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News

Swedish Steel reduces Italian car seat weight

SSAB Tunnpl : 21 February, 2002  (New Product)
By using thin-walled tubing in extra high strength steel from SSAB Swedish Steel, Lear Corporation in Italy has succeeded in reducing the weight of the Alfa Romeo 147 rear seat by 25 per cent. The new car seat design, which was completed in record time and which recently won the Swedish Steel Prize, the international engineering industry accolade, is now being exhibited. In addition to reduced weight, the Italian designers have succeeded in improving the seat's rigidity and shock-absorbing capacity, which contributes to enhanced safety in a collision.
By using thin-walled tubing in extra high strength steel from SSAB Swedish Steel, Lear Corporation in Italy has succeeded in reducing the weight of the Alfa Romeo 147 rear seat by 25 per cent. The new car seat design, which was completed in record time and which recently won the Swedish Steel Prize, the international engineering industry accolade, is now being exhibited. In addition to reduced weight, the Italian designers have succeeded in improving the seat's rigidity and shock-absorbing capacity, which contributes to enhanced safety in a collision.

The body of the new Alfa Romeo 147 back seat is constructed around a steel tubing frame in SSAB Swedish Steel's extra high strength steel Docol 600 DP which has a minimum tensile strength of 600 N/mm2. The dual-phase steel has excellent ductility in combination with its high strength. The result is a rear seat design which is three-quarters the weight of previous designs. It is also more rigid and has a greater shock absorption capacity.

'The steel's properties have proven decisive in meeting Alfa Romeo's rear seat design requirements,' says Dario Castellano, head of product development at Lear Corporation in Turin. 'The time schedule was also unusually tough,' he continues. 'We had 18 months in which to complete the assignment, half the time normally allocated to development projects.'

The back support, the section of the seat most exposed to shock, has a steel tubing frame.

The 30-millimetre, thin-walled tubing has a wall thickness of 1.5 millimetres, and is bent into the right shape for the frame.

'The steel is so strong that we could have made the tubing walls thinner without compromising on the strength requirements, but that would have involved more complicated welding,' comments Mr Castellano. 'As it is now, the tubing can be bent, welded and worked in other ways without problems. Production costs are therefore optimal.'

A divided rear seat makes considerable demands on both the material used and the design. In a collision there is considerable stress in the middle, where the seat support is divided. This is also the place where the middle passenger is belted and where the safety belt, in turn, is connected to the seat. In addition, forces are created by luggage items in the rear of the vehicle which are thrown forward in a collision. In the crash tests, Lear's auto designers placed 18 kilograms of loose, heavy cubes in the car's luggage compartment. When the vehicle is in a frontal collision, the cubes must not penetrate the back support more than a few millimetres behind the crash test dummy.

The frame of the two back sections is bent into shape from a single-piece section of tubing. The frame of the widest of the two back support sections is welded to a beam in Domex 700 MC, a hot-rolled extra high strength steel, which has a minimum tensile strength of 750 N/mm2. The material thickness of the bar is 3 millimetres. The back support is then attached to the autobody using a bracket in the same hot-rolled steel as the bar, but with a material thickness of 4 millimetres. The bracket functions as a robust hinge and is one of the five anchorage points for the back support.

The housing for the middle passenger belt is fitted to a separate bar in the top of the back support. The bar, like the tubing, is manufactured in Docol 600 DP. The material thickness is 1.5 millimetres.

'The strength of the steel is impressive and the project has confirmed our conviction that still stronger and lighter designs can result from the use of high strength steel without prices soaring. But when it comes to design it is important to think along new lines and to continue following materials research and development,' Mr Castellano concludes.
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