Complete Thesis on Segmented Object Manufacturing

Segmented Object Manufacturing

Submitted in the partial fulfillment of the requirements

of the degree of

Masters in Engineering

(CAD/CAM & Robotics)

by

Pratik Rajesh Soni

Roll No: 1205008

Guide

Prof. R.R.Lekurwale

DEPARTMENT OF MECHANICAL ENGINEERING

K.J.SOMAIYA COLLEGE OF ENGINEERING, VIDYAVIHAR

UNIVERSITY OF MUMBAI

(2014)

Dedicated To

My Family

ii

Certificate

This is to certify that the dissertation entitled Segmented Object Manufacturing is a bona fide

record of the dissertation work done by Mr. Pratik Rajesh Soni in the year 2013-14 under the

guidance of Prof. R.R.Lekurwale of Department of Mechanical Engineering in partial fulfillment

of requirement of the Masters of Engineering in Mechanical Engineering with specialization in

CAD-CAM and Robotics.

--------------------------------------- ---------------------------------------

Guide Head of the Department

(Prof. R.R.Lekurwale)

---------------------------------------

Principal

Date:

Place: Mumbai

iii

Dissertation Approval for M. E.

This dissertation report entitled Segmented Object Manufacturing by Pratik R.

Soni is approved for the degree of Master of Engineering in CAD/CAM and

Robotics.

Examiners

1.---------------------------------------------

2.---------------------------------------------

Guide

1.---------------------------------------------

Chairman

-----------------------------------------------

Date:

Place:

iv

Declaration

I declare that this written submission represents my ideas in my own words and where others' ideas

or words have been included, I have adequately cited and referenced the original sources. I also

declare that I have adhered to all principles of academic honesty and integrity and have not

misrepresented or fabricated or falsified any idea/data/fact/source in my submission. I understand

that any violation of the above will be cause for disciplinary action by the Institute and can also

evoke penal action from the sources which have thus not been properly cited or from whom proper

permission has not been taken when needed.

----------------------------

Pratik R. Soni

Roll No. 1205008

University Registration No.: KJSCE/173

Date:

v

Abstract

Rapid Prototyping (RP) is a process where one manufactures a model of the product with limited

or complete functionality. It is done by additive manufacturing rather than conventional subtractive

manufacturing. In all commercial RP processes, the part is fabricated in the x-y plane and stacked

along the z axis. This results in very exact prototypes in the x-y plane but stair-casing along the z-

axis. Segmented Object Manufacturing (SOM) is a Rapid Prototyping (RP) process meant for

making foam patterns. Unlike traditional rapid prototyping where the objects are built in several

thin slices, SOM builds objects in thick slices. In spite of that, the objects are free from stair-steps

owing to its novel visible slicing. SOM is typically a hybrid process involving hot wire cutting for

slicing the stock, CNC machining and gluing. SOM is useful for building larger prototypes.

A study and complete overhaul of the machine was carried out and various sub-systems of the

machine were tested. As the machine gradually became functional, the focus shifted to integration

of all the sub-systems of the machine, viz. milling, hot wire slicing and gluing into one Automatic

Program. Multiple softwares have been used to create, edit, test and execute the program. The

softwares used are Delcam Powermill 2013, Notepad, Cimco and SurfCAM DNC.

This report explains each software used in detail .It explains why certain methods are more

appropriate as compared to others. The settings required for each software to work properly have

also been described. The project concludes with a comparison of the CAD model and the actual

object obtained and provides justifications for the inaccuracies. It also elaborates future scope for

development in the SOM machine.

Key words: Rapid Prototyping, Segmented Object Manufacturing, Automatic Program

vi

CONTENTS

List of figures ................................................................................................................................. ix

List of tables .................................................................................................................................... x

Nomenclature ................................................................................................................................. xi

1 Introduction ............................................................................................................................. 1

1.1 Outline .............................................................................................................................. 1

1.1.1 Different Rapid prototyping technologies ................................................................ 2

1.2 Background and motivation ............................................................................................. 3

1.2.1 Stamping dies ............................................................................................................ 3

1.2.2 Stratos concepts, LLC ............................................................................................... 5

1.3 Scope and application....................................................................................................... 6

1.3.1 Scope ......................................................................................................................... 6

1.3.2 Applications .............................................................................................................. 6

1.4 Objectives of study ........................................................................................................... 8

1.5 Organization of thesis....................................................................................................... 8

2 Literature review .................................................................................................................... 10

2.1 Shapemaker II ................................................................................................................ 10

2.2 Free-form thick-layered object manufacturing (FF-TLOM) .......................................... 10

2.3 Flexible blade cutting ..................................................................................................... 11

2.3.1 Requirements for flexible blade .............................................................................. 11

2.4 Rough machining strategies ........................................................................................... 12

2.4.1 Model rest area clearance ........................................................................................ 13

2.5 Finishingstrategies .......................................................................................................... 13

2.5.1 Raster, Radial, Spiral, and Pattern Finishing .......................................................... 14

3 Methodology .......................................................................................................................... 16

3.1 Flowchart for methodology ............................................................................................ 16

4 Segmented object manufacturing (SOM) machine ............................................................... 18

4.1 Overall view of the machine .......................................................................................... 18

4.2 Principle of working ....................................................................................................... 19

4.2.1 Algorithm for visible slicing ................................................................................... 21

4.3 Machine kinematics........................................................................................................ 22

4.4 Machine specifications ................................................................................................... 22

vii

4.4.1 Machine tool ........................................................................................................... 24

4.4.2 Controller ................................................................................................................ 25

4.4.3 Software and interfacing ......................................................................................... 25

4.5 The structure of the machine .......................................................................................... 29

4.5.1 Proposed alteration.................................................................................................. 29

4.6 The slides........................................................................................................................ 30

4.7 The brakes ...................................................................................................................... 30


4.8 The ATC ......................................................................................................................... 31

4.9 The Spindle .................................................................................................................... 31

4.10 Cutter .............................................................................................................................. 32


4.11 Glue gun ......................................................................................................................... 33

4.11.1 Operation of the glue gun and the type of glue to be used ..................................... 33


4.12 Area filling algorithm ..................................................................................................... 34

4.13 Hot wire system .............................................................................................................. 34

4.13.1 Functioning of the system ....................................................................................... 34

4.13.2 Parameters that dictate the cutting action of the wire ............................................. 35

4.14 Work done to bring the machine into working condition .............................................. 36

4.14.1 Establishing communication between the controller and a computer .................... 36

4.14.2 Improvising the cable to connect via USB ............................................................. 36

4.14.3 Repairing the axis controller ................................................................................... 36

4.14.4 Repairing the coupling that connects the motor with the x-axis ............................. 36

4.14.5 Replacing the battery that helps memorize the zero position of the machine ........ 37

4.14.6 Replacing rubber components................................................................................. 37

4.14.7 Oiling the various joints to get the machine in working order ............................... 37

4.15 Case study ...................................................................................................................... 37

4.15.1 Steps 0 and 1 ........................................................................................................... 38

4.15.2 Steps 2,3 and 4 ........................................................................................................ 38

4.15.3 Steps 5 and 6 ........................................................................................................... 39

4.15.4 Steps 7,8 and 9 ........................................................................................................ 39

4.15.5 Steps 10 and 11 ....................................................................................................... 40

viii

5 Implementation and execution of code .................................................................................. 41

5.1 Description of the bracket that will be manufactured .................................................... 41

5.2 Steps to create the bracket (brief overview) ................................................................... 41

5.2.1 Importing the model slices into Powermill ............................................................. 41

5.2.2 Creating and simulating the code ............................................................................ 42

5.2.3 Mounting the themocole block onto the machine ................................................... 42

5.2.4 Selecting and mounting of tool ............................................................................... 42

5.2.5 Interface and transfer of program ........................................................................... 43

5.3 Tools used to create and execute the code ..................................................................... 43

5.3.1 DelcamPowermill ................................................................................................... 43

