Research On The Method Of NC Machining For Spiral Bevel Gear Of Half-hobbing Helix

Aiming at the problems of the spiral bevel gear: the bias of tooth contact,the complex parameter adjustment and the low machining efficiency.This paper adopts the method of half-hobbing helix to machine spiral bevel gears.The passive gear is machined by generating method,the drive gear is machined by the method of helix modified roll,conducting the research of cutting principle and NC machining for spiral bevel gears:Firstly,the forming theory and cutting calculation of half-hobbing helix are conducted.The reason of the bias of tooth contact of traditional generating method is interpreted.The principle that the bias of tooth can be eliminated by the half-hobbing helix is analyzed.With the point of passive gear cone section for calculating point that is located in the center of the tooth,the passive gear mathematical cutting model is established on the basis of local conjugate principle.Normal vector and curvature of the calculation point and the machine settings of passive gear are gained.By applying principle of gearing and differential geometry,normal vector and curvature of the calculation point on pinion tooth surface are determined.Finally,the pinion mathematical cutting model is established and the machine settings of the pinion is determined.Secondly,the mathematical processing model of the five-axis machining center is established.The cutting coordinate system of the traditional machine and the five-axis machining center are respectively established.Based on space coordinate transformation,the relative attitude and position matrix of the work piece and the cutter,which is in the coordinate system of the traditional machine and the five-axis machining center,is obtained.The motion expression of NC axis is deduced,accomplishing the transformation from traditional machine setting parameters to the input parameters of five-axis machining center.Thirdly,the simulation processing of the spiral bevel gear is conducted.The threedimensional model of the cutter,blank of passive gear and pinion are established respectively,which are imported VERICUT through the format conversion.Based on the motion expression of NC axis,conducting programming by C++,to generate NC code needed for the simulation with the demand of NC program.Finally,the simulation processing model of passive gear and pinion are gained,which proves the accuracy and feasibility of NC program and the mathematical processing model of five-axis machining center.Finally,the research of cutting on the five-axis machining center is accomplished.According to the principle of the half-hobbing helix,conducting processing for a pair of spiral bevel gear in the double turntable five-axis NC machining center and rolling test for the passive gear and pinion after processed.It proves that the method of half-hobbing helix contributes to improve the quality of the tooth contact,simplified processing adjustment and improve the machining efficiency.