Rapid prototyping and manufacturing is an incredibly varied and exciting area.
Opportunities abound. During the past year, our members and faculty have refocused our
efforts on four main areas: Rapid Tooling, Rapid Inspection and Computer-Aided
Verification (CAV), RPM within Product Realization, and Alternative Applications of SLA.
Additionally, new projects in surface finish and machining have also begun.
Rapid prototyping technologies are
increasingly being used to fabricate patterns and tools for making parts in end-use
materials. Rapid tooling was the first focus area for the RPMI and continues to generate
the most interest in industry. By utilizing both high-pressure/high-temperature polymer
injection molding and low-pressure/low-temp powder injection molding, we can fabricate
parts in a variety of polymers, metals, and ceramics! Our projects this year span
fundamental studies of molding and material behavior to polishing and curing SLA parts.
Polishing and Post Build Cure of Stereolithography
Post-processing of SLA parts and molds remains a time-consuming and somewhat
problematic necessity. Typically, SLA parts and molds must be post-cured in a UV
oven for 1 - 1.5 hours. After that, sanding, filing, and polishing are often
necessary to produce nice surfaces. Research performed by Bryan Blair, led by Dr. Jon
Colton, studied both the post-cure and polishing of SLA parts and molds. Bryan graduated
with his MSME degree in Spring 1998.
Current SLA technology is limited in surface roughness and finish by the thickness of
each layer, which is approximately 127 microns (0.005 inches). Smooth surfaces of SLA
parts and molds are critical to producing parts in injection molding. An average roughness
of 1.27 microns (50 micro-inches) is required. The best surfaces that Bryan achieved in
his work had roughnesses consistently under 20-microinches. For polishing with an
abrasive, results indicate the use of 500 -1200 grit. For polishing by pumping abrasive
pastes, a viscoelastic media such as borax/glue mixtures mixed with 30-micron abrasive. A
pressure of 600 psi should be used. This work indicates that an automated polishing device
could be made that would quickly finish SLA parts and molds.
The UV energy imparted by the SLA laser does not fully cure the resin in parts. Because
of this, it is necessary to post-cure SLA parts. This research investigated two modes of
post-cure: the conventional UV chamber and thermal post-curing. Mold hardness will vary
according to the degree of cure, and a more fully cured part is harder. Therefore, it is
hypothesized that a greater degree of cure will result in molds that can produce more
parts before failure. DSC (differential scanning Calorimeter) tests indicate that even
parts that were cured 1.6 hours in the UV chamber still had some uncured material. A
series of DSC tests were performed on various SLA parts and material samples after just UV
curing or both UV and thermal curing. As a result of this work, a thermal cure at 150
degrees C for 30 minutes is recommended. Results also show that improved surface finishes
are possible with parts that are thermally cured.
The Effect of Rapid Tooling on Final Product
The development of a plastic part frequently involves several prototype iterations.
Production of these prototypes with conventional metal tooling often results in high costs
and long lead-times. A group of materials and processes known as rapid tooling can produce
a limited number of prototypes faster and more economically than conventional tooling.
However, the differences in the material properties of conventional and rapid tooling
result in mechanical property differences in the final plastic parts.
In order to understand the reasons underlying this phenomenon, the effect of mold
material on the tensile and flexural properties of two polystyrene stereoisomers molded in
H13 steel, fiber-reinforced epoxy, and backfilled stereolithography (SL) tools were
When molded in backfilled SL and fiber-reinforced
epoxy molds, both isomers exhibited an average of 17% lower ultimate tensile stress,
similar Youngs modulus, and 20% lower ultimate elongation than parts produced from a
steel mold. In flexural testing, both isomers produced in the fiber-reinforced epoxy mold
exhibited an average of 19% higher flexural strength, 39% higher flexural modulus, and 27%
lower ultimate flexural elongation than parts produced in the steel mold.
