials research has advanced so far that there are varieties of wear resistant white

cast iron that cannot be economically cut by traditional methods. High chromium white

cast iron commonly used in mining equipment has a hardness of 650 Brinell and higher.

Machining of such hard materials can be problematic and expensive. Traditionally hard

materials have been cut by either grinding or diamond machining to get the accuracy

and finish required, which can contribute up to 60%-90% of the final cost of a part [1].

The mining industry in Australia is one of the countries largest manufacturing groups

and exporters. Weir Warman Ltd. is a world leader in the design and manufacture of

slurry pumps, selling throughout Australia and worldwide. Weir Warman Ltd. pumps

are commonly used in the copper, iron, aluminium, cement, palm oil, paper and pulp,

uranium, water and sewerage industries. Any improvement in performance, efficiency,

lifespan, design and manufacturing of these slurry pumps will be of direct benefit to the

Australian economy, which depends greatly on the productivity of its mining sector.

The benefits from increasing the life span of these pumps will flow through to benefit

the mining industry worldwide.

Weir Warman Ltd. slurry pumps are designed with a split outer casing and easily

removable linings and impellers. The inner parts of the pumps are made from either

rubber or hard metal depending on the application. Figure 1-1 is an example of the

replaceable inner lining and impeller of a Warman pump. Figure 1-2 shows the outer

casing of a Warman L slurry pump with a black rubber lining, which can be seen around

the inlet and outlet of the pump. When the impellers or linings of a pump are worn, the

Page 14

outer casing is opened; the lining and impellers are removed and replaced with new

parts. This design reduces downtime and is much cheaper than replacing the whole

pump.

Figure 1-1. Replaceable inner components of a Warman pump [2].

Figure 1-2. Warman L rubber/metal lined slurry pump [2].

Although the design of the pump allows for quick changeovers, the linings and

impellers still need to have a long life. The inner components of slurry pumps need to

be wear resistant and chemically stable, not reacting with the slurries that they are

pumping. Most slurries contain sand, which effectively acts like millions of miniature

cutting tools, constantly being thrown onto the pumps inner surfaces. This results in

high abrasive wear on the inner parts of the pump. No one material is suitable for all

Page 15

slurry pumping applications so there are several different options. High chromium

white cast iron is often used because of its high wear resistance and hardness, which is

between 650 and 700 Brinell hardness. However, with some slurries it is susceptible to

chemical wear and rubber liners are used instead.

At Weir Warman Ltd., inner parts of pumps, made of high chromium white cast iron are

cut at high speeds with cubic boron nitride (CBN) tools in a process otherwise known as

hard turning. CBN tools are also quite expensive and brittle and can break easily during

the cutting process. A new way of machining hard materials such as high chromium

white cast iron is needed.

Laser assisted machining has been considered as an alternative way of cutting very hard

materials. It combines high power laser technology with traditional cutting methods.

The laser is used as a concentrated heat source, which heats and softens the surface

layer of the workpiece before the cutting tool removes it. It has proven successful in

machining of advanced ceramics and other metallic materials, reducing forces, tool

wear and overall cost [4-8]. However, it has never been tried on high chromium white

cast irons.

1.2 THE OBJECTIVE OF RESEARCH

Thus the objective of this research is to investigate and determine if laser assisted

machining of AS2027 high chromium white cast iron is a feasible alternative to current

machining methods and if the theory and results obtained by previous studies into laser

assisted machining of ceramics and other hard materials apply to laser assisted

machining of high chromium white cast iron. Also, to find an operating window, giving

parameters that reduce forces in laser assisted machining compared to conventional

machining using industry parameters as used at Weir Warman Ltd.

An Nd:YAG laser and a lathe will be used to conduct laser assisted machining

experiments on samples of high chromium white cast iron. Experiments will also be

conducted without the laser and turning forces from both experiments will be compared

to determine the effectiveness of laser assisted machining. Laser assisted machining

experiments will be conducted varying cutting and laser parameters to determine which

operating parameters give the greatest reduction in cutting forces.

Page 16

This research considers only AS2027-1985 Cr27 high chromium white cast iron as used

in slurry pumps manufactured in Australia. At the conclusion of this study it may be

appropriate to consider other variations of high chromium white cast iron.

1.3 THESIS OUTLINE

Chapter 2 looks at structure and properties of high chromium white cast iron. It also

discusses the traditional methods of cutting hard materials such as high chromium white

cast iron. Finally it investigates alternate methods of machining hard materials including

laser assisted machining.

Chapter 3 discusses the theory behind laser assisted machining and evaluates the

advantages and disadvantages of the method for machining hard materials. It also

includes a review of literature published on laser assisted machining and its relevance to

machining high chromium white cast iron.

Chapter 4 details experiment design including equipment setup for both preliminary and

secondary experiments. It also discusses parameter selection and further tests and

experiments conducted including hardness tests and tool wear measurements.

Chapter 5 discusses the temperature model that was used to estimate temperatures in the

work piece due to the laser. It details the method used to verify the model and the input

data required to produce accurate results. Finally it outlines the usefulness of the model

and the experiment design used to obtain results.

Chapter 6 includes all results obtained from preliminary, secondary, hardness and

temperature model experiments. Results include the effect of laser power on surface

profile, force reduction versus laser power density and the effect of laser spot diameter

on temperature in the work piece.

Chapter 7 is a discussion of the results detailed in the previous chapter. It discusses the

effect of forces due to heal in the primary shear zone and the distance between the

cutting tool and laser. It also discusses the effect of heat on chips and the finished

surface as well as the effect of laser and cutting parameters. It concludes by outlining

the limitations of the study.

Chapter 8 outlines the conclusions reached as a result of this study and makes

recommendations for future work.

Page 17

1.4 LIST OF PUBLICATIONS

K. Armitage, S. Masood, M. Brandt, “Laser Assisted Machining of High Chromium

White Cast Iron”, Proceedings of the 1st Pacific International Conference on

Applications of Lasers and Optics, 19-21 Apr 2004

K. Armitage, S. Masood, M. Brandt, “Laser Assisted Machining of Wear Resistant

White Cast Irons”, Proceedings of the 9th International Conference on Manufacturing

Excellence, Melbourne, 13-15 Oct 2003

K. Armitage, S. Masood, M. Brandt, “An Investigation on Laser Assisted Machining of

Hard to Wear Materials”, Proceedings of the 2nd Pacific International Conference on

Applications of Lasers and Optics, 3-5 Apr 2006

Page 18

Chapter 2

MACHINING OF HIGH CHROMIUM WHITE CAST IRON

2.1 INTRODUCTION

The applications for hard materials such as advanced ceramics, hardened steels and

white cast irons are continually growing. New harder materials are being developed for

use in the aerospace and mining industries. However, as these materials are being

developed methods of shaping them accurately and machining them have not advanced

as quickly. For some materials the machining methods may not be very cost efficient or

effective. One such material is high chromium white cast iron, which is used in the

manufacture of mining pumps and components.

This chapter discusses the structure and properties of high chromium white cast iron and

the pros and cons of the current and alternative methods of cutting such hard materials.

2.2 HIGH CHROMIUM WHITE CAST IRON

High chromium white cast iron has a structure typical of cast irons with hard carbide

rods surrounded by a softer matrix phase. Figure 2-1 shows the Iron-Carbon phase

diagram. The addition of chromium changes the diagram, however the general shape is

similar.

A cast iron is any iron-carbon alloy with greater than 2% Carbon. There are different

types of cast iron depending on the carbon content and other alloying elements. In white

cast iron all the carbon is present in carbides (Fe3C) rather than in graphite as in other

cast irons. Increasing the carbon content in a cast iron increases the carbides and hence

the hardness and wear resistance of the casting. However with more than 4% carbon,

the cast iron becomes too brittle to be of any use. An alternative is to add chromium to

increase the amount of carbides and change their constitution from Fe3C to M7C3 (M

represents the metallic species, mainly Fe and Cr).

Page 19

The high chromium white cast iron used in this study is Weir Warman Ltd. A05, which

conforms to AS2027 Grade Cr27 and ASTM A532 Grade IIIA. It has 3% carbon and

27% chromium with silicon, manganese, phosphorous, sulphur, and molybdenum as

additional alloying elements. The carbides have a Vickers hardness ranging between

1200-1500HV and the surrounding matrix has a hardness of approximately 700 Vickers

hardness, which gives A05 an overall hardness of approximately 650 Brinell hardness

[9].

[Figure removed for copyright reasons]

Figure 2-1. Iron-carbon phase diagram [10].

A05 is a eutectic alloy with a melting temperature of approximately 1275°C [11]. The

matrix surrounding the carbides is primarily martensite with some residual

austenite[12]. For optimum wear characteristics, the alloy should be free of any pearlite

formation [11]. Figure 2-2 shows the microstructure of high chromium white cast iron.

The white sections are the M7C3 carbides while the surrounding grey is the martensite

matrix.

Figure 2-2. Microstructure of AS2027 grade Cr27 high chromium white cast iron .

Page 20

2.2.1 Variations of High Chromium White Cast Iron Bedolla Jacuinde & Rainforth [13] found that it is the form and size of the carbides in

high chromium white cast iron that have the most effect on its wear resistance. By

increasing the number and length of chromium carbide rods the overall hardness can be

increased. Weir Warman Ltd. has patented casting methods, which use inoculants to

control the size and number of carbide rods during casting. Their patented technology

can produce cast irons with up to 75% chromium carbide. [9]. The resultant increased

hardness of the material makes it very difficult and expensive to cut, so much so that it

is not used commercially as no economical method of cutting it has been developed.

This research project focuses on Weir Warman Ltd. A05, which has 25% chromium

carbide rods.

2.3 MACHINING HIGH CHROMIUM WHITE CAST IRON

2.3.1 Hard Turning The high hardness of high chromium white cast irons makes them highly abrasive wear

resistant materials. This makes them difficult and expensive to machine. The abrasive

wear resistant material drastically reduces the life of ceramic and tungsten carbide tools

making them ineffective in cutting it. They are currently machined by a method known

as hard turning. Hard turning incorporates high cutting speeds and cubic boron nitride

(CBN) tools and is used in situations where the more common ceramic coated and

tungsten carbide tools are not effective. CBN tools have been commercially available

now since the 1970’s and they have brought a great change in hard machining

technology because of their many favourable properties [14]. CBN has a hardness and

wear durability second only to diamond and it has good thermal resistance, a high

coefficient of thermal conductivity and high hot hardness [15]. A negative rake angle,

high speeds and no coolant cause the temperature in the small cutting zone to rise to

temperatures above 900°C [14-18]. Ng et al. [19] has stated that “During metal cutting

heat is generated in the primary shear zone and the secondary deformation zone” of the

materials being cut. The high temperatures reduce the shear stress in the primary shear

zone reducing cutting forces. The majority of heat generated is removed in the chip.

However, this is to the detriment of the tool wear [14]. During hard turning a negative

Page 21

rake angle is used as the chamfered edge gives greater strength to the brittle CBN

material [14].

Figure 2-3 shows the yield strength versus temperature for high chromium white cast

iron. It can be seen that increasing the temperature reduces the yield strength.

Although data is limited it shows that there is a drop of 150MPa over 600°C therefore it

can be assumed that at 900°C the yield strength would be significantly lower, allowing

for easier cutting.

0

50

100

150

200

250

300

350

400

450

0 50 100 150 200 250 300 350 400 450 500 550 600 650

Temperature (Deg C)

Yiel

d St

reng

th, 0

.2%

(Mpa

)

Yield Strength 0.2% Mpa

Figure 2-3. Yield strength versus temperature for high chromium white cast iron [20].

Hard turning is used for machining hard materials, which cannot be cut with

conventional tools. Ng and Aspinwall [21] measured the cutting forces generated by

CBN tools on bars of AISI H13 hot work die steel heat treated to various hardness

values (28, 35, 42 and 49 HRC) and cut at various speeds. Figure 2-4 is a graph of their

results showing that increasing the cutting speed caused the resultant cutting force to

drop. This is because of the increased heat generated in the shear zone, which causes

greater plastic deformation. Hence, the cutting forces are reduced when the temperature

in the cutting zone is increased.

Page 22

[Figure removed for copyright reasons]

Figure 2-4. The effect of workpiece hardness and cutting speed on resultant force when machining AISI H13 hot

worked die steel [21].

CBN inserts are very expensive and can be one of the highest contributors to the final

cost of a machined part. It has been stated that diamond machining and grinding can

contribute between 60% and 90% of the final cost of the part [1] and it has been

estimated that CBN inserts are one of the largest costs associated with machining high

chromium white cast iron at Weir Warman Ltd. It is no surprise then that the wear

mechanisms of CBN tools have been widely investigated.

2.3.2 CBN Wear Mechanisms There are four main mechanisms of wear when machining with CBN tools. They are

thermal, chemical, abrasive and impact, however the only acceptable method of wear is

abrasion [22].

There were found to be two main forms of CBN tool wear during hard machining. One

was that the workpiece material adheres to the CBN tool. This may be the result of

small chemical reactions or diffusion between parts of the workpiece material and the

binder material of the CBN tool. The other way was typical built up edge (BUE)

adhesion. Both of these increase the forces and hence the friction heat generated,

softening the binder of the CBN tool. The softening allowed the BUE or adhesion to

break away pulling out the harder CBN particles or rods. These particles then worked

to increase the abrasion wear on the tool face. Majority of studies have found that

increasing the cutting speed increased the tool life to a point after which the tool life

was reduced [13]. This may be because at this point the friction heat raised the cutting

edge to a temperature at which the binder phase began to soften and the tool began to

wear more quickly.

Page 23

2.3.3 Surface Finish A general consensus among research groups is that the surface roughness produced

during hard turning with CBN is generally acceptable. In some circumstances it is

comparable to grinding. However, as the tool begins to wear the surface roughness

begins to increase. The flank wear is a main cause of this.

While all parameters have some effect on the tool wear and surface roughness, some

have a much greater effect. The feed rate has the greatest effect and the hardness of the

workpiece is also a main contributor.

2.3.4 Cutting Forces and Machine Rigidity Cutting forces in hard turning with negative rake CBN tools are lower than forces

generated with positive rake angles, because of the small tool-chip contact length and

the small plastic deformation of the tool [23]. While cutting forces may not be an issue

the rigidity of the machine definitely is. Hard turning with CBN requires a very rigid,

high precision, high horse power machine. Lack of rigidity can cause increased tool

wear due to chipping because of the brittle nature of the tool. [24]

2.4 ALTERNATIVE METHODS OF MACHINING HARD

MATERIALS

2.4.1 Grinding and Diamond Machining Grinding and diamond machining are two alternative methods of machining hard

materials. However, they are not commonly used for machining high chromium white

cast iron. This is most likely because of the high costs associated with them. While

CBN tools are expensive they are not as expensive as diamond tools and grinding. It has

also been reported that grinding reduces the strength of ceramic materials by 10-20

percent [25].

2.4.2 Hot Machining It was mentioned in Section 2.3.1 that Ng and Aspinwall [26] found that increasing

cutting speed increased the temperature in the shear zone and hence reduced the cutting

forces. Hot machining is a process where a heat source is used to heat the workpiece

prior to cutting with the aim of increasing the temperature in the shear zone. It was

Page 24

recognised over 100 years ago that hot machining might make finishing hard materials

easier. In 1898 Tilghman [7] filed a US patent using electrical resistance to heat a

workpiece. It is not known if his experiment was successful, however, many people

have followed his example and investigated hot machining using various different

heating techniques. Some of these include using furnaces, induction coils, gas torches,

resistance heating and plasma arc heating [7;27;28]. For hot machining to be most

effective, there needs to be sufficiently large heat transferred to a small area directly in

front of the machining point [7]. Most of the above mentioned heating methods do not

do this effectively [29], and therefore hot machining is not currently a viable alternative

for machining high chromium white cast iron. However the use of the laser as a heat

source in hot machining does have good prospects and research has been conducted into

it. This is investigated further in Chapter 3 of this thesis.

2.4.3 Laser Machining Laser machining is another method that has been trialled on hard materials. The

problem with laser machining is that it works by melting the surface of the material to

remove it. The large amount of heat added by the laser can cause the microstructure of

the surface to change, which may require finish machining in some cases [1]. It can

also result in subsurface cracks affecting the integrity of the part. Also, laser machining

is limited to producing simple shapes making it unsuitable for finishing of objects like

high chromium white cast iron slurry pumps.

2.5 CONCLUSIONS

The development of new or improved cutting techniques for high chromium white cast

iron is essential for the continued prosperity of the mining industry in Australia. Much

time and money has been spent on developing harder materials for use in this industry

with little time spent on developing methods of cutting them.

Precision cutting of high chromium white cast iron with good surface finish and long

tool life is difficult to achieve with present hard turning methods. A new method of

cutting is needed if tool life is to be increased and costs reduced.

Studies conducted on hard turning demonstrate that when the temperature in increased

in the shear zone the cutting forces are reduced.

Page 25

It is obvious that a new cheaper method of machining high chromium white cast iron is

needed. Of the alternatives mentioned in Section 2.4, hot machining offers the most

potential for an improved method of machining high chromium white cast iron.

Page 26

Chapter 3

LASER ASSISTED MACHINING OF HARD TO WEAR MATERIALS

3.1 INTRODUCTION

Cutting hard materials economically has always been an issue for machinists. Cutting

tools are constantly improving and more efficient methods of cutting hard materials are

being sought. It was mentioned in Chapter 2 that hot machining has been investigated

as a possible method of cutting hard materials for over 100 years and that the one factor

holding it back has been the availability of a heat source which can provide high power

localized heat [7]. The 1960’s brought the invention of the laser and the perfect heat

source for hot machining. Known as laser assisted machining (LAM), the process

heralded a new era in hot machining.

In recent years there has been a lot of investigation into the benefits and effects of laser

assisted machining, however, much of the research has been material specific in its

application, with most studies being done on advanced ceramics such as silicon nitride.

There has, however, been some experimental work done using laser assisted machining

on metal matrix composites and hardened steels. Fortunately, the results appear to be

similar across all materials. Little research has been done on laser assisted machining of

high chromium white cast iron. Most of the discussion that follows is in regards to

ceramic materials unless stated otherwise.

Research has shown that laser assisted machining increases tool life and reduces

machining time, thus reducing the cost to manufacture parts. It also makes it possible to

machine extremely hard materials such as ceramics, which currently cannot be used

because the cost to machine is too high. If similar results are found for high chromium

white cast iron these benefits will flow through the pump manufacturing industry to

benefit the mining industry worldwide.

This chapter explains how laser assisted machining works and discusses the benefits

and disadvantages of the machining method. It starts by explaining what a laser is and

Page 27

how it works. Section 3.3 explains the theories about how laser assisted machining

works and the rest of the chapter discusses the previous research conducted on laser

assisted machining to date including the advantages and disadvantages of the new

cutting method.

3.2 INDUSTRIAL LASERS

Two types of lasers dominate in industrial applications; the carbon dioxide (CO2) laser

and the neodymium yttrium aluminium garnet (Nd:YAG) laser. The reason for their

dominance is because of their relatively high efficiency, high output power, relatively

low cost and good reliability.

Nd:YAG lasers have flash pumps that are used to excite electrons in a material raising

them to a higher energy level. When they drop back down to a lower energy level light

is emitted. Gas lasers use gas as the active medium contained in a resonant cavity

whereas solid state lasers contain the active medium in crystals. Mirrors on either side

of the crystal or resonant cavity are used to amplify the light emitted and they can be

used in parallel to obtain the required laser power.

The CO2 laser is a gas laser, whose active medium is a mixture of about 5% carbon

dioxide, 10% nitrogen and the balance helium. The active component is the carbon

dioxide molecule. The nitrogen acts as a catalyst, transferring the energy to the CO2

molecule and enabling it to remain in the upper laser level. The helium cools the gas

mixture through the collision and transfer of stored energy from the CO2 molecule. The

CO2 laser produces a wavelength of 10.6 μm with an electrical efficiency of 10%. It is

commonly used for cutting, welding and surface engineering applications.

The Nd:YAG laser is a solid state laser with a wavelength of 1.06 μm. The crystal is

usually shaped as a rod. A YAG crystal contains positively charged neodymium ions as

the active material. Neodymium is a rare earth metal that is a good laser material

because it is not affected by the containing material, in this case YAG [30]. The overall

efficiency of the Nd:YAG laser output is between 3%-5%.

The advantage of the Nd:YAG laser compared to the CO2 laser when processing metals

is the higher absorption of its energy by metal surfaces due to its shorter wave length

[31].

Page 28

3.3 WHAT IS LASER ASSISTED MACHINING

Laser assisted machining (LAM) combines laser technology with traditional cutting

methods such as turning or milling. With small laser spot diameters and a power

density of up to 106W/cm2, the laser provides the high power, localised heat source

required for laser assisted machining [3]. Figure 3-1 is a simple diagram showing the

basic setup of laser assisted machining.

Figure 3-1. Laser assisted machining.

A laser beam is directed onto the surface of the workpiece immediately in front of the

cutting tool. The laser heats the surface layer softening the primary shear zone. The

primary shear zone is the area along which the material shears to form a chip. It

stretches from the tool tip to the unmachined surface directly in front of the chip. As

mentioned in Section 2.3.1 the cutting temperature when cutting high chromium white

cast iron with CBN is around 900°C. Also, it is estimated that the temperature of

hardened tool steel is in the range of 600°C and 800°C when machined with CBN [32].

These high temperatures are due to friction and plastic strain in the shear zone [7]. The

high temperatures in the shear zone reduce the high yield strength of the material so that

it is below the fracture strength. Figure 3-2 shows the effect temperature has on a

typical stress-strain curve. As the temperature rises the material will have greater strain

at lower stresses.

Page 29

[Figure removed for copyright reasons]

Figure 3-2. Effect of temperature on stress – strain curve [33].

[Figure removed for copyright reasons]

Figure 3-3. Temperature distribution in AISI H13 hot work die steel at 3333mm/sec, CBN tool (SNMN090316T2020)

[19].

Figure 3-3 is the temperature distribution in H13 hot work, die steel being cut by a

negative rake CBN tool. It was generated by a model created by Ng et.al. [19]. It

shows that when cutting with CBN the maximum temperature is generated at the tool-

chip interface along the rake of the tool. The temperature in the shear zone is 25%-35%

less than that. It also shows that the majority of the heat generated is removed in the

chip.

The theory behind laser assisted machining is that the laser adds heat to the workpiece,

which raises the temperature in the shear zone, thus softening it. This reduces the yield

strength within the shear zone and hence the amount of heat that the cutting tool needs

to generate which in turn reduces the cutting forces. Rozzi et al. [4] conducted laser

assisted machining experiments on silicon nitride and found that the reduction in

strength allows visco-elastic flow to occur, reducing the cutting forces and the friction

between the tool face and the material. They also calculated the total energy, including

both laser and cutting energy, required to remove a unit volume of silicon nitride under

certain conditions. They found that just 7% of the energy was added by the cutting

process, while 93% of the energy was added by the laser. While there were no turning

experiments to compare with, they did state that compared to grinding (the only other

Page 30

alternative to finishing ceramics) the specific cutting energy of laser assisted machining

is significantly lower. This strengthens the idea that during laser assisted machining,

the heat generated by the cutting tool will be reduced and hence cutting forces will be

reduced.

The addition of thermal energy by the laser can cause a steep temperature gradient

between the surface and the depth of the cut near the tool. Knowledge of the

temperature gradient is essential to determine the optimum parameters for laser assisted

machining [1;3]. It is also needed to ensure that the temperature at depth does not get

so high that it causes microstructural changes and damage the machined surface [7].

3.4 RESEARCH AND DEVELOPMENT USING LASER

ASSISTED MACHINING

3.4.1 General Laser assisted machining has proven to be a feasible method of machining advanced

ceramic materials under specific conditions in experimental and lab conditions. Further

investigation into controlling the process is needed before it can be applied in industrial

applications [1]. Several reseach investigations have shown that with the right

conditions, laser assisted machining can reduce forces, increase material removal rate,

reduce chatter, minimize residual stresses, reduce tool wear, avoid tool breakage and

produce a crack free surface [1;6]. Laser assisted machining of various materials has

been found to give a reduction in cutting forces of between 20%-50% [34]. Ma et al.

[35] investigated laser assisted machining of cold hard cast iron and his results showed

a reduction of 24% of the main cutting force compared to conventional machining.

Konig and Zaboklicki [3] found laser assisted machining of Stellite 6 coatings gave a

70% reduction in cutting forces and a 90% reduction in tool wear when compared with

conventional machining.

3.4.2 Cutting Forces Why look at cutting forces To understand the cutting mechanisms and deformation behaviour of a material the

cutting force components are important [3]. They also assist in determining the

optimum operating parameters. That is why most studies, including this one, look at

Page 31

cutting force components as an initial indication of the effectiveness of laser assisted

machining, when it is actually increased tool life and material removal that industry is

interested in.

