Title: Permeation Controlled Concurrent Consolidation Inventor: Lawrence J. Rhoades

Background of the Invention

Field of the Invention: The present invention relates to methods for producing useful articles from powders. More specifically, the present invention relates to methods employing solid free-form fabrication techniques for producing articles from powder that minimize layer- specific defects.

Description of the Related Art: Three dimensional printing was developed beginning in the late 1980' s as a method for quickly creating an article from an electronic representation of the article in a layerwise fashion. The basic principles of the process are described in detail in United States Patent No. 5,204,055, which was issued to Sachs et al. on April 20, 1993. In some ways, three dimensional printing is similar to inkjet printing, but instead of printing ink upon paper, a binder material is printed upon powder layers.

In brief, three dimensional printing involves first spreading a layer of powder across the top of a surface. A printhead then prints a binder material, e.g., a polymeric binder, onto the powder layer in the pattern of a first two dimensional slice of the article that is to be built. After the printing is done, another layer of powder is spread atop the first. The printhead then prints the binder material onto this layer in the pattern of the spatially next successive two dimensional slice of the article. This cycle is repeated until the entire article is built out of powder and binder material. After the building steps are completed, the article is usually sintered and/or infiltrated with a hardenable liquid, e.g., a curable polymer or a molten metal, in order to strengthen and density the article. At some point during the post-building processing, the unbound powder is removed from around the article and from any internal passageways that the article may contain.

Three dimensional printing is only one of many methods that have been developed to date for building useful articles from computer representations thereof in a layerwise fashion. In the art, these various methods are referred to as "solid free-form fabrication" techniques, processes, or methods. Other examples of solid free-form fabrication techniques include stereolithography, which uses successive thin layers of a photopolymer resin that are selectively hardened by an ultraviolet laser beam in desired areas; fused deposition modeling, in which a plastic filament is forced through a hot nozzle that selectively deposits the material in successive layers; laminated object manufacturing, in which cut sheets of paper or other laminate material are stacked to form an article; selective laser sintering, in which a laser is used to selectively bond powder on each successive layer; the selective laser melting process, in which a laser is used to selectively melt and fuse together powder on successive powder layers; and electron beam free-form fabrication processes, in which an electron beam is used to melt and fuse together powder on successive powder layers.

Some solid free-form fabrication methods, for example, three dimensional printing, selective laser sintering, selective laser melting, and electron beam free-form fabrication processes, build the article from a powder. All solid free-form fabrication methods that use powder to build an object are susceptible to defects that are layer-specific or that affect interlayer bonding. The types of defects are several, as are their sources. For example, incorrect or missing data in the electronic representation of the article will cause omissions in the scanned or printed pattern, just as extraneous data may cause some unwanted scanning or printing. Similar defects may occur from transient malfunctions of the scanning or printing mechanism. Stresses can develop within and between layers due to localized binding, thermal changes, or evaporation and may cause weaknesses or cracks in the article. The depth of bonding may vary due to localized variations in the depth of penetration of the scanned radiation or the applied binder.

Many of these problems are eliminated by solid free-form fabrication methods which create a negative of the article, rather than the article itself, from powder and then globally consolidate the remaining powder to form the article. The term "negative" is used herein in the context of a three dimensional article to refer to the three dimensional shape or shapes formed by the remainder of the powder bed that is the complement to the portion of the powder bed that forms the desired article (or articles, in cases where multiple articles are being simultaneously formed). A negative includes any internal passages and voids the article or articles may contain. In conventional three dimensional printing, the negative consist of the unprinted portions of the powder bed. When used in the context of a two dimensional powder layer, the term "negative" means the portion of the powder layer that is the complement of the portion of the layer that comprises the relevant two dimensional cross section of the article. The phrase "globally consolidate" is used herein to mean to substantially simultaneously bind together powder that lays within more than just a single powder layer and the adjacent underlying layer. To the inventor's knowledge, prior to the present invention only two methods utilizing negative creation and global consolidation were known to exist in the art and each has limiting drawbacks.

One of the methods is described in United States Patent No. 6,147,138, which issued to Hόchsmann et al. on November 14, 2000, (hereinafter "the ' 138 patent"). The ' 138 patent teaches making casting molds and cores from a powder that has been coated with a binder. This method involves depositing a binding energy moderating agent onto sequential layers of the coated powder in patterns that are the negatives of the relevant cross-sectional slices of the desired mold or core. The moderating agent is said to positively or negatively shift the level of specific energy necessary for bonding the coated powder together by melting or chemical reaction of the binder coating. After all of the layers of the negative have been deposited, a defined amount of energy is globally induced, i.e., introduced or released, to

form the article by causing the coated particles in the untreated areas to bind together. However, the method of the ' 138 patent suffers from the inherent disadvantage of having to control the amount of globally induced energy within very specific levels - too little energy resulting in no consolidation and too much energy resulting in the consolidation of the entire powder mass. Moreover, the ' 138 patent does not describe how such specific amounts of energy are to be globally induced. Another disadvantage of the method taught by the ' 138 patent is that it relies entirely on the binding of the point-to-point contact areas between the powder binder coatings of adjacent powder particles to provide the strength of the article. This can result in a very weak and delicate article having very little structural integrity. Another disadvantage is that the method of the '138 patent can only be utilized with powder that has been coated with a binder.

