Artem Komarov clarified that seam welding is a resistance welding process in which two metals are joined by applying heat generated by resistance to electrical current and pressure applied by electrodes. The resulting weld is a series of overlapping spot welds made progressively along the joint by rotating round electrodes.
Komarov Artem explained how seam welding works.
Seam welding is similar to spot welding, except that circular rolling electrodes are used to produce a continuous, airtight seam of lap welds. Lap (spot) seams are made by rotating electrodes and regularly interrupted current.
Step 1: The parts to be seam welded are cleaned, stacked in an appropriate manner and placed between two round electrodes which press the parts together with the force of the electrode.
Step 2. A current pulse is applied through the rollers to the material in contact with them. The heat released in this way makes the metal ductile, and the pressure of the electrodes completes the welding.
Step 3. When the first current pulse is applied, the power-driven circular electrodes are rotated and the workpieces move forward evenly. During the entire welding period, the electrodes rotate, and work passes through them at a certain speed.
Current is applied to the welding electrodes for a certain period. If the current is turned off and on quickly, a continuous melting zone of overlapping nuggets is obtained, a process known as stitch welding.
If individual spot welds (or nuggets) are obtained by continuous and regular interruptions of the welding current, this process is known as roll (spot) welding. Roll welding simply connects two workpieces, while stitch welding creates gas-tight and liquid-tight joints.
There are two methods of seam welding. One involves continuous motion and the other includes intermittent motion during the welding operation.
Continuous Motion / Seam Welding
In continuous motion seam welding, the electrodes rotate at a constant speed and the current flows continuously. The workpiece passes through the electrodes and a uniform weld is formed on the workpiece. Continuous motion is generally used for welding workpieces less than 4.5mm thick.
Intermittent seam welding
In intermittent motion welding, the electrodes travel the distance required for each successive weld and then stop. Then the current is turned on and welding is carried out, while the whole process is controlled automatically. Intermittent motion is usually used for welding workpieces with a thickness of more than 4.5 mm.
Rotating welding electrodes are cooled to prevent overheating, minimizing subsequent problems with dressing, and changing the wheel. In addition, the use of water-cooled nozzles immediately before and after the electrodes reduces warping of the materials to be joined.
Advantages of Seam Welding
• It can produce gas-tight or liquid-tight connections.
• Overlap may be less than for spot or raised seams.
• A single seam or several parallel seams can be sewn at the same time.
• This is a fast-welding process that can be automated.
• No filler metal required.
Disadvantages of Seam Welding
• Welding can only be done in a straight line or evenly curved line.
• Thicknesses over 3 mm are difficult to weld.
• A redesign of the electrode wheels is required to avoid obstacles in the way of the wheels during welding.
Application of seam welding
• Girth welds can be made in round, square or rectangular parts.
• Most general industrial metals can be welded with the exception of copper and high copper alloys.
• In addition to overlap welding, seam welding can also be used to make butt welds.Metals that can be welded
The following metals are satisfactorily welded by seam welding:
• Low carbon, high carbon and low alloy steels.
• Stainless steel and many coated steels.
• Aluminum and its alloys.
• Nickel and its alloys.
• Magnesium alloys.
Seam welding machines are similar in design to spot welding machines, except that the electrodes are mechanically driven rotating disks. As a rule, seam welding is performed on a pressure-type resistance welding machine with means for driving the electrode wheels or moving the workpiece between the electrodes and using a direct-acting pneumatic or hydraulic cylinder to provide the necessary electrode force.
Seam welding machines usually run-on single-phase AC, although some are designed to run on a three-phase power source. The equipment required for seam welding consists of:
Source of power
A power source capable of supplying low voltage, high current, and similar to that used in spot welding machines.
Electrode strength and support
The lower electrode is fixed on the support bracket. The top electrode is mounted and isolated from the working head, which is driven by a direct acting air or hydraulic cylinder. The working head applies the force of the electrode.
Electrode or workpiece drive
A job can be moved in one of the following ways:
Electrode rotation with knurling or friction drive. Such a drive gives a constant linear speed regardless of the change in the diameter of the electrode. The knurling drive is not suitable when the highest welding quality and appearance is required
Electrode rotation by direct drive.
Direct drive is applicable to small diameter electrodes that cannot be driven by knurled or friction wheels due to workpiece gap interference or when the application (e.g., weld appearance) does not allow the use of an electrode pulley that has been roughened by the drive with rolling wheel.
Due to problems with the speed synchronization of the two welding electrodes, only one of them is activated. Welding speed can be kept constant despite electrode wear by means of a variable speed gear drive.
Controls for adjusting, synchronizing, and sequencing the application of welding current and force, as well as the speed of movement of the workpiece between the welding electrodes. There are three main types of seam welding machines:
Circular in which the ends of the electrode wheels are at right angles to the neck of the machine. This machine is used for circular jobs such as welding container lids, as well as for flat jobs that require long seams.
Longitudinal, in which the surfaces of the electrode wheels are parallel to the mouth of the machine, and the depth of the neck is usually 30 to 90 cm. This machine is used for welding short seams in containers, etc.
Versatile in which the electrode wheels can be mounted in either a circular or longitudinal position using a swivel type top head, in which the top wheel and its bearing can be rotated 90 degrees. The bottom mount could consist of two interchangeable lower arms, or both could be permanently attached to the machine via hinges or a swivel strut, so could be rotated into place, Komarov Artem specified.