Resistance Spot Welding-Introduction

A sub type of Resistance welding, resistance spot welding or RSW is probably the simplest one among the welding processes, and it is best suited to weld simple sheet steel. However, the quality and strength of the weld depends largely upon the cleanliness of the surfaces of the parts to be welded. The electrodes used to perform the welding process are made up of high strength.

The very basic advantage of this method is that it can be used for both ferrous and non-ferrous metals. However, the current to be passed and the pressure to be applied depend upon the materials to be welded. For materials having higher thermal conductivity, higher current for short span of time is required than for materials having lower thermal conductivity. Similarly, ductile and dissimilar metals can be welded only if the difference between conductivity and the melting point is not too much.

The size and the shape of the weld depend largely on the electrodes used. The equipment used for resistance spot welding is simple even for complex welding; however, for mass production, a press type machine is used, which constitutes multiple guns holding the electrode tips.

Process of Resistance Spot Welding

The process involves holding the pieces to be welded between two electrodes and pressed, a low voltage and sufficient amperage current is allowed to pass through the electrodes making the pieces to attain stage where they could be welded, and pressure is applied. After a short time, current is switched off but the pressure is still there until the weld cools and attains full strength. Then the job piece is removed from the machine and the next job piece is placed.

Different time periods involved

Weld Time

It means the time for which the current is passed between the electrodes.

Hold Time

It is the time for which the pieces are held by electrodes even after the current is switched off.

Off time

It is the time that involves removing the finished job from the machine and placing a new one.

Squeeze time

After placing the new job piece, current is allowed to pass; and this time is known as squeeze time.

Advantages of resistance spot welding

Resistance spot welding is advantageous over other techniques commonly used, and some of them are listed below:

" High speed
" Ease of automation
" Energy efficiency

Risks involved in resistance spot welding

As with almost all types of welding processes, there are some risk factors involved with resistance spot welding also. However, with care and attention, these can be avoided or reduced. Some of the risk factors involved are listed below:

" The process involves handling and setting the equipments and jobs, which can sometimes crush fingers or hands of the operator.
" There is potential threat to the eyes from splash metal.
" The production of harmful fumes while working with oil or organic materials makes it risky for the operator. Proper and adequate safety measures should be addressed.

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