Q. In most of the articles I see in Sport Aviation, I see builders using gas to weld tube for aircraft fuselages. I recently bought a Lincoln 220V wire-feed MIG welder for a business venture with the thought that, at some point in the future, I would be able to use it to build other projects, one of which might be an airplane. It will accept a gas bottle for shielding although I have not used that option yet. Can this type of welder be used to weld tubing in an aircraft fuselage?
A: Yes, a properly welded MIG (GMAW) joint will be more than acceptable for an aircraft fuselage. However, amateur builders need to think about more than just the strength of a properly welded joint. MIG welding's primary advantage over TIG (GTAW) or oxyacetylene "gas" (OFW) welding is speed. From a production standpoint, speed makes MIG the preferred welding process. Speed isn't as important to homebuilders compared to price and ease of attaining and maintaining proficiency.
MIG is more expensive than gas welding but about half the price of TIG. From a cost standpoint, MIG sounds like a reasonable option, and it's probably the easiest method to learn for welding thick, flat material (just pull the trigger and go!). But for a fuselage, you need to weld thin wall tubing, and this is probably the most difficult use of the MIG process. Even experienced, professional MIG welders have difficulty the first time they attempt to MIG weld thin wall tubing.
For builders learning to weld so they can build their fuselages, learning and maintaining TIG or gas welding proficiency is easier than MIG. This is one reason why most of the articles mention these welding methods. However, because you'll be using MIG regularly in your business, all it will take is practice to be able to transition to MIG welding thin wall tubing.
In researching this answer, we spoke with Richard Finch, an aerospace engineer, Technical Counselor, Flight Advisor, and author of Performance Welding and Welder's Handbook (both available from EAA at 800-843-3612), and he agreed with the above. "The only thing that I would add is that most of the kit-plane manufacturers use MIG for speed and accuracy, but they practice, practice, practice before they turn a welder loose on a salable MIG weldment." For detailed information about the pros and cons of welding thin wall 4130 tubing with MIG, see Performance Welding.