Metal additive manufacturing method

Abstract

To provide a metal additive manufacturing method capable of suppressing oxidation of a molded object and reused powder.SOLUTION: A metal additive manufacturing method includes: a concentration adjustment step of adjusting an oxygen concentration in an atmosphere to 10 vol.ppm or less and a moisture concentration in the atmosphere to 10 vol.ppm or less; a supply step of supplying a metal powder having a moisture content of 30 mass.ppm or less into the adjusted atmosphere to form a metal powder layer; and a layer forming step of supplying heat to the metal powder layer by using an energy beam in the adjusted atmosphere to form a metal layer.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to metal additive manufacturing methods. [Background technology]

[0002] Patent Document 1 discloses an additive manufacturing system and an additive manufacturing method. This additive manufacturing system includes an additive manufacturing unit that uses energy rays to heat a powder material in the presence of a shielding gas to form layers and sequentially stack the formed layers, and a concentration adjustment unit that adjusts the concentration of gas components in the shielding gas. The additive manufacturing unit includes an irradiation unit that includes an energy ray irradiation source that irradiates the powder material, and a modeling unit that includes a chamber filled with shielding gas and a modeling stage where layers are formed and stacked. The concentration adjustment unit includes a purification unit that removes a first gas component that becomes an impurity in the shielding gas depending on the powder material, and a supply unit that supplies a second gas component selected depending on the powder material into the chamber as needed.

[0003] Patent document 1 also discloses that the powder material remaining after modeling within the chamber is the powder material remaining in the parts of the modeling stage that were not irradiated with the laser (energy ray), but that the powder material surrounding the powder material irradiated with the laser on the modeling stage may be altered by the high heat conducted from the part irradiated with the laser, even if it is not directly irradiated with the laser, and that the powder material remaining after modeling can be reused after undergoing a process such as reduction. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-079550 Summary of the Invention [Problem to be solved by the invention]

[0005] In conventional techniques such as that disclosed in Patent Document 1, there is a problem in that the object and recycled powder in metal additive manufacturing are oxidized by impurities in the atmosphere during manufacturing or by moisture contained in the metal powder used as the material for manufacturing. Therefore, it is desirable to provide a metal additive manufacturing method that can suppress the oxidation of the object and recycled powder.

[0006] The present disclosure has been made in consideration of the above-mentioned circumstances, and its purpose is to provide a metal additive manufacturing method that can suppress oxidation of the molded object and recycled powder. [Means for solving the problem]

[0007] In order to achieve the above object, the metal additive manufacturing method according to the present disclosure includes: a concentration adjusting step of adjusting the oxygen concentration of the atmosphere to 10 ppm by volume or less and the moisture concentration to 10 ppm by volume or less; a supplying step of supplying metal powder having a moisture content of 30 mass ppm or less into the adjusted atmosphere to form a metal powder layer; and a layer forming step of supplying heat to the metal powder layer using energy rays in the adjusted atmosphere to form a metal layer. [Effects of the Invention]

[0008] According to the present disclosure, it is possible to provide a metal additive manufacturing method that can suppress oxidation of the molded object and recycled powder. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram illustrating a configuration of an additive manufacturing apparatus. DETAILED DESCRIPTION OF THE INVENTION

[0010] A metal additive manufacturing method according to an embodiment of the present disclosure will be described with reference to the drawings.

[0011] The metal additive manufacturing method according to this embodiment includes a concentration adjustment process for adjusting the oxygen concentration of the atmosphere to 10 ppm by volume or less and the moisture concentration to 10 ppm by volume or less, a supply process for supplying metal powder having a moisture content of 30 ppm by mass or less into the adjusted atmosphere to form a metal powder layer, and a layer formation process for supplying heat to the metal powder layer using energy rays in the adjusted atmosphere to form a metal layer.

[0012] According to the metal additive manufacturing method of this embodiment, it is possible to suppress oxidation of the molded object and the recycled powder. The metal additive manufacturing method of this embodiment will be described in detail below.

