2015 International Solid Freeform Fabrication Symposium
Permanent URI for this collectionhttps://hdl.handle.net/2152/88478
Proceedings for the 2015 International Solid Freeform Fabrication Symposium. For more information about the symposium, please see the Solid Freeform Fabrication website.
The Twenty-Sixth Annual International Solid Freeform Fabrication (SFF) Symposium – An Additive Manufacturing Conference, held at The University of Texas in Austin on August 10-12, 2015, was attended by 388 researchers from 19 countries. The organizers are pleased that 175 of the attendees were students, representing 45% of the audience. The number of oral and poster presentations increased to 289 this year, an increase of almost 50% over 2014. The meeting was held on the camps of The University of Texas at Austin in the AT&T Executive Education and Conference Center.
The meeting consisted of a Monday morning plenary, 25 parallel technical sessions and a poster session. This year’s best oral presentation was entitled, “Thermographic Measurements of the Commercial Laser Powder Bed Fusion Process at NIST”, authored by B. Lane, S. Moylan, E. Whitenton and L. Ma from the National Institute of Standards and Technology. Selection is based on the overall quality of the paper, the presentation and discussion at the meeting, the significance of the work and the manuscript submitted to the proceedings. Selected from 256 oral presentations, the associated manuscript appears on Page 575. The best poster presentation selected from 33 posters was given by L.B. Bass, N.A. Meisel and C.B. Williams from Virginia Polytechnic Institute and State University. Titled, “Exploring Variability in Material Properties of Multi-Material Jetting Parts”, the paper is included in the Proceedings on Page 993. Posters are judged based on the quality and organization of the poster as well as the discussion of the poster by the author during the poster session.
The recipient of the International Outstanding Young Researcher in Freeform and Additive Manufacturing Award was Dr. Ibrahim T. Ozbolat from The Pennsylvania State University. Dr. Richard J.M. Hague from the University of Nottingham won the International Freeform and Additive Manufacturing Excellence (FAME) Award.
The editors would like to thank the Organizing Committee, the session chairs, the attendees for their enthusiastic participation, and the speakers both for their significant contribution to the meeting and for the relatively prompt delivery of the manuscripts comprising this volume. We look forward to the continued close cooperation of the additive manufacturing community in organizing the Symposium. We also want to thank the Office of Naval Research (N00014-15-1-0071) and the National Science Foundation (CMMI-1536671) for supporting this meeting financially. The meeting was co-organized by The University of Connecticut at Storrs, and the Mechanical Engineering Department/Lab for Freeform Fabrication under the aegis of the Advanced Manufacturing and Design Center at The University of Texas at Austin.
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Item Using Design of Experiments in Finite Element Modeling to Identify Critical Variables for Laser Powder Bed Fusion(University of Texas at Austin, 2015) Ma, Li; Fong, Jeffrey; Lane, Brandon; Moylan, Shawn; Filliben, James; Heckert, Alan; Levine, LyleInput of accurate material and simulation parameters is critical for accurate predictions in Laser Powder Bed Fusion (L-PBF) Finite Element Analysis (FEA). It is challenging and resource consuming to run experiments that measure and control all possible material properties and process parameters. In this research, we developed a 3-dimensional thermal L-PBF FEA model for a single track laser scan on one layer of metal powder above a solid metal substrate. We applied a design of experiments (DOE) approach which varies simulation parameters to identify critical variables in L-PBF. DOE is an exploratory tool for examining a large number of factors and alternative modeling approaches. It also determines which approaches can best predict L-PBF process performance.Item 2015 International Solid Freeform Fabrication Symposium Table of Contents(2015) Laboratory for Freeform Fabrication and University of Texas at AustinItem Parameter Estimation Based Real-Time Metrology for Exposure Controlled Projection Lithography(University of Texas at Austin, 2015) Zhao, Xiayun; Rosen, David W.Exposure Controlled Projection Lithography (ECPL) is a layerless mask-projection stereolithography process, in which parts are fabricated from photopolymers on a stationary transparent substrate. To enable advanced closed-loop control for ECPL, an in-situ interferometric curing monitoring (ICM) system has been developed to infer the output of cured height. However, the existing ICM method based on an implicit model and rough phase counting is not fast and accurate enough. This paper reports on a new ICM method to address the modeling and algorithms issues confronted by the current ICM method. The new ICM model includes two sub-models: a sensor model of instantaneous frequency based on interference optics and a calibration model. To solve the models, a moving horizon exponentially weighted online parameter estimation algorithm and numerical integration are adopted. As a preliminary validation, offline analysis of interferograms acquired in an ECPL curing experiment is presented. The agreement between ICM estimated cured