Extrusion internal thread of titanium alloy plate: Multi-objective optimization of material flow-induced defects

Material flow-induced defects in extrusion internal thread can significantly reduce the bearing capacity and sealing reliability of threaded connections. To address this issue, this study focuses on titanium alloy plates (Ti-6Al-4V) and analyzes the effects of optimization variables (bottom hole diameter, chamfering depth, and chamfering angle) on optimization objectives (tooth height rate, upper surface defect height, and lower surface defect height) using a single-factor method. Based on the Box-Behnken design response surface method, a regression response model between the optimization variables and the optimization objective is established and multi-objective optimization is carried out, and a set of optimal parameters are obtained (bottom hole diameter of 19.221 mm, chamfering depth of 1.421 mm, and chamfering angle of 38.252°). The numerical simulation results show that the optimized tooth height rate is 76.51%, with the upper surface defect height being −0.048 mm and the defect height on the lower surface −0.026 mm. The prediction error is less than 5%, indicating a good model fit. This study provides theoretical support for high-precision internal thread forming of titanium alloy in the aerospace field.