Additive manufacturing method and additive manufacturing device

Abstract

This additive manufacturing method comprises: a step for, when forming a bead layer, detecting whether or not there is a bead (BD) in a lower layer, such detection performed for each processing path; a step for skipping processing from the first processing path (Pn) in which it was detected that there is no bead (BD) to the last processing path (Pn +1) in which it was detected that there is no bead (BD); a step for forming a bead (BD) having a second cross-sectional area in a corrected processing path (Pcn1) obtained by correcting the position of the processing path (Pn); and a step for forming a bead (BD) or a bead (BD) having a third cross-sectional area in a processing path from the processing path (Pn +1) subsequent to the corrected processing path (Pcn1) to the last processing path (Pn +1) at which it was detected that there is no bead (BD).

Description

Additive manufacturing method and additive manufacturing device

[0001] The present disclosure relates to an additive manufacturing method and an additive manufacturing apparatus for producing a three-dimensional object.

[0002] Additive manufacturing (AM) is a well-known technique for manufacturing three-dimensional objects. In directed energy deposition (DED), one of the various additive manufacturing techniques, a beam is irradiated onto the material and workpiece while supplying the material to a specified position, forming a bead, and the bead is then stacked to manufacture the object.

[0003] There is a demand for the use of such additive manufacturing methods to manufacture hollow-shaped objects with elongated holes. The hollow-shaped object is used, for example, as a mold, and a coolant is circulated through the circular cavity to control the temperature of the mold. In Non-Patent Document 1, the cross-sectional shape of the cavity is made teardrop-shaped, and the angle of the apex of the cavity is made small, thereby preventing beads from dripping into the cavity in the molded object.

[0004] Jack Holmes, Joe Pike, "Autodesk study Class_Handout_TR501949_ClassHandout-TR501949-Holmes-AU2022", [online], Autodesk University, [Retrieved June 19, 2023], Internet, <URL: Using Autodesk Fusion 360 and Metal AM to Optimize Automotive Mold Cooling Solutions | Autodesk University>

[0005] When a molded object with a teardrop-shaped cavity is manufactured using conventional manufacturing methods, stress is concentrated at the corners of the teardrop shape, which can shorten the product's lifespan. In addition, there are problems such as the accumulation of impurities, which can cause deterioration in the product's dimensions and shape.

[0006] The present disclosure has been made in consideration of the above, and aims to provide an additive manufacturing method that can prevent sagging of the bead at the top of the cavity due to the effects of gravity and thermal distortion.

[0007] In order to solve the above-mentioned problems and achieve the objectives, the additive manufacturing method disclosed herein moves a processing point along multiple processing paths extending in a first direction to form a bead layer in which multiple first beads of a first cross-sectional area are arranged in a second direction perpendicular to the first direction, and stacks the bead layers in a third direction perpendicular to the first and second directions to form a three-dimensional object having a cavity that is a deposit of the bead layers. The additive manufacturing method includes, when forming a bead layer, a detection process for detecting whether or not a first bead is present in the lower layer for each processing pass; a skip process for skipping processing in processing passes arranged in a second direction from a first processing pass, which is the first processing pass at which it is detected that the first bead is not present in the lower layer, to a second processing pass, which is the last processing pass at which it is detected that the first bead is not present in the lower layer; a second bead formation process for forming a second bead having a second cross-sectional area in the first processing pass after correction, in which the position of the first processing pass is corrected; and a third bead formation process for forming the first bead or a third bead having a third cross-sectional area in the processing pass from the processing pass next to the first processing pass after correction to the second processing pass.

[0008] The additive manufacturing method disclosed herein has the advantage of being able to prevent sagging of the bead at the top of the cavity due to the effects of gravity and thermal distortion.

[0009] FIG. 1 is a diagram showing the configuration of an additive manufacturing apparatus according to a first embodiment; FIG. 2 is a perspective view showing an example of a design model of a finished product formed by the additive manufacturing apparatus according to the first embodiment; FIG. 3 is a perspective view showing a molding model of a finished product formed by the additive manufacturing apparatus according to the first embodiment; FIG. 4 is a diagram for explaining intermediate machining passes introduced in the additive manufacturing apparatus according to the first embodiment; FIG. 5 is a diagram for explaining a machining pass skip procedure and an intermediate machining pass formation procedure in the additive manufacturing apparatus according to the first embodiment; FIG. 6 is a diagram for explaining a machining position and a cross-sectional area of ​​a bead in an intermediate machining pass in the additive manufacturing apparatus according to the first embodiment; 1. Flowchart showing a first example of an overall operation procedure performed by a control device in an additive manufacturing apparatus according to the first embodiment. 2. Flowchart showing a second example of an overall operation procedure performed by a control device in an additive manufacturing apparatus according to the first embodiment. 3. Perspective view showing an example of a design model of a finished product formed by an additive manufacturing apparatus according to the second embodiment. 4. Cross-sectional view showing a modeling model of a finished product formed by an additive manufacturing apparatus according to the second embodiment. 5. Cross-sectional view showing a modeling model of a finished product formed by an additive manufacturing apparatus according to the second embodiment. 6. Cross-sectional view showing a modeling method in a comparative example. 7. Cross-sectional view showing a modeling method in an additive manufacturing apparatus according to the second embodiment.

