Patent Publication Number: US-2022212264-A1

Title: Three-Dimensional Powder Bed Fusion Additive Manufacturing Apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to Japanese Patent Application No. 2021-001226 filed Jan. 7, 2021, the disclosure of which is hereby incorporated by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a three-dimensional powder bed fusion additive manufacturing (PBF-AM) apparatus. 
     Description of Related Art 
     In recent years, a three-dimensional PBF-AM apparatus has been developed which irradiates metal powder spread on a stage with an electron beam to melt and solidify the powder, and sequentially stacks solidified layers by moving the stage to form a three-dimensional build object. 
     Regarding the three-dimensional PBF-AM apparatus, for example, JP 2003-531034 A describes a technique in which a window is provided in a vacuum chamber, and temperature distribution of a surface layer in a powder bed is recorded through the window. JP 2003-531034 A also describes a technique for protecting the window with a film and feeding the film along the window to maintain transparency of the window. 
     SUMMARY OF THE INVENTION 
     However, the techniques described in JP 2003-531034 A have the following problems. 
     In a case where the powder is melted in the three-dimensional PBF-AM apparatus, the temperature inside the chamber is high, and the film for protecting the window is thus required to have heat resistance. However, since a film having heat resistance is generally colored, the film is not suitable for observation of the inside of the chamber. 
     The present invention has been made to solve the above problems, and an object thereof is to provide a three-dimensional PBF-AM apparatus capable of protecting a window provided in a chamber without using a colored film. 
     A three-dimensional powder bed fusion additive manufacturing apparatus according to the present invention includes a chamber provided therein with a stage for forming a three-dimensional build object, a window provided in the chamber for observation of the inside of the chamber, and a shutter arranged inside the chamber to open and close the window. 
     According to the present invention, a window provided in a chamber can be protected without using a colored film. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a side cross-sectional view schematically illustrating a configuration of a three-dimensional PBF-AM apparatus according to an embodiment of the present invention; 
         FIG. 2  is a schematic view of the three-dimensional PBF-AM apparatus illustrated in  FIG. 1  as viewed in direction A; 
         FIG. 3  is a longitudinal cross-sectional view illustrating a main part of the three-dimensional PBF-AM apparatus according to the embodiment of the present invention; 
         FIG. 4  is a view illustrating a state in which a window is closed by a shutter; 
         FIG. 5  is a view illustrating a state in which the window is opened by the shutter; 
         FIG. 6  is a schematic side cross-sectional view illustrating arrangement of a shutter mechanism; 
         FIG. 7  is a perspective view of the arrangement of the shutter mechanism as viewed further from the upper side than an upper wall of a chamber; 
         FIG. 8  is a perspective view of the arrangement of the shutter mechanism as viewed further from the lower side than the upper wall of the chamber; 
         FIG. 9  is a block diagram illustrating a configuration of a shutter control circuit according to the embodiment of the present invention; and 
         FIG. 10  is a flowchart illustrating a method for forming a build object using the three-dimensional PBF-AM apparatus according to the embodiment of the present invention in order of steps. 
     
    
    
     DESCRIPTION OF THE INVENTION 
     Hereinbelow, an embodiment of the present invention will be described in detail with reference to the drawings. In the present specification and the drawings, elements having substantially the same function or configuration are denoted by the same reference signs, and redundant description is omitted. 
       FIG. 1  is a side cross-sectional view schematically illustrating a configuration of a three-dimensional PBF-AM apparatus according to an embodiment of the present invention.  FIG. 2  is a schematic view of a three-dimensional PBF-AM apparatus  10  illustrated in  FIG. 1  as viewed in direction A. 
     In the following description, in order to clarify the shape, positional relationship, and the like of each unit of the three-dimensional PBF-AM apparatus, the right-left direction in  FIG. 1  is referred to as an X direction, the depth direction in  FIG. 1  is referred to as a Y direction, and the up-down direction in  FIG. 1  is referred to as a Z direction. The X direction, the Y direction, and the Z direction are directions perpendicular to each other. Also, the X direction and the Y direction are parallel to the horizontal direction, and the Z direction is parallel to the vertical direction. The definitions of the directions are similar in the other drawings. 