Figure 3-4 shows the three cutting force components acting on the cutting tool, which

are dependant on the operating parameters. The cutting force (Fc) is the main force

acting downwards on the tool. The feed force or thrust force (Ff) acts along the axis of

the workpiece in the same direction as the feed. The radial (passive) force (Fr) acts in

the radial direction as shown in Figure 3-4. All of these components can be measured

using a force dynamometer. The resultant force is the product of the feed force and the

cutting force. The radial force is usually smaller than the feed and cutting forces and

the change measured is insignificant compared to the change in the other two

components. To avoid confusion, from this point on ‘turning forces’ will be the

general term used to describe all force components.

[Figure removed for copyright reasons]

Figure 3-4. Force directions Ff – feed (thrust) force, Fc – cutting force, Fr – radial (passive) force [33].

When looking at the variable parameters that affect the turning forces, there are two

different sets. The first being the machine variables, namely cutting speed, feed rate

and depth of cut. The other variables are those associated with the laser including laser

power, spot diameter and its position in relation to the cutting tool.

The effect of machine variables on turning forces Rozzi et at. [4] conducted laser assisted machining experiments on silicon nitride

ceramics varying all parameters and comparing results to a standard cut. A specific

cutting energy ratio was calculated for each cut and he found that changing the depth of

cut during laser assisted machining of silicon nitride ceramics had very little effect on it.

This led to the conclusion that there is a small temperature gradient in proximity to the

cut. If the temperature gradient was large then there would be a significant difference in

Page 32

temperature and the yield strength of the material would also be significantly different

increasing the turning forces and specific cutting energy ratio. This also highlights the

need to have knowledge of the temperature gradients within the workpiece.

König and Zaboklicki [3] investigated the effect of cutting speed and feed rate on the

turning forces during laser assisted machining of silicon nitride. They found with fixed

laser parameters the turning forces increased with increasing feed rate and decreased

with increasing cutting speed. Ben Salem et al. [5] conducted similar experiments on

hardened XC42 steel and obtained the same outcome.

Effect of laser based parameters on turning forces There are several laser-based parameters that are variable and may have an effect on the

turning forces. They are laser power, laser spot size, axial and radial laser position.

König and Zaboklicki [7] state that during machining, cutting energy is mostly

converted into heat due to friction and plastic strain in the shear zone. Therefore the

temperature in the shear zone is dependant on energy added by the laser and the cutting

energy converted to heat. Rozzi et al. [4] found that increasing the laser power

increases the surface temperature and reduces the turning forces. This is supported by

experiments conducted by Lei et al. [25], who found that turning forces decrease

linearly with increasing workpiece temperature, indicating that the added heat from the

laser is reducing the yield strength of the material. Ben Salem et al. [5] also found that

when laser assisted machining both hardened XC42 steel and Inconel 718, the reduction

of turning forces increased with increasing laser power.

Rozzi [4] did note, however, that increasing the laser power does raise the chances of

surface melting and microstructure changes resulting in subsurface cracks and poor

surface finish. So, obviously there is a limit to how high the laser power can be raised

without causing other problems. The aim is to add the heat in such a way that the

majority of it is removed with the chip [5]. To achieve this, knowledge of the

temperature gradient within the workpiece is needed.

Another observation from Lei et al. [25] is that the decrease in forces reduces deflection

and chatter in the machine, which is a big issue when machining hard materials.

The position of the laser spot relative to the cutting tool is another important variable to

be considered. Rozzi et al. [4] found that with silicon nitride ceramics, small changes to

Page 33

the laser tool lead distance of 1 mm had a negligible effect on the turning forces, surface

temperature and specific cutting energy ratio. His experiments were set up with the

laser leading the tool by 1mm to start with. On the other hand Ben Salem et al. [5]

conducted laser assisted machining experiments on hardened XC42 steel and found that

when the distance between the laser spot and the tool was 3mm the reduction in forces

were 85%-90% for feed force and 65% for both the radial force and the cutting force

when compared to conventional cutting methods. When that distance was increased to

8mm the force reductions decreased to 30%, 35% and 20% respectively. This indicates

that this distance may be more crucial for some materials than it is for others and so

must be considered in the machining of high chromium white cast iron.

Preheat time Some of the studies conducted on ceramic materials had a preheat phase where the

workpiece was rotated under the laser for several seconds before the feed and cutting

tool were initiated. Other studies on ceramic materials used a preheat time where the

laser passed over the same spot several times so that the heat penetrated deeper into the

workpiece. This was done to preheat the material, thus giving time for the heat to

penetrate into the workpiece. This prevented the cutting tools from fracturing on initial

impact with the workpiece [35]. This was not necessary in this study because tool

breakage on impact only occurs occasionally when machining high chromium white

cast iron with CBN tools.

3.4.3 Temperature Models From discussion so far it is clear that knowledge of the temperature distribution in the

workpiece is important in understanding what is happening at the cutting point and

determining the optimum cutting parameters. Modelling laser assisted machining is

complex as in involves both the moving heat source of the laser as well as the cutting

mechanism, which is especially difficult. It was mentioned in Section 3.3 that in this

case only 7% of the energy was due to the cutting process, therefore looking only at a

thermal model of the moving laser is still helpful.

3.4.4 Other Benefits of Laser Assisted Machining Tool wear Industry is mostly concerned with increasing material removal rates and reducing tool

wear. Laser assisted machining reduces tool wear under the right conditions. By

Page 34

adding heat to the workpiece via a laser, the shear plane can be heated without

excessively heating the cutting tool face [6]. Rozzi et al. [4] found that wear below a

certain temperature resulted in pitting on the rake and flank surfaces due to brittle

fracture of the CBN tool. Whereas above this temperature the wear was predominantly

flank wear and it was found that flank wear versus linear distance cut is a linear

relationship. Lei et al. [25] looked at tool wear of a CBN tool used in laser assisted

machining of silicon nitride ceramics and found that flank wear decreased with

increasing temperature to a maximum temperature of 1570°C after which the tool

experienced rapid tool wear. Lei et al. [25] also found that the main cause of tool wear

was due to adhesion of the glassy phase of the ceramic material to the tool rake face,

which then breaks off taking some of the CBN material with it. At high temperatures,

the strength of the CBN is reduced and when the glassy phase breaks away it takes more

of the CBN with it. Therefore for any application the right parameters need to be found

to give maximum tool life. Tool life is not always increased in laser assisted machining.

Surface quality The increased temperature in laser assisted machining raises questions about the

integrity of the surface and subsurface quality of the finished part. It has been shown

that as long as the temperature near the cutting tool is above a lower limit, which allows

the material to deform in a visco-elastic manner, the machining parameters do not have

a significant effect on the surface roughness of a laser assisted machined surface [4].

Experiments on silicon nitride ceramics conducted by Lei et al. [25] show that

workpiece temperature has little effect on the surface roughness, which is more

dependant on the size and distribution of the silicon nitride grains. König and

Zaboklicki [7] agreed with Lei et al. [25], as neither found any detectable subsurface

cracks in silicon nitride after laser assisted machining and under the right conditions, the

surface roughness is comparable to that of grinding. Chryssolouris et al. [1] on the

other hand state that surface melting can compromise the surface integrity and can cause

micro cracking which can be undesirable. This stresses the importance of finding the

right parameters for laser assisted machining for each application. In some

circumstances it can increase the problems associated with hard machining.

Chips Ben Salem et al. [5] found that chips produced during laser assisted machining of

Inconel 718 are thinner and the shear area smaller than conventional machining. The

Page 35

smaller shear area indicates that the chip flowed easier in laser assisted machining

compared to conventional machining.

3.5 LASER MATERIAL INTERACTION

3.5.1 Reflectivity Reflectivity of the material is an important parameter in laser assisted machining as it

determines how much of the energy supplied by the laser beam is absorbed into the

material. Reflectivity is a percentage value and is dimensionless. For an opaque

material Reflectivity = 1 – Absorptivity. Reflectivity is dependant on many factors such

as the material, the surface finish, the wavelength of the laser and the angle of

incidence. For example copper has a higher reflectivity than steel. Migliore [30] states

“a clean steel surface reflects 96% of normally incident 10.6μm light, while it reflects

70% at 1.06μm.” Also a polished surface will reflect much better than a dull or painted

surface. In many laser-processing applications a layer is added to the material to reduce

the reflectivity and increase absorptivity.

3.6 CONCLUSION

In order to determine if laser assisted machining is going to be an economical and easier

method of machining hard materials, it was required to determine what effect laser

assisted machining is going to have on the machining process. The best way of doing

this is to look at the turning forces.

The literature survey shows cutting forces in laser assisted machining of various

materials results in force reductions of 20% to 65% without any significant surface or

subsurface damage. The crucial parameters giving maximum force reduction are the

feed rate and the distance between the laser spot and the cutting tool. As laser assisted

machining has not been trialled on hard white cast irons, results may vary, however,

previous studies indicate that a reduction in forces will occur.

It is expected that the addition of heat in the primary shear zone by the laser will reduce

the heat required to be generated by the cutting tool and hence it will reduce the turning

forces. Therefore, it is essential to have some knowledge of the temperature gradient

Page 36

within the workpiece to assist in determining the optimum parameters. Therefore a

thermal model of the moving laser source is needed.

Page 37

Chapter 4 RESEARCH DESIGN

4.1 INTRODUCTION

Chapter 3 discussed the literature review on research into laser assisted machining, most

of which resulted in a reduction in turning forces. Published works have shown that

laser assisted machining has not been trialled on white cast iron. However it is expected

that with the right parameters, laser assisted machining of high chromium white cast

iron will also result in reduced turning forces

This chapter presents the research methodology undertaken and details the experimental

set up and procedures needed to perform laser assisted machining of high chromium

white cast iron.

4.2 EXPERIMENTAL PLAN

The only way to determine if laser assisted machining is a feasible method of machining

high chromium white cast iron is to test it experimentally. Modelling the complete

system is very difficult, as consideration has to be given to both the cutting mechanism

as well as the heat added by the laser. A simple model of a moving heat source giving

the temperature distribution within the workpiece is helpful as it assists with optimising

the cutting and laser parameters.

To determine if laser assisted machining is having any effect on the cutting mechanism

of high chromium white cast iron the turning forces must be measured. The forces

acting on the cutting tool give an indication of what is happening at the cutting tip. A

reduction in forces is desirable as it means that the visco-elastic flow is occurring and

the heat from the laser is making a difference to the cutting process. The previous

chapter also discussed many of the benefits associated with this change in cutting

mechanism including the reduction in tool wear.

Once turning forces are successfully reduced, then investigation of the material removal

rate and tool wear can be conducted.

Page 38

Preliminary experiments were conducted with the cutting parameters used as close as

possible to those currently used at Weir Warman Ltd. and laser parameters used in

studies done on ceramic material by other researchers.

The preliminary experiments showed that the position of the laser spot was crucial and

also helped to determine the operating window for the laser power and spot size. The

experimental set up was modified and further experiments conducted, this time with

greater understanding and knowledge of the process.

4.3 EQUIPMENT SETUP

4.3.1 Preliminary Equipment Set up The experimental equipment was initially set up as shown in Figure 4-1. The workpiece

was mounted in a 3.5hp Hafco Metal Master lathe (Model AL540). It was supported at

both ends as shown.

Figure 4-1. Experimental set up.

A 2.5kW Neodymuim Doped Yttrium Aluminium Garnet (Nd:YAG) laser was used for

heating the workpiece in all experiments. The focusing head was positioned directly

above the workpiece, 15mm off centre towards the cutting tool, as shown in Figure 4-2.

This resulted in approximately 110mm separation between the laser spot and the cutting

tool.

Page 39

Figure 4-2. Radial Laser Position.

Figure 4-3. Axial laser position during preliminary experiments.

The laser spot was positioned on the chamfer of the cut as shown in Figure 4-3.

A pyrometer was mounted coaxially with the laser beam to measure the surface

temperature of the workpiece in the centre of the laser spot within the range of 800°C

and 2400°C. During preliminary experiments a temperature control system (Temcon

für Windows© 2001 LZH) was used to control the laser power according to the surface

temperature measured by the pyrometer. The controller allowed a constant temperature

in the centre of the laser spot to be maintained allowing the effects of temperature to be

investigated.

A 3-component dynamic force sensor (PCB Model 260A01) was mounted below the

tool holder measuring the cutting force (Fc) and the feed force (Ff) acting on the tool as

shown in Figure 4-4. The sensor was connected to a signal conditioner (PCB Model

482A22) that was connected to an oscilloscope, which gave the force as a voltage.

Page 40

Figure 4-4. Force sensor position.

The force sensor instructions specified that it be installed with a 5000lb (2267kg)

preload however it was not possible to measure the preload on the sensor so it needed to

be calibrated. It was calibrated by applying a series of known weights to the cutting tool

and recording the resultant voltage change. Plotting the voltage against the force

resulted in a straight line and the gradient of this line was used as a conversion factor to

convert amplitude to a force measurement. Figure 4-5 shows the graph used to find the

conversion factor for the cutting force direction.

y = 31.489x

0

100

200

300

400

500

600

0 2 4 6 8 10 12 14 16

Mass (kg)

Volta

ge (m

V)

Figure 4-5. Calibration of force senor. Cutting force conversion factor, preliminary experiments.

This conversion factor was used for all preliminary experiments. To modify the set up

for secondary experiments the sensor was removed and had to be calibrated again.

Therefore the conversion factors for cutting and feed forces were different for the

Page 41

secondary experiments. Appendix A contains the graphs for the feed force for

preliminary experiments and both cutting and feed force graphs for the secondary

experiments.

The force sensor output is displayed on an oscilloscope and measures a change in

voltage only when the force is not constant. Figure 4-6 a) and b) is an example of the

sensor output for the cutting force and the feed force. Measuring the amplitude of the

initial peak and applying the conversion factor gives the force acting on the tool. In the

cutting conditions shown in Figure 4-6, the laser was applied approximately 12.5

seconds after the start of the cut and this can be seen by the visible change in the

amplitude at this point. This change in amplitude corresponds to a change in the force

when the laser is turned on. Adding or subtracting this change of force from the initial

force gives the force acting on the tool during laser assisted machining. It is clear that

in the example shown the cutting force increases slightly and the feed force decreases

when the laser is turned on.

a). b).

Figure 4-6. Force Sensor output.

The cutting tool insert used in all experiments is a Seco CBN300 RNMN120300S

insert, which is a round, solid PCBN tool, 12mm in diameter and 3.18mm height with a

20° x 0.2mm chamfer on all edges (Figure 4-7). This allows the insert to be used for

many cuts as once an edge is worn the insert can be rotated to a new edge. Once the

tool is worn all the way around on one side, it can be turned over to use the other side.

The tool holder is a Seco CRSNR3225P12 giving the insert a compound rake angle of -

6° x -6°.

Page 42

Figure 4-7. Seco CBN300 RNMN120300S insert.

The workpiece used is high chromium white cast iron (AS2027 Grade Cr27, ASTM

AS32 Grade IIIA), which has a hardness of approximately 650HB. It is a hollow

section with an outer diameter of 190mm and an internal diameter tapering from

130mm to 115mm (Figure 4-8). The workpiece was mounted at both ends due to its

large weight. The outer layer of the workpiece was removed with a different lathe, as

the lathe used for experiments was unable to cope with the intermittent cutting required

to remove the name, which was cast into the workpiece.

Figure 4-8. High chromium white cast iron workpiece.

As the lathe and the laser were not integrated it was not possible to start them

simultaneously. Therefore because of safety reasons the laser was started 10-20

seconds after the lathe had started cutting. The time delay allowed the signal to the force

Page 43

sensor to decay so that the force change due to the laser was more noticeable and easy

to measure.

4.3.2 Equipment Set Up Modifications The preliminary experiments gave unexpected results so changes to the experimental set

up were needed. It was discovered that in most cases cutting and feed forces increased

with laser assisted machining compared to hard turning. One reason for this was

thought to be the large distance between the cutting tool and the laser spot. Hence it

was decided to move the laser spot closer to the cutting tool as shown in Figure 4-9. It

was also thought that the increase in forces might be due to slow cutting speeds used

compared to those used at Weir Warman Ltd., however, resources were not available to

eliminate this problem.

Figure 4-9. Radial laser position in secondary experiments

Figure 4-10 shows the modified set up with the laser mounted in such a way that it

could be rotated around the workpiece to move the laser spot. This allowed the laser

spot to be positioned a minimum of 22mm away from the tool.

Figure 4-10. Revised experimental set-up.

Page 44

With the new setup a different optical fibre was used and it was not possible to use the

pyrometer as it required a 90° bending cube which could not be incorporated into the

mounting arm. Therefore the temperature controller was not used for secondary

experiments. The lathe, laser, tool holder, insert and workpieces did not change.

4.4 CUTTING PARAMETERS

Cutting parameters were kept as close as possible to Weir Warman Ltd. industry

standards as the equipment permitted. Table 4-1 shows both the industry standard

parameters as used at Weir Warman Ltd. as well as those used in experiments. The

lathe used in experiments is not a large lathe and does not have the rigidity or power

required to cut materials with such a high hardness. In industry, the depth of cut can be

as deep as 5mm but due to flexing in the lathe it was not possible to cut deeper than

2mm in the laboratory. The actual depth of cut was approximately half of the dialled

depth of cut.

Table 4-1. Cutting Parameters.

Industry Standard Used for Project

Cutting Speed 1500mm/sec 830mm/sec –

1500mm/sec

Feed Rate 0.25mm/rev 0.256mm/rev

Depth of Cut 1-3mm 0.8-2mm

A cutting speed of 830mm/sec was used during experiments because of the limitations

of the lathe. While this is almost half the cutting speed used in industry it is still within

the recommended machining parameters for the cutting tool [37].

The cutting speed is dependant on the rpm of the lathe. In the preliminary experiments

it was kept constant at 90rpm.

Table 4-2 shows all the parameters used in initial experiments. Experiments were

conducted varying the depth of cut, laser power, temperature and axial laser spot

position. The Temcon temperature controller was used to regulate the laser power and

Page 45

keep the temperature constant. The temperature was varied between 1300˚C and

2300˚C, which was the maximum and minimum capability of the pyrometer used. The

laser spot size was varied between 2.5mm and 3.5mm for the initial experiments.

Table 4-2. Experiment design parameters.

Speed (mm/sec)

Feed (mm/rev)

Depth of cut

(mm)

Spot size (mm)

Surface Temperature

(°C) 830 0.256 0.8, 1.2, 1.6 None None

830 0.256 0.8, 1.2, 1.6 3.1 1300

830 0.256 0.8, 1.2, 1.6 3.1 1400

830 0.256 0.8, 1.2, 1.6 2.8 1400

830 0.256 0.8, 1.2, 1.6 2.8 2300

830 0.256 0.8, 1.2, 1.6 2.6 2300

During each cut the cutting and feed forces and surface temperature were recorded and

chips were collected. Hard turning experiments (without laser) were also conducted as a

standard to compare against laser assisted machining results and to measure tool wear.

Results obtained during the preliminary experiments were not repeated for verification

as they were done to find an operating window where laser assisted machining would be

beneficial.

Preheat phase It was not possible to have a preheat phase in this study because the large diameter of

the workpiece meant that it was able to cool significantly between each pass of the laser.

It was not possible to get a smaller workpiece to overcome this problem because at Weir

Warman Ltd., part diameters is generally no smaller than the workpiece supplied in this

study.

4.4.1 Cutting Parameters in Secondary Experiments For secondary experiments the cutting parameters did not change from those listed in

Table 4-1 except that the rpm was kept constant at 90rpm, which meant the cutting

speed varied between 729mm/sec and 860mm/sec because of the change in diameter of

the workpiece. The new laser assisted machining parameters are listed in Table 4-3.

The cutting speed varied between 729mm/sec and 854mm/sec for each cut. Ideally the

Page 46

speed would be kept constant for all experiments however it was not possible due to the

difference in diameter of the workpiece after each cut.

The laser spot size varied between 1.4mm and 3mm. The range of laser spot sizes

differed in secondary experiments because when the laser spot was closer to the cutting

tool the reflected laser light was directed towards the operator. This meant that the laser

spot size was restricted.

The axial position of the laser spot with respect to the centre of the cutting tool was also

varied. Figure 4-11 shows the position of the laser spot with respect to the cutting tool.

In this figure the cutting tool and laser would be moving in a vertical path, removing the

un-machined material on the left of the tool. The right side of the laser spot was aligned

against the centre of the laser tool visually with the use or a ruler. Three positions were

trialled as shown in Figure 4-11. In position A the right side of the laser spot was 1mm

to the right of the centre of the cutting tool. In this position a large portion of the laser

beam fell on the machined surface. In position B the right side of the laser spot was

aligned with the centre of the cutting tool, with approximately half of the laser beam

falling on the machined surface. In position C the right side of the laser beam was 1mm

to the left of the centre of the cutting tool. This allowed the majority of the laser beam

to fall on the unmachined surface of the workpiece with a small area falling on the

chamfered cutting edge.

Table 4-3. Secondary experiment design.

Speed (mm/sec)

Feed (mm/rev)

Depth of cut

(mm)

Spot size (mm)

Laser Power (W)

Axial Laser Position

729-854 0.256 1.6 1.4 1500 C

729-854 0.256 1.6 1.4 1500 A

729-854 0.256 0.8, 1.2, 1.6 1.4 1500 B

729-854 0.256 1.6 1.5 500,1000,1300 C

729-854 0.256 1.6 3 1500 C

729-854 0.256 0.8, 1.2, 1.6 3 1500, 2000 A

729-854 0.256 1.6 3 1500, 2000 B

Page 47

The reason for this variation in position is to determine if it is more important to direct

the heat at the chamfer or at the unmachined surface and to see which position gives the

greatest force reduction.

Figure 4-11. Axial laser position of laser spot with respect to the centre of cutting tool.

4.5 LASER SCANS

4.5.1 Hardness Testing As well as using different cutting experiments, several laser scans were conducted

where the laser passed over the workpiece without the cutting tool engaged. The

secondary experiment set up was used to conduct the laser scans. The equipment was

set up so that even though the tool was not cutting the workpiece, the laser still tracked

across the workpiece when the feed was engaged.

The laser scans were done so that the heat-affected zone due to the laser could be

determined. Table 4-4 shows the laser scan parameters used for this. The speed varied

Page 48

because the diameter of the workpiece varied slightly. The change in speed between

experiments is only 3% of the maximum speed used which is not a significant

difference therefore results are able to be correlated.

Laser power was varied between 1000W and 1750W which is based on the range of

powers used in previous experiments. Two spot sizes were chosen that were

sufficiently different to get variation in results.

Table 4-4. Laser scan parameters.

Scan Feed

(mm/rev)

Speed

(mm/sec)

Spot Size

(mm)

Dialed laser

Power (W)

1 0.256 669 1.5 1000

2 0.256 669 1.5 1300

3 0.256 674 1.5 1500

4 0.256 674 2.5 1000

5 0.256 679 2.5 1300

6 0.256 683 2.5 1500

7 0.256 693 2.5 1750

Once the scans were completed the workpiece was then sectioned so that the hardness

could be measured at different depths below the surface. A microhardness tester was

used to measure the Knoop hardness with a testing weight of 500g. Hardness tests are

done by indenting the material with an elongated pyramid shaped diamond and

measuring the length of the indent through a microscope. The measurements were

made 0.05mm from the surface and every 0.1mm thereafter. The results are detailed in

Chapter 6 of this thesis. A temperature model was used to predict the temperature

within the workpiece due to the laser passing over its surface. The temperature model is

detailed in Chapter 5 including validation and experimental design. The model was

used to predict the temperature at different depths within the workpiece. These results

Page 49

were compared with the hardness results to determine if there is any correlation between

hardness and temperature. Details of the model experiments are included in Section 5.7.

4.6 SURFACE PROFILE MEASUREMENTS

A micrometer was used to measure and record the surface profile after both hard turning

and laser assisted machining cuts. The micrometer was mounted on a retort stand,

which was mounted on the tool post of the lathe. The micrometer was in contact with

the workpiece surface at the start of the cut and set to zero. The measurement on the

micrometer was recorded every 1mm by adjusting the position of the tool post with the

lathe. This was done for several experiments and results are detailed in section 6.2.2.

4.7 TOOL WEAR MEASUREMENT

There are two main types of tool wear – crater wear on the rake face which is usually

caused by chips sliding over it and flank wear, which is on the flank of the tool caused

by the rubbing of the tool over the machined surface. Tool wear and tool life is usually

calculated by measuring the width of the wear on the flank of the tool. The wear band

will not be constant with VBmax being the maximum width and VB being the average

width.