The other attempt to utilize the advantages inherent in the negative build concept is found in United States Patent No. 6,589,471, which issued to Khoshnevis on July 8, 2003 (hereinafter "the '471 patent"). The '471 patent teaches the layerwise building of the negative of an article by selectively depositing a sintering inhibitor, e.g., by inkjet printing, until the negative of the article is built. Alternatively, the '471 patent teaches depositing the sintering inhibitor in the outline of the article cross-section on each consecutive layer. In some embodiments, each powder layer is exposed to a radiation source that will sinter together the powder in the desired portions of the layer, hi other embodiments, the entire powder bed is then placed into a sintering oven after all of the layers have been set down. In either case, the heating causes all powder particles, other than those affected or separated by the sintering inhibitor, to be sintered together, thus forming a sintered article. The disadvantages of this method include the fact that the method can only be used with powders which are amenable to sintering and for forming articles from sintered powder. Another disadvantage is that the layer-wise heating embodiments may require a controlled atmosphere

to prevent the undesired oxidation or nitriding of the powder from occurring during sintering. The layer-wise heating embodiments may also require the layer to cool down before the next layer is applied. A disadvantage with the embodiments that employ full article sintering is that they can only be used with powder beds which can fit into a sintering furnace. Attendant to this is the disadvantage that post-processing must contend with the long cycle times, expenses, and control problems associated with operating a sintering furnace.

An additional drawback in the aforementioned conventional solid free-form fabrication methods that create a negative or an outline of the article and then bond together the positive of the article en masse is the susceptibility of the article to experience the formation of internal voids, non-uniform shrinkage, and other dimensional distortions, e.g., non-flatness of the article's top surface, due to powder particle rearrangement as the entire article becomes bonded together in a single operation. In contrast, there is less susceptibility to these defects with the conventional solid free-form fabrication methods in which the particle bonding occurs one layer at a time. This is because the application of each successive powder layer provides an opportunity for the accommodation of the particle rearrangement that occurred during the bonding of the underlying layers. This accommodation results because, in layer-by-layer bonding processes, many of the defect- causing effects arising from bonding-induced powder movement are confined to the layer that is currently being bonded since the powders of the preceding layers are already locked into place by the binder. But as described above, these layer-wise bonding solid free-form fabrication processes have drawbacks of their own.

Summary of the Invention

The present invention overcomes one or more of the aforementioned drawbacks of the prior art solid free-form fabrication methods by providing a new solid free-form fabrication

method, which is referred to herein as "permeation controlled concurrent consolidation" or "PCCC."

In PCCC, a first layer of powder is applied over a surface, such as a conventional vertically indexable build table. A permeation control agent is then deposited onto the first layer in a predetermined pattern. The phrase "permeation control agent" is used herein to mean a material that controls the permeability of the powder to which it is applied with respect to the binding agent which is to be used to form the article. The predetermined pattern may be the negative of a cross-sectional slice of the article that is to be built. Alternatively, it may be the outline of a cross-sectional slice of the article that is to be built. In either case, the permeation control agent divides the powder layer into (1) one or more regions which are permeable to the intended binding agent, i.e., the "untreated powder," and (2) one or more regions which are substantially impermeable to the intended binding agent, i.e., the "treated powder." The term "treated powder" is used herein to refer to the powder to which the permeation control agent has been applied. Correspondingly, the term "untreated powder" is used herein to refer to the powder to which the permeation control agent has not been applied.

Another layer of powder is applied over the first layer and the permeation control agent is deposited thereon in another predetermined pattern which corresponds to the spatially next cross-sectional slice of the article as a negative or an outline thereof. The steps of applying powder layers and depositing a permeation control agent in predetermined patterns are continued for a predetermined number of times. Together, all of the applied layers form a powder bed containing regions of treated powder and untreated powder. A bonding agent is then permeated throughout the untreated powder in one or more predetermined portions of the bed to globally consolidate the untreated powder. The permeation control agent prevents the bonding agent from substantially permeating the

treated powder. The permeation control agent may also provide a barrier to prevent the binding agent from flowing through a treated powder region into an untreated powder region in which bonding is undesired.

For articles for which no significant amount of dimensional variation is expected to result from the particle rearrangement incident to the global consolidation, e.g., small articles, it is preferred that the steps of applying powder layers and depositing a permeation control agent be continued until the entire article is built. In other words, the predetermined number of times the steps of applying an additional powder layer and depositing a permeation control agent in predetermined patterns over the first such layer is equal to the number of cross- sectional slices into which the article has been rendered, minus one, the one that is subtracted accounting for the first layer. Thus, if the entire article consists of X number of layers, the number of times the steps of applying an additional powder and depositing a permeation control agent in predetermined patterns is equal to the number X-I.

However, for articles for which a significant amount of dimensional variation from particle rearrangement may be expected, it is preferred that the global consolidation be done in multiple multi-layer increments. The number of layers to be globally consolidated in each increment is preferably the maximum number that can be globally consolidated without producing a significant amount of dimensional distortion. Thus, the predetermined number of times the steps of applying an additional powder layer and depositing a control agent in a predetermined pattern over the first such layer before the untreated powder is permeated with a binding agent is preferably less than X-I for such articles. After the untreated powder has been permeated with the binding agent, a new layer of powder is applied over the globally consolidated powder and a permeation control agent is deposited in a predetermined pattern which corresponds to the spatially next cross-sectional slice of the article as a negative or an outline thereof. These steps of applying powder and depositing a permeation control agent

are continued for a predetermined number of times to form a new powder bed upon the original powder bed. A binding agent is then permeated through predetermined regions of the untreated powder of this new powder bed to globally consolidate that untreated powder. Additional cycles of applying powder layers, depositing a permeation control agent on these powder layers, and globally consolidating selected portions of the untreated powder in the powder beds formed by these powder layers may be conducted until the construction of the article is completed.

Once the entire article has been formed, whether through one or multiple cycles, it may be separated from the treated powder and used for its intended purpose or processed further, as desired.

It should be understood that where the preselected patterns in which the permeation control agent is deposited are those of the outlines of the cross-sectional slices of the article to be built, it is preferred that the binding agent be permeated through only those regions of untreated powder which are to form the article. This procedure conserves the binding agent and better enables the unpermeated portions of the untreated powder to be recycled.

