MANUFACTURING AND APPLICATION OF PA11-GLASS FIBER COMPOSITE PARTICLES FOR SELECTIVE LASER SINTERING

Maximilian A. Dechet #‡, Lydia Lanzl †‡, Yannick Werner #, Dietmar Drummer †‡, Andreas Bück #‡, Wolfgang Peukert #‡, Jochen Schmidt #‡*

# Institute of Particle Technology (LFG), Friedrich-Alexander-Universität Erlangen-Nürnberg, Cauerstr. 4, D-91058 Erlangen, Germany

† Institute of Polymer Technology, Friedrich-Alexander-Universität Erlangen-Nürnberg, Am Weichselgarten 9, 91058 Erlangen, Germany

‡ Collaborative Research Center 814 – Additive Manufacturing, Am Weichselgarten 9, D-91058 Erlangen, Germany

Abstract Selective laser sintering (SLS), a powder-based additive manufacturing technology, employs micron-

sized polymer particles, which are selectively fused by a laser. SLS yields excellent part qualities with good mechanical properties. However, a persistent challenge in this layer-by-layer process is a reduction of mechanical properties in the z-direction. This is often caused by insufficient layer adhesion. One way to strengthen the layer adhesion in z-direction is the incorporation of glass fibers, which exceed from one layer into another. However, most commercially available glass-fiber enhanced materials are dry blends of the polymer powders and the fibers. In order to enhance the isotropic mechanical properties of parts manufactured via selective laser sintering, the manufacturing of glass fiber-filled PA11 particles is shown in this contribution. We present a single-pot approach to produce glass fiber-filled polyamide 11 (PA11) composite particles. The particles are manufactured via liquid-liquid phase separation and precipitation [1] (also known as solution-dissolution process) from ethanol glass fiber dispersions. Bulk polymer material of PA11 is directly converted to composite microparticles in a single process. The produced particles are characterized regarding their size and morphology. The amount of glass fibers in the bulk is assessed via thermogravimetric analysis and the effect of the fibers on the processing window is investigated via differential scanning calorimetry (DSC). As a proof of concept, the powder is employed in the SLS process to produce glass fiber-enhanced test specimens for mechanical testing.

Introduction Powder-based additive manufacturing technologies, especially laser powder bed fusion (aka. selective

laser sintering (SLS)) yields parts of high quality and stability, without the need for support structures. In this process, a homogeneous layer of powder is spread via doctor blade or roller onto a building platform. The particles in the spread powder are selectively fused with a laser, according to the cross section of the part to be built in this layer, before the building platform is lowered by the height one powder layer and the process is repeated. The process is operated at elevated temperatures, namely between the onset of melting and the onset of crystallization, the so called sintering window [1]. The most obvious material requirement is that the feedstock must be a powder. However, the requirements on the material to obtain parts of high quality are much more demanding. Suitable powders must be optimized with regard to their flowability and packing properties, particle size and shape, but also thermal and rheological properties. Therefore, the most widely and most successfully employed material for SLS is polyamide 12 with a market share of around 90%, while the rest is made up of e.g. polyamide 11, polypropylene, PEEK and others [2]. For SLS they show good intrinsic properties (aging behavior, sintering window, crystallization kinetics) rendering them very suitable for SLS [3]. To overcome some of the PA12 or PA11 specific drawbacks, like mediocre mechanical properties, it is possible to add fiber materials to the polymer powder, in order to obtain fiber-reinforced parts with high stiffness for applications like housing in automotive [4]. As fibers might reduce the flowability of a dry blended powder system due to their large diameter-length ratio [5], it is desirable to incorporate the fibers into the polymer particle. By that, process properties, like flowability as well as optical properties of the powder are hardly

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Solid Freeform Fabrication 2019: Proceedings of the 30th Annual InternationalSolid Freeform Fabrication Symposium – An Additive Manufacturing Conference

Reviewed Paper

influenced by the fillers. A comprehensive overview on advantages and challenges of fiber reinforced additive manufacturing is given in a recent article by Fidan et al. [6]. While the commercially available polyamide 11 is produced via cryogenic grinding, the largest portion of the PA12 powder used in SLS is precipitated using the thermally-induced liquid-liquid phase separation (TIPS), or solution-dissolution, process [3,7]. This process is based in the dissolution of the polymer in a moderate solvent. Such a solvent dissolves the polymer only at elevated temperatures, so that upon cooling the homogenous solution, the solvent cannot dissolve the polymer anymore. Subsequently, during cooling, the system reaches a miscibility gap, where TIPS sets in, dependent on the system composition and process parameters. Droplets of high polymer concentration form in a matrix of high solvent concentration. Consequently, the polymer in the droplets crystalizes or solidifies and polymer microparticles are precipitated. The resulting size distribution and shape are governed, among other parameters, on the polymer-solvent pairing, the polymer concentration, droplet coarsening by coalescence and Ostwald ripening, stirring conditions etc. More information on this process can be found in [8–12]. In a recent publication, we investigated this process for the manufacturing of PA11 particles and performed a thorough particle and material characterization before applying the material in the SLS process, where we could show its processability [13]. The advantage of this process is the possibility to add stabilizers, fillers or other compounds easily during the TIPS process, which get incorporated into the particles. Based on this work, in this study we investigate the manufacturing of glass fiber-filled PA11 particles with a fiber concentration of 25 vol.%. The fiber length distribution of the employed milled glass fiber material is assessed via light microscopy and the particle size distribution (PSD) of the manufactured composite powder is investigated via laser diffraction particle sizing. The incorporation of the glass fibers into the polymer particles, as well as the resulting particle shape, is studied via SEM imaging. The glass content in the manufactured and sieved powder is determined via thermogravimetric analyses. Furthermore, the thermal properties, namely the sintering window, as well as a possible effect of the fiber material on the polymer crystallization, is investigated via DSC. Based on the performed powder characterization, appropriate laser sintering parameters for the manufacturing of test specimens with a desktop laser sintering device could be identified. As a proof of concept, thereby manufactured test specimens made from neat PA11 powder and the glass-filled PA11 composite powder respectively, are mechanically tested to assess the strengthening effect of the glass fibers. The resulting part morphology, especially the fiber distribution in the laser sintered specimens, is investigated via light microscopy on resin embedded cross sections.

