17.6.2004 Pressing & Sintering

High Performance Gears

PM²TEC 2004, in Chicago, USA. Authors: Sven Bengtsson, Linnéa Fordén, Magnus Bergström. The past decades have seen an increased use of P/M components in passenger cars and light trucks. However, only a limited number of applications have been found in heavy trucks. P/M technology have so far not met the performance requirements of transmission gears. Forging of a blank, followed by turning, hobbing, shaving, heat treatment and finally grinding are the manufacturing steps normally used for the planetary gear of a hub reduction unit of a heavy truck. The large size of the gear means that a lot of material is machined away before the component is finished.  Using a net shape process offers the potential of significant cost savings. Normally conventional cold compaction cannot deliver the fatigue performance and tolerances required, but other techniques can increase these properties to new levels.  Warm compaction improves the density and exhibits an excellent pore size distribution. This means that the fatigue properties improve at a moderate cost increase. Surface densification is an additional process step in the manufacture of a P/M component. By introducing this step the net shape capability of the P/M technology is utilized while at the same time the highly loaded regions benefit from increased density. Also tolerances of the densified regions can be improved.