A simplified approach for distinguishing between spring-back and spring-go in free U-die bending process of SPFC 440 sheets

This study proposed a simplified approach to distinguish between spring-back and spring-go in free U-die bending process of SPFC 440 sheets. A U-die bending model for unloading process is developed based on an elementary bending theory. The accuracy of prediction for distinguishing between spring-back and spring-go approaches 91.67%. A series of experiments are carried out to verify the proposed model, and further to explore the effects of process parameters on the conversion of the unloading behavior from spring-back to spring-go. Experimental results show that spring-back angle increases as sheet thickness decreases. The thin sheet is easier to induce spring-back than the thick sheet. In addition, spring-back angle increases as punch corner radius increases. Accordingly, spring-back angle slightly increases as the radius of die corner increases. Moreover, the key factor to distinguish between spring-back and spring-go seems the clearance between punch and die. The small clearance is easier to induce spring-go than the large clearance under the small radius of punch corner. A better understanding for distinguishing between spring-back and spring-go is achieved.