Finishing methods

Roughing vs. finishing

Roughing – removing material as fast as

possible, without special demands on

surface and low demand on precision –

high Q, high IT, high Ra

Finishing – making final surface with

wanted properties. Remowing residual

material, improving geometrical and

dimensional tollerance – low Q, low IT,

better Ra

3

GRINDING

the finishing method with very wide use area;

grinding wheel is a multiple cutting edges tool consisting from abrasive grains and a bondingmaterial;

grinding can be likened to the milling process

4

Grinding process

t – chip thickness

d – depth of cut

5

Grinding wheels

Abrasive grains:

Al2O3 – tough – most common material

for: steel, Fe alloys

SiC – hard

for ductile metals (Al, brass,

stainless steel) and brittle metals

(cast iron)

cBN – for fine grinding

diamond dtto

GRAIN SIZE (grit): 0,003 – 3 mm

6

Grinding wheels

Bonding material:

vitrified bond – clay + ceramic materials

(„baked“)

silicate bond – Na2SO3

metallic bond – bronze

(for cBN and diamond)

rubber bond – (for cBN and diamond)

7

Grinding methods

A) surface grinding – plain flat surfaces

- horizontal grinding – horizontal spindle

- vertical grinding – vertical spindle

B) cylindrical grinding – rotational surfaces

8

Surface grinding

9

Surface grinder

10

Grinding methods

A) surface grinding – plain flat surfaces

- horizontal grinding – horizontal spindle

- vertical grinding – vertical spindle

B) cylindrical grinding – rotational surfaces

1. external grinding

- centre grinding – a workpiece is rotated between centres

- centreless grinding – a part is supported by a grinding wheel and a regulating wheel

2. internal grinding

11

Cylindrical grindinga) external

b) internal

12

External cylindrical grindingFeed motion types in centre grinding:

a) traverse feed

b) plunge cut

13

Center grinding with an inclined in-feed –

an operation example

14

External centreless grinding

15

Internal grinding – traverse feed

16

Internal grinding – plunge cut

17

Grinding – tolerances and surface finish

Type of cut IT Ra

roughing 9 – 11 0,8 – 6,3

finishing 5 – 7 0,2 – 1,6

fine finishing 3 – 4 0,025 – 0,4

Finishing methods

With material removal – generative

methods

(fine machining, honing, superfinishing,

lapping)

Without material removal – forming

methods

(glazing, blasting, tumbling, polishing)

1. Fine machining

Machining process

Turning or milling with depth of cut close

to minimum depth of cut

Fine cylindrical of flat surfaces

Fine machining

Tools

Turning – high precision inserts (PCD -

alluminium, coated SC)

Milling – special shaped inserts, large

diameter facing milling heads

Fine machining - examples

Video 001

Fine machining properites

Low depth of cut

Ap = 0,01 – 0,05 mm

High cutting speeds – up to 1000 m.min-1

High cutting forces, high spindle load

IT = 4 – 6

Ra = 0,1 – 0,4

2. Honing

Abrassive process

Small amout of material is removed by

honing stones

Mainly internal holes (bored and ground

holes)

Honing

Tool:

Honing head with honing stones

Honing stones:

Made of abrasive material

Adjustable

Seated on pushing springs

Honing

Material of stones

Any abrasive material can

Be used for a honing stone

- Same materials like grinding stones

(corundum, SiC, CBN, PCD)

- more precise shape, smaller grain (10-50 μm)

- Cutting fluids are used for lubrication

Honing

Available as tool for CNC machines

Various diameters (4-40 mm)

Spring mounted (to adapt to hole)

Movement with CNC

cycle

Small tools (1-20mm)

Honing – process mechanics

Honing head is

1) Rotating –

reciprocitive

2) Oscilating – up and

down

3) Honing stones are

pushed to the

surface

Video 002

Honing – process mechanics

Two speeds combined

together make unique

movement and special form

of tool path.

Honing – machine tools

Special horizontal or vertical honing machines

Honing – machine tools

CNC horizontal or vertical honing machines

Honing - examples

Honing - properties

Improving the geometrical accuracy (IT)

mainly

Setting certain surface pattern

(lubrication)

Expensive and time consuming

IT = 3 to 6

Ra = (0,025)0,1 – 0,4

3. Superfinishing

Abrassive process

Small amount of material is removed by

moving superfinishing stone

Both cylindrical and planar surfaces

Superfinishing

Tool:

Superfinishing stone

Has the negative shape of the machined

surface (or it can be flat for large

surfaces)

Abrasive material again – fine grained (to

20 μm)

Principle

The superfinishing stone is sliding on a layerof lubricant on the surface and pushed by certain force

1) The surface is rough – peaks looking outof the lubracant layer

2) The stone cuts the peaks – the surface forlubricant is bigger, more sliding

3) The stone cuts all peaks, no more materialremoval

Superfinishing - surface

Superfinishing - methods

Cylinders

Cones

Flat surface

Shape surface

Superfinishing - properties

Not improving the geometry!!! (IT remains)

Lower speeds and force than gringing or

honing

MethodCut. Speed

(m.min-1)Move Presure (MPa)

Grinding 1800-3500 None (infeed) 14-140

Honing 100 - 250

50 cycles (length

of hole – 150

mm)

