Feedability in GMAW Welding of Aluminum

Understanding Feedability in GMAW Welding of Aluminum

Feedability is probably the most common problem experienced when moving from GMAW welding of steel to GMAW welding of aluminum. Welders mostly experience equipment problems such as fusion of the aluminum welding wire to contact tip. This requires the breakdown of the feeding system and replacement of the contact tip. Further, these problems are time-consuming and costly. The present article covers the various issues associated with feedability in GMAW welding of aluminum and how to overcome the issues.

What is Feedability?

Feedability, in this instance, can be described as the ability to consistently feed the spooled welding wire when GMAW welding, without interruption, during the welding process.

Feedability in Steel vs Aluminium

Feedability is a far more significant issue with aluminum than steel. This is primarily due to the difference between the material’s mechanical properties. Steel welding wire is rigged, can be fed more easily over a greater distance, and can withstand far more mechanical abuse when compared to aluminum.

Aluminum is softer, more susceptible to being deformed or shaved during the feeding operation. Therefore, it consequently, requires far more attention when selecting and setting up a feeding system for GMAW welding. Feedability problems can be increased when using the smaller diameter wires and the softer aluminum alloys such as the 1100 and 4043 over the harder alloys such as 5356.

Understanding the Feeding System

Feedability problems often express themselves in the forms of irregular wire feed or as burn-backs (the fusion of the welding wire to the inside of the contact tip). To prevent excessive problems with feedability of this nature, it is important to understand the entire feeding system and its effect on aluminum welding wire.

Spool - If we start with the spool end of the feeding system, we must first consider the brake settings. Brake setting tension is required to be backed off to a minimum. Only sufficient brake pressure, to prevent the spool from free-wheeling when stopping welding, is required. Any pressure over and above this will increase the potential for feeding problems and burn-backs. Electronic braking systems and electronic and mechanical combinations have been developed to provide more sensitivity within the braking system. They are particularly useful for the improved feeding of aluminum wire.

Inter and Outlet Guides and Liners - Inlet and outlet guides, as well as liners, which are typically made from metallic material for steel welding, must be made from a non-metallic material such as Teflon or nylon to prevent abrasion and shaving of the aluminum wire.

Drive Rolls - Drive rolls designed specifically for feeding aluminum should be used. These often have U-type contours with edges that are chamfered and not sharp. They should be smooth, aligned, and provide correct drive roll pressure. Drive rolls that have sharp edges can shave the soft aluminum wire. These shavings can collect within the feeding system and cause burn-backs from blockages within the liner. Excessive drive roll pressure and/or drive roll misalignment can deform the aluminum wire and increase friction drag through the liner and contact tip.

Contact Tip - Contact tip I.D. and quality are of immense importance. You should only use contact tips that are made specifically for aluminum wire welding. The contact tip should have smooth internal bores and the absence of sharp burrs on the inlet and outlet ends of the tips which can easily shave the softer aluminum alloys. Contact tip bore diameter should be approximately 10% to 15% larger than the electrode diameter.

Feedability Chart

Significance of Welding Wire Quality in Feedability

The quality of the welding wire used for GMAW welding can influence the feedability characteristics. Such things as surface smoothness, wire diameter control, and final treatment of the wire during the spooling operation can assist or detract from the ability to easily deliver the wire through the feeding system. The consistent quality characteristics of the aluminum welding wire should be considered to minimize feedability problems.

Aluminum Wire Feeding System

In terms of aluminum wire feeding, there are four recognized feeding systems used:

• push feeders
• pull feeders
• push-pull feeders and
• spool-on-gun feeding systems

Push Feeders and Pull Feeders

For aluminum welding, with the push and the pull feeders, limitations are recognized dependent on application and feeding distance. These systems are generally limited to a practical length of about 12 feet. With the push feeders, the feeding distance limit is a result of the flexibility of the aluminum wire and its tendency to buckle and bend in the liner, and with the pull feeders from a rapid increase in friction drag in the liner, particularly if there are bends in the conduit.

Push-Pull Feeders

Push-pull feeders were developed to overcome the wire feeding problems experienced by the other systems and are the most positive method of feeding aluminum welding wire. The push-pull systems can improve feedability in many applications and are often essential for more critical/specialized operations such as robotic and automated applications to ensure consistent feedability.

Spool-On-Gun Feeding System

The spool-on-gun feeding system is usually designed to use 1-lb spools of wire that are mounted in the gun. These guns are usually air-cooled and generally limited to smaller wire sizes and light-duty service. Because of their relatively low current rating, they are not perfectly suited to heavy-duty continuous production welding. But are often quite effective for tack welding and other light-duty applications.

The choice of the most suitable feeding system for each application is based on such factors as the type of welding (light or heavy-duty), the electrode size and alloy (large or small diameter / hard or soft filler alloy), the need for a long flexible conduit, and the importance of minimizing electrode cost (larger diameter wire is generally lower priced than smaller diameter).

The Bottom Line

The demands of welding applications vary extensively, and the cost of each feeding system varies also. The cost of downtime from feeding problems and replacement parts can also be significant. For these reasons, you should choose the feeding system that is best suited to your application and set it up to optimize its feeding capability.