Advanced Forming Process for High Density PM Gears
Powder metallurgy is a well-established technology for manufacturing a variety of complex shaped parts in the gearbox of a passenger car. However, using standard PM technology it is not possible to reach the mechanical properties necessary for gear components. Combining the net shape capability of powder metallurgy and cold forming by a burnishing operation provides a method of producing transmission gears for automotive gearboxes at a low cost with mechanical properties equivalent to conventionally produced gears. Powder and process selection is discussed, including the influence of core density on densification and quality. The mechanical performance of a helical and a spur gear are compared to their respective reference gears made of case hardening steels. The endurance limit in tooth root bending fatigue testing of the surface densified helical PM gear reaches 94% of the reference material, while the surface densified spur gear reaches 106% of its reference gear. The gear quality of the two gears is DIN class 8 after heat treatment and the surface roughness of the gear tooth and root is Ra=1,2 µm.