(1) In the process of drawing, the blank holder force should not be too large or too small, and should be uniform everywhere. If the blank holder force is too small, it is easy to wrinkle the drawing part. If the blank holder force is too large, it will break the drawing part. If the blank holder force is not uniform, one side of the drawing part will wrinkle. Therefore, it is necessary to adjust the BHF properly in drawing.
(2) If the measured material thickness is not correct or the negative difference is too large, the drawing part is easy to wrinkle, and the uneven material thickness will cause one side of the drawing part to wrinkle. The material with uneven thickness can be rolled once before drawing.
(3) If the clearance between punch and die is too large, the straightening effect will be reduced and the material is easy to wrinkle. However, if the gap is not uniform, one side of the drawing part will wrinkle. The gap between punch and die can be adjusted properly.
(4) The fillet of die is too large, which reduces the contact area between blank holder and material, and makes the drawing parts wrinkle.
(5) For some complex curved surface drawing parts, especially small flange parts, drawbead can be set on the die to increase the flow resistance of the material and prevent the parts from wrinkling
(6) For spherical parts, conical parts and parabolic parts, reverse drawing method is used to increase the deformation resistance of materials to prevent wrinkling
(7) If the lubricant is applied too much, it may cause local feeding and wrinkling, so it should be lubricated correctly.
(8) The pressing surface, die surface or drawbead are worn seriously, which makes it difficult to control the feeding speed and cause wrinkling. The pressing surface, die surface and drawbead shall be trimmed.
(9) When the blank holder force is 1 ~ 2 times of the drawing force for stainless steel and other workhardening plates, if the punch is not rigid enough, no matter how to increase the blank holder force, the wrinkling of the drawing parts can not be eliminated. At this time, large tonnage punch can be used, and closed punch or hydraulic press can be used for deep drawing.
2020-12-13