Understanding Resistance Spot Welding!

Posted on Aug 20, 2020

Resistance Spot Welding

Resistance spot welding is a technology that uses heat generated by resistance to weld two pieces of metal together. The welding material is fixed together from above and below by copper electrodes connected to the welding power source for energization. When current passes through the part to be welded, the heat generated by the resistance melts and is incorporated into the material. In factory automation, automatic resistance spot welding machines have been widely used in the connection process of production lines.

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 that will be 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 to learn more about resistance spot welding? Let us begin with the construction of these types of machines.


Construction of Resistance Spot Welding Machines

The resistance spot welding device includes a transformer, a workpiece, two copper electrodes, and two pliers. Under certain circumstances, a transformer can be used to increase or decrease the voltage. The power source will reach the electrode through two pliers. When it comes to resistance spot welding copper, tungsten, and copper-tungsten alloy 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 and shaping of current that leads to the formation of a connection between the two metal parts or workpieces. The machine that performs such a technique is called a Resistance Spot Welder.


Thermal Properties of Elements Used in Resistance Spot Welding

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 (I) through the resistance (R) of the metal workpiece within a specified time (t). The welding current is applied under a controlled force through copper electrodes. The diameter of the electrode in contact with the workpiece will determine the current density. The applied electrode force will also affect the resistance between all interface layers (including the weld nugget area and the electrode-to-workpiece interface area). In practice, the force is adjusted so that heat is generated immediately in the interface area. Although it is important to start to accumulate heat at the joint surface of the workpiece, it is not desirable to generate excessive heat marks at the electrode-workpiece interface. Therefore, it is very important that the electrode cooling system should remove heat as efficiently as possible from the surface of the workpiece in contact with the electrode. An efficient cooling system will retain electrodes to control the current density.


:: Read More: Resistance Spot Welding Machine for Buyers

Working Principle of Resistance Spot Welding

But how exactly does resistance spot welding work? We have broken down the concept into a few simple stages:

In the process, two or more metal plates are joined together by spot welding. The workpiece to be welded is pressed between the tips of the copper electrodes, and a high current under low pressure passes through the workpiece. Due to the resistance of the workpiece (sheet metal) to the current, the temperature of the contact surface rises to the fusion point, and the weld is formed as a nugget. The nugget is the weld formed between the workpieces. No filler material is used during the process. Repeat the operation "n". The time for spot welding at the desired location.


Pros and Cons of Resistance Spot Welding

• Pros

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 by spot welding, and there is no unsafe open flame. It can be done without any special capabilities. 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, and different types 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.

• Cons

The electrodes must be able to touch both sides of the metal sheets which 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. Whether the current is not high enough, not hot enough, or if the metal is not held together with enough force, the spot welding will be low or weak.

• Limitations

Even though it has certain drawbacks, spot welding is useful in many cases. Only partial connections that may not be particularly strong can be created. The efficiency of the spot welding 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 of Resistance Spot Welding

• Connection of vehicle body parts

• Barrels of gasoline

• Railway tracks

• Gas, oil, and water pipes

• Household radiators

• Turbine blades

…and many more!

We hope this article was helpful for you and gave you an overview of the resistance spot welding technology.


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