Materials

As feed material polyamide 11 granules (Rilsan BMN O natural, Arkema) were used. Ethanol (99.5 %, denatured with 1 % MEK, VWR) was used as a moderate solvent without further purification. The fibers used for filling the PA11 were milled glass fibers of the type OK-7904 FM with a nominal fiber length of 0.2 mm (WELA Handelsgesellschaft mbH).

Methods Precipitation of glass fiber-filled PA11 particles DAB-3 (Berghof) steel autoclaves equipped with PTFE liners placed on stirrer hotplates were used as reactors for particle manufacturing. A detailed description of the particle precipitation procedure can be found in [13]. In all reported experiments 18 g PA11 granules and 82 g ethanol were used. Furthermore, in order to obtain a PA11-glass fiber composite material with 25 vol.% of glass fibers, 13.5 g of glass fiber material was added. The autoclaves were then heated to 190 °C, where the system was held for 15 min, to ensure complete dissolution of the PA11, before heating was turned off. The system was then cooled to 130 °C, where an isothermal step was applied for 30 minutes. Stirring inside the autoclaves was realized via magnetic stirring bars (6mm x 25 mm) at 300 rpm. The autoclaves were opened at temperatures below 60°C and the product particles were collected by filtration via a Büchner funnel (Grade 1 filter, Whatman). The recovered wet particles were subsequently dried in an oven and sieved with a 160 μm sieve. 1023

Laser diffraction particle sizing Particle size distributions (PSDs) of the glass fiber-filled PA11 particles were measured by laser

diffraction using a Mastersizer 2000 equipped with a Scirocco 2000 dry dispersion unit (Malvern). The dispersion gas pressure was 2 bar.

Glass fiber size analysis Since size measurement of fibers is not feasible via laser diffraction, the fiber lengths were measured via

light microscopy under 10X magnification with a Morphologi G3 (Malvern). For the measurement, around 60,000 particles are dry-dispersed and then measured optically.

Scanning Electron Microscopy (SEM) Shape and surface morphology of the PA11 particles were characterized by scanning electron

microscopy (SEM) with a GeminiSEM 500 (Carl Zeiss) operated at an acceleration voltage of 1.0 kV. A secondary electron detector was used for imaging.

Differential scanning calorimetry (DSC) Differential scanning calorimetry (DSC) for the glass fiber-filled PA11 powders was performed using a

DSC8000 (PerkinElmer). The samples were placed in standard aluminum pans with covers and measured at a heating rate of 10 K/min from 30°C to 210°C followed by cooling to 30°C at 10 K/min. Measurements were conducted under continuous nitrogen purge gas flow (25 mL/min).

He-pycnometry Solid density was determined using the helium pycnometer AccuPyc 1330 (Micromeritics) equipped

with a 1 cm3 sample cell.

Thermogravimetric analysis (TGA) Determination of glass fiber content in the filled PA11 powders was realized by measuring the weight of

the ash residue via TGA. Experiments were performed in synthetic air using a TGAQ50 (TA Instruments). A ceramic pan with a volume of 250 μl was used and the sample weight was approximately 60 mg. The measurement was conducted in a temperature range of 30–900 °C with a heating rate of 10 K/min. Measurements were conducted once with powder sample mixtures of at least 6 single powder precipitation samples.

Powder bed fusion To investigate the processability of the manufactured glass-filled PA11 powder in the powder bed fusion

process, five test specimens were manufactured on a SnowWhite (Sharebot). The test specimens were tensile specimens according to DIN EN ISO 527-2 type 5A. The device is equipped with a CO2 laser (wavelength 10.6 μm) with a maximum nominal power of 14 W, the maximum scanning speed is 3500 mm/s and the distance between the laser tip and the powder bed is approx. 20 cm. No information on laser spot size and hatching distance is specified by the device manufacturer. The device is not flushed with nitrogen and operated under air atmosphere. Before and after each experiment, the lens was cleaned with dust-free tissues and absolute ethanol.

Mechanical Testing

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All tensile tests were performed on a Z050 (Zwick) tensile testing machine according to DIN EN ISO 527-1. In accordance with the norm, the test speed was 20 mm/min, the clamping length L0 50 mm and thepreload 0.1 N for all samples, to ensure comparability.

Specimen and particle cross section inspection For analyzing the spatial fiber distribution, cross-sections of the particles and the test specimen are

made. The tensile bar and the particles were embedded in epoxy and then grinded and polished. Then, the cross-section of the middle of the tensile bar was analyzed by light microscopy (AxioImagerM2m, Zeiss) under bright field illumination with a magnification of 10x. The prepared particles are analyzed via SEM (Ultra Plus, Zeiss).

