Multi-material Approach with Integrated Joining Technologies in the New Volvo S80 1999-01-3147
In May 1998 Volvo launched its most exclusive car model so far, the Volvo S80, which is aimed to compete with upper luxury segment products. The car is produced in the new production facility in the Torslanda plant in Sweden. Among the more highlighted features were a transversely mounted in-line six cylinder engine with a specially designed gearbox, electronic multiplex technology with 18 computers in the network, and safety features like stability and traction control (STC), front seats with integrated antiwhiplash system (WHIPS) and inflatable curtain (IC) for improved side impact protection.
To fulfill the product's high demands on safety, quality and environmental care, the design, materials selection and assembly of the car body with high precision had to be very carefully engineered. As in previous product-/process development a holistic and concurrent engineering approach was necessary.
In order to minimize car body weight as a consequence of lower fuel consumption, but maintain high product properties in terms of stiffness, energy absorption and fatigue, some 40% of the overall body weight is represented by various grades of high strength steels, such as rephosphorized and dualphase qualities. For the rear bumper beam, a Boron alloyed steel with >1000MPa in ultimate strength was chosen. For these material qualities, welding process data had to be adjusted to assure superior weld quality.
To lighten the BIW even more, aluminium was used for hang-on parts like the hood and trunk-lid. No welding is used for these parts, but only mechanical joining methods such as clinching and riveting. To meet security demands, and protect from burglary in the trunk-lid, self-piercing rivet technique was used for the attachment of the locking reinforcement.
The S80 has particularly distinctive treatment of the rear wing. The trunk-lid is stepped higher than the wing, something that gave the S80 the visual individualism essential to separate it from more traditional shapes. To solve this trunk lid design an injection moulded part made of PC/PBT was attached to the conventionally stamped aluminium part.
Laser welding, utilized by Volvo since 1991, was further improved for the S80 production. The laser welding cell, situated in the main production line, is equipped with two laser sources and adherent robotized beam guidance system. These robots are working in parallel in order to shorten cycle time. The flexible body shop, with multi-tooling for high precision reasons, gave the possibility to launch and ramp up the S80 production as the second product (1.product Volvo S70) on the same line without loosing S70 customer cars.
This paper will describe some of the topics mentioned above, with a specific attention to the interactive work between materials development and the choice of adequate joining processes. A new system for quality assurance of joints will also be reviewed. A 3D model, Digital Shape Model (DSM), is the sole document describing the position and requirements for each joint. Linked to this is also all information necessary for the plant operators, e.g. robot identification, weld process data etc.