Understanding Voltage & Amperage in Welding

Gas metal arc welding (GMAW) is a welding process that happens when an electrical arc is established between a base material and a continuously fed wire electrode. The molten weld pool is protected from the atmosphere by a shielding gas that flows around the wire filler metal in the weld pool and the weld pool itself. The heat from the electrical arc melts the base metal and the wire filler metal being fed into the weld pool.

While many variables can influence a weld's quality, including the type and thickness of the base material, the four primary factors affecting it are welding current, welding voltage, contact-to-work distance, and travel speed.

Of all the welding factors, voltage and amperage cause the most confusion, especially in the novice welder. And since they are considered among the primary aspects that impact a GMAW weld, we will take a more detailed look at them.

What is amperage in welding?

The welding current is the variable that mainly controls the amount of weld metal deposited during the welding process. Amperage measures the strength of the electrical current, with its primary effect on welding being the melt-off rate of the electrode and the depth of penetration into the base material.

Wire feed speed (WFS), another of the welding variables, controls amperage and the amount of weld penetration. WFS and current are directly related: as one increases, so does the other and vice versa. If the WFS is set too high, it can lead to burn-through. That's because as the welding current increases, the weld penetrates deeper into the base material.

Take a look at Table 1: Welding Current Data to see how this works in practice. As you can see, the WFS was incrementally increased from Weld 1 through Weld 5, which, in turn, increased the welding current. Keep in mind that the welding operator sets the WFS--not the current level--on a GMAW-CV power supply. The primary way of adjusting the current is by changing the WFS.

You can see from the table that as the wire feed speed increased, so did the amperage. The results are evident in Figure 1: Cross-Sectional View of Welds 1 through 5.

Welding Voltage
Weld ID Number	Tager Welding Voltage	Welder Settings			Data Acquisition			Heat Input (kJ/in)
		WFS (ipm)	Voltage (v)	Travel Speed (ipm)	WFS (ipm)	Voltage (v)	Current (A)
1	100	150	24	15	151	24.5	111	10.88
2	150	250			252	24.7	162	16.01
3	175	325			331	24.8	193	19.15
4	200	300			462	24.9	212	21.12
5	250	615			618	25	254	24.40

 Table 1 shows the welding data from the following welds

Figure 1: Cross-Sectional View of Welds 1-5 (Table and Image Courtesy of EWI.org)

Notice the increase in weld penetration from Weld 1 to Weld 5. With the voltage and travel speed variables held constant, the increase in WFS and current indicates a substantially deeper weld moving from the 1st to the 5th.

Also, note the fingerlike penetration in Welds 3-5 caused by the metal transfer mode in the welding arc changing to "spray metal" transfer mode. The metal transfer mode typically transitions from globular to spray mode transfer above 190 amps of welding current for specific metal and shielding gas combinations.

What is welding voltage?

If amperage measures the volume of electrons flowing through an electrical current, voltage measures the pressure that allows them to flow. In other words, it's the carrying force of the electrical current. So, what effect does this electrical "pressure" (voltage) have on the weld? Welding voltage controls the arc length: the distance between the weld pool and the wire filler metal at the point of melting within the arc. As the voltage increases, the weld bead will flatten out, and its width-to-depth ratio will increase. Check out the weld data in Table 2:

Welding Voltage
Weld ID Number	Tager Welding Voltage	Welder Settings			Data Acquisition			Heat Input (kJ/in)
		WFS (ipm)	Voltage (v)	Travel Speed (ipm)	WFS (ipm)	Voltage (v)	Current (A)
7	18	325	17.5	15	328	18	177	12.74
8	21		20.4		328	21.1	174	14.69
9	23		22		327	22.7	173	15.71
10	26		25.2		328	26	185	19.24
11	30		29.2		328	30.1	208	25.04

 Table 2 shows the welding voltage data from the following welds

 Figure 2: Cross-Sectional View of Welds 7-11 (Table and Image Courtesy of EWI.org)

While the travel speed, wire feed speed, and amperage remained constant, the voltage varied. Clearly, the voltage has little impact on penetration. You can see the effects of voltage on the weld's surface, helping it lay flat and wash in at the edges. Too much voltage can produce a weld that is flat, concave or undercut. Too little voltage could yield a shoddy weld bead, or it can contribute to a lack of fusion.

Figure 2 shows this widening of the weld beads from 7 to 11 as the voltage is increased. You can see the penetration remained constant for Welds 7-9 since the current was unchanged. Welds 10 and 11 showed the same increase in fingerlike penetrations as in Welds 3-5, as well as an increase in welding current. As the arc length increases in proportion to the rise in voltage, the electrode extension, the distance from the contact tip to the point where the welding wire is melting in the arc, consequently decreases.

Welding amps per thickness of common types of metal

Anyone wishing to achieve optimal welding results should know how to set the proper amps according to the type and thickness of each metal. Refer to the chart below for welding amps per thickness for carbon steel and stainless steel.

Carbon Steel With 75 Percent Argon/25 Percent CO2 Shielding Gas

Thickness (ga.)	Wire Diameter (Inch)	Wire Feed Speed (IPM)	Current (amps)	Voltage
24	0.023	140-170	40-50	14-15
24	0.030	110-120	45-50	13-14
20	0.030	125-135	55-60	13-14
20	0.035	105-115	50-60	15-16
18	0.035	140-160	70-80	16-17
16	0.035	180-220	90-110	17-18
16	0.045	90-110	90-110	17-18
14	0.035	240-260	120-130	17.5-18
10	0.035	280-300	140-150	18-19
10	0.045	140-150	140-150	18-19
3/16	0.035	320-340	160-170	18.5-19.5
3/16	0.045	160-175	160-170	18.5-19.5

 

Stainless Steel With 90 Percent Helium/7.5 Percent Argon/2.5 Percent CO2

Thickness (ga.)	Wire Diameter (Inch)	Wire Feed Speed (IPM)	Current (amps)	Voltage
18	0.030	130-160	30-40	15-16.5
18	0.035	105-115	50-60	18-18.5
16	0.035	140-160	70-80	18-19
14	0.035	180-220	90-110	18.5-19
14	0.045	90-110	90-110	18.5-19
10	0.035	240-260	120-130	19-20
10	0.045	120-130	120-130	19-20
3/16	0.035	280-300	140-150	19-20
3/16	0.045	140-150	140-150	19-20

 

Remember the rule of thumb: Material thickness determines amperage, and each .001 inch of material thickness requires approximately 1 amp of output. (1/4" thickness, or .25" = 250 amps)

Do you have questions on amperage and voltage?

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