Additive manufacturing method and additive manufacturing apparatus

Abstract

This invention provides a method for additive manufacturing of three-dimensional objects that can suppress adverse effects caused by misalignment between the build table and the base plate. [Solution] A build plate manufacturing method is provided, comprising: a heating step of heating the build plate to a preheating temperature; a building step of alternately repeating the process of forming a material layer and irradiating it with laser light or an electron beam to form a solidified layer to form a predetermined number of solidified layers; a cooling step of cooling the build plate to a cooling temperature; a cutting step of performing cutting on the end faces of the solidified layers; a first correction step of measuring the horizontal and rotational displacement of the base plate with a measuring device after the heating step and before the building step and correcting the coordinate system used in the building step; and a second correction step of measuring the horizontal and rotational displacement of the base plate with a measuring device before the cutting step after the cooling step and correcting the coordinate system used in the cutting step.

Description

Technical Field

[0001] The present invention relates to a layered manufacturing method and a layered manufacturing apparatus.

Background Art

[0002] Various methods are known as layered manufacturing methods for three-dimensional objects. For example, a layered manufacturing apparatus that performs powder bed fusion and sintering forms a material layer by leveling a powdery material, and irradiates a laser beam or an electron beam to sinter or melt the material layer to form a solidified layer. The formation of the material layer and the formation of the solidified layer are repeated, and a plurality of solidified layers are stacked to manufacture a desired three-dimensional object. Generally, a three-dimensional object is formed with a plate-like member called a base plate as a base. The base plate is fixed to a manufacturing table configured to be movable in the vertical direction, and the material layer and the solidified layer are formed on the base plate. When forming the solidified layer, for the purpose of stress relaxation or the like, it is preferable that the manufacturing table is heated to a predetermined temperature and the material layer is preheated.

[0003] In order to obtain a three-dimensional object with higher precision, cutting may be performed on the end face of the solidified layer during layered manufacturing. Also, for various purposes, cooling of the solidified layer may be performed during layered manufacturing. For example, when metal is used as the material, by cooling the solidified layer under predetermined temperature conditions during layered manufacturing, martensitic transformation is intentionally advanced, and a layered manufacturing method is known that controls the residual stress generated in the three-dimensional object by reducing the tensile stress due to the shrinkage of the metal with the compressive stress due to martensitic transformation. Patent Document 1 discloses a layered manufacturing method that performs cooling of the solidified layer, cutting of the solidified layer, and reheating of the solidified layer every time a predetermined number of solidified layers are formed. In this layered manufacturing method, the temperature of the manufacturing table is set relatively high when forming the solidified layer, and the temperature of the manufacturing table is set relatively low when performing cutting.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

[0005] Repeated heating and cooling of the build plate during additive manufacturing can cause horizontal or rotational displacement between the build plate and the base plate due to thermal displacement. While fixing the center of displacement of the build plate and the center of displacement of the base plate at a single point could suppress this displacement, such fixing is practically difficult.

[0006] One might consider setting a larger material removal allowance to account for positional misalignment, but this would require extra time for molding and machining. Furthermore, there is a risk of larger-than-expected positional misalignment resulting in insufficient dimensions that prevent machining, or excessive material that increases the load on the tool.

[0007] This invention has been made in view of these circumstances, and aims to provide an additive manufacturing method and an additive manufacturing apparatus that can suppress adverse effects caused by positional misalignment between the build table and the base plate due to thermal displacement. [Means for solving the problem]

[0008] The present invention provides an additive manufacturing method comprising: a heating step of heating a build table to which a base plate is fixed to a preheating temperature; a manufacturing step of alternately repeating the following steps to form a predetermined number of solidified layers: supplying material onto the build table to form a material layer and irradiating the material layer heated to the preheating temperature with laser light or an electron beam to form a solidified layer; a cooling step of cooling the build table to a cooling temperature lower than the preheating temperature; a cutting step of performing cutting on the end face of the solidified layer cooled to the cooling temperature; a first correction step performed after the heating step and before the manufacturing step, in which the horizontal and rotational positional displacement of the base plate is measured by a measuring device and the coordinate system used in the manufacturing step is corrected; and a second correction step performed after the cooling step and before the cutting step, in which the horizontal and rotational positional displacement of the base plate is measured by a measuring device and the coordinate system used in the cutting step is corrected.