The present invention has the advantage in various of its embodiments of being amenable for use with both coated and uncoated powders.

The present invention also has the advantage of providing wide latitude in the selection of the binding agent that is to be used to achieve global consolidation. Moreover, PCCC processes are able to utilize binding agents that are not easily employed by other solid free-form fabrication methods. For example, the present invention permits the use of binding agents which comprise fragile long chain molecules, e.g., red blood cells, as well as those which comprise elastic fluids which resist breaking up into droplets.

Another advantage provided by the present invention is that the partial consolidation it permits during multi-cycle building is particularly beneficial when powders with poor flowability are used.

Moreover, the global consolidation employed by the present invention, whether done for just a few layers at a time or for all layers of the article at once, allows powder particle reorientation to take place in a larger scale than is typical of other solid free-form fabrication processes. This presents an opportunity for the achievement of better dimensional accuracy in parts that are to be subsequently sintered than is achievable for such parts in which the layers of the part have bound together one at a time during the solid free-form fabrication process. This dimensional accuracy may be enhanced in some embodiments of the present invention by the use of powder reservoirs in the form of sprues to supply powder to the article as its powder is globally consolidated by the binding agent.

Brief Description of the Drawings The criticality of the features and merits of the present invention will be better understood by reference to the attached drawings. It is to be understood, however, that the drawings are designed for the purpose of illustration only and not as a definition of the limits of the present invention.

FIGS. IA through IH are schematic representations of cross-sections of a build chamber illustrating steps of the PCCC process for making a bell-shaped article according to an embodiment of the present invention.

FIG. IA shows the process as the first powder layer is about to be applied to the build platform.

FIG. IB shows the process as the permeation control agent is being deposited from a printhead into the first powder layer.

FIG. 1C shows the process after a powder bed comprising a preselected number of layers has been formed.

FIG. 1 D shows the build platform being lowered to create a space above the powder bed. FIG. IE shows the binding agent being applied to fill the space above the powder bed.

FIG. IF shows the binding agent as having permeated into the untreated powder.

FIG. IG shows the removal of a top layer of the powder bed to remove excess binding agent from the top surface of the powder bed after the global consolidation of the untreated powder has been completed. FlG. IH shows the process after additional layers have been applied over the globally consolidated powder to form a second powder bed.

FIG. 11 shows the process after the binding agent has been applied and permeated into the untreated powder of the second powder bed.

FIG. IJ shows the build platform being raised to remove the built article from the build chamber after the global consolidation of the untreated powder of the second powder bed has been completed.

FIG. 2 is a perspective drawing of the bell-shaped article of FIGS. 1A-1H, 3A-3C, 4A-4C, and 5.

FIGS. 3A through 3C are schematic drawings which illustrate examples of various terminology used herein.

FIG. 3 A is a perspective drawing of the cross-sectional slice which has as its top surface the cross-section taken along line 3A-3A in FIG. 2.

FIG. 3B illustrates what is meant by the permeation control agent being deposited in a pattern that is the negative, or complement, of the cross-sectional slice of FIG. 3 A.

FIG. 3C illustrates what is meant by the permeation control agent being deposited in a pattern that is the outline of the cross-sectional slice of FIG. 3 A.

FIGS. 4A through 4C are schematic representations of cross-sections of a build chamber illustrating steps of the PCCC process for making the bell-shaped article of FIG. 2 according to another embodiment of the present invention. In this embodiment, the permeation control agent has been deposited to form the outline of the article. Also, sprues have been provided for conducting the binding agent into the untreated powder and to act as a reservoir of untreated powder to accommodate settling that may occur during the global consolidation process. FIG. 4A shows the process at the completion of the building of the powder bed.

FIG. 4B shows the introduction of the binding agent into the untreated powder via the sprues.

FIG. 4C shows that the binding agent has permeated all of the untreated powder in the selected region. FIG. 5 is a schematic representation of the cross-section of a build chamber illustrating the binding agent infiltration step of the PCCC process for making the bell-shaped article of FIG. 2 according to another embodiment of the present invention.

Description of Preferred Embodiments In this section, some preferred embodiments of the present invention are described in detail sufficient for one skilled in the art to practice the present invention. It is to be understood, however, that the fact that a limited number of preferred embodiments are described herein does not in any way limit the scope of the present invention as set forth in the appended claims.

An embodiment of the PCCC process of the present invention is illustrated schematically in FIGS. IA through U for creating the bell-shaped article 2 shown in FIG. 2 from a powder material. FIG.1A shows the beginning of the PCCC process. A vertically indexable build platform 4 is shown contained within a build chamber 6. The build platform 4 is positioned a distance T from the top of the build chamber 6, the distance T corresponds to the thickness of one powder layer. A pile 8 of powder is about to be spread across the top surface of build platform 6 by counter-rotating roller 10.

Referring to FIG. IB, it is seen that the first powder layer 18 has been applied to the top surface of the build platform 4. The printhead 12 is shown in the process of depositing a permeation control agent 14 to a preselected region 16 of the first powder layer 18 in a pattern that corresponds to the negative of a first cross-sectional slice of the article 2, leaving the powder region 20 as untreated powder. Although the article 2 may be built in any desired orientation compatible with the dimensions of the build chamber 6, for illustration purposes, the article 2 is shown being built in an inverted position. Thus, this first cross-sectional slice corresponds to the topmost portion of the article 2. After the deposition of the permeation control agent 14 onto the first powder layer 18 has been completed, the build platform 4 is lowered the distance T, another layer of powder is applied over the first powder layer 18, and then the printhead 12 is operated to deposit the permeation control agent 14 onto the second powder layer in a pattern which corresponds to the negative of the second cross sectional slice of the article 2.