5.3.2 Microsoft Notepad .................................................................................................. 49

5.3.3 Cimco Edit V5 ........................................................................................................ 53

5.3.4 SurfCAM DNC ....................................................................................................... 55

6 Results and Discussion .......................................................................................................... 57

6.1 Comparison between the dimensions of the CAD model and the actual model ............ 57

6.2 Observations ................................................................................................................... 57

6.3 Justifications for the inaccuracies .................................................................................. 58

6.3.1 Coupling error ......................................................................................................... 58

6.3.2 Material addition due to gluing ............................................................................... 58

6.3.3 Heating loss ............................................................................................................. 58

6.3.4 Machine instability.................................................................................................. 59

6.3.5 Optimum feed and spindle speed ............................................................................ 59

6.3.6 Vibration due to eccentric cutter shank, because of manual grinding .................... 59

7 Conclusion and future scope .................................................................................................. 60

7.1 Conclusion ...................................................................................................................... 60

7.2 Future scope ................................................................................................................... 61

References ..................................................................................................................................... 63

Authors publications ..................................................................................................................... 65

Acknowledgement ........................................................................................................................ 66

ix

LIST OF FIGURES

Figure 1-1: Broad classification of rapid prototyping technologies ............................................... 2

Figure 1-2: Stamping dies prepared by assembling and gluing smaller parts ................................ 3

Figure 1-3 Stratoconcepts (layered manufacturing) procedure ...................................................... 5

Figure 1-4: Applications of SOM ................................................................................................... 6

Figure 2-1: FF-TLOM head and Figure 2-2: FF-TLOM process simulation .......................... 11

Figure 2-3: Rough machining strategies (isometric view) ............................................................ 12

Figure 2-4: Rough machining strategies (front view) ................................................................... 13

Figure 2-5: Material left on product after roughing ...................................................................... 14

Figure 2-6: Finishing patterns ....................................................................................................... 15

Figure 3-1: Flowchart for methodology ........................................................................................ 17

Figure 4-1: SOM Machine (overall view) .................................................................................... 18

Figure 4-2: Possible slices obtained by visible slicing ................................................................. 19

Figure 4-3: Settings required to machine the bracket on a three axis machine ............................ 20

Figure 4-4: Kinematics of the som machine ................................................................................. 22

Figure 4-5: Character framing ...................................................................................................... 26

Figure 4-6: Pin diagram to connect the fanuc controller to a computer ....................................... 28

Figure 4-7: Photograph of the automatic tool changer (atc) ......................................................... 31

Figure 4-8: Photograph of the glue gun ........................................................................................ 33

Figure 4-9: Photograph of the hot wire slicing system ................................................................. 34

Figure 4-10: Hot wire locking mechanism ................................................................................... 35

Figure 4-11: Proposed case study ................................................................................................. 37

Figure 4-12: steps 0 and 1 ............................................................................................................. 38

Figure 4-13: steps 2, 3 and 4 ......................................................................................................... 38

Figure 4-14: steps 5 and 6 ............................................................................................................. 39

Figure 4-15: steps 7, 8 and 9 ......................................................................................................... 39

Figure 4-16: steps 10 and 11 ......................................................................................................... 40

Figure 5-1: CAD model of the object to be machined .................................................................. 41

Figure 5-2: Powermill interface .................................................................................................... 43

Figure 5-3: Object to be machined (slice 1).................................................................................. 44

Figure 5-4: Object to be machined (slice 2).................................................................................. 44

Figure 5-5: Object vector .............................................................................................................. 45

Figure 5-6: Settings for rough machining ..................................................................................... 47

Figure 5-7: Settings to create the nc code file............................................................................... 48

Figure 5-8: Cimco interface .......................................................................................................... 53

Figure 5-9: Simulation of the program on cimco .......................................................................... 54

Figure 5-10: Surfcam dnc interface .............................................................................................. 55

Figure 5-11: Surfcam dnc settings for communication................................................................. 56

Figure 6-1: Comparison between the cad model and the actual model obtained ......................... 57

x

LIST OF TABLES

Table 6-1: Dimensional and surface comparison of cad model and machined object ..................... 57

xi

NOMENCLATURE

3D - Three Dimensional

2D Two Dimensional

SLA Stereo Lithography Apparatus

SLS Selective Laser Sintering

ABS Acrylonitrile Butadiene Styrene

RP Rapid Prototyping

CAD Computer Aided Drafting

RM Rapid Manufacturing

EB Electron Beam

SRM Silicon Rubber Molding

LM Layered Manufacturing

HLM Hybrid Layer Manufacturing

RC Rapid Casting

STL StereoLithography file format

DXF Drawing Interchange Format

CNC Computer Numerical Control

SOM Segmented Object Manufacturing

EPC Evaporative Pattern Casting

FF-TLOM Free form thick layered object manufacturing

PM Prototype Model

ATC Automatic Tool Changer

UART Universal Asynchronous Receiver/Transmitter

AC Alternating Current

USB Universal Serial Bus

HSS High Speed Steel

CAM Computer Aided Manufacturing

1

1 INTRODUCTION

Till 1987, manufacturing was dominated by material subtraction. Material was removed from a

pre-defined block of raw material. Not only machining but also formative processes like forming

and casting had to be finished using subtractive machining. The sign change in manufacturing

happened with the advent of Additive Manufacturing by 3D Systems. It led to total automation in

converting art-to-part (design-to-manufacturing or virtual-to-physical). It is as

easy/simple/analogous as 2D printing. So, many prefer to call it as 3D Printing. Additive

manufacturing revolutionized the way products are designed and manufactured today. It is an

effective tool to compress product development time and hence gives an edge over the competitors.

[1]

1.1 OUTLINE

Rapid manufacturing is a subset in the field of rapid prototyping. The most commonly used method

for rapid manufacturing is rapid casting. The process works as follows.

Initially a prototype is created using any of the 3D technologies like SLA, SLS, etc. A silicon mold

is prepared out of this pattern. So now we have a silicon mold in two parts (cope and drag). The

gating system is built into the silicon mold. The vacuum casting machine has two compartments,

one is where the silicon mold is kept (the lower compartment) and the other is where the molten

material is kept (the upper compartment). A near zero vacuum is created in the machine. This

along with gravity enables the flow of the material from the upper chamber into the mold. This

process is used to cast plastics, ABS, rubber and wax.[2,3]

Whenever a new product is developed, there is a need to develop a functional sample of the

product. This sample is called a prototype. This is done before investing a huge amount of money

in developing assembly lines, special tooling etc. because of the following reasons:

This chapter presents an introduction to segmented object manufacturing. It starts with a

description of what 3D printing is and the various technologies available in the market for 3D

printing. It then describes in brief, the machine that has been used for the project. It starts by

defining the scope of the project, then elaborates the problem statement and finally the

objectives of the project are listed.

2

1. Capital cost is very high

2. Production tooling takes considerable time to prepare

3. Design evaluation

4. Troubleshooting

The advantages of RP:

1. Physical models of parts produced from CAD data files can be manufactured in a matter of

hours and allow the rapid evaluation of manufacturability and design effectiveness. In this way,

rapid prototyping serves as an important tool for visualization and concept verification.

2. With suitable materials, the prototype can be used in subsequent manufacturing operations to

produce the final parts. This also serves as a manufacturing technology

3. RP operations can be used in some applications to produce actual tooling for manufacturing

operations (rapid tooling). [3]

1.1.1 DIFFERENT RAPID PROTOTYPING TECHNOLOGIES

The basic steps while constructing a prototype are as follows

1. Solid model

Figure 1-1: Broad classification of rapid prototyping technologies [4]

3

2. STL file generation

3. Rapid manufacturing system (error checking, orientation, support, slicing)

4. RP machine.

The tree above gives a classification of various rapid prototyping technologies used. [3]

1.2 BACKGROUND AND MOTIVATION

1.2.1 STAMPING DIES

Stamping dies are the large shape components that are manufactured through casting followed

byCNC machining process. The casting is obtained by evaporative pattern casting process. For

thisexpanded polystyrene is used. The figure below shows the patterns fromGanesh Pattern, Pune

and that of Jyoti Tooling, Pune. The patterns are made by dividing the larger object into small

segments. These segments are then glued together to get the complete pattern.

