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.
(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.
(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.
(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.
(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.
(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.
(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.
(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.
(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.
(University of Texas at Austin, 2014) Gribbins, Cassandra; Steinhauer, Heidi M.
A study on the plastic behavior of an additively manufactured acrylonitrile butadiene
styrene (ABS) living hinge was conducted using a MakerBot 2X. Initial research included
numerical and analytical linear analyses on a typical living hinge design. This paper introduces the
portion of the research that explores the application of traditional design practices to entry-level
additive manufacturing machines. Tensile testing for material properties was conducted to refine
the numerical model. Experimental rotational testing was conducted for data on the non-linear,
plastic behavior experienced during application. Verification of the numerical model with
experimental results will be used to guide future work on exploring alternate design geometries
that leverage the advantages of additive manufacturing’s design freedom for smoother stress
distribution on the hinge.
An emerging international engineering design trend has resulted from widespread use of
social media: a large number of people are engaged in collaborative engineering design activities
to build their design expertise through interaction with other designers, to compete for
recognition or prizes, or simply for the enjoyment of doing so. The term “crowdsourcing” was
introduced in 2005 and implies soliciting contributions from a large group of people, usually an
online community, in order to get a broad perspective from various points of view. This
community-generated creativity is contrary to conventional practice in most manufacturing
companies, which prefer tight control of engineering designs and practices because they
represent key intellectual property and know-how. Recognizing that crowdsourcing represents a
potential resource, GE embarked on an experiment to see how a for-profit company might
benefit from soliciting new design approaches from this non-traditional source. The design of a
specific part, an aircraft engine bracket, was released to an online community of engineers with
an invitation to submit improved designs in an open competition. Entrants were encouraged to
consider additive manufacturing as the fabrication method. Hundreds of designers submitted
concepts and some achieved 80% reduction in weight.
(University of Texas at Austin, 2014) Gupta, Sulabh; Rui, Rahul
A Plethora of user generated 3D models are available online. With rapid proliferation and
diffusion of additive manufacturing machines in households, it has now become possible to
download these virtual objects and print them out as physical parts. Although printing small size
parts (within print volume of low cost 3D printers) is relatively an easy task, additive fabrication
of large size parts (part volumes greater than print volume of low cost 3D printer) remains a
challenging task for novice 3D printer users. In this paper the authors present a computational
pipeline to 3D print large size 3D models that can be easily downloaded from online websites.
The pipeline essentially enables decomposition of large objects into smaller parts that can be 3D
printed and then assembled. To assemble the printed parts a three-pronged approach is outlined.
First, an interface based on graph grammar rules has been developed to generate assembly
instructions. Second, an interactive segmentation of the desired 3D model is carried out using a
Segmentation Guide Interface (SGI). SGI has been developed to assist a user to carry out
component to sub-component segmentation. Third, we have also developed an interface that aids
a user in printing small size pieces that can be printed in print volume of a commercial 3D printer
(such as Makerbot®) and then assembled to create components that are too large to be printed in
print volumes of low cost 3D printers. We demonstrate the efficacy of developed pipeline by
creating assembly instructions for multiple large sized 3D table models available online.
(University of Texas at Austin, 2014) Kuhn, Joshua; Green, Matthew; Bashyam, Sanjai; Seepersad, Carolyn Conner
The Innovation Station is designed to provide on-demand, web-enabled 3D printing
securely in a public space. The overarching goal is to lower the barriers to 3D printing at a
university, to facilitate innovation and creativity, and to inspire future engineers. Both hardware
and software innovations were required to realize this capability. From the hardware side, we
invented a process to automatically remove parts from the 3D printer and sweep them into a bin
from which users can retrieve them without directly accessing the 3D printer. From the software
side, in partnership with the Faculty Innovation Center (FIC) at UT Austin, we created a web
portal that allows students to upload parts remotely and access detailed directions for creating
parts. It also allows administrators to remotely manage the queue and initiate builds. Together,
the hardware and the software innovations enable printing multiple jobs continuously without
user intervention and remote cancellation of jobs. Plans for the entire station, both hardware and
software, are intended to be open source, with a startup cost of less than $4,000 for recreating the
station at a new location.
(University of Texas at Austin, 2014) Park, Sang-in; Rosen, David W.; Duty, Chad E.
To design lattice structure, a uniform voxel based approach is widely used which divides
a part into unit volumes (e.g., cubes) and maps lattice topology into those volumes. In contrast,
conformal lattice structures represent a second design method for constructing lattices in which
unit cells are constructed parallel to the surface to be reinforced and are deformed in a manner
that enables them to conform to the surface. In this paper, the strength of lattice structures
designed using these two methods (uniform voxel based and conformal) are compared based on
additive manufacturing (AM) process effects. For this purpose, spheres filled with three types of
lattice structure are fabricated using electron beam melting technology and tested in compression.
