Optimization of Processing Parameters for a Reverse Drawing–Flanging Combined Process for a B550CL High-Strength Steel Spoke Based on Grey Relational Analysis

Undesired wall thickness distribution and flanging cracking easily occur in reverse drawing–flanging combined processes of steel spokes when improper process parameters are used. Thus, based on GRA (grey relational analysis) and FEM (finite element method), a GRA model for a reverse drawing–flanging combined process for high strength steel B550CL spoke was established and validated. The results show that: (1) the most significant factors affecting uneven wall thickness distribution and excessive thinning in the mounting zone and center hole cracking are the friction coefficient and the shape of punch, respectively; (2) the non-uniformity of wall thickness U increases with the increase of the friction coefficient. The conical punch has a lower thinning ratio T, the spherical punch has a lower value of damage D; (3) considering synthetically the indexes of uneven wall thickness distribution, the excessive thinning in the mounting zone and center hole cracking, optimal results for the process parameters are obtained.