STUDY OF TUBE REDUCTION USING DIE-LESS DRAWING

A study of die-less tube sinking is carried out in which the conventional reduction die is replaced by a die-less stepped bore reduction unit (DRU). The DRU is a single cylinder of two concentric bores with different diameters, where the smallest bore diameter is slightly greater than the outer tube diameter before deformation. The gap between the drawn tube and the DRU is filled with a polymer melt.

The reduction of tube diameter is effected by means of the plastohydrodynamic action of the polymer melt. Since the smallest bore size of such a device is dimensionally greater than the outer tube diameter, the leading end is not needed, also metal-to-metal contact, and hence wear, is not longer problem. On the other hand a layer of polymer coats the drawn tube, which is important in protecting the tube. In this study the method of solution is based on the principle of minimum work rate, where the total work rate required for the die-less drawing process is divided into two parts, the first is for shearing the polymer melt (which in this study is considered as non-Newtonian fluid), and the second part of the work rate is for deformation of the tube material. The profile of deformation is needed to be assumed, the nearest assumed profile to the true profile is that which gives minimum work rate. In this study the assumed profile is chosen to be quadratic equation. It was found that for a given DRU dimensions and shear stress constant of polymer melt, increasing the drawing speed raises slightly the reduction ratio in the tube diameter, coating thickness, and the drawing stress. The reduction ratio I as well as the coating thickness, and the drawing stress are also increased when the gap or/and length ratios of the unit are increased. However increasing the shear stress constant decreases the reduction ratio, coating thickness and the drawing stress.