height and ex-situ microscope measurement indicates that the overall scheme of the new ICM measurement method with a well-established model, evolutionary estimation and incremental accumulation, is promising as a real-time metrology system for ECPL. The new ICM method is also shown to be able to measure multiple voxel heights consistently and simultaneously, which is desired in global measurement and control of ECPL.Item Selective Heat Sintering Versus Laser Sintering: Comparison of Deposition Rate, Process Energy Consumption and Cost Performance(University of Texas at Austin, 2015) Baumers, M.; Tuck, C.; Hague, R.The Selective Heat Sintering (SHS) process has become available as a low cost alternative to Laser Sintering (LS) for the additive deposition of polymer objects. While both processes belong to the powder bed fusion variant of Additive Manufacturing (AM) technology, their operating principles vary significantly: SHS employs a thermal print head to selectively fuse material powder, whereas the LS approach utilizes a laser beam coupled with a galvanometer. Based on a series of build experiments, this research compares these technology variants along three dimensions of process efficiency: deposition rate (measured in cm³/h), specific process energy consumption (MJ/kg) and specific cost ($/cm³). To ensure that both platforms are assessed under the condition of efficient technology utilization, an automatic build volume packing algorithm is employed to configure a subset of build experiments. Beyond reporting absolute and relative process performance, this paper additionally investigates how sensitive the compared processes are to a variation in the degree of capacity utilization and discusses the application of different levels of indirect cost in models of low cost AM.Item Direct Laser Deposition of Ti-6Al-4V from Elemental Powder Blends(University of Texas at Austin, 2015) Yan, Lei; Chen, Xueyang; Li, Wei; Liou, Frank; Newkirk, JoeA thin-wall structure composed of Ti-6Al-4V has been deposited using direct laser deposition (DLD) from blended Ti, Al, and V elemental powders. The microstructure and composition distribution along the build height direction were intensively investigated using optical microscopy, scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS), and Vickers hardness testing. The microstructures of the as-deposited Ti-Al-V were studied using EDS to determine appropriate weight percentage for Al and V in the blended powders before mixing. The effects of laser power and laser transverse speed on the microstructure were investigated and optimized laser processing parameters were concluded.Item Feedforward Control for Polymer Laser Sintering Process Using Part Geometry(University of Texas at Austin, 2015) Abdelrarhman, Mostafa; Starr, Thomas L.For the polymer laser sintering process, achieving optimum mechanical properties requires that every volume element of a part experience a temperature history sufficient to reach full density. This history must include a peak temperature high enough to fully melt, but not degrade, the polymer and a cool-down period that ensures elimination of porosity, interlayer bonding and relaxation of stress. Real-time thermal monitoring of the laser sintering process has shown that this temperature history depends on the geometries of both the current and prior layers. In this paper we demonstrate a feed-forward control system that improves uniformity of the temperature history for parts with variable cross-sections. The control algorithm for this system will utilize information from layerwise geometry models for parts in a multi-part build. The cross-sectional area for every layer will be used at run-time for feed forward control the laser scan parameters. The results confirmed maintaining constant peak temperature throughout the part. This control system ensures optimized sintering for parts with complex geometries.Item An Algorithm-Based Method for Process-Specific Three-Dimensional Nesting for Additive Manufacturing Process(University of Texas at Austin, 2015) Arndt, Alexander; Hackbusch, Heike; Anderl, ReinerTo achieve optimal and high-quality results through additive manufacturing, the process-and technology-specific orientation and positioning of components within the virtual space, the so-called nesting, is essential. Primarily the nesting step is examined in this paper. From a scientific perspective it is a matter of examining this process and furthermore to analyze the optimal insertion of supporting structures, since the critical machine-specific parameters have been insufficiently studied. Within this paper a new multi-criteria optimization based on a conceptual algorithm is proposed. The most important point is the consideration of a technical and not only geometric nesting process. The objective is the demonstration of restrictions and boundary conditions and a first developing for a new approach for the nesting process. As an example, the influence of the orientation of the spring rate is presented with a sample component here. Furthermore, there will be a prototype implementation and a short validation. Finally, a brief conclusion and an outlook is given.Item Towards High-Quality Selective Beam Melting Technologies: Modeling and Experiments of Single Track Formations(University of Texas at Austin, 2015) Yan, Wentao; Ge, Wenjun; Smith, Jacob; Wagner, Gregory; Lin, Feng; Kam Liu, WingAdditive manufacturing technologies are promising but