Eight Common Problems with Stamped Parts and Their Solutions

This article summarizes various defects found in stamped part production at stamping plants, analyzes their causes, and provides preventive measures in hopes of helping readers.

1. Burrs: Burrs may occur when the die clearance is too large, too small, or uneven; when the punch or die edges are not sharp enough; or when the punching condition is poor.

2. Warping or uneven parts:
    a. During punching, large stretching and bending forces can cause parts to warp. Improvements include firmly clamping with the punch and blank holder and maintaining sharp cutting edges.
        b. When the part shape is complex, uneven shearing forces around the part can produce inward forces that cause warping. The solution is to increase the blank holder force.
    c. Oil, air, or other substances trapped between the die and the part can cause warping, especially with thin or soft materials. Apply oil evenly and provide exhaust holes to eliminate warping.

3. Wrinkling:
    a. Excessive draw depth can cause the material to flow too quickly during feeding, resulting in wrinkles.
    b. If the die R-radius is too large during drawing, the punch may fail to hold the material, causing excessive material flow and wrinkles.
    c. Unreasonable or improperly positioned blank holders cannot effectively prevent excessive material flow, resulting in wrinkles.
    d. Improper die alignment or small blank holder edges during drawing can fail to hold the material, causing wrinkles. The remedy is to use appropriate blank holder devices and properly positioned draw beads.

4. Dimensional accuracy errors:
    a. Inaccurate cutting edge dimensions in die manufacturing may cause part dimensions to exceed tolerances.
    b. Springback during stamping may cause misalignment between locating surfaces and the part, resulting in deformation and dimensional inaccuracies in subsequent processes.
    c. Poor part locating design can allow part movement during stamping, affecting dimensional accuracy. Defective part design may also cause inaccurate locating.
    d. For multi-step parts, improper adjustments or wear of rounded corners in previous steps can create uneven deformation and dimension changes after piercing. To control dimensional accuracy, take necessary measures such as reasonable part shapes and tolerance grades, improved die manufacturing precision, and designing springback compensation.

5. Indentation:
    a. Surface contaminants on material. Inspect and clean material surfaces with an air gun and cloth before stamping.
    b. Foreign objects on the die surface. Clean die surfaces and select appropriate die clearance based on material thickness.
    c. Magnetic material sticking to the die. Change processing order, stamp parts from outside to inside or row by row. First trim (shear) then punch holes. For special forming operations that deform, excessive pressure may be the cause and die springs may need replacement.
    d. Stamping oil that does not meet requirements. Replace with appropriate stamping oil that contains sulfur extreme pressure additives.

6. Scratches: Scratches on parts are mainly caused by sharp burrs or metal dust in the die. Preventive measures include polishing die marks and removing metal dust.

7. Bottom cracks: Bottom cracks are mainly caused by poor material ductility or overly tight blank holder rings. Preventive measures include using materials with good ductility or loosening the blank holder.

8. Sidewall wrinkling: Sidewall wrinkling is mainly caused by insufficient material thickness during die assembly (which may allow relative thinning) or eccentricity causing uneven clearances. One side gap becomes larger and the other smaller. Preventive measures include replacing the material immediately and readjusting the die.