In order to understand how different mold materials and construction techniques
affected the heat transfer characteristics of the part and mold, a one-dimensional heat
transfer model for composite injection molds was developed to predict the heating and
cooling rates of the injected polymer and mold material. The model provided a very
accurate prediction of experimental data for the first 100 seconds. Additionally, the
model indicated that SL shell thickness (1.02 - 2.54 mm), backfill material (Aluminum
filled epoxy, low melting point alloy, and solid SL), and cooling distance (2.79 - 6.35
mm) exerted negligible effects on the surface temperature of the mold over a single
Future work will utilize more rigorous mold filling, heat transfer, and fracture models
to develop a quantitative relationship between the mold material, injection molding
conditions, and the mechanical properties of the final part. See the web page:
Predicting the number of parts that can be molded in a SLA tool is very difficult due
to the complexity of the molding process and the nature of SLA resins. The goal of this
project is to reliably mold 50 parts in SLA tools. To do so, we must understand the
failure mechanisms of SLA tools and relate these failures to molding process variables,
mold material properties, part geometries, and the polymer being molded. We hypothesize
that four failure mechanisms predominate: part shrinkage onto the core, thermal cycling of
the mold, mechanical interlocking of the part and mold due to stair-stepping, and adhesion
between part and mold.
Jon Colton is leading this project. Currently, two visiting students from GT Lorraine
(in France), Yann Lebaut and Thomas Cedorge, are working on this project. Additionally,
Anne Palmer is assisting with the molding experiments and with instrumentation. Yann is
focused on the thermal aspects of the investigation. He is performing a set of experiments
to relate the cooling time of a molded part, the level of cure of the mold (thermal curing
of the SLA mold occurs during molding), and the number of parts produced from the mold.
Objectives include finding the temperature for ejection with minimum part shrinkage
without part damage, and finding process variable settings such that no modifications of
the material properties occur as the number of parts increases.
Thomas is conducting experiments to relate surface finish to mold and process factors.
More specifically, mold layer thickness and build style will be related to draft angle and
number of parts. Ejection force, pre- and post-molding surface roughness, and mold
hardness will be monitored. Does ejection force increase or decrease as surface roughness
decreases, or as layer thickness decreases? These are some of the questions that will be
answered by this research.
An Ejection Mechanism Design Method for Rapid
Injection Molding Tools
There are two goals of this research. The first goal is to develop a
mathematical model that effectively characterizes the forces and stresses that the mold
core undergoes as a result of part ejection. The second goal is to develop a system that
uses the aforementioned model to determine an ejection procedure for a part given its
geometry. This ejection design system will have two main functions. First it will
determine the feasibility of ejection for that particular geometry. Second it will
determine the number of pins and recommend locations for these pins.
Sunji Jangha is the graduate student leading this project, supervised by David Rosen.
The approach taken to accomplish this will consist of a combination of analytical,
computational, and physical experiments. Analytical models of part shrinkage during
cooling and adhesion are being developed that will enable us to approximate forces on the
mold core that result from parts shrinking and sticking to the mold. With a qualitative
understanding of shrinkage and forces, we will develop computational models that enable
the calculation of forces on the mold much more accurately. This has proven to be
non-trivial to date. However, we are confident that the COSMOS/M or Moldflow packages will
enable the development of shrinkage and force models. A set of physical experiments is
being run to aid our understanding of molding and ejection issues. For these experiments,
we are using the instrumented mold base that Anne Palmer has developed.
Given that an estimation of ejection forces on different areas and features of a part,
it will be possible to develop ejection strategies for the part. We plan to develop a
synthesis package that will determine the number of ejector pins, their sizes, and
locations. Sunji should finish his Masters thesis early in 1999.
Rapid Tooling using Powder Injection Molding and
Electrodes for electrodischarge machining (EDM) applications are often difficult and
expensive to machine. Also, traditional carbon material used to make electrodes wears too
quickly. This project addresses both of these issues by using the Powder Injection Molding
(PIM) process we developed for molding ceramic parts to form a zirconium diboride (ZrB2)
An undergraduate MSE student, Jennifer Vucic, and her advisor, Tom Starr, completed
this project in June 1998. An initial molding study with the ZrB2 material was completed;
10 bars were molded, debinded, and infiltrated with copper. Tim Lloyd, one of Tom
Kurfess students, helped with measurement of the bars. Subsequently, several EDM
electrodes were molded. This 4-post electrode design exhibited difficulties in ejection.
