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Flashcards in Lec11 Deck (43)
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1

disadv of traditional machining

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

2

Adv of traditional machining

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

3

Types of nontraditional machining

chemical
electrochemical
mechanical
thermal

4

Chemical non traditional machining

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

5

Electro chemical

an electrolytic reaction at the
workpiece surface is responsible for material removal

6

Mechanical

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

7

Thermal

high temp. in very localised region evaporates materials

8

General chemical machining steps

cleaning
masking
etching
stripping

9

Cleaning for chemical machining

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

10

Masking for chemical machining

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

11

Etching for chemical machining

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

12

Stripping for chemical machining

maskant is removed from the workpiece and its surface is cleaned

13

Etch rate proportional to

etchant concentraction adjadcent to the region of machining

14

disadv of chemical machining x2

1 MRR is very slow in terms of unit area exposed
2 handling of dangerous chemicals and disposal of harmful products

15

Photochemical machining is a type of

chemical machining

16

How does photochemical machining work

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

17

Types of photoresists

dry film - use a hot roller lamination
lquid - dipping flowing rolling electrophoresis

18

adv of chemical machining x6

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

Electro chemical maching removes material by

anodic dissolution with rapidly flowing electrolyte
deplating process tool is the cathode workpiece is the anode

20

Electro chemical process x3

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

Electro chemical machining what happens to metal particles

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

22

electro chemical machining tool advance rate

constant penetration rate that matches deplating rate of the workpiece

23

What happens to heat and waste product

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

24

adv of ECM x4

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

Disadv of ECM x2

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

26

How is material removed by water jet cutting WJC

removed by impact of high velocity water jet

27

Speed and pressure of water in WJC and kerf

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

Adv of WJC

cut materials without burning or crushing
inexpensive

29

disadv of WJC

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

30

abrasive in WJC (abrasive water jet cutting AWC)

abrasives added to waterjet in mixing chamber
required for most metal working process