Analysis and Design of Profiled Dies for the Polymer Wire Die-Drawing Process

Abstract

In the standard polymer die-drawing process, using conventional conical dies, the strain and strain rate are maximum at the die exit where the stress state in the material, now oriented, is predominantly tensile in nature. This leads to fracture of the material at the die exit at high drawing speeds. In this paper, the plastic flow of the polymer in profiled dies, where the strain and strain rate are controlled along the die-length, is analysed theoretically and it is shown that the design of profiled dies can be chosen to reduce the strain rate at the die exit. A coupled thermo-mechanical finite-element model has been developed to study the detailed temperature, strain and strain rate distributions in conical and profiled die-designs and their effect on important processing parameters such as draw load and speed. The performance of conical and profile die designs has also been compared experimentally under identical drawing conditions for the specific case of die drawing of polyoxymethylene wire. Both the analytical and experimental results demonstrate the ability of the profile die designs to significantly increase the processing speed while retaining the high degree of orientation and enhanced properties of the die-drawn product.