A projection weld is a spot weld deformation in which a projection point is usually rushed out on one of two plates and then welded. Due to the concentration of current, the defect of spot welding deviating from the nucleus is overcome and the thickness ratio of the workpiece can reach 6:1 during the projection welding process. During the projection welding process, the electrode must drop rapidly with the compression of the projection point, otherwise spattering will occur due to pressure loss, so a larger electrode pressure should be selected. To prevent displacement of the projection, a smaller welding current should also be selected.
Process parameters of the projection welding machine:
Electrode pressure: The electrode pressure for projection welding depends on the properties of the weld metal, the size of the bump and the number of bumps to be welded at one time. When the bump reaches the welding temperature, the electrode pressure should be sufficient to complete the pressure and make a tight fit between the two pieces. Due to the effectiveness of the current density, too much electrode pressure can result in premature compression of the bump losing the role of the bump and reducing the strength of the joint. Too little pressure can cause severe spatter, so the higher the mobility of the protrusion welder, the better. The main ways to improve mobility are to reduce the mass of the moving parts of the pressurized system and to use rolling friction.
Welding time: For the given material and thickness of the workpiece, the welding time is determined by the welding current and the bump stiffness. Welding time is secondary to electrode pressure and welding current when bump welding low carbon and low alloy steels. After determining the proper electrode pressure and welding current, adjust the welding time to obtain a satisfactory weld joint. If you want to shorten the welding time, you need to increase the welding current accordingly, but excessive increases in welding current may result in overheating and spattering of the metal. Generally speaking, projection welding takes longer than spot welding, while the current is lower than spot welding. Multi-point projection welding takes a little longer than single-point projection welding, thus reducing the inconsistent height of heating at each point.
Welding current: The current required for each weld joint is less than the current required for the same weld joint. However, the current must be able to melt the projection before the projection can be fully compressed. The recommended current should be the maximum current to avoid squeezing too much metal at the proper polar pressure. For some projection sizes, the amount of extruded metal increases as the current increases. Using an increased amplitude regulated current can reduce the amount of extruded metal. As with spot welding, the properties and thickness of the weld metal are still the primary basis for selecting the welding current.
