FE Impact Model and Simulation of the Shot Peening Effect on Cylindrical Gear Topland and Profile Edge Rollover

Author:  E. Garijo, F.B. Lobato, J.C. Sánchez
Source:  ICSP-13
Doc ID:  2017098
Year of Publication:  2017
Introduction: When mechanical current production transmissions are subjected to a load increase by product upgrades or additional functionalities, usually the envelope and working environment of the transmission is already restricted by other elements of the machine where it is used. For those cases,or wherever the space constrains force us to have high power and torque transmitted in a relatively small space, the shot peening can be applied as an additional improvement for the existing or new gears. If the design of the gear to be improved by shot peening is already in production and its manufacturing process does not take into account any preparation for the shot peening, some issues with sharp edges can be found. The bending fatigue improvement is achieved when the shot peening is extended from the bottom of the root fillet past the tangent point between the root and flank. The pitting fatigue improvement is required on the active profile area where the maximum contact pressure is reached [1]. Although the topland of the gear is not the objective of the shot peening treatment, in reasonable volumes of part production, the shot peening cannot be localized to the area of the gear tooth that is desired to be treated. So, profile geometry, root and topland of the gear are evenly treated. In a standard shot peening process of a gear, any sharp edge is prone to present issues. The general recommendation by the shot peening industry is to avoid functional areas with sharp edges to be treated [2]. That is the case of the gear tip edges where the impact of the shots can produce a small protrusion on the side of the tooth active profile. This protuberance generated on the active profile near the tip edge is known as profile edge rollover. The dimension of the generated protrusion can be taken into account as a deviation from the perfect shape of the involute profile, that eventually will result in a wrong contact between the tip of the shot peened gear tooth and the contact area of the mating gear tooth. The effect of the edge rollover is directly affecting the behaviour of the gearmesh in the EAP (End of Active Profile) of the shot peened gear and the area close to the SAP (Start of Active Profile) of the mating gear in mesh with it. If microgeometry corrections, such as tip relief, have been performed during the manufacturing process prior to shot peening, the effect of the edge rollover can be less critical, but should be evaluated for any specific case.

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