1.How should the process and mold be adjusted?
Optimizing Blank Holder Force (BHF)
Principle: Find the optimal balance between preventing wrinkling and tearing. Insufficient blank holder force will cause wrinkling, while excessive force will cause tearing.
Operation: Gradually increase the blank holder force until wrinkles are eliminated. If using a nitrogen cylinder or hydraulic cushion, ensure uniform and stable pressure.
Properly Setting Draw Beads
Function: Controlling the speed and flow of sheet metal into the die is a key means of adjusting local material flow resistance.
Solutions:
Add or raise draw beads in areas prone to wrinkling (such as near die corners or flat areas).
Reduce or eliminate draw beads in areas requiring smooth material flow (such as punch corners).
Use segmented draw beads for precise control of different areas.
Adjusting Die Clearance
The die clearance on one side is typically 1.1 ± 0.1 times the sheet metal thickness. Excessive clearance weakens the constraint on the sheet metal, leading to wrinkling.
Check and ensure the clearance between the punch and die is uniform.
2.How should materials and lubrication be managed?
Choosing the Right Material
Materials with high plasticity and a high coefficient of thickness anisotropy (r-value) have stronger resistance to wrinkling. A high r-value means the sheet metal is less prone to thinning in the thickness direction and flows more easily in the planar direction.
Appropriately Increasing Material Thickness: Within the limits allowed by the part design, increasing the material thickness can directly improve resistance to instability.
Optimizing Lubrication Strategy
Key Principle: Lubricate areas where material flow is needed; avoid or minimize lubrication in areas requiring resistance.
Operation:
Apply lubricant to areas where material needs to flow, such as the die fillet and the contact surface of the blank holder.
Avoid lubricating the top of the punch or overhanging areas prone to wrinkling, as this increases frictional resistance in these areas.
3.What are the main causes of wrinkling at the flange and what are the solutions?
Insufficient blank holder force, excessive tangential compressive stress
Solution: Increase blank holder force
Strengthen or add outer drawbeads
4.What are the causes and solutions for wrinkling on the sidewalls of parts?
Excessive mold clearance causes material to become unstable and suspended in mid-air.
Adjust and reduce mold clearance; optimize die radius; increase process allowance for subsequent removal.
5.What are the solution process and checklist?
Step 1: Verify Material Condition
Confirm that the material has undergone sufficient recrystallization annealing (i.e., high-temperature tempering) and possesses good plasticity (elongation).
Check if the material thickness and grade meet the process requirements.
Step 2: Inspect the Die and Equipment
Is the die surface smooth and undamaged?
Is the blank holder force uniform, adjustable, and stable? (Check the nitrogen cylinder/hydraulic cushion)
Is the die clearance uniform?
Step 3: Adjust Process Parameters (Core)
Gradually increase the blank holder force from low to high, observing the wrinkling changes.
Adjust the drawbead settings (e.g., use shims to adjust the height).
Optimize the lubrication area and oil quantity.
Step 4: Consider Design Changes
If the above methods are ineffective, consult with the design department:
Add additional process surfaces or wrinkle-reducing ribs.
Modify the shape of parts of the product to avoid large flat surfaces.
If permissible, use a material with a higher r-value or a slightly thicker material.