Results

To study the manufacturing of glass fiber-filled PA11 particles, it is crucial to obtain information on the fiber length distribution, since the used fiber material is a milled glass fiber powder. While we aim for incorporation of the glass fiber material into the particle matrix, only fibers smaller than the particle can be enclosed fully in the particle matrix. Longer fibers might protrude from the particle and even longer fibers might only be coated by the polymer. In Table 1, the representative number- and volume-weighted fiber length distribution, given as x10, x50, and x90 values, as determined via light microscopy are listed.

Table 1: Fiber length distribution x10 / μm x50 / μm x90 / μm

Number-weighted 1.87 4.45 23.88 Volume-weighted 20.94 66.91 240.3

It is obvious, that the milled fiber material displays a broad length distribution, with a large portion of very small sub 5 μm fiber fragments, which are formed during milling. The large number of small fiber fragments is beneficial for filling the particles, as the mean particle size obtained from the precipitation of PA11 from ethanol employing comparable parameters is larger (c.f. 80 μm to 130 μm [13]). However, the large x90,3 length shows, that also very long fibers must be present in the fiber material. The longest observed fiber even measured 571.9 μm. Such long fibers, while beneficial for macroscopic strengthening, as they extend over several particles or powder layers in the SLS process, can hardly be incorporated into single particles and might negatively influence powder flowability or spreadability and subsequently SLS processability. To assess the incorporation of the glass fiber material and the resulting PA11 composite particle shape and morphology, SEM imaging was conducted. In Figure 1, three representative images are shown.

Figure 1: SEM images of the manufactured glass-filled PA11 powder.

The images support the assumptions made based on the fiber lengths distribution. Particles with nearly enclosed or protruding fiber fragments can be identified, as well as larger fibers, which are coated with polymer. Also fibers with particles attached at the end are visible. While these observations proof, that our approach to manufacture PA11-glass fiber composite particles via TIPS is successful, they also show, that employing a

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milled glass fiber material leads to a wide variety of particle shapes and sizes, as well as polymer-coated fibers. Coating of fibers with polymer via TIPS for application in SLS has previously been reported by Yang et al. [14], where carbon fibers were coated with PA12. They found enhanced mechanical properties due to the homogeneous distribution of the fibers and the strong interfacial bonding. These effects will be investigated for our PA11 composite powder in the following via mechanical testing and cross-section imaging of parts manufactured via SLS.

However, in order to identify appropriate process parameters for SLS, the particles size distribution of the manufactured particles, which is linked to the applicable layer height in the CAD model and the sintering machine, must be known. In previous studies concerning laser sintering of PA11 particles manufactured via TIPS, we found the removal of a coarse fraction larger than 160 μm to be a viable method to ensure good SLS processability [13]. The volume-weighted particle size distribution of the PA11-glass fiber composite powder is depicted in Figure 2 (left). The powder exposes a mean particle size of 65.4 μm, which is well comparable to commercial SLS powders [3,13,15,16]. With a x10,3 of 21.2 μm and a x90,3 of 145.7 μm, the fine fraction is smaller and the coarse fraction larger than commercial powders (c.f. non-sieved: x10,3 = 19.8 μm, x50,3 = 66.0 μm and x90,3= 155.4 μm). The distribution width, given as span calculated as (x90,3 - x10,3)/x50,3, is 1.9 (c.f. non-sieved: 2.1), indicating a rather broad distribution. However, this could be easily overcome by further removal of fine and coarse fraction via sieving and classification. In this study, we refrain from doing so, as the goal is a proof of principle of the process route to obtain glass fiber-filled PA11 composite particles, which can be employed in SLS, and not optimized material development. While the SEM images showed, that the incorporation of the glass fibers was successful, no information on the final glass concentration is obtained. To check, if the intended glass fiber concentration of 25 vol.%, added during the initial manufacturing process, is still present in the dried and sieved powder, TGA measurements were performed. The recorded progression of weight loss over temperature is depicted in Figure 2 (right).

Figure 2: Particle size distributions of the manufactured sieved and non-sieved PA11-glass fiber composite powder (left) and progression of weight loss over temperature as obtained by TGA (right). Onset of degradation is 424 °C for the glass-fiber composite and 415 °C for neat PA11.

The ash residue, which can be correlated to the weight concentration of the glass fibers, was determined to be 42.5 wt.%. With a density, as obtained by He-pycnometry, of 2.598 g/cm3 and 1.110 g/cm3 for the glass fiber material and the PA11 particles [13], respectively, the volume concentration of the glass in the powder bulk is 24.7 vol.%. This matches the intended volume concentration of 25 vol.% nearly perfect, even though the bulk powder obtained after the TIPS process was washed, dried and sieved. The powder yield after production and these post processing steps was higher than 90%, rendering the TIPS process and the subsequent post processing quite efficient. The TGA shows, that it is possible to tailor the glass concentration in the PA11-glass fiber composite powder by mere addition of the desired glass content to the initial TIPS process in a one pot approach. Furthermore, the glass reinforced particles exhibit a slightly higher onset of degradation, with 424 °C compared to 415 °C for the neat PA11.

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1.0 PA11-GF (160µmsieved) ,,, ___ _ ------ PA11 -GF (non-sieved) /

0.8 x10,J = 21 .2 µm x

50_3 = 65.4 µm -,..._0.6

>< -o("f)o.4 0.2

x90

_3

= 145.7 µm

Span= 1.9

10 100 1000

Particle size / µm

100,----- = -----.======

90

~ 80 o 70 -_, 60 "5, 50 . (1) 40

$ 30 20

10

Neat PA11

42.5 wt.% ~ 24 .7 vol.°/4

0 -l--,-~---,-~-,---~....;:::::::$===,;,e==;-____j 0 200 400 600 800 1000

Temperature/ °C

Another important material characteristic, which is crucial for successful SLS processing, is the thermal sintering window, given as the temperature difference between the onset of melting and the onset of crystallization (often determined with heating and cooling rates of 10 K/min). The processing temperature in the building chamber should be in this window, to mitigate premature crystallization of the molten polymer after laser exposure. A thermogram depicting the first heating and cooling of the glass fiber-filled PA11 powder and the appropriate sintering window is displayed in Figure 3.

