resistance welding

Resistance welding

Resistance welding is a process in which heat is generated at the interface by passing an electric current through it. It is performed under control time and pressure. The term is derived from the fact that the resistance between the workpiece and electrodes are used to generate the heat at the interface. This technology is used in the manufacturing industry of metal sheets and components. It has been part of industrial processes nowadays.

History of resistance welding
There was a time when metal welding was done by heating the metals to their melting points and then pressed together. Welding technology has advanced considerably after the launch of electricity. Resistance welding, arc welding, and gas welding are advanced forms of this phenomenon. Now ultrasonic, electronic beam and laser welding are also present. Resistance welding with enormous benefits has been contributing to the growth of industries for many years.

Principle of resistance welding
It works on simple principles. Force and current are applied through the electrodes. The resistance heat is generated at the interface of the metal parts. It results in the melt joints. Although the huge amount of current flows. Yet, there is no danger of electric shock. Because low voltage is present.

Features of resistance welding
• One of the interesting features of resistance welding is that it uses no flux. Such as solder. Welded parts are easily recycled.
• Ultraviolet rays are not generated during the process. So a neat and clean work site is Available
• It is an easy operation to perform. Only pressing the buttons leads to automation. It does not require trained skills like arc welding and gas welding.
• It is a low cost and high volume production process. Welding can be performed efficiently not taking much time.
• The duration of the process is short. Workpieces are affected less by the heat.
• The optimization of the process depends upon the material and thickness of the part to be welded. The electric facility should be present due to the use of a large current.

Applications of resistance welding
• Resistance welding is used in the automotive industry. It is specially used to design nuts and bolts.
• Seam welding is used to make water tanks and boilers.
• Resistance welding is used in the welding of tubes and pipes

Types of resistance welding
The process of resistance welding is classified into many variants depending upon the shape of the workpiece and form of electrodes. Commonly used resistance welding processes are
• Spot welding
• Projection welding
• Seam welding
• Butt welding

Spot welding
It is a predominant process in the automobile industry. It is used in the assembling of automobile bodies and its large components. It is used for the manufacturing of furniture and other domestic products. In this process, the current and heat generation is localized in the form of electrode.

Projection welding
This type of resistance welding is done with specially designed electrodes to shift the shape of the workpiece. Projection welding is used in electrical equipment, electronics, automotive, and construction industries. This process is used in the manufacturing of sensors, valves, and pumps.

Seam welding
In this resistance welding process, the joints are leak-tight by continuous opposing force with electrodes consisting of rotatory wheels. Seam welding is applied in manufacturing containers, radiators and heat exchangers, etc.

Butt welding
It is a forging operation applied to the workpiece when heated. Racks it is a resistance welding process to join metal plates or bars with an applied force of electrodes clamping the workpiece at the ends. It is applied for the manufacturing process of wheel rims, wire joints, and railway track joints.

Characteristics of a welding machine
The electrical and mechanical characteristics of the welding machine greatly affect the welding resistance process.
• The total welding time is very short. So the up-slope welding time is critical. It is critical to consider the factor of magnetic loss in spot welding.
• One of the main mechanical characteristics includes acceleration as well as the stiffness of the frame.
• The dynamic reaction time of welding is important. The loss of induction due to the size of the welding window and the material consumed.
• The current density is dependent upon the geometry of the electrodes.
• There is a need for different welding current for the thickness of metal.
• Special parameters are required for the adjustment in resistance welding. According to the surface coating of the workpiece.

Material properties
• The resistivity of the material affects heat generation.
• The thermal conductivity of the material and the heat capacity control the heat transfer.
• In silver and copper with low resistivity and high thermal conductivity, only a little heat generates with high welding current.
• Silver and copper are considered good materials for electrodes. More heat generates with high resistivity.
• Hardness of the material affects the contact resistance.

Low- frequency and high-frequency electric resistance welding
It is a method of welding seams in oil and gas pipelines. The pipe made through this method forms a sheet of steel into a cylindrical shape. The current is passed to the edges of the steel to heat the steel so that a bond can be formed without the use of welding filler material. It uses low-frequency A.C current. In recent years it has been replaced by a high-frequency process that produces a high-quality weld. The welds manufactured by this process do not corrode and do not develop hook cracks in pipeline construction high-frequency process is used to manufacture pipes. High-frequency methods include flash welding, resistance projection welding, and upset welding.

Advantages
There are myriads of benefits of resistance welding to use it in industry and on commercial scale. These advantages have increased its use in every filed.
• Welding speed is high
• No flux or protecting gases are required
• Rate of production is high
• The method is simple and does not need high expert labor
• All types of metals can be weld.

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