Patent Description:
In recent years, there has been known a three-dimensional powder bed fusion additive manufacturing (PBF-AM) apparatus that irradiates a powder material spread in layers with a beam to melt and solidify the powder material, and sequentially stacks solidified layers to form a manufactured object having a three-dimensional structure (see, for example, Patent Literature <NUM>.

<CIT> discloses an additive manufacturing device with: a stage on which material powder s placed; a raising and lowering part which raises and lowers the stage; a side wall part surrounding the stage; and a side wall heating part which is embedded in the side wall part and which heats the side wall part from the inside. The stage includes: an upper plate part having an upper surface on which the material powder is placed; an upper plate heating part which heats the lower surface of the upper plate part; and a heat insulation part interposed between the upper plate heating part and the raising and lowering part.

<CIT> discloses a powder bed fusion apparatus in which an object is built in a layer-by-layer manner. The apparatus includes a build sleeve, a build platform for supporting a powder bed and the build platform lowerable in the build sleeve. A heating element is integrated in or located on the build platform or the build sleeve. A seal is provided for sealing a gap between the build platform and the build sleeve to prevent powder from passing through the gap. A build chamber is provided for maintaining an inert atmosphere both above and below the build platform.

In the three-dimensional PBF-AM apparatus, a powder material is spread on a stage surrounded by a build box, and the powder material is irradiated with a beam to heat the powder material. At this time, heat input by the irradiation of the beam is desirably as small as possible from the viewpoint of the quality of the manufactured object, building time, environmental load, and the like.

However, in the conventional three-dimensional PBF-AM apparatus, a part of the heat input by the irradiation of the beam flows out from the build box as radiant heat. Therefore, it cannot be said that the heat input during building is always efficiently used.

The present invention has been made to solve the problems above, and an object of the present invention is to provide a three-dimensional PBF-AM apparatus capable of more efficiently using the heat input during the building than before.

The present invention is a three-dimensional PBF-AM apparatus including a stage on which a powder material is spread, and a tubular build box disposed in a state of surrounding the stage. The build box includes a side wall portion having a first tubular member that surrounds the stage and a second tubular member that surrounds the stage via the first tubular member and forms a space with the first tubular member, and is configured to be able to form a vacuum heat insulating layer inside the side wall portion by vacuuming the space. The upper and lower ends of the build box are sealed, and a groove is formed on at least one of an outer surface of the first tubular member and an inner surface of the second tubular member. The outer surface of the first tubular member and the inner surface of the second tubular member face each other with a gap interposed therebetween except for a formation portion of the groove, and the space is formed by the groove, the apparatus further comprising: a vacuum pump arranged to vacuum the groove; and a refrigerant supply unit arranged to supply a refrigerant to the groove.

According to the present invention, the heat input during the building can be more efficiently used than in the conventional art.

In the present description and the drawings, elements having substantially the same function or configuration are denoted by the same numerals, and redundant description is omitted.

<FIG> is a side view schematically illustrating a configuration of a three-dimensional PBF-AM apparatus according to a first embodiment of the present invention. In the following description, in order to clarify shapes, positional relationship, and the like of each part of the three-dimensional PBF-AM apparatus, a horizontal direction in <FIG> is referred to as an X direction, a depth direction in <FIG> is referred to as a Y direction, and a vertical direction in <FIG> is referred to as a Z direction. The X direction, the Y direction, and the Z direction are directions orthogonal to each other. Furthermore, the X direction and the Y direction are parallel to a horizontal direction, and the Z direction is parallel to a vertical direction.

As illustrated in <FIG>, the three-dimensional PBF-AM apparatus <NUM> includes a vacuum chamber <NUM>, a beam irradiation device <NUM>, a powder supply device <NUM>, a building table <NUM>, a build box <NUM>, a collection box <NUM>, a stage <NUM>, and a stage moving device <NUM>.

The vacuum chamber <NUM> is a chamber for creating a vacuum state by evacuating air in the chamber using the vacuum pump (not illustrated).

The beam irradiation device <NUM> is a device that irradiates a manufactured surface 32a with the electron beam <NUM>. The manufactured surface 32a corresponds to an upper surface of a metal powder <NUM> spread on the stage <NUM>. Although not illustrated, the beam irradiation device <NUM> includes an electron gun that is a generation source of the electron beam and an optical system that controls the electron beam generated by the electron gun. The optical system includes a focusing lens, an objective lens, a deflection lens, and the like. The focusing lens is a lens that focuses an electron beam <NUM> generated by the electron gun. The objective lens is a lens for focusing the electron beam <NUM> focused by the focusing lens in the vicinity of the manufactured surface 32a. The deflection lens is a lens that deflects the electron beam <NUM> to cause the electron beam <NUM> to scan on the manufactured surface 32a.

