Lecture 10 - Abrasive Machining and Polishing

Question 1

Abrasive machining definition

Answer 1

Method to produce parts with high dimensional accuracy

Removes small amounts of material from surface by cutting process that produces tiny chips

Question 2

Abrasive definition

Answer 2

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

Question 3

Abrasive bonds

Answer 3

Each grain removes small amount of material. bonded together to form grinding wheel for higher MMR

Clay and feldspar bonds. Glassy amorphous structure (removing heat quickly)
Strong, stiff, resistant to oil acid and water

Question 4

Bond fracture

Answer 4

Too strong - dull grains cannot be dislodged for sharp grains to perform grinding

Too weak - grains dislodged too easily and dimensional accuracy becomes difficult

Question 5

Attritious wear

Answer 5

Wear of grains caused by friction

Contact of grain and workpiece material involving physical and chemical reactions

Question 6

Porosity

Answer 6

Provides clearance for minute chips being produced

Provides cooling

Question 7

Grinding process

Answer 7

Chip removal process

Grinding tool made of irregular shaped grains spaced randomly along periphery of cutting wheel

Question 8

Selection of grinding process criteria

Answer 8

Part shape
Part size
Ease of fixing
Production rate

Question 9

Ultrasonic machining definition

Answer 9

Material removed from surface by microchipping or erosion with fine abrasive grains

Question 10

Ultrasonic machining

Answer 10

Tip of tool vibrates at frequency 20kHz and ampl. 0.05mm (High f low a)
Stress produced by abrasive particles is high
- Contact time between particle and workpiece is short
- Area of contact small

Question 11

What materials is ultrasonic machining ideal for and what are limitations?

Answer 11

Ideal for hard, brittle materials eg glass, ceramics, silicon carbides, precious stones etc.

Limitations: special tools needed

Question 12

Finishing operations examples

Answer 12

Sanding
Honing
Lapping
Polishing
Electropolishing

Question 13

Sanding

Answer 13

Coated abrasives
Grains electrostatically deposited on backing material
coating made of resin
Process widely used

Question 14

Honing

Answer 14

Stock-removal process using abrasive stones to remove small amounts of metal
Used to size and finish bored holes
remove errors left by boring
remove tool marks left by grinding

Question 15

Lapping

Answer 15

Fine abrasive particles embedded into relatively soft material called lap
Lap made out of leather, cloth, cast iron, copper
Used on flat/cylindrical surfaces of metal and non-metal parts

Question 16

Polishing

Answer 16

Produces smooth, lustrous surface finish

Done with disks or belt of fabric or leather coated with fine powders of Al2O3 or diamond

Question 17

Electropolishing

Answer 17

DC electric circuit constructed using workpiece as anode, submerged in electrolyte
Current applied, material is oxidised and dissolved by electrolyte
Does not require mechanical contact
Suitable for polishing irregular shaped workpieces

Question 18

Economics of machining

Answer 18

Costs increase with higher surface finish