Audi ultra lightweight technology reduces weight by as much as 90 kilograms, compared with the previous Sportback model.
The five-door model with the 1.4 TFSI engine has a kerb weight of just 1,225 kilograms. Hot-shaped high-tensile steels are used in the occupant cell of the new A3 Sportback and the bonnet and front guards are made of aluminium.
The complete occupant cell is 37 kilograms lighter overall than in the previous model. Further weight reductions were achieved throughout the interior and in the engines.
Many of the A3’s design principles and individual components are based on the group’s new modular transverse platform which offers a great deal of technical and financial freedom for ultra-lightweight design.
The ultra-lightweight design principle is not an obligation for engineers, but rather a state of mind, says Audi. Its engineers always consider the vehicle as a whole, making every gram count in every area.
Many interior trim elements, for instance, are now fastened with plastic expansion rivets; each one saves four grams
of weight compared with the steel screws used in the previous model.
The air conditioning system has shed 4.0 kilograms because the fan motor now requires fewer coils. The housing for the passenger airbag is made from plastic and the frame of the MMI monitor from magnesium – both components have dropped a combined weight of 0.6 kilograms.
Engineers also made substantial weight savings on the chassis of the new Audi A3. The front axle subframe is cast in a single piece from aluminium.
In the press shop and bodyshell shop, the forming of the aluminium components and their connection with the steel parts present particularly tough challenges.
The same applies to the form-hardened components, which are coated with an anti-corrosive layer made from an aluminium-silicon alloy. The bodyshell of the new A3 features a wide array of jointing technologies, including adhesive bonding, clinching and punch riveting.
The joint between the side wall and the roof of the Audi A3, which are both made from steel, is created by a plasmatron-soldered seam, with the permitted tolerance reduced to just a few tenths of a millimeter.
The finished seam is polished with brushes to create a “zero joint” that is virtually invisible. In contrast to the previous model, the doors and window frames are pressed in a single piece, which also saves weight.
The largest single component on any car is the bodyshell, which offers particular potential for weight saving.
In accordance with the principle of “the right material in the right place for optimum function”, a steel cell was created for the new A3 using a multi-material construction.
The outcome is 25 kilograms lighter than for the preceding model. At its core are form-hardened steels; prior to being formed, they are heated to almost 1,000 degrees Celsius in a continuous furnace and then quenched to around 200 degrees immediately afterward in a water-cooled press tool.
This temperature drop creates an extremely stiff iron-carbon structure – form-hardened steels can handle low wall thicknesses, and the associated parts weigh 18 kilograms less than conventional components.
Form-hardened steels are used in the transition from the front section to the occupant cell, in the A-pillars, B-pillars, roof arches, center tunnel, sills and floorpan. Altogether, they constitute 26 percent of the occupant cell. A tailored rolled blank forms the transition from the floor to the rear section; its eleven segments are rolled to five different thicknesses.
High-strength and ultra-high-strength steel grades are used in many other bodyshell areas, such as the floor of the occupant cell. At the front of the vehicle, the hood and fenders are made from aluminium – making the hood 7.0 kilograms lighter and saving 1.1 kilograms on each of the fenders.
Aluminium fans since 1913
Early Audi engineers were fascinated by aluminium often drawing inspiration from aeronautical engineering.
In 1913, NSU built the Type 8/24, with an all-aluminium body. Ten years later, the Audi Type K wore an experimental aluminium streamlined skin.
In the 1930s, specialists from the Racing department of Auto Union manufactured aluminium panels by hand and used them to build the bodies and streamlining panels for their spectacular racing cars and land speed record cars.
Lightweight design advanced to the level of a strategic project at Audi in 1982, at which time the company established a joint venture with an aluminium company from the United States.
The mission was nothing more and nothing less than to once again reinvent the self-supporting body, but this time with a material that is roughly two-thirds lighter than conventional steel and also with a new geometry tailored to this material – the Audi Space Frame (ASF).
The new technology was ready for series production in 1993 when a shining silver showcar with an unpainted body of polished aluminium was on display at the International Motor Show in Frankfurt am Main, Germany.
The A8 paved the way for Audi into the premium league, and it also sparked new developments for the traditional material of steel.
ASF: the reversal of the weight spiral
The reversal of the weight spiral that Audi initiated with the ASF principle has major secondary effects.
In fabrication, traditional spot welding is being replaced by joining methods developed by Audi, including punch riveting, bonding or laser-MIG hybrid welding.
In the TT and the R8, self-tapping screws are used to join many of the components. Another innovation is the laser-welded invisible seam on the roof of the TT.
Lightweight Design Centre
Around 180 employees at the Audi Lightweight Design Centre in Neckarsulm work in close collaboration with research institutions and partners in industry.
The company has a new FRP Technical Center for fiber-reinforced polymers. Officially inaugurated in 2012, it now employs more than 50 experts. Audi engages in an intensive technology transfer with other group brands such as Lamborghini for the materials CFRP (carbon fiber-reinforced polymer) and aluminium.
Aluminium, high-strength and ultra-high-strength steels, magnesium and fiber-reinforced polymers – from its development work, Audi researches all the materials used in the construction of automobile bodies, with all of their advantages and disadvantages.
Audi philosophy is: “The right material in the right location in only the amount necessary.”
The engineers at the Neckarsulm Lightweight Design Center continue to drive the competition between these materials, always on the lookout for an optimised solution.
The Audi body of the future will use these high-end materials, with the mix varying depending on the model.
Audi says lightweight construction not only means material engineering, it also means full competence in process technology and quality assurance, the development of new joining technologies and ease of both service and repair.