The basic procedure in the manufacture of PM consists of:
(1) The metal powder(s) has/have to be mixed with a suitable lubricant.
(2) This mixture is loaded into a die or mould before pressure is applied. This result is called compact, which requires sufficient cohesion enabling it to be handled safely as well as being transferred to the next stage. Such compacts are also called green meaning unsintered.
(3) Now the compact is heated within a protective atmosphere at a temperature below the melting point of the main constituent. The powder particles will weld together and confer sufficient strength to the object for the user’s requirements. This process is called sintering. A minor constituent becomes molten at the sintering temperature sometimes which process is called liquid phase sintering. The amount of liquid phase has to be limited to ensure the part retains its shape.
The second and third step can also be combined in form of a compaction done at an elevated temperature so that sintering occurs during the process. This is called termed hot pressing, or pressure sintering.
This process can be performed in various variants.
Loose powder sintering means that no pressure is used but the powder is sintered within a suitable shaped mould.