1, the fillet radius of the die is too small (rd). When bulging is the main deformation and a small amount of material flows in, if the rd of the lower die is too small, work hardening will occur due to bending and straightening, and the rd part will often break, so the rd part of the drawing die should be carefully polished, and if it still breaks, the rd should be appropriately increased.

2. The blank holder is not adjusted properly. When rd is small and BHF is too small, the flange will appear tiny wrinkles, which will often lead to rd fracture in the later stage of processing. Generally speaking, it can be solved by increasing BHF.