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.
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
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 welding methods
There are two welding methods, One involves continuous motion and the other intermittent motion during the welding operation.
In this method, the electrodes rotate at a constant speed and the current flows continuously or is interrupted.
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
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.
Several metals can be welded by seam welding such as