Three-dimensional printing excess deposited particulate handling

A three-dimensional printing apparatus is disclosed has one or more troughs for receiving excess deposited particulate. Such troughs may be positioned to receive the excess deposited particulate into a particulate receiving chamber of the trough. An evacuation chamber is located at the bottom of each trough. A partition separates the evacuation chamber from the receiving chamber of the trough. The partition is selectively perforated to permit a desired amount of the particulate to flow into the evacuation chamber from the receiving chamber. The evacuation chamber is connected to a vacuum source to periodically or continuously draw ambient gas from a gas inlet to the evacuation chamber and/or from the receiving chamber through the perforations of the partition and then through the evacuation chamber toward the vacuum source to entrain an amount of the particulate and carry the entrained particulate out of the evacuation chamber.

FIELD OF THE INVENTION

The present invention relates to apparatuses for handling excess deposited build particulate from the spreading of particulate layers in three-dimension printers. The present invention also relates to methods of handling such excess deposited particulate.

BACKGROUND OF THE INVENTION

Conventional three dimensional printing processes take various forms. Nearly all involve the slicing of a software representation of a three-dimensional article into software representations of two-dimensional slices of the article and then building the article in three-dimensions by sequentially transforming such two-dimensional representations into physical layers built one upon another. Several three-dimensional printing processes make use of particulates (also sometimes referred to in the art as “powder” or “particles”) for building the article in three dimensions. Among these processes are the binder jetting process (also known as the inkjet printing process), selective layer sintering process, selective laser melting process, direct metal laser sintering process, electron beam melting process, and the selective heat sintering process.

In the three-dimension printing processes that use particulates, a first layer of the particulates is deposited onto the top surface of a build platform. This deposition is sometimes referred to in the art as “spreading” a particulate layer. An image of the two-dimensional representation of the first slice of the article may then be imparted to this first particulate layer or the first particulate layer may be covered over with one or more additional particulate layers before the image of the first slice of the article is imparted to the then-topmost particulate layer. After that, the sequence of applying a particulate layer and imparting the image of the two-dimensional representation of a subsequent slice of the article is performed until the three-dimensional article is formed. The top surface of the bare build platform or of the then-topmost particulate layer is referred to herein as the “build surface”. Often, more than one article or multiple copies of the same article are produced at the same time by simultaneously imparting the respective two-dimensional slices of the articles onto the build surface particulate layers. At the end of the particulate layer-placing plus image-imparting iterative sequence, particulate-based versions of the article or articles are surrounded by a bed of the unbonded particulates. This bed is sometimes referred to as a “build bed” or as a “powder bed” or as a “particulate bed”.

The particulate processes commonly use a support platform which is designed to be step-wise lowered into a walled cavity. At the start of the process, the support platform is positioned so that the support surface is flush with the top of the cavity walls. After each particulate layer-placing plus image-imparting iteration, the support platform is indexed down into the cavity so that the then-topmost particulate layer is flush with the cavity walls so that the next particulate layer can be deposited.

Various techniques have been devised for depositing the particulate layers, but a common problem occurs with particulate layer deposition that is due to the nature of particulate flow in normal-level gravity fields. Unlike layers of continuous solid materials, e.g. sheets of metal, plastic, or paper, the particulate layers do not terminate in sharply-defined vertical walls, but rather in somewhat irregular edges with generally downwardly-outward sloping walls, the contours of which roughly relate to the angle of repose of the particulates and depend on various material and dynamic factors, e. g. the inter-particle attractive/repulsive forces of the particulates, the velocity vectors active on the particulates during layer deposition, the presence of additives, coatings, or absorbed or adsorbed chemical species on the particulates, environmental forces such as vibrations, etc. Usually, in order to assure that the build surface always has the same predictable dimensions of the initial support surface, an excess amount of particulates is deposited for each layer. However, unless some provision is made for removing the excess deposited particulates, it is likely that the accumulation of the excess deposited particulates after the deposition of one or more layers will interfere with the desired deposition of additional layers.

