1.How to adjust process parameters?
Increase Blank Holder Force
Reason: Blank holder force (BHF) is the most direct way to prevent wrinkling. If the blank holder force is too small, the blank holder ring will not hold the material tightly, and the material will arch under tangential compressive stress.
Solution: Gradually increase the blank holder force until the wrinkles disappear. Be careful not to increase it too much, otherwise it will cause the material to tear.
Adjust Draw Ribs
Reason: Draw ribs are used to increase feed resistance. If feeding is too easy, the material will flow too quickly and accumulate in the cavity.
Solution: Increase the resistance of the draw ribs (e.g., replace with thicker ribs or increase the bite depth), or add draw ribs to the mold to slow down the material flow.
Reduce Draw Depth
Reason: Too large a single draw depth can easily cause material instability.
Solution: If the part allows, it can be drawn in two or more steps, first shallowly and then deeply, or the part design can be modified to reduce the single draw depth.
2.How to improve the condition of the mold?
Check Die Clearance
Cause: If the clearance between the punch and die is too large (more than 1.1 to 1.2 times the material thickness), the material is not adequately constrained within the clearance, easily causing wrinkling.
Solution: Adjust the die to ensure a uniform and reasonable clearance.
Adjust Die Corner Radius (R-angle)
Cause: If the die corner radius is too large, material is easily "swallowed" in, causing excessively fast flow and accumulation; worn corners also reduce friction, leading to uncontrolled material movement.
Solution: Appropriately reduce the die corner radius, or repair worn corners by welding or grinding to increase surface roughness and provide appropriate resistance.
Check Die Wear
Cause: Wear on the surface of the blank holder or the tension rib prevents the provision of uniform blank holder force.
Solution: Repair worn areas by welding and re-grind the blank holder to ensure good fit.
3.How to optimize lubrication conditions?
Reduce Lubricant Amount or Change Lubricant
Reason: This is a common misconception. While more lubricant is needed for cracking, too much lubrication is detrimental to wrinkling. Too much or too slippery lubricant allows material to flow too smoothly, leading to buildup and wrinkling.
Solution: Reduce the amount of lubricant applied, or use a lower viscosity, less lubricating oil to increase friction and control material flow.
Local Lubrication Strategy
Solution: Areas where wrinkling prevention is needed (such as flange edges) can be left unlubricated or treated with a dry lubricant, while lubricating the more vulnerable, crack-prone sections. This is a balanced approach.
4.How to inspect materials and billets?
Increase Blank Size
Reason: If the blank is too small, the blank holder may not be able to hold the material, causing the blank holder force to fail.
Solution: Appropriately increase the diameter or overall dimensions of the blank to ensure sufficient material is held in place by the blank holder.
Change Material Grade
Reason: If the material's yield strength is too low or its n-value (hardening index) is too high, the material is prone to flow in the early stages of deformation, which may also lead to wrinkling.
Solution: While meeting forming requirements, try using a material with a slightly higher yield strength, or increase the sheet thickness to resist instability.
Check Material Shape
Reason: The incoming material itself has edge waviness or center waviness, and is already in an uneven state before stamping, making it more prone to wrinkling during stamping.
Solution: Ensure the flatness of the sheet material meets the standards after leveling.
5.If wrinkles are encountered on-site, how can they be quickly identified and addressed?
Observe the location: If wrinkles appear at the flange edge or clamping ring, it's usually because the clamping force is too weak; simply increase the clamping force.
Observe the oil level: If too much oil has been added, wipe it dry and test. If the wrinkles disappear, there's excessive lubrication, and the oil level needs to be reduced.
Listen to the sound: If the material flows in very quickly, it indicates insufficient resistance. Check if the tension ribs are worn or if the clamping force is insufficient.