When machining spiral bevel gear by forming method, under the condition of constant feed speed, the cutting force on the workpiece increases gradually with the increase of cutting depth. In the process of single tooth machining, the tangential cutting force changes greatly, which is easy to lead to abnormal vibration and noise of the gear milling machine, reduce the quality of the tooth surface, and even accelerate and damage the tool wear and reduce the service life of the tool.
The mathematical model of the cutting force of spiral bevel gear NC machining by forming method is established. If the G code of NC machining can be improved by using the linear (or polynomial) constraints of feed speed and cutting force, the speed of feed motion can be variable and the cutting force can be basically constant in the NC machining process of spiral bevel gear, so as to reduce or even eliminate the abnormal vibration of machine tool and tool wear caused by the gradual increase of cutting force, Prevent the cutting tool from breaking and pricking the workpiece, and improve the machining efficiency and quality. According to the milling characteristics of ball end milling cutter, Shi Lei established the mechanical model of milling. Using the empirical formula, under the constraint of keeping the cutting force basically constant, the feed rate of NC code for machining free-form surface is optimized, so as to reduce the movement of cutting force, improve the quality and machining efficiency of NC machined parts, prolong the service life of tools and avoid tool damage. Therefore, a machining optimization prototype system under the constraint of basically constant cutting force is established and verified by an example. Peng Haitao et al. Proposed a new feed rate optimization method, applied the milling force simulation model to the feed rate optimization algorithm, determined the target value of metal removal rate from the set peak force, calculated the corresponding feed rate value according to the actual cutting volume of each tool path, and verified that this method has a good optimization effect through experiments.
There are two methods to control cutting force with variable feed rate: on-line control and off-line control. The main problems of on-line control are: high hardware requirements; The servo control of feed rate has time delay, which can not avoid the emergency; Installing a force sensor will reduce the rigidity of the processing system. Off line control mainly uses macro program to process G code, and constantly modifies the value of feed rate keyword according to the calculation results of optimization algorithm. Off line optimization has no special requirements for machine tool hardware and simple operation, so it is widely used. The feed speed optimization method described in this chapter is changed to offline control.