A common way of handling the excess deposited particulate problem is to provide one or more receiving troughs into which the excess deposited particulate can fall or be pushed. However, sizing the receiving troughs can be problematic. Making the troughs too large requires making the overall size of the three-dimensional printing apparatus larger than it needs to be. Making the troughs too small may result in the troughs becoming ineffective upon overfilling or require the use of reservoirs which take in the particulates directly or indirectly from the trough or troughs. Also, adding to the problem is the fact that the effective bulk density of the particulate as deposited can change from one type of particulate to another and even from batch-to-batch for the same type of particulate. Furthermore, in order to prevent cross-contamination, the troughs and associated reservoirs must be thoroughly cleaned before the three dimensional printing apparatus can be utilized with another type of particulate.

SUMMARY OF THE INVENTION

The present invention addresses the above-stated sizing problem by providing a three-dimensional printing apparatus which has one or more troughs for receiving the excess deposited particulate. Preferably such troughs are positioned parallel or perpendicular to the particulate deposition direction to receive the excess deposited particulate into a particulate receiving chamber of the trough. An evacuation chamber is located at the bottom of each trough. A partition separates the evacuation chamber from the receiving chamber of the trough. The partition is selectively perforated to permit a desired amount of the particulate to flow into the evacuation chamber from the receiving chamber. The evacuation chamber is connected to a vacuum source to periodically or continuously draw ambient gas (usually air) from a gas inlet to the evacuation chamber and/or from the receiving chamber through the perforations of the partition and then through the evacuation chamber toward the vacuum source so as to entrain a desired amount of the particulate and carry the entrained particulate out of the evacuation chamber where it may be collected in a collection vessel or otherwise disposed of.

Some preferred embodiments of the present invention also address the above-stated cleaning problem. In these embodiments, the inventive apparatus includes a build box having one or more troughs of the character described in the previous paragraph. The build box is designed to be removable from the three-dimensional printer apparatus. The build box includes walls configured to confine the particulate bed from lateral flow and a build platform which is adapted to be raised or lowered.

The present invention also includes methods of removing excess deposited particulate by capturing the particulate in a trough which has a receiving chamber and an evacuation chamber separated by a selectively perforated partition, and connecting the evacuation chamber to a vacuum source so that ambient gas is drawn from the receiving chamber through the perforations of the partition and the gas entrains a desired amount of the particulate and carries the entrained particulate out of the evacuation chamber.

In some preferred embodiments of the present invention, the perforations in the partition are adapted to be selectively opened and closed, thus providing the user with the ability to adjust the gas flow path through the partition through selected perforations.

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 without undue experimentation. 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 claims. It is to be understood that whenever a range of values is described herein or in the claims that the range includes the end points and every point therebetween as if each and every such point had been expressly described. Unless otherwise stated, the word “about” as used herein and in the claims is to be construed as meaning the normal measuring and/or fabrication limitations related to the value which the word “about” modifies. Unless expressly stated otherwise, the term “embodiment” is used herein to mean an embodiment of the present invention.

Prior to describing preferred embodiments,FIGS. 1A-1DandFIG. 2are presented to provide a better understanding of the excess deposited particulate problem. It should be understood that the particulates may range in nominal size from about a micron to about a millimeter in effective diameter and usually consist of a range of sizes, the smallest of which may be submicron in effective diameter.

FIG. 1Ashows a schematic top planar view of a work table surface2of a three-dimensional printer that uses a particulate build material. The work table2here forms a curtilage around a build platform4that is configured to be step-wise lowered into a build cavity (not shown). Also shown in the drawing is a particulate dispenser6which is adapted to move above and across the work table surface2and the build platform4in the direction of arrow8(seeFIG. 1B), i.e., the particulate layer “deposition direction” or “spread direction”, and to selectively deposit a predetermined amount of particulate as it moves along. The work table surface2is shown prior to the deposition of a first particulate layer and does not have troughs for receiving excess deposited particulate material.

FIG. 1Bshows the scene ofFIG. 1Awhen the particulate dispenser6is partway in its journey and has partially deposited a first particulate layer10(indicated by hashing).FIG. 1Cshows the scene after the particulate dispenser6has completed depositing the first particulate layer10. Note that first particulate layer10covers the build platform4and extends onto portions of the work table surface2immediately surrounding the build platform4. The excess deposited particulate12(indicated by double hashing) beyond the particulate needed to just cover the build platform4(indicated by single hashing) serves no purpose other than to assure that the first particulate layer10fully covers the build platform4.

