Rapid tool manufacturing

A method for rapid tool manufacturing comprising the steps of first building an SFF pattern made of plastic to be used to make a first die half. Then there is the step of spraying metal onto the pattern to form a first metal substrate. Next, there is the step of separating the substrate from the SFF pattern to form the first die half. Then there is the step of building a second SFF pattern to be used to make a second die half. Next, there is the step of spraying metal onto the second SFF pattern to form a second metal substrate. Then there is the step of separating the second metal substrate from the second SFF pattern to form the second die half. In a preferred embodiment, the method for rapid tool manufacturing the second die half is formed by first the step of building an SFF model of a part to be molded. Then, there is the step of inserting the model into the first die half. Next, there is the step of spraying metal onto the model in the first die half to form a second metal substrate. Then there is the step of separating the second metal substrate from the model and the first die half to form the second die half.

FIELD OF THE INVENTION 
The present invention is related to rapid tool manufacturing. More 
specifically, the present invention is related to rapid tool manufacturing 
using solid freeform fabrication, such as stereolithography, and thermal 
spray deposition. 
BACKGROUND OF THE INVENTION 
The capability to manufacture a wide variety of quality products in a 
timely and cost-effective response to market requirements is a key to 
global competitiveness. The opportunities for improving manufacturing 
technology range across the entire spectrum of industries, materials, and 
manufacturing techniques. There is no single technological innovation 
which, by itself, will significantly improve productivity; rather it is a 
systems issue which involves rethinking many manufacturing activities. One 
such activity is the manufacture of tooling (i.e., design, prototype, and 
fabrication) such as dies required for the high-volume production methods 
that generate most of our manufactured products. Tooling manufacture is 
typically an expensive and time-consuming process. The reasons lie not 
only in the fabrication costs and time constraints imposed by conventional 
machining methods, but also in the organizational framework. In most 
organizations, different groups employ different processes to design and 
manufacture tools and products, and the expertise in tool design and 
product design reside in different groups, impeding communications between 
them. The representational and physical models used in design, 
prototyping, and manufacturing are often incompatible with one another, so 
that transitions between the stages are time-consuming and error-prone. 
Products often make several complete cycles through design, prototyping, 
and fabrication before reaching production. Thus, new product development 
or product modification implies a series of iterative changes for both 
product manufacturers and toolmakers. For all these reasons, a rapid and 
smooth transition from product concept to production remains a challenge. 
The present invention describes the development of a unified CAD/CAM tool 
manufacturing system. In this system, both prototyping and tooling 
fabrication are based upon compatible solid freeform fabrication, while 
the underlying geometric and process models share a common 
representational scheme. 
Solid freeform fabrication (SFF) builds three-dimensional shapes by 
incremental material buildup of thin layers, and can make geometrically 
complex parts with little difficulty. These processes include selective 
laser sintering (Deckard, C. R. (1987). Recent Advance in selective laser 
sintering, in Fourteenth conference on production research and technology, 
NSF, Ann Arbor, Mich. October), laminated object manufacturing (Colley, D. 
P. (1988). Instant Prototypes, Mechanical Engineering, July), ballistic 
powder metallurgy (Hauber, D. (1987). Automated fabrication of net shape 
microcrystalline and composite metal structures without dies, in 
Manufacturing processes, systems and machines: 14th conference on 
production research and technology, S. K. Samanta, Ed., NSF, Ann Arbor, 
Mich., October), three-dimensional printing (Sachs, E. (1989). Three 
dimensional printing: rapid tooling and prototypes directly from a CAD 
model, in Advances in manufacturing systems engineering, ASME, Winter 
Annual Meeting, 1989), stereolithography, and near-net thermal spraying. 
The present invention incorporates commercially available technologies: 
stereolithography apparatus (SLA) and arc spray equipment. 
Stereolithography, which has been commercialized by 3D Systems, Inc. 
(Valencia, Calif.), is a new process which creates plastic prototype 
models directly from a vat of liquid photocurable polymer by selectively 
solidifying it with a scanning laser beam. In arc spraying, metal wire is 
melted in an electric arc, atomized, and sprayed onto a substrate surface. 
