An analytical method for hydrofilm extrusion of axisymmetric tubes through optimized curved dies is proposed. The upper-bound method and hydrodynamic lubrication theory are used in combination. The work-hardening effect of metal and the variation of fluid viscosity are taken into consideration. The optimal film thickness and the optimal die profile are found through energy minimization, and also pressure distributions of the fluid are obtained. A new mandrel system is devised for the film formation at the mandrel-billet interface. Experiments were carried out at room temperature for various diameter ratios of the tube, using the axisymmetric curved die. The theoretical prediction of extrusion pressure shows good agreement with experimental measurements for mild steel specimens, using castor oil as the lubricant.

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