The displayed thermogram is typical for PA11 particles obtained via TIPS, with the double -phase melting endotherm and a sintering window in the range of 17 °C to 19 °C [13]. The glass fiber composite material shows an onset of melting at 184.6 °C and an onset of crystallization at 166.3 °C, which corresponds to a sintering window of 18.3 K. The glass fiber material, even though its large number concentration of sub-5 μm fragments, does not act as a nucleating agent causing premature crystallization. Considering the thermal properties of the composite powder, sufficient processability can be expected, as the sintering window is large enough to compensate minor deviations on temperature during processing and the glass fiber material does not affect the crystallization negatively.

Figure 3: Thermogram of the first heating and cooling cycle of the PA11-glass fiber composite material and neat PA11 material determined with a scanning rate of 10 K/min. The heat flow of the composite material has not been correct for the mass of glass, thus yielding lower absolute enthalpy as compared to the native PA11 material.

Based on the preceding powder characterization, suitable processing parameters for SLS with the SnowWhite desktop sintering machine can be chosen. In the slicer software, a layer height of 0.3 mm was used, which correlates roughly to twice the x90,3, a value often used as rule of thumb. Under consideration of the DSC results, the building chamber temperature, given in the device as environmental temperature, was set to 157 °C, which correlates to a powder bed temperature in the device of approx. 177 °C. Since the glass might absorb some of the laser light and our particles are larger than standard PA12 powder material, we deviate from the processing parameters given by the device manufacturer for sintering of PA12. In Table 2, a comparison between the most important processing parameters given for PA12 and our settings can be found. After a few test runs, sufficient sintering results could be obtained with a laser power of 4.2 W and a scanning rate of 825 mm/s in the bulk and 550 mm/s at the part borders. Furthermore, a waiting time of 20 seconds, after laser illumination and before the next powder layer is deployed, was set.

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Table 2: Comparison between the most important processing parameters given for PA12 and the settings employed for sintering of our PA11-glass fiber composite powder. Material Standard PA12 PA11-GF composite Temperature (environmental) / °C 138 - 143 157 Laser power / W 2.8 4.2 Scanning Speed / mm/s 2188 825 Scanning Speed (border) / mm/s 2188 550

These parameters are not optimized and the resulting part qualities are hardly comparable to industrial laser sintering machines. Thorough processing parameter optimization could not be realized, because due to the air atmosphere present in the SnowWhite device and the well-known aging of polyamide powder materials, virgin material was only used once for each experiment. This increased material demand had to be met with the present production rate of 18g polymer material per precipitation experiment. However, we were able to manufacture multi-layered test specimens from our produced PA11-glass fiber composite powder and could show its basic SLS processability.

To assess the effect of the glass fiber material on the part properties, mechanical testing of the manufactured test specimens was conducted. For better comparison, also test specimens manufactured under identical parameters via SLS from neat PA11 powder, produced via TIPS, were investigated. The resulting ultimate tensile strength and elongation at break for the neat PA11 and the PA11-glass fiber composite are listed in Table 3.

Table 3: Mechanical properties of the test specimens manufactured from neat PA11 and PA11-glass fiber composite. Sample (n = 5) Ultimate tensile strength / MPa Elongation at break / % Neat PA11 7.1 ± 0.5 5.9 ± 0.5 PA11-glass fiber composite 21.4 ± 1.1 6.3 ± 0.2

Even though the mechanical properties, as compared to injection molding or laser sintering with optimized parameters on industrial devices, are rather weak, a strong increase in ultimate tensile strength can be observed for the composite powder. The elongation at break was apparently not affected by the addition of glass fiber material. For the neat PA11 specimens, we observed a fracture behavior governed by delamination, which could explain the weak ultimate tensile strength and the low elongation at break. The employed processing parameters lead to subpar layer adhesion and thus, delamination under tensile stress. This causes the unexpected low elongation at break in the same range as the much more brittle glass fiber composite. For the composite material, the employed manufacturing parameters yield stronger parts without any observed delamination under stress. This could be caused by the longer fibers extending between the layers and thus, linking the layers, which would benefit the layer adhesion. Furthermore, glass absorbs light very well in the CO2-laser wavelength (10.6 μm) [17]. Since some glass fibers protrude from the polymer particle, they are directly exposed to the laser during illumination, which could increase the effective energy input into the powder bed. This could lead to better sintering and therefore overall increased layer adhesion. Due to the limited amount of material and the temperature-induced ageing of polyamides [18] (especially under air, as it is the case in the desktop sintering device), we refrained from an extended parameter study to identify optimized processing parameters. To study the unaged, pristine powder properties, each powder batch was only used once for laser sintering. Nevertheless, it can be observed, that the fibers strengthen the material, even though they are smaller than typically used fiber material [19,20]. Via mechanical testing, we could show the basic SLS processability of our PA11-glass fiber composite powder and the strengthening effect of the fibers. However, no information on the fiber orientation in the polymer matrix could be gained. Therefore, a small fragment of a previously tested tensile specimen was embedded in epoxy, grinded and polished, until a plane cross section of the laser sintered specimen could be investigated under the light microscope. Images of the analyzed cross sections can be found in Figure 4 (left). Furthermore, a SEM image of the glass-filled particle cross-section is depicted in Figure 4 (right).

