Method of making lamination-formed body

Abstract

To provide a method of making a lamination-formed body that allows for forming a lamination-formed body at high quality and is effective for a metal material having a martensitic-transformation initiating temperature of 200°C or higher.SOLUTION: There is provided a method of making a lamination-formed body according to the present invention including: a solidified-layer forming step of laying solidified layers by repeating a material-layer forming step of forming a material layer by supplying a material powder containing a metal material that expands with tempering processing onto a formation table regulated at a forming temperature T1 and a solidification step of forming a solidified layer by irradiating the material layer with laser light or the like; and a thermal expansion processing step of, each time a predetermined number of or a predetermined thickness of solidified layers are newly formed, raising the temperature of the solidified layers from a forming temperature T1 to a heating temperature T2 to be maintained for predetermined time and then lowering the temperature down to the forming temperature T1. In the method, the metal material has a martensitic transformation initiating temperature of 200°C or higher so as to satisfy a relationship of T1<T2≤350°C and 50°C≤T2-T1≤200°C.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a laminated object.

Background Art

[0002] In the laminated manufacturing of three-dimensional objects, various methods are known. For example, in the powder bed fusion method, a material layer composed of a material powder is formed in a shaping area on a shaping table, and a laser beam or an electron beam is scanned and irradiated to a predetermined position of the material layer to sinter or melt the material layer to form a solidified layer. Then, by repeating the formation of the material layer and the solidified layer, the solidified layers are laminated to manufacture a desired three-dimensional object.

[0003] Patent Document 1 discloses a method for manufacturing a laminated object capable of suppressing deformation and cracking of the shaped object by intentionally advancing the martensitic transformation each time one or a plurality of solidified layers are formed, reducing the tensile stress due to the shrinkage of the metal by the compressive stress due to the expansion accompanying the martensitic transformation, and controlling the residual stress of the shaped object. Specifically, when the first temperature is T1, the second temperature is T2, the martensitic transformation start temperature of the solidified layer is Ms, and the martensitic transformation end temperature of the solidified layer is Mf, the solidified layer is cooled from the first temperature to the second temperature to advance the martensitic transformation under the temperature conditions satisfying Mf≦T1, T2<T1, and T2≦Ms. The amount of martensitic transformation (expansion amount) can be controlled by appropriately setting the first temperature and the second temperature under the above temperature conditions. Further, the temperature adjustment of the solidified layer is possible, for example, by providing a temperature adjustment device composed of a heater and a cooler on the shaping table and adjusting the shaping table to a set temperature corresponding to the first temperature or the second temperature by the temperature adjustment device.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

[0005] In an additive manufacturing device of general specifications, the upper limit of the set temperature of the modeling table is about 200 to 350°C. Therefore, when the method of Patent Document 1 is applied to additive manufacturing using a metal material with a relatively high martensitic transformation start temperature of 200°C or more, the settable range of the first temperature that satisfies the above-mentioned temperature conditions is limited, making it difficult to sufficiently suppress deformation and cracking of the modeled object. Although it is possible to introduce a modeling table with special specifications that has a higher upper limit of the set temperature, there is a concern about the influence of thermal displacement of surrounding members due to the modeling table being set at an extremely high temperature.

[0006] The present invention has been made in consideration of the above circumstances, and aims to provide a method for manufacturing additive objects that is capable of producing high-quality additive objects and is effective for metal materials with a martensitic transformation start temperature of 200°C or higher. [Means for solving the problem]

[0007] According to the present invention, the following inventions are provided. [1] A method for manufacturing an additive manufacturing object, comprising: a material layer forming step of supplying a material powder containing a metallic material that expands with a tempering process onto a modeling table adjusted to a modeling temperature to form a material layer; a solidification step of irradiating a predetermined region of the material layer with a laser beam or an electron beam to form a solidified layer; and a thermal expansion treatment step of raising the temperature of the solidified layer from the modeling temperature to a heating temperature, holding the heating temperature for a predetermined time, and then lowering the temperature to the modeling temperature each time a predetermined number or thickness of the solidified layer is newly formed, the martensitic transformation start temperature of the metallic material is 200°C or higher, and the relationship between the following formulas (1) and (2) is satisfied, where T1 is the modeling temperature and T2 is the heating temperature. <T2≦350℃(1)50℃≦T2-T1≦200℃(2) [2] The manufacturing method according to [1], wherein the heating temperature is 200°C or higher and 350°C or lower. [3] The manufacturing method according to [1] or [2], wherein the metal material is high speed steel. [4] A manufacturing method described in any one of [1] to [3], further comprising a post-modeling heating process in which, after completion of modeling of the layered object, the solidified layer is heated from the modeling temperature to the heating temperature and maintained at the heating temperature for a predetermined period of time, and a slow cooling process in which, after the post-modeling heating process, the solidified layer is slowly cooled from the heating temperature to room temperature. Effect of the Invention

