Analysis Of The Causes Of Stamping Cracks in Galvanized Steel Sheets And Key Points Of Process Control

First, annealing temperature is a key variable determining the mechanical properties of a material. During continuous annealing, controlling the temperature and holding time allows the cold-rolled structure to recrystallize and achieve the desired grain size. When the annealing temperature is too low, recrystallization is insufficient, resulting in fine grains, high yield strength, and insufficient elongation. Materials in this state have limited plasticity reserves during stamping and are prone to cracking in stress concentration areas.

Conversely, if the annealing temperature is too high, it may lead to abnormally coarse grains. Although the yield strength decreases, the tensile strength decreases even more significantly, resulting in an imbalance between overall strength and toughness, making the material prone to instantaneous fracture during tensile testing. For cold-rolled carbon steel stampings, a stable annealing regime is fundamental to ensuring stamping performance; therefore, the temperature is typically controlled within a reasonable range, and furnace temperature fluctuations are kept manageable.

Second, processing lubrication conditions directly affect the material's flow behavior in the die. The surface roughness of galvanized steel determines its oil retention capacity; appropriate surface morphology helps form a stable oil film and reduce the coefficient of friction. In the production of customized sheet metal stamping and bending parts, insufficient oil application increases the frictional resistance between the sheet metal and the die, significantly raising local tensile stress and inducing cracking. Excessive oil application causes slippage during slitting or continuous forming, affecting positioning accuracy and cycle stability. Therefore, oil application control should be systematically matched with sheet metal thickness, stamping depth, and die structure.

Third, the coordinated design of material thickness and die clearance is a key technical factor in preventing stamping cracks. During stamping, a reasonable die clearance ensures uniform deformation of the material in the shear and tension zones. Too small a clearance increases shear stress and exacerbates material hardening; too large a clearance may cause burrs or stress concentration. For carbon steel stamped parts or GI stamping parts, die design must fully consider the actual material thickness deviation and coating effects to avoid edge cracking due to improper fit.

Fourth, metallurgical quality has a fundamental impact on stamping performance. Inclusions, non-metallic particles, or foreign matter indentation defects in molten steel can form microcrack initiations during subsequent forming. When materials are subjected to tensile loads, inclusion areas, due to insufficient local elongation, are highly susceptible to becoming crack propagation initiation points. This problem is particularly prominent in the production of structural components such as Zinc Coated Steel Stamping or Galvanized Steel Bracket Stamping. Therefore, strengthening cleanliness control during steelmaking and continuous casting is a prerequisite for improving stamping safety.

To address these causes, the industry typically adopts systematic improvement measures. First, the annealing process is optimized, stabilizing the target temperature at approximately 850℃, and ensuring temperature fluctuations are within acceptable limits through online monitoring systems to obtain a uniform grain structure. Second, the type and amount of stamping rust-preventive oil are appropriately selected to match lubrication conditions with the stamping depth. Third, controlling the rolling force during the finishing process, for example, maintaining it above 1200kN, can improve sheet shape and surface condition, enhancing subsequent forming stability. Simultaneously, the verification and maintenance of die clearances are strengthened to ensure that the material's deformation capacity is consistent with the die design.

In the field of electrical equipment, such as galvanized steel stamping for relay enclosures, high requirements are placed on dimensional accuracy and surface integrity. Cracks can not only affect structural strength but also potentially reduce the protection level. Similarly, in the manufacturing of galvanized steel mounting plate stamping or steel electrical parts, the stamping quality directly affects the subsequent welding and assembly results. For steel-welded stamped parts requiring welding, the impact of the coating on the welding heat input must also be considered to avoid localized performance degradation.