Formability of Steel Tubes in Corner Fill Hydroforming

Corner fill is a benchmark test intended to gain knowledge of tube hydroforming and to evaluate hydroforming parameters. The tests are used to compare steel grades, tube thickness and lubricants in tube hydroforming in this paper. The performance of the above variables were assessed by the final corner radius, radial displacement, burst pressure, burst location and thickness variations attained at burst. The formability of the tubes were indicated by the final corner radius and radial displacement attained at burst. The tests were simulated by finite element analysis using the measured coefficients of friction and mechanical parameters of the steel tubes. It was found that the pressure-expansion relations can be accurately predicted. However, burst pressures predicted by forming limit diagram and plastic strain criterion are too low for the AKDQ steel tubes compared to the experimental results. The discrepancy is due to the fact that the burst criteria used are not developed for tube hydroforming in a die where the radial stress and shear deformation can not be neglected. The need of better prediction methods is addressed.