Research On The Technology Of Slow Tool Servo Turning For Complex Surface

With the development of industrial technology,compared with traditional plane and spherical surface,the advantage of complex surface with higher degree of design freedom becomes more and more obvious.Various complex surfaces are gradually applied in many fields,such as national defense and military field,celestial observation field and civil life field.Slow tool servo(STS)turning technology belongs to the category of single-point diamond precision turning technology,as a surface machining technology,is gradually applied to various complex surface machining.The complex surface with high accuracy can be directly machined by using the STS precision turning technology,and the machining efficiency is high.The research on STS technology started early abroad,and some mature commercial lathes came out,while the research in our country started late,and our research was mostly carried out on the basis of foreign commercial lathe platforms,the STS turning technology is not yet fully mature in our country.This paper takes STS turning of complex surface as the research object,the construction of STS turning platform,the tool path generation(TPG)and the workpiece surface measurement were studied.The major research works include the following points.1)TPG for STS turning of complex surfaces.High qualify TPG for STS turning directly affect the machining accuracy,and its related theories have always been the focus of research in this field.Three methods of cutting contact points(CCPs)discretization were analyzed,and a method to determine the maximum discretion angle in integrated discretization by limiting the maximum discrete error was proposed in this paper.For the mathematical expression of discrete surface and surface fitting in subsequent surface measurement,a Zernike polynomial local fitting algorithm was proposed,meanwhile,the support domain in local fitting was optimized.Aiming at the problems of high complexity and poor universality of traditional cutting tool shape compensation algorithm,a cutting tool shape compensation algorithm based on tool projection to surface was proposed.The algorithm not only satisfied the compensation accuracy,but also reduced the complexity of the algorithm and had better generality.It was suitable for conical and cylindrical diamond cutting tools with different rake angles.The principle,advantages and disadvantages of different entrance parameters generation algorithms for PVT interpolation were summarized based on the research of different cutting location points(CLPs)interpolation algorithms.2)Simulation analysis of TPG for typical surfaces.Toric surface,sinusoidal array surface,off-axis parabolic surface and progressive-addition lenses(PAL)were selected as simulation surfaces,and the research content of TPG was simulated and analyzed with MATLAB software.The distribution of discrete error with equal angle discretization and equal arc length discretization was analyzed,and the maximum discretion angle of integrated discretization was determined by quantitative method.The result showed that the absolute value of maximum discrete error of integrated discretization was less than the set error threshold.The simulation results of fitting error showed that the fitting error of Zernike polynomial local fitting algorithm was smaller than that of moving least squares method,which met the accuracy requirements.Meanwhile,the fitting error can be further reduced by using the improved dynamic support domains.The cutting tool shape compensation algorithm based on tool projection to surface was simulated,and the result showed that the compensation algorithm had good generality and the compensation accuracy of the algorithm met the requirements of actual machining.The accuracy of PVT interpolation with the entrance parameters which were generated by the three-bending moment method was better than that of the three-point method.3)STS turning experiment for typical surfaces and measurement of workpiece surface.Independently designed and constructed STS turning platform with the core of motion control card and the system PID parameters were debugged.Based on C#programming language and MATLAB software,the NC program generating software and script for complex surface were written.Taking toric surface,sinusoidal array surface,off-axis parabolic surface and PAL surface as examples,turning experiments were carried out with the TPG theories in this paper.The surface roughness of workpieces were measured by JB4C roughness meter.The workpieces were automatically measured by coordinate measuring machine(CMM)using circular measuring path and measuring path programming.The measured data were fitted and divided into meridians with Zernike polynomial local fitting algorithm,and the measuring head radius was compensated by meridian radius compensation method,thus the surfaces error were obtained.The measurement results showed that the surface roughness of the four surfaces can be maintained within 100nm,and the surface error of the toric surface can be maintained at ±0.010mm,the sinusoidal array surface error can be maintained at ± 0.022mm,the off-axis parabolic surface error can be maintained at± 0.013mm,the PAL surface error can be maintained at±0.015mm.