What are different types of subtracting techniques
- EDM electro discharge machining (Ra = 0.02-8 μm)
- laser processing
- water jet (abrasion)
- chemical machining
What are different types of deformation techniques
- injection moulding
What are different types of addition techniques
- electroforming
- MEMS
- additive manufacturing (3D printing)
Explain how EDM removes material
- workpiece and electrode are set up with a gap , immersed in a dielectric fluid
- voltage is applied
- high frequency electrical pulses create sparks
- intense heat is generated melting the workpiece
- molten material is vaporised (due to high temp)
- fluid carries debris away
What is the trade off to using a high voltage when preforming EDM
+ bigger crackers
+ bigger spark gap
+ high material removal rate
- rougher surface finish
What are the 4 types of EDM
- wire EDM
- die sinking EDM
- EDM drilling
- EDM milling
Explain die sinking
- two steps used, roughing (removes large amount of material quick) and finishing (slow) steps
- 3D shapes
advantages:
- high quality surfaces
- any conductive material can be used
disadvantages:
- slow process
- expensive
- tools difficult to produce
- wear on tools is difficult to control
Explain wire EDM
- cuts using electrified wire
- diameter = 0.02mm - 0.3mm
advantages:
- no wear
- easy flushing
- high quality surfaces
disadvantages:
- can only machine conductive materials
- produce 2D shapes
Explain EDM drilling
- can produce very deep holes (ratio = ⌀1mm:100mm deep)
- flushing is crucial, fluid is run through center of drill/tube
Explain EDM milling
- can produce 3D shapes
Compared to die sinking: - improved flushing more accurate geometry
- more tie consuming
- used more for smaller cavities (< 100mm^2)
What is overburn
When more material is removed than intended
roughing tool width equation
= target width - 2 x (finishing layer (rough layer) + spark gap)
finishing tool width equation
target width - 2 x spark gap
