Research On Plastic Deformation Law Of Square Hole Hydropiercing

Due to the advantages of lightweight,high performance and low cost,tube hydroforming parts are widely used in automobile manufacturing industry,and the processing of holes in hydroforming parts has become an urgent problem to be solved.Hydro-piercing is the process of punching the first mock exam after the hydroforming.It has the advantages of high production efficiency and low cost,and has great advantages over other drilling technologies.In this paper,based on the hydraulic forming,the plastic deformation law of square hole hydraulic punching is studied.Taking DP600 high-strength steel tube as the research object,the deformation sequence,collapse behavior,"bending" phenomenon and orifice characteristics in the process of square hole hydraulic punching are studied by mechanical analysis,finite element simulation and experiment.Firstly,the stress state around the hole and the deformation behavior of the material in the process of punching are analyzed,the generation and distribution of the collapse around the hole are explored,and the influence law of the internal pressure and the radius of square hole fillet on the collapse around the hole is verified by the simulation analysis combined with the experiment.On this basis,the deformation law of the porous punching is analyzed.The results show that when the square hole is punched,it is in the state of two-way compression and one-way tension and thick shear stress,and the deformation process is the collapse around the hole corner corner fracture straight edge fracture;with the increase of internal pressure,the amount of collapse around the hole decreases,the collapse area also decreases,and the coincidence degree of collapse contour lines in all directions increases;with the increase of fillet radius,the collapse at the fillet increases,the square hole is gradually round,and the hole is gradually round The distribution of circumferential stress is more uniform,and the deformation of material around the hole tends to be the same with the increase of internal pressure and the radius of square hole fillet;Then through the finite element simulation,the mechanism of "bending" phenomenon is revealed,the influence of internal pressure and the radius of square hole fillet on "bending" phenomenon is summarized,and the improvement method of improving the quality of the boat is put forward.The results show that the phenomenon of "bending" is caused by the unsynchronized fracture between the symmetrical points on the square hole.The smaller the fillet ratio of the square hole is,the larger the internal pressure is,the more likely the phenomenon of "bending" will appear.The larger the fillet ratio is,the smaller the internal pressure is,the less likely the phenomenon of "bending" will appear,which is the opposite relationship with the change of collapse.By using the transition circle with larger taper The angle punch can effectively improve the collapse and orifice quality after "bending".Finally,through the observation of the micro morphology of the characteristic points of the square hole,the fracture form and order of each point are analyzed,and through the observation of the macro morphology of each side,the fracture order and fracture quality of each side are analyzed.The fracture quality after punching under different internal pressure and square hole fillet radius is compared,and the crack defects after punching square hole are analyzed.The results show that the fracture at the corner of the first fracture is composed of shear fracture,tensile fracture and cleavage fracture,and the fracture at the middle point of the straight edge of the second fracture is almost shear fracture.The macro morphology of the fracture of the square hole is composed of the first bright zone,shear fracture zone and the second bright zone,no matter whether there is "bending" phenomenon or not The fracture of the four sides of the square hole is sequential;increasing the internal pressure and the radius of the round corner of the square hole can increase the area of the bright zone in the fracture of the square hole and improve the quality of the fracture after punching;the crack defects of the square hole after punching appear on the last fracture surface of the hole,and improving the stress and deformation of the last fracture surface can effectively reduce the crack defects.