In a resistance welding, heat is generated by passing electric current through high resistance. The amount of heat generated depends on the value of current and resistance as shown in the formula.
H = I2 · R · t Joul
where I = Current in ampere, R = Resistance in ohm, and t = Time in second.
When the electric current is passed through the welding members, they offer maximum resistance at the interface in comparison to other parts of the member. Hence largest heat is generated at the interface. When the proper temperature is reached, the pressure is applied to complete the weld. Because of application of pressure, the process requires lower temperature as compared to oxyfuel gas or arc welding as the metal has to reach the softened state, not in the molten state.
There are six types of resistance welding: spot welding, seam welding, projection welding, flash welding, percussion welding, Butt welding.
Advantages
- This is fast process and suitable for mass production.
- No fluxes or filler materials are required.
- Less skilled operators may be employed.
- Practically all conductive materials can be welded by this method.
Limitations
- Few metals like tin, zinc, and lead are difficult to weld by this method.
- Control of pressure and current during the process is critical.
- Equipment cost is high.
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