Seam welding process

Seam welding is a resistance welding process wherein coalescence is produced by heating the job with an electrical resistance (obtained by an electric current (flow) through work parts) held together under pressure by circular rolling electrodes on the fraying surface.

Seam welding

Usually, an overlapped resistance-spot weld is produced by Resistance seam welding. In this process, a weld formed with a joint by rotating the circular electrode.

 

Principle of operation

The seam welding process is similar to the spot welding process, but the used electrodes are different from spot welding. In this welding process

seam welding, circular rolling electrodes are used to produce a continuous air-tight seam of overlapping welds.

As indicated in the figure, a step-down transformer (low voltage, high current) is used in this process that supplies energy to the weld joint in the form of AC power. The joint has a high electrical resistance relative to other circuits by which it is heated to the melting point and the semi-molten surfaces are pressed together. Water cooling systems are used to cool most of the heat generated.
 

 

A current impulse is driven through the rollers to the workpiece in contact with them. The heat generated thus makes the metal plastic and the pressure from the electrodes completes the weld.

As the first current impulse is applied the power-driven circular electrodes are set in rotation and the workpieces steadily move forward. Throughout the welding period, the electrode’s role, and the work passes through them at a specific speed. The current applied to welding electrodes is intermittent i.e. it is on for a definite length of time and then off for another definite and short period.

 seam weldingFor stitch welding, the current is put off and on speedily, as a result, a continuous fusion zone creates overlapping nuggets.
but using constant and regularly timed interruptions of the welding current, individual spot welds(or nuggets) are obtained, this process is known as Roll(spot)welding.

 

Seam welding methods

 

There are two welding methods, One involves continuous motion and the other intermittent motion during the welding operation.

Continuous motion 

In this method, the electrodes rotate at a constant speed and the current flows continuously or is interrupted.

Intermittent motion

In this method, the entire process is being controlled automatically. Continuous motion is used for welding workpieces less than 4.5 mm thick.

Equipment used in Seam welding

 seam welding
Seam welding machines generally operate on single-phase A.C., though some are designed to operate on three-phase supply also.
The equipment needed for seam welding consists of :

Power supply 

A step-down(low voltage, high amperage current ) welding transformer and similar to the one used in the spot welding machine is used for the seam welding process.

Supporting element of electrodes

The lower electrode is connected to a supporting arm. that can be adjustable whereas the upper electrode is connected with and insulated from the operating head that is actuated by a hydraulic cylinder. The operating head applies the electrode force.

 

Advantages and limitations

The main advantage of this process is that gas-tight or liquid-tight joints can be welded by this process also single seam weld or several parallel seams may be produced.

The seam welding process has some limitations also, such as it can weld only with a straight or uniformly curved line.

Conclusion

Several metals can be welded by seam welding such as 

Low carbon, High carbon, low alloy, stainless steels, Aluminium, and its alloys, Nickel and its alloys, Magnesium and its alloys, etc.