The temperature field in the welding area of a spot welding machine is the result of the combined action of heating and heat dissipation processes. The heat generated in the welding area cannot be used entirely to melt the base material. The effective heat required to form a sufficiently sized fusion core only accounts for 10% to 30% of the total amount. The majority of the remaining heat will be lost due to heat conduction and radiation to adjacent substances (including air, the interior of the plate, metal electrodes, etc.), forming a dynamic thermal balance in the welding process and maintaining the appropriate temperature in the welding area of the spot welding machine.
The factors that affect the effective heat capacity of spot welding machines include the specific heat capacity of the material, melting temperature, and volume of the melting core. In general, the heat lost by conduction to the metal around the solder joint accounts for about 20% of the total heat, the heat lost by conduction to the inside of the electrode accounts for 30% to 50% of the total heat, and the heat lost by radiation convection on the surface of the electrode plate to the air medium accounts for about 5% of the total heat.
1. Welding quality of spot welding machine: The adjustment cycle of power frequency AC welding machine is relatively long, and for a 50Hz power grid, the welding time adjustment resolution is 20ms. The time adjustment resolution of the inverter DC spot welding machine can reach 0.25ms (4kHz inverter frequency), with high control accuracy. The response speed of the feedback control of the inverter welding machine is significantly accelerated, and the output stability is good. Due to the influence of zero crossing current, the thermal efficiency of power frequency AC welding machines is low. Thyristors are used to regulate the current. When the current percentage is small, the zero crossing time is long and the impact is greater; The output current of the inverter DC spot welding machine is pulsating DC, and under the action of the circuit inductance, it is continuous DC output, with high thermal efficiency and stable welding heat input.
2. Welding speed of spot welding machine: Due to the influence of zero crossing current, the heating time of power frequency AC welding machine is relatively long. The inverter resistance spot welding machine has DC output, centralized heating, and shortened welding time.
3. Energy saving effect of spot welding machine: The power frequency AC spot welding machine operates at 50Hz, with high transformer losses, low welding machine power factor, and high circuit losses. The inverter welding machine transformer operates at a high frequency (1-4kHz) with minimal loss, and the DC output improves the power factor, resulting in significant energy-saving effects.
4. Volume and weight of spot welding equipment: The transformer iron core of the power frequency AC welding machine is relatively large, and the equipment is bulky under the same power conditions. The transformer of the inverter DC resistance spot welding machine is greatly reduced, and the equipment is relatively lightweight.
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