Occurrence and effect of ironing in the hole-flanging process

The effect of the clearance-thickness ratio on the hole-flanging process was investigated to determine the occurrence of ironing. A 2 mm thick 1000 series aluminium alloy sheet was considered. An elastic-plastic finite element model using remeshing option was developed. Experiments were conducted to verify the reliability of the developed finite element model. A critical clearance-thickness ratio which is a limit between two conditions of hole-flanging was found: hole-flanging with edge stretching and hole-flanging with ironing in which the metal is squeezed between the punch and the die. The effect of the hole-flanging condition on the punch load, the forming kinematics, the flange geometry and the boring quality was studied. The finite element results were validated by experimental results.