2014 International Solid Freeform Fabrication Symposium

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Proceedings for the 2014 International Solid Freeform Fabrication Symposium. For more information about the symposium, please see the Solid Freeform Fabrication website.

The Twenty-Fifth Annual International Solid Freeform Fabrication (SFF) Symposium – An Additive Manufacturing Conference, held at The University of Texas in Austin on August 4-6, 2014, was attended by 334 researchers from 16 countries. This is a significant increase from the record-setting 2013 attendance of 218, over 50% growth in one year. The organizers are pleased that 90 of the attendees were students, representing 27% of the audience. The number of oral and poster presentations increased as well, from 118 in 2013 to 196 this year. In anticipation of the increase, the conference organizers relocated the meeting from the University of Texas Thompson Conference Center, the venue for the meeting’s first 24 years. The AT&T Executive Education and Conference Center was able to handle the increased number of attendees.

The meeting consisted of plenary and parallel technical sessions. To celebrate the 25th anniversary of the conference, the morning plenary sessions on the first two days were given over to looking back at the first 25 years of additive manufacturing and looking forward to the next 25 years, respectively. The Monday morning session was an inventor’s forum with talks by the technology inventors/founders: Chuck Hull (vat polymerization), Michael Cima (Binder Jetting), Lisa Crump (Material Extrusion) and Carl Deckard (Powder Bed Fusion). The session was opened by Harris Marcus, founder of the SFF Symposium, who gave a brief history of the conference. Terry Wohlers followed with perspectives on the origins of additive manufacturing. Terry deserves special credit for giving his entire presentation the way we did presentations 25 years ago: completely using 35 mm slides which were produced and archived by him in the 1980s-1990s. For a significant number of attendees, this was the first time they had seen a 35 mm presentation. The Tuesday morning plenary session was a series of short presentations contrasting how we did research 25 years ago with how we do research today. The topic areas and speakers were Process Development (Phill Dickens, Then; Brent Stucker, Now), Computational Methods (Rich Crawford, Then; Jack Beuth, Now), Materials (Gideon Levy, Then, Tom Starr, Now), Design (David Rosen, Then, Carolyn Seepersad, Now). Gideon Levy then chaired a short panel on the subject of the next 25 years of additive manufacturing to transition from the past and present to the future. While these presentations do not have associated papers in this conference Proceedings, the organizers have arranged for many of the presentations themselves to be included in the flash drive. These appear in the folder “Plenary Presentations”.

Tuesday evening, Hod Lipson gave an outstanding plenary presentation on the future of additive manufacturing. This was followed by the International Digital Sculpture and Engineered Forms Exhibit, curated by Mary Visser of Southwestern University. The art show included digital art by 20 digital artists from around the world. Also shown were 10 engineered pieces that have an artistic quality. The attendees were invited to enjoy the pieces and to consider the amorphous interface between art and engineering.

This year’s best oral presentation was entitled, “A Survey of Sensing and Control Systems for Machine and Process Monitoring of Directed-Energy, Metal-Based Additive Manufacturing”, authored by E.W. Reutzel and A.R. Nassar from Pennsylvania State University. 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 171 oral presentations, the associated manuscript appears on Page 309. The best poster presentation selected from 25 posters was given by Y. Bai and C.B. Williams from Virginia Polytechnic Institute and State University. Titled, “An Exploration of Binder Jetting of Copper”, the paper is included in the Proceedings on Page 793.

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. Adam T. Clare from The University of Nottingham. Dr. Joseph Beaman won the International Freeform and Additive Manufacturing Excellence (FAME) Award. He holds the Earnest F. Gloyna Regents Chair in Engineering at The University of Texas at Austin.

