Patent Publication Number: US-2021178472-A1

Title: Additive manufacturing apparatuses and powder storage vessels for additive manufacturing apparatuses

Description:
BACKGROUND 
     Field 
     The present specification generally relates to additive manufacturing apparatuses and, more specifically, to additive manufacturing apparatuses with powder storage vessels and methods for using the same. 
     Technical Background 
     Additive manufacturing apparatuses may be utilized to “build” an object from build material, such as organic or inorganic powders, in a layer-wise manner. Early iterations of additive manufacturing apparatuses were used for prototyping three-dimensional objects. While there is an increased interest in utilizing additive manufacturing apparatuses for large-scale commercial production of objects, there continues to be a need for smaller additive manufacturing apparatuses for prototyping. 
     Powder material is typically supplied to the additive manufacturing apparatuses using a hopper or other powder storage vessel. The hopper may store the powder material and also control release of the powder material from the hopper. A need exists for powder storage vessels that provide increased control of release of the powder material within the additive manufacturing apparatuses. 
     SUMMARY 
     In a first embodiment, an additive manufacturing apparatus for forming a three-dimensional article through successive fusion of parts of layers of a powder material, which parts correspond to successive cross-sections of the three-dimensional article is provided. The additive manufacturing apparatus includes a process chamber housing with a process chamber. An energy beam source is arranged for at least one of heating or fusing a powder material located on a build platform within the process chamber in a predetermined pattern layer-by-layer to form the three-dimensional article. A powder storage vessel is in the process chamber. The powder storage vessel includes a vessel body including a powder storage volume, a floor including a powder delivery opening extending therethrough and a bottom cap including a powder delivery opening extending therethrough. In an open configuration, the powder delivery opening of the bottom cap is aligned with the powder delivery opening of the floor to allow powder material to flow from the powder storage vessel through the powder delivery openings. In a closed configuration, one or both of the vessel body and the bottom cap is rotated relative to the other to misalign the powder delivery openings and inhibit powder material from flowing from the powder storage vessel through the powder delivery openings. 
     In another embodiment, a powder storage vessel for an additive manufacturing apparatus includes a vessel body including a powder storage volume, a floor having a powder delivery opening extending therethrough and a bottom cap having a powder delivery opening extending therethrough. In an open configuration, the powder delivery opening of the bottom cap is aligned with the powder delivery opening of the floor to allow powder material from the powder storage volume to flow through the powder delivery openings. In a closed configuration, one or both of the vessel body and the bottom cap is rotated relative to the other to misalign the powder delivery openings and inhibit powder material from flowing from the powder storage volume through the powder delivery openings. 
     In another embodiment, a method of delivering powder material to a build platform of an additive manufacturing apparatus is provided. The method includes placing a powder storage vessel into a process chamber of the additive manufacturing apparatus. The powder storage vessel includes a vessel body including a powder storage volume, a floor having a powder delivery opening extending therethrough and a bottom cap having a powder delivery opening extending therethrough. In an open configuration, the powder delivery opening of the bottom cap is aligned with the powder delivery opening of the floor to allow powder material to flow from the powder storage volume through the powder delivery openings. In a closed configuration, one or both of the vessel body and the bottom cap is rotated relative to the other to misalign the powder delivery openings and inhibit powder material from flowing from the powder storage volume through the powder delivery openings. One or both of the vessel body and the bottom cap is rotated relative to the other thereby moving the powder storage vessel from the closed configuration to the open configuration. 
     Additional features and advantages of the additive manufacturing apparatuses described herein, and the components thereof, will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the embodiments described herein, including the detailed description which follows, the claims, as well as the appended drawings. 