     As illustrated in  FIG. 1 , the three-dimensional PBF-AM apparatus  10  includes a chamber  12 , a beam irradiation device  14 , a powder supply device  16 , a build table  18 , a build box  20 , a stage  22 , and a stage moving device  24 . The powder supply device  16 , the build table  18 , and the stage  22  are arranged inside the chamber  12 . 
     The chamber  12  is a chamber that creates a vacuum state by evacuating air in the chamber by means of a not-illustrated vacuum pump, that is, a vacuum chamber. The chamber  12  includes an upper wall  12   a , a side wall  12   b , and a bottom wall  12   c . The upper wall  12   a  and the bottom wall  12   c  are opposed to each other in the Z direction. 
     The beam irradiation device  14  is a device that irradiates a build surface  32   a  with an electron beam  15 . The build surface  32   a  is equivalent to the upper surface of powder  32  spread on the stage  22 . The beam irradiation device  14  includes an electron gun  26  that serves as a generation source of the electron beam and an optical system  27  that controls the electron beam  15  generated by the electron gun  26 . 
     The optical system  27  includes a focusing lens  28 , an objective lens  29 , and a deflection lens  30 . The focusing lens  28  is a lens that focuses the electron beam  15  generated by the electron gun  26 . The objective lens  29  is a lens that focuses the electron beam  15  focused by the focusing lens  28  on the build surface  32   a . The deflection lens  30  is a lens that deflects the electron beam  15  to cause the electron beam  15  focused by the objective lens  29  to be scanned over the build surface  32   a . Note that the beam is not limited to the electron beam, and may be a laser beam. In addition, the arrangement of the lenses  28 ,  29 , and  30  in the optical system  27  can be changed as necessary, and the configuration of the optical system  27  can also be changed as necessary. 
     The beam irradiation device  14  is attached to the upper wall  12   a  of the chamber  12 . The beam irradiation device  14  is arranged so that a center axis  31  of the electron gun  26  and the optical system  27  is parallel to the Z direction. The lower end portion of the beam irradiation device  14  is provided with a beam emission port  34 . The beam emission port  34  is an opening that causes the electron beam  15  controlled by the optical system  27  to be emitted. That is, the electron beam  15  is emitted from the beam emission port  34 . The beam emission port  34  may be formed in an optical component (such as a lens) that controls the electron beam  15 , or may be formed in a chassis that holds the optical component. 
     The beam emission port  34  is formed in a circular shape as viewed in the direction of the center axis of the optical system  27 . The beam emission port  34  is formed in a shape in which the diameter gradually increases from the upstream side to the downstream side in the traveling direction of the electron beam  15 , that is, in a trumpet shape. The reason why the beam emission port  34  is formed in a trumpet shape is to allow the electron beam  15  to be deflected by the deflection lens  30 . Specifically, an inner peripheral surface  34   a  of the beam emission port  34  is inclined at a predetermined angle with respect to the center axis  31  so that the electron beam  15  does not interfere with (contact) the inner peripheral surface  34   a  of the beam emission port  34  when the electron beam  15  is deflected by the deflection lens  30 . 
     The beam irradiation device  14  includes a shield member  36 . The shield member  36  is a member that covers the inner peripheral surface  34   a  of the beam emission port  34 , and is formed in a trumpet shape to conform to the shape of the beam emission port  34 . The shield member  36  is a member that prevents an evaporated substance to be described below from adhering to the inner peripheral surface  34   a  of the beam emission port  34 . The shield member  36  covers the entire inner peripheral surface  34   a . The components constituting the optical system  27  have limited heat-resistant temperatures and cannot thus be subjected to a very high temperature. On the other hand, in a case where the inner peripheral surface  34   a  of the beam emission port  34  is covered with the shield member  36 , the shield member  36  exerts a heat insulating (heat shielding) effect on the optical system  27 . Therefore, the components of the optical system  27  can be protected from heat. 
