Addressing Aluminum

Tackling the challenges of welding aluminum in auto body repair begins with the right equipment

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Aluminum is gaining in popularity in many applications in the automotive industry, as manufacturers seek to provide improvements in fuel efficiency without sacrificing vehicle integrity or performance.

The industry’s move toward lighter-weight vehicles is driven, in part, by the Corporate Average Fuel Economy (CAFE) regulations. Intended to improve the average fuel economy of cars and lightweight trucks sold in the United States, the CAFE regulations were first enacted by Congress in 1975. Increasingly stringent standards recently issued by the U.S. Department of Transportation and the U.S. Environmental Protection Agency added to those regulations, requiring the average fuel economy to be the equivalent of 54.5 mpg for cars and light-duty trucks by model year 2025.

2015 Ford F-150 frame and body
The F-150’s military-grade, aluminum alloy body is made of the same 5000/6000-series high-strength aluminum used in industries such as aerospace, commercial transportation and energy. It reduces weight and increases strength while also maintaining resistance to dents and corrosion.

Because aluminum can be used at thinner gauges while still providing high strength, it can help automotive manufacturers reduce total vehicle weight in order to meet these increasingly strict fuel economy requirements.

Aluminum often is used for frames and body panels, especially in larger vehicles, and now some auto manufacturers are fabricating entire bodies from aluminum, the 2015 Ford F-150 all-aluminum-body truck, for instance. This transition makes aluminum welding a growing market in auto body repair as well because vehicles in service will inevitably need to be repaired.

Welding thin-gauge aluminum like that used in many of the automotive applications poses several challenges. These issues are difficult for experienced aluminum welding operators to address and even more so for auto body technicians who may not have prior experience welding aluminum.

To undertake these challenges, it’s important to use equipment and consumables designed specifically for aluminum and to keep in mind some best practices that can help drive success when welding aluminum for auto body repairs.

Challenges of aluminum

The main challenges posed by welding thin-gauge aluminum are warping, distortion and burn-through.

Because aluminum quickly transfers heat away from the weld area, establishing the weld pool takes more energy than when welding steel. However, because aluminum has a relatively low melting point, thin sections of aluminum are also especially prone to burn-through and warping.  Therefore, controlling heat input during the welding process is key to addressing these issues.

Millermatic 350P
Controlling heat input during the weld is key. Choosing a machine with the capability for pulsed MIG welding provides a process that helps control the heat input.

Another common issue when welding aluminum is the feedability of aluminum wire, which is softer and can be harder to feed through a gun than other filler metals. Depending on the application and the specific aluminum wire, it may be necessary to use a spool gun, push-pull gun or standard MIG gun when welding this material.

Using larger diameter wires can provide more consistent wire feeding and reduce the chance of wire “birdnesting,” or tangling of the wire, between the drive roll and the liner. Clearing it requires the welding operator to stop welding, cut the wire, discard the wire in the gun and re-feed new wire through the line, which makes it a time-consuming and costly problem to address.

Auto body prep

As more auto manufacturers use aluminum in vehicles and aluminum welding in auto body repair becomes more common, shops will need to train technicians and welding operators who typically haven’t welded aluminum as to the proper techniques, power source settings and welding parameters. Those making the repairs will also need to be certified to weld on aluminum vehicles or those with aluminum components.

Along with employee training, auto body shops should be prepared to invest in new equipment specifically designed for welding aluminum as the material becomes more common in the industry.

Choosing a machine with the capability for pulsed MIG welding is critical as this process is among the best options to control the heat input. Auto body shops should have an aluminum-dedicated machine that is at least 230 V and has pulsed MIG capabilities for welding 18-gauge to 1/8-in.-thick aluminum. It is important to use the machine only for aluminum as sharing it for other welding projects, such as steel for example, can cause dust, dirt or other contaminants to be pulled into the wire feeder, resulting in quality issues.