Figure 1-2: Stamping dies prepared by assembling and gluing smaller parts [5]

In the RM lab at IIT-Bombay, a team has designed and developed a RP (rapid prototyping)

machine that can produce the 3D model of the given design. The raw material used is expanded

polystyrene. The principle of manufacturing is the same. It divides the given object into segments

using the help of an algorithm called the visible slicing algorithm. The segments are then glued

together to give us the desired object. The machine is known as Segmented Object Manufacturing

(SOM) machine. The 3D model thus obtained can be used for making patterns through evaporative

pattern casting process.

4

The proposed process is a hybrid process which uses subtractive as well as additive processes. The

subtractive process is the CNC machining of the segments and the additive process is gluing of the

segments.

5

1.2.2 STRATOS CONCEPTS, LLC

This UNIQUE stratoconcept process (layer manufacturing) was developed in partnership with

CIRTES(European Center for Rapid Prototyping and Tools).

Stratoconcept allows hollow core forms and internal details for big size real (no flat surface

necessary with CNC machines) 3D objects. [6]

Figure 1-3 Stratoconcepts (layered manufacturing) procedure [6]

6

1.3 SCOPE AND APPLICATION

1.3.1 SCOPE

To make the SOM machine fully functional and integrate all the subsystems into the controller and

to develop and execute a CNC code to create a complete object with the press of a single button

(from CAD model to actual object).

1.3.2 APPLICATIONS

The following figure indicate some of the applications of the SOM machine

Figure 1-4: Applications of SOM [4]

7

1.3.2.1 EVAPORATIVE PATTERN CASTING (EPC)

Evaporative Pattern Casting (EPC) is a class of processes that use pattern materials that evaporate

during the pour, which means there is no need to remove the pattern material from themocole

before casting. The two main processes are lost-foam casting and full-mold casting.Lost-foam

casting is a type of evaporative-pattern casting process that is similar to investment casting except

foam is used for the pattern instead of wax. This process takes advantage of the low boiling point

of foam to simplify the investment casting process by removing the need to melt the wax out of

the mold.

Full-mold casting is an evaporative-pattern casting process which is a combination of sand casting

and lost-foam casting. It uses an expanded polystyrene foam pattern which is then surrounded by

sand, much like sand casting. The metal is then poured directly into the mold, which vaporizes the

foam upon contact. [2]

1.3.2.2 MILITARY DECOY (MOCKUPS OF PLANES, SHIPS, TANKS)

The patterns resulting out of the SOM machine can be used as decoys on a battle field. Themocole

components can be readily painted to resemble tanks and artillery. This would create a distraction,

it could provide additional times to the army and prove lifesaving in certain instances. It would

also be easy to carry around since themocole is light weight. A real tank which would weigh

thousands of kilos would be only a couple of kilos on themocole. Mock-ups of ships could also be

made. It could be designed and painted so that it resembles a real ship. This would give an illusion

of a much larger army than it actually is.

1.3.2.3 FESTIVALS

Ganesh Chaturthi is a widely celebrated festival in the state of Maharashtra. Every year lakhs of

idols of lord Ganesh are made out of plaster of Paris and immersed into the sea. This has created

a lot of problems for the environment. The plaster of Paris does not decompose into the sea and it

is toxic to the sea life. Plaster of Paris is heavy to move around.

The concept of SOM could be applied to create themocole idols. They would be very light weight

and hence very easy to move around. The making would take place by CNC programming which

would be highly accurate and fast as compared to manual labor. They could be painted just like

regular idols. And the best part would be environmental friendliness. Themocole decomposes in

acetone. Instead of immersion, we could have a small tray with acetone, the idol could be placed

in the tray and it would slowly melt away giving the effect of immersion.

8

1.4 OBJECTIVES OF STUDY

The objectives of the project are as follows:

-To study the rapid prototyping technologies in the market and to find out drawbacks in them. A

review of the current technologies has been done and it has been concluded that long build times

and stair casing are two of the most significant drawbacks of current technologies. The Segmented

Object Manufacturing (SOM) machine overcomes these.

-To get the SOM machine into working condition by fixing the following sub-systems

1. Braking mechanism

2. Hot wire mechanism

3. Gluing mechanism

4. Automatic tool changer

5. Interfacing the controller with a computer

-To create a method to create the complete program from CAD model to actual component for a

specific component. (This involved using 4 softwares to create an integrated program).

1.5 ORGANIZATION OF THESIS

The thesis has been organized into seven chapters for the convenience of the reader.

The first chapter introduces the concept. It briefly discusses rapid prototyping technologies and

draws a comparison between them. It introduces segmented object manufacturing, illustrates the

scope of the project and finally presents the objectives of the study along with the problem

definition.

The second chapter is the literature reviews. It describes previous research done on machines

which are similar to the one available here. It draws a comparison between those machines. It also

presents machining strategies that have been used in the latter part of the project.

The third chapter shows the methodology used. It explains the project step by step in the form of

a flowchart

The fourth chapter sums up the work done during the initial phase of the project. It explains how

the SOM machine was revived. The components that were replaced. The studies done to interface

the controller with a computer. It finally explains the steps required to machine a specific object

on the machine.

9

The fifth chapter describes the tools required to create and implement the CNC code. It describes

the softwares and the steps required to create a code which can be custom run on this machine.

The SOM machine is unique in the sense that it has two work tables. Certain modifications need

to be done to enable running of code on this machine.

The sixth chapter presents a tabular and pictorial comparison between the object actually

manufactured and the CAD model. It lists down the observations and provides the probable reasons

that have caused deviation between the actual object and its CAD model.

The seventh chapter presents a conclusion and describes scope for future work.

10

2 LITERATURE REVIEW

2.1 SHAPEMAKER II

Thomas and co-workers developed a new rapid prototyping system for a large object called the

Shape-Maker II. The system employs a heated wire to cut layers with sloped edges from sheets of

25mm thick poly-styrene foam to fabricate large-scale prototypes. The heated wire is controlled

by two plotter heads, which simultaneously trace the top and bottom contours of a part slice.

However, the difficulties associated with the shape maker II in cutting of a multiple-connected

domain are due to the mechanism of cutting in which the heated wire cutter goes through the foam.

Other draw backs associated with the mechanism of the heated wire cutter are the slow response

in each rotation of axis when using the two plotter heads and the difficulties in the melted area due

to an inconsistency of power for heated wire, which is induced by a change of wire tension and

wire length during the rotation. Thomas and Chamberlain also developed the latest version of the

thick-layered ruled edge machine called Shape maker 2000. It is a four-axis water jet cutter

capable of building prototypes of 20 ft. or more in size [7, 8].

2.2 FREE-FORM THICK-LAYERED OBJECT MANUFACTURING

(FF-TLOM)

The principle of the proposed FF-TLOM technology is based on the shaping of the front faces of

each layer, which is performed in a free-form way. At a later stage, the machined layers are

assembled or stacked to obtain the Prototype Model (PM). The PM fabrication with the FF-TLOM

technology is achieved in such a way that possibly little or no finishing effort is needed for a proper

functional usage. The proposed technology uses thick high-density polystyrene foam layers, whose

front faces are shaped according to the principle of free-form cutting. In this method, the foam

layers are shaped with a flexible hot knife, which is heated by electrical current. The cutting blade

This chapter presents the literature survey done on rapid prototyping. It also describes existing

machines for themocole prototyping and the existing work on machining strategies which has

been used for the latter part of the project.

11

is flexible and its curvature is adjusted according to the local shape requirements set by the nominal

shape of the CAD-model.