[0009] Furthermore, the present invention provides an additive manufacturing apparatus comprising: a build table to which a base plate is fixed; a temperature control device for heating the build table to a preheating temperature or cooling it to a cooling temperature lower than the preheating temperature; a material layer forming device for supplying material onto the build table to form a material layer; an irradiation device for irradiating the material layer heated to the preheating temperature with laser light or an electron beam to form a solidified layer; a processing device for performing cutting on the end face of the solidified layer cooled to the cooling temperature; a measuring device configured to measure the horizontal and rotational positional displacement of the base plate; and a control device that corrects the coordinate system used to control the irradiation device based on the positional displacement measured by the measuring device between the time the build table is heated to the preheating temperature and the time the solidified layer is formed, and corrects the coordinate system used to control the processing device based on the positional displacement measured by the measuring device between the time the build table is cooled to the cooling temperature and the time cutting is performed on the end face of the solidified layer. [Effects of the Invention]

[0010] In the additive manufacturing method and apparatus of the present invention, the positional displacement of the base plate is measured after the temperature of the build table is adjusted and the coordinate system is corrected. As a result, even if positional displacement occurs due to thermal displacement, its effects can be suppressed, and the formation of the solidified layer and the cutting of the solidified layer can be performed. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic diagram of the additive manufacturing system. [Figure 2] This is an exploded view of the build plate and temperature control device. [Figure 3] This is a schematic diagram of the irradiation device. [Figure 4] This is a perspective view of the solidified layer and measurement reference material formed on the base plate. [Figure 5] The following are examples of modified measurement standards. [Figure 6] This is a magnified view of the measurement reference object on which the reference mark has been formed. [Figure 7] This is a magnified view of a measuring reference object whose reference surface has been formed by machining. [Figure 8] The following are examples of modified measurement standards. [Figure 9] This is a block diagram of the control device. [Figure 10] This is a flowchart of the additive manufacturing method. [Figure 11] This shows an example of the measurement position when measuring the reference mark. [Figure 12] This shows an example of the measurement position when measuring a reference surface. [Modes for carrying out the invention]

[0012] Embodiments of the present invention will be described below with reference to the drawings. The various modifications described below can be implemented in any combination.

[0013] The additive manufacturing apparatus 1 of the present embodiment shown in FIG. 1 is specifically an apparatus that performs powder bed fusion bonding, and manufactures a desired three-dimensional object by alternately repeating the formation of the material layer 63 and the formation of the solidified layer 65. As the material, for example, metal powder is used. The additive manufacturing apparatus 1 includes a chamber 11, a material layer forming device 2, a modeling table 22, an irradiation device 3, a processing device 4, a removal nozzle 47, a measurement device 49, and a control device 5.

[0014] The additive manufacturing apparatus 1 of the present embodiment is controlled by the control device 5 based on a predetermined coordinate system. The coordinate system may be a rectangular coordinate system, and in the following, the horizontal axis directions orthogonal to each other are respectively taken as the X axis and the Y axis. In the present embodiment, one coordinate system is shared as the coordinate system used for the control related to the formation of the solidified layer 65 of the irradiation device 3 and the coordinate system used for the control related to the cutting process of the processing device 4. However, the coordinate system used for the control of the irradiation device 3 (hereinafter, the optical coordinate system) and the coordinate system used for the control of the processing device 4 (hereinafter, the cutting coordinate system) may be provided separately. At this time, the optical coordinate system and the cutting coordinate system are set to be aligned with each other.

[0015] The chamber 11 is configured to be substantially sealed and covers a modeling region which is a region where a desired three-dimensional object is formed. During additive manufacturing, an inert gas is supplied to the chamber 11 from an inert gas supply device (not shown), and the chamber 11 is filled with an inert gas at a predetermined concentration. The inert gas supply device is, for example, an inert gas generation device that generates an inert gas from air or a gas cylinder in which an inert gas is stored. Also, the inert gas containing the fumes generated during the formation of the solidified layer 65 is discharged from the chamber 11. Desirably, the inert gas discharged from the chamber 11 is returned to the chamber 11 after the fumes are removed by a fume collector (not shown). The fume collector is, for example, an electrostatic precipitator or a filter. The inert gas refers to a gas that does not substantially react with the material layer 63 or the solidified layer 65, and an appropriate one is selected from nitrogen gas, argon gas, helium gas, etc. according to the type of the material.

[0016] The material layer forming device 2 is provided in the chamber 11 and forms a material layer 63 with a desired thickness on the forming region on the forming table 22. The material layer forming device 2 includes a base 21, a recoater head 25, a recoater head driving device 26, and a blade 27.

[0017] The base 21 has a forming region. The forming table 22 is disposed in the forming region and is configured to be movable in the vertical direction by a forming table driving device 23 having an arbitrary actuator. The forming table 22 and the tank wall surrounding the forming table 22 hold the uncured material. As the laminated forming proceeds, the base plate 61 and the cured layer 65 are buried in the uncured material. In the laminated forming, the base plate 61 is placed on the upper surface of the forming table 22, and the material layer 63 and the cured layer 65 are formed on the base plate 61. The base plate 61 may be a plate-shaped member of any shape. In the present embodiment, the base plate 61 has a rectangular shape. The base plate 61 may be fixed to the forming table 22 by any fixing means. Typically, mechanical fixing means such as bolts and clamps are used, but it is not limited thereto.

