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Lightweight Design worldwide

, Volume 11, Issue 3, pp 42–47 | Cite as

Additively manufactured hood hinges

  • Martin Hillebrecht
  • Eric Klemp
  • Patrick Mehmert
  • Sebastian Flügel
Design Hood Hinge
  • 179 Downloads

Edag, voestalpine and Simufact have developed an additively manufactured engine hood hinge. As well as being half the weight of conventional designs, it also incorporates a pedestrian protection function. The component can be manufactured without tools, is optimized for warp and requires only minimum post-processing.

Compact and Sports Car Segments

Stringent safety and functionality demands imposed on active hinge systems for engine hoods mean they are very complex, Figure 1 (right). In the event of an accident with a pedestrian, they extend the distance between the impacting object and any hard engine components by raising the engine hood. A pyrotechnically triggered actuator kicks in within fractions of a second and raises the hood. These hinge systems can be manufactured from sheet metal or cast or forged for large-scale production series in excess of 30,000 units p.a. [1]. The complex kinematics involved require many individual parts (approx. 40 components per vehicle) and high assembly and tooling costs. Active hinges made from sheet metal nowadays weigh around 1500 g each and thus generate considerable additional weight in vehicles. However, economic constraints prevent small production runs of between 80 and 30,000 units p.a. being covered using large-scale production technologies [1]. Furthermore, design reasons and the lack of assembly space in the front section of sports cars generally prevent sheet-metal methods being used for active engine hood hinges. Carry-over strategies aiming to minimize investments for small production runs usually cause package and design problems due to the adoption of active hinges from large-scale production.
Figure 1

Engine hood hinge in additive manufacturing (left) and in sheet-metal design (right) (© Edag)

The collaboration between Edag, voestalpine and Simufact was thus intended to exploit the potential of additive manufacturing to solve this issue and demonstrate the following:
  • ▸ ultra-lightweight design and pedestrian protection in the compact and sports car segments

  • ▸ maximum integration of components and functions

  • ▸ tool-free and flexible manufacturing with minimum post-processing

  • ▸ maximum precision from the very first production batch.

Close cooperation between the three partners was crucial to achieving these goals. As project initiator and engineering expert in the automotive field, Edag oversaw project management and the virtual development of the so-called LightHinge+, Figure 2 and Table 1. As the partner responsible for production, voestalpine Additive Manufacturing contributed its expertise in laser beam melting, metal powders and machine parameters. Simufact is a software specialist in the simulation of metal production processes and contributed its Simufact additive software to improve the design, validation and warp optimization of the additively manufactured hinge.
Figure 2

Besides technical benefits, the engine hood hinge also offers a visually attractive design (© Edag)

Table 1

Comparison of the essential characteristics (© Edag)

Sheet metal construction (reference)

LightHinge+

Weight per hood hinge [g]

1490

720 (−52 %)

Number of parts, including standard parts

19

6 (−68 %)

Capital employed

High

Very low

Assembly space

High

Low

Manufacturing process

Sheet metal forming, stamp, screws, rivets (inter alia)

Powder bed-based metallic laser additive manufacturing

Engineering

Edag first performed a competitive analysis of different hinge systems before preparing a number of new conceptual solutions using creative methods. Accordingly, an interdisciplinary team was established, comprising Edag specialists from areas of lightweight design, safety construction and body-making, production experts from voestalpine and simulation experts from Simufact. Meeting the high stability and rigidity demands imposed given the limited space available was accomplished through the choice of 316L stainless steel. A second step — optimizing topology — involved calculating minimum material requirements based on actual loads. The resultant complex geometries are usually only possible through laser beam melting with considerable support structure. For the hinge under development, the share of support structures that would have had to be subsequently removed would have comprised over half the total volume. In the course of the collaboration, this share could be removed in several iterations, to initially 30 %, Figure 3 and finally to under 18 %, thanks to optimum component alignment and other design measures. In other words, more or less eliminating most of the processing steps and achieving considerable material efficiency. These post-processing measures normally comprise approximately 30 % of production costs. [2]
Figure 3

Systematic and simulation-based minimization of the support structures with more than 50 % (left) and less than 30 % of the material volume (© Simufact)

The hinge also comes complete with an automatic hood function.

