Three-dimensional additive manufacturing device and method for controlling the three-dimensional additive manufacturing device

Abstract

To provide a three-dimensional lamination shaping device capable of performing correction work without deteriorating throughput and to provide a method for controlling the three-dimensional lamination shaping device.SOLUTION: A three-dimensional lamination shaping device comprises a shaping plate, a powder supply device, a beam irradiating device, a detection part, and a control part controlling the powder supply device and the beam irradiation device. The control part obtains a reflected electron signal before main melting which is a reflected electron signal detected by the detection part before main melting the powder material by the electron beam after the powder material is laid down by the powder supply device. Further, the control part obtains a reflected electron signal after main melting of a previous layer which is a reflected electron signal detected by the detection unit after main melting the powder material by the electron beam in the shaping step of the previous layer of the current layer. Then, the control part sets a supply amount of powder material from the powder supply device in the shaping step of a subsequent layer based on the reflected electron signal before main melting and the reflected signal after main melting of the previous layer.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a three-dimensional additive manufacturing apparatus and a method for controlling the three-dimensional additive manufacturing apparatus. [Background technology]

[0002] In recent years, 3D additive manufacturing technology, which creates objects by stacking thin layers of powder material one by one, has been attracting attention, and many types of 3D additive manufacturing technology have been developed, depending on the powder material and manufacturing method.

[0003] In a conventional 3D additive manufacturing device, for example, powder material is spread layer by layer on a base plate installed on the upper surface of a stage. Next, only the two-dimensional structure portion of the powder material spread on the base plate, which corresponds to one cross section of the object, is melted using a heating mechanism consisting of an electron beam or laser. Then, the layer of powder material is stacked one by one in the height direction (Z direction) to form the object (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-138653 Summary of the Invention [Problem to be solved by the invention]

[0005] However, with conventional 3D additive manufacturing devices, if the powder material was not properly spread during the manufacturing process, the manufacturing operation had to be temporarily stopped and the powder material had to be spread again, which resulted in a problem of reduced throughput for the manufacturing operation.

[0006] In consideration of the above problems, an object of the present invention is to provide a three-dimensional additive manufacturing apparatus and a control method for a three-dimensional additive manufacturing apparatus that can perform correction work without deteriorating throughput. [Means for solving the problem]

[0007] To solve the above problems and achieve the object of the present invention, a three-dimensional additive manufacturing apparatus of the present invention includes a modeling plate, a powder supplying device that supplies powder material to the modeling plate to form a powder layer, and a beam irradiation device that irradiates the powder layer with an electron beam. The three-dimensional additive manufacturing apparatus also includes a detection unit that detects backscattered electrons generated when the powder material is irradiated with the electron beam, and a control unit that controls the beam irradiation device. The control unit acquires a reflected electron signal after main melting of the previous layer, which is a reflected electron signal detected by the detection unit after the powder material is main melted by the electron beam during the manufacturing process of the layer previous to the current layer. Then, the control unit sets the control conditions of the beam irradiation device for the main melting step in the modeling step of the current layer based on the electronic signal after the main melting of the previous layer.

[0008] The three-dimensional additive manufacturing method of the present invention includes the following steps (1) to ( 3 ) (1) A process in which powder material is supplied to a build plate by a powder supply device to form a powder layer. (2) A process for acquiring a reflected electron signal after main melting of the previous layer, which is a reflected electron signal detected by the detection unit after the powder material is main melted by the electron beam in the manufacturing process of the layer before the current layer. (3) The main melting process involves using a beam irradiation device to irradiate the powder layer with an electron beam to melt the powder material. Then, based on the electronic signal after the main melting of the previous layer, the control conditions of the beam irradiation device for the main melting step in the modeling step of the current layer are set. [Effects of the Invention]

[0009] According to the three-dimensional additive manufacturing device and the control method for the three-dimensional additive manufacturing device of the present invention, correction work can be performed without deteriorating throughput. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic cross-sectional view showing a three-dimensional additive manufacturing apparatus according to an embodiment of the present invention. [Figure 2]FIG. 2 is a block diagram showing an example of the configuration of a control system of a three-dimensional additive manufacturing apparatus according to an embodiment of the present invention. [Figure 3] 1 is a plan view showing the position of a detection unit in a three-dimensional additive manufacturing device according to an embodiment of the present invention. FIG. [Figure 4] 4 is a flowchart showing an example of operation of the three-dimensional additive manufacturing device according to the embodiment of the present invention. [Figure 5] 1 shows an example of a backscattered electron image acquired after powder heating. [Figure 6] Backscattered electron image taken after powder heating, showing an example of improperly packed powder material. [Figure 7] 1 is a backscattered electron image taken after the actual melting, showing an example of the powder material being melted. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of a three-dimensional additive manufacturing device and a method for controlling a three-dimensional additive manufacturing device according to the present invention will be described with reference to Figures 1 to 7. Note that common members in the figures are given the same reference numerals.