[0018] The build table 22 is configured to be temperature-controllable. In this embodiment, as shown in Figure 2, a temperature control device 24 is built into the build table 22. The temperature control device 24 includes at least one of a heater 24a and a cooler 24b. The heater 24a is, for example, an electric heater or piping through which a heating medium can flow. The cooler 24b is, for example, piping through which a refrigerant can flow. The temperature control device 34 is configured to heat the build table 22 to a predetermined preheating temperature and to cool it to a predetermined cooling temperature which is lower than the heating temperature. In this specification, "heating" means adjusting to a relatively high temperature, and "cooling" means adjusting to a relatively low temperature. When forming the solidified layer 65, the build table 22 is temperature-controlled to the preheating temperature. When cutting the end face of the solidified layer 65, the build table 22 is temperature-controlled to the cooling temperature. When adjusting the temperature of the build table 22 with the aim of controlling residual stress in a three-dimensional object by intentionally promoting martensitic transformation and reducing tensile stress due to metal shrinkage with compressive stress due to martensitic transformation, the preheating temperature may be higher than the martensitic transformation completion temperature of the solidified layer 65, and the cooling temperature may be lower than the martensitic transformation start temperature of the solidified layer 65. The cooling temperature may also be, for example, room temperature. In this specification, room temperature means a temperature of substantially 5°C or higher and 35°C or lower. When the temperature of the build table 22 is adjusted, thermal displacement may cause misalignment at the fixing points of the base plate 61, or misalignment of the build table 22 or its surrounding components. Consequently, relative misalignment in the horizontal or rotational direction may occur between the build table 22 and the base plate 61.

[0019] The recoater head 25 is positioned on a base 21 and is configured to reciprocate horizontally on the build table 22 by a recoater head drive device 26 having an arbitrary actuator. A blade 27 is attached to the side of the recoater head 25. The recoater head 25 only needs to have the function of moving the blade 27. In this embodiment, the recoater head 25 is configured to move while discharging the material stored inside. As the recoater head 25 moves, the material supplied onto the build table 22 is leveled by the blade 27, forming a material layer 63 of a predetermined thickness.

[0020] The irradiation device 3 is located above the chamber 11. The irradiation device 3 irradiates the material layer 63 with laser light L to melt or sinter it and form a solidified layer 65. The irradiation device 3 of this embodiment includes a light source 31, a collimator 33, a focus control unit 35, and a scanning device 37, as shown in Figure 3.

[0021] The light source 31 generates laser light L. Here, the type of laser light L is not limited as long as it can sinter or melt the material layer 63, for example, a fiber laser, CO2 laser, YAG laser, green laser, or blue laser. The collimator 33 converts the laser light L output from the light source 31 into parallel light. The focus control unit 35 has a focusing lens, a lens actuator that moves the focusing lens back and forth, and a focusing lens fixed in a predetermined position. The laser light L output from the light source 31 passes through the focusing lens and the focusing lens and is adjusted to a desired spot diameter. The scanning device 37 is, for example, a galvanometer scanner. The scanning device 37 has an X-axis galvanometer mirror 371, an X-axis actuator 373 that rotates the X-axis galvanometer mirror 371, a Y-axis galvanometer mirror 375, and a Y-axis actuator 377 that rotates the Y-axis galvanometer mirror 375. The X-axis galvanometer mirror 371 and the Y-axis galvanometer mirror 375 have their rotation angles controlled and scan the laser light L output from the light source 31 in two dimensions.

[0022] The laser light L that has passed through the X-axis galvanometer mirror 371 and the Y-axis galvanometer mirror 375 passes through a window 13 provided on the upper surface of the chamber 11 and irradiates the material layer 63 formed in the fabrication area. The window 13 is made of a material that can transmit the laser light L. For example, if the laser light L is a fiber laser or a YAG laser, the window 13 can be made of quartz glass.

[0023] A contamination prevention device 15 is provided on the upper surface of the chamber 11 so as to cover the window 13. The contamination prevention device 15 includes a cylindrical housing and a cylindrical diffusion member placed inside the housing. An inert gas supply space is provided between the housing and the diffusion member. An opening is also provided on the bottom surface of the housing inside the diffusion member. The diffusion member has numerous pores, and clean inert gas supplied to the inert gas supply space fills the clean chamber through these pores. The clean inert gas that has filled the clean chamber is then ejected downwards from the contamination prevention device 15 through the opening. In this way, fumes are prevented from adhering to the window 13.