Effects of AM processes are studied in two ways – volumetric and structural performance
equivalence. Struts in lattice structures are observed through a microscope to examine volume-equivalence and tests are simulated numerically and compared to identify structural equivalence.
(University of Texas at Austin, 2014) Ashby, Kathryn; Fieldman, Zack; Kenney, Pat; Rockstroh, Todd
One of the key factors for development and optimization of direct metal laser
melting (DMLM) is the analysis of process parameters on reentrant build geometry and
surface finish. Recent studies have focused on the optimization of standard build
parameters with only minor emphasis on reentrant geometries. Parameters that are not
optimized often contribute to poor surface finish, difficult to remove supports, and failed-to-build geometries of reentrant surfaces that limit the capabilities of DMLM. Through the
analysis of multiple studies with varying process parameters and input scan path
geometry, open loop methods for creation and control of reentrant build geometries are
assessed and presented.
(University of Texas at Austin, 2014) Karnati, Sreekar; Sparks, Todd; Liou, Frank
Primitive stages of studies on and with additive manufacturing techniques popularly involve thin
wall geometry. In the current effort attempts were made to capture various thermal aspects
during deposition of a thin wall geometry. The thermo-graphic data was captured using a FLIR
A615 infrared camera. Post processing using edge detection algorithms and image processing
techniques, the geometric and thermal aspects of meltpool and tail of the meltpool were obtained.
The effect of geometry and power on shape of the meltpool and its tail were obtained. The
depositions of SS 316 with varying power. These observations were discussed and analyzed in
aim to perform planned deposition of functionally gradient materials in future.
(University of Texas at Austin, 2014) Boudreaux, J.C.
To maintain the forward momentum of additive manufacturing technology, it is necessary to thoroughly evaluate
new and potentially useful technological developments in this field. One such development is the intense interest being
directed to the field of hybrid automata (HA). Hybrid automata combine both the discrete processing behavior of finite
automata as well as the continuous, or flow, behavior of dynamical systems. At this point, some important results on hybrid
automata have been obtained, but many open questions remain, including those concerning the decidability of HS
operational procedures. (Recall that decidability is directed to a decision problem, that is, a definite true-or-false response
given by an effective procedure.) Some important decidability results for HAs have been obtained. For example, in
[Henzinger et al.1998] the reachability problem for timed automata (an HA class) has been convincingly shown to be
decidable. However, it should also be noted that subtle and difficult issues have been identified, e.g., [Fraenzle 1999],
[Asarin, Collins, 2005]. This paper will provide a summary review of the operational features of HAs as they might pertain
to additive manufacturing, and then briefly consider the following technical issues: (i) are the classical models of the real
numbers best suited to deal with the necessarily approximate measures of physical systems or would non-standard analysis
of [Robinson 1996] be a better fit; and (ii) would the introduction of “noisy semantics” and finite arithmetic precision,
following [Freidlin, Wentzell 1984], be a better work around?
(University of Texas at Austin, 2014) Ahsan, Nazmul; Habib, Ahasan; Khoda, Bashir
Three dimensional free-form geometric shapes can be built by putting layers upon layer in a
predefined direction via Additive Manufacturing (AM) processes. The fabrication processes
require computational as well as physical resources and can vary not only upon the product but its
process plan. Overly simplified process plan may expedite the pre-fabrication techniques, but may
create difficulty during fabrication of those slices. For an example, slices with concavity or discrete
contour plurality may introduce deposition discontinuity, over deposition, and higher build time
during the fabrication. These issues demand more resources there by affecting the part quality and
fabrication cost. In this work, we focus upon the build direction of AM process plan to address the
fabrication and resource utilization. First, a set of uniform build direction is identified and the
object is discretized using a set of critical points considering the object concavity along the build
direction. Cutting planes are generated and the object is discretized into strips and each strip is
analyzed for contour plurality and the build directions are quantified through the allocation of
importance factors. The optimal build direction thus found will result in lowest possible fabrication
complexity. The proposed methodology is implemented and presented with a sample example in
(University of Texas at Austin, 2014) Mohajeri, Babak; Khajavi, Siavash H.; Nyberg, Timo; Khajavi, Siamak H.
Additive manufacturing (AM) offers unique production characteristics which among those,
toollessness and production of complex geometries are potentially significant to operations
efficiency. Previous research has illustrated the potential sufficiency of this technology to affect the
supply chains‟ arrangements and enabling decentralized production configurations. While, one of
the important advantages of AM enabled distributed production is the increased flexibility, which is
a necessity in today‟s competitive and ever changing global supply chains, number of obstacles
have kept this method from wide implementation. In this paper, we study the possible supply chain
modifications to decrease the cost of an AM-enabled decentralized production system. In other
words, we perform a cost-benefit analysis on various AM supply chain strategies in a spare parts
context to realize the independent operational factors affecting the implementation cost of additive
manufacturing. Moreover, we analyze the ways to adapt the supply chain management to enable full
potential of AM considering the present technology.