This led to a study of molded part adhesion and ejection. Several electrodes were
successfully molded, infiltrated, and tested. Testing at Kodak demonstrated the
superiority of ZrB2 over carbon. For more information, see the web page: http://rpmi.marc.gatech.edu/project/description/Power_inj_mold.html
Rapid Inspection & Computer-Aided
Many have made claims about the merits of new RP and RT related developments, but few
can back up those claims with comprehensive dimensional data. We have a significant effort
underway to develop better and faster ways to measure what we produce.
Verification of Conformance to
Target Geometric Parameters Using Three Dimensional Coordinate Metrology
This project, supervised by Tom Kurfess, is to develop algorithms and procedures for
extracting artifact quality information from the combination of a set of three-dimensional
coordinates with the design CAD model. Significant developments to date include:
- least squares best fit of rigid body transformation variables to localize the
measurement coordinate frame to the design coordinate frame,
- data reduction methods to reduce the analysis cycle times for the copious data generated
by scanning equipment (rather than touch probe equipment),
- Matlab tools for fitting the coordinate frame and geometric parameters of geometric
- software for quick verification of rapid prototyping and rapid tooling using point-set
to point-set registration methods.
The ACIS solid modeling kernel is also used
for analysis of general solid models.
Future directions include the application of statistical sampling methods to inspection
planning for touch probe CMMs, confidence interval determination for measurement results,
development of more efficient methods for data analysis and new methods for analyzing
spline surfaces. Another interesting direction is the use of Product Data Management to
integrate inspection considerations in every aspect of a computer aided manufacturing
operation. The requirements for Ph.D. research will make the project more general in
nature over the next year. See the web page: http://rpmi.marc.gatech.edu/project/description/meas_verif_CAD.html
Computer-Aided Build Style Decision Support for SLA
When building parts in an SLA machine, the user is faced with many decisions regarding
how the part will be built. The user can control the quality of the build by changing
numerous SLA process variables, such as layer thickness, by reorienting the part, or even
by changing resins. A user will probably have preferences for the part build (i.e.,
accuracy or speed), but may not understand how to vary the process variables to produce
the desired results. The overall goal of this project was to develop a process planning
method for SLA, and to generate accuracy data to support this. Two main objectives
included: (1) to relate SLA process variables to the build goals (surface finish, build
time, and accuracy), emphasizing accuracy, through quantitative models, and (2) to extend
a previous problem formulation and solution algorithm enabling the user to attain the
appropriate trade-off among the build goals.
Charity Lynn-Charney extended our work in this area,
under the supervision of Dr. David Rosen. She graduated with a MSME degree in September
1998. Through a series of Design of Experiments, Charity identified the key process
variables that affect part accuracy. She builds a
series of blocks, cylinders, and cones (almost 100 total) and measured each surface on
each part using our CMM. From the measurement data, she developed response surface
equations that quantitatively capture the relationships between these variables and
geometric tolerances. With these response surfaces, we can predict how well a specific
tolerance on a specific surface can be achieved. By predicting achievement for all
tolerances on a part, an overall measure of accuracy can be generated.
We began by investigating the effect that eight SLA variables had on accuracy: hatch
spacing, blade gap, z level wait time, layer thickness, hatch overcure, fill overcure, and
sweep period. Planar, cylindrical, and conical surfaces were studied. As a result of a
variable screening experiment, four of these variables were identified as most influential
on accuracy: z level wait time, hatch overcure, fill overcure, and sweep period. Somewhat
surprisingly, layer thickness was not one of the most influential variables.
Charity also developed a trade-off decision support tool for SLA process planning. The
accuracy response surfaces comprised the accuracy aspect of the tool. Methods for
predicting build time and surface finish were borrowed from Joel McClurkins work.
Results indicate that the method is useful in supporting build style decisions.
Charitys tool can fine-tune variable settings, such as fill and hatch overcures,
beyond that which human users typically utilize. This work is being integrated into the
Rapid Tooling TestBed.
Dimensional Accuracy in Rapid Prototyping of
Ceramics using Injection Molding
A new method of ceramic prototyping has been derived from traditional low-pressure
ceramic injection molding and solid epoxy tooling produced overnight by stereolithography.
