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Aluminum Workshop: What to know when changing shielding gas with pulsed GMAW

Q: Recently I bought a new high-end pulsing power supply, which has different modes for all of the common materials and wire diameters. I was getting great results with 3/64-in. 5356 wire and 100 percent argon shielding gas. When I changed to a mixture of 70 percent argon/30 percent helium, the arc became very long and almost uncontrollable. Can you tell me what the problem is?

A: I think I can. First of all, I will try to give a general description here, rather than use any one company’s equipment as an example. The most important thing to remember in gas metal arc welding (GMAW) is that you must feed wire at exactly the same rate as you burn it off. Constant-voltage (CV) GMAW power supplies do this by allowing the current to vary. In synergic pulsing power supplies, the pulsed waveform is usually programmed by attaching a computer to the power supply and using the computer to program the pulsed waveform.

The welder/programmer chooses a wire feed speed (WFS), then adjusts some or all of the detailed pulsing parameters so that he has the right amount of arc energy at that WFS to burn off the preset WFS. He does this for a number of WFSs. The computer then interpolates between the data points and you have a smooth waveform at all WFSs.

It’s important to understand that the arc, which was so carefully programmed, depends on a number of variables, one of those being shielding gas composition. Changing the gas mixture can increase or decrease the arc voltage significantly. If that happens, you will not have the correct arc energy to burn off the preset WFS. The consequence is the arc will become either really long or really short.

Be aware that you cannot change shielding gas mixtures indiscriminately when using pulsing power supplies. You must use the same gas mixture that the manufacturer used to develop the waveform. If you need or want to use a different gas mixture, contact the power supply manufacturer. It might have a waveform developed for your shielding gas mixture.

By the way, you can also play this “mode” game to your advantage. Remember that the power supply is only putting out energy—it doesn’t know what material it is welding. So, if no preprogrammed mode fits your application, try other modes. It is common to find carbon steel or stainless steel modes for specific aluminum applications. We recently had need of a pulsed mode for 3/16-in.-dia. 5183. We didn’t have one, but we found out that a mode for 1/8-in.-dia. carbon steel worked fine. Don’t be afraid to experiment.

About the Author
Aluminum Consulting Inc.

Frank Armao

President

Aluminum Consulting Inc.

440-479-0239

Frank Armao was an active member of the AWS D1 Committee, chairman of the AWS D1 Aluminum Subcommittee, and member of the Aluminum Association Committee on Welding and Joining. He also was the author of The WELDER's "Aluminum Workshop" column from 2001 to 2020.