Formability of 6k21-T4 car panel sheet for viscoelastic–plastic flexible-die forming

The service performance of a car body is obviously improved by using aluminum alloy panels. Because of the lower hardness and elastic modulus of aluminum alloy sheets, the car panels are easily scraped to reduce the surface quality, and the dimensional accuracy of sheet parts is affected due to higher spring-back after forming. In order to overcome forming problems of aluminum alloy panels, the viscoelastic–plastic flexible-die forming method is proposed to form the aluminium alloy panels in this paper. The scrape defect and the spring-back are improved by making use of the characteristics of the viscoelastic–plastic flexible-die. The forming limit curve of 6k21-T4 sheet is obtained through viscoelastic–plastic flexible-die bugling experiments. The car outer door with scale-down simulating dimensions is chosen as experimental parts for panels, and the viscoelastic–plastic flexible-die forming experiments are carried out to analyze the effect of the relationship between viscoelastic–plastic flexible-die pressure and BHF on the formability of aluminum panels. Experimental results indicate that the viscoelastic–plastic flexible-die forming can meet the formability of the aluminium alloy panels by using the proper BHF.