[0008] In the method for manufacturing an additive manufacturing object according to the present invention, a material powder containing a metal material that expands with a tempering process is used, and in the thermal expansion process, each time a predetermined number or thickness of solidified layers are newly formed, the solidified layer is heated from the molding temperature to the heating temperature, held for a predetermined time, and then cooled to the molding temperature. This reduces the tensile stress caused by the contraction of the metal by the compressive stress caused by the expansion caused by the heat treatment in the thermal expansion process, thereby controlling the residual stress of the molded object and suppressing deformation and cracking of the molded object. The manufacturing method of the present invention is effective for metal materials that expand with a tempering process and have a martensitic transformation start temperature of 200°C or higher. In addition, since the molding temperature and the heating temperature are set so as to satisfy the relationship between the above-mentioned formulas (1) and (2), the method can be carried out by an additive manufacturing device of general specifications in which the upper limit of the set temperature of the molding table is about 200 to 350°C. [Brief description of the drawings]

[0009] [Figure 1] 1 is a schematic configuration diagram of an additive manufacturing apparatus 100 according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a perspective view of a material layer forming apparatus 3. [Diagram 3] 2 is a perspective view of a recoater head 32 of the material layer forming apparatus 3 from above. [Figure 4] 2 is a perspective view of a recoater head 32 of the material layer forming apparatus 3, seen from below. [Diagram 5] FIG. 2 is an exploded perspective view of the modeling table 4 equipped with a temperature adjustment device 42. [Figure 6] 1A to 1C are diagrams illustrating a method for manufacturing a layered object using the layered object manufacturing apparatus 100. [Figure 7] 1A to 1C are diagrams illustrating a method for manufacturing a layered object using the layered object manufacturing apparatus 100. [Figure 8] 13 is a graph showing changes in the set temperature of the modeling table 4 in the method for manufacturing a layered object using the layered modeling apparatus 100. [Figure 9] 11 is a graph showing temperature changes in the upper layer of a model on a modeling table 4 during a solidified layer formation process and a thermal expansion treatment process. [Figure 10] 11 is a graph showing temperature changes of an upper layer of an object on a modeling table 4 in a post-modeling heating process and a post-cooling process. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Each feature described in the following embodiment can be combined with each other. Also, each feature can be an invention independently.

[0011] 1. Additive manufacturing device 100 FIG. 1 shows an example of an additive manufacturing apparatus 100 used in the additive manufacturing method of this embodiment. The additive manufacturing apparatus 100 includes a chamber 1, a material layer forming apparatus 3, and an irradiation apparatus 5. In a modeling region R provided on a modeling table 4 arranged in the chamber 1, a material layer 91 and a solidified layer 92 are repeatedly formed to form a desired additive manufacturing object. The application of the additive manufacturing object manufactured by the additive manufacturing apparatus 100 is not particularly limited, but the present invention is particularly suitable for use in manufacturing an additive manufacturing object used as a mold. The present invention is particularly suitable for use in manufacturing an additive manufacturing object used as a mold that requires higher strength and higher rigidity, such as a mold for press processing (hereinafter referred to as a press mold).

[0012] 1.1.Chamber 1 The chamber 1 covers a modeling region R where a desired layered object is formed. The chamber 1 is connected to an inert gas supply / exhaust device (not shown). The inert gas supply / exhaust device supplies a predetermined concentration of inert gas to the chamber 1, thereby filling the chamber 1 with the inert gas. The inert gas containing fumes generated with the formation of the solidified layer 92 is exhausted from the chamber 1 and subjected to a fume removal process in the inert gas supply / exhaust device before being supplied to the chamber 1 and reused. In this specification, the inert gas is a gas that does not substantially react with the material layer 91 or the solidified layer 92, and is appropriately selected from nitrogen gas, argon gas, helium gas, etc. depending on the type of molding material.

[0013] 1, for example, a window 1a serving as a transmission window for the laser light L output from the irradiation device 5 is provided on the upper surface of the chamber 1. The window 1a is made of a material capable of transmitting the laser light L, and is selected from quartz glass, borosilicate glass, or crystals of germanium, silicon, zinc selenide, or potassium bromide, etc., depending on the type of laser light L. For example, when the laser light L is a fiber laser or a YAG laser, the window 1a can be made of quartz glass.

[0014] As shown in FIG. 1, a contamination prevention device 17 is provided on the upper surface of the chamber 1 so as to cover the window 1a. The contamination prevention device 17 includes a cylindrical housing 17a and a cylindrical diffusion member 17c arranged in the housing 17a. An inert gas supply space 17d is provided between the housing 17a and the diffusion member 17c. An opening 17b is provided on the inside of the diffusion member 17c on the bottom surface of the housing 17a. The diffusion member 17c has a large number of fine holes, and clean inert gas supplied from the inert gas supply / exhaust device to the inert gas supply space 17d fills the clean room 17e through the fine holes and is ejected from the opening 17b toward the lower side of the contamination prevention device 17. This configuration prevents fumes from adhering to the window 1a and can eliminate fumes from the irradiation path of the laser light L.

