Expecting good results on aluminum with a system designed for carbon steel is like asking a carpenter to frame a house with a wrench instead of a hammer. Both tools will make a weld or drive a nail, but only one optimizes productivity, profitability, quality and operator satisfaction.
Pulsed MIG welding systems can address the differences between aluminum and steel and help increase productivity, reduce downtime and deliver better weld quality.
Aluminum’s properties differ greatly from those of steel, which can create challenges. Some common issues include:
Because aluminum quickly transfers heat away from the weld area, establishing the weld puddle takes more energy than with steel. However, because aluminum has a relatively low melting point, thin sections of aluminum (which have less mass to transfer heat) are especially prone to burn-through and warping. In short, there’s a fine line between providing sufficient energy to ensure good fusion, yet controlling the heat input to prevent problems.
In many aluminum applications, such as trailer, truck body and components (e.g., cargo boxes), boat and sign fabrication, material thicknesses tend to be 3/8-inch and thinner. For thin components, the pulsed MIG welding process solves heat control issues.
Pulsed MIG works well with thin and thick sections because it is a modified spray transfer process. The welder switches between a high peak current and a low background current 30 to 400 times per second (see Fig. 1). The peak current pinches off a spray transfer droplet and propels it toward the weldment. The background current maintains the arc, but the heat input is too low for metal transfer to occur.
The peak current pulse ensures good fusion, overcoming concerns related to cold lap, which is a common issue with short circuit MIG on aluminum. It also provides faster travel speeds, helping improve productivity. The background current lowers overall heat input (see Fig. 2), addressing the burn-through and warping issues commonly associated with spray transfer MIG.
||Travel Speed (inches per minute)
||Heat Input (kilojoules/inches)
| Spray MIG*
||69 A (average)
Fig. 2: Heat control. The pulsed MIG process provides better control over heat input. It can enable fabricators to eliminate burn-through and warping issues, weld out-of-position, use larger diameter filler wires and improve productivity while lowering operating costs. *Filler wire: 3/64-in. diameter 4043 aluminum.
A cooler weld puddle also permits all-position welding (the puddle is less likely to sag or look excessively convex), and it helps bridge gaps when fit-up is less than optimal. Pulsed MIG also provides the operator with excellent directional control over the molten weld puddle, which improves bead appearance.
As an economic benefit, pulsed MIG welding allows using larger filler wire diameters, such as.047 inch instead of .030 inch, to weld thin-gauge material. An .047 wire improves feeding performance — because larger wires are stiffer and feed better — while also increasing the deposition rate and saving money, since larger diameter wires are often less expensive to purchase than smaller diameter wires. Add in the decreased time and materials for rejected parts, and pulsed MIG may be the best welding process for your application.
Pulsed MIG systems like the XR-AlumaFeed® systems feature built-in pulsing programs for 4,000 and 5,000 series aluminum wires in .035, 3/64- (.047) and 1/16- (.062) inch diameters. Most importantly, the systems are operator-friendly. In many cases, all operators do is set wire feed speed to match the application. Use faster speeds for thicker material and slower speeds for thinner material. The systems adjust all other voltage and pulsing variables automatically.
In this respect, pulsed MIG systems where operators only need to adjust wire feed speed are actually easier to use than conventional MIG systems, which require operators to fine-tune both wire feed speed and voltage.
Pulsing technology enables operators to easily adapt to different joint configurations by adjusting arc cone width, which in turn controls bead width. A wider bead can tie-in both sides of a joint or help with an outside corner; a narrow bead helps provide good fusion at the root of a joint.
One of biggest differences with new pulsing technology compared to old pulsing technology is that it does not force operators to hold a longer arc. It adapts to individual preferences so they don’t have to change welding style. Using an arc length control function on the front panel, operators can set the arc length they want. Even better, the machine holds arc length constant regardless of electrode stickout, which helps when welding in deep corners.
With just three variables to adjust — wire feed speed, arc length and arc control — experienced MIG welders can learn to use pulsed MIG systems with just a few hours of training. They often become more productive in just one day. For companies that struggle to find and train new welders, pulsed MIG can reduce the learning curve.
