Tooth surface Hobbing analysis for unconventional gears with ultrasonic-assisted motion

Abstract

As an atypical conventional gear pair, non-circular gear has a variable transmission ratio, which can be used to improve the structure and transmission characteristics in some applications, such as variable speed grinding mechanism, wool blending machine guide mechanism, continuously variable transmission structure and so on. According to the friction theory of conjugate surfaces, the transmission characteristics will be affected by the micro topography of tooth surface, but the shaped tooth surface of non-circular gear with normal hobbing method is not uniform, because of its variable radius and flank orientations of tooth surface. The research on the relationship between micro topography and parameters of non-circular gear is necessary, thus an improved manufacturing method with ultrasonic-assisted motion was presented in this paper, the mathematical equations for the theoretical tooth surface of non-circular gear with and without ultrasonic-assisted motion have been derived in this paper, also the equations for cutting parameters (step displacement, step rotating angle) have been proposed, shown that all the parameters (initial parameters of gear and gear hob, cutting parameters in manufacturing process) will affect the formed micro surfaces. In detail, the height Hm and width Sm of micro undulating tooth surface periodically increase and decrease, getting the maximum value at θn=π, where is the maximum radius. The height Hm and width Sm of micro tooth surface will increase with any control parameter increase, the height Hm of most micro peaks is near 6.5um in normal hobbing process. While, the tooth surface with ultrasonic-assisted motion is more regular and clearer with the maximum height Hm decrease from 6.5 um to 2.7 um, getting more compact cutting tracks and lower surface roughness. The experimental results shows that ultrasonic-assisted hobbing has obviously positive influence for micro tooth surface, provides the theoretical support for a further analysis and better application of unconventional gear pair.