[0015] 1.2. Material layer forming device 3 The material layer forming apparatus 3 is provided inside the chamber 1. As shown in Fig. 2, the material layer forming apparatus 3 includes a base 31 and a recoater head 32 disposed on the base 31. The recoater head 32 is configured to be reciprocable in one horizontal axial direction by a recoater head driving device 33 incorporating a driving mechanism such as a motor.

[0016] As shown in FIG. 3 and FIG. 4, the recoater head 32 includes a material storage section 32a, a material supply port 32b, and a material discharge port 32c. The material supply port 32b is provided on the upper surface of the material storage section 32a, and serves as a receiving port for the material powder supplied from a material supply unit (not shown) to the material storage section 32a. The material discharge port 32c is provided on the bottom surface of the material storage section 32a, and discharges the material powder in the material storage section 32a. The material discharge port 32c has a slit shape extending in the longitudinal direction of the material storage section 32a. Flat blades 32fb and 32rb are provided on both side surfaces of the recoater head 32. The blades 32fb and 32rb flatten the material powder discharged from the material discharge port 32c to form a material layer 91.

[0017] 1.3.Irradiation device 5 The irradiation device 5 irradiates the material layer 91 with a laser beam L or an electron beam to form a solidified layer 92. For example, as shown in Fig. 1, the irradiation device 5 of this embodiment is provided above the chamber 1, and irradiates the irradiation region of the material layer 91 formed in the modeling region R with the laser beam L to melt or sinter and solidify the material powder, thereby forming a solidified layer 92. As shown in Fig. 2, the irradiation device 5 of this embodiment includes a laser light source 51, a focus control unit 53, an X-axis galvanometer mirror 55a and a Y-axis galvanometer mirror 55b, and actuators (not shown) that rotate the X-axis galvanometer mirror 55a and the Y-axis galvanometer mirror 55b, respectively.

[0018] The laser light source 51 generates laser light L. The laser light L may be any light capable of sintering or melting the material powder, and may be, for example, a fiber laser, a CO2 laser, a YAG laser, or the like. The focus control unit 53 includes a focus control lens therein and can focus the laser light L to adjust the spot diameter.

[0019] The laser light L that has passed through the focus control unit 53 is scanned two-dimensionally in an X-axis direction, which is one horizontal axis direction, and a Y-axis direction, which is another horizontal axis direction and is perpendicular to the X-axis direction. Specifically, the laser light L is reflected by the X-axis galvanometer mirror 55a and scanned in the X-axis direction of the modeling region R, and is reflected by the Y-axis galvanometer mirror 55b and scanned in the Y-axis direction of the modeling region R. The laser light L reflected by the X-axis galvanometer mirror 55a and the Y-axis galvanometer mirror 55b passes through the window 1a and is irradiated onto the material layer 91 in the modeling region R, thereby forming a solidified layer 92.

[0020] The irradiation device 5 is not limited to the above-mentioned form. For example, an fθ lens may be provided instead of the focus control unit 53. The irradiation device 5 may be configured to form the solidified layer 92 by irradiating the material layer 91 with an electron beam instead of the laser light L to solidify the material layer 91. Specifically, the irradiation device 5 may be configured to include a cathode electrode (not shown) that emits electrons, an anode electrode (not shown) that converges and accelerates the electrons, a solenoid (not shown) that forms a magnetic field to converge the direction of the electron beam in one direction, and a collector electrode (not shown) that is electrically connected to the material layer 91, which is the irradiated body, and applies a voltage between the cathode electrode. In this case, the cathode electrode and the anode electrode serve as an output source that outputs the electron beam, and the solenoid serves as a scanning means that scans the electron beam. The window 1a and the contamination prevention device 17 may be omitted, and the cathode electrode may be provided so as to protrude into the chamber 1. When an irradiation device that irradiates an electron beam is used, the atmosphere in the chamber 1 may be a noble gas atmosphere in a state close to vacuum. The noble gases are sometimes called rare gases.

[0021] 1.4. Modeling table 4 1, a modeling table 4 is placed in a chamber 1, and a model is formed in a modeling region R on the modeling table 4. The modeling table 4 is driven by a modeling table driving device 41 and is movable in the vertical direction. During modeling, a base plate 90 is placed in the modeling region R, and material powder is supplied to an upper surface of the base plate 90 by the material layer forming device 3, forming a material layer 91.

[0022] The additive manufacturing apparatus 100 includes a temperature adjustment device 42 for adjusting the temperatures of the material layer 91 and the solidified layer 92. In this embodiment, the temperature adjustment device 42 is provided inside the modeling table 4, and the modeling table 4 is adjusted to a predetermined temperature by the temperature adjustment device 42, thereby adjusting the temperatures of the material layer 91 and the solidified layer 92 on the modeling table 4. As shown in FIG. 5, the temperature adjustment device 42 includes a heater 43 for heating the modeling table 4 and a cooler 44 for cooling the modeling table 4.