     It is to be understood that both the foregoing general description and the following detailed description describe various embodiments and are intended to provide an overview or framework for understanding the nature and character of the claimed subject matter. The accompanying drawings are included to provide a further understanding of the various embodiments, and are incorporated into and constitute a part of this specification. The drawings illustrate the various embodiments described herein, and together with the description serve to explain the principles and operations of the claimed subject matter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of an additive manufacturing apparatus, according to one or more embodiments shown and described herein; 
         FIG. 2  is a section view of a powder storage vessel for use with the additive manufacturing apparatus of  FIG. 1 , according to one or more embodiments shown and described herein; 
         FIG. 3  is a perspective, exploded view of the powder storage vessel of  FIG. 2 , according to one or more embodiments shown and described herein; 
         FIG. 4  is a schematic plan view of operation of a bottom cap of the powder storage vessel of  FIG. 2  in an open configuration, according to one or more embodiment shown and described herein; 
         FIG. 5  is a schematic plan view of operation of the bottom cap of  FIG. 4  in a closed configuration, according to one or more embodiments shown and described herein; 
         FIG. 6  is a perspective view of the additive manufacturing apparatus of  FIG. 1  with a separable process housing portion removed showing the powder storage vessel of  FIG. 2 , according to one or more embodiments shown and described herein; 
         FIG. 7  is a perspective view of the additive manufacturing apparatus of  FIG. 6  with the powder storage vessel removed, according to one or more embodiments shown and described herein; 
         FIG. 8  is a perspective view of a powder distributor, according to one or more embodiments shown and described herein; 
         FIG. 9  is a bottom view of a rotatable support conveyor of the additive manufacturing apparatus of  FIG. 7  with the powder distributor of  FIG. 8 , according to one or more embodiments shown and described herein; 
         FIG. 10  is a section view of the additive manufacturing apparatus of  FIG. 1  with a separable process chamber housing in a closed configuration, according to one or more embodiments shown and described herein; 
         FIG. 11  is a perspective view of the additive manufacturing apparatus of  FIG. 10  with the separable process chamber housing in an open configuration, according to one or more embodiments shown and described herein; and 
         FIG. 12  is a method of operating the additive manufacturing apparatus of  FIG. 1 , according to one or more embodiments shown and described herein. 
     
    
    
     DETAILED DESCRIPTION 
     Whenever possible, the same reference numerals will be used throughout the drawings to refer to the same or like parts. One embodiment of an additive manufacturing apparatus includes separable process chamber housing portions in order to provide greater access to within the process chambers for cleaning and other operations where access to within the process chamber is needed. Another embodiment of an additive manufacturing apparatus includes a powder storage vessel having a closed configuration where metal powder is inhibited from leaving the powder storage vessel and an open configuration where metal powder is allowed to leave the powder storage vessel. Various embodiments of additive manufacturing apparatuses, additive manufacturing apparatuses including the separable process chambers and/or the powder storage vessels, and methods for using the same are described in further detail herein with specific reference to the appended drawings. 
     Ranges can be expressed herein as from “about” one particular value, and/or to “about” another particular value. When such a range is expressed, another embodiment includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent “about,” it will be understood that the particular value forms another embodiment. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint. 
     Directional terms as used herein—for example up, down, right, left, front, back, top, bottom, upper, lower,—are made only with reference to the figures as drawn and are not intended to imply absolute orientation unless otherwise expressly stated. 
     Unless otherwise expressly stated, it is in no way intended that any method set forth herein be construed as requiring that its steps be performed in a specific order, nor that with any apparatus specific orientations be required. Accordingly, where a method claim does not actually recite an order to be followed by its steps, or that any apparatus claim does not actually recite an order or orientation to individual components, or it is not otherwise specifically stated in the claims or description that the steps are to be limited to a specific order, or that a specific order or orientation to components of an apparatus is not recited, it is in no way intended that an order or orientation be inferred, in any respect. This holds for any possible non-express basis for interpretation, including: matters of logic with respect to arrangement of steps, operational flow, order of components, or orientation of components; plain meaning derived from grammatical organization or punctuation, and; the number or type of embodiments described in the specification. 
     As used herein, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a” component includes aspects having two or more such components, unless the context clearly indicates otherwise. 
     Reference will now be made in detail to embodiments of additive manufacturing apparatuses, and components thereof, examples of which are illustrated in the accompanying drawings. The additive manufacturing apparatuses may include a process chamber housing that houses a build platform onto which a powder material is delivered and an electron beam source that is used to fuse powder together layer-by-layer. A powder storage vessel is provided in the process chamber that can be delivered to the build platform to dispense the powder material thereon. A rotatable support conveyor may be used to both hold the powder storage vessel and also to move the powder storage vessel toward and away from the build platform as layers of fused powder material are being formed. 
     As can be appreciated, powder material may build up in and may need to be cleaned from the process chamber from time-to-time. To facilitate access to the process chamber for cleaning or any other reason, the process chamber housing is divided into process chamber housing portions including a first process chamber housing portion and a second process chamber housing portion, where the first and second process chamber housing portions are separable from one another to provide increased access to within the process chamber. 
     As used herein, the term “three-dimensional structures” and the like refer generally to intended or actually fabricated three-dimensional configurations (e.g., of structural material or materials) that are intended to be used for a particular purpose. Such structures may be, for example, designed with the aid of a computer aided design (CAD) program. 
