Hybrid processes and materials made of fibre-reinforced plastic (FRP) and metal for the automotive lightweight construction of tomorrow are the focus of the LEIKA research project, which KraussMaffei is advancing in collaboration with the Institute for Lightweight Engineering and Polymer Technology at Dresden University of Technology and other partners from industry and research academia.
A new lab system at the Institute for Lightweight Engineering and Polymer Technology stands at the centre of the development work. This system allows FRP-metal hybrid materials to be formed and back injected in one step.
Hybrid ready for series production
LEIKA stands for “Leichtbau in Karosseriebauteilen” or lightweight construction in auto body components. The objective of the research project supported by the German Federal Ministry of Education and Research is to decrease the structural mass in electric vehicles by using innovative hybrid materials with a focus on processes ready for large-scale series production.
“The new lab system at the Institute for Lightweight Engineering and Polymer Technology allows us to form and back-inject FRP-metal hybrid materials in one step. The resulting process and structure quality, together with the achieved cycle times of significantly less than two minutes, supports the potential of such hybridisation on both the material and production end,” says Martin Würtele, Director of Injection Moulding Technology Development at KraussMaffei.
Another great advantage of the new test system is its flexibility. KraussMaffei served as the system provider and has been closely involved in project engineering from the beginning. The new lab system is suited both for the manufacturing of components by injection moulding and for the back injection of semi-finished products.
Furthermore, plastics can be used for compression in the mould or reinforcement for local areas in the component. This process sequence is implemented through the integration of a flat sheet die as well as a conveyor belt with an insertion robot. “The new test system lets us project a large number of incredibly varied processes on a single system. This lets us offer significant added value to our partners from the automotive industry,” says Dr Michael Krahl, Project Manager and person in charge of LEIKA at the Institute for Lightweight Engineering and Polymer Technology.
Combined expertise in injection moulding and extrusion
Flexibility is also a subject of major interest in the implementation of individual system components. This is why KraussMaffei designed a bolt-on unit of reduced height which is completely integrated with the production line including a press, infrared oven, robot and conveyor belt. The unit is capable of both injection moulding and extrusion, portioning the injection volume in the process. As stated in the requirements specifications, up to five areas can be reinforced locally in one cycle.
Another feature of note is the conveyor belt’s full integration into the system to make it possible to deposit the individual portions of plastic. “The speed of the conveyor belt results directly from the process parameters, such as injection speed or throughput. This is a clear advantage for the Institute for Lightweight Engineering and Polymer Technology because there is no longer any need to set the conveyor belt manually beforehand and there is no discharged melt. In the event of a change in discharge speed, the conveyor belt speed adapts automatically and with deliberate control,” says Würtele.
One control system and high shot weight consistency
The software for the system has been completely rewritten. The MC6 from KraussMaffei acts as an open control system that handles the integration of the bolt-on and conveyor belt modules. In addition, it is also completely integrated into the production line electrically.
Another advantage is the high shot weight consistency of the associated SP 12000 injection unit with direct drive. The motors for plasticising and injection are arranged in a series and directly flange-mounted on the screw, making it possible to prevent transverse forces opposing the flow of force. The result is very accurate metering and precise material discharge shot by shot.
Mass structure reduced by 25%
Using the floor structure for electric vehicles as an example, the partners demonstrated the suitability of real-world implementation in series production for the innovative hybrid materials and their processes. For the centre tunnel, the scientists combined metallic outer layers of steel with a core of CFRP. “The first test results are excellent. The mass is reduced by 25 percent compared to an all-metal lightweight construction solution. Simultaneously, it was possible to demonstrate comparable performance under the most important load conditions with regard to stiffness and crash situations for components with significantly lower mass,” explains Würtele.