Adhesion's Dilemma? Challenges and Solutions for Auto Body Welding

Resistance welding Yolo Materials Industry 27th, Oct 2023 11:00 am

With the ongoing development of the modern automotive industry, the use of galvanized steel sheets has become increasingly prevalent in a wide range of automotive components. In the domestic automotive manufacturing sector, chromium-zirconium-copper is commonly used as the electrode material for welding these galvanized steel sheets. While this material exhibits reliability when welding low-carbon steel, complications arise when welding galvanized steel. This is primarily due to the occurrence of metallurgical bonding between copper and zinc at high temperatures, resulting in the formation of zinc brass and, consequently, the adhesion of the electrode to the galvanized sheet. In addition to material properties, several other factors need to be taken into consideration to minimize electrode adhesion.

Excessive Current Causing Electrode Adhesion

High Current: When the welding current is excessive, the current density in the welding circuit exceeds the normal working current of the electrode’s surface. This leads to a temperature gradient between the electrode and the workpiece, causing the fusion connection between the electrode and the workpiece and resulting in electrode adhesion.
Non-parallel Electrode Faces: If the upper and lower electrode surfaces are not parallel, localized contact points between the electrode and the workpiece increase contact resistance. This decreases the current in the circuit, but the local contact point’s current density is higher than that during regular welding, leading to localized temperature increase and electrode adhesion.
Rough Electrode Working Surfaces: The presence of a rough electrode cap can cause localized contact, resulting in excessive local current and, consequently, electrode adhesion.

Insufficient Electrode Pressure Leading to Electrode Adhesion

Insufficient pressure on the electrode causes an increase in contact resistance between the electrode and the workpiece, resulting in resistance heating at the contact site. This raises the temperature of the electrode’s contact surface with the workpiece to the weldable temperature, leading to fusion between the electrode and the workpiece and the subsequent electrode adhesion.

Inadequate Electrode Cooling and its Effects on Electrode Adhesion

Prolonged usage of welding equipment can lead to issues like blocked cooling channels. Inadequate cooling affects the electrode temperature, especially during continuous welding. As the temperature reaches the weldable temperature of the electrode and the workpiece, fusion occurs, resulting in electrode adhesion.

Conclusion

When dealing with electrode adhesion during spot welding of low-carbon steel workpieces, it is important to address the factors mentioned above. However, the most effective solution to tackle electrode adhesion when welding galvanized steel sheets is to consider a change in electrode material. Traditional chromium-zirconium-copper is prone to electrode adhesion due to metallurgical bonding with zinc at high temperatures. Currently, the most suitable material for welding galvanized sheets is tungsten-embedded CuCrZr. So, why Tungsten?

1. High Melting Point: Tungsten has an exceptionally high melting point, making it suitable for withstanding the intense heat generated during resistance welding processes. This property ensures that the electrode maintains its structural integrity even in high-temperature environments.
2. Excellent Thermal Conductivity: Tungsten possesses excellent thermal conductivity, allowing it to efficiently dissipate heat generated during welding. This characteristic aids in preventing overheating and ensures consistent performance throughout the welding process.
3. Chemical Stability: Tungsten is chemically stable and resistant to corrosion, ensuring the longevity of the electrode. It can withstand the potentially harsh welding environments without degrading, which is vital for maintaining electrode quality over time.

Tungsten’s special properties, like its high melting point, great heat conductivity, and low electrical resistance, work together to prevent adhesion problems in resistance welding. Its non-stick characteristics and durability keep it from sticking to the materials being welded, resulting in clean, high-quality welds without adhesion issues. This is why tungsten is a preferred choice in resistance welding.