By combining these technologies, it is possible to produce functional ceramic prototypes
in one week. Other important advantages to this technique are that the same material is
used as in the final part, and that multiple parts can be made in the same time it takes
to make one part with other rapid prototyping technologies. There are two important
challenges currently facing the ceramic injection molding industry. One is the high cost
and long lead time for tooling, and the other is the ability to predict the shrinkage of a
new geometry in order to meet manufacturing tolerances for the final part.
While rapid tooling technology addresses the first
challenge, Beth Judsons work with her advisor, Tom Starr, addresses the second
challenge for ceramic injection molding using new SLA rapid tooling. Current injection
molding design-modeling software assumes isotropic shrinkage, or allows the introduction
of anisotropic shrinkage through manual modification of dimensions only. In the real
world, anisotropy is a result of process dynamics, due to the viscoelastic behavior of the
molten feedstock under an applied stress causing particles and molecules to orient in a
direction influenced by shear flow.
The result of not accounting for anisotropic shrinkage is the inaccurate prediction of
final dimensions. In ceramic injection molding this problem is magnified when compared to
plastic injection molding because the shrinkage is an order of magnitude higher. Results
to date include:
- Shrinkage was less variable in parts with a center gate versus end-gated parts.
- A model was developed that reduced the error in predicting the dimensions of the fired
part to less than 0.7%.
- The theoretical basis for anisotropy was explained by work from Brady and Morris on the
microstructure of pressure driven-flow of particles in suspensions.
Remaining work will involve the
generalization of the developed anisotropic shrinkage model to make it independent of
material type. See the web page: http://rpmi.marc.gatech.edu/project/description/dim_accracy_of_ceramics.html
RPM within Product Realization
As use of RPM technologies is becoming more widespread, the issue of how to effectively
use the tools has become more important. Specifically, we are interested in helping users
to better understand when and how to use these tools - and when it is better not to use
Assessing RP/RT Usefulness in Product
Development and the RT Survey
Rapid prototyping is quickly becoming a key factor in reducing the cost and time to
market associated with new product development. It allows the designer to evaluate aspects
of a proposed designs form, fit and function using a prototype made in days instead
of weeks. This means that design flaws can be detected, corrected and the new design
tested again much faster than was previously possible. Unfortunately a lot of the time and
cost savings associated with rapid prototyping are often lost due to the use of processes
that are incompatible with the type of information needed by the designer at any given
point in the product development process. A common example is using a relatively expensive
Stereolithography (SLA) model to check the overall form of a proposed design when a
concept model costing much less and built in a fraction of the time would have provided
the necessary information.
The goal of this research is to improve the selection of prototyping techniques in
order to reduce both the costs and cycle times associated with product development
processes. In order to accomplish this we must understand and quantify the value
associated with each prototyping technique at any given stage in the design process. For
the purposes of this research value will be defined as the benefit (the amount of useful
information generated) divided by the cost (resources used) associated with creating the
prototype. Of particular interest is the development of a benefits metric, which requires
two sets of attributes: one that describes the capabilities of the individual prototyping
technologies (prototype attributes) and another that describes the designs informational
needs (design attributes). The final step is to correlate the two sets of attributes in an
attempt to model the informational content of a given prototype.
The major result of this research to date is the completion of a value model for
prototyping activities. The first task accomplished was identifying a set of attributes
that can be used to describe a wide array of prototyping technologies. The attributes were
selected based on our experiences as well as the examination of industry case studies
conducted with both Siemens and NCR. The second task completed was identifying the major
attributes that drive prototyping needs/decisions. The next step in creating this model
was the construction of mathematical relationships that correlate individual prototyping
technologies to the informational needs of a given design process. Finally these
relationships were combined with an existing metric for measuring informational content
during the design process to construct a quantitative measure of rapid prototyping
technology benefits and cost.
