Plastic and nonmetallic article shaping or treating: processes – Stereolithographic shaping from liquid precursor
Reexamination Certificate
2002-01-17
2003-12-02
Tentoni, Leo B. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Stereolithographic shaping from liquid precursor
C264S113000, C264S234000, C264S308000, C425S078000, C425S174400, C425S404000
Reexamination Certificate
active
06656410
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates in general to a recoating system for use by any solid freeform fabrication technique and, in particular, to a recoating system capable of establishing a uniform layer of a high viscosity build material prior to being solidified by a solid freeform fabrication apparatus. The recoating system is unique in that previously formed layers are not substantially disturbed when applying a new layer of build material to establish a layer of high viscosity build material.
2. Description of the Prior Art
Recently, several new technologies have been developed for the rapid creation of models, prototypes, and parts for limited run manufacturing. These new technologies can generally be described as Solid Freeform Fabrication techniques, herein referred to as “SFF.” Some SFF techniques include stereolithography, selective deposition modeling, laminated object manufacturing, selective phase area deposition, multi-phase jet solidification, ballistic particle manufacturing, fused deposition modeling, particle deposition, selective laser sintering, and the like. Generally in SFF techniques, complex parts are produced from a modeling material in an additive fashion as opposed to traditional fabrication techniques, which are generally subtractive in nature. For example, in traditional fabrication techniques material is removed by machining operations or shaped in a die or mold to near net shape and then trimmed. In contrast, additive fabrication techniques incrementally add portions of a build material to specific locations, layer by layer, in order to build a complex part. The additive process varies depending on the technique used, whether by selective deposition of a build material or by selective solidification of a build material.
SFF technologies typically utilize a computer graphic representation of a part and a supply of a build material to fabricate the part in successive layers. SFF technologies have many advantages over the prior conventional manufacturing methods. For instance, SFF technologies dramatically shorten the time to develop prototype parts and can quickly produce limited numbers of parts in rapid manufacturing processes. They also eliminate the need for complex tooling and machining associated with-the prior conventional manufacturing methods, including the need to create molds in casting operations. In addition, SFF technologies are advantageous because customized objects can be produced quickly by processing computer graphic data.
There are a wide variety of build materials that are used in various SEE techniques. These materials are typically applied in the form of a powder, liquid, paste, foam, or gel. Recently, there has developed an interest in utilizing highly viscous paste materials in SEE processes. One of the main purposes of using paste materials is to take advantage of their unique material properties which result in improved properties of the resultant parts formed. These pastes may be obtained by blending a solid charge or filler material in the form of a particulate or powder with a bonding agent. For some pastes the bonding agent is comprised of a photosensitive or heat-cured liquid resin, such as a photopolymerizable resin composed of various combinations of acrylates, epoxies, and vinyl ethers. The powders, typically having a particle size of less than 45 &mgr;m, may be a polymer, mineral, metallic, ceramic, or any combination thereof. Some polymer powders that may be used are thermoplastics such as ABS. Nylon, polypropylene, polycarbonate, polyethcrsulfate, and the like. Some metallic powders that may be used are steel, steel alloy, stainless steel, aluminum, aluminum alloy, titanium, titanium alloy, copper, tungsten, tungsten carbide, molybdenum, nickel alloy, lanthanum, hafnium, tantalum, rhenium, rubidium, bismuth, cadmium, indium, tin, zinc, cobalt, manganese, chromium, gold, silver, and the like. Some ceramics that may be used are aluminum nitride, aluminum oxide, calcium carbonate, fluoride, magnesium oxide, silicon carbide, silicon dioxide, silicon nitride, titanium carbide, titanium earbonitride, titanium diboride, titanium dioxide, tungsten carbide, tungsten trioxide, zirconia, and zinc suiphide, and the like. Some rare earth mineral powders thai may be used are cerium oxide, dysprosium oxide, erbium oxide, gadolinium oxide, holmium oxide, lutetium oxide, samarium oxide, terbium oxide, yttrium oxide, and the like. Alternatively, these pastes may also be obtained by blending high viscosity photosensitive or heat-cured liquid resins without a solid charge of filler material, These high viscosity liquids or pastes can be obtained by blending, for example, photopolymerizable resins composed of acrylates, epoxies, and/or vinyl ethers wit any desired toughening agent, such as, for example, polybutadiene, polyethylene, fiberglass, and the like.
The pastes, typically having a viscosity of greater than 10,000 centipoise at ambient conditions, are selectively cured layer by layer by exposure to radiation. Generally, the radiation cures the bonding agent in the paste. The uncured pastes may exhibit a linear stress-strain relationship, a Bingham type linear stress-strain relationship having a threshold yield stress to overcome, a non-linear pseudoplastic stress-strain relationship (shear thinning), or a non-linear dilatant fluid stress-strain relationship (shear thickening). It has been discovered that pastes have significant advantages over other materials used in SFF techniques. For example, the pastes can contain concentrations of a solid charge material, such as a metallic powder, of greater than 50% by volume, which in turn can produce extremely dense green parts. These green parts are well suited for further post processing, such as sintering and infiltration, to produce mechanical properties in the resultant parts that are substantially similar to those achieved by conventional forming techniques such as casting or forging. Thus, it is believed that the utilization of pastes is a significant step forward in achieving rapid manufacturing by solid freeform fabrication techniques.
Recently, there has also developed an interest in utilizing highly viscous liquid materials in SFF processes. For example, in stereolithography a liquid photopolymer resin is used comprising both high and low molecular weight monomers and oligomers. When solidified, the high molecular weight monomers and oligomers provide greater mechanical properties in the resultant objects than the low molecular weight monomers. Thus, it is desirable to maximize the quantity of high molecular weight monomers and oligomers in the resin in order to increase the mechanical properties of the parts formed, and/or include toughening agents to increase the properties. However, when the quantity of high molecular weight monomers and oligomers are increased in a liquid photopolymer resin, the viscosity of resin is also increased. Undesirably, the increase can far exceed the acceptable viscosity range of the resin coating system, since most conventional stereolithography resin coating systems are generally able to work only with low viscosity liquid resins whose behavior is similar to that of a Newtonian liquid. In order to compensate for this, current liquid photopolymer resins used in stereolithography include low molecular weight monomers so as keep the viscosity of the resin within the acceptable viscosity range of the resin coating system. Thus, there is a need to be able to work with high viscosity liquids in order to substantially enhance the mechanical properties of objects formed from liquid photopolymer resins used in stereolithography.
There are number of difficulties that must be overcome when working with high viscosity pastes and liquids in SFF techniques. For example, in order to make a highly viscous material flow, the material must be subjected to a significant amount of shear stress. When attempting to form a uniform layer of a highly viscous material in SFF, the recoater or spreading device invariably induces
Hull Charles W.
Newell Kenneth J.
3-D Systems, Inc.
Curry James E.
D'Alessandro Ralph
Tentoni Leo B.
LandOfFree
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