Study On Surface Roughness Formation Mechanism And Simulation Of Centerless Lathe Turning

In surface finishing,surface roughness is one of the important criteria to judge the quality of the workpiece after machining,which has a great influence on the wear resistance,fatigue strength and matching accuracy of the workpiece.Using the data information during machining,the simulation of the surface morphology of the machined workpiece has been a hot research topic.In this paper,a simulation model based on the vibration characteristics of different turning positions combined with the tool contour trajectory is proposed.The specific work is as follows:(1)The formation mechanism of the workpiece surface was analyzed,and the influence of different parameter changes on the workpiece surface roughness was compared.The actual workpiece surface roughness profile was decomposed into the superposition of the ideal workpiece surface profile and the relative vibration between the tool and the workpiece by simulation method.According to the influence degree of the vibration of different parts of the machine tool on the workpiece surface roughness,the simulation model of workpiece roughness topography was built.The experimental platform of turning superalloy with centerless lathe was built,orthogonal experiments of different cutting parameters were designed,vibration acceleration sensors were arranged at the tool and rear guide,roughness profile measuring instrument and white light interferometer were used to collect the surface roughness topography of the machined workpiece.The collected vibration signals are smoothed and denoised and converted into vibration displacement signals by quadratic integration.The vibration displacement signals are decomposed and reconstructed by using wavelet packet,and the energy ratio of different frequency bands is obtained to obtain the frequency band occupied by the main energy,and the vibration displacement signals are reconstructed.(2)In the process of turning,the cutter head and the back guide of the centerless lathe directly contact the surface of the workpiece,and the vibration of these two places directly affects the surface roughness of the workpiece.The dynamics model of the 2-DOF turning system of the centerless lathe is established,and the fourth order Runge Kutta equation in MATLAB is used to solve the dynamics equation.The variation trends of vibration displacement and vibration acceleration under different cutting parameters were analyzed,and the vibration displacement signals obtained were compared with those obtained by experiments to verify the accuracy of the dynamic model.(3)Analyze the significant influence of vibration at different positions on surface roughness,extract the root mean square value of vibration displacement signal to reflect the strength of the signal,and compare the change trend of the root mean square value of vibration displacement signal at the tool and the rear guide under different cutting parameters with the change trend of the workpiece surface roughness.Principal component analysis(PCA)was used to quantify the contribution rate of the vibration displacement at the cutter head and the vibration displacement at the rear guide to the surface roughness.(4)Two simulation models of surface roughness were established for comparative study according to different acquisition methods of turning vibration displacement:Tool profile trajectory-simulated vibration model,(Tool profile trajectory-simulated vibration model,PTS)and Tool profile trajectory-measured vibration model(PTM).According to the PTM model,the simulated roughness profile under different cutting parameters was compared with the workpiece surface roughness profile measured in the actual experiment.The arithmetic mean deviation R_a and fractal dimension D were used to analyze the accuracy of the model.The average error of Ra was 1.978%,and the average error of D was 3.8818%.It shows that the simulation model of surface contour curve has high accuracy and can accurately reflect the surface quality of the workpiece.By comparing the actual measured roughness value and the simulated roughness value calculated by the PTS model,the average error of R_a is 9.326%and the average error of D is 9.813%.The simulation accuracy is lower than that of the PTM model.However,the vibration displacement signal solved by the dynamic model of the PTS model reduces the conditions for the simulation of the workpiece surface profile.The surface quality of the workpiece can be reflected in the error range,and the surface roughness can be evaluated in the design of experimental parameters.