[0010] An additive manufacturing method and an additive manufacturing device according to an embodiment will be described in detail below with reference to the drawings.

[0011] First Embodiment. FIG. 1 is a diagram showing the configuration of an additive manufacturing apparatus 100 according to a first embodiment. The additive manufacturing apparatus 100 is a DED-type additive manufacturing apparatus. The additive manufacturing apparatus 100 supplies material to a workpiece 9 and manufactures a molded object 1 by stacking beads formed from the material melted using a beam. The beam is a heat source that melts the material, such as a laser beam L or an electron beam. The heat source is not limited to a beam and may be an arc. In the first embodiment, a case will be described in which the heat source is a laser beam L. In the first embodiment, the material is a metal wire 3. The material is not limited to a wire 3 and may be a powder. Furthermore, a layering method other than the DED method may be used.

[0012] The additive manufacturing apparatus 100 forms a bead by irradiating the wire 3 and the workpiece 9 with a laser beam L while supplying the wire 3 to the commanded processing point 13. The bead is a solidified product obtained by solidifying molten material on the workpiece. The bead is formed in a molten pool. The molten pool is a pool of molten metal that is formed by melting the workpiece 9 and wire 3 through irradiation with the laser beam L.

[0013] A bead layer is formed on the substrate 2 by arranging multiple beads. The bead layers are stacked to form the object 1, which is a deposit of beads. In this way, the additive manufacturing apparatus 100 manufactures the object 1, which is a three-dimensional object, by stacking the bead layers. The workpiece 9 is an object to which molten material is added, and includes the substrate 2 and the object 1 in the process of being modeled. The object 1 is formed on the substrate 2.

[0014] The X-axis, Y-axis, and Z-axis are three axes that are perpendicular to each other. The X-axis and Y-axis are two horizontal axes. The Z-axis is a vertical axis. In each of the X-axis direction, Y-axis direction, and Z-axis direction, the direction indicated by the arrow is positive, and the direction opposite to the arrow is negative. The positive Z-direction is assumed to be the vertically upward direction. The beads BD are stacked in the positive Z-direction. In the first embodiment, for the sake of convenience of explanation, it is assumed that the beads extend in the Y-direction as a first direction, and that the beads extending in the Y-direction are arranged in the X-direction as a second direction to form a bead layer, and that the bead layers are stacked in the Z-direction as a third direction.

[0015] The additive manufacturing apparatus 100 includes a laser oscillator 11, a gas supply device 20, a wire supply device 30, a processing head 7, a stage 40, a head drive device 50, a height measuring device 8, and a control device 15. The control device 15 is, for example, a numerical control (NC) device, and is connected to an external computer 16. The external computer 16 is equipped with CAD (Computer Aided Design) and CAM (Computer Aided Manufacturing).

[0016] A laser oscillator 11, which is a beam source, outputs a laser beam L. The laser beam L output by the laser oscillator 11 propagates through a fiber cable 10, which is an optical transmission path, and enters the processing head 7. An optical system (not shown) is arranged inside the processing head 7.

[0017] The processing head 7 is provided with a beam nozzle (not shown) through which the laser beam L emitted from the processing head 7 toward the processing point 13 passes, and a gas nozzle 14 that sprays shielding gas toward the processing point 13. The laser beam L passes through an optical system inside the processing head 7 and is emitted from the processing head 7 through the beam nozzle. The processing point 13 is the position on the workpiece 9 that is irradiated with the laser beam L and is the area where the wire 3 is added. The additive manufacturing device 100 moves the processing point 13 along a processing path, which is a movement path, during an additive processing process that adds molten material. The position of the processing point 13 is the position where the heat source and material are supplied, and is a position on the central axis of the beam nozzle. The processing path, which is a movement path, is specified by a processing program.

[0018] The gas supply device 20 supplies shielding gas from a gas supply source (not shown) to the gas nozzle 14. The gas supply device 20 can change the flow rate of the shielding gas based on a gas supply command from the control device 15. The injection of the shielding gas reduces oxidation of the material and the workpiece 9 and cools the molded object 1. The shielding gas is preferably an inert gas such as argon gas.

