# Influence of Metal Fear Tooth Geometry on Load and Wear within Metal-Polymer Fear Pairs
###### Abstract  
Gear pairs made of the material pairing metal-polymer provide advantages, such as a reduced weight, beneficial damping properties and the possibility to be operated in dry running conditions. However, the service life of the pairing is limited due to wear. The properties of the metallic gearing have a significant influence on the wear behavior of the material pairing. From previous investigations, the influence of the surface topography and the flank hardness of the metal pinion is known. With regard to resource saving and efficient manufacturing of the metal pinion, cold forging offers benefits. Through cold forging, metallic gears for the material pairing can be produced ready-to-use in a process suitable for serial production. In order to enable manufacturing by extrusion, the application of gear radii is necessary. The gear radii significantly affect the extrusion process and the achievable gear properties. However, the influence of gear radii on wear within the metal-polymer material pairing has not yet been investigated. Within this contribution, the influence of the gear radii on the contact behavior as well as the resulting local load and wear of the tooth flank is determined. For this purpose, wear tests with aluminum (AlMgSi1) and steel (16 MnCr5) gears with different gear radii within the pairing with polyamide (PA66) gears were performed. It has been shown that the local wear of the tooth flank can be attributed to the local load and that adjusted gear radii lead to a varying load and wear of the metal and polymer gears. Based on the findings, functional relationships regarding the choice of gear radii and the wear behavior are derived which can be applied in the design of cold forged gears. g 2021 2021 2021 2022 2021 2022 2021 2022 2021 2022 2 metal-polymer can be produced ready-to-use by cold forging with sufficient accuracy in a highly productive and resource efficient process [8]. In addition to steel, aluminum offers potential as a metallic material due to its low density and cold formability [8]. During operation of gear pairs of the material combination, the occurring wear limits the lifetime and compliance of the functionally relevant tolerances [9]. Previous studies determined the influence of the mechanical component properties and the surface topography of the metal gear [10]. Hardness [11] and roughness [12] are of importance. In addition, model tests have identified the load resulting from surface pressure and sliding velocity as influencing variables [13]. Insufficient knowledge exists about the influence of tooth geometry on the wear behavior. In order to enable gear production by extrusion, it is necessary to adapt the involute tooth geometry by adding gear radii [14]. The gear radii have a significant influence on the extrusion process and the achievable component properties. From the perspective of the forming process, large radii are advantageous [15]. Reasons for this are a more homogeneous material flow and reduced die stress. The influence of gear radii on wear within the metal-polymer material pairing has not yet been investigated, and the effects of modified gear radii are not known. In previous studies on the effects of contact behavior on wear, it was shown that the specific sliding within the gear pair has an influence on wear and that the wear occurring locally on the tooth could be reduced by adapting the tooth profile [16]. The influence of gear radii has only been investigated regarding the load carrying capacity of polymer gears, but not on wear. It has been shown that increased radii reduce stresses in the tooth root and increase the load carrying capacity [17]. Against the background of the use of extrusion for the production of metallic gears for the material pairing, the application of preferably large gear radii is required. Since the length of the active tooth flank is changed by the gear radii, an influence on the load situation and wear is also to be expected.