Research On Tool Path Planning Of Improved Genetic Algorithm For Free-form Surface Based On Reverse Engineering

Free-form surface parts are widely used in aerospace,shipbuilding,automobile,mold manufacturing and other fields because of their excellent aerodynamics,hydrodynamics and thermodynamics.Free-form surface modeling technology has been relatively mature,but relatively speaking,the development of free-form surface processing technology is slightly backward.As a bridge between free-form surface design and multi-axis machining,with the development of multi-axis machining center,NC programming of free-form surface has become more and more important.Especially,the research on the tool path planning technology has become a hot and difficult topic in this field.For the free-form surface model without clear parameter expression,the three-dimensional point cloud information on its surface is obtained by using the coordinate measuring machine,and then the point cloud data is fitted with MATLAB software to obtain the parameter expression of the free-form surface model.Finally,the surface model is reconstructed in the NX software according to the parameter expression.Aiming at the disadvantages of route redundancy,low efficiency and large error in the method of equal parameter step length,step length screening and bow height error,an improved bow height error method is proposed.According to the relation between the bow height error and the curvature of the surface,the minimum step size of the surface satisfying the bow height error is calculated as the initial step size.Based on the constraint condition that the bow height error between two adjacent contacts is constant and the maximum allowable bow height error,an adaptive step size adjustment mechanism is proposed.On the basis of ensuring the discrete maximum length of surface,the quick solution of cutter contact is realized.The experimental results show that the efficiency of improved bow high error method is 29 times higher than that of step length screening method when the accuracy is the same.Under the condition that the solving efficiency is almost the same,the number of cutter contacts obtained by the improved bow high error method is small and the accuracy is high.The improved bow high error method can solve the problems of high efficiency and low accuracy of the traditional algorithm.Aiming at the problems of slow convergence speed and easy to fall into local optimal solution when traditional genetic algorithm optimizes tool path,an improved genetic algorithm is proposed.Aiming at the loss of excellent individuals due to high crossover and mutation probability in the late iteration period of traditional genetic algorithm,adaptive adjustment of crossover and mutation probability is realized from two aspects of individual fitness distribution and individual fitness value.In order to solve the problems that the traditional genetic algorithm is too slow in the face of a large number of knife contact path optimization,the greedy crossover operator and greedy inversion mutation operator are designed with the constraint condition that the fitness value of the child is better than that of the parent.The experimental results show that in terms of path length optimization,the improved genetic algorithm can shorten by 8.82%compared with the traditional genetic algorithm,and in terms of program time,the improved genetic algorithm can reduce by 91.18% compared with the traditional genetic algorithm.The improved genetic algorithm improves the algorithm efficiency,reduces the prematurity probability,and can complete the free-form surface tool path planning more efficiently and with high quality.In order to verify the actual machining efficiency and accuracy of the tool path planned by the improved bow high error method and the improved genetic algorithm,a group of actual machining control experiments are carried out on the curved parts.Firstly,on the basis of improving the discretization of tool contacts by the bow high error method,the simulation machining of the tool paths planned by the traditional genetic algorithm and the improved genetic algorithm is carried out in NX software,and compared with the machining of streamline milling and area milling commonly used in parts machining,and then the actual machining of curved parts is carried out.Finally,the surface accuracy of the machined parts is measured by the coordinate measuring machine.The experimental results show that,on the basis of improving the discrete tool contacts of the bow high error method,the parts machined by the improved genetic algorithm meet the requirements of machining accuracy,and the actual machining efficiency of the improved genetic algorithm is increased by 12.66% compared with other tool path generation methods.