Quick Test - MIG Welding AluminumWritten by on October 3, 2013 Wrenchin' @ Random
If you want to weld aluminum, you might think skill-intensive TIG welding is the only way. However, if you already own a MIG welder, an add-on spool gun is a viable option. Retailing for $276, Miller Electric’s Spoolmate 100 Series gun costs far less than $1,000-plus TIG welders. We borrowed Miller’s Millermatic 211 Auto-Set MIG welder with a Spoolmate to find out what it’s like to MIG aluminum.
Why is a spool gun needed? A MIG normally pushes steel welding wire from the welder through the same cable that feeds current and gas to the handle. If you try to push soft aluminum through that cable, it bends and bird-nests inside. The add-on, 1-pound, 4-inch-diameter spool of wire mounted to a pistol-grip-style gun shortens the distance the welding wire needs to travel to prevent that problem.
There are still limitations with a MIG and aluminum. The thickness of weldable material is limited to 3⁄8 inch, and anything above ¼ inch requires preheating. On the other end of the spectrum, 18-gauge is the thinnest the spool gun can handle, although “it takes quite a bit of experience and detail to weld that thin,” says Ben Romenesko, Miller Electric’s product manager of integrated MIG systems.
Aluminum requires more heat to weld because it has different thermal conductivity than steel. MIG-aluminum welding uses the much hotter spray-transfer method, where the wire vaporizes before hitting the base material. Traditional steel MIG welding uses short-circuit transfer, where the wire repeatedly shorts out and burns back. When properly done, spray transfer doesn’t produce a weaker weld, but it does produce a lot more heat. “Because thermal conductivity with aluminum is so much higher than steel, you get a lot of burn-through with thin material,” Ben says.
Another cause for burn-through is the inability to adjust heat while MIG welding, like you can when using foot controls on a TIG welder. “You can’t get a great puddle going because wire-feed speed isn’t adjustable like with the foot pedal of a TIG welder. Also why TIG welding is more complicated and requires more skill, because there are so many variables the operator must maintain,” Ben says.
TIG welding is more complicated than MIG welding, no matter the base material; however, the MIG with an aluminum spool is still a MIG, meaning technique is basically the same—hold the gun with one hand and use your index finger to operate. This is why we liked the add-on spool: It’s easy! After one pass, we had stacked dimes like our dad taught us. Only slight changes needed to be made for MIG welding aluminum compared to steel: the gun-to-work distance needs to be slightly increased, beads can only be pushed (move the gun away from yourself while making a pass), and operation has to be much faster. “People often travel too slow, that’s most of their frustration,” Ben says. If you know how to MIG weld, then you know how to MIG weld aluminum. The spool add-on is tremendously easy to use.
Our Millermatic 211 Auto-Set can operate on either 110V or 220V when welding mild steel. Miller suggests that all MIG-aluminum welding be performed on 220V, but we found out it can be done on 110V—it just limits your range of material thickness even more. Max is roughly 1⁄8 inch, depending on preheating, wire size, and cleanliness. We didn’t try anything thinner than ¼ inch on 110V.
For a full-tilt hot rod shop, nothing beats a TIG welder, but for the guy with a single-car garage, multiple projects, and limited funds, an aluminum-spool add-on is a cost-effective alternative. “You don’t need the skills like a TIG welder,” says Ben. “A do-it-yourselfer can do a lot of different things with a MIG spool gun.”