Additive manufacturing method and device

Abstract

The additive manufacturing method includes, when forming a bead layer, a step of detecting whether or not a bead (BD) is present in the lower layer for each machining pass, a step of skipping machining from the first machining pass (Pn) where it is detected that no bead (BD) is present to the last machining pass (Pn+1) where it is detected that no bead (BD) is present, a step of forming a bead (BD) having a second cross-sectional area in a corrected machining pass (Pcn1) in which the position of the machining pass (Pn) is corrected, and a step of forming a bead (BD) or a bead (BD) having a third cross-sectional area in the machining passes from the next machining pass (Pn+1) after the corrected machining pass (Pcn1) to the last machining pass (Pn+1) where it is detected that no bead (BD) is present.

Description

[Technical field]

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

[0002] Additive manufacturing (AM) is one of the known technologies for manufacturing 3D objects. In the Directed Energy Deposition (DED) method, which is one of the multiple methods in additive manufacturing, beads are formed by irradiating the material and the workpiece with a beam while supplying the material to a commanded position, and the beads are stacked in order to manufacture the object.

[0003] There is a demand for manufacturing a hollow-shaped object having a long hole using such an additive manufacturing method. The hollow-shaped object is used, for example, as a mold, and a coolant is flowed in the cavity with a circular cross section to control the temperature of the mold. In Non-Patent Document 1, the cross section of the cavity is made teardrop-shaped and the angle of the top of the cavity is made small to prevent beads from dripping into the cavity in the object. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] 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> Summary of the Invention [Problem to be solved by the invention]

[0005] When a molded object having a teardrop-shaped cavity is manufactured using conventional manufacturing methods, stress is concentrated at the corners of the teardrop shape, which can reduce the product's lifespan, and impurities can accumulate, deteriorating the product's dimensions and shape. [Means for solving the problem]

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

[0007] In order to solve the above-mentioned problems and achieve the objective, 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 a processing pass from the next processing pass after the first processing pass to the second processing pass after correction. Effect of the Invention

[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. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram showing a configuration of an additive manufacturing apparatus according to a first embodiment. [Diagram 2] FIG. 1 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; [Diagram 3] FIG. 1 is a perspective view showing a model of a finished product formed by the additive manufacturing apparatus according to a first embodiment; [Figure 4] FIG. 1 is a diagram for explaining an intermediate machining path introduced in the additive manufacturing apparatus according to the first embodiment. [Diagram 5] FIG. 1 is a diagram for explaining a procedure for skipping a machining path and a procedure for forming an intermediate machining path in an additive manufacturing apparatus according to a first embodiment. [Figure 6] FIG. 1 is a diagram for explaining a machining position and a cross-sectional area of ​​a bead in an intermediate machining pass in an additive manufacturing apparatus according to a first embodiment; [Figure 7] A flowchart for explaining a process for skipping a machining path and a process for forming an intermediate machining path performed by a control device in an additive manufacturing device according to a first embodiment. [Figure 8] 1 is a flowchart showing a first example of an overall operation procedure performed by a control device in an additive manufacturing device according to a first embodiment. [Figure 9] 1 is a flowchart showing a second example of an overall operation procedure performed by a control device in an additive manufacturing apparatus according to a first embodiment. [Figure 10] FIG. 11 is a perspective view showing an example of a design model of a finished product formed by the additive manufacturing apparatus according to the second embodiment; [Figure 11] FIG. 11 is a cross-sectional view showing a model of a finished product formed by the additive manufacturing apparatus according to the second embodiment; [Figure 12] FIG. 11 is a cross-sectional view showing a model of a finished product formed by the additive manufacturing apparatus according to the second embodiment; [Figure 13] 1 is a cross-sectional view showing a molding method in a comparative example; [Figure 14]FIG. 11 is a cross-sectional view showing a modeling method in the additive manufacturing apparatus according to the second embodiment. [Figure 15] FIG. 13 is a diagram showing an example of a height measurement result of a height measuring device in the additive manufacturing apparatus according to the second embodiment; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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

[0011] Embodiment 1 FIG. 1 is a diagram showing a 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 a material to a workpiece 9, and manufactures a molded object 1 by stacking beads formed by the material melted using a beam. The beam is a heat source that melts the material, and is a laser beam L, an electron beam, or the like. The heat source is not limited to a beam, and may be an arc. In the first embodiment, a case where the heat source is a laser beam L will be described. In the first embodiment, the material is a metal wire 3. The material is not limited to the wire 3, and may be a powder. Also, 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 the 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 the wire 3 by irradiation with the laser beam L.