[0024] In this embodiment, the irradiation device 3 is configured to form a solidified layer 65 by irradiating with laser light L, but the irradiation device may irradiate with an electron beam. For example, the irradiation device may be configured to include a cathode electrode that emits electrons, an anode electrode that focuses and accelerates electrons, a solenoid that forms a magnetic field to focus the direction of the electron beam in one direction, and a collector electrode that is electrically connected to the material layer 63 which is the object to be irradiated and applies a voltage between itself and the cathode electrode.

[0025] The processing device 4 performs cutting on the end face of the solidified layer 65, etc. The processing device 4 comprises a processing head 41, a processing head drive device 43, a spindle 45, and a removal nozzle 47. The processing head 41 is configured to be movable to a desired position within the chamber 11 by the processing head drive device 43. The processing head drive device 43 is configured to include, for example, an X-axis drive device for moving the processing head 41 in the X-axis direction, a Y-axis drive device for moving the processing head 41 in the Y-axis direction, and a Z-axis drive device for moving the processing head 41 in the vertical direction. The X-axis drive device, Y-axis drive device, and Z-axis drive device may each have any actuator. The spindle 45 is provided on the processing head 41 and is configured to grip and rotate a cutting tool such as an end mill. Cutting is performed on the surface of the solidified layer 65 and unwanted parts by the cutting tool rotated by the spindle 45. An automatic tool changer may be provided to change the cutting tool as needed during additive manufacturing. The removal nozzle 47 is provided on the machining head 41 and is configured to remove material by suction or injection of an inert gas. By removing material around the area to be machined using the removal nozzle 47, it is possible to prevent material from getting caught in the cutting tool. When removing material by injection of an inert gas, it is preferable to inject the inert gas at a low pressure so as not to cause the material to fly up.

[0026] The measuring device 49 is a sensor that measures the horizontal and rotational displacement of the base plate 61. The measuring device 49 may be an optical sensor such as a CCD camera, or a contact-type sensor such as a touch probe. In this embodiment, the measuring device 49 is configured to be movable by the machining head 41. When the measuring device 49 is an optical sensor, it may be provided on the lower surface of the machining head 41. When the measuring device 49 is a contact-type sensor, it may be held by the spindle 45 and may be attached in place of a cutting tool by an automatic tool changer. A dedicated drive device may be provided to move the machining head 41, but by installing the measuring device 49 on the machining head 41 or configuring it to be attachable, the machining head 41 can also be used as a drive device for the measuring device 49. If the measuring device 49 is an optical sensor and can image the entire object to be measured at once, the measuring device 49 may be fixed inside the chamber 11.

[0027] When the measuring device 49 measures the displacement of the base plate 61, it may directly measure the base plate 61, measure the solidified layer 65, or measure the measurement reference object 7 formed on the base plate 61. The measurement reference object 7 is a laminated object provided at a position separated from the solidified layer 65 and fixed to the base plate 61. In this embodiment, the measurement reference object 7 is used as the direct object to measure for determining the displacement of the base plate 61, and the coordinates related to the measurement reference object 7 are acquired to measure the horizontal and rotational displacement of the base plate 61. By using the measurement reference object 7 as the object to measure, the measurement position can be fixed regardless of the shape of the three-dimensional object, and the advantages of not requiring or requiring only a small amount of material removal at the measurement position can be enjoyed.

[0028] In this embodiment, the irradiation device 3 irradiates the material layer 63 to melt or sinter it, similar to the formation of the solidified layer 65, and forms a measurement reference object 7 on the base plate 61. The formation of the measurement reference object 7 is performed simultaneously with the formation of the solidified layer 65. That is, when the nth solidified layer 65 is formed, the nth measurement reference object 7 is also formed. The laser irradiation conditions for the measurement reference object 7 may be the same as or different from the laser irradiation conditions for the solidified layer 65. To improve the accuracy of the measurement, it is preferable to provide multiple measurement reference objects 7 so that the coordinates of each measurement reference object 7 can be obtained. In this embodiment, as shown in Figure 4, measurement reference objects 7 are formed at each of the three corners of the rectangular base plate 61.

[0029] The shape of the measurement reference object 7 is not particularly limited, and any shape can be used, such as a polygonal prism, cylindrical shape, polygonal pyramidal shape, or conical shape. If the measurement reference object 7 is subjected to machining as described later, it is sufficient that the measurement reference object 7 has sufficient strength to withstand the machining. In this embodiment, the measurement reference object 7 has a triangular prism shape. Alternatively, it may be configured to gradually taper upwards, as shown in the triangular pyramidal measurement reference object 7 in Figure 5. This allows the measurement reference object 7 to be firmly fixed to the base plate 61 and reduces the amount of material used to form the measurement reference object 7.

[0030] The measuring device 49 may measure the coordinates of the reference mark 71 or reference surface 72 formed on the upper part of the measurement reference object 7 as the coordinates of the measurement reference object 7. The reference mark 71 can be suitably measured by the measuring device 49, which is an optical sensor. The reference surface 72 can be suitably measured by the measuring device 49, which is either an optical sensor or a contact sensor.

