1. Wall rupture
This kind of defect generally appears on the side wall near the corner of the square tube, usually, it appears near the corner radius (rcd) of the die. In the mold design stage, it is generally difficult to predict. That is, an inverted W shape, and a cross grid that is 45° with the drawing direction appears above it. The cross grid is like scoring with a scribing needle. When looking for the cause of wall rupture, if you don’t pay attention, you will often miss it. It is a relatively clear and rare defect.
2. The square tube is deep drawn, and the straight edges and corners are deformed unevenly. As the drawing progresses, the plate thickness only increases at the corners. As a result, in the ground blank holder, the blank holder force is concentrated on the corners, and at the same time, work hardening is also promoted. For this reason, the force required for bending and straightening increases, the drawing load is concentrated on the corners, and the load peak of this drawing stroke load curve appears twice.
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