The powder supply device <NUM> is a device that supplies a metal powder <NUM> as a powder material to be a raw material of the manufactured object onto the building table <NUM>. The powder supply device <NUM> includes a hopper 16a, a powder drop device 16b, and an arm 16c. The hopper 16a is a container for storing the metal powder. The powder drop device 16b is a device that drops the metal powder stored in the hopper 16a onto the building table <NUM>. The arm 16c is a long-shaped member elongated in the Y direction. The arm 16c spreads the metal powder dropped by the powder drop device 16b on the building table <NUM> and the stage <NUM>. The arm 16c is provided to be movable in the X direction in order to uniformly spread the metal powder on the entire surface of the building table <NUM> and the stage <NUM>.

The building table <NUM> is horizontally disposed inside the vacuum chamber <NUM>. The building table <NUM> is disposed below the powder supply device <NUM>. A central portion of the building table <NUM> is opened. An opening shape of the building table <NUM> is circular in plan view or angular in plan view.

The build box <NUM> is a box that forms a space for manufacturing. The build box <NUM> is formed in a tubular shape. The build box <NUM> is disposed in a state of surrounding the stage <NUM>. A cross-sectional shape of the build box <NUM> is the same as the opening shape of the building table <NUM>. For example, when the opening shape of the building table <NUM> is circular in plan view, the cross-sectional shape of the build box <NUM> is circular, and when the opening shape of the building table <NUM> is angular in plan view, the cross-sectional shape of the build box <NUM> is angular. In the present embodiment, as an example, it is assumed that the cross-sectional shape of the build box <NUM> is circular, that is, the build box <NUM> is formed in a tubular shape. An upper end portion of the build box <NUM> is connected to an opening edge of the building table <NUM>.

The collection box <NUM> is a box that recovers the excess metal powder <NUM> among the metal powders <NUM> supplied onto the building table <NUM> by the powder supply device <NUM>. One collection box <NUM> is provided on each of one side and the other side in the X direction.

The stage <NUM> is provided to be movable in the vertical direction (the Z direction). The stage <NUM> slides in the vertical direction along an inner peripheral surface of the build box <NUM>. A seal member <NUM> is attached to an outer peripheral portion of the stage <NUM>. The seal member <NUM> is a member that maintains slidability and sealability between the outer peripheral portion of the stage <NUM> and the inner peripheral surface of the build box <NUM>. The seal member <NUM> is made of a material having heat resistance and elasticity.

The stage moving device <NUM> is a device that moves the stage <NUM> in the vertical direction. The stage moving device <NUM> includes a shaft 26a and a drive mechanism unit 26b. The shaft 26a is connected to a lower surface of the stage <NUM>. The drive mechanism unit 26b includes a motor and a power transmission mechanism (not illustrated), and drives the power transmission mechanism using the motor as a drive source to move the stage <NUM> integrally with the shaft 26a in the vertical direction. The power transmission mechanism includes, for example, a rack and pinion mechanism, a ball screw mechanism, and the like.

Next, basic procedures in a case of forming the manufactured object having a three-dimensional structure using the three-dimensional PBF-AM apparatus <NUM> having the configuration described above will be described.

First, the metal powder <NUM> is spread in layers on the stage <NUM> in a state where the upper surface of the stage <NUM> is lower than the upper surface of the building table <NUM>. At this time, the powder supply device <NUM> operates as follows. First, the metal powder stored in the hopper 16a is weighed by the powder drop device 16b, so that a predetermined amount of the metal powder <NUM> is dropped from the powder drop device 16b onto the building table <NUM>. Next, the arm 16c reciprocates in the X direction. Specifically, the arm 16c moves from a home position HP to a turning position TP, and then returns from the turning position TP to the home position HP. Accordingly, the metal powder <NUM> is uniformly spread over the entire surfaces of the building table <NUM> and the stage <NUM>. In addition, the excess metal powder <NUM> is recovered in the collection box <NUM>.