Additional powder layers are applied and permeation control agent is deposited thereto in patterns which correspond to the negatives of successive cross-sectional slices of the article 2 as the PCCC process continues. FIG. 1C shows the process after a number of layers have been so applied to form a powder bed 22, which has treated powder regions 16a, 16b and an untreated powder region 20.

Referring now to FIG. ID, it is seen there that the build platform 4 has been lowered a distance D to create a space S between the top surface of the powder bed 22 and the top of the build chamber 6. Space S is selected to have a volume that is at least equal to that of the cumulative interparticle void space of the region of untreated powder 20. Referring to FIG. IE, a binding agent 24 is provided from outlet 26 to fill the space S. The binding agent 24 is able to permeate into untreated powder region 20, but is not able to substantially permeate into treated powder regions 16a, 16b due to the presence therein of the permeation control agent 14. FIG. IF shows the powder bed 22 after the binding agent 24 has fully permeated the untreated powder region 20. The binding agent 24 binds together the untreated powder in powder region 20.

Referring now to FIG. IG, it is seen that the global consolidation of the untreated powder region 20 has been completed, as indicated by the hatching in powder region 20. If desired, the top surface of the powder bed 22 may be conditioned to remove any remaining trace of undesired binding agent, e.g., by removing the topmost layer or layers of the powder bed 22 in the manner shown in FIG. IG. In that drawing, the build platform 4 is shown to have been raised so as to bring the top of the powder bed 22 a distance T above the top of the build chamber 6. A doctor blade 27 is shown as being used to remove the portion of the powder bed 22 which extends above the top of the building chamber 6.

Those persons who are skilled in the arts of infiltration and solid free-form fabrication will recognize that the infiltration of binding agent 24 into the untreated powder in powder region 20 may be accomplished in ways other than that described above, and all such ways are within the scope of the present invention. For example, the infiltrant binding agent 24 may be introduced from the bottom and/or the sides of the powder bed 22 so that it wicks upwardly and/or inwardly into the untreated powder region 20 by capillary action or by vacuum- or pressure-assisted capillary action. The use of a removable build box in place of

build box 6 facilitates such alternate infiltration methods as the bottom of the removable build box may be brought into fluid communication with a reservoir of the infiltrant binding agent 24 or the removable build box may be submersed, at least in part, in such a reservoir. One or more sprues may be incorporated into the design of the article 2 that is being built so as to extend the untreated powder region 20 to contact the periphery of the removable build box and act as a conduit or conduits of the infiltrant binding agent 24 into the untreated powder region 20.

After the infiltration step has been completed, a preselected number of additional layers of powder are applied over the powder bed 22 and additional permeation control agent 14 is applied in patterns corresponding to the negatives of the successive cross-sectional slices of the article 2. In cases where a portion of the top of the powder bed 22 have been removed to eliminate undesired excess binding agent 24, the removed layer or layers of the article 2 are to be rebuilt. In the embodiment shown in FIG. IH, the preselected number of additional layers was chosen to be the number of remaining cross-sectional slices needed to complete the building of the article 2, including the rebuilding of the removed layers. These new layers form a second powder bed 28 atop the first powder bed 22. The demarcation line between these two powder beds is indicated by dashed line 30.

The infiltration steps described above are then performed to cause the binding agent 14 to permeate through the untreated powder region 32 of the second powder bed 28. FIG. 11 shows that after these steps have been completed, the untreated powder region 32 has been globally consolidated by binding agent 24, as indicated by the hatching in powder region 32. The build platform 4 is then indexed upward to permit the article 2 along with the rest of the powder bed 22 to be removed from the build chamber 6, as illustrated in FIG. U.

In some embodiments of the present invention, the permeation control agent is deposited to form the outline of the article, rather than its negative. The difference between the negative of an article and the outline of the article is illustrated in FIGS. 3A through 3C.

Referring to FIG. 3A, there is shown a depiction of a cross-sectional slice 40 of the article 2 which has as its top surface 42 the cross-section taken along line 3A-3A in FIG. 2.

The cross-sectional slice 40 has a slice thickness t. Those who are skilled in the art of solid free-form fabrication will recognize that the slice thickness t may be chosen to be the same or different for each of the slices into which the article 2 is divided.

FIG. 3B illustrates what is meant by the permeation control agent being deposited in the pattern of the negative of a cross-section of the article 2 with regard to the cross-sectional slice 40. A powder layer 44 is shown as being contained within the build chamber 6. The negative 44, or complement, of the cross-sectional slice 40 in powder layer 44 is shown as the shaded regions 46a, 46b, and it is in these regions that the permeation control agent is deposited to form the negative of the cross-sectional slice 40. FIG. 3C illustrates what is meant by the permeation control agent being deposited in the pattern of the outline of the cross-sectional slice of the article to be built. The outline of the cross-sectional slice 40 is depicted by lines 48a, 48b, and it is along these lines that the permeation control agent is deposited to form the outline of the cross-sectional slice 40. The thickness chosen for the lines 48a, 48b depends on such factors as the characteristics of the permeation control agent, of the binding agent that is to be used, and of the powder comprising layer 44 as well as the degree of definition desired for the article that is being made and the operating characteristics of the printhead which deposits the permeation control agent. The thickness also must also be sufficient so that there is sufficient overlap of the outlines of adjacent layers for the deposited permeation control agent to form a continuous

boundary between the untreated powder that is to comprise the article being built and the untreated powder that comprises the remainder of the powder bed.

