Study On Relife Grinding Theory Of Hob Cutters And Dressing Machine Design For Form-grinding Wheels

Gear hobbing is the most widely used method in gear machining, the precise hob relief grinding is one of the most important premises for high accuracy gear machining, and the reasonable hob regrinding can prolong the tool life of hob and improve the accuracy of tooth surface.The researched relief grinding theory and dressing system is mainly aimed at the medium module hobs, the full tooth-surface of hob is derived from once radial overall relief grinding by the hob grinding wheel. As the gear hobbing processes, the cutting edge of hob will be worn, so the hob should be reground for ensuring precise hobbing. For the effect of the grinding wheel feeding in hob radial direction, the regrinding error between the practical tooth edge and the theoretical tooth edge is formed, and the excessive regrinding error will lead to decrease the accuracy of gear. Therefore, it is necessary to research once radial overall grinding, including the accurate calculation of grinding wheel sectional contour and the analysis of hob regrinding error; the results may provide valuable reference for hob machining.In the practical application, the tooth profile on the rake face of hob is regarded as the benchmark tool shape. In this paper, a hob cutter with single-head and right-lateral is took as illustration, the tooth profile on the rake face of hob is discrete, then, analyzing the motion in the hob grinding processing, calculating the sectional contour of grinding wheel based on meshing theory, the section contour of the grinding wheel is obtained. According to the obtained section contour of grinding wheel, the practical relief grinding tooth surface equation is established by meshing theory, and the regrinding error in regrinding section is acquired by comparing with the theoretical tooth surface. In case of constant permissible regrinding error, using the theoretical tooth profile under specified optimized angle replaces the rake face as the benchmark tool shape, the regrinding angle is capable of maximization, and the corresponding section contour and regrinding error of grinding wheel are calculated.The obtained section contour of grinding wheel is a series of discrete dots. In order to obtain the smooth section contour, this paper proposes double-arc fitting method which ensures the fitting error is within permitted, then, directly converting the fitted arcs into G-code for dressing the section contour in the dressing machine.Applying the precise technology of forming grinding wheel, the machine system and control system are designed respectively based on the expected motion and the control requirement, and the brief calculative process and the selection description are presented. Finally, a kind of dressing machine is designed successfully for the precise dressing of forming grinding wheel.Taking a kind of straight slot dextral zero double-arc hob cutter with single head as the research subject, the theoretical tooth edge with the optimized angle 0°, 0.5°and 1o is regarded as the benchmark tool shape, the corresponding section contour of grinding wheel and the regrinding error of hob are calculated. The section contour of grinding wheel with the optimized angle 0.5°is fitted with double-arc fitting method, the obtained double-arc fitting curve is magnified by ten times and converted into the corresponding G-code for executing the simulation experiment in the designed dressing machine, and the motion of the worktable is draw.