FIG. 1Dshows the scene after the image14of the first slice of the article that is being built has been imparted to the first particulate layer10and the build platform4has been indexed downward a distance equal to a layer thickness and the particulate dispenser6has been moved back into position to deposit the second particulate layer. Unless an operation has been conducted to remove the excess deposited particulate12—and none has been removed in the scene shown inFIG. 1D—the excess deposited particulate12remains on the surface of the work table2and may interfere with the deposition of a second particulate layer and the movement of the particulate dispenser6as it deposits the second particulate layer.

Various schemes have been developed to handle the excess deposited particulate. Such schemes typically involve using some sort of a trough and/or reservoir that is part of the three-dimensional printer apparatus to collect the excess deposited particulate. The reservoir or reservoirs may be fed by troughs in the curtilage area or directly receive the excess deposited particulate. The excess deposited particulate may fall into a trough or reservoir directly or be mechanically pushed into a trough or reservoir, e.g. by the particulate dispenser or blades attached to the particulate dispenser.

FIG. 2shows a schematic top planar view of the work table surface2which has been modified to include troughs16a-16dsurrounding the build platform4. The inner walls of the troughs16a-16d, e.g. inner wall18, separate the interiors of the troughs16A-16D from the build platform4. The troughs16a-16dare sized to receive the excess deposited particulate described above with regard toFIGS. 1C and 1D. The troughs16a-16dmay be sized to contain all of the excess deposited particulate that is expected to be deposited during the building of an article. Alternatively, one or more of the bottoms of the troughs16a-16dslope toward an exit, e.g. exit20of the trough16d, to convey the excess deposited particulate to one or more collection reservoirs (not shown).

Descriptions of preferred embodiments will now be presented.FIG. 3is a schematic, perspective, cross-sectional view of a trough30in accordance with the present invention. The trough30has four vertical walls, e.g. vertical wall32, a bottom wall34, and a top opening36. The trough30also has a perforated partition38which contains a plurality of through-holes, e.g. hole40. The partition38divides the space within the trough30into a particulate receiving chamber42and an evacuation chamber44. An optional gas inlet46is located at one end of the evacuation chamber44and a gas outlet48is located at the opposite end of the evacuation chamber44. A nipple50is connected to the gas outlet48and is adapted to be attached to a vacuum source (not shown). The gas inlet46is preferably provided with some form of a particulate outflow restrictor52which controls the amount of particulate which can flow out of the evacuation chamber44through the gas inlet46. The particulate outflow restrictor52shown is in the form of hollow box having one side in communication with the gas inlet46and its top side open so as to permit inflow of the ambient atmosphere. The streamline arrows54show the direction of gas flow when the evacuation chamber44is operatively connected to the vacuum source. As indicated by the streamline arrows54, the pressure differential imposed by the vacuum source causes ambient gas (e.g. air) to flow into the evacuation chamber44through the open top side of the particulate outflow restrictor52and then the gas inlet46and in through the holes in the partition38and exit the evacuation chamber44through the nipple50. Particulates which are in the evacuation chamber44or about to enter the evacuation chamber44through the holes in the partition38may be entrained in the gas flow and exit the evacuation chamber44through nipple50to be carried off to a collection device, e.g. a cyclone or a screen separator, or otherwise disposed of.

The partition38is shown inFIG. 3as being flat and horizontally disposed within the space of the trough30. However, other configurations and dispositions of a trough's partition are within the scope of the present invention. For example, the partition may be disposed at any desired acute angle from the horizontal.FIGS. 4-6 and 11-12give examples of some of the various configurations the partitions of the present invention can take.

Referring toFIG. 4, there is shown a schematic perspective view of a partition60. The top surface62of partition60is concave across its width. This shape encourages the flow of particulate down into each of the holes64located along the length of the partition60.

