Optimization of structural parameters for elliptical cross-section spiral equal-channel extrusion dies based on grey theory

 The elliptical cross-section spiral equal-channel extrusion (ECSEE) process is simulated by using Deform-3D finite element software. The ratio m of major-axis to minor-axis length for ellipse-cross-section, the torsion angle φ, the round-ellipse cross-section transitional channel L₁, the elliptical rotation cross-section transitional channel L₂ and the ellipse-round cross-section transitional channel L₃ are destined for the extrusion process parameters. The average effective strain ε_ave on cross-section of blank, the deformation uniformity coefficient α and the value of maximum damage δ_max are chosen to be the optimize indexes, and the virtual orthogonal experiment of L₁6 (4⁵) is designed. The correlation degree of the process factors affecting ε_ave, α and δ_max is analyzed by the numerical simulation results using the weights and grey association model. The process parameters are optimized by introducing the grey situation decision theory and the ECSEE optimal combination of process parameters is obtained: φ of 120°, m of 1.55, L₁ of 7 mm, L₂ of 10 mm, and L₃ of 10 mm. Simulation and experimental results show that the material can be refined with the optimized structural parameters of die. Therefore, the optimization results are satisfactory.