In order for PM to increase market share there are two factors that have a significant influence. The two factors are strength and cost. For PM to work in the most demanding environments such as gears in gearboxes they sometimes need more strength than can be obtained by the Compaction-Sinter-Case hardening route. There are methods on the market such as Surface Densification by rolling, shot peening, powder forging and some other proprietary methods that will increase strength but the common denominator for all methods are cost and certain draw backs.
In this paper a method for Hot Isostatic Pressing (HIP) of PM parts is presented. HIP is not a new method for increasing strength in solid steel or aluminum parts for off-shore, nuclear or aerospace products. It has previously been demonstrated in a Rally car that HIP:ed transmission gears in PM can perform equal or better than the solid steel gears. In that vehicle the gear material was HIP:ed in a solid steel container since the porosity of the material excluded the possibility of HIP:ing without a container. The container is very costly and impossible to make in the shape of a gear wheel. This paper will demonstrate a method for HIP:ing gears in PM without a container thus eliminating a big part of the cost for the HIP process. The strength benefits will be demonstrated as well as the cost situation for HIP:ing of a gear to fully dense. Also some very interesting future developments will be presented for the whole process chain of HIP:ed gears or components.