Research On Effects Of Boss Forming On Cylindrical Parts Bottom In Plate Forging Process

With the improvement of manufacturing level,requirements for processing metal parts of higher assembling accuracy,energy-saving and environment protection have recently been the creatively hot subjects in plastic forming industry,which constantly actuate the reform and innovation of new processes and technologies.Plate forging as a new class of manufacturing process is applied for controlling the metal flow to forming three-dimensional local structure with sheet or semi-finished product in stamping process.It is an advanced technology to be used for forming boss structure on thinning plate.In present study,forming boss on cylindrical parts bottom in plate forging process is researched,and the slab method(SM)is used to analyze the stress characteristics of metal formation in drawing region,punch profile radius region and part bottom region.The stress distribution of thickness direction and the principle of metal flow on bottom sheet and at the punch radius bottom corner are meanly studied,the mechanical model of boss bottom dimple is established,the theoretical formula for predicting the limit thickness of boss bottom part is deduced,and the concept of plastic bending moment effecting on solid boss is proposed in this paper.Based on the platform of DEFORM finite element software,the subprogram module of Swift constitutive model is developed to simulate the plate forging process for manufacturing the boss on cylindrical part bottom.Besides,the stress and metal flow velocity distribution of thickness direction are compared in both back-extrusion and plate forging process.As the simulation results shown,the stresses in boss bottom region linearly increase along the thickness and radial direction for both forming process;the punch load of back-extrusion is about two times larger than that of plate forging with forming same height boss,while the metal flow velocity in back-extrusion process is dozens of times larger than that of plate forging.Meanwhile,the influence of fraction conditions,boss structure and blank thickness on the boss dimple effect is investigated,and a dimple mechanism diagram of plate forging boss is developed.The results indicate that the dimple is easily appeared under bad lubrication fraction,larger boss radius,smaller boss profile radius and thinner blank;the depth of first appeared dimple increases with boss bottomthickness thinning as the boss profile radius is too larger.In addition,the plate forging experiments are carried on to form boss structure and verify the reliability of theoretical and FEM simulation results.At last,the plate forging swing bolster process is put forward,and an optimized structure of forming die and blank has proposed,which successfully reduces the forming process,saves material and improves formability of part.