Laser-based manufacturing of ceramic matrix composites
Willy Kunz, Clemens Steinborn, Stefan Polenz, Benjamin Braun

A novel fabrication route for ceramic matrix composites (CMCs) was investigated. This was based on laser-induced melting of a Y-Si-O matrix between SiC fibers. Scanning electron microscopy studies showed that melting and solidification of the matrix is possible without damaging the fibers. Thus, the feasibility of the process in principle was demonstrated. Due to the strong inhomogeneities in the microstructure, samples were prepared for mechanical characterization using FAST/SPS. Bending and tensile tests were performed on them at room temperature and at 1000 °C in air atmosphere. The mechanical behavior was damage tolerant and showed the dependencies between strength and fiber orientation typical for CMC.

Keywords: Ceramic matrix composites; laser-based fabrication; mechanical properties

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Polymer powders with enhanced absorption in the NIR for laser powder bed fusion with diode lasers
Michael Willeke, Carlos Donate-Buendia, Tim Hupfeld, Stephan Barcikowski, Bilal Gökce

Additive manufacturing techniques represent an ideal manufacturing process for series components, for example in the automotive industry when good mechanical properties and precision are needed. In that sense, Laser Powder Bed Fusion (LPBF) is a manufacturing technique already employed in several applications where polymer parts with complex geometries are required. However, since the employed polymer powders exhibit a low absorption in the visible and NIR wavelength range, the laser sources employed in polymer LPBF are limited.
To address this difficulty, the addition of near-infrared absorbing LaB6 nanoparticles is proposed and tested on the most employed polymer powder for LPBF, i.e. polyamide 12 (PA12). The nanoparticles are generated by laser ablation in liquid and homogeneously dispersed on the polymer surface by dielectrophoretic deposition. The resulting nanoadditivated polymer powder exhibits an absorption maximum at 800 nm, suitable for its processability by LPBF with NIR laser sources.

Keywords: Laser powder bed fusion; nanoparticles; near-infrared absorption

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Additive manufacturing of magnetic parts by laser powder bed fusion of iron oxide nanoadditivated polyamide powders
Carlos Doñate-Buendía, Alexander Sommereyns, Jochen Schmidt, Michael Schmidt, Stephan Barcikowski and Bilal Gökce

Laser powder bed fusion (LPBF) allows the processing of polymer powders with design freedom achieving highly complex geometries that are relevant for medical and aerospace applications. The characteristics of the generated parts as well as the processability by LPBF depends on the initial polymer powder properties. A route to achieve a controlled modification of the polymer powders and adapt the properties of the final parts to the desired application is the nanoparticle-additivation of the powders. The generation of superparamagnetic iron oxide nanoparticles by laser fragmentation and supporting on polyamide (PA12) is shown to transfer the magnetic response of the nanoparticles to the resulting nanoadditivated powder even when the nanoparticle loading is only 0.1 wt%. The characterization of the as-built parts confirms that the saturation magnetization and structure of the iron oxide nanoparticles are not influenced by LPBF processing, proving the successful transfer of the initial nanoparticle properties to the 3D-printed part.

Keywords: Laser powder bed fusion, Laser fragmentation in liquids, Magnetic Nanoparticles, Selective laser melting, Iron oxide.

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Manufacturing of fused silica parts by means of Laser Glass Deposition
Katharina Rettschlag, Simon Stieß, Peter Jäschke, Stefan Kaierle, Roland Lachmayer

Additive manufacturing (AM) of polymers and metals is already established in the industry. Materials such as glass create significant challenges based on their material properties. Especially mechanical and thermal properties as well as the viscosity behavior are difficult to handle. So far, only few specialized glass AM processes exist and are established in research and development.
The Laser Glass Deposition (LGD) process offers the possibility to deposit glass fibers without using binder materials. For the application area of optical components, manufactured parts must fulfill high requirements for transparency, surface quality, material purity and homogeneity of the material. Investigations on the printing of individual single-layer quartz glass structures have already been carried out with the LGD process. Within this article the influence of laser power, axis speed and fiber feeding speed on the deposition characteristics is investigated shortly. Subsequently, a multilayer deposition is investigated to manufacture solids with an optical transparency.