[0013] 1 is a schematic diagram showing the configuration of an additive manufacturing apparatus 100 that can implement the metal additive manufacturing method according to this embodiment. The additive manufacturing apparatus 100 includes a laser oscillator 1, an optical system 2, a chamber 3 with an adjusted internal atmosphere, a storage chamber 4, a manufacturing chamber 5, a recovery chamber 6, a recoater 7, a storage stage 8, a manufacturing stage 9, a first densitometer C1, and a second densitometer C2. The additive manufacturing apparatus 100 uses the laser oscillator 1 to irradiate a laser L (an example of an energy beam) to supply heat to metal powder M on the manufacturing stage 9 to manufacture metal layers (hereinafter sometimes simply referred to as layers), and then sequentially stacks the manufactured metal layers to produce an additive manufactured object X (an example of a manufactured object).

[0014] As the metal powder M, powders of metals such as chromium, copper, iron, manganese, molybdenum, cobalt, nickel, hafnium, niobium, titanium, and aluminum, and alloys thereof are preferred.

[0015] Examples of alloys suitable for the metal powder M include stainless steel alloys, nickel alloys, aluminum alloys, titanium alloys, etc. The metal powder M is more preferably a powder of iron, nickel, or copper, or an alloy thereof.

[0016] Metal powder M is heated to a temperature where the equilibrium oxygen partial pressure is 10 -2It is preferable that the metal powder M is a powder of a metal having an equilibrium oxygen partial pressure of 0.1 Pa or more. Iron, nickel, or copper has a high equilibrium oxygen partial pressure, which suppresses the progress of oxidation reactions and is suitable for promoting reduction reactions. Therefore, when the metal powder M is iron, nickel, or copper, it is easy to perform manufacturing using the metal additive manufacturing method according to this embodiment. The equilibrium oxygen partial pressure is a threshold value that determines whether an oxidation reaction or a reduction reaction will proceed. If the oxygen partial pressure in the atmosphere is higher than the equilibrium oxygen partial pressure, oxidation of the metal will proceed, and if the oxygen partial pressure in the atmosphere is lower than the equilibrium oxygen partial pressure, the metal oxide will be reduced.

[0017] The particle diameter of the metal powder M is, for example, 10 μm or more and 200 μm or less. When the particle diameter of the metal powder M is on this order, the flowability is good and the handling is excellent, and when it is molded into a metal layer, a dense metal layer can be obtained. In other words, the mechanical properties of the additive manufacturing product are improved, and deterioration of the shape can be reduced, thereby improving the quality of the additive manufacturing product.

[0018] The layered manufacturing apparatus 100 has an irradiation unit and a modeling unit. The irradiation unit includes an irradiation source of energy rays that are irradiated onto the metal powder M. The layered manufacturing apparatus 100 includes a laser oscillator 1 and an optical system 2 as an example of the irradiation unit.

[0019] The manufacturing unit includes a chamber 3 filled with a shielding gas and a manufacturing stage 9 where layers are manufactured and stacked. The additive manufacturing apparatus 100 includes the chamber 3, a manufacturing chamber 5, and the manufacturing stage 9 as the manufacturing unit.

[0020] The laser oscillator 1 is an example of an energy beam irradiation source. The laser oscillator 1 irradiates the metal powder M with a laser L as an energy beam. The laser oscillator 1 is not particularly limited as long as it can irradiate the metal powder M on the modeling stage 9 with the laser L. The laser oscillator 1 irradiates the metal powder M in the chamber 3 with the laser L via the optical system 2. In this way, the additive manufacturing apparatus 100 can sinter or melt and solidify the metal powder M at the position irradiated with the laser L. As a result, a layer containing a sintered product of the metal powder M or a melt and solidified product of the metal powder M (hereinafter referred to as a "modeling layer") is formed as an example of a metal layer.

[0021] The optical system 2 is not particularly limited as long as it can control the irradiation position of the laser L on the metal powder M on the modeling stage 9 in accordance with preset data. An example of the optical system 2 is one that has one or more reflecting mirrors. The additive manufacturing apparatus 100 can control the irradiation position of the laser L on the metal powder M by controlling the optical system 2 in accordance with preset data. This allows the additive manufacturing apparatus 100 to manufacture model layers of any shape.

[0022] The modeling unit includes a chamber 3, a modeling chamber 5, and a modeling stage 9. In addition to the chamber 3, the modeling chamber 5, and the modeling stage 9, the storage chamber 4, the recovery chamber 6, the recoater 7, and the storage stage 8 may also be considered to constitute the modeling unit of the additive manufacturing apparatus 100.

