Heat distribution during welding with resistance welding machine

UnderstandResistance welding machineThe heat distribution during welding allows everyone to better control them, and equipped with suitable electrodes and cooling methods to weld good products faster and better.

Resistance welding spot weldingThermal Balance and Temperature Distribution

When spot welding with a resistance spot welding machine, part of the heat generated by the welding is used to heat the metal in the welding area to form a nugget of sufficient size, and the other part is used to compensate for the heat loss caused by conduction and radiation to the surrounding materials to form a dynamic heat balance in the welding process.
The balanced equation is as follows: Q=Q1+Q2
1) Effective heat Q1: It mainly depends on the thermophysical properties such as low resistivity of the workpiece, heat dissipation capacity, and the amount of melted metal, and has nothing to do with other welding parameters.Q1=(10%~30%)Q, take the lower limit for metals with low resistivity and strong heat dissipation ability; take the high limit for metals with high resistivity and poor thermal conductivity.
2) The lost heat Q2: mainly includes the heat conducted by the electrode and the heat conducted through the workpiece, and a small amount of heat radiated into the air.
The heat loss through electrode conduction generally accounts for 30% to 50% of the total heat, which is the part with the largest heat loss. This part of the heat loss is related to the electrode material, shape and cooling conditions, as well as the welding conditions. The heat loss of welding with strong conditions is less than that of weak conditions. The heat loss radiated from the workpiece surface is very small and can be ignored.

The temperature field in the welding zone is the comprehensive result of heat generation and heat dissipation.Due to the heat dissipation effect of the electrode, the axial growth rate of the molten nugget is slower than the radial growth rate, so it takes the shape of an ellipsoid.

Resistance weldingTemperature distribution of seam welding

It is slightly different from spot welding. Since the nugget is continuously formed, it has a post-heating effect on the welded parts and a preheating effect on the unwelded parts. Therefore, the temperature distribution is more average than that of spot welding. Also, due to the shunt heating of the welded parts and the deterioration of heat dissipation conditions after the disc electrode leaves, the temperature distribution is asymmetrical along the forward direction of the workpiece. The side that has just left under the disc electrode has a higher temperature. The higher the welding speed, the worse theThe symmetry is more obvious. This phenomenon can be improved by using strong conditions (i.e. hard specifications) or step seam welding, which is close to the temperature distribution of spot welding.
The flatter the temperature distribution curve, the larger the heat-affected zone of the joint, the easier it is for the workpiece surface to overheat, and the easier it is for the electrode to wear. Therefore, strong condition welding should be used when the welding power allows.

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