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MEC130 2 4 8 10 15 > Lec 10 > Flashcards

Lec 10 Flashcards

1
Q

Abrasive machining adv

A

High dimensional accuracy

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2
Q

What is abrasive machining

A

Abrasion used to remove small amounts of material by cutting processes that introduce tiny chips
Each abrasive grain removes only small amount of material
A method used to produce parts with high
dimensional accuracy
Each particle acts as a cutting tool

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3
Q

Types of bond (grinding wheel)

A

Clay and Feldspar crystalline material

vitrification used to produce a glassy amorphous structure strong and stiff resistant to oil acid and water

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4
Q

Bond too strong (grinding wheel)

A

Dull grains cannot be dislodged to

allow other sharp grains to perform grinding

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5
Q

Bond too weak (grinding wheel)

A

Grains become dislodged easily,
hence maintaining dimensional accuracy
becomes difficult

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6
Q

What is attritious wear (grinding wheel)

A

Wear of grains (flank wear of cutting tool) caused by friction between grain and workpiece involving chemical and physical reactions

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7
Q

Why are abrasive grains brittle (grinding wheel)

A

if grains dull grinding inefficient therefore should fracture moderately to expose new sharp grains
continuously being sharpened

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8
Q

Why is porosity important (grinding wheel)

A

Essential in bonded wheels provides cooling and clearance for minute chips produced

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9
Q

What is grinding?

A

chip removal process - The grinding tool is made up of irregular shaped grains spaced randomly along the
periphery of the cutting wheel
Range of machines available for different workpiece geometries - CNC automation load - unload clamp repeat cycle path will sharpen wheel between processes

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10
Q

Ultrasonic machining (drawing)

A

removal by micochipping or erosion with fine abrasive grains

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11
Q

Ultrasonic machining process

A

high freq
Tip of tool vibrates
amplitude 0.05
vibration drives grain at workpiece high velocity
high stress between grain and workpiece - small area short contact time

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12
Q

Tool vibration speed 20kHz or 3000000kHz ultrasonic machining

A

20kHz

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13
Q

Ultrasonic machining best suited for

A

Brittle materials as high enough stresses causes microchipping - glass ceramics silicon hardened steels precious tones

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14
Q

What is a Finishing operations how do they affect a design

A

These are used to improve the surface finish of a
workpiece
Can contribute significantly to production time
and product cost

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15
Q

Finishing operations What is Sanding

A

Uses coated abrasives sand paper emery cloths

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16
Q

Construction of sandpaper (diagram)

A

The grains are electro-statically deposited on backing
material
Coating is made of resin

17
Q

What types of surface can sanding be used on?

A

Any! Widely used in finishing flat or curved metallic non metallic

18
Q

What is honing (diagram)

A

stock removal process abrasive stones remove smallamounts of metal

19
Q

What is honing used for

A

Size and finish bored holes (engine cylinders)
remove errors left by boring
tool marks left by grinding

20
Q

What is lapping? (diagram)

A

fine abrasive particles embedded in relatively soft material called lap (leather/cloth/cast iron/copper)

21
Q

Shapes and materials used for lapping

A

Flat cylindrical metal and non metal

22
Q

What is polishing

A

Produces a smooth, lustrous surface finish - takes time costs alot of money

23
Q

What is an abrasive

A

Is a small, non-metallic hard particle with sharp

edges and irregular in shape

24
Q

For higher material removal rates what is done

A

Abrasives are bonded together to form a grinding

wheel

25
Q

What is Vitrification

A

Used to produce a glassy, amorphous

structure

26
Q

The selection of a grinding process depends

on x4

A

Part shape Part size Ease of fixing Production rate

27
Q

Limitations of Ultrasonic machining

A

Each job requires special tooling

28
Q

Purpose of grooves in lapping plate

A

serve to hold slurries, removing cutting chips and evenly supply slurry to workpiece
uniformly distribute pressure across workpiece - improves flatness accuracy

29
Q

How is polishing done

A

It is done with disks or belts of fabric or leather coated

with fine powders of aluminium oxide or diamond

30
Q

What is electro-polishing

A

polishing using electrolysis

31
Q

What is electro-polishing

A

polishing using electrolysis

32
Q

How is electro-polishing done (diagram)

A

A DC electric circuit 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

33
Q

Order of surface finish highest to lowest; Finish turn, Hone, Rough turn, Grind Semi-finish turn, As cast
or cut

A

Process/surface finish micrometres/machining cost (%)

As cast or cut/500/0, Rough turn/500-10/20, Semi-finish turn/5-4/70, Finish turn/2/100, Grind/0.8/250, Hone/0.4/400

MEC130 2 4 8 10 15 (6 decks)

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