2.3 FLEXIBLE BLADE CUTTING

The cutting is performed with a cutter, which consist of a flexible cutting blade supported at both

ends. This is shown in Figure 5 where the supports are rotatable and introduce an inclination at

both blade ends in respect to the U-shaped support structure. The shape and curvature of the blade

are defined by the inclination of the blade at both supporting ends, the length of the blade, the

endpoints and the assumption that the blade will take up a shape related to the minimal strain

energy inside the blade.

The cutting blade is electrically heated. Due to heat radiation towards the foam, the foam melts

locally and creates a gap in which the cutting blade can proceed. This is a continuous process,

which requires continuous energy input into the cutting blade to prevent the blade cooling down.

The amount of power required depends, amongst other things, on the cutting speed and the

electrical properties of the cutting blade. When the applied cutter speed is too high the melting

does not have proper time to have effect, the gap is not sufficiently shaped and the foam material

opposes the blade. This will create higher cutting forces, which will deform the blade shape. On

the other hand, when the speed is too low the foam melts away in a wide gap, which will have also

a negative effect on the cutting accuracy. Cutting speed, surface quality and provided heat are

important items and need thorough investigations to achieve a feasible cutting technology [9]

Figure 2-1: FF-TLOM head [9] Figure 2-2: FF-TLOM process simulation [9]

2.3.1 REQUIREMENTS FOR FLEXIBLE BLADE

12

The cross-section of the blade is considered constant having a high aspect ratio (thickness/width

ratio).

The cutting blade has to be flexible enough to take up the requested tool profile, referred

to as tool shape, in order to give the required shape curve.

The cutting blade should be rigid enough to sustain that tool shape during cutting.

The blade material should be electrical resistance in order to be heated up and also have

good dynamic heating characteristics.

The blade material is thus very important and it seems to be most likely that the requested

material properties cannot be achieved in one specific type of material and the application

of compound material for the blade will thus be considered. [9]

2.4 ROUGH MACHINING STRATEGIES

The main strategies for roughing a 3D component Model are called 3D Area Clearance. These

provide a choice of 2D material removal methods, which progressively machine the area (Slice),

up to the component contour, down a sequence of user-defined Z Heights. [10]

Figure 2-3: Rough machining strategies (isometric view) [12]

Sometimes known as Waterline Roughing the cutter steps down to a specified Z Height and

13

Fully clears an area (Slice) before stepping down to the next Z Height to repeat the process.

Figure 2-4: rough machining strategies (front view) [12]

For some components a secondary Area Clearance strategy is applied using the Rest Machining

options in conjunction with a smaller roughing tool. This will locally remove pockets of excess

material inaccessible to the original Reference Toolpath or Stock Model. This will reduce the

degree of tool overload and provide a more consistent material removal rate for any subsequent

Finishing operations. If the original material is in the form of a casting or fabrication then it may

not be necessary to apply any Area Clearance machining but to go directly for a semi-Finishing

strategy [11]

2.4.1 MODEL REST AREA CLEARANCE

It is generally good practice to use as larger diameter tool as possible for the initial Area Clearance

operation. This ensures that the maximum amount of material is removed as quickly as possible.

In many cases however the larger diameter tool may not have full access to certain internal corners

or pockets within the component. As a result these areas will require further roughing out with one

or more, smaller diameter tool before sufficient material is removed prior to running the Finish

Machining strategies. In the Model Rest Area Clearance options a smaller diameter tool is

referenced to a previously created machining strategy such that tool tracks will only be produced

locally within the remaining material (stock).[11]

2.5 FINISHINGSTRATEGIES

Finishing strategies machine the actual component form and where applicable, follow on from the

Area Clearance operation. Suitable values are required to control the accuracy and amount of

excess material to be left on a component by a tool path. The parameters used for this purpose are

called Thickness and Tolerance. Thickness is the amount of extra material specified to remain on

14

the work-piece after machining. This can be applied generally (as shown), or independently as

separate Radial and Axial values within the machining options. It is also possible to assign

additional Thickness values to groups of Surfaces on the actual model [12]

Figure 2-5: Material left on product after roughing [12]

2.5.1 RASTER, RADIAL, SPIRAL, AND PATTERN FINISHING

This section will cover Finishing strategies created by the downward projection of a Pattern, which

include four types, Raster, Radial, Spiral and (user defined) Pattern. Powermill generates the

toolpaths by projecting a wireframe form down the Z-axis onto the model. The standard patterns

applied in Raster, Radial, and Spiral are achieved by entering values directly into the Finishing

Form. The resultant Pattern can be displayed by selecting Preview before executing the command

by selecting Calculate. The Pattern option requires a user-defined geometric form (active Pattern),

which is projected down Z onto the model as a toolpath. Typical previews of the our Pattern

strategies are shown below as viewed down Z. [12]

15

Figure 2-6: Finishing patterns [12]

Out of the above strategies, the one that we shall use the raster strategy because:

1. Radial causes uprooting of grains and non-uniform surface finish, it results in more

material removed at the centre

2. Spiral takes a long time and the distance between adjacent spirals is limited by machine

ability

3. A user defined pattern is not required in this case as the object is not as complex

16

3 METHODOLOGY

Kinematic Analysi

3.1 FLOWCHART FOR METHODOLOGY

This chapter presents the methodology used for the project. It presents the steps that have been

used to fulfil the objectives in the form of a flow chart

Study of various machines and techniques available to manipulate themocole

Create the model in Solidworks and import the model to

Powershape

and slicing it

Literature Review

Study the programs to generate and test the code like Powermill,

Powershape, Surfcam DNC, Cimco and Solidworks to create the

CAD model

Manipulating the programs using notepad and Cimco to

enable running the program on our machine

Creating the programs for individual slices (machining

from both sides top and bottom)

B

A

Problem Definition

To make the SOM machine fully functional by

integrating all the sub-systems into the controller

and also Development of CNC code for making a

fully automatic conversion from CAD model into

expanded polystyrene prototype

17

Figure 3-1: Flowchart for methodology

Program works

as intended?

As intended?

Run the program

A

B

Creating and placing code for the functions of slicing and

gluing

Is the object as

per the

specifications?

Results and discussion

B

18

4 SEGMENTED OBJECT MANUFACTURING (SOM)

MACHINE

4.1 OVERALL VIEW OF THE MACHINE

The SOM machine and its components:

Figure 4-1: SOM Machine (overall view)

This chapter describes the SOM machine in detail. All its subsystems have been explained in

detail. The interfacing between the controller of the machine and computer has been explained

and the work that has been done during the initial phase of the project has been described

19

4.2 PRINCIPLE OF WORKING

The purpose of the machine is to manufacture prototypes out of themocole. This is done in multiple

stages using a novel concept of slicing which is explained below.

In conventional slicing strategies, the slice thickness and part accuracy are closely related. As

against this, in visibility based slicing, visibility is used as the criteria for determining the slice

thickness or segment geometry to be more precise. For this the given object is split into visible

slices, also known as segments. The intersection of any vertical ray with the v-slice will always

give us a pair of points. When the faces encountered by the ray happen to be vertical, one gets a

line segment as intersection in which case the end points of this line segment can be treated as the

pair of intersection points. This characteristic of v-slice ensures its machinability by a vertical

cutter from two opposite directions. Following figure illustrates the concept of v-slicing for an

object shown in Figure. [13, 14]

Figure 4-2: Possible slices obtained by visible slicing [13, 14]

20

Figure shows us the given object. Since the object can have multiple set of visible slices all

possible combination are shown in figures b,c,d,e. Figures b,c gives us equal and opposite 2pairs

of slices and the raw material required would be equal for both of these but figure d has the least

amount of raw material. Hence after obtaining all possible combinations of slices, a post

processing is done so as to give us a minimum amount of the raw material required.

