When the general drawing shape is a square tube, near the center of the straight side wall, there may be a large-scale drawing cracking.
1.1 Height of drawing too large:
For the use of reducing the depth of drawing to prevent cracking, other causes must be verified first. After all the conditions are checked and if the problem still occurs, the method of reducing the stretching height can be used, and a set of stretching and shaping procedures can be added.
1.2, Die fillet radius is too small
When the square tube is deep-drawn, the measure to prevent the spring back sag on the side wall of the straight side is generally to use the method of drawing the bead, but it has the defect of causing a bead scar.
Therefore, when drawing without using draw beads, as a measure for drawing forming, make the gap slightly smaller than the plate thickness, and at the same time, select the drawing method in the state where the angle is too small. If cracks occur beyond the tensile limit, the angle can be slightly increased and a trial drawing can be performed.
2, Stamping conditions
2.1 Blank holder force is too large:
The flange surface is all shiny, indicating that the blank holder force is too large, and the force can be reduced to the point where the material is allowed to flow in without wrinkling.
2.2 Poor lubrication of the die surface:
To make it easy for materials to flow in, it is necessary to check the type and amount of lubricating oil.
3, Problems with mold
3.1 Poor processing and matching of the die surface:
While the product is cracked, there are scratches on the flange surface. It is thus necessary to use a grinding wheel to polish it well to achieve the condition that the material flows easily.
3.2 The gap is too small:
When the side wall of the product is shiny and cracked, it is because the side wall is too thin, and the gap needs to be adjusted.
3.3 Poor position and shape of draw beads:
Due to the excessive force of the drawn bead, there are many cases of rupture, so the force of the drawn bead should be reduced.
3.4 Poor mold precision:
The precision of the mold is poor, and the core is offset. The parallelism and verticality of the punch and the die are not ideal. If the mold is checked in advance, there should be no problems in the test drawing.
3.5 Insufficient rigidity of blank holder:
When the rigidity of the blank holder is insufficient, only a few buffer pins will be violently stretched and cracked.
3.6 Poor press accuracy:
When the precision of the press is not ideal, it will produce the same defects as the poor precision of the mold. Before the test drawing, the machine tool must be kept in a high-precision state, and the test drawing must be carried out.
When the defect is caused due to insufficient tensile strength of the material and excessive grain size, it is necessary to change the material.
When defects occur due to insufficient thickness of the sheet, it is necessary to increase the thickness of the sheet.
Cracking during stretching is a common technical problem, such as thin-wall cracking, corner cracking and product wrinkling.