     As used herein, the term “two-dimensional structures” and the like refer generally to layers of the three-dimensional structure that when built, one over the other, form the three-dimensional structures. While referred to as “two-dimensional structures,” it should be understood that each layer includes an accompanying thickness in a third dimension, albeit the structures have a relatively planar configuration compared to a fused stack of the two-dimensional structures that form the three-dimensional structures. 
     As used herein, the term “electron beam” refers to any charged particle beam. The sources of a charged particle beam can include an electron gun, a linear actuator, etc. 
     Various embodiments of the additive manufacturing apparatuses relate to methods for producing three-dimensional objects by layering two-dimensional structures one on the other by powder additive manufacturing, such as using electron beam melting (EBM), selective laser sintering (SLS) and/or selective laser melting (SLM). 
     Referring to  FIG. 1 , an additive manufacturing apparatus  10  includes a process chamber housing  12  defining a process chamber  14  that includes a first process chamber housing portion  52  and a second process chamber housing portion  54 . A vacuum system  20  may be provided that provides a vacuum within the process chamber  14 . The vacuum system  20  is capable of maintaining a vacuum environment within the process chamber  14 . The vacuum system  20  may include, for example, a turbomolecular pump, a scroll pump, an ion pump and one or more valves that controls ingress and egress or air and/or other gases into and out of the process chamber  14  through the vacuum system  20 . In some embodiments, the process chamber  14  may be back filled with another gas other than air, such as helium. 
     An electron beam gun  22  generates an electron beam that is used for melting or fusing together powder material provided on a build platform  24 . A control unit  26  is provided for controlling and managing the electron beam gun  22  and the electron beam that is emitted. The control unit  26  may include a processor and memory for storing a CAD program and CAD design that can be executed by the processor. A focusing coil, deflection coil, astigmatic coil and an electron beam power supply (all represented by element  28 ) may be electrically connected to the control unit  26 . In some embodiments, the electron beam gun  22  generates a focusable electron beam with an accelerating voltage of between about 15 kV and 120 kV and with a beam power of between about three Kw and about 10 kW. The pressure in the process chamber may be about 1×10 −3  mbar or lower when building the three-dimensional structure by fusing the powder layer-by-layer with the electron beam. 
     In another embodiment, a laser beam may be used for melting or fusing the powder material. In such a case, tiltable mirrors may be used in the beam path in order to deflect the laser beam to a predetermined position. As used herein, a laser beam, electron beam or any other energy suitable in building a three-dimensional structure as discussed herein may be referred to as an energy beam. 
     A powder storage vessel  30  houses the powder material to be provided on the build platform  24 . The powder material may be, for example, pure metals or metal alloys, such as titanium, titanium alloys, aluminum, aluminum alloys, stainless steel, Co—Cr alloys, nickel based super alloys, etc. Additional details of the powder storage vessel are described below. 
     A powder distributor  29  is arranged to rake a thin layer of powder material that falls from the powder storage vessel  30  onto the build platform  24 . During a work cycle, the build platform  24  is lowered successively in relation to a fixed point in the process chamber  14 . In order to make this movement possible, the build platform  24  can translate in a vertical direction, i.e., in the direction indicated by arrow P. This means that the build platform  24  starts in an initial position, in which a first powder material layer of necessary thickness is laid down. An actuation system  32  is provided that lowers and then raises the build platform  24 . The actuation system  32  may, for example, include any suitable linear actuator. 
     The energy beam may be directed over the build platform  24  causing a first powder layer to fuse in selected locations to form a first cross-section of the three-dimensional structure. The energy beam is directed over the build platform  24  in accordance with instructions given by the control unit  26 . In the control unit  26 , instructions for how to control the electron beam for each layer of the three-dimensional structure is stored in memory. 
     After a first layer is finished, i.e., the fusion of powder material for making a first layer of the three-dimensional structure, a second powder layer is provided on the build platform  24 . The second powder layer is distributed according to the same manner as the previous layer in some embodiments. However, there may be other methods in the same additive manufacturing machine for distributing powder onto the build platform  24 . 
     After having distributed the second powder layer on the build platform  24 , the energy beam is directed over the build platform  24  causing the second powder layer to fuse in selected locations to form a second cross section of the three-dimensional article. Fused portions in the second layer may be bonded to fused portions of the first layer. The fused portions in the first and second layer may be melted together by melting not only the powder in the uppermost layer but also re-melting at least a fraction of a thickness of a layer directly below the uppermost layer. 
     In some embodiments, a shield  36  (e.g., formed of stainless steel) may be provided between the build platform  24  and the powder storage vessel  30 . The shield  36  may inhibit heated metal powders from sputtering into the process chamber  14 . 