If the slicing is accurate enough, the horizontal surfaces of the object can be obtained during the

slicing operation itself whereas the non-horizontal surfaces will require machining in scan milling.

Therefore, after obtaining the set of v-slices that have the least heights, we prefer to split them

further if any of the slices have large horizontal surfaces. Accordingly, the preferred set of slices

for this object will be the one shown in Figure 4.2 e. This is obtained from Figure d by splitting

the bottom slice at its horizontal surface. But the one that we will implement here would be d. The

reason being a larger number of slices reduces part accuracy along the z-direction.

Figure 4-3: Settings required to machine the bracket on a three axis machine [14]

The proposed v-slices can be correlated with the number of setups required in CNC machining to

produce the object by scooping out material from its bounding box. Figure a shows the blank of

this object in 1st setting. Figure 4.3 b shows the blank at the end of 1st setting. After reversing the

object, the remaining surfaces are machined except the eye-end hole (Figure c). Machining this

21

hole requires a separate setting as shown in Figure d. Therefore, CNC machining, which is purely

a subtractive process, requires three settings to make this piece from a blank. The same object can

be made through SOM in just two V-slices (Figure d), each requiring machining from top as well

as bottom; hence this object will have essentially four settings in SOM. SOM has one setting more

since the eye end hole is realized in two settings of different layers.

4.2.1 ALGORITHM FOR VISIBLE SLICING

Karunakaran et al [13] have developed an algorithm based on the principle of visible slicing that

decides the location of the slice, thickness of slices needed and post processing to combine

segments to give us the desired object. A face of the solid will be called invisible face if (i) its

normal is upward and (ii) it is shadowed by its other faces; otherwise, it will be called a visible

face. These are illustrated in Figure a. A contiguous set of invisible faces is called invisible patch.

While the segmenting can proceed in either the top-down or bottom-up manner, the building will

happen in a bottom-up manner only. The author has chosen segmentation in the top-down manner

in this algorithm. Algorithm for determining the V slices: [13]

The above algorithm produces v-slices but they could be more in number with the possibility of

combining some of the segments into one segment without affecting the visibility.

22

4.3 MACHINE KINEMATICS

The machine is a 3-axis machine. It has independent AC servo motors for movement along each

axis. The x and z axis have 2 lead screws of 5mm.The y axis has just one lead screw.

There are two work tables for machining, one is at the bottom of the frame and fixed rigidly and

the other is at the top and is movable. The top table can slide along the z-axis and uses brake pads

to hold its position. The raw material is mounted using double sided tape.

Figure 4-4: Kinematics of the som machine [4]

The figure above presents a schematic of the kinematics of the machine. The machine has a table

at the bottom where the work-piece will be deposited. The top table is for machining a visible slice

from the bottom.

4.4 MACHINE SPECIFICATIONS

23

The motion along the three axes takes place by means of three motors, the specifications of which

are as follows:

Fanuc AC servo motor

Model: is 8/3000

Motor specs:

A06B-0075-B503

No. C089X4228

Output: 1.2KW

Voltage: 153

Frequency: 133 Hz

Current: 4.9 Amp

Speed: 2000 min-1

Manual part number: B-65302

The motor uses the following encoder for positioning:

Pulsecoder iA128

Type A860-2020-T301

The motor is connected to the lead screw by using a beam coupling.

A beam coupling, also known as helical coupling, is a flexible coupling for transmitting torque

between two shafts while allowing for angular mis-alignment, parallel offset and even axial

motion, of one shaft relative to the other. This design utilizes a single piece of material and

becomes flexible by removal of material along a spiral path resulting in a curved flexible beam of

helical shape.

Wherever 2 lead screws have been used, they have been connected using a timer belt.

The hot wire gets a current of 4.5 A at a voltage of 24, DC.

The machine has 3, 3/2 single acting valves and 1, 5/2 double acting valve from FESTO.

The glue gun and the ATC are operated by 3/2 valves. The glue gun requires 1 and the ATC

requires 2. One to change position and the other to lock the tool in place.

The brake table is operated by a 5/2 valve.

The entire machine can be divided into three subsections

1. Machine tool

2. Controller

24

3. Software and interfacing

4.4.1 MACHINE TOOL

The machine tool includes all the mechanical systems of the machine, viz. ATC,spindle and cutter,

glue, hot-wire and chip disposal. Below is a brief description.

4.4.1.1 AUTOMATIC TOOL CHANGER (ATC)

The machine has a six tool ATC which is pneumatic. The pressure at which everything works is 5

bar. It is mounted on a frame which can move along the z axis. The ATC has been designed such

that two vertically opposite tools can run at the same time. There is a switch which enables the

ATC to do this. A plate depresses a roller when the ATC is indexed and vertically opposite tools

can spin simultaneously. The ATC also has a locking plate which gets engaged into a plastic

groove. The groove is part of the hot wire cutting system. When the locking plate is engaged, the

wire moves along with the ATC.

4.4.1.2 HOT WIRE CUTTING

There is a nichrome wire which runs parallel to the x axis of the machine. It can be heated and

the themocole can be sliced. The voltage of the wire is 4.5V.Nichrome is a nonmagnetic alloy of

nickel and chromium. It is silvery- grey in color, corrosion resistant and has a high melting point.

Due to its high electric resistance and resistance to oxidation at high temperature it is used as a

heating element.

4.4.1.3 GLUE GUN

The glue gun is used to attach the various machined slices of the themocole together. It uses

thermoplastic beads of glue from a company called Jowart. Thermoplastic meaning the beads

can be melted and dried repeatedly without significantly affecting their characteristics.

4.4.1.4 TOP TABLE MOVEMENT AND BRAKING

The top table is the second work table which can move along the z-axis. It is held in position by

four pneumatic brake pads which are normally closed (When air supply is off, the brakes are

clamped, and when the air supply is on, the brakes are released). The ATC table has four plates at

the four corners which support the top table. As the ATC frame moves upwards, a metal sensor

gets activated and the brakes are released. This causes the top table to move down with the ATC.

The entire top table comes down with the ATC frame. This feature is used to stick the slice on the

top table to the slice on the bottom table.

25

4.4.2 CONTROLLER

The controller is what enables the hardware of the machine to be controlled.

The controller and the three motors have come as a complete set. The operating manual for the

machine is attached at [15]. The controller is supplied by Fanuc. The model number is Fanuc series

Oi Mate-MC. It accepts inputs through a 25 pin parallel female port. It has been programmed to

perform certain unique to this machine functions as follows

M11: brake table release

M10: lock brake table

M21: hot wire on

M22: hot wire off

M12: glue gun on

M13: glue gun off

Some part of PLC programming was used to allocate these codes. This was done with the help of

a CNC controller expert.

4.4.3 SOFTWARE AND INTERFACING

The software used is SurfcamDNC. It is used to transmit data from a PC to the controller. A

detailed description of the interfacing follows.

4.4.3.1 BRIEF DESCRIPTION OF WHAT IS A SERIAL/PARALLEL INTERFACE

Since the subject of interfacing is quite vast we will limit our discussion to the interfacing used

between the SOM machine and the computer. For this particular connection. we used a DB9 male

connector at the PC end and a DB25 female connector at the machine end. This connection uses

the RS-232 protocol. Length of RS-232 links can be 80 feet or more depending on cable

specifications and required data transfer rates.

A UART (Universal Asynchronous Receiver/Transmitter) is a piece of computer hardware that

translates data between serial and parallel forms. A UART is present at the sending and the

receiving terminal. The basic job of a UART is converting data from parallel to serial for

transmission and from serial to parallel on reception. [17, 18].

