Classification
Based on the rotation of the rollers, seam welding can be categorized as continuous, intermittent, and step-by-step seam welding:
1. Continuous Seam Welding: In continuous seam welding, the workpiece moves continuously between two rollers (i.e., the rollers rotate continuously), and the welding current also flows continuously through the workpiece. This method can easily overheat the workpiece surface and the vicinity of the weld nugget, causing severe motor wear and deep craters in the weld, and is therefore rarely used.
2. Intermittent Seam Welding: In intermittent seam welding, the rollers rotate continuously, the workpiece moves continuously, and the current flows intermittently. The resulting weld consists of overlapping weld nuggets. The intermittent flow of current allows the rollers and workpiece to cool during the rest period, thus extending roller life, reducing the width of the heat-affected zone and workpiece deformation, and achieving better weld quality without the drawbacks of continuous seam welding. In intermittent seam welding, the rollers leave the weld zone while the weld nugget cools, preventing sufficient forging. The weld nugget crystallizes under reduced pressure, which can easily lead to surface overheating, shrinkage, and cracks. 3. Step Roller Welding: During step roll welding, the roller rotates intermittently, and current flows through the workpiece while the workpiece remains stationary. Because the metal melts and crystallizes while the roller is stationary, pressure is present throughout the crystallization process, improving heat dissipation and consolidation. This effectively improves weld quality, extends roller life, and produces denser welds. This method is commonly used for welding aluminum and magnesium alloys. It can also effectively improve weld quality when seaming high-temperature alloys. However, this type of roll welding requires a relatively complex mechanical device to rotate the roller intermittently.
Depending on the joint type, roll welding can be categorized as lap roll welding, flattening roll welding, butt roll welding with foil pads, copper wire electrode roll welding, and auxiliary fixture roll welding.
1. Lap roll welding: Similar to spot welding, lap joints can be welded using a pair of rollers or a single roller and a mandrel electrode. The minimum overlap is the same as for spot welding. In addition to the commonly used double-sided roll welding, lap roll welding also includes single-sided single-seam roll welding, single-sided double-seam roll welding, and small-diameter circumferential roll welding. Single-sided roll welding can be used when the plate is wide or other factors restrict the rollers from approaching the workpiece from both sides. When welding small parts such as mounting brackets on the surface of a large part and requiring airtightness, roll welding with rollers placed perpendicular to each other can be used.
2. The overlap during flattening roll welding is much smaller than in standard roll welding, approximately 1 to 1.5 times the plate thickness. The joint is flattened during welding, resulting in a welded joint thickness of 1.2 to 1.5 times the plate thickness. Cylindrical rollers are typically used, and their width should fully cover the overlapped portion of the joint. High welding pressure and continuous current are used during welding.
3. To save metal, reduce weight, minimize deformation of the welded structure, and improve fatigue strength, butt roll welding using foil as a gasket can be used. The foil can be stainless steel, titanium alloy, or a similar metal.
4. Copper wire electrode roll welding is an effective method for preventing the coating from sticking to the roller during roll welding of coated steel plates. During welding, a round copper wire is continuously fed between the roller and the plate. The copper wire is continuously fed in its original shape, passing through the roller and then unwinding without contaminating the roller.
5. When welding bellows and diaphragm boxes, auxiliary clamps are often used for roll welding due to the thinness, low rigidity, and narrow weld zone of the parts. Typically, the clamp is made of copper alloy to ensure good conductivity and heat dissipation.
