**4. Discussion and Conclusions**

The case study consisted in the manufacture of a full-scale high-detail model (HDM) for its conservation as part of the aerospace heritage, through the low-cost digital manufacturing of the PHI instrument for the Solar Orbiter mission. This project was carried out under a collaborative approach, low cost manufacturing, and graphic engineering planning. For the collaboration of different teams and their supervision, techniques of organization and distribution of subassemblies were applied. This organization was essential to know at all times of the project what was the location of each element and its state of manufacture.

Aerospace engineering entails complexity that cannot be transmitted simply through texts, photographs, or simplified scale models. Although, these modalities serve for the conceptual preservation and the diffusion in educative environments of this heritage of engineering, the development of models of HDMs are necessary for the scientific and professional panorama. For this reason, it is proposed to add these scale models to the current categories [22].

Other authors have promoted digital graphic representation techniques such as augmented reality for the conservation of industrial heritage [15] or the application of BIM techniques for the representation of architectural heritage with a high level of detail [16], but the materialization of the work in a physical element can test and evaluate it [19]. This research generates a proposal that combines the level of detail in CAD modeling and benefits of its materialization.

This complexity has also been reflected in the need to solve problems through collaborative work and planning, with the particularity of working with geometric modeling in 3D. In this sense, results are presented that agree with Vila, Ugarte, Ríos, and Abellán [25], Fusion 360 has worked and allowed team work both synchronous and asynchronous, so that supervision tasks could be done through Fusion 360. In addition, printing times were optimized, as there were no downtimes between the low-cost digital manufacturing of highly complex engineering projects is possible, but far from being an instantaneous process. This experience fosters the generation of seven stages of graphic engineering and planning for the elaboration of models of high level of detail from the reception of a 3D digital model: identification and organization of subassemblies, analysis of the digital files, digital model repair, digital model restructuration to optimize their manufacture, adaptation of the models to the means of manufacturing, pre-allocation of the digital models to the manufacturing, and manufacturing and finishing.

The importance of HDM is supported by its role as a source of information in historical investigations [21]. However, the models have usually led to geometric simplifications due to the cost involved in representing the engineering project in detail [20,22]. This research contributes to the achievement of this high-detail model by the combination of two 3D printing types: fused deposition modeling and digital light processing (DLP). DLP have allowed to manufacture elements in photosensitive resin with very small dimensions at full-scale, being reproduced in the environment of the engineering project. This means a step forward in the detailed representation of engineering projects as opposed to architectural scale models that require geometric simplifications because they cannot be uniformly scaled [3].

This research has developed a full-scale high-detail model of the SO/PHI instrument for the Solar Orbiter mission of the European Space Agency through low-cost digital fabrication techniques and collaborative work. The HDM is presented as a tool that contains complex information that seems especially suitable for the aerospace sector, in which most of the designs are launched into space and there is no record beyond the digital model, texts, and photographs. In addition, seven engineering graphics procedures for the manufacture of HDMs have been provided to enable other professionals and scientists to contribute to the transfer and conservation of industrial heritage.

**Author Contributions:** Conceptualization, J.L.S. and V.L.C.; Methodology, software investigation and resources, J.d.l.T.-C. and M.D.D.-A.; Formal analysis and the writing of the manuscript, J.L.S. and V.L.C.; Supervision, project administration, and funding acquisition, M.D.D.-A. and J.d.l.T.-C.

**Funding:** This research was partially funded by Ministerio de Ciencia e Innovación, grant number HAR2017-85169-R: Fundición artística de micro esculturas diseñadas por ordenador, mediante el desarrollo de técnicas de impresión 3D basadas en el procesado digital de luz". It has also been funded by National Institute of Aerospace Technology (INTA) and Andalusian Astrophysics Institute (IAA) through the project "Réplicas Dummies a escala 1:1 del instrumento espacial PHI para la misión Solar Orbiter de la ESA".

**Conflicts of Interest:** The authors declare no conflict of interest.

## **References**


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