Despite the extensive structural changes vis-à-vis topology optimization for eliminating post-processing, the final result successfully achieved weight savings of 50 % compared with the reference sheet metal construction, thanks to applying bionic principles. According to Mattheck, the method of tensile triangles and the tree-branching principle had a particularly positive effect on weight reduction. [3]

In addition to reducing weight and post- processing, structures developed in this way also look attractive, Figure 2. Considering that sports car engine bays in particular are increasingly becoming design objects, engine hood hinges developed in this way can help highlight the sporty and exclusive nature of the car.

Functional Integration

The hinge also comes complete with an automatic hood function. The geometric freedoms of additive manufacturing allowed Edag engineers to develop complex predetermined breaking point structures through experienced-based and therefore non- automatable vehicle engineering, Figure 4. These points are designed such as to yield when a specific force exerted by the pyrotechnic actuator is applied, releasing a swivel joint and generating even more free movement. This enables the actuator to raise the engine hood in the event of a collision with a pedestrian. The free space created acts as a crumple zone, cushioning the impact on the pedestrian and protecting them from hard vehicle components. Furthermore, it was also possible to integrate the connection point for the gas pressure spring and the mounts for the wash-wiper tubing and collar screw into the hinge. This functional integration reduces the number of parts by 68 % compared to the sheet-metal reference part, eliminating much of the assembly’s original weight.
Figure 4

Functional integration of components and the active pedestrian protection functions, together with the operating principle of additively manufactured predetermined breaking point structures (detail, extreme right) (© Edag)

This integrated hinge function can be deployed in significantly more compact spaces in sports cars or other high-performance vehicles, where such solutions for active hood functions were previously not possible for reasons of space.

A component test was able to confirm that the virtual development of the active hood function was successful and the simulation-based forecast of component and material behavior was valid. For this purpose, Edag set up a pyrotechnical test and simulated an accident with a pedestrian. The result shows the engine hood lifting by around 50 mm within around 25 ms of triggering the actuator, Figure 5. In other words, in around a quarter of the time that it takes a human to blink. In the process, the predetermined breaking point was released and the required degree of freedom was met. All of which means the functional requirements for an active hood hinge were met and it shows that new functions and operating principles can be implemented with additive manufacturing.
Figure 5

Test execution of the active hinge function in component testing (© Edag)

Process Simulation

The concentrated input of heat during the additive manufacturing process results in warping and internal stress, due to high rates of heating and cooling. A hinge without warp compensation may thus deviate by between 1 and 2 mm from the CAD model, as measurements showed, Figure 6. An important interim step when designing and manufacturing additive components is thus to simulate the actual laser melting process during the additive 3-D manufacturing process. The software solution that Simufact Additive created specially for additive manufacturing was used for this purpose.
Figure 6

Before and after warp compensation in the lower section: Deviation from the CAD model (left) and warping of the compensated component based on simulation results (right) (© Simufact)

It allows the actual printing process and subsequent process steps to be simulated and warping and internal stresses to be predicted [4]. In an initial step, only the warping of the printed test items is made available to the simulation and is then used to calibrate the influence of the production parameters. Based on the simulated warping of the component , the geometry is negatively pre-deformed to minimize form deviations of the printed hinge parts on target geometry. A subsequent comparison of the warp-compensated components showed that this process also delivered the desired results. Three-dimensional measurements performed by Aicon 3D Systems were able to demonstrate the dimensional accuracy of the parts.

Process simulation allowed an overall reduction in engine hood hinge warping of around 80 % [5]. Additional iterations of the simulation can be used to further improve warp compensation until the desired tolerance is reached.

Simulating the construction process was crucial in helping improve the design, safety and warp optimization of the additively manufactured hinge. It also eliminated the need for costly and time-consuming production experiments, since the components were within the required tolerance from the very first production batch.

