Push or Pull’ Feeding Aluminum Wire

Compared to TIG welding, MIG welding offers several benefits when it comes to welding aluminum. It’s quicker, has a higher deposition rate and requires less operator training. It has its own challenges though, one being the best way to feed the aluminum wire. Aluminum has low columnar strength, and feeding it through a MIG gun has been likened to pushing a wet noodle through a straw. To address this issue, a few options include push systems, spool guns, and push pull systems. Choosing the right one will depend on your specific needs.

First, aluminum as a filler metal has the same oxidation problems as all aluminum and needs to be stored correctly for optimal use. Leaving aluminum wire exposed to air, either on the shelf or installed on the welder, will lead to oxidation, which adds resistance, can produce soot and can change the wire’s ability to feed smoothly. Before changing contact tips or checking the shielding gas to address feeding problems, make sure the problem isn’t oxidized wire.

PUSHING THE WIRE

In a standard MIG gun, wire is pushed from the drive motor in the welder or wire feeder through the gun cable. With aluminum wire, however, any resistance to pushing the wire, such as a bend in the gun cable, can lead to “birdnesting,” or the tangling of the wire between the drive roll and the liner. This is a common, time-consuming and costly problem. To clear it, the operator must stop welding, cut the wire, discard the wire in the gun, and re-feed new wire through the liner. Often, if the wire stops feeding, the wire may burn back to the gun tip. These “burnbacks” require the welder to clean or replace the tip before continuing.

The ability to successfully use a push system is in direct proportion to the wire thickness. Pushing the wire is not very dependable for thinner gauge (.030 in) aluminum wires. There’s little columnar strength and any resistance will most likely cause the wire to birdnest. To improve your aluminum wire feeding performance with this system, you should use U-groove drive rolls for greater surface contact with the wire, a Teflon liner to decrease resistance, keep the gun cable straight and free of bends, and maintain adequate drive-roll pressure. Thicker wire, such as 1/16 in, may be fed consistently in a push-feed system.

SPOOL GUNS

Many fabricators (especially in the boat and trailer markets), maintenance professionals and DIY’ers choose spool guns for their aluminum welding needs. A spool gun carries a 4 in (1 lb) spool and eliminates birdnesting and other issues associated with pushing thin aluminum wire through the cable. Spool guns can accommodate aluminum wire diameters from .023 in to 1/16 in and allow the operator to use longer cables (15 ft to 50 ft).

A spool gun with a direct connect feature allows you to switch between steel and aluminum set-ups fairly quickly. Note, however, that a spool gun needs to have the roll changed after every pound of wire is used, where a push or push-pull system can hold 8 lb or 15 lb spools. If you’re using several pounds of aluminum per day, the few minutes needed to change spools can add up. Plus, if you’ll be welding for long periods of time, holding a 1 lb spool of aluminum in your hand may become an issue. For heavy-duty fabrication needs, push-pull guns may be a better choice.

PUSH-PULL GUNS

A push-pull gun has one motor in the gun to pull the wire through the liner and uses the motor in the welder or feeder control to push. This system maintains a consistent tension on the wire to ensure smooth feeding and eliminate birdnesting.

Since the most commonly used aluminum wires, 4000- and 5000 series, have different mechanical properties (4000 series is softer; 5000 series is harder and more abrasive) they require different tension settings. While some welders believe more is always better and add as much tension as possible, too much tension can deform the wire, create metal shavings and lead to feeding problems. However, some push-pull guns have series-specific tension settings to eliminate the guesswork.

Push-pull guns are more ergonomic than spool guns, since the weight of the spool is not in the operator’s hands. For higher volume aluminum fabricators, that may be a prime consideration. In addition, the spool needs to be changed less often than on a spool gun and allows the purchase of larger spools.

One welding distributor, picked at random, lists a 1 lb spool of .035 in 5356 aluminum wire at $5.42. A 16 lb roll lists for $73.92 ($4.62/lb), which works out to a difference of $0.80 per pound or $12.80 per 16 lb. Now, add the time for 16 spool changes (and possibly burnbacks) for the spool gun, as compared with one change for the larger spool. At 5 minutes to change a spool, that’s 75 minutes of extra time for each 16 lb of filler wire used. For high-volume use, a push-pull system makes financial sense.

Chris Roehl is a product manager for Miller Electric Manufacturing Co., 1635 W. Spencer Street, P.O. Box 1079, Appleton, WI 54912-1079, 920-734-9821,www.millerwelds.com.