     A rotatable support conveyor  40  may be used to both hold the powder storage vessel  30  and also to move the powder storage vessel  30  toward and away from the build platform  24  as layers of fused powder material are being formed. A motor  42  may be provided that is used to rotate the rotatable support conveyor  40  based on instructions from the control unit  26 . After each layer of material is formed, the control unit  26  instructs the motor  42  to rotate the rotatable support conveyor  40 , which moves both the powder storage vessel  30  and the powder distributor  29  that is underneath the powder storage vessel  30  toward the build platform  24 . At onset of an additive manufacturing process, the build platform  24  may be below a floor  44  of the process chamber housing  12  a predetermined amount (e.g., about 20-100 μm per layer). This allows a layer of powder material of a predetermined thickness to be raked over the build platform  24 . The rotatable support conveyor  40  then returns the powder storage vessel  30  to its initial position while the electron beam gun  22  fuses the powder material in a predetermined pattern. 
     The layer of powder material provided on the build platform  24  may have a working diameter of about 100 mm or less. The build platform  24  may move down in the direction P a total distance of about 100 mm or less thereby capable of building a 100 mm×100 mm×100 mm three-dimensional structure. In this regard, the additive manufacturing apparatus  10  may be referred to as compact. As used herein, the term “compact additive manufacturing apparatus” refers to additive manufacturing apparatuses having a working area (i.e., area of the build platform  24 ) of no greater than about 785 cm 2  for a working area having a diameter of 100 mm. While the work area is shown as circular herein, the work area may be any suitable shape, such as rectangular, irregular, or any other suitable shape. In some embodiments, the compact additive manufacturing apparatuses may be defined by the size of the process chamber, which may be no greater than about 31400 cm 3 . 
     Because the size of additive manufacturing apparatus  10  may be relatively small, the additive manufacturing apparatus may be provided with separable process chamber housing portions, such as a first separable process chamber housing portion  52  and a second separable process chamber housing portion  54 . The process chamber housing  12  may be separable so that an operated does not have to rely on presence of an openable door of limited area to enter into the process chamber  14 , for example, for a cleaning operation or to exchange components, such as the powder storage vessel  30 . An actuation device  56  is connected to one or both of the first and second separable process chamber housing portions  52  and  54 . The actuation device  56  may include a first linear actuator  58  and a second linear actuator  60  on a side of the process chamber housing  12  that is opposite the first linear actuator  58 . The first linear actuator  58  includes a first housing connection  62  that is connected to the first process chamber housing portion  52  and a second housing connection  64  that is connected to the second process chamber housing portion  54 . Likewise, the second linear actuator  60  includes a first housing connection  66  that is connected to the first process chamber housing portion  52  and a second housing connection  68  that is connected to the second process chamber housing portion  54 . Additional details of the separable process chamber housing portions  52  and  54  are described in greater detail below. 
     Powder Storage Vessel 
     Referring to  FIG. 2  where a section view of the powder storage vessel  30  is shown and also to  FIG. 3  where a perspective exploded view of the powder storage vessel  30  is illustrated, the powder storage vessel  30  includes a vessel body  70  that, in the illustrated embodiment, is generally cylindrical having a width or diameter and a height. The vessel body  70  has a bottom  72  with a floor  74  that is primarily closed and a top  76  that may be open-ended. A sidewall  88  extends between the top  76  and the bottom  72 . A top cap  78  may be used to close the top  76 . A bottom cap  80  may be used to cover the bottom  72  and the floor  74 . The bottom cap  80  includes guide pins  82 , which may be threaded, that can be received within guide openings  84  within the floor  74 . The guide openings  84  are elongated in a circumferential direction and are located nearer to sidewall  88  than to a central axis of the vessel body  70 . 
     The floor  74  has a pair of powder delivery openings  90  and  92  (see  FIG. 4 ) in the form of slots that have elongated dimensions that extend in a radial direction. The powder delivery openings  90  and  92  may be spaced-apart from one another providing a gap  97  at a center of the floor  74 . The bottom cap  80  also includes powder delivery openings  94  and  96  in the form of slots that have elongated dimensions that extend in the radial direction. The powder delivery openings  94  and  96  may be spaced apart from one another providing a gap  98  at a center of the bottom cap  80 . The powder delivery openings  94  and  96  and the powder delivery openings  90  and  92  may have substantially the same dimensions in both the radial and circumferential directions. While openings in the form of elongated slots are shown, any suitable shape for the openings may be used. Further, the openings may be divided into multiple, individual openings. 
