THE HYDRODYNAMIC DRAWING OF WIRE AT ELEVATED-TEMPERATURES

The flow stress in a metal-forming operation will be reduced by increa sing the working temperature. However, this brings with it tribology p roblems which may cause severe die wear. It has been shown that when w ire surrounded by a lubricant is drawn at high speed through an orific e whose diameter is slightly larger than that of the incoming wire a h ydrodynamic pressure is established which may reach the flow stress of the wire. In this way the diameter may be reduced without its making contact with the die. If a wire is heated and this system of wire-draw ing is applied, the tribology problems associated with drawing at elev ated temperatures are considerably reduced. This paper describes a dra wing programme of mild-steel wire using molten polymer and glass mater ials as lubricants and using a 'double bore' non contacting die at tem peratures varying from ambient to 600 degrees C. A stress analysis mod el of the deforming wire is developed which rakes into consideration l ubricant viscosity, the flow stress and the strain-hardening exponent of the wire. The bore diameters are calculated using information from this model. Up 12% reductions were achieved when using this method.