Concepts for Manufacturing a Seat Backrest Structure Dominated by an Extruded Magnesium Alloy

Abstract

In large-scale production of vehicle seats, high and ultra-high strength steel alloys prevail because of challenging requirements, mainly concerning passenger safety. The potentials of metal lightweight structures using steel and aluminum are exhausted to a large extent. The national project FUMAS (Functionally integrated magnesium lightweighting for automobile seat structures) aims at weight reduction of a seat structure by using extruded magnesium (an alloy of the type MgMnCe) and novel process routes in manufacturing. Concepts for a lighter seat back structure have been developed, dimensioned and evaluated. The underlying predevelopment process is based on numerical as well as experimental methods on different levels. On component level, profile tests in bending reveal large deformation without local failure. This deformation makes the use of closed rectangular profiles promising for the application in seat frame structures. In FUMAS, the developed backrest structure consists of a three-part magnesium frame and a so-called mobile steel gusset at the transition to the seat area. Two alternative structural concepts have been developed utilizing different joining technologies - a primary concept using friction stir welding and a secondary one basing on injection adhesive bonding. Both concepts use the same magnesium frame. In the consideration and development of associated process routes, the major challenge has been the magnesium-steel joint between frame and gusset. For welding, the joining direction is essential. Therefore, the magnesium material needs to be accessible. On the other hand, injection adhesive bonding demands sufficient joint areas and a filling concept to perform the bonding process. The two alternative concepts respectively illustrate and demonstrate engineering solutions.