     The bottom cap  80  can rotate relative to the vessel body  70  to place the powder storage vessel  30  in the open configuration or the closed configuration. Referring particularly to  FIG. 4 , in the open configuration, the powder delivery openings  94  and  96  of the bottom cap  80  align with the powder delivery openings  90  and  92  of the floor  74  of the vessel body  70 , which allows powder material to exit the powder storage vessel  30 . As represented by  FIG. 5 , rotating the vessel body  70  and/or the bottom cap  80  relative to each other places the powder delivery openings  90  and  92  of the floor  74  of the vessel body  70  out of alignment with the powder delivery openings  94  and  96  of the bottom cap  80 , which disallows powder material from exiting the powder storage vessel  30 . Shown by  FIG. 3 , a lock member  100  (e.g., a nut) may be provided that can be connected to the guide pins  82  and used to lock the powder storage vessel either in the closed or open configurations. Access openings  102  may be provided through the sidewall  88  that provides access to the lock member  100  for tightening or loosening operations in order to allow or disallow rotation of the vessel body  70  and bottom cap  80  relative to one another. 
     Referring again to  FIG. 2 , the powder storage vessel  30  is provided with guide walls  104  and  106  that extend downward from the sidewall  88  toward the floor  74  forming a funnel-like shape. The guide walls  104  and  106  terminate at opposite edges of the powder delivery openings  90  and  92 . The guide walls  104  and  106  utilize gravity to reliably deliver powder material to the powder delivery openings  90  and  92 . 
     Referring now to  FIG. 6 , the interior of the process chamber  14  including the powder storage vessel  30  with the separable process housing portion  52  removed for clarity is illustrated. The powder storage vessel  30  is received by a cavity structure  110  that is provided in the rotatable support conveyor  40 . A support wall  112  surrounds a perimeter of the cavity structure  110  to provide additional support for the powder storage vessel  30 . Referring also to  FIG. 7 , a raised support ledge  114  is provided about the perimeter of the cavity structure  110  and is raised from a floor  116  of the cavity structure  110  providing some clearance between the powder storage vessel  30  and the floor  116  when located thereon. A central raised ledge  118  extends radially through the cavity structure  110  and includes an opening  120  that also extends radially along the central raised ledge  118 . The opening  120  aligns with the powder delivery openings  90 ,  92 ,  94  and  96  of the powder storage vessel  30  with the powder storage vessel  30  in the open configuration. 
     As shown most clearly by  FIG. 7 , a vessel support bracket  122  is mounted at least partially within the cavity structure  110 . The vessel support bracket  122  includes mounts  124  and  126  that mount the vessel support bracket  122  to the rotatable support conveyor  40  using fasteners  128  and  130 . A pair of clips  132  and  134  are mounted adjacent the vessel support bracket  122 . In some embodiments, the clips  132  and  134  may be part of the vessel support bracket  122 . The clips  132  and  134  include oppositely oriented U-shaped clip portions  136  and  138  that receive opposite ends  140  and  142  of a dowel rod  140  ( FIG. 3 ) that extends through and is fixedly connected to the vessel body  70 . 
     The cavity structure  110  further includes tab receiving recesses  144  and  146 . The tab receiving recesses  144  and  146  are located on opposite sides of the cavity structure  110  and are oriented about 90 degrees offset from the clip portions  136 . As can be seen in  FIG. 3 , the bottom cap  80  includes tabs  148  and  150 . The tabs  148  and  150  are located on opposite sides of the bottom cap  80 . The tabs  148  and  150  are sized and located to be received within the tab receiving recesses  144  and  146 . When the tabs  148  and  150  are located within the tab receiving recesses  144  and  146  and the ends  140  and  142  of the dowel rod  140  are received by the clip portions  136  and  138 , the powder storage vessel  30  is placed in the open configuration and powder material flows through the openings  90 ,  92 ,  94  and  96  and passes through the opening  120  into a space  154  beneath the rotatable support conveyor  40  and adjacent the powder distributor  29  ( FIG. 1 ). The space  154  may have a height of between about five mm and about 6 mm, for example. 
     Referring briefly to  FIGS. 8 and 9 , the powder distributor  29  includes a relatively flexible rake portion  156  and a relatively rigid connecting portion  158 . The relatively rigid connecting portion  158  mounts to an underside of the rotatable support conveyor  40  such that powder material can be carried by the rake portion toward the build platform  24 . The powder distributor  29  mounts at a location adjacent the opening  120  to push the powder material toward the build platform  24  as the rotatable support conveyor  40  rotates. In some embodiments, the powder distributor  29  may be curved in the direction of its long axis; however, the powder distributor  29  may be straight in other embodiments. 
