The Mechanics of Drawing Polygonal Tube From Round on a Cylindrical Plug

Abstract

Economic factors such as the expense of raw materials, labour and power, are compelling manufacturers of polygonal section rod and tube to seek new production routes. One such method generating considerable industrial interest is the drawing of any regular polygonal tube from round stock on a cylindrical plug in a single pass. Although much work has been done on the drawing of round tube, no theoretical or experimental work has been done on the drawing of a polygonal tube directly from round stock on a cylindrical plug. This project studies this process experimentally and establishes a general theoretical solution based on the principle of least work of deformation. The theoretical and experimental investigations shewed the practicability of the drawing process. The design of the die profile, i.e. the curves of the interpenetration between the undrawn circular workpiece and the drawn polygonal tube, with the bore remaining circular, was found to be critical. A gradual transformation of the external surface of the round stock to the final section with minimum energy dissipation was found to be essential. A semi-analytical method, which was developed to determine the mean coefficient of friction in the drawing process, produced values which were comparable with those from the direct measurement using the split rotating die. Upper and lower bound solutions were developed to predict the maximum and the minimum values of the draw force. The upper bound value over-estimates the actual load to effect the process; the lower bound on the other hand is an under-estimate. A computer programme was written to enumerate the results for a variety of drawing parameters including, for example, the mean coefficient of friction and the geometry of the deformation zone. The theoretical results compared well with the experimental data.