Wire feeders for aluminum
As has been shown, many (if not most) aluminum fabricators would benefit from upgrading to systems with pulsed MIG capabilities. The same holds true for their wire feed system. Many fabricators first enter the aluminum marketing by purchasing a spool gun. A spool gun eliminates the possibility of bird-nesting by putting a 4-inch (1 pound) spool on the gun, so the wire only feeds a few inches.
However, a spool gun needs to have the roll changed after every pound of wire is used, compared with the 8- to 20-pound spools on a push-pull system. If the operator is using several pounds of aluminum per day, the few minutes needed to change spools can add up.
Also, the chance of burnback exists when the end of a spool is reached, so many operators stop when a few turns are left on the spool. For any fabricator using several spools of aluminum per day, a push-pull system makes better economic sense.
With a push-pull gun, a motor in the gun pulls the wire through the liner, while the motor in the welder or feeder control becomes an assist motor. By maintaining consistent tension on the wire, the push-pull system helps eliminate bird-nesting. It is more ergonomic than the spool gun since the weight of the spool is not in the operator’s hands. Also, the spool needs to be changed less often than on a spool gun and allows the purchase of larger spools.
The only disadvantage to a push-pull system is their relatively higher initial purchase price, but the increased productivity and the financial advantage of buying larger spools usually provide a quick return on investment. When you compare the cost of 20 1-pound spools of 3/64-inch 4043 aluminum filler wire with one 20-pound spool of the same diameter wire (plus the time to change 20 spools versus one spool) you’ll see that for high-volume use, a push-pull system makes financial sense.
New gun for aluminum welding
In addition to welding power source technologies, new advances exist with wire feeders and guns for aluminum.
For example, the updated XR-Aluma-Pro™ push-pull guns are balanced and have a natural feel, so welders have improved joint access and can maintain proper gun angles, stickout and travel speeds. These guns optimize feeding performance for 4,000 and 5,000 series aluminum through a two-position, series-specific tension control (see Fig. 3). Proper drive roll tension solves problems related to wire burnback, erratic feeding and arc fluctuations, helping aluminum fabricators improve productivity.
| Fig. 7: Top gun. The XR-Aluma-Pro provides different tension settings for 4,000 and 5,000 series aluminum wire. Proper tension eliminates many causes of poor feeding.
Miller factory-tests and presets the tension on every XR-Aluma-Pro gun for 4,000 series aluminum (which is a softer wire requiring a lighter setting), and 5,000 series aluminum (a harder, more abrasive wire requiring more tension). When switching wire types, operators change tension using a screwdriver to turn a control on the side of the gun to one series-specific tension setting or the other — no in-between is possible.
Other guns let operators fully adjust tension settings, and operators may tighten the tension as much as possible. Unfortunately, too much tension deforms the wire and creates metal shavings, which clog drive rolls and work their way into the head tube. This results in feeding problems and micro arcing.
The air-cooled XR-Aluma-Pro is the first push-pull gun rated for welding at 300 amps/100 percent duty cycle. A higher duty cycle can eliminate the need for a water-cooled gun when welding aluminum up to 3/8-inch thick.
For welding thicker aluminum at higher amperages, Miller offers the water-cooled XR-Aluma-Pro, rated for welding at 400 amps/100 percent duty cycle. Features common to both guns include a 3-3/4 turn potentiometer for wire feed speed control that provides better resolution and is easy to adjust while wearing welding gloves. An easy-to-rotate, self-seating head tube allows better access to tight spots, while a replaceable feed cable liner reduces parts cost and service time.
Pulsed welding aluminum
When MIG welding aluminum, obtaining good quality and productivity depends on using the right welding process and system. This may seem like common sense, but many fabricators get hung up on purchase price vs. life cycle costs, or they try to weld aluminum with the same processes and systems used for steel.
The newest generation of pulsed MIG welding systems address the differences between aluminum and steel and generally provide a quick return on investment through increased productivity, reduced downtime and better weld quality.