     The powder supply device  16  is a device that supplies the powder  32  of metal, which is a raw material for a build object  38 , onto the build table  18 . The powder supply device  16  includes a hopper  16   a , a powder dropper  16   b , and a squeegee  16   c . The hopper  16   a  is a chamber for storing powder. The powder dropper  16   b  is a unit that drops the powder stored in the hopper  16   a  onto the build table  18 . The powder dropper  16   b  drops a predetermined amount of powder to the end of the build table  18 . The squeegee  16   c  is an elongated member elongated in the Y direction. The squeegee  16   c  spreads the powder dropped by the powder dropper  16   b  on the build table  18 . The squeegee  16   c  is provided to be movable in the X direction in order to uniformly spread the powder on the entire surface of the build table  18 . 
     The build table  18  is horizontally arranged inside the chamber  12 . The build table  18  is arranged further on the lower side than the powder supply device  16 . An opening portion  18   a  is formed at the center portion of the build table  18 . The opening portion  18   a  is formed in a circular shape in a planar view or in a quadrangular shape in a planar view. In the present embodiment, as an example, the opening portion  18   a  is formed in a circular shape in a planar view. 
     The build box  20  is a box that forms a build space on the lower side of the opening portion  18   a  of the build table  18 . The upper end portion of the build box  20  is connected to the lower surface of the build table  18  at the edge of the opening portion  18   a . The lower end of the build box  20  is connected to the bottom wall  12   c  of the chamber  12 . 
     The stage  22  is a stage for forming the three-dimensional build object  38  using the powder  32  of metal. The stage  22  is formed in a circular shape in a planar view to conform to the shape of the opening portion  18   a  of the build table  18 . The stage  22  includes an upper surface  22   a  and a lower surface  22   b . In a case where the build object  38  is formed by the three-dimensional PBF-AM apparatus  10 , the powder  32  is spread with a predetermined thickness on the upper surface  22   a  of the stage  22 . The predetermined thickness corresponds to a thickness of one layer in a case where the three-dimensional build object is formed by stacking one layer at a time. The upper surface  22   a  of the stage  22  is arranged to be opposed to the beam irradiation device  14  in the Z direction. The lower surface  22   b  of the stage  22  is arranged to be opposed to the bottom wall  12   c  of the chamber  12  in the Z direction. 
     The stage moving device  24  is a device that moves the stage  22  in the up-down direction. The stage moving device  24  includes a shaft  24   a  and a drive mechanism  24   b . The shaft  24   a  is connected to the lower surface  22   b  of the stage  22 . The drive mechanism  24   b  is driven using a not-illustrated motor as a drive source to move the stage  22  in the up-down direction integrally with the shaft  24   a . Note that the drive mechanism  24   b  can be arranged outside the chamber  12  by allowing the shaft  24   a  to penetrate the bottom wall  12   c  of the chamber  12 . 
     As illustrated in  FIG. 2 , a window  39  is provided in the upper wall  12   a  of the chamber  12 . The window  39  is provided for observation of the inside of the chamber  12 . The observation performed using the window  39  may be or may not be accompanied by measurement, and any of the cases may be employed in the present embodiment. That is, in the present embodiment, the purpose of the observation, the manner of the observation, and the method of the observation are not limited. The window  39  may have any configuration as long as transparency suitable for observation of the inside of the chamber  12  is secured, and the number of the windows  39  is not limited to one and may be plural. For example, although not illustrated, the window  39  has a configuration in which at least one opening formed in the upper wall  12   a  of the chamber  12  is closed using colorless and transparent lead glass for X-ray shielding. The lead glass for X-ray shielding may be directly attached to the upper wall  12   a  of the chamber  12 , or may be attached to an observation member attached to the upper wall  12   a  so as to close the opening portion of the chamber  12 . 
     The window  39  is provided to be displaced in the horizontal direction (Y direction in the illustrated example) from the beam irradiation device  14 . A device (not illustrated) for observation of the inside of the chamber  12  through the window  39  is attached to the upper surface of the upper wall  12   a  of the chamber  12 . Examples of the device for observation include a camera and lighting, and various sensors. 
       FIG. 3  is a longitudinal cross-sectional view illustrating a main part of the three-dimensional PBF-AM apparatus according to the embodiment of the present invention. 
