The large class science mission NewATHENA, rescoped by the European Space Agency (ESA) in November 2023, will explore the hot and energetic universe using advanced X-ray technology. The key components of the telescope will be hundreds of Silicon Porous Optics (SPO) modules arranged in an optical bench with a diameter of around 2.7 metres. Considering the overall size, the delicate cell structure and the high aspect ratio in combination with the material-related challenges of Ti6Al4V, additive manufacturing using Direct Energy Deposition (DED) is a promising alternative to conventional processing. In addition to discussing fundamental challenges (e.g. shielding), the development of a highperformance hybrid DED process and associated equipment for robust long-term production will be presented. The developed end-to-end manufacturing approach will be verified by manufacturing and analysing test specimens, geometric demonstrators and representative large breadboards [1], [2].
The need for ever increasing process temperatures during combustion in space engines and gas turbines to increase efficiency requires the use of thermally resistant materials and novel cooling solutions. For the improved cooling of thermally highly stressed components, the technology of transpiration cooling, in which a cooling medium flows through a porous structure, has been known for a long time. Additive manufacturing and, in particular, laser powder bed fusion (LPBF) offers great potential for the near-net-shape production of porous structures compared to complex conventional manufacturing. In this contribution, porous structures were manufactured and the process parameters were optimized to increase the quality of the pores. The study discloses an adapted exposure parameter set for the improved fabrication of cylindrical pores in an INCONEL® 718 material and the associated mechanical properties of porous and dense components.
Advanced Manufacturing (AM) has the potential to improve existing technologies and applications in terms of performance, light-weighting and costs. In the context of the SME4ALM initiative, launched by DLR and ESA, the company Kampf Telescope Optics GmbH (KTO) in cooperation with the Fraunhofer Institute for Material and Beam Technology (IWS) have assessed the feasibility of AM to build a high-performance optical mirror for space applications.
For the assessment of the AM potentials, a mirror design concept for cryogenic instruments for observations in the IR and NIR range was baselined. In a second step, Nickel-Phosphorus (NiP) was selected as optical coating. The combination of coating and mirror material is a primary design driver for optical performance. Both materials must have a very similar CTE as well as be compliant to modern optical manufacturing (diamond turning, polishing). As a promising candidate for NiP coating the AlSi40 was selected for the mirror structure.
The potential advantages of AM for optical mirrors in terms of mechanical performance, cost, and manufacturing time were exploited. The achievement of those objectives was / will be demonstrated by:
1. verifying AM material properties and manufacturability of AM mirrors by material sample tests and subcomponent tests
2. designing AM mirror demonstrator by structural, thermal, and optical performance analysis
3. applying and elaborating AM specific design methods (topology optimization, sandwich structures with internal microstructures, monolithic design, etc.)
4. manufacturing, assembling, and testing AM mirror demonstrator to verify manufacturability and optical performance
5. comparing optical and mechanical performance of the AM mirror demonstrator to a conventional mirror by numerical analysis to exploit potential advantages of AM
Additive Manufacturing (AM) processes as Laser Metal Deposition (LMD) addresses various benefits such as the build-up of complex shaped parts, the possibility of functional integration, reduced lead times or the use of difficult machinable materials compared to conventional manufacturing possibilities. Beside mentioned advantages, the use of more than one material in a component strongly increases the field of applications. Similar to structures in nature, multi-material arrangements can be realized by (I) sharp intersections from one material to the other (e. g. in the case of a thin corrosion protection), (II) graded structures enabling smoother material transitions (e. g. dissimilar materials joined together without defects), (III) composite structures with enclosed particles in a matrix material as well as by (IV) in-situ alloying of different material compositions. Due to varying material properties (e.g. thermo-physical, mechanical, optical), the combination of materials often requires a detailed investigation of occurring process phenomena and well-chosen modifications of the process regimes. Within this paper, (a) the right material feeding as well as powder interaction between various materials in Laser Metal Deposition, (b) the suitable selection of laser wavelengths for different materials, (c) process window adjustments by means of additional sensor equipment, (d) limitations of material combinations as well as (e) results and material characterization of multi-material parts are discussed. Phenomena are discussed by means of exemplary industrial applications, e.g. from the jet engine or medical business.
Diffraction-limited high power lasers represent a new generation of lasers for materials processing, characteristic traits of
which are: smaller, cost-effective and processing "on the fly". Of utmost importance is the high beam quality of fiber
lasers which enables us to reduce the size of the focusing head incl. scanning mirrors. The excellent beam quality of the
fiber laser offers a lot of new applications. In the field of remote cutting and welding the beam quality is the key
parameter. By reducing the size of the focusing head including the scanning mirrors we can reach scanning frequencies
up to 1.5 kHz and in special configurations up to 4 kHz. By using these frequencies very thin and deep welding seams
can be generated experienced so far with electron beam welding only. The excellent beam quality of the fiber laser offers
a high potential for developing new applications from deep penetration welding to high speed cutting. Highly dynamic
cutting systems with maximum speeds up to 300 m/min and accelerations up to 4 g reduce the cutting time for cutting
complex 2D parts. However, due to the inertia of such systems the effective cutting speed is reduced in real applications.
This is especially true if complex shapes or contours are cut. With the introduction of scanner-based remote cutting
systems in the kilowatt range, the effective cutting speed on the contour can be dramatically increased. The presentation
explains remote cutting of metal foils and sheets using high brightness single mode fiber lasers. The presentation will
also show the effect of optical feedback during cutting and welding with the fiber laser, how those feedbacks could be
reduced and how they have to be used to optimize the cutting or welding process.
The present paper reviews recent progress in productivity, precision and quality of laser-based cladding and additive
layer manufacturing. Recently, we have demonstrated the great benefits obtained from induction assisted laser cladding.
This novel hybrid technology combines high deposition rates with excellent cladding properties. Laser-based direct
metal deposition is a novel concept for the fabrication of components and repair as well as geometrical surface
modifications. Newly developed nozzle design allows focused powder spots to generate wall thicknesses of about
30 μm. An in-depth understanding of the processes and the resulting materials properties is key for the development of
technically viable and economically reasonable customized solutions.
Cracking in laser cladding caused by inhomogeneous thermal expansion and/or phase transformations restricts the feasible feed rates and the use of high-strength coating materials. In order to better understand the physical reasons of thermal stress and cracking and to reduce the restrictions mentioned, the formation of beads and the evolution of the temperature and stress fields in laser cladding are simulated with and without inductive pre- or post-weld heating. The results of a semi-analytical analysis of the cladding process are transferred to a finite element model which calculates the temperature field, the phase transformations, and the residual stress and strain. These results show that both the danger of cracking due to high residual stress and strain and the distortion of the workpiece by irreversible plastic and thermo-metallurgical strain may be reduced by pre- or post-weld heating using inductors which can be directly integrated into the cladding process.
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