The editors would like to extend a warm “Thank You” to Rosalie Foster for her detailed handling of the logistics of the meeting, as well as her excellent performance as registrar during the meeting. We 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 (N00014-14-1-0691) and the National Science Foundation (CMMI-1433422) 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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    2014 International Solid Freeform Fabrication Symposium Table of Contents
    (2014) Laboratory for Freeform Fabrication and University of Texas at Austin
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    A Review of Hybrid Manufacturing
    (University of Texas at Austin, 2015) Lorenz, K.A.; Jones, J.B.; Wimpenny, D.I.; Jackson, M.R.
    In recent years the combination of laser-based Additive Manufacturing and Computer Numerical Controlled (CNC) machining has become increasingly popular, with several machine tool manufacturers exhibiting products based on different machine tool configurations. This technology, widely known as Hybrid Manufacturing, generally exploits Directed Energy Deposition processes using powder feedstock that is fed into a melt pool created by a laser. Although Directed Energy Deposition processes predate powder bed fusion Additive Manufacturing (at least in terms of coating and repair applications), commercialization of Hybrid Manufacturing systems is still very much in its infancy. However, they do offer clear advantages, combining a high deposition rate together with the accuracy and surface finish associated with machining. This paper presents the history of the development of Hybrid Manufacturing Systems (HMS), dating back from work undertaken in the mid 1990s through to the present day. The relative merits of different material deposition approaches are compared and some of the key technical challenges which remain are highlighted and discussed.
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    Understanding the Dynamics of Ultrasonic Additive Manufacturing
    (University of Texas at Austin, 2015) Mao, Qing; Coutris, Nicole; Gibert, James; Fadel, Georges
    Ultrasonic Additive Manufacturing (UAM) is an additive manufacturing technique that uses ultrasound to merge metal foils (150 µm thick, 24 mm wide) layer by layer to fabricate three-dimensional bodies. As new layers are deposited and the height-to-width ratio of the built feature changes, the dynamics of UAM changes accordingly. Prior research suggested the existence of a limit for the height-to-width ratio. Above this limit, additional layers fail to bond because the built feature reaches its resonance frequency. Specifically, the bond failure is affected by the lack of plastic shear deformation between two foils which is essential to the generation of true metallic bonds. As the height-to-width ratio falls in the critical range, the built feature becomes resonant under the high-frequency excitations (20 kHz) of the sonotrode, leading to large-amplitude oscillations matching those of the sonotrode, and resulting in reduction of differential motion and therefore plastic shear deformation between the foils. In order to develop a model incorporating plasticity, heat transfer, and friction to study UAM, 2-D and 3-D lump parameter models consisting of mass-spring networks are proposed to study the dynamics of the elastic part of the built feature. The models are established such that they preserve the modal parameters of the built feature in free vibration. The lumped parameter models are validated by comparing their modal predictions with those from 2-D and 3-D finite element models. The lumped parameter model will be coupled with a 3-D finite element model to describe an elasto-plastic bonding layer introducing the friction and thermal aspects of UAM. By examining the deformation of the bonding layer under the combined effects of the excitation of the sonotrode and the vibration of the built feature, the bond failure due to geometry change of the built feature will be better understood and quantified in the future.
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    Selective Separation Sintering (SSS) A New Layer Based Additive Manufacturing Approach for Metals and Ceramics
    (University of Texas at Austin, 2015) Zhang, Jing; Khoshnevis, Behrokh
    Selective Separation Sintering (SSS) is a powder layer based Additive Manufacturing approach. SSS can fabricate high temperature ceramic and metallic parts at comparatively lower cost with high quality. In the printing process a dry powder of higher sintering temperature is deposited into the base material which makes up the part. The inserted powder defines the boundary of the part and separates the part from its surroundings. When printing of all layers is completed the deposited dry powder serves as a separation coating which defines the shape of the part. In the sintering process the base material is sintered into a solid part while the separation coating remains as loose powder. The part is then separated from the surrounding area at the separation coating surfaces, and is post processed if necessary. Preliminary results have proven the capability of SSS in successfully printing ceramic and metallic parts. Future experiments are planned for improving the process resolution.
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    Support-less Horizontal Filament-Stacking by Layer-less FDM
    (University of Texas at Austin, 2015) Kanada, Yasusi
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    High Viscosity Jetting of Conductive and Dielectric Pastes for Printed Electronics
    (University of Texas at Austin, 2015) Ledesma-Fernandez, J.; Tuck, C.; Hague, R.
