Collision Repair Training | Australia
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Collision Repair Training | Australia
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Current Events/News: Advantage Online: 2005 Archives
WORKING WITH UHSS ALLOYED WITH BORON - AN UPDATE
August 22, 2005 - On May 10, 2004, I-CAR produced an article entitled "Working with Boron Steel." Since then, vehicle makers have continued to increase their use of ultra-high-strength steel (UHSS) alloyed with boron. This has prompted some tool and equipment makers to address a few of the issues related to repairing collision damaged parts made of UHSS alloyed with boron. During research at the I-CAR Tech Centre, some of this equipment has proven effective when drilling, cutting, straightening, and welding UHSS alloyed with boron. Removing Spot Welds on UHSS Alloyed with Boron One type of spot weld drill bit has three flutes (see Figure 1). This bit is made from tungsten carbide steel, a material even stronger than UHSS alloyed with boron. When used in combination with a pneumatic C-clamp-style spot weld drill (see Figure 2), this bit effectively removes spot welds. Precision and control of the drill is key to preserving the longevity of the drill bit. A speed of 800-1000 rpm is recommended for removing the spot weld and preventing heat buildup of the bit. Even when used cautiously, the drill bit will become dull after drilling approximately 100 spot welds. The C-clamp-style drill with the tungsten carbide bit is also effective for making plug weld holes in a part made from UHSS alloyed with boron (see Figure 3). Using plasma arc cutting equipment has also shown some effectiveness, although extensive practice on the technique is required. The technique requires making a circular cut around the spot weld through the outer layer, yet leaving the spot weld and the inner panel intact (see Figure 4). Caution must be used to prevent cutting into the inner panel. Before attempting to cut spot welds on a vehicle, it is helpful to practice on a scrap part to obtain the proper settings of the equipment and to practice the technique. Other methods, including using a cutoff wheel or a die grinder to grind through the weld, have also been proven effective. Straightening UHSS Alloyed with Boron The previous article stated that parts made with UHSS alloyed with boron should not be straightened. In some instances, however, it may be necessary to pull on the UHSS part to remove indirect damage from a collision. Due to the extensive strength, straightening should usually be limited to parts that will be either partially or completely replaced (see Figure 5). When straightening parts made from UHSS alloyed with boron, it is crucial that the entire vehicle dimensions are monitored and that the vehicle is visually inspected during the pulling operation. This prevents pulling damage into an undamaged area of the vehicle. Welding UHSS Alloyed with Boron As the previous article also stated, UHSS alloyed with boron does weld easily, although there are a few items to consider. To maintain the high strength characteristics of the steel, it is important to limit the heat-affected area in the weld zone. When GMA (MIG) welding UHSS alloyed with boron, a skip/stitch technique should be used, allowing the metal to cool after approximately 13 mm (1/2") of welding. When using squeeze-type resistance spot welding (STRSW) (see Figure 6), some equipment makers have specific settings for welding UHSS alloyed with boron. These settings pulse the welding output once to preheat the weld zone, and then welds the metal together. This creates a weld with less heat buildup in the weld zone, helping to maintain the strength of the metal. Conclusion Vehicle makers are continuing to use UHSS alloyed with boron to reduce vehicle weight while maintaining occupant protection in the event of a collision. Although the metal may be difficult to work with, some product and equipment makers have provided tools and equipment that make it a little less challenging.
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