[0013] A bead layer is formed on the substrate 2 by arranging a plurality of beads. The bead layers are stacked to form the object 1, which is a deposit of beads. In this manner, 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 the molten material is added, and includes the substrate 2 and the object 1 during modeling. The object 1 is formed on the substrate 2.

[0014] The X-axis, Y-axis, and Z-axis are three axes 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, Y-axis, and Z-axis directions, the direction indicated by the arrows is positive, and the direction opposite to the arrows 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 convenience of explanation, it is assumed that the beads extend in the Y direction as a first direction, and the beads extending in the Y direction are arranged in the X direction as a second direction to form a bead layer, and 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 injects a 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 irradiation position of the laser beam L on the workpiece 9, 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 in which the molten material is added. 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 supplying device 30 includes a wire supplying machine 5 and a wire nozzle 4. The wire 3 is supplied to the processing point 13 through the wire nozzle 4 by the wire supplying machine 5. The wire nozzle 4 is supported so as to be at a constant angle with respect to the object 1 on the stage 40.

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

[0021] The shaped 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 may rotate around the Z axis and the X axis.

[0022] The height measuring device 8 as a detection device detects whether or not a bead exists in the lower layer for each processing pass. In this case, the height measuring device 8 detects the height of the processing pass, i.e., the height of the object 1 during the processing, along the processing pass for each processing 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 processing pass, along the processing path. The height measuring device 8 detects a cavity in the object 1 based on the detected height. The processing path is the moving path of the processing point 13 as described above. The height measuring device 8 determines that a cavity exists when it is recognized that a bead of the previous layer does not exist at the XY position to be processed this time based on the detected height. Although it depends on the detection principle of the height measuring device 8, in the case of the height measuring device 8 in which height detection is impossible at a position where a bead of the previous layer does not exist, it detects the presence of a cavity when height detection is impossible. In addition, in the case of the height measuring device 8 in which height detection is possible even at a position where a bead of the previous layer does not exist, it detects the presence of a cavity when the detected height is smaller than a preset threshold value. For example, a laser displacement meter or an imaging camera is used as the height measuring device 8. The height measuring device 8 is also used when measuring the formation position of a bead formed by a processing pass immediately before a processing pass of interest when forming an intermediate processing pass described later.

[0023] The control device 15 drives and controls the laser oscillator 11, the wire supply device 5, the head drive device 50, the gas supply device 20, the height measuring device 8, and the stage 40. Note that since the stage 40 below the model 1 is rotatable, it is possible to perform height measurement and additive manufacturing with the model 1 tilted to an appropriate position.

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

[0025] In the first embodiment, when a cavity is detected in the model 1 by the height measuring device 8, the machining path is skipped until the cavity is eliminated. If a machining path 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 path 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. After that, the skipped bead portion is machined, for example, at the original machining position and with the original bead diameter. Machining performed in the skipped machining path is called machining in an intermediate machining path. The details will be described 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 is a circular pipe shape having a through-hole K with a circular cross section. In this design model, the element shape of a water pipe is extracted to form 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. A plurality of bead layers are laminated 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 diagrams of FIG. 4 show a case where machining corresponding to the model shown in FIG. 3 is performed. In FIG. 4, each bead BD extends in the Y direction. In the left diagram of FIG. 4, the machining path of the top layer includes three machining paths Pn-1, Pskip, and the machining path for forming the bead BD shown by the dashed line is the skipped machining path Pskip. In the right diagram of FIG. 4, the machining path for forming the bead BD surrounded by a thick line among the machining paths of 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 the measurement of the height measuring device 8. In the machining path of the top layer for filling the cavity K, after a bead BD is formed by the machining path Pn-1 at the end, machining is skipped by the machining path Pskip. In the machining path Pe at the opposite end, a bead BD is already formed in the previous layer, so next, a bead BD is formed by the intermediate machining path Pcn. In the intermediate machining path Pcn, first, machining of the machining path that is in contact with the machining path Pn-1 at the end is performed, and then machining of the machining path that is in contact with the machining path Pe at the opposite end is performed. 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 machining path Pn-1 at the end is larger than the cross-sectional area of ​​the bead BD that is not in contact with the cavity K at the lower part. The cross-sectional area of ​​the bead BD generated by the intermediate machining pass Pcn in contact with 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, that is, in the order indicated by the arrows. In FIG. 5, each bead BD extends in the Y direction perpendicular to the paper surface.

