How to set the parameters of the spot welding machine

When using a power frequency AC power supply, the spot welding parameters of the spot welding machine mainly include welding current, welding (energizing) time, electrode pressure, and electrode size.

① Welding current Iw: The heat released from the welding piece is proportional to the square of the current, so the welding current is the most sensitive to the performance of the solder joint. When other parameters remain unchanged, when the current is less than the corresponding value, the molten nucleus cannot form, causing detachment. After exceeding this value, as the current increases, the molten nucleus rapidly increases, and the strength of the solder joint increases. Then, due to the increase in heat dissipation, the growth rate of the molten nucleus slows down, and the strength of the solder joint increases slowly. If the current is further increased, it will cause splashing and the strength of the solder joint will actually decrease. Therefore, it is generally recommended to choose a moderate current that is not sensitive to changes in the diameter of the molten core for welding. In actual production, the fluctuation of welding current is sometimes very large, and the reasons are: A. It is the fluctuation of the grid voltage itself or multiple welding machines being powered on simultaneously; B. Changes in the extension of ferromagnetic weldments into the welding circuit; C. Diversion of front to back points, etc; D. Conductive welding fixtures come into contact with welding machine electrodes, resulting in shunt flow.

② Welding time tw: The length of the power on time directly affects the amount of input heat. In the widely used synchronous control spot welding machines, the power on time is measured in multiples of the number of cycles (one cycle in China is 0.02s, and some welding machine manufacturers use computer controllers, and the power on time is measured in half a cycle). In the case of fixed other parameters, only when the power on time exceeds a certain minimum value does the appearance of molten nuclei begin, thus achieving the welding connection of the workpiece. As the electrification time increases, the melt nucleus first rapidly increases, and the tensile shear force also increases. When the selected current is high, splashing will occur when the molten nucleus grows to a certain limit.

Choosing the shortest possible welding time is a priority process for the welding process, but according to factors such as different welding machine powers, welding workpiece forms, welding workpiece materials, and the number of welding points, the welding time must meet the conditions for the formation of molten nuclei.

③ Electrode pressure F: The magnitude of electrode pressure affects the numerical value of the workpiece contact resistance, the amount of heat evolution from the surface, and on the other hand, it affects the heat dissipation from the weldment to the electrode. From the perspective of energy conservation, the minimum electrode pressure that does not generate splashing should be selected.

When multiple welding machines are continuously welding, special attention should be paid to the stability of the compressed air flow rate and pressure output of the air source. When the flow rate and pressure output are unstable, it is easy to generate splashing or detachment.

④ Electrode working surface size: When the welding current is constant, a smaller electrode working size increases the current density and enhances the welding ability. Therefore, it is necessary to repair the electrodes of the intermediate frequency spot welding machine in a timely manner after a certain period of welding to ensure the consistency of welding current density and the stability of welding quality.

The size of the electrode working surface has a significant impact on the surface aesthetics of the weldment and the stability of the weld nugget size, and special attention should be paid.

It should be noted that during point (row) welding, various parameters are interdependent. For different welding materials and working conditions, various combinations of parameters can be selected for most occasions.