[0023] Specifically, the modeling table 4 comprises a top plate 4a and three support plates 4b, 4c, and 4d, and a heater 43 capable of heating the top plate 4a is disposed between the top plate 4a and the support plate 4b disposed below it, and a cooler 44 capable of cooling the top plate 4a is disposed between the two support plates 4c and 4d below the support plate 4b.

[0024] The heater 43 is, for example, an electric heater having a heating element, or a tubular member configured to allow a high-temperature heat medium to flow therethrough. The cooler 44 can be configured by arranging, on the support plate 4d, a tubular member configured to allow a refrigerant supplied from a refrigerant circulation device (not shown), such as a chiller or a cooling tower, to flow therethrough. With this configuration, the top plate 4a on the top surface of the modeling table 4 can be heated or cooled to adjust the temperature to a predetermined level. The material layer 91 and the solidified layer 92 are temperature-adjusted by direct heat transfer between the top plate 4a and the material layer 91 and the solidified layer 92, or by indirect heat transfer via a base plate 90 arranged on the top plate 4a and a layer formed on the lower side.

[0025] The configuration of the temperature adjustment device 42 is not limited to that of the embodiment described above. In this embodiment, the tubular member of the cooler 44 is arranged to be sandwiched between the support plates 4c and 4d. However, for example, a pipe for circulating a refrigerant may be formed inside one or both of the support plates 4c and 4d, and the cooler 44 may be configured by the pipe. Alternatively, the top plate 4a and the three support plates 4b, 4c, and 4d may be integrated into a structure, and the heater 43 and the cooler 44 may be configured within the structure. In addition, in order to prevent thermal displacement of the modeling table driving device 41, a constant temperature unit maintained at a constant temperature may be provided between the temperature adjustment device 42 and the modeling table driving device 41.

[0026] 2.Metal materials The material layer 91 is formed using a material powder containing a metallic material that expands with tempering and has a martensitic transformation start temperature of 200°C or higher. Tempering refers to a process in which a metallic material having an unstable structure after quenching is reheated to a predetermined temperature, held at that temperature, and then cooled to promote transformation or precipitation of the structure, stabilize the structure, and improve toughness. By using a material powder containing a metallic material having the above-mentioned properties, in the thermal expansion process described below, the tensile stress caused by the contraction of the metal due to the temperature drop immediately after irradiation with the laser light L is reduced by the compressive stress caused by the volume expansion due to the heat treatment in the thermal expansion process, thereby controlling the residual stress of the molded object and suppressing deformation and cracking of the molded object.

[0027] The metal material used as the material powder has a martensitic transformation start temperature of 200° C. or higher, preferably 300° C. or higher, and more preferably 350° C. or higher. As described above, when the martensitic transformation start temperature is relatively high, in an additive manufacturing apparatus of general specifications in which the upper limit of the set temperature of the modeling table 4 is about 200 to 350° C., it is difficult to sufficiently suppress deformation and cracking of the modeled object by the method disclosed in Patent Document 1, but by applying the present invention, it is possible to realize high-quality modeling.

[0028] As an example of a metal material that expands with tempering and has a martensitic transformation start temperature of 200°C or higher, there is high-speed steel as defined in JIS G4403. Specific examples of high-speed steel include molybdenum-based high-speed steel (SKH50, SKH51, SKH52, SKH53, SKH54, SKH55, SKH56, SKH57, SKH58, SKH59, SKH40) and tungsten-based high-speed steel (SKH2, SKH3, SKH4, SKH10). High-speed steel is used, for example, as a material for dies. High-speed steel is used, for example, as a material for dies such as press dies that require higher strength and higher rigidity.

[0029] High-speed steel contains a relatively large amount of carbon, 0.73 to 1.60 mass %. Therefore, in the process of quenching the solidified layer 92 from a very high temperature state after irradiation with the laser light L or the electron beam to room temperature, cracks tend to develop from the places where carbides are precipitated, and cracks tend to occur. In order to avoid quenching, the molding table 4 has been set to a relatively high temperature of about 300°C and molding has been performed while adjusting the temperature of the material layer 91 and the solidified layer 92. However, when the size of the molded object is large, the temperature control is insufficient and it is very difficult to suppress cracks. In addition, since the martensitic transformation start temperature of high-speed steel is relatively high, 300 to 400°C, the technical significance of applying the present invention is particularly remarkable as described above.

[0030] The material powder preferably contains at least 50 mass % of the metallic material that expands with tempering and has a martensitic transformation start temperature of 200° C. or higher, more preferably at least 80 mass % of the metallic material, and even more preferably at least 95 mass % of the metallic material. The material powder may be composed only of metallic material that expands with tempering and has a martensitic transformation start temperature of 200° C. or higher.