     Separable Process Chamber Housing 
     Referring to  FIG. 10 , a section view of the additive manufacturing apparatus  10  is illustrated including the process chamber housing  12  defining the process chamber  14 , the rotatable support conveyor  40 , the powder storage vessel  30 , the shield  36  and the build platform  24 . As discussed above, a space  154  is provided beneath the rotatable support conveyor  40  where a limited amount of powder material can accumulate from the powder storage vessel  30  and then be pushed by the powder distributor  29  to the build platform  24 . 
     As noted above, the size of the process chamber housing  12  may be relatively small. Because of this, it may be difficult to access all areas of the process chamber  14  through an access opening  160  provided at a front of the process chamber housing  12 . For example, the access opening  160  may have a height/width/diameter that is less than about 500 mm, such as less than about 250 mm, such as less than about 200 mm, such as less than about 175 mm, such as less than about 150 mm. A door  162  may be provided that closes the access opening  160 . The door  162  may include a latch  164  that allows for latching and unlatching the door  162  to the process chamber housing  12 . An average human hand breadth where the fingers meet the palm may be about 80 mm for illustrative purposes. It can be appreciated that reaching into the process chamber  14  through the access opening  160  may be somewhat cumbersome. 
     The process chamber housing  12  includes the first separable process chamber housing portion  52  and the second separable process chamber housing portion  54 . The first separable process chamber housing portion  52  includes a top  164  of the process chamber housing  12  and at least a portion of a side  166  of the process chamber housing  12 . The second separable process chamber housing portion  54  includes a bottom  168  of the process chamber housing  12  and may include a portion of the side  166  of the process chamber housing  12 . The first separable process chamber housing portion  52  meets the second separable process chamber housing portion  54  at a junction  170 . The junction  170  is formed between a first flange  172  at a terminal end of the first separable process chamber housing portion  52  and a second flange  174  at a terminal end of the second separable process chamber housing portion  54 . A seal  176  (e.g., an O-ring seal) may be provided within a recess  178  between the first and second flanges  172  and  174 . The seal  176  may be provided to help maintain an air-tight environment within the process chamber  14  through the junction  170  with the process chamber housing  12  in a closed configuration, as shown by  FIG. 10 . 
     Referring to  FIG. 11 , the process chamber housing  12  is illustrated in an open configuration. The additive manufacturing apparatus  10  includes the first linear actuator  58  and the second linear actuator  60 . The first linear actuator  58  includes a pair of cylinders  180  and  182  and a pair of rods  184  and  186 . The cylinders  180  and  182  are connected to the first separable process chamber housing portion  52  using a bracket  188  that is connected to the side  166  of the process chamber housing  12 . The rods  184  and  186  are connected to the second separable process chamber housing portion  54  using a bracket  190  that is connected to the side  166  of the process chamber housing  12 . Likewise, the second linear actuator  60  includes a pair of cylinders  192  and  194  and a pair of rods  196  and  198 . The cylinders  192  and  194  are connected to the first separable process chamber housing portion  52  using a bracket (similar to bracket  188 ) that is connected to the side  166  of the process chamber housing  12 . The rods  196  and  198  are connected to the second separable process chamber housing portion  54  using a bracket  202  that is connected to the side  166  of the process chamber housing  12 . 
     In some embodiments, the first linear actuator  58  and the second linear actuator  60  may be gas springs. A gas spring is a type of spring that uses compressed gas contained within an enclosed cylinder sealed by a sliding piston to pneumatically store potential energy. For example, a pull-type gas spring may be used that holds the process chamber housing  12  in the closed configuration. When a tension above a predetermined level is applied to the first linear actuator  58  and the second linear actuator  60 , the rods  184 ,  186 ,  196 ,  198  are forced to move relative to the cylinders  180 ,  182 ,  192 ,  194 , and the gas spring assists the operator in placing the process chamber housing  12  in the open configuration. Further, the gas springs can hold the process chamber housing  12  in the open configuration until a compressive force of a predetermined amount is applied to the first linear actuator  58  and the second linear actuator  60 . 
