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 εave on cross-section of blank, the deformation uniformity coefficient α and the value of maximum damage δmax 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 εave, α and δmax 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.