Effect Of Tool Wear And Thermal Deformation On Form Accuracy In Ultraprecision Cutting Of Large-scale Aluminum-alloy Mirrors

Large aluminum mirrors are important component to guarantee the high resolution of the space optical system,its machined form error directly affects the service performance of mirrors.Because of deterministic machining advantages,ultraprecision diamond cutting technology has become an important method to realize the high efficiency ultraprecision machining of large aluminum mirrors.In ultraprecision cutting of large aluminum mirrors,the large size of mirrors,long cutting distance,unchanging of cutting tool and great cutting speed variation at the different position of workpiece result in serious tool wear and thermal elongation of tool,which have become a key problem to restrict the machined form accuracy of large aluminum mirrors.So it has important theory significance and actual application values to investigate the related problems.In ultraprecision cutting of large aluminum mirrors,the analysis of the wear mechanism and the tool wear rule is the basic problems to explore reducing the influence of tool wear on the machined form accuracy of mirrors.In this paper,the molecular dynamics simulation model in ultraprecision cutting of single crystal aluminum with single crystal diamond tool was established.And the wear mechanism of diamond tool was analyzed by simulation.Then the cutting experiments were carried out to verify the correctness of the simulation results.Finally the main influence factor and influence law of cutting parameters and tool geometry parameters on tool wear were investigated through molecular dynamics simulation and diamond tool wear experiments.It provided a basis for investigating the influence of tool wear on the machined form accuracy of large aluminum mirrors.The degree of tool wear is the key factor directly influencing the machined form accuracy of large aluminum mirrors.In this paper,internal relation between tool wear form and effective cutting depth was analyzed based on the investigation of the forming of machined surface in ultraprecision cutting with round nosed diamond tool.The characterization parameter of tool wear which reflects the changing degree of cutting edge shape caused by tool wear was proposed through the detecting and analysis of micro-morphology of tool wear.And the characterization parameter of tool wear was obtained through 3D surface reconstruction method and the 2D contour section method.The mathematical model of the characterization parameter of tool wear in ultraprecision cutting of aluminum was established.The ultraprecision cutting experiments of large aluminum mirrors were carried out to investigate the influence law of cutting distance on the characterization parameter of tool wear and the machined form accuracy.It provided a basis for exploring reducing the influence of tool wear on the machined form accuracy of large aluminum mirrors.Thermal deformation of the tool is the important factor influencing the machined form accuracy of large aluminum mirrors.In this paper,the influence of tool wear and machining parameters on the cutting temperature was analyzed by the finite element simulation and experiments of ultraprecision cutting of aluminum.On this basis,the thermal elongation model of tool considering tool wear in ultraprecision cutting of aluminum was established based on the analysis of metal cutting theory and finite element simulation.Then the major and minor relationship of the influence of cutting parameters,tool geometry parameters and tool wear on thermal elongation of tool was analyzed.It provided a basis for investigating the influence of thermal elongation of tool on the machined form accuracy of large aluminum mirrors.Based on the above research,the influence law of cutting speed and flank angle on the machined form accuracy of large aluminum mirrors was obtained through the ultraprecision cutting experiments of large aluminum mirrors.Based on the mathematical model of the characterization parameter of tool wear and the thermal elongation of tool,the optimized cutting parameters and tool geometry parameters in ultraprecision cutting of large aluminum mirrors were obtained using the non-dominated sorting genetic algorithm.Finally,the ultraprecision cutting experiments were carried out to verify the effectiveness of optimized method.The investigation results provided basis for the selection of machining parameters in the ultraprecision machining of large aluminum mirrors.