Another embodiment of the PCCC process of the present invention will now be described, again with reference to the bell-shaped article 2 shown in FIG. 2. In this embodiment, the permeation control agent is deposited upon individual powder layers that are built upon the build platform 4 in patterns which correspond to the outline of the cross- sectional slices of the article 2. Another characteristic of this embodiment is that the binding agent is applied to form the entire article in one stage rather than in multiple stages as it was in the embodiment described with respect to FIGS. 1 A-IJ. FIGS. 4A through 4C schematically illustrate certain aspects of this embodiment.

FIG. 4A illustrates the point in time at which the application of the powder layers to form a powder bed 50 upon a build platform 4 within a build chamber 6 has been completed and the permeation control agent 14 has been deposited layer-by-layer in the outline 52 of the article 2. Note that the sprues 54a, 54b have been added to the design of the article 2. The sprues 54a, 54b connect the untreated powder region 56 that is in the shape of the article 2 to the top surface 58 of the powder bed 50. The sprues 54a, 54b have been formed by depositing the permeation control agent 14 along their outlines 60a, 60b.

FIG. 4B shows the introduction of the binding agent 62 to the untreated powder region 56 through the nozzles 64a, 64b. The nozzles 64a, 64b have been positioned so that they are in fluid communication with the untreated powder within the sprues 54a, 54b and in the region 56. However, they are not in fluid communication with the untreated powder in the rest of the powder bed 50. The binding agent 62 is shown being flowed through the nozzles 64a, 64b into the sprues 54a, 54b. The flow is continued until the untreated powder in region 56 has been fully permeated by the binding agent 62. The nozzles 64a, 64b are then moved away from the powder bed 50. FlG. 4C shows the point in time when this has been

completed. As depicted there, the untreated powder in region 56 has been fully permeated with the binding agent 62. Some binding agent 62 is also present within the sprues 54a, 54b.

However, the permeation control agent 14 which makes up the outline 52 of the article 2 and the outlines 60a, 60b of the sprues 54a, 54b has prevented the binding agent 62 from substantially permeating into the untreated powder in the remainder of the powder bed 50.

After the binding agent 62 has had sufficient time to globally consolidate the untreated powder in region 56 so that the article 2 possesses enough strength to be handled, the build platform 4 is indexed upward to permit the article 2 to be removed from the build chamber 6.

Note that in FIG. 4C the level of the powder in the sprues 54a, 54b is depicted as having fallen below the level of the top surface 58 of the powder bed 50 as the binding agent fully permeated the untreated powder region 56. This is because, in addition to acting as conduits for the binding agent 62, the sprues 54a, 54b act as reservoirs from which powder may flow downward into region 56 to accommodate settling that may occur due to particle rearrangement as the binding agent 62 consolidates the powder in region 56. The present invention also contemplates that in some embodiments it is beneficial to apply vibrations to the powder bed assist in powder settling during the global consolidation process. Such vibrations may be applied before, during, and/or after the introduction of the binding agent. In such embodiments, it is important to configure the powder bed so that any settling that might occur within it does not eliminate any necessary support that the powder bed provides to the powder that is to form the article or articles that are being built. However, in embodiments of the present invention in which the permeation control agent unifies the portions of the powder bed that do not comprise the powder that is to become the article or articles such that no settling occurs in those portions during the use of vibration, the need for such configuration is obviated.

It is also to be noted that the sprues 54a, 54b are useful for accommodating erosion effects that may attend the inflow of the binding agent 62 at the surface of the powder bed 50.

The present invention also includes embodiments which facilitate the infiltration of the binding agent by providing one or more exit passages for the binding agent to exit the region or regions of untreated powder that is to become the article or articles. Such exit passages extend from the region or regions of the untreated powder that is to become the article or articles and through the treated powder to an outer surface of the powder bed or to a region of untreated powder that is in fluid communication with an outer surface of the powder bed. The powder bed outer surface is at the end of such exit passages, in turn, in fluid communication with a portion of the build chamber and/or build box that is permeable to the binding agent. Such exit passages are useful in cases where the binding agent is a transient activating gas that is to pass through the untreated powder region or regions that are to become the article or articles. They are also useful in cases where the binding agent is a liquid, as they allow excess binding agent to exit the untreated powder region or regions that are to become article or articles, thus permitting wider latitude in controlling the amount of binding agent that is metered into such region or regions during the permeation step or steps. Such exit passages are also useful in providing an escape for the air or other gas that is being displaced from the interparticle interstices of the powder bed by the introduction of the binding agent into the region or regions of untreated powder that are to become the article or articles.

FIG. 5 illustrates an embodiment of the present invention that utilizes exit passages. FIG. 5 shows the same article 2 in the same stage of processing as is shown in FIG. 4B, but with some important differences. As in FIG. 4B, the binding agent 62 is introduced into the untreated powder region 56 through the nozzles 64a, 64b. These nozzles have been positioned so that they are in fluid communication with the untreated powder within the

sprues 54a, 54b and within the region 56 and so that they are not in fluid communication with the untreated powder within the rest of the powder bed 50. Again, the binding agent 62 is shown being flowed through the nozzles 64a, 64b into the sprues 54a, 54b and into the untreated powder in region 56. What is different is the following. First, the exit passages 70a, 70b have been added to the design of the article 2. These exit passages 70a, 70b extend to the bottom surface of the powder bed 50. Second, the powder bed 50 is contained within a removable build box 72. The build box 72 consists of a cylinder 74 and a bottom plate 76. The cylinder 74 lines the interior of the build chamber 6. The cylinder 74 has a lower lip 78 for supporting the bottom plate 76. During the article- building operation, however, the bottom plate 76 is supported by the vertically indexable piston 80 and slides along the interior wall of cylinder 74 as the piston 80 is indexed downward. By the conclusion of the article-building operation, the piston 80 has lowered the bottom plate 76 to rest upon the lower lip 78. This permits the build box 72 and the powder bed 50 that is contained within it to be removed from the build chamber 50 as a single unit. The bottom plate 76 is designed to retain the powder on its top surface while being permeable to the binding agent 62, at least in the regions which are contacted by the exit passages 70a, 70b.