[0012] 1. Example of implementation 1-1.Configuration of 3D additive manufacturing equipment First, a first embodiment of a three-dimensional additive manufacturing device according to an embodiment of the present invention (hereinafter referred to as "this example") will be described with reference to FIG. Fig. 1 is a schematic cross-sectional view showing a three-dimensional additive manufacturing apparatus according to this embodiment. In the following description, in order to clarify the shapes and positional relationships of the various components of the three-dimensional additive manufacturing apparatus, the left-right direction in Fig. 1 is referred to as the X direction, the depth direction in Fig. 1 as the Y direction, and the up-down direction in Fig. 1 as the Z direction. The X direction, Y direction, and Z direction are perpendicular to each other. Furthermore, the X direction and Y direction are parallel to the horizontal direction, and the Z direction is parallel to the vertical direction.

[0013] The 3D additive manufacturing device 1 shown in Figure 1 is a device that irradiates powder material made of metal powder such as titanium, aluminum, iron, etc. with an electron beam to melt the powder material, and then stacks layers of this solidified powder material to form a three-dimensional object.

[0014] 1, the 3D additive manufacturing apparatus 1 includes a vacuum chamber 3, a beam irradiation device 2, a powder supply device 16, a modeling table 18, a modeling box 20, and a collection box 21. The 3D additive manufacturing apparatus 1 also includes a modeling plate 22, an inner base 24, a plate moving device 26, a radiation shield cover 28, a mask cover 30, a camera 42, and a shutter 44. The 3D additive manufacturing apparatus 1 also includes a plurality of detection units 46 that detect reflected electrons.

[0015] The vacuum chamber 3 is a chamber for creating a vacuum state by evacuating the air inside the chamber with a vacuum pump (not shown).

[0016] The beam irradiation device 2 is a device that irradiates an electron beam 15 onto a build surface 32a of a powder layer formed from a build plate 22 or a powder material 32. The build surface 32a corresponds to the upper surface of the powder layer. The state of the powder layer changes as the 3D additive manufacturing process progresses. Although not shown, the beam irradiation device 2 has an electron gun that generates the electron beam 15, a focusing lens that focuses the electron beam generated by the electron gun, and a deflection lens that deflects the electron beam 15 focused by the focusing lens. The focusing lens is configured using a focusing coil and focuses the electron beam 15 by the magnetic field generated by the focusing coil. The deflection lens is configured using a deflection coil and deflects the electron beam 15 by the magnetic field generated by the deflection coil.

[0017] The powder supplying device 16 is a device that supplies powder material 32, which is an example of a powder material that serves as a raw material for the molded object 38, onto the molding plate 22 to form a powder layer. The powder supplying device 16 has a hopper 16a, a powder dropper 16b, and a squeegee 16c. The hopper 16a is a container for storing metal powder. The powder dropper 16b is a device that drops the powder material 32 stored in the hopper 16a onto the molding table 18. The squeegee 16c is an elongated member that is long in the Y direction and has a blade 16d for spreading the powder. The squeegee 16c spreads the powder material 32 dropped by the powder dropper 16b over the molding table 18. The squeegee 16c is movable in the X direction to spread the powder material 32 over the entire surface of the molding table 18.

[0018] The modeling table 18 is arranged horizontally inside the vacuum chamber 3. The modeling table 18 is arranged below the powder supply device 16. The center of the modeling table 18 is open. The shape of the opening of the modeling table 18 is circular in plan view or angular in plan view (for example, rectangular in plan view).

[0019] The modeling box 20 is a box that forms a space for modeling. The upper end of the modeling box 20 is connected to the edge of the opening of the modeling table 18. The lower end of the modeling box 20 is connected to the bottom wall of the vacuum chamber 3.

[0020] The recovery box 21 is a box for recovering the powder material 32 that has been supplied onto the modeling table 18 by the powder supplying device 16 in excess of what is needed.

[0021] The shaping plate 22 is a plate for forming a shaped object 38 using the powder material 32. The shaped object 38 is formed by stacking on the shaping plate 22. The shaping plate 22 is formed to be circular or angular in plan view to match the shape of the opening of the shaping table 18. The shaping plate 22 is connected (grounded) to the inner base 24 by an earth wire 34 to prevent it from being electrically floating. The inner base 24 is maintained at GND (ground) potential. The powder material 32 is spread over the shaping plate 22 and the inner base 24.

[0022] The inner base 24 is provided so as to be movable in the vertical direction (Z direction). The shaping plate 22 moves vertically together with the inner base 24. The inner base 24 has larger outer dimensions than the shaping plate 22. The inner base 24 slides vertically along the inner surface of the shaping box 20. A sealing member 36 is attached to the outer periphery of the inner base 24. The sealing member 36 is a member that maintains slidability and airtightness between the outer periphery of the inner base 24 and the inner surface of the shaping box 20. The sealing member 36 is made of a heat-resistant and elastic material.

[0023] The plate moving device 26 is a device that moves the shaping plate 22 and the inner base 24 in the vertical direction. The plate moving device 26 includes a shaft 26a and a drive mechanism unit 26b. The shaft 26a is connected to the underside of the inner base 24. The drive mechanism unit 26b includes a motor and a power transmission mechanism (not shown), and moves the shaping plate 22 and the inner base 24 together with the shaft 26a in the vertical direction by driving the power transmission mechanism using the motor as a drive source. The power transmission mechanism is configured, for example, by a rack and pinion mechanism, a ball screw mechanism, or the like.

