1.What causes insufficient anti-adhesion?
Mechanism: Carbide particles in cold-rolled coils act like "hard abrasive grains." If the matrix hardness of the die steel is insufficient, or if the carbide particles in the die are smaller than the hard particles in the material, the hard particles in the material will act like a file, microscopically cutting the die.
Solution: If ordinary Cr12MoV is used to stamp 65Mn, wear will be rapid. It is recommended to upgrade to powder high-speed steel (such as ASP23) or cemented carbide, and perform deep cryogenic treatment to eliminate retained austenite and improve matrix hardness.
2.How to deal with coating peeling or improper selection?
Phenomenon: Many people believe that any coating will provide wear resistance.
Analysis: If a TiN coating (golden yellow) is used to stamp thick plates, the coating is prone to peeling off under impact due to TiN's poor toughness. The peeling coating fragments themselves become abrasive particles, exacerbating wear. For thick cold-rolled coils, CrN coatings or TD coatings (vanadium carbide VC) generally offer better wear resistance and stronger adhesion to the substrate.
3.What are the causes of lubrication failure?
Oil film rupture:
Mechanism: Cold-rolled coil stamping involves boundary lubrication under high pressure. If the extreme pressure performance (EP) of the lubricating oil is insufficient, or the oil application is inadequate, direct contact will occur between the die and the sheet metal, resulting in microscopic metal welding and tearing, i.e., "adhesive wear."
On-site assessment: Observe the surface of the punch or die. If fine scratches (ploughing grooves) parallel to the stamping direction or metal smears (built-up edge) appear, it indicates lubrication failure.
Improper lubrication method:
Manual oiling is often uneven. During continuous production, localized temperature increases cause lubricating oil to evaporate or leak, resulting in a "dry running" state in the latter half of the process.
4.What are the issues related to oxide scale and inclusions?
Residual Iron Oxide Scale:
Phenomenon: If the annealing process is not properly controlled, a very thin oxide layer (Fe3O4/FeO) will remain on the surface of the cold-rolled coil.
Consequence: Although this oxide layer is not very hard, it is brittle. During stamping, it breaks into hard particles that enter the die gaps, becoming a medium for abrasive wear and accelerating the wear of the die edges.
Carbide Segregation:
Mechanism: Especially for high-carbon steel cold-rolled coils (such as SK85, C75S), if there are large banded carbides inside the material (steel mill smelting and rolling defects), these large carbides are equivalent to "sand grains." When they pass through the die gaps, they directly scrape the die surface.
5.How to deal with a gap that is too small?
Logic: During blanking, if the clearance on one side is less than 3%-4% of the material thickness (for high-strength steel), the extrusion pressure will increase exponentially. This enormous extrusion pressure causes a rapid rise in the die surface temperature (up to 200-300℃), resulting in thermal softening, decreased die hardness, and accelerated wear.
Inspection: If the wear is concentrated at the cutting edge tip and accompanied by fine thermal cracks (crazing), it is very likely that the clearance is too small, causing overheating.