[0023] The chamber 3 is a container filled with a shielding gas, and the atmosphere inside the chamber 3 is controlled by the shielding gas.

[0024] To the chamber 3, for example, a supply line L1 which is a pipe for supplying a shielding gas to the chamber 3 and a discharge line L2 which is a pipe for discharging the shielding gas from the chamber 3 may be connected.

[0025] As described above, the shielding gas is a gas for adjusting the atmosphere within the chamber 3. The shielding gas adjusts the oxygen concentration of the atmosphere within the chamber 3 to 10 ppm by volume or less, and also adjusts the moisture concentration of the atmosphere within the chamber 3 to 10 ppm by volume or less (an example of a concentration adjusting step). This makes it possible to suppress oxidation of the layered object X and the recycled powder used when manufacturing the layered object X. The atmosphere within the chamber 3 preferably has an oxygen concentration of 1 ppm by volume or less and a moisture concentration of 5 ppm or less.

[0026] Examples of the shielding gas include nitrogen gas, helium gas, argon gas, and mixed gases containing any combination of these. To adjust the atmosphere in chamber 3 as described above, the oxygen concentration and moisture concentration of the shielding gas may be adjusted to 10 ppm by volume or less.

[0027] The atmosphere inside the chamber 3 may be monitored by an oxygen concentration meter (first concentration meter C1) or a moisture concentration meter (second concentration meter C2). In the additive manufacturing apparatus 100, the first concentration meter C1 and the second concentration meter C2 may be disposed inside the chamber 3, for example.

[0028] Specific target values ​​for adjusting the atmosphere inside the chamber 3 can be determined by referring to an Ellingham diagram. The Ellingham diagram is a graph in which the standard Gibbs energy of reaction is plotted on the vertical axis and the temperature on the horizontal axis, with the standard Gibbs energy of reaction of various oxides at each temperature. Based on the Ellingham diagram, it is possible to determine whether a metal can exist without being oxidized under a specific oxygen partial pressure.

[0029] A storage chamber 4, a modeling chamber 5, and a recovery chamber 6 are formed on the bottom surface B of the chamber 3. The storage chamber 4, the modeling chamber 5, and the recovery chamber 6 each have, for example, a columnar space formed downward from the bottom surface B of the chamber 3 (formed so as to extend downward from the bottom surface B). The shape of the columnar space is not particularly limited. The shape may be, for example, a cylindrical shape or a polygonal pillar shape.

[0030] In the layered manufacturing apparatus 100, a storage chamber 4, a manufacturing chamber 5, and a recovery chamber 6 are formed below the bottom surface B of the chamber 3, as an example.

[0031] The storage chamber, the modeling chamber, and the recovery chamber may be provided on the upper surface of a pedestal provided on the bottom surface B of the chamber 3. The pedestal is used for operations such as storing, supplying, and recovering the metal powder M, modeling by supplying heat to the metal powder M, and stacking modeling layers. The storage chamber, the modeling chamber, and the recovery chamber may be provided outside the chamber 3 so as to be in communication with the space inside the chamber 3.

[0032] As described above, the manufacturing chamber 5 has a space formed below the bottom surface B of the chamber 3. The manufacturing stage 9 is disposed within the manufacturing chamber 5. The manufacturing stage 9 is supported by a movable rod 9a that can move up and down. As the movable rod 9a moves up and down, the manufacturing stage 9 moves up and down within the space within the manufacturing chamber 5 along the inner wall of the manufacturing chamber 5.

[0033] As will be described later, metal powder M, which is a material for modeling and is to be irradiated with a laser L, is placed in the form of a metal powder layer on the upper side of the modeling stage 9.

[0034] As described above, the storage chamber 4 has a space formed below the bottom surface B of the chamber 3. The storage stage 8 is arranged inside the storage chamber 4. Metal powder M is placed above the storage stage 8 before the formation of a modeling layer. In this way, the storage chamber 4 stores unused metal powder M in the space above the storage stage 8.

