Go Back to the Basics: Machine Setup for GMAW Aluminum

When fabricating with aluminum, it is essential to understand some critical differences between aluminum and other materials. To develop a firm foundation, it is crucial to be aware of the differences in mechanical properties, feedability, material handling, and equipment configuration.

Mechanical Properties 

One of the many differences between steel and aluminum is aluminum’s relative lack of column strength, a term used in structural engineering to describe the amount of compressive load a column can support before it buckles. Even within aluminum, there is a notable difference in the column strength of 5XXX series alloys when compared to 4XXX series alloys.  

In a typical gas metal arc welding (GMAW) setup, there are multiple areas the wire must pass through to get to the arc. The wire feed speeds used when welding aluminum are often higher than those used for most steel wire setups. If there is a restriction in the feeding system, the result is generally a burnback (if the wire can’t feed properly and ends up melting to the end of the contact tip) and/or a bird’s nest (if the wire bends between the drive rolls and the outlet guide, it will build up in that small area). 

Wire Spools 

Aluminum welding wire is commonly offered on 1-, 5-, 16-, 20-, or 32-lb plastic spools. In an ideal world, the wire feeds without interruptions. Assuming the wire package was not damaged in shipping, it is recommended to handle the spools in a way that ensures the most robust ability to pay off the aluminum wire. 

Spools should be lifted by the hub or bottom flange. Additionally, ensure the brake tension on the spool spindle is only tight enough so that the spool does not spin freely when the drive rolls stop. 

Wire Drums 

Customers looking for a bulk wire option can use 50-lb mini drums or full-size drums that weigh 311 lb. Do not tip or shake the drums, and avoid dragging them by the straps. Also, never allow the drums to get wet. When moving drums, use a forklift, pallet jack, or a cart designed for drums. To lift drums, use a lifting yoke. Keep the drum in a warm, dry location and keep it closed until ready to use. 

Setting up a drum for reliable, uninterrupted feeding requires special accessories, which are unique to either 4XXX or 5XXX series wires. Always follow the manufacturer’s recommendations.

The most common feeding issue with drum wire is tangles. Some of the usual suspects that cause them are as follows: 

• The drum was set up incorrectly

• Worn conduit 

• Shifting wire during transport 

• Wire twist getting pushed back into the drum 

Wire Twist 

When the wire is put into the drums, a twist must be applied to ensure the wire lies flat in the drum. When the wire is pulled through the system, the twist must be allowed to release. The most common cause of wire twisting in the drum is excessive pressure on the drive roll. 

Machine Setup 

Because wire feeding problems are not as common in steel GMAW applications, and most systems are setup at the factory for steel wire, machine setup is often overlooked as the culprit. By taking the time to convert the system to aluminum mode, the operator can reduce wire feeding issues. Some key elements of machine configuration include wire guides, drive wheels, liners, and contact tips. 

Wire Guides 

When feeding aluminum, eliminate all areas where the wire is not supported or encapsulated. One way to understand the differences is to think of steel wire as rigid, uncooked spaghetti and aluminum wire as cooked spaghetti. 

On most wire feeders, the wire passes through an inlet guide before reaching the drive rolls. First, the guide should be nonmetallic, as metal guides can scrape the wire and create shavings. Inspect the inlet guide; if it has worn a groove due to rubbing, replace it. Center guides (if present) and outlet guides should be tapered with a contour that matches the drive rolls, allowing their ends to be as close to the drive rolls as possible. Additionally, ensure there is no gap between the back of the torch liner and the exit end of the outlet guide. 

Drive Rolls

When using steel wires with a V-groove drive roll, opt for a U-groove drive roll for aluminum to prevent wire deformation and the creation of shavings. 

Select a drive roll that matches the diameter of the wire. To evaluate quality, inspect the geometry of the grooves under magnification to ensure the grooves are smooth (a 10x eye loupe usually offers enough magnification). 

How much drive roll pressure should be used for aluminum? There is no standard answer. The technique used for steel, where you feed the wire into an obstruction and increase pressure until it curls, is not usually recommended for aluminum because that much pressure can cause the soft wire to crush.  

Guns and Liners 

One of the more common misunderstandings is that aluminum requires a push-pull gun. Some experts argue that the need for a push-pull gun is a function of the gun length; however, the stiffness of aluminum wire can vary significantly depending on the alloy. 

Use a nonmetallic gun liner, nylon, or graphite. Be certain the inner diameter of the liner is correct for the application. 

Contact Tip 

The most frequent set-up errors are oversized tips and poorly manufactured tips. The inside diameter of the tip should be approximately 10% more than the wire diameter. There are numerous aftermarket tips; while they may appear the same on the outside, many are made from lower-quality copper alloys that are softer and wear out faster. 

Summary 

The information presented here is based on more than three decades of troubleshooting GMAW aluminum systems over a wide range of applications. The bottom line is if a shop’s approach works, great; however, if there are feeding issues, hopefully the topics covered will aid in troubleshooting and optimizing the system. 

This article was written by Rob Krause (territory sales manager, ESAB) and Thomas Pfaller (applications engineer, AlcoTec Wire Corp.) for the American Welding Society.