Lightweight design has been a driving force at Audi for many years. The brand has been building cars with the Audi Space Frame (ASF) body continuously since 1994. And over the years it has time and again precisely tailored and improved the technology for use with the various vehicle concepts and their new requirements – right up to the latest stage, the multi-material ASF.
The Audi A8 (1994)
For the first generation of the Audi A8, the company once again completely reinvented the unitary body – using aluminum as a material and a concept tailored to the lightweight metal. The development work, which got started in 1982, yielded 40 patent applications. In the role of the production model’s forerunner was a technical study with the “ASF” designation, which caused a sensation at the 1993 IAA – its unpainted body of polished aluminum gleamed like silver.
The aluminum unitary body of the Audi A8, which followed in 1994, weighed only 249 kilograms (549.0 lb). And it was endowed with the fundamental ASF design principle, which still applies today: Extruded profiles – many with closed multi-chamber profiles – formed a lattice together with complex die-castings. Aluminum panels gave the structure rigidity. Of the 334 individual components, they were dominant, making up 71 percent of the total mix and far surpassing the share of profile and cast components. Roughly 75 percent of the assembly work at the Neckarsulm plant was done by hand.
The Audi A2 (1999)
The Audi A2 was the second model from Audi in the ASF design – and the premium compact model stood out by virtue of its remarkably low weight. The base version had a curb weight (without driver) of no more than 895 kilograms (1,973.1 lb), and the “3-liter” A2 1.2 TDI weighed in at just 825 kilograms (1,818.8 lb). The key factors behind this were the Audi Space Frame and the aluminum add-on parts with a total weight of just 153 kilograms (337.3 lb).
The A2 was conceived to be built in higher volumes than the A8, with up to 360 cars per working day. Its ASF showcased improvements and new developments that simplified the structure. The number of individual parts decreased to 225, and the B-pillar was made as a single large casting for the first time – for the luxury sedan it had still comprised eight components. Hydroforming was used to produce the profiles for the roof line, whose cross-section changed several times over its entire length. The underbody frame was welded together from extruded profiles, which were directly joined to one another.
The sheets also made up the largest share of the Audi A2 body, at 81 percent. Three joining processes dominated – punch riveting, MIG welding and the new laser welding, enabling Audi to achieve an 80-percent degree of automation.
The Audi A8 (2002)
For the second generation of the A8, the engineers improved the static torsional rigidity by 61 percent with the further developed Audi Space Frame, while the number of individual parts was reduced compared to the predecessor. The ASF body of the flagship model weighed only 220 kilograms (485.0 lb), more than 40 percent lighter than equivalent steel bodies at that time.
Audi also achieved major advances with the large castings. Their share of the total weight of the ASF rose from 22 to 31 percent, and a few of them integrated new functions like the door hinge mounts in the castings of the A-pillars. As in the Audi A2, the big side wall frame from the A-pillar to the rear end was made of a single low-drawn aluminum sheet, although even considerably larger and more ambitious in the A8.
The joining techniques also were further optimized, and a new technology came into play – laser hybrid welding. This technology’s special strengths – minimal distortion, good performance when filling gaps, and high process speed – make it particularly well-suited for large component joints susceptible to distortion, like where the roof is joined to the side wall frame, to name one example.
The Audi TT (2006)
The TT of the second generation displayed a major new innovation from the brand – the multi-material Audi Space Frame. The front body module, middle floor and superstructure of the compact sports car are made of aluminum. As a result, the material accounted for 68 percent of the total weight of the coupé.
Steel was used for the rear section of the floor assembly, the rear end, and the bulkhead (on the roadster). And to ensure good weight distribution, the doors and the tailgate were also made of steel.
Compared to the predecessor model with its all-steel body, the new concept reduced the curb weight by up to 90 kilograms (198.4 lb), depending on the version. In addition, it allowed outstanding axle load distribution and thus dynamic handling typical of a sportscar, bolstered by greatly increased torsional rigidity. The ASF body of the TT Coupé weighed only 206 kilograms (454.2 lb). Aluminum’s share of the mix comprised 63 kilograms (138.9 lb) of sheet panels, 45 kilograms (99.2 lb) of castings and 32 kilograms (70.5 lb) of extruded profiles.
