Collision Repair Training | United States
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Current Events/News: Advantage Online: 2005 Archives
HOW NEW TECHNOLOGIES AFFECT PARTIAL PART REPLACEMENT
September 19, 2005 - A vehicle with side impact damage is being analyzed. The B-pillar, which is made of ultra-high-strength steel, has a kink. Taking into consideration that the part is made from ultra-high-strength steel, can the part be sectioned, or does it need to be replaced at factory seams? Over the past several years, many advancements have been made in regards to the construction of full-frame and unibody vehicles. We have seen new joining methods, increased use of aluminum and advanced high-strength steels, and alternative part designs. Each of these innovations brings with them new considerations for part repairability. These new materials and construction methods may have a significant effect on your repair decisions. Joining Methods
One type of OEM joining method that is gaining popularity is laser welding. Laser welding is a process that uses the heat of a laser beam to fuse two panels, typically without the use of filler metal. Some vehicle makers use laser welding in areas where gaining access to both sides of a panel joint is challenging. These areas include trunk floor-to-rear rail joints, and floor pan-to-front rail assembly joints, windshield pinchwelds, and roof panel joints (see Figure 1). Because this process currently cannot be duplicated during collision repairs, the laser-welded panel is typically removed by grinding the laser welds away with a cutoff wheel, and replacing them with plug welds, slot welds, adhesives, or a combination of these processes. The use of laser-welded joints can reduce the vehicle weight by reducing the number of flanges. Laser welds can also increase the stiffness of the structure. Laser welds are also used to form tailor-welded blanks. This type of construction joins thinner gauge metal to thicker gauge metal for collision energy management purposes (see Figure 2). Tailor-welded blanks may also incorporate different alloys of the same or different thicknesses to increase the strength of an assembly without the need to add internal reinforcements. To maintain the integrity of the tailor-welded joint, most vehicle makers are recommending sectioning away from the laser-welded joint, leaving the laser weld intact. For example, on the 2006 Audi A3, the sectioning joint for the lower front rail is several centimeters ahead of the laser-welded factory seam. Advanced High-Strength Steel Vehicle makers are continuously looking for ways to reduce vehicle weight while maintaining or increasing part strength. To accomplish this, there is an increasing presence of advanced high-strength steel (AHSS) in vehicle construction. AHSS body panels are not necessarily lighter when compared to lower-strength steel body panels of the same size and thickness. The weight savings is accomplished by reducing the thickness of the AHSS panel. If stronger steel is used, the panel can be made thinner while maintaining the same strength of a thicker, lower-strength steel panel. Some of these types of steel include dual-phase steel (400–600 MPa), high-strength steel alloyed with boron (1500 MPa), high-strength, low-alloy steel (upward of 700 MPa), and a number of other advanced high-strength steels. Recent encounters with some of these advanced steels have provided some unique repair challenges. It may be difficult to cut and drill. It is very difficult, if not impossible, to straighten, and also weakens when exposed to heat. Therefore, many pose the question, "Can this material be repaired or sectioned?" The answer is yes, but it is dependent on the vehicle maker’s recommendations. For example, the 2005 Volvo XC90 has B-pillar reinforcements and inner and outer lower rear body panels made from ultra-high-strength steel alloyed with boron (see Figure 3). Each of these panels can be sectioned. The rear body panels have a choice of three sectioning locations. The B-pillar reinforcement can be sectioned about 100 mm from the roof rail. Always refer to the vehicle maker‘s recommendations before attempting a sectioning procedure on AHSS panels. Laminated Steel To reduce the amount of noise in the passenger compartment, some vehicle makers are adding laminated steel to their vehicle designs. Laminated steel is basically two pieces of cold-rolled steel with a layer of visco-elastic polymer sandwiched between them. Examples of vehicles that have laminated steel include the 2001 Ford Explorer Sport Trac, the 2004 Ford F-150, and the 2006 Cadillac CTS and DTS. All have laminated steel in the cowl (see Figure 4), but some vehicles may have it in the floorpan, such as the Chrysler Town and Country "STOW 'N GO" seating system. To date, there are no sectioning recommendations available for this type of material. Repair recommendations require complete replacement at factory seams. The attachment methods of laminated steel vary. The vehicle maker may recommend GMA (MIG) welding, adhesive bonding, or rivet bonding. Hydroformed Parts Hydroformed parts have a tubular design with no flanges. They’re formed by forcing high pressure fluid through a steel tube. The tube is inside a die, and as the tube expands from the pressure of the fluid, it takes the shape of the die and forms the part. There has been speculation that perhaps these parts cannot be sectioned. This is not the case. There are several vehicle makers that offer sectioning procedures for their hydroformed structural parts. Several full-frame vehicles now have partial part replacement procedures from the vehicle makers for hydroformed frames. Examples include the front frame on the 2002 Oldsmobile Bravada and the upper fender rail and shotgun rail on the 2004 Dodge Durango (see Figure 5). There are also a number of other sectioning procedures available. Always follow the vehicle maker’s recommendations when sectioning any hydroformed parts. In addition to providing partial replacement guidelines for hydroformed frames, many vehicle makers have come onboard in regard to providing sectioning procedures for many of the non-hydroformed sections of the frames on their full-frame vehicles. From frame tips to rear H-sections, several vehicle makers have developed alternatives to replacing frames that have damaged areas that are unrepairable (see Figure 6). When sectioning full frames, however, make sure the welder being used has the capability of welding thicker gauge metal, and make sure to use the recommended electrode wire type and diameter. Recommended Sectioning Joints Two types of sectioning joints commonly used include the open butt joint, or butt joint with insert. If inserts are used, follow the vehicle maker’s recommendation for the insert length and attachment method. Some vehicle makers recommend that the insert be plug welded on either side of the continuous weld that closes the sectioning joint, while others recommend a short insert that functions as a weld backer only. Some replacement parts, such as the replacement crush cap for the GM C/K trucks and SUVs, ship the replacement part with the insert already welded into the end. Vehicle Maker Partial Part Replacement Recommendations When making repair or replace decisions, it is recommended to follow the vehicle maker recommendations. Many of the OEM web sites can be accessed online for a nominal fee. Visit this I-CAR web page for a list of vehicle maker web links: /html_pages/about_icar/industry_links/technical_info.html Some vehicle makers have specific statements about sectioning structural parts on their vehicles. For example, Honda recommends replacing parts at factory seams unless otherwise stated in a Honda body repair manual. DaimlerChrylser has a similar statement and Toyota has stated that they do not want sectioning procedures performed on their full-frame vehicles. Conclusion New construction materials and construction processes have presented unique repair challenges to the collision industry. However, many vehicle makers are providing guidelines on how to make a safe and quality repair that doesn’t affect the safety or performance of these innovative designs.
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