[0024] The radiation shield cover 28 is disposed between the build plate 22 and the beam irradiation device 2 in the Z direction. The radiation shield cover 28 is made of a metal such as stainless steel. The radiation shield cover 28 shields against radiant heat generated when the electron beam 15 is irradiated onto the powder material 32 by the beam irradiation device 2. When the electron beam 15 is irradiated onto the powder material 32 for sintering, the powder material 32 melts. However, if the heat radiated from the build surface 32a of the powder layer at this time, i.e., the radiant heat, is widely dispersed within the vacuum chamber 3, thermal efficiency deteriorates. In contrast, when the radiation shield cover 28 is disposed above the build plate 22, the heat radiated from the build surface 32a is shielded by the radiation shield cover 28, and the shielded heat is reflected by the radiation shield cover 28 and returned to the build plate 22. This allows for efficient use of the heat generated by the irradiation of the electron beam 15.

[0025] The radiation shield cover 28 also functions to prevent evaporated material generated when the powder material 32 is irradiated with the electron beam 15 from adhering (depositing) onto the inner wall of the vacuum chamber 3. When the powder material 32 is irradiated with the electron beam 15, part of the molten metal turns into mist-like evaporated material and rises from the building surface 32a. The radiation shield cover 28 is arranged to cover the space above the building surface 32a to prevent this evaporated material from diffusing inside the vacuum chamber 3.

[0026] The mask cover 30 has an opening 30a and a mask portion 30b. When forming the molded object 38, the mask cover 30 is placed over the top surface of the powder material 32, i.e., the molded surface 32a. The opening 30a exposes the powder material 32 spread on the molded object 38, while the mask portion 30b shields the powder material 32 located outside the opening 30a. The shape of the opening 30a is set to match the shape of the molded object 22. For example, if the molded object 22 is circular in plan view, the opening 30a is set to be circular in plan view accordingly, and if the molded object 22 is rectangular in plan view, the opening 30a is set to be rectangular in plan view accordingly.

[0027] The mask cover 30 is disposed below the radiation shield cover 28. The opening 30a and mask portion 30b of the mask cover 30 are disposed between the build plate 22 and the radiation shield cover 28 in the Z direction. The mask cover 30 has an enclosure portion 30c. The enclosure portion 30c is disposed so as to enclose the space above the opening 30a. A portion (upper portion) of the enclosure portion 30c overlaps with the radiation shield cover 28 in the Z direction. The enclosure portion 30c functions to shield radiant heat generated from the build surface 32a and to suppress the diffusion of evaporated materials generated from the build surface 32a. In other words, the enclosure portion 30c functions similarly to the radiation shield cover 28.

[0028] The mask cover 30 is made of a metal with a higher melting point than the powder material 32 used as the raw material for the molded object 38. The mask cover 30 is also made of a material that is less reactive with the powder material 32. Titanium, for example, can be used as a material for the mask cover 30. The mask cover 30 may also be made of the same metal as the powder material 32 used. The mask cover 30 is electrically grounded to GND. The mask cover 30 serves as an electrical shield when the powder material 32 is pre-sintered by irradiating it with an electron beam 15 in a pre-heating step prior to the main sintering step, which will be described later, thereby minimizing powder scattering.

[0029] The camera 42 is a camera capable of capturing an image of the powder layer's building surface 32a. The camera 42 is positioned offset in the Y direction from the beam irradiation device 2 so as not to interfere with the position of the beam irradiation device 2. The camera 42 is preferably configured as a visible light camera such as a digital video camera. The camera 42 captures an image of the powder layer's building surface 32a to generate an image (image data) of the powder layer. Therefore, the image generated by the camera 42 is an image that shows the state of the powder layer's building surface 32a. The image is captured by the camera 42 with illumination light emitted by an illumination light source (not shown) included in the 3D additive manufacturing device 1 irradiating the powder layer's building surface 32a.

[0030] The shutter 44 protects the camera 42 and the observation window so that evaporated substances generated from the manufacturing surface 32a do not adhere to the camera 42 or the observation window when the powder material 32 is melted by irradiation with the electron beam 15. The camera 42 photographs the manufacturing surface 32a with the shutter 44 open. Furthermore, in processes in which evaporated substances are likely to be generated or in which a large amount of evaporated substances are generated, i.e., when the powder material 32 is melted by the electron beam 15, the shutter 44 is closed.

[0031] A plurality of detectors 46 for detecting reflected electrons are disposed below the beam irradiation device 2. Specifically, the detectors 46 are disposed between the beam irradiation device 2 and the build surface 32a of the object 38 formed on the build plate 22.

[0032] FIG. 3 is a plan view showing the position of the detection unit 46. As shown in FIG. 3, the multiple detectors 46a, 46b, 46c, and 46d are arranged to surround the periphery of the object 38. The first detector 46a is arranged on one side of the object 38 in the X direction, and the second detector 46b is arranged on the other side of the object 38 in the X direction. The first detector 46a and the second detector 46b face each other with the object 38 between them. The third detector 46c is arranged on one side of the object 38 in the Y direction, and the fourth detector 46d is arranged on the other side of the object 38 in the Y direction. The third detector 46c and the fourth detector 46d face each other with the object 38 between them.

[0033] Although an example in which a plurality of detectors 46 are arranged has been described, the present invention is not limited to this, and the number of detectors 46 may be one, three or less, or five or more.