[0031] As shown in Figure 6, the reference mark 71 is a mark with a shape that can identify the coordinates of a predetermined point formed on the upper surface of the measurement reference object 7. The shape of the reference mark 71 may be a combination of line segment shapes, such as a cross shape or an X shape, and the measuring device 49 may measure the coordinates of the intersection of the line segment shapes as the coordinates of the measurement reference object 7. More precisely, since the line segment shapes that make up the reference mark 71 have thickness, the intersection of the line passing through the center of the line segment shape may be considered as the intersection of the line segment shape. The shape of the reference mark 71 may also be circular or polygonal, and the measuring device 49 may measure the coordinates of the center, such as the centroid of the reference mark 71, as the coordinates of the measurement reference object 7. The reference mark 71 may be formed by cutting the upper part of the measurement reference object 7 with the processing device 4. The reference mark 71 may also be a shape created by the irradiation device 3. That is, when forming the measurement reference object 7, laser light L or an electron beam may be selectively irradiated so that the reference mark 71 is formed. The reference mark 71 may be formed as a recess or a protrusion, but it is preferable that it be a shallow recess that allows for the continued additive manufacturing of the measurement reference object 7 on the reference mark 71.

[0032] The reference surface 72 is a surface located on the upper side of the measurement reference object 7, as shown in Figure 7. The reference surface 72 may be formed by cutting the end face of the measurement reference object 7 with the processing device 4. However, if a sufficiently smooth surface is obtained when it is formed by the irradiation device 3, the side surface of the measurement reference object 7 may be used as the reference surface 72 without cutting it. Furthermore, even if there are irregularities on the side surface of the measurement reference object 7, a straight line approximating the upper edge of the side surface may be calculated by regression analysis such as the least squares method, and the coordinates on that straight line may be considered as the coordinates of the reference surface 72.

[0033] The measurement reference object 7 may be a shape that combines multiple plate-like shapes. The measurement reference object 7 shown in Figure 8 is a shape that combines two plate-like shapes, and the measuring device 49 may measure the coordinates relating to the intersection of the plate-like shapes, that is, the intersection of the cross shape in a top view, as the coordinates relating to the measurement reference object 7. More precisely, the intersection of the lines passing through the centers of the line segments that make up the cross shape may be considered as the coordinates relating to the measurement reference object 7. With such a measurement reference object 7, cutting of the measurement reference object 7 is unnecessary, and the amount of material used to form the measurement reference object 7 can be reduced. In addition, since the area fixed to the base plate 61 can be made small, it is easy to remove. The thickness of the plate-like shape may be equivalent to the spot diameter of the laser light L or electron beam.

[0034] The measurement reference object 7 may be cut and removed from the base plate 61 by machining, such as wire electrical discharge machining, after the additive manufacturing is complete. Alternatively, if a measurement reference object 7 with relatively low adhesion force to the base plate 61 is used, such as the measurement reference object 7 shown in Figure 8, the measurement reference object 7 may be pressed to separate it from the base plate 61.

[0035] The control device 5 controls each part of the additive manufacturing apparatus 1 based on the molding program. The control device 5 also corrects the coordinate system based on the horizontal or rotational displacement of the base plate 61 measured by the measuring device 49. As shown in Figure 9, the control device 5 includes a calculation unit 51 and a storage unit 53. The control device 5 can be configured by combining any hardware and software. The calculation unit 51 is, for example, a calculation processing unit such as a CPU. The calculation unit 51 has a command unit 511, a coordinate transformation unit 512, and a coordinate correction unit 513. The storage unit 53 can be configured by combining RAM, ROM, auxiliary storage devices, etc. The control device 5 may be configured by combining multiple control devices; for example, a control device that controls the irradiation device 3 and a control device that controls other devices may be configured separately.

[0036] The command unit 511 controls each part according to the molding program, etc. Specifically, the command unit 511 outputs control commands to the molding table drive unit 23 and the recoater head drive unit 26, controlling the material layer forming device 2 and the molding table 22 to form the material layer 63. The command unit 511 also outputs control commands to the light source 31, the focus control unit 35, the X-axis actuator 373, and the Y-axis actuator 377, controlling the irradiation device 3 to form the solidified layer 65. At this time, the command unit 511 refers to the coordinate system correction data and corrects the control commands. The command unit 511 also outputs control commands to the machining head drive unit 43 and the spindle 45, controlling the machining device 4 to cut the solidified layer 65 and the measurement reference object 7. At this time, the command unit 511 refers to the coordinate system correction data and corrects the control commands. The command unit 511 also controls the measuring device 49. Furthermore, when the command unit 511 controls the irradiation device 3 and the processing device 4, it may correct the control commands based on the predicted value of the thermal displacement amount corresponding to the temperature of the molding table 22.