[0035] The storage stage 8 is supported by a movable rod 8a that can move up and down. As the movable rod 8a moves up and down, the storage stage 8 moves up and down in the space within the storage chamber 4 along the inner wall of the storage chamber 4. As the storage stage 8 moves upward, the metal powder M placed on the upper surface of the storage stage 8 protrudes above the bottom surface B of the chamber 3. In the additive manufacturing device 100, the metal powder M on the storage stage 8 that protrudes above the bottom surface B of the chamber 3 is transported above the manufacturing stage 9 by the left-right movement of the recoater 7.

[0036] The metal powder M stored in the storage stage 8 has a moisture content adjusted to 30 ppm by mass or less. From the storage stage 8, the metal powder M with the moisture content adjusted in this manner is supplied by the recoater 7 into the chamber 3, the atmosphere of which has been adjusted in terms of oxygen concentration and moisture concentration, and is then placed in the form of a layer on the modeling stage 9 (an example of a supplying step). By adjusting the moisture content of the metal powder M to 30 ppm by mass or less, oxidation of the layered object X and the reused powder when modeling the layered object X can be suppressed. Note that the moisture content of the metal powder M is preferably 10 ppm by mass or less.

[0037] In the additive manufacturing device 100, a laser L is irradiated onto the metal powder layer of the metal powder M placed on the manufacturing stage 9 as described above to supply heat, thereby heating the metal powder M as the metal powder layer and manufacturing (forming) a manufacturing layer (an example of a layer formation process).

[0038] In the additive manufacturing device 100, a process (supply process) of forming a metal powder layer of metal powder M on the manufacturing stage 9 and a process (layer formation process) of heating the metal powder M as the metal powder layer to manufacture a manufacturing layer are sequentially repeated, and the manufacturing layers are sequentially stacked to construct a metal laminated structure.

[0039] Below, we will explain the formation of a forming layer on the forming stage 9 and the stacking of a metal laminate structure, using as an example a state in which a laser L is irradiated onto a metal powder layer of metal powder M on the forming stage 9 to form a forming layer of an arbitrary shape.

[0040] After a certain modeling layer of an arbitrary shape has been modeled, the movable rod 9a moves downward, causing the modeling stage 9 to move downward, and new metal powder M is supplied from the storage stage 8 by the recoater 7 to be spread over the upper side of the modeling layer of the arbitrary shape. In this state, when a new modeling layer is further modeled by irradiating the laser L, a new modeling layer is formed on top of the modeling layer of the arbitrary shape that has already been modeled. Thereafter, the modeling stage 9 moves further downward, and new metal powder M is further supplied from the storage stage 8. Next, when the laser L is further irradiated, a new modeling layer is further formed on top of the already layered modeling layer and is layered. In this way, modeling and layering of modeling layers are performed sequentially on the modeling stage 9.

[0041] The additive manufacturing device 100 includes a laser oscillator 1, a storage stage 8, and a manufacturing stage 9, and can repeatedly emit a laser L, lower the manufacturing stage 9, and supply new metal powder M, thereby sequentially stacking manufacturing layers to manufacture an additive manufactured object X. When the additive manufactured object X is completed, the manufacturing stage 9 has lowered to a position where the top end of the additive manufactured object X is at the same height as the bottom surface B of the chamber 3.

[0042] In the areas on the building stage 9 that are not irradiated with the laser L, unmodeled (unused in modeling) metal powder M (metal powder to be reused, i.e., recycled powder) remains. The metal powder M surrounding the metal powder M irradiated with the laser L on the building stage 9 may be heated by the high heat conducted from the area irradiated with the laser L, even if it is not directly irradiated with the laser L. However, by adjusting the atmosphere in the chamber 3 to an oxygen concentration of 10 ppm by volume or less and a moisture concentration of 10 ppm by volume or less as described above, oxidation of the metal powder M surrounding the metal powder M irradiated with the laser L on the building stage 9 is suppressed. Furthermore, by adjusting the moisture content of the metal powder M supplied into the chamber 3 to 30 ppm by mass or less, oxidation of the metal powder M surrounding the metal powder M irradiated with the laser L on the building stage 9 is further suppressed. Therefore, the unmodeled metal powder M can be reused as a material for modeling without undergoing treatment such as reduction. The unshaped metal powder M may be transported to and recovered in a recovery chamber 6 for recovering used powder material, for example. Hereinafter, the metal powder M recovered in the recovery chamber 6 may be referred to as recovered powder.

