The powder metal forming process performed by heating compacted metal powders to just below their melting points. The forming technology involves a production cycle comprising:
- Filling a die cavity with a known volume of the powder feedstock, delivered from a fill shoe
- Compaction of the powder within the die with punches to form the compact. Generally, compaction pressure is applied through punches from both ends of the toolset in order to reduce the level of density gradient within the compact.
- Ejection of the compact from the die, using the lower punch(es)
- Removal of the compact from the upper face of the die using the fill shoe in the fill stage of the next cycle.
The size of forming of powder metal:
The size and weight of the part is limited by the maximum tonnage capacity of available forming presses (around 1000 tones capacity). A 2 kg. ferrous PM part would be regarded as being a large one.
A number of alternative forming processes have been developed, which have sought to attack one or more of these limitations.
1. Isostatic pressing can tackle all four limitations in that very large components can be formed,
2. Cold isostatic pressing: the powder is contained in a flexible mold, commonly of polyurethane, which is immersed in liquid.
3. Hot isostatic pressing: the pressuring medium is a gas, normally argon. The powder is contained in a metallic can, which is subjected to the hydrostatic pressure in the pressure vessel.
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