[0031] Furthermore, the base plate 90 may be made of the same metal material as the material powder, or may be made of a metal material with a different composition, such as iron.

[0032] 3. Manufacturing method of additive manufacturing 6 to 10, a method for manufacturing an additive manufacturing object using the additive manufacturing apparatus 100 will be described. The manufacturing method according to this embodiment includes a material layer forming step of supplying a material powder containing a metal material that expands with a tempering process onto a modeling table 4 adjusted to a modeling temperature T1 to form a material layer 91, and a solidification step of irradiating a predetermined region of the material layer 91 with a laser beam L or an electron beam to form a solidified layer 92, thereby stacking the solidified layers 92, and a thermal expansion process of increasing the temperature of the solidified layer 92 from the modeling temperature T1 to a heating temperature T2, maintaining the heating temperature T2 for a predetermined time, and then decreasing the temperature to the modeling temperature T1 every time a predetermined number or thickness of solidified layers 92 are newly formed. In addition, the manufacturing method according to this embodiment further includes a post-modeling heating process in which, after completion of the modeling of the additive manufacturing object, the solidified layer 92 is heated from the modeling temperature T1 to a heating temperature T2 and maintained at the heating temperature T2 for a predetermined period of time, and a slow cooling process in which, after the post-modeling heating process, the solidified layer 92 is slowly cooled from the heating temperature T2 to room temperature Tn.

[0033] 3.1. Solidified layer formation process The solidified layer forming process includes a material layer forming process and a solidifying process. In the material layer forming process, a material layer 91 made of material powder is formed in the modeling region R. In the solidifying process, a laser beam L is irradiated onto a predetermined irradiation region of the material layer 91 to form a solidified layer 92. The material layer forming process and the solidifying process are repeatedly performed. In the following description, a predetermined number or thickness of solidified layers 92 newly formed in the solidified layer forming process may be referred to as an upper surface layer.

[0034] First, the first material layer forming process is performed. FIG. 8 is a graph showing the temperature change of the modeling table 4 in the manufacturing method of this embodiment. FIG. 9 is a graph showing the temperature change of the upper surface layer in the solidified layer forming process and the thermal expansion treatment process. In the solidified layer forming process including the material layer forming process, the modeling table 4 is adjusted to the modeling temperature T1. In this embodiment, the top plate 4a is heated by the heater 43 of the temperature adjustment device 42, so that the modeling table 4 is adjusted to the modeling temperature T1. Then, the height of the modeling table 4 is adjusted to an appropriate position with the base plate 90 placed on the modeling table 4 adjusted to the modeling temperature T1. In this state, the recoater head 32 is moved from the left side to the right side of FIG. 6, so that the first material layer 91 is formed on the base plate 90 as shown in FIG. 7. The material layer 91 is preheated to the modeling temperature T1 by heat transfer from the top plate 4a through the base plate 90.

[0035] Next, the first solidification step is performed. As shown in FIG. 7, the first material layer 91 is solidified by irradiating a predetermined irradiation area of ​​the first material layer 91 with the laser light L, to obtain a first solidified layer 92. Here, in the solidification step, the modeling table 4 is maintained at the modeling temperature T1. As shown in FIG. 9, the newly formed solidified layer 92 is at a very high temperature (temperature Ts) of about 1400°C to 1600°C immediately after irradiation with the laser light L, but after completion of irradiation, the temperature drops to reach thermal equilibrium with the modeling table 4, and after a predetermined time has passed, the temperature reaches the modeling temperature T1. Since metal has a positive thermal expansion coefficient, the volume shrinks with such a temperature drop. However, the amount of shrinkage is limited by the base plate 90 and adhesion with the adjacent layers, so that tensile stress remains in the model.

[0036] Next, a second material layer forming process is performed. After the first solidified layer 92 is formed, the height of the modeling table 4 is lowered by one material layer 91. In this state, the recoater head 32 is moved from the right side to the left side of the modeling region R in FIG. 7, thereby forming a second material layer 91 so as to cover the first solidified layer 92. Then, a second solidification process is performed. In the same manner as described above, the second material layer 91 is solidified by irradiating a predetermined irradiation region of the second material layer 91 with the laser light L or the electron beam, thereby obtaining the second solidified layer 92.

[0037] Until a desired three-dimensional object is obtained, the material layer forming step and the solidifying step are repeated to stack a plurality of solidified layers 92. Adjacent solidified layers 92 are strongly bonded to each other.

[0038] 3.2. Heat expansion treatment process The thermal expansion treatment step is carried out each time a predetermined number or a predetermined thickness of the solidified layer 92 is newly formed in the solidified layer forming step.