[0019] The wire supply device 30 includes a wire supply machine 5 and a wire nozzle 4. The wire 3 is supplied to the processing point 13 by the wire supply machine 5 through the wire nozzle 4. The wire nozzle 4 is supported so as to be at a fixed angle relative to the object 1 on the stage 40.

[0020] The head driving device 50 moves the processing head 7 in the X-axis direction, the Y-axis direction, and the Z-axis direction based on commands from the control device 15 .

[0021] The object 1 is placed and fixed on a base material 2 of a stage 40. The stage 40 may rotate around the Z axis or around both the Z axis and the X axis.

[0022] The height measuring device 8, which serves as a detection device, detects whether or not a bead exists in the lower layer for each machining pass. In this case, the height measuring device 8 detects the height of the machining pass, i.e., the height of the object 1 during molding, along the machining path for each machining pass. In other words, the height measuring device 8 detects the height of the bead of the previous layer, which is the object 1 of the previous layer, at the XY position corresponding to the current machining pass along the machining path. The height measuring device 8 detects a cavity in the object 1 based on the detected height. As described above, the machining path is the movement path of the machining point 13. The height measuring device 8 determines the presence of a cavity when it recognizes, based on the detected height, that no bead of the previous layer exists at the XY position to be machined this time. Depending on the detection principle of the height measuring device 8, a height measuring device 8 that is unable to detect the height at a position where no bead of the previous layer exists will detect the presence of a cavity when height detection is impossible. Furthermore, a height measuring device 8 that is able to detect the height even at a position where no bead of the previous layer exists will detect the presence of a cavity when the detected height is smaller than a preset threshold. A laser displacement meter or an imaging camera, for example, is used as the height measuring device 8. The height measuring device 8 is also used to measure the formation position of a bead formed by a machining pass immediately before a machining pass of interest when forming an intermediate machining pass, which will be described later.

[0023] The control device 15 controls the driving of the laser oscillator 11, the wire feeder 5, the head drive device 50, the gas supply device 20, the height measuring device 8, and the stage 40. Note that the stage 40 below the object 1 is rotatable, so that the height can be measured and the object 1 can be layer-modeled with the object 1 tilted to an appropriate position.

[0024] With this configuration, the object 1 rotates and the processing head 7 can move in the X, Y, and Z axes, so that the laser beam L can be irradiated at any position on the object 1 while the metal wire 3 is fed out to perform build-up welding, thereby forming the desired three-dimensional object.

[0025] In the first embodiment, when a cavity is detected in the object 1 by the height measuring device 8, machining passes are skipped until the cavity is eliminated. If a machining pass exists at a position where the cavity is eliminated, machining is performed and then the system returns to the first skipped position. Then, at the first skipped position, the normal machining pass set in the machining program is corrected, and machining is performed at the corrected machining position with a bead diameter different from the normal bead diameter. Thereafter, the skipped bead portion is machined, for example, at the original machining position and with the original bead diameter. Machining performed in a skipped machining pass is called machining in an intermediate machining pass. This will be described in detail below.

[0026] 2 is a perspective view showing an example of a design model of a finished product formed by the additive manufacturing apparatus 100 according to the first embodiment. The design model has a circular pipe shape with a circular cross section and a through-hole K. In this design model, the element shape of a water pipe is extracted and used as the design model.

[0027] 3 is a perspective view showing a molding model of a finished product formed by the additive manufacturing apparatus 100 according to the first embodiment. In this case, in the molding model, one bead layer is formed by arranging beads BD extending in the Y direction in the X direction. Multiple bead layers are stacked in the Z direction. In the molding model, the cavity K is formed by not providing a machining path in a part of the intermediate layer corresponding to the cavity K and not performing machining.

[0028] FIG. 4 is a diagram for explaining intermediate machining paths introduced in the additive manufacturing apparatus 100 according to the first embodiment. The left and right views of FIG. 4 illustrate a case where machining corresponding to the molding model shown in FIG. 3 is performed. In FIG. 4, each bead BD extends in the Y direction. In the left view of FIG. 4, the machining path in the top layer includes three machining paths Pn-1 and Pskip, and the machining path for forming the bead BD indicated by the dashed line is the skipped machining path Pskip. In the right view of FIG. 4, the machining path for forming the bead BD surrounded by a thick line among the machining paths in the top layer is the intermediate machining path Pcn described above.

