One trademarked material, named Quiet Steel®, is used on some of the newer General Motors, DaimlerChrysler, and Ford vehicles. The core of Quiet Steel has a "viscoelastic" property that effectively reduces vibration transferred through the panel. By reducing vibration, noise is also reduced.
History of modern steel
The UltraLight Steel Auto Body (ULSAB) consortium developed a similar type of material in the 1990s. This worldwide consortium consisted of 35 steel producers from 18 different countries with the common goal of designing an all-steel lightweight vehicle while maintaining structural integrity and affordability.
The ULSAB version of laminated steel was developed along with other innovations including tailor-welded blanks, advanced high-strength steels, and the hydroforming processes used to form steel. This material had a polymer core of 0.650 mm between two sheets of steel. It was used for the dash insert panel and spare tire tub on the ULSAB unibody concept structure that was completed in 1998. Both laminated steel parts were lightweight and had sound-absorbing capabilities, but neither could be welded because the polymer core was too thick. The parts were attached to the structure with bolts, rivets, and adhesive. The polymer core of the ULSAB laminated steel was much thicker than the 0.025 mm core of Quiet Steel panels (see Figure 2).
The first body application of Quiet Steel in a production vehicle was the cowl panel of the 2001 Ford Explorer Sport Trac. This type of application of Quiet Steel later won the Premier Automotive Suppliers' Commitment to Excellence (PACE) Award for the cowl panel on the Cadillac CTS.
Benefits of laminated steel
Currently, some of the body parts made using laminated steel include cowl panels, lower plenums, storage tubs, and for other areas where noise, vibration, and harshness (NVH) is a concern. Some mechanical parts, such as the oil pan on the 2004 Ford F-150 Triton V8, are made with laminated steel.
Using this material allows vehicle makers to produce quieter vehicles without adding extra steps during assembly. Another benefit is that the material is 100% recyclable compared to other non-recyclable materials like thick carpeting, cotton shoddy, foam, and mastics. Replacing non-recyclable materials with laminated steel may also increase the amount of interior space in the vehicle.
Characteristics of steels are similar
Characteristics of the steel, and total thickness, typically remain the same when a part is made with laminated steel. The laminated material is shipped to
stamping plants in a continuous coil or steel sheets. There, the parts are stamped, E-coated, and shipped for assembly. The material can be welded because the core is only 0.025 mm thick. Parts are commonly attached at the factory with squeeze-type resistance spot welding (STRSW). Other attachment methods may also be used. Daimler-Chrysler uses a windshield urethane adhesive for attaching the laminated steel seat tubs on mini-vans with Stow N' Go™ seating (see Figure 3).
Some repairability issues include identifying parts made of laminated steel, varying recommended repair procedures, and different joining techniques. Currently, most locations of parts made of laminated steel do not provide adequate accessibility for using STRSW equipment during repairs. GMA (MIG) plug welds are sometimes recommended, but weld contamination from the polymer core may arise.
Achieving adequate penetration through both layers of steel into the backside may be another problem. Practice welds help to identify the proper settings and techniques used to reduce contamination and achieve proper penetration in the weld, but this can only be done if laminated steel is available. A good practice is to keep a piece of this material in the facility for future repairs that require sample welds.
When making test welds, it is important to use a piece of laminated steel that closely matches the thickness of the intended repair. The total thickness of laminated steel can range from 0.8 mm to 3.0 mm and the polymer core can be specifically "tuned" for the type of noise the part is designed to absorb.
Differences in thickness or composition may affect the welding characteristics of the part. To avoid these concerns, General Motors recommends rivet bonding for repairs that involve laminated steel parts. When repairing laminated steel Stow N' Go seat tubs, DaimlerChrysler recommends that the repaired or replaced tubs be reattached with a urethane adhesive. GMA (MIG) welds are recommended for attaching the apron to the laminated steel cowl panel on the 2004 F-150.
The I-CAR Online Training program, 2006 Cadillac DTS Front Lower Rail Replacement, provides detailed information for replacing a front lower frame rail and explains the attachment process of the rail to the laminated steel cowl panel. This program also includes a sectioning procedure for the same front lower frame rail. Other General Motors vehicles that use a similar rivet-bonding procedure for repairing laminated steel include the 2005 Buick LaCrosse and the 2005 Chevrolet Cobalt.
Identifying laminated steel parts
At first glance, laminated steel parts may look identical to parts made of non-laminated steel. A closer look at the edges of the panel may show two separate pieces of steel sandwiched together (see Figure 4). To confirm, a firm tap on the part may also help identify that the part is laminated steel. Of course, vehicle maker service information is the best method to identify and determine proper repair processes for this new material.
Laminated steel is a sandwich-type material designed to reduce vibration and noise. Laminated steel has helped vehicle makers design quieter vehicles without adding additional assembly steps. It is a recyclable material and can reduce the amount of other non-recyclable sound-absorbing materials added to a vehicle. Repair technicians should be aware of the proper joining techniques to use when working with laminated steel. Vehicle makers may also have different recommendations for repairing these parts. It is important for repair technicians to stay informed of the latest technologies vehicle makers are using on their vehicles.
This Advantage Online article first appeared in the I-CAR e-newsletter, which is published and distributed free of charge. I-CAR, the Inter-Industry Conference on Auto Collision Repair, is a not-for-profit international training organization that researches and develops quality technical education programs related to collision repair. To learn more about I-CAR, and to subscribe to the free e-newsletter, visit http://www.i-car.com or contact I-CAR Marketing Communications Specialist Brandon Eckenrode at Brandon.Eckenrode@i-car.com.