Numerical Simulation Research On The Multi-point Punch Active Loading Stretch-forming

Multi-point stretch-forming is a new flexible forming technology.This forming method can save manufacturing costs,shorten the parts manufacturing cycle.However,due to multi-point stretch-forming technology and the traditional stretch-forming technology has similar limitations,for example,the deformation of sheet is not uniform,and prone to slip lines,wrinkles etc.Therefore,it is necessary to explore the new loading method to improve the uniformity of sheet deformation.With the development of multi-point technology,the height of multi-point punch element can be ajusted under pressure,so as to achieve actively continuous loading in the vertical direction of sheet,which makes the sheet formed continuously.Based on the above characteristics of the multi-point punch,it is applied to the stretch-forming,and studies the effects of the multi-point punch active loading stretch-forming on the forming quality of the sheet.In this forming method,all multi-point punch is always contact with the sheet material,which can effectively improve the uniformity of the deformation of the sheet,avoid forming defects,obtain qualified parts.The study of multi-point punch active loading stretch-forming for the actual production has important guiding significance.The main contents and conclusions are as follows:1.Force analysis of the sheet metal and finite element model establishmentBasic assumptions of the deformation condition of the sheet was made.The stretch-forming process of the sheet metal was analyzed by means of mechanical analytical method.The expression formula of stress,strain and thickness of the sheet during the forming process were obtained.At the same time,the finite element model was established,and the boundary condition was determined.2.Multi-point punch active loading stretch-forming and loading path designThis paper introduced the characteristics of multi-point punch active loadingstretch-forming,and analyzed its similarities and differences with multi-point stretch-forming.Based on the run time,the speed of punch and the deformation curvature of the sheet,three loading paths were designed,such as constant velocity punch active loading,isochronous punch active loading and equidifferent-curvature punch active loading.At the same time,the stress state of AL sheet between the multi-point stretch-forming and the equidifferent-curvature punch active loading stretch-forming were compared and analyzed.The results show that the equidifferent-curvature punch active loading can effectively improve the deformation uniformity of the sheet.3.Numerical simulation analysis of the multi-point punch active loading stretch-formingBased on the multi-point punch active loading stretch-forming and the multi-point stretch-forming,the numerical simulation of the spherical and saddle parts was analyzed.The influence of different loading paths on the forming effect of sheet metal was studied.Conclusions can be made that,compared with the multi-point stretch-forming,constant velocity punch active loading,isochronous punch active loading and equidifferent-curvature punch active loading can not only reduce the stress concentration in the position between the sheet metal and jaw,but also improve the uniformity of the distribution of stress,strain,thickness and elongation,and reduce the springback.4.The study of parameters of the multi-point punch active loading stretch-formingThe effect of process parameters on the quality of saddle was studied through numerical simulation.The process parameters involved the pretension,cushion thickness,length of transition zone,forming time and basic element parameters.The results show that,the reasonable combination on process parameters can make sheet metal deformation more uniformity,and enhanced the quality of the parts.