Research On Forming Laws Of Tube Hydro-pressing Of SAPH440

With the increasing demand for light-weight processing in the automotive and aerospace fields,hollow structural parts are getting more and more applications in recent years.At present,hollow structural parts are mainly manufactured by integrated forming methods such as hydroforming and hydro-pressing.Compared with hydroforming,The pressure of hydro-pressing and the required tonnage of the mold clamping press are smaller,and the wall thickness distribution is more uniform.It gradually replaces hydroforming and is applied to the forming of most hollow structural parts.It has a very broad application prospectThis article first classifies the typical structural characteristics of hydro-pressing shaped parts,including outer corners,inner corners and straight edges.Based on the rigid-plastic material model,the mechanical analysis models of the fillet forming stage and the section compression stage were established,and the critical internal pressure and its influencing factors required for the forming were studied.Through research,it was found that in the fillet forming stage,there is a critical internal pressure in inner corners.The critical internal pressure is related to factors such as wall thickness ,fillet radius ,and yield strength of the material.In the section compression stage,the increase of the hoop force will cause the straight edge buckling defect and the fillet to detach from the mold defect.In addition to the material,wall thickness ,fillet radius and hoop strain εθ,the critical internal pressure of the fillet is affected.On this basis,the numerical simulation and experimental research of hydro-pressing of SAPH440 material rectangular cross-section tube and V-shaped cross-section tube are carried out.The typical defects generated in the forming are summarized.The effects of the internal pressure of the support and the compression ratio of the cross-section on the cross-sectional shape change,fillet filling,and wall thickness distribution are analyzed,as well as the stress and strain at typical locations are analyzed.The rectangular section tube is composed of inner corners and straight edges.The typical defects of hydro-pressing are flash and buckling.The critical internal pressure increases continuously with the increase of the compression rate;the relative radius of the radius increases with the support internal pressure or the compression rate.Compared with hydroforming,the internal pressure of hydro-pressing to form the same fillet is only 1/30 of hydroforming the internal pressure and compression rate have a significant effect on the wall thickness distribution,and the wall thickness increases with the compression rate.While increasing,the minimum wall thickness is located in the up and down straight side area,which is always maintained at about 1%.As the internal pressure increases,the uniformity of the wall thickness becomes worse.The V-shaped cross-section tube is composed of inner corners,outer corners and straight edges.When there is a outer corner structure in the molded part and the compression rate exceeds the maximum compression rate that can be achieved by the current internal pressure,Defects of outer corners out of the mold will occur first instead of the straight edge area buckling Defects require a high internal pressure to achieve perimeter compression;the wall thickness of the V-shaped cross-section tube increases with the increase of the cross-sectional circumference compression rate,and the maximum thinning is located at the center of the lower rounded area.In the mold clamping stage,the pipe is in a "two-tension –one-compression" stress state,and the wall thickness of some areas will be slightly reduced.In the compression stage,the pipe is in a "three-directional compression" stress state,and the wall thickness of all areas has increased significantly.