[0029] In FIG. 4 , the intermediate machining path Pcn is a machining path that is replaced with the skipped machining path Pskip when a cavity K is detected by measurement by the height measuring device 8. In the machining path of the top layer for filling the cavity K, a bead BD is formed by the end machining path Pn-1, and then machining is skipped by the machining path Pskip. In the machining path Pe at the opposite end, a bead BD has already been formed in the previous layer, so the bead BD is then formed by the intermediate machining path Pcn. In the intermediate machining path Pcn, first, machining is performed by the machining path that is tangent to the end machining path Pn-1, and then machining is performed by the machining path that is tangent to the opposite end machining path Pe. The lower part of the bead BD generated by the intermediate machining path Pcn is in contact with the cavity K, and the cross-sectional area of ​​the bead BD generated by the intermediate machining path Pcn that is in contact with the end machining path Pn-1 is larger than the cross-sectional area of ​​the bead BD whose lower part does not contact the cavity K. The cross-sectional area of ​​the bead BD generated by the intermediate machining pass Pcn that contacts the machining pass Pe at the opposite end is approximately the same as the cross-sectional area of ​​the bead BD that does not contact the cavity K at the bottom.

[0030] Next, the procedure for skipping a machining pass and forming a bead of an intermediate machining pass Pcn will be described in more detail with reference to FIG. 5. FIG. 5 is a diagram for explaining the procedure for skipping a machining pass and the procedure for forming an intermediate machining pass in the additive manufacturing apparatus 100 according to the first embodiment. FIG. 5 includes an upper left diagram, an upper middle diagram, an upper right diagram, a lower left diagram, and a lower middle diagram, and machining is performed in this order, i.e., in the order indicated by the arrows. In FIG. 5, each bead BD extends in the Y direction, which is perpendicular to the paper surface.

[0031] In the upper left diagram of Figure 5, in the machining pass of the top layer for filling the cavity K, the presence or absence of the cavity K is detected in the end machining pass Pn-1 based on the height measurement in the Z direction along the Y direction by the height measuring device 8. The path of the height measuring device 8 along the Y direction is the same as the machining pass Pn-1. In this machining pass Pn-1, it is determined that the cavity K does not exist, so a bead BD is formed in the machining pass Pn-1. Thereafter, the presence or absence of the cavity K is detected in the machining pass Pn based on the height measurement in the Z direction along the Y direction by the height measuring device 8. In the machining pass Pn, the bottom of the cavity K is measured, so the presence of the cavity K is detected. Therefore, machining of the machining pass Pn is skipped. As shown in the upper middle diagram of Figure 5, the presence of the cavity K is also detected in the next machining pass Pn+1 by the measurement by the height measuring device 8, and machining of the machining pass Pn+1 is skipped.

[0032] 5, in machining path Pe, a bead BD has already been formed in the previous layer. Machining path Pn, which is the first machining path where it is detected that no bead BD exists in the lower layer, corresponds to the first machining path, and machining path Pn-1, which is the last machining path where it is detected that no bead BD exists in the lower layer, corresponds to the second machining path.

[0033] Next, the process returns to the initially skipped machining path Pn. Then, an intermediate machining path Pcn1 is generated as a corrected first machining path between the initially skipped machining path Pn and the machining path Pn-1 immediately before the skip, and machining is performed. The machining path Pn-1, which is the machining path immediately before the first machining path Pn, corresponds to the third machining path. In the intermediate machining path Pcn1, the XZ position of the skipped original machining path Pn is corrected to obtain the XZ position, and the cross-sectional area of ​​the generated bead BD is made larger than the bead cross-sectional area of ​​the machining path Pn set in the molding model shown in FIG. 3. In other words, the bead cross-sectional area of ​​the intermediate machining path Pcn1 is made larger than the cross-sectional area of ​​the bead BD that does not contact the cavity K at its lower part. A normal bead BD that does not contact the cavity K at its lower part or each bead BD specified in the design model corresponds to the first bead, and the cross-sectional area of ​​the first bead corresponds to the first cross-sectional area. The bead BD formed in the intermediate machining pass Pcn1 corresponds to the second bead, and the cross-sectional area of ​​the second bead corresponds to the second cross-sectional area.

[0034] Thereafter, for the skipped machining path Pn+1, a bead BD is formed in the intermediate machining path Pcn2 at the position and with the original bead cross-sectional area of ​​the original machining path Pn+1. Note that, as will be described later, in the machining path Pn+1, a third bead having a third cross-sectional area larger than the first cross-sectional area may be formed by changing the machining path position and the cross-sectional area of ​​the bead BD.

[0035] Next, the position and bead cross-sectional area of ​​the intermediate machining pass Pcn1 described above will be explained. Figure 6 is a diagram for explaining the machining position and bead cross-sectional area in the intermediate machining pass Pcn1 in the additive manufacturing device 100 according to the first embodiment. Figure 6 includes an upper left diagram, an upper right diagram, a lower left diagram, and a lower right diagram, and will be explained in this order.