[0039] 9, in the thermal expansion treatment step, first, the solidified layer 92, which is in thermal equilibrium with the modeling table 4 in the material layer formation step and is maintained at the modeling temperature T1, is heated from the modeling temperature T1 to a heating temperature T2 and maintained at the heating temperature T2 for a predetermined time. In this embodiment, the modeling table 4 is adjusted to the heating temperature T2 by heating the top plate 4a with the heater 43 of the temperature adjustment device 42, and the solidified layer 92 is adjusted to the heating temperature T2 and maintained at the temperature by heat transfer from the top plate 4a via the base plate 90 and the layer formed on the lower side.

[0040] Next, the temperature of the solidified layer 92 is decreased to the modeling temperature T1. In this embodiment, the top plate 4a is cooled by the cooler 44 of the temperature adjustment device 42, whereby the modeling table 4 is adjusted from the heating temperature T2 to the modeling temperature T1, and the solidified layer 92 is adjusted to the modeling temperature T1 by heat transfer from the top plate 4a through the base plate 90 and the layer formed on the lower side. In the following description, a series of processes in which the solidified layer 92 is heated from the modeling temperature T1 to the heating temperature T2 in the thermal expansion treatment step, maintained at the heating temperature T2 for a predetermined time, and then cooled from the heating temperature T2 to the modeling temperature T1 may be referred to as the thermal expansion treatment.

[0041] The modeling temperature T1 and the heating temperature T2 are set so as to satisfy the relationship of the following formulas (1) and (2). T1 <T2≦350℃ (1) 50℃≦T2-T1≦200℃ (2) In this embodiment, the modeling temperature T1 is set to 200°C, and the heating temperature T2 is set to 300°C, for example.

[0042] The thermal expansion treatment is performed only on the upper surface layer. In this embodiment, since the temperature adjustment device 42 is provided on the modeling table 4, the thermal expansion treatment is performed on the entire solidified body obtained by stacking the solidified layers 92, that is, the upper surface layer and the solidified layers 92 below the upper surface layer.

[0043] The heating temperature T2 in the heat expansion treatment is set to a much lower temperature compared to the heating temperature in a general tempering treatment (for example, 500 °C or higher in the case of high-speed steel). Therefore, the above-mentioned heat expansion treatment is a heat treatment different from the tempering treatment and does not exhibit the effects of the tempering treatment such as improvement of toughness. However, when using a material powder containing a metal material that expands with the tempering treatment and has a martensite transformation start temperature of 200 °C or higher, by performing a heat expansion treatment on the solidified layer 92 at the shaping temperature T1 and the heating temperature T2 set to satisfy the above-mentioned relationship, a volume expansion similar to that during the tempering treatment can be generated. Thereby, the tensile stress due to the shrinkage of the metal can be reduced by the compressive stress due to the expansion accompanying the heat expansion treatment, controlling the residual stress of the shaped article, and suppressing deformation and cracking of the shaped article.

[0044] Note that the shaping temperature T1 and the heating temperature T2 satisfy the relationship T1 < T2 ≤ 350 °C, and preferably satisfy the relationship T1 < T2 ≤ 300 °C. In this case, it is possible to easily execute the heat expansion treatment even in a laminated manufacturing apparatus with a general specification, and it is also possible to suppress the thermal influence on the peripheral members constituting the laminated manufacturing apparatus 100.

[0045] The lower limit value of the shaping temperature T1 is not particularly limited, but the shaping temperature T1 is, for example, 100 °C or higher, and preferably 150 °C or higher. The heating temperature T2 is preferably 200 °C or higher in order to more effectively control the residual stress of the shaped article. Note that the volume expansion amount accompanying the heat expansion treatment depends on the difference (T2 - T1) between the shaping temperature T1 and the heating temperature T2, and the larger the difference (T2 - T1), the larger the volume expansion amount.

[0046] 9, in the thermal expansion treatment step, the time required to raise the temperature of the solidified layer 92 from the modeling temperature T1 to the heating temperature T2 (temperature rise time) is t1, the time required to hold the temperature at the heating temperature T2 (temperature retention time) is t2, and the time required to lower the temperature from the heating temperature T2 to the modeling temperature T1 (temperature fall time) is t3. The temperature rise time t1 is preferably 1 hour or more, and is set to 1 hour in this embodiment. The temperature retention time t2 is preferably 1 hour or more, and is set to 1 hour in this embodiment. The temperature fall time t3 is preferably 1 hour or more, and is set to 1 hour in this embodiment.

[0047] The thermal expansion treatment step may be performed during modeling, and may be performed each time one solidified layer 92 is formed, each time multiple solidified layers 92 are newly formed, or each time a solidified layer 92 of a predetermined thickness (for example, 1 to 10 mm) is newly formed. The implementation cycle of the thermal expansion treatment step may be changed during the modeling process. In addition, in a test modeling performed as a preliminary investigation of additive modeling, modeling may be performed without performing the thermal expansion treatment, and the number of layers or the stacking height at the time when cracks occur in the modeled object due to stacking of the solidified layers 92 may be investigated, and the implementation cycle of the thermal expansion treatment step may be set based on the number of layers or the stacking height. In this case, for example, the thermal expansion treatment step may be performed each time a solidified layer 92 of a number or thickness not exceeding the number of layers or the stacking height is newly formed.

