Short Answer:

Resistance welding is a process in which heat is generated by the resistance offered to the flow of electric current through the metal pieces that are to be joined. The metal parts are pressed together, and the combination of heat and pressure creates a strong joint. It does not require any filler material or flux for joining the metals.

This welding method is widely used in the manufacturing of automobile parts, wire mesh, and sheet metal products. It is clean, fast, and can easily be automated, making it suitable for mass production. Common types include spot welding, seam welding, and projection welding.

Detailed Explanation :

Resistance Welding

Resistance welding is a type of fusion welding process that joins metals by applying both electrical and mechanical energy. The basic principle behind this process is the generation of heat due to the resistance offered by the metals to the passage of electric current. When a high current passes through the contact surfaces of two metal sheets under pressure, the localized heat generated at the interface melts the metal, and upon cooling, a strong joint is formed.

This process requires two main components: electrodes and a power source. The electrodes apply both pressure and current to the workpieces, while the power source supplies the required electrical energy. Resistance welding is particularly suitable for joining thin metal sheets and similar materials where quick, consistent, and clean joints are required.

Principle of Operation

The working principle of resistance welding is based on Joule’s Law, which states that the amount of heat generated is directly proportional to the square of the current, the resistance, and the time for which the current is applied:

H = I² × R × t

Where:

H = Heat generated
I = Current
R = Electrical resistance
t = Time of current flow

When the metal pieces are pressed together between two electrodes, the contact area offers electrical resistance. The current passing through this small area generates heat, causing localized melting. When the current is stopped, the molten metal solidifies and forms a permanent joint under the continuous pressure of the electrodes.

Equipment Used

A typical resistance welding setup includes:

Power Supply: Provides a high current at low voltage.
Electrodes: Made of copper alloy to conduct current and apply pressure.
Workpieces: Metal sheets or wires to be joined.
Control Unit: Regulates the duration of current and pressure applied.

The electrodes also serve as clamps to hold the workpieces together and ensure uniform current distribution.

Types of Resistance Welding

Spot Welding:
This is the most common type of resistance welding. It joins metal sheets at small points using two electrodes. It is mainly used in car bodies and sheet metal fabrication.
Seam Welding:
This process is similar to spot welding, but instead of separate spots, it produces a continuous seam using rotating wheel electrodes. It is used for making leak-proof joints like in fuel tanks and pipes.
Projection Welding:
In this method, small projections or raised points are made on one of the workpieces. When pressure and current are applied, the projections concentrate the heat and form the joint. It is often used for fasteners or nuts.
Butt Welding:
The ends of two rods or wires are pressed together, and the current flows through the joint, fusing them end to end. It is commonly used in the wire and rail industries.

Advantages

No filler material or flux is required.
The process is fast and can be easily automated.
Produces clean and strong joints.
Suitable for thin metal sheets.
Little or no fumes, sparks, or smoke are produced.

Disadvantages

Not suitable for thick sections.
High initial equipment cost.
Limited to electrically conductive materials.
Precise control of current and pressure is required.

Applications

Automotive body manufacturing.
Production of wire meshes and grids.
Joining of metal containers and pipes.
Fabrication of household appliances.
Electrical and electronic components assembly.

Conclusion

Resistance welding is an efficient, clean, and economical process widely used for joining sheet metals. It works on the principle of heat generation through electrical resistance, eliminating the need for filler materials. Although it has certain limitations, its ability to produce strong and consistent joints at high speed makes it one of the most popular welding methods in modern manufacturing and mass production industries.