The future goals of this project include the completion of several industry case
studies and the validation of the value metric. In order to validate the metrics used in
the construction of the value model, it is imperative to compare the results of real
design efforts to the results generated by the model for a wide variety of possible
scenarios. The final goal is to develop a web based selection aid that will allow
designers to plan prototyping activities prior to starting product development. See the
web page: http://rpmi.marc.gatech.edu/project/description/rp_rt_use_and_survey.html
Benchmarking Rapid Prototyping Technology/ Process
and Assessing its Impact on New Product Development Performance
Today, many firms are faced with a high rate of technological change, shrinking product
life cycles, and intense competition in global, dynamic, and fragmented markets comprised
of discerning customers. There is overwhelming evidence in the business world to show that
a majority of technology based initiatives, in spite of scoring high marks on technical
performance metrics, fall short of achieving their intended business objectives. A lack of
understanding of the fundamental drivers of successful implementation results in their
failure to accomplish the established business goals.
Under the guidance of Nagesh Murthy, we are identifying best practices in the
development and implementation of RP technology. Bill Griffin and Atul Mandal are
researching different methods through literature search. At the same time we are
scheduling site visits in order to develop a more thorough understanding of the use of RP
and its relation to the overall design process.
After completion of some preliminary site visits, we will develop a survey for further
investigation. At the same time we will prepare case studies. With the survey and case
studies we will develop a report that will further best practices in the incorporation of
RP technology into the design process.
Rapid Tooling Test Bed
The product realization process, driven by market factors, is changing dramatically.
Increased competition is forcing product realization to become faster, enabling shorter
time to market. At the same time, globalization, core-competencies, out-sourcing, etc. are
changing the structure of the product realization process--it is becoming distributed,
both organizationally and geographically. Rapid prototyping has the potential to
dramatically reduce time to market by shortening the time required to produce tooling.
Realizing this potential, however, requires creating a technological infrastructure for
both rapid tooling and distributed product realization. In response, a Rapid Tooling
TestBed (RTTB) is proposed in order to focus on injection-molded
products and processes. A team of eight Georgia Tech faculty from three units on campus
have been funded by a three-year NSF Distributed Design and Fabrication Initiative grant
to develop the RTTB.
The key question to be investigated in this proposal is: How early in the
product realization process, and under what conditions, can design be separated safely
from manufacture? This question will be investigated from the manufacturing viewpoint
by (1) developing a distributed fabrication testbed for rapid tooling (injection molds)
and (2) experimenting with different product realization processes for injection molds and
molded components. Several product decomposition strategies will be developed and tested
to ensure that these molds and components are manufacturable. As a result of this proposed
project, customers of the rapid tooling testbed will receive nearly
production-representative components in a variety of polymer, ceramic, and metal materials
within three days of submitting a product model.
The RTTB project has several thrust areas, as outlined below. See the web page: http://rpmi.marc.gatech.edu/project/description/rapid_tooling_test_bed.html
Product and Mold Design Methods
Janet Allen, Farrokh Mistree, and David Rosen are leading this thrust area. The goal is
to translate a product design description into fabrication process plans, including
process plans for polymer or powder injection mold tooling. A series of activities are
required to perform this translation. Given a preliminary part design as input, our
testbed will select the appropriate component material and fabrication process, tailor the
design to that material and process, design molding tools for the parts, design the tool
fabrication process, fabricate those tools, design the molding process, and mold the part.
The primary activity over the first four months of the project was to design the RTTB,
to map the information flows through the various activities required to design and product
rapid tools in a distributed environment. Present work is focused on three primary
decisions, Resource Selection, Mold Design, and Fabrication Process
Design, and on information modeling to support those decisions. A new selection
decision formulation has been developed to match target values of attributes, which is
necessary when trying to select materials and RP/RT processes that will yield production
representative parts. This new formulation will be used for Resource Selection. SLA
rapid tools act differently than conventional steel tools and must be designed somewhat
differently. Based on Kent Dawsons and Anne Palmers work in rapid tooling, a
set of mold design rules are being developed to enable tailoring SLA mold designs.
Additionally, Sunji Jangha is developing an ejection system design tool for use with SLA
rapid tools and our standard mold bases. Under Fabrication Process Design, Aaron
West is developing a method for selecting favorable values of SLA process variables to
achieve build goals of accuracy, surface finish, and build time. This work extends that of
Charity Lynn-Charney and Joel McClurkin.
As part of this work, a Fabrication Description Language (FDL) is being developed to
serve as the medium of communication among all modules of the RTTB. FDL can describe the
capabilities of RP technologies and materials. It is being developed in XML so that it is
easily interpretable by applications running in web browsers.
