Numerical Simulation And Experimental Research On End Effect Of Curved Parts By Multi-point Forming

With the continuous development of society,people pay more attention to travel facilitation.The development of automobile,ship,and aerospace technology is constantly moving towards the public's vision.The product manufacturing industry is constantly updating technology,improving product quality and increasing production capacity to gain greater industry competitiveness.The sheet metal is widely used,and the forming of sheet metal has always been the top priority of industrial production.The traditional sheet metal forming uses integral die stamping,which is relatively difficult to produce and debug.It is only suitable for volume-produce.For small batches and individual demand,the integral die forming can't meet the requirements of rapid prototyping and cost saving.Flexible multi-point forming is a major breakthrough compared with traditional sheet metal forming methods.It uses the idea of discretization,discretizes the traditional mold surface into separate element bodies,and forms an envelope surface by combining the element bodies to replace the overall mold,which reduces the production and debugging cycle of the overall mold and greatly improves the productivity.Various forming defects often occur when sheet metal is formed,and the forming defect of sheet metal has always been a major problem that countless engineers and technicians eager to solve.This paper mainly researches the abnormal deformation of the end in the process of sheet metal bending.In allusion to this phenomenon,the concept of end effect is proposed.The causes of this phenomenon are analyzed and verified by experiments through multi-point forming technology.The finite element numerical simulation test is designed for some influence factors of sheet metal forming.The influence of each factors on the end effect is studied,which provides a certain basis for future research and analysis.The main research contents and conclusions are as follows:(1)Discuss the principle of multi-point forming and the general situation of numerical simulation of sheet metal,and expound the finite element theory of sheet metal forming and numerical simulation theory of multi-point forming.Taking the forming cylindrical part as an example,a multi-point forming finite element model is established,and the specific setting of each parameter is discussed.(2)The cylindrical sheet bending is carried out through multi-point die forming and integral die forming.The numerical simulation results show that after loading and unloading of the sheet metal under the two forming methods,the central axis of the extracted axial direction(i.e.the longitudinal direction)exhibits end effects.The reason for this phenomenon is obtained through analysis: the degree of deformation of the sheet in the circumferential direction(i.e.the width direction)is different in the bending deformation.Because the sheet metal will be accompanied by the thinning of the sheet thickness,the elongation of the material in the length direction and the internal movement of the neutral layer during the forming process.The small elongation of the small deformation area at the circumferential end will limit the elongation of the material in the central large deformation area,and the different tensile and compressive stresses on the inside and outside surfaces of the sheet will also lead to different material elongations on the inner and outer surfaces.With these factors combined,the formed part exhibits the end effect of abnormal arching at both ends.(3)Multi-point forming test is carried out to verify the end effect in sheet metal bending forming.The conclusion is that the curve of the extracted test piece shows the macroscopic abnormal arching phenomenon at the end,and the numerical value is consistent with the numerical value of the curve extracted by the numerical simulation.The error is within the specified range,and the end effect has been verified by experiments.(4)It can be obtained by analyzing the formed parts with different curvature radii.With the increases of the radius of curvature,the formed parts all show end effect when pressed down,and the change of the maximum value is inversely proportional to the value of the radius of curvature.And the influence range of the end effect in the length direction accounts for 2/3 of the length of the whole formed part(1500mm),which has a great impact on the forming of the sheet metal.After the formed part springs back,within a certain radius of curvature,the maximum value of its end effect is still inversely proportional to the radius of curvature.And its length influence range also occupies 2/3 of the length of the formed part(1500mm).However,as the radius of curvature increases to a certain extent,the overall deformation of the formed part is small,and the formed part no longer has end effect and shows the warpage phenomenon of bending deformation.(5)It can be obtained by forming analysis of forming parts with different thicknesses.When other conditions like curvature radius unchanged,as the thickness increases,the relative bending radius decreases and the degree of bending deformation of the sheet increases continuously.The curves at the central axis are extracted after forming,and all demonstrates end effects.And the maximum value of its height increases with the increase of the plate thickness,and the end effect also increases continuously in the lengthwise direction until it reaches the position of about500 mm from the edge.Its influence area also accounts for about 2/3 of the length of the whole sheet(1500mm).(6)Forming analysis of formed parts with different lengths shows that when the plate length is less than the influence length of the end effect,the formed parts are completely warped.When the plate length is increased to the same length as the end effect,it fully exhibits the end effect with no flat part in the middle region.When the plate length continues to increase,it exhibits an end effect with the ends arched and the middle straight.When the plate length is increased to a certain range,the middle part of the formed part shows warping phenomenon,and the end part also has the end effect of arching.The overall analysis shows that as the plate length reaches the influence area of the end effect,the longer the plate is,the greater the end effect height value is.When the length reaches a certain level,the sheet not only exhibits end effect at the end but also shows warpage deformation in the middle of the sheet,and the warpage degree also increases with the length of the sheet.