Plastic article or earthenware shaping or treating: apparatus – Means applying electrical or wave energy directly to work – Sonic or supersonic wave energy
Reexamination Certificate
2001-06-08
2004-09-07
Drodge, Joseph (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
Means applying electrical or wave energy directly to work
Sonic or supersonic wave energy
C425S174000
Reexamination Certificate
active
06786711
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to stereolithography methods and systems involving the application of lithographic techniques to three-dimensional objects, and more particularly to providing structural reinforcement of such three-dimensional objects.
(2) Brief Description of the Prior Art
Stereolithography is a “printing” process invented by Charles Hull in 1986 by which three-dimensional copies of solid models are fabricated in plastic. This process is disclosed in U.S. Pat. No. 4,575,330 to Hull, the contents of which are incorporated herein by reference. The Hull patent discloses a system for generating three-dimensional objects by creating a cross sectional pattern of the object to be formed at a selected surface of a fluid medium. This fluid medium is capable of altering its physical state in response to appropriate synergistic stimulation by impinging radiation, particle bombardment or chemical reaction. Successive adjacent laminae, representing corresponding successive adjacent cross sections of the object, are automatically formed and integrated together to provide a step-wise laminar buildup of the desired object. A three-dimensional object is thereby formed and drawn from a substantially planar surface of the fluid medium during the forming process. This process was the first solid imaging process that allowed the fabrication of highly complex physical parts directly from computer generated topology data as is disclosed by Jacobs in
Rapid Prototyping and Manufacturing: Fundamentals of StereoLithography
(1992).
In fact, the advantages of stereolithography prototyping over traditional machining become even more prominent with increasing part complexity. For example, parts involving intricate internal cavities or encased subparts that are impossible to machine as one part are easily fabricated with stereolithography. Physical application of the stereolithography printing process for rapid prototyping takes place via a commercial system known as a stereolithography apparatus (SLA), manufactured by 3D Systems, Inc., Valencia, Calif., which is shown in FIG.
1
.
Referring to
FIG. 1
, a liquid photopolymer
10
in a vat
12
is positioned beneath a moveable HeCd laser
14
. The SLA part
16
is positioned on an elevator
18
. The upper surface
20
of the SLA part
16
is positioned just below the top surface
22
of the liquid photopolymer
10
so that successive layers can be added to the SLA part
16
.
To produce a physical part, the SLA receives solid or surface model geometry data via a specifically formatted input data file known as an STL file. The STL file contains a topological representation of the part in terms of many small triangular flat-faced facets whose dimensions and orientation in space are precisely defined. The STL file “virtual” part is then mathematically “sliced” by computer software into very thin horizontal cross sections or layers. The lowest cross section data is sent to a computer-controlled optical scanning system controlling the helium cadmium (HeCd) laser
14
. The laser
14
draws out the shape of the cross section down onto the surface of the vat
12
of photosensitive liquid resin. Ultraviolet radiation solidifies the resin surface wherever the laser strikes, thereby precisely transforming the cross section into a thin solid layer. The process repeats itself, layer by layer, with each polymerized layer adhering to the layer below it, until a final three-dimensional physical part is produced; this layer-wise assembly is accomplished on elevator platform
18
within the vat
12
which is lowered incrementally with the creation of each new layer. Finally, the full part is removed from the liquid vat and exposed to high intensity ultraviolet light to fully cure it and complete the polymerization process.
The SLA process was originally intended to produce prototypes for conceptual and 3D visualization purposes only. However, users of stereolithography quickly began to desire to actually test the prototypes in the laboratory. Since the first generation stereolithography polymer resins were typically brittle, low-strength, and prone to warping, second generation epoxy-based photopolymers were developed with improved mechanical properties and dimensional stability. One of these is disclosed in U.S. Pat. No. 5,437,964 to Lapin et al. However, except for very carefully designed experiments as is reported, for example, by W. H. Dornfeld, (1994), “Direct Dynamic Testing of Scaled Stereolithographic Models”
International Gas Turbine and Aeroengine Congress and Exposition
, The Hague, Netherlands (ASME Prepromt 94-GT-271), the improved polymers to date still have not achieved the mechanical strength necessary for general laboratory testing loads (e.g., high-speed in-water testing for marine applications, high-speed centrifugal loading, etc.).
Other prior art related to stereolithography and mixing materials into the fluid medium used in that process are summarized as follows.
U.S. Pat. No. 5,248,456 to Evans, Jr. et al. discloses an improved stereolithographic apparatus and method. In one embodiment, the improvement includes immersing at least a portion of a part in a volume of a liquid solvent in a vapor degreaser while subjecting the portion to ultrasonic agitation to substantially remove excess resin. Several examples of solvents are provided, including ethanol, and FREON™. In a second embodiment, the improvement includes building the part on a layer of liquid resin supported by a volume of a dense, immiscible and UV transparent intermediate liquid, and integratably immersing at least a portion of the built part in the intermediate liquid, and then either subjecting the immersed portion to ultrasonic agitation to substantially remove excess resin, or subjecting the immersed portion to UV light. Several examples of intermediate liquids are provided, including prefluorinated fluids, such as FLUORINER™ FC-40 and water-based salt solution, such as solution of magnesium sulfate or sodium chloride in water.
U.S. Pat. No. 5,296,335 to Thomas et al. discloses a method of manufacturing a three-dimensional fiber-reinforced part utilizing the single-tool method of stereolithography. The tool is fabricated by designing the tool on a computer-aided design system and curing successive layers of a fluid medium via a computer-controlled irradiation source to form the three-dimensional tool. The desired part is generated by applying layers of resin-wetted fabric to the tool, curing the fabric on the tool, removing the tool from the designed part, and cleaning, trimming and inspecting the designed part.
U.S. Pat. No. 5,688,464 to Jacobs et al. discloses a method and apparatus for providing a vibrational enhancement to the recoating process in stereolithography. The formation of a thin layer of building material over a previous layer of structure of a partially completed three-dimensional object, in preparation for formation of an additional layer of structure is enhanced by the use of vibrational energy imparted to the building medium. In a first preferred apparatus, vibration is induced into the surface of the material by a plurality of vibrating needles that penetrate below the working surface to a sufficient depth to ensure adequate coupling but not deep enough to come into contact with the surface of the partially completed part. In a second preferred apparatus, vibration is coupled directly to the object support. The vibrational energy is then transmitted through the part to the surface of the building material. In a first preferred method, the partially completed object is overcoated with material and vibration is used to reduce the coating thickness. In a second preferred method, the partially completed object is under-coated with material and vibration is used to increase the coating thickness.
U.S. Pat. No. 5,731,388 to Suzuki et al. discloses photocurable resins containing unsaturated urethane of a specified form and vinyl monomer which is N-(meth)acryloylmorpholine or its mixture with di-ol di(meth)a
Koch Robert M.
Kuklinski Robert
Drodge Joseph
Kasischke James M.
Luk Emmanuel
Nasser Jean-Paul A.
Oglo Michael F.
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