Abrasive Machining and Finishing Operations

Question 1

When using a computer controlled grinding machine, which features can be automated?

Answer 1

Load/unload workpiece
Clamp workpiece
Repeat cycle path
Sharpen wheel between passes

Question 2

What does the selection of a grinding process depend on?

Answer 2

Part shape
Ease of fixing
Part size
Production rate

Question 3

Describe lapping

Answer 3

A process wherein fine abrasive particles are embedded into a relatively soft material called lap
The lap can be made out of leather, cloth, cast iron, copper
It is used on flat or cylindrical surfaces of both metal and non-metal parts

Question 4

Describe sanding

Answer 4

Uses coated abrasives i.e. sand paper and emery cloth
The grains are electro-statically deposited on backing material
Coating is made of resin
The process is widely used in finishing flat or curved surfaces of metallic and non-metallic parts

Question 5

What’s the main difference between electro-polishing and other finishing operations?

Answer 5

For other finishing operations, the peaks of rough bits are grinded down. Whereas for electo-polishing the troughs are also broken down

Question 6

List the general finishing operations by increasing machining cost

Answer 6

As cast or cut
Rough turn
Semi-finish turn
Finishing turn
Grinding
Honing

Question 7

Describe the grinding process

Answer 7

A chip removal process

The grinding tool is arranged of irregular shaped grains spaced randomly along the periphery of the cutting wheel

Question 8

Briefly describe Ultrasonic machining

Answer 8

Material is removed from a surface by micro-chipping or erosion with fine abrasive grains

Question 9

What material is ultrasonic welding best suited to?

Answer 9

Hard and brittle materials as the impact stresses are high enough to cause microchipping and erosion of the workpiece surface
e.g. glass, ceramics, silicon, carbides, precious stones, composites and hardened steels

Question 10

What will happen if the bond between abrasives is too strong or too weak?

Answer 10

Too strong - Dull grains cannot be dislodged to allow other sharp grains to perform grinding
Too weak - Grains become dislodged easily, hence maintaining dimensional accuracy becomes difficult

Question 11

What’s an abrasive?

Answer 11

A small, non-metallic hard particle with sharp edges and irregular in shape

Question 12

What is abrasion used for?

Answer 12

To remove small amounts of material from a surface by a cutting process that produces tiny chips
To hone, lap, and polish workpieces

Question 13

What is attritious wear?

Answer 13

The wear of the grains, the flank wear of a cutting tool
Caused by friction
It is the contact of grain and workpiece material involving physical and chemical reactions

Question 14

What is honing used for?

Answer 14

To size and finish bored holes e.g. engine cylinders
To remove errors left by boring
To remove tool marks left by grinding

Question 15

List 5 examples of abrasive finishing operations

Answer 15

Sanding
Honing
Lapping
Polishing
Electropolishing

Question 16

Which has the slowest MRR, polishing and abrasive machining or electro-polishing?

Answer 16

Electro-polishing, but you get a smoother surface finish

Question 17

Describe the vibrating process of ultrasonic machining

Answer 17

The tip of the tool vibrates at a frequency of ~20kHz and an amplitude of ~0.05mm
The vibration drives the abrasive grains at high velocity into the workpiece

Question 18

Why is electro-polishing suitable for polishing irregular shaped workpieces?

Answer 18

Polishing is accomplished without mechanical contact with the workpiece

Question 19

Describe bonded abrasives

Answer 19

Each abrasive grain removes only a very small amount of material at a time
Abrasives are boned together to form a grinding wheel for higher material removal rate

Question 20

What’s abrasive machining?

Answer 20

A method used to produce parts with high dimensional accuracy

Question 21

Describe honing

Answer 21

A stock-removal process using abrasive stones to remove very small amounts of metal

Question 22

What is the limitation of ultrasonic welding?

Answer 22

Each job requires special tooling

Question 23

Describe electro-polishing

Answer 23

A DC electric current is constructed using the workpiece as the anode, usually submersed in electrolyte
As current is applied, material is oxidised and then dissolved by the electrolyte , stripping it from the surface

Question 24

Name and describe the bond type used for bonding abrasives

Answer 24

Clay and feldspar (crystalline structure)
Vitrification (substance to liquid) is used to produce a glassy, amorphous structure (removing heat quickly or using additives)
Strong, stiff, resistant to oil, acid and water

Question 25

Why is the stress produced by abrasive particles hitting the workpiece high?

Answer 25

The contact time between particle and workpiece is short

The area of contact is very small

Question 26

Why is porosity essential in bonded wheels?

Answer 26

It provides clearance for the minute chips being produced

It provides cooling

Question 27

What type of material iselectro-polishing good for?

Answer 27

Brittle as it makes no contact

Question 28

Describe grain fracture

Answer 28

Abrasive grains are brittle
If grains become dull, grinding becomes inefficient
Therefore the grains should fracture moderately to expose sharp grains

Question 29

Why is electro-polishing expensive?

Answer 29

Surface needs to be as pure as possible (washing, cleaning, de-greasing etc.) before it goes into the electrolyte.
Then it has to be cleaned again to remove the electrolyte.
More steps makes it more epensive

Question 30

Describe polishing

Answer 30

A process that produces a smooth, lustrous surface finish

It is done with disks or belts of fabric or leather coated with fine powders of aluminium oxide or diamond