Influence Of Mold Parameters On Residual Stresses In304Stainless Steel Drawing Cylindrical Parts

The residual stress directly affects the parts’ fatigue strength, dynamic load strength,static load strength, fracture toughness, dimensional stability and resistance to corrosioncracking etc. The residual stress also can cause larger deformation of the parts duringprocessing or using, which may bring considerable impacts on assembly and repair. Thusthe residual stress has gradually aroused the great attention of researchers. It is of veryimportant significance to reduce and eliminate residual stress in the parts.Firstly in this paper, a new theoretical model for split-ring test to measure the residualstress in the ring was developed, and the theoretical model was verified to be reasonableand reliable by the simulation of closing the split ring with software ABAQUS. Secondly,seven groups, three cylindrical drawing cups of each group, and a total of21qualifiedcylindrical drawing cups were made from0.94mm thick SUS304stainless steel sheet withfour different punch-die clearance (C0.9mm, C1.0mm, C1.1mm, C1.2mm) and fourdifferent die corner radius (R3mm, R5mm, R7mm, R9mm). Then the closed rings were cutfrom the wall of cups and each ring was split along the radial direction. Almostsimultaneously two ends of the split ring opened a distance to release the circumferentialresidual stress in the closed ring. The opening distance and central angle were measuredand the residual stress in each cup was calculated by newly developed theoretical model.Thirdly, the drawings of seven group cylindrical cups were simulated by softwareABAQUS, and the residual stress of cylindrical drawing cups were obtained with differentmold parameters. The results showed as follows.1) The circumferential residual stresses were very large in the wall of304stainlesssteel cylindrical drawing cups (the maximum was801MPa on outer surface and-823MPaon inner surface), and circumferential residual stresses in the middle wall was larger thanthose at the mouth of cups.2) The die corner radius almost had no influence on the circumferential residual stress,and the circumferential residual stress first increased with the increase of the punch-dieclearance, then almost remained unchanged when the punch-die clearance increasedgreater than1mm.The circumferential residual stress calculated by split ring tests were much greaterthan those in simulations. Reasons for the difference may be as follows:1) As martensite phase transformation occurs in the deep drawing process of304stainless steel sheet, the density of martensite is smaller than austenite. So the martensite phase transformation will lead to volume expansion, which increases the circumferentialresidual stress in the wall of the304stainless steel cylindrical drawing cups. But thecircumferential stress of phase transformation was not considered in the finite elementmodel of304stainless steel cylindrical deep drawing.2) Material model may be a big uncertain factor. In this paper, Mises isotropichardening model was used in finite element simulations, whose yield surface may existsome differences and the true yield surface of the material in the304stainless steelcylindrical deep drawing.3) Due to the punch-die clearance is smaller in the deep drawing process, cylindricalcup wall was extruded by mold so that the circumferential residual stress inner larger thansurface sometimes, therefore increased the results of calculation.