ULSAC MAKES CAR DOOR 42% LIGHTER THAN CURRENT DESIGNS
29 October 2000 - Corus Automotive

These findings have been confirmed by the actual manufacture of a 'window frameless' door that is 33 per cent lighter than the benchmarked average for all door types in the concept phase and 42 per cent lighter than the benchmarked average for frameless doors in the validation.

The ULSAC study has been commissioned by an international consortium of 30 sheet steel producers to assist their automotive customers with viable lightweighting solutions. The consortium has contracted Porsche Engineering Services to provide engineering management for the programme.

To create a lightweight mass-efficient closure, while exceeding the crash safety requirements for lateral stiffness and side intrusion, the ULSAC study has completely reappraised the typical car door. This new approach has enabled the Porsche engineering team to reduce weight in key areas, while strengthening important strategic locations such as hinges and latches.

The high strength required for the basic structure has been achieved by replacing the normal steel inner panel with four steel tubes. Two hydroformed tubes in 280MPa high-strength steel form the latch and hinge uprights, while two straight tubes in 800MPa ultra-high-strength steel form the adjoining upper and lower longitudinal members. A stamped laser-welded tailored blank of 1.2mm and 1mm gauge 140MPa mild steel provides an additional reinforcing inner front member, which incorporates the mirror flag.

The resulting mass of the basic steel structure, at 10.5kg, is almost 2kg lighter than the target mass of 12.3kg. Independent studies by Massachusetts Institute of Technology show the closures can be manufactured in high volume (+250,000) with no cost penalty. The manufacturing cost for a pair of ULSAC door structures built to the target mass is £91 (133 Euros). The investment in innovative processes like hydroforming and laser welding are compensated through huge savings in material costs.

Commenting on the success of the ULSAC design, Simon Kragtwijk of Corus Light Strip Products, said: 'The preliminary results of the study, showing that significant mass reduction with steel closure structures can be achieved with high structural performance and no cost penalty, are indeed remarkable.'

He added: 'Interestingly, the ULSAC study is a microcosm of virtually all the technologies applied throughout the UltraLight programmes. These complementary studies are playing a pivotal role in the transfer of advanced steel technologies to the motor industry, which is under enormous pressure to provide personal transportation at affordable cost.'

The ULSAC design has changed significantly between the concept and validation phase, which has led to the application of a plethora of new materials and processes that are available but not yet commonly used in today's cars. This includes ultra high strength steels (800MPa), roll and tubular hydroforms, and laser-welded tailored blanks. Laser welding was also used extensively in the assembly of the door.

The ULSAC study is now seeking to maximise the stiffness benefits of the sheet hydroforming process for the door outer panel, to consider how steel's excellent strain hardening characteristics can be further utilised and to apply the experience gained so far to other closures including the bonnet (hood) and bootlid (decklid) on a saloon and the tailgate on a hatchback or estate.

To ensure total functionality, the ULSAC frameless door includes designs for the complete door package incorporating similarly highly developed features for the non-steel parts including the trim, mirror, latch assembly, electronic locking, glass, regulator mechanism, wiring harness and speaker.

Working on aspects of the programme, Corus Research, Development & Technology (RD&T) performed sophisticated strain measurements called 'circle grid analysis' using the Phast system jointly developed with Geodelta, which can process and measure millions of surface points simultaneously and very rapidly over a complete structure.

Corus IJmuiden Technology Centre (IJTC) in the Netherlands and Welsh Technology Centre (WTC) at Port Talbot are also helping to determine steel's dynamic resistance to denting, essentially by firing bullets at the door panel. The shape and depth of the resulting dents are then measured using highly accurate coordinate measuring machines and ultrasonic equipment. The findings will have a major influence on determining the optimum thickness and geometry of the panel to minimise denting.

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