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Figure 4: Cross-section of laser sintered specimen made from PA11-glass fiber composite (left). SEM image of PA11-glass fiber composite particle cross sections (right).

The investigated cross sections show, that the glass fibers are distributed homogeneously throughout the part. No segregation effects or one-direction fiber orientation can be detected, which is important for isotropic part properties. In addition, the part exhibits a dense structure, which means that the powder composite offers a high packing density and proper flowability. The black spots in Figure 4 (left) result from sample preparation as some of the fibers fall out during grinding. The inspection of the particle cross sections supports the observation made by SEM imaging of the particles, as glass fiber fragments and glass fibers can be identified in the polymer particle matrix.

Conclusions

In this study, we could show a one-pot approach to manufacture a PA11-glass fiber composite powder based on a TIPS process, where small fiber fragments are incorporated into the polymer particle and larger fibers are coated with the polymer. Furthermore, via TGA we could show, that it is possible to tailor the glass fiber concentration by simply adding the desired amount during the initial TIPS process. Even though the powder was washed and sieved, the measured amount of glass in the composite powder agreed perfectly with the desired amount of 25 vol.%. With a mean particle size 65.4 μm, the manufactured composite powder was in the typical size range for SLS materials, even though the size distribution was not optimized by narrowing via sieving and classification. The DSC analysis showed, that the fiber material does not influence the crystallization and that the composite powder displays a sintering window of 18 °C. Following the powder characterization, processing parameters for laser sintering in the desktop SLS device could be identified, whereby the basic SLS processability of our composite powder could be proven. Though the laser sintering parameters are not optimized yet, a clear strengthening effect of the glass fiber material could be observed for the absolute mechanical properties of the parts. Via light microscopy on cross sections of laser sintered specimens, homogeneous distribution and good adhesion could be shown. For future studies, a thorough comparison between glass-filled PA11 and dry-blended PA11 particle glass fiber mixtures is envisioned, where parts manufactured with optimized sintering parameters in industrial SLS machines are investigated to assess the differences between dry blends and composites.

Acknowledgement This study has been funded by the Deutsche Forschungsgemeinschaft (DFG, German Research

Foundation) – Project-ID 61375930 – SFB 814, Subproject A1, A3 and A6. The financial support is gratefully acknowledged. We thank Franz J. Lanyi and Dirk W. Schubert for performing the mechanical testing.

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WelcomeTitle PagePrefaceOrganizing CommitteePapers to JournalsTable of ContentsBroader Impacts and EducationDesign for Additive Manufacturing: Simplification of Product Architecture by Part Consolidation for the LifecycleAn Open-Architecture Multi-Laser Research Platform for Acceleration of Large-Scale Additive Manufacturing (ALSAM)Large-Scale Identification of Parts Suitable for Additive Manufacturing: An Industry PerspectiveImplementation of 3D Printer in the Hands-On Material Processing Course: An Educational PaperConceptual Design for Additive Manufacturing: Lessons Learned from an Undergraduate CourseAn Empirical Study Linking Additive Manufacturing Design Process to Success in ManufacturabilityInvestigating the Gap between Research and Practice in Additive Manufacturing

Binder JettingInfluence of Drop Velocity and Droplet Spacing on the Equilibrium Saturation Level in Binder JettingProcess Integrated Production of WC-Co Tools with Local Cobalt Gradient Fabricated by Binder JettingThe Effect of Print Speed on Surface Roughness and Density Uniformity of Parts Produced Using Binder Jet 3D PrintingExperimental Investigation of Fluid-Particle Interaction in Binder Jet 3D PrintingBinder Saturation, Layer Thickness, Drying Time and Their Effects on Dimensional Tolerance and Density of Cobalt Chrome - Tricalcium Phosphate Biocomposite

Data AnalyticsPredicting and Controlling the Thermal Part History in Powder Bed Fusion Using Neural Networks‘Seeing’ the Temperature inside the Part during the Powder Bed Fusion ProcessConditional Generative Adversarial Networks for In-Situ Layerwise Additive Manufacturing DataIn-Situ Layer-Wise Quality Monitoring for Laser-Based Additive Manufacturing Using Image Series AApplications of Supervised Machine Learning Algorithms in Additive Manufacturing: A ReviewReal-Time 3D Surface Measurement in Additive Manufacturing Using Deep LearningRoughness Parameters for Classification of As-Built and Laser Post-Processed Additive Manufactured SurfacesApplication of the Fog Computing Paradigm to Additive Manufacturing Process Monitoring and ControlSpectral X-ray CT for Fast NDT Using Discrete Tomography

Hybrid AMPart Remanufacturing Using Hybird Manufacturing ProcessesIntegration Challenges with Additive/Subtractive In-Envelope Hybrid ManufacturingRobot-Based Hybrid Manufacturing Process ChainIntegrated Hardfacing of Stellite-6 Using Hybrid Manufacturing ProcessInkjet Printing of Geometrically Optimized Electrodes for Lithium-Ion Cells: A Concept for a Hybrid Process ChainUltrasonic Embedding of Continuous Carbon Fiber into 3D Printed Thermoplastic Parts

