Optimized density profiles for powder metallurgical gears

Abstract

In gear production, resource efficiency considering material, energy and time can be achieved using a powder metallurgical process chain. Furthermore, powder metallurgical gears have a lower weight, which will improve the fuel efficiency of a gear box as well. Currently powder metallurgical gears are not used in series-production automobile gear boxes. The main reason for this is a lower expected tooth root fatigue strength, which can be increased using surface densification by rolling. The investigation of how the powder metallurgical (PM) gear manufacturing has to improve in order to gain the possible resource efficiency, is funded in the Priority Program "Resource efficient machine elements”. This paper considers a two-step approach to increase the tooth root fatigue strength of PM gears. The first step is to calculate the fatigue strength considering the density profile of the gear. This first step will result in a description of the optimal density profile. The second step is an investigation of how the density profile and the manufacturing properties can be influenced using different process designs. This step will result in a guideline to change the density profile to the one described in the first step. The combined knowledge of which density profile is necessary and how it can be achieved will give the chance to increase the tooth root fatigue strength of powder metallurgical gears. This paper considers the first part of both steps of the approach.