Manufacturers are currently required to integrate an increasing number of drive concepts and energy storage systems into vehicle structures. The vehicle bodies of tomorrow will not only need to be lighter, but also require a highly flexible design. The consequence is an increasing number of vehicle derivatives, which demand adaptable bodywork concepts that are economical to manufacture. In the foreseeable future, additive manufacturing could offer entirely new approaches to vehicle manufacturing.
The EDAG concept car “Light Cocoon” is a compact sports car with a bionically designed and additively manufactured vehicle structure, covered with an outer skin made from weatherproof textile material. The bodywork structure embraces bionic patterns which allows for a lightweight frame.
In a joint project, EDAG Engineering GmbH (Wiesbaden, DE), Laser Zentrum Nord GmbH (Hamburg, DE), Concept Laser GmbH (Lichtenfels, DE) and the BLM Group (Cantù, IT) created the bionically optimized spaceframe produced by hybrid manufacturing to highlight a new way in which a bodywork concept can be manufactured.
Additively manufactured bodywork nodes and intelligently processed profiles are combined. Thanks to additive manufacturing, the nodes can be configured to be highly flexible and multifunctional so that different versions of a vehicle can be produced “on demand” without any additional tooling, equipment and start-up costs. Steel profiles are used as connecting elements. They too can easily be adapted on an individual basis to the specified load levels by providing them with different wall thicknesses and geometries.
The NextGen spaceframe is a combination of additively manufactured 3D nodes and intelligently processed steel profiles. The nodes can be manufactured on site for the particular version, along with the profiles, which are cut to the appropriate shape and length initially using 3D bending and then by employing 2D and 3D laser cutting processes.
The focus is on joining together individual components to create a hybrid structure in order to produce topologically optimized structures that are not yet possible at present. The method used is laser welding, which is characterized by intricate welded seams and low thermal input. The components are welded together with a fillet weld on the lap joint. This joint enables circumferential welding to produce a connection over a long length along with excellent prepositioning of the components. The profiles are automatically aligned and fixed in place by the node. A high-brightness laser with robot-guided optics is used. In addition, the laser techniques used to produce profiles and nodes can largely be automated in assembly. This concept offers great potential when it comes to the manufacturing cost structure and the possibility of saving time.
The additively manufactured nodes can be adapted to reflect each load stage, e.g. by incorporating additional stiffening elements to cater for high load requirements. This means that each version is designed for the optimum weight and function. The hybrid design spans the required distances of the structure with the profiles, while the nodes are used to connect the profiles together. Both elements were optimized using CAE/CAD and guarantee the requirements that are demanded of a bodywork structure. In the present case, as well as playing a coordinating role, EDAG Engineering GmbH was responsible for devising and optimizing the spaceframe concept, Laser Zentrum Nord GmbH did the laser welding, the BLM Group undertook the 3D bending and laser cutting, and Concept Laser GmbH performed the additive manufacturing of the nodes.
The LaserCUSING process from Concept Laser generates components in layers directly from 3D CAD data. This method allows the production of components with complex geometrical shapes without the use of any tools. It is possible to produce components, which it would be very difficult or impossible to fabricate by conventional manufacturing. With this type of design, the nodes cannot be manufactured by conventional steel casting. In order to be able to guarantee a fault-free structure, a support structure should be provided on planes with an angle of less than 45° in relation to the build platform. As well as providing simple support, the support itself absorbs in particular internal stresses and prevents the components from warping. Due to the complex geometry of the nodes, clean support preparation is the absolute basis of successful production.
After preparing the support, the component is virtually cut into individual slices. Once the data has been transferred to the LaserCUSING machine, the corresponding process parameters are assigned, and the build process is started. The nodes were manufactured on an X line 1000R machine from Concept Laser, which has the appropriate build envelope (630 x 400 x 500 mm3) for such projects and operates with a 1kW laser. Only the new X line 2000R (800 x 400 x 500 mm3), likewise from Concept Laser, has a larger build envelope for powder-bed-based laser melting with metals and it is also equipped with 2 x 1kW lasers.
The spaceframe concept combines the advantages of 3D printing, such as flexibility and the potential for lightweight construction, with the efficiency of proven conventional profile designs. The topologically optimized nodes enable the maximum lightweight construction that is possible at the present time, and a high degree of functional integration. Both the nodes and the profiles can be adapted to new geometries and load requirements. The basic idea then is to have a node/profile design which can be optimally customized to reflect what the particular model requires. The result is a spaceframe structure with an optimized load path. By employing processes, which do not involve much use of apparatus or tools, it will be possible in future to manufacture all bodywork versions economically and with the greatest possible flexibility.