[0036] As shown in the upper left diagram of Figure 6, in the design model of the finished product, machining paths Pn-1, Pn, and Pn+1 are arranged at equal intervals along the circumference. When machining path Pn-1, immediately preceding machining path Pn where cavity K is detected by height measuring device 8, actually forms bead BDn-1, the center position O'n-1 of bead BDn-1 deviates from the XZ position of machining path Pn-1 due to the effects of gravity and thermal distortion, as shown in the upper right diagram of Figure 6. Therefore, if the bead of the next machining path Pn is formed in this state, the first overlap amount θ, which is the original overlap amount between machining path Pn-1 and machining path Pn, cannot be maintained, resulting in defects such as gaps and reduced strength. The first overlap amount θ is a preset angle representing the overlap between two adjacent beads BD, centered on the center C of the design model of the finished product.

[0037] Therefore, as shown in the lower left diagram of Figure 6, when forming the next bead BDn, the original machining path Pn is corrected, and an intermediate machining path Pcn, which is a corrected machining path, is introduced. In the intermediate machining path Pcn, the center position O'n and bead radius R (bead cross-sectional area) of the bead BDn are derived so that the bead BDn-1 of the previous machining path Pn-1 overlaps the next-next machining path Pn+1 by a first overlap amount θ. The derived center position O'n of the bead BDn is determined as the XZ position of the intermediate machining path Pcn. The formation position of the bead BDn-1 is derived based on the measurement results of the height measuring device 8. The cross-sectional area of ​​the bead BDn can be adjusted by changing the machining conditions, including the laser output of the laser oscillator 11, the wire feed speed of the wire feeder 5, and the XY axis movement speed of the head driver 50. The XZ position of the intermediate machining path Pcn is on the circumference of a circle centered at the center C, the same as the original machining path Pn. Then, a bead BDn of radius R is formed on the derived intermediate machining path Pcn.

[0038] Next, as shown in the lower right diagram of Figure 6, for the next intermediate machining pass Pcn+1, a bead BDn+1 having the same cross-sectional area as the original machining pass Pn+1 is formed on the original machining pass Pn+1. However, the formation position of the bead BDn may be derived based on the measurement results of the height measuring device 8, and the center position and bead radius R (bead cross-sectional area) of the bead BDn+1 may be derived and machining may be performed so that the bead BDn overlaps the bead BDe already formed on the machining pass Pe by the first overlap amount θ.

[0039] In FIG. 6, the intermediate machining path Pcn is calculated based on a position on the circumference, but as long as it is possible to maintain the overlap amount θ that is set based on the formation position of the bead BDn-1 in the previous machining path Pn-1 and the formation position of the bead Bn+1 in the next-next machining path Pn+1, the calculation is not limited to being based on the circumference, and calculation based on a polygon or an arbitrary curve may also be used.

[0040] 7 is a flowchart for explaining the procedure for skipping a machining path and the procedure for forming an intermediate machining path performed by the control device 15 in the additive manufacturing apparatus 100 according to the first embodiment. The control device 15 determines whether the current machining path contacts the cavity K (step S10). The flowchart shown in FIG. 7 explains only the procedure for skipping a machining path and the procedure for forming an intermediate machining path, and omits the explanation of the normal machining procedure. If the control device 15 determines that the current machining path does not contact the cavity K (step S10: No), it ends the processing in this flowchart and performs machining using the normal machining path according to the machining program.

[0041] If the current machining path contacts the cavity K (step S10: Yes), the control device 15 causes the height measuring device 8 to measure the height of the machining path (step S20). If the control device 15 determines based on the measurement result of the height measuring device 8 that the layer below the current machining path is not a cavity (step S30: No), it terminates the processing in this flowchart and performs machining using the normal machining path in accordance with the machining program. If the control device 15 determines that the layer below the current machining path is a cavity (step S30: Yes), it skips the current machining path (step S40) and moves the machining point to the next machining path (step S50). Next, the control device 15 causes the height measuring device 8 to measure the height of this machining path (step S60). If the control device 15 determines based on the measurement result of the height measuring device 8 that the layer below the current machining path is a cavity (step S70: Yes), it skips this machining path (step S40) and moves the machining point to the next machining path (step S50). In this way, machining passes are skipped until it is determined that the lower layer is not hollow.

[0042] If the control device 15 determines that the lower layer is not hollow (step S70: No), it performs normal machining if a machining path still exists for that layer. If no machining path exists for that layer, it proceeds to the next step S90 (step S80). Next, the control device 15 generates the intermediate machining path Pcn1 described above between the machining path Pn whose machining was initially skipped and the machining path Pn-1 immediately before it (step S90), moves the machining point to the position of the generated intermediate machining path Pcn1 (step S100), and performs machining at the position of the intermediate machining path Pcn1 (step S110). Note that when forming this intermediate machining path Pcn1, the height measuring device 8 measures the formation position of the bead BDn-1 of the machining path Pn-1, and determines the position and bead cross-sectional area of ​​the intermediate machining path Pcn1 so that the bead BDn-1 and the bead formed by the machining path Pn+1 overlap by the first overlap amount θ. The generation of the intermediate machining paths is executed by the external computer 16 via the control device 15.

