How to Solve Wrinkling Problems in Deep Drawn Parts
Wrinkling is one of the most common defects in deep drawing and sheet metal forming. It usually appears in the flange area, side walls, or bottom corners of the drawn part. Wrinkles not only affect appearance but may also reduce dimensional accuracy and structural performance.
The root cause of wrinkling is excessive compressive stress that causes the sheet metal to buckle during material flow. Effective control requires optimization of tooling, process parameters, and material flow conditions.
1. Main Causes of Wrinkling
1.1 Insufficient Blank Holder Force
When the blank holder force is too low, the material flows too freely into the die cavity, creating compressive instability and wrinkles.
1.2 Excessive Material Flow
Improper blank size or die design may leave excess material in the flange area, causing buckling during drawing.
1.3 Uneven Material Flow
Uneven friction or improper lubrication can cause localized accumulation of material, resulting in wrinkles.
1.4 Improper Die Design
Large die clearance
Poor draw bead design
Insufficient guidance of material flow
These issues reduce control over deformation.
1.5 Thin or Soft Material
Thin sheets have lower rigidity and are more likely to wrinkle under compression.
2. Effective Solutions to Prevent Wrinkling
2.1 Increase Blank Holder Force
This is the most direct and commonly used method.
Benefits:
Restricts excessive material flow
Stabilizes the flange area
Reduces compressive buckling
However, excessive holding force may lead to cracking, so adjustment must be balanced carefully.
2.2 Optimize Draw Bead Design
Draw beads help control material flow into the die cavity.
Key improvements include:
Adjusting bead height and shape
Increasing resistance in wrinkle-prone areas
Achieving more uniform deformation
Proper draw bead design is especially important in complex deep drawing parts.
2.3 Improve Die and Punch Geometry
Recommended measures:
Optimize die radius and punch radius
Maintain reasonable die clearance
Ensure smooth transitions in forming areas
Improved geometry helps guide material flow more evenly.
2.4 Optimize Blank Shape and Size
Reducing excess material in the flange area minimizes compressive stress.
Methods include:
Modifying blank outline
Using tailored blanks
Adjusting trimming allowance
2.5 Control Lubrication Conditions
Proper lubrication helps achieve stable and uniform material flow.
Key points:
Avoid excessive lubrication that allows uncontrolled flow
Ensure even lubricant distribution
Select lubricants suitable for the material and process
2.6 Use Multi-Step Drawing Processes
For parts with large drawing depth or complex shapes, multi-stage drawing reduces deformation per step.
Advantages:
More uniform strain distribution
Lower compressive stress concentration
Reduced wrinkling risk
2.7 Increase Material Thickness or Strength
If design permits, using thicker or slightly stronger material improves rigidity and resistance to buckling.
3. Advanced Control Technologies
Modern manufacturers often use advanced methods to reduce wrinkling:
3.1 Finite Element Simulation (FEA)
Simulation software predicts wrinkle-prone areas before tooling production, reducing trial-and-error.
3.2 Servo Press Technology
Servo presses allow flexible control of speed and force during different forming stages.
3.3 Variable Blank Holder Systems
Adaptive blank holder pressure improves material flow control dynamically during drawing.
4. Balancing Wrinkling and Cracking
Wrinkling and cracking are closely related defects:
Increasing blank holder force reduces wrinkles but may cause cracking
Decreasing blank holder force reduces cracking but may increase wrinkles
Therefore, optimization must balance both issues through careful testing and process adjustment.
Conclusion
Wrinkling in deep drawn parts is primarily caused by uncontrolled compressive stress and uneven material flow. Effective prevention requires coordinated optimization of blank holder force, die design, lubrication, material selection, and process parameters. By combining traditional process control with advanced simulation and intelligent forming technologies, manufacturers can significantly improve forming quality and production stability.
References
Altan, T., & Tekkaya, A. E. Sheet Metal Forming: Fundamentals. ASM International.
Hosford, W. F., & Caddell, R. M. Metal Forming: Mechanics and Metallurgy. Cambridge University Press.
Lange, K. Handbook of Metal Forming. McGraw-Hill.
Kalpakjian, S., & Schmid, S. R. Manufacturing Engineering and Technology. Pearson Education.
Keeler, S., Kimchi, M., & Mooney, P. Advanced Sheet Metal Forming. SAE International.