Keywords: Laser Glass Deposition; Fused silica; Glass fibers; Multilayer deposition

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Process strategies on laser-based melting of glass powder
Thomas Schmidt, Susanne Kasch, Fabian Eichler, Laura Katharina Thurn

This paper presents the laser-based powder bed fusion (L-PBF) using various glass powders (borosilicate and quartz glass). Compared to metals, these require adapted process strategies. First, the glass powders were characterized with regard to their material properties and their processability in the powder bed. This was followed by investigations of the melting behavior of the glass powders with different laser wavelengths (10.6 μm, 1070 nm). In particular, the experimental setup of a CO2 laser was adapted for the processing of glass powder. An experimental setup with integrated coaxial temperature measurement/control and an inductively heatable build platform was created. This allowed the L-PBF process to be carried out at the transformation temperature of the glasses. Furthermore, the component’s material quality was analyzed on three-dimensional test specimen with regard to porosity, roughness, density and geometrical accuracy in order to evaluate the developed L-PBF parameters and to open up possible applications.

Keywords: 3D-printing; glass; additive manufactureing; laser based powder fusion;

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Fabrication strategies with fixed diffractive optical elements for high speed two-photon polymerization
Francisco J. Gontada, Sara M. Vidal, Nerea Otero-Ramudo, Pablo M. Romero-Romero

The benefits of Two-Photon Polymerization (TPP) are well known for the fabrication of 3D structures with micron and even submicron sizes However the fabrication time of these structures is still far from being competitive with other techniques. In this work, the use of fixed Diffractive Optical Elements (DOEs) is presented as valid approach to boost the fabrication speed of TPP. In this way, the fabrication strategy for different 2.5D and 3D microstructures, taking advantage of the use of DOEs with different optical configurations, is presented and discussed. The results of this study suggest that the fabrication speed can be increased up to 20 times through the correct combination of DOE and path planning, without the need of an excessive average power.

Keywords: Two-Photon Polymerization;

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Experimental investigation on lateral path overlay and the degree of mixing of additively manufactured soda-lime and borosilicate glass structures.
Fabian Fröhlich, Jörg Hildebrand, Jean Pierre Bergmann

In the presented paper, the influence of the lateral distance between the deposited lines on the geometric dimensions and the degree of mixing of additively manufactured glass structure is investigated. Initial experimental investigations have shown that additive manufacturing of quartz, soda-lime and borosilicate glass is possible when material- and process-specific process parameters are taken into account. Using a CO2-laser, the silicate glasses and the rod-based additive material are melted. For this experimental investigation, the ratio between welding and feeding speed of the filler material, as well as the laser power, is kept constant. The fabricated structures are subjected to post heat treatment to relieve thermally induced stresses and are examined with photoelasticity. Geometrical dimensions, such as layer height, width and bond angle, as well as the degree of mixing are quantified after materialographic sample preparation. The knowledge is used to optimise near-net-shape additive manufacturing of glass components.

Keywords: soda-lime-glass; borosilicate glass; CO2-laser; 3D-Printing;

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Additive manufacturing for minimally invasive endomicroscopy
Jürgen Czarske, Elias Scharf, Robert Kuschmierz

Flexible endoscopes commonly employ coherent fiber bundles (CFB), which are indispensable in biomedicine. However, the footprint of the endoscope is limited because of the used bulky lens systems. We present a novel approach of lensless ultrathin fiber endoscopy using 3D-printed diffractive optical elements (DOE) at the fiber facet for aberration compensation. Using 2P-polymerization axial resolutions better than 20 nm can be achieved. This enables robust and cost efficient, endoscopes for biomedicine. The influence of the DOE quality especially the axial resolution towards the image quality is discussed. With a total endoscope diameter below 400 μm, novel applications for instance for in-vivo cancer diagnostics in the brain can be envisioned.

Keywords: Endoscopy, holography, 3D printing

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Powder bed fusion of ultra-high molecular weight polyethylene using ultra-short laser pulses
Tobias Ullsperger, Yannick Wencke, Burak Yürekli, Gabor Matthäus, Gerrit A. Lunistra, Stefan Nolte

Laser powder bed fusion (L-PBF) of ultra-high molecular weight polyethylene (UHMWPE) is a new approach to fabricate complex components for medical implants. CO2 laser radiation is the method of choice to selectively heat up the powder particles above the melting point. Although previous studies have shown the feasibility to fuse UHMWPE, the produced specimen lack of warping and degradation. Moreover, the achievable geometrical resolution is limited by the large spot size of several 100 μm. In this paper, we demonstrate an alternative approach for L-PBF of UHMWPE by using 500 fs laser pulses at a wavelength of 1030 nm. The peak intensity of several 100 MW/cm2 allows for efficient multi-photon absorption in the transparent polymer. Thus, it was possible to completely melt the powder with less degradation. Furthermore, the achieved tensile strength of 4 MPa is 60 % higher in comparison to produced samples using conventional CO2 L-PBF.

Keywords: Laser powder bed fusion; Additive manufacturing; Selective laser sintering; UHMWPE; Ultrashort laser pulses