[0034] The detector 46 is not limited to a semiconductor detector, but may be a Ti electrode having a low secondary electron emission rate due to electron excitation, etc. The detector 46 may also detect backscattered electrons incident on the electrode as a current using a current detection amplifier, and detect an increase or decrease in this current.

[0035] FIG. 2 is a block diagram showing an example of the configuration of a control system of the three-dimensional additive manufacturing apparatus 1 of this embodiment. As shown in Figure 2, the 3D additive manufacturing device 1 has a polarization amplifier control circuit 101 which represents an electron beam control unit, an analog-to-digital conversion circuit (ADC) 102, a preamplifier (Pre-AMP) 103, a personal computer (PC) 104 which represents an example of a control unit, and a display unit 105.

[0036] The polarization amplifier control circuit 101 is connected to the beam irradiation device 2 and the PC 104. The polarization amplifier control circuit 101 controls the beam irradiation device 2 based on the set beam scanning information. As a result, the beam irradiation device 2 irradiates the electron beam 15 at a predetermined position. The polarization amplifier control circuit 101 also transmits beam irradiation position information indicating the irradiation position of the electron beam 15 to the PC 104.

[0037] The Pre-AMP 103 is connected to the detection unit 46 and the ADC 102. The Pre-AMP 103 converts the reflected electron current detected by the detection unit 46 from a current signal to a voltage signal. The voltage signal converted by the Pre-AMP 103 is transmitted to the ADC 102. The ADC 102 converts the reflected electron signal, which has become a voltage signal, from an analog signal to a digital signal and transmits it to the PC 104.

[0038] PC 104 has an image processing unit and a storage unit (not shown). The image processing unit of PC 104 captures images generated by camera 42 and performs predetermined image processing on the captured images. PC 104 then outputs the camera images that have been processed by the image processing unit to display unit 105.

[0039] The memory unit stores camera images generated by the image processing unit. Furthermore, the memory unit stores beam irradiation position information transmitted from the polarization amplifier control circuit 101. The memory unit also stores a plurality of arithmetic expressions for performing arithmetic processing on backscattered electron signals acquired from the plurality of detectors 46a, 46b, 46c, and 46d.

[0040] The PC 104 selects a predetermined arithmetic expression from a plurality of arithmetic expressions according to the modeling process. Then, the PC 104 performs arithmetic processing on the backscattered electron signal using the selected arithmetic expression to calculate the arithmetic signal. Then, the image processing unit visualizes the arithmetic signal to acquire a backscattered electron image (BSE image). The PC 104 outputs the acquired backscattered electron image (BSE image) to the display unit 105. The backscattered electron image (BSE image) is also stored in the storage unit.

[0041] The display unit 105 is configured with a display such as a liquid crystal display (LCD) or an organic ELD (Electro Luminescence Display), etc. The display unit 105 displays the BSE image and the camera image output from the PC 104 on a display screen 106 (see FIG. 4, etc.).

[0042] 1-2. Example of operation of 3D additive manufacturing equipment Next, an example of the operation of the three-dimensional additive manufacturing device 1 having the above-described configuration will be described with reference to FIG. FIG. 4 is a flowchart showing an example of the operation of the three-dimensional additive manufacturing device 1.

[0043] 4, the beam irradiation device 2 operates based on a control command given from the PC 104 to heat the build plate 22 (step S1). In step S1, the beam irradiation device 2 irradiates the build plate 22 with the electron beam 15 through the opening 30a of the mask cover 30, and scans the build plate 22 with the electron beam 15. As a result, the build plate 22 is heated to a temperature at which the powder material 32 is pre-sintered.

[0044] Next, the powder material 32 is spread on the building plate 22 (step S2). In step S2, the plate moving device 26 operates based on a control command given from the PC 104 to lower the building plate 22 by a predetermined amount. The plate moving device 26 lowers the inner base 24 by a predetermined amount so that the upper surface of the building plate 22 is slightly lower than the upper surface of the powder material 32 spread on the building table 18. At this time, the building plate 22 is lowered by the predetermined amount together with the inner base 24.

[0045] The powder supplying device 16 then drops the powder material 32 supplied from the hopper 16a to the powder dropper 16b onto the modeling table 18 using the powder dropper 16b, and then spreads the powder material 32 over the inner base 24 by moving the squeegee 16c from one end to the other in the X direction. At this time, the powder material 32 is spread over the modeling table 18 to a thickness equivalent to ΔZ. Any excess powder material 32 is collected in the collection box 21. At this time, the powder material 32 set in step S8 of the previous layer is spread over the entire surface. For example, if the PC 104 determines that the powder material 32 was not properly spread over the entire surface in step S8 of the previous layer, two layers of powder material 32 are spread over the entire surface.

[0046] Next, the beam irradiation device 2 operates based on control commands given by the polarization amplifier control circuit 101 and the PC 104 to preheat the powder layer on the build plate 22, a process known as powder heating (PH) (step S3). In step S3, the powder layer is preheated to pre-sinter the powder material 32. Pre-sintering the powder material 32 makes the powder material 32 conductive. This makes it possible to suppress powder scattering during the sintering process that follows the pre-heating process.

