Seam Welding Machine

For some welding processes, heavy industrial welding devices are necessary, which are generally not available to small operators, whether these are home users interested in welding or independent welders who specialize in small-scale fabrication or repair. One of the welding processes that needs massive pieces of equipment and a precisely-calibrated manufacturing procedure is seam welding.

Seam welding produces long, extremely tough welds between two pieces of metal (although there is also a secondary branch of ultrasonic seam welding used for plastics). This type of welding is used in the construction of fuel tanks, pipes, and other metal tubes and cylinders, where a long, tough weld is essential to the stability of the finished workpiece. A seam welding machine can produce a continuous weld of almost any length, as long as more metal sheeting continues to be fed through it.

There is a practical upper limit to the thickness of the pieces that can be welded together, because seam welding makes use of the electrical resistance principle to heat and fuse the metal. If the metal were too thick, the electricity would be diffused too much laterally and heat would not be generated properly to effect the weld. A seam welding machine is an interesting application of electricity’s properties to make a weld that could not be created by standard means.

Seam welding machines and electrical resistance

Seam welding machines operate in somewhat the same way as spot welding machines – the weld is created by bracketing the two metal parts with electrodes that have a strong current passing between them. The metal parts resist this current, and its energy is transferred to them in the form of sudden, intense heat throughout their thickness, since the current passes entirely through them, forming a circuit through both the upper and lower electrodes.

A seam welding machine uses two copper rollers or wheels as the electrodes. These rollers are electrified with a charge that is low in voltage, but very high in amperage – as much as 100,000 amperes may be used, depending on the type and thickness of metal pieces that are to be joined. The two pieces of metal are passed between these rollers, which travel along the seam between the two pieces, guided by precise computer adjustments of the roller position and the metal sheets’ position.

The rollers perform no less than three different tasks at once, all of which, when combined, form the seam welding process. The electrode rollers or wheels actually move the pieces of metal, sliding them forward so that new areas of the join are continuously brought in contact with the electrodes. They also squeeze the pieces of metal powerfully together, and they serve as electrodes, passing the powerful electric welding current through the metal in a continuous circuit.

The resistance welding effect of the electrodes is caused by the metal’s resistance to the electricity, which converts some of the electrical energy into heat energy at the point immediately between the upper and lower rollers. The metal is heated to a semi-molten state, and is simultaneously squeezed together by the rollers. This has the effect of literally squeezing the substance of both pieces of metal into each other – since they are semi-molten, both pieces are mashed together so that they flow into each other and occupy the same space, combined into a single piece by a combination of heat and pressure.

Of course, the seam welding machine does not simply do this at one point. It continues to roll the metal sheets forward between the electrodes, passing a continuous electric current through them as it does so. There is no pause in the welding process – the machine welds steadily, forming a constant seam that has no breaks in it and is completely uniform down its whole length.
 
There are a few variations on this process as well. Some machines perform a rapid series of spot welds in place of using electrode rollers, with each spot weld overlapping the last so that the welds form a continuous ribbon rather than a ‘stitching’ pattern. Plastic seam welding machines make use of an ultrasonic sonotrode in place of the electrode, with the mechanical vibration of the ultrasound replacing the electric current of the metal-fusing versions. The principle is largely the same, however – reducing the weld area of both pieces of material to a semi-molten state, then squeezing them so hard that they combine.