Influence of Metal Flank Hardness of Machined and Cold Forged Gears on Wear within a Metal-Polyamide Gear Pair and Targeted Process Adaptation

Abstract

Metal-polyamide gear pairs provide advantages but their application is limited due to wear. The properties of the metallic gearing significantly affect the wear behavior. However, the influence of varying metallic materials as well as flank hardness is not known. Within this contribution, the occurring wear mechanisms when applying steel, brass and aluminum with varying hardness resulting from manufacturing by machining and cold forging were identified. Depending on the hardness of the metallic tooth flank, the release of metallic particles (3-body abrasion) or surface roughening (2-body abrasion) results. The formation of a wear-reducing transfer film is only possible with sufficient strength of the metallic tooth flank and tribological compatibility. Maximum wear occurs at a metal hardness of about 120 HV due to 3-body abrasion with high abrasive effect of the metallic particles. The adaptation of the cold forging process enables a local increase in the plastic strain of the tooth flank by 84% resulting in an elevated tooth flank hardness (+ 53%) for aluminum and significantly reduced wear. Furthermore, the formation of a wear-reducing transfer film results. Aluminum pinions produced in the adapted cold forging process achieve performance level of steel within the investigated load case.