On contact, the sprayed material solidifies and forms a surface coating. 
Spray coatings can be built up by depositing multiple fused layers which, 
when separated from the substrate, form a free-standing shell with the 
shape of the substrate surface. By mounting the shell in a frame and 
backing it up with appropriate materials, a broad range of tooling can be 
fabricated including injection molds, forming dies, and EDM electrodes. 
For example, the cavities of injection molds can be fabricated by direct 
deposition of metal onto plastic SLA models of the desired part and 
backing the framed shell with epoxy resins. Relative to conventional 
machining methods, the sprayed metal tooling approach has the potential to 
more quickly and less expensively produce tools, particularly for those 
parts with complex shapes or large dimensions,. Thus, with 
stereolithography, an initial part shape or prototype is quickly created. 
Thermal spraying is then used to make tools based on the part shapes 
produced by stereolithography. 
The potential effect of combining thermal spraying with stereolithography 
to build tooling is enhanced by integrating and automating these processes 
within a unified CAD/CAM environment. The goal of integration is to reduce 
the number of interactive cycles through design, prototyping, and 
fabrication. CAD-based evaluation and modification tools can operate on 
design models to help the designer create manufacturable designs on the 
basis of requirements and limitations of the downstream processes. For 
example, there are certain shape features in thermally sprayed parts which 
are difficult to spray. The system should identify these features so that 
the designer may modify them before reaching the fabrication stage. 
Another example is to automatically critique ejectability by analyzing 
whether there is sufficient draft for part ejection from an injection mold 
or mold die. If drafts are not sufficient, the system should identify this 
geometric problem and bring it to the designer's attention. 
Another step in the CAD/CAM approach is to automate the thermal spray 
process with robotics. Tooling manufacture by thermal spraying is 
currently a labor-intensive artform. Shifting emphasis to robotic 
spraying, driven by an off-line trajectory and process planner, will 
improve tooling quality by achieving consistent and predictable 
performance of the sprayed metal shell. 
Finally, the level of integration and the number of different models, in 
this CAD/CAM system requires geometric representations that can be 
abstracted at several levels and that can be manipulated over several 
dimensions. Rather than use several different modeling environments 
customized for the demands of each subsystem, the models in our framework 
for design, analysis, and fabrication share a single common unifying 
geometric representation implemented in the software modeling system 
NOODLES ("Vertex-based representation of non-manifold boundaries" by E. 
Levent Gursoz, Young Choi, Frederick D. Prinz; IFIP WG 5.2/NSF working 
conference on geometric modeling RPI, Sept. 1988, pp. 107-130). With this 
approach, model manipulation capability is robust and models need not be 
transformed between subsystems. 
The present invention represents a significant departure in tool 
manufacturing compared with conventional methodologies. The majority of 
ongoing research (Hayes, C. and Wright, P. (1989) Automating process 
planning: using feature interactions to guide search, Journal of 
Manufacturing Systems, 8(1); Cutkosky, M. R. and Tenenbaum, J. M. CAD/CAM 
integration through concurrent product and process design, in Proceedings 
of the symposium on intelligent and integrated manufacturing, ASME, 
December), 1987 focuses on automating numerical control (NC) fabrication 
by removing material from metal blanks. Manufacturing a broad class of 
complex geometries is difficult without extensive programmer and operator 
intervention, so that NC fabrication remains expensive and relatively 
time-consuming. In addition, the fabrication of prototype parts has 
remained disjoint from the processes to fabricate the production part. In 
contrast, geometric complexity is not an issue with SLA, so that complex 
metal shapes can be fabricated by direct metal deposition onto the SLA 
models. Also, tooling fabrication builds directly upon the prototyping 
process. Such process compatibility and system integration will facilitate 
a continuous transition from design to prototyping to mass production 
within a single manufacturing enterprise. 
SUMMARY OF THE INVENTION 
The present invention pertains to a method for rapid tool manufacturing. 
