1.What are the core reasons for this analysis?
Insufficient or failed lubrication: An effective pressure- and shear-resistant barrier cannot be formed between the die and the sheet metal.
Poor die condition: Inappropriate surface hardness, roughness, or material, failing to resist adhesion.
Material property mismatch: The surface condition or mechanical properties of the steel sheet itself are unsuitable for this stamping process.
Inappropriate process parameters: Overly stringent forming conditions, exacerbating friction and temperature rise.
2.How to optimize lubrication?
Upgrade Lubricants:
Increase Viscosity or Use Extreme Pressure Additives: Use specialized stamping oils/lubricants containing extreme pressure (EP) additives such as chlorine, sulfur, and phosphorus. Under high pressure, these additives react with the metal to form a shear-resistant chemical reaction film.
Change Lubricant Type: Switch from oil-based to dry film lubricants, wax-based lubricants, or polymer coatings, which provide a thicker, more durable protective layer.
Ensure Cleanliness: Prevent lubricant contamination or the introduction of impurities.
Improve Coating Method and Amount:
Uniform and Sufficient Application: Ensure uniform and sufficient lubricant coverage in deformed areas of the sheet metal (especially flange areas).
Double-Sided Coating: Apply lubricant to both sides of the sheet metal, especially for deep-drawn parts.
Die Spraying: In continuous production, add an automatic die oil/wax spraying system.
3.How to improve the condition of the mold?
Improving Mold Surface Hardness and Smoothness:
Surface Treatment: Apply TD treatment (vanadium/niobium infiltration in salt bath) or PVD/CVD coating (such as CrN, TiCN, DLC diamond-like carbon coating) to the mold. These treatments significantly improve the surface hardness, wear resistance, and anti-adhesion properties of the mold, making them one of the most effective methods to solve the problem of high-strength steel and stainless steel sticking to the mold.
Surface Polishing: Polish the working surfaces of the mold (especially the rounded corners) to a mirror finish (Ra ≤ 0.2μm) to reduce scratching of the sheet metal by microscopic protrusions.
Optimizing Mold Materials:
Use powder high-speed steel or cemented carbide inserts in critical locations, as they have higher hardness and red hardness.
Enhancing Mold Maintenance:
Regular Cleaning: Promptly remove any metal particles adhering to the mold (use copper or brass scrapers to avoid damaging the mold substrate).
Ensuring Cooling: Design cooling channels within the mold to control the mold's operating temperature and prevent lubricant failure due to high temperatures.
4.How to check and adjust materials?
**Confirm Surface Roughness:** Check the surface roughness (Ra value) of the cold-rolled coil. An excessively smooth surface (Ra value too low) has poor oil retention capacity, easily leading to lubrication failure; an excessively rough surface will increase friction. Generally, cold-rolled sheets for stamping have a suitable roughness range.
**Check Surface Cleanliness:** Confirm that the steel sheet surface is free of residual rolling oil, rust-preventive oil, or contaminants, which may react adversely with the stamping oil.
**Verify Mechanical Properties:** Confirm that the material's yield strength, tensile strength, n-value (hardening index), and r-value (plastic strain ratio) meet stamping requirements. Materials that are too soft or too hard can cause forming difficulties and increase the risk of mold sticking.
5.How to optimize stamping process parameters?
Reduce blank holder force: Use the lowest possible blank holder force while ensuring no wrinkling to reduce frictional resistance in the flange area.
Adjust clearance: Check and optimize the clearance between the punch and die. Insufficient clearance will exacerbate shearing and scraping.
Control stamping speed: Appropriately reduce stamping speed to minimize instantaneous high temperatures generated by high-speed friction.
Improve draw bead design: Optimize the radius and height of the draw bead to facilitate smoother material flow and reduce localized severe friction.