Next, the beam irradiation device <NUM> irradiates the upper surface (the manufactured surface 32a) of the metal powder <NUM> with the electron beam <NUM> to pre-sinter the metal powder <NUM>. At this time, the beam irradiation device <NUM> irradiates a wider range than a target manufactured object with the electron beam <NUM>, and defocuses the electron beam <NUM> such that the metal powder <NUM> is not excessively heated.

Next, the beam irradiation device <NUM> irradiates the upper surface of the metal powder <NUM> with the electron beam <NUM> to melt and solidify the metal powder <NUM> as a presintered body. This step is also referred to as a main sintering step. In the main sintering step, the beam irradiation device <NUM> scans the electron beam <NUM> based on two-dimensional data obtained by slicing three-dimensional Computer-Aided Design (CAD) data of the target manufactured object to a certain thickness, thereby selectively melting the metal powder <NUM> on the stage <NUM>. The metal powder <NUM> melted by the irradiation of the electron beam <NUM> is solidified after the electron beam <NUM> passes.

Next, as a preparation for spreading the metal powder <NUM> of the next layer, the beam irradiation device <NUM> irradiates the upper surface of the metal powder <NUM> with the electron beam <NUM> to preheat the metal powder <NUM>. At this time, the beam irradiation device <NUM> defocuses the electron beam <NUM>.

Next, the stage moving device <NUM> lowers the stage <NUM> by a predetermined amount. The predetermined amount corresponds to a thickness of one layer when the manufactured object is built by lamination.

Thereafter, the above operation is repeated until the building of the manufactured object is completed. The building of the manufactured object is completed when the metal powder <NUM> is melted and solidified by the number of layers necessary for the building of the manufactured object.

Thus, the target manufactured object is obtained.

As described above, it is necessary to repeatedly perform the pre-sintering, the main sintering, or the preheating of the metal powder <NUM> and to input the heat by irradiation of the electron beam <NUM> each time until the building of the manufactured object is completed. At this time, when a part of the heat input flows out from the build box <NUM> to the outside as the radiant heat, it is necessary to input a larger amount of heat, which is not preferable from the viewpoint of thermal efficiency. Therefore, in the present embodiment, the following configuration is adopted.

<FIG> is a perspective view illustrating a configuration of the build box <NUM> included in the three-dimensional PBF-AM apparatus <NUM> according to the first embodiment of the present invention, and <FIG> is a longitudinal sectional view in which a part of the build box <NUM> illustrated in <FIG> is enlarged.

As illustrated in <FIG> and <FIG>, the build box <NUM> is formed in a tubular shape. The build box <NUM> includes a side wall portion <NUM>. The side wall portion <NUM> has an appropriate thickness in order to secure mechanical strength enough to withstand pressure received from the metal powder <NUM> during the building and to suppress deformation due to heat. The side wall portion <NUM> has a two-layer structure. Specifically, the side wall portion <NUM> includes a tubular inner pipe <NUM> and a tubular outer pipe <NUM> having an outer diameter larger than that of the inner pipe <NUM>. As illustrated in <FIG> above, when the stage <NUM> is disposed inside the build box <NUM>, the inner pipe <NUM> is disposed in such a way to surround the stage <NUM>, and the outer pipe <NUM> is disposed in such a way to surround the stage <NUM> via the inner pipe <NUM>.

The inner pipe <NUM> corresponds to the first tubular member, and the outer pipe <NUM> corresponds to the second tubular member. Furthermore, the inner peripheral surface of the inner pipe <NUM> corresponds to the inner surface of the first tubular member, and an outer peripheral surface of the inner pipe <NUM> corresponds to an outer surface of the first tubular member. Moreover, the inner peripheral surface of the outer pipe <NUM> corresponds to the inner surface of the second tubular member, and the outer peripheral surface of the outer pipe <NUM> corresponds to the outer surface of the second tubular member.

The inner pipe <NUM> and the outer pipe <NUM> are both made of metal (including alloy). As an example of the metal constituting the inner pipe <NUM> and the outer pipe <NUM>, stainless steel can be exemplified.

