Plastic flow in extrusion and drawing through conical and wedge-shaped dies: Prediction of central bursting

Abstract

In this article, the plastic flowfields for extrusion and drawing - for rigid plastic materials forced through conical and wedge-shaped dies - are analysed on the basis of Shield's work. A modification to Shield's analysis is developed to account for the redundant deformation. Solutions for axisymmetric and plane strain flows are given. The total forces estimated for both drawing and extrusion operations are compared favourably with available experimental data. On the basis of the present modified Shield's analysis, expressions for the stresses within the die are then derived. These expressions are then employed to predict central bursting by applying two fracture criteria, namely: the hydrostatic stress criterion and the plastic instability criterion. The deformation zone geometry criterion has also been used for comparison. The predictions fairly agree with the experimental results.

Design of Dies of Minimum Length Using the Ideal Flow Theory for Pressure-Dependent Materials

“…The distribution of p affects ductile fracture (see, for example, [30]). A typical example is central bursting, which can appear at the symmetry axis in extrusion and drawing processes [31]. The effect of the reduction ratio and the angle of internal friction on the distribution of p along the axis of symmetry of ideal flow dies is illustrated in Figure 10 (h 0 /h = 2 in Figure 10a, h 0 /h = 1.5 in Figure 10b, and h 0 /h = 1.2 in Figure 10c).…”