Tool Technology for Lightweight Structures in 3-D Hybrid Designs
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Novel construction methods for the series-capable production of hybrid lightweight structures demand innovative tool technologies. The builder of models and molds Siebenwurst is developing suitable tool solutions for the large series-compatible production of intrinsically bonded hybrid structures in 3-D hybrid construction.
3-D Hybrid Technology
The automotive industry is constantly looking for new solutions to reduce vehicle weight. It is especially important to find intelligent construction methods in the bodywork structure so that they are not only lighter but can also be manufactured economically in large series-compatible volumes. From the classic pure steel construction of the past, hybrid constructions have increasingly become established in automotive building over the last few years. The intelligent combination of different materials such as aluminum, magnesium and steel means that their specific properties can be used in a more targeted manner, improving component performance and increasing the proportion of lightweight materials used in the bodywork structure.
The potential of this construction was highlighted in an impressive way as part of the sponsored 3-D hybrid project using the example of a lightweight-design B-pillar. Compared to a conventional B-pillar, the number of parts was reduced significantly, the weight of the component reduced by 14 % and the energy absorption increased by 25 %. All of the required load constraints were demonstrated successfully in component and bodywork tests.
Pressing Tools for 3-D Hybrid Structures
In production trials, the functionality of the tool concept was demonstrated for automated component production. Safeguarding reproducible component quality, however, requires precise coordination of the tool and handling system. The transfer and defined depositing of the individual plasticized LFT compound strands, as well as the organo sheet sections, are an extremely challenging task in terms of process technology that leads to increased process complexity.
3-D Hybrid in Thermoplastic Injection Molding
This is why, in a follow-up project, the expertise gained will be used to further improve the 3-D hybrid technology in terms of component quality, reproducibility and cost-effectiveness. To this end, in 2015, seven industrial companies (Porsche, Volkswagen, Siebenwurst, Mitras Composites, ESI, Trumpf, Hengstmann Solutions) and three German research organizations (TU Dresden's ILK, University of Stuttgart's IKT and the Bavarian Laser Center) came together as part of a research consortium on the Forel joint project "Q-Pro." The group focused on a number of different goals. For the process-integrated bonding of the organo-reinforcements to the sheet metal shells, the use of laser-structured surfaces was also investigated alongside firmly bonded solutions. To minimize future development efforts and to improve component quality, an end-to-end process chain was also established and extensively investigated for the simulative and experimental mapping of the 3-D hybrid production process.
Both with the basic profile and on the A-pillar, the tolerances of the sheet metal shells from the upstream metal forming process were a major challenge when it came to the design of the molding tools. To address this challenge, extensive geometry measurements were carried out on the sheet metal shells. If deviations from the specified sheet metal tolerances are not adequately accommodated, this can result in costly damage to the tool and to reduced component quality. Under-sized sheet metal shells, for example, can lead to increased tool wear since the shells are widened and shaped as a result of the closing movement and injection pressure. After the de-molding of the component, there is also the risk of the steel sheet springing back, and tension in the component can lead to loosening of the injection-molded ridge structures.
To de-mold the finished component, sleeve ejectors were installed at the crossover points of the ridges. One key challenge of the Q-Pro project was the implementation of end-to-end quality assurance. To achieve this, a range of different sensors were installed to capture the process parameters in the individual process stages throughout the entire process chain. To measure the internal tool pressures and temperatures during the filling process and the cooling phase, combined pressure and temperature sensors from Kistler were installed in the lower tool cavity at selected positions using small molded inserts to integrate them into the tool.
For the electric vehicles of the future especially, innovative solutions for component structures exposed to high levels of mechanical stress are needed so that the strict crash requirements can be met while maintaining the maximum installation space. The potential of 3-D hybrid technology for this was demonstrated very impressively in the development projects listed above. In addition to the wide range of material, design and simulation issues, however, it has also become clear that tool technology is an essential component in order to ensure a manufacturing process that can be used in large series production runs and reproducible component quality. With its solutions, Siebenwurst was able to make a considerable contribution to this, allowing the transfer to series applications to take place without any obstacles from a technical perspective. |
Kellner, P.; Steinbach, K.: Die 3D-Hybrid Leichtbautechnologie: Eine neuartige Stahl-GFK-Hybridbauweise für höchstbelastete Karosseriestrukturen. Conference: 18. Dresdner Leichtbausymposium, Dresden, 2014
The authors are grateful to the project partners Porsche, Volkswagen, ESI, Mitras, Trumpf, Hengstmann, the Bavarian Laser Center, the ILK Dresden and the IKT Stuttgart for their highly successful cooperation. The authors are also grateful for the sponsorship of the Q-Pro project (sponsorship identifier 02P14Z040 - 02P14Z049) by the Federal Ministry for Education and Research (BMBF) and the project sponsor Karlsruhe (PTKA), as well as for the sponsorship of the 3-D hybrid project by the Sächsische Aufbaubank (SAB).