Finite element analysis of piercing process of piercing extrusion for titanium alloy solid ingots

Metal flow and penetration fracture behavior is important for application of piercing extrusion process of solid ingots for high-performance seamless tube. A piercing extrusion process from a solid ingot (Φ200 mm) to a titanium alloy tube (Φ80 mm×10 mm) has been studied. Based on FE software of DEFORM-2D, a thermo-mechanical coupling model being able to describe the metal flow and penetration fracture behavior was developed for the piercing process of piercing extrusion of solid ingots. The piercing processes by two kinds of piercing punches were analyzed. The results indicate that at the initial stage of piercing process, the deformation characteristic is similar to forward extrusion, and then metal reverse flows, and the backward extrusion remains until the end cap is removed; the piercing force increases rapidly under forward extrusion, and backward extrusion occurs when the force rises to the stable value, and the piercing force decreases rapidly at the penetration fracture stage after removing the end cap; under backward extrusion, the piercing force has a little change by a cylindrical piercing punch, but the force will significantly increase again after a short stable stage by a bottle piercing punch, and thus the piercing force by the bottle piercing punch is much greater than that by the cylindrical piercing punch; at the penetration fracture stage, fracture behavior by the cylindrical piercing punch is similar to that in blanking process, but the fracture face by the bottle piercing punch presents an approximate L-shape.