The Twelfth Solid Freeform Fabrication (SFF) Symposium, held at The University of Texas
in Austin on August 6-8, 2001, was attended by over 130 national and international researchers.
Papers addressed SFF issues in computer software, machine design, materials synthesis and
processing, and integrated manufacturing. The diverse domestic and foreign attendees included
industrial users, SFF machine manufacturers, university researchers and representatives from the
government. The Symposium organizers look forward to its being a continuing forum for technical
exchange among the expanding body of researchers involved in SFF.
A special plenary session on the state of SFF was organized to present overview talks on
various aspects of the field. Invited speakers were Joseph Beaman (University of Texas) who gave
a historical perspective, Emanuel Sachs (MIT) who related SFF to manufacturing, Phill Dickens
(DeMontfort University) who gave a presentation on the role of SFF in design, Kevin Lyons
(NIST) who spoke on software developments and Fritz Prinz (Stanford) who discussed the future
The Symposium was again organized in a manner to allow the multi-disciplinary nature of
the SFF research to be presented coherently, with various sessions emphasizing modeling, process
development, and materials. We believe that documenting the changing state of SFF art as
represented by these Proceedings will serve both those presently involved in this fruitful technical
area as well as new researchers and users entering the field.
The editors would like to extend a warm “Thank You” to Rosalie Foster for her detailed
handling of the logistics of the meeting and the Proceedings, as well as her excellent performance as
registrar and problem solver during the meeting. We would like to thank the Organizing
Committee, the session chairs, the attendees for their enthusiastic contributions, 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
SFF community in organizing the Symposium. We also want to thank the Office of Naval
Research (N00014-01-1-0637) and the National Science Foundation (DMI-0117072) for
supporting this meeting financially. The meeting was co-organized by the University of
Connecticut at Storrs, and the Mechanical Engineering Department, Laboratory for Freeform
Fabrication and the Texas Materials Institute at The University of Texas at Austin.
Browsing 2001 International Solid Freeform Fabrication Symposium by Title
Over the past few years, improvements in equipment, materials, and processes have enabled
significant improvements in the accuracy of Fused Deposition Modeling (FDM) technology.
This project will investigate the present in-plane accuracy of a particular FDM machine using the
benchmark “User Part” developed by the North American StereoLithography User Group
(NASUG) and show the effect of optimal Shrinkage Compensation Factors (SCF) on the
accuracy of the prototyped parts.
The benchmark parts were built on the FDM-1650 prototyping machine and a total of 46
measurements were taken in the X and Y planes using a Brown & Sharpe Coordinate Measuring
Machine (CMM). The data was then analyzed for accuracy using standard formulas and
statistics, such as mean error, standard deviation, residual error, rms error, etc. The optimal SCF
for the FDM-1650 machine was found to be 1.007 or 0.7%.
Solid Freeform Fabrication (SFF) and related techniques are used at the Naval Research
Laboratory (NRL) for a variety of materials related investigations. Research and applications
conducted over the past few years are described including: Helisys Laminated Object
Manufacturing System (LOMS) fabrication of: ceramic piezoelectric actuators, tooling for
multifunctional materials, and anatomical prototypes for surgical visualization; fabrication of
mesoscale electronic and sensor components using a laser forward transfer direct write
technique; and visualization of complex, 3-D microstructures using a Stratasys Fused-Deposition
Modeler. The paper closes with a brief overview of future SFF related work at the NRL.
This paper presents some concepts and initial investigation of a novel construction
automation approach using the Contour Crafting (CC) layered fabrication process, developed at
the University of Southern California. CC uses computer control to take advantage of the
superior surface forming capability of trowels, used by craftsmen and builders since ancient
times, to create large intricate structures with smooth and accurate surfaces. The potential of CC
became evident from the initial investigations and experiments with various materials and
geometries. Using this process, a single house or a colony of houses, each with possibly a
different design, may be automatically constructed in a single setup.