Materials: MetalsComparison of Fatigue Performance between Additively Manufactured and Wrought 304L Stainless Steel Using a Novel Fatigue Test SetupElevated Temperature Mechanical and Microstructural Characterization of SLM SS304LFatigue Behavior of Additive Manufactured 304L Stainless Steel Including Surface Roughness EffectsJoining of Copper and Stainless Steel 304L Using Direct Metal DepositionSS410 Process Development and CharacterizationEffect of Preheating Build Platform on Microstructure and Mechanical Properties of Additively Manufactured 316L Stainless SteelCharacterisation of Austenitic 316LSi Stainless Steel Produced by Wire Arc Additive Manufacturing with Interlayer CoolingEffects of Spatial Energy Distribution on Defects and Fracture of LPBF 316L Stainless SteelEnvironmental Effects on the Stress Corrosion Cracking Behavior of an Additively Manufactured Stainless SteelEffect of Powder Chemical Composition on Microstructures and Mechanical Properties of L-PBF Processed 17-4 PH Stainless Steel in the As-Built And Hardened-H900 ConditionsPowder Variation and Mechanical Properties for SLM 17-4 PH Stainless SteelFatigue Life Prediction of Additive Manufactured Materials Using a Defect Sensitive ModelEvaluating the Corrosion Performance of Wrought and Additively Manufactured (AM) Invar ® and 17-4PHComparison of Rotating-Bending and Axial Fatigue Behaviors of LB-PBF 316L Stainless SteelA Study of Pore Formation during Single Layer and Multiple Layer Build by Selective Laser MeltingDimensional Analysis of Metal Powder Infused Filament - Low Cost Metal 3D PrintingAdditive Manufacturing of Fatigue Resistant Materials: Avoiding the Early Life Crack Initiation Mechanisms during FabricationAdditive Manufacturing of High Gamma Prime Nickel Based Superalloys through Selective Laser Melting (SLM)Investigating the Build Consistency of a Laser Powder Bed Fused Nickel-Based Superalloy, Using the Small Punch TechniqueFatigue Behavior of Laser Beam Directed Energy Deposited Inconel 718 at Elevated TemperatureVery High Cycle Fatigue Behavior of Laser Beam-Powder Bed Fused Inconel 718Analysis of Fatigue Crack Evolution Using In-Situ TestingAn Aluminum-Lithium Alloy Produced by Laser Powder Bed FusionWire-Arc Additive Manufacturing: Invar Deposition CharacterizationStudy on the Formability, Microstructures and Mechanical Properties of Alcrcufeniᵪ High-Entropy Alloys Prepared by Selective Laser MeltingLaser-Assisted Surface Defects and Pore Reduction of Additive Manufactured Titanium PartsFatigue Behavior of LB-PBF Ti-6Al-4V Parts under Mean Stress and Variable Amplitude Loading ConditionsInfluence of Powder Particle Size Distribution on the Printability of Pure Copper for Selective Laser MeltingInvestigation of the Oxygen Content of Additively Manufactured Tool Steel 1.2344The Porosity and Mechanical Properties of H13 Tool Steel Processed by High-Speed Selective Laser MeltingFeasibility Analysis of Utilizing Maraging Steel in a Wire Arc Additive Process for High-Strength Tooling ApplicationsInvestigation and Control of Weld Bead at Both Ends in WAAM

Materials: PolymersProcess Parameter Optimization to Improve the Mechanical Properties of Arburg Plastic Freeformed ComponentsImpact Strength of 3D Printed Polyether-Ether-Ketone (PEEK)Mechanical Performance of Laser Sintered Poly(Ether Ketone Ketone) (PEKK)Influence of Part Microstructure on Mechanical Properties of PA6X Laser Sintered SpecimensOptimizing the Tensile Strength for 3D Printed PLA PartsCharacterizing the Influence of Print Parameters on Porosity and Resulting DensityCharacterization of Polymer Powders for Selective Laser SinteringEffect of Particle Rounding on the Processability of Polypropylene Powder and the Mechanical Properties of Selective Laser Sintering Produced PartsProcess Routes towards Novel Polybutylene Terephthalate – Polycarbonate Blend Powders for Selective Laser SinteringImpact of Flow Aid on the Flowability and Coalescence of Polymer Laser Sintering PowderCuring and Infiltration Behavior of UV-Curing Thermosets for the Use in a Combined Laser Sintering Process of PolymersRelationship between Powder Bed Temperature and Microstructure of Laser Sintered PA12 PartsUnderstanding the Influence of Energy-Density on the Layer Dependent Part Properties in Laser-Sintering of PA12Tailoring Physical Properties of Shape Memory Polymers for FDM-Type Additive ManufacturingInvestigation of The Processability of Different Peek Materials in the FDM Process with Regard to the Weld Seam StrengthStereolithography of Natural Rubber Latex, a Highly Elastic Material

Materials: Ceramics and CompositesMoisture Effects on Selective Laser Flash Sintering of Yttria-Stabilized ZirconiaThermal Analysis of Thermoplastic Materials Filled with Chopped Fiber for Large Area 3D PrintingThermal Analysis of 3D Printed Continuous Fiber Reinforced Thermoplastic Polymers for Automotive ApplicationsCharacterization of Laser Direct Deposited Magnesium Aluminate Spinel CeramicsTowards a Micromechanics Model for Continuous Carbon Fiber Composite 3D Printed PartsEffect of In-Situ Compaction and UV-Curing on the Performance of Glass Fiber-Reinforced Polymer Composite Cured Layer by Layer3D Printing of Compliant Passively Actuated 4D StructuresEffect of Process Parameters on Selective Laser Melting Al₂O₃-Al Cermet MaterialStrengthening of 304L Stainless Steel by Addition of Yttrium Oxide and Grain Refinement during Selective Laser MeltingApproach to Defining the Maximum Filler Packing Volume Fraction in Laser Sintering on the Example of Aluminum-Filled Polyamide 12Laser Sintering of Pine/Polylatic Acid CompositesCharacterization of PLA/Lignin Biocomposites for 3D PrintingElectrical and Mechancial Properties of Fused Filament Fabrication of Polyamide 6 / Nanographene Filaments at Different Annealing TemperaturesManufacturing and Application of PA11-Glass Fiber Composite Particles for Selective Laser SinteringManufacturing of Nanoparticle-Filled PA11 Composite Particles for Selective Laser SinteringTechnique for Processing of Continuous Carbon Fibre Reinforced Peek for Fused Filament FabricationProcessing and Characterization of 3D-Printed Polymer Matrix Composites Reinforced with Discontinuous FibersTailored Modification of Flow Behavior and Processability of Polypropylene Powders in SLS by Fluidized Bed Coating with In-Situ Plasma Produced Silica Nanoparticles