     As illustrated in  FIG. 3 , a shutter  42  is arranged inside the chamber  12 . Specifically, the shutter  42  is arranged on the lower surface side of the upper wall  12   a  of the chamber  12 . The shutter  42  operates in accordance with driving of a motor  44  to open and close the window  39 . The opening and closing of the window  39  includes both a case where the window  39  is closed for protection of the window  39  from contamination due to adhesion of an evaporated substance, heat accompanying beam irradiation, and the like, and a case where the window  39  is opened for observation of the inside of the chamber  12  through the window  39 . 
     The shutter  42  operates in a space between a closed position to shield the window  39  as illustrated in  FIG. 4  and an open position to expose (open) the window  39  as illustrated in  FIG. 5  as the upper wall  12   a  of the chamber  12  is viewed from the lower side. In the present embodiment, as an example, the operation of the shutter  42  is a rotational movement operation. However, the operation of the shutter  42  is not limited to the rotational movement operation, and may be, for example, a linear movement operation or an opening/closing movement operation using a not-illustrated hinge. That is, the operation of the shutter  42  may be any operation as long as the shutter  42  can open and close the window  39 . 
     The operation of the shutter  42  in the present embodiment is a rotational movement operation about the rotation center axis of a connecting shaft  46 . The connecting shaft  46  is a shaft that rotates in accordance with driving of the motor  44 . The motor  44  is provided as an example of a drive source for operating the shutter  42 . The connecting shaft  46  constitutes a shutter mechanism  40  together with the shutter  42  and the motor  44 . Hereinbelow, the configuration of the shutter mechanism  40  will be described in detail. Note that, in the following description, opening and closing the window  39  and opening and closing the shutter  42  have substantially the same meaning. 
       FIG. 6  is a schematic side cross-sectional view illustrating arrangement of the shutter mechanism  40 . Also,  FIG. 7  is a perspective view of the arrangement of the shutter mechanism  40  as viewed further from the upper side than the upper wall  12   a  of the chamber  12 , and  FIG. 8  is a perspective view of the arrangement of the shutter mechanism  40  as viewed further from the lower side than the upper wall  12   a  of the chamber  12 . Note that reference sign  11  in  FIG. 6  schematically indicates a portion serving as a contamination source or a heat source inside the chamber  12 . A main contamination source or heat source when a build object is formed in the three-dimensional PBF-AM apparatus  10  is present on the stage  22  irradiated with the electron beam  15 . 
     As illustrated in  FIGS. 6 to 8 , the shutter mechanism  40  includes a motor mount unit  48 , a rotary motion feedthrough  50 , and an arm  52  in addition to the shutter  42 , the motor  44 , and the connecting shaft  46  described above. The motor  44  is mounted on the motor mount unit  48 . 
     The motor mount unit  48  is attached to the upper wall  12   a  of the chamber  12  by a plurality of (four in the present embodiment) support legs  49 . As illustrated in  FIG. 3 , an output shaft  44   a  of the motor  44  is connected to the connecting shaft  46  by a coupling member  54 . The output shaft  44   a  of the motor  44  and the connecting shaft  46  are coaxially arranged. As a result, the connecting shaft  46  rotates integrally with the output shaft  44   a  of the motor  44 . 
     The connecting shaft  46  is a shaft that connects the motor  44  with the arm  52 . The rotary motion feedthrough  50  is a unit that conducts the connecting shaft  46  from the outside to the inside of the chamber  12  while maintaining airtightness in the chamber  12 . The arm  52  is attached to the lower end of the connecting shaft  46 . The arm  52  is arranged further on the lower side than the upper wall  12   a  of the chamber  12  and parallel to the lower surface of the upper wall  12   a . When the connecting shaft  46  is rotated by driving of the motor  44 , the arm  52  swings in accordance with the rotation of the connecting shaft  46 . 