A pilot study was undertaken to evaluate the clinical acceptance of prosthetic limb sockets
manufactured using solid freeform fabrication (SFF). The fabrication of sockets for amputees is a
natural application for SFF. The socket is the part of the prosthetic limb that fits onto the
amputee’s residual limb. Each socket is custom manufactured for each individual amputee. Four
amputees were successfully fit with sockets created using selective laser sintering. The scope of
the study included software development, finite element analysis, materials testing, and clinical
evaluation. This paper discusses socket design issues and clinical testing results.
In this paper, a heat input closed-loop control system based on infrared image sensing for 3D
laser cladding is introduced. A high frame-rate (up to 800 frames/s) camera is installed coaxially
on the top of the laser-nozzle setup. Complete of the infrared images of the molten pool can be
acquired with a short nozzle-substrate distance in different scanning directions, eliminating the
noise from the metal powder. The characteristics of the images show a clear relationship with the
parameter variations of the cladding process. A closed-loop control system is built based on the
feedback of the infrared image sensing. The control results show a great improvement in the
geometrical accuracy of the part being built
Inaccuracies in the selective laser sintering (SLS) process using polymer materials are typically
caused by inhomogeneous shrinkage due to inhomogeneous temperature distribution in the
powder bed of the SLS machine. These shrinking effects lead to stress in the sintered parts,
causing the part to distort. The inhomogeneous shrinkage of benchmark parts has been
compensated empirically in a former work. The results cannot been transferred to all geometries,
because each geometry requires a specific temperature for laser sintering and, thus, has its own
related shrinkage distribution. In a new theoretical approach, shrinkage behavior is to be
integrated in a thermal simulation of the SLS process and the thermal shrinkage calculated prior
to the building process. In the following, experimental data of the temperature- and pressuredependent shrinkage of laser-sintered powder samples is presented. Possible theories for a
physical model of thermal shrinkage are discussed. In particular, these models have to consider
granular characteristics such as internal friction, particle sliding, and powder compaction.
Solid Freeform Fabrication technologies have potential to manufacture parts with locally controlled properties (LCP), which would allow concurrent design of part’s geometry and desired
properties. To a certain extent, Fused Deposition Modelling (FDM) has the ability to fabricate
parts with LCP by changing deposition density and deposition orientation. To fully exploit this
potential, this paper reports a study on the mechanical properties of FDM prototypes, and related
materials and fabrication process issues. Both theoretical and experimental analyses of mechanical
properties of FDM parts were carried out. To establish the constitutive models, a set of equations
is proposed to determine the elastic constants of FDM prototypes. An example is provided to
illustrate the model with LCP using FDM.
This paper discusses the application of adaptive slicing algorithm and computer vision technology on Rapid Prototyping (RP) system to enhance fabrication performance of Model Maker (MM) RP system. Usually, the layer number determines the RP system performance in terms of fabrication time and accuracy. In this research, a new practically adaptive slicing algorithm is developed and easily implemented for RP system, because it only recalculates the scanning path according to the criterion of adjacent profile variation. The experimental results of the proposed adaptive slicing algorithm show that saving of 54% fabrication time is achieved and the model accuracy is still remained in the same level. MM presents a problem of stability because of a tiny nozzle. Computer vision technology is employed in this paper to on line inspect the layer accuracy and defect of a model fabricated by RP system. The results of vision inspection is used to close-loop monitor the process to increase the processing stability and accuracy. These new practically adaptive slicing algorithm and machine vision technology are implemented in the commercial Model Maker (MM) RP system to increase its fabrication speed, accuracy and stability, but not accuracy sacrifice. Hence, the performance of the MM RP system can be significantly enhanced using vision and practically adaptive slicing techniques.
(2001) Boddu, Mallikharjuna R.; Landers, Robert G.; Liou, Frank W.
Lasers have wide–ranging applications in the manufacturing field (e.g., cladding,
welding, cutting, machining, drilling). Extensive work is being conducted to apply laser cladding
as a Rapid Prototyping (RP) process. In this paper the authors illustrate various principles of
laser cladding in rapid prototyping. Important process parameters for the control of the laser
cladding process are discussed as well as the experimental methods adopted, and results obtained
by, various authors.