ModelingAnalysis of Layer Arrangements of Aesthetic Dentures as a Basis for Introducing Additive ManufacturingComputer-Aided Process Planning for Wire Arc Directed Energy DepositionMulti-Material Process Planning for Additive ManufacturingCreating Toolpaths without Starts and Stops for Extrusion-Based SystemsFramework for CAD to Part of Large Scale Additive Manufacturing of Metal (LSAMM) in Arbitrary DirectionsA Standardized Framework for Communicating and Modelling Parametrically Defined Mesostructure PatternsA Universal Material Template for Multiscale Design and Modeling of Additive Manufacturing Processes

Physical ModelingModeling Thermal Expansion of a Large Area Extrusion Deposition Additively Manufactured Parts Using a Non-Homogenized ApproachLocalized Effect of Overhangs on Heat Transfer during Laser Powder Bed Fusion Additive ManufacturingMelting Mode Thresholds in Laser Powder Bed Fusion and Their Application towards Process Parameter DevelopmentComputational Modelling and Experimental Validation of Single IN625 Line Tracks in Laser Powder Bed FusionValidated Computational Modelling Techniques for Simulating Melt Pool Ejecta in Laser Powder Bed Fusion ProcessingNumerical Simulation of the Temperature History for Plastic Parts in Fused Filament Fabrication (FFF) ProcessMeasurement and Analysis of Pressure Profile within Big Area Additive Manufacturing Single Screw ExtruderNumerical Investigation of Extrusion-Based Additive Manufacturing for Process Parameter Planning in a Polymer Dispensing SystemAlternative Approach on an In-Situ Analysis of the Thermal Progression during the LPBF-M Process Using Welded Thermocouples Embedded into the Substrate PlateDynamic Defect Detection in Additively Manufactured Parts Using FEA SimulationSimulation of Mutually Dependent Polymer Flow and Fiber Filled in Polymer Composite Deposition Additive ManufacturingSimulation of Hybrid WAAM and Rotation Compression Forming ProcessDimensional Comparison of a Cold Spray Additive Manufacturing Simulation ToolSimulated Effect of Laser Beam Quality on the Robustness of Laser-Based AM SystemA Strategy to Determine the Optimal Parameters for Producing High Density Part in Selective Laser Melting ProcessRheology and Applications of Particulate Composites in Additive ManufacturingComputational Modeling of the Inert Gas Flow Behavior on Spatter Distribution in Selective Laser MeltingPrediction of Mechanical Properties of Fused Deposition Modeling Made Parts Using Multiscale Modeling and Classical Laminate Theory

Process DevelopmentThe Use of Smart In-Process Optical Measuring Instrument for the Automation of Additive Manufacturing ProcessesDevelopment of a Standalone In-Situ Monitoring System for Defect Detection in the Direct Metal Laser Sintering ProcessFrequency Inspection of Additively Manufactured Parts for Layer Defect IdentificationMelt Pool Monitoring for Control and Data Analytics in Large-Scale Metal Additive ManufacturingFrequency Domain Measurements of Melt Pool Recoil Pressure Using Modal Analysis and Prospects for In-Situ Non-Destructive TestingInterrogation of Mid-Build Internal Temperature Distributions within Parts Being Manufactured via the Powder Bed Fusion ProcessReducing Computer Visualization Errors for In-Process Monitoring of Additive Manufacturing Systems Using Smart Lighting and Colorization SystemA Passive On-line Defect Detection Method for Wire and Arc Additive Manufacturing Based on Infrared ThermographyExamination of the LPBF Process by Means of Thermal Imaging for the Development of a Geometric-Specific Process ControlAnalysis of the Shielding Gas Dependent L-PBF Process Stability by Means of Schlieren and Shadowgraph TechniquesApplication of Schlieren Technique in Additive Manufacturing: A ReviewWire Co-Extrusion with Big Area Additive ManufacturingSkybaam Large-Scale Fieldable Deposition Platform System ArchitectureDynamic Build Bed for Additive ManufacturingEffect of Infrared Preheating on the Mechanical Properties of Large Format 3D Printed PartsLarge-Scale Additive Manufacturing of Concrete Using a 6-Axis Robotic Arm for Autonomous Habitat ConstructionOverview of In-Situ Temperature Measurement for Metallic Additive Manufacturing: How and Then WhatIn-Situ Local Part Qualification of SLM 304L Stainless Steel through Voxel Based Processing of SWIR Imaging DataNew Support Structures for Reduced Overheating on Downfacing Regions of Direct Metal Printed PartsThe Development Status of the National Project by Technology Research Assortiation for Future Additive Manufacturing (TRAFAM) in JapanInvestigating Applicability of Surface Roughness Parameters in Describing the Metallic AM ProcessA Direct Metal Laser Melting System Using a Continuously Rotating Powder BedEvaluation of a Feed-Forward Laser Control Approach for Improving Consistency in Selective Laser SinteringElectroforming Process to Additively Manufactured Microscale StructuresIn-Process UV-Curing of Pasty Ceramic CompositeDevelopment of a Circular 3S 3D Printing System to Efficiently Fabricate Alumina Ceramic ProductsRepair of High-Value Plastic Components Using Fused Deposition ModelingA Low-Cost Approach for Characterizing Melt Flow Properties of Filaments Used in Fused Filament Fabrication Additive ManufacturingIncreasing the Interlayer Bond of Fused Filament Fabrication Samples with Solid Cross-Sections Using Z-PinningImpact of Embedding Cavity Design on Thermal History between Layers in Polymer Material Extrusion Additive ManufacturingDevelopment of Functionally Graded Material Capabilities in Large-Scale Extrusion Deposition Additive ManufacturingUsing Non-Gravity Aligned Welding in Large Scale Additive Metals Manufacturing for Building Complex PartsThermal Process Monitoring for Wire-Arc Additive Manufacturing Using IR CamerasA Comparative Study between 3-Axis and 5-Axis Additively Manufactured Samples and Their Ability to Resist Compressive LoadingUsing Parallel Computing Techniques to Algorithmically Generate Voronoi Support and Infill Structures for 3D Printed ObjectsExploration of a Cable-Driven 3D Printer for Concrete Tower Structures

