Lec11

Question 1

disadv of traditional machining

Answer 1

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

Question 2

Adv of traditional machining

Answer 2

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

Question 3

Types of nontraditional machining

Answer 3

chemical
electrochemical
mechanical
thermal

Question 4

Chemical non traditional machining

Answer 4

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

Question 5

Electro chemical

Answer 5

an electrolytic reaction at the

workpiece surface is responsible for material removal

Question 6

Mechanical

Answer 6

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

Question 7

Thermal

Answer 7

high temp. in very localised region evaporates materials

Question 8

General chemical machining steps

Answer 8

cleaning
masking
etching
stripping

Question 9

Cleaning for chemical machining

Answer 9

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

Question 10

Masking for chemical machining

Answer 10

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

Question 11

Etching for chemical machining

Answer 11

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

Question 12

Stripping for chemical machining

Answer 12

maskant is removed from the workpiece and its surface is cleaned

Question 13

Etch rate proportional to

Answer 13

etchant concentraction adjadcent to the region of machining

Question 14

disadv of chemical machining x2

Answer 14

1 MRR is very slow in terms of unit area exposed

2 handling of dangerous chemicals and disposal of harmful products

Question 15

Photochemical machining is a type of

Answer 15

chemical machining

Question 16

How does photochemical machining work

Answer 16

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

Question 17

Types of photoresists

Answer 17

dry film - use a hot roller lamination

lquid - dipping flowing rolling electrophoresis

Question 18

adv of chemical machining x6

Answer 18

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

Question 19

Electro chemical maching removes material by

Answer 19

anodic dissolution with rapidly flowing electrolyte

deplating process tool is the cathode workpiece is the anode

Question 20

Electro chemical process x3

Answer 20

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

Question 21

Electro chemical machining what happens to metal particles

Answer 21

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

Question 22

electro chemical machining tool advance rate

Answer 22

constant penetration rate that matches deplating rate of the workpiece

Question 23

What happens to heat and waste product

Answer 23

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

Question 24

adv of ECM x4

Answer 24

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

Question 25

Disadv of ECM x2

Answer 25

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

Question 26

How is material removed by water jet cutting WJC

Answer 26

removed by impact of high velocity water jet

Question 27

Speed and pressure of water in WJC and kerf

Answer 27

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)

Question 28

Adv of WJC

Answer 28

cut materials without burning or crushing | inexpensive

Question 29

disadv of WJC

Answer 29

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

Question 30

abrasive in WJC (abrasive water jet cutting AWC)

Answer 30

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

Question 31

How are abrasives mixed

Answer 31

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)

Question 32

Type of material that can be cut

Answer 32

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

Question 33

adv of AWC

Answer 33

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

Question 34

disadv of AWC

Answer 34

more expensive than normal WJC

Question 35

Remove method for abrasive jet machining (AJM)

Answer 35

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

Question 36

Applications of AJC

Answer 36

processing hard brittle materials glass silicon tungsten | not suitable for soft and elastic materials

Question 37

Abrasive flow machining AFM | involves

Answer 37

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

Question 38

AFM setup

Answer 38

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

Question 39

applications of AFM

Answer 39

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

Question 40

AFM should be considered if

Answer 40

workpiece req laborious hand finishing of complex shapes | internal edges difficult to reach

Question 41

Non tradition machining produes

Answer 41

exceptionally smooth surfaces and complex shapes | allows machining of brittle materials

Question 42

chemical machining

Answer 42

req a lengthy process of masking protecting etching and washing

Question 43

abrasives can be

Answer 43

added to water or other media to create useful machining methods