Influence of die angle on containerless extrusion of CP titanium rods

As the name implies containerless extrusion is done without container and the total force consists of three individual terms namely ideal force, shear force and die friction force. Container wall billet friction is absent. The shear force varies directly with die angle, die friction force varies inversely with Sine of twice the die angle and ideal force is independent of angle. At a particular angle the total force is minimum. This is termed as optimum die angle. This can be understood from slab analysis of the process. Theoretically the optimum die angle varies only with extrusion strain and friction factor. It is found to change from 25° at a strain of 0.15 to 30° at a strain of 0.42. Experimentally the optimum angle is found to be independent of strain and at all strains it is found to be 25° at a constant friction factor of 0.14. More over the experimental pressure is less than that-predicted by theory. This is attributed to the temperature rise in the deformation zone and a consequent decrease in flow stresses of titanium.