Numerical and Experimental Investigation of Forming Limit Diagram in Warm Incremental Forming Process of Aluminum Tubes

Incremental tube forming process is capable of manufacturing tubes with different cross sections and dimensions using simple and inexpensive forming tools. In the current study, seven different ductile failure criteria are used in finite element simulations in order to obtain the forming limit diagram (FLD) of Al6063 aluminium tubes at high temperatures. The predicted FLD using these criteria are compared with experimental data to select the optimum criterion. Standard universal tensile tests in different temperatures and strain rates along with Zener-holloman parameter are performed to calibrate the failure criteria. The effects of process parameters including temperature, forming depth and forming feed are considered. The results showed that failure criteria can predict the time and location of rupture in incremental tube forming process with a good accuracy. In high temperatures, Cockroft-Latham and normalized Cockroft-Latham criteria which consider the effect of the largest tensile stress had the best prediction. Investigation of temperature and strain rate showed that by increasing temperature, the forming limit goes higher but increasing strain rate causes to decrease it.