    Ink-jet printing of multiple materials in 3 dimensions is a promising alternative to traditional patterning methods due to its flexibility, scalability and accuracy. However, the printability of the inks is strongly restricted by material properties such as surface tension and viscosity. Dispensing high viscosity fluids on a drop-on-demand approach is a potential solution that can facilitate the incorporation of new materials to the jetting catalogue. Consequently, in this study 2 micro-dispensing valves are used in combination with a mechanical stage to deposit conductive and dielectric pastes with viscosities of 15.3 ± 0.2 and 0.638 ± 0.005 Pa·s (at 25°C and 10 s-1 shear rate) respectively. Crucial printing parameters such as pressure, temperature, pulse shape and drop spacing are studied in order to optimise the process. Additionally, post-printing characteristics such as contact angle of different materials and cured layer profiles are also measured and taken into account during the designing of the 3D patterns to minimise the negative effects of the thickness miss-match of different materials. Finally, the manufacturing capability of the set-up is demonstrated by the fabrication of a functional device using a combination of “pick-and-place” components and high viscosity jetting.
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    Active Device Fabrication Using Fiber Encapsulation Additive Manufacturing
    (University of Texas at Austin, 2015) Saari, M.; Galla, M.; Cox, B.; Richer, E.; Krueger, P.; Cohen, A.
    Fiber Encapsulation Additive Manufacturing (FEAM) is a novel solid freeform fabrication process in which a fiber and a matrix are co-deposited simultaneously within a single printer along straight and curved 2-D and 3-D paths. Using a FEAM approach in which the fiber is a metal wire and the matrix is a thermoplastic polymer, simple electromechanical devices such as voice coils, inductive sensors, and membrane switches have been successfully produced. This paper will present an overview of the FEAM process, describe several fabricated devices, and discuss recent developments in controllably stopping and starting the wire, and in creating electrical junctions between individual wires, which together enable much more complex devices to be made.
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    Electrostatic Stabilisation of Drop on Demand Bio‐Ink through the Cationic Encapsulation of Cells
    (University of Texas at Austin, 2014) Benning, Matthew; Dalgarno, Kenny
    The ability to formulate bioprinting inks in which suspensions of cells and other biological materials can be maintained, without affecting biological response, is crucial in producing robust printing strategies for tissue fabrication. A piezoelectrically actuated drop‐on‐demand printing system has been used to deposit electrostatically stabilised cells from a human osteosarcoma cell line (U2OS). Experiments were intended to investigate the effectiveness of a polyelectrolyte cell encapsulant to maintain cell dispersion within a bio ink. Cells were coated with a number of thicknesses of a Cationic Poly‐l‐lysine (PLL) encapsulant and their ability to release studied over 7 days, with the thinner coatings proving to be more favourable. Printing of both coated and uncoated cells indicated the dispersion and printability of coated cells was significantly better than that of uncoated cells. Preliminary results suggest that electrostatic stabilisation of bio inks could provide a solution to cell aggregation, increasing viable printing time and decreasing poor yields due to orifice obstruction.
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    Separation Force Analysis Based on Cohesive Delamination Model for Bottom-Up Stereolithography Using Finite Element Analysis
    (University of Texas at Austin, 2014) Liravi, Farzad; Das, Sonjoy; Zhou, Chi
    Bottom-up (constrain-surface) Additive Manufacturing (AM) systems have been widely used in industry. Compared to traditional open-surface AM technology, properties like better vertical resolution, higher material filling rate, less production time, and less material waste make bottom-up AM technology a suitable candidate for fabrication of complex three dimensional materials with high accuracy. However during the pulling up stage, the substantial force generated between the formed part and the material container has high risk of breaking the part and therefore reduces the process reliability. In this paper, an optimization-based method is developed to model bottom-up AM process using finite element analysis (FEA). The FEA model is developed using ABAQUS to model the behavior of the cohesive delamination at the interface of the formed part and a hyper-elastic intermediate which has been used to reduce the pulling up force. An optimization model is also established to evaluate the cohesive stiffness parameters that cannot be calculated directly from closed formulas or mechanical tests. The results of this work will be used to develop an adaptive closed-loop mechanics-based system to control the pulling up process and achieve a reliable technology.
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    Stereo Vision Based Hybrid Manufacturing of Ti-6Al-4V in Component Repair Process
    (University of Texas at Austin, 2014) Liu, Renwei; Wang, Zhiyuan; Sparks, Todd; Liou, Frank
    Parts or products from high performance metal are very expensive, partly due to the processing complexities during manufacturing. Recent studies have indicated that hybrid processes of additive manufacturing and machining process can be used to repair titanium parts, thus extending the service life. In order to implement these methods automatically, it is necessary to obtain the spatial geometry information of component with defects to generate the tool path. The purpose of this paper is to summarize the research on hybrid manufacturing with stereo vision function which can be applied to the component repair process. Stereo vision is adopted to detect the location and the size of the defect area which is marked by color marker. And then laser displacement sensor is applied to scan the defect area. Therefore, automated alignment, reconstruction of the defect area and tool path planning could be implemented based on the spatial geometry information. Finally, a Ti64 part repair experiment is done to verify the method. This work provides an automatic method for repairing damaged parts by hybrid manufacturing.