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MEC130 Other > Lec11 > Flashcards

Lec11 Flashcards

1
Q

disadv of traditional machining

A

1 large amount of energy goes into producing unwanted chips
2 a lot of energy ends up was undesirable heat
3 unwanted residual stress burs req further processing
4 some geometries are too delicate

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2
Q

Adv of traditional machining

A

ability to machine
1 Complex geometries beyond simple planar or cylindrical features
2 extreme surface finish and tolerance
3 components that cannot withstand large cutting forces
4 no burs or residual stresses
5 brittle materials or very high hardness

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3
Q

Types of nontraditional machining

A

chemical
electrochemical
mechanical
thermal

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4
Q

Chemical non traditional machining

A

a chemical reaction between liquid reagent and the workpiece results in etching

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5
Q

Electro chemical

A

an electrolytic reaction at the

workpiece surface is responsible for material removal

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6
Q

Mechanical

A

high velocity abrasives or liquids are used to remove materials e.g. Ultrasound, water jet
etc

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7
Q

Thermal

A

high temp. in very localised region evaporates materials

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8
Q

General chemical machining steps

A

cleaning
masking
etching
stripping

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9
Q

Cleaning for chemical machining

A

contaminants on surface are removed to permit uniform etching
pickling rinsing degreasing

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10
Q

Masking for chemical machining

A

etch resistant maskant to cover a certain region of a workpiece - uncovered is exposed to etching

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11
Q

Etching for chemical machining

A

Spraying etchant onto a workpiece or immersing workpiece in etchant
chemical reaction stopped by rinsing

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12
Q

Stripping for chemical machining

A

maskant is removed from the workpiece and its surface is cleaned

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13
Q

Etch rate proportional to

A

etchant concentraction adjadcent to the region of machining

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14
Q

disadv of chemical machining x2

A

1 MRR is very slow in terms of unit area exposed

2 handling of dangerous chemicals and disposal of harmful products

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15
Q

Photochemical machining is a type of

A

chemical machining

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16
Q

How does photochemical machining work

A

Photoresist used as mask
CAD used to develop design
develop photographic negative (phototool)
bring phototool in contanct with workpiece using vacuum frame
expose workpiece to intense UV light
expose regions more resistant to solvents
dip or spray in etchant
remove mask

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17
Q

Types of photoresists

A

dry film - use a hot roller lamination

lquid - dipping flowing rolling electrophoresis

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18
Q

adv of chemical machining x6

A

1 simple no highly skilled operator req
2 no induced stress in material
3 large areas can be machined
4 virtually any shape part
5 thin section can be machined as no forces
6 materials that cannot sustain large cutting forces

19
Q

Electro chemical maching removes material by

A

anodic dissolution with rapidly flowing electrolyte

deplating process tool is the cathode workpiece is the anode

20
Q

Electro chemical process x3

A

1 tool is the cathode
workpiece is the anode
2 electrolyte pumped through hole in tool
3 electrolyte in the tool work piece gap washes away metal ions on workpiece away

21
Q

Electro chemical machining what happens to metal particles

A

washed metal particles are flushed away by the flow of electrolyte prevent them from plating onto the tool

22
Q

electro chemical machining tool advance rate

A

constant penetration rate that matches deplating rate of the workpiece

23
Q

What happens to heat and waste product

A

sweeped away by electrolyte, sludge is caputred and removed from electrolyte through filtration

24
Q

adv of ECM x4

A

1 complex shapes and conductive materials that cannot withstant high machining forces
2 good surface finish
3 no residual stress or thermal damage
4 no tool wear

25
Q

Disadv of ECM x2

A

preparation of tool electrode can by time consuming and costly
disposal of environmental harmful by products

26
Q

How is material removed by water jet cutting WJC

A

removed by impact of high velocity water jet

27
Q

Speed and pressure of water in WJC and kerf

A

high pressure 400 MPa
velocity greater than speed of sounds
small nozzle (0.1 - 0.4 mm dia) produce very narrow width of cut (kerf)

28
Q

Adv of WJC

A

cut materials without burning or crushing

inexpensive

29
Q

disadv of WJC

A

noisy - operators need ear protection
cannot cut brittle materials (will crack)
limited to thin sheets of metal

30
Q

abrasive in WJC (abrasive water jet cutting AWC)

A

abrasives added to waterjet in mixing chamber

required for most metal working process

31
Q

How are abrasives mixed

A

abrasives fed into centre of the nozzle with converging set of angled water jets imparting momentum to the abrasives
(better mixing and increases nozzle life)

32
Q

Type of material that can be cut

A

flat sheet but any material with right choice of abrasive jet pressure and feed rate

33
Q

adv of AWC

A

cut through composite without delaminating the layers - airplane industry to cut CF sections of airfract
thick materials up to 8 inch

34
Q

disadv of AWC

A

more expensive than normal WJC

35
Q

Remove method for abrasive jet machining (AJM)

A

removes material by a focused jet of abrasives - similar to AWC but momentum transferred by jet of inert gas no water
abrasive producing micro scale chipping action on workpiece

36
Q

Applications of AJC

A

processing hard brittle materials glass silicon tungsten

not suitable for soft and elastic materials

37
Q

Abrasive flow machining AFM

involves

A

use of semisolid liquid or gel laden with abrasives to flow over workpiece

38
Q

AFM setup

A

workpiece mounted in machines and pistons drive the abrsive back and forces

39
Q

applications of AFM

A

edge finishing deburring radiusing polishing or minor surfacing machining
features normally inaccessibly in internal passageways

40
Q

AFM should be considered if

A

workpiece req laborious hand finishing of complex shapes

internal edges difficult to reach

41
Q

Non tradition machining produes

A

exceptionally smooth surfaces and complex shapes

allows machining of brittle materials

42
Q

chemical machining

A

req a lengthy process of masking protecting etching and washing

43
Q

abrasives can be

A

added to water or other media to create useful machining methods

MEC130 Other (13 decks)

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