Learning proper aluminum cleaning techniques is another way auto body shops can prepare for the transition to aluminum welding. Getting the material as clean as possible and removing the layer of aluminum oxide on the surface of the material is key.

This cleaning process, however, may pose a challenge in repairing vehicles that have been in service on the road, where dirt and gravel can become embedded into the base material. Greater care and attention to detail during the cleaning process is absolutely essential.

In a media demonstration Tuesday, Ford’s new 2015 F-150, with an all-aluminum alloy body and bed and high-strength steel frame, weighed 732 pounds less than the steel-bodied 2014 F-150 it will replace.
Aluminum is gaining in popularity in many applications in the automotive industry with some manufacturers now fabricating entire vehicles from aluminum. As is true with the Ford F-150, an aluminum body offers improvements in vehicle performance and fuel efficiency.

When cleaning the material, technicians or welding operators must first use a solvent such as acetone to remove grease or other impurities, then use a stainless steel brush to remove the aluminum oxide prior to welding to help achieve a good quality weld.

Designed for aluminum

When it comes to choosing welding equipment and consumables for aluminum welding, many manufacturers simplify the selection process by offering entire systems or welding packages designed to work together. These packages include the power source, wire, gun and other consumables, such as the nozzle, contact tip and liner.

These complete aluminum-welding packages are designed as a sort of turnkey welding solution, which is particularly helpful for those without much experience welding aluminum. These systems feature simplified setup, intuitive interfaces and consistent arc performance, making it easier to execute quality repairs even for those with less experience welding aluminum.

For these systems, there are some considerations when it comes to the gun. Some dedicated aluminum systems use a push-pull or spool gun, while others, including newer ones designed for aluminum body repairs, require a standard MIG gun because auto manufacturers have specified a thicker, stronger aluminum wire for these auto body repair jobs (0.047 in. diameter, 5554 or 5356 alloy).

Auto body shops, however, should always consult the manufacturer for proper wire specifications and gun requirements. For those systems using a standard MIG gun, it is important to use a nylon or plastic liner as it helps the aluminum wire slide through easier. It also prevents shaving of the soft aluminum wire, which can lead to clogs in the liner that cause poor wire feeding. A standard gun with a head tube that has a 30° angle instead of a 45° angle is a good option as it creates less drag for more consistent wire feeding.

Choosing the most appropriate power source, wire, gun and other consumables are all important factors for success in welding aluminum. Choosing the right welding process is another key step.

Because aluminum is such a good conductor of heat, conventional short circuit transfer isn’t a good method for welding this material. Pulsed MIG is a modified spray transfer process that is preferred and more consistent for welding aluminum.

Ensuring success

Depending on the wire feed speed during the pulsing process, the power source switches between a high peak current and a low background current 30 to 400 times per second. The peak current pinches off a spray transfer droplet and propels it toward the weldment. The background current maintains the arc, but because the heat input is too low, metal transfer will not occur. The peak current pulse ensures good fusion, overcoming concerns related to cold lap, a common weld defect. The background current lowers heat input, addressing the burn-through and warping issues commonly associated with spray transfer MIG welding of aluminum.

A close-up of an aluminum weld produced by using a complete aluminum-welding package.
A close-up of an aluminum weld produced by using a complete aluminum-welding package.

Because the surrounding structure must be protected from the heat of the arc during the aluminum welding repairs, pulsing technology offers a distinct advantage in these applications. Namely, it controls heat input. As a result, a technician or welding operator can make the welds required to complete the repair without damaging surrounding parts on a vehicle that will go back into service.

Even for experienced welding operators, welding new aluminum can pose challenges. Repair welding on aluminum that has been in service on a vehicle exposed to dirt, mud, gravel and other impurities can prove even more challenging.

To help ensure success in welding aluminum in auto body repair applications as this material becomes more popular, proper cleaning of the material, training of welding operators and choosing the most appropriate aluminum-specific welding equipment and consumables are all critical steps.

Miller Electric Mfg. Co.

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