The inner pipe <NUM> is formed to be thicker than the outer pipe <NUM>. The inner peripheral surface of the inner pipe <NUM> is a curved surface without unevenness such that the stage <NUM> can smoothly move by sliding of a seal member <NUM> described above. On the other hand, a groove <NUM> is formed on the outer peripheral surface of the inner pipe <NUM>. The groove <NUM> is formed in a spiral shape around a center axis of the build box <NUM>. The groove <NUM> has a depth represented in units of mm, that is, a depth having a dimension on the order of mm. As a longitudinal cross-sectional shape of the groove <NUM>, for example, any shape such as a quadrangle, a semicircle, or a triangle can be adopted. Furthermore, the width and depth of the groove <NUM> can be arbitrarily changed within a range in which a refrigerant to be described later can flow. Moreover, the groove <NUM> is preferably formed in the spiral shape in consideration of ease of flow of a refrigerant to be described later or the like, but may be formed in a shape other than the spiral shape.

One end portion 45a in a length direction of the groove <NUM> is disposed in the vicinity of the upper end portion of the build box <NUM>, and the other end portion 45b in the length direction of the groove <NUM> is disposed in the vicinity of the lower end portion of the build box <NUM>. Furthermore, the groove <NUM> is formed continuously from the one end portion 45a to the other end portion 45b. In the present embodiment, since the groove <NUM> is formed in the spiral shape on the outer peripheral surface of the inner pipe <NUM>, the length direction of the groove <NUM> is a spiral direction along the outer peripheral surface of the inner pipe <NUM>.

Furthermore, ridge units <NUM> are formed on the outer peripheral surface of the inner pipe <NUM>. The ridge units <NUM> are formed adjacent to the groove <NUM> in the Z direction. The ridge units <NUM> are formed in a spiral shape similarly to the groove <NUM>. The ridge units <NUM> protrude radially outward from a bottom surface of the groove <NUM> with the same dimension as the depth of the groove <NUM>. In other words, the outer peripheral surface of the inner pipe <NUM> has an uneven structure in which the grooves <NUM> and the ridge units <NUM> are alternately arranged in the Z direction.

The outer pipe <NUM> is disposed in such a way to cover the entire outer peripheral surface of the inner pipe <NUM>. The outer pipe <NUM> is joined to the inner pipe <NUM> by welding, thereby sealing upper and lower ends of the build box <NUM>. More specifically, the upper end portion of the build box <NUM> is sealed in a way not to leak fluid such as gas or liquid by welding an upper end surface of the inner pipe <NUM> and the upper end surface of the outer pipe <NUM> over the entire circumference of the build box <NUM>. Similarly, the lower end portion of the build box <NUM> is sealed in a way not to leak the fluid by welding the lower end surface of the inner pipe <NUM> and the lower end surface of the outer pipe <NUM> over the entire circumference of the build box <NUM>. In addition, as a method of joining the inner pipe <NUM> and the outer pipe <NUM>, a method other than welding may be adopted as long as the upper and lower ends of the build box <NUM> can be sealed.

The inner peripheral surface of the outer pipe <NUM> is curved without unevenness. Thus, when the outer pipe <NUM> is put on the outer peripheral surface of the inner pipe <NUM>, a space <NUM> is formed between the inner pipe <NUM> and the outer pipe <NUM>. The space <NUM> is a space formed by the groove <NUM> inside the side wall portion <NUM>. Therefore, the space <NUM> is continuously connected from the one end portion 45a to the other end portion 45b in the length direction of the groove <NUM>.

Furthermore, as illustrated in <FIG>, the outer peripheral surface of the inner pipe <NUM> and the inner peripheral surface of the outer pipe <NUM> face each other with a gap <NUM> interposed therebetween except a formation portion of the groove <NUM>. In other words, the ridge units <NUM> of the inner pipe <NUM> face the inner peripheral surface of the outer pipe <NUM> via the gap <NUM>. The gap <NUM> is a minute gap represented in units of um, that is, a gap having a dimension on the order of um. In other words, the dimension of the gap <NUM> is sufficiently smaller than the depth of the groove <NUM>. In addition, even when cross-sectional areas of the groove <NUM> and the gap <NUM> are compared, the cross-sectional area of the gap <NUM> is sufficiently smaller than the cross-sectional area of the groove <NUM>.

Two connection pipes 51a and 51b are connected to the outer pipe <NUM>. One of the two connection pipes 51a and 51b corresponds to a first connection pipe, and the other corresponds to a second connection pipe. The connection pipe 51a communicates with the one end portion 45a of the groove <NUM> via a joint 52a, and the connection pipe 51b communicates with the other end portion 45b of the groove <NUM> via a joint 52b. Here, the "communicate" refers to a state of being spatially connected. The joint 52a is attached to the outer pipe <NUM> to connect the connecting pipe 51a, and the joint 52b is attached to the outer pipe <NUM> to connect the connecting pipe 51b.

