Spot welding by resistance welding machine is a pressure welding method that uses electric current to weld according to the resistance heat generated by the joint, after matching through the workpiece according to the pressure applied by the electrode. It belongs to the high efficiency of pressure welding production and manufacturing and is suitable for processing and manufacturing industries such as light industry.
The actual nature of the resistance spot welding process is to use the resistive heat and the large amount of plastic deformation energy in the weld area itself to create metal bonds between two separate surfaces with metal atoms close to each other at lattice distance. The resistivity of spot welding depends not only on the type of metal, but also on the heat treatment, production processing method and temperature of the metal. Contact resistance exists for a short period of time and is usually present in the early stages of welding, in about two layers: when a thick oxide layer on the surface of the workpiece and electrode accumulates to a corresponding degree, it causes the resistance to expand, making it impossible to direct the current.
If the surface of the workpiece is relatively clean, the workpiece can only produce contact points locally on the rough surface due to the microscopic inhomogeneity of the surface, and the current at the contact point becomes smaller, resulting in the closure of the current lines at the contact point, thus increasing the resistance at the contact point. The resistivity and hardness of copper alloys are usually lower than that of workpieces compared to the resistance between workpieces REW and RC, and therefore have less influence on the melting core.
When the workpiece and electrode are determined, the resistance of the workpiece depends on its resistivity. Therefore, resistivity is an important component of the weld material. Metals with high resistivity (e.g. stainless steel) metals with low conductivity have good electrical conductivity (e.g. aluminum alloys). Resistivity depends not only on the type of metal, but also on the heat treatment, production processing method and temperature of the metal. Each spot welding electrode has its own individual pressurization system to ensure the quality of each spot welding joint.