FIG. 5shows a schematic longitudinal mid-plane cross-sectional view of another partition70disposed within a trough72. The profile of the partition70has a semi-parabolic slope from its first end74to its second end76. When the partition's70first end74is placed adjacent to the gas inlet end78of the evacuation chamber80, this profile shapes the evacuation chamber80to enhance the acceleration of gas flow and the sweeping away of particulates through the evacuation chamber80as indicated by the streamline arrows82.

FIG. 6shows a schematic longitudinal mid-plane cross-sectional view of another partition90. The partition90slopes from its first and second ends92,94down toward its middle to encourage particulate flow toward the middle of the partition90.

FIG. 11shows a schematic perspective view of another partition150. The partition150has a flat bottom wall152, two sidewalls154,156, and an optional horizontal stiffener158. The bottom section152has a plurality of perforations, e.g. perforation160. Each of the sidewalls154,156extends upward from the bottom wall152at a preselected included angle. Preferably the included angle is in the range of from about 5 to 90 degrees. Each of the sidewalls is shown as having an optional extension, e.g., sidewall extension162of sidewall154, which is adapted to be parallel to the trough vertical wall in which the trough is used (e.g. vertical wall32of trough30inFIG. 3). When used, a sidewall extension allows the sidewall to better seal against the sides of the trough with which the partition is used. The horizontal stiffener158is attached to the bottom152and the perforations extend through the horizontal stiffener158. When used, a horizontal stabilizer preferably extends horizontally to engage the vertical wall of the trough into which the partition used so as to help position the partition within the trough in which the partition is used.

In some embodiments, one or more of the perforations of one or more of the partitions are adapted to be selectively opened or closed, thus providing the user with the ability to adjust the gas flow path through the partition through selected perforations. Selectively closing selected partition perforations has the effect of controlling the amount particulate flow through the partition.

Selectively closing a perforation may be done by securing a plug into the selected perforation and opening a closed perforation is done by removing a plug from the perforation. The plug may be secured by any conventional securing strategy, e.g. by threading the plug and the perforation, by compressing the plug within the perforation, etc.FIG. 12, which is a cross-sectional view of partition150ofFIG. 11taken along cutting plane12-12, shows an example of a perforation164which is adapted to receive plug166. The perforation164has threads168which are sized to cooperate with the threads of the plug166to reversibly secure plug166(also shown in cross-section) within the perforation164(as indicated by arrow) to close off the perforation164.

Selectively closing groups of two or more adjacent perforations may be done by attaching a strip to the partition so that the strip covers the selected group of perforations. Preferably, the strip is removably secured to the partition by way of one or more plugs that securingly engage one or more perforations.FIG. 13shows a schematic perspective view of a strip170that is designed to be used in conjunction with the partition shown inFIGS. 11 and 12. The strip170has two through-holes172,174which are sized to receive screws (not shown) which extend through through-holes172,174and thread into threaded perforations (e.g. perforation164shown inFIG. 11) of partition150to secure the strip170to the partition150. The strip170is long enough to close five perforations of the partition150including the two perforations which are closed off by the screws which secure the strip170to the partition150.

The placement of a trough's partition within the trough's interior space determines both the relative and absolute sizes of the trough's particulate receiving chamber and evacuation chamber. The placement is selected to balance the expected rate of influx of particulate material into the particulate receiving chamber with the expected rate of particulate removal from the evacuation chamber so that the receiving chamber is not allowed to overflow during the three-dimensional printing operation. The rate of influx of particulate into the particulate receiving chamber is dependent on the amount and deposition rates of the excess deposition particulate. The rate of removal of particulate from the evacuation chamber depends, among other things, on the gas flow rate through the evacuation chamber, the particulates' propensity to become entrained in the gas flow, and the amount of time the gas flow is continuously or periodically sustained. Although it is within the scope of the present invention to have the inter-chamber transfer rate of particulates equal that of the particulate receiving chamber's influx rate, it is also within that scope for the transfer rate to be less than that influx rate, so long as this does not result in the overflow of the particulate receiving chamber during the three-dimensional printing operation.

It is to be understood that while it is preferable for the particulate removal rate from the evacuation chamber to be such that particulates do not accumulate within the evacuation chamber over the course of the three-dimensional printing operation, such accumulations are within scope of the present invention, so long as the accumulations do not result in the overflow of the trough during the three-dimensional printer operation.

