Part of what makes MIG welding what it is, is the transfer of metal, via heat, from the electrode (or welding wire) to the base metal(s) being welded. There are four different transfer types available to MIG welders, and each has its benefits, uses, and drawbacks. Each type is a result of the voltage settings and shielding gases used, so it’s crucial to be aware of how your voltage and gas selection will interact to generate the transfer type.
Short Circuit Transfer
Short circuit transfer occurs when, as the name suggests, the welding wire touches the metal(s) being welded. Electricity from the gun courses through the wire and creates a short circuit. Within the circuit, the welding wire heats up and drips onto the base metal(s), creating a “puddle” that welds the joint. The welding wire heats and drips multiple times a second, and the process produces a fast crackling sound, like something frying in a very hot pan.
Short circuit transfer is achieved using a combination of low voltage and a carbon dioxide shielding gas or gas mixture. One benefit of the short circuit transfer is that the required shielding gases are less expensive. The limitation is the thickness of the base metals this type of weld can handle. It’s used on sheet metals or thin metals measuring a quarter of an inch or less – anything thicker will prevent the low-voltage weld to penetrate the joint well.
Globular transfer is similar to short circuit transfer, with the main difference being the speed and intensity of the dripping from the welding wire to the joint. With a globular transfer, the wire melts and collects in a “glob” at the end of the wire, dripping into the joint only a few times per second. Rather than sounding like a sizzle or a crackle, globular transfer pops.
Globular transfer happens with a combination of high voltage and an argon shielding gas or gas mixture. One benefit of globular transfer is that it can handle welding thicker metals, but a drawback is that the drops aren’t always easily controlled and can lead to spatter.
Spray transfer happens when the welding wire melts into very fine droplets and sprays, or “mists,” onto the base metals being welded together. A good spray transfer will make a hissing sound, rather than a crackle or popping sound. Another characteristic of a good spray transfer is a clean arc from the welding gun to the base metals.
Spray transfer is achieved with a combination of high voltage and an argon shielding gas or gas mixture, though if carbon dioxide is more than about 15% of the gas mixture, the electrode will never make the transition from globular to spray, no matter how high the voltage goes. This type of transfer is often preferred for welding thicker metals because, when done correctly, it has no spatter. The shielding gas or gas mixture can be expensive due to the high argon content, however.
Pulsed Spray Transfer
Pulsed spray transfer, unlike the other transfer types, requires a high-end welder. The welder, when set to pulse, pulses the voltage instead of providing the usual steady flow of voltage. The pulses occur many times a second, and the result is a transfer that alternates between spray and globular transfer.
Because the voltage is pulsed, it doesn’t have to be quite as high as with regular spray transfer. This is beneficial because it decreases the overall amount of heat being applied to the weld, allowing for a smaller, neater weld pool and joint. The smaller weld pool also allows for greater flexibility with weld positions, making it ideal for welding pipe and other difficult projects. The main drawback is the greater expense associated with welders that provide this function.