[0047] In step S3, the beam irradiation device 2 irradiates the powder material 32 on the building plate 22 with the electron beam 15. The beam irradiation device 2 also scans the electron beam 15 over an area wider than the area for forming the object 38 (hereinafter also referred to as the "building area"). As a result, the powder material 32 present in the building area and the powder material 32 present around the building area are both pre-sintered.

[0048] If the PC 104 determines that the powder material 32 was not properly spread in step S8 of the previous layer, two layers of powder material are spread in step S2. Therefore, the powder heating time in step S3 is extended longer than normal. This allows the powder material 32 for two layers to be completely pre-sintered.

[0049] Next, a backscattered electron image (BSE image) before the main melting is acquired (step S4). In step S4, first, the beam irradiation device 2 operates based on control commands given by the polarization amplifier control circuit 101 and the PC 104 to scan the electron beam 15 over the pre-sintering region where the pre-sintered powder material 32 exists. At this time, the beam irradiation device 2 minimizes the electron beam current of the electron beam 15 and focuses the electron beam 15 on the manufacturing surface 32a. Then, the detection unit 46 detects the backscattered electrons generated by the electron beam 15.

[0050] The detector 46 outputs the detected backscattered electron signal to the PC 104 via the Pre-AMP 103 and the ADC 102. The image processor of the PC 104 then performs arithmetic processing on the backscattered electron signal (backscattered electron information) acquired from the detector 46 to acquire a backscattered electron image (BSE image). The image processor also stores the acquired BSE image before main melting (before melting) in a memory unit.

[0051] Next, the PC 104 evaluates the BSE image after melting of the previous layer and sets the melting conditions to be performed in step S6 (step S5). These melting conditions are the control conditions of the beam irradiation device 2 in the main melting process in step S6 (described later). In step S5, the PC 104 acquires from the memory the BSE image acquired in step S7 when the previous layer was formed (hereinafter referred to as the BSE image after melting of the previous layer). The BSE image after melting of the previous layer may be determined, for example, by using an unevenness analysis of the building surface 32a. That is, the frequency of the unevenness is detected, and if the frequency is higher than a threshold, it is determined to be unmelted, and if the frequency is lower than the threshold, it is determined to be overmelted. The PC 104 then sets melting conditions, such as the irradiation spot diameter and scanning speed of the electron beam 15, and the thermal energy value supplied by the electron beam 15, depending on the degree of melting of the powder material 32.

[0052] Furthermore, if the PC 104 determines that the powder material 32 was not properly spread in step S8 of the previous layer, two layers of powder material 32 are spread in step S2. Therefore, the PC 104 sets the melting conditions so that two layers of powder material 32 can be melted.

[0053] The melting condition setting process in step S5 may be performed between the acquisition of a post-melting BSE image in step S7 described later during the modeling work of the previous layer and the main melting process in step S6 during the modeling work of the current layer.

[0054] Next, the beam irradiation device 2 operates based on the melting conditions set in step S5 to melt and solidify the powder material 32 for final sintering (melting) (step S6). In step S6, the powder material 32 that has been provisionally sintered as described above is irradiated with the electron beam 15 to melt and solidify, thereby final sintering the powder material 32 as a provisionally sintered body.

[0055] In step S6, the beam irradiation device 2 identifies a printing area based on two-dimensional data obtained by slicing the three-dimensional CAD data of the target object 38 at a certain thickness (a thickness corresponding to ΔZ), and selectively melts the powder material 32 on the printing plate 22 by scanning the electron beam 15 over this printing area. The powder material 32 melted by irradiation with the electron beam 15 solidifies after the electron beam 15 has passed through. This forms the first layer of the object.

[0056] After step S6 is completed, a backscattered electron image (BSE image) after the actual melting, i.e., a post-melt BSE image, is acquired (step S7). In step S7, the beam irradiation device 2 first scans the electron beam 15 over the pre-sintering region where the pre-sintered powder material 32 exists, by operating based on control commands given by the polarization amplifier control circuit 101 and the PC 104. At this time, the beam irradiation device 2 minimizes the electron beam current of the electron beam 15 and focuses the electron beam 15 on the manufacturing surface 32a. The detection unit 46 then detects the backscattered electrons generated by the electron beam 15.

[0057] The detection unit 46 also outputs the detected backscattered electron signal to the PC 104 via the Pre-AMP 103 and the ADC 102. The detection unit 46 also outputs the detected backscattered electron signal to the PC 104 via the Pre-AMP 103 and the ADC 102. The image processing unit of the PC 104 then performs arithmetic processing on the backscattered electron signal acquired from the detection unit 46 to acquire a backscattered electron image (BSE image).

[0058] Next, PC 104 compares the post-melt BSE image of the previous layer with the current pre-melt BSE image, and sets the supply amount of powder material 32 from powder supply device 16 for the next layer (step S8). In step S8, PC 104 obtains from the memory the BSE image acquired in step S7 when the previous layer was formed (hereinafter referred to as the post-melt BSE image of the previous layer). PC 104 also obtains from the memory the pre-melt BSE image acquired in step S4 when the current layer was formed. PC 104 then compares the two BSE images, determines the degree of spreading of powder material 32, and sets the powder supply amount for step 2, in which the next layer is formed.

