Effect of ground tire rubber media's viscoelasticity and flow passage geometry on the abrasive flow finishing of helical gear

Abstract

This work aims to elucidate the behavior of viscoelastic ground tire rubber media (GTRM) under abrupt contraction and expansion of the media at the entry and exit of the gear flow channel and its influence on polishing results. Due to the inherent nature of the abrasive flow finishing (AFF) process, the media flow converges at the entrance of the gear tooth as it flows from a larger fixture cross-section to a narrower volumetric space between gear teeth. The material removal and subsequent surface roughness rely heavily on the flow's pressure and velocity. A numerical simulation was performed to obtain the pressure and velocity along the gear flank face width (FFW). To investigate the effect of variation in the media deformation rate along the gear flow channel on AFF results, the material removal height and improvement in average surface roughness at different locations along the tooth flank face width were measured. AFF results reveal that the material removal near the two edges of the gear tooth is higher and has an inferior surface finish compared to the tooth's center. Due to the abrupt compression of the media at the flow channel entrance, the media act elastically dominant, resulting in high pressure and flow velocity near the tooth edge (flow channel's entry). Additionally, the effect of the helix angle on the AFF of various helical gear (HG) was investigated. Among the three HGs chosen, the 30° HG produces the lowest surface roughness under moderate pressure and high velocity. The microhardness and fretting wear analyses further confirm that the AFF polishing increases the microhardness and wear resistance of the gear tooth surface as a result of work hardening and minimizing surface defects.