Deep Drawing Failures: Comprehensive Analysis and Solutions

Rapid Analysis of the Causes of Deep Drawing Part Fractures

Fractures in deep-drawn parts most commonly occur at the end of the radius on the wall of the workpiece, or slightly below it, at what is known as the critical section. The main causes of fractures include:

1) Uneven dies.

2) Non-parallel upper and lower worktable surfaces.

3) Insufficient material elongation.

4) Too small a radius on the punch and die corners.

5) Too small a deep-drawing coefficient, resulting in excessive deformation.

6) Excessive blank holder force.

Experienced individuals can quickly determine the cause by observation. For instance, if the fracture circumference is between half and two-thirds, it is likely due to uneven dies; if the fracture circumference is equal to or greater than two-thirds, it suggests that the upper and lower dies are essentially parallel, and attention should be focused on the fourth to sixth reasons mentioned above.

When the die corner radius is too small, the material thinning is obvious and the fracture zone moves closer to the corner of the die, which can be directly observed at the fracture site.

With excessive blank holder force, the original luster of the material’s surface is completely destroyed, replaced by a sheen created by the sliding under heavy pressure. By holding the workpiece up to a light and adjusting the angle of the blank holder surface, a clear reflection can be seen.

Auditory cues can also assist in diagnosis. Fractures due to uneven dies start from one side or point, producing a softer, drawn-out sound; whereas fractures caused by reasons three to six occur almost simultaneously across the entire section, resulting in a louder and more abrupt sound.

If multiple adjustments fail to achieve the desired outcome, the following steps can be taken:

1) Switch the relative positions of the die and the press worktable. If the starting point of the fracture does not change relative to the die, it indicates that the upper and lower worktable surfaces are parallel and the die surfaces are uneven. If the starting point of the fracture remains constant relative to the worktable, it means the die is flat and the upper and lower worktable surfaces are not parallel.

2) If the starting point of the fracture is not fixed but varies around the circumference, material elongation should be considered after ruling out the issue of a too small die corner radius.

3) Additionally, if severe flange deviation occurs, the following should be considered: slight unevenness in the die, inconsistent roughness at the die corner radius, and uneven roughness on the blank holder surface or die face.

Analysis of Causes for Defective Deep Drawing Products

The analysis of the causes of defects in deep drawing is presented in Table 1.

Table 1: Analysis of Causes for Defective Deep Drawing Products