Properties of Surface Densified P/M Gears

A helical PM gear for a passenger car gear box was manufactured by pressing, sintering and selective surface densification by transverse rolling. The evolution of the gear properties in terms of microstructure, gear geometry, surface roughness and DIN-quality is monitored at each step of the processing sequence. The geometry of the PM gear is compared to a conventional wrought steel gear (DIN-quality 7) being currently used in the gear box. It is shown that PM gears can be manufactured well within the DIN quality 8 tolerance fields. Furthermore it is demonstrated that alignment and profile errors is reduced in the sequence of processing. While wrought gears have less alignment and profile errors, PM gears are superior in terms of run-out and pitch errors as well as surface roughness.