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What is Spot Welding? â€“ Working and Applications
The welding process which is used for welding two or more metal sheets together by applying pressure and heat from an electric current to the weld area is known as spot welding.
Spot welding is a type of resistance welding process, which is why it is also known as the resistance spot welding.
The figure below shows the schematic diagram of resistance spot welding −
Spot welding is the simplest and most universally adopted method of making lap joints in thin sheet up to a maximum thickness of 12.7 mm.
A typical spot welding machine consists of a transformer to produce high current at low voltage and the electrodes are connected to the ends of the secondary winding for leading the current to the work.
There is also an arrangement to bring the electrodes in contact with the work and to apply the necessary mechanical pressure.
Spot Welding Process
In the spot welding process, the materials to be welded are overlapped and pressed between two water-cooled electrodes and a high electric current is passed through the assembly. The metals in the zone of pressure gets heated up to their melting temperature and the joint so made gets cooled under pressure.
For spot welding process, the required welding current is about 5000 A and the voltage between the electrodes is usually less than 3 V. Also, the open circuit voltage is less than 12 V. To regulate the secondary voltage and current, tapings are provided on the primary winding of the transformer.
The main factors affecting the quality of the spot weld are −
Value of welding current
Time for which the current flows
Pressure between the electrode tips
Advantages of Spot Welding
The main advantages of spot welding are as follows −
Spot welding has high compatibility with efficiency and uniformity.
Spot welding is economical, i.e., it is relatively cheap to operate.
Spot welding provides a much more efficient way of utilizing electrical energy for welding process.
Spot welding is a fast welding process.
Disadvantages of Spot Welding
The disadvantages of spot welding are as follows −
Spot welding requires a large working area.
The welding gun used in the spot welding is heavy and require great strength when using it. Therefore, spot welding may be very dangerous to the aged welders.
Spot welding is not suitable for the thicker materials.
Applications of Spot Welding
Some of the applications of spot welding are given as follows −
Spot welding is used in various industries such as automotive, aerospace, metal furniture, electronics, building construction, etc.
Spot welding is used in high volume production applications.
It is applied for welding of thin sheets.
Spot welding is also used for fabricating all types of sheet metal structures where high mechanical strength is required.
Spot welding can also be applied to all types of boxes, cores and enclosing cases, etc.
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