Manufacture

Additive manufacturing was performed on a standard machine. 316L stainless steel was chosen due to its availability. It was then possible to implement the building process with the existing material and machine parameters. A key first step involved choosing a starting point with existing knowledge, so that in the course of development one can move towards the use of other, possibly optimized materials. Another essential aspect when choosing this material is also eliminating the need for heat treatment. This has the advantage of ensuring no additional influencing factors arise. However, at this point, it is already clear that this approach is the right one for this design because work can be performed on a standard machine. It was also possible to make extensive use of the available space, meaning that eight components could be manufactured simultaneously on a single construction platform. This ultimately led to four complete hinges in a single production batch. The manufacturing took place with the standard laser beam melting process, which includes coating with metallic powder, exposing the points to be melted, lowering the construction platform and subsequent coating. The platform had to be extracted from the machine after the construction process and the residual powder removed. The subsequent removal of the support structures was performed manually under prototype conditions.

Additive manufacturing is only economically viable with a high degree of functional integration.

Summary

The project demonstrates that additive manufacturing can only succeed commercially when functional integration can be maximized in the component. Performing topology analysis in a purely automated manner without taking functional integration or an efficient manufacturing concept into consideration is of little value for the development process. It is better to forget old ways of thinking and design and rethink components completely from scratch, harnessing the potential of additive manufacturing.

Using this concept, Edag, voestalpine and Simufact are now addressing further bilateral collaboration with high-end automotive manufacturers interested in the tool-free, variant- intensive manufacture of complex products. The engine hood hinge developed clearly shows the exceptional potential of additive manufacturing for overtaking rapid prototyping and tooling and adding a whole new dimension to classic production processes and engineering design possibilities for small production runs.

New simulation-based approaches along the development process are key to a controlled, laser-based additive manufacturing process and compliance with tolerance thresholds. The hood hinge ultimately combines increased safety and lightweight design in a production-ready and visually attractive design.

Notes

Thanks

The authors would like to thank the entire interdisciplinary team for their close cooperation: Edag Engineering: Martin Rüde, Team Leader BE Sindelfingen; Fabian Baum, Development Engineer BE Sindelfingen; Fabian Möller, Calculation Engineer CAE Sindelfingen; Julia Schäfer-Koch, Department Head Testing Böblingen; Reinhard Bolz, Head of Measurements.

voestalpine Additive Manufacturing Center: Jens Christoffel. Simufact Engineering GmbH: Michael Wohlmuth, Dr. Hendrik Schafstall, Volker Mensing.

A special thank you also to Hirtenberger as an associate partner for providing the pyrotechnic equipment: Horst Weinkopf, Director Research and Development; Kurt Aigner, Product Pre-Development.

References

  1. [1]
    Hillebrecht, M.: LightHinge+: Engineering und Herstellung eines ultraleichten Motorhauben-Scharniers. Fachvortrag auf formnext Messe, VDMA Stage, Frankfurt, November 14, 2017Google Scholar
  2. [2]
    Leupold / Glosser: 3D Printing: Recht, Wirtschaft und Technik des industriellen 3D-Drucks, C. H. Beck, 2017Google Scholar
  3. [3]
    Mattheck, C.: Die Körpersprache der Bauteile: Enzyklopädie der Formfindung nach der Natur. Karlsruhe: Karlsruher Institut für Technologie, 2017Google Scholar
  4. [4]
    Mehmert, P., Escobar, E., Tateishi, M.: Optimization of the AM Process Chain by Scalable Practice Orientated Simulation. Conference NAFEMS Seminar: Virtual and Real, Wiesbaden 2017Google Scholar
  5. [5]
    Mehmert, P.; Escobar, E.; Tateishi, M.: Simulation Mehmert, P.; Escobar, E.; Tateishi, M.: Simulation of the Additive Manufacturing Process Chain for Metals. In: Kynast, M.; Eichmann, E.; Witt, G. (eds.): Rapid.Tech — International Trade Show & Conference for Additive Manufacturing: Proceedings of the 14th Rapid.Tech Conference Erfurt, 20.-22.6.2017. Munich: Carl Hanser, 2017, S. 185-201Google Scholar

Copyright information

© Springer Fachmedien Wiesbaden 2018

Authors and Affiliations

  • Martin Hillebrecht
    • 1
  • Eric Klemp
    • 2
  • Patrick Mehmert
    • 3
  • Sebastian Flügel
    • 1
  1. 1.Edag Engineering GmbHFuldaGermany
  2. 2.voestalpine Additive Manufacturing Center GmbHDüsseldorfGermany
  3. 3.Simufact Engineering GmbHHamburgGermany

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