Describe friction stir welding
The joining of materials without the need for filler materials
List advantages and disadvantages of friction stir welding
A:
- excellent mechanical properties
- no porosity or distortion
- non consumable tool
- can perform on the spot repair work
- can work at high temperatures
D:
- costly equipment
- same materials are hard to FSW
What is the advantage of powder metallurgy processes over casting
PMP have a very low scrap rate compared to casting processes
List advantages of additive layer manufacturing
- Design friendly
- Low lead times
- Reduces buy-to-fly ratio
- Near-net shape products
Powder metallurgy processes - laser system
applies heat only the part slice, therefore don’t get uniform heating. This leads to residual stresses.
Impossible to do thin walls.
Powder metallurgy processes - Electron beam
Most promising technology. Uses Ti-6Al-4V and CoCr.
Preheats every layer so properties are very good.
Have to build supports, but these are recyclable.
Must be very careful with parameters.
Need skilled workers
Disadvantages to additive layer manufacturing
- its expensive
- certain powders are expensive
- cannot have every material in powder form
- highly skilled workers needed
Describe metal injection moulding
- Start with powder
- Add Binder and heat
- form granules and inject into mould
- remove Binder
- Sinter
Why is sintering needed in metal injection moulding
After debinding, the material is very brittle and only 70% dense.
Sintering compacts product and makes it 100%
General equation for mechanical effects of porosity
X = Xo * e^(βρ)
Describe hot isostatic pressing (HIP)
Simply: put powder in chamber and squeeze creating 100% dense product and eliminating porosity