[Figure removed for copyright reasons]

Figure 4-12. Tool wear - flank wear VBmax & VB [33]

4.8 CONCLUSION

Preliminary experiments were conducted by using an Nd:YAG laser and a 3.5hp lathe

on Weir Warman Ltd. A05 high chromium white cast iron. A dynamic sensor was used

Page 50

to record the cutting and feed forces and a pyrometer measured the surface temperature

in the centre of the laser spot. The laser beam was directed at a position approximately

110mm from the cutting tool, and several parameters were varied to find out the effect

they had on cutting and feed forces.

The experiment setup was modified so that the laser beam was positioned 22-42mm

from the cutting tool. Results detailed in Chapter 6 show that this laser assisted

machining set up resulted in a reduction of cutting and feed forces.

The cutting parameters were kept as close as possible to those used at Weir Warman

Ltd.. However, the depth of cut and cutting speed were substantially less because of the

limitations of the lathe. The axial position of the laser beam with respect to the cutting

tool was also varied to determine the optimum position.

A mathematical temperature model of a moving heat source was also used to predict the

temperature on the surface and at depth within the workpiece. This will be discussed

further in Chapter 5.

Page 51

Chapter 5

TEMPERATURE MODEL

5.1 INTRODUCTION

A simple thermal model program was used to calculate the temperatures on the surface

and at depths within the workpiece due to the laser. The model was used to determine

the effect the laser has on the temperature of the workpiece at the cutting point. It was

also used to predict the temperatures within the workpiece generated during the laser

scans used in hardness experiments.

The model uses a gaussian heat source moving in a straight line over an infinite

workpiece. The thermal model program uses the command prompt terminal in

Microsoft Windows and has no graphics capabilities. Results are generated that can be

opened in notebook or imported into Microsoft Excel or another spreadsheet program

where they can then be graphed. It is only capable of modelling the heat added by the

laser and does not take the temperatures generated by the cutting tool into account.

It has the capability to determine the temperature change due to the heat source at any

point on the surface or within the workpiece at any position in time. It can also

calculate temperature change at any point over time.

This chapter discusses the method used to validate the model including the selection of

model input parameters. It also details the method used to model temperatures at depth

within the workpiece for comparison to experimental results. Results of the model with

respect to the temperature at the cutting point are covered in Chapter 6.

The model was developed by Dr Charles Johnson and is based on the equations for

transient heat transfer through a body by conduction.

5.2 EXPERIMENTAL DATA

To validate the model experiments were conducted with a Weir Warman Ltd. A05

workpiece placed in a rotating chuck. A pyrometer was mounted coaxially with the

Page 52

Nd:YAG laser directed on the top of the workpiece. The pyrometer measured the

surface temperature in the centre of the laser spot. This measurement could then be

compared with the temperature predicted by the model. During these experiments the

laser spot diameter was kept constant at 4.6mm, the speed of the laser beam with respect

to the workpiece was varied between 83mm/sec and 167mm/sec and the axial feed of

the laser was varied between 0 and 1.5mm/rev. When the feed was zero the laser spot

passed over the same tracks. This gave an increasing temperature for each revolution

and also changed the surface characteristics so the absorption factor would also vary.

For this reason, only results obtained when the feed was 1.5mm/rev were used.

Table 5-1 shows the experiments run and results used to validate the model. Detailed

results can be found in Appendix B.

Table 5-1. Model validations experimental results.

Run Laser power

(W)

Feed

(mm/rev)

Speed

(mm/sec)

Surface

Temperature

°C

1 1000 0 166 1079

2 1000 0 166 1095

3 852 0 166 1049

4 852 0 166 1056

5 1000 0.25 166 1082

6 1000 0.5 166 1088

7 1000 1.5 166 961

8 1000 1.5 166 947

9 1000 1.5 84.3 1482

10 852 1.5 84.3 945

11 852 1.5 125 806

12 852 1.5 166 751

13 852 1.5 166 911

Page 53

Figure 5-1 is a photo of the workpiece surface after the experiments had been

conducted. The numbers in the figure correspond to the run number in Table 5-1. It

shows the effect different laser powers, feed rates and speeds have on the surface of the

workpiece. Runs 1, 2, 5, 6 and 9 melted the surface. Runs 7, 8 and 10 show the surface

beginning to melt and the remaining runs show only marking of the surface.

Figure 5-1. Laser scans used for validating temperature model.

Figure 5-2 is an example of the temperature on the surface of the workpiece in the

centre of the laser spot measured by the pyrometer. The workpiece was rotated three

times, so the temperature output was split into the three revolutions and then a trend line

was plotted for each section. The trend line was then averaged to get an approximation

of the measured surface temperature. The average surface temperature changed for

each revolution as the laser passed over previously heated material. As the model is

Page 54

only capable of calculating the temperature for one pass, only the results from the first

revolution were used to validate the model.

The peak at the end is due to the fact that the laser spot finishes on the same spot it

started on. At that spot the reflectivity is low so the material absorbs more energy

producing a peak in the temperature.

Runs 12 and 13 were done with the same parameters but at the opposite ends of the

workpiece. The difference in temperature indicates a difference in absorption factor at

the two points. Absorption factor will change slightly in every cut depending on how

clean the surface is and how reflective it is. In this case the difference is less than 18%,

which is not excessive.

0 1 2 3 4 5 6 7 8 9 10 11400

600

800

1000

1200

1400

1600

Tem

pera

ture

(o C)

Time (sec)

Laser power 1300WSpot size 4.6mmSpeed 10m/minFeed 1.5mm/rev3 rotations100 point smoothing

Figure 5-2. Surface temperature in the centre of the laser spot measured by pyrometer.

Page 55

5.3 MODEL INPUT DATA

5.3.1 Material Properties The model does not take into consideration the changes that temperature has on the

workpiece properties such as thermal conductivity, thermal diffusivity and density.

From experimental results it was found that the surface temperature in the centre of the

laser spot varied between 750°C and 1000°C. At these temperatures the average

thermal conductivity is approximately 30W/m·K [36]. This conductivity was used

when measuring the temperature near the heat source. At points away from the heat

source the temperature would be much lower and hence the thermal conductivity would

be different. To validate the model only predicted temperatures in the centre of the laser

spot were used. Therefore the effect of varying conductivity with temperature was

reduced. For the same reason the density was kept constant at 7400kg/m3 [38] for all

runs. Thermal diffusivity was calculated from

pC

kρ

ν =

Where =ν diffusivity, =k thermal conductivity, =ρ density and =pC Specific heat

capacity.

Table 5-2. Diffusivity calculation.

Temperature

°C

Cp

J/KgK

[17]

k

W/mK

[39]

ρ

kg/m3

[38]

ν

m2/s

20 514.6* 13.75 7400 3.6x10-6

230 644 17.5 7400 3.7x10-6

600 780 23.74 7400 4.1x10-6

750 955 28.7 7400 4.1x10-6

900 800 28.26 7400 4.8x10-6

1000 960 31.46 7400 4.4x10-6

* Ref. [40]

Page 56

As these values change with temperature, diffusivity was calculated over several

different temperatures shown in Table 5-2. The drop in specific heat capacity and

thermal conductivity at 900°C is due to a phase change in the material. As mentioned

the temperatures measured during experiments varied between 750°C and 1000°C.

Therefore the diffusivity used for validating the model was 4.4x10-6 m2/s with 4.8x10-6

m2/s and 4.1x10-6 m2/s used to calculate the error in the model.

5.3.2 Laser Parameters Laser parameters include laser beam diameter, laser power and speed. During

experiments the laser spot diameter was kept constant for all passes, however the other

equipment parameters were varied. To validate the model, the laser power was kept

constant at 825W, the laser spot diameter was set at 4.6mm and the speed of the laser

beam was set at 84mm/s, 125mm/s and 166mm/s.

Sigma The temperature model uses a Gaussian heat source where σ is the standard deviation of

the heat source.

In reality the laser spot is closer to a “top hat” shaped heat source. Ideally the model

would use a “top hat” shaped heat source however this was not available. A comparison

of the heat source shapes can be seen in Figure 5-3. With a top hat heat source the

energy is constant over the radius of the source. In a gaussian heat source the energy

varies normally with the radius of the source.

The different shaped heat sources give similar temperature profiles at a distance away

from the centre of the heat source, however they produce very different temperature

profiles close to the heat source. To validate the model an equivalent gaussian heat

source was needed to model the top-hat profile. This was done by finding a gaussian

curve with the equivalent heat flux to the top-hat curve. The peak value of each curve

below is equal to the heat flux and power is the area under the curve.

Page 57

0

0.3

0 1 2 3 4 5 6

radius (arbitrary units)

Top HatGaussian

Figure 5-3. Top hat and equivalent gaussian heat source.

The area under a gaussian curve shown in Figure 5-3 is given by the equation:

∫∞ −

=0

2 2

2

2 drreAPr

gσπ 5-1

Where P = laser power, Ag = Peak power of gaussian curve, r = radius, σ = standard

deviation of Gaussian heat source,

Using the chain rule and substituting 2

2

2σru = 5-2

Then 2σr

drdu

= 5-3

durdr 2σ= 5-4

So PdueA ug =∫∞

−

0

22 σπ 5-5

When 0=r then 0=u and when ∞=r then ∞=u

[ ]∞−= 022 u

g eAP σπ 5-6

22 σπ gAP = 5-7

Page 58

22πσPAg = 5-8

The peak value of the top hat design is calculated

2rPAh π

= 5-9

Let hg AA =

∴ 222 rππσ = 5-10

∴ 22

2 rr==σ 5-11

Sigma can then be found by substituting r (radius) of the top hat. The radius of the laser

spot in experiments was mmr 3.2= which gives mm63.1=σ . This value of sigma

could then be used to validate the model against experimental results. Sigma was given

a 10% error when modelling to allow for variations in the radius measured in

experiments ( 163.063.1 ±=σ ). The model requires sigma values for the x,y and z

component of the laser beam. As the beam is round the x and y values are the same and

are entered as calculated. Sigma in the z direction indicates the depth of the laser beam.

As the workpiece is not being melted the z component is almost zero and so was entered

as 0.1mm.

5.3.3 Basic Data Input Page The material properties and equipment parameters constitute the basic data required by

the model. All of this basic data was entered into the programs input page as shown in

Figure 5-4.

Page 59

Figure 5-4. Basic data input page.

Figure 5-4 shows that the first data required is the material data including conductivity

and diffusivity. This is followed by the laser parameters, laser beam diameter, laser

power and laser absorption coefficient. The laser absorption coefficient is the fraction

of light absorbed by the material. It must be less than or equal to one. The model asks

if the laser beam is pulsed. In all experiments in this study the laser beam is continuous

not pulsed and so the answer to this prompt was always no.

The model has the ability to process heat source speed in three dimensions, however

only one dimension was used in experiments. The model calculates the length, time and

temperature scales shown, which are used for calculation purposes. The final input

required is sigma. As shown in Section 5.3.2 22

2 rr==σ . This equation was used

to calculate sigma in the x and y axis for each radius used. The Sigma_z value must be

greater than zero, it was therefore kept constant at 0.1mm for every model experiment

conducted.

5.3.4 Operational Information Once the basic data is entered the model program asks what type of operational mode to

proceed with. For validation “Tabulate temperature over plane for fixed values of the

time” was selected. Then the model required the maximum and minimum x and y

Page 60

values and the interval where temperatures would be calculated. The area entered for

all validation runs was x=-2mm,+10mm and y=-5mm,+5mm both axis incremented

over 0.5mm. The time at which temperatures were calculated was 3seconds. Figure 5-5

shows the operational data input page.

Figure 5-5. Operational input page.

5.4 MODEL OUTPUT

The model gives results in table form, which can then be imported into a spreadsheet

program and plotted. Some examples of results generated by the model are shown in

Appendix C. A typical 3D surface temperature plot is shown in Figure 5-6 using 100%

absorption of laser power. The laser was travelling in the negative

x-direction with x=0 representing the centre of the laser spot. The temperature at x=10

represents the temperature at a point 10 mm from the centre of the laser spot, that the

laser spot has passed over.

Page 61

-2

-0.5 1

2.5 4

5.5 7

8.5

10-5

-1.5

20

200400600800

10001200140016001800200022002400

Tem

p ch

ange

(deg

C)

x dist (mm)

y dist (mm)

2200-24002000-22001800-20001600-18001400-16001200-14001000-1200800-1000600-800400-600200-4000-200

Absorptivity 1Power 852WSpeed 84.3mm/sLaser spot 4.6mmDiffusivity 4.4E-6Conductivity 32

Figure 5-6. 3D surface temperature plot.

5.5 VALIDATING THE MODEL

The model was initially run with an absorption factor of 1, which assumes that all of the

energy from the laser is absorbed into the workpiece. This is unrealistic as the

machined surface of the workpiece is shiny and will reflect a lot of the laser energy.

Therefore the predicted temperature would be significantly larger than the measured

temperature. The absorption factor could then be calculated from this difference.

Figure 5-7 shows the temperature measured experimentally and the temperature change

calculated by the model with an absorption factor of 1 and 0.53. The error bars on the

model temperature are calculated by running the model, varying sigma by ±10% and

thermal diffusivity set to maximum of 4.8x10-6m2/s and minimum of 4.1x10-6m2/s. It

can be seen that as predicted the temperature calculated by the model is significantly

larger than that measured by the pyrometer during experiments when the absorption

factor was 1.

Page 62

400600800

100012001400160018002000220024002600

70 80 90 100 110 120 130 140 150 160 170 180

Speed (mm/sec)

Tem

pera

ture

(°C

)

Measured Absorption 1 Absorption 0.53

k = 30 W/mKν = 4.4m^2/sPower 852W

Figure 5-7. Modelled surface temperature versus laser speed

The absorption factor is calculated by the ratio of predicted temperature over measured

temperature and is then averaged over all speeds. Table 5-3 shows the absorption factor

calculations with the average absorption being 0.53.

Table 5-3. Absorption factor calculations.

Speed

Measured

Temperature

(°C)

Predicted

Temperature

(°C)

Absorption factor

Measure/Predicted

84.3 945.0 1940.7 0.49

125 806.2 1530.7 0.53

166 751.2 1283.1 0.58

Average Absorption factor 0.53

The model was then run again at the three speeds with an absorption factor of 0.53. To

calculate the error the model was also run at the same absorption factor, varying sigma

by ±10% and diffusivity set at 4.8x10-6m2/s and 4.1x10-6m2/s. These results can be seen

Page 63

in Figure 5-7. Whilst the gradient of the measured temperature and the predicted

temperature is slightly different, taking the error into account the model adequately

predicts the measured temperature.

5.6 USEFULNESS OF THE MODEL

The temperature gradient on the surface of the model is very steep and the surface

temperature 25mm away from the centre of the laser spot is significantly cooler than the

peak. Ideally the model would take into account the difference in temperature and the

effect this would have on thermal conductivity and diffusivity. Unfortunately it does

not have that capability. To calculate the temperature at a distance the standard thermal

conductivity and diffusivity (k = 32W/m·K and ν = 4.4x10-6m2/s) that were used in the

validation process were used. More appropriate thermal conductivity and diffusivity

values were selected from the predicted temperatures and the model run again. These

iterations were done several times. Although this method is not ideal it is satisfactory

for this project.

5.7 THERMAL MODEL EXPERIMENT DESIGN

5.7.1 Input Parameters Material parameters

Once the model was validated it was used to predict the temperature at depth at certain

points away from the laser spot. Thermal conductivity and thermal diffusivity vary with

temperature so several iterations were done to determine the right parameters for the

temperature calculated by the model. The initial values used were 30W/mK for

conductivity and 4.4x10-6m2/s for diffusivity, which are the same as those used in the

validation process. Table 5-4 is an example of the iterations conducted for one

temperature profile calculated by the model. It shows the parameters used for each

iteration to determine the appropriate conductivity and diffusivity parameters. After

each run the conductivity and diffusivity values were modified to suit the calculated

temperature and the model was run again. Appendix E shows the thermal properties of

high chromium white cast iron at various temperatures including the conductivity and

diffusivity. This continues until the calculated temperature was within 5°C of the

Page 64

previous run. The final conductivity values and diffusivity values were then used in the

model to calculate the desired temperature profile. Occasionally this process would

give divergent temperatures. In these cases the mean temperature was used to

determine the input values. Often this step was also repeated to determine the most

appropriate conductivity and diffusivity values.

This iteration process had to be done for each temperature profile required because the

temperature calculated is also dependant on all other material and operational

parameters. Detailed tables of the iterations conducted for each temperature profile are

shown in Appendix F.

Table 5-4. Temperature calculated by thermal model for various values of conductivity and diffusivity.

Conductivity

(k)

W/mK

Diffusivity

(ν)

m2/s

Calculated

Temperature

°C

30 4.4x10-6 468

20.7 3.9 x10-6 332

18.7 3.9 x10-6 366

19.4 3.8 x10-6 352

19.1 3.9 x10-6 358

19.2 3.8 x10-6 356

All calculations done using the following

parameters:

Laser spot size – 1.5mm

Laser power – 1100W

Absorption coefficient – 0.53

Laser speed – 729mm/sec

Sigma – 0.53

X distance – 42mm

Page 65

Operational parameters The model can calculate temperatures over a plane for fixed values of time, which was

the mode used in the validation process. It can also calculate temperature at depths

below a given surface point.

Figure 5-8. Operational mode for calculating temerature at depths under a given surface point.

Figure 5-8 shows the operational mode input screen for calculating temperature at

depths under a specified surface point. It requires the user to input the x, y and z

components of the surface point, the time value and depth coordinate range. The x

component of the surface point represents the distance position of the cutting tool

relative to the laser spot. For all model runs the y and z components were zero. The

time value used in most model runs was 100sec. This is an arbitrary number that is

large enough to allow the model to reach steady state conditions. The depth coordinate

range specifies the depths that the model will calculate temperatures at. For all models

the minimum depth was specified as 0 and the maximum varied to 10mm. Delta z

relates to the distance between each measurement. In most cases it was 0.2mm.

Table 5-5 shows the operational parameters used to calculate the temperature model

results. The temperature at depths under a specified surface point was calculated for all

of these parameters. The parameters from the second set of experiments that gave the

Page 66

highest reduction in forces were used as a starting point for modelling. Results from the

temperature model are detailed in Chapter 6.

Table 5-5. Parameters used for temperature model experiments

Laser Spot

Size Laser Power Absorption Speed Sigma

Distance

from laser

1.5 0.517, 0.917, 1.1, 1.38kW 0.53 729 0.53 42

1.5

0.517, 0.917, 1.1, 1.38,

2.3kW 0.53 729 0.53 25

1.5 1.38kW 0.53 729 0.53

0, 0.8, 25,

42

3.1 1.78 0.53 729 1.1 1.5, 25, 110

1.5, 3 1.38 0.53 729 0.53, 1.06 0.8, 25

1.5 1.38 0.53

100, 729,

850 0.53 25

1.5 1.1 0.53 729 0.53 42

3.1 1.7 0.53 729 1.1 110

5.7.2 Modelling Hardness Results The temperature model was also used to calculate temperatures at depths within the

workpiece to compare with the hardness results obtained from the laser scan parameters

listed in Table 4-4.

To take axial feed rate into account the temperature was taken at a particular point for

15 revolutions of the workpiece. Figure 5-9 shows the position of the centre of the laser

beam and its path after several revolutions of the workpiece. The feed rate used for all

experiments was 0.256mm/rev and the laser spot diameter was no less than 1.5mm,

which means that the laser will pass over the same point more than once.

Page 67

Figure 5-9. Path of laser beam

The model was used to calculate the temperature at point A when the laser beam was at

position B. To do this the surface field point coordinates of point A relative to point B

were needed. The thermal modelling program assumes the heat source is moving in a

straight line over an infinitely large workpiece. Therefore X coordinate is simply the

circumference of the workpiece. The Y coordinate is the feed rate because that is how

far the laser beam has moved in one revolution. To calculate each subsequent x

position the circumference of the workpiece was added to the previous x position.

Similarly the initial y position was y=0 and the feed rate were added for each

subsequent revolution.

Table 5-6 shows the coordinates for each revolution of the workpiece for laser hardness

scans 1 and 2. Spreadsheets for the other scans are in Appendix G. As the aim of this

exercise was to determine the depth of heat penetration into the workpiece the initial

position was at the point where maximum surface temperature was reached. In the case

of scan one this was located at x=0.8mm.

The temperature at depths under each of these surface points was calculated and then

added together to calculate the temperatures under the peak surface temperature. This

method was repeated for each laser scan. The results are detailed in Chapter 6 of this

thesis.

Page 68

Table 5-6. Surface positions taking feed into consideration.

Laser Scan 1 and 2

Laser spot size 1.5 mm

Circumference 446.11 mm

Feed 0.256 mm/rev

Revolution 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

x= (mm) 0.8 446.9 893.0 1339.1 1785.2 2231.4 2677.5 3123.6 3569.7 4015.8 4461.9 4908.0 5354.1 5800.2 6246.3

y= (mm) 0 0.256 0.512 0.768 1.024 1.28 1.536 1.792 2.048 2.304 2.56 2.816 3.072 3.328 3.584

Page 69

5.8 CONCLUSION

A temperature model has been validated against measured temperatures of the surface

of the sample. Temperatures were measured in the centre of the laser spot for speeds

between 84.3mm/sec and 166mm/sec. The model does not take into consideration the

variation of material properties with temperature change, however, the temperatures

calculated will give a sufficient indication of the temperatures in the regions to be

investigated.

The temperature model was used to calculate the temperature at depths below the peak

surface temperature taking into account the heat added by previous passes of the laser.

Temperatures predicted from these calculations will be compared with the micro

hardness results.

Page 70

Chapter 6

RESULTS

6.1 INTRODUCTION

This investigation involved cutting high chromium white cast iron with both the

traditional hard turning method and the new laser assisted machining method.

Experiments were conducted under a variety of different conditions with turning forces

being the main outcome measured. Changes were made to the power density of the

laser spot and its axial and radial position relative to the cutting tool.

Preliminary experiments were conducted with the laser approximately 110mm from the

cutting tool (Figure 4-2). As detailed in Chapter 4, secondary experiments were

conducted with the laser spot positioned within 25-42mm from the cutting tool.

A simple temperature model was also used to determine the temperature at depth within

the workpiece and experiments were conducted to record surface temperatures, which

were used to validate the model.

This chapter summarises the results obtained from preliminary and secondary

experiments as well as the temperature model.

6.2 PRELIMINARY EXPERIMENTS

6.2.1 Force Measurement The three graphs in Figure 6-1, Figure 6-2 and Figure 6-3 show the cutting force versus

the depth of cut at three different temperatures. Feed force results are shown in Figure

6-4, Figure 6-5 and Figure 6-6. Cuts were made at 0.8mm, 1.2mm and 1.6mm depth of

cut with the Temcon temperature controller keeping the temperature constant at

1400°C, 2000°C and 2300°C. Detailed tables of results are in Appendix H. In all cuts

the laser was turned on several seconds after cutting had begun. The initial force is the

force reached before the laser was applied. When the laser beam became incident on

Page 71

the surface the force either increased or decreased. The laser assisted machining force

is the force recorded after the laser started.

0

20

40

60

80

100

120

0.6 0.8 1 1.2 1.4 1.6 1.8

Depth of Cut (mm)

Forc

e (N

)

Initial Force LAM force

Figure 6-1. Cutting force versus depth of cut at 1400°C showing initial force and laser assisted machining force.

0

20

40

60

80

100

120

0.6 0.8 1 1.2 1.4 1.6 1.8

Depth of Cut (mm)

Forc

e (N

)

Initial Force LAM Force

Figure 6-2. Cutting force versus depth of cut at 2000°C showing initial force and laser assisted machining force.

Page 72

0

20

40

60

80

100

120

0.6 0.8 1 1.2 1.4 1.6 1.8

Depth of Cut (mm)

Forc

e (N

)

Initial Force LAM Force

Figure 6-3. Cutting force versus depth of cut at 2300°C showing initial force and laser assisted machining force.

The above figures show that in the preliminary experimental set up, the cutting force

increased once the laser was turned on over all depths of cut and temperatures except

0.8mm depth at 2300°C. From the literature discussed in Chapter 3 it was expected that

the cutting forces would decrease when the laser was turned on. Although experiments

were not repeated, the increase in force is consistent at all but one variation of the

parameters.

The feed force output (Figure 6-4, Figure 6-5 and Figure 6-6) showed similar results

with the laser increasing the forces in most cases. It was only at large depth of cuts and

high temperatures that the feed force was reduced by the addition of the laser. This can

be seen in Figure 6-5 and Figure 6-6 at 1.6mm depth of cut where the laser reduced the

feed force. The reduction was greatest in Figure 6-6, which was at the highest

temperature.

One reason for the increase in forces may be that the laser hardened the material rather

than softening it. The high temperatures combined with rapid cooling, aided by the

large workpiece acting as a heat sink, may have changed the microstructure of the

material. Ben Salem et al. [5] found that the closer the laser to the workpiece the

greater the reduction in forces, which is why the experimental set up was changed and

further experiments conducted.

