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Understanding Resistance Spot Welding!

Posted on Jul 27, 2021

Resistance Spot Welding

Resistance spot welding is a technology that uses heat to weld two pieces of metal together. The welding material is fixed together from above and below by electrodes connected to the power source. When current passes through the parts, the heat generated by the resistance melts and fuses the parts.

Metal objects have various electrical and thermal properties, which makes resistance welding processes possible. Electrically, metal objects have a certain degree of resistance to the flow of electric current. When current passes through the workpiece, the resistance causes heat energy.

The higher the current carrying capacity and duration, the higher the heat energy generated. In this article, we will talk about the basics of resistance spot welding and the pros and cons of this method. Are you ready? Let us begin with the construction of these types of machines.
 

Construction

Resistance spot welding machines include a transformer, a workpiece, two copper electrodes, and two pliers. The transformer can adjust the voltage. The power source will reach the electrode through two pliers. When it comes to resistance spot welding, copper, tungsten, and copper-tungsten alloys are the most common metals that are used for the electrodes.

As pressure is applied to the pliers, heat is generated between the workpieces due to the passage of the current that leads to the formation of a connection between the two metal workpieces.
 

Working Principle

In terms of heat, metal objects have a melting point, specific heat content, thermal conductivity, etc. By using these properties, an environment can be created to generate a molten pool, which will freeze into a weld block. Melting a certain amount of metal will produce a welding nugget, which requires a lot of energy.

Resistance spot welding is done by passing a controlled current through the resistance of the metal workpiece within a specified time. The current is applied under a controlled force through the electrodes. The diameter of the electrode in contact with the workpiece determines the current density. The force will also affect the resistance between all interface layers. In practice, the force is adjusted so that heat is generated immediately in the interface area.

Although accumulating heat at the joint of the workpieces is the key to the process, it is not desirable to generate excessive heat marks at the electrode-workpiece interface. Therefore, it is important that the cooling system removes heat as efficiently as possible from where the workpiece contacts the electrode. An efficient cooling system will retain electrodes to control the current density.
 


Spot Welding, AniMech

Advantages & Disadvantages

The process of resistance spot welding is not applicable under every circumstance. Before practicing such a technique, it is necessary to understand the advantages and disadvantages.
 

Advantages

One of the biggest advantages of resistance spot welding is that it is a very quick and simple process. There is no need to use any metal flux or filler to form joints, and there is no unsafe open flame. Automated machines can be spot-welded in the factory to speed up production.

Machinery used in car factories produces up to 200 spot welds in six seconds. Resistance spot welding can be used to connect several different metals that can be linked to one another. It can spot thin plates as thin as 1/4 inch, and at the same time connect multiple thin plates together.
 

Disadvantages 

The electrodes must be able to touch both sides of the metal sheets that are bound together. Only a certain thickness of metal (5 to 50 inches) can be carried by a particular spot welder. While the location of the electrode can be changed, in most electrode holders only minimal movement is possible.

The size and shape of the electrode define the size and strength of the weld. The relation is formed only when the electrode is in contact with the metal. If the current is not high or hot enough, or if the metal is not held together with enough force, the spot welding will be weak.
 

Limitations

Only partial connections that may not be particularly strong can be created. The efficiency of the process depends on the intensity and temperature applied and the cleanness of the electrodes and metal. The challenge of binding electrodes to oddly formed metals can be prevented by using a compact spot welder. The electrodes are attached to long cables so that they can reach areas that are hard to access.
 

Applications

Resistance spot welding machines are frequently involved in the automotive, oil and energy, transportation, and aerospace industries. They connect vehicle body parts in assembly lines. They weld barrels and pipelines for gasoline and water supply. They are also used to connect railway tracks.
 

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