Polymer Injection Molding Characterization and
Jon Colton is leading this research thrust. The goal is to characterize polymer
injection molding in support of the molding process design activity. This enables testing
and verification of DFM rules and process designs. With SLA and other RP technologies,
resulting molds suffer from two main problems: low strength and poor thermal conductivity.
A prerequisite for good experimental studies is state-of-the-art experimental
equipment. In the past year, we have a new insert mold with flexible cavity size and
ejector pin pattern. Plus, a data acquisition system has been added with transducers for
indirect cavity pressure measurement, in-cavity melt temperature, screw position and
velocity, and hydraulic pressure. Several sets of experiments have been run, studying the
effect of draft angle on ribs and slots on mold failure. Also, the resin flow direction
relative to ribs and slots is critical for mold life. One set of experiments demonstrated
that fan gates are far superior to pin gates. Additional experiments are underway to study
feature height, width, depth, and draft angle interactions. Design rules for SLA molds
will be developed that are analogous to those for steel tools. Results will be integrated
with the Mold Design Methods RTTB thrust.
Metal Powder Injection Molding
Tom Starr leads this research area. As described in the Rapid Prototyping of Ceramics
project, the powder molding and sintering process differs from polymer molding. A ceramic
or metal powder, mixed with suitable thermoplastic binder, is molded under relatively low
temperature and pressure. After cooling and removal from the mold, the body is heated to
high temperature, eliminating the binder and the inter-particle porosity to form a fully
dense ceramic or metal part. The sintering step produces additional and significant
dimensional changes in the as-formed shape. The primary research issue of this project is
to develop a detailed understanding of these changes and the computational methods for
predicting as-formed shapes. Our near-term focus will be on processing of stainless steel
materials using a methodology similar to that outlined in the RP of Ceramics project.
One drawback in using SLA-fabricated molds for powder injection molding is the reported
greater difficulty of part removal as compared to using steel or aluminum molds. We have
designed and fabricated a mold and test stand for quantitative measurement of part/mold
adhesion for various materials, surface treatments and molding conditions. Initial
measurements with our stainless steel powder feedstock, molding into an SLA epoxy mold,
suggest that the low thermal conductivity of the mold material plays a role in bond
formation due to the resulting slower heat removal rate and longer contact time with
liquid feedstock. This effect will need to be incorporated into the mold design algorithm.
RP Error Characterization
Tom Kurfess is leading this thrust from the perspective of three-dimensional metrology.
The objective is to characterize rapid prototyping processes and encode their
characteristics for use in the SLA process design. We will also enable on-line monitoring
and control of SLA builds. Research issues include: (1) quantification of systematic
errors of SLA systems, (2) development of methods by which SLA systems can be validated
and calibrated, and (3) direct feedback to SLA controller from metrology systems to
invert anticipated deviations from target geometry.
Software using the ACIS 3D Modeling Kernel has been developed to enable the metrology
team to fit measurement data from the CMM or laser scanner to CAD models and provide
differential shrinkage values. The work has been applied to the products of various RP
processes, with an emphasis on stereolithography. This research recognized differences in
the results of different measurement methods and interpreted results of the algorithm. On
a related topic, data selection and reduction from dense point clouds can provide for
substantially faster computational analysis. Work in this area lends itself to more
effective use of data fitting methods and new methods of form verification.
Distributed Computing Environment
Richard Fujimoto and Karsten Schwan from the College of Computing are leading this
thrust. Their goal is to develop the distributed computing environment that enables the
RTTB to function across the web. As required by the NSF Initiative, the RTTB must support
distributed design and fabrication. It should be possible to search for materials and
manufacturing processes on the web. Designers in one geometric location should be able to
collaborate with manufacturers and tool makers in other locations. Mold-filling
simulations and mold design optimization runs should be observable and controllable from
remote locations. These challenges call for a new approach to developing distributed
Our approach to this environment involves the application of the Distributed
Laboratories work in the College of Computing. Several technologies will be developed: (1)
Foundations, Shared Event Formats, and Objects. We will develop techniques for describing
and utilizing the interactivity attributes of distributed programs and develop
portable tools using these descriptions. (2) Distributed Architecture Managers: we will
develop mechanisms that support the creation and management of the environment at
cooperating locations and of specific processes performed at those locations so that
design, planning, and fabrication components can be plugged in and jointly
executed easily. (3) Distributed Optimization and Fabrication Architectures: we will
develop a framework for the establishment, management, and growth of distributed
optimization and fabrication by applying these distributed simulation technologies.