Page 73

0

200

400

600

800

0.6 0.8 1 1.2 1.4 1.6 1.8Depth of Cut (mm)

Forc

e (N

)

initial force LAM force

Figure 6-4. Feed force versus depth of cut at 1400°C showing initial force and laser assisted machining force.

0

200

400

600

800

0.6 0.8 1 1.2 1.4 1.6 1.8Depth of Cut (mm)

Forc

e (N

)

initial force LAM force

Figure 6-5. Feed force versus depth of cut at 2000°C showing initial force and laser assisted machining force.

Page 74

0

200

400

600

800

0.6 0.8 1 1.2 1.4 1.6 1.8Depth of Cut (mm)

Forc

e (N

)

initial force LAM force

Figure 6-6. Feed force versus depth of cut at 2300°C showing initial force and laser assisted machining force.

6.2.2 Effect of Laser Power on Surface Profile A micrometer was used to measure and record the surface profile after both hard turning

and laser assisted machining cuts. Figure 6-7 is a plot of the surface profile and laser

power versus time. During this particular cut the laser power was increased by 250W

every 15 seconds starting at 1500W. It is clear that as the laser power was stepped up

the micron measurement was reduced therefore the amount of material removed

increased. However there is little correlation between the actual step in laser power and

a significant step in the surface profile. The random nature of micro flow during

localized melting may be the reason for this.

Compare this to a cut made without the assistance of the laser. It can be seen that the

surface profile of the machined edge is much more uniform, as shown in Figure 6-8.

This is possibly due to the increase in temperature and the change in material

deformation characteristics.

Page 75

0

20

40

60

80

100

120

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75

time (sec)

surf

ace

prof

ile (μ

m)

0

500

1000

1500

2000

2500

lase

r pow

er (W

)

Surface Profile Laser power

Figure 6-7. Surface profile and laser power. Depth of cut 0.6mm, speed 800mm/sec, feed 0.256mm/rev.

0

100

200

300

400

500

600

0 20 40 60 80 100

time (sec)

surf

ace

prof

ile (m

icro

n)

Figure 6-8. Surface profile of hard machining. Depth of cut 1.2mm, speed 800mm/sec, feed 0.256mm/rev.

6.2.3 Tool Wear To measure tool wear a series of cuts were made keeping parameters constant at

90RPM, 1.2mm depth of cut and 0.256mm/rev feed rate. The length of the cut was

60mm, which was also kept the same for each cut. After each cut was made the tool

was photographed through a microscope and the tool flank wear measured with ImageJ,

a graphics program with measurement capabilities. Figure 6-9 is typical of the

photographs taken of the flank wear on the edge of the CBN tool. The flank wear

Page 76

measured is that on the right edge of the tool. The wear on the left edge of the tool is

from previous experiments.

Figure 6-9. Flank wear of CBN tool after 62.5 minutes

cutting time. (Right side of the tool).

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0 5 10 15 20 25 30 35 40 45 50 55 60 65Time (min)

Flan

k w

ear (

mm

)

Figure 6-10. Flank wear progression.

The flank wear progression over time is plotted in Figure 6-10 and is relatively linear

which is what was expected. The flank wear at zero time is 0.1mm this is because the

Page 77

cutting tool needs to be worn in at slow speeds before it can cut at the high speeds

required for laser assisted machining. The tool was still cutting satisfactorily after 62

min of cutting and experience suggested that it would continue cutting satisfactorily for

a lot longer. So due to time constraints the experiment finished at this point.

6.2.4 Chips The geometry of the chips produced by laser assisted machining is evidence that the

process is causing the material to deform differently.

A scanning electron microscope (SEM) was used to observe the chips produced by a

new tool edge for both hard turning and laser assisted machining. Figure 6-11 and

Figure 6-12 are photographs of the chips collected in initial experiments taken through

the SEM. In both cases the chips are saw-toothed, however, Figure 6-11 shows that the

chips from hard turning seems to have sheared a lot cleaner than the laser assisted

machining chips. The surface temperature in the laser spot during that cut was

approximately 1800°C, however, the temperature at the cutting tool would be

significantly less due to heat dissipating into the workpiece. These pictures are

evidence that the laser is softening the surface of the workpiece. The softer and more

ductile a material is the lower its yield stress and hence it will shear more often as is

seen in Figure 6-12. The effect of this on forces will be discussed in the Chapter 7.

a). b).

Figure 6-11. Chip from hard turning with a new tool edge. a) Side view. b) Top view.

Page 78

a). b).

Figure 6-12. Chip from laser assisted machining with a new tool edge. a) Side view. b) Top view

6.3 MODIFIED EXPERIMENTS

6.3.1 Force Reduction vs. Laser Power Density Power density is calculated by dividing the laser power (W) by the laser spot area

(mm2).

As mentioned in Section 6.2.1 the addition of the laser to hard turning caused the forces

to increase in most cases. It was also mentioned that Ben Salem et al. [5] found that

force reduction was greatest when the laser was closer to the tool. For this reason the

experimental set up was modified to position the laser as close to the tool as possible

(Figure 4-10). Detailed results from secondary experiments are located in Appendix I.

Figure 6-13 and Figure 6-14 show the change in cutting and feed force due to the

addition of the laser. The change in force was used rather than the actual force

recorded, as the hard turning forces varied up to 26N between each cut. This was due to

the difference in hardness within the workpiece. Also as cuts were made, the diameter

of the workpiece was reduced and so the speed of each cut was slightly slower than the

previous one. A positive force change indicates that the laser increased the cutting

forces and a negative change represents a reduction in forces.

Page 79

-150

-100

-50

0

50

100

150

200

0 200 400 600 800 1000

Laser Power density (W/mm2)

Forc

e ch

ange

(N)

A - trailingB - centreC - leading

Figure 6-13. Cutting force vs laser power density, 1.6mm depth of cut.

-250

-200

-150

-100

-50

0

50

100

150

200

250

0 200 400 600 800 1000

Power density (W/mm2)

Forc

e C

hang

e (N

)

A - trailingB - centreC - leading

Figure 6-14. Feed force change vs laser power density, 1.6mm depth of cut.

Page 80

The force change is plotted against power density, which is calculated from the laser

spot size and the laser power. This allows all cuts to be compared together. All cuts

were made with 1.6mm depth of cut. The greatest force change averaged over both the

feed and cutting forces is at a power density of approximately 896W/mm2, with the

laser leading the cutting tool. The cutting parameters, which gave the greatest overall

force reduction, are shown in Table 6-1.

Table 6-1. Cutting parameters giving greatest force reduction.

Laser spot size 1.4mm

Power incident on work piece 1380W

Cutting speed 792mm/sec

Feed rate 0.256mm/rev

Distance between laser spot and

cutting tool 25mm

It is clear from Figure 6-13 and Figure 6-14 that the force reduction is greatest when the

laser is leading the cutting tool.

Results from modified experiments over all depths of cut give an average cutting force

reduction of 8.3%, with a maximum reduction of 24%. The average feed force

reduction was 12%, with a maximum reduction of 22%.

These results prove that moving the laser spot closer to the cutting tool reduces turning

forces, confirming that this distance is a critical factor in the success of laser assisted

machining.

The limitations of the equipment meant that the laser could be positioned no closer than

22mm to the cutting tool. The spot size of the laser was also restricted. When the laser

was positioned 25mm from the cutting tool the spot size was restricted to 1.4mm

because of limitations in the clamping mechanism holding the laser head. When the

distance was 22mm the spot size was 3mm and at 42mm from the tool the laser spot

size was restricted to 1.5mm. It would have been preferable to conduct experiments

Page 81

with the laser within 10mm of the tool, however that was not possible due to safety

issues. When the laser spot was positioned closer than 22mm the reflections of the

beam were directed back towards the laser head and operator. Therefore 22mm was as

close as the laser spot could be positioned to the cutting tool.

6.3.2 Hardness of Machined Surface The hardness results from the laser scan experiments are shown in Figure 6-15 to Figure

6-21. Detailed tables of results are shown in Appendix J. For scans 1, 2 and 3 (Figure

6-15, Figure 6-16 and Figure 6-17) only the laser power was changed. All other

parameters including laser spot size were kept constant. The figures show that the

higher laser power resulted in higher hardness near the surface of the material. This is

possibly due to the formation of martensite like structure caused by rapid cooling.

Figure 6-15 and Figure 6-16 representing scan one and two also show a small peak in

hardness at approximately 0.15mm then a larger peak at approximately 0.45mm. For

scan three (Figure 6-17) there is only one large peak at approximately 0.25mm then

dropped off rapidly to a minimum at 0.35mm before gradually increasing. This is

possibly due to hard phases in the material. The temperature model shows that the

temperature of the work piece at a depth of 0.3mm is less than 200°C therefore any

changes in hardness beyond this depth is not due to laser assisted machining.

The laser spot size was increased to 2.5mm for scans four to seven (Figure 6-18, Figure

6-19, Figure 6-20 and Figure 6-21). Again the only parameter changed between these

scans was the laser power. Figure 6-18, Figure 6-19, Figure 6-20 and Figure 6-21 all

show a small hardness peak between 0.25mm and 0.35mm, which increased with

increasing power. As in the first three scans the hardness near the surface increased

with increasing laser power.

It is clear that, in general, the higher the laser power the higher the hardness near the

surface of the workpiece. This result is therefore independent of any changes to

hardness caused by grinding or cutting of the sample or hardness variations due to

casting.

The testing surface was not polished and on the mirco level there were small grooves

created when the sample was cut. There were also many small cracks created during

either the casting or cutting process. It is also possible that they were caused by laser

assisted machining, however, as they were mostly found near the internal diameter of

Page 82

the workpiece, it is most likely that they were caused by other processes. High

chromium white cast iron is a very brittle material and cracks easily. As much as

possible, cracks and large grooves were avoided when conducting hardness tests.

It was expected that the hardness would correlate with the temperature over depth

however there is no apparent correlation from the results obtained. A more detailed

analysis may reveal some correlation between hardness and temperature penetration.

The melting temperature of the material is approximately 1275°C [10] which is why

there are burn marks on the surface of the sample for the first three scans. The seventh

scan (Figure 6-21) reached the melting temperature however no burn marks appeared.

This may be due to the fact that an individual pass of the laser did not raise the surface

temperature beyond the melting temperature. It was only the heat added by previous

passes that raised the temperature above the melt point.

0

200

400

600

800

1000

1200

1400

1600

1800

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2Depth (mm)

Tem

pera

ture

(°C

)

400

450

500

550

600

650

700

750

800

850

900

950

1000

Har

dnes

s H

V0.

5

Model Temperature HardnessLaser power 822WSpot size 1.5mm

Figure 6-15. Hardness results for laser scan 1.

Page 83

0

200

400

600

800

1000

1200

1400

1600

1800

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

Depth (mm)

Tem

pera

ture

(°C

)

4004505005506006507007508008509009501000

Har

dnes

s H

V0.

5

Model Temperature HardnessLaser Power 1190WSpot size 1.5mm

Figure 6-16. Hardness results for laser scan 2.

0

200

400

600

800

1000

1200

1400

1600

1800

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

Depth (mm)

Tem

pera

ture

(°C

)

400

450

500550

600

650

700

750

800

850

900

950

1000

Har

dnes

s H

V0.

5

Model Temperature HardnessLaser Power 1400WSpot size 1.5mm

Figure 6-17. Hardness results for laser scan 3.

Page 84

0

200

400

600

800

1000

1200

1400

1600

1800

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

Depth (mm)

Tem

pera

ture

(°C

)

400

450

500

550

600

650

700

750

800

850

900

950

1000

Har

dnes

s H

V0.

5

Model Temperature Hardness

Laser Power 822WSpot size 2.5mm

Figure 6-18. Hardness results for laser scan 4.

0

200

400

600

800

1000

1200

1400

1600

1800

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

Depth (mm)

Tem

pera

ture

(°C

)

400

450

500

550

600

650

700

750

800

850

900

950

1000

Har

dnes

s H

V0.

5

Temperature HardnessLaser Power 1194WSpot 2.5mm

Figure 6-19. Hardness results for laser scan 5.

Page 85

0

200

400

600

800

1000

1200

1400

1600

1800

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

Depth (mm)

Tem

pera

ture

(°C

)

400450

500550

600650

700

750800850

900950

1000

Har

dnes

s H

V0.

5

Temperature HardnessLaser Power 1400WSpot size 2.5mm

Figure 6-20. Hardness results for laser scan 6.

0

200

400

600

800

1000

1200

1400

1600

1800

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

Depth (mm)

Tem

pera

ture

(°C

)

400

450

500

550

600

650

700

750

800

850

900

950

1000

Har

dnes

s H

V0.5

Temperature HardnessLaser Power 1584WSpot size 2.5mm

Figure 6-21. Hardness results for laser scan 7.

These results show that the laser does have an effect on the hardness of the material.

Results from the secondary experiments also confirm this. Figure 6-22, Figure 6-23 and

Figure 6-24 show the voltage output from the force sensor from three consecutive cuts.

In all three cuts the depth of cut was 1.6mm and the speed was approximately

Page 86

817mm/sec. In Figure 6-22 and Figure 6-24 no laser was used however in Figure 6-23 a

laser beam of 1380W was directed at the workpiece 25mm from the cutting tool.

In Figure 6-22 no laser was used and the sensor output shows an almost smooth decay.

There is a small rise at 20 seconds indicating a small hard spot in the workpiece as a

result of the casting process. Figure 6-23 clearly shows the force increase due to the

laser being turned on at 25 seconds, which is obviously not desirable. The final cut

(Figure 6-24), which had no laser, shows s small levelling out of the signal at

25seconds. This is a slight residual hard spot from the previous cut. This indicates that

in these conditions the laser is probably hardening the material beyond the depth of the

cut.

These results were only noticed when the laser increased cutting forces which indicates

poor operational parameters. There was no evidence of this occurring when the laser

reduced the cutting forces.

0 5 10 15 20 25 30 35 40-0.05

0.00

0.05

0.10

0.15

0.20

0.25

Am

plitu

de (V

)

Time (sec)

Depth of cut 1.6mmSpeed 817mm/sec

Figure 6-22. Cutting force versus time. Depth of cut 1.6mm,

cutting speed 817mm/sec, no laser.

Page 87

0 5 10 15 20 25 30 35 40-0.05

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

Am

plitu

de (V

)

Time (sec)

Depth of cut 1.6mmSpeed 817mm/secLaser power 1380WLaser-tool distance 25mm

Figure 6-23. Cutting force versus time. Laser incident on workpiece at 25 sec. Depth of cut 1.6mm, speed 817mm/sec,

laser power 1380W, distance between laser spot and tool 25mm.

0 5 10 15 20 25 30 35 40-0.05

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

Am

plitu

de (V

)

Time (sec)

Depth of cut 1.6mmSpeed 817mm/sec

Figure 6-24. Cutting force versus time. Depth of cut 1.6mm, cutting speed 817mm/sec, no laser.

Page 88

6.4 THERMAL MODEL RESULTS

6.4.1 Effect of Laser Spot Position on Temperature The temperature model was used to predict the temperature change at various depths

from the surface of the workpiece and at various distances from the laser spot. This

distance represents the distance between the laser spot and the cutting tool during laser

assisted machining. These predictions give an indication of the depth of heat

penetration due to the laser at the tool tip under various laser conditions. They do not

take into consideration the heat generated by friction and shear strain caused by the

cutting tool.

Figure 6-25 shows the temperature versus depth at various laser powers and a laser spot

size of 1.5mm, 25mm from the centre of the laser spot. It can be seen that increasing

laser power increases the peak surface temperature and increases the maximum depth of

heat penetration. The increasing surface temperature creates a steeper temperature

gradient over depth. At a depth of 1mm the temperature is 40°C when the laser power

is 0.52kW compared to a temperature of 220°C when the laser power is 2.3kW. This

proves that the higher the laser power the higher the temperatures at depth in the

workpiece.

0

100

200

300

400

500

600

700

800

900

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3

Depth (mm)

Tem

pera

ture

(°C

)

0.52 kW 0.92 kW 1.1 kW 1.38kW 2.3kW

Spot size 1.5mmSpeed 729mm/secAbsorption 0.53

Figure 6-25. Temperature versus depth. 1.5mm laser spot, 25mm from the centre of heat source.

Page 89

Figure 6-26 shows similar results when calculating the temperature 42mm from the

laser spot, the main differences being the reduction in surface temperature and the

increase in the depth of penetration. This can be seen more clearly in Figure 6-27,

which compares the temperature within the workpiece at several distances from the

laser spot including the centre of the laser spot and 0.8mm from the centre, which is

where the peak surface temperature occurs. The laser power used is 1.38kW.

0

50

100

150

200

250

300

350

400

450

500

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3

Depth (mm)

Tem

pera

ture

(°C

)

0.52 kW 0.92 kW 1.1 kW 1.38 kW

Spot size 1.5mmSpeed 729mm/secAbsorption 0.53

Figure 6-26. Temperature versus depth. 1.5mm laser spot, 42mm from the centre of the laser spot.

0

200

400

600

800

1000

1200

1400

1600

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3

Depth (mm)

Tem

pera

ture

(°C

)

42mm 25mm 0.8mm 0mm

Laser Power 1.38kWLaser Spot size 1.5mmSpeed 729mm/secAbsorpt ion 0.53

Figure 6-27. Temperature versus depth at various points from laser spot. Laser power 1.38kW.

Page 90

Figure 6-27 shows that the temperature at the surface drops as the distance from the heat

source increases. Also, the temperature gradient is steeper close to the laser spot. As

the distance from the laser spot increases, the heat has more time to dissipate into the

workpiece, which lowers the temperature at the surface and increases the depth of

penetration. At depths less than 0.2mm the temperature within the work piece is

significantly higher closer to the heat source.

Figure 6-28 is a similar graph, which shows the temperature change versus depth at

three distances from the laser spot. The laser spot size and laser power are based on

cuts made during the preliminary experiments so the laser power is 1.78kW compared

to 1.38kW used in Figure 6-27 and the laser spot size is 3.1mm instead of 1.5mm.

However in both these figures the surface temperature decreased and the depth of heat

penetration increased as the distance from the laser spot increased. The temperature

was predicted at a point 110mm from the laser spot, which represents the position of the

cutting tool in preliminary experiments. It was under these conditions that the cutting

forces increased when the laser was turned on.

0

200

400

600

800

1000

1200

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3Depth (mm)

Tem

pera

ture

(°C

)

110mm 25mm 1.5mm

Laser power 1.78kWLaser spot 3.1mmAbsorption 0.53

Figure 6-28. Temperature versus depth at various points from laser spot. Laser power 1.78kW.

Figure 6-27 shows that at a depth of 0.8mm the temperature change is approximately

200°C at both 25mm and 42mm. This corresponds to the depth of the tool tip during

Page 91

many experiments. This is a significant increase in temperature when considering that

CBN tools cut best at temperatures over 900°C. Therefore it can be said that for 0.8mm

depth of cut the laser is heating the shear zone significantly. Figure 6-28 shows that the

temperature change at 0.8mm deep is approximately 160°C, which is still a significant

increase in temperature in the shear zone. Experimental results however found that

when the distance between the cutting tool and the laser spot was 110mm the cutting

forces increased. This will be discussed further in Chapter 7.

6.4.2 Effect of Laser Spot Diameter on Temperature Figure 6-29 shows the effect that different laser spot diameters have on the temperature

at 0.8mm and 25mm from the heat source. Increasing the spot diameter reduces the

power density, which reduces the peak surface temperature. However, the model shows

that the temperature difference between the different spot diameters is minimised as the

depth increases.

0

200

400

600

800

1000

1200

1400

1600

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2Depth (mm)

Tem

pera

ture

(°C

)

1.5mm spot, 25mm dist. 3mm spot, 25mm dist1.5mm spot, 0.8mm dist 3mm spot, 0.8mm dist

Laser power 1.38kwSpeed 729mm/secAbsorption 0.53

Figure 6-29. Temperature change versus depth from 1.5mm and 3mm laser spot predicted at 0.8mm and 25mm from the

laser beam.

At 0.8mm from the laser, the depth at which the temperature is approximately 0°C is

0.1mm greater when using a 3mm spot size, however, at 25mm from the laser source

the difference is minimal. This results in a lower temperature gradient within the

Page 92

workpiece. Therefore a 1.5mm spot size is more ideal for laser assisted machining than

a 3mm spot because it results in higher temperatures within the workpiece and a

negligible change to the maximum depth of heat penetration. Reducing the spot size

even further will result in even higher temperatures within the workpiece. There is a

limit to how small the spot size can be due to the fact that at small spot sizes it begins to

melt the material. Equipment restrictions was the main reason that the spot size was not

reduced further in these experiments.

6.4.3 Effect of Varying the Cutting Speed on Temperature

During experiments the radius of the workpiece kept decreasing as material was cut

away. This resulted in reduced speeds for each cut, as the lathe did not have a variable

speed drive. No two cuts were done at exactly the same speed. The speed used for the

majority of temperature models was 729mm/sec. This was chosen because it was the

speed at which the greatest reduction in forces was recorded during experimental

results. This also was the slowest speed recorded for secondary experiments. The

maximum speed was approximately 850mm/sec. To assess the impact of speed on

surface temperature the system was modelled using these two speeds. Figure 6-30

presents the results from the model. The figure also shows the temperature at

100mm/sec.

There is very little change in the surface temperature between 729mm/sec and

850mm/sec, however there is a big difference in the depth of heat penetration. It was

thought that the change in speed caused by the changing diameter would be negligible,

but these results prove otherwise. At a depth of 1mm, the temperature is approximately

100°C at a speed of 729mm/sec and is zero at 850mm/sec. This will be discussed

further in Section 7.4.3.

As expected, reducing the cutting speed significantly from 729mm/sec to 100mm/sec

increased the depth of heat penetration by approximately 2.5mm. The surface

temperature also increased at the slower speed because the slower moving laser allows

more energy to be transferred to the workpiece, therefore the temperature of the surface

is much higher.

Page 93

0

100

200

300

400

500

600

700

800

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

Depth (mm)

Tem

pera

ture

(°C

)

100mm/sec 729mm/sec 850mm/sec

Laser Pow er 1.38kWLaser spot size 1.5mmAbsorption 0.53

Figure 6-30. Temperature change versus depth at 25mm for the same laser power and various cutting speeds.

6.4.4 Comparison of Temperature Profile in Preliminary and Secondary Experiments

The temperature as a function of depth calculated for the cut that gave the highest

reduction of forces is shown in Figure 6-31. The figure also shows the temperature

calculated for a cut made at a similar speed in the preliminary experiments. The cutting

parameters and force change for both cuts are shown in Table 6-2.

The results in Figure 6-31 show that when the cutting tool is located 42mm from the

laser spot, the temperature at a depth of 1.6mm is approximately 25°C when the laser

power is 1.1kW. If the depth of cut is 1.6mm the laser is contributing little to raise the

temperature at the point of the cutting tool. However, because of lack of rigidity in the

lathe the actual depth of cut was approximately half of the dialled depth of cut and was

therefore 0.8mm. At this point the temperature due to the laser was approximately

175°C, which is significant considering the temperature of the cutting tip during cutting

is to approximately 900°C. The temperature at the surface is just over 350°C. These

two temperatures represent the temperature increase caused by the laser across the shear

plane.

Page 94

Table 6-2. Cutting parameters from cut giving the highest reduction in forces and a comparable cut from preliminary experiments.

Preliminary

Experiment

Secondary

Experiment

Speed (mm/sec) 733 729

Feed (mm/rev) 0.256 0.256

Depth of Cut (mm) 0.8mm 1.6mm

Laser spot diameter (mm) 3.1 1.5

Laser Power (kW) 1.78 1.1

Distance between tool and

laser spot (mm) 110 42

Cutting Force change (N) 15.3% -24.1%

Feed Force change (N) 7.7% -21.9%

0

50

100

150

200

250

300

350

400

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.6 3.8 4

Depth (mm)

Tem

pera

ture

(°C

)

Secondary Experiment Preliminary Experiment

Reduction in forcestool-laser dist. 42mmLaser pow er 1.1kWSpot size 1.5mmSpeed 729mm/sec

Increase in forcestool-laser dist. 110mmLaser pow er 1.7kWSpot size 3.1mmSpeed 729mm/sec

Figure 6-31. Temperature as a function of depth at tool position for two different cuts producing a force reduction

and a force increase.

Page 95

The depth of cut that was shown on the lathe dial for the preliminary cut was 0.8mm,

which means the actual depth of cut would have been closer to 0.4mm. At this depth

the temperature is 204°C and 220°C at the surface. These temperatures are both

significant considering the hard turning temperature of 900°C, however for these

parameters the cutting and feed force both increased. The reason for this is discussed

in Chapter 7.