[0059] If the difference between the two BSE images is small, the PC 104 determines that the powder material 32 was not properly spread in this step 2. Then, in step S2 for the next layer, the amount of powder to be supplied for two layers is set.

[0060] The step of setting the powder supply amount shown in step S8 may be performed after the step of acquiring the pre-melt BSE image in step S4. In this case, if the powder is not properly spread, the melt current used in the immediately following melt can be reduced to minimize the impact on the model 38.

[0061] Next, in preparation for spreading the powder material 32, afterheating (AH) is performed to heat the build surface 32a (step S9). In step S9, the beam irradiation device 2 operates under the control of the polarization amplifier control circuit 101 and the PC 104 to irradiate the build surface 32a with the electron beam 15 through the opening 30a in the mask cover 30. At this time, the polarization amplifier control circuit 101 defocuses the electron beam 15 using an objective lens or the like provided in the beam irradiation device 2. This defocusing causes the focal position of the electron beam 15 to be shifted downward from the build surface 32a, i.e., an underfocus state.

[0062] Furthermore, the polarization amplifier control circuit 101 and the PC 104 control the beam irradiation device 2 to scan the electron beam 15 over an area wider than the opening 30a of the mask cover 30. As a result, the electron beam 15 is irradiated onto the entire surface 32a to be molded that is exposed through the opening 30a. The surface 32a to be molded is heated to a temperature sufficient to temporarily sinter the powder material 32. Once the surface 32a to be molded has been heated to a predetermined temperature, the beam irradiation device 2 stops irradiating the electron beam 15.

[0063] Furthermore, if it is determined in step S8 that the powder material 32 was not properly applied, two layers of powder material will be applied in the next layer. Therefore, the afterheating time in step S9 is made longer than normal to increase the temperature of the printing surface 32a. This prevents the temperature of the printing surface 32a from dropping too much even if two layers of powder material 32 are applied in step S2 of the next layer.

[0064] Next, the shaping plate 22 is lowered by a predetermined amount (ΔZ) (Step S10). In Step S10, the plate moving device 26 lowers the inner base 24 by ΔZ so that the shaping surface 32a is slightly lower than the upper surface of the powder material 32 spread on the shaping table 18.

[0065] Thereafter, the above steps S2 to S11 are repeated until the final layer is formed in step S11, i.e., until the formation of the object 38 is completed. The formation of the object 38 is completed when the powder material 32 has been melted and solidified for the number of layers required to form the object 38. In this way, the desired object 38 is obtained.

[0066] As described above, according to the operation example of the 3D additive manufacturing apparatus 1 of this example, the degree of spreading of the powder material 32 and the degree of melting of the model 38 are determined in steps S5 and S8 before and after the main melting in step S6. Then, the supply amount of powder material 32 and melting conditions for the next layer are set and corrected as necessary. This reduces the number of times the modeling of the model 38 fails.

[0067] Furthermore, corrections to the molding process for problems such as the powder material 32 not being properly laid or melted are performed on the next layer, not on the layer where the problem occurred. Furthermore, the corrections are performed by changing the supply amount of powder material 32 in the next layer or the melting conditions of the main melting process. This allows the throughput of the molding operation to always be performed at the same timing, and corrections can be made without deteriorating the throughput.

[0068] Furthermore, by performing the correction work on the next layer, there is no need to perform a heating process to accelerate the preliminary sintering after the preliminary sintering of the same layer. This prevents the preliminary sintered body from becoming harder than necessary, making it easier to perform the blasting process that is performed after the 3D printing operation. Furthermore, it is possible to prevent the mechanical properties of the model 38 that has undergone the correction work from differing from those of the model 38 that has been produced without the correction work.

[0069] Although the example in which a BSE image is used to make the determinations in steps S5 and S8 has been described, the present invention is not limited to this. For example, the determinations in steps S5 and S8 may be made using the backscattered electron signal (backscattered electron information) detected by the detection unit 46 without performing image conversion processing on the backscattered electron signal.

[0070] 2. Example of backscattered electron image Next, examples of backscattered electron images (BSE images) acquired in steps S4 and S7 will be described with reference to FIGS. FIG. 5 shows an example of a backscattered electron image acquired after powder heating.

[0071] The image processing unit performs arithmetic processing on the backscattered electron signals acquired from the multiple detectors 46a, 46b, 46c, and 46d to generate a backscattered electron image. In the backscattered electron image acquired after powder heating in step S4, the image processing unit adds the first backscattered electron signal A from the first detector 46a and the second backscattered electron signal B from the second detector 46b, which are arranged opposite each other. That is, the arithmetic expression is A + B. Alternatively, the third backscattered electron signal C from the third detector 46c and the fourth backscattered electron signal D from the fourth detector 46d, which are arranged opposite each other, may be added (C + D). Using this arithmetic expression, a backscattered electron image in which the contour of the model 38 is emphasized can be acquired. As a result, it becomes easier to confirm whether the powder material 32 has been properly spread, and the PC 104 can accurately determine whether the powder material 32 has been properly spread in step S8.

[0072] FIG. 7 shows an example of a backscattered electron image acquired after the main melting. In the backscattered electron image acquired after the main melting in step S7, the image processing unit subtracts the first backscattered electron signal A from the second backscattered electron signal B, or subtracts the third backscattered electron signal C from the fourth backscattered electron signal D. This makes it possible to acquire a backscattered electron image in which the unevenness of the printing surface 32a of the object 38 is emphasized.

