Spot welding is a type of press welding and a traditional form of resistance welding. It is an important part of metalworking and is used in many industries. This article will explain the principles and working methods of spot welding in detail to help you better understand what spot welding is.

 What Is Spot Welding?

Spot welding is a metal joining technique where pressure is applied to metal workpieces by upper and lower electrodes, and an electric current heats them for a set time, causing the metal to weld at the contact points. The electrodes are typically made of copper because of its high thermal conductivity and low resistance. When current passes through the electrodes and the metal workpieces, heat is concentrated at the contact points, melting them into a plastic state. The current is then stopped, but pressure is maintained, bonding the contact points together. Spot welds are relatively small, with each weld spot’s diameter ranging from about 3 to 20 mm.

How Does Spot Welding Work?

We divide the spot welding process into four steps: setting parameters, placing the workpieces, applying pressure, and passing current.

Setting Parameters

A crucial step in spot welding is setting the welding parameters. The heat generated during spot welding is primarily determined by three parameters: current, resistance, and time. The relationship between these parameters is expressed by the following equation: 

Q = I²Rt

Q = heat generated

I = welding current

R = resistance in the electrode

T = duration of current flow

These parameters influence each other and determine the welding quality. The current has the greatest impact; its squared value in the equation significantly affects the heat generated. Therefore, controlling the current is crucial. If the welding current is too high, it can cause deformation and bubbles in the weld. If the current is too low, the workpieces won’t melt properly.

The resistance in the electrode is challenging to adjust during welding, as it mainly depends on the electrode’s shape and size. The duration of current flow is also important and should be set in coordination with the other parameters to achieve the desired results. Additionally, welding pressure is another key factor. Without adequate pressure, successful spot welding is difficult to achieve.

 Aligned The Metal

After adjusting the parameters, the welding process begins. First, place the workpieces between the two electrodes, aligning the metal so the electrodes target the spot to be welded. This step is crucial because if the welding point is misaligned, the weld will be off, possibly causing the product to be defective. When the metal pieces have a special shape or require high precision, it can be challenging to align the weld spot visually. In such cases, it is necessary to create a specialized jig. This way, you only need to place the metal pieces in the jig to ensure proper alignment for welding.

Apply Pressure

The third step in welding is applying pressure to the metal workpieces. The electrodes move towards the metal workpieces and apply pressure, ensuring that the workpieces and the electrodes are tightly in contact with each other.

Passing Current

Once the electrodes are fully pressed against the metal, you can start the current. During this time, the current flows from the electrodes to the metal workpieces, causing the metal to melt. When the set time for the current ends, the current automatically stops. At this point, the electrodes continue to apply pressure, allowing the heated metal to fuse together. Finally, the electrodes are released, completing the weld.

Common Materials Appropriate for Spot Welding

Low-carbon steel is widely used in automotive parts and sheet metal enclosures. For this type of material, you can set a high current and a short welding time to help form solid weld spots.

Aluminum has good heat dissipation and conductivity, with very low resistance. However, its surface easily oxidizes. When welding aluminum sheets, choose higher-powered welding equipment and use low current with long welding time settings.

Stainless steel welding, pulse welding is usually used to minimize the heat-affected zone’s impact on the appearance, ensuring the weld meets aesthetic requirements.

When welding galvanized sheets, the zinc layer on the surface has a low melting point, which is easily reached, causing significant splatter and electrode sticking, leading to unstable welding current. We use a two-step welding current process: the first step uses a smaller current to break through the zinc layer, and the second step adjusts the current to suitable welding parameters to reduce splatter and electrode sticking, improving welding stability.

In addition to these, copper wires and plates, high-strength steel, iron, and other metals can also be welded using spot welding techniques. Different materials may require different welding parameters.

The Applications of Spot Welding

Spot welding is widely used in various fields such as the automotive, electronics, home appliance, and sheet metal industries. In the automotive industry, spot welding is used for car body assembly, which has a complex structure, often utilizing portable spot welders or automated spot welding systems. Many metal parts in cars, like seat side panels, shock absorbers, and brake pads, also require spot welding. Spot welding is generally suitable for high-volume metal part production. If you need to weld 20,000 metal sheets per month, spot welding is an ideal choice.

Advantages of Spot Welding

Spot welding has a long history of development and is indispensable in many industrial sectors for metal joining. Compared to other welding methods, spot welding offers several advantages:

1. Fast Welding Speed: Spot welding is significantly faster than other welding methods. While other methods may take several minutes to complete a weld, spot welding can finish in just a few seconds. With advancements in welding technology, spot welding times have become even faster.

2. Aesthetic Welds: Products welded using spot welding are aesthetically pleasing with high precision. They are less prone to deformation, free from weld splatter, and have minimal visible seams. This quality is crucial for industries like automotive where high aesthetic standards are important.

3. Safe Operation: Spot welding has a low technical difficulty in its operation process, making it easy for ordinary workers to be trained and operate safely.

4. Automation Feasibility: Spot welding is suitable for mass production of metal products and can be easily integrated with robotic systems for automation, reducing manual labor.

5. No Filler Material Required: Unlike many other welding methods that require constant filler material, spot welding directly joins two workpieces together without the need for additional material.

These advantages make spot welding a preferred choice in industries requiring efficient, aesthetic, safe, automated, and material-efficient metal joining processes.

Limitations of resistance spot welding

While spot welding is powerful, its application is limited due to specific structural constraints:

1. Accuracy in Positioning: Spot welding completes with a single discharge. Without precise positioning systems, misalignment can lead to product defects and scrap.

2. Thickness and Shape Constraints: Spot welding is generally suitable for welding thin sheets (0-6mm). Thick or uniquely shaped materials are challenging to weld using spot welding, prompting the use of other welding technologies for thicker plates or pipes.

3. Joint Strength: Welded joints in spot welding may not be as strong because it is a localized welding process, focusing on welding one spot at a time.

4. Quality Control Challenges: Spot welding involves numerous parameters, each affecting the welding quality. Improper adjustment of parameters, such as pressure, can result in imperfect welding outcomes.

These limitations necessitate careful consideration of material type, thickness, and welding requirements when choosing spot welding or alternative methods for different manufacturing needs.

Spot Welding Machine

To complete spot welding tasks, you need a spot welding machine. Spot welding machines generally come in several forms: Stationary spot welders, benchtop spot welders, portable gun spot welder, and multi spot welder. The choice of spot welding machine depends largely on the shape and size of your metal materials. For simple 2 mm thick sheets, a vertical spot welder is sufficient. However, for welding car bodies where the workpieces are difficult to move, portable welding tongs are used. If you need to weld several spots on metal materials at once, a multi-spot welder is ideal.

Summary

Here is an explanation about spot welding. Metal welding is a crucial stage in metal processing, and spot welding techniques are widely used across various industries. If you want to learn more about spot welding, you can visit our website or directly consult with our technical staff.