The basic procedure in the manufacture of PM parts is:

1. Mix the metal powder or powders with a suitable lubricant.

2. Load the mixture into a die or mould and apply pressure.

This gives what is called a compact which requires only to have sufficient cohesion to enable it to be handled safely and transferred to the next stage. Such compacts are referred to as green, meaning unsintered: hence the terms green density and green strength.

3. Heat the compact, usually in a protective atmosphere, at a temperature below the melting point of the main constituent so that the powder particles weld together and confer sufficient strength to the object for the intended use.

This process is called sintering hence the term sintered parts. In certain cases a minor constituent becomes molten at the sintering temperature in which case the process is referred to as liquid phase sintering.

The amount of liquid phase must be limited so that the part retains its shape. In certain special cases stages 2 and 3 are combined i.e. compaction is done at an elevated temperature such that sintering occurs during the process.

This is termed hot pressing, or pressure sintering. In many cases the sintered part is subjected to additional processing - repressing, plating etc. and these will be dealt with in the appropriate sections below. In certain special cases, e.g. in the manufacture of filter elements from spherical bronze powder, no pressure is used, the powder being placed in a suitably shaped mould in which it is sintered.

This process is known as loose powder sintering.