[0043] It should be noted that when the laser L is irradiated onto the metal powder M on the building stage 9, i.e., during building, spatter may occur. This spatter may be mixed into the recovered powder described above. By adjusting the oxygen concentration and moisture concentration of the atmosphere in the chamber 3 to 10 ppm by volume or less, and further adjusting the moisture content of the metal powder M supplied into the chamber 3 to 30 ppm by mass or less, oxidation of this spatter is also suppressed. Therefore, even if spatter is mixed into the recovered powder, the recovered powder can be reused as a building material (i.e., the metal powder M supplied into the chamber 3) without requiring treatment such as reduction. [Example]

[0044] The metal additive manufacturing method according to this embodiment will be described below based on examples.

[0045] In the examples and comparative examples shown below, the metal species of the metal powder used as the material for manufacturing using energy beams, the atmosphere in the chamber where this manufacturing was performed, and the moisture content (ppm by mass) of the metal powder used as the material for manufacturing were changed, as shown in Table 1. Additive-modeled objects were manufactured for each case, and the manufactured objects and manufacturing conditions were evaluated. An additive-modeling device similar to the additive-modeling device 100 shown in FIG. 1 was used for manufacturing. The laser output used for manufacturing was 300 W, and the laser scanning speed during manufacturing was 700 mm / s. The temperature of the powder bed (manufacturing chamber) during manufacturing (laser irradiation) was 195°C. The additive-modeled objects were manufactured into cylindrical shapes with a diameter of approximately 12 mm and a height of approximately 85 mm.

[0046] [Table 1]

[0047] The atmosphere in the chamber was changed by changing the oxygen concentration [ppm by volume] of the shielding gas in the chamber and the moisture concentration [ppm by volume] of the shielding gas in the chamber. To evaluate the molded object, the oxygen concentration [ppm by mass] in the manufactured object was measured. To evaluate the molding conditions, the oxygen concentration [ppm by mass] during sputtering was measured, and the amount of sputtering generated [g] was also measured. The lower the oxygen concentration of the molded object and the oxygen concentration during sputtering, the better. The lower the amount of sputtering generated, the better.

[0048] Table 1 also shows the equilibrium oxygen partial pressure [Pa] near the melting point of the metal used as the material for molding in each example or comparative example. The equilibrium oxygen partial pressure shown in Table 1 is a value determined from an Ellingham diagram. The examples and comparative examples will be described in detail below.

[0049] Example 1 In Example 1, a nickel alloy (Inconel 718, hereinafter simply referred to as nickel) was used as the metal powder used as the material for molding. The equilibrium oxygen partial pressure of this metal powder (nickel) was 1 Pa. The volumetric median diameter of this metal powder was 33 μm. The median diameter was measured by dispersing the powder in water using a laser diffraction particle size distribution analyzer (Shimadzu Corporation, model: iSpect DIA-10).

[0050] The metal powder was used after adjusting the moisture content in advance, i.e., drying. Specifically, the moisture was removed by holding the powder at 200°C for 240 minutes in an argon gas atmosphere as an inert gas (hereinafter referred to as pre-treatment drying). The moisture content of the metal powder after moisture removal was determined by the Karl Fischer method. In this example, the moisture content of the metal powder was measured using a Karl Fischer moisture meter manufactured by Nitto Seiko Analytech Co., Ltd. The moisture content of the metal powder after moisture removal was 10 ppm by mass.

[0051] The oxygen concentration of the shielding gas was 10 ppm by volume, and the moisture concentration was 10 ppm by volume. The oxygen and moisture concentrations were measured using an oxygen and dew point meter (model: AMTrace) manufactured by Michell.

[0052] The oxygen concentrations of the metal powder used for manufacturing, the oxygen concentration in the manufactured object, and the oxygen concentration of the spatter generated by manufacturing were measured using an oxygen / nitrogen analyzer manufactured by Leco, and were found to be 237 ppm by mass, 136.7 ppm by mass, and 207 ppm by mass, respectively.

[0053] The amount of spatter generated by a series of molding processes (total amount of spatter generated by multiple laminations) was determined as follows. First, the metal powder remaining in the chamber after molding (metal powder not used in molding) was collected and sieved using a sieve with a mesh opening diameter of 100 μm. The weight of the coarse particles collected by the sieve (particles remaining on the mesh) was then measured, and this weight was used as the amount of spatter generated for evaluation. The amount of spatter generated was 52.9 g. The evaluation results are also shown in Table 1.

