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Sustainable production technologies of emission reduced light weight car concepts

Final Report Summary - SLC (Sustainable Production Technologies of Emission reduced Light weight Car Concepts)

SUPERLIGHT-CAR (SLC) was a collaborative Research & Development project, running from 2005 to 2009, where 37 leading organisations from 9 European countries have worked together to bring lightweight automotive technologies closer to high volume car production. It featured the full title: 'Sustainable production technologies of emission reduced lightweight car concepts' and demonstrated one efficient solution for the distribution of dissimilar materials in an existing compact class vehicle. As the project comes to a conclusion, it can display an impressive car-body weight reduction of 35 % in a compact car that can be produced at 1000 units per day.

The European automotive industry is world leading in technologies for energy efficiency and CO2 reduction in vehicles; important factors for an industry that seeks to radically reduce its environmental footprint. One key to reinforce these strengths is to decrease the vehicle weight, and thereby the fuel consumption. The concept of lightweight vehicles is nothing new; sports cars have been produced with lightweight materials for decades. Yet steel remains the main material of mass-produced cars, due to the lack of technologies for bringing lightweight vehicle production up to scale.

To show the feasibility of the SUPERLIGHT-CAR concept and to gain in operating experiences, several prototypes have been built up. These prototypes are not only testing objects but learning supports too. Several technologies have been demonstrated by producing parts under prototyping and industrial like conditions. This includes:
- Warm formed Magnesium roof panel and front and rear roof crossbeams (in AZ31 Mg).
- Roof crossbeam middle in carbon fibre reinforced plastic pultrusion technology.
- Tunnel press hardened steel part with lengthwise integrated tailor welded blank technology.
- Tunnel reinforcement as press hardened steel with tailor rolled blank technology.
- Front longitudinal rail using aluminium tailor welded blank technology.

The biggest and most important prototype is a complete body in white (BIW) with a 1:1 scale. This BIW have been engineered with the materials, material grades, gauges and joining methods as defined in the project. However, to actually build the final model a feasibility study of the individual parts has to be carried out. For all aluminium parts a finite element simulation is done.

Advanced joining technologies are the key for cost-efficient high-volume assembling of multi-material structures. The joining work in the SUPERLIGHT-CAR project was focussed on:
- continuous joining (welding/brazing), in particular optimisation towards high strength steels as well as aluminium with laser and laser induction, and multimaterial solutions with hybrid technologies;
- cold joining (adhesive structural bonding, pulse magnetic welding, friction spot stir welding) well suited for multi-material joints (and steel-aluminium joints);
- mechanical fasteners and insert techniques;
- high speed joining (>3m/min) enlarging process tolerances (hybrid welding) for mono-side access joining on thinner wall hollow section (profile, roll formed hollow section);
- body assembly sequence optimisation.

Assembly of front end physical demonstrator was performed by using multi-materials joining techniques. Precision positioning of shaped parts was ensured by assembly station with 0,3 mm geometrical accuracy. This was checked by 3D metrological measurement on assembled front end. Different joining techniques were used: 2K adhesive glue ensures continuous joining needed for body high structural integrity. Self Piercing Riveting & Screwing ensure clamping of assembled during adhesive glue reticulation. Cold Metal Transfer and Melt Inert Gas weld brazing were successfully used for joining Hot Press Steel parts as rocker transverse beam with Aluminium long front rail.

The SUPERLIGHT-CAR project has successfully tackled the challenge of a feasible car-body concept suitable for high volume production, with an achieved weight reduction of 35 %. A multi-material approach was used where each specific body part is made from the most suitable material to fulfil the requirements while minimising the weight. The car-body is composed from aluminium, new steel, magnesium, and fibre reinforced plastics. Appropriate design and manufacturing technologies were developed to allow for the production of high volume series.

The body-in-white concept developed by SUPERLIGHT-CAR has exceeded the initial target and offers, with a weight of 180 kg, a weight reduction of 101 kg compared to the reference car (Golf V), showing an equivalent performance. The full body-in-white prototype was recently presented at the international conference 'Innovative Developments for Lightweight Vehicle Structures', where it was enthusiastically received by the automotive industry.

The SUPERLIGHT-CAR concept also demonstrates economic potential. Originally targeted at EUR5-10 per kg of weight saved, the final additional cost landed at EUR 7,8 per kg of weight saved. Based on the expected fuel savings of 0,3 - 0,5 l/km that the SUPERLIGHT-CAR concept implies, a fully economic solution would require a reduction of the additional cost to EUR 5 per kg of weight saved. Future research based on the findings of SUPERLIGHT-CAR is expected to overcome this economic challenge, while advancing lightweight technologies even further. Clearly, the SUPERLIGHT-CAR consortium has taken a significant step towards the sustainable mass-produced vehicles of tomorrow.