Additively manufactured hood hinges
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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
▸ 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.
Comparison of the essential characteristics (© Edag)
Sheet metal construction (reference)
Weight per hood hinge [g]
720 (−52 %)
Number of parts, including standard parts
6 (−68 %)
Sheet metal forming, stamp, screws, rivets (inter alia)
Powder bed-based metallic laser additive manufacturing
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. 
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.
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.
It allows the actual printing process and subsequent process steps to be simulated and warping and internal stresses to be predicted . 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 % . 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.
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.
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.
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.
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