4.4.3.2 PURPOSE OF VARIOUS PINS

The pin description is as follows

DB 9 Connector

26

1 - Data carrier detect

2 - Receive data

3- Transmit data

4 - Data terminal ready

5 - Signal ground

6 - Data set ready

7 - Request to send

8 - Clear to send

9 - Ring indicator

DB 25 Connector

2 - Transmit

3 - Receive

4 - Request to send

5 - Clear to send

7 - Signal ground

6 - Data set ready

8 - Data carrier detect

20 - Data terminal ready

[16]

The character framing is as follows

Figure 4-5: Character framing

If at all the parity bit is used, it comes after the data bits but before the stop bits. [16]

4.4.3.3 BYTES

A byte is a unit of digital information that consists of 8 bits.

4.4.3.4 BAUD RATE

The baud rate is nothing but the rate at which data is transmitted. It represents the number of bits

that are actually being sent over the media. It includes the overhead bits Start, Stop and Parity that

27

are generated by the sending UART and removed by the receiving UART. This means that seven-

bit words of data actually take 10 bits to be completely transmitted. In this case we use a baud rate

of 9600

4.4.3.5 PARITY

A parity bit, or check bit, is a bit added to the end of a string of binary code that indicates whether

the number of bits in the string with the value one is even or odd. Parity bits are used as the simplest

form of error detecting code. In this machine, we use even parity

4.4.3.6 STOP BITS

The bits that come after the data bits are called as stop bits. There may be one or two stop bits

depending on the system. Until the end of the last stop bit, there can be no new characters. Once

the last stop bit or bits are completed, the transmitter is ready to repeat the entire process again

from the start bit. In this machine, we used two stop bits.

4.4.3.7 HANDSHAKING

Handshaking determines the communications protocol that will be used to govern the flow of

information between the computer and the other side of the cable. Originally, serial ports used

handshaking to signal to the sending device that it was OK to send more information. This was

done because it is possible that the receiver may not be ready to receive more information.

However, as the speed of computers has increased substantially, they can easily outrun even the

fastest serial communication. In our case, we used XON/XOFF handshaking. XON enables

transmission and XOFF disables it. When the slave is ready to receive data, it sends an XON signal

to the master and when its input buffer is full, it sends an XOFF.[17, 18]

28

4.4.3.8 PIN DIAGRAM TO CONNECT THE CONTROLLER TO A COMPUTER

This was made according to the instructions of a CNC controller expert.

Figure 4-6: Pin diagram to connect the fanuc controller to a computer

4.4.3.9 MACHINE PARAMETERS

The machine parameters need to be configured as follows

0000 - 00000110

This parameter is used to set:

a) TV check

b) Code used for data output

c) Unit of input

d) Automatic insertion of sequence numbers

0020 - 0

This is used for selection of an input/output device or selection of input device in the foreground

0100 - 00000000


a) Character counting

29

b) EOB to be output in the ISO code

c) Output of the end of block in ISO code

d) Whether a program is read block by block or continuously

e) How to stop program operations

f) Action taken when a null code is formed during reading of code

0101 - 10000001


a) Number of stop bits

b) Whether the alarm for internal handy file is displayed or not

c) Code used for data input

d) Feed before and after data

0102 - 0

This parameter is used to set the number specified for the input/output device

0103 - 11

This parameter is used to set the baud rate[19]

4.5 THE STRUCTURE OF THE MACHINE

The machine structure is a box which has a metal plate at the bottom and four, one inch solid rods

on which the movement of the ATC takes place. There are three tables in all. At the very bottom

is the work table where themocole blocks are mounted. The mounting is done using double sided

tape. The next table holds the ATC and the y-axis. The third table is for machining a visible slice

from below. The machine is 900x900x1000 mm.

4.5.1 PROPOSED ALTERATION

We propose to increase the dimensions of the machine to 2000x2000x2500 mm. This will provide

more volume for machining thus making it suitable for large scale prototyping. The four supporting

rods are solid 25 mm ones. We propose to have 50mm hollow rods. This would improve rigidity

of the machine and wouldnt lead to an increase in weight.

30

4.6 THE SLIDES

The machine is a 3-axis machine. The controller came with three AC servo motors for the x, y and

z axis. The x and z axis have 2 lead screws of 5mm. The y-axis has just one lead screw.

The work table is not mobile but the ATC is.

4.7 THE BRAKES

The bottom table of the machine is fixed. The top table can move. The top table can slide along

the four rods mentioned in the previous section. The top table is held in position by four pneumatic

brakes. These brakes are normally closed (engaged when there is no air supply). When air is

supplied to the brakes, they are released and the table becomes free to slide down. This enables

the deposition of the slice onto the work table below.


Currently the brakes are released by one metal sensor at one vertex of the table. When this detects

a metal, it activates the air supply to the brakes thus releasing them. This however is risky and not

fool proof. It could lead to a fatal accident when someone inadvertently activates the switch while

working on the machine. We propose to activate it using a CNC code and sensor. This would

enhance the safety of the system. This has been accomplished by PLC programming with the help

of a CNC controller expert.

31

Figure 4-7: Photograph of the automatic tool changer (atc)

4.8 THE ATC

The automatic tool changer (ATC) assembly can house 6 different tools. It can be indexed at 60

degrees. At any given time, two opposite tools can be run. This is facilitated by using three rollers

which get depressed at a particular position of the ATC. This enables machining at both the tables,

the upper and the lower table. The ATC is operated by air. It occupies a volume of approximately

500x500x500 mm, considering the unusable space as well. The ATC has an inlet and an outlet for

the spindle and an inlet and an outlet for the indexing.

4.9 THE SPINDLE

There are six pneumatic motors which power the spindle. The rpm obtained is about 2500. We

require above 15000 rpm. This could either be obtained by increasing the flow rate or the pressure.

The pressure cannot be increased because it raises safety concerns. A higher pressure would

require replacement of the plastic pipes with metal pipes. This would raise the expense as well. So

we would increase the rpm by increasing the flow rate. Currently, the pipes that carry air are too

thin to handle increased flow. They need to be replaced with pipes of a larger diameter.

32

The current pipes have a diameter of 6mm. We have replaced them with 8mm pipes.

4.10 CUTTER

The cutters that we use currently are either milling cutters or drill bits. They have not been designed

to cut themocole, they are metal cutters. This results into undesired surface finish and chipping of

the themocole. Themocole is made up of granules, the surface finish is inversely proportional to

the granule size i.e. higher the surface finish, smaller should be the granule size. So the feed rate

and the rpm have to be perfectly optimized to get desired parameters.


There is a wide variety of cutters available for metal cutting. Checking each and every cutter to

optimize parameters would be time consuming. So we intend to make our own cutter. At present,

there is aFused Deposition Modeling (FDM) machine present in the lab. This could be used to

print out the plastic body of the cutter. We could have a cutter having the exact dimensions as

required. The cutter would have a ball nosed tip. It could have a single cutting point which is made

out of a paper cutter. This way the weight of the cutter would be very low thus assisting in reaching

higher rpms. It would be cheap as well.

33

Figure 4-8: Photograph of the glue gun

4.11 GLUE GUN

The glue is attached at the back of the ATC. It is required to stick the slices of the object together.

It operates using thermoplastic beads of glue from a company called Jowart. The beads melt on

application of heat and solidify on cooling down. The beads are thermoplastic meaning they can

be heated and cooled a number of times with no significant changes to their properties. The glue

melts at approximately 120 degrees Celsius. The melting takes place by using a cylinder wrapped

with a heating coil. The glue is dispensed using air pressure.

4.11.1 OPERATION OF THE GLUE GUN AND THE TYPE OF GLUE TO BE USED

Various properties need to be kept in mind while using the glue gun. In applications where the

SOM product is used as pattern for casting, the ash content needs to be low. If the glue has

significant ash content, it can cause defects in the casting. The slices are deposited from the top

layer to the bottom layer. After deposition the top table moves up. When the glue is being deposited

on the slice, it should not dry out before application is completed. So it needs to have a sufficient

setting time. And while the top table moves up, the slice should not get disturbed from its position,

34

so the drying has to be sufficiently quick as well. The glue should not react thermally or chemically

with the themocole or disturb the shape and finish in any way.


