Lec12 Flashcards Preview

MEC130 Other > Lec12 > Flashcards

Flashcards in Lec12 Deck (33)
Loading flashcards...
1

Types of thermal machining x4

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

2

EDM removes metal by

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

EDM process

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

What causes tool wear in EDM

high temp spark melts or vaporises the tool

5

How are chips removed in EDM

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

6

two types of EDM

Ram EDM
Wire EDM

7

Ram EDM

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

Wire EDM

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

Wire EDM material vs wire

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

10

applications of EDM

manufacture of punches and dies
low volume high performance components

11

adv of EDM

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

12

disadv of EDM

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

13

PBM or electron beam welding

high energy electrons focused on workpiece to melt and vaporise it

14

Where is PBM performed

vacuum chamber

15

PBM how is electron beam produced

electron gun via thermionic emission
tungsten filament heated to 2000 C electrons emitted and focused using electrostatic optics

16

Adv of PBM

recast material and depth of heat damage very small
small features - micoron level precision

17

disadv of PBM

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

18

LBM uses

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

Two types of material removal mechanism

thermal evaporation - material vaporised
chemical ablation bonds bronze by excessive energy (no HAZ)

20

Adv of LBM

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

21

disadv of LBM

safety implications of lasers

22

applications

drilling microholes in turbine engines
machining complex shapes in sheet metal

23

PAC uses

superheated stream of electrically ionised gas to melt and remove materials

24

plasma

10,000 25,000 C created inside a water cooled nozzle
mixture of free electrons and positively charged ions and neutral atoms

25

adv of PAC

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

26

disadv

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

27

What sustains the plasmc arc

high voltage dc power
high velocity gases melt and blow away molten metal chips

28

applications of plasma arc cutting

cutting structural materials
either handheld or CNC machines

29

economics of non traditional machining factors to consider x 5

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

Chemical machining economics

chemicals maskants disposal and cleaning of chemical