Metal injection moulding (MIM) has over the past decade established itself as a competitive manufacturing process for small precision components which would be costly to produce by alternative methods.

It is capable of producing

• in both large and small volumes
• complex shapes
• from almost all types of materials including metals, ceramics, intermetallic compounds, and composites

• The standard PM process is to compact a lubricated powder mix in a rigid die by uniaxial pressure, eject the compact from the die, and sinter it.

Quite complicated shapes can be and are regularly being produced by the million, but there is one significant limitation as regards shape.

• After compaction in the die the part must be ejected, i.e. pushed out of the die cavity.

  It will be obvious, therefore, that parts with undercuts or projections at right angles to the pressing direction cannot be made directly.

  That limitation is substantially removed by the metal injection moulding process developed during the last decade and now expanding rapidly.

The use of injection moulding for the production of quite intricate parts in a number of plastic materials has been known for many years, and most of us come into contact with them in some form or other every day.

One important feature of such parts is that they are relatively cheap.

However, for engineering applications these thermo-plastic materials have quite inadequate mechanical properties.

Some improvement is made possible by the use of solid fillers - ceramic or metal powders - but the real breakthrough occurred when it was found possible to incorporate a very high volume fraction of metal powder in a mix so that, instead of a filled plastic part, a plastic-bonded metal or ceramic part is produced.

Careful removal of the plastic binder leaves a skeleton of metal or ceramic which, although fragile, can be handled safely and sintered in much the same way as traditional die compacted parts.

After sintering densities of 95% or more are reached and the mechanical properties are, for that reason, generally superior to those of traditional PM parts.