Instead of the current glue, we intend to use 3M scotch-weld polystyrene foam insulation adhesive

which has been specifically formulated to stick themocole. The glue is available as 54 gallon

drums.

4.12 AREA FILLING ALGORITHM

The glue cannot be applied in a haphazard manner. The path of application needs to be planned

for accuracy and efficiency. An area filling algorithm would help determine the best possible way

to apply glue.

4.13 HOT WIRE SYSTEM

Figure 4-9: Photograph of the hot wire slicing system

4.13.1 FUNCTIONING OF THE SYSTEM

Themocole melts on application of heat. The system works on this very principle. There are two

holders for the nichrome wire which supply current to it. The wire gets heated and it is fed through

35

the themocole to produce a cut. The movement of the hot wire takes place according the following

mechanism

Figure 4-10: Hot wire locking mechanism

There is a block at the back of the ATC which engages in a slot as shown. As the ATC moves, the

cutting system also moves.

4.13.2 PARAMETERS THAT DICTATE THE CUTTING ACTION OF THE WIRE

The parameters influencing the hot-wire cutting of EPS are:

1. Foam material

The softer the material (i.e. lower density), the easier it is to cut

2. Supply voltage

3. Feed rate

If you move the wire faster, less themocole gets burnt in the process. If you move the wire slowly,

more of it gets burnt.

4. Wire Tension

The more taut the wire, the more planar the surface

5. Wire Material

6. Wire Diameter

A thicker wire would have a lower resistance so according to the equation q=i*i*r, heat generated

would be lower and vice-versa.

Apart from these parameters, there are other things which influence the cutting.

Due to heat, the wire elongates noticeably and forms a downward bow (because of gravity), this

causes a similar effect on the surface being cut. So a planar surface will look like a concave

36

surface. In order to take care of this, we have two springs at each end of the wire to keep it taut at

all times.

While cutting the themocole, because of material resistance, the wire forms a bow in the cutting

plane as well. This, however does not affect the surface of the work piece.

4.14 WORK DONE TO BRING THE MACHINE INTO WORKING

CONDITION

The following sub-sections describe the work done to bring the machine into working condition.

4.14.1 ESTABLISHING COMMUNICATION BETWEEN THE CONTROLLER AND A

COMPUTER

Since the machine has been lying unused for about three years, there was very little information

available about how to connect the controller with a computer. We managed to make a new wire

with the required pin connections and made a successful connection by changing certain

parameters (mentioned in the previous chapter) in the controller.

4.14.2 IMPROVISING THE CABLE TO CONNECT VIA USB

Since most computers these days have USB ports and serial ports are not popular anymore, we

need to have an interface that has a USB connector on one side and a DB25 pin on the other. There

is a USB to serial convertor readily available in the market which was used for this purpose.

4.14.3 REPAIRING THE AXIS CONTROLLER

The axis controller controls the motors that provide movement to the axis. This controller was sent

to Fanuc, Bangalore for repairs.

4.14.4 REPAIRING THE COUPLING THAT CONNECTS THE MOTOR WITH THE X-

AXIS

The motor is connected to the lead screw by a coupling, this coupling has become loose so we

were not getting motion along the x-axis, and this was fixed by removing the entire assembly with

the motor and re-tightening it.

37

4.14.5 REPLACING THE BATTERY THAT HELPS MEMORIZE THE ZERO POSITION OF

THE MACHINE

The machine zero can be set from the parameters. This is required to be done only once and then

the controller memorizes it. However, because of a faulty battery, the machine did not memorize

the zero position and it had to be reset every time we started the machine. The battery was replaced

and the problem was solved.

4.14.6 REPLACING RUBBER COMPONENTS

Because of non-usage, the rubber components of the machine were spoilt and had to be replaced

4.14.7 OILING THE VARIOUS JOINTS TO GET THE MACHINE IN WORKING ORDER

The hot wire cutting mechanism was not functioning properly. The hot wire is supported at two

ends and whenever one end moves, the other has to move automatically. This was not happening

before because the pulley was not tightly attached on the rod that connects both ends. Also, some

of the moving parts had rust on them, so we opened the assembly, cleaned it and oiled it

4.15 CASE STUDY

The sub-sequent sections describe an object that is proposed to be built on the SOM machine using

the concept of visible slicing.

We will describe the building of the object with 11 figures and 11 steps as follows

Figure 4-11: Proposed case study

38

Figure 4-12: steps 0 and 1

4.15.1 STEPS 0 AND 1

Attach the themocole block at the top worktable and machine the bottom of the first slice

Figure 4-13: steps 2, 3 and 4

4.15.2 STEPS 2,3 AND 4

Bring the top worktable down, attach the bottom of the first slice to the bottom worktable and slice

it. Bring the top worktable back up.

39


4.15.3 STEPS 5 AND 6

Machine the top of the first slice and the bottom of the second slice

Figure 4-15: steps 7, 8 and 9

4.15.4 STEPS 7,8 AND 9

Get the top table down, attach the bottom of the second slice to the top of the first slice and take

the top worktable back up

40


4.15.5 STEPS 10 AND 11

Machine the top of the second slice and the required component is ready

This chapter gave the reader, an overall idea the SOM machine. The case study presented has been

implemented after the machine is brought to working condition. The next chapter describes the

complete process to create the code. It describes all the stages of manufacturing and gives reasons

for making specific decisions.

41

5 IMPLEMENTATION AND EXECUTION OF CODE

5.1 DESCRIPTION OF THE BRACKET THAT WILL BE

MANUFACTURED

A CAD model of the object was provided by our guide, it has been displayed in the figure below

Figure 5-1: CAD model of the object to be machined

It is a bracket which is used to mount large doors onto hinges. The task was to slice the given

object into visible slices [13] and then create a program which would create the entire object

automatically by pressing a single button.

The slices have been shown in the latter part of the chapter.

5.2 STEPS TO CREATE THE BRACKET (BRIEF OVERVIEW)

5.2.1 IMPORTING THE MODEL SLICES INTO POWERMILL

The two slices of the model have to be imported into Powermill. Powermill accepts a lot of

standard formats including, but not limited to .stl, .iges, .psmodel, .step. Out of these, we require

compatibility for .stl as that is the format in which our model is. In-order to import the model, just

drag and drop the model file into Powermill interface.

This chapter deals with giving an overview of the steps to manufacture the bracket followed by

a detailed explanation of the tools that have been used to prepare the code. The steps required

in each software to generate the required code have been described.

42

5.2.2 CREATING AND SIMULATING THE CODE

Subsection 5.3 describes the entire process used to create the code. It describes the softwares that

are required for the creation of the code. Since this is a custom machine, the code making process

is also customized and various softwares have been used. The steps to be performed in each

software along with screenshots have been given in this section. The various settings required have

also been specified. Every step has been explained in detail.

5.2.3 MOUNTING THE THEMOCOLE BLOCK ONTO THE MACHINE

The dimensions of the object are 300mm,170mm and 88mm in the X,Y and Z directions

respectively. Because of machine limitations, there needs to be extra material of 35mm in the z

direction. The machine has two movable platforms and the lower platform supports the upper

platform. When the upper platform is resting on the lower, the nichrome wire used for slicing is

35mm away from the base of the upper worktable. Hence the extra material. The type of themocole

used here is standard, 22 density and fine grain. It is denser than the one that is commonly used

(density 16). The density is basically the weight in kgs of a 1x1x1 meter block. The size of block

mounted was 320x190x100mm. It is mounted on the upper work table using double sided adhesive

tape.

5.2.4 SELECTING AND MOUNTING OF TOOL

The automatic tool changer can hold 6 tools at a time. The tools are held using a collet and nut

type of tool holder. The maximum diameter of the shank that the holder can hold is 6mm.

For machining themocole, we require two types of tools, one for roughing and the other for

finishing. The tool that we used for roughing is a 10mm end mill cutter. This type of cutter has a

flat bottom and so machining of flat surfaces can be done faster and a larger step over can be used.