[0043] Next, the control device 15 moves the machining point to the position of the next machining path Pn+1 (step S120).The control device 15 then generates an intermediate machining path Pcn2 between the machining path Pn+1 and the intermediate machining path Pcn1 formed immediately before it (step S130), moves the machining point to the position of the generated intermediate machining path Pcn2 (step S140), and performs machining at the position of the intermediate machining path Pcn2 (step S150).When forming this intermediate machining path Pcn2, the height measuring device 8 measures the formation position of the bead BDcn1 of the intermediate machining path Pcn1, and determines the position and bead cross-sectional area of ​​the intermediate machining path Pcn2 so that the bead BDcn1 and the bead formed on the machining path Pn+2 overlap by the first overlap amount θ.

[0044] The control device 15 moves the machining path to the position of the next machining path (step S160). Next, the control device 15 determines whether machining of the skipped machining path has been completed (step S170). If machining of the skipped machining path has been completed (step S170: Yes), the processing in this flowchart is terminated, and the next processing is then executed according to the machining program. If machining of the skipped machining path has not been completed (step S170: No), n is updated to n+1 (step S180), and the procedure proceeds to step S130.

[0045] Next, the control device 15 generates an intermediate machining path Pcn3 between the machining path Pn+2 and the intermediate machining path Pcn2 formed immediately before it (step S130), moves the machining point to the position of the generated intermediate machining path Pcn3 (step S140), executes machining at the position of the intermediate machining path Pcn3 (step S150), and moves the machining path to the position of the next machining path (step S160). This process is repeated until the determination in step S170 becomes Yes.

[0046] Next, the overall operation performed by the control device 15 will be described with reference to Figures 8 and 9. Figure 8 is a flowchart showing a first example of the overall operation procedure performed by the control device 15 in the additive manufacturing device 100 according to the first embodiment. In the flowchart of Figure 8, intermediate machining paths are generated in advance.

[0047] Using the CAD of the external computer 16, a molding model shown in Figure 3 is created from the design model of the finished product shown in Figure 2 (step S200). Next, using the CAM of the external computer 16, multiple machining paths are created to realize the molding model (step S210). Next, a simulation of the machining paths is performed using the CAM of the external computer 16, and the presence or absence of cavities is detected during this simulation (step S220). If cavities are detected in the molding model, the CAM of the external computer 16 generates the intermediate machining paths described above (step S230). Next, using the CAM of the external computer 16, the machining shape and interference between the machining head 7 and the wire nozzle 4, etc., are confirmed on the CAM (step S240).

[0048] Next, the control device 15 of the additive manufacturing device 100 checks for interference between the machining head 7 and the wire nozzle 4, etc. on the actual device (step S250). Next, the control device 15 of the additive manufacturing device 100 actually executes machining in steps S260 to S280. At this time, as described above, the height is measured by the height measuring device 8 (step S260), a cavity is detected (step S270), and the intermediate machining path generated in step S230 is selected (step S280).

[0049] 8, if a cavity is detected during simulation of the machining path, the intermediate machining path described above is created in advance using the molding model, and if a cavity is detected during actual machining, machining is performed using the intermediate machining path created in advance. Therefore, depending on the shape and size of the cavity, creating an enormous number of intermediate machining paths may require a lot of calculation time and a lot of data communication time in the external computer 16, but this calculation time and data communication time can be eliminated, thereby shortening the machining time.

[0050] FIG. 9 is a flowchart showing a second example of the overall operation procedure performed by the control device 15 in the additive manufacturing apparatus 100 according to the first embodiment. In the flowchart of FIG. 9, intermediate machining paths are formed during actual machining. In FIG. 9, steps S200, S210, and S240 to S270 are the same as those in FIG. 8, and redundant explanations will be omitted. In step S225, intermediate machining paths are not created, but a machining path is simulated. If a cavity is detected, intermediate machining paths are generated during actual machining in step S285.

[0051] 9, the intermediate machining paths are created during actual machining, so that the actual machining results can be measured by the height measuring device 8 to create intermediate machining paths, and more accurate intermediate machining paths can be created, reducing machining defects. When machining is not possible with the intermediate machining paths created in advance as explained in FIG. 8, the actual machining results may be measured using the method shown in FIG. 9 to create intermediate machining paths.