The method comprises the steps of first building an SFF pattern made of 
plastic to be used to make a first die half. Then there is the step of 
spraying metal onto the pattern without any solid layer between the 
pattern and the metal to form a first metal substrate. Next, there is the 
step of separating the substrate from the SFF pattern to form the first 
die half. Then there is the step of building a second SFF pattern to be 
used to make a second die half. Next, there is the step of spraying metal 
onto the second SFF pattern to form a second metal substrate. Then there 
is the step of separating the second metal substrate from the second SFF 
pattern to form the second die half. 
In a preferred embodiment, the method for rapid tool manufacturing of the 
second die half is formed by first the step of building an SFF model of a 
part to be molded. Then, there is the step of inserting the model into the 
first die half. Next, there is the step of spraying metal onto the model 
in the first die half to form a second metal substrate. Then there is the 
step of separating the second metal substrate from the model and the first 
die half to form the second die half. 
In a more preferred embodiment, after the step of spraying metal onto the 
pattern, there are the steps of applying a water-soluble release agent on 
the pattern and the step of pouring backing material onto the first metal 
substrate to support it. The step of separating the substrate from the 
pattern then preferably includes the step of dissolving the water-soluble 
release agent. It is also preferably before the pouring step, the step of 
laying in place on the first metal substrate tubing for cooling channels. 
In an even more preferred embodiment, after the step of building the SFF 
pattern, there is the step of placing a metal frame onto the pattern. The 
step of spraying metal on the pattern then includes the step of spraying 
metal around the inside edge of the metal frame. Furthermore, after the 
inserting step, there is the step of applying a water-soluble release 
agent on the model, and placing a second metal frame on the first die 
half. After the step of spraying metal onto the model and around the 
inside edge of the frame, there are preferably the steps of laying in 
place on the model tubing for cooling channels; the step of pouring 
backing material on the model to support the second metal substrate and 
the step of dissolving the water-soluble release agent between the second 
metal substrate and the model. In general, there are applications 
utilizing both single dies and complementary die sets. 
The invention is also a method for rapid tool manufacturing which is 
characterized by the steps of building an SFF pattern from a 
computer-based geometrical model followed by robotically spraying metal 
onto the SFF pattern in correspondence with the computer based geometric 
model. Preferably, before the building step, there is the step of creating 
the computer-based geometric model on a CAD/CAM system.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawings wherein like reference numerals refer to 
similar or identical parts throughout the several views and more 
specifically to FIG. 4 thereof there is shown a method for rapid tool 
manufacturing. The method comprises the steps of first building an SFF 
pattern made of plastic such as an SLA pattern 52 to be used to make a 
first die half 60. Then there is the step of spraying metal onto the 
pattern 52 without any solid layer between the pattern and the metal to 
form a first metal substrate 58. Next, there is the step of separating the 
substrate 58 from the SFF pattern 52 to form the first die half 60. If a 
single die is being manufactured, such as an EDM electrode or a 
superplastic forming die, then the die is essentially complete at this 
point. 
In a first embodiment, there is then the step of building a second SFF 
pattern to be used to make a second die half. Next, there is the step of 
spraying metal onto the second SFF pattern to form a second metal 
substrate 58. Then there is the step of separating the second metal 
substrate 58 from the second SFF pattern 52 to form the second die half. 
In a preferred embodiment, the method for rapid tool manufacturing the 
formation of the second die half 63 is formed by first the step of 
building an SFF model 62 of a part to be molded. Then, there is the step 
of inserting the model 62 into the first die half 60. Next, there is the 
step of spraying metal onto the model in the first die half 60 to form a 
second metal substrate 65. Then there is the step of separating the second 
metal substrate 65 from the model 62 and the first die half 60 to form the 
second die half 63. 