<FIG> is a schematic view illustrating a configuration example of a fluid pressure circuit included in the three-dimensional PBF-AM apparatus <NUM> according to the first embodiment of the present invention.

As illustrated in <FIG>, a fluid pressure circuit <NUM> includes two connection pipes 51a and 51b connected to the outer pipe <NUM> in such a way to communicate with the groove <NUM> described above, three valves <NUM>, <NUM>, and <NUM>, a vacuum pump <NUM>, and a refrigerant supply unit <NUM>. The valve <NUM> is provided in the connection pipe 51a. A terminal portion of the connection pipe 51a is opened to the atmosphere.

On the other hand, the connection pipe 51b has a branch unit <NUM>, and is branched into a connection pipe 51b-<NUM> and a connection pipe 51b-<NUM> at the branch unit <NUM>. The valve <NUM> is provided in the connection pipe 51b-<NUM>, and the valve <NUM> is provided in the connection pipe 51b-<NUM>. The connection pipe 51b-<NUM> is connected to the vacuum pump <NUM> via the valve <NUM>. The connection pipe 51b-<NUM> is connected to the refrigerant supply unit <NUM> via the valve <NUM>.

The vacuum pump <NUM> is a pump for vacuuming the groove <NUM>. The refrigerant supply unit <NUM> is a portion that supplies the refrigerant to the groove <NUM>. The refrigerant supplied by the refrigerant supply unit <NUM> may be liquid such as water or gas such as air. Each of the valves <NUM>, <NUM>, and <NUM> is desirably configured by a vacuum valve in such a way to withstand the vacuuming using the vacuum pump <NUM>.

Next, a three-dimensional PBF-AM method using the fluid pressure circuit <NUM> having the configuration above will be described.

To start with, when starting the building of the manufactured object by the three-dimensional PBF-AM apparatus <NUM>, the valve <NUM> and the valve <NUM> are both closed at the very beginning, then the valve <NUM> is opened, and the vacuum pump <NUM> is operated. Accordingly, the space <NUM> formed by the groove <NUM> is vacuumed in the side wall portion <NUM> of the build box <NUM>. Furthermore, the space <NUM> formed by the groove <NUM> is connected to the gap <NUM>. Accordingly, when the groove <NUM> is vacuumed by the vacuum pump <NUM>, the portion of the gap <NUM> is also vacuumed. As a result, the vacuum heat insulating layer is formed inside the side wall portion <NUM> of the build box <NUM>. The vacuum heat insulating layer is formed on both the portions where the groove <NUM> and the space <NUM> are formed and the formation portion of the gap <NUM>, that is, on the entire region of the side wall portion <NUM>.

By forming the vacuum heat insulating layer inside the side wall portion <NUM> in this manner, heat insulating property of the build box <NUM> is greatly improved. Therefore, the heat in the build box <NUM> is difficult to escape to the outside of the build box <NUM>. When forming the manufactured object by the three-dimensional PBF-AM apparatus <NUM>, the building of the manufactured object is started in a state where the vacuum heat insulating layer is formed in the side wall portion <NUM>, and this state is maintained until the building of the manufactured object is completed. In other words, during the building of the manufactured object, a state in which the vacuum heat insulating layer is formed inside the side wall portion <NUM> is maintained. Accordingly, it is possible to reduce the heat flowing out to the outside as the radiant heat from the build box <NUM> among the heat input by the irradiation of the electron beam <NUM> during the building. Therefore, the heat input during the building can be more efficiently used than in the conventional art.

However, when a state in which the vacuum heat insulating layer is formed is maintained in the side wall portion <NUM> after the building of the manufactured object is completed, the temperature of the molding object is difficult to lower. Therefore, it takes a long time until the manufactured object can be taken out of the build box <NUM>.

Therefore, when the building of the manufactured object is completed by the three-dimensional PBF-AM apparatus <NUM>, the valve <NUM> and the valve <NUM> are both opened, the valve <NUM> is closed, and the refrigerant supply unit <NUM> is operated while maintaining the vacuum state in the vacuum chamber <NUM>. Accordingly, the refrigerant is supplied from the refrigerant supply unit <NUM> to the groove <NUM> in the side wall portion <NUM> of the build box <NUM> through the connection pipe 51b.