[0052] As described above, according to the first embodiment, if it is detected that no bead is present in the lower layer, machining passes are skipped until a bead is present in the lower layer, and then a bead with a larger cross-sectional area than a normal bead is formed in the skipped machining pass, thereby preventing the bead from sagging in the upper part of the cavity due to the effects of gravity and thermal distortion.

[0053] Second Embodiment. In the first embodiment, a cavity shape at an open end was machined. In the second embodiment, however, a cavity shape at a closed end, in which the front and rear ends in the Y direction of the cavity are completely capped, is machined. The second embodiment is applicable to a molded object in which a cavity exists at a partial position in the Y direction along which the bead BD extends. The additive manufacturing apparatus 100 of the second embodiment has the same configuration as the additive manufacturing apparatus 100 of the first embodiment shown in FIG. 1. FIG. 10 is a perspective view showing an example of a design model of a finished product formed by the additive manufacturing apparatus 100 according to the second embodiment. This design model has a closed-end cylindrical tubular shape having a circular cross-section cavity K at the center in the Y direction. FIG. 11 is a cross-sectional view showing a molding model of a finished product formed by the additive manufacturing apparatus 100 according to the second embodiment. FIG. 11 is a cross-sectional view taken along line XI-XI in FIG. 10, which is a position in the Y direction where there is no cavity K. FIG. 12 is a cross-sectional view showing a molding model of a finished product formed by the additive manufacturing apparatus 100 according to the second embodiment. Fig. 12 is a cross-sectional view taken along line XII-XII in Fig. 10, which is the Y-direction position where cavity K is located. In Fig. 11, cavity K is not visible, but in Fig. 12, cavity K is visible.

[0054] 11 and 12, attention will be focused on the bead BDq in the Nth layer indicated by the thick line. As shown in Fig. 11, this bead BDq does not contact the cavity K at the closed end in the Y direction, but as shown in Fig. 12, at the center in the Y direction, the lower part of the bead BDq contacts the cavity K. The XZ position of the bead BDq in the Nth layer corresponds to the XZ position of the bead formed in the machining path Pn in Fig. 5.

[0055] FIG. 13 is a cross-sectional view showing a molding method in a comparative example. In FIG. 13, the Nth layer of the molding model in FIGS. 11 and 12 is cut along the XZ plane. In FIG. 13, Lb indicates the length of one bead in the Y direction. In the comparative example shown in FIG. 13, the bead BDq is formed by a single bead with a length of Lb. For this reason, with the method of the comparative example, the bead BDq is likely to lose its shape and sag at the center in the Y direction that contacts the cavity K.

[0056] FIG. 14 is a cross-sectional view illustrating a molding method in the additive manufacturing apparatus 100 according to the second embodiment. In FIG. 14, the Nth layer of the molding model in FIGS. 11 and 12 is cut along the XZ plane. In the second embodiment, when a bead formed by one machining pass includes a bead having a portion that contacts the cavity K at its lower part, the bead is divided into a first region that contacts the cavity K and a second region that does not contact the cavity K. Therefore, the machining pass for forming the bead BDq is divided into a machining pass for forming the bead BDq2 that contacts the cavity K and a machining pass for forming the beads BDq1 and BDq3 that do not contact the cavity K. In the second embodiment, based on the height measurement results of the height measuring device 8, the machining pass for forming the bead BDq is divided into a machining pass for forming the bead BDq1, a machining pass for forming the bead BDq2, and a machining pass for forming the bead BDq3.

[0057] Fig. 15 is a diagram showing an example of the height measurement results of the height measuring device 8 in the additive manufacturing apparatus 100 according to the second embodiment. In Fig. 15, the horizontal axis represents time T, and the vertical axis represents the measured height. Fig. 15 shows, for example, the results of measuring the machining path for forming bead BDq along the Y direction by the height measuring device 8. In the region of the machining path for forming bead BDq2, the height measurement result is smaller than in other regions, and the presence of cavity K is detected.

[0058] In some regions where the height measuring device 8 detects the presence of a void K, the intermediate machining path Pcn1 described in embodiment 1 is introduced. In embodiment 2, the machining path for forming the bead BDq2 is divided within the same bead BDq, so that by changing the machining conditions including the laser output of the laser oscillator 11, the wire feed speed of the wire feeder 5, and the XY axis movement speed of the head drive device 50, as described above, only the machining path for forming the bead BDq2 can be machined using the intermediate machining path Pcn1 with a changed bead cross-sectional area.

[0059] 15, the area where the presence of a void K is detected is identified by, for example, recording the program number of the machining program. The program number corresponds to the coordinate in the Y direction, and when the area where the presence of a void K is detected corresponds to program number N10 to program number N20, even in the newly selected machining path, only program number N10 to program number N20 out of program number N1 to program number N30 is changed to machining using intermediate machining path Pcn1. In this way, even when a void K is contacted midway through a single bead, by dividing the machining path, machining can be performed using the optimal intermediate machining path.