Preferably after the step of spraying metal onto the pattern 52, there are 
the steps of applying a water-soluble release agent 54 on the pattern 52 
and the step of pouring backing material 61 onto the first metal substrate 
58 to support it. The step of separating the substrate 58 from the pattern 
52 then preferably includes the step of dissolving the water-soluble 
release agent 54. It is also preferable before the pouring step, the step 
of laying in place on the first metal substrate 58 tubing 59 for cooling 
channels. 
After the step of building the SFF pattern 52, there is preferably the step 
of placing a metal frame 56 onto the pattern 52. The step of spraying 
metal on the pattern 52 then includes the step of spraying metal around 
the inside edge of the metal frame 56. Furthermore, after the inserting 
step, there is the step of applying a water-soluble release agent 54 on 
the model 62, and placing a second metal frame 67 on the first die half 
60. After the step of spraying metal onto the model 62 and around the 
inside edge of the frame 67, there are preferably the steps of laying in 
place on the model 62 tubing 59 for cooling channels; the step of pouring 
backing material 61 on the model 62 to support the second metal substrate 
65 and the step of dissolving the water-soluble release agent 54 between 
the second metal substrate 65 and the model 62. 
The invention is also a method for rapid tool manufacturing which is 
characterized by the steps of building an SFF pattern from a 
computer-based geometrical model followed by robotically spraying metal 
onto the SFF pattern in correspondence with the computer based geometric 
model. Preferably, before the building step, there is the step of creating 
the computer-based geometric model on a CAD/CAN system. 
In the operation of the preferred embodiment, stereolithography is a 
process which quickly makes plastic prototypes of arbitrary geometric 
complexity directly from the computer models of the parts. The 
stereolithography SLA does not require experienced model makers, and the 
machine runs unattended once the building operation is started. It is 
relatively straightforward for the designer to program and run the SLA. 
SLA is the product of 3D Systems, Inc. of Valencia, Calif. Their system for 
SLA 12 (FIG. 1) is composed of a vat 14 of photosensitive liquid polymer 
16, an x-y scanning ultraviolet laser 18 beam 19 with a 0.25 mm (0.01 in.) 
beam diameter, and a z-axis elevator 20 in the vat 14. The laser 18 beam 
19 is focused on the liquid's surface 22 and cures the polymer, making 
solid forms 24 wherever the beam 19 has scanned. The depth of cure is 
dosage-dependent. The physical object to be created, as described by a 
boundary representation model (in the 3D Systems device, this is a 
triangulated, planar surface PHIGS B-Rep.), is first "sliced" into thin 
cross-sectional layers along the z-axis. For each slice, the laser's 18 
trajectory is dictated by the cross sections boundary and by the bounded 
region. 
The elevator platform 26 is initially positioned at the surface 22 of the 
liquid 16. As the laser 18 draws a cross section in the x-y plane, a solid 
layer is formed on the elevator platform 26. The platform 26 is lowered 
and then the next layer is drawn in the same way and adheres to the 
previous layer. The layers are typically between 0.13 and 0.5 mm (0.005 
and 0.020 in.) thick. A three-dimensional plastic object 24 thus grows in 
the vat 14, starting at the object's bottom and building to the top. 
To save time, the SLA laser 18 does not fully cure each cross section. 
Rather, the laser 18 cures the boundary of a section, and then cures an 
internal structure, or honeycomb, that traps the uncured fluid 16. Top and 
bottom surfaces, on the other hand, are fully cured. These surfaces are 
cured by commanding the laser 18 to draw the whole surface with 
overlapping lines; the result of this operation is called skin-fill. Final 
curing under separate ultraviolet lights solidifies the complete part. The 
current accuracy of SLA objects 24 is of the order of 0.25 mm (0.010 in.), 
while surface texture is dependent on the building orientation. Additional 
postprocessing, such as carefully sanding and grinding the part, is 
therefore required for making accurate and smooth models. 
There is an engineering cost to preparing a part design for SLA 
construction. Support structures are added to the part to hold it together 
while it is being built, the part must be oriented in the vat 14 for best 
surface quality and fastest build time, and SLA process parameters must be 
planned. One example of the latter is the choice of layer thicknesses in 
the part; they do not have to be constant throughout the part, and their 
choice has a first-order effect on the accuracy, the surface quality, and 
the build time of the part. 
