What to Know about Aluminum GMAW Setup
Aluminum gas metal arc welding (GMAW) requires attention to detail and a base of knowledge to be successful. It’s also necessary to take precautions to avoid common mistakes.
Common challenges include feedability due to the softness of the aluminum welding wire, which can be exacerbated if the operator coils the welding gun or overtightens the drive rolls. Lack of cleaning and shielding gas leaks can lead to porosity. Melt-through on thin sections of material and incomplete fusion on thicker sections can also occur if the welding operator uses the wrong settings or technique.
Those new to welding aluminum need to be cognizant of cleaning requirements, proper setup of drums or spools, the correct equipment to use, and more.
Steps for Successful Setup
When getting ready for aluminum GMAW, it’s necessary to look at every component of the welding system. Each has requirements that vary, and there are best practices to follow.
1. SPOOLS AND DRUMS
Spools are generally straightforward to install. Periodically, a tangle may accidentally occur when attaching a spool to the wire feeder; however, the operator can remedy the problem by removing the spool from the feeder and pulling one to two layers of wire off it. Hold the spool from below (rather than by the rim) and place it on the spool assembly, aligning the hole on the spool with the dowel on the wire feeder. Put the retaining clip in place to secure the spool.
Setting up a welding wire drum for aluminum takes a bit of time and know-how because the wire tends to flip when it is pulled out of the drum. If that flip can’t escape through the contact tip, it will tangle inside the drum. Each manufacturer has its own style of drum and instructions for setup that welding operators should always follow. It’s important to note that different aluminum alloys may require different drum-feeding components. A 4XXX series filler typically requires a device inside the drum that spins around while feeding the wire, while a 5XXX series filler only needs a ring or cone that sits on top of the drum and directs the wire through the center.
Regardless of the manufacturer’s style of aluminum welding drum, it is necessary that all conduits from a drum to a feeder are straight to provide the smoothest feeding. When making a turn with a conduit, the radius of the turn should be at least 2 to 3 ft and no tighter. This allows twists to flow through the conduit. It is important to make the conduit the right length so that there aren’t any humps or bows in the path to the feeder.
2. WIRE FEEDER AND WELDING DRIVE ROLLS
Some wire feeders used in aluminum GMAW have electric brakes in them to prevent over-spooling when the wire feeder stops pulling. Others have a form of tensioner on the hub so the more the welding operator tightens it, the harder it is to spin. This style should be set so that it takes very little force to get the spool spinning; however, the spool should stop spinning as soon as the feeder stops pulling.
Always use U-groove welding drive rolls when welding aluminum because the wire is soft and other styles can easily shave it. The drive roll pressure should be set at a minimum to reduce distortion or the possibility of shaving the wire. A simple test can determine the correct tension. When the operator feeds the wire out of the gun into a gloved hand, it should coil into a 2- to 3-in.-diameter coil. A smaller diameter coil indicates too much drive roll pressure, and the operator needs to loosen the drive rolls. When the drive roll tension is set correctly, the drive rolls should slip and stop feeding wire when the operator applies more pressure with his hand than it takes to make the 2- to 3-in.-diameter coil.
3. WELDING GUN AND CONSUMABLES
Push-pull guns are the most common for aluminum GMAW, as they provide reliable feedability when paired with a nylon or plastic liner. These liners help alleviate wire shaving that causes clogs and, ultimately, poor wire feeding. Push-pull guns are also well suited for all diameters of wire. Spool guns are a more affordable option for smaller projects, but they require frequent welding wire spool changeover. In some instances, welding operations choose a standard push welding system using a mono-coil D-wound steel liner and larger-diameter wires (e.g., 0.047 to 0.062 in.) along with shorter power cables. When using this option, it’s important to deburr the ends of any cut steel liner to prevent shaving issues.
Aluminum GMAW requires specific contact tips. These tips have a bore diameter that is ap-proximately 10 to 15% larger than the wire diameter. They are also polished to remove any burrs that could potentially cause shavings. It is important to note that 3/64-in. aluminum wire is not 0.045 in., but rather 0.047 in. Using a standard 0.045-in. contact tip can lead to meltback and feeding issues.
Understanding Power Sources, Parameters, and More
Any direct current electrode positive (DCEP) GMAW power source is capable of welding aluminum. When welding with a small power source, the largest limiting factor will be material thickness because aluminum is thermally conductive and requires a lot of energy to complete the welding process. For welding on thin sections of aluminum, it’s a good idea to invest in a power source with pulsed welding capabilities as this helps minimize the risk of melt-through and distortion.
There is no set rule of thumb for setting welding parameters for aluminum GMAW. Figuring wire feed speed (WFS) and amperage, along with voltage and travel speed, depends on the application, aluminum alloy, base material thickness, and wire diameter. For example, 5XXX series aluminum wires require much higher wire feed speeds to reach the same amperages as 4XXX series wires. This is due to the electrical conductivity differences between the two series of alloys. Because 5XXX series aluminum requires higher WFS, it’s also necessary for operators to use faster travel speeds to accomplish the targeted weld size and stay ahead of the weld pool.
Some filler metal manufacturers provide a chart on their spec sheets that offers starting points for welding parameters for different wire diameters and base material thicknesses. There are also power sources in the marketplace that allow welding operators to select such variables as material thickness and alloy. The machine, in turn, provides the starting parameter point, which can be adjusted as needed to gain the desired results.
The most common shielding gas for aluminum GMAW is 100% argon. Argon provides good shielding from the atmosphere, has consistent cleaning properties, and is cost effective. An argon/helium mixture is another option for welding aluminum that is 1 in. or thicker. The mixture increases the ionization potential and thermal conductivity of the gas, generating a hotter arc. This results in deeper depth of fusion and reduces the opportunity for porosity because the weld pool remains fluid for longer.
Filler metal selection depends on the aluminum alloy being welded and the service conditions the part will encounter. Consult a filler metal chart for assistance.
Cleanliness is Key
Even if every component of the aluminum GMAW process is in order, lack of proper cleaning will lead to poor results.
Moisture removal is the first step in cleaning and material preparation. Even the smallest amount of moisture on aluminum can cause porosity. Ideally, welding operations should pre-vent moisture from developing in the first place. This is done by watching the dew point and humidity in the storage area to avoid condensation and bringing the material into the welding area 24 hours in advance. This allows the material to transition to the ambient temperature and avoids cold-to-warm temperature shocks.
After ensuring that the aluminum base material is moisture free, the welding operator should apply a solvent with a clean cloth to degrease it. Oil, grease, and paint contain hydrocarbons that produce porosity when welded over.
Last, use a stainless-steel wire brush dedicated to cleaning aluminum to further prevent porosity. The wire brushing is necessary to remove the aluminum oxide from the surface of the aluminum. It is good practice to brush in one direction to prevent embedding contaminants. Some welding operators prefer power tools over a stainless-steel wire brush, but these must be operated at a low pressure and low rpm. An electric die grinder is a better choice than a pneumatic tool because the exhaust on the latter can contain small amounts of oil that could contaminate the base material.
Gaining the Best Results
While there are many steps to successfully weld aluminum, careful setup and practice can yield positive results. For the GMAW process, pay close attention to all components that contribute to smooth wire feeding as well as the parameters recommended by the equipment and filler metal manufacturers.
This article was written by Sean Walkowski (aluminum applications engineer and AWS certified welding inspector at Hobart Filler Metals) for the American Welding Society.