The formability of Galvanized plate is influenced by both the characteristics of their zinc coating and the mechanical properties of the substrate. According to laboratory tests, for steel plates with standard G90 coating (zinc coating mass approximately 275g/m²), when the bending radius is equal to 0.8 times the plate thickness, the cracking probability of the surface zinc coating is approximately 18% (ASTM A653 standard data). However, if the optimized process, such as hot-dip galvanizing followed by alloying treatment (GA process), is adopted, the critical bending radius can be reduced to 0.5 times the plate thickness, and the surface crack rate can be lowered to within 5%, significantly enhancing the processing flexibility. For instance, General Motors’ 2022 body production line data shows that the stamping yield of galvanized steel sheets using the GA process reached 96.7%, which is 12 percentage points higher than that of traditional galvanized sheets. The annual rework cost for a single model was saved by approximately 2.3 million US dollars.
In the bending processing stage, the surface friction coefficient of galvanized steel sheets is approximately 0.12-0.15 (in the zinc coating state), and the bending springback compensation amount needs to be increased by 15%-20% compared with cold-rolled sheets. In actual cases, during the construction of the main venue for the 2020 Tokyo Olympics, the construction unit selected 1.2mm thick galvanized steel plates for the curved roof. Through a CNC bending machine, the pressing pressure was increased to 650 tons (25% higher than the processing pressure of conventional cold-rolled steel plates), and the mold gap accuracy was controlled within ±0.03mm. Ultimately, a complex three-dimensional modeling with a curvature radius of 0.5 meters is achieved. This technical solution enables the material utilization rate to reach 91.5%, an increase of 8% compared to the traditional method.
The forming limit diagram (FLD) of galvanized steel sheets indicates that its ultimate strain is approximately 8% to 12% lower than that of cold-rolled sheets, especially in the tension-compression compound strain region. The 2023 research report of the China Steel Construction Association indicates that when performing roll forming on 0.8mm thick galvanized steel sheets and the feeding speed exceeds 15m/min, the occurrence rate of edge wrinkles increases to 7.2%. Sany Heavy Industry successfully controlled the bending accuracy error of the 6-meter-long C-shaped galvanized steel purlin within 1mm/ meter by optimizing the forming process: keeping the roller temperature at 120±5℃, reducing the forming speed to 12m/min, and combining it with a 0.6‰ roller taper correction design. The production efficiency was only sacrificed by 5%.
The key control points lie in the adhesion strength of the zinc coating (requiring ≥3MPa) and the management of processing temperature. Actual measurements show that when the temperature of the bending die is below 10℃, the risk of zinc coating peeling increases by 40%. The stamping specifications for galvanized sheets formulated by ThyssenKrupp of Germany stipulate that when processing materials with a thickness of ≥2mm, the preheating temperature of the die should be maintained at 60℃, and the single die repair cycle should not exceed 15,000 strokes. This standardized management has kept the bending Angle deviation of a certain model of building support products within ±0.5° and controlled the scrap rate below 0.8%. Current technological trends indicate that the adoption of laser-assisted local heating (with a power density of 200W/cm²) can reduce the bending springback of galvanized sheets by 35%, further enhancing design freedom.