[0073] The calculation formula may be (AB) / (A+B) or (CD) / (C+D). That is, by dividing the subtraction signal of two backscattered electron images by the addition signal of two backscattered electron images, fluctuations in the electron beam current and the effects of noise can be suppressed. As a result, as shown in FIG. 7, a backscattered electron image can be acquired in which the unevenness of the printing surface 32a of the molded object 38 is emphasized. As a result, it becomes easier to confirm whether the powder material 32 has been properly melted, and the process of determining the degree of melting of the powder material 32 by the PC 104 can be accurately performed in step S5.

[0074] 3. Example of determining the degree of powder material spreading Next, an example of determining the degree of spreading of the powder material 32 performed in step S8 will be described with reference to FIGS. Fig. 6 is a backscattered electron image acquired after powder heating, showing an example in which the powder material 32 was not properly spread. The backscattered electron image shown in Fig. 6 is acquired using the calculation formula A+B.

[0075] If the powder material is properly laid, the backscattered electron image will be almost entirely black (see Figure 5). If no powder material is laid at all, the entire area melted in the previous layer will be white, and the other areas will be black, as shown in Figure 6. If only a portion of the powder material is laid, the part of the area melted in the previous layer (the area where the powder material was laid) will be black, the remaining melted area (the area where the powder material 32 was not laid) will be white, and the remaining area of ​​the powder material 32 will be all black.

[0076] Here, consider the three-dimensional coordinate system of xyz. Then, the data of the post-melt BSE image of the previous layer and the pre-melt BSE image of the current layer are digitized in the form of (x, y, z) for all pixel counts to create three-dimensional data of xyz. In other words, the position of the BSE image as the x coordinate, the position of the BSE image as the Y coordinate, and the brightness values ​​of the BSE image corresponding to the X and Y coordinates are set. At this time, the whiter the image, the higher the brightness value, and the darker the image, the lower the value.

[0077] Then, 3D data is derived by taking the difference between the z coordinate values ​​(brightness / darkness values ​​of the BSE image corresponding to the X and Y coordinates) corresponding to the same x and y coordinates of the two 3D data. If no powder material is laid, the z coordinate values ​​(brightness / darkness values) of the two 3D data obtained by taking the difference between the post-melt BSE image of the previous layer and the pre-melt BSE image of the current layer will be nearly the same at any x or y coordinate. Therefore, it is expected that the z coordinate value will be close to 0 at any x or y coordinate.

[0078] On the other hand, if the powder material 32 is properly spread, the white portions of the object in the previous layer will turn black. Therefore, the z-coordinate value of the subtracted 3D data, which indicates the position of the object in the x-y coordinate system, will be a brightness value indicating the difference between white and black (a value greater than 0). Therefore, two values ​​are considered. The first value is the z-coordinate of the 3D data from which the subtraction data was taken (the difference between brightness and darkness between the two BSE images). A threshold value is then set for this value. The second value is the sum of the number of pixels in the z-coordinate of the 3D data from which the subtraction data was taken (the difference between brightness and darkness between the two BSE images) that exceed a threshold, divided by the sum of the number of pixels in the white portions of the BSE image due to the presence of the object in the previous layer (hereinafter referred to as the powder spreading ratio). A threshold value can also be set for this powder spreading ratio. If the powder spreading ratio value is smaller than this threshold, it is determined that the powder was not properly spread. This allows the degree of spreading of the powder material 32 to be determined in step S8.

[0079] 4. Example of determining the degree of melting of powder materials Next, an example of determining the melting degree of the powder material 32 performed in step S5 will be described with reference to FIG. Figure 7 shows a backscattered electron image acquired after the actual melting. Figure 7 shows an example that includes both a portion (i) where the powder material was relatively properly melted and portions (j) to (q) where the powder material was not properly melted. The backscattered electron image shown in Figure 7 was acquired using the formula (AB) / (A+B).

[0080] If the powder material 32 is properly melted, the top surface of the build surface 32a will be flat, as shown in part (i) of Figure 7. If the powder material 32 is not properly melted, the top surface of the build surface 32a will be very uneven, as shown in parts (j) to (q) of Figure 7. The unevenness of the top surface can be considered as a three-dimensional wave. The maximum amplitude and maximum period of this three-dimensional wave are then calculated. Furthermore, the top surface unevenness can be quantified for all pixels in the form of three-dimensional coordinates (x, y, z) of x, y, and z, and converted into three-dimensional data of x, y, and z. In other words, the brightness and darkness values ​​of the BSE image corresponding to the position as the X coordinate of the BSE image and the position as the Y coordinate of the BSE image are set.

[0081] The maximum amplitude and maximum period are then calculated from the three-dimensional data. Threshold values ​​are set for the amplitude and period, and when either or both of these thresholds are exceeded, it is determined that the powder material 32 is not properly melted. This allows the degree of melting of the powder material 32 to be determined in step S5.

[0082] The present invention is not limited to the embodiments described above and shown in the drawings, and various modifications can be made without departing from the spirit of the invention as set forth in the claims.