The selection of the number, size, shape, and locations of the holes in the partition of a trough may be made depending on several factors. Two closely related factors are the size distribution range and the shapes of the particulates that are to be used during the three-dimensional printing operation. It is preferable that the holes be sized and shaped to allow passage of all shapes and sizes within the size distribution range without the occurrence of particulate bridging of the holes. Additional factors are the partition's profile and its angle of disposition. It is preferred that the number and distribution of holes be chosen to avoid the accumulation of particulates on the portion or portions of the partition to which the partition's profile and/or angular disposition direct greater numbers of particulates. Two more factors are the gas flow rate through the evacuation chamber and whether or not a gas inlet (e.g., gas inlet46ofFIG. 3) has been provided to the evacuation chamber. It is desirable to size, shape, and distribute the holes to promote particulate entrainment in the vacuum-induced gas flow through the holes. It is to be understood that in embodiments wherein the optional gas inlet of the evacuation chamber is omitted, there is no need for a particulate outflow restrictor, e.g. the particulate outflow restrictor52shown inFIG. 3. Also, in that case, all gas inflow into the evacuation chamber is through the holes in the partition.

In some embodiments, the partition may be removed from its trough and replaced with a substitute partition. The substitute partition may have holes which are different in number, size, shape, and/or locations from the holes of the original partition and/or have a configuration that is different from that of the original partition and/or be adapted to have an angle of disposition which is different from that of the original partition. It is preferable to seal the partition against the sides of the trough so that the only passageways for particulate from the particulate receiving chamber to the evacuation chamber is through the holes in the partition.

The present invention includes three-dimensional printing apparatuses having of one or more of the inventive troughs which are adapted to directly and/or indirectly collect the excess deposited particulates appurtenant to the deposition of particulate layers during the three-dimensional printing operation. Preferably, the trough or troughs are positioned adjacent to the build platform so as to directly receive the excess deposited particulate, e.g. in the relative locations of conventional troughs16a-16dshown inFIG. 2. In some embodiments, one or more inventive troughs (i.e. troughs having some version of the evacuation chamber system described above) are used in conjunction with one or more conventional troughs. In some of these embodiments, at least one of the conventional troughs conveys some or all of the excess deposited particulate into one or more of the inventive troughs.FIG. 7shows such an embodiment.

Referring toFIG. 7, there is shown a schematic top view of a work table100of a three-dimensional printer that uses a particulate build material. A build platform102is located within the work table100. A particulate dispenser104is located above the work table100and is adapted to deposit layers of particulate material onto the build platform102. In contrast to the particulate dispenser6ofFIG. 1A-1Dwhich was adapted to deposit particulate layers only when moving in the one direction indicated by arrow8inFIG. 1B, the particulate dispenser104is adapted to deposit particulate layers when moving in either of the directions indicated by the arrow106, so that the particulate dispenser104has two alternate deposition directions. Two inventive troughs108a,108bare positioned adjacent to the build table and parallel to the deposition directions of the particulate dispenser104. Two conventional troughs110a,110bare positioned adjacent to the ends of the build platform and are adapted to feed excess particulate material into the inventive troughs108a,108b. Thus, in this arrangement, each of the inventive troughs108a,108bare adapted to receive excess deposited particulate directly from the particulate dispenser104and to receive excess deposited particulate indirectly by way of the conventional troughs110a,110b.FIG. 8presents a schematic cutaway side view taken across cutting plane8-8ofFIG. 7.

Referring toFIG. 8, the conventional trough110ais positioned between inventive troughs108a,108b. The inventive troughs108a,108b, have, respectively, particulate receiving chambers112a,112b, partition plates114a,114b(having through holes such as holes116a,116b), and evacuation chambers118a,118b. The conventional trough110ahas a peaked bottom119which slopes so as to direct excess deposited particulate toward the particulate receiving chambers112a,112bof the inventive troughs108a,108b.