     It can be appreciated that providing a separable process chamber housing  12  with the first separable process chamber housing portion  52  and the second separable process chamber housing portion  54  increases access area with the process chamber housing  12  in the open configuration compared to the closed configuration. Further, because many of the components discussed above, such as the powder storage vessel  30 , rotatable support conveyor  40 , build platform  24  and shield  36  travel with the second separable process chamber housing portion  54  and out of the first separable process chamber housing portion  52 , added access is provided to those components. In some embodiments, the first and second linear actuators  58  and  60  may be operated automatically, e.g., using the control unit  26 . For example, the first and second linear actuator  58  and  60  may be pneumatic cylinders or be motor-operated. In some embodiments, the linear actuators  58  and  60  may be sized to separate the first and second separable process chamber housing portions a distance D of at least about 80 mm, such as a distance of at least about 100 mm, such as a distance of at least about 150 mm, such as a distance of at least about 200 mm, such as a distance of at least about 250 mm, such as a distance of at least about 300 mm. In some embodiments, the distance D may be about a height of the process chamber  14  or more. 
     Referring to  FIG. 12 , a method  210  of operating the additive manufacturing apparatus  10  is represented. The method  210  includes placing the powder storage vessel  30  into the process chamber  14  with the powder storage vessel  30  in the closed configuration so that powder material does not exit the powder storage vessel  30  at step  212 . At step  214 , the tabs  148  and  150  of the bottom cap  80  are aligned with and inserted into the tab receiving recesses  144  and  146  of the cavity structure  110  of the rotatable support conveyor  40 . With the bottom cap  80  held in place by the tabs  148  and  150  in the tab receiving recesses  144  and  146 , the vessel body  70  is rotated relative to the bottom cap  80  until the ends  140  and  142  of the dowel rod  140  are received by the clip portions  136  and  138  of the clips  132  and  134  thereby aligning the powder delivery openings  90 ,  92 ,  94  and  96  and also aligning the powder delivery openings  90 ,  92 ,  94  and  96  with the opening  120  through the rotatable support conveyor  40  at step  216 . At step  218 , powder material is delivered to the space  154  beneath the rotatable support conveyor  40  and adjacent the powder distributor  29 . The powder distributor  29  then rakes the powder material onto the build platform  24 . 
     After a three-dimensional structure is built, as described above, it may be desirable to clean or otherwise access the process chamber  14 . At step  220 , an operator may grasp one or both of the first and second separable process chamber housing portions  52  and  54  and pull one away from the other providing a tensioning force to the first linear actuator  58  and the second linear actuator  60 . The tensioning force may cause the process chamber housing  12  to move into the open configuration at step  222 . The first and second separable process chamber housing portions  52  and  54  may then be held in the open configuration until a compressive force is applied to the first linear actuator  58  and the second linear actuator  60  thereby causing the process chamber housing to move into the closed configuration. 
     The above-described additive manufacturing apparatuses include powder storage vessels that can be used to control egress of the powder material stored therein from their powder storage volumes. The powder storage vessels have a closed configuration where powder is inhibited from leaving the powder storage vessels and an open configuration where powder is allowed to leave the powder storage vessels. 
     Further aspects of the invention are provided by the subject matter of the following clauses: 
     1. An additive manufacturing apparatus for forming a three-dimensional article through successive fusion of parts of layers of a powder material, which parts correspond to successive cross-sections of the three-dimensional article, the additive manufacturing apparatus comprising: a process chamber housing with a process chamber; an energy beam source arranged for at least one of heating or fusing a powder material located on a build platform within the process chamber in a predetermined pattern layer-by-layer to form the three-dimensional article; and a powder storage vessel in the process chamber, the powder storage vessel comprising: a vessel body comprising a powder storage volume; a floor comprising a powder delivery opening extending therethrough; and a bottom cap comprising a powder delivery opening extending therethrough; wherein, in an open configuration, the powder delivery opening of the bottom cap is aligned with the powder delivery opening of the floor to allow powder material to flow from the powder storage vessel through the powder delivery openings; and wherein, in a closed configuration, one or both of the vessel body and the bottom cap is rotated relative to the other to misalign the powder delivery openings and inhibit powder material from flowing from the powder storage vessel through the powder delivery openings. 
     2. The additive manufacturing apparatus of any preceding clause, wherein the bottom cap further comprises a guide pin received within a guide opening formed through the floor of the vessel body. 
     3. The additive manufacturing apparatus of any preceding clause, wherein the vessel body comprises a sidewall having an access opening extending therethrough, the access opening providing access to the guide pin from outside the vessel body. 
     4. The additive manufacturing apparatus of any preceding clause, wherein the guide pin is threaded to receive a lock member. 
     5. The additive manufacturing apparatus of any preceding clause, wherein the vessel body comprises a sidewall and a pair of guide walls that extend downward toward the floor adjacent to opposite sides of the powder delivery opening. 
     6. The additive manufacturing apparatus of any preceding clause, wherein the powder delivery opening of the floor is a first powder delivery opening of the floor, the floor further comprising a second powder delivery opening. 
