1.What is the fundamental reason for deformation?
The deformation after leveling, whether it is horizontal wrinkling, vertical bending, or diagonal warping, is essentially an imbalance in the internal stress distribution of the material. When the leveling process (such as straightening or cutting) breaks the original stress balance, and the material itself does not have sufficient "resistance," it will release the stress through deformation.
2.What are the common causes of horizontal wrinkles and creases?
Internal Causes (Material):
- Low yield strength or coarse grains: The material itself is "soft," and improper annealing processes lead to coarse grains, resulting in poor resistance to deformation and easy wrinkling when stretched.
- Presence of yield plateaus: Annealed low-carbon steel has yield plateaus, causing sudden yielding in localized areas during uncoiling, forming Lüders bands (the surface pattern).
- Poor sheet shape: The incoming material has edge waviness and center waviness, indicating uneven internal stress.
- Interlayer adhesion: During annealing, the layers of the steel coil adhere to each other, causing plastic deformation when uncoiling and tearing.
3.How can we control horizontal wrinkles and creases at the source?
1. Re-inspect materials: Verify the quality certificate to confirm whether the yield strength meets the standard. For high-requirement stamping parts, specify the use of sheet metal with a no-yield platen or that has undergone surface finishing and tempering.
2. Standardize the annealing process: Ensure that the annealing temperature, time, and cooling rate are reasonable to avoid coarse grains and interlayer adhesion.
3. Check the shape of incoming materials: If obvious waviness is found in the incoming materials, communicate with the supplier immediately.
4.What are the causes of sickle-shaped bends, single-sided waves, and warping?
Incoming material wedge shape: The cross-sectional thickness of the steel plate is uneven, with one side being thicker than the other. After this material is leveled, it may appear flat, but once the stress is released, the edge waviness will immediately return.
5.How can we control it at the source?
Measure the cross-section: If in doubt, use a micrometer to measure the thickness on both sides and in the middle of the steel plate to confirm whether there is a significant wedge shape (thickness difference > 0.5%-1%).
Equipment Maintenance and Operation:
1. Check Equipment Accuracy: Regularly calibrate the leveling machine to ensure the roller system is parallel and level.
2. Improve Storage: Leveled steel plates should be laid flat on flat, dry wooden blocks, avoiding suspension or prolonged side storage, especially for thin plates.