[0037] The coordinate transformation unit 512 analyzes and digitizes the coordinate data measured by the measuring device 49. The coordinate correction unit 513 determines the amount of horizontal and rotational displacement of the base plate 61 from the digitized coordinate data and generates coordinate system correction data.

[0038] The memory unit 53 stores data necessary for controlling the molding program, data that needs to be stored during the calculation process by the calculation unit 51, and coordinate system and its correction data.

[0039] Here, the additive manufacturing method of this embodiment shown in Figure 10 will be described. The additive manufacturing method of this embodiment comprises a heating step, a first correction step, a molding step, a cooling step, a second correction step, and a cutting step, and these steps are repeated in order to manufacture a desired three-dimensional object.

[0040] Before starting additive manufacturing, the base plate 61 is placed on the build table 22 and fixed to the build table 22 by any fixing means. At this time, the temperature of the build table 22 is usually room temperature. The position and number of fixing points are not particularly limited. According to this embodiment, a certain degree of displacement of the base plate 61 is permissible, so the position and number of fixing points can be set relatively freely. After fixing the base plate 61, the chamber 11 is sealed and inert gas is supplied. During additive manufacturing, the chamber is maintained under an inert gas atmosphere of a predetermined concentration. Also, before proceeding to the heating process, the origin of the coordinate system and the X and Y axes are set. The origin of the coordinate system may be the center of the base plate 61. Also, when the base plate 61 has a rectangular shape, each side of the base plate 61 may be parallel to the X or Y axis. When setting the origin and the X and Y axes, the end faces of the base plate 61 can be measured by the measuring device 49.

[0041] First, a heating process is performed. In the heating process, the build plate 22 is heated to a preheating temperature by the temperature control device 24. The temperature of the build plate 22 is maintained at the preheating temperature until the next cooling process begins.

[0042] After the heating process and before the molding process, a first correction process is performed. In the first correction process, the horizontal and rotational positional displacement of the base plate 61 is measured by the measuring device 49, and the coordinate system used for the molding process, i.e., the coordinate system used to control the irradiation device 3, is corrected. If separate optical coordinate systems and cutting coordinate systems are provided, the coordinate system corrected by the first correction process may be only the optical coordinate system. The detailed procedure of the first correction process will be described later. However, when the measurement reference object 7 or the solidified layer 65 is used as the object to be measured, since the measurement reference object 7 and the solidified layer 65 have not yet formed immediately after the first heating process, the first correction process immediately after the first heating process may be performed with the base plate 61 as the object to be measured. In other words, the first first correction process may use the base plate 61 as the object to be measured, and subsequent first correction processes may use the measurement reference object 7 or the solidified layer 65 as the object to be measured.

[0043] When performing the first correction step, if the measurement position is embedded in the material, the material at the measurement position may be removed by the removal nozzle 47 before measurement by the measuring device 49.

[0044] Next, the molding process is carried out. The molding process consists of alternating material layer formation and irradiation processes, which are repeated to form a predetermined number of solidified layers 65 and measurement reference objects 7. In the material layer formation process, the molding table 22 is positioned at a predetermined height, and the recoater head 25 moves on the molding table 22. In this way, material is supplied onto the molding table 22, and the material is leveled by the blade 27 to form a material layer 63. In the irradiation process, a laser beam L or electron beam is irradiated onto the material layer 63, which has been heated to a preheating temperature, based on a coordinate system, to form a solidified layer 65. In addition, the measurement reference object 7 is also formed in parallel with the formation of the solidified layer 65 during the irradiation process. That is, a laser beam L or the electron beam is irradiated onto a material layer 63 located away from the solidified layer 65, forming a measurement reference object 7 fixed to the base plate 61.

[0045] When a reference mark 71 or reference surface 72 is formed on the measurement reference object 7 by cutting, the cutting process is performed on the measurement reference object 7 after the molding process and before the cooling process. When performing the cutting process on the measurement reference object 7, the material around the part to be cut, i.e., the material at the measurement position, may be removed by the removal nozzle 47.

[0046] After forming a predetermined number of solidified layers 65, a cooling process is performed. During the cooling process, the build plate 22 is cooled to a cooling temperature by the temperature control device 24. The temperature of the build plate 22 is maintained at the cooling temperature until the next heating process begins.

[0047] After the cooling process and before the cutting process, a second correction process is performed. In the second correction process, the horizontal and rotational positional displacement of the base plate 61 is measured by the measuring device 49, and the coordinate system used for the cutting process, i.e., the coordinate system used to control the processing device 4, is corrected. If the optical coordinate system and the cutting coordinate system are provided separately, the coordinate system corrected by the second correction process may be only the cutting coordinate system. The detailed procedure of the second correction process will be described later.