[0048] 3.3. Post-molding heating process and slow cooling process The post-modeling heating process is performed after the completion of modeling, that is, after all the solidified layers 92 are formed. As shown in FIG. 10, in the post-modeling heating process, the solidified layer 92 is heated from the modeling temperature T1 to the heating temperature T2 and is maintained at the heating temperature T2 for a predetermined time. In the slow cooling process, which is a process performed after the post-modeling heating process, the solidified layer 92 is slowly cooled from the heating temperature T2 to a room temperature Tn (5°C to 35°C). In this embodiment, as shown in FIG. 10, the solidified layer 92 is gradually cooled by repeatedly lowering the temperature by a predetermined temperature from the heating temperature T2 to the room temperature Tn at predetermined time intervals and then maintaining the temperature. This makes it possible to control the residual stress of the model by performing a heat treatment similar to the thermal expansion process on the upper surface layer formed in the final stage of modeling. In addition, the solidified layer 92 is rapidly cooled to the room temperature Tn after the completion of modeling, which can suppress the occurrence of cracks in the modeled object.

[0049] The temperature of the solidified layer 92 in the post-modeling heating step and the slow cooling step can be adjusted by adjusting the temperature of the modeling table 4, as shown in FIG.

[0050] 10, in the post-modeling heating step, the time required to raise the temperature of the solidified layer 92 from the modeling temperature T1 to the heating temperature T2 (temperature rise time) is t4, and the time required to hold the solidified layer 92 at the heating temperature T2 (temperature retention time) is t5. The temperature rise time t4 is preferably 1 hour or more, and is set to 1 hour in this embodiment. The temperature retention time t5 is preferably 1 hour or more, and is set to 1 hour in this embodiment.

[0051] In the slow cooling process, the temperature drop time t6, which is the time required for one temperature drop when the solidified layer 92 is gradually cooled, is preferably 1 hour or more, and is set to 1 hour in this embodiment. The temperature holding time t7 after the temperature drop is preferably 1 hour or more, and is set to 1 hour in this embodiment. The temperature drop width ΔT, which is the temperature width in one temperature drop, is, for example, 30 to 70°C, and is set to 50°C in this embodiment.

[0052] The slow cooling step is not limited to the configuration of gradually lowering the temperature of the solidified layer 92 as in the present embodiment. For example, the slow cooling step may be performed by continuously lowering the temperature of the solidified layer 92 over a relatively long period of time. Moreover, modeling may be completed without performing the post-modeling heating step and the slow cooling step.

[0053] In addition, during or after the modeling is completed, the surface and unnecessary parts of the solidified body obtained by stacking the solidified layers 92 may be machined, such as cut or polished, by a machining device 95 provided in the chamber 1. After the above-mentioned steps are completed, the unsolidified material powder and cutting chips are discharged to obtain a modeled object.

[0054] 4. Other embodiments The present invention can also be carried out in the following manner.

[0055] In the above embodiment, the temperature adjustment device 42 is provided inside the modeling table 4, and the material layer 91 and the solidified layer 92 are heated or cooled from below through the base plate 90 and the lower layer to adjust the temperature. The configuration of the temperature adjustment device 42 is not limited to this example, and may be configured to heat or cool the material layer 91 and the solidified layer 92 from above. In this case, for example, a halogen lamp or the like can be used as the heater 43. In addition, the cooler 44 may be configured to be a blower that blows the same type of cooling gas as the inert gas filled in the chamber 1 onto the material layer 91 and the solidified layer 92 from above, or a cooling plate cooled by a Peltier element or the like that contacts the material layer 91 and the solidified layer 92 from above. With such a temperature adjustment device 42, the material layer 91 and the part of the solidified layer 92 that constitutes the upper surface layer can be directly adjusted to the modeling temperature T1 and the heating temperature T2 without going through the base plate 90 and the lower layer, and the temperature can be adjusted quickly even after a large number of solidified layers 92 are formed. EXAMPLES

[0056] The following detailed description will be given using examples, but the present invention is not limited to the following examples.

[0057] In Example 1, Example 2, and Comparative Example 1, a model was formed by additive manufacturing on the upper surface of a base plate 90 placed on a modeling table 4 equipped with a temperature adjustment device 42, and the occurrence of cracks was confirmed.