In this manner, the build box <NUM> is cooled by supplying the refrigerant to the groove <NUM> in the side wall portion <NUM> of the build box <NUM>. In this way, the temperature of the manufactured object can be quickly lowered. Therefore, the time until the manufactured object can be taken out of the build box <NUM> can be shortened. Furthermore, in the conventional art, a technique of supplying an inert gas into the vacuum chamber <NUM> and cooling the manufactured object in the inert gas is also known, but in this conventional art, the manufactured object may be oxidized due to influence of impurities contained in the inert gas. On the other hand, in the present embodiment, since the inside of the vacuum chamber <NUM> is maintained in the vacuum state even after the building is completed, and the manufactured object is cooled in the vacuum, there is no concern that the manufactured object is oxidized.

In addition, in the present embodiment, the dimension of the gap <NUM> is very small as compared with the depth of the groove <NUM>, and the cross-sectional areas of both are greatly different accordingly. Therefore, the refrigerant supplied through the connection pipe 51b easily flows to a portion where the groove <NUM> and the space <NUM> are formed, and is difficult to flow to the formation portion of the gap <NUM>. Accordingly, even when the space <NUM> and the gap <NUM> passing thereto that are formed by the groove <NUM> are formed in the side wall portion <NUM> of the build box <NUM>, the refrigerant can preferentially flow into the groove <NUM>. Furthermore, even when a long refrigerant flow path is secured by the groove <NUM>, the refrigerant can flow from one end to the other end in the length direction of groove <NUM>. Thus, the entire build box <NUM> can be cooled by the refrigerant by forming the groove <NUM> over the entire build box <NUM>. In particular, when the groove <NUM> is formed in the spiral shape, a curve of the groove <NUM> becomes gentle, the refrigerant easily flows, and a long flow path length of the refrigerant can be secured. Therefore, the manufactured object can be efficiently cooled by sufficient heat exchange.

From above, the three-dimensional PBF-AM apparatus <NUM> according to the first embodiment of the present invention can simultaneously obtain a first effect of improving the heat insulating property of the build box <NUM> and a second effect of shortening cooling time of the manufactured object, that is, two opposite effects.

Furthermore, in the first embodiment above, the connection pipe 51b is branched into two, the vacuum pump <NUM> is connected to the connection pipe 51b-<NUM>, and the refrigerant supply unit <NUM> is connected to the connection pipe 51b-<NUM>; but the configuration of the fluid pressure circuit <NUM> can be changed into many types. For example, the connection pipe 51a may be branched into two, the vacuum pump <NUM> may be connected to one connection pipe, and the refrigerant supply unit <NUM> may be connected to the other connection pipe. Furthermore, the vacuum pump <NUM> may be connected to one of the connection pipe 51a and the connection pipe 51b, and the refrigerant supply unit <NUM> may be connected to the other connection pipe.

Furthermore, in the first embodiment above, the terminal portion of the connection pipe 51a is opened to the atmosphere, but the present invention is not limited thereto; and the terminal portion of the connection pipe 51a may be connected to the refrigerant supply unit <NUM> by a circulation pipe (not illustrated) to circulate the refrigerant in the fluid pressure circuit <NUM>.

In addition, the second embodiment of the present invention is different from the first embodiment described above in the structure of the side wall portion <NUM> of the build box <NUM>. Specifically, in the second embodiment of the present invention, as illustrated in <FIG>, between the inner pipe <NUM> and the outer pipe <NUM> constituting the side wall portion <NUM> of the build box <NUM>, a fine unevenness <NUM> is formed on a top surface of the ridge units <NUM>, which is a part of the outer peripheral surface of the inner pipe <NUM>, and a gap 48A is formed by the unevenness <NUM>. Furthermore, the outer peripheral surface of the inner pipe <NUM> and the inner peripheral surface of the outer pipe <NUM> face each other with the gap 48A formed by the fine unevenness <NUM> except the formation portion of the groove <NUM>.

The fine unevenness <NUM> may be recesses and protrusions having a sufficiently smaller height difference between the protrusion portions and the recess portions than the depth of the groove <NUM> such that the refrigerant preferentially flows into the groove <NUM> when the refrigerant is supplied from one end side in the length direction of the groove <NUM>. Specifically, the depth of the groove <NUM> may be on the order of mm (for example, several mm to ten-something of mm), and the height difference of the unevenness <NUM> may be on the order of um (for example, several um to tens of um). The fine unevenness <NUM> may be formed by mechanically or chemically roughening the top surface of the ridge units <NUM>.

