Hybrid manufacturing of functionally integrated car body parts via robotic screw extrusion additive manufacturing

Abstract

Additive manufacturing (AM) processes are technologies that have already established themselves for the rapid, cost-effective production of design and functional prototypes. AM processes have only made the step to industrial production in a few areas, in particular for high-performance applications and in design, architecture or tool production. This is mainly due to the low quantities required and the fact that no component-specific tools are needed for additive manufacturing, thus saving investment costs and time. AM processes also enable a high degree of geometric freedom, which allows the optimization of components in terms of lightweight construction and functional integration, without significant cost increases with increasing complexity. Limiting factors for most processes, however, are the still low productivity as well as the relatively small selection of available materials and their high costs. The Robotic Screw Extrusion Additive Manufacturing (SEAM) used in the presented work aims at extending the scope of application towards series production. The use of a screw extruder allows the processing of a large number of available standard thermoplastic pellets, which greatly expands the material selection and reduces raw material costs. In addition, much higher plasticizing rates can be realized relative to other extrusion processes such as fused deposition modeling. The combination with a 6-axis industrial robot as positioning system as well as a turn-tilt table as build platform enables the fast build-up of even large components or additive manufacturing on existing structures. In addition, the tool changing system of the SpaceA type system, besides the use of several extruders, also allows the use of a milling spindle and a gripper in a closed process. Despite the increased productivity of the SEAM process, large components with low complexity in particular can, in some cases, be produced more economically with conventional processes even at relatively low volumes. A hybrid manufacturing approach, as a combination of conventional processes with AM, offers the opportunity to combine the advantages of both worlds. Hybrid manufacturing thus opens up new possibilities for the flexible and economical production of components and structures with multiple variants and derivatives. In addition, it supports the principle of multi-material design: the right material in the right place. In this process, a conventionally manufactured basic structure is printed with variant-specific, additive substructures. This process variant places high demands, not only on the component design, but also on the planning and execution of the manufacturing process. In this presentation, this hybrid manufacturing process will be demonstrated using the example of a functionally integrated roof structure. The roof structure is taken from the Inter Urban Vehicle concept, which was developed in the DLR project "Next Generation Car". The body is mainly made of thermoplastic FRP materials, in particular polyamide 6 carbon fiber organo sheets, and partly in sandwich construction. In this case, the core of the sandwich roof structure is additively applied to the organo sheet top layer to integrate air ducts for air conditioning/ventilation of the vehicle interior. The presentation will provide insights into the studies on the adhesion between the organo sheet and the additively manufactured structure, the process planning and manufacturing of the demonstration part.