Powdered Metallurgy Process
The three basic steps for producing conventional density parts by the powder metallurgy process are Mixing, Compacting, and Sintering. A brief explanation of each step follows:
Step One: Mixing
Elemental or pre-alloyed metal powders are first mixed with lubricants or other alloy additions to produce a homogeneous mixture of ingredients. The initial mixing may be done by either the metal powder producer or the P/M parts manufacturer.
Step Two: Compacting
A controlled amount of mixed powder is automatically gravity-fed into a precision die and is compacted, usually at room temperature. Normally, compacting pressures in the range of 30 - 50 tons per square inch are used. Compacting the loose powder produces a "green compact" which, with conventional pressing techniques, has the size and shape of the finished part when ejected from the die, and sufficient strength for in-process handling and transporting to a sintering furnace. Typical compacting techniques use rigid dies set into special mechanical or hydraulic presses.
Step Three: Sintering
In the typical sintering step, the green compact is placed on a wide-mesh belt and slowly moved through a controlled atmosphere furnace. The parts are heated to below the melting point of the base metal, held at the sintering temperature, and then cooled.
Basically a solid state process, sintering transforms compacted mechanical bonds between the powder particles to metallurgical bonds. This provides the P/M part's primary functional properties.
P/M parts are generally ready for use after sintering. However, to provide special properties, the parts can be repressed, impregnated, machined, tumbled, plated, heat treated, or welded.