6.5 CONCLUSION

Results obtained during the preliminary experiments show that laser assisted machining

does not reduce the cutting forces as expected when the distance between the laser beam

and the cutting tool is approximately 110mm. Therefore secondary experiments were

conducted with the laser spot positioned closer to the cutting tool. Secondary

experiment results gave maximum cutting force reduction of 24% and a maximum feed

force reduction of 22%. This proves that moving laser spot closer to the cutting tool

reduces forces.

The temperature model results show that as expected the heat penetration increases as

the distance between the laser spot and the cutting tool is increased, however, the

surface temperature is reduced. This is because the heat has more time to dissipate into

the workpiece.

Secondary experiments also show that increasing the laser power resulted in an increase

in surface hardness and that there is no apparent correlation between hardness and

temperature over depth.

Also increasing the laser power resulted in an increase in surface temperature and depth

of heat penetration. However increasing the laser spot diameter reduced the surface

temperature and had little effect on the depth of penetration. Reducing the cutting speed

increases the surface temperature and the depth of heat penetration

These results are discussed further in Chapter 7.

Page 96

Chapter 7

DISCUSSION OF RESULTS

7.1 INTRODUCTION

Laser assisted machining does show promise as an alternative method of machining

high chromium white cast iron. Results show that with the right parameters laser

assisted machining results in lower turning forces than hard machining without laser

assistance.

This chapter discusses the results obtained, the effect of the added heat on the cutting

characteristics, the industry applications and the limitations of this study.

7.2 EFFECT ON FORCES

7.2.1 Effect of Heat on Primary Shear Zone As discussed in Chapter 3 laser assisted machining has been proven to reduce turning

forces on certain ceramics and hard metals. Results of this study show that with the

right parameters this is also true for laser assisted machining of high chromium white

cast iron.

Ng and Aspinwall [19] stated that “During metal cutting heat is generated in the

primary shear zone and the secondary deformation zone”. The primary shear zone is

the area along which the material shears to form a chip. It stretches from the tool tip to

the unmachined surface directly in front of the chip (Figure 3-1). The principle behind

laser assisted machining is that the laser heats the shear plane, reducing the yield

strength so that turning forces are reduced. Research shows that the temperature needed

in the shear plane for CBN to cut white cast iron is approximately 900°C [15-18].

The results in Figure 7-1 show the temperature calculated by the temperature model for

two cuts. The parameters used are from the secondary experimental cut which gave the

highest reduction in forces and a preliminary cut that had a similar cutting speed and

resulted in an increase in forces. The actual depth of cut for the preliminary experiment

Page 97

was approximately 0.4mm at which point the predicted temperature was 204°C and at

the surface the temperature was 220°C. Whereas for the secondary experiment the

depth of cut was 0.8mm and the predicted temperature was 175°C at the tool tip and the

surface temperature just over 350°C. These temperatures are purely due to laser

heating. The actual temperature would be higher because of the heat generated by

shearing and friction along the tool-chip interface. It was shown in Figure 3-2 that as

the temperature of a material increases the yield stress decreases. Therefore, it would be

expected that for both cuts the turning force would be reduced, however, this was not

the case as forces in the preliminary experiments increased.

0

50

100

150

200

250

300

350

400

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.6 3.8 4Depth (mm)

Tem

pera

ture

(°C

)

Secondary Experiment Preliminary Experiment

Reduction in forcestool-laser dist. 42mmLaser power 1.1kWSpot size 1.5mmSpeed 729mm/sec

Increase in forcestool-laser dist. 110mmLaser power 1.7kWSpot size 3.1mmSpeed 729mm/sec

Figure 7-1. Temperature as a function of depth at tool position for two different cuts producing a force reduction

and a force increase.

7.2.2 Laser Surface Hardening There are several possible reasons why the forces increased in preliminary experiments

where the distance between the laser spot and the tool was approximately 110mm.

Page 98

The most obvious possibility is that the laser is hardening the surface of the workpiece

before the cutting tool removes the material. To do this the phase change temperature

would have to be reached and then sufficient cooling would have to occur. In

preliminary experiments the pyrometer recorded surface temperatures between 900°C

and 2000°C in the centre of the laser spot. The melting temperature of the material is

approximately 1275°C. In most cases the surface temperature is above this. It takes

approximately 0.14 seconds for this material to pass from the laser spot to the cutting

tool. For the preliminary cut modelled in Figure 7-1 the surface temperature was

measured at 1900°C in the centre of the laser spot during laser assisted machining.

According to the model the surface temperature drops to 220°C at the cutting tool,

110mm away. The bulk of the workpiece acts like a heat sink causing a rapid drop in

temperature.

In the secondary experiments the temperature in the laser spot was also higher than the

melting point in many cases, but with the closer distance between the laser and the tool,

there was less time for the heat to dissipate into the workpiece and so the hardening

effect did not occur as readily. Reducing the distance between the tool and the laser

would reduce this effect even more.

Whilst surface hardening is a possible reason for the force increase it is not likely

because the surface hardness results shown in Figure 6-15 to Figure 6-21 do not show

any correlation between laser power and surface hardness.

7.2.3 Distance Between Tool and Laser Whilst it is not possible to conclude from this study that the closer the laser spot is to

the cutting tool the greater the force reduction, it does go someway to confirm this.

Results show that when the laser spot-tool distance is 110mm the cutting forces increase

whereas when that distance is reduced to 42mm or 25mm the cutting forces are reduced.

This is similar to results obtained by Ben Salem [5], which show that when cutting

hardened XC42 steel by laser assisted machining, a greater force reduction was obtained

when the laser was closer to the cutting tool.

Moving the laser spot even closer to the tool than 25mm will result in a higher surface

temperature and a reduced depth of penetration. As the majority of heat generated by

the tool is concentrated at the tip of the cutting tool, the depth of heat penetration from

Page 99

the laser may not be as crucial as first thought. When the laser is closer to the cutting

tool the heat added by the laser has less time to penetrate into the workpiece hence the

temperature in the shear zone due to the laser will be higher near the surface of the

workpiece. The heat generated by the cutting tool is greatest at the tip of the cutting

tool. This means that temperature in the shear zone due to the cutting tool will be

highest at the depth of the cut. Adding the laser to the cutting process causes a

reduction in the yield strength near the surface beyond what it would be in normal hard

turning. This results in reduced cutting forces as demonstrated in the secondary

experiments. So it is likely that reducing the distance between the laser spot and the

cutting tool further would reduce the turning forces further. However, in this study the

laser-tool distance was restricted to 22mm due to safety issues caused by reflection of

the laser beam.

In the preliminary experiments the surface temperature was lower beyond 0.9mm

compared to secondary experiments, therefore the yield strength in the shear zone near

the surface was higher. The depth of heat penetration was greater, and therefore,

depending on the depth of cut, the temperature at the tool tip would be higher. In Figure

7-1 the temperature curves of the two cuts cross at approximately 0.9mm. If the depth

of cut was less than 0.9mm, the temperature at the tool would be higher in the

secondary experiment cut when the distance between the tool and the laser spot was

42mm. Whereas if the depth of cut were greater than 0.9mm, the temperature at the tool

would be higher in the preliminary experiment, when the distance between the laser and

the tool was 110mm. So it cannot be said that the temperature at the depth of cut

increases as the distance between the tool and laser spot increases as it depends on the

depth of the cut.

The depth of cut used by Ben Salem [5] varied between 0.15mm and 0.4mm, the laser

power used was between 1.5kW and 3kW and the speed between 1-2.8mm/sec. The

slow speed combined with the shallow depth of cut means that the heat added by the

laser would have significantly increased the temperature near the tool tip. Therefore it

is understandable that reducing the laser-tool distance and increasing the laser power

resulted in a greater force reduction, as they would both increase the temperature in the

shear zone. The deeper cuts and the high speeds used in this study mean that the heat

from the laser did not increase the temperature at the tool tip as much.

Page 100

The depths of cut Ben Salem [5] used are very small and so the depth of heat

penetration would not be a concern. The temperature gradient is relatively flat near the

surface of the workpiece so the difference in temperature between the surface and the

depth of cut would be minimal. In this study the depths of cut were up to 2mm and so

heat penetration did influence results. As the distance between the laser spot and the

cutting tool is reduced, the surface temperature increases and the temperature at the

depth of cut is reduced. High surface temperatures reduces the yield strength near the

surface of the workpiece.

Depth of heat penetration It was expected that raising the temperature within the shear zone at the tip of the tool

would reduce the shear stress and hence the turning forces. This would be the case if

increasing the distance between the laser and the tool resulted in a greater reduction in

forces but it did not.

In preliminary experiments the forces were increased this is possibly due to the surface

of the work piece being heated to high temperatures and then cooled rapidly before

being cut. Although the heat will have penetrated deeper into the workpiece giving a

reduction of yield stress at the tip of the cutting tool, the hardeneing of the surface

increases the cutting forces.

Ideally the laser would provide a good depth of penetration (to the depth of cut) and

would not have given the surface sufficient time to cool and harden. Reducing the

distance between the tool and the laser spot gave less time for cooling and increasing

the power gave a deeper initial depth of penetration.

7.3 EFFECT OF HEAT ON CHIPS AND FINISHED SURFACE

7.3.1 Heat Removal A simple temperature model was used to determine the depth of heat penetration into

the workpiece at various speeds, spot sizes and laser powers. The results displayed in

Figure 7-2 show that the maximum depth of heat penetration into the workpiece was

approximately 0.4mm under the peak surface temperature (at 0.8mm from the centre of

the laser source) and 1.6mm deep at a point 42mm from the heat source. The actual

depth of cut in secondary experiments was 0.8mm where the temperature was

Page 101

approximately 200°C both 25mm and 42mm away from the laser spot. The majority of

the heat is removed in the chip, but there is still some remaining in the workpiece. This

residual heat expands the workpiece making it difficult to machine to the correct

tolerance. This is an issue that occurs in industry as well with large workpieces.

In addition to this, during the preliminary experiments the chamfer between the laser

spot and the tool was darkened because of heat added by the laser. This visibly

darkened material was removed in the swarf.

Notter and Heath [18] noted that a negative rake angle and high cutting speeds generates

heat which continuously softens the workpiece in the very small volume of the cutting

zone. They go on to say that virtually all of the heat generated is removed with the

chip. Therefore, the only remaining heat in the workpiece is that due to the laser

penetrating beyond the depth of cut.

0

200

400

600

800

1000

1200

1400

1600

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4

Depth (mm)

Tem

pera

ture

(°C

)

42mm 25mm 0.8mm 0mm

Laser Power 1.38kWLaser Spot size 1.5mmSpeed 729mm/secAbsorption 0.53

Figure 7-2. Temperature as a function of versus depth at various distances from laser spot.

7.3.2 Chip Formation The increased temperature in the shear zone results in greater plastic deformation and

hence chips do not shear as cleanly. When machining ductile materials the chips

formed are continuous due to plastic deformation in the shear zone. When machining

Page 102

hard materials, cracks form causing local shear producing a saw-tooth chip [13;23].

This can be seen in Figure 6-12 and Figure 6-11, which shows the difference between

chips, generated by hard turning and by laser assisted machining.

The added heat from the laser increases the temperature in the shear plane making it

more ductile. This causes it to form a more continuous chip, whereas without the added

laser heat, the chips shear much cleaner as shown in Figure 6-12 and Figure 6-11.

7.3.3 Micro-Hardness of Subsurface Removing the majority of heat with the swarf means that minimal surface damage on

the machined surface is expected.

Figure 6-15 to Figure 6-21 show hardness variation as a function of depth together with

predicted temperature as a function of depth. There appears to be no correlation

between the depth of heat penetration and the hardness. Figure 6-17, Figure 6-20 and

Figure 6-21 did show a small increase in the hardness within the first millimetre of

depth. It appears predominantly in those with higher laser power, however, when

considering the power density, it is a random occurrence. This indicates that the rise in

hardness in some samples is simply due to material hard spots. Throughout this study

the workpieces have shown themselves to be inconsistent with many hard spots

encountered.

The increased hardness near the surface of the workpiece is most likely due to the

casting process and the wire wheel cutting of the test sample. The surface will naturally

be harder due to the casting process.

7.3.4 Surface and Subsurface Integrity While testing the hardness several cracks were visible within the workpiece. It is

uncertain what caused these cracks. It may have been due to the casting process, the

preparing of the sample or the laser assisted machining of the workpiece. The cracks

extend right through the sample from the interior to the machined surface. This

indicates that they are most likely due to the casting process and not laser assisted

machining. Results obtained by Lei et al. [25] and Konig and Zaboklicki [7] show that

laser assisted machining causes minimal surface and subsurface damage.

Page 103

7.4 EFFECT OF LASER AND CUTTING PARAMETERS

7.4.1 Laser Spot Position Axial position The effect of the axial position of the laser was investigated in the secondary

experiments. The laser was aligned with the cutting tool in three different positions as

shown in Figure 7-3. When the laser spot was leading the tool, the spot was falling

predominately on the chamfer with a small proportion falling on the unmachined and

machined surfaces on either side of the chamfer. When the laser spot was aligned with

the centre of the cutting tool, it was half covering the chamfer and half on the

unmachined surface. When the laser spot was trailing the cutting tool, the majority of

the spot was on the unmachined surface with a small amount on the chamfer.

Results are shown in Figure 6-13 and Figure 6-14. They show that in all cases the force

reduction is greatest when the laser spot was leading the tool. It also shows that in all

but one experiment the forces were increased when the laser was trailing the cutting

tool.

Page 104

Figure 7-3. Axial laser position of laser spot with respect to the centre of cutting tool.

The shear zone is located in the unmachined surface directly in front of the cutting tool.

When the laser beam is trailing the cutting tool the centre of the laser spot is directed at

the machined surface and hence it is not heating the shear zone efficiently. It is

therefore not surprising that when the laser was in this position the cutting forces were

not reduced.

When the laser was leading the cutting tool the laser spot was directed onto the

unmachined surface with a small proportion hitting the chamfer and the machined

surface. This is the ideal position to ensure that the majority of energy added by the

laser heats the shear zone. When the laser spot is aligned with the centre of the cutting

tool half the spot is over the chamfer. The laser beam hits the chamfer at a different

angle of incidence, which contributes to more of the energy being reflected away from

the workpiece. Heating too much of the chamfer allows heat to dissipate into the

machined section of the workpiece easier. This is demonstrated in the fact that when

the laser spot was in position A and B it was more difficult to determine when the laser

Page 105

was turned on when looking at the force sensor output. The majority of heat was not

directed at the shear zone and force changes were smaller and more difficult to detect.

7.4.2 Laser Parameters For ideal laser assisted machining the depth of heat penetration needs to be similar to

the depth of cut without allowing time for the surface temperature to drop rapidly and

cause surface hardening. To do this a high power density is required. Results in Figure

6-13 and Figure 6-14 show that the best power density to reduce both cutting and feed

forces is approximately 896W/mm2. The reduction in forces generally increased with

increasing power density. However, there is not a large reduction in forces when the

power density increases from 620W/mm2 to 896W/mm2.

Either increasing the laser spot power or reducing the laser spot size can increase the

power density. Both these parameters are limited by the constraints of the laser and

delivery fibres.

0

100

200

300

400

500

600

700

800

0 0.5 1 1.5 2 2.5 3

Depth (mm)

Tem

pera

ture

(°C

)

1.5mm Spot 1.38kW 1.9mm Spot 2.3kW

Figure 7-4. Surface temperature vs Depth – for two different spot diameters and the same power density of 1564W/mm2.

Thermal model results found that equal power densities do not give equal temperature

distributions as shown in Figure 7-4. It shows that increasing the spot size and the laser

Page 106

power gives a higher surface temperature but it has a similar maximum depth of heat

penetration reducing to ambient temperature at approximately 1.5mm. Therefore, to

increase the surface temperature and the power density it is best to increase the laser

power rather than reduce the spot size.

7.4.3 Machining Parameters Speed One method of increasing the depth of heat penetration is to slow the cutting speed

down. The cutting speed in this study is approximately 729±100mm/sec compared to a

maximum speed of 0.5mm/sec used by Rozzi and Pfefferkorn et al. [4] when laser

assisted machining of Silicon Nitride. Model results show that slowing the speed from

729mm/sec to 100mm/sec gave a 2.5mm increase in the depth of heat penetration

25mm from the laser spot (Figure 6-30). It also shows that a small reduction in cutting

speed from 850mm/sec to 729mm/sec produces little difference in the surface

temperature but has a large effect on the depth of heat penetration. A large reduction in

cutting speed however, would not be economical due to the increase in machining time.

The cost of a small increase in machining time would need to be weighed up against the

cost saving generated by the reduction in turning forces to find the optimum cutting

speed.

Depth of cut and feed rate In secondary experiments when the laser spot was leading the cutting tool the depth of

cut was kept constant. For this reason the effect of depth of cut on the force reduction

cannot be compared. Preliminary experiments showed that when the depth of cut was

shallow the CBN tool scraped along the surface rather than cut the material. It is a

characteristic of CBN tools that they do not cut shallow depths of cut well because the

reduction in forces ensures the temperature within the shear zone does not reach the

900°C range that is required for efficient cutting.

Preliminary experiments also showed that increasing the depth of cut increased the

cutting and feed forces. It is expected that this would also occur when the laser-tool

distance is reduced as in secondary experiments. As the depth of cut increases, the

depth of heat penetration due to the laser remains the same, therefore the average

temperature in the shear zone would be lower and hence the cutting forces would

increase.

Page 107

7.5 TOOLING

The reduction in turning forces obtained during laser assisted machining opens up the

possibility of alternative cutting tools employed rather than CBN tools. The reduction

of yield stress may mean that tool with a lower hardness such as ceramic or carbide

tools can be used to cut high chromium white cast iron. CBN tools have a very high hot

hardness meaning that they maintain a high hardness at high temperatures. Further

experimentation is needed to determine if ceramic or carbide tools maintain their

hardness at the temperatures experienced in laser assisted machining. Ng and

Aspinwall [19] found that when the thermal conductivity of the cutting tool was reduced

the temperature in the primary shear zone increased. This is because the tool with the

higher thermal conductivity channelled the heat away from the primary shear zone.

7.6 MATERIAL REMOVAL RATE

Material removal rate is a function of depth of cut, cutting speed and feed rate. As

mentioned in Section 7.4.3, increasing the cutting speed results in a smaller depth of

heat penetration. Therefore, it is more beneficial to reduce cutting speeds, however, this

will reduce the material removal rate. The effect of depth of cut and feed rate on

turning forces during laser assisted machining needs to be investigated further before

any material removal calculations can be made.

Results from preliminary experiments indicate that increasing the laser power causes the

cutting tool to dig in deeper and remove more material. It is also possible that

increasing laser power caused an increase in expansion of the workpiece. However, this

would result in a shallower surface profile step not a deeper one. Increasing the laser

power would result in reduced shear stresses and so reduced forces, which reduced the

flexing of the lathe causing the tool to take a deeper cut. This phenomenon would not

be as prevalent when machining on a stronger more rigid lathe.

7.7 LIMITATIONS OF THE STUDY

In industry the lathes used are large industrial lathes able to machine hard white cast

irons relatively easily. Due to space and financial restrictions the lathe used during

these experiments was not able to easily machine the large sample parts. The lack of

Page 108

rigidity and strength meant that at high speeds chattering would occur and at large

depths of cut the motor was unable to cope with the large forces and the cutting would

stop.

Although the results obtained are not achieved under the same operating conditions as

those used in industry, they are still an indication of the feasibility of laser assisted

machining of high chromium white cast iron.

Chatter was also a problem when a new tool edge was used. It was not until the tool

had some wear that it would cut the material properly. Therefore it was difficult to

measure and compare tool wear progression.

The fact that it was not possible to use a new tool edge for each cut also means that tool

wear will contribute to the forces recorded. Therefore it is difficult to compare hard

turning experiments with laser assisted machining experiments. That is why in the

modified experiments a laser assisted machining run was always followed by a hard

turning run. The tool wears during each cut, and so even comparing these results can be

questionable. Therefore, in all results the comparison between hard turning and laser

assisted machining is made between the initial part of the cut before the laser is turned

on and the second part of the cut after the laser has started. This gives the best

comparison of forces under the circumstances available.

A pyrometer was used to measure the surface temperature during the preliminary

experiments. However it was discovered that the vibrations of the lathe might have

caused the lens to move giving discrepancy in results. It was also difficult and costly to

modify the laser optics to accommodate the pyrometer. Therefore the pyrometer was

not used during the secondary experiments.

The high chromium white cast iron workpieces supplied by Weir Warman Ltd. had the

same composition, however, there was noticeable differences in hardness between

samples. All secondary experiments were conducted on the same workpiece to reduce

the errors involved.

Due to space restrictions a new force sensor had to be purchased for the project. The

sensor was small enough to fit in the space required, however, it was a dynamic sensor

measuring the change in force not the actual force. This made the measurement of the

Page 109

forces difficult, as the changes in turning forces due to hard spots in the workpiece were

often larger than the change in force due to the laser.

The thermal model assumes an infinite flat surface with a moving gaussian heat source,

however, in reality the workpiece is not flat. The chamfer created by the cutting tool is

in close proximity to the heat source as shown in Figure 7-5. This would restrict the

diffusion of heat into the bulk of the workpiece in that direction creating a build up of

heat along the edge of the chamfer. This means that the temperature within the

workpiece would most likely be slightly higher than predicted. This buildup of heat

was visible as a dark line along the edge of the chamfer during experiments, which was

removed by the cutting process.

Figure 7-5. Position of laser beam and chamfer.

For the majority of modelling the cutting speed was kept constant at 729mm/sec, that

was also the minimum speed used. Results show that increasing the cutting speed gives

a small reduction in temperature but a large reduction in the depth of heat penetration.

Therefore the depth of heat penetration and surface temperature would be slightly less

than that predicted for most secondary experiments. This has little impact on the final

results as the purpose of the model was to obtain information about how the temperature

changed with various cutting and laser parameters.

Page 110

Chapter 8

CONCLUSION AND RECOMMENDATIONS

8.1 MAJOR CONCLUSIONS

The objective of this study was to investigate and determine if laser assisted machining

of AS2027 high chromium white cast iron is a feasible alternative to current machining

methods and to determine the operating parameters where laser assisted machining of

high chromium white cast iron results in a reduction in turning forces. The following

major conclusions and observations are drawn from the thesis:

• With the right parameters laser assisted machining does reduce the cutting and

feed forces. Results have shown that the heat added by the laser is increasing

the temperature within the shear zone which reduces the yield strength and

hence the cutting and feed forces. Increasing the power density increases the

surface temperature, which increases the reduction in forces. To increase the

power density it is more beneficial to increase the laser power rather than reduce

the laser spot size. The same power density does not result in the same

temperature profile over depth.

• The distance between the laser spot and the cutting tool is a crucial factor in

reducing forces. If the distance is too large (eg.110mm), the force actually

increases rather than decrease. This is attributed to the high initial surface

temperature followed by rapid cooling which results in surface hardening. The

larger the distance between the cutting tool and the laser, the greater the depth of

heat penetration, however, the hardening of the surface overrides any benefit in

increasing the temperature near the tool tip.

• The fact that the laser is reducing the yield strength is evidenced in the chips

collected during laser assisted machining. They show that when compared to

chips from hard turning they did not shear as cleanly indicating greater plastic

flow.

Page 111

• The axial position of the laser with respect to the cutting tool and the chamfer is

also important in maximizing the reduction in forces. The laser spot should be

positioned so that it is leading the tool and the majority of it is hitting the

unmachined surface not the chamfer or machined surface.

• A reduction in turning forces was obtained using the following parameters:

729-850mm/sec cutting speed

195-896W/mm2 power density (500-1785W power and 1.5-3mm laser spot)

1.2-1.6mm depth of cut

0.256 mm/rev feed rate

The results obtained indicate that laser assisted machining of high chromium white cast

iron does reduce turning forces and therefore shows potential to be a feasible alternative

to hard turning. However, further investigation is needed to determine if it is an

economical alternative before it can be introduced into industry.

8.2 RECOMMENDATIONS FOR FURTHER RESEARCH

The limitations of the equipment used in this study placed several constraints on the

parameters used in experiments. It is for this reason that further investigation is needed

into the effect of laser assisted machining before it can be successfully implemented in

industry.

In industry the cutting speed is typically 90m/min which is almost twice the speed used

in this study (50m/min). At these speeds the depth of heat penetration would be

drastically reduced. Combining this with the increased depth of cut in industry and

there will be a significant difference in the temperature profile within the shear zone.

Higher surface temperatures will be obtained however the depth of heat penetration due

to the laser will not reach the depth of cut. This may have a significant impact on the

force reduction results obtained which needs to be investigated. Increasing the laser

power will increase the depth of heat penetration, as would reducing the cutting speed.

