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What is Resistance Welding?

Felicia Dye
Felicia Dye

Resistance welding refers to processes that use electrically generated heat and pressure to create bonds between materials. Such processes usually pertain to connecting metals but the term resistance welding may also be used in plastic bonding. This type of welding is regarded as quick and efficient when done properly. Mistakes during such a process can result in problems such as cracking, deformed surface appearance, and cavities.

The machines normally used for resistance welding utilize copper electrodes. These are used to inject the materials with electrically generated heat. The machine’s operator can control the amount of heat and the heating period. After a sufficient amount of heat is injected, the materials may be cooled on the outside while the inner, molten materials are left to cool more gradually. When this phase is complete, bonds should be formed.

A welding mask protects a welder's eyes and face.
A welding mask protects a welder's eyes and face.

Generally, the higher the melting point of the metal, the less heat that is needed. A metal that conducts heat well, such as aluminum, requires more heat for resistance welding. This is because the heat tends to spread through the material instead of being trapped at the melting point.

Resistance welding also requires force. Pressure is used to hold layers of metal together while they are cooling. If this is not done, cohesion may never occur. The necessary pressure is usually applied by the machine that supplies the electrical current. The machine’s operator can also usually control the amount of pressure.

Spot welding is an example of a resistance welding process. It can be used to connect multiple layers of metal without filler materials. Since copper is an excellent conductor of heat, pointed, copper electrodes, are used to clamp the metal together and send electrical currents through them.

Many metals do not conduct heat well. The heat created within the layers of the project is therefore trapped and results in melting. Pressure from the electrodes then causes the layers to connect.

Seam welding is similar to spot welding. Instead of creating bonds at various points, however, this process allows the creation of long, continuous bonds. Round electrodes are used in this process to roll over the outsides of the materials, feeding them with electrical current and applying pressure.

There are several types of resistance welding bonds. Fusion bonding involves materials that bind because their melting points are reached, allowing the molten materials to mix together. A solid state bond, on the contrary, is one that involves minimal melting.

Discussion Comments


I work for a welding company. We use resistance welding most of the time and let me tell you, resistance welding is no easy thing.

When the company started using this system, we were getting a lot of complaints from our customers about cracking and it took us a long time to figure out what exactly was going wrong during the welding process.

We eventually figured out that high levels of humidity in the air and an issue with our power supply was the cause.

There are so many factors that have to be just right and the people running the resistance welding machines have to know what they're doing for it to work properly. It's definitely not easy.


@anamur-- I think that depends on the metals being used and what is being manufactured. The article already mentioned that different metals require different amounts of heat and pressure from welding machines because they conduct electricity in different ways.

In addition to seam and spot resistance welding, there are also other types like projection welding and flash welding. In flash welding, for example, the entire surface of the metal is fused together through heat and afterward, pressure is applied to weld them together.

So it really depends on the metals and the purpose of welding.


This is interesting. So which type of resistance welding is the best in terms of quality and life?

I feel like resistance seam welding with fusion bonds would be the best combination. Spot welding might cause the metals to break off at that point if a lot of weight and pressure is applied on it. I think the same goes for solid state bond because the metals are not one uniform piece at any point.

Seam welding on the other hand would give the metals more support with multiple connecting spots. And fusion bonds will melt and merge the two metals together which I think will make it really difficult for them to separate, even if there is a lot of pressure.

What do you think? Am I right?

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    • A welding mask protects a welder's eyes and face.
      By: Dmytro Sukharevskyy
      A welding mask protects a welder's eyes and face.