The development and application of modern numerical control technology provides a foundation for the development of spiral bevel gear machining towards high efficiency, high precision, automation, flexibility and intelligence. Aiming at improving the cutting efficiency and machining quality of spiral bevel gear NC milling machine, this paper carries out theoretical and Experimental Research on the calculation of cutting force, the optimization of cutting parameters and the influence of cutting parameters on the residual height of spiral bevel gear in spiral bevel gear NC machining. Based on the principle from easy to difficult, firstly, the dynamic cutting force modeling and machining parameter optimization method of forming method are studied, and then the cutting force modeling and machining parameter optimization of spiral bevel gear pinion processed by hobbing method, the calculation of average residual height of spiral bevel gear tooth surface and the evaluation method of tooth surface roughness during finish machining are studied.
(1) According to the geometric theory of machining spiral bevel gear by forming method, the calculation formulas of undeformed chip thickness and chip width at any time are deduced, the dynamic milling force model of machining spiral bevel gear by forming method is established, the milling force coefficient is calibrated through orthogonal experiment, and the dynamic cutting force simulation program of machining spiral bevel gear by forming method is compiled. In order to verify the effectiveness of the dynamic cutting force model, an experimental device is designed. The relative error between dynamic cutting force calculation results and experimental results is less than ± 15%, which proves the correctness of cutting force modeling and simulation.
(2) Based on the geometric principle of hobbing spiral bevel gear with four axis NC gear milling machine, the calculation formula of instantaneous undeformed chip area of cutting layer in the process of rough milling small gear is deduced. Using the traditional cutting force model, the calculation method of cutting force for hobbing spiral bevel gear pinion is established, the cutting force simulation program is developed, and the verification scheme is designed. The results show that when different cutting parameters are used, the calculated results of the corresponding main motor power input power are basically consistent with the measured results of the main motor frequency converter output power.
(3) A variable feed rate control method under the constraint of basically constant instantaneous tangential cutting force is proposed. This method is based on the instantaneous cutting force model of machining spiral bevel gear by forming method. By dynamically changing the value of feed speed keyword of NC code of gear milling machine, the variable feed speed control is realized, so as to reduce the fluctuation of cutting force, reduce the vibration and abnormal noise in the process of NC gear milling, improve the quality and machining efficiency of NC gear milling, and prolong the service life of tools. The feasibility of this method is verified by forming experiment.
(4) An optimization scheme of rough milling parameters of spiral bevel gear based on harmony search algorithm (HSA) is presented. It takes the shortest process time (maximum productivity) and the lowest processing cost of a single piece as the objective function, takes the allowable maximum cutting speed, cutting power and tool durability of the blade as the constraints, and takes the cutting speed, X and Y axis moving speed and single step interpolation degree as the optimization variables, The cutting parameter optimization model of NC Hobbing rough milling spiral bevel gear is established. The optimization program is written in MATLAB, and finally the best rough milling cutting parameters are obtained. The effectiveness of the model is verified by a specific example.
(5) According to the machining principle of precision milling spiral bevel gear by NC Hobbing method, the analytical relationship between the average residual height of spiral bevel gear tooth surface and cutting parameters (cutting speed, moving speed of linkage shaft, single-step interpolation degree) is established, the influence law of cutting parameters on the average residual height of spiral bevel gear tooth surface is analyzed, and the correctness of the results is verified by experiments. The results show that the average residual height of spiral bevel gear tooth surface can be reduced with the increase of blade cutting speed, but the effect is not obvious; When the moving speed of the linkage shaft increases, the average residual height of the tooth surface increases slightly; Single step interpolation degree can significantly affect the average residual height of tooth surface. The average residual height of spiral bevel gear tooth surface can be used as an index to predict the tooth surface roughness.