However, as mentioned above slowing the cutting speed down is undesirable as it

increases machining time. Also, there is a limit to how high the laser power can be

Page 112

increased. It may be necessary to purchase a higher power laser, which is more

expensive. This is definitely one area, which needs further investigation.

When introducing a laser into the workplace safety must be a primary concern. The

beam from the Nd:YAG laser is harmful to the naked eye so appropriate shielding is

needed around any machines using this type of laser. Also, laser reflections off the

workpiece surface can be hazardous as discovered during this study. Machined surfaces

are quite reflective and the laser beam could be reflected onto the surrounding

machinery or operators. During this study the distance between the laser and the tool

was restricted to greater than 22mm due to the reflection of the laser beam. When this

distance was reduced the laser beam was reflected towards the operator or back onto the

lens on the end of the optical fiber. Therefore these issues must be considered for each

individual application.

There are many opportunities for further research into laser assisted machining of high

chromium white cast iron.

Further investigation of laser assisted machining is needed before it can be introduced to

industry as an alternative to hard machining. Research is needed to determine the effect

of faster cutting speeds and deeper depths of cut on the turning forces. To do this

appropriate machinery is needed including a high power industrial lathe with high

rigidity, a more appropriate force sensor that does not have a decaying signal and

workpieces with a more uniform hardness and consistency.

Investigation into the effect of laser assisted machining on CBN tool wear as well as the

possibility of using alternative tool material is also critical before laser assisted

machining can be implemented into industrial application. Once this data is available a

full economical analysis of laser assisted machining of high chromium white cast iron

can be undertaken.

Page 113

REFERENCES

[1] Chryssolouris, G., Anifantis, N., and Karagiannis, S., "Laser assisted

machining: an overview", Journal of Manufacturing Science & Engineering,

Transactions of the ASME, Vol. 119, Iss. 4(B), 1997, p.766-769

[2] Weir Warman Ltd, viewed on 3 July. 2002, http://www.warman.com.au

[3] König, W. and Zaboklicki, A. K., "Laser-assisted hot machining of ceramics

and composite materials", NIST Special Publication 847. Proceedings of the

International Conference on Machining of Advanced Materials. Vol. 847, 1993,

p.455-463

[4] Rozzi, J. C. , Pfefferkorn, F. E., Shin, Y. C., and Incropera, F. P.,

"Experimental Evaluation of the Laser Assisted Machining of Silicon Nitride

Ceramics.", Journal of Manufacturing Science & Engineering, Transactions of

the ASME, Vol. 122, Iss. 4, 2000, p.666-670

[5] Ben Salem, W., Marot, G., Moisan, A., and Longuemard, J. P., "Laser Assisted

Turning during Finishing Operation Applied to Hardened Steels and Inconel

718", Laser Assisted Net Shape Engineering. Proceedings of the LANE'94, Vol.

1, 1994, p.455-464

[6] Jau, B. M., Copley, S. M., and Bass, M., "Laser Assisted Machining",

Manufacturing Engineering Transactions, 1981, p.12-15

[7] König, W. and Zaboklicki, A. K., "Laser-Assisted Hot Machining Processes:

Technological Potentials", Laser Assisted Net Shape Engineering. Proceedings

of the LANE'94, Vol. 1, 1994, p.389-404

[8] Wang, Y., Yang, L. J., and Wang, N. J., "An investigation of laser-assisted

machining of Al2O3 particle reinforced aluminum matrix composite", Journal

of Materials Processing Technology, Vol. 129, Iss. 1-3, 2002, p.268-272

Page 114

[9] Dolman, K. F., Private conversation, Chief Development Metallurgist, Weir

Warman Ltd., 29 Sept. 2002

[10] Yescas-Gonzalez, M. A. and Bhadeshia, H. K. D. H., University of Cambridge,

2001, viewed on 4 Sept. 2002

http://www.msm.cam.ac.uk/phase-trans/2001/adi/cast.iron.html

[11] Tabrett, C. P., Sare, I. R., and Ghomashchi, M. R., "Microstructure-property

relationships in high chromium white cast iron alloys", International Materials

Reviews, Vol. 41, Iss. 2, 1996, p.59-82

[12] Weir Warman Ltd. and Emms, Sarah, "Metallography Sheet", 2002

[13] Bedolla Jacuinde, A. and Rainforth, W. M., "The wear behaviour of high-

chromium white cast irons as a function of silicon and Mischmetal content",

Wear, Vol. 250, Iss. 1-12, 2001, p.449-461

[14] Chou, Y. K. , Evans, C. J., and Barash, M. M., "Experimental investigation on

CBN turning of hardened AISI 52100 steel", Journal of Materials Processing

Technology, Vol. 124, Iss. 3, 2002, p.274-283

[15] Lin, Z. C. and Chen, D. Y., "A study of cutting with a CBN tool", Journal of

Materials Processing Technology, Vol. 49, Iss. 1-2, 1995, p.149-164

[16] Wells, P., O'Loughlin, W., Hinckley, B., and Emms, S., Private conversation,

Weir Warman Ltd., 9 Mar. 2004

[17] Albert, M., "Taking the Fear out of Hard Turning", Modern Machine Shop, Vol.

68, Iss. 11, 1996, p.102-105

[18] Notter, A. T. and Heath, P. J., 'The Selection of Machining Parameters Using

Amborite', Ultrahard Materials in Industry machining with Amborite, De Beers

Industrial Diamond Division, London, 1985,

[19] Ng, E., Aspinwall, D. K., Brazil, D., and Monaghan, J., "Modelling of

temperature and forces when orthogonally machining hardened steel",

International Journal of Machine Tools and Manufacture, Vol. 39, Iss. 6, 1999,

Page 115

p.885-903

[20] Emms, Sarah, personal email, 29 July 2002

[21] Ng, E. and Aspinwall, D. K., "The Effect of Workpiece Hardness and Cutting

Speed on the Machinability of", Journal of Manufacturing Science and

Engineering [H.W. Wilson - AST], Vol. 124, Iss. 3, 2002, p.588

[22] Broskea, T. J., "Analyzing PcBN tool wear", Modern Machine Shop, Vol. 73,

Iss. 8, 2001, p.86

[23] Nakayama, K., Arai, M., and Kanda, T., "Machining Characteristics of Hard

Materials", CIRP Annals., Vol. 37, Iss. 1, 1988, p.89-92

[24] König, W., Komanduri, R., Tönshoff, H. K., and Ackershott, G., "Machining of

hard materials", CIRP Annals, Vol. 33, Iss. 2, 1984, p.417-427

[25] Lei, S., Shin, Y. C., and Incropera, F. P., "Experimental Investigation of

Thermo-Mechanical Characteristics in Laser-Assisted Machining of Silicon

Nitride Ceramics", Journal of Manufacturing Science & Engineering,

Transactions of the ASME, Vol. 123, Iss. 4, 2001, p.639

[26] Ng, E. and Aspinwall, D. K., "Evaluation of cutting force and temperature when

turning hardened die steel with AMBORITE AMB90 and DBC50 tooling",

Industrial Diamond review, Iss. 3, 1999, p.183-195

[27] Ozler, L., Inan, A., and Ozel, C., "Theoretical and experimental determination

of tool life in hot machining of austenitic manganese steel", International

Journal of Machine Tools & Manufacture, Vol. 41, Iss. 2, 2001, p.163-172

[28] Madhavulu, G. and Ahmed, B., "Hot machining process for improved metal

removal rates in turning operations", Journal of Materials Processing

Technology, Vol. 44, Iss. 3-4, 1994, p.199-206

[29] Barrow, G., "Machining of High Strength Materials at Elevated Temperatures

using Electric Current Heating", CIRP Annals., Vol. 14, 1966, p.145-151

[30] Migliore, L, Laser Materials Processing, Marcel Dekker, Inc, New York, 1996

Page 116

[31] Emmelmann, C (Ed.), Introduction to Laser Materials Processing, Rofin Sinar

Laser, 1998

[32] Narutaki, N. and Yamane, Y., "Tool wear and cutting temperature of CBN tools

in machining of hardened steels", CIRP Annals, Vol. 28, Iss. 1, 1979, p.23-28

[33] Kalpakjian, S., Manufacturing Engineering and Technology, Addison Wesley

Publishing Company, Inc, USA, 1989

[34] Jau, B. M., "Laser Assisted Machining of Hard to Machine Materials",

University of Southern California, California, USA, 1981

[35] Ma, L., Wang, Y., Xie, D., Yang, L., and Liu, X., "Laser assisted hot machining

of cold-hard cast iron", Harbin Gongye Daxue Xuebao/Journal of Harbin

Institute of Technology, Vol. 34, Iss. 2, 2002, p.228-231

[36] Rozzi, J. C., Pfefferkorn, F. E., Incropera, F. P., and Shin, Y. C., "Transient,

three-dimensional heat transfer model for the laser assisted machining of silicon

nitride: i. Comparison of predictions with measured surface temperature

histories", International Journal of Heat & Mass Transfer, Vol. 43, Iss. 8, 2000,

p.1409-1424

[37] Seco Tools, Secomax PCBN Technical Guide, Seco Tools AB, Sweden, 2003

[38] ASM, ASM Metals Reference Book, American society for metals, Metals Park,

Ohio, 44073, 1983

[39] ASM, Metals Handbook, Desk Edition, ASM International, Materials Park, Ohio

44073, 1998

[40] Hinckley, Brook, "A05 Thermal conductivity", Weir Warman Ltd., 2004

[41] Hinckley, Brook, personal email, 15 Mar. 2004

Page 117

APPENDICES

Page 118

Appendix A

FORCE SENSOR CALIBRATION CURVES

y = 31.489x

0

100

200

300

400

500

600

0 2 4 6 8 10 12 14 16

Mass (kg)

Volta

ge (m

V)

Figure A-1. Force sensor calibration curve for cutting force in preliminary experiment set up.

y = 8.6531x

0

20

40

60

80

100

120

140

160

0 2 4 6 8 10 12 14 16

Mass (kg)

Volta

ge (m

V)

Figure A-2. Force sensor calibration curve for feed force in preliminary experiment set up.

Page 119

y = 0.0057x

0

0.02

0.04

0.06

0.08

0.1

0.12

0 2 4 6 8 10 12 14 16 18

Mass (kg)

Volta

ge c

hang

e (V

)

Z axis Linear (Z axis)

Figure A-3. Force sensor calibration curve for cutting force in secondary experiment set up.

y = 0.0073x

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0 2 4 6 8 10 12 14 16 18

Mass (kg)

Volta

ge c

hang

e (V

)

X axis Linear (X axis)

Figure A-4. Force sensor calibration curve for feed force in secondary experiment set up.

These curves were generated by applying known forces to each axis of the force sensor

and measuring the resultant voltage change with an oscilloscope.

Page 120

Appendix B

MODEL VALIDATION RESULTS

Table B-1. Results of model validation experiments.

Material Warman A05 Lens 200mm Initial material temperature 20 Diameter 180.50mm Program clad rotary1 Laser Nd:YAG Pyrometer 500-1500C Fibre 10m with bending cube

Temp. - recorded by pyrometer averaged over

each revolution

Temp. – predicted by the model with various absorption factors

Run Preset laser power (W)

Laser power (W)

Lens position

(mm) Laser Spot size (mm)

Speed (m/min) Rev’s

feed (mm/rev)

Speed (mm/sec) 1sr rev 2nd rev 3rd rev Abs.=1 Abs.=0.9 Abs.=0.8 Abs.=0.7

4 1000 852 217 4.6 9.937 3 0 166 1056 857 850 1063.3 1002.3 890.9 779.6 3 1000 852 217 4.6 10 3 0 167 1049 862 864 1063.3 1002.3 890.9 779.6 1 1300 1000 217 4.6 9.937 3 0 166 1079 1363 1476 1307.1 1176.4 1045.7 915.0 2 1300 1000 217 4.6 10 3 0 167 1095 1382 1473 1307.1 1176.4 1045.7 915.0 5 1300 1000 217 4.6 10 3 0.25 167 1082 1330 1461 1307.1 1176.4 1045.7 915.0 6 1300 1000 217 4.6 10 3 0.5 167 1088 1291 1405 1307.1 1176.4 1045.7 915.0

10 1000 852 217 4.6 5.062 3 1.5 84 945 943 947 1700.5 1530.4 1360.4 1190.3 9 1300 1000 217 4.6 5.062 3 1.5 84 1482 1253 1017 1995.1 1796.3 1596.7 1397.1

11 1000 852 217 4.6 7.5 3 1.5 125 806 800 813 1334.4 1200.9 1067.5 934.1 12 1000 852 217 4.6 9.937 3 1.5 166 751 751 773 1063.3 1002.3 890.9 779.6 13 1000 852 217 4.6 9.937 3 1.5 166 911 830 834 1063.3 1002.3 890.9 779.6 8 1300 1000 217 4.6 9.937 3 1.5 166 947 952 975 1307.1 1176.4 1045.7 915.0 7 1300 1000 217 4.6 10 3 1.5 167 961 957 978 1307.1 1176.4 1045.7 915.0

Page 121

Appendix C

EXAMPLES OF THERMAL MODEL OUTPUT FILES

Table C-1. Example of thermal model output file for temperature variation with depth below a given surface

point.

Gaussian Heat Source General three parameter distribution centered on the origin

Compute isotherms through a given point for a series of time values

SERIAL : Thermal conductivity = 30 SI

Thermal diffusivity = 4.4E-06 SI

Laser diameter = 1.5 mm Laser power = 0.92 kW

Laser Absorption coefft = 0.53 Laser is continuous and is not pulsed

Velocity components (mm/sec) U = 729 V = 0 W = 0

Scales:

length = 1.50E-03 meter time = 5.11E-01 seconds speed scale = 2.93E-03 meters/second temperature = 2.16E+04 deg

Gaussian function parameters: sigma_x = 0.53 mm sigma_y = 0.53 mm Sigma_z = 0.1 mm

Compute temperature variation with depth below a given surface point. Surface point at 42 mm, 0 mm, 0 mm

Time value = 100 seconds. Depth range: z_min = 0 mm, z_max = 4 mm, delta_z = 0.1

Depth (mm) Temperature (deg) Temp. x2

0 97.5395 195.079 0.1 96.6003 193.2006 0.2 93.8364 187.6728 0.3 89.4048 178.8096 0.4 83.55 167.1 0.5 76.5824 153.1648 0.6 68.8509 137.7018 0.7 60.7141 121.4282 0.8 52.5134 105.0268 0.9 44.5505 89.101 1 37.0714 74.1428

1.1 30.2574 60.5148

Page 122

Table C-2. Example of thermal model output file for temperature variation with depth below a given surface

point continued.

Depth (mm)

Temperature (deg) Temp. x2

1.3 19.0214 38.0428 1.4 14.651 29.302 1.5 11.069 22.138 1.6 8.2029 16.4058 1.7 5.9628 11.9256 1.8 4.2516 8.5032 1.9 2.9737 5.9474 2 2.0401 4.0802

2.1 1.373 2.746 2.2 0.9064 1.8128 2.3 0.587 1.174 2.4 0.3729 0.7458 2.5 0.2324 0.4648 2.6 0.142 0.284 2.7 0.0852 0.1704 2.8 0.0501 0.1002 2.9 0.0289 0.0578 3 0.0145 0.029

3.1 0.0081 0.0162 3.2 0.0044 0.0088 3.3 0.0023 0.0046 3.4 0.0012 0.0024 3.5 0.0006 0.0012 3.6 0.0003 0.0006 3.7 0.0002 0.0004 3.8 0.0001 0.0002 3.9 0 0

*** Steady temperature has been reached ***

Page 123

Table C-3. Example of thermal model output file for the temperature over a set of surface points at a discrete value of time.

Mode_Type[2]. Tabulate temperature at a set of surface points at a discrete value of the

time. Field point x_range: x_min = -2 mm x_max = 25 mm del_x = 1 mm Field point y_range: y_min = -5 mm y_max = 5 mm del_y = 0.5 mm Time step value (seconds): t_min = 3.00, t_max = 3.00, delta = 1 x values (mm) -2 -1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 y values (mm) -5 -4.5 -4 -3.5 -3 -2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 Temperature distribution at time = 3 seconds x y -2 -1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 -5 33 53 74 89 97 96 91 83 77 72 67 64 62 60 58 56 55 54 53 52 52 51 50 50 49 49 48 48

-4.5 52 83 115 139 150 148 139 128 117 109 102 97 92 89 86 84 81 79 78 76 75 73 72 71 70 69 69 68-4 77 124 170 205 221 219 205 187 171 158 147 139 133 127 123 119 115 112 109 107 104 102 100 99 97 95 94 93

-3.5 110 175 242 291 313 309 288 263 239 219 204 192 183 174 168 162 156 152 147 144 140 137 134 131 129 126 124 122-3 149 238 327 393 422 416 387 352 319 292 271 254 241 229 220 211 204 197 191 186 181 176 172 168 164 161 158 155

-2.5 193 307 422 507 544 535 497 450 407 372 344 322 304 289 276 265 255 246 238 231 224 218 213 207 202 198 194 190-2 238 379 521 625 670 658 610 551 497 453 418 391 368 349 333 319 306 295 285 276 268 260 253 246 240 234 229 224

-1.5 280 446 613 735 787 772 715 645 581 529 487 454 427 405 385 368 354 340 328 317 307 298 289 281 274 267 261 255-1 315 502 688 826 884 866 801 722 650 590 543 506 475 450 428 409 391 376 363 350 339 328 318 310 301 293 286 279

-0.5 338 538 738 885 947 927 858 773 694 630 580 540 507 479 455 435 416 400 385 372 359 348 337 328 319 310 302 2950 346 551 756 906 969 949 877 790 710 644 593 551 518 489 465 444 425 408 393 379 366 355 344 334 325 316 308 300

Page 124

Table C-4. Example of thermal model output file for the temperature over a set of surface points at a discrete value of time continued.

x y -2 -1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

0.5 338 538 738 885 947 927 858 773 694 630 580 540 507 479 455 435 416 400 385 372 359 348 337 328 319 310 302 2951 315 502 688 826 884 866 801 722 650 590 543 506 475 450 428 409 391 376 363 350 339 328 318 310 301 293 286 279

1.5 280 446 613 735 787 772 715 645 581 529 487 454 427 405 385 368 354 340 328 317 307 298 289 281 274 267 261 2552 238 379 521 625 670 658 610 551 497 453 418 391 368 349 333 319 306 295 285 276 268 260 253 246 240 234 229 224

2.5 193 307 422 507 544 535 497 450 407 372 344 322 304 289 276 265 255 246 238 231 224 218 213 207 202 198 194 1903 149 238 327 393 422 416 387 352 319 292 271 254 241 229 220 211 204 197 191 186 181 176 172 168 164 161 158 155

3.5 110 175 242 291 313 309 288 263 239 219 204 192 183 174 168 162 156 152 147 144 140 137 134 131 129 126 124 1224 77 124 170 205 221 219 205 187 171 158 147 139 133 127 123 119 115 112 109 107 104 102 100 99 97 95 94 93

4.5 52 83 115 139 150 148 139 128 117 109 102 97 92 89 86 84 81 79 78 76 75 73 72 71 70 69 69 68 5 33 53 74 89 97 96 91 83 77 72 67 64 62 60 58 56 55 54 53 52 52 51 50 50 49 49 48 48

Page 125

Appendix D

ABSORPTION CALCULATIONS FOR THERMAL MODEL

Table D-1. Absorption calculation table.

POWER = 852W CONDUCTIVITY = 30 Predicted temperature (°C) when Absorption = 1 Predicted temperature (°C) when

Absorption = 0.53 Diffusivity 4.8E-06 4.4E-06 4.4E-06 4.4E-06 4.1E-06 Error 4.8E-06 4.4E-06 4.1E-06 Error

Temp change (°C) Speed

(mm/sec)

Temperaure (°C) measured by pyrometer Sigma 1.467 1.467 1.63 1.793 1.793 + - 1.467 1.63 1.793 + -

84.3 945 2360.5 2241.6 1940.7 1702.8 1635.8 419.8 304.9 1260.5 1038.0 876.4 222.5 161.6 125 806 1861.3 1764.0 1530.7 1345.8 1291.0 330.7 239.6 995.9 820.6 693.6 175.3 127.0 166 751 1559.6 1475.7 1283.1 1130.1 1082.9 276.5 200.1 836.0 689.4 583.4 146.5 106.1 Diffusivity 4.8E-06 4.4E-06 4.4E-06 4.4E-06 4.1E-06

Speed (mm/sec)

Temperaure (°C) measured by pyrometer Sigma 1.467 1.467 1.63 1.793 1.793

84.3 945 0.40 0.42 0.49 0.55 0.58 125 806 0.43 0.46 0.53 0.60 0.62

Absorption Estimates (measured

temp/predicted temp) 166 751 0.48 0.51 0.59 0.66 0.69

Total average absorption Average Absorption 0.44 0.46 0.53 0.61 0.63 0.53

Page 126

Appendix E

HIGH CHROMIUM WHITE CAST IRON THERMAL PROPERTIES

Table E-1. Thermal properties of high chromium white cast iron.

Temp. °C

Cp J/KgK [39]

k W/mK

[41]

ν m2/s

Temp. °C

Cp J/KgK [39]

k W/mK

[41]

ν m2/s

Temp. °C

Cp J/KgK [39]

k W/mK

[41]

ν m2/s

20 514.6 13.75 3.6E-06 500 722 21 3.9E-06 960 894 30.2 4.6E-06110 579 15.2 3.5E-06 510 728 21.3 4.0E-06 970 914 30.5 4.5E-06130 584 15.6 3.6E-06 530 744 21.8 4.0E-06 980 933 30.8 4.5E-06180 617 16.3 3.6E-06 540 745 22.1 4.0E-06 990 944 28.1 4.0E-06190 622 16.5 3.6E-06 550 750 22.3 4.0E-06 1010 969 31.5 4.4E-06200 622 16.7 3.6E-06 560 756 22.6 4.0E-06 1020 978 31.6 4.4E-06210 633 16.8 3.6E-06 570 761 22.9 4.1E-06 1030 989 31.7 4.3E-06220 633 17 3.6E-06 580 767 23.2 4.1E-06 1040 1000 31.7 4.3E-06230 644 17.1 3.6E-06 590 772 23.5 4.1E-06 1050 1017 31.73 4.2E-06240 644 17.3 3.6E-06 600 780 23.74 4.1E-06 1060 1033 31.8 4.2E-06260 644 17.6 3.7E-06 610 783 24 4.1E-06 1080 1059 31.9 4.1E-06270 656 17.8 3.7E-06 640 811 24.8 4.1E-06 1090 1078 31.9 4.0E-06280 656 17.9 3.7E-06 650 822 25.1 4.1E-06 1100 1086 32 4.0E-06290 656 18 3.7E-06 670 844 25.6 4.1E-06 1110 1105 32.1 3.9E-06300 661 18.3 3.7E-06 680 850 25.9 4.1E-06 1120 1119 32.2 3.9E-06310 667 18.4 3.7E-06 700 867 26.4 4.1E-06 1130 1133 32.3 3.9E-06330 667 18.7 3.8E-06 710 889 26.8 4.1E-06 1160 1175 32.6 3.7E-06340 667 18.9 3.8E-06 730 944 27.6 4.0E-06 1170 1189 32.7 3.7E-06350 667 19.1 3.9E-06 750 955 28.7 4.1E-06 1180 1203 32.8 3.7E-06360 678 19.2 3.8E-06 760 711 28.8 5.5E-06 1190 1217 32.9 3.7E-06370 683 19.4 3.8E-06 770 711 29.2 5.5E-06 1200 1231 33 3.6E-06380 683 19.5 3.9E-06 780 711 30 5.7E-06 1210 1245 32.9 3.6E-06390 689 19.7 3.9E-06 800 711 30.339 5.8E-06 1220 1259 32.7 3.5E-06400 690 19.8 3.9E-06 820 717 29.9 5.6E-06 1240 1287 32.4 3.4E-06410 693 19.9 3.9E-06 830 733 29.7 5.5E-06 1260 1315 32.1 3.3E-06420 694 20.1 3.9E-06 860 767 29.1 5.1E-06 1380 1483 31.7 2.9E-06430 700 20.2 3.9E-06 880 788 28.7 4.9E-06 1400 1511 31.748 2.8E-06440 706 20.3 3.9E-06 900 800 28.26 4.8E-06 1410 1525 31.8 2.8E-06450 711 20.4 3.9E-06 910 822 28.6 4.7E-06 1430 1553 31.9 2.8E-06460 711 20.5 3.9E-06 920 839 28.9 4.7E-06 1440 1567 31.9 2.8E-06470 711 20.7 3.9E-06 930 855 29.2 4.6E-06 1470 1609 32 2.7E-06480 711 20.8 4.0E-06 940 872 29.5 4.6E-06 1480 1623 32 2.7E-06490 717 20.9 3.9E-06 950 877 29.9 4.6E-06 1490 1637 32.0 2.6E-06

Page 127

Appendix F

THERMAL MODEL ITERATIONS AND RESULTS

Table F-1. Thermal model iterations.

