by Jason Becker
Every welder should have a good understanding of modes of metal transfer (MOMT). In this video, we discuss three different modes of metal transfer and their purpose. In GMAW, modes of metal transfer rely heavily on the shielding gas composition, and the welding parameters. Voltage and wire feed speed will vary greatly from one mode to the next.
The globular mode of metal transfer is often used with 100% CO2 as it is a much cheaper gas than bi-nary (mix of two gases) or ternary (mix of three gases). The globular MOMT is just as it sounds, during the welding process, large irregular shaped globs of metal are formed at the end of the wire and fall into the weld pool. with this mode of transfer, spatter is highly prevalent because of the large dropplets of metal falling into the weld pool. Globular was used extensively in the past for high production sheetmetal welding due to the higher rates of travel that could be accomplished. Some of the disadvantages of this method of transfer is the higher levels of spatter, cold lap, incomplete fusion and bead appearance. Globular is also position restricted to flat fillets and grooves and horizontal fillets. Globular occurs between current levels of short circuit and axial spray.
Short circuit is exactly what it sounds like. The wire is creating a short-circuit 20-200 times per second during welding by making physical contact with the weld pool. Short-circuit is mostly run using a 75/25 mix of Argon (an inert gas) and C02 (an active gas)75% being Argon with CO2 as the remainder. Short-circuit is mostly used on thinner materials 5/16" and under and is not recommended on materials 1/4" or thicker due to it being prone to lack of fusion. Short circuit has the advantage of high travel speeds and no position limitations. Short-circuit is also used frequently in root welds on pipe due to its rapid solidification. The short circuit MOMT takes place with lower current values compared than globular and axial spray.
The Axial Spray MOMT is primarily used for thicker materials but is restricted to flat fillets and grooves, and horizontal fillets. Due to the higher current required for Axial Spray, the wire forms fine dropplets which are "sprayed" into the weld joint. Travel speeds are another added benefit of this MOMT. Axial spray is a great choice when weld appearance is a factor as it produces high quality aesthetic welds. Spatter is also almost completely eliminated with this method of transfer.
For additional information on the different modes of metal transfer, check out the video in the link above. I hope that you found the information in the video and article of value and that you learned something along the way. On behalf of the weld.com crew, we thank you for your support and until next time Make Every Weld Better Than Your Last!