The third difference is that a reservoir pan 82 resides in the lower portion of build chamber 6. The reservoir pan 82 has a center hole 84 to accommodate the through passage of the shaft 86 of piston 80. An o-ring seal 88 is located in the wall of the reservoir pan 82 which defines the center hole 84 and sealingly contacts the shaft 86. The reservoir pan 82 also seals against the bottom surface of the lower Hp 78 of the build box 72 with seal 90.

Continuing to refer to FIG. 5, during the infiltration of the untreated powder in the region 56, the binding agent 62 permeates downwardly through the untreated powder of region 56. Excess binding agent 62 is able to flow through the exit passages 70a, 70b and the

bottom plate 76 into the reservoir pan 82. The reservoir pan 82 may be equipped with a sensor (not shown) to detect the presence or the level of the binding agent 62 therein and the detection may be used to as a signal for terminating the flow of the binding agent 62 into the nozzles 64a, 64b. After the flow has been terminated, the build box 72 may be removed from the build chamber 6 and placed upon a surface which is impermeable to the binding agent 62 to retain the binding agent 62 within the region 56.

Note that the seal 90 in this embodiment prevents the binding agent 62 from overflowing from the reservoir pan 82 and flowing down the sidewall of the build chamber 6. However, such a seal is unnecessary where such overflow is of no significant consequence or sensors are used that prevent the overflow from occurring. Furthermore, as mentioned above, exit passages may be employed to provide an escape route for the air or other gas that is being displaced from the interparticle interstices of the powder by the introduction of the binding agent into the region of the untreated powder that is to become the article or articles. In such cases, the absence of a seal, or even of a reservoir pan, may be beneficial where the escape of such displaced gases is an objective. Moreover, in some preferred embodiments of the present invention, the permeation control agent is selected so such displaced gases can escape through the treated powder portion of the powder bed.

Although the embodiments of the present invention described with regard to FIGS. 1A-1H, FIGS. 4A-4C, and FIG. 5 utilize a printhead to deposit patterns of a permeation control agent into the individual powder layers, the present invention also embraces all other ways known in the art that are suitable for making such depositions. The suitability of a particular deposition method will depend on factors such as the geometrical dimensions and shapes of the involved patterns, the physical characteristics of the permeation control agent, especially its viscosity, surface tension, and volatility, and the physical characteristics of the powder, especially its susceptibility to disturbance by flowing fluids and its chemical

stability. For example, in some embodiments of the present invention, the step of creating a three dimensional negative of the article includes the use of a mask or masks for creating a two dimensional negative on at least one powder layer. In these embodiments, a mask or masks, whose combined masking area corresponds in shape to the cross-section of the relevant cross-sectional slice of the article, is placed over the powder layer. While the mask is in place, a permeation control agent may be applied across the entire exposed portion of the powder layer, e.g., as a spray, to create the negative. Similarly, masks may be used in some embodiments of the present invention to deposit the permeation control agent in the outline of the article or articles that are to be built. The PCCC process of the present invention may be used with any type of powder that is amenable to being applied in layers and for which there is a suitable combination of a permeation control agent and binding agent. Thus, metallic, ceramic, polymeric, biomimetic, and organic powders may be used in practicing embodiments of the present invention.

The choice of the permeation control agent or agents to be used in practicing the PCCC process of the present invention depends on the binding agent or agents and on the powder or powders that are to be used, as there must be compatibility among all of these. A permeation control agent is selected so as to prevent substantial ingress of the binding agent into and/or through the portions of the powder bed that have been treated with the permeation control agent. In some cases, the permeation control agent completely prevents such ingress, while in others it reduces the rate of ingress to a level that is substantially slower than it is in the untreated powder portion of the bed. In either case, the permeation control agent sufficiently controls ingress of the binding agent into treated powder to permit the article or articles to be globally consolidated by the binding agent with the desired degree of shape and feature definition.

In some cases the permeation control agent controls permeation of the binding agent into and/or through the treated powder by acting as a physical barrier to the flow of the binding agent, e.g. by substantially filling the interparticulate porosity of the treated powder. Examples of permeation control agents that control in this fashion are waxes and polymers. In other cases the permeation control agent controls the permeation of the binding agent into and/or through the treated powder by acting as an anti-wetting agent that greatly reduces or eliminates the ability of the binding agent to wet the treated powder. Examples of permeation control agents that act in this fashion are surfactants that eliminate the wetability of powder to aqueous-based binding agents. The effect of the permeation control agent on the flowability of the treated powder may be taken into consideration in choosing the permeation control agent. Some permeation control agents may have little or no effect on the flowability of the treated powder. Such permeation control agents make it very simple to remove the built article from the powder bed. Other permeation control agents may act to unify the treated powder into a single mass. Such permeation control agents are useful when long times or additional processing is needed for the binding agent to cure as they facilitate the powder bed removal from the build chamber and allow it to be handled as a unit, even without the use of a removeable build box. Of course, where a removable build box is used, this concern is of reduced or no importance. Ancillary processes, such as, for example, exposure to a solvent or a heat treatment, may be used to remove such permeation control agents so as release the built article or articles from the treated powder mass. Machining methods may also be employed to remove the article or articles from the rest of the powder bed.

