The Cold Forming Analysis of Stainless Battery Bolts

A multi-stage cold forming process for the manufacture of battery stainless bolts is studied numerically with AISI 316 stainless steel in this study. The cold forming process through five stages includes preparation and centering for backward extrusion, backward extrusion over die pin, two upsetting operations, and square trimming. The numerical simulations of cold forming are carried out using the finite element code of DEFORM-3D. The formability of the workpiece is studied, such as the effect on forming force responses, maximum forming forces, effective stress and strain distributions and metal flow pattern. In the five-stage forming process, in the two upsetting and the square trimming forming stages, the effective stresses in the head of the workpiece are significantly high, and the effective strains are also significantly high due to large deformation. The flow line distributions are also very complex in which the flow lines in the trimming region of the upset head are severely bent, highly compacted, and eventually fractured due to excessive trimming. For the maximum axial forming force, the fourth stage of secondary upsetting to form a cylindrical head to a larger outer diameter is 347.2 kN, which is the largest among the five stages due to the large amount of upsetting. However, for the forming energy, the third stage, which the workpiece is firstly upset into a conical shape, is 530.1 J, which is the largest among the five stages due to longer acted axial forming stroke. The total maximum axial forming forces from the first to the last stages are 597.1 kN and the total forming energies are about 1.36 kJ.