Optimization design of process parameters for cold and hot composite roll forming of the AHSS square tube using response surface methodology

Advanced high-strength steel (AHSS) is a highly competitive material for the automobile industry to resolve the challenge of weight reduction and passenger safety. Cold and hot composite roll forming is a newly developed manufacturing technology, which aims to overcome the defects such as microcrack, severe work hardening, thickness reduction, and large corner radius in the traditional cold roll forming process of AHSS. In this paper, the mathematical models that represent the effect of line velocity, heating power, and deformation amount on the yield strength, outer corner radius, and microcrack length in the corner section of cold and hot composite roll-formed AHSS square tube are investigated by the response surface methodology with Box-Behnken design. The analysis of variance shows that the linear velocity has the greatest influence on the three responses, followed by the heating power and deformation amount. Furthermore, the experimental verification is carried out under the optimal combination of process parameters to manufacture the AHSS square tube with the desired performance. Compared to the cold roll-formed AHSS square tube, the product of strength and elongation in the corner section is increased by 53%, the corner thickness is increased by 60%, the outer corner radius is decreased by 94%, and the microcrack defect is not generated. The average magnitude of errors between the predicted and actual values is about 5%, which implies that the optimization design is accurate and reliable.