Double-sided spot welding and spot welding is usually divided into two major categories of single-sided spot welding. Double-sided spot welding, the electrode on both sides by the workpiece fed to the welding. A typical two-sided spot welding as shown in Figure 11-5. A chart is the most common way to have electrodes on both sides of the workpiece when the indentation. Figure b said welding area with large plate made of conductive lower electrode, which can eliminate or reduce the following parts of the indentation. Commonly used in the decorative panel spot. The figure for the same c spot welding two or more two-sided spot welding, using a transformer to the electrodes in parallel, this time, the impedance of all current paths to be almost equal, and each welding wires of the surface state, material thickness, electrodes are subject to the same pressure to ensure that the current through all basically the same spot. D more than the figure for the introduction of double-sided multi-spot welding transformer, so to avoid c deficiency.
Single-sided spot welding, the mig electrode was in the same side of the workpiece feed welding, a typical single-sided spot welding as shown in Figure 11-6, Figure in a single-sided single-spot welding, the electrode is not formed solder joints large diameter and large contact surface to reduce the current density. Figure b is no double-sided shunt little welding, all welding current flows through the welding time zone. Figure C are double-sided shunt little welding, the workpiece above the current flowing through the welding zone without form romantic. In order to provide a low resistance welding current path, in the copper plate underneath the workpiece. Figure d is the distance l when the two large joints, such as frame components and complex plate during welding, in order to avoid undue heating caused by multiple board warpage and reduce resistance between two electrodes, using a special Copper Bridge A, and also pressed on the workpiece electrode.
In mass production, the single multi-spot welding is widely available. At this time can be powered by a transformer, to suppress the rotation of the workpiece electrode pattern (Figure 11-7a), also can be used by each of the separate transformer power supply electrodes, all electrodes simultaneously press and hold the workpiece type (Figure 11-7b). The latter type has more advantages, applications are more widely used. Its advantages are: the transformer can be obtained from the joint placement of electrodes recently, so.
The power and size can significantly decrease; each solder process parameters can be individually adjusted; all joints can welding, production rate; all electrodes simultaneously press and hold the workpiece, can reduce the deformation; more than one power transformer at the same time, to ensure the three-phase load balancing.
Aluminium welding electrode is divided into two categories, the first class to the main heat-resistant surface coated with a 20-25 micron thick Al-Si alloy (containing Si6-8.5%), resistant to high temperature of 640 degrees. The second category of corrosion mainly for the pure aluminum coating, the coating thickness is 2-3 times the first class. When these two types of welding galvanized steel can get a good solder joint strength.
As the conductive coating, thermal conductivity, therefore requires a large welding current. And copper alloys should be hard spherical electrode. The following table Aluminium welding wire for the first spot welding conditions. For the second category, the coating thickness should be used in a larger current and a lower electrode pressure.