By forming the fine unevenness <NUM> on the top surface of the ridge units <NUM> in this manner, the following effects in addition to the same effects as in the case of the first embodiment, can be obtained.

To start with, when the inner peripheral surface of the outer pipe <NUM> is brought into contact with the outer peripheral surface of the inner pipe <NUM>, the gap 48A due to the fine unevenness <NUM> can be secured between the inner pipe <NUM> and the outer pipe <NUM>. Furthermore, the ridge units <NUM> of the inner pipe <NUM> and the inner peripheral surface of the outer pipe <NUM> are brought into point contact or line contact by the fine unevenness <NUM>. Therefore, a contact area between the inner pipe <NUM> and the outer pipe <NUM> can be reduced as much as possible to suppress the transfer of heat from the inner pipe <NUM> to the outer pipe <NUM>. Moreover, when the inner pipe <NUM> is covered with the outer pipe <NUM>, the shape of the outer pipe <NUM> can be held by the fine unevenness <NUM>. In addition, when the groove <NUM> is vacuumed, the deformation and sticking of the outer pipe <NUM> can be suppressed by the presence of the fine unevenness <NUM>.

Furthermore, in the second embodiment above, the fine unevenness <NUM> are formed on the top surface of the ridge units <NUM> of the inner pipe <NUM>, but the present invention is not limited thereto, and fine irregularities may be formed on the inner peripheral surface of the outer pipe <NUM>.

Next, the third embodiment of the present invention will be described. In addition, the third embodiment of the present invention is different from the first embodiment described above in the structure of the side wall portion <NUM> of the build box <NUM>. Specifically, in the third embodiment of the present invention, as illustrated in <FIG>, a spiral groove 45A is formed in the inner peripheral surface of an outer pipe 42A, and a space 47A is formed inside a side wall portion 40A by the groove 45A. Even in a case where such a configuration is adopted, the same effects as those of the first embodiment can be obtained.

The technical scope of the present invention is not limited to the embodiment described above, and includes a mode in which various modifications and improvements are added within a range in which specific effects obtained by the constituent elements of the invention and the combination thereof can be derived.

For example, in the first embodiment and the second embodiment, the groove <NUM> is formed on the outer peripheral surface of the inner pipe <NUM>, and in the third embodiment, the groove 45A is formed on the inner peripheral surface of the outer pipe 42A; however, the present invention is not limited thereto, and the groove may be formed on both the outer peripheral surface of the inner pipe and the inner peripheral surface of the outer pipe.

Furthermore, in the second embodiment, the fine unevenness <NUM> is formed on the top surfaces of the ridge units <NUM>, but the same technical idea can be applied to the third embodiment above. Specifically, in the inner peripheral surface of the outer pipe 42A illustrated in <FIG>, fine irregularities may be formed on a surface excluding the formation portion of the groove 45A, or the fine irregularities may be formed on the outer peripheral surface of the inner pipe 41A.

Claim 1:
A three-dimensional powder bed fusion additive manufacturing (PBF-AM) apparatus (<NUM>), comprising:
a stage (<NUM>) on which a powder material (<NUM>) is spread;
a tubular build box (<NUM>) disposed in a state of surrounding the stage (<NUM>),
wherein
the build box (<NUM>) includes a side wall portion (<NUM>) having a first tubular member (<NUM>) surrounding the stage (<NUM>) and a second tubular member (<NUM>) surrounding the stage (<NUM>) with the first tubular member (<NUM>) interposed therebetween and forming a space (<NUM>) with the first tubular member (<NUM>), and is configured to be able to form a vacuum heat insulating layer inside the side wall portion (<NUM>) by vacuuming the space (<NUM>);
the upper and lower ends of the build box (<NUM>) are sealed,
a groove (<NUM>) is formed on at least one of an outer surface of the first tubular member (<NUM>) and an inner surface of the second tubular member (<NUM>),
the outer surface of the first tubular member (<NUM>) and the inner surface of the second tubular member (<NUM>) face each other with a gap (<NUM>) interposed therebetween except for a formation portion of the groove (<NUM>), and
the space (<NUM>) is formed by the groove (<NUM>), the apparatus further comprising:
a vacuum pump (<NUM>) arranged to vacuum the groove (<NUM>) ; and
a refrigerant supply unit (<NUM>) arranged to supply a refrigerant to the groove (<NUM>).