Model Name Cond. Diff.

Laser Spot size

(mm)

Laser Power

(W) Absorp. Speed

(mm/sec) Sigma

X Distance

(mm) Temp. (°C)

26Oct test1 30 0.0000044 1.5 1100 0.53 729 0.530 42 468 20.7 0.0000039 1.5 1100 0.53 729 0.53 42 332 18.7 0.0000039 1.5 1100 0.53 729 0.530 42 366 19.4 0.0000038 1.5 1100 0.53 729 0.53 42 352 19.1 0.0000039 1.5 1100 0.53 729 0.530 42 358

22dec test2 19.2 0.0000038 1.5 1100 0.53 729 0.53 42 356 3Nov test1 30 0.0000044 1.5 917 0.53 729 0.53 42 0

19.7 0.0000039 1.5 917 0.53 729 0.53 42 290 18 0.0000037 1.5 917 0.53 729 0.53 42 314

22dec test3 18.4 0.0000037 1.5 917 0.53 729 0.53 42 308 3Nov test5 30 0.0000044 1.5 917 0.53 754 0.53 42 388

19.7 0.0000039 1.5 917 0.53 754 0.53 42 288 18 0.0000037 1.5 917 0.53 754 0.53 42 312

22dec test4 18.4 0.0000037 1.5 917 0.53 754 0.53 42 306 3Nov test9 30 0.0000044 1.5 517 0.53 729 0.53 42 220

17 0.0000036 1.5 517 0.53 729 0.53 42 186 22dec test5 16.5 0.0000036 1.5 517 0.53 729 0.53 42 192 3Nov test13 30 0.0000044 1.5 1380 0.53 729 0.53 42 587

23.5 0.0000041 1.5 1380 0.53 729 0.53 42 370 19.4 0.0000038 1.5 1380 0.53 729 0.53 42 442 20.3 0.0000039 1.5 1380 0.53 729 0.53 42 424 20.1 0.0000039 1.5 1380 0.53 729 0.53 42 428

22dec test6 20.2 0.0000039 1.5 1380 0.53 729 0.53 42 426 4Nov test1 30 0.0000044 1.5 1100 0.53 729 0.530 25 701

26.4 0.0000041 1.5 1100 0.53 729 0.530 25 390 19.7 0.0000039 1.5 1100 0.53 729 0.530 25 516 21.5 0.000004 1.5 1100 0.53 729 0.530 25 476 20.8 0.000004 1.5 1100 0.53 729 0.530 25 492

22dec test7 20.9 0.0000039 1.5 1100 0.53 729 0.530 25 488 4Nov test7 22.3 0.000004 1.5 917 0.53 729 0.53 25 767

29.5 0.0000055 1.5 917 0.53 729 0.53 25 314 18.4 0.0000037 1.5 917 0.53 729 0.53 25 454 20.4 0.0000039 1.5 917 0.53 729 0.53 25 416

22dec test8 20.1 0.0000039 1.5 917 0.53 729 0.53 25 422

Page 128

Table F-1. Thermal model iterations continued.

Model Name Cond. Diff.

Laser Spot size

(mm)

Laser Power

(W) Absorp. Speed

(mm/sec) Sigma

X Distance

(mm) Temp. (°C)

4Nov test11 20 0.0000039 1.5 517 0.53 729 0.53 25 479 20.8 0.000004 1.5 517 0.53 729 0.53 25 232 17.1 0.0000036 1.5 517 0.53 729 0.53 25 274 17.8 0.0000037 1.5 517 0.53 729 0.53 25 264 17.6 0.0000037 1.5 517 0.53 729 0.53 25 268 17.8 0.0000037 1.5 517 0.53 729 0.53 25 264

22dec test9 17.7 0.0000037 1.5 517 0.53 729 0.53 25 266 4Nov test14 20.9 0.0000039 1.5 1380 0.53 729 0.53 42 1222

32.7 0.0000035 1.5 1380 0.53 729 0.53 42 258 17.6 0.0000037 1.5 1380 0.53 729 0.53 42 484 20.8 0.000004 1.5 1380 0.53 729 0.53 42 416 20 0.0000039 1.5 1380 0.53 729 0.53 42 430

22dec test10 20.2 0.0000039 1.5 1380 0.53 729 0.53 42 426 26dec test1 20.9 0.0000039 1.5 1380 0.53 729 0.53 25 612

24 0.0000041 1.5 1380 0.53 729 0.53 25 540 22.1 0.000004 1.5 1380 0.53 729 0.53 25 582 23.2 0.0000041 1.5 1380 0.53 729 0.53 25 558 22.6 0.000004 1.5 1380 0.53 729 0.53 25 570

26dec test1 22.9 0.0000041 1.5 1380 0.53 729 0.53 25 566 3jan test1 30 0.0000044 3 517 0.53 729 1.06 25 105

15.2 0.0000034 3 517 0.53 729 1.06 25 186 16.5 0.0000036 3 517 0.53 729 1.06 25 176

3jan test1 16.3 0.0000036 3 517 0.53 729 1.06 25 178 3jan test2 30 0.0000044 3 917 0.53 729 1.06 25 187

16.5 0.0000036 3 917 0.53 729 1.06 25 312 18.4 0.0000037 3 917 0.53 729 1.06 25 284 17.9 0.0000037 3 917 0.53 729 1.06 25 292

3jan test2 18 0.0000037 3 917 0.53 729 1.06 25 290 4jan test1 30 0.0000044 3 1100 0.53 729 1.06 25 224

17 0.0000036 3 1100 0.53 729 1.06 25 364 19.2 0.0000038 3 1100 0.53 729 1.06 25 330 18.7 0.0000038 3 1100 0.53 729 1.06 25 338

4jan test1 18.9 0.0000038 3 1100 0.53 729 1.06 25 334 4jan test2 30 0.0000044 3 1380 0.53 729 1.06 25 282

17.9 0.0000037 3 1380 0.53 729 1.06 25 438 20.3 0.0000039 3 1380 0.53 729 1.06 25 396 19.8 0.0000039 3 1380 0.53 729 1.06 25 406 19.9 0.0000039 3 1380 0.53 729 1.06 25 404

4jan test3 30 0.0000044 1.5 1380 0.53 729 0.53 0 1468 32 0.0000027 1.5 1380 0.53 729 0.53 0 896 28.3 0.0000048 1.5 1380 0.53 729 0.53 0 1676 32.8 0.0000037 1.5 1380 0.53 729 0.53 0 1158

Page 129

Table F-1. Thermal model iterations continued.

Model Name Cond. Diff.

Laser Spot size

(mm)

Laser Power

(W) Absorp. Speed

(mm/sec) Sigma

X Distance

(mm) Temp. (°C)

4jan test3 32.6 0.0000037 1.5 1380 0.53 729 0.53 0 1162 4jan test4a 32.6 0.0000037 1.5 1380 0.53 729 0.53 0.8 1878

32 0.000002 1.5 1380 0.53 729 0.53 0.8 1162 32 0.0000026 1.5 1380 0.53 729 0.53 0.8 1444 31.9 0.0000028 1.5 1380 0.53 729 0.53 0.8 1538

4jan test4 32 0.0000027 1.5 1380 0.53 729 0.53 0.8 1490 5jan test1 30 0.0000044 3 1380 0.53 729 1.06 0.8 920

28.9 0.0000047 3 1380 0.53 729 1.06 0.8 1002 31.5 0.0000044 3 1380 0.53 729 1.06 0.8 876 28.7 0.0000049 3 1380 0.53 729 1.06 0.8 1042 29.5 0.0000046 3 1380 0.53 729 1.06 0.8 966 30.4 0.0000045 3 1380 0.53 729 1.06 0.8 920 29.2 0.0000046 3 1380 0.53 729 1.06 0.8 976 30.8 0.0000045 3 1380 0.53 729 1.06 0.8 910 28.6 0.0000047 3 1380 0.53 729 1.06 0.8 1012 29.7 0.0000046 3 1380 0.53 729 1.06 0.8 960

5jan test1 29.9 0.0000046 3 1380 0.53 729 1.06 0.8 954 6jan test1 30 0.0000044 1.5 2300 0.53 729 0.53 25.0 732

27.6 0.000004 1.5 2300 0.53 729 0.53 25.0 776 6jan test1 30 0.0000057 1.5 2300 0.53 729 0.53 25.0 780 6jan test2 30 0.0000044 3 2300 0.53 729 1.06 25.0 468

20.7 0.0000039 3 2300 0.53 729 1.06 25.0 646 25.1 0.0000041 3 2300 0.53 729 1.06 25.0 544 22.1 0.000004 3 2300 0.53 729 1.06 25.0 612 24 0.0000041 3 2300 0.53 729 1.06 25.0 570 22.9 0.0000041 3 2300 0.53 729 1.06 25.0 596 23.7 0.0000041 3 2300 0.53 729 1.06 25.0 576 23.2 0.0000041 3 2300 0.53 729 1.06 25.0 588

6jan test2 23.4 0.0000041 3 2300 0.53 729 1.06 25.0 584 6jan test2 30 0.0000044 1.9 2.3 0.53 729 0.68 25 640

24.8 0.0000041 1.9 2.3 0.53 729 0.68 25 756 28.8 0.0000055 1.9 2.3 0.53 729 0.68 25 714 27.6 0.000004 1.9 2.3 0.53 729 0.68 25 674 25.6 0.0000041 1.9 2.3 0.53 729 0.68 25 734 26.4 0.0000041 1.9 2.3 0.53 729 0.68 25 710 26.8 0.0000041 1.9 2.3 0.53 729 0.68 25 700 26.6 0.0000041 1.9 2.3 0.53 729 0.68 25 706

10jan test1 30 0.0000044 1.5 1380 0.53 100 0.53 25 584 23.2 0.0000041 1.5 1380 0.53 100 0.53 25 752 28.7 0.0000041 1.5 1380 0.53 100 0.53 25 608 24 0.0000041 1.5 1380 0.53 100 0.53 25 726 25.6 0.0000041 1.5 1380 0.53 100 0.53 25 682 25.9 0.0000041 1.5 1380 0.53 100 0.53 25 672 25.8 0.0000041 1.5 1380 0.53 100 0.53 25 676

Page 130

Table F-1. Thermal model iterations continued.

Model Name Cond. Diff.

Laser Spot size

(mm)

Laser Power

(W) Absorp. Speed

(mm/sec) Sigma

X Distance

(mm) Temp. (°C)

17jan test1 30 0.0000044 3.1 1781 0.53 729 1.1 110 132 15.6 0.0000036 3.1 1781 0.53 729 1.1 110 240 17.3 0.0000036 3.1 1781 0.53 729 1.1 110 216

17jan test1 17 0.0000036 3.1 1781 0.53 729 1.1 110 220 17jan test2 30 0.0000044 3.1 1781 0.53 729 1.1 25 352

19.1 0.0000039 3.1 1781 0.53 729 1.1 25 526 28.1 0.000004 3.1 1781 0.53 729 1.1 25 362 19.2 0.0000038 3.1 1781 0.53 729 1.1 25 518 20.3 0.0000039 3.1 1781 0.53 729 1.1 25 494 20.9 0.0000039 3.1 1781 0.53 729 1.1 25 480 20.8 0.000004 3.1 1781 0.53 729 1.1 25 488

17jan test2 20.8 0.0000039 3.1 1781 0.53 729 1.1 25 482 17Jan test3 30 0.0000044 3.1 1781 0.53 729 1.1 1.5 1210

32.9 0.0000036 3.1 1781 0.53 729 1.1 1.5 956 30.2 0.0000046 3.1 1781 0.53 729 1.1 1.5 1240 32.4 0.0000034 3.1 1781 0.53 729 1.1 1.5 932 31.9 0.000004 3.1 1781 0.53 729 1.1 1.5 1064 31.8 0.0000042 3.1 1781 0.53 729 1.1 1.5 1106

17jan test3 31.9 0.0000041 3.1 1781 0.53 729 1.1 1.5 1084 20jan test1 32.6 0.0000037 1.5 1.38 0.53 729 0.53 0 20jan test2 32 0.0000027 1.5 1.38 0.53 729 0.53 0.8 20jan test3 22.9 0.0000041 1.5 1.38 0.53 729 0.53 25 20jan test4 20.2 0.0000039 1.5 1.38 0.53 729 0.53 42 20jan test5 30 0.0000044 1.5 1.38 0.53 729 0.53 110 128

15.6 0.0000036 1.5 1.38 0.53 729 0.53 110 240 17.3 0.0000036 1.5 1.38 0.53 729 0.53 110 218 17 0.0000036 1.5 1.38 0.53 729 0.53 110 220

21Feb test1 30 0.0000044 1.5 1100 0.53 850 0.53 25 336 18.9 0.0000038 1.5 1100 0.53 850 0.53 25 512 21.3 0.000004 1.5 1100 0.53 850 0.53 25 460 20.5 0.0000039 1.5 1100 0.53 850 0.53 25 476 20.8 0.000004 1.5 1100 0.53 850 0.53 25 472

21Feb test1 20.7 0.0000039 1.5 1100 0.53 850 0.53 25 470 21Feb test2 30 0.0000044 1.5 1100 0.53 850 0.53 0 1024

31.6 0.0000044 1.5 1100 0.53 850 0.53 0 972 30.5 0.0000045 1.5 1100 0.53 850 0.53 0 1028 31.5 0.0000044 1.5 1100 0.53 850 0.53 0 974 28.1 0.000004 1.5 1100 0.53 850 0.53 0 1006 31 0.0000045 1.5 1100 0.53 850 0.53 0 1010

21Feb test2 31.7 0.0000043 1.5 1100 0.53 850 0.53 0 950 21Feb test3 30 0.0000044 1.5 1100 0.53 850 0.53 42 228

17.1 0.0000036 1.5 1100 0.53 850 0.53 42 382 19.5 0.0000039 1.5 1100 0.53 850 0.53 42 340 18.9 0.0000038 1.5 1100 0.53 850 0.53 42 350

21Feb test3 19.1 0.0000039 1.5 1100 0.53 850 0.53 42 348

Page 131

Table F-1. Thermal model iterations continued.

Model Name Cond. Diff.

Laser Spot size

(mm)

Laser Power

(W) Absorp. Speed

(mm/sec) Sigma

X Distance

(mm) Temp. (°C)

21Feb test4 30 0.0000044 1.5 1100 0.53 729 0.53 0 1170 32.7 0.0000037 1.5 1100 0.53 729 0.53 0 924 28.9 0.0000047 1.5 1100 0.53 729 0.53 0 1284 32 0.000004 1.5 1100 0.53 729 0.53 0 1010 31.5 0.0000044 1.5 1100 0.53 729 0.53 0 1114 32.6 0.0000037 1.5 1100 0.53 729 0.53 0 926 29.2 0.0000046 1.5 1100 0.53 729 0.53 0 1248

21Feb test5 30 0.0000044 1.5 1100 0.53 850 0.53 5 896 28.3 0.0000048 1.5 1100 0.53 850 0.53 5 992 28.1 0.000004 1.5 1100 0.53 850 0.53 5 912 28.6 0.0000047 1.5 1100 0.53 850 0.53 5 972 30.5 0.0000045 1.5 1100 0.53 850 0.53 5 892 29.9 0.0000046 1.5 1100 0.53 850 0.53 5 920 28.9 0.0000047 1.5 1100 0.53 850 0.53 5 960 29.5 0.0000046 1.5 1100 0.53 850 0.53 5 932 29.2 0.0000046 1.5 1100 0.53 850 0.53 5 940

21Feb test5 29.4 0.0000046 1.5 1100 0.53 850 0.53 5 936 21Feb test6 29.4 0.0000046 1.5 1100 0.53 729 0.53 5 1008

31.5 0.0000044 1.5 1100 0.53 729 0.53 5 920 30.2 0.0000046 1.5 1100 0.53 729 0.53 5 982 30.8 0.0000045 1.5 1100 0.53 729 0.53 5 952 30.5 0.0000045 1.5 1100 0.53 729 0.53 5 962 30.4 0.0000045 1.5 1100 0.53 729 0.53 5 964

24Feb test1 30 0.0000044 1.5 1380 0.53 850 0.53 5 1124 32.2 0.0000039 1.5 1380 0.53 850 0.53 5 984 30.8 0.0000045 1.5 1380 0.53 850 0.53 5 1108 32.1 0.0000039 1.5 1380 0.53 850 0.53 5 988

24Feb test1 31.7 0.0000042 1.5 1380 0.53 850 0.53 5 1052 24Feb test2 30 0.0000044 1.5 1380 0.53 850 0.53 25 422

20.1 0.0000039 1.5 1380 0.53 850 0.53 25 608 24 0.0000041 1.5 1380 0.53 850 0.53 25 516 21.5 0.000004 1.5 1380 0.53 850 0.53 25 572 22.9 0.0000041 1.5 1380 0.53 850 0.53 25 542 22.1 0.000004 1.5 1380 0.53 850 0.53 25 558 22.6 0.000004 1.5 1380 0.53 850 0.53 25 544 22.3 0.000004 1.5 1380 0.53 850 0.53 25 552

24Feb test3 30 0.0000044 1.5 1380 0.53 850 0.53 25 284 17.9 0.0000037 1.5 1380 0.53 850 0.53 25 460 20.5 0.0000039 1.5 1380 0.53 850 0.53 25 406 19.9 0.0000039 1.5 1380 0.53 850 0.53 25 418 20.1 0.0000039 1.5 1380 0.53 850 0.53 25 414 20 0.0000039 1.5 1380 0.53 850 0.53 25 416

Page 132

Appendix G

LASER SCAN SURFACE POINT COORDINATES

Table G-1. Laser scan surface point coordinates for scans 1 & 2.

Laser Scan 1 and 2 Spot 1.5 mm

circumference 446.11 mm Feed 0.256 mm/rev

rev1 rev 2 rev3 rev4 rev5 rev6 rev7 rev8 rev9 rev10 rev11 rev12 rev13 rev14 rev15 x= 0.8 446.9 893.0 1339.1 1785.2 2231.4 2677.5 3123.6 3569.7 4015.8 4461.9 4908.0 5354.1 5800.2 6246.3 y= 0 0.256 0.512 0.768 1.024 1.28 1.536 1.792 2.048 2.304 2.56 2.816 3.072 3.328 3.584

Table G-2. Laser scan surface point coordinates for scan 3.

Scan 3 Spot 1.5 mm

circumference 449.25 mm Feed 0.256 mm/rev

rev1 rev 2 rev3 rev4 rev5 rev6 rev7 rev8 rev9 rev10 rev11 rev12 rev13 rev14 rev15 x= 0.8 450.0 899.3 1348.5 1797.8 2247.0 2696.3 3145.5 3594.8 4044.0 4493.3 4942.5 5391.8 5841.0 6290.3 y= 0 0.256 0.512 0.768 1.024 1.28 1.536 1.792 2.048 2.304 2.56 2.816 3.072 3.328 3.584

Page 133

Table G-3. Laser scan surface point coordinates for scan 4.

Scan 4 Spot 2.5 mm

Circumference 449.25 mm Feed 0.256 mm/rev

rev1 rev 2 rev3 rev4 rev5 rev6 rev7 rev8 rev9 rev10 rev11 rev12 rev13 rev14 rev15 x= 1.2 450.4 899.7 1348.9 1798.2 2247.4 2696.7 3145.9 3595.2 4044.4 4493.7 4942.9 5392.2 5841.4 6290.7 y= 0 0.256 0.512 0.768 1.024 1.28 1.536 1.792 2.048 2.304 2.56 2.816 3.072 3.328 3.584

Table G-4. Laser scan surface point coordinates for scan 5.

Scan 5 Spot 2.5 mm

circumference 452.39 mm Feed 0.256 mm/rev

rev1 rev 2 rev3 rev4 rev5 rev6 rev7 rev8 rev9 rev10 rev11 rev12 rev13 rev14 rev15 x= 1.2 453.6 906.0 1358.4 1810.8 2263.1 2715.5 3167.9 3620.3 4072.7 4525.1 4977.5 5429.9 5882.3 6334.7 y= 0 0.256 0.512 0.768 1.024 1.28 1.536 1.792 2.048 2.304 2.56 2.816 3.072 3.328 3.584

Page 134

Table G-5. Laser scan surface point coordinates for scan 6.

Scan 6 Spot 2.5 mm

circumference 455.53 mm Feed 0.256 mm/rev

rev1 rev 2 rev3 rev4 rev5 rev6 rev7 rev8 rev9 rev10 rev11 rev12 rev13 rev14 rev15 x= 1.2 456.7 912.3 1367.8 1823.3 2278.9 2734.4 3189.9 3645.4 4101.0 4556.5 5012.0 5467.6 5923.1 6378.6 y= 0 0.256 0.512 0.768 1.024 1.28 1.536 1.792 2.048 2.304 2.56 2.816 3.072 3.328 3.584

Table G-6. Laser scan surface point coordinates for scan 7.

Scan 7 Spot 2.5 mm

circumference 461.81 mm Feed 0.256 mm/rev

rev1 rev 2 rev3 rev4 rev5 rev6 rev7 rev8 rev9 rev10 rev11 rev12 rev13 rev14 rev15 x= 1.3 463.1 924.9 1386.7 1848.6 2310.4 2772.2 3234.0 3695.8 4157.6 4619.4 5081.3 5543.1 6004.9 6466.7 y= 0 0.256 0.512 0.768 1.024 1.28 1.536 1.792 2.048 2.304 2.56 2.816 3.072 3.328 3.584

Page 135

Appendix H

PRELIMINARY EXPERIMENT RESULTS

Table H-1. Preliminary experiment results - Cuting forces.

Preliminary Experiments - Cutting Force 13/06/2003 Sensitivity 0.03149 V/kg All cuts made using the Tempcon laser controller Cutting Forces with Tool only Cutting Forces with Laser and Tool

Run Cutting Speed

(m/min) Feed

(mm/rev) Depth of Cut

(mm) Laser Height

(mm) Temp (°C) Zero max peak Force (N) min max peak

Force Change (N)

Laser Force (N)

1 51 0.256 0.8 -0.020 0.163 0.183 57 no laser 2 51 0.256 0.8 -0.027 0.142 0.169 53 no laser 3 50 0.256 1.2 212 1300 -0.010 0.216 0.226 70 0.188 0.236 0.048 15 85 4 50 0.256 1.6 212 1300 -0.038 0.304 0.342 107 0.226 0.3 0.074 23 130 5 51 0.256 0.8 212 1400 -0.008 0.140 0.148 46 0.094 0.138 0.044 14 60 6 51 0.256 1.2 212 1400 0.004 0.186 0.182 57 0.157 0.197 0.04 12 69 7 50 0.256 1.6 212 1400 -0.023 0.275 0.298 93 0.21 0.246 0.036 11 104 8 50 0.256 0.8 207 1400 -0.016 0.116 0.132 41 0.079 0.115 0.036 11 52 9 50 0.256 1.2 207 1400 -0.009 0.198 0.207 64 0.153 0.194 0.041 13 77

10 49 0.256 1.6 207 1400 -0.010 0.269 0.279 87 0.188 0.249 0.061 19 106 11 49 0.256 0.8 207 2000 -0.004 0.142 0.146 45 0.116 0.164 0.048 15 60 12 49 0.256 1.2 207 2000 -0.006 0.200 0.206 64 0.128 0.171 0.043 13 78 13 48 0.256 1.6 207 2000 -0.015 0.290 0.305 95 0.205 0.242 0.037 12 107 14 48 0.256 0.8 207 2300 -0.031 0.123 0.154 48 0.093 0.069 -0.024 -7 40 15 48 0.256 1.2 207 2300 -0.020 0.198 0.218 68 0.136 0.174 0.038 12 80 16 47 0.256 1.6 207 2300 -0.016 0.289 0.305 95 0.196 0.24 0.044 14 109 17 47 0.256 0.8 202 2300 -0.022 0.126 0.148 46 0.0727 0.121 0.0483 15 61 18 47 0.256 1.2 202 2300 -0.016 0.190 0.206 64 0.111 0.155 0.044 14 78 19 46 0.256 1.6 202 2300 -0.014 0.262 0.276 86 0.178 0.217 0.039 12 98

Page 136

Table H-2. Preliminary experiment results - Feed force.

