Arc voltage is also one of the important welding parameters in CO2 gas shielded welding. When the wire feeding speed is constant, adjust the external characteristics of the power supply, the welding current is almost unchanged, the arc length will change, and the arc voltage will also change. Figure 《Influence of arc voltage on welding seam shows》 the influence of arc voltage on weld forming.
U-welding voltage ; vD-wire feed rate ; I-welding current
With the increase of arc voltage, the weld width increases obviously, the weld depth and residual height decrease slightly, and the weld forming is good, but the oxidation and spatter of weld metal increase, and the mechanical properties decrease. In order to ensure good weld forming, the arc voltage must be properly matched with the welding current. Usually when welding current is small, arc voltage is low; When the welding current is high, the arc voltage is high, and this relation is called matching. When welding bottom weld or space position weld, short circuit transition is often adopted. In vertical welding and inverted welding, the arc voltage should be slightly lower than the horizontal welding position to ensure the stability of short circuit transition process. During the short circuit transition, the droplet transitions drop by drop in the short circuit state, the molten pool is sticky, and the short circuit frequency is 5~10Hz. When the arc voltage increases, the short circuit frequency decreases. Figure 《The relationship between arc voltage and welding current during short circuit transition》 shows the relationship between arc voltage and welding current in short-circuit transition mode. Normally, the arc voltage is 17~24V.
As shown in Figure《The relationship between arc voltage and welding current during short circuit transition》, the arc voltage increases with the increase of welding current. Too high or too low arc voltage has adverse effects on weld forming, spatter, porosity and arc stability. It should be noted that welding voltage and arc voltage are two different concepts and should not be confused. Arc voltage is the voltage measured between the conductive tip and the weldment; The welding voltage is the voltage shown by the voltmeter on the welder. It is the sum of the arc voltage and the voltage drop on the connecting cable between the welder and the welder. Obviously the welding voltage is higher than the arc voltage, but for the same welding machine, when the cable length and section is unchanged, the difference between them is easy to calculate, especially when the cable is short, thick section, because of the cable voltage drop is very small, can be used to replace the arc voltage welding voltage; If the cable is very long and the cross section is small, the voltage drop on the cable cannot be ignored. In this case, replacing the arc voltage with the welding voltage read from the welder voltmeter will cause a large error. Strictly speaking, the voltage read on the coal miner voltmeter is welding voltage, not arc voltage. If you want to know the arc voltage, you can calculate it by following the formula:
Arc voltage = welding voltage – correction voltage
The corrected voltage can be obtained from Table 《Fixed voltage and cable length 》.
Welding speed is also one of the important welding process parameters of CO2 gas shielded welding. During welding, the arc blows the molten metal apart, forming a pit under the arc, and then the molten wire metal is filled in. If the welding speed is too fast, the pit cannot be completely filled, resulting in defects such as edge and sag. On the contrary, if the welding speed is too slow, the deposited metal is piled up below the arc, so that the welding depth is reduced, and the defects such as uneven pass, incomplete fusion and incomplete penetration will occur. Figure 《Influence of welding speed on weld forming》 shows the influence of welding speed on weld forming.
As can be seen from Figure《Influence of welding speed on weld forming》, when the diameter of welding wire, welding current and arc voltage remain unchanged, the weld width and weld depth decrease as the welding speed increases. If the welding speed is too high, in addition to the defects such as edge biting, incomplete welding, incomplete fusion, due to the deterioration of the protection effect, there may be air holes; If the welding speed is too low, in addition to reducing productivity, welding deformation will increase. General semi-automatic welding welding speed within the range of 5-60m/h.