[0048] When performing the second correction step, if the measurement position is embedded in the material, the material at the measurement position may be removed by the removal nozzle 47 before measurement by the measuring device 49. However, as mentioned above, if cutting is performed on the measurement reference object 7, the material at the measurement position may be removed at the time of cutting.

[0049] Next, a cutting process is performed. In the cutting process, cutting is performed on the edge face of the solidified layer 65, which has been cooled to the cooling temperature, based on a coordinate system. The cutting process allows for the creation of a three-dimensional object with higher precision.

[0050] In this way, the heating process, the first correction process, the molding process, the cooling process, the second correction process, and the cutting process are repeated to produce the desired three-dimensional object. The heating and cooling processes may cause horizontal or rotational displacement between the molding table 22 and the base plate 61, but the coordinate system is corrected each time by the first and second correction processes, allowing additive manufacturing to continue while suppressing the effects of the displacement.

[0051] The first correction step is performed after the completion of the heating step, and the second correction step is performed after the completion of the cooling step. Whether or not the temperature adjustment related to the heating step or the cooling step has been completed can be determined, for example, as follows: The elapsed time since the start of temperature adjustment can be measured with a timer 24c, and it can be determined that the temperature adjustment has been completed when a predetermined time has elapsed. Alternatively, the temperature of the measurement reference object 7, the solidified layer 65, or the molding table 22 can be measured with a contact-type or non-contact-type temperature sensor, and it can be determined that the temperature adjustment has been completed when a predetermined temperature is reached. Alternatively, an arbitrary position on the measurement reference object 7 or the solidified layer 65 can be measured with a measuring device 49, and it can be determined that the temperature adjustment has been completed when the position change falls below a threshold.

[0052] Here, the procedures for the first and second correction steps will be described in detail. Figures 11 and 12 are top views of the measurement reference object 7, the base plate 61, and the solidified layer 65, illustrating the measurement positions when measuring the reference mark 71 and the measurement positions when measuring the reference surface 72, respectively.

[0053] In this embodiment, the measurement reference objects 7 are formed at each of the three corners of the rectangular base plate 61. The measuring device 49 then obtains the coordinates of the two diagonally positioned measurement reference objects 7 to measure the horizontal displacement, and obtains the coordinates of the two measurement reference objects 7 located at both ends of the same side to measure the rotational displacement. More specifically, the coordinates of the two diagonally positioned measurement reference objects 7 are obtained, and their midpoint is calculated based on these coordinates. The measured value of the midpoint coordinates is compared with the control target value, and the deviation is taken as the amount of horizontal displacement, and coordinate system correction data is created. According to the correction data, the origin of the control coordinate system is shifted by an amount corresponding to the amount of horizontal displacement. Even if the base plate 61 has expanded or contracted as a whole, the central part of the base plate 61 is relatively less affected by the expansion or contraction, so by taking the midpoint of the coordinates of the two diagonally positioned measurement reference objects 7, the amount of horizontal displacement can be determined with greater accuracy. By taking the midpoint of the coordinates of two diagonally positioned measurement reference objects 7, the amount of horizontal displacement can be determined with greater accuracy, even if the base plate 61 has expanded or contracted overall. In addition, the coordinates of the two measurement reference objects 7 located at both ends of the same side are obtained, and the slope, and thus the angle, of the line passing through these coordinates is calculated. The measured angle is compared with the control target value, and the deviation is taken as the amount of displacement in the rotational direction, and coordinate system correction data is created. According to the correction data, the angle of the control coordinate axis is shifted by an amount corresponding to the amount of displacement in the rotational direction.

[0054] In the embodiment shown in Figure 11, the reference marks 71 on the diagonally opposite measurement reference object 7 are designated as the first reference mark 71a and the second reference mark 71b, respectively, and the reference marks 71 on the measurement reference object 7 located at both ends of the same side are designated as the second reference mark 71b and the third reference mark 71c, respectively. The coordinates of the first reference mark 71a and the second reference mark 71b are obtained, and the amount of horizontal displacement is calculated based on the coordinates of their midpoint 71m. In addition, the coordinates of the second reference mark 71b and the third reference mark 71c are obtained, and the amount of rotational displacement is calculated based on the angle of the straight line passing through them. In this way, in the first and second correction steps, coordinate system correction data is created based on the horizontal and rotational positional displacement amounts of the base plate 61.

[0055] In the embodiment shown in Figure 12, the measurement positions of the reference plane 72 relating to the diagonally positioned measurement reference objects 7 are defined as measurement points 72a, 72b and 72c, 72d, respectively, and the measurement positions of the reference plane 72 relating to the measurement reference objects 7 located at both ends of the same side are defined as measurement points 72d and 72e, respectively. The coordinates of measurement points 72a, 72b and measurement points 72c, 72d are obtained, and the amount of horizontal displacement is calculated based on the coordinate of their midpoint 72m. In addition, the coordinates of measurement points 72d and 72e are obtained, and the amount of rotational displacement is calculated based on the angle of the straight line passing through them. In this way, in the first and second correction steps, coordinate system correction data is created based on the horizontal and rotational positional displacement amounts of the base plate 61.

