Initial position optimization of preform for large-scale strut forging

The titanium alloy strut is a key load-bearing part for landing gear in aircraft. Closed-die forging with flash is adopted to manufacture the titanium alloy strut. The initial position of preform also has a notable influence on the cavity fill and metal lost into flash in the forging process. Complete die filling and even metal lost into flash at different portions of forging are the best forging process. Thus, an optimization method of initial position of preform for large-scale strut forging was developed based on the cavity fill and flash size. According to the geometrical characteristics and the deformation characteristics, a design variable x (description of initial position) and the fill indexes η₁ and η₂ were selected and defined. The objective function y consists of fill indexes. Numerical simulation combining algorithm of dichotomy to generate sampling data, and then the objective function can be produced. The finite element analysis was carried out for the optimum initial position searched by the objective function. If the simulation results is in the error range (such as < 5%), the optimum initial position was obtained, else the simulation results were added into sampling data to improve the objective function and the above steps were repeated. By using a developed optimization method, the initial position of preform for a large-scale titanium alloy strut forging process was determined after one improvement for objective function, where 5% is adopted as stop criteria in optimization procedure.