Key electrical parameters of welding power sources include open-circuit voltage and duty cycle. CO2 gas shielded welding power sources use flat or gradually decreasing external characteristics, with an open-circuit voltage of 38–70V. Duty cycle refers to the welding power source's ability to operate continuously at a given current. National standards stipulate a rated duty cycle of 60% for manual welding and 60% and 100% for automatic or semi-automatic welding, respectively.
In CO2/MAG/MIG welding, the welding current and arc voltage must be strictly matched. Adjusting the welding current adjusts the wire feed rate, and adjusting the arc voltage adjusts the wire melting rate. Equal values of both ensure stable arc welding. At a constant welding current, a high arc voltage leads to large droplets and increased spatter; a low arc voltage leads to wire embedding in the molten pool, excessive spatter, and poor weld formation. Optimal matching of welding current and arc voltage results in a high droplet transition frequency, minimal spatter, and a beautiful weld formation.
Important operating parameters include wire extension length and wiring polarity. The longer the welding wire extension length (dry extension), the greater the resistance heat consumption, and the smaller the welding current displayed value compared to the actual welding current. Therefore, it is generally set within the range of 12-20mm. CO2 welding typically uses the DC reverse polarity method, meaning the workpiece is connected to the negative terminal of the power supply.
Power supply characteristics include static characteristics, dynamic characteristics, and arc self-regulation characteristics. The static characteristics (external characteristics) of CO2/MAG/MIG arc welding power supplies are required to be flat characteristics (constant voltage characteristics). Dynamic characteristics refer to the relationship between the output current and output voltage of the arc welding power supply and time when the load condition changes instantaneously, used to characterize the responsiveness to load transients. In a constant speed wire feeding system, the effect of arc length recovery caused by changes in current and melting speed due to changes in arc length is called the self-regulation effect of the power supply arc system. The finer the welding wire diameter used, the stronger this regulation effect and the more stable the arc.
Modern digital welding power supplies offer system flexibility; the same hardware circuitry can achieve different welding process controls, and has better stability and higher control precision. To adapt to harsh working environments, modern welding power supplies must have overcurrent, overvoltage, and overheat protection functions.
