Details of a programme to investigate the outgassing rate of additively manufactured (AM) aluminium alloys are presented. AM has significant potential benefits to applications in ground- and space-based instrumentation, particularly in mass optimisation, part consolidation and increased design freedom. However, its use in high-risk projects is often curtailed by lack of heritage and an imperfect understanding of the materials. The programme goal was to address one of the most significant topics preventing wider adoption of AM technology in cryogenic and space-based applications; uncertainty about material outgassing. The sensitivity of outgassing rates to various key parameters was characterised, including print method, post-processing and geometrical complexity. Correlation of outgassing rates against other measurable properties, such as sample porosity and surface roughness, was also investigated via the use of X-ray computed tomography and profilometry. Finally, the test apparatus, experimental design and implications of the findings on design and process control are discussed.
Additive Manufacturing (AM) has several potential advantages for astronomical instrumentation: particularly the ability to create custom parts with optimised geometries that cannot be produced with traditional manufacturing. The goal of the EU H2020 funded OPTICON (Optical Infrared Coordination Network for Astronomy; grant agreement 730890) A2IM (Additive Astronomy Integrated-component Manufacturing; PI H. Schnetler) project completed in June 2021, was to develop prototypes demonstrating these benefits. This paper presents the design and additive manufacture of a piezoelectric stack actuator driven, monolithic flexure for the active array of the Freeform Active Mirror Experiment (FAME). Flexure geometry had previously proved difficult to repeatedly produce and AM was considered as a potential solution. Two AM processes were used: powder bed fusion where metal powder is bonded using a laser, and binder jetting where powder is bonded using a polymer adhesive. A topology optimised, flexure hinged frame was designed based on the minimum feature size of each AM machine. This geometry was produced in Aluminium (AlSi10Mg), Titanium (Ti64Al4V) and Stainless Steel 316L. Porosity is a known issue with AM and Hot Isostatic Pressing (HIP): a post process whereby parts are subject to increased temperature and pressure was identified as a way of reducing this, thereby increasing the predictability of flexure behaviour and suitability for vacuum applications. Conformity of AM parts to their original geometry was assessed using external dimensional metrology. X-ray Computed Tomography (XCT) was used to identify internal porosity.
Additive manufacture (AM), also known as 3D printing, builds an object, layer-by-layer, from a digital design file. The primary advantage of the layer-by-layer approach is the increase in design-space, which enables engineers and scientists to create structures and geometries that would not be practical, or possible, via conventional subtractive machining (mill, drill and lathe). AM provides more than prototyping solutions: there are a broad range of materials available (polymers, metals and ceramics); software capable of creating lightweight structures optimised for the physical environment; and numerous bureaux offering AM as a service on a par with subtractive machining. In addition, AM is an ideal method for bespoke, low-count parts, which are often the foundation of astronomical instrumentation. However, AM offers many challenges as well as benefits and, therefore, the goal of the OPTICON A2IM Cookbook is to provide the reader with a resource that outlines the scope of AM and how to adopt it within astronomical hardware, with an emphasis on the fabrication of lightweight mirrors. The Cookbook was an open access deliverable of the EU H2020 funded OPTICON (Optical Infrared Coordination Network for Astronomy; grant agreement #730890) A2IM (Additive Astronomy Integrated-component Manufacturing; PI H. Schnetler) work package and it was completed in June 2021. This paper will introduce the Cookbook, its scope and methodology, and highlight the paradigm shift required to design and AM lightweight mirrors for astronomy and space-science.
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