Alternative Applications of SLA
Overall, this project area is concerned with extending the suite of
applications of SLA machines, particularly in the fabrication of functional assemblies and
mechanisms. Generally, it is necessary to build each part in an assembly separately, then
assemble them after the build outside of the SLA vat. It would be of significant benefit
to eliminate the secondary assembly steps. Furthermore, functional assemblies and
mechanisms may require stronger materials in high-stress areas, such as joints, in order
to operate effectively. In the context of SLA, one solution is to incorporate inserts (of
a different material) into SLA parts or assemblies that are placed into the build vat
during or prior to the start of a build. Another is to fabricate mechanisms entirely out
of SLA resin, taking care not to fuse the parts together. A second application is the
production of smooth surfaces on SLA parts directly out of the vat. A meniscus smoothing
approach will be taken.
In order to achieve functional assembly fabrication and smooth surfaces, the SLA
machines themselves will require additional functionality. We will investigate the use of
additional degrees of freedom in the operation of SLA machines, working up to 5-axes of
motion. If successful, such a result brings us much closer to our long-term objective of rapid
manufacturing. All of the projects under this Alternative Application heading are
being run as one large project. The project began in October 1998. See the web page: http://rpmi.marc.gatech.edu/project/current1.html
Building Around Inserts
It is sometimes necessary to build prototype assemblies that operate as
mechanisms or that have multiple materials in them. In the context of SLA, one solution is
to incorporate inserts into SLA parts or assemblies that are placed into the build vat
during or prior to the start of a build. Imagine fabricating a working mechanism with
metal shafts and bearings directly in a SLA machine. This vision requires both small and
large changes in the operation of a SLA machine, and may require hardware changes as well.
Alok Kataria, with his advisor David Rosen, is leading the
investigation into these issues. Many difficult issues arise in this project, including:
addressing laser beam shadowing problem when an insert is in the build vat, how to
position and fixture inserts during builds, and methods to recoat the SLA vat with inserts
sticking above the resin surface. Alok is currently developing a SLA simulation
environment for testing building-around-inserts concepts. Tests to measure adhesion
strength of SLA resin to inserts will be performed in the near future to provide a basis
for subsequent work.
Improved Surface Finish by Meniscus Smoothing
The idea here is to lessen the effects of stair stepping by solidifying resin in the
crevices between the stairs while the part is in the vat. In order to smooth the resin
meniscus, a suitable scan vector type needs to be developed. It is necessary to
investigate modifications to the optics system or to the elevator in the SLA machine so
that laser shadowing effects are minimized. We will investigate the use of off-line
process planning for meniscus smoothing. And we will explore real-time control of meniscus
solidification through partial redesign of the optics, elevator, and control systems of
R&D will be completed that will define processes and methods to achieve SLA part
smoothness of 50 micro-inches RMS or better without sacrificing part accuracy. The
processes and methods will not be conventional sanding and painting, but will be part of
the SLA building process or an automated post processing method. Specific objectives
- Understand the capabilities and limitations of standard SLA machines in meniscus
smoothing (surface angles, process variable ranges).
- Develop an analytical model of the SLA process, at least one that explains the meniscus
- Utilize this process model as the basis for the development of an off-line process
planning capability for meniscus smoothing.
A new student, Sameer Joshi, is expected to
start work on this project in January 1999, under the supervision of David Rosen.
In order to achieve functional assembly fabrication and smooth
surfaces, SLA machines will require additional functionality. We will investigate the use
of additional degrees of freedom in the operation of SLA machines, investigating 5-axes of
motion or more. Conventional RP machines have 3 degrees of freedom; for example, the SLA
has two DOF in the laser beam (scans XY), plus a third DOF with the elevator translating
in Z. Additional DOFs could include platform swivel and tilt. Two broad approaches
are being taken to provide additional DOFs. The first involves modifying the
mechanical subsystem to provide platform motions beyond simple elevation. The second
involves adding additional capabilities to the optics system.