[0083] For example, in the above-described embodiment, an example was described in which metal powder such as titanium, aluminum, or iron was used as the powder material, but the present invention is not limited thereto, and resin or the like may also be used as the powder material. Also, an example was described in which an electron gun that irradiates an electron beam was used as the heating mechanism for preheating or melting the powder material, but the present invention is not limited thereto. For example, a laser irradiation unit that irradiates a laser may also be used as the heating mechanism.

[0084] In the above-described embodiment, the detection unit 46 is disposed inside the radiation shield cover 28, but the present invention is not limited to this. The detection unit 46 may also be disposed outside the radiation shield cover 28.

[0085] Although the example in which the PC 104 is used as the control unit has been described, the present invention is not limited to this. As the control unit, a control unit having various kinds of calculation functions, such as an electron beam control unit that controls the beam irradiation device 2, can be used.

[0086] Furthermore, some or all of the above-described components, functions, processing units, etc. may be implemented in hardware, for example, by designing an integrated circuit. Furthermore, the above-described components, functions, etc. may be implemented in software by a processor interpreting and executing a program that implements each function. Information such as the programs, tables, and files that implement each function can be stored in a storage device such as a memory, a hard disk, or an SSD (Solid State Drive), or in a storage medium such as an IC card, SD card, or DVD.

[0087] In this specification, the words "parallel" and "orthogonal" are used, but these do not mean only "parallel" and "orthogonal" in the strict sense, but also include "parallel" and "orthogonal" and may also mean a "substantially parallel" or "substantially orthogonal" state within a range in which the functions can be exerted. [Explanation of symbols]

[0088] 1...3D additive manufacturing device, 2...beam irradiation device, 3...vacuum chamber, 15...electron beam, 16...powder supply device, 16a...hopper, 16b...powder dropper, 16c...squeegee, 16d...blade, 18...build table, 20...build box, 21...recovery box, 22...build plate, 24...inner base, 26...plate moving device, 32...powder material, 32a...build surface, 38...build object, 42...camera, 44...shutter, 46...detection unit, 101...polarization amplifier control circuit, 102...digital conversion circuit (ADC), 103...preamplifier (Pre-AMP) 104...personal computer (PC, control unit), 105...display unit, 106...display screen

Claims

1. A shaping plate and a powder supplying device that supplies powder material to the build plate to form a powder layer; a beam irradiation device that irradiates the powder layer with an electron beam; a detection unit that detects reflected electrons generated when the electron beam is irradiated onto the powder material; a control unit for controlling the beam irradiation device, the control unit acquires a reflected electron signal after main melting of the previous layer, which is a reflected electron signal detected by the detection unit after the powder material is main melted by the electron beam in a modeling process of the previous layer of the current layer, The control unit determines whether the powder material has been properly melted based on the post-main melting reflected electron signal of the previous layer, and when it determines that the powder material has not been properly melted in the modeling process of the previous layer, does not perform a correction operation for the melting of the previous layer in the modeling process of the previous layer; The control unit corrects the control conditions of the beam irradiation device for the main melting step in the modeling step of the current layer based on the reflected electron signal after the main melting of the previous layer. 3D additive manufacturing device.

2. the control unit controls the powder supplying device to acquire a pre-main-melting backscattered electron signal, which is a backscattered electron signal detected by the detection unit after the powder material is spread by the powder supplying device and before the powder material is main-melted by the electron beam; The supply amount of the powder material from the powder supply device in the molding process of the next layer is set based on the pre-main-melting reflected electron signal and the post-main-melting electron signal of the previous layer. The three-dimensional additive manufacturing apparatus according to claim 1 .

3. The control unit has an image processing unit that generates a backscattered electron image based on a backscattered electron signal before main melting and a backscattered electron signal after main melting of the previous layer. The three-dimensional additive manufacturing apparatus according to claim 2 .

4. The detecting unit is provided in plurality, The control unit performs arithmetic processing on a plurality of backscattered electron signals detected by the plurality of detection units. The three-dimensional additive manufacturing apparatus according to claim 1 .

5. supplying powder material to a build plate by a powder supply device to form a powder layer; acquiring a reflected electron signal after main melting of the previous layer, which is a reflected electron signal detected by a detection unit after the powder material is main melted by an electron beam in a modeling process of the previous layer of the current layer; determining whether the powder material has been properly melted based on the reflected electron signal after the melting of the previous layer; a main melting step of irradiating the powder layer with the electron beam using a beam irradiation device to melt the powder material; Including, If it is determined that the powder material was not properly melted in the manufacturing process of the previous layer, the control conditions of the beam irradiation device for the main melting process in the manufacturing process of the current layer are corrected based on the reflected electron signal after the main melting of the previous layer, without performing the work of correcting the melting of the previous layer in the manufacturing process of the previous layer. A method for controlling a three-dimensional additive manufacturing device.

6. acquiring a pre-main-melting backscattered electron signal, which is a backscattered electron signal detected by a detection unit after the powder material is spread by the powder supplying device and before the powder material is main-melted by an electron beam; and setting a supply amount of the powder material from the powder supply device in the modeling step of the next layer based on the pre-main-melting reflected electron signal and the post-main-melting reflected electron signal of the previous layer. The method for controlling the three-dimensional additive manufacturing apparatus according to claim 5 .

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