Research On The Impact-contact Mechanism And Surface Quality In The Process Of Low-frequency Vibration Cutting

The requirements about machining accuracy and surface quality of all kinds ofprecision machinery parts become higher, with the development of mechanicalmanufacturing industry. The efficiency of traditional machining method is very lowand unable to machine difficult-to-cut materials like titanium alloy, high temperaturealloy, stainless steel, high strength steel, ultra-high strength steel, composite materials,hard brittle materials and precision machinery parts with poor manufacturability.However, the technological effect of low-frequency vibration cutting process issuperior. It has been recognized by domestic and foreign experts. Ultrasonic vibrationcutting has been researched widely at home and abroad, and the low-frequencyvibration cutting is less studied. Especially the research on the impact-contactmechanism of low-frequency vibration cutting is singularity. This basic research willundoubtedly affect the effective and wide application of low-frequency vibrationcutting technique. The impact-contact mechanism of low-frequency vibration cuttingwas studied on this article from the following aspects: the impact system model oflow-frequency vibration cutting, local stress changes during the cutting process, finiteelement simulation, cutting experiments, the prediction of surface roughness.(1) Study on nonlinear impact system model of low-frequency vibration cuttingimpact-contact process.The dynamic impact on the material exposure in low-frequency vibration cuttingand the process of the impact of the cutting tool on the material were analyzed in thispaper, and the equivalent impact model was also built here. Based on Hertz contacttheory, the nonlinear shock system model was constructed. The model was simplifiedcertain and sought its analytical solution. According to the stress wave theory, thestress wave production and propagation in the workpiece under impact-contact effectwere studied. The impact model was used to find the change of force anddisplacement in the process of impact. It was also applied to solve the proportion ofsteady state force to the total impact force, and then study how the dynamic impactaffects the stiffness of the system. (2) Studying on cutting degree and machining simulation based on impact contacteffect of low-frequency vibration cutting process.Based on the properties of low-frequency vibration cutting process impact-contact,the concept of "cutting degree" was proposed to rule the change of local stress in thecutting surface. Based on analyzing the material nonlinearity and geometricnonlinearity of metal-cutting issues, elastic-plastic finite element method for solvinglarge deformation process was researched; low-frequency vibration cutting finiteelement model, friction model, re-meshing model and others were established; Thechange values of stress of the same node on finished surfaces during the cuttingprocess was achieved by using nonlinear finite element simulation software tosimulate low-frequency vibration cutting process and based on dynamic impactproperties and finite element theory. The change of local stress of the same node onthe finished surface was researched by using three different cutting ways:low-frequency vibration cutting with frequency150Hz and200Hz and generalcutting.(3) Study on surface micro-topography and chip cross section micro-morphologybased on impact contact effect of low frequency vibration cutting process.The contrast experimental of low-frequency vibration cutting and conventionalcutting was studied by CA6140. The variation of Rockwell hardness on finishedsurface, processed by three different cutting ways: low-frequency vibration cuttingwith frequency150Hz and200Hz and general cutting, was studied throughexperimental. The different effects, produced by machining under the role of shockand vibration exposure in different cutting ways, were compared and analyzed, basedon observing the machined surface and chip section by SEM. The change rule of localstress on machined surface during cutting process of low-frequency vibration wasverified through the experiments. The effect and mechanism of impact-contact forworkpiece during low-frequency vibration were revealed according to themicro-topography of finished surface and chip section.(4) The prediction algorithm of machined surface roughness was studied based onthe effect of impact-contact in the process of low-frequency vibration cutting, theprinciple of least squares support vector machine and the intrinsic parameters of the low-frequency vibration cutting experiment.The input parameters of forecasting model were designated by the experiment ofintrinsic parameters of low-frequency vibration. The cutting parameters, vibrationparameters, and surface roughness of workpiece were achieved by the experiment oflow-frequency vibration cutting. The forecasting model and algorithm betweensurface roughness with vibration parameters and cutting parameters duringlow-frequency vibration cutting were established, based on the effect ofimpact-contact in the process of low-frequency vibration cutting, the principle of leastsquares support vector machine and the intrinsic parameters of the low-frequencyvibration cutting experiment. The performance of the prediction algorithm ofmachined surface roughness basing on least square support vector was researchedthrough comparing with BP neural network and support vector machine.