Tooling can be fabricated with arc spraying upon appropriate substrate 
patterns. Examples which demonstrate this process for fabricating 
injection dies using SLA patterns are described below and compared with 
conventional pattern-making techniques. The combination of 
stereolithography with thermal spraying provides a tooling fabrication 
process which builds directly upon prototype models. These models are 
rapidly produced and the ability to modify them for spraying applications 
is straightforward. 
The concept of sprayed metal tooling 30 has been in existence for decades 
(Garner, P. J., New die making technique, SPE Journal, 27(5), May 1971). 
Current commercial technology uses electric arc spraying. The arc spray 
process (FIG. 2) uses two spools of metal wire 32 which are fed to a spray 
gun 34 where the wire tips 36 form consumable electrodes. A high current 
is passed through the electrodes creating an arc 38 which melts the wire 
tips 36. The molten particles 42 are atomized by a high pressure air jet 
40 directed at the arc and are accelerated in the air stream. These 
particles strike the surface of a substrate 44 where they flatten out and 
quickly solidify. 
A conventional machined injection mold die set 46 is shown in cross section 
in FIG. 3. The holes 48 represent cooling/heating channels, and the 
injection geometry is that of a simple sprue gate 50. Alternatively, the 
fabrication steps for building a sprayed mold using SLA patterns are 
depicted in FIG. 4. 
The steps are: 
STEP 1 
Build SLA pattern 52 used to make one die half. This pattern is the 
complement of the interior of this die half. In this example, the die 
pattern 52 includes the partial part shape, a parting plane, and sprue 
gate. 
STEP 2 
Apply a water-soluble release agent 54 onto the plastic pattern 52, such as 
polyvinyl alcohol (PVA), to facilitate separation of metal from plastic. 
STEP 3 
Place a metal frame 56 onto the pattern 52. 
STEP 4 
Spray metal onto the pattern and around inside edge of frame. Alloyed zinc 
compositions are typically used for this particular process because their 
relatively low residual stress permits thick shells to be deposited. 
Sprayed shell thicknesses are typically on the order of 2-7 mm. Fine 
pattern details are accurately replicated by this spray process. 
STEP 5 
Lay in place copper tubing 60 for cooling channels for the injection 
molding process. Additional injection mold components, such as 
prefabricated ejector pin assemblies (not shown), can be added in STEP 1 
and sprayed in place in STEP 4. 
STEP 6 
Pour in a backing material 61 to support the metal substrate 58. Typical 
backing materials include epoxy mixed with aluminum shot. 
STEP 7 
Separate the substrate pattern 58 from the die half. This is aided by 
dissolving the PVA in water. This completes the fabrication of the first 
die half 60. 
STEP 8 
With SLA, build a model 62 of the whole part to be molded, including 
runners and gates, and insert the model 62 into the first die half 60. 
This forms the pattern for spraying the second die half. 
STEP 9 
The second die half is completed by repeating STEPS 2-7. 
The die set fabrication is completed by removing the SLA insert. 
Using these steps, there has been fabricated, for instance, the injection 
mold in FIG. 5 for making a polyethylene turbine blade. This example is 
interesting because of this shape's complexity and useful since molded 
plastic blades can be used for making castings for metal blades. This tool 
also includes a nonplanar parting surface and a complex runner system. The 
fabrication of this tool requires three SLA patterns, shown in FIG. 6 
which can be built simultaneously in the vat. The first pattern in FIG. 6 
is sprayed to make the first half of the mold. In contrast to the planar 
parting surface in the first example, the blade mold requires a nonplanar 
parting surface to permit ejection of the molded blade from the tool. To 
create this pattern, the computer models of the blade and runner are 
embedded into the parting plane model in FIG. 7 using simple union 
operators. Another major advantage of using SLA to create spray patterns 
is demonstrated by this nonplanar parting plane example. Conventionally, 
the first die half can be prepared by partially embedding a complete 
prototype model of the part into, say, melted paraffin. The paraffin then 
cools to form a planar parting surface around the remaining partial part 
shape. With this approach it is difficult to sculpt nonplanar surfaces. 
