Lec12

Question 1

Types of thermal machining x4

Answer 1

1 electrical discharge machining (EDM)
2 Particle beam machining (PBM)
3 Laser beam machining (LBM)
4 Plasma arc cutting (PAC)

Question 2

EDM removes metal by

Answer 2

discharing electrical cutten from dc power supply across a thin inter electrode gap between a tool a workpiece
removal is based on spark erosion process

Question 3

EDM process

Answer 3

1 dielectric fluid in gap
2 fluid locally ionised at narrowest gap
3 ionisation creates conduction path - spark produced
4 spark produces tiny crater by vaporisation and melting
5 spherical chips produced by resolidifcation of melted workpiece

Question 4

What causes tool wear in EDM

Answer 4

high temp spark melts or vaporises the tool

Question 5

How are chips removed in EDM

Answer 5

dielectric fluid pumped through theinterelectrodge gap to flush out chips and bubbles while confining the sparks

Question 6

two types of EDM

Answer 6

Ram EDM

Wire EDM

Question 7

Ram EDM

Answer 7

electrode is a die shape of the negative of the cavity made from copper or copper alloy
by feeding die into the workpiece shape of the die is produced

Question 8

Wire EDM

Answer 8

electrode used is wire
used only once made of brass copper tungsten
travels along prescribed path cutting workpiece with discharge sparks acting like teeth
should have sufficient tensile strength fracture toughes and high electrical conductivity

Question 9

Wire EDM material vs wire

Answer 9

wire does not contact workpiece therefore tool does not need to be harder than material

Question 10

applications of EDM

Answer 10

manufacture of punches and dies

low volume high performance components

Question 11

adv of EDM

Answer 11

complex geometries (especially hardened tool materials)
no burrs on edges
able to cut intricate openings tight ridius contours and corners

Question 12

disadv of EDM

Answer 12

slow compared to conventional
thin recast and heat affected layers
hazardous fumes

Question 13

PBM or electron beam welding

Answer 13

high energy electrons focused on workpiece to melt and vaporise it

Question 14

Where is PBM performed

Answer 14

vacuum chamber

Question 15

PBM how is electron beam produced

Answer 15

electron gun via thermionic emission

tungsten filament heated to 2000 C electrons emitted and focused using electrostatic optics

Question 16

Adv of PBM

Answer 16

recast material and depth of heat damage very small

small features - micoron level precision

Question 17

disadv of PBM

Answer 17

intercations of beam wtih surface produce exrays - need shielding
needs vacuum

Question 18

LBM uses

Answer 18

intensly focused coherent stream of light to remove material from workpiece surface
material removal process dependent upon type of laser used and how it is operated

Question 19

Two types of material removal mechanism

Answer 19

thermal evaporation - material vaporised

chemical ablation bonds bronze by excessive energy (no HAZ)

Question 20

Adv of LBM

Answer 20

increadibly precise and accurate
no mechanical contact - no contamination good clean edge and surface finish and no tool wear
small or no HAZ

Question 21

disadv of LBM

Answer 21

safety implications of lasers

Question 22

applications

Answer 22

drilling microholes in turbine engines

machining complex shapes in sheet metal

Question 23

PAC uses

Answer 23

superheated stream of electrically ionised gas to melt and remove materials

Question 24

plasma

Answer 24

10,000 25,000 C created inside a water cooled nozzle

mixture of free electrons and positively charged ions and neutral atoms

Question 25

adv of PAC

Answer 25

high cutting speed one electrode can be used to machine a wide variety of materials and thicknesses

Question 26

disadv

Answer 26

poor tolerances tapered cuts and double arcing leading to premature wear on nozzle

Question 27

What sustains the plasmc arc

Answer 27

high voltage dc power

high velocity gases melt and blow away molten metal chips

Question 28

applications of plasma arc cutting

Answer 28

cutting structural materials

either handheld or CNC machines

Question 29

economics of non traditional machining factors to consider x 5

Answer 29

1 cost of tool and equipment (chemicals and acids)
2 MRR (slow for many)
3 Operational cost
4 operator skill req (high for some and have to be protected)
necessary secondary and 5 finishing operations (req for some

Question 30

Chemical machining economics

Answer 30

chemicals maskants disposal and cleaning of chemical

Question 31

EDM economics

Answer 31

cost of consumables electrodes/wire

Question 32

laser and plasma machining

economics

Answer 32

main cost is investment of equipment

production rate feasibility of other methods

Question 33

economics of machinig non traditional processes

Answer 33

choose them are they only feasible method - as traditional methods probably faster