What is Resistance Welding?

What is resistance welding? What are the application scope and advantages and disadvantages?
Answer: After the workpieces are combined, pressure is applied through the electrode, and the resistance heat generated by the current passing through the contact surface of the joint and the adjacent area is used for welding. This method is called resistance welding. Common ones include butt welding, spot welding, projection welding and seam welding machines.
The characteristics of resistance welding are large welding current, short power-on time, expensive and complex equipment, but extremely high production efficiency, no auxiliary materials and special protection are required during welding, so the cost is very low. It is mainly used for welding thin plate components with a thickness of less than 3 mm, or welding nuts and other components on thin plate materials. Resistance butt welding can be used to weld various types of steel and non-ferrous metals such as aluminum, magnesium, copper, and stainless steel.

Resistance welding generally makes the workpiece under a certain electrode pressure, and uses the resistance heat generated when the current passes through the workpiece to melt the contact surface between the two workpieces, thereby realizing the welding method of connection. Usually a larger current is used. In order to prevent arcing on the contact surface and to forge the weld metal, pressure must always be applied during the welding process. When performing this type of electric welding, the surface condition of the workpiece to be welded is of primary importance for obtaining stable welding quality. Therefore, the contact surface between the electrode and the workpiece and between the workpieces must be cleaned before welding. The characteristics of spot welding, seam welding and projection welding are that the welding current (single phase) is large (several thousand to tens of thousands of amperes), the power-on time is short (several cycles to several seconds), the equipment is expensive and complex, and the production efficiency is high, so it is suitable for mass production. It is mainly used for welding thin plate components with a thickness of less than 3mm. All kinds of steel, aluminum, magnesium and other non-ferrous metals and their alloys, stainless steel, etc. can be welded.

Spot welding (resistance spot welding) is mainly to pass a large current between the two electrodes instantly, using the resistance between the two welded metals is much greater than the electrode resistance, so when a large current passes, it will also instantly produce a fusion of liquid metal between the two welded metals, and then connect the two plates together.

The electrodes of seam welding are generally a pair of disc-shaped electrodes. Each time a large current passes through the electrodes, the metal to be welded between the two wheels is melted and connected. Then the electrodes roll at an angle and pass a large current for a moment to form a weld that overlaps with the previous weld. In this way, the electrodes move forward continuously to form a continuous weld. In order to prevent the wheels from pulling out arcs when they rotate, the electrodes of the seam welding machine are generally energized intermittently, and the wheels stop rotating at the moment of energization.

Projection welding mainly uses the convex points stamped on the workpiece, which melt rapidly when a large current passes through them instantly, and then apply a rapid clamping force to connect the welded metals after the predetermined convex points are melted. Because there are generally several convex points that are shunted at the same time, the input capacity of the general projection welding machine is much larger than that of the ordinary spot welding machine. At the same time, the clamping is generally no longer pedaled, but pneumatic pressure is used.

The principle of flash welding is similar to projection welding in the early stage of welding, but no excessive forging force is applied in the early stage of strong current. In the early stage of power-on, the two welded metals only maintain a small contact surface, and the metal on this contact surface is quickly heated to vaporization by the current, causing the metal in the molten metal pool to boil and explode and spray out to the surroundings. A small concave area will be formed on the original contact surface, and the original non-contact area will have a slight contact, and then boiling and explosion will occur again, and spray out to the surroundings. When the liquid metal is sprayed outward, it will continuously heat the surrounding metal and clean the two sides of the welded metal. In this way, boiling and explosion are continuously generated, and the two welded surfaces are continuously heated and cleaned until the two welded surfaces become pure liquid metal. Then a larger forging force is applied to quickly press the two welded metals, the liquid metal part bulges, and the connecting part is quickly cooled and connected together.