The present invention provides wide latitude in the selection of the binding agent that is to be used to achieve global consolidation. The binding agent should be selected to be compatible with the powder that is to comprise the article, the permeation control agent that

is to be used, and whatever use or further processing is desired for the globally consolidated article. The binding agent may be a liquid, a gas, or some other flowable substance, so long as it is able to permeate through the untreated powder and produce the desired degree of global consolidation. The binding agent may be chosen to be one that either: (1) permanently remains in the article; (2) is removed in subsequent processing; or (3) does not remain in the article at all, but only facilitates powder bonding. An example of the first type is an elastomeric binder or a molten metal that is subsequently solidified. An example of the second type is a polymeric binder that is volatized during a subsequent heat treatment to sinter the article. An example of the third type is a gas that reacts with a polymeric coating on the powder to cause the powder to become bound together.

In some embodiments of the present invention, the binding agent may be a body fluid, e.g., blood, or a slurried cellular material, e.g., ground bone matter in a saline solution, or a biomimetic fluid. The binding agent may include one or more compatible polymer adhesives. Examples of such biocompatible polymer adhesives include, without limitation: (a) surgical adhesives which comprise (i) a NCO-terminated hydrophilic urethane prepolymer derived from a fluorine-containing polyisocyanate and a hydrophilic polyether polyol of higher oxyethylene content, or a combination of (i) with (ii) an unsaturated cyano compound containing a cyano group directly bonded to a polymerizable double bond; (b) surgical adhesives, which contain NCO-terminated (i.e., containing terminal NCO groups) hydrophilic urethane prepolymers derived from organic polyisocyanates, such as tolylene diisocyanates (TDI) and diphenylmethane diisocyanates (MDI), and hydrophilic polyether polyols of higher oxyethylene content, or combinations thereof with unsaturated cyano compounds containing a cyano group directly bonded to a polymerizable double bond; (c) polymethyldisiloxane; and (d) biodegradable polymer gels. The biocompatible adhesives of group (a) are preferred, especially those which comprise a mixture of isocyanate capped

molecules having an average isocyanate functionality of at least 2.1 and which are formed by reacting biocompatible multi-cyanate functional molecules with biocompatible multifunctional precursor molecules including terminal functional groups selected from the group consisting of a hydroxyl group, a primary amino group, and a secondary amino group. Note that the biocompatible adhesives of group (b) in which aromatic polyisocyanates, such as tolylene diisocyanates and diphenylmethane diisocyanates are used as the starting materials are less desirable for use in the present invention because they possess a high activity in a microbial mutagenicity test (Ames test). Similarly, biocompatible adhesives of group (b) are also less desirable in which heavy metal compounds and amines are used as catalysts for aliphatic or cycloaliphatic polyisocyanates because they may pose some toxicity problems. The binding agent may also comprise natural cell substrate materials, e.g., hydroxyapatite, and biocompatible materials, e.g., polymethylmetacrylate, especially in conjunction with a biocompatible polymer adhesive.

The biodegradable polymer gels of group (d) include thermogelling, biodegradable polymers. Examples of such thermogelling biodegradable polymers are those which contain a polyethylene glycol (PEG) block linked to a biodegradable polyester block. The polymer may have a general formula of A _n (B), where n is greater than 2, A is selected from a polyethylene glycol block and a biodegradable polyester block, B is selected from the group consisting of a polyethylene glycol block and a biodegradable polyester block, and A is different from B, and an aqueous solution. The biodegradable polyester block is preferably poly(DL-lactic acid), poly(L-lactic acid), poly(glycolic acid), poly([epsi]-caprolactone), poly(gamma-butyrolactone), poly(alpha-valerolactone), poly(beta-hydroxybutyric acid), and their copolymers or terpolymers. The copolymers and/or terpolymers may also be selected from poly(DL-lactic acid-co-glycolic acid), poly(L-lactic acid-co-glycolic acid), poly([epsi]- caprolactone-co-DL-lactic acid), and copoly([epsi]-caprolactone-co-DL-lactic acid-glycolic

acid). The biodegradable polyester blocks may have a maximum molecular weight of about 100,000, in some embodiments from about 1 ,000 to about 30,000, and in some embodiments, from about 1,000 to about 10,000. The polyethylene glycol (PEG) block may have an average molecular weight of from about 300 to about 20,000, and in some embodiments, from about 500 to about 10,000. Other exemplary thermogelling polymers are poly[N- isopropylacrylamide-co-2-(N,N-dimethylamino)-ethyl acrylate] copolymers,

The biodegradable polymer gels of group (d) also include crosslinked hydrogels. Any of a variety of known crosslinking techniques may be utilized, such as chemical crosslinking, irradiation crosslinking (e.g., electron beam), and so forth. In most embodiments, chemical crosslinking using a crosslinking agent is particularly desired. Some examples of suitable crosslinkable hydrogel polymers are believed to include, but are not limited to, hyaluronic acid, alginic acid, carrageenan, chondroitin sulfate, dextran sulfate, pectin, chitosan, polylysine, collagen, alginate, carboxyethyl chitin, fibrin, poly(ethylene glycol-lactic acid- ethylene glycol), poly(lactic acid-ethylene glycol-lactic acid), poly(lactic glycolic acid- ethylene glycol-lactic glycolic acid, poly(hydroxy butyrate), poly(propylene fumarate-co- ethylene glycol), poly(ethylene glycol-butylene oxide-terephtalate), poly(methylrnethacrylate-co-hyroxyethylmethacrylate, poly(ethylene glycol-bis-(lactic acid- acrylate), poly(ethylene glycol-g-(acrylamide-co-vamine)), polyethylene glycol+/- cyclodextrins, polyacrylamide, poly(N-isopropyl acrylamide-co-acetic acid), poly(N- isopropyl acrylamide-co-ethylmethacrylate), poly(vinylacetate/vinylalcohol), poly(N-vinyl pyrrolidone), poly(biscarboxy-phenoxy-phospazene), poly(acrylonitrile-co-allyl sulfonate), poly(ethylene glycol dimethacrylate-sulfate), poly(ethylene glycol-co-peptides), alginate-g- poly(ethylene oxide-propylene oxide-ethylene oxide), chitosan-g-poly(ethylene oxide- propylene oxide-ethylene oxide), poly(lactic glycolic acid-c-serine), poly(hydoxypropylacrylamide-g-peptide), poly(hydroxyethylmethacrylate/Matrigel),