still not widely used. One major problem is the unsatisfying quality e.g. surface roughness and dimensional accuracy. The discontinuous droplets and distortions in single track formations, which influence both surface roughness and dimensional accuracy, were investigated. The physical mechanisms of the formations of the droplets and distortions were proposed and the heat transfer simulations based on the Finite Element Method were established to predict the possibility of the droplet formation and the magnitude of the distortion. Experiments using Electron Beam Melting were then conducted to validate the physical and numerical models. The good agreements of the simulated and experimental results demonstrated that the proposed models are simple and efficient to provide quantitative predictions of the distortions.Item Thermographic Measurements of the Commercial Laser Powder Bed Fusion Process at NIST(University of Texas at Austin, 2015) Lane, Brandon; Moylan, Shawn; Whitenton, Eric; Ma, LiMeasurement of the high-temperature melt pool region in the laser powder bed fusion (LPBF) process is a primary focus of researchers to further understand the dynamic physics of the heating, melting, adhesion, and cooling which define this commercially popular additive manufacturing process. This paper will detail the design, execution, and results of high speed, high magnification in-situ thermographic measurements conducted at the National Institute of Standards and Technology (NIST) focusing on the melt pool region of a commercial L-PBF process. Multiple phenomena are observed including plasma plume and hot particle ejection from the melt region. The thermographic measurement process will be detailed with emphasis on the ‘measurability’ of observed phenomena and the sources of measurement uncertainty. Further discussion will relate these thermographic results to other efforts at NIST towards L-PBF process finite element simulation and development of in-situ sensing and control methodologies.Item Feasibility Study of Small Scale Production Based on Additive Manufacturing Technologies(University of Texas at Austin, 2015) Cunico, Marlon Wesley Machado; de Carvalho, JonasAlong the last years, the complexity of products has been growing progressively, while the product development life-cycle tended to be reduced. In addition to that, additive manufacturing technologies increased their role in the product development process, resulting in reduction of errors and products release time. In spite of these benefits, the main application of these technologies is still focused on initial phases of projects and results in high costs of parts and low volumes. On the other hand, although conventional productivity processes results in low costs and high volumes, the investment related to these processes are high and the implementation time are long. For that reason, the main goal of this work is to investigate the possibility of application of additive manufacturing technologies for small and medium scale production. Along this work, the main direct and indirect processes which are used for small and medium scale production were studied and a numerical cost model were developed for each one. In order to compare the benefits and disadvantages among the processes, 3 parts were selected and analysed through such models. By the end, the main cost, payback; amortization and takt time were identified and the most suitable process was found in accordance with annual part demand.Item Evaluation of 3D Printable Sustainable Composites(University of Texas at Austin, 2015) Roberson, David A.; Rocha, Carmen R.; Piñon, MonicaPolylactic acid (PLA) is rapidly becoming the mainstay material for use in desktop grade 3D printers based on FDM technology in part due to the environmental sustainability of this polymer. While biodegradability is an advantage; as compared to other materials used by FDM-type platforms, there is a lack of desirable physical attributes. The work presented here evaluates the altering of the physical properties of PLA through the addition of sustainable additives. Here, the physical properties of PLA were modified while, at the same time the two desirable aspects of 3D printer compatibility and biodegradability were retained. Rheological analysis of the material systems was performed by dynamic mechanical analysis and failure analysis of 3D printed tensile specimens was carried out through the use of scanning electron microscopy. Finally, biodegradability of the novel PLA-based material systems was assessed based on in-soil exposure testing.Item FE-Optimization and Data Handling for Additive Manufacturing of Structural Parts(University of Texas at Austin, 2015) Reiher, Thomas; Koch, RainerAdditive Manufacturing (AM) offers high potential due to its freedom of design for structural parts. Especially in combination with FE-based topology optimization an optimal use of material and thus significant weight reductions can be expected. However, the application of AM is hampered by different additional manufacturing processes along the entire production chain and data handling induced restrictions. Disadvantages emerge from a lack of adjustment of the entire design process for AM. First the optimization algorithms are not targeted to the opportunities and restrictions of AM – represented by design rules – like the design of support structures. Secondly, the CAD software is not adjusted to AM in particular. Creating freeform shaped