     The shutter  42  is detachably attached to the arm  52 . The shutter  42 , the arm  52 , and the connecting shaft  46  are each made of metal (including alloy) for antistatic purposes. As illustrated in  FIG. 3 , a positioning screw  53  as a positioning member is attached to the arm  52 . The positioning screw  53  is a screw for positioning the shutter  42 . The positioning screw  53  is secured to the arm  52  by engaging the positioning screw  53  with a screw hole formed in the arm  52  and fastening the positioning screw  53 . The male screw portion of the positioning screw  53  penetrates the arm  52  and protrudes downward. On the other hand, a positioning hole  55  is formed in the shutter  42 . The positioning hole  55  penetrates the shutter  42  in the thickness direction. The shutter  42  is positioned by fitting the positioning hole  55  to the male screw portion of the positioning screw  53 . 
     As illustrated in  FIGS. 4 and 5 , the shutter  42  is provided with a cutout portion  56 . 
     The cutout portion  56  is formed in an arc shape, centering on the positioning hole  55 . A rotary fastener  57  is attached to the cutout portion  56 . The fastener  57  is a member having a T-shaped cross section and having a screw hole  57   a  (refer to  FIG. 3 ). The male screw portion of a set screw  58  (refer to  FIG. 3 ) is engaged with the screw hole  57   a  of the fastener  57 . The male screw portion of the set screw  58  is engaged with the screw hole  57   a  of the fastener  57  through a through hole formed in the arm  52  and the cutout portion  56  formed in the shutter  42 . 
     In order to attach the shutter  42  to the arm  52 , the end of the cutout portion  56  of the shutter  42  first abuts on the male screw portion of the set screw  58  in a state where the positioning hole  55  of the shutter  42  is fitted to the male screw portion of the positioning screw  53 . Subsequently, the fastener  57  is rotated in one direction (for example, a clockwise direction) to be tightened. As a result, the shutter  42  and the arm  52  are sandwiched between the fastener  57  and the set screw  58 . The shutter  42  is thus secured by the tightening force of the fastener  57 . In this manner, the shutter  42  can be attached to the arm  52 . 
     On the other hand, in order to detach the shutter  42  from the arm  52 , the fastener  57  is first rotated in the other direction (for example, a counterclockwise direction) to loosen the tightening force of the fastener  57 . Subsequently, the shutter  42  is rotated about the male screw portion of the positioning screw  53  to detach the cutout portion  56  of the shutter  42  from the fastener  57 . In this manner, the shutter  42  can be detached from the arm  52 . 
     In the shutter mechanism  40  configured as described above, in a case where the window  39  of the chamber  12  is to be protected, the shutter  42  is closed by driving of the motor  44 . As a result, the window  39  is shielded by the shutter  42 . Therefore, the window  39  provided in the chamber  12  can be protected without using a colored film. Also, in a case where the inside of the chamber  12  is to be observed through the window  39 , the shutter  42  is opened by driving of the motor  44 . As a result, the window  39  is opened. Therefore, the inside of the chamber  12  can directly be observed through the window  39  provided in the chamber  12 . Therefore, it is possible to accurately observe the appearance and state of the inside of the chamber  12  as compared with a case of observing the inside of the chamber  12  through a colored film. 
     Also, the shutter  42  is formed to be detachable from the arm  52 . Accordingly, in a case where the shutter  42  is contaminated due to adhesion of an evaporated substance (described below) generated from the contamination source, the shutter  42  can be replaced. 
       FIG. 9  is a block diagram illustrating a configuration of a shutter control circuit according to the embodiment of the present invention. 
     As illustrated in  FIG. 9 , a control unit  60  is connected to the motor  44  of the shutter mechanism  40 . The control unit  60  controls the operation of the shutter  42  by driving the motor  44  on the basis of a preset condition. The control unit  60  includes, for example, computer hardware such as a CPU, a ROM, and a RAM. 
     An instruction receiving unit  62  is connected to the control unit  60 . The instruction receiving unit  62  includes, for example, a user interface such as an operation panel, and receives an opening/closing instruction of the shutter  42 . The opening/closing instruction of the shutter  42  includes an instruction to open the shutter  42  and an instruction to close the shutter  42 . The instruction to open the shutter  42  is an instruction to open the window  39  by moving the shutter  42  arranged at the closed position to the open position. The instruction to close the shutter  42  is an instruction to shield the window  39  by moving the shutter  42  arranged at the open position to the closed position. The instruction receiving unit  62  notifies the control unit  60  of the content of the opening/closing instruction received from the user. In response to this notification, the control unit  60  controls the operation of the shutter  42  in accordance with the opening/closing instruction that the instruction receiving unit  62  has received. 
