Agile production of vehicles with multi-material structures

Abstract

Increasingly strict requirements regarding fuel efficiency and increasing customer demands introduce new challenges in car manufacturing. On the one hand more and more car model derivatives are introduced in order to satisfy customer demands. This dimension of variance is continuously expanding since several years. On the other hand, due to increasing fuel efficiency requirements new dimensions of variance are introduced in car manufacturing. Firstly, alternative drive systems, such as hydrogen cars, LPG cars, hybrid cars and electric cars, have different manufacturing requirements when compared to traditional gasoline cars as new systems, traditionally not found in passenger cars, such as electric energy storage and pressurized gas storage tanks are introduced. Secondly, new materials are increasingly used in car manufacturing. While aluminum has already been used in particular in small series cars it is now commonly found also in mass produced vehicles [1]. However, also nonmetal materials, in particular carbon fiber reinforced plastic (CFRP) are finding their way in to mass production [2]. Together with these new materials come new joining processes with disruptively different properties when compared to the traditionally employed processes. Combining these new dimensions of variance Ieads to cars that are not only geometrically different, but also different with respect to their mechanical structure and build procedure. This intensifies change drivers related to product variance tremendously. To cope with these challenges current production need to be transformed into agile production systems [3] Addressing these challenges requires fundamental changes in how cars are uced. This paper discusses how the above mentioned challenges can be in car manufacturing. lt is suggested to modularize the vehicle and accordingly. ln order to realize this modularization on production side it is to abandon the fixed interlinking of production cells resulting from the currently conveyors in order to flexible control the path a specific product takes through the factory. A related planning method basing on Axiomatic Design [4], an approach commonly used in product design, is presented. This new production paradigm has also a profound effect on the means of production which are discussed. In order to encapsulate the complexity of variants of the product in manufacturing it is suggested to establish product modules that are pre-assembled aside the manufacturing line. ln order to treat the material and process variance the establishment of production modules with loose coupling is proposed Figure 1 shows the proposed production structure and used nomenclature. The production consists of different production modules. Production modules are production sections that are homogenous in terms of executed processes for one variant or a range of variants. A production module can consist of a single station, resembling workshop manufacturing, or multiple stations, resembling a short manufacturing line. The production segments themselves are composed of modules to allow fast reconfiguration of production modules if demand changes. The single production modules are interlinked loosely using autonomously guided vehicles (AGV) allowing the individual control of products through the production. The proposed production setup generates new degrees of freedom in production planning and production control. For this purpose a design method based on Axiomatic design has been developed that allows developing the production structure based on the product structure. The method starts from the manufacturing requirements of the product (functional requirements), develops principles for the means of production (design parameters) and finally the actual production system structure (process variables). The correspondence of the tree structures developed on these three Ieveis Ieads to production systems that resemble the modular structure of the product