[0054] (Comparative Example 1) In Comparative Example 1, the oxygen concentration and moisture concentration of the shielding gas were changed to 1500 ppm by volume and 1500 ppm by volume, respectively, as shown in Table 1, and otherwise molding and evaluation were carried out in the same manner as in Example 1. The evaluation results are also shown in Table 1.

[0055] (Comparative Example 2) Comparative Example 2 differed from Example 1 in that the oxygen concentration of the shielding gas was changed to 1500 ppm by volume, as shown in Table 1, but otherwise was molded and evaluated in the same manner as Example 1. The evaluation results are also shown in Table 1.

[0056] (Comparative Example 3) Comparative Example 3 differed from Example 1 in that the moisture concentration of the shielding gas was changed to 1500 ppm by volume, as shown in Table 1, but otherwise was molded and evaluated in the same manner as Example 1. The evaluation results are also shown in Table 1.

[0057] Comparative Example 4 Comparative Example 4 differed from Example 1 in that the retention time in the argon gas atmosphere in the pre-drying process was shortened and the moisture content of the metal powder was changed to 70 ppm by mass, as shown in Table 1. Otherwise, the molded product was shaped and evaluated in the same manner as Example 1. The evaluation results are also shown in Table 1.

[0058] (Comparative Example 5) Comparative Example 5 differs from Comparative Example 4 in that the oxygen concentration and moisture concentration of the shielding gas were changed to 1500 ppm by volume and 1500 ppm by volume, respectively, as shown in Table 1. Otherwise, the molded product was manufactured and evaluated in the same manner as Comparative Example 4. The evaluation results are also shown in Table 1.

[0059] Example 2 In Example 2, as shown in Table 1, the metal type of the metal powder was changed to an iron-based alloy (SKD61, hereinafter simply referred to as iron), and otherwise, molding and evaluation were carried out in the same manner as in Example 1. The equilibrium oxygen partial pressure of this metal powder (iron) was 0.1 Pa. The volume-based median diameter of this metal powder was 34 μm. The moisture content of the metal powder after moisture removal was approximately 10 ppm by mass. The oxygen concentration of the metal powder was 348 ppm by mass. The evaluation results are also shown in Table 1.

[0060] (Comparative Example 6) Comparative Example 6 differs from Example 2 in that the oxygen concentration and moisture concentration of the shielding gas were changed to 1500 ppm by volume and 1500 ppm by volume, respectively, as shown in Table 1. Otherwise, the molded product was manufactured and evaluated in the same manner as Example 2. The evaluation results are also shown in Table 1.

[0061] As shown in Table 1, in Example 1 (nickel), the oxygen concentration in the molded object was approximately 42% lower than that of the metal powder used as the molding material, indicating that oxidation during molding was suppressed and that a reduction reaction actually occurred during molding.

[0062] Furthermore, when molding in a typical atmosphere such as Comparative Example 1 (nickel) (oxygen concentration and moisture concentration of the shielding gas were 1500 volume ppm and 1500 volume ppm, respectively), the oxygen concentration of the sputter increased by approximately 983% compared to the metal powder used as the molding material, and there was a significant tendency for oxidation.However, in Example 1, the oxygen concentration of the sputter decreased by approximately 13% compared to the metal powder used as the molding material, suppressing oxidation and rather causing a reduction reaction.Furthermore, in Example 1, the amount of sputter generated was reduced by approximately 60% compared to Comparative Example 1.

[0063] The oxygen concentration in the shaped object, the oxygen concentration in the sputtering, and the amount of sputtering in Example 1 were all lower than the oxygen concentration in the shaped object, the oxygen concentration in the sputtering, and the amount of sputtering in Comparative Examples 1-5, and were therefore favorable.

[0064] Furthermore, in Example 2 (iron), the oxygen concentration in the molded object was approximately 77% lower than that of the metal powder used as the molding material, indicating that oxidation during molding was suppressed and that a reduction reaction actually occurred during molding.

