Effect of plug shape on forming square tube by expansion drawing

Abstract This study clarifies the plug shape for forming a square tube with high dimensional accuracy from a circular tube using expansion drawing, with the effects of plug parameters — width, corner angle, and corner radius of the plug — on the thickness distribution and dimensional accuracy of the drawn tube (aluminum alloy 1070) evaluated using finite element analysis and experiments. When the plug width was large, local thinning occurred at the corners of the drawn tube; when the plug width was small, a gap appeared between the plug and the drawn tube. Local thinning and gaps can be suppressed by decreasing the half-angle. In addition, the local thinning at the corner of the drawn tube increased when the corner radius was small. The experimental results were consistent with the analysis results. An evaluation based on Japanese industrial standards showed that both the experimental and analytical results of the drawn tubes met these standards.