Forming defect control and optimization of multi-step spinning thickening process considering the variation of spinning gap

Spinning thickening is a novel metal-bulk forming technology for sheet metal, which gains successful applications in the net-shape manufacture of the structural parts with thin web plates and thick rims in automobile industry. However, through-process design of the forming scheme considering the possible variation of relative position of the plate is still lacking. To this end, the instantaneous stress-strain distribution of the plate, the bending force of the plate, and the order of the metal filling into roller groove were analyzed. Additionally, forming quality of the Eigen-structure with different spinning gaps was studied and quantitatively evaluated by experiments and FE simulation. It is found that pit, flash, hump, and depression are the dominant forming defects that influence the surface quality and performance of the parts. With the increase of positive spinning gaps, the area of the pit increases firstly and then decreases. With the increase of the absolute value of negative spinning gaps, the area of the pit increases continuously. By employing weighting method, a new index is proposed to evaluate the combined forming quality of the Eigen-structure. In addition, a phenomenological model was established for characterizing the correlation between the spinning gap and the quality index. Finally, taking the variation of spinning gap into consideration, process optimization of a two-step spinning thickening process was carried out under the constraint of multiple defects. The optimized range of spinning gap was obtained and experimentally validated. Results show that the quality of thick rim is improved by utilizing the optimized scheme and the target parts were formed with high quality under the reasonable range of spinning gap.