Precision cold extrusion with controlled elastic deformation of die.

In cold forward extrusion, dimensional errors are caused in products by elastic expansion of the die exit and elastic recovery (expansion) of the billet after extrusion. To improve accuracy, an extrusion method using a ring-shaped die is proposed. Thc outer surface of the ring-shaped die is of a conical shape and is fitted to a conical holder. By the axial extrusion force, the die moves slightly in the direction of extrusion so that the die exit is reduced in diameter. The dimensional error due to elastic recovery of the billet after extrusion is canceled by the decrease in exit diameter during extrusion. The deformation of the ring-shaped die during extrusion is calculated using the elastic finite element method, and the effects of die dimensions on the degree of reduction in the diameter of the diameter of the die exit are investigated. Extrusion tests are carried out for dies with various conical angles of the outer surface. It is confirmed that the present extrusion method is effective in decreasing the diametral error of an extruded bar, especially the error due to fluctuation of the extrusion load.