ApplicationsTopology Optimization for Anisotropic Thermomechanical Design in Additive ManufacturingCellular and Topology Optimization of Beams under Bending: An Experimental StudyAn Experimental Study of Design Strategies for Stiffening Thin Plates under CompressionMulti-Objective Topology Optimization of Additively Manufactured Heat ExchangersA Mold Insert Case Study on Topology Optimized Design for Additive ManufacturingDevelopment, Production and Post-Processing of a Topology Optimized Aircraft BracketManufacturing Process and Parameters Development for Water-Atomized Zinc Powder for Selective Laser Melting FabricationA Multi-Scale Computational Model to Predict the Performance of Cell Seeded Scaffolds with Triply Periodic Minimal Surface GeometriesMulti-Material Soft Matter Robotic Fabrication: A Proof of Concept in Patient-Specific Neurosurgical SurrogatesOptimization of the Additive Manufacturing Process for Geometrically Complex Vibro-Acoustic MetamaterialsEffects of Particle Size Distribution on Surface Finish of Selective Laser Melting PartsAn Automated Method for Geometrical Surface Characterization for Fatigue Analysis of Additive Manufactured PartsA Design Method to Exploit Synergies between Fiber-Reinforce Composites and Additive Manufactured ProcessesPreliminary Study on Hybrid Manufacturing of the Electronic-Mechanical Integrated Systems (EMIS) via the LCD Stereolithography TechnologyLarge-Scale Thermoset Pick and Place Testing and ImplementationThe Use of Smart In-Process Optical Measuring Instrument for the Automation of Additive Manufacturing ProcessesWet-Chemical Support Removal for Additive Manufactured Metal PartsAnalysis of Powder Removal Methods for EBM Manufactured Ti-6Al-4V PartsTensile Property Variation with Wall Thickness in Selective Laser Melted PartsMethodical Design of a 3D-Printable Orthosis for the Left Hand to Support Double Bass Perceptional TrainingPrinted Materials and Their Effects on Quasi-Optical Millimeter Wave Guide Lens SystemsPorosity Analysis and Pore Tracking of Metal AM Tensile Specimen by Micro-CtUsing Wax Filament Additive Manufacturing for Low-Volume Investment CastingFatigue Performance of Additively Manufactured Stainless Steel 316L for Nuclear ApplicationsFailure Detection of Fused Filament Fabrication via Deep LearningSurface Roughness Characterization in Laser Powder Bed Fusion Additive ManufacturingCompressive and Bending Performance of Selectively Laser Melted AlSi10Mg StructuresCompressive Response of Strut-Reinforced Kagome with Polyurethane ReinforcementA Computational and Experimental Investigation into Mechanical Characterizations of Strut-Based Lattice StructuresThe Effect of Cell Size and Surface Roughness on the Compressive Properties of ABS Lattice Structures Fabricated by Fused Deposition ModelingEffective Elastic Properties of Additively Manufactured Metallic Lattice Structures: Unit-Cell ModelingImpact Energy Absorption Ability of Thermoplastic Polyurethane (TPU) Cellular Structures Fabricated via Powder Bed FusionPermeability Analysis of Polymeric Porous Media Obtained by Material Extrusion Additive ManufacturingEffects of Unit Cell Size on the Mechanical Performance of Additive Manufactured Lattice StructuresMechanical Behavior of Additively-Manufactured Gyroid Lattice Structure under Different Heat TreatmentsFast and Simple Printing of Graded Auxetic StructuresCompressive Properties Optimization of a Bio-Inspired Lightweight Structure Fabricated via Selective Laser MeltingIn-Plane Pure Shear Deformation of Cellular Materials with Novel Grip DesignModelling for the Tensile Fracture Characteristic of Cellular Structures under Tensile Load with Size EffectDesign, Modeling and Characterization of Triply Periodic Minimal Surface Heat Exchangers with Additive ManufacturingInvestigating the Production of Gradient Index Optics by Modulating Two-Photon Polymerisation Fabrication ParametersAdditive Manufactured Lightweight Vehicle Door Hinge with Hybrid Lattice Structure

Attendee ListAuthor Index