Study On Forming Mechanism And Control Method Of Stretch Bending Forming Surface Distortion Of Aluminum Trim Strip For Aotobody

In recent years,with the development of the automobile industry and the improvement of people’s living standards,people have put forward higher aesthetic requirements for the appearance of automobiles,and the shape design of exterior trim of automobiles is more complex.Different from traditional exterior trim strips with large bending radius and narrow cross-section width,integrated upper trim strip design with variable crosssection appears.As the bending radius decreases(up to 150 mm)and the cross-section width gradually increases(up to 50 mm),forming defects such as springback,wrinkling and surface distortion are more likely to occur.Among them,surface distortion defects during tension bending process under decorative conditions are usually manifested as narrow and long depressions on surface A with depths ranging from tens of microns to millimeters and widths of about 2-3 mm,which seriously affect the exterior quality of the autobody.In actual production,surface distortion defects are improved by manual grinding,with low efficiency,high labor intensity and poor working environment.Therefore,it is of great theoretical and engineering significance to study the mechanism and control method of surface distortion during tension bending.Aiming at the surface distortion defect of F-section aluminium alloy trim during stretch bending,this paper carries out research on evaluation method,forming mechanism,influencing factors and control method.The main work completed includes:(1)Numerical simulation of distortion defects on stretch bending forming surfaceBased on ABAQUS simulation platform,finite element model of distortion defect of stretch bending surface of aluminium ornament parts was established,and local coordinate system was established on fixture to simulate actual conditions of stretch bending process.The potential area of surface distortion is obtained by preliminary simulation results and refined to ensure simulation efficiency and accuracy.An experimental system for stretch bending of aluminum trim parts was established and experiments were carried out.The accuracy of the simulation model was verified by comparing the simulation results with the experimental results.(2)Study on forming mechanism of stretch bending forming surface distortionThe F-shaped feature is designed,the geometric and technological conditions of the feature surface distortion are analyzed,the local deformation and stress-strain characteristics of the surface distortion parts in the process of forming are analyzed,and the process of surface distortion is obtained.The research results show that when the ratio of cross-section width to bending radius is more than 30%,the warping tendency of the part is caused by the thinning of the outer side and the thickening of the inner side of the part during the stretching and bending process.During the pressing down process of the upper die,the material between the two reinforcing bars can not be adequately supported by the gasket,resulting in surface distortion.(3)Study on influence of process parameters on distortion of stretch bending forming surfaceThe influence laws of key factors such as loading history,material properties of parts,material properties of padding and section shape of padding on surface distortion defects were studied.During stretch bending process of aluminium trim strip: the change of pre-tension and supplementary tension has no obvious effect on the surface distortion defect,while the change of main tension has significant effect on the surface distortion defect;in terms of material properties,the influence of each parameter on the surface distortion defect is from large to small according to the following: elastic modulus of pad > yield strength of part > elastic modulus of part > hardening index of part;the increase of arc of pad can make the surface distorted.Distortion depression is greatly improved.(4)Research on optimization control method of stretch bending forming defectsThe face distortion compensation method is simulated and analyzed,and the simulation results of upper and lower die compensation are compared.Based on the analysis of influencing factors of surface distortion defects and by means of multi-objective optimization method,the prediction and control model of surface distortion defects in stretch bending of aluminium trim strips under multi-parameters is established,and the optimal parameters are obtained.By combining the traditional die compensation method with the parameter optimization scheme,the optimal control method for the surface distortion defect is obtained.The experimental verification proves that the scheme can effectively improve the surface distortion defect.