1.How to increase the blank holder force?
The direct cause of wrinkling is excessive material flow.
Operation: Increase the blank holder force by 10%-20% and observe whether the wrinkles disappear.
Verification: If wrinkling lessens but the sidewalls begin to whiten (thinning), it indicates that the blank holder force is approaching its critical point and requires adjustment with lubrication.
Tip: For dies with draw beads, increasing the blank holder force can be equivalent to increasing the draw bead groove by grinding the bead groove.
2.How to adjust the lubrication strategy?
Reduce lubrication in the flange area: Wrinkling indicates that the material is flowing too quickly. Wipe off the lubricant in the flange area with a dry cloth, or switch to a lower viscosity oil to increase friction resistance.
Spot application: Lubricate only the areas that do not wrinkle, and dry-wipe the wrinkled areas.
3.How to polish the radius (R) of a die cavity?
Symptoms: Flange wrinkling, with a risk of sidewall tearing.
Solution: Reduce the radius (R) of the die inlet-a smaller R angle increases resistance and suppresses wrinkling. However, note that an excessively small R angle can cause cracking; a balance must be found.
Recommended value: Usually 4~6 times the plate thickness; in severe cases of wrinkling, it can be reduced to 3 times the plate thickness.
4.What are the effects of having too low a yield strength?
The material is too soft and lacks rigidity, causing wrinkling even with slight resistance.
Threshold: When the yield strength of deep-drawing material is <140MPa, the tendency to wrinkle increases significantly.
Solution: Use a batch of the same grade but with a yield strength closer to the upper limit (e.g., for SPCC, choose ≥180MPa).
5.What are the effects of thickness deviation (negative tolerance)?
Symptoms: Unstable wrinkling throughout the roll, sometimes good, sometimes bad.
Mechanism: Thinner sheet → relatively larger gap between pressure rings → unable to hold the sheet in place.
Solution: Measure the actual thickness. If the negative tolerance is >5% and wrinkling persists, return or downgrade is recommended.