This project is being co-supervised by Tom Kurfess and Imme
Ebert-Uphoff. Imme is a new faculty member in Mechanical Engineering. They are each
supervising one student, Chad Moore and Brad Geving, respectively. Chad will be focusing
on the system design and development of a suitable machine controller. Brad will be
investigating alternative mechanical subsystem configurations, including simple swivel and
tilt motions, plus more general Stewart platform-type mechanisms.
Machining of Non-Traditional Materials for Rapid Tooling
In contrast to SLA based rapid tooling approaches, high speed machining is often used
to fabricate tools for short runs or for prototype parts. This project will investigate
the machinability characteristics of CIBA tooling board materials, specifically the
CIBA-Express epoxy tooling board materials. Applications of machined tooling boards
include injection and blow molding and sheet metal forming.
The objectives of this project are to
- Develop an understanding of the process and material related factors influencing surface
finish, dimension/form stability, machining time, and tool wear.
- Develop an understanding of the effect of process variables on surface integrity of the
materials. Sub-surface deformation and other changes in mechanical properties are of
- Compare and contrast with CNC machining of aluminum tooling.
Shreyes Melkote is supervising this project
and has hired a new graduate student, Ruben Lanz, to start this project in January 1999.
Surface Coatings for Smooth Surfaces
Prototypes produced by stereolithography (SL) have "stair-step" surfaces as a
result of the layered SL build process. This pattern leads to a rough surface that reduces
the utility of the SLA prototype. In contrast to the meniscus smoothing approach, this
proposed solution involves a post-processing step of coating SLA part and processing that
coating. Powder coating provides a means for adding polymer similar to the SLA substrate.
Electrostatics can temporarily hold the powder coating on the surface until the coating
melts and wets the surface. This liquid resin should preferentially fill in the
"stair steps", thereby smoothing the surface. In addition, a second material
system, liquid UV coatings, will also be investigated.
This project is on hold until a suitable student is identified.
Other RPMI-Related Activities
Rapid Manufacture of Composite Structures
NASA has sponsored a first phase of work to investigate the feasibility of creating new
methods for building large composite structures more quickly than current methods allow.
The work is ongoing.
Jon Coltons research will develop the science underlying the rapid production of
composite structures, specifically those of carbon fiber-epoxy materials. The goal is to
provide a minimum 100x reduction in the time required to produce arbitrary, laminated
products. This scientific understanding will be reduced to practice in a demonstration
device that will produce a part on the order of 12" by 12" by 12".
Long lead times and high labor contents characterize current composite manufacturing
processes. This makes it difficult to produce parts quickly. A method similar to the
tape-laying process has the potential to make composite structures, and rapid prototyping
processes currently use fiber-reinforced papers to make composite-like products. The
incorporation of carbon fibers and epoxy resins is problematic. Issues such as storage,
dispensing, cutting, orientation, consolidation and curing within a reasonable amount of
time and with minimal operator intervention are a few.
Laser Chemical Vapor Deposition for RP
A laser CVD rapid prototyping system is capable of fabricating complex net-shaped
metallic and ceramic structures. In contrast to most metal and ceramic RP systems, LCVD
bonding occurs at the atomic level, producing a material that is fully dense, ultra-pure,
and mechanically sound. Since LCVD can also produce fibers or layers in any given
direction, the proposed system will mimic a production part in form, fit, and
function. Furthermore, a capacity for multiple materials permits composite structures and
functionally-graded materials and alleviates traditional material restrictions imposed by
a given prototyping technique.
Theoretically, enormous possibilities exist, and Jack Lackey will ask the RPMI members
and faculty for input to guide this work. Thus far, Lackey's team has performed extensive
research into current laser CVD technology, leading to a design for the first LCVD rapid
In the coming year, we will complete construction and begin operation. Several
geometric modeling issues will need to be resolved in the representation of multiple
material parts. Studies will also be conducted to understand the influence of process
variables on the synthesis of LCVD structures for various applications.