Process Encyclopaedia

Other names / variants: Sintering, HIPping, Reaction bonding

One of the first uses for powder metal forming was the manufacture of tungsten filaments for light bulbs. Advances in the technology mean even structural parts for aircraft (e.g. landing gear) can be made this way.
Much of the research in powder forming is to obtain good quality powder, as this helps to achieve a good quality component.

Pressureless sintering involves only heat. It can be used for any shape.

Pressure sintering involves heat and axial pressure, but can only be used for 2D components.

HIPping (hot isostatic pressing) is a variant used for 3D shapes; it uses a foil bag and a hydrostatic pressure chamber.

Reaction bonding involves using a binder (so it can be moulded like plasticine) which is later burnt off; it can used for most shapes.

Possible sizes range from balls in ball point pens up to 25kg.
Mostly used for small (<2kg) complex components that are difficult to make from solid stock or where uniform properties are desired.
All metals can be processed this way, though extra care is required for some which burn or oxidise easily.
Sides must be parallel to allow ejection of part.
Very good dimensional accuracy (near net-shape process) with 100% material utilisation.
There can be problems with porosity – although sometimes this can be beneficial (e.g. filter, bearings).

The machinery is expensive, and can cost well over Ł100,000.
The dies are dedicated, expensive (Ł5,000+) and need to be replaced after about ten thousand uses. They can take several weeks to manufacture, mean prototype testing is slow.
The production rate is dominated by the sintering stage and is therefore quite slow (2-20 per hour).
Tends only to be economic for large batches (50,000+) or processing high-strength alloys.