The New Aston Martin DB9 | Part Two

The bonding has enormously high stiffness, so that shakes and rattles are obliterated. Bonding also has excellent durability offering better stress distribution than welding - which is more prone to crack. The process is also used in the aircraft industry and Formula One.

There are also advances in the welding procedure. On the DB9, the upper and lower C-pillars are joined by advanced ultrasonic welding. It works by using a vibrating probe, called a sonotrode, which oscillates at 20,000 Hz. This high frequency of vibration agitates the molecules of the two aluminium panels to be joined, allowing them to form a molecular bond.

Because the bond takes place at a molecular level, it is 90 per cent stronger than a conventional spot weld. It also requires only five per cent of the energy of conventional welding, and as it generates no heat, there is no contamination or change in the characteristics or dimensions of the metal. Aston Martin is the first car company in the world to use this technique.

Lightweight frame helps performance and handling

In addition to the aluminium frame, other lightweight or high-technology materials are used extensively. The bonnet, roof and rear wings are aluminium. The front wings and bootlid are composite. Cast aluminium is used in the windscreen surround, another industry first. Magnesium alloy, which is even lighter than aluminium, is used in the steering column assembly and inner door frames. The driveshaft is made from carbon fibre. It is part of the torque tube that rigidly connects the front engine to the rear gearbox. This arrangement helps the DB9 achieve perfect 50:50 weight distribution, further improving handling.

Lightweight suspension, brakes and wheels

The DB9 uses all-round independent double-wishbone suspension. As the body frame is brand new, the chassis designers were able to start from scratch - rather than be forced to develop a suspension for an adapted saloon car platform. The front suspension is mounted on a cast aluminium subframe. At the rear, another subframe carries the rear suspension as well as the rear transaxle. Forged aluminium wishbones are used front and rear, as are aluminium-bodied dampers. This is rare, even on top-end sports and GT cars.

The steering rack is mounted ahead of the front wheels, which provides better control under extreme steering loads and heavy braking. Magnesium alloy is used in the construction of the steering column.Even the wheels have been specially designed to save weight. The 19-inch alloys are made using flow forming rather than casting. This saves about 1kg per wheel, benefiting unsprung mass, overall vehicle weight, and reducing rotational inertia. The tyres have been specially developed by Bridgestone.

continues... | Part Three
Published 9 January 2004 Melanie Carter
 

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