Preliminary Experiments - Feed Force 13/06/2003 Sensitivity 0.0086531 V/kg All cuts made using the Temcon laser controller Feed Forces with Tool only Feed Forces with Laser and Tool

Run Cutting Speed

(m/min) Feed

(mm/rev) Depth of Cut (mm)

laser height (mm)

Temp (°C) Zero max peak

Force (N) min max peak

Force Change (N)

Laser Force (N)

1 51 0.256 0.8 212 0 -0.014 0.267 0.281 319 no laser 0 2 51 0.256 0.8 212 0 -0.025 0.25 0.275 312 no laser 0 3 50 0.256 1.2 212 1300 -0.01 0.41 0.42 476 0.281 0.326 0.045 51 527 4 50 0.256 1.6 212 1300 -0.042 0.57 0.612 694 0.315 0.424 0.109 124 817 5 51 0.256 0.8 212 1400 -0.005 0.273 0.278 315 0.0783 0.094 0.0157 18 333 6 51 0.256 1.2 212 1400 0 0.356 0.356 404 0.189 0.15 -0.039 -44 359 7 50 0.256 1.6 212 1400 -0.052 0.6 0.652 739 0.303 0.368 0.065 74 813 8 50 0.256 0.8 207 1400 -0.013 0.22 0.233 264 0.0939 0.11 0.0161 18 282 9 50 0.256 1.2 207 1400 0 0.365 0.365 414 0.198 0.235 0.037 42 456

10 49 0.256 1.6 207 1400 -0.01 0.52 0.53 601 0.28 0.341 0.061 69 670 11 49 0.256 0.8 207 2000 0 0.25 0.25 283 0.097 0.14 0.043 49 332 12 49 0.256 1.2 207 2000 -0.008 0.388 0.396 449 0.18 0.21 0.03 34 483 13 48 0.256 1.6 207 2000 -0.013 0.59 0.603 684 0.35 0.275 -0.075 -85 599 14 48 0.256 0.8 207 2300 -0.036 0.25 0.286 324 0.118 0.075 -0.043 -49 275 15 48 0.256 1.2 207 2300 -0.015 0.385 0.4 453 0.189 0.206 0.017 19 473 16 47 0.256 1.6 207 2300 -0.008 0.57 0.578 655 0.34 0.377 0.037 42 697 17 47 0.256 0.8 202 2300 -0.02 0.234 0.254 288 0.061 0.094 0.033 37 325 18 47 0.256 1.2 202 2300 -0.017 0.377 0.394 447 0.166 0.192 0.026 29 476 19 46 0.256 1.6 202 2300 -0.01 0.53 0.54 612 0.285 0.32 0.035 40 652

Page 137

Appendix I

SECONDARY EXPERIMENT RESULTS

Table I-1. Secondary experiment results - Cutting force.

Secondary experiment results – Cutting Force X sensitivity 0.0073 V/kg 13/01/2004 X-Feed

Run

Lase

r or N

o la

ser

Dia

met

er (m

m)

RPM

Spee

d (m

m/s

ec)

Feed

(mm

/rev)

doc

(mm

)

Spot

size

(mm

)

Dia

lled

lase

r po

wer

(W)

Act

ual P

ower

(W)

axia

l las

er

posi

tion

(mm

fr

om c

entre

of

tool

) ra

dial

lase

r po

sitio

n (m

from

to

ol)

Pow

er d

ensi

ty

W/m

m2

Vol

tage

pea

k

Forc

e pe

ak

Vol

tage

poi

nt o

ne

Vol

tage

poi

nt tw

o

Vol

tage

cha

nge

Forc

e ch

ange

Lase

r For

ce

% C

hang

e

14-13 l 163.2 90 769.1 0.256 1.6 3 1500 1380 2-left 22 195.2 0.515 692.0753 10-14 l 168.1 90 792.2 0.256 1.6 1.4 1500 1380 1mm left 25 896.5 0.725 974.2808 0.183 0.035 -0.148 -199 775 -20.4 12-14 l 160 90 754 0.256 1.6 1.5 1000 917 1mm left 25 518.9 0.645 866.774 0.208 0.104 -0.104 -140 727 -16.1 13-14 l 90 0.256 1.6 1.5 1000 917 1mm left 42 518.9 14-14 l 156.5 90 737.5 0.256 1.6 1.5 500 517 1mm left 42 292.6 0.645 866.774 0.203 0.098 -0.105 -141 726 -16.3 15-14 l 154.7 90 729 0.256 1.6 1.5 1300 1100 1mm left 42 622.5 0.639 858.711 0.268 0.128 -0.14 -188 671 -21.9 8-14 l 172.2 90 811.5 0.256 1.6 1.4 1500 1380 1mm right 25 896.5 0.706 948.7479 0.107 0.261 0.154 207 1156 21.8 2-13 l 180.6 90 851.1 0.256 0.8 3 1500 1380 1-right 22 195.2 0.26 349.3973 -0.042 0.026 0.068 91 441 26.2 3-13 l 179 90 843.5 0.256 0.8 3 2000 1785 1-right 22 252.5 0.158 212.326 5-13 l 177.2 90 835 0.256 1.2 3 1500 1380 1-right 22 195.2 0.361 485.1247 0.031 -0.028 -0.059 -79 406 -16.3 6-13 l 176.1 90 829.9 0.256 1.2 3 2000 1785 1-right 22 252.5 0.339 455.5603 0.0282 -0.0193 -0.0475 -64 392 -14.0

10-13 l 169.2 90 797.3 0.256 1.6 3 2000 1785 1-right 22 252.5 0.601 807.6452 8-13 l 173 90 815.2 0.256 1.6 3 1500 1380 1-right 22 195.2 0.499 670.574 0.14 0.0728 -0.0672 -90 580 -13.5 2-14 l 180.5 90 850.6 256 0.8 1.4 1500 1380 centre 25 896.5 0.181 243.2342 -0.073 -0.13 -0.057 -77 167 -31.5 4-14 l 90 0.256 1.2 1.4 1500 1380 centre 25 896.5 0.446 599.3507 0 -0.052 -0.052 -70 529 -11.7 6-14 l 90 0.256 1.6 1.4 1500 1380 centre 25 896.5 0.705 947.4041

Page 138

Table I-2. Secondary experiment results - Cutting force continued.

Run

Lase

r or N

o la

ser

Dia

met

er (m

m)

RPM

Spee

d (m

m/s

ec)

Feed

(mm

/rev)

doc

(mm

)

Spot

size

(mm

)

Dia

lled

lase

r po

wer

(W)

Act

ual P

ower

(W)

axia

l las

er

posi

tion

(mm

fr

om c

entre

of

tool

) ra

dial

lase

r po

sitio

n (m

from

to

ol)

Pow

er d

ensi

ty

W/m

m2

Vol

tage

pea

k

Forc

e pe

ak

Vol

tage

poi

nt o

ne

Vol

tage

poi

nt tw

o

Vol

tage

cha

nge

Forc

e ch

ange

Lase

r For

ce

% C

hang

e

12-13 l 166.7 90 785.6 0.256 1.6 3 1500 1380 centre 22 195.2 0.582 782.1123 0.131 0.0707 -0.0603 -81 701 -10.4 13-13 l 165.1 90 778 0.256 1.6 3 2000 1785 centre 22 252.5 0.522 701.4822 0.058 0.0028 -0.0552 -74 627 -10.6 1-13 nl 181 90 852.9 0.256 0.8 0.213 286.237 1-14 nl 181.4 90 854.8 0.256 0.8 0.206 276.8301 3-14 nl 90 0.256 1.2 0.376 505.2822 4-13 nl 178.4 90 840.7 0.256 1.2 0.357 479.7493

11-14 nl 161.8 90 0.256 1.6 0.582 782.1123 16-14 nl 90 0.256 1.6 0.665 893.6507 5-14 nl 178.2 90 0.256 1.6 0.614 825.1151 7-13 nl 174.8 90 0.256 1.6 0.541 727.0151 7-14 nl 90 0.256 1.6 0.543 729.7027 9-13 nl 90 0.256 1.6 0.538 722.9836 9-14 nl 90 0.256 1.6 0.622 835.8658

Page 139

Table I-3. Secondary experiment results - Feed force.

Secondary experiment results Z sensitivity 0.0057 V/kg 13/01/2004 Z - Cutting

Run

Lase

r or N

o la

ser

Dia

met

er (m

m)

RPM

Spee

d (m

m/s

ec)

Feed

(mm

/rev)

doc

(mm

)

Spot

size

(mm

)

Dia

lled

Lase

r po

wer

(W)

Act

ual P

ower

(W)

axia

l las

er p

ositi

on

(mm

from

cen

tre

of to

ol)

radi

al la

ser

posi

tion

(m fr

om

tool

)

Pow

er d

ensi

ty

W/m

m2

Vol

tage

pea

k

Forc

e pe

ak

Vol

tage

poi

nt o

ne

Vol

tage

poi

nt tw

o

Vol

tage

cha

nge

Forc

e ch

ange

Lase

r For

ce

% C

hang

e

14-13 l 163.2 90 769.1 0.256 1.6 3 1500 1380 2-left 22 195.2 0.225 302.363 0.067 0.026 -0.041 -55 247 -18.2 10-14 l 168.1 90 792.2 0.256 1.6 1.4 1500 1380 1mm left 25 896.5 0.34 456.9041 0.12 0.044 -0.076 -102 355 -22.4 12-14 l 160 90 754 0.256 1.6 1.5 1000 917 1mm left 25 518.9 0.296 397.7753 13-14 l 90 0.256 1.6 1.5 1000 917 1mm left 42 518.9 0.255 342.6781 0.104 0.027 -0.077 -103 239 -30.2 14-14 l 156.5 90 737.5 0.256 1.6 1.5 500 517 1mm left 42 292.6 0.289 388.3685 0.121 0.07 -0.051 -69 320 -17.6 15-14 l 154.7 90 729 0.256 1.6 1.5 1300 1100 1mm left 42 622.5 0.29 389.7123 0.12 0.05 -0.07 -94 296 -24.1 8-14 l 172.2 90 811.5 0.256 1.6 1.4 1500 1380 1mm right 25 896.5 0.292 392.4 0.059 0.189 0.13 175 567 44.5 2-13 l 180.6 90 851.1 0.256 0.8 3 1500 1380 1-right 22 195.2 0.181 243.2342 0.056 0.022 -0.034 -46 198 -18.8 3-13 l 179 90 843.5 0.256 0.8 3 2000 1785 1-right 22 252.5 0.1019 136.9368 5-13 l 177.2 90 835 0.256 1.2 3 1500 1380 1-right 22 195.2 0.2089 280.7273 0.0731 0.032 -0.0411 -55 225 -19.7 6-13 l 176.1 90 829.9 0.256 1.2 3 2000 1785 1-right 22 252.5 0.1889 253.8505 0.0654 0.0386 -0.0268 -36 218 -14.2

10-13 l 169.2 90 797.3 0.256 1.6 3 2000 1785 1-right 22 252.5 0.32 430.0274 8-13 l 173 90 815.2 0.256 1.6 3 1500 1380 1-right 22 195.2 0.27 362.8356 0.05 0.108 0.058 78 441 21.5 2-14 l 180.5 90 850.6 256 0.8 1.4 1500 1380 centre 25 896.5 0.085 114.226 0.016 -0.003 -0.019 -26 89 -22.4 4-14 l 90 0.256 1.2 1.4 1500 1380 centre 25 896.5 0.208 279.5178 0.0801 0.0824 0.0023 3 283 1.1 6-14 l 90 0.256 1.6 1.4 1500 1380 centre 25 896.5 0.32 430.0274 0.175 0.117 -0.058 -78 352 -18.1

12-13 l 166.7 90 785.6 0.256 1.6 3 1500 1380 centre 22 195.2 0.266 357.4603 0.095 0.054 -0.041 -55 302 -15.4 13-13 l 165.1 90 778 0.256 1.6 3 2000 1785 centre 22 252.5 0.247 331.9274 0.086 0.061 -0.025 -34 298 -10.1 1-13 nl 181 90 852.9 0.256 0.8 0.142 190.8247 1-14 nl 181.4 90 854.8 0.256 0.8 0.094 126.3205 3-14 nl 90 0.256 1.2 0.169 227.1082

Page 140

Table I-4. Secondary experiment results - Feed force continued.

Run

Lase

r or N

o la

ser

Dia

met

er (m

m)

RPM

Spee

d (m

m/s

ec)

Feed

(mm

/rev)

doc

(mm

)

Spot

size

(mm

)

Dia

lled

Lase

r po

wer

(W)

Act

ual P

ower

(W)

axia

l las

er p

ositi

on

(mm

from

cen

tre

of to

ol)

radi

al la

ser

posi

tion

(m fr

om

tool

)

Pow

er d

ensi

ty

W/m

m2

Vol

tage

pea

k

Forc

e pe

ak

Vol

tage

poi

nt o

ne

Vol

tage

poi

nt tw

o

Vol

tage

cha

nge

Forc

e ch

ange

Lase

r For

ce

% C

hang

e

4-13 nl 178.4 90 840.7 0.256 1.2 0.2139 287.4464 11-14 nl 161.8 90 0.256 1.6 0.289 388.3685 16-14 nl 90 0.256 1.6 0.302 405.8384 5-14 nl 178.2 90 0.256 1.6 0.29 389.7123 0 0 7-13 nl 174.8 90 0.256 1.6 0.2912 391.3249 7-14 nl 90 0.256 1.6 0.204 274.1425 0 0 9-13 nl 90 0.256 1.6 0.29 389.7123 9-14 nl 90 0.256 1.6 0.249 334.6151 0 0

Page 141

Table I-5. Secondary experiments - Resultant forces.

Run Laser or No laser

Diameter (mm) RPM

Speed (mm/sec)

Feed (mm/rev)

doc (mm)

Spot size (mm)

power (W)

Actual Power (W)

axial laser position (mm from centre of

tool)

radial laser position (mm

from tool)

Power density W/mm2

Resultant force

Average Force

reduction 14-13 l 163.2 90 769.1 0.256 1.6 3 1500 1380 2-left 22 195.2 10-14 l 168.1 90 792.2 0.256 1.6 1.4 1500 1380 1mm left 25 896.5 852.7 -150.5 12-14 l 160 90 754 0.256 1.6 1.5 1000 917 1mm left 25 518.9 727.0 -69.9 13-14 l 90 0.256 1.6 1.5 1000 917 1mm left 42 518.9 14-14 l 156.5 90 737.5 0.256 1.6 1.5 500 517 1mm left 42 292.6 793.0 -104.8 15-14 l 154.7 90 729 0.256 1.6 1.5 1300 1100 1mm left 42 622.5 732.9 -141.1 8-14 l 172.2 90 811.5 0.256 1.6 1.4 1500 1380 1mm right 25 896.5 1287.3 190.8 2-13 l 180.6 90 851.1 0.256 0.8 3 1500 1380 1-right 22 195.2 483.0 22.8 3-13 l 179 90 843.5 0.256 0.8 3 2000 1785 1-right 22 252.5 0.0 5-13 l 177.2 90 835 0.256 1.2 3 1500 1380 1-right 22 195.2 464.3 -67.3 6-13 l 176.1 90 829.9 0.256 1.2 3 2000 1785 1-right 22 252.5 448.2 -49.9 10-13 l 169.2 90 797.3 0.256 1.6 3 2000 1785 1-right 22 252.5 0.0 8-13 l 173 90 815.2 0.256 1.6 3 1500 1380 1-right 22 195.2 728.7 -6.2 2-14 l 180.5 90 850.6 256 0.8 1.4 1500 1380 centre 25 896.5 188.8 -51.1 4-14 l 90 0.256 1.2 1.4 1500 1380 centre 25 896.5 600.2 -33.4 6-14 l 90 0.256 1.6 1.4 1500 1380 centre 25 896.5 -39.0 12-13 l 166.7 90 785.6 0.256 1.6 3 1500 1380 centre 22 195.2 763.5 -68.1 13-13 l 165.1 90 778 0.256 1.6 3 2000 1785 centre 22 252.5 694.6 -53.9 1-13 nl 181 90 852.9 0.256 0.8 1-14 nl 181.4 90 854.8 0.256 0.8 3-14 nl 90 0.256 1.2 4-13 nl 178.4 90 840.7 0.256 1.2 11-14 nl 161.8 90 0.256 1.6 16-14 nl 90 0.256 1.6 5-14 nl 178.2 90 0.256 1.6 7-13 nl 174.8 90 0.256 1.6 7-14 nl 90 0.256 1.6 9-13 nl 90 0.256 1.6 9-14 nl 90 0.256 1.6

Page 142

Appendix J

RESULTS OF HARDNESS TESTS

Table J-1. Hardness results - Scan 1.

Scan 1 Weight 500g

Time applied 15sec Distance from

edge y Hardness 1 (HV0.05)

Hardness 2 (HV0.05)

0.05 16.01 514.4 510 0.13 15.93 560 541.7 0.13 15.93 553.2 569.1 16.33 -0.27 528.7 525 16.33 -0.27 615.6 624.9 16.33 -0.27 501.5 504.9 32.61 -16.55 598.8 556.1 32.61 -16.55 579.5 578.4 32.61 -16.55 579.5 594.4 48.89 -32.83 604 582.6 48.89 -32.83 751.4 696 48.89 -32.83 664.1 673.2 65.17 -49.11 640.4 634.3 1.25 14.81 633.1 624.8 1.33 14.73 587.9 582.6 1.40 14.66 619 621.4 1.48 14.58 624.9 624.9 1.55 14.51 666.7 664.1 1.63 14.43 718.6 751.4 1.63 14.43 705.7 700.2 1.63 14.43 667.1 686.5 1.63 14.43 702.9 710 1.63 14.43 705.7 725.8 1.63 14.43 743.8 734.7

Page 143

Table J-2. Hardness results - Scan 2.

Scan2 Weight 500g

Time applied 15sec Distance from

edge y Hardness 1 (HV0.05)

Hardness 2 (HV0.05)

0.05 16.23 603.2 617.9 0.15 16.13 627.2 644 0.25 16.03 612.2 619 0.35 15.93 633.1 636.7 0.45 15.83 689.2 694.6 0.55 15.73 655.4 661.5 0.65 15.63 627.2 624.9 0.75 15.53 608.8 616.7 0.85 15.43 581.6 593.3 0.95 15.33 659 623.7 1.05 15.23 628.4 636.7 1.15 15.13 606.5 608.8 1.25 15.03 611 603.2 1.35 14.93 664.1 682.4 1.45 14.83 674.5 660.3 1.55 14.73 593.3 595.5 1.65 14.63 533.3 527.8 1.75 14.53 623.7 627.2 1.85 14.43 601 602.1 1.95 14.33 602.1 555.2 2.05 14.23 689.2 701.5 2.15 14.13 666.7 670.6

Page 144

Table J-3. Hardness results - Scan 3.

Scan3 Weight 500g

Time applied 15sec Distance from

edge y Hardness 1 (HV0.05)

Hardness 2 (HV0.05)

0.05 16.16 592.2 580.5 0.15 16.06 679.8 682.4 0.25 15.96 815.5 796.6 0.35 15.86 671.9 679.8 0.45 15.76 734.7 757.6 0.55 15.66 781.7 786.6 0.65 15.56 826.1 861 0.75 15.46 840.5 849.7 0.85 15.36 798.3 808.6 0.95 15.26 649 661.5 1.05 15.16 749.9 767.1 1.15 15.06 598.8 607.7 1.25 14.96 570.2 570.2 1.35 14.86 556.1 562.1 1.45 14.76 567.1 565.1 1.55 14.66 526.9 516.1 1.65 14.56 645.3 644 1.75 14.46 585.8 584.7 1.85 14.36 459.7 491.6 1.95 14.26 464.1 462.7 2.05 14.16 441 450.2 2.15 14.06 540.7 538.8

Page 145

Table J-4. Hardness results - Scan 4.

Scan 4 Weight 500g

Time applied 15sec Distance from

edge y Hardness 1 (HV0.05)

Hardness 2 (HV0.05)

0.05 16.25 693.3 686.5 0.15 16.15 737.7 731.7 0.25 16.05 691.9 694.6 0.35 15.95 743.8 746.8 0.45 15.85 656.5 669.3 0.55 15.75 697.4 698.8 0.65 15.65 702.9 715.7 0.75 15.55 659 671.9 0.85 15.45 751.4 759.2 0.95 15.35 711.4 728.8 1.05 15.25 595.5 603.2 1.15 15.15 580.5 595.5 1.25 15.05 561.1 571.2 1.35 14.95 596.6 604.3 1.45 14.85 661.5 657.7 1.55 14.75 597.7 593.3 1.65 14.65 542.6 547.4 1.75 14.55 601 598.8 1.85 14.45 556.1 569.1 1.95 14.35 564.1 560.1 2.05 14.25 627.2 635.5 2.15 14.15 534.2 542.6

Page 146

Table J-5. Hardness results - Scan 5.

Scan 5 Weight 500g

Time applied 15sec Distance from edge y Hardness 1 (HV0.05) Hardness 2 (HV0.05)

0.05 17.37 803.4 794.9 0.15 -601.63 739.2 754.5 0.25 -1220.63 805.1 775.1 0.35 -1839.63 817.2 812 0.45 -2458.63 767.1 757.6 0.55 -3077.63 639.2 634.3 0.65 -3696.63 749.9 742.2 0.75 -4315.63 730.3 736.2 0.85 -4934.63 793.3 798.3 0.95 -5553.63 645.3 646.5 1.05 -6172.63 705.7 700.2 1.15 -6791.63 731.7 721.5 1.25 -7410.63 748.4 731.7 1.35 -8029.63 667.1 666.7 1.45 -8648.63 798.3 775.1 1.55 -9267.63 696 696 1.65 -9886.63 740.7 742.2 1.75 -10505.6 711.4 722.9 1.85 -11124.6 653.9 659 1.95 -11743.6 542.6 549.3 2.05 -12362.6 619 615.6 2.15 -12981.6 677.1 666.7 2.25 -13600.6 653.9 659 2.35 -14219.6 634.3 639.2 2.45 -14838.6 635.5 637.9 2.55 -15457.6 652.7 650.2 2.65 -16076.6 639.2 649 2.75 -16695.6 611 604.3 2.85 -17314.6 619 633.1 2.95 -17933.6 583.7 581.6 3.05 -18552.6 516.1 557.1 3.15 -19171.6 546.4 548.3 3.25 -19790.6 489.9 484.3 3.35 -20409.6 565.1 563.1 3.45 -21028.6 581.6 557.1 3.55 -21647.6 656.5 651.4 3.65 -22266.6 702.9 693.3 3.75 -22885.6 718.6 722.9 3.85 -23504.6 628.4 634.3 3.95 -24123.6 698.8 693.3 4.05 -24742.6 620.2 622.5 4.15 -25361.6 683.8 673.2

Page 147

4.25 -25980.6 645.3 644 4.35 -26599.6 591.1 593.3

Page 148

Table J-6. Hardness results - Scan 6.

Scan 6 Weight 500g

Time applied 15sec Distance from

edge y Hardness 1 (HV0.05)

Hardness 2 (HV0.05)

0.05 17.89 733.2 724.4 0.15 17.89 771.9 778.4 0.25 17.89 870.5 872.5 0.35 17.89 824.3 808.6 0.45 17.89 796.6 788.3 0.55 17.89 922.9 920.8 0.65 17.89 1008.2 994 0.75 17.89 686.5 687.8 0.85 17.89 825.1 822.5 0.95 17.89 708.6 702.9 1.05 17.89 697.4 694.6 1.15 17.89 655.2 647.7 1.25 17.89 599.9 590.1 1.35 17.89 539.8 530.5 1.45 17.89 577.4 585.8 1.55 17.89 575.3 578.4 1.65 17.89 511.8 507.5 1.75 17.89 522.3 523.2 1.85 17.89 525 527.8 1.95 17.89 445.2 436.9 2.05 17.89 453.8 453.8 2.15 17.89 428.1 429.5 2.25 17.89 485.9 487.5 2.35 17.89 455.3 450.2 2.45 17.89 505.7 504 2.55 17.89 435.5 438.3

Page 149

Table J-7. Hardness results - Scan 7.

Scan 7 Weight 500g

Time applied 15sec Distance from

edge y Hardness 1 (HV0.05)

Hardness 2 (HV0.05)

0.05 20.13 763.9 756.1 0.15 20.13 728.8 721.5 0.25 20.13 739.2 748.4 0.35 20.13 746.8 786.6 0.45 20.13 916.6 912.4 0.55 20.13 822.5 822.5 0.65 20.13 762.4 781.7 0.75 20.13 734.7 736.2 0.85 20.13 754.5 756.1 0.95 20.13 689.2 694.6 1.05 20.13 696 687.8 1.15 20.13 570.2 563.1 1.25 20.13 548.3 547.4 1.35 20.13 568.1 574.3 1.45 20.13 527.8 524.1 1.55 20.13 592.2 590.1 1.65 20.13 560.1 547.4 1.75 20.13 616.7 617.9 1.85 20.13 653.9 653.9 1.95 20.13 611 621.4 2.05 20.13 633.1 646.5 2.15 20.13 639.2 630.8 2.25 17.93 615.6 620.2