Galvanized steel sheets are widely used in industries such as automotive manufacturing, home appliance production, and construction due to their excellent corrosion resistance and cost-effectiveness. However, the zinc coating on the surface of galvanized steel sheets is prone to damage during bending and welding, which may affect the protective performance and appearance quality of the sheets. Mastering the key process points of bending and welding of galvanized steel sheets is crucial to ensuring processing quality.
I. Key Points of Bending Process for Galvanized Steel Sheets
(1) Selection of Bending Equipment and Molds
The precision of bending equipment directly affects the accuracy of bending angles and dimensions. It is recommended to use CNC bending machines to ensure operational stability and repeatability. For molds, upper molds with a larger fillet radius should be selected to avoid zinc coating cracking caused by stress concentration during bending. Generally, the fillet radius of the upper mold should be no less than 1.5 times the thickness of the sheet. For example, for a 1mm-thick galvanized steel sheet, the fillet radius of the upper mold should be at least 1.5mm.
(2) Control of Bending Process Parameters
Before bending, the bending angle and pressure should be adjusted according to the thickness and material of the sheet. The springback angle of galvanized steel sheets is usually larger than that of ordinary steel sheets. In practical operations, the compensation angle can be determined through trial bending, generally ranging from 2° to 5°. In addition, the bending speed should not be too fast, as excessive speed will aggravate the separation of the zinc coating from the base material. It is recommended to control the speed at 10–20 mm/s.
(3) Common Problems and Solutions
Zinc coating peeling is the most common problem during bending, mainly caused by the dual stress of tension and extrusion on the zinc coating during bending. In addition to selecting appropriate molds and controlling process parameters, annealing treatment can be carried out on the sheets before bending to reduce their hardness and improve plasticity. For slight zinc coating peeling, zinc-rich coatings can be used for repair after bending.
II. Key Points of Welding Process for Galvanized Steel Sheets
(1) Selection of Welding Methods
Common welding methods for galvanized steel sheets include arc welding, gas shielded welding, and resistance welding. Arc welding is suitable for thicker sheets, but the heat-affected zone is large, easily causing zinc coating evaporation and porosity; gas shielded welding (such as CO₂ welding) is efficient and low-cost, making it a commonly used method, but attention should be paid to controlling the gas flow to prevent air from entering and causing weld oxidation; resistance welding (such as spot welding and seam welding) has a small heat-affected zone and less damage to the zinc coating, making it suitable for thin sheet welding.
(2) Optimization of Welding Parameters
Taking gas shielded welding as an example, the welding current should be adjusted according to the sheet thickness. Generally, the current for a 1mm-thick sheet should be controlled at 80–100A, and that for a 2mm-thick sheet at 120–150A. The welding speed should not be too fast, as excessive speed will result in insufficient weld penetration, while too slow speed will cause excessive evaporation of the zinc coating. It is recommended to control the speed at 20–30 cm/min. At the same time, the protective gas flow should be maintained at 15–25 L/min to ensure effective protection of the welding area.
(3) Weld Treatment and Protection
After welding, the zinc coating on and around the weld is often damaged and requires secondary protection treatment. First, use a wire brush or sandpaper to remove welding slag, scale, and residual zinc slag from the weld surface; then, apply zinc-rich primer or perform thermal spraying zinc treatment to restore the corrosion resistance of the sheet. In addition, for important structural components, weld flaw detection should be carried out to ensure that the welding quality meets the standards.
III. Safety and Environmental Protection Considerations in Processing
During the bending and welding of galvanized steel sheets, special attention should be paid to safety and environmental protection. Zinc vapor and fumes generated during welding are harmful to the human body, so operators should wear gas masks and protective gloves; bending equipment should be equipped with protective devices to prevent operator injuries. At the same time, waste zinc slag, waste coatings, and other materials generated during processing are hazardous wastes and need to be collected and disposed of in accordance with environmental protection regulations to avoid environmental pollution.
Mastering the key points of bending and welding processes for galvanized steel sheets can not only improve processing efficiency and product quality but also effectively reduce production costs. In actual operations, it is necessary to continuously summarize experience according to specific working conditions and optimize process parameters to ensure that galvanized steel sheets still maintain good protective performance and mechanical properties after processing.