     Next, a method for forming a build object using the three-dimensional PBF-AM apparatus according to the embodiment of the present invention (a three-dimensional PBF-AM method) will be described. 
     A process for forming a three-dimensional build object using the three-dimensional PBF-AM apparatus  10  is performed in the order of a stage heating step→a powder spreading step→a first preheating step→a melting step→a second preheating step, as illustrated in  FIG. 10 , when a manufacture preparation step and a build object taking-out step are excluded. After the second preheating step is performed, the process returns to the powder spreading step, and thereafter, the first preheating step, the melting step, and the second preheating step are repeated every time one layer of the powder  32  is spread on the stage  22  in the powder spreading step. Also, the steps from the powder spreading step to the second preheating step are repeated a predetermined number of times (the number of layers). Hereinbelow, each of the steps will be described in order. 
     (Stage Heating Step) 
     In the stage heating step, the upper surface  22   a  of the stage  22  is irradiated with the electron beam  15  by the beam irradiation device  14  to heat the stage  22 . 
     (Powder Spreading Step) 
     In the powder spreading step, the powder  32  of metal is supplied onto the build table  18  by the powder supply device  16  in a state where the upper surface  22   a  of the stage  22  is lowered further by a predetermined amount than the upper surface of the build table  18 . At this time, the powder stored in the hopper  16   a  is dropped onto the build table  18  by the powder dropper  16   b . The powder  32  dropped on the build table  18  is spread on the build table  18  by movement of the squeegee  16   c . The squeegee  16   c  passes over the stage  22  during the movement. Therefore, the powder  32  is spread on the stage  22  as well. 
     (First Preheating Step) 
     In the first preheating step, the powder  32  on the stage  22  is irradiated with the electron beam  15  by the beam irradiation device  14  to calcine the powder  32 . At this time, the beam irradiation device  14  causes the electron beam  15  to be scanned in a wider range than the target build object, for example, the entire powder  32  on the stage  22  to calcine the powder  32  on the stage  22 . The first preheating step is also referred to as a powder-heat step. 
     (Melting Step) 
     In the melting step, the powder  32  on the stage  22  is irradiated with the electron beam  15  by the beam irradiation device  14  to melt and solidify the powder  32 . At this time, the beam irradiation device  14  causes the electron beam  15  to be scanned based on two-dimensional data obtained by slicing three-dimensional CAD (Computer-Aided Design) data of a target build object to a certain thickness to selectively melt the powder  32  on the stage  22 . The powder  32  melted by the irradiation of the electron beam  15  is solidified after the electron beam  15  passes. Consequently, manufacture of one layer is completed. Also, when the powder  32  of metal is irradiated with the electron beam  15  in the melting step, part of the melted metal becomes an evaporated substance and rises in a mist form. The evaporated substance adheres to the inner wall of the chamber  12  and contaminates the inner wall. That is, the evaporated substance becomes a contaminant. 
     (Second Preheating Step) 
     In the second preheating step, the build object on the stage  22  is irradiated with the electron beam  15  in preparation for formation of a subsequent layer to raise the temperature of the build object. The second preheating step is also referred to as an after-heat step. 
     In a step, out of the aforementioned steps, in which a predetermined number or more of contaminants are estimated to be generated, the control unit  60  controls the operation of the shutter  42  so that the window  39  is closed by the shutter  42 . The predetermined amount or more of contaminants refer to contaminants that may adversely affect observation of the inside of the chamber  12  due to adhesion to the window  39 . Also, in a step in which a predetermined amount or more of heat is estimated to be generated, the control unit  60  controls the operation of the shutter  42  so that the window  39  is closed by the shutter  42 . The predetermined amount or more of heat refers to an amount of heat that may damage the window  39  due to direct incidence of heat. In the present embodiment, a case will be described as an example in which both the step in which a predetermined number or more of contaminants are estimated to be generated and the step in which a predetermined amount or more of heat is estimated to be generated are the melting step. 
