Deel 2:
The innovative direct-fibre-layering process specially developed for this purpose makes it possible to entirely dispense with the normally needed intermediary step of manufacturing entire sheets of carbon fibre. Using another newly developed process, the layered panel is wetted with epoxy resin and cured within minutes. Finish is smooth, precise and neat although just-auto has only seen the polymer base, not the fully-fitted sub-assembly.
Metals
A high-strength combination of hot-formed steel components make up the occupant cell, which comprises the lower section of the front bulkhead, the side sills, the B-pillars and the front section of the roof line. Some of these sheet metal blanks are manufactured in varying thicknesses by means of tailoring technologies while others also undergo partial heat treatment. That reduces weight and increases the strength, especially in safety-critical areas.
As always with A8s, aluminium components in the form of cast nodes, extruded profiles and sheets, elements long characteristic of the ASF design, make up the biggest share of the new body, at 58%. New heat-treated cast alloys attain a tensile strength of over 230MPa. The corresponding yield strength in the tensile test is over 180MPa and for the profile alloys it is higher than 280MPa and 320MPa significantly higher than previously.
Rounding out the intelligent mix of materials is the magnesium strut brace, 28% lighter than before. Aluminium bolts secure the connection to the strut tower domes, making them a guarantor of the body's high torsional rigidity. In the event of a frontal collision, the forces generated are distributed to three impact buffers in the front end.
New body shop
Not content with redesigning the shell from top to bottom, Audi has built a brand new body shop for it - sadly operating only in 'ghost' mode for our visit with all the (mostly Kuka) robots going through all their motions but not actually handling any parts, though a lot of pre-production sub-assemblies were on display.
The shop was designed to ensure maximum energy efficiency and conservation of resources. The new spot welding tongs are powered by electric motors, and they weigh 35kg (77.2 lb) less than their predecessors – allowing the use of smaller robots, which in turn use less electricity. The halls are equipped with LED lighting (switched off by area when not needed as robots don't require lighting to work), and intelligent concepts for ventilation and shutting down equipment further reduce energy requirements.
The plant is equipped with about 500 robots, 90 adhesive systems, 60 machines for self-tapping screws, 270 punch riveting systems and 90 resistance spot welding tongs. Many robots perform several process steps, and in the intervals they autonomously switch to the tools needed, such as gripping arms and adhesive guns.
In plan view, the two directly adjoining buildings resemble an equilateral triangle. There are three production levels in the new building, which is 41m (134.5 ft) high. Each level encompasses 50,000 square metres (538,195.5 sq ft) of floor space. Supporting columns divide the floor space of each level into a grid of 500m (1640.4 ft) sections. Beneath one of the halls is the plant's railway loading station, where girders span a distance of 36m.
As noted earlier, there are 14 different joining processes to assemble the multi-material body, including roller hemming, grip punch riveting, and remote laser welding of aluminium which is a claimed Audi world first.
Roller hemming is used all the way around the complete front and rear door cutouts which allows larger openings (up to 36mm or 1.4 inches) for easier entry and exit and a wider driver's field of vision around the A-pillar.
Grip punch riveting, which fixes the side wall frame in its position, accompanies the roller hemming process, which in turn is supported by structural bonding. It was the development and adaptation of these joining technologies to this specific application that first made it possible to use the material concept and to combine the aluminium side wall frame with the hot-formed, high-strength steel sheets at the B-pillar, the roof line and the sills with their thin flanges.
With remote laser welding of aluminium, exact positioning of the laser beam in relation to the welding edge considerably reduces the risk of hot cracking because the heat input can be precisely controlled. The size of the gap between parts being joined can immediately be determined and effectively filled in by means of process control. The laser beam's high feed rate and low energy use reduce CO2 emissions by about one quarter. This new process also results in a 95% saving on recurring costs in series production because it eliminates the need for the costly process controls required with conventional laser welding
Used at the rear, at the water drain channels, is a further development of the conventional aluminium MIG (metal inert gas) welding process based on the established CMT (cold metal transfer) process. The development approach is essentially a geometric modification of the inert gas nozzle which makes it possible to achieve process speeds of up to 50mm/s and a very fine weld seam appearance. Compared to conventional MIG welding, this triples speed and also results in considerably reduced heat input, and therefore also less risk of component distortion. To ensure the welding wire is positioned at the component edge with the required precision, the process is performed in combination with a system for automatic seam detection and seam tracking.
Resistance spot welding (RSW) of aluminium is a highly versatile joining process. High-performance plant technology combined with control technology adapted to the requirements of working with aluminium are delivering improvements in process stability and reproducibility of welding results. Use of welding tongs with higher electrode forces makes it possible to reduce undesirable adhesions from the copper electrode onto the aluminium component.
Laser welding is used to join the sides of the A8 roof to the side walls along a practically invisible zero gap.