The Audi R8 (2007)
For its R8, Audi transferred the ASF concept to a high-performance sports car for the first time. The results speak for themselves: The body weight of the coupé was 206 kilograms (454.2 lb). Extruded profiles play the lead role in the ASF sports car concept, at around 70 percent. Castings accounted for eight percent in the coupé, and aluminum sheets made up the remaining 22 percent.
And the ASF of the new Audi R8 also incorporated new ultra-lightweight materials. Made of magnesium, a rear cross-member in the engine compartment lent rigidity to the upper section of the rear module. For the Spyder, the rear side walls and the hood compartment cover – both load-bearing components – are made of carbon fiber-reinforced polymer (CFRP).
The Audi A8 (2010)
The third generation of the A8 – once again presenting impressive advances. Thirteen different grades of aluminum are used in the ASF, which is built from 243 individual parts. The B-pillars are made of ultra-high-strength, hot-stamped steel. The sedan body with the standard wheelbase weighs only 231 kilograms (509.3 lb).
The composition of the Audi flagship’s ASF works out to be 35 percent cast components, 35 percent sheets, 22 percent extruded profiles, and eight percent steel. Most of its cast components are made of improved alloys, produced using vacuum die-casting – a process that makes it possible to achieve mechanical properties with high values but also good ductility and good joining characteristics. For the higher strength components Audi increased the strength by up to 25 percent while also reducing the material thickness and the weight by up to 20 percent.
The Audi TT (2014)
With their multi-material design, the bodies of the current Audi TT and TT Roadster represent a new stage in the evolution of the ASF. The front end, and particularly the floor of the passenger compartment, contain many hot-formed steel components, which thanks to their extreme strength can perform with relatively thin walls, so they are lightweight. For the second time in a row, Audi succeeded in significantly reducing the curb weight of the TT while also increasing the torsional rigidity.
The characteristic ASF lattice of aluminum forms the superstructure of the occupant cell. Four castings comprise the nodes of the coupé – two at the A-pillars and two above the rear window – and the body, complete with the aluminum outer skin, weighs just 276 kilograms (608.5 lb).
The Audi R8 (2015)
With the new R8, Audi once again lowered the ASF’s weight, this time down to 200 kilograms (440.9 lb) for the coupé. The decisive factor behind this achievement is the new combination of aluminum and CFRP. The CFRP components – the rear wall, the center tunnel and the three-part B‑pillars – are produced using the highly efficient resin transfer molding (RTM) process.
The dry fiber matting and local reinforcements are first laid down, formed and then inserted into closed, heated tools. After they are closed, liquid epoxy resin is injected into the form and completely soaks the matting – and the components are then cured under pressure and temperature. The CFRP components form the functional backbone of the ASF and account for a 13-percent share of the materials. Considered in detail, they serve a number of different purposes, which is why they vary greatly from one another in their number and arrangement of the webbing layers.
The front and rear body modules of the new R8 are constructed of aluminum – from semi-finished goods that include castings, profiles and sheets. Cast nodes make up 21 percent of the ASF, the extruded profiles account for a 47-percent share, and the sheet panels 12 percent (numbers apply to the coupé). The remaining seven percent comprises other materials and connecting elements. The outer skin, including the doors and lids, is made entirely of aluminum.
The Audi Q7 (2015)
The current Q7 is the first Audi model based on the second-generation modular longitudinal platform (MLB evo). Its curb weight is up to 325 kilograms (716.5 lb) lighter than that of the predecessor, due also to the considerable reduction of the body weight – the multi-material body integrates large parts made of hot-formed steel and aluminum, and that alone saves 71 kilograms (156.5 lb). Also contributing to the weight savings are the body add-on parts, which account for a reduction of 24 kilograms (52.9 lb).
While ultra-high-strength steel components are used for the occupant cell’s safety cell, aluminum makes up a 41-percent share of the body structure. Parts such as the strut tower domes in the engine compartment and the connecting parts between the sills and longitudinal members are die-cast. The front and rear longitudinal members are made of aluminum profiles.
Aluminum sheets take up large sections of the floor, the rear wheel arches, the roof and the side wall frame. All components including doors, front fenders, engine hood and tailgate are made entirely of the lightweight metal.
The equipment, data and prices specified in this document refer to the model range offered in Germany. Subject to change without notice; errors and omissions excepted.