Other approaches which build up parting planes with sheet-wax, clay, or 
plaster are tedious and difficult. Machining complex patterns is 
time-consuming and expensive. With SLA it is straightforward and 
relatively quick to build complex patterns, with nonplanar parting 
surfaces, and include the runner system in these models. 
Once the first half of the mold is completed, the initial pattern is 
removed and SLA models of the blade with tab gates and the runner with the 
injection sprue gate are inserted into the die cavities. The process is 
then repeated to build the second die half. 
The need to execute accurately spray paths based on process knowledge and 
to repeat consistently operations makes a robotic system preferable in the 
rapid tool manufacturing domain. Arc spraying robots currently provide 
repeatability in surface coating applications (Metco Inc., Six axis robot 
developed for thermal spray coating, Robotics World, February, 1985; Tafa 
Inc., Arc spray robot can coat at twice manual speed, Robotics World, 
March, 1985). However, the spray paths are manually generated with a teach 
pendant for all but the simplest of part geometries. Automated and 
intelligent decision making capabilities, using design models and process 
knowledge for off-line path generation, are absent from these systems. 
Automated thermal spraying requires the scheduling of the arc spray 
parameters and the selection of the robot path. These parameters include: 
arc voltage, wire feed rate, atomizing gas pressure, atomizing gas type, 
wire diameter, and nozzle geometry. Many of these parameters are directly 
affected by the type of material being sprayed. Because the number of 
parameters is high, an experimental testbed is crucial to study 
systematically how these parameters affect shell quality. Some insight 
into this problem may be gained from published statistical methods for 
tuning the thermal spray process parameters to produce optimal thin 
surface coatings (Van Doren, S. L., A statistical method of plasma spray 
parameter testing in Proceedings of the second national conference on 
thermal spray, ASM, Long Beach, Calif., October, 1984). 
Although arc parameters directly affect the sprayed shell quality (Thorpe, 
M. L., How recent advances in arc spray technology have broadened the 
ranges of applications, in Thermal spray technology: new ideas and 
processes, ASM International, October, 1988), the path of the gun is of 
equal importance. Robot paths must be found that traverse the substrate to 
deposit a uniform layer even when the substrate presents geometric 
features that make spraying difficult. 
For example, consider overspray as shown in FIG. 8. Particle trajectories 
should align with the surface normals to assure maximal splattering of the 
molten particles. As the angle of impingement increases, that is, as the 
angle between the particle trajectory and the surface normal increase, the 
shell quality degrades. After some critical impingement angle 
.theta..sub.c, the particles bounce off the surface 70 as wasted overspray 
or become entrapped in the shell reducing its strength or shadow effects 
are accentuated. Although .theta..sub.c is a function of the spray 
parameters, .theta..sub.c =45.degree. has been used as a rule-of-thumb 
(Franklin, J., Designing for thermal spraying, Engineering, July/August, 
1986). The amount of overspray generated is therefore dependent upon the 
gun orientation relative to the part surface. The following examples 
illustrate how this information can be accounted for in planning. 
For a simple planning algorithm, the spray path is defined by a grid on the 
surface of the substrate. In this algorithm, the spray gun is oriented 
normal to the surface and follows each line of the grid with a constant 
standoff distance. This strategy is referred to as the surface-normal 
tracking strategy. To analyze the overspray performance of this strategy, 
consider the convex corner of the cross section shown in FIG. 9 (A). 
.theta. is defined as the spray divergence angle. There is no overspray so 
long as all of the spray hits a flat surface, the gun axis is 
perpendicular to the flat surface, and .theta..ltoreq..theta..sub.c. 
However, this strategy produces overspray on both the vertical and 
horizontal surfaces as the gun negotiates the corner. 
An alternative two-step strategy (FIG. 9B) eliminates overspray for this 
example. As the gun approaches the corner, it is oriented so that the 
trailing edge of the spray cone makes an incident angle of .theta..sub.c. 
