Three Steps for Powdered Metallurgy Excellence

Here at Volunteer Sintered Products, our 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 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 manufacturer of the P/M parts.

Step Two: Compacting

A controlled amount of mixed powder is automatically gravity-fed into a precision die and is compacted, usually at room temperature. Compacting pressures of 30 - 50 tons per square inch are typically used. Compressing 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 into metallurgical bonds. This provides the P/M part's primary functional properties.

P/M parts are generally ready for use after sintering. However, the pieces can be repressed, impregnated, machined, tumbled, plated, heat treated, or welded to provide special properties.