Design and analysis for topologically modified helical gear finished by gear-hobbing

A design and an analysis of topologically modified helical gears were proposed to improve the machining efficiency and reduce the noise and vibration. Firstly, the topologically modified pinion tooth surfaces finished by hobbing was established according to the meshing theory of three independent motion parameters of the tight rational meshing between work-gear and hobbing cutter and the traverse motion of work-gear along the axis of the work gear and tangential feed along the axis of the hobber. Besides, the modified teeth were determined by the profile gear-hob, the center distance between work-gear and hobbing cutter, the hob tangential feed and additional rotation angle of work gear. Secondly, the parameters were individually determined based on TCA and LTCA by optimizing the aim of minimum the amplitude of loaded transmission error of drive gears. Finally, a numerical simulation of example was performed. The characteristics of amplitude of LTE curves were investigated by analyzing the contact ratio with increasing loads on modified gears. The results show that the optimal modified tooth surfaces can reduce sensitivity caused by errors of axes alignment and prevent the gear's meshing teeth from colliding with each other at the boundary, and make lower amplitude of LTEs reduce by 44%, which contributes to a lower vibration and noise. Besides, an accurate tangential feed of the hob with longitudinal correction can attain an anti-twist helical gear tooth flank with longitudinal tooth crowning, because continuous changes in profile along longitudinal of hobber contribute to reducing distortion of profile due to variable center distance hobbing without compensation of profile.