1.What are the material factors?
Excessive Material Strength: With the development of lightweight automobiles, the application of ultra-high-strength steel (such as third-generation high-strength steel) is becoming increasingly widespread. These materials have extremely high strength, generating enormous frictional stress and contact pressure on the die surface during cold stamping, leading to a dramatic acceleration of die wear.
Surface Cleanliness and Adhesives: If hard impurities, such as iron powder, oxide scale, or sand particles, adhere to the surface of the cold-rolled coil, these hard particles will act like abrasives during stamping, causing severe abrasive wear between the die and the sheet metal, directly scratching the die surface.
Material Thickness Deviation: If the sheet metal thickness fluctuates significantly (especially negative deviations), the actual blanking clearance may exceed the reasonable range, resulting in excessively large burrs. These burrs, in turn, exacerbate die wear.
2.What are the factors related to mold design?
Insufficient mold hardness and wear resistance: If the hardness of the working parts of the mold is too low, its wear resistance will naturally be poor. For example, one case indicated that when the surface hardness layer is below HRC 50, wear resistance decreases by 40%. Choosing a higher-quality mold material (such as powder metallurgy steel ASP-23) or increasing the hardness of key parts to 58-62 HRC can effectively improve this.
3.What are the consequences of improper mold design and clearance?
Too small or too large a clearance: If the blanking clearance exceeds the reasonable range for material thickness (usually 8%-12%), it will not only lead to abnormal blanking force but also cause abnormal wear of the cutting edge. Too small a clearance intensifies extrusion; too large a clearance will produce excessive burrs, which in turn will damage the die.
Stress concentration in the design: Sharp corners or excessively small transition fillet radii in the die shape will cause localized stress concentration, which will not only easily lead to cracking but also accelerate wear in that area.
4.What are the consequences of inadequate mold surface treatment?
No matter how good the die substrate material is, without proper surface treatment (such as nitriding, PVD coating, TD coating, etc.), it is difficult to resist the intense friction during high-strength steel stamping. For example, Kobe Steel's HKS-G technology is a surface modification treatment technology specifically developed to solve the problem of die wear in high-strength steel stamping. Toolox materials also require appropriate surface nitriding treatment to achieve excellent wear resistance.
5.What are the process factors?
Poor lubrication: This is one of the most common causes of mold wear. Lubricant effectively isolates the mold and sheet metal from direct contact, carrying away frictional heat. If the lubricant is improperly selected, applied unevenly, or insufficiently, the coefficient of friction will increase sharply, generating high temperatures, causing the mold surface material to soften and accelerating wear. Good lubrication can extend mold life several times or even more than ten times.
Local temperature rise and adhesion: Under high pressure and sliding friction, the temperature in localized areas rises sharply, which may cause material transfer between the mold and the sheet metal, forming "adhesive nodules." These nodules are very hard and can severely scratch subsequently passing sheet metal (i.e., roughening). They also represent a loss of mold material, i.e., "biting wear."
Improper process parameters: For example, excessive blank holder force increases the resistance to sheet metal flow, causing a significant increase in friction, thereby accelerating mold wear. Excessive stamping speed also leads to heat accumulation, exacerbating wear.