The prediction of central burst defects in extrusion and wire drawing

Central burst defects cause very serious problem in the quality control of products, because it is impossible to detect the defects by means of a simple surface inspection of the workpiece. Since the occurrence of these kinds of defects is, therefore, troublesome in industrial practice, it is important to predict the conditions that may lead to the defects, and by using this prediction it may be possible to choose appropriate process conditions and to modify the forming processes to produce sound and reliable products. This paper suggests an approach to simultaneously accomplish both the prediction of central burst defects and the analysis of deformation in extrusion and wire drawing. The proper ductile fracture criterion is employed in this investigation to estimate the occurrence of central burst defects. Based on the results of analyses, it has been possible to obtain the numerical boundaries that divide the safe and danger zones in reduction in area vs. semi-die angle plane for central burst defects. To verify the effectiveness of the proposed approach, numerical predictions and experimental results are compared, the latter showing a good agreement with the former.