[0056] As several examples have already been specifically shown, the present invention is not limited to the configuration of the embodiments shown in the drawings, and various modifications or applications are possible without departing from the technical spirit of the present invention. [Explanation of symbols]

[0057] 1. Additive manufacturing device 22 Build Table 24 Temperature adjustment device 2 Material layer forming device 3 Irradiation device 4 Processing equipment 49 Measuring device 5 Control device 61 Base Plate 65 Solidified layer 63 Material layer L Laser light

Claims

1. A heating step in which the build table to which the base plate is fixed is heated to a preheating temperature, A molding process that alternately repeats the following steps to form a predetermined number of solidified layers: supplying material onto the molding table to form a material layer, and irradiating the material layer, which has been heated to the preheating temperature, with laser light or an electron beam to form a solidified layer. A cooling step of cooling the molding table to a cooling temperature lower than the preheating temperature, A cutting step in which cutting is performed on the end face of the solidified layer that has been cooled to the aforementioned cooling temperature, A first correction step is performed after the heating step and before the molding step, in which the horizontal and rotational positional displacement of the base plate is measured by a measuring device, and the coordinate system used in the molding step is corrected. A method for additive manufacturing comprising: a second correction step performed after the cooling step and before the cutting step, in which the horizontal and rotational positional displacement of the base plate is measured by the measuring device and the coordinate system used for the cutting step is corrected.

2. In the molding process, the laser light or electron beam is irradiated onto the material layer at a position separated from the solidified layer, and a measurement reference object fixed to the base plate is formed. The additive manufacturing method according to claim 1, wherein the measuring device is configured to acquire coordinates relating to the measurement reference object and measure the positional displacement of the base plate.

3. The base plate has a rectangular shape, The additive manufacturing method according to claim 2, wherein the measurement reference is formed at each of the three corners of the rectangular shape.

4. The additive manufacturing method according to claim 3, wherein the measuring device is configured to obtain coordinates relating to two diagonally positioned measuring reference objects to measure horizontal displacement, and to obtain coordinates relating to two measuring reference objects located at both ends of the same side to measure rotational displacement.

5. The additive manufacturing method according to claim 2, wherein the measuring device acquires the coordinates of a reference mark formed on the upper surface of the measuring reference object.

6. The additive manufacturing method according to claim 5, wherein the reference mark is formed by cutting the upper surface of the measurement reference object after the molding process and before the cooling process.

7. The additive manufacturing method according to claim 5, wherein the reference mark is a shape formed in the molding process.

8. The additive manufacturing method according to claim 2, wherein the measuring device acquires the coordinates of a reference surface located on the side surface of the measuring reference object.

9. The additive manufacturing method according to claim 8, wherein the reference surface is formed by cutting the end face of the measurement reference object after the molding process and before the cooling process.

10. The additive manufacturing method according to claim 1, wherein the material at the measurement position of the measuring device is removed before measurement.

11. The additive manufacturing method according to claim 10, wherein the removal of the material is performed by suction or injection of an inert gas.

12. The additive manufacturing method according to claim 1, wherein the measuring device is an optical sensor.

13. The additive manufacturing method according to claim 1, wherein the measuring device is a contact-type sensor.

14. The preheating temperature is higher than the martensitic transformation completion temperature of the solidified layer. The additive manufacturing method according to claim 1, wherein the cooling temperature is lower than the martensitic transformation initiation temperature of the solidified layer.

15. The additive manufacturing method according to claim 1, wherein the cooling temperature is room temperature.

16. A build table to which the base plate is fixed, A temperature control device that heats the molding table to a preheating temperature or cools it to a cooling temperature lower than the preheating temperature, A material layer forming apparatus that supplies material onto the molding table to form a material layer, An irradiation device that irradiates the material layer heated to the preheating temperature with laser light or an electron beam to form a solidified layer, A processing apparatus for performing cutting on the end face of the solidified layer cooled to the aforementioned cooling temperature, A measuring device configured to measure the horizontal and rotational positional displacement of the base plate, Additive manufacturing apparatus comprising: a control device that corrects the coordinate system used to control the irradiation device based on the positional deviation measured by the measuring device between the time the molding table is heated to the preheating temperature and the time the solidified layer is formed; and a control device that corrects the coordinate system used to control the processing device based on the positional deviation measured by the measuring device between the time the molding table is cooled to the cooling temperature and the time cutting is performed on the end face of the solidified layer.

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