surfaces based on the optimization results is significantly less convenient than building defined blocks or turning parts following the needs of conventional machining. The indispensable subsequent interpretation of optimization results regarding the design rules and the possibilities of CAD-tools counteracts optimal results. This paper considers different approaches for a Topology Optimization (TO)-shape regaining on different sample parts including telecommunication satellite parts. An innovative design methodology is presented getting crucial for creating high quality designs.Item Computational Modeling and Experimental Validation of Melting and Solidification in Equiaxed Superalloys Processed through Scanning Laser Epitaxy(University of Texas at Austin, 2015) Basak, Amrita; Acharya, Ranadip; Bansal, Rohan; Das, SumanThis paper focuses on simulation-based optimization of the Scanning Laser Epitaxy (SLE) process applied to gas turbine hot-section components made of nickel-base superalloys. SLE creates equiaxed, directionally-solidified and single-crystal microstructures from superalloy powders melted onto like-chemistry substrates using a fast scanning, high power laser beam. In this paper, a transient coupled flow-thermal approach is implemented to accurately simulate the melting and solidification process in SLE. The laser movement is modeled as a Gaussian moving heat source, and the thermophysical properties of the alloys are adjusted based on the thermal field. Simulations for different superalloys such as IN100, René 80 and MAR-M247 are performed and the instantaneous melt pool characteristics are recorded. Comparisons of the simulations with experimental results show reasonably good agreement for the melt depth. Feedback control is implemented, and demonstrated to produce superior quality SLE deposits.Item Functional Gradient Material of Ti-6Al-4V and γ-TiAl Fabricated by Electron Beam Selective Melting(University of Texas at Austin, 2015) Ge, Wenjun; Lin, Feng; Guo, ChaoAdditive Manufacturing (AM) technologies are very promising in fabricating functionally graded materials. Electron Beam Selective Manufacturing (EBSM) is one widely used AM technology capable of fabricating a variety of materials especially titanium alloys. Previous studies on EBSM process were focused on the manufacturing of one single material. In this study, a novel EBSM process capable of building gradient structures with dual metal materials was developed. Ti6Al4V powders and Ti47Al2Cr2Nb powders were used to fabricate Ti3Al/TiAl and Ti6Al4V/Ti3Al dual metal structures. The chemical compositions, microstructure and micro-hardness of the dual material samples were investigated employing Optical Microscope (OM), Scanning Electronic Microscope (SEM), Electron Probe Micro-Analyzer (EPMA). Results showed that the thickness of the transition zone was about 300μm. The transition zone was free of cracks, and the chemical compositions exhibited a staircase-like change. The microstructure and chemical compositions in different regions were studied. Microhardness was affected by the microstructure. The microstructures turned out to be full lamellar at the TiAl region and basket-weave structure at the Ti3Al and Ti6Al4V region.Item Systematical Determination of Tolerances for Additive Manufacturing by Measuring Linear Dimensions(University of Texas at Austin, 2015) Lieneke, T.; Adam, G.A.O.; Leuders, S.; Knoop, F.; Josupeit, S.; Delfs, P.; Funke, N.; Zimmer, D.Additive manufacturing offers many technical and economical benefits. In order to profit from these benefits, it is necessary to consider the manufacturing limits and restrictions. This applies in particular to the geometrical accuracy. Therefore, the achievable geometrical accuracy needs to be investigated, which enables the determination of realistic tolerances. Thus, two different aims are considered. The first aim is the determination of dimensional tolerances that can be stated if additive manufacturing is used under normal workshop conditions. Within the second aim, relevant process parameters and manufacturing influences will be optimized in order to reduce dimensional deviations. To achieve both aims a method was developed first. This method identifies relevant influential factors on the geometrical accuracy for the processes Fused Deposition Modeling (FDM), Laser Sintering (LS) and Laser Melting (LM). Factors were selected that are expected to affect the geometrical accuracy mainly. The first investigations deal with measuring linear dimensions on a designed test specimen and the derivation of achievable dimensional tolerances. This paper will present both, the developed method and the first results of the experimental investigations.Item A Framework for Large Scale Fused Pellet Modeling (FPM) by An Industry Robot(University of Texas at Austin, 2015) Wang, Zhiyun; Liu, Renwei; Sparks, Todd; Liou, FrankFused pellet modeling (FPM) is an important method in additive manufacturing technology, where granular material is used instead of filaments. In FPM, prototypes are constructed by the sequential deposition of material layers. As the size of the part increases, the problem of long build times and part deformation becomes critical. In this paper, methods for eliminating the void density during deposition and accuracy control principles for large scale FPM processes are studied. By analyzing the ab initio principles of this process, a mini extruder with variable pitch and