     The control unit  60  controls driving of the motor  44  in the following manner. 
     First, the control unit  60  controls driving of the motor  44  so that the shutter  42  is arranged at the open position in each of the stage heating step, the powder spreading step, the first preheating step, and the second preheating step and so that the shutter  42  is arranged at the closed position in the melting step. Also, when starting the melting step, the control unit  60  drives the motor  44  to move the shutter  42  from the open position to the closed position. As a result, the window  39  is covered by the shutter  42 . Also, when ending the melting step, the control unit  60  drives the motor  44  to move the shutter  42  from the closed position to the open position. As a result, the window  39  is opened. 
     In this manner, the shutter  42  is automatically opened and closed by means of the control unit  60  to enable the window  39  to be protected from the contamination source and the heat source in the melting step. Specifically, the window  39  can be protected by the shutter  42  so that the evaporated substance generated in the melting step does not adhere to the window  39 . In addition, the window  39  can be protected by the shutter  42  so that the heat generated in the melting step is not directly incident on the window  39 . Also, the control unit  60  controls the operation of the shutter  42  on the basis of a preset condition. Therefore, it is not necessary for the user to manually operate the shutter  42 . Accordingly, the window  39  can be protected from the contamination source and the heat source without user intervention. In particular, in a case of forming a build object using the three-dimensional PBF-AM apparatus  10 , the number of times of stacking the powder  32  is very large, and it may thus take several hours to several days from the start to the end of manufacture. Even in such a case, the control unit  60  automatically opens and closes the shutter  42  on the basis of a predetermined condition to enable the window  39  of the chamber  12  to be reliably protected from contamination and heat. 
     Also, when the instruction receiving unit  62  receives an opening/closing instruction of the shutter  42  from the user, the control unit  60  drives the motor  44  on the basis of the instruction content to control the operation of the shutter  42 . 
     For example, when the instruction receiving unit  62  receives an instruction to open the shutter  42  from the user under a situation where the shutter  42  is arranged at the closed position, the control unit  60  drives the motor  44  to move the shutter  42  from the closed position to the open position. Also, when the instruction receiving unit  62  receives an instruction to close the shutter  42  from the user under a situation where the shutter  42  is arranged at the open position, the control unit  60  drives the motor  44  to move the shutter  42  from the open position to the closed position. 
     In this manner, by operating the shutter  42  in accordance with an opening/closing instruction of the shutter  42  by the user, the inside of the chamber  12  can be observed when the user wishes, and the window  39  can be protected from the contamination source and the heat source. Therefore, the usability of the three-dimensional PBF-AM apparatus  10  can be improved. 
     Modification Examples and the Like 
     The technical scope of the present invention is not limited to the above-described embodiment, and includes a mode in which various modifications and improvements are added within a range in which specific effects obtained by the components of the invention and the combination thereof can be derived. 
     For example, in the above embodiment, the window  39  is closed by the shutter  42  when the melting step is started, but the timing of closing the shutter  42  does not necessarily coincide with the start timing of the melting step, and may be slightly before or slightly after the start of the melting step. Similarly, the timing of opening the shutter  42  does not necessarily coincide with the end timing of the melting step, and may be slightly before or slightly after the end of the melting step. 
     Also, in the above embodiment, only the melting step has been given as the step of closing the window  39  by the shutter  42 , but the present invention is not limited thereto, and the window  39  may also be closed by the shutter  42  in a step other than the melting step, for example, the first preheating step and the second preheating step. That is, the number of steps to close the shutter  42  is not limited to one, and may be plural. In addition, since process parameters applied to each step differ depending on the material used as the powder  32  of metal, controls may be taken so that the shutter  42  is closed in a plurality of steps depending on the material. An example case of closing the shutter  42  in a plurality of steps may include a case of using the powder  32  of a high melting point metal. 
     Also, in the above embodiment, the configuration in which the shutter  42  is automatically opened and closed by the control unit  60  has been described as an example, but the present invention is not limited thereto, and a configuration in which the shutter  42  is opened and closed by a manual operation of the user may be employed. Also, a drive source for opening and closing the shutter  42  may be an actuator other than the motor.