Tooth contact analysis for helical gear pairs generated by a modified hob with variable tooth thickness

•We propose a mathematical model of the modified hob with variable tooth thickness.•The model of the modified hob can be simulated the traditional and the VTT hob.•The related coordinate systems are established for a CNC hobbing mechanism.•The gear tooth contact simulations are investigated by applying the TCA method.

Conventionally, the longitudinal crowning of helical gears can be accomplished by varying the center distance between the hob and work gear in gear hobbing process. Without a crossed angle compensation, however, this center distance variation produces twisted tooth flanks on the work gear. A methodology is thus proposed herein to reduce the tooth flank twisting of a longitudinal crowning gear by applying a modified variable tooth thickness hob and having a diagonal feed without varying the center distance. This study also investigates the gear tooth surface topologies, contact ellipses and transmission errors of the work gear pairs, generated by a conventional hob and the proposed modified hob with variable tooth thickness, respectively. Three numeral examples are presented to illustrate and verify the merits of the proposed gear hobbing method with longitudinal crowning.