[0060] Thus, according to the second embodiment, when a cavity K exists in a portion of the bead layer in the Y direction, the machining path extending in the Y direction is divided into a first region where the cavity K exists and a second region where no cavity exists, and an intermediate machining path in which the bead cross-sectional area described above is changed is introduced in the machining path corresponding to the first region. Therefore, even when a cavity K exists in a portion of the bead layer in the Y direction, sagging of the bead above the cavity due to the effects of gravity and thermal distortion can be prevented.

[0061] The configurations shown in the above embodiments are examples of the contents of the present disclosure, and may be combined with other known technologies, or embodiments may be combined with each other, and some of the configurations may be omitted or modified within the scope of the gist of the present disclosure.

[0062] 1 Object, 2 Base material, 3 Wire, 4 Wire nozzle, 5 Wire feeder, 7 Processing head, 8 Height measuring device, 9 Workpiece, 10 Fiber cable, 11 Laser oscillator, 13 Processing point, 14 Gas nozzle, 15 Control device, 16 External computer, 20 Gas supply device, 30 Wire supply device, 40 Stage, 50 Head drive device, 100 Additive manufacturing device, BD Bead, K Cavity, L Laser beam, Pcn, Pcn1, Pcn2, Pcn3 Intermediate processing path.

Claims

1. An additive manufacturing method for forming a three-dimensional object having a cavity which is a deposit of the bead layers by moving a processing point along a plurality of processing passes extending in a first direction to form a bead layer in which a plurality of first beads having a first cross-sectional area are arranged in a second direction perpendicular to the first direction, and stacking the bead layers in a third direction perpendicular to the first and second directions, the method comprising: a detection step for detecting whether the first bead is present in a lower layer for each processing pass when forming the bead layer; a skip step for skipping processing in processing passes arranged in the second direction from a first processing pass which is the first processing pass at which it is detected that the first bead is not present in the lower layer to a second processing pass which is the last processing pass at which it is detected that the first bead is not present in the lower layer; a second bead formation step for forming a second bead having a second cross-sectional area in the first processing pass after correcting the position of the first processing pass; and a third bead formation step for forming the first bead or a third bead having a third cross-sectional area in a processing pass from the processing pass next to the first processing pass after correction to the second processing pass. An additive manufacturing method characterized by:

2. The additive manufacturing method of claim 1, wherein the second cross-sectional area is greater than the first cross-sectional area, and the third cross-sectional area is greater than the first cross-sectional area.

3. The additive manufacturing method described in claim 1 or 2, characterized in that in the second bead forming process, the position on a surface including the second direction and the third direction of the first bead after formation formed by a third processing pass, which is the processing pass immediately before the first processing pass, is detected, and the second bead is formed by correcting the first processing pass so that the second bead overlaps the first bead after formation formed by the third processing pass and the first bead formed by the processing pass next to the first processing pass by a first overlap amount.

4. An additive manufacturing method as described in any one of claims 1 to 3, characterized in that if the cavity exists in a part of the bead layer in the first direction, the machining path extending in the first direction is divided into a first region where the cavity exists and a second region where the cavity does not exist, and the detection process, the skip process, the second bead formation process, and the third bead formation process are performed using the machining path corresponding to the first region.

5. An additive manufacturing method according to any one of claims 1 to 4, characterized in that the corrected first machining path is created during simulation using a model.

6. An additive manufacturing method according to any one of claims 1 to 4, wherein the corrected first machining path is created during machining.

7. An additive manufacturing device that moves a processing point along multiple processing passes extending in a first direction to form a bead layer in which multiple first beads having a first cross-sectional area are arranged in a second direction perpendicular to the first direction, and stacks the bead layers in a third direction perpendicular to the first and second directions to form a shaped object having a three-dimensional cavity, which is a deposit of the bead layers, comprising: a detection device that detects whether the first bead is present in a lower layer for each processing pass when forming the bead layer; and a control device that skips processing in processing passes arranged in the second direction from a first processing pass that is the first processing pass at which it is detected that the first bead is not present in the lower layer to a second processing pass that is the last processing pass at which it is detected that the first bead is not present in the lower layer, forms a second bead having a second cross-sectional area in the first processing pass after the position of the first processing pass is corrected, and forms the first bead or a third bead having a third cross-sectional area in processing passes from the processing pass next to the first processing pass after the correction to the second processing pass.

8. The additive manufacturing device of claim 7, wherein the second cross-sectional area is larger than the first cross-sectional area, and the third cross-sectional area is larger than the first cross-sectional area.

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