As the leading edge starts traversing the curved surface, its incident 
angle increases and spraying is stopped when it becomes .theta..sub.c. At 
this time both the leading and the trailing edges make incident angles of 
.theta..sub.c so that there is no overspray on any surface. The gun is 
then reoriented so that the leading edge makes an incident angle of 
.theta..sub.c with the vertical surface, and repositioned so that the 
trailing edge makes an incident angle of .theta..sub.c with the curved 
surface. Spraying is restarted from this position and proceeds down the 
vertical surface. 
These two strategies demonstrate spray planning for a simplified 
two-dimensional case. In practice, strategies will have to be synthesized 
which account for the interaction of the spray cone with three-dimensional 
and more complex shapes, and which address a range of spray performance 
requirements. However, these examples demonstrate one important result. 
The first strategy only considers geometry, while the second strategy also 
considers process limitations; the framework of considering both geometry 
and process resulted in a superior strategy. 
Robot paths must be found to traverse the workpiece given these process 
limitations. The basis of one approach to this problem is a planner based 
on geometry features, such as the corner feature of the example. A 
feature-based strategy uses extracted features to recognize spray problem 
areas, and then uses successful strategies, predetermined for each 
feature, to generate a robot path plan. The capability to define and 
extract three-dimensional features is being developed within the NOODLES 
environment. (NOODLES is a data structure which implements a non-manifold 
geometric representation. The ability to model non-homogeneous entities, 
i.e. different dimensions and to perform non-regular operations on them, 
i.e. boolean operations between different dimensions facilitates geometric 
reasoning and geometrics manipulation geometrics. Shape feature 
description and recognition using an augmented topology graph grammer, in 
Engineering design research conference, NSF, Amherst, Mass., June 1989). 
The discovery of a good path for the spray torch is critical to successful 
robotic spraying. Equally critical is the translation of the torch's path 
into a complete, reachable, and smooth robot trajectory. It is simple to 
create trajectories that are unreachable by the robot. A second difficulty 
coming from off-line generated paths is the problem of creating paths that 
result in smooth robot motion. The tool manufacturing system will build 
upon robot motion. The tool manufacturing system will build upon robot 
path optimization research at Carnegie Mellon (Hemmerle, J. S. (1989). 
Optimal path placement for kinematically redundant manipulators, PhD 
dissertation, Carnegie Mellon University). 
The representational requirements for modeling systems, including the 
levels of abstraction, the nature of the analyses, and the geometric 
manipulations, vary with the context of the model's use. In CAD/CAM 
applications, the models for design, analysis, and evaluation, and 
fabrication are quite different for each subsystem. In typical systems 
numerous modeling environments are incorporated to satisfy the 
requirements of each subsystem. An approach which incorporates several 
different modeling environments has several drawbacks. First, it is 
error-prone and inefficient since models must be transformed between each 
separate environment. Second, nonuniform data structures make the software 
difficult to manage. 
Finally, it is not easily extendible to new system applications which may 
require a mixture of the attributes of different environments. The key to 
successful integration is to provide a modeling environment in which 
design models, description of prototype models, and manufacturing methods 
are uniformly treated. To address this issue, manufacturing system is 
built upon a geometric modeling environment, NOODLES (Gursoz, E. L., Choi, 
Y. and Prinz, F. B., Vertex-based representation of non-manifold 
boundaries, in Second workshop on geometric modelling, M. J. Wozny, J. 
Turner and K. Preiss, Ed., IFIP, New York, September, 1988), where 
subsystem models share a common representational and manipulation scheme. 
The following examples demonstrate some of the diverse modeling 
requirements for this CAD-based manufacturing system: 
The user designing a part should be allowed to select the appropriate 
modeling description paradigm depending upon the immediate need. For 
example, designs, at times, can best be synthesized using constructive 
solid geometry, or building solids up from sets of surfaces, while, at 
others, sweeping lower-dimensional elements, such as curves and surfaces, 
into solid representations produce more satisfactory results. 
