Stamping–forging hybrid forming of double layer cup with different wall thicknesses

A double layer cup with different wall thicknesses was studied. The wall thickness of the inner cylinder was 4 mm and that of the other sections was 2 mm. According to this characteristic, the outer cylinder was first formed by forward drawing, then the inner cylinder was formed by powerful backward drawing and, finally, the inner cylinder was thickened by upsetting to meet the requirements. The finite element simulation software Marc was used to analyse the effect of shape and size of blank holder, specific velocity and fillet on the forming. The results show that a blank holder with filleting can effectively promote the material flow from the wall of the outer cylinder to that of the inner cylinder during the powerful backward drawing, that the minimum and maximum values of the wall thickness of the inner cylinder increase with increasing specific velocity and that the corner with filleting can guide the material flow effectively to avoid folding during the thickening forming.