3,5 – 7

superfinishing 6-14200-1000 cycles

(1-5 mm)0,02 – 0,07

Superfinishing - properties

Ra = 0,025 – 0,1

Lubricant is used to carry away chips and

minimize heat (deformation) – kerosene

is used

Superfinishing – machine tool

Superfinishing device

– mounted on lathe

Superfinishing

Machines – special,

Expensive type (multi-

ple parts, long travel

distance)

Video 003 Video 004

4. Lapping

Abrassive process

Removing very small amount of material

Removing surface undulations,

roughness, tool marks and surface fuzz

from grinding

For all types of surfaces

Lapping Tool:

A flat disc or plate made of cast iron, al-

alloy, copper, brass (low strength

material)

Abrasive particles are carried by an agent

– grease, oil, water (higher viscosity

means higher abrasion)

Lapping - methods

The lapping tool is rotated (oscilated) and

moved irregularly across the machined

surface

- Equalising laping – removing previous

surface shape, flatening (spur, helical

gears)

- Forming laping – lap is the negative

shape of the surface

Lapping - methods

For:

Holes

Flat surfaces

cylinders

Made:

Manually

mechanically

Lapping - methods

Flat surfaces

Lapping plate (different sizes, manual,

machine operated

- Moved irregularly along the surface

Lapping - methods

Machine lapping

Part are placed between a rotary and stationary

lap. Part are carried by a workpiece holder. Part

are placed excentrically so is the rotating lap.

This makes the parts rotate and move

Lapping - examples

Video 005

Video 006

Lapping - properties

Lapping removes all tool traces –

improves durability, lowers friction

Gives best surface quality (glass, mirror

lapping)

IT = 1 – 5

Ra = 0,01 – 0,16

6. Blasting

Two forms

- Forming (angle 80°)

- machining method (for angle of impact

bellow 45°)

Particles are thrown at surface

All kinds of shape

Blasting - tool

Blasting elements are transported by high

presure air to the surface

Hardened steel balls

cast iron balls

Steel wire pieces (rounded)

Glass balls – aerospace industry

Blasting - examples

Video 007

Video 008

Blasting - Aerolap

7. Tumbling

Forming method, abrassive method

Part to be machined and tumbling

particles are placed in rotating cylinders

Non defined surfaces

Tumbling - method

Abbrasive particles and parts mixed

together

Special rotary or vibrational mills

steel cylinders, inner rubber linning (to

prevent abrasion)

Sometimes active cutting fluid (water,

NaCl, NaNO3, H2SO4 ) helping to

remove the surface layer

Tumbling – surface quality

Tumbling - tools

Abbrasive particles – non-uniform

pieces of grinding stones, porcelain,

ceramics (5-20 mm)

Hardened steel balls (4-10) little surface

hardnes improvement

Soft particles for tumbling-polishing (dry

corn peels, palm bark, wood chips)

Video 009

Video 010

Tumbling - machines

8. Polishing

Abrasive method

A friction between the polishing tool and

part is caused by polishing media

(paste) heat melts the peaks of surface

All surface mainly flat surface with no

strength demands

Polishing

Abbrasive material is bond

to a tool (disc, belt) or it is a

media (paste) freely between

tool (textile disc, belt) and

part

NO improve in shape or

accuracy!!

Just improves the surface quality

Polishing - tools

Discs

– multi-plated : of fabric, leather, cotton

- Solid : rubber, wood, cork, mild metal

Brushes

- Made of fibres : plastic, metal wire (0,1-1,2 mm)

Belts

- Endless belt pushed to the part. Betterand more productive than discs.

Video 011

Video 012

Video 013

Polishing - properties

Cutting speed

25-40 m.sec-1

No IT improvement

Ra 0,2 - 0,4 (removes tool paths)

!!! Implicates residual stress due to high

temperature !!!

Schedule WS 2016/2017

lesson 11 – 5.1.2017

Lesson 12 – 10.1.2017 (Tuesday)

Lesson 13 – 12.1.2017

Video links:

Fine turning

001 - http://www.youtube.com/watch?v=do6BJA7G3R0

https://www.youtube.com/watch?v=cTCegI1HvJo

Honing

002 - http://www.youtube.com/watch?v=IuzBQlYFgXo

Superfinishing

003 - http://www.youtube.com/watch?v=WNkNgsnov7o

004 - http://www.youtube.com/watch?v=ePhAIJDjouE

Lapping

005 - http://www.youtube.com/watch?v=RfC5H4dA-ds

006 - http://www.youtube.com/watch?v=fnoVV-RWIWY

Blasting

007 - http://www.youtube.com/watch?v=zK258AM2Axo

008 - http://www.youtube.com/watch?v=Q8qN9QYlzvI

Video links:

Tumbling

009_http://www.youtube.com/watch?v=QR1mBCFhlpM

010_http://www.youtube.com/watch?v=iIdc2YhkG5o

Polishing

011_http://www.youtube.com/watch?v=TnzEMkkCxpw

012_http://www.youtube.com/watch?v=G4xC_GzYAKM

INOX polishing

013_http://www.youtube.com/watch?v=l-Zf2AAgA5U