hyaluronic acid-g-N-isopropyl polyacrylamide, collagen-acrylate, and alginate-acrylate. Crosslinking agents for polymers, such as described above, may include, but are not limited to, magnesium chloride, calcium chloride, cationic polymers, anionic polymers, buffering salts, glutaraldehyde, ethylene glycol dimethacrylate, diisocyanate, and so forth. It is to be understood that the multiple cycle embodiments of the present invention permit the use of different powders, different permeation control agents, and different binding agents in each build-global consolidation cycle.

The PCCC process of the present invention may be used to make articles of any kind as prototypes, production parts, or objects d'art. The PCCC process is particularly useful for making parts that cannot be practically made by other solid free-form fabrication processes, such as cell scaffolds that use a patient's own cells as part of the binding agent of the scaffold.

Examples The following four prophetic examples illustrate some of the many ways in which the present invention may be carried out. Examples 1-3 demonstrate how the same article, i.e., a bone implant made from hydroxyapatite powder, can be made by three different variations of the present invention. Example 4 shows how another variation of the present invention may be used to make a much different article, i.e., a metal ring gear.

Example 1

In this example a powder comprising a mixture of hydroxyapatite powder and polymethyl methacrylate is used to make a small bone implant. The permeation control agent is selected to be an alginate dissolved in an aqueous sodium hydroxide solution. The binding agent is selected to be acetone vapor.

A device that is similar to a conventional three-dimensional printing solid free-form fabrication device is used to create a powder bed comprising layers of the powder imprinted with the patterns of the permeation control agent which correspond to the negatives of consecutive cross-sectional slices of the bone implant. For each layer, the pattern is formed by using the printhead to deposit the permeation control agent at a level that saturates the printed areas with the permeation control agent and radiant heat is applied to dry the deposited permeation control agent. As the permeation control agent dries, it forms a gel structure that congeals the treated powder together into a single mass.

After the entire negative of the bone implant has been built, the operation is continued to create a plurality of sprues that provide fluid communication from the surface of the powder bed to the untreated powder that is to become the bone implant.

The powder bed is then removed from the build chamber and a nozzle is placed above one or more of the sprues. The powder bed is gently vibrated to settle the untreated powder and to assist powder flow from the sprues to fill in the voids caused by the powder settling. The acetone vapor binding agent is flowed from the nozzle and through the sprues and the untreated powder regions and exits by way of another sprue or sprues. As it permeates through the untreated powder, the acetone vapor dissolves the polymethyl methacrylate to form a solution that coats the hydroxyapatite powder particles. The powder bed is then gently heated to evaporate the acetone. As the acetone evaporates from the solution, the polymethyl methacrylate is left behind as a coating that binds together the hydroxyapatite particles into the bone implant. The powder bed is then submerged in an aqueous sodium hydroxide solution to dissolve the gel so as to free the completed bone implant.

Example 2

In this example, again the powder is hydroxyapatite and the article to be built is a small bone implant. The permeation control agent is an aqueous solution of lauryl dimethylamine oxide, which is a surfactant that makes the surface of hydroxyapatite unwettable by water. The binding agent is an aqueous solution of polyvinyl alcohol.

The negative of the article is built in the manner described in Example 1. Because the permeation control agent in this example does not unify the treated powder, a removeable build box is used to enhance the utilization rate of the three-dimensional printing solid free- form fabrication device. The removeable build box containing the powder bed is removed from the build chamber after the article is built and prior to the addition of the binding agent to the untreated powder.

Nozzles are placed above the sprues and the binding agent is flowed through the nozzles and into the untreated powder regions via the sprues. The powder bed is gently heated to evaporate the aqueous portion of the binding agent, leaving behind the polyvinyl alcohol to bind together the hydroxyapatite particles to become the bone implant. The completed implant is then removed from the powder bed by pouring away the loose treated powder.

Example 3 In this example, again the powder is hydroxyapatite and the article to be built is a small bone implant. The permeation control agent is paraffin wax. The binding agent is an aqueous solution of polyvinyl alcohol.

The process described in Example 2 is used. However, because the wax permeation control agent unifies the treated powder into a single mass, the powder bed is able to be removed from the build chamber without the use of a removable build box. After the bone

implant has been consolidated, the powder bed is heated to melt the wax, thus releasing the bone implant for removal.

Example 4 In this example, the powder is grade 304 stainless steel that has been coated with sodium chloride to polarize its surface. The permeation control agent is an aqueous solution of lauryl dimethylamine oxide. The binding agent is an aqueous solution of polyvinyl alcohol. The article to be built is a small ring gear.

The process described in Example 2 is used at the conclusion of which the completed ring gear is removed from the powder bed by pouring away the loose treated powder.

While only a few embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that many changes and modifications may be made thereunto without departing from the spirit and scope of the present invention as described in the following claims. All United States Patents, United States Patent Applications, United States Patent Publications, and Patent Cooperation Treaty Published Patent Applications identified herein are incorporated herein by reference in their entireties.

Some of the following claims identify elements by using the phrase "the of step (_)" _> wherein the first blank contains the name of an element identified in the step identified by the letter which fills in the second blank. These phrases are to be interpreted as referring to the element that is identified in the specified step. Thus, for example, the phrase "the pattern of step (b)" is to be interpreted as referring to the pattern identified in step (b) and the phrase "the region of step (f)" is to be interpreted as referring to the region that is identified in step