The tool used is made of High Speed Steel (HSS). Since we are machining themocole, there is no

special requirement for the material of the tool. The tool that we used was available in the lab.

Only the shank size had to be reduced by grinding to fit it into the tool holder.

The tool that was used for finishing was a ball-nose type with diameter 5mm. a ball-nose type of

tool, as the name indicates has a hemi-spherical end. Instead of a flat end, it has a point end. This

results into better accuracy, and more flexibility in terms of machining profile. Hence it is used as

a finishing cutter.

43

5.2.5 INTERFACE AND TRANSFER OF PROGRAM

The program is transmitted using a cable which has a 25 pin male port at one end and a 9 pin

female port at the other. The 9 pin end is connected to a serial to USB converter (manufactured by

BAFO). Once connected, the machine is put into remote mode and transfer is initiated using

SurfcamDNC. It has been explained in detail in the latter part of this chapter.

5.3 TOOLS USED TO CREATE AND EXECUTE THE CODE

5.3.1 DELCAMPOWERMILL

Figure 5-2: Powermill interface

5.3.1.1 INTRODUCTION TO POWERMILL

Delcam covers many aspects of the product development process within its software portfolio, but

its core focus continues to be on CAM. The companys flagship product, PowerMill, has long been

one of the most advanced systems for machining highly complex 3-axis mould and die type

components, but in recent years the system has evolved and now handles five-axis machining as

well as more routine production machining tasks such as hole drilling, and basic pocketing. [10]

44

5.3.1.2 APPLICATIONS

Typical applications of Powermill include but are not restricted to

Aerospace components

De-featuring models

Repairing holes and gaps

Creating reference surfaces for multi-axis parts

5.3.1.3 TYPICAL STEPS INVOLVED FOR MAKING A PROGRAM IN POWERMILL

The steps have been outlined assuming that the model is ready in a compatible format. The best

option would be to use Delcams in-house software, PowerShape to model components. If that is

not possible, other softwares like Solidworks, Catia or Autocad can be used.

The component has to be sliced into a number of slices, which can be independently machined

using the SOM machine layout. This slicing needs to be done manually.

For our purposes, we wanted a bracket to be machined. This bracket is used to hinge doors to their

frames. The bracket model was obtained from our guide. The model was in the .stl format. The

model was sliced using the create new plane feature in PowerShape and then exported to the

.iges format.

Programs need to be created individually for each slice. For our purposes, the given object was

broken into two slices.

Figure 5-3: Object to be machined (slice 1)

Figure 5-4: Object to be machined (slice 2)

The first slice was imported first. Since we start by machining from the bottom of the slice, the

slice needs to be inverted and a block needs to be defined around it. This is done using the create

block feature select the style as box and then letting it calculate the block automatically. The

45

block gets calculated considering the maximum dimensions of the object along the x, y and z

directions.

Let us define the vector of the object as the line perpendicular to the floor on which the object is

resting upright and pointing upwards.

Figure 5-5: Object vector

Once this gets done, we can see a faint box around the object. The next step is to define the work

plane. We have oriented the first slice such that the bottom is facing up. The z-axis has to be

aligned such that it points out of the object. There is a tree on the left side of the screen, called

Explorer pane with a subtitle work plane. Right click on it and choose create and orient work

plane using center of block. Once you do this, you can see dots at all the important points of the

block. Select the one at the center of the block. Orient the work-plane using the work-plane editor

and such that the z-axis points upwards, the x-axis is along the longer side of the object (as there

is more space available in the x-direction on the machine as compared to the y-direction).

5.3.1.4 DEFINING THE TOOL

Now let us define the tool. The type of tool has to be defined. There are many alternatives, but for

our purposes we define it as either a ball nosed tool or an end mill. The ball nosed tool has a semi-

circular end and is usually used for finishing purposes. The end mill has a flat end and is used for

roughing purposes. Since we are starting the machining we shall select an end mill tool.

The diameter of the tool has to be defined, the one that is available with us has a diameter of 5mm.

define the shank and the holder for the tool and give them appropriate values.

5.3.1.5 MACHINING

Machining themocole is different from machining metal because the tool can be used with lesser

restrictions. It can plunge into themocole without any consequences. The material also need not

be machined completely from the raw block. The tool can be run along the border only, the rest of

46

the block may not be machined. This would separate the object from the rest of the block. But the

separation would not be total. It would be attached to the block at some places. Total separation

would be attached when the block is sliced.

The next step would be to create a boundary. The boundary would be created using a subtitle in

from the same tree. Next, recreate a block using the boundary. The block gets reformed along the

border of the block.

5.3.1.6 SELECTING THE TOOL-PATH STRATEGY

Depending on the type of machining required, there are many machining strategies available in

Powermill. There are 5 main strategy titles available and each in turn has sub-strategies.

The main strategies available are:

1. 2.5D area clearance

2. 3D area clearance

3. Blisks (Blade+Disk)

4. Drilling

5. Finishing

Out of these, 3D area clearance is the most relevant for our job and after that, we shall use a

strategy to finish it.The 3D Area Clearance tab on the Strategy Selector dialog contains the main

strategies for roughing a 3D component. In general, Powermill machines a series of slices at user-

defined Z heights. The tool steps down to a specified Z height and fully clears an area (slice)

before stepping down to the next Z height to repeat the process.

In 3D area clearance, the sub-strategy used is model area clearance. This strategy clears each

slice in 2D and follows the feature profile. Then it steps down and machines the next slice and so

on until everything has been machined. The dialogue box looks as follows

47

Figure 5-6: Settings for rough machining

The parameters of the dialogue box need to be set appropriately. The work plane has to be selected,

the block needs to be selected. The style that we select here is offset all. The step over needs to

be calculated according to the formula: 80% of the cutter diameter.

The thickness box indicates the amount of material which will be left over the component to be

removed while finishing. For our purpose, a thickness of 1mm is sufficient. Fill up the parameters

for speed, feed etc in the dialogue box.

Next, we set up the rapid move heights, this would be the height until which the tool can travel

using a rapid feed rate, and then it slows down to linear interpolation. After setting up all the

parameters, we click on calculate. The program them calculates the tool path. The tool path can be

simulated using Viewmill. Viewmill is a tool which can simulate how the machining operation is

going to take place. Error can be rectified using this tool and the surface finish can be observed to

a certain extent.

48

Once the tool path has been modified and calculated to satisfaction, we proceed to compute the

program.

5.3.1.7 GENERATING THE NC CODE

The code is generated using the following steps.

1. Right click on the tool path in the Explorer Pane.

2. Go to the tool path you have generated and click on activate

3. Once, the tool path is active, you shall see lines along the object which shows the tool paths

4. Right click on the tool path again and select create individual NC programs.

5. This creates indivicudal NC programs.

6. Go back to the NC program sub title in the Explorer pane and right click on the program

that has just been created.

7. You will find an option called settings, click on it, you shall get a window like this:

Figure 5-7: Settings to create the nc code file

8. Change the name of the output file as desired and select the Machine Option File as

Fanuc.opt. The machine option file is decided by the machine on which the code will be

run. For example, if we wish to run the code on a Hermle controller, we choose the

appropriate machine option file. In this particular case, the controller is Fanuc so we need

to use that machine option file.

49

9. Click on accept, the code gets generated as a .tap file.

Let us name this code as code I.

Now import the next slice into the program and delete the previous slice. Keep the origin at the

same point as before. And repeat all the steps that we performed for slice I.

5.3.1.8 CREATING THE FINISHING CODE

The roughing codes that have been created would leave 1mm of material over the finished product.

This would need to be removed using a finishing strategy. Delete the previous toolpath for each

slice. We shall use the same work plane and tool to create the new tool path. Go to machining

strategies, select finishing strategies and select raster finishing. This is a strategy that is commonly

Documents

Complete Thesis on Segmented Object Manufacturing