diff --git a/uni/mmme/1029_materials_and_manufacturing/manufacturing.md b/uni/mmme/1029_materials_and_manufacturing/manufacturing.md index d1128a7..bab3f6a 100755 --- a/uni/mmme/1029_materials_and_manufacturing/manufacturing.md +++ b/uni/mmme/1029_materials_and_manufacturing/manufacturing.md @@ -21,3 +21,113 @@ $$cost < price < value$$ Cost modelling equation: $$C = \frac{mC_m}{1-f} + \frac{C_t}{n} + \frac{1}{\dot n} \left[ \dot C_{oh} + \frac{C_c}{L\cdot t_{wo}} \right]$$ + +# Shaping Processes + +## Casting + +- Can be used for large size range +- Molten metal poured into solid mould to give shape +- Heat removed leads to shrinkage +- We need to be able to melt the metal and handlethe molten metal +- Mould degradation by the liquid metal needs to be considered +- Heat flowing from the molten metal into the mould causes a drop in temperature so solidification + starts from outside inwards +- Rate of solidification depends on rate of heat flow into mould + +### Types of Mould + +- Expendable mould (sand, plaster, ceramic) + + - The mould is used once, being broken to release the casting + - Can have multiple use or single use pattern (investment and lost foam casting + +- Multiple mold casting + + - Die casting (pressure die casting) + - Permanent mould casting (gravity die casting) + +#### Sand Casting + +![](./images/vimscrot-2022-02-21T16:36:48,640821636+00:00.png) + +- Wide range of metals can be cast +- Almost no limit to size and shape of casting +- Poorer tolerances than other proces, rough surface texture +- Slow +- Economic for a low number of castings +- Applications include cylinder blocks and large pipe fittings + +#### Investment Casting + +- A high cost process +- Used mostly for complex shapes, such as sculptures, jewellery, and gas turbine blades +- Can be used for a wide range of metals +- Very high precision and surface finish + +1. Make a master die +2. Make wax pattern by casting wax into master die +3. Coat wax pattern with investment material + + 1. First with a slurry of water and fine ceramic to capture fine details + 2. Then coat with stucco, which is a thicker coating for strength + +4. Heat mould to melt wax out, bake and preheat mould +5. Pour in molten metal +6. Wait for solidification, break mould when done + +#### Permanent Mould Casting (Gravity Die Casting) + +- Mould cavity is machined into mating metal blocks +- Molten material poured into mould +- Mould material is cast iron, steel, bronze, graphite +- Mould must disassebmble without locking +- Mould is expensive but can be reused (typically around 25k times) +- Mould life is reduce by casting high meling point metals +- Good surface finish and dimensional accuracy +- Cooling is rapid therefore high production rates +- Example use is a piston + +#### Die Casting (High Pressure Die Casting) + +- Dies must be able to withstand high pressure +- 0.1 mm slits at parting lines provide escape for air +- Dies are made of expensive tool steels +- High volume production is necessary to justify costs +- Generally limited to low viscosity, low melting point, non ferrous metals like Al, Zn, Mg, and Pb +- Good surface finish +- Precision castings with thickness between 0.75 mm and 12 mm + +### Design of Castings + +- Distribute castings evently around parting planes +- Need to be able to get patterns out of moulds and casting out of moulds where applicable +- No re-entrants (complex multi-part moulds may be able to avoid this restriction) +- Draft angle between surfaces + + - Need to be able to get solid patternout of mould in sand casting + - Need to be able to get solid casting out of mould in die casting + +- Allow for shrinkage --- dimensions of casting mould/pattern needs to be made so that part is + desired size after shrinkage +- Avoid rapid change in section or direction: + + ![](./images/vimscrot-2022-02-21T17:12:20,117329889+00:00.png) + +### Solifidification of Metals + +- How well the liquid fills detail depends on viscosity of liquid +- During freezing, latent heat of fusion is removed +- During freezing, material is a solid/liquid mixture +- There is a significant (~7 %v) shrinkage during solidification +- Heat flows down steepest thermal gradient so usually there is an actively cooled section +- Thin sections freeze faster than thick sections + +### Castability + +- Low melting point +- Low viscosity and surface tension +- Low solidification contraction +- Low thermal capacity and high conductibity +- Low solubility +- Not contaminated by air