[0058] <Example 1> In Example 1, a molded object (cubic shape of 20 mm long x 20 mm wide x 20 mm thick) was molded on the upper surface of a base plate 90 (material: S50C, rectangular parallelepiped shape of 125 mm long x 125 mm wide x 15 mm thick) using a material powder (high speed steel powder M2, manufactured by Höganäs) equivalent to SKH51 high speed steel, by an additive manufacturing device 100 (OPM250L, manufactured by Sodick Co., Ltd., upper limit of the set temperature of the molding table 4: 300°C). In the solidified layer forming process, the molding temperature T1 was set to 200°C. During molding, a thermal expansion treatment process was carried out every time a 1 mm solidified layer 92 was newly formed. In the thermal expansion treatment process, the heating temperature T2 was set to 300°C, the temperature rise time t1 was set to 1 hour, the temperature holding time t2 was set to 1 hour, and the temperature fall time t3 was set to 1 hour. After the molding was completed, a post-molding heating process and a slow cooling process were carried out. In the post-molding heating process, the temperature rise time t4 was set to 1 hour, and the temperature holding time t5 was set to 1 hour. In the slow cooling process, the temperature fall time t6 was set to 1 hour, the temperature holding time t7 was set to 1 hour, and the temperature fall width ΔT was set to 50°C, and the solidified layer 92 was gradually cooled.

[0059] <Example 2> In Example 2, the object was molded under the same conditions as in Example 1, except that the molded object was a rectangular parallelepiped with dimensions of 80 mm long, 80 mm wide, and 10 mm thick.

[0060] <Comparative Example 1> In Comparative Example 1, the size of the molded object was a substantially cylindrical shape with a bottom radius of 10 mm and a height of 45 mm. In the solidified layer forming process, the molding temperature T1 was set to 300°C. The thermal expansion treatment process, the post-molding heating process, and the slow cooling process were not performed. The other molding conditions were the same as those of Example 1.

[0061] <Result> No cracks occurred during modeling, after modeling was completed, or one week after the implementation of the slow cooling step in the molded objects of Examples 1 and 2. In the molded object of Comparative Example 1, cracks occurred during modeling when the molded object reached a height of 35 mm.

[0062] Generally, the larger the horizontal size of the object, the more likely it is that cracks will occur due to tensile stress caused by metal contraction accompanying a temperature drop immediately after irradiation with the laser light L. While cracks occurred in the object in Comparative Example 1, no cracks occurred in Example 2, where the object was larger in size, which shows that carrying out a thermal expansion treatment step is effective in suppressing cracks in the object.

[0063] Various embodiments of the present invention have been described above, but these are presented as examples and are not intended to limit the scope of the invention. The novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. The embodiments and modifications thereof are included in the scope and spirit of the invention, and are included in the scope of the invention and its equivalents described in the claims. [Explanation of symbols]

[0064] 1: Chamber 1a: Window 3: Material layer forming device 4: Modeling table 4a: Tabletop 4b: Support plate 4c: Support plate 4d: Support plate 5: Irradiation device 17: Pollution prevention equipment 17a: Housing 17b: Opening 17c: Diffusion material 17d: Inert gas supply space 17e: Clean room 31: Bass 32: Recoater head 32a: Material storage section 32b: Material supply port 32c: Material discharge port 32fb: Blade 32rb: Blade 33: Recoater head drive unit 41: Modeling table drive unit 42: Temperature adjustment device 43: Heater 44:Cooler 51: Laser light source 53: Focus control unit 55a: X-axis galvanometer mirror 55b: Y-axis galvanometer mirror 90: Base plate 91: Material layer 92: Solidified layer 95: Machining equipment 100: Additive manufacturing equipment L: Laser light R: Printing area

Claims

1. A method for manufacturing a layered object, comprising the steps of: a material layer forming step of forming a material layer by supplying a material powder containing a metal material that expands with a tempering process onto a modeling table adjusted to a modeling temperature, and a solidification step of forming a solidified layer by irradiating a predetermined region of the material layer with a laser beam or an electron beam, thereby stacking the solidified layers; and a thermal expansion treatment step of increasing the temperature of the solidified layer from the modeling temperature to a heating temperature, maintaining the temperature at the heating temperature for a predetermined time, and then decreasing the temperature to the modeling temperature every time a predetermined number or thickness of the solidified layer is newly formed. The martensitic transformation start temperature of the metallic material is 200° C. or higher, If the molding temperature is T1 and the heating temperature is T2, A production method in which the relationships of the following formulas (1) and (2) are satisfied. T1<T2≦350℃ (1) 50°C≦T2-T1≦200°C (2)

2. The method according to claim 1, The manufacturing method, wherein the heating temperature is 200° C. or higher and 350° C. or lower.

3. The method according to claim 1 or 2, The method of manufacturing, wherein the metallic material is high speed steel.

4. The method according to claim 1 or 2, a post-modeling heating process in which, after completion of modeling of the layered object, the solidified layer is heated from the modeling temperature to the heating temperature and maintained at the heating temperature for a predetermined period of time; The manufacturing method further includes, after the post-shaping heating step, a slow cooling step of slowly cooling the solidified layer from the heating temperature to room temperature.

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