     7. The additive manufacturing apparatus of any preceding clause, wherein the powder delivery opening of the bottom cap is a first powder delivery opening of the bottom cap, the bottom cap further comprising a second powder delivery opening. 
     8. The additive manufacturing apparatus of any preceding clause, wherein, in the open configuration, the first and second powder delivery openings of the bottom cap are aligned with the respective first and second powder delivery openings of the floor to allow powder material to flow from the powder storage vessel through the first and second powder delivery openings of the bottom cap, wherein, in the closed configuration, one or both of the vessel body and the bottom cap is rotated relative to the other to misalign the first and second powder delivery openings of the bottom cap and the floor and inhibit powder material from flowing from the powder storage vessel through the first and second powder delivery openings of the bottom cap. 
     9. The additive manufacturing apparatus of any preceding clause, wherein the vessel body comprises a dowel rod extending therethrough, wherein ends of the dowel rod are received by clips on opposite sides of the vessel body located within the process chamber. 
     10. The additive manufacturing apparatus of any preceding clause, wherein the bottom cap comprises a tab that is received within a tab receiving recess thereby inhibiting rotation of the bottom cap as the vessel body rotates while locating the ends of the dowel rod in the clips. 
     11. A powder storage vessel for an additive manufacturing apparatus, the powder storage vessel comprising: a vessel body comprising a powder storage volume; a floor having a powder delivery opening extending therethrough; and a bottom cap having a powder delivery opening extending therethrough; wherein, in an open configuration, the powder delivery opening of the bottom cap is aligned with the powder delivery opening of the floor to allow powder material from the powder storage volume to flow through the powder delivery openings, wherein, in a closed configuration, one or both of the vessel body and the bottom cap is rotated relative to the other to misalign the powder delivery openings and inhibit powder material from flowing from the powder storage volume through the powder delivery openings. 
     12. The powder storage vessel of any preceding clause, wherein the bottom cap further comprises a guide pin received within a guide opening formed through the floor of the vessel body. 
     13. The powder storage vessel of any preceding clause, wherein the vessel body comprises a sidewall having an access opening extending therethrough, the access opening providing access to the guide pin from outside the vessel body. 
     14. The powder storage vessel of any preceding clause, wherein the guide pin is threaded to receive a lock member. 
     15. The powder storage vessel of any preceding clause, wherein the vessel body comprises a sidewall and a pair of guide walls that extend downward toward the floor adjacent to opposite sides of the powder delivery opening. 
     16. The powder storage vessel of any preceding clause, wherein the powder delivery opening of the floor is a first powder delivery opening of the floor, the floor further comprising a second powder delivery opening. 
     17. The powder storage vessel of any preceding clause, wherein the powder delivery opening of the bottom cap is a first powder delivery opening of the bottom cap, the bottom cap further comprising a second powder delivery opening. 
     18. The powder storage vessel of any preceding clause, wherein, in the open configuration, the first and second powder delivery openings of the bottom cap are aligned with the respective first and second powder delivery openings of the floor to allow powder material to flow from the powder storage vessel through the first and second powder delivery openings of the bottom cap, wherein, in the closed configuration, one or both of the vessel body and the bottom cap is rotated relative to the other to misalign the first and second powder delivery openings of the bottom cap and the floor and inhibit powder material from flowing from the powder storage vessel through the first and second powder delivery openings of the bottom cap. 
     19. A method of delivering powder material to a build platform of an additive manufacturing apparatus, the method comprising: placing a powder storage vessel into a process chamber of the additive manufacturing apparatus, the powder storage vessel comprising: a vessel body comprising a powder storage volume; a floor having a powder delivery opening extending therethrough; and a bottom cap having a powder delivery opening extending therethrough; wherein, in an open configuration, the powder delivery opening of the bottom cap is aligned with the powder delivery opening of the floor to allow powder material to flow from the powder storage volume through the powder delivery openings, wherein, in a closed configuration, one or both of the vessel body and the bottom cap is rotated relative to the other to misalign the powder delivery openings and inhibit powder material from flowing from the powder storage volume through the powder delivery openings; and rotating one or both of the vessel body and the bottom cap relative to the other thereby moving the powder storage vessel from the closed configuration to the open configuration. 
     20. The method of any preceding clause, wherein the step of rotating includes rotating the vessel body until ends of a dowel rod are received by clips on opposite sides of the vessel body located within the process chamber. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the embodiments described herein without departing from the spirit and scope of the claimed subject matter. Thus, it is intended that the specification cover the modifications and variations of the various embodiments described herein provided such modification and variations come within the scope of the appended claims and their equivalents.