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3.jpg In the previous article, the Wick welder explained the welding processes and the principles behind welding cycles; here, we will go on to explain the principles of seam welding and spot welding. Resistance welding can be divided into spot welding, seam welding, and butt welding. There is no fundamental difference between seam welding and spot welding; seam welding can also be considered a variation of spot welding. In both cases, an appropriate combination of heat and mechanical force is applied to the welding area. Seam welding is sometimes used to weld ordinary, non-hermetically sealed sheet metals, with the thickness of the metal materials to be welded ranging from 0.1 to 2.5 mm. It is primarily used in the production of sealed containers and pipes. However, since a seam weld joint consists of continuously overlapping weld points, and since the formation of these weld points as well as the application of welding current and electrode pressure occur as the roller electrodes move while rotating (except in the case of step-seam welding), this makes the seam welding process more complex than spot welding, with its own set of characteristics. Additionally, there are more standard parameters for seam welding compared to spot welding. As for spot welding, it operates on the principle of two-sided, two-point current flow. During operation, the two electrodes apply pressure, causing the two layers of metal to come into contact with each other, thereby creating a certain contact resistance. When the welding current flows from one electrode to the other, this contact resistance generates heat that leads to instantaneous melting of the metals. The welding current then flows back from one electrode along the two workpieces to the other electrode, completing a circuit. This process does not damage the workpieces or their internal structures. Moreover, it features a simple metallurgical process, making it easy to automate and mechanize the welding process, as well as improving working conditions. Spot welding can generally be divided into two main categories: double-sided spot welding and single-sided spot welding. In double-sided spot welding, electrodes supply electricity to the welding area from both sides of the workpiece. In this typical method, there are electrode impressions at both ends of the workpiece; a conductive pad with a large surface area is used as the lower electrode, which helps to eliminate or reduce the impressions on the workpiece below. This method is often used for spot welding decorative panels. For double-sided spot welding that involves welding two or more points simultaneously, a single transformer is used with all electrodes connected in parallel. In this case, the impedance of all currents must be essentially the same, and the surface condition, material thickness, and electrode pressure at each welding site must also be identical in order to ensure that the current flowing through each weld point is roughly the same. Double-sided spot welding using multiple transformers is also an option. In single-sided spot welding, the electrodes are located on one side of the material to be welded, which is why it is called single-sided spot welding. For electrodes that do not form weld spots during welding, large diameters and large cross-sectional areas are used to reduce the current density. In single-sided double-spot welding without current splitting, the entire welding current flows into the welding area; in single-sided double-spot welding with current splitting, the current flowing through the upper workpiece does not pass through the welding area. To provide a low-resistance path for the welding current, copper shims are placed under the workpiece. When the distance between the two weld spots is large, during the welding of frame components and replicas, special copper bridges A are used – these are pressed against the workpiece together with the electrodes – in order to avoid improper heating that could cause the replica to warp and to reduce the resistance between the two electrodes. In mass production, single-sided multi-spot welding is widely used. At this time, a configuration in which one transformer supplies power and each pair of electrodes takes turns pressing on the workpiece can be used; or a configuration in which each pair of electrodes is powered by its own separate transformer, with all electrodes pressing on the workpiece simultaneously, can also be employed. The latter configuration has more advantages and is therefore more widely used. Its advantages include: each transformer can be placed as close as possible to the connected electrode. Its power and size can be significantly reduced ； The process parameters for each solder joint can be adjusted individually ； All solder joints can be welded simultaneously, resulting in high productivity ； Pressing all electrodes against the workpiece at the same time can reduce deformation ； Powering multiple transformers simultaneously ensures a balanced three-phase load. Summary: In fact, it’s not only the working principle of resistance welding that is like this; equipment from other brands also operates based on the same principles. I’ll have the chance to explain more about other resistance welding principles to everyone in the future!