Part II: The New BMW 6 Series - In Depth

Press Release

Part II: The New BMW 645Ci - In Depth

Article contents - Page reference
Part I: The New 645Ci - In Depth
6 Series Photo album - 40 Photos added

Bodyshell:

Intelligent Lightweight Construction for a New Dimension of Dynamic Motoring To be really dynamic, a modern car requires not only a powerful engine and an excellent chassis, but also lightweight components reducing weight to a minimum. The name of the game, therefore, is intelligent lightweight technology also on the body of the car, "intelligent" meaning that lightweight components serve not only to reduce weight, but also to enhance the various functions of the vehicle. An intelligent mix of materials saving weight and enhancing crash safety.
The key concept on the body of the car is to use the right mix or combination of materials. Precisely this is why the bodyshell is a combination of steel, aluminium and plastic components offering huge advantages in terms of weight reduction. And at the same time the body of the car is stiffer and firmer than ever before, serving to enhance crash safety and providing even more precise dynamic driving characteristics. The Weight-Reduced Aluminium Front (WRAF) is a good example of intelligent lightweight construction. Weighing approximately 45 kilos or 99 lb, this entire module is about 20 per cent lighter than a conventional steel structure of the same kind. Building the new 6 Series, BMW is also entering new terrain in the use of aluminium: The spring supports housing the front axle springs and dampers are made of a pressure-cast aluminium alloy composed mainly of aluminium and small amounts of magnesium, silicon and manganese. This alloy combines superior strength and stiffness with strong resistance to any change in shape. The two doors are also made of aluminium, saving approximately 10 kilos on the car but nevertheless outperforming all of BMW's internal stiffness and safety requirements. Front lid in new bonding technology.
The front lid is also made of aluminium and at the same time incorporates a world-first achievement currently only available from BMW: The inner and outer panels forming the lid are joined not by a single-component glue, but rather by a two-component glue bond allowing the use of thinner aluminium panels reducing the overall weight of the front lid by 9 per cent. A further advantage is that this two-component bond makes the front lid extremely stiff, which minimises wind noise in the process. The two front side panels made of thermoplastic save approximately 4 kilos in contributing to the excellent driving dynamics of the new 6 Series. And an equally important point is that the use of such a sophisticated synthetic material enables the designers to consistently continue the line of BMW's large coupé throughout the side panel area, since it would not have been possible with a conventional steel structure to integrate the side trim into the side panels in the same way. A further advantage is that thermoplastic, being a regenerating synthetic material, is less sensitive than steel to minor bumps. And last but not least, this special material provides a better potential in meeting pedestrian safety requirements to be expected in future, yet a further point being that it is absolutely rustproof in the interest of a long service life. SMC plastics saving weight and providing new design options.
SMC, a special synthetic material used on the rear lid of the BMW 6 Series Coupé, also offers a wide range of benefits. This duroplastic material referred to in technical terms as a sheet moulding compound is approximately 25 per cent lighter than steel and offers far greater freedom in design, allowing the outer skin of the rear lid to be made of one single piece even integrating the rear spoiler and aerials. Tailored rolled blanks to keep body panels as slim as possible.
Last but certainly not least, a new process used on the rolled components also saves a lot of weight on the 6 Series: Tailored rolled blanks, that is panels rolled in a dynamic process, come in exactly the right thickness at all crucial points. This means that they do not require any additional reinforcements at highly exposed points, but are rather tailored to specific requirements and are made thicker only where really necessary. This process is now being used in a BMW model series for the first time on the transverse and longitudinal seat supports and on the heel crossbars, not only saving weight, but also enhancing the car's safety above all on the crossbar elements. Innovative production methods allowing an intelligent mix of metals.
Innovative production methods are required to provide the right combination of materials on the body of the car. A special insulating glue, for example, had to be developed for bonding steel and aluminium and is applied over a distance of approximately 60 metres or almost 200 feet on the 6 Series. Then there are approximately 4,000 welding points and almost 70 bolted connections. Depending on load conditions and the material involved, other joining technologies applied on the new 6 Series Coupé are MAG welding (MAG = a reactabale protective gas), MIG soldering (MIG = an inert protective gas), laser-soldering and welding, beading, riveting, sublining, sealing, clinching, and clipping. Overall, the body of the 6 Series is made up of almost 500 steel and aluminium components and weighs less than 350 kg or 770 lb together with all attachments and add-on parts.