What You Need to Know About: Seam Welding
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SEAM WELDING
Resistance seam welding is a type of electric resistance welding in which two sheets pass through discs, similar to the rolling process. However, these discs are energized conductive electrodes which, upon receiving electric current, cause the sheets to heat up by the Joule effect.
SEAM WELDING MACHINES
A seam welding machine is of similar construction to a spot welding machine, except that the discs are replaced by spot welding electrodes. Most seam welding machines are powered by alternating current (AC), some are designed for use with direct current (DC), others with high frequency (16.5 kHz) in the basic supply line. There are also stored energy seam welding machines, but this type is rarely used in the market. Power supplies with DC frequency converters are used for better control of welding pulses.
TYPES OF MACHINES
There are 03 basic types of resistance seam welding machines: Transverse, longitudinal, and universal.
Transverse: The rotation axis of the discs works at a transverse angle with the front of the machine. This type of machine is used, for example, for closure welding in containers, boiler covers, among others.
Longitudinal: The rotation axis of the rollers is parallel to the front. This type of machine is used for welding longitudinal seams, for fixing parts, for fixing coils, for welding tanks, reservoirs, cylindrical parts, flat sheets, etc.
Universal: A swivel-type head and interchangeable lower arms allow the rotation axis of the copper discs (electrodes) to rotate perpendicularly or in parallel.
ABOUT PROCESS VARIATIONS
Resistance seam welding is a process in which the heat generated by resistance to the flow of electric current in the workpiece is combined with pressure to produce a welded seam. Variations in the seam welding process can be classified as:
• Spot welding with discs (relatively large unwelded spacing between lenses)
• Spot welding with reinforced disc (small unwelded spacing between lenses)
• Watertight seam welding (no spacing between weld lenses) Two disc-shaped electrodes are used to apply current, force, and cooling to the metal to be welded.
When two discs are used, the drive can be performed on one or both; this drive can be direct through coupled shafts.
Other electrode systems for seam welding include a disc and a flat bar opposite the metal to be welded, or a wire feed system, where a copper wire is introduced into a groove of the disc. In this process, the feed wire continuously provides a new copper surface for contact with the metal to be welded.
In seam welding, a series of weld spots is made without retracting the discs (electrodes) or releasing the force between spots. The discs can rotate continuously or intermittently. The welding speed, working current, cooling system, application force, shape, and diameter of the copper disc are all interconnected and must be carefully selected to optimize the process and produce a quality weld.
ADVANTAGES AND LIMITATIONS
The advantages of resistance seam welding, compared to spot, projection, and laser resistance welding, are:
• Gas-tight joints can be produced (not possible with spot or projection welding).
• The width of the seam weld can be smaller than the diameter of the spot weld lens, as the electrode contour can be continuously profiled, determining the electrode/part contact area.
• High-speed welding (especially on thin sheets).
• The cost is generally favorable per meter of welded part.
• Coated steels are generally more weldable and used in seam welding compared to spot welding, as coating residues can be continuously removed from the discs (electrode) if special provisions are made.
• Coated steels are generally more weldable with seam welding compared to laser welding, as the volatilization of the coating is minimized by the intense pressure field in the weld zone.
• The hardness of air-cooled seam welds is lower than that of laser welds.
The limitations of seam welding, compared to spot and projection welding, are:
• Welding must normally be performed on a single plane or on a uniform surface.
• Obstruction along the disc (electrode) path must be avoided or compensated for in the roller design.
• External water cooling on the electrodes and in the welded zone may be required for high-speed welding. External cooling can increase costs due to the device for containing and removing water after welding.
• Materials requiring quenching heat treatment should not be seam welded without special considerations.
• Chrome-plated and painted parts are not seam welded.
SUKHA manufactures seam welding machines in transverse, longitudinal, and universal models, as well as the seam welding + roll bending model, suitable for welding motor housings, automotive reservoirs, and various cylindrical parts with a maximum bending diameter of 300mm.
In addition to the equipment in our portfolio, we also develop machines according to the client's needs, for seam, spot, butt, projection welding solutions, welding robots, TIG/MIG welding robots, welding centers, among others.
Contact us:
(51) 3075-9570