[0031] In the upper left diagram of FIG. 5, in the machining pass of the top layer for closing the cavity K, the presence or absence of the cavity K is detected based on the height measurement in the Z direction along the Y direction by the height measuring instrument 8 in the machining pass Pn-1 at the end. The path of the height measuring instrument 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. After this, the presence or absence of the cavity K is detected based on the height measurement in the Z direction along the Y direction by the height measuring instrument 8 in the machining pass Pn. In the machining pass Pn, the bottom of the cavity K is measured, so the presence of the cavity K is detected. For this reason, the machining pass Pn is skipped. As shown in the upper center diagram of FIG. 5, in the next machining pass Pn+1, the presence of the cavity K is also detected by the measurement of the height measuring instrument 8, and the machining pass Pn+1 is skipped.

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

[0033] Next, the process returns to the machining path Pn that was skipped first. Then, between the machining path Pn that was skipped first and the machining path Pn-1 immediately before the skip, an intermediate machining path Pcn1 is generated as a first machining path after correction, and machining is performed. The machining path Pn-1, which is the machining path immediately before the machining path Pn that is the first machining path, corresponds to the third machining path. In the intermediate machining path Pcn1, the XZ position of the original machining path Pn that was skipped is corrected to obtain the XZ position, and the cross-sectional area of ​​the bead BD to be generated 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 the lower part. The normal bead BD that does not contact the cavity K at the 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 position of the machining path 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. Fig. 6 is a diagram for explaining the machining position and the cross-sectional area of ​​the bead in the intermediate machining pass Pcn1 in the additive manufacturing apparatus 100 according to the first embodiment. Fig. 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 FIG. 6, in the design model of the finished product, the machining paths Pn-1, Pn, and Pn+1 are arranged at equal intervals along the circumference. In the machining path Pn-1 immediately before the machining path Pn where the cavity K is detected by the height measuring device 8, when the bead BDn-1 is actually formed by machining, the center position O'n-1 of the bead BDn-1 deviates from the XZ position of the machining path Pn-1 due to the influence of gravity and thermal distortion, as shown in the upper right diagram of FIG. 6. Therefore, if the bead of the next machining path Pn is formed as it is, the first overlap amount θ, which is the original overlap amount, cannot be maintained between the machining path Pn-1 and the machining path Pn, and defects such as gaps are generated, resulting in a decrease in strength. The first overlap amount θ is expressed as an angle of the overlapping portion of two adjacent beads BD with the center C of the design model of the finished product as the center, and is set in advance.

[0037] Therefore, as shown in the lower left diagram of FIG. 6, when the next bead BDn is formed, the original machining path Pn is corrected, and an intermediate machining path Pcn, which is a machining path after the correction, is introduced. In the intermediate machining path Pcn, the center position O'n of the bead BDn and the bead radius R (bead cross-sectional area) are derived so that the bead BDn-1 of the previous machining path Pn-1 and the next next machining path Pn+1 overlap by the 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 result 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 movement speed of the XY axis by the head driving device 50. The XZ position of the intermediate machining path Pcn is on the circumference centered on 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 Fig. 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 in the original machining pass Pn+1. However, the formation position of the bead BDn may be derived based on the measurement result 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 with the bead BDe in the already formed 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 a circumference. However, 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 calculations based on a polygon or an arbitrary curve may also be used.

[0040] FIG. 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 judges whether the current machining path contacts the cavity K (step S10). In the flowchart shown in FIG. 7, only the procedure for skipping a machining path and the procedure for forming an intermediate machining path are explained, and the explanation of the normal machining procedure is omitted. When it is judged that the current machining path does not contact the cavity K (step S10: No), the control device 15 ends the processing in this flowchart and executes machining with the normal machining path according to the machining program.

[0041] If the current machining path is in contact with 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 that the lower layer of the current machining path is not a cavity based on the measurement result of the height measuring device 8 (step S30: No), it ends the processing in this flowchart and executes machining with a normal machining path according to the machining program. If the control device 15 determines that the lower layer of 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 that the lower layer of the current machining path is a cavity based on the measurement result of the height measuring device 8 (step S70: Yes), it skips this machining path (step S40) and moves the machining point to the next machining path (step S50). In this manner, machining passes are skipped until it is determined that the lower layer is not hollow.

[0042] When the control device 15 determines that the lower layer is not hollow (step S70: No), if a machining path still exists in the layer, it executes normal machining, and when a machining path does not exist in the layer, it shifts the procedure to the next step S90 (step S80). Next, the control device 