The SLA process planner must convert solid models into an ordered set of 
21/2 D cross sections (i.e., cross sections with an associated depth or 
thickness) and span these ross sections with appropriate drawing vectors. 
This operation dimensions since one generates planes from solid models, 
and then vectors, or line segments, from the planes. 
The robotic spray planner operates with yet other abstractions. Grids are 
projected onto the object's shell to produce surface patches which are 
analyzed for spraying action. In turn, the spraying actions are molded as 
curvilinear paths which sweep the relevant portions of the tool geometry 
into volumes for interference testing. At this level, assessing the 
interference is not constrained to be intersections between solids, but 
also intersections between surfaces and surfaces, or surfaces and solids. 
Features are the most complex level of abstraction for this system. The 
spray planning system, for example, needs to extract convex corner 
features from the geometric descriptions in order to aim properly the 
spray to avoid overspray. 
Geometric modeling can be performed at various levels, such as wire-frame, 
surface, or solid modeling. The previous examples suggest that all levels 
are required in the system. Although solid modeling approaches have the 
richest information, the representation of lower level elements such as 
lines and surfaces is not explicit. Furthermore, operations provided 
within solid modeling approaches do not apply when nonsolid elements are 
used. The ideal geometric modeling system should uniformly represent and 
operate on nonhomogeneous (i.e., mixed dimensions) elements such as 
vertices, lines, surfaces, and solids. NOODLES offers an environment where 
nonhomogeneous elements are uniformly represented and permits Boolean 
operations between elements of any dimensionality. 
One example which uses nonhomogeneous representations is the planning of 
the layered shape deposition processes. The first step is to obtain the 
cross sections of the object. These sections are obtained from the Boolean 
intersection between the object and a stack of planar faces that are 
appropriately spaced. FIG. 10 shows that the result of this nonregular 
operation is a collection of cross sections. Identification of the 
interior and skin-fill areas for SLA applications can also be achieved 
with set operations. The intersection between the projections of 
contiguous cross sections identifies the interior area; the differences 
between these cross sections produce the skin-fill areas (FIG. 11). 
Finally, the vectors to be scanned by the laser are obtained by 
intersecting appropriate grids with the portions of the cross section. For 
example, as shown in FIG. 12, the interior area of a cross section is 
intersected with a ross hatch grid. The object boundaries for the laser 
are quickly found from the perimeters of the cross sections. Similarly, 
the grids for robotic path planning are defined by the perimeters of the 
intersection of the surface boundary of the object with two perpendicular 
sets of stacks of planar faces. 
A feature extraction algorithm is also being developed which automatically 
recognizes form features of objects represented in NOODLES (Pinilla, J. 
M., Finger, S. and Prinz, F. B., Shape feature description and recognition 
using an augmented topology graph grammar, in Engineering design research 
conference, NSF, Amherst, Mass., June, 1989). This algorithm uses a graph 
grammar to describe and recognize shape features, based on an augmented 
topology of the modeled objects which contain these features. The NOODLES 
representation provides the information for construction for the augmented 
topology graphs. These graphs constitute the search space for the 
recognition of the subgraphs which correspond to the features. In 
injection molding, features like ribs and bosses are recognized in this 
manner (20). Once a feature is recognized by mapping the descriptive 
subgraph into the object graph, various regimes in the subgraph are also 
identified with their counterparts in the surface model. The relevant 
attributes for a feature can thus be evaluated by referring to the actual 
representation. For instance, the draft angle attributes of the rib 
features in an injection molded part is very relevant for assessing 
ejectability. When a rib is recognized by identifying certain surfaces on 
the object with the opposing sides of the rib, the draft angle can be 
computed using the geometric information in the model. 
Although the invention has been described in detail in the foregoing 
embodiments for the purpose of illustration, it is to be understood that 
such detail is solely for that purpose and that variations can be made 
therein by those skilled in the art without departing from the spirit and 
scope of the invention except as it may be described by the following 
claims.