progressive diameter screw for the large scale fused deposition is proposed. Based on polymer extrusion theory and non-Newtonian fluid properties, each of the design parameters are analyzed, such as the length of different function sections of screw, die shape of extruder nozzle, and the material properties. According to these analysis results, an extrusion process simulation for controlling the filament shape is carried out with multi-physics modeling software and proved the FPM could increase the building efficiency and deposition quality for large size parts.Item Selective Laser Sintering of Diamond Lattice Structures: Experimental Results and FEA Model Comparison(University of Texas at Austin, 2015) Neff, Clayton; Hopkinson, Neil; Crane, Nathan B.Nature utilizes multiple materials with varying properties to create high performance, integrated systems. In contrast, most additive manufacturing processes are limited to a small set of compatible materials to fabricate a device. However, the large geometric freedom of AM could be used to create the effect of multiple properties by creating lattice structures. Prior work has focused on using this concept to reduce weight in high stiffness structures. This paper will consider the use of a diamond lattice structures to create the effect of materials with a low elastic modulus materials. Low stiffness regions are advantageous for energy absorption, vibration isolation, and reduction of stress due to dimensional or temperature mismatches. The diamond lattice possesses Face-Centered-Cubic (FCC) elemental configuration possessing tetrahedral angles of 109° between elements. This allows for a pliable moment exerted on the structure yielding a flexible and energy absorbent arrangement. A range of devices was fabricated in Nylon 12 (PA 2200) through Laser Sintering (LS) process with variable element size (thickness) and unit cell size. The effective stiffness of the structures is compared as a function of these parameters and compared to numerical simulation. The results show the possibility of tuning the effective elastic modulus by over four orders of magnitude.Item In Situ Printing - An Alternative Three Dimensional Laden Structure Fabrication Method(University of Texas at Austin, 2015) Liu, W.; Sun, W.Recapitulating a structure that mimics the anatomic geometries and intratissue cell distribution as in live organism is a major challenge of tissue engineering nowadays. Solid freeform fabrication (SFF) has been demonstrated as an efficient tool for this purpose. In this paper we presented a SFF based in situ printing method that is free of fabrication time frame and fabrication environment constrains. The fabrication parameters on strut formability, fabricated structural stability against gentle fluidic disturbance, and the integrity of the fabricated structure in cell culture environment were studied to assess the potential of the fabrication method on biomedical application. Based on the results, controlled strut formability can be achieved in an appropriate cross-linking deposition range. Alginate composition is the main parameter that dominates the stability and integrity of the fabricated structure. A parameter set that can produce a stable scaffold with the ability to maintain its structure in cell culture environment for at least 15 days was optimized.Item Development of Powder Bed Fusion Additive Manufacturing Test Bed for Enhanced Real-Time Process Control(University of Texas at Austin, 2015) Vlasea, M.L.; Lane, B.; Lopez, F.; Mekhontsev, S.; Donmez, A.Laser powder bed fusion (PBF) is emerging as the most popular additive manufacturing (AM) method for producing metallic components based on the flexibility in accommodating a wide range of materials with resulting mechanical properties similar to bulk machined counterparts, as well as based on in-class fabrication speed. Although this approach is advantageous, the current limitations in achieving predictable and repeatable material and structural properties, geometric and surface roughness characteristics, and the occurrence of deformations due to residual stresses results in significant variations in part quality and reliability. Therefore, a better understanding and control of PBF AM processes is needed. The National Institute of Standards and Technology (NIST) is developing a testbed to assess in-process and process-intermittent metrology methods and real-time process control algorithms, and to establish foundations for traceable radiance-based temperature measurements that support high-fidelity process modeling efforts. This paper will discuss functional requirements and design solutions to meet these distinct objectives.Item 3D Printing with Natural Fiber Reinforced Filament(University of Texas at Austin, 2015) Montalvo, J.I.; Hidalgo, M.A.An initial study of 3d printing with compound filament using different plastic matrices and sugar cane bagasse as the filler was conducted. In order to do this, a reverse engineering process was made to several 3d printer extruders to determine how to change the extruder in order to be able to print with the filament. To obtain the filament, a plastic extruder was modified to obtain a compound filament of 1.75 mm using a 3x4 design of experiments with the factors percentage of fiber (10% 20% 30%) and type of matrix(PE,PP,ABS,PLA). The filaments obtained were tested to determine the mechanical properties and finally were used in a 3d printing to compare results.