1.How to reduce the interference of coating on welding?
Removing the coating of the welding area: Use mechanical grinding, chemical cleaning or laser cleaning to remove a certain width of coating on both sides of the welding line to expose the clean substrate surface, ensure good contact between the electrode and the substrate during welding, and avoid the coating interfering with the formation of the molten pool.
Substrate surface cleaning: If there is oxide scale, oil stains, etc. on the surface of the substrate, it needs to be cleaned simultaneously to prevent pores and cracks during welding.
2.How to reduce heat affected zone damage?
Resistance welding
Including spot welding, seam welding, etc., through the electrode pressure and current, the heat generated by the contact resistance of the substrate is used for local melting welding. The heat input is small, the heat-affected zone is narrow, and the damage to the coating is small. It is suitable for the connection of thin plate color-coated coils.
Note: The electrode pressure, current and power-on time that are suitable for the thickness of the substrate must be matched to avoid false welding or overheating of the welding point.
Laser welding
The energy is concentrated, the welding speed is fast, the heat-affected zone is extremely small, the weld is smooth, and the damage to the coating is small. It is suitable for scenes with high precision and high appearance requirements. However, the equipment cost is relatively high, and it is necessary to ensure that the laser focus is accurate to avoid weld defects caused by coating residue.
Gas shielded welding
Applicable to medium and thick color coated coils, inert gas or mixed gas is required to protect the molten pool and reduce oxidation. However, the heat input is large, and the welding current and speed need to be controlled to avoid excessive heat-affected zone, which may lead to a decrease in the strength of the substrate or large-scale burning of the coating.
Note: When welding, the welding wire needs to be directly aimed at the substrate to prevent the coating from mixing into the molten pool and forming slag inclusions.
3.How to control heat input and weld quality?
Heat input control: Excessive heat input will lead to overheating of the substrate, coarse grains, and a wider range of coating decomposition; too little heat input may not be welded through. It needs to be adjusted according to the thickness of the substrate. For example, when spot welding a 1mm thick galvanized color-coated coil, the current is usually controlled at 5-10kA and the power-on time is 0.1-0.3 seconds.
Pressure and speed: In resistance welding, the electrode pressure must be sufficient to keep the substrate in close contact to avoid sparks caused by gaps; the welding speed of laser welding or gas shielded welding must match the heat input to ensure that the penetration depth meets the standard.
4.How to repair coating and improve corrosion resistance?
Coating repair
The exposed substrate and heat-affected zone in the welding area need to be covered with special repair paint:
The repair paint must be compatible with the original coating of the color-coated coil (if the original coating is polyester, the repair paint should be polyester type; avoid peeling later.
Before repairing, the welding slag and oxide scale in the welding area need to be cleaned, and then the repair paint should be applied. The dry film thickness should be close to the original coating to ensure consistent protective performance.
5.How to reduce welding risks from the source?
Substrate selection: Priority should be given to substrates with excellent welding performance, such as low carbon steel or low alloy high strength steel, which have low thermal sensitivity during welding, are not prone to cracking, and have stable mechanical properties after welding.
Coating type: Some manufacturers provide "welding-resistant color-coated coils", whose coating decomposes slowly at high temperatures and has less residue, which can reduce smoke and weld slag during welding, and is suitable for scenes with high requirements for welding efficiency.