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Flashcards in Lec12 Deck (33)
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1
Q

Types of thermal machining x4

A

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

2
Q

EDM removes metal by

A

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

3
Q

EDM process

A

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

4
Q

What causes tool wear in EDM

A

high temp spark melts or vaporises the tool

5
Q

How are chips removed in EDM

A

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

6
Q

two types of EDM

A

Ram EDM

Wire EDM

7
Q

Ram EDM

A

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

8
Q

Wire EDM

A

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

9
Q

Wire EDM material vs wire

A

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

10
Q

applications of EDM

A

manufacture of punches and dies

low volume high performance components

11
Q

adv of EDM

A
complex geometries (especially hardened tool materials)
no burrs on edges
able to cut intricate openings tight ridius contours and corners
12
Q

disadv of EDM

A

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

13
Q

PBM or electron beam welding

A

high energy electrons focused on workpiece to melt and vaporise it

14
Q

Where is PBM performed

A

vacuum chamber

15
Q

PBM how is electron beam produced

A

electron gun via thermionic emission

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

16
Q

Adv of PBM

A

recast material and depth of heat damage very small

small features - micoron level precision

17
Q

disadv of PBM

A

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

18
Q

LBM uses

A

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

19
Q

Two types of material removal mechanism

A

thermal evaporation - material vaporised

chemical ablation bonds bronze by excessive energy (no HAZ)

20
Q

Adv of LBM

A

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

21
Q

disadv of LBM

A

safety implications of lasers

22
Q

applications

A

drilling microholes in turbine engines

machining complex shapes in sheet metal

23
Q

PAC uses

A

superheated stream of electrically ionised gas to melt and remove materials

24
Q

plasma

A

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

mixture of free electrons and positively charged ions and neutral atoms

25
Q

adv of PAC

A

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

26
Q

disadv

A

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

27
Q

What sustains the plasmc arc

A

high voltage dc power

high velocity gases melt and blow away molten metal chips

28
Q

applications of plasma arc cutting

A

cutting structural materials

either handheld or CNC machines

29
Q

economics of non traditional machining factors to consider x 5

A

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

30
Q

Chemical machining economics

A

chemicals maskants disposal and cleaning of chemical

31
Q

EDM economics

A

cost of consumables electrodes/wire

32
Q

laser and plasma machining

economics

A

main cost is investment of equipment

production rate feasibility of other methods

33
Q

economics of machinig non traditional processes

A

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