What is the power heating stage of a medium frequency spot welding machine?

The power heating stage of a medium frequency spot welding machine is designed to create the required molten core between the workpieces. When the electrodes are powered with pre-applied pressure, the metal cylinder between the contact surfaces of the two electrodes experiences the highest current density.

This generates significant heat due to the contact resistance between the workpieces and the inherent resistance of the welding parts. As the temperature gradually increases, the contact surfaces between the workpieces begin to melt, forming the molten core. While some heat is generated at the contact resistance between the electrodes and the workpieces, most of it is dissipated by the water-cooled copper alloy electrodes. As a result, the temperature at the contact point between the electrodes and the workpieces is much lower than between the workpieces.

Under normal circumstances, the temperature does not reach the melting point. The metal around the cylinder experiences lower current density and thus lower temperatures. However, the metal near the molten core reaches a plastic state and, under pressure, undergoes welding to form a plastic metal ring tightly surrounding the molten core, preventing the molten metal from splattering outward.

There are two situations during the power heating process that can cause splattering: when the pre-pressure of the electrodes is too low initially, and no plastic metal ring forms around the molten core, resulting in splattering outward; and when the heating time is too long, causing the molten core to become too large. As a result, the electrode pressure decreases, leading to the collapse of the plastic metal ring, and the molten metal spills out from between the workpieces or the workpiece surface.

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