Data processing: generic control systems or specific application – Specific application – apparatus or process – Product assembly or manufacturing
Reexamination Certificate
2000-05-05
2003-06-03
Picard, Leo (Department: 2125)
Data processing: generic control systems or specific application
Specific application, apparatus or process
Product assembly or manufacturing
C345S420000
Reexamination Certificate
active
06574523
ABSTRACT:
FIELD OF INVENTION
The present invention is directed to methods for forming three-dimensional objects on a layer-by-layer basis and, more particularly, is directed to a method of controlling part mechanical properties for stereolithographic and other three-dimensional photocured objects by using an improved method of curing the photocurable medium or photopolymer liquid from which the three-dimensional build object is generated.
BACKGROUND OF THE INVENTION
In recent years, many different techniques for the fast production of three-dimensional models have been developed for industrial use. These are sometimes referred to as rapid prototyping and manufacturing (“RP&M”) techniques. In general, rapid prototyping and manufacturing techniques build three-dimensional objects layer by layer from a working medium utilizing a sliced data set representing cross-sections of the object to be formed. Typically, an object representation is initially provided by a Computer Aided Design (CAD) system.
Stereolithography, presently the most common RP&M technique, may be defined as a technique for the automated fabrication of three-dimensional objects from a fluid-like material utilizing selective exposure of layers of the material at a working surface to solidify and adhere successive layers of the object (i.e. laminae). In stereolithography, data representing the three-dimensional object is input as, or converted into, two-dimensional layer data representing cross-sections of the object. Layers of material are successively formed and selectively transformed or solidified (i.e. cured) using a computer controlled laser beam of ultraviolet light (UV) light into successive laminae according to the two-dimensional layer data. During transformation, the successive laminae are bonded to previously formed laminae to allow integral formation of the three-dimensional object.
The basic stereolithographic approach to forming three-dimensional objects is described in U.S. Pat. No. 4,575,330, (C. W. Hull), issued on Mar. 11, 1986, and later reexamined (certificate issued on Dec. 19, 1989). This patent describes a system for generating three-dimensional objects by creating a cross-sectional pattern as described above.
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 CAD/CAM. However, such systems have encountered difficulties relating to shrinkage, curl and other distortions, as well as resolution, accuracy, and difficulties in producing certain object shapes. Additionally, until the present time these systems have not been able to create build parts with different properties in different regions of the object.
Although stereolithography has shown itself to be an effective technique for forming three-dimensional objects, various improvements addressing the technology's difficulties have been desired for some time. Many improvements have addressed the aforementioned difficulties and have been made to object accuracy, speed and appearance of the build object over the years. However, there still remains a need for further improving the build object appearance and ease of making certain object shapes with different build object properties in different regions of the same part. Various aspects of the stereolithographic building process can impact the build object appearance, ease of generation, and properties of the three-dimensional object. For instance, two aspects and areas for needed improvement are the ability to control the thermal resistance and the tensile elongation or durability of a part built using stereolithography or of a region built within a part.
The problem of being able to build a stereolithographic part with different mechanical properties from a single photopolymer material has not been achievable until now. Prior approaches have produced models or parts from different photopolymer materials and glued them together. Recently, the fabrication of supports, which act like fixtures in conventional machining and hold the build object or part in place during the build process, have employed differential curing to create weak areas at the point of attachment to the build object to facilitate part removal. This differential curing exposes the supports to the laser for varying lengths of time to obtain different cure depths of the photopolymer material at different locations. The less cured areas are at the weak points. This is described in co-pending U.S. application Ser. No. 09/493,938 filed Jan. 28, 2000. These supports are removed from the green part prior to postprocessing and curing. However, there has been no ability to produce a build object or part having discrete mechanical properties in different regions from a single photopolymer material.
One form of three-dimensional object modeling that addresses the issue of producing desirable characteristics in build parts by controlling the depth of penetration of the actinic radiation into a vat of photopolymer uses a technique known as beam profiling. U.S. Pat. Nos. 5,058,988 and 5,182,056 discuss the control of the depth and width of photopolymer cured by a computer controlled laser beam. The '988 patent discloses a method and apparatus that determines the net exposure of the photopolymer by sensing the intensity of the laser beam and then calculating the cure parameter or depth based on the determined net exposure and properties of the photopolymer. The '056 patent discloses the use of two different wavelength exposure beams to cure the photopolymer to different cure depths. Neither patent teaches the creation of a stereolithographic part with discrete mechanical properties in different regions.
These problems are solved in the method of forming a three-dimensional object using the present invention.
SUMMARY OF THE INVENTION
It is an aspect of the present invention that a build object or part is created with different mechanical properties in discrete regions from a single photocurable medium by employing a method of curing the photocurable medium liquid to form the build object that employs differential curing of discrete regions of the build.
It is another aspect of the present invention that differential curing of the build object or part can be employed to create parts with tailored durability having greater tensile elongation or durability in certain areas of the part where required while preserving faster build speeds overall.
It is a feature of the present invention that varying the exposure as the part or build object is made provides different properties in the part.
It is another feature of the present invention that the stereolithographic build method and apparatus tailors the durability of the part by controlling the applied exposure, laser spot size, the laser firing or repetition rate, and the laser power.
It is yet another feature of the present invention that the stereolithographic build method and apparatus to control the exposure of the photocurable medium while creating the part or build object by employing wider hatch spacing, use of different laser repetition firing rates and use of different laser spot sizes.
It is an advantage of the present invention that a build object or part is obtained which has graded mechanical properties.
It is another advantage of the present invention that more delicate build objects or parts may be obtained.
It is yet another advantage of the present invention that the heat deflection temperature under load (HDT) can be selectively increased in selected part regions, as required.
It is still another advantage of the present invention that the entire part or build object is not softened in the green or uncured postprocessed state to achieve high heat deflection resistance in one or more desired regions of the part.
These and other aspects, features, and advantages are obtained by the present invention through the use of a method of differential curing of the photocurable medium forming the part or build
Hanna Stephen D.
Moussa Khalil M.
3-D Systems, Inc.
Cabrera Zoila
D'Alessandro Ralph
Ervin Michael A.
Picard Leo
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