In some embodiments, the inventive troughs are built directly into the three-dimensional printing apparatus so that they are a permanent part of the apparatus.FIG. 7illustrates one such embodiment. In other embodiments, one or more of the inventive troughs are disposed in a removable unit which is adapted to be inserted into the three-dimensional printing apparatus during a particular three-dimensional printing operation and then removed thereafter. In some particularly preferred embodiments, the removable unit also includes a build box having walls designed to laterally confine the particulate bed and a build platform which is adapted to be raised or lowered.FIG. 9is a perspective view of a build box120of such an embodiment.

Referring toFIG. 9, the build box120is adapted to be inserted and withdrawn through the side of a three-dimensional printing apparatus in the directions indicated by the first arrow122a(insertion direction) and the second arrow122b(withdrawal direction). The third arrow124indicates the particulate spreading or deposition direction during the operation of the three-dimensional printing apparatus. The build box120has a build cavity126which is adapted to receive a particle bed during the building of a three-dimensional article. The build cavity126is bordered along its sides by four vertical walls, e.g. wall128, and along its bottom by a vertically-movable build platform (not shown). The build box120also has two conventional troughs130a,130band two inventive troughs132a,132b. The build box120also has nipple134which is adapted to connect the inventive trough132bto a vacuum source and a particulate outflow restrictor136which has an open top138and is in communication with the gas inlet (not shown) for inventive trough132b. Although they are not visible in FIG.9, the build box120also includes a corresponding nipple and particle outflow restrictor with a gas inlet for inventive trough132a.

FIG. 10shows a schematic perspective view of a three-dimensional printer140into which the build box120has been inserted.

It is to be understood that the present invention includes within its scope three-dimensional printers that have build cavities that have one or more non-planar walls for laterally confining the build bed. For example, one or more of the walls may be curved. The build cavity may have a circular cross-section circumscribed by a continuously curved wall. Such non-planar walled build cavities may be either a permanent part of the three-dimensional printing apparatus of part of a removable build box.

It is also to be understood that the troughs of embodiments may have curved shapes. Such curved shaped troughs are preferred for use adjacent to a curved build cavity wall. Such curved troughs may be either a permanent part of the three-dimensional printing apparatus or removable, e.g., as part of a build box. Troughs having a curved shape may be either the troughs having an evacuation chamber or troughs not having an evacuation chamber.

In some embodiments, the particulates which are removed from a trough's evacuation chamber are subsequently collected in a collection device, e.g. a cyclone, screen separator, electrostatic precipitator, scrubber, etc. Preferably, the collection device is chosen so as to permit reuse of the collected particulate in the three-dimensional printing process with little or no subsequent conditioning operation. Although the collection device may be an integral part of the three-dimensional printer apparatus, preferably the collection device is either removably attached to the three-dimensional printer apparatus or is separate from the three-dimensional printer apparatus. These latter two configurations make it easier to avoid cross-contamination when the three-dimensional printer apparatus is first used for one type of particulate and then another type.

The present invention also includes methods of making articles with a three-dimensional printer apparatus which utilizes one or more of the inventive troughs. In such embodiments, the methods include providing a three-dimensional printer apparatus with at least one trough having a particulate receiving chamber, an evacuation chamber, and a selectively perforated partition separating the particulate receiving chamber from the evacuation chamber. The trough is positioned to receive excess deposited particulate material during the three-dimensional printing operation and is connected to a vacuum source. A vacuum source is intermittently or continuously operatively connected to the evacuation chamber and to cause a flow of ambient gas through the evacuation chamber which entrains at least a portion of the excess deposited particulate which entered the trough's particulate receiving chamber and removes the entrained particulate from the evacuation chamber. Some method embodiments also include the steps of inserting a removable build box into the three-dimensional printing apparatus prior to the printing operation and then removing the build box after the completion of the printing operation.

Some method embodiments also include the step of selectively closing one or more partition perforations so as to control the gas flow through the partition in which the perforation is located. The step has the effect of controlling the amount particulate flow through the partition. The closing may be done by selectively and removably inserting a plug into one or more of the perforations. The closing may also be done by selectively and removably attaching a strip that is adapted to attach to the partition so as to close a plurality of perforations.

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 invention as described in the claims. All United States patents and patent applications, all foreign patents and patent applications, and all other documents identified herein are incorporated herein by reference as if set forth in full herein to the full extent permitted under the law.