Third-Generation Audi Space Frame
In 1994, Audi became the first automaker to successfully produce the world’s first mass-produced, aluminum-bodied car — the A8. Its concept refuted the notion that weight equals strength. Today, after a more than $300-million investment in the Audi Aluminum Competence Center and production facilities in Germany, the 2004 Audi A8 L is setting a new benchmark for lightweight automotive design and construction with an exclusive, third-generation Audi Space Frame (ASFâ). The ASF is approximately 300 pounds lighter than a comparable car’s conventional steel frame, and provides a backbone that increases the torsional rigidity of the all-new Audi flagship by 60 percent over the previous model. This accomplishment is even more impressive considering ASF uses 17 percent fewer parts, while demonstrating increased stability, strength and safety properties. The latest version of the ASF is the product of systematic refinement, with newly developed materials and imaginative use of aluminum in automobile production. The New Audi Space Frame (ASF) The ASF consists of large multi-functional castings, long and continuous profiles and a high proportion of straight, extruded sections that replace multi-part elements of previous iterations. By reducing the overall parts count to 267 from the previous 334, approximately ten percent in parts weight is saved. A fewer number of parts also simplifies construction, which improves production results and helps control costs. The smaller number of elements also mean fewer part joints, improving overall rigidity as the frequency of connections is reduced and the number of potential flex points is lowered. The reduced number of parts and part joints results in increased overall strength, enhancing crashworthiness. Improved structural integrity as a result of fewer parts and part joints helps prevent vibrations that are sometimes felt through the passenger seats or steering wheel. Reducing these vibration tendencies helps ensure a solid, comfortable ride and feel. A unique feature of the ASF is the combined use of several semi-finished aluminum elements. Castings, profiles and panels form a self-supporting frame into which each connecting component is integrated, achieving maximum stability with minimal mass. Audi engineers employed new production techniques for the construction of the space frame. Newly developed joining techniques are also employed for superior fusion of parts. A Vacular die-casting process used in previous versions also is employed for ASF construction, as well as a hydroforming technique developed by Audi for the world’s first high-volume production aluminum-bodied car, the Audi A2. Advanced Structure ASF consists of a single unit divided into front and rear sections and joined to the underbody of the vehicle. The revolutionary, fully pneumatic Audi Adaptive Air Suspension system of the A8 L necessitated development of an entirely new rear section. (Please refer to the Audi Adaptive Air Suspension release for complete details.) The rear structure of ASF consists of two large, central castings that connect the side sills, along with the C- and D-pillars, to a longitudinal member. The larger of the two castings supports the entire rear sub-frame and connects the sills at the back to protect the fuel tank in a rear-end collision. The other casting connects the C- and D-pillars and serves as the top mount for the suspension and forms the outside edge of the roof frame. The rear castings also form part of the air spring suspension mount points, and also are connected with the rear shelf to provide a base for mounted audio components. The forward structure of the ASF contains a single casting that replaces an eight-part assembly and several support components in the previous version. This large, multi-functional casting serves as the support for the air conditioning system, pedal mount and windshield frame cross-member. The front and rear structures are joined to the side of the roof frame, the sills, the seat cross-members, the B-pillars and the floor panels to form the continuous space frame. The side of the roof frame is a hydroformed extrusion with varying cross-sectional diameter to meet different load limits along its length. To ensure a high degree of roof shaping with minimal machining, a separate sheet metal element replaces a door seal flange and also serves as a connection point for interior components. The longitudinal members of the ASF also are divided into front and rear sections. These sections are joined by a casting that serves as the mount for the sub-frame and engine cross-member, and as the support for the fender bracket and the air spring suspension strut mount. For ease of repair, the front longitudinal member is bolted on. The A-pillars — consisting of two large, cast shell-halves clasped together beneath the sill and at the top through the side of the continuous roof frame — are connected with the tunnel structure to help prevent body twist and flex. The B-pillars are designed for strength in the event of a side collision. The castings serve as rear door hinge mounts and front door striker mounts. Whereas the B-pillars of previous ASF versions consisted of eight parts each, the new-generation Audi Space Frame B-pillars are each a single, multi-functional piece. When joined to the roof, these single-piece B-pillars significantly increase body rigidity and strength compared to earlier models. Finally, a single-section roof is laser welded to the structure along the length of the side rails, completing the upper structure connecting the front and rear sections, which in turn are connected to the underbody, completing the contiguous ASF. Advanced Materials Rapid-hardening alloys developed specifically for use in the ASF construction eliminate a separate heat exposure process during body production. These new alloys achieve comparable strength to conventional alloys, but cure at lower temperatures and in less time, preserving integrity and tensile strength and virtually eliminating flow lines. The new alloys are used exclusively in interior structural areas where its higher strength and energy-absorption potential is especially beneficial. The new alloys are heat-treated at the paint shop, eliminating steps in the build process, saving time and cost. Alloy panels, both delivered as blanks and on a roll, are heat-treated after forming. This increases tensile strength while affording weight savings as compared to panels that are not exposed to heat-treating. The process also has an aesthetic benefit: post-form heat exposure renders the alloy panels almost impervious to permanent dents, such as those caused by hailstones and parking lot “dings.” Advanced Production Techniques New in ASF production — and another world-first — is a laser-MIG hybrid joining technology. Laser-MIG hybrid welding combines the joining techniques of MIG and laser welding for higher-quality seams, enhanced process reliability and gap-bridging capacity. The process is faster, so there is less thermal distortion of parts, and more economical, as it allows for a single joining technique in production of multiple body versions, and satisfies legal requirements for global build processes. Green-sand casting is another new production technology used in this version of ASF. Green-sand casting is a “box-less” process that permits freedom in component design while producing parts that exhibit outstanding welding properties. Green-sand castings are also suitable for heat treatment, making them ideal for manufacture of strength-relevant structural components. A Lighter, Smarter Design The third generation Audi Space Frame improves on the already impressive designs of previous versions of the ASF, and passes on to Audi owners even more of the inherent benefits of aluminum in automobile production: design flexibility, lighter weight, superior strength, outstanding safety properties and, ultimately, enhanced driving performance. |