Collision Repair Training | Australia
|
Collision Repair Training | Australia
|
Current Events/News: Advantage Online: 2005 Archives
WELDING ALUMINUM - A KEY ASPECT TO STRUCTURAL REPAIRS ON ALUMINUM-INTENSIVE VEHICLES
February 20, 2006 - When vehicle makers started using aluminum as a structural part of the vehicle, the advantages were numerous, including the great energy-absorbing characteristics and weight-reducing ability. There were also some disadvantages, including the many differences that technicians would encounter between aluminum and steel when performing structural repairs, primarily the welding process. As the aluminum-intensive vehicles have evolved, so have the welding processes used during repairs. The majority of aluminum vehicle makers require extensive training, especially for aluminum welding. In this article, we will take a look at some of the issues that may arise when welding aluminum. Equipment
The welding process commonly used for aluminum welding is gas metal arc (GMA) or metal inert gas (MIG) welding. Tungsten inert gas (TIG) or gas tungsten arc welding is typically not used for aluminum structural repairs because the high frequency generated during the welding could potentially damage electronic modules and computers. Most collision repair technicians are trained on the GMA (MIG) process for steel. The equipment required for GMA (MIG) welding aluminum has changed since the inception of the aluminum-intensive vehicle. The transfer method of the welding machines used originally was spray arc transfer. With this method, the welding output current remains constant and tiny droplets of molten metal are sprayed across the arc continuously to fuse the metal. Technological advancements in welding equipment have made it possible to use the pulsed spray arc transfer technique. With this process, the welding output current rapidly pulses from high peak current, which allows the metal transfer to take place by spraying the aluminum across the arc, to a low background current to maintain the arc while allowing the weld puddle to solidify between each pulse (see Figure 1). Technique Welding aluminum poses a whole new set of technique challenges. Probably the most important consideration when welding aluminum is that the metal must be clean. Aluminum is naturally corrosion resistant. A layer of oxide forms almost instantly after contact with air. This oxide protects the metal from corrosion, but also inhibits the welding process. The aluminum oxide has a melting point of 1,650°C (3,000°F) and will not burn away until a temperature of 2,050°C (3,725°F). The melting point of aluminum is 660°C (1,220°F). Due to the extreme differences in melting temperature, the oxide must be removed before welding can take place. Failure to do so will lead to a weld bead with a great deal of porosity (see Figure 2). The first step is to use a wax and grease remover to remove any oils and other surface contaminants from the weld zone. Next, the oxide layer can be removed using a stainless steel wire brush or other abrasive. There are several differences when welding aluminum as opposed to steel; the biggest being aluminum doesn’t change color before it reaches the melting point. Therefore, it is very difficult to see how the weld puddle is flowing and whether proper fusion between the metals is occurring. Aluminum will not begin fusing until the metal temperatures have approached the melting point. This is what is called a cold start. A few welding techniques help reduce the effect of the cold start. A technique called “tailing in” is where the weld bead is started off to the side of the weld seam. When the metal has been pre-heated and the weld puddle begins to flow, the bead is run along the weld joint. Another method is to use run-on tabs. This method uses small aluminum tabs placed at the beginning and end of the weld seam (see Figure 3). The bead is started on the tabs and by the time the weld reaches the seam, a molten bead of aluminum is flowing, causing fusion between the metals. This helps make a weld that completely joins the metals. The welding torch is generally pushed at a 5–15° angle (see Figure 4), allowing the weld to penetrate into the base metal. If the proper gun angle is not maintained, fusion between the base metals may not take place. Pulling or dragging the torch, as commonly done when welding steel, does not allow the weld zone to be pre-heated, creating a weld that may not fuse the metals together. Visual appearance of an aluminum weld can be deceiving. It is possible for a weld to appear strong, yet still fail the destructive tests due to lack of penetration into the base metal (see Figures 5 and 6). Training The time to get training on aluminum welding is before an aluminum vehicle arrives at your facility. The I-CAR Automotive Aluminum GMA (MIG) Qualification Test (AWQT) series (see Figure 7) introduces collision industry professionals to the aluminum welding process through a knowledge-based classroom training program, followed by a (required) practice session with “hands-on” welding of aluminum. During the practice session, three different weld types are made in both the vertical and overhead positions. Following the practice session is the actual qualification test. During the test, the candidate is allowed to make two of each weld in each position, and turn in one of each for visual inspection and destructive testing. Some aluminum vehicle makers require additional training on specific welding applications. Jaguar has requested that each student successfully complete both the I-CAR AWQT as well as the I-CAR Automotive Steel Welding Qualification Test (SWQT) before attending the vehicle specific welding training. Jaguar requires 32 hours of training on aluminum welding. With the Jaguar aluminum welding test, technicians are required to complete the following welds in the overhead, vertical, and horizontal positions:
Audi requires 40 hours of training on aluminum welding for structural repairs to the Audi A8. Audi technicians are also required to complete the following welds:
At the end of the training, a weld inspector from an outside testing organization completes an evaluation of each weld. If the welds pass the evaluation, the Audi technician is Audi certified for aluminum welding by the testing organization. General Motors requires the I-CAR AWQT and a four-hour I-CAR training program, Collision Repair Overview for the Chevrolet Corvette Z06 (GEN01), specific to repairs to the new, aluminum-framed Corvette Z06, for body structural technicians at Chevrolet dealerships that sell this vehicle. The welds that are made during the AWQT may also apply when repairing structural damage to a Corvette Z06. Conclusion Aluminum welding isn’t a required task for structural repairs on the vast majority of vehicles. As vehicles evolve due to stricter fuel economy and crashworthiness requirements, aluminum will play a larger role. The I-CAR AWQT series allows collision industry professionals the ability to demonstrate that they have the technical skills and ability to weld aluminum. Visit the class schedules search on the I-CAR web site to see when an AWQT is scheduled in your area. Want to learn more? The following I-CAR training programs/topics were mentioned in the above article:
Visit the I-CAR home page at www.i-car.com, utilize the “Quick Search” function by entering your Zip/Postal Code, and find an I-CAR training program near you! Don’t see the program you want in your area? Simply complete a “class request form” at the bottom of the search results page.
|
|||||||||||||||||||||||||||
|
|||||||||||||||||||||||||||
|
Page Last Revised: |
|||||||||||||||||||||||||||
