1.Why are galvanized coils suitable for shallow stamping?
Excellent Substrate Performance:
The substrate for galvanized coils is typically high-quality low-carbon steel (such as SPCC, DC01, etc.). This type of steel possesses excellent plasticity and ductility, making it the preferred material for stamping (including shallow stamping).
Lubricating Effect of the Zinc Layer:
The zinc layer acts as a solid lubricant during stamping, reducing friction between the die and the sheet metal, facilitating material flow, reducing stamping pressure and die wear, thereby improving stamping quality and die life.
Surface Quality:
Electro-galvanized coils, in particular, have a smooth, uniform surface with fine zinc blooms, making them ideal for shallow-stamped parts requiring high aesthetic appeal and subsequent painting or coating processes.
Combined Formability and Corrosion Resistance:
This is the biggest advantage of galvanized steel coils. While providing excellent stamping performance, they also impart outstanding corrosion resistance to the parts, eliminating the need for subsequent electroplating or painting for rust prevention. They are widely used in home appliances, automobiles, construction, and other fields.
2.How to choose the type of galvanized coil?
Electro-galvanized coils: The zinc layer is thinner (usually less than 30μm), uniform, and has a smooth surface with strong adhesion to the substrate. For parts requiring shallow stamping and high aesthetic standards, electro-galvanized coils are generally preferred because the zinc layer is less prone to cracking or peeling during forming.
Hot-dip galvanized coils: The zinc layer is thicker (usually 35-200μm), providing stronger corrosion resistance, but the surface is relatively rough, with noticeable zinc spangles, and a brittle alloy layer forms between the zinc layer and the iron. During stamping, the thicker zinc layer is more prone to micro-cracks and even peeling, affecting appearance and localized corrosion resistance. If hot-dip galvanizing is chosen, varieties with no or small zinc spangles should be selected, and the stamping depth must be strictly controlled.
3.How does the adhesion of the zinc coating affect stamping performance?
Stamping deformation causes the zinc layer to be stretched. If the adhesion between the zinc layer and the substrate is poor, peeling and flaking are likely to occur. Therefore, it is necessary to select materials with high adhesion grades (e.g., verified by bending tests and cupping tests).
4.What are the effects of surface treatment and lubrication on stamping performance?
Passivation layer: This comes in different types, such as chromium-free passivation and oil-coated passivation. Some passivation layers are quite hard and may flake off into powder during stamping, accelerating die wear. The appropriate passivation treatment method needs to be selected based on the complexity of the stamping process, or consultation with the material supplier is necessary.
Lubrication: Even if the galvanized coil contains its own rust-preventive oil, additional stamping oil may be required during stamping to provide more adequate lubrication, ensure forming quality, and prevent scratches.
5.What are the effects of mold design and condition on stamping performance?
Die Clearance: The die clearance for stamping galvanized steel sheets needs to be slightly larger than that for stamping cold-rolled sheets of the same thickness. Because the zinc layer itself has thickness, if the clearance is too small, it will compress the zinc layer, leading to zinc scraping, zinc layer peeling, and even die blockage.
Die Material and Hardness: It is recommended to use die materials with better wear resistance (such as powder metallurgy steel) and perform surface treatments (such as TD treatment or PVD coating) to resist abrasive wear from the zinc layer.
Die Surface Finish: The die cavity and cutting edge should have a high surface finish to reduce friction and prevent scratches on the galvanized surface.