Numerical and experimental analysis of defects control in cross wedge rolling for titanium alloy workpieces

Through the optimization of tool parameters and the wedge shape, titanium alloy workpieces free of internal and external defects were formed by flat cross wedge rolling (CWR) adopting tools without surface grooves. Firstly, the thermomechanical coupled model of CWR for TC11 (Ti-6.5Al-3.5Mo-1.5Zr-0.3Si) titanium alloy was established in the finite element (FE) software DEFORM-3D, and the effects of forming angle alpha, stretching angle beta, and section reduction Psi were studied. The results showed that in the conventional empirical range of tool parameters, the defect-free workpiece is hard to be rolled by the typical tool structure. To optimize the forming quality of rolled workpieces, a modified tool structure was proposed by introducing an inclined plane with a width of lambda (2-5 mm) on the top of the wedge shape and revising the side wedge plane alpha to a combination of two inclined planes alpha(1) and alpha(2) (alpha >= alpha(1) > alpha(2)). Simulations and experiments demonstrated that the modified tools without surface grooves can achieve TC11 alloy workpieces with smooth surface. When the distance between the top and bottom tools is too large, the rolled workpiece axis is prone to being bent, and the gap from the top tool to the billet should be controlled in the range of 0-0.2 mm to ensure its straightness. Finally, the necking-free TC11 alloy rolled workpieces (Psi = 67.9% and Psi = 82.3%) with smooth surface and excellent internal quality were manufactured by IM500 flat CWR mill at 900 degrees C, 500 mm/s.