Method of making a three-dimensional object by...

Details Method of making a three-dimensional object by... Method of making a three-dimensional object by...

1999-09-24

2001-07-24

Tentoni, Leo B. (Department: 1732)

Plastic and nonmetallic article shaping or treating: processes

Stereolithographic shaping from liquid precursor

C700S120000

Reexamination Certificate

active

06264873

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to the field of stereolithography, which is a technique for making solid, three-dimensional objects (or “parts”) from solidifiable materials (e.g. fluid or fluid-like material such as photopolymers, sinterable powders, and bindable powders).
In recent years, stereolithography systems, such as those described in U.S. Pat. No. 4,575,330, issued Mar. 11, 1986 and entitled “Apparatus for Production of Three-Dimensional Objects by Stereolithography,” have come into use. Basically, stereolithography is a method for automatically building complex three-dimensional parts by successively solidifying thin cross-sectional layers. These layers may be composed of photopolymer resin, powdered materials, or the like. Some types of powder materials are converted from a fluid-like medium to a cohesive cross-section by melting and solidification. The layers are solidified on top of each other consecutively until all of the thin layers are joined together to form a whole part. Photocurable polymers change from liquid to solid upon exposure to synergistic stimulation. Many photopolymers exist whose photospeed (rate of transformation from liquid to solid) upon irradiation with ultraviolet light (UV) is fast enough to make them practical model building materials. In a preferred system, a radiation source (e.g., an ultraviolet laser) generates a beam which is focused to a small intense spot which is moved across the liquid photopolymer surface by galvanometer or servo type mirror x-y scanners. The scanners are driven by computer-generated vectors or the like. The material that is not polymerized when a part is made is still functional and remains in the vat for use as successive parts are made. With this technology, the parts are literally grown from a vat of fluid-like material (e.g. resin or powder). Specifically, the parts are grown from a thin layer near a surface of the vat of fluid-like material. In this manner precise complex three-dimensional patterns can be rapidly produced. This method of fabrication is extremely powerful for quickly reducing design ideas to physical form for making prototypes.
This technology typically utilizes a stereolithography apparatus, referred to as an “SLA,” which generally includes a laser and scanner, a photopolymer vat, an elevator, and a controlling computer. The SLA is programmed to automatically make a three-dimensional part by forming it as a sequence of built-up cross-sectional layers.
Stereolithography represents an unprecedented way to quickly make complex or simple parts without tooling. Since this technology depends on using a computer to generate its cross-sectional patterns, there is a natural data link to computer aided design and manufacture (CAD/CAM). However, such systems have presented challenges relating to structural stress, shrinkage, curl and other distortions, as well as resolution, speed, accuracy and difficulties in producing certain object shapes.
The techniques to be described herein are also useful in other Solid Modeling, or Rapid Prototyping and Manufacturing, technologies. One of these other technologies builds up objects from sheets of materials, as described in U.S. patent application Ser. No. 07/803,681, now U.S. Pat. No. 5,182,715. In some embodiments these sheets of material are transformed upon exposure to appropriate radiation. These transformations can benefit from the techniques to be described herein.
RELATED PATENTS AND APPLICATIONS
The following patents and patent applications are incorporated by reference into this disclosure as though fully set forth herein:
U.S. Pat. No. 5,130,064 describes some methods of practicing stereolithography involving continuous skinning and weave patterns. U.S. Pat. No. 5,184,307 describes in great detail the presently preferred stereolithographic apparatus, as well as various methods to form parts therewith. This application is incorporated herein by reference, including its appendices, as though fully set forth herein to facilitate handling due to its relatively lengthy disclosure. Two reference manuals, The SLA-250 User Reference Manual and The SLA-500 Reference Manual are hereby incorporated into this disclosure by reference as though fully set forth herein. These manuals accompanied U.S. patent application Ser. No. 429,435 (now U.S. Pat. No. 5,130,064) as Appendices B and C respectively.
U.S. Pat. No. 4,575,330 to Hull discusses stereolithography in general. It teaches complete polymerization of each cross-section in the formation of a stereolithographically-formed object.
U.S. Pat. No. 5,076, 974, and U.S. patent application Ser. No. 07/415,134, now abandoned, describe off-absorption-peak wavelength post curing of parts which were formed based on the primary approach to building stereolithographic parts.
U.S. Pat. No. 5,104,592 describes several methods of reducing curl distortion.
U.S. Pat. No. 4,999,143 describes the use of web supports to support and minimize curl in a part being formed.
U.S. Pat. No. 5,015,424 describes the use of “smalleys” to minimize curl in a
U.S. Pat. No. 5,182,056 describes the use of multiple penetration depths in the stereolithographic process, along with the use of beam profile characteristics in combination with resin parameters to predict various cure parameters associated with the creation of stereolithographic parts. This application also describes the role of beam profile information in the creation of skin fill and discusses various multiple wavelength curing methods for reducing part distortion.
U.S. patent application Ser. Nos. 07/415,168, 07/268,428, and 07/183,012, all of which are now abandoned, and U.S. Pat. No. 5,234,636, disclose various methods of finishing a stereolithographic part surface to smooth out discontinuities in a post-processing step.
U.S. patent application Ser. Nos. 07/265,039, which is now abandoned, and 07/249,399 which together form the basis of PCT Application Ser. No. PCT/US89/04096, WIPO Publication No. WO 90/03255, disclose the use of a doctor blade for obtaining a uniform coating of resin of known thickness over each cross-section of a stereolithographic part as well as a system for maintaining a known surface level of the building material as the part is being built.
U.S. patent application Ser. No. 07/429,301 discusses post-processing techniques.
In the normal practice of stereolithography, objects or “parts” are built on a layer-by-layer basis, where each layer represents a thin cross-section of the part to be formed. Initial approaches to stereolithographic part building were based on the complete filling (e.g. substantial polymerization of all regions of a cross-section to a thickness at least as deep as the layer thickness) of layers. This filling was either done by the scanning of a pencil of light, by a focused or defocused pencil of light, or by flood exposure of an appropriate cross-sectional image. The pencil of light approach strictly used complete filling of cross-sections based on the scanning of adjacent overlapping vectors until the entire cross-sectional pattern was cured. These initial approaches suffered from several drawbacks, including distortion, curl, inaccurate sizing, lack of structural integrity, and lack of uniformity in down-facing surface appearance.
Later stereolithographic techniques used an internal lattice of partially cured building material (“cross-hatch” or “hatch”) in place of completely filling the successive cross-sections. The internal structures primarily consisted of cross-hatch separated by untransformed building material (e.g. liquid photopolymer or the like). In this approach, the outer and inner edges of each layer are solidified by scanning of what are called “boundary vectors” (also termed, “boundaries” or “border vectors” or “borders”). These vectors separate the interior cross-hatched regions of a cross-section from exterior untransformed building material. Cross-sections or portions of cross-sections that bound external regions of the part are completely filled with skin fill (termed “fill” or “skin”) after being cross-hat

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