Weld Aluminum with a MIG Welder
TIG (GTAW) welding is not the only process capable of producing high-quality welds on aluminum alloys. The high degree of control that the process provides makes it well-suited to tackling very thin materials, but as material thickness increases, the relatively slow speed of the process becomes more apparent. When ease-of-use and cost-effectiveness are prime considerations in an aluminum welding application, many fabricators choose to implement MIG (GMAW). While the process fundamentals are unchanged from MIG welding steel, MIG welding aluminum requires some specialized equipment and additional care to achieve high-quality results with minimal frustration.
Delivering the Aluminum Wire
Much of the additional care required is focused within the wire delivery system, since the lower columnar strength of aluminum wire makes it susceptible to burn-back and bird’s nesting. MIG welding aluminum typically requires fabricators to choose between “push-pull” or “spool gun” welding torches.
The Push Pull Gun:
- Ideal when the workpiece can be brought within 15-25 feet of the power source
- Advantages: Lighter and more maneuverable; can utilize wire packaging of any size (meaning reduced changeover cost)
- Disadvantages: Reduced forgiveness to compounding issues in the feeding system
- Example: Spoolmatic 30A Spool Gun
The Spool Gun:
- Ideal when the workpiece cannot be brought close to the power source
- Advantages: Improved forgiveness in the wire feeding system
- Disadvantages: Less ergonomic; use is limited to 2# spools (meaning increased changeover cost).
- Example: Miller XR-Aluma-Pro Push-Pull Gun
Regardless of the MIG welding gun being used, it is critical to ensure that the MIG consumables used are properly sized and in good condition. For example, both gun types require contact tips. Ensure that the wire diameter stamped on the contact tip matches the wire diameter being used and that the contact tip is inspected periodically for the formation of a keyhole shape at either end that is an indicator of wear. As the contact tip wears, micro-arcing between the contact tip and wire can lead to costly burn-backs that are prevented by a quick change of consumables.
A typical carbon steel MIG welding setup will typically use steel liners, brass inlet and intermediate wire guides, and either V-groove or V-knurled drive rolls. Users of a push-pull gun will need to go beyond simply changing contact tips. When MIG welding aluminum, it is important to use ALL the following: U-groove drive rolls, Teflon inlet and intermediate wire guides, and Teflon liners. Ensuring that these components are properly installed (and dedicated for aluminum use only) will help to minimize the potential for wire shaving that can cause the liner to become clogged and complicate wire feeding. Likewise, users of bulk wire packaging such as drums should carefully read the drum’s set up instructions and carefully consider the drum placement and conduit routing to help keep the overall “drag” in the system as low as possible.
Selecting Aluminum Welding Parameters
As with welding steel, it is possible to weld aluminum using one of several “transfers” depending on the specific wire feed speed and voltage combinations used.
- Thin materials typically require a short circuit transfer that is the result of low wire feed speed and low voltage. These “low” settings help to minimize penetration to prevent burn-through from occurring. Attempting to use short-circuit on thick material without proper base metal preparation may lead to lack-of-fusion defects.
- Thicker aluminum is best welded using a spray transfer. The higher wire feed speeds and voltages required to achieve the stable spray transfer provides additional penetration. Attempting to use spray transfer on thin aluminum will require significantly higher travel speeds than when welding using short-circuit.
Aluminum & Modern Pulsed Waveforms
“Pulse” is a feature found on many modern power sources where the output of the power source is “pulsed” between a low “background” and high “peak” current. By offering the “best of both worlds”, pulsed waveforms are beneficial when welding a wide range of common aluminum thicknesses. Using thinner material as an example: the “peak” current maintains a stable arc when welding at the “low” settings needed for thin material while the “background” current helps to keep overall heat input low to further minimize the risk of both distortion and burn-through.
Looking through a welder rental supplier’s catalog will reveal that there are many choices to be made when selecting aluminum MIG welding equipment. Consult with these experts to learn which combinations are best for your application; they may even have MIG welding packages which can help to alleviate some guesswork by bundling popular options together.
Before pulling the trigger, make sure to purchase some 100% Argon (or 75% Helium/25% Argon shielding gas for a little extra “punch”), set the flow rate to 35-50 cubic feet per hour, and always remove the oxide layer from the weld zone! With some modern technology and a little knowledge, achieving great results when MIG welding aluminum doesn’t necessarily have to be difficult.
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