Welding aluminum with MIG
MIG welding is most often used to join steel or stainless steel together. But with the properly equipped MIG, aluminum can be easily welded as well. Many MIGs use a device known as a spool gun to weld aluminum. It is a small, pistol shaped device that holds its own small spool of wire. The spool is approximately 4 inches in diameter and for aluminum use, the spool weighs in at about a pound. Welding aluminum requires the same DC+ polarity as other solid wire fillers. However, 100% pure argon is normally used. At times Helium can be added to improve the penetration. However for thin material, pure Argon is preferred. Aluminum MIG welding takes place in the spray transfer mode, which happens at a lower threshold than in Steel. Spray transfer is different from short circuit MIG. Trying to weld aluminum in short circuit mode, can make a terrible, wadded up mess. Spray transfer is smooth, quite, and the molten ball of aluminum pinches off before a “short” is ever created. It is a very hot process and fairly rapid and requires a much higher wire speed rate. One of the most overlooked details is that usually, the next size up contact needs to be used with aluminum wire. The greater swelling that aluminum exhibits, will cause the wire to seize up in the tip, if room for heat expansion is not left. There are other methods of welding aluminum with a MIG, including simply using the standard gun with a Teflon liner installed. In this type of setup, the cable has to be kept very straight and free from kinks or tight loops to feed properly. Of course a larger tip should be used as well. Also a similar device to the spool gun is used called a push-pull gun, which uses the cabinet to hold and push the wire, while a drive roller in the gun’s body “pulls” the wire to keep the wire from bird’s nesting inside the liner.