Plastic article or earthenware shaping or treating: apparatus – Means applying electrical or wave energy directly to work – Radiated energy
Reexamination Certificate
1994-03-31
2001-03-27
Chiesa, Richard L. (Department: 1724)
Plastic article or earthenware shaping or treating: apparatus
Means applying electrical or wave energy directly to work
Radiated energy
C264S484000
Reexamination Certificate
active
06206672
ABSTRACT:
BACKGROUND OF THE INVENTION
Numerous systems for the freeform fabrication of three dimensional objects under computer control have been proposed. This field has become known by the general terms “rapid prototyping” and “desktop manufacturing” over the last several years.
While existing or proposed three dimensional freeform fabrication systems differ from each other in the materials used to build objects in the specific process, the form or state of these materials, and the particulars of the mechanics to form objects and the properties of the resulting objects themselves, almost all of the methods are based upon the layerwise superposition and bonding of materials to form the object. The numerical information required to control a freeform fabrication apparatus and thus to form and bond together each such layer of an object is commonly obtained by performing additional mathematical processing upon the data file which defines the desired object from a three dimensional computer aided design (CAD) system. These additional mathematical steps define the layers of the object as required to perform a freeform fabrication process. It is also possible to use as a starting point a physical object, digitize the spatial coordinates of the object and in a similar fashion perform additional mathematical processing on this data to define layers of the object for a freeform fabrication process. Thus, a second object can be generated that may be different in scale, materials or design from the first.
The uses for three dimensional freeform fabrication systems include, but are not limited to: the rapid fabrication of prototype parts for use as engineering or design models, both for functional and visual design verification; the rapid fabrication of investment and other types of casting patterns; fabrication of unique objects to be used as casting patterns or even functional objects, as for example from CAT scan or NMR data for prosthetic and other medical uses; the fabrication of objects of geometries that would be difficult or impossible to realize using typical subtractive machining processes such as milling or turning on a lathe.
Such systems in addition possess the virtue of allowing rapid realization of a three dimensional object from data supplied by a computer aided design (CAD) system without the preparation of intervening tooling and thereby lower the time for the overall design cycle in many cases from months to a few days or hours. This results in great savings in tooling costs, especially in cases where several iterations may be required to be performed until an acceptable final design or tool is realized, and also results in a highly-desirable, more timely introduction of the so-designed products to market.
Among the processes that have been proposed are those which use layerwise hardening of a photopolymer as the object medium such as stereolithography, U.S. Pat. No. 4,575,330, solid ground curing, U.S. Pat. No. 4,961,154, and design controlled automatic fabrication, U.S. Pat. No. 4,752,498, and others. Another group of proposed technologies is based on layerwise material deposition and includes ballistic particle manufacturing, U.S. Pat. No. 4,665,492, fused deposition modeling, U.S. Pat. No. 5,121,329, inkjet methods, U.S. Pat. No. 5,059,266, weld metal deposition, U.S. Pat. No. 5,207,371, masked plasma spray, U.S. Pat. No. 5,126,529, and others. The object materials in these techniques include melt extruded plastics and waxes, photopolymers, ballistically jetted waxes and metals, and other materials. Still other methods have been proposed based upon the bonding of powders. Selective laser sintering, U.S. Pat. No. 4,863,538, uses the energy of a laser to layerwise bond particles of plastic, wax, or metal together until the desired object is formed. Three dimensional printing, U.S. Pat. No. 5,204,055, is similar, but replaces the laser with a high speed inkjet system which ejects bonding material layerwise into a bed of ceramic powder. The object so formed may subsequently be sintered and may be used to produce a metal article by means of an investment casting-like process without the requirement for an intervening wax or other material pattern.
Additional three dimensional freeform fabrication methods are based on the cutting out of cross sections of the desired object from sheet or web fed material and subsequent lamination of these cross sections to form the object. The most commercially successful of these techniques to date is laminated object manufacturing, U.S. Pat. No. 4,752,352. Paper, plastic films of various kinds and metal foils may be used in this process to form the desired object.
While there are, as described above, many proposed methods for three dimensional freeform fabrication, and indeed some of these have reached a significant level of commercialization, there are many disadvantages to the existing and proposed methods. Examination of these methods and their characteristics, advantages and disadvantages, permits the desirable properties of an improved freeform three dimensional object fabrication method to be listed:
a. It is desirable that an improved method of freeform fabrication be a slice-based technology. This allows the rate of construction of the object to be independent of the geometry of the object and shortens fabrication time by eliminating the need for calculating and individually positioning vectors as is required for stereolithography or fused deposition modeling. It would be a further advantage if the layers did not require the fabrication of an intervening mask as required by solid ground curing or design controlled automatic fabrication.
b. A solid support material is desirable in an improved method of freeform fabrication in order to produce desired objects with the most generalized geometric capability, to minimize built in stress and to improve accuracy by preventing wandering and swelling of the fabricated object as occurs with some methods that use liquid photopolymers. A solid support also dispenses with the need to design a support structure for overhanging or other geometrically awkward volumes of the desired object as is required in stereolithography or fused deposition modeling.
c. It is desirable in an improved method of freeform fabrication that the support material be subjected to the same physical processes as the build or object material in order to result in minimum differences in physical properties between the support and the object materials. The reasons are similar to those set forth above. Note that in the case of selective laser sintering, while a solid support structure is provided by the powder which remains unsintered, the difference in density between this unsintered support and the sintered object powders can lead to inaccuracies in object geometry.
d. An improved method of freeform fabrication should be capable of providing high resolution and accuracy. High resolution will result in better surface finish.
e. High speed operation should be possible with an improved method of freeform fabrication. It is very desirable to be able to build objects much more quickly than previously known methods are capable.
f. Object materials used in an improved method of freeform fabrication should be safe, non-toxic and inexpensive. Unlike the situation with some existing methods, it is highly desirable to be able to build objects in materials which are suitable for the actual application envisioned for the object. It is further desirable that there results no emission of smoke or vapors requiring venting as with some methods such as laminated object manufacturing which uses a carbon dioxide laser for material cutting. Many photopolymers used in present methods can irritate the skin or respiratory tract and are suspected carcinogens. It is thus desirable to avoid the use of these materials.
g. An improved method of freeform fabrication should utilize existing technology and not require expensive or exotic components. Many present methods such as stereolithography require expensive and/or limited-life lasers, expensive laser bea
Chiesa Richard L.
Choate Hall & Stewart
Grenda Edward P.
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