[0065] Furthermore, in the case of Comparative Example 6 (iron) where the oxygen concentration of the shielding gas was 1500 volume ppm and the moisture concentration was 1500 volume ppm, respectively, the oxygen concentration of the sputter increased by approximately 312% compared to the metal powder used as the material for manufacturing, and there was a significant tendency for oxidation. However, in Example 2, the oxygen concentration of the sputter decreased by approximately 29% compared to the metal powder used as the material for manufacturing, and oxidation was suppressed, and a reduction reaction rather occurred, a tendency similar to that of Example 1, was observed. Furthermore, in Example 2, the amount of sputter generated was reduced by approximately 30% compared to Comparative Example 6, and a tendency similar to that of Example 1 was observed.

[0066] Thus, the oxygen concentration in the molded object, the oxygen concentration in the sputtering, and the amount of sputtering in Example 2 were all lower and better than those in Comparative Example 6. These trends were similar to those in Example 1.

[0067] As such, in the above examples and comparative examples, oxidation during molding was suppressed for the two metal species, nickel and iron, and the effects of promoting the reduction reaction and suppressing the generation of spatter were observed.

[0068] Based on this result and the information from the Ellingham diagram, it can be seen that copper and lead have a higher equilibrium oxygen partial pressure than iron in Example 2, and therefore can provide the same effect as iron.

[0069] Thus, in the metal additive manufacturing method, oxidation of the molded object and the reused powder (sputter) can be suppressed by adjusting the oxygen concentration of the atmosphere to 10 ppm by volume or less and the moisture concentration to 10 ppm by volume or less. Also, in the metal additive manufacturing method, oxidation of the molded object and the reused powder (sputter) can be suppressed by adjusting the moisture content of the metal powder to 30 ppm by mass or less.

[0070] Furthermore, by adjusting the oxygen and moisture concentrations of the atmosphere and the moisture content of the metal powder, it is possible to suppress the occurrence of spatter during metal additive manufacturing and also to suppress the oxidation of the spatter. This improves the utilization efficiency of the metal powder. Specifically, the proportion of metal powder used in additive manufacturing increases, and even if there is metal powder (including spatter) that is not used in additive manufacturing, oxidation of the metal powder is suppressed and no reduction treatment is required, so the metal powder can be easily reused as a material for additive manufacturing.

[0071] In this way, it is possible to provide a metal additive manufacturing method that can suppress oxidation of the shaped object and the recycled powder.

[0072] It should be noted that the embodiments disclosed in this specification are merely examples, and the embodiments of the present disclosure are not limited to these, and can be modified as appropriate within the scope of the purpose of the present disclosure. [Industrial Applicability]

[0073] The present disclosure is applicable to metal additive manufacturing methods. [Explanation of symbols]

[0074] 1: Laser oscillator 100: Additive manufacturing equipment 2:Optical system 3: Chamber 4: Storage room 5: Modeling room 6: Recovery Room 7: Recoater 8: Storage Stage 8a: Movable rod 9: Modeling stage 9a: Movable rod B: Bottom C1: First concentration meter C2: Second concentration meter L: Laser L1: Supply line L2: Discharge line M: Metal powder X: Additive manufacturing

Claims

1. a concentration adjusting step of adjusting the oxygen concentration of the atmosphere to 10 ppm by volume or less and the moisture concentration to 10 ppm by volume or less; a supplying step of supplying metal powder having a moisture content of 30 mass ppm or less into the adjusted atmosphere to form a metal powder layer; a layer formation process in which, in the adjusted atmosphere, heat is supplied to the metal powder layer using energy rays to form a metal layer.

2. The metal additive manufacturing method according to claim 1 , wherein in the concentration adjusting step, the oxygen concentration is set to 1 volume ppm or less and the water concentration is set to 5 ppm or less.

3. The metal additive manufacturing method according to claim 1 , wherein the metal powder supplied in the supplying step has a moisture content of 10 ppm by mass or less.

4. The metal powder has an equilibrium oxygen partial pressure of 10 －２ The metal additive manufacturing method according to claim 1, wherein the metal powder has a viscosity of Pa or higher.

5. The metal additive manufacturing method according to claim 1 , wherein the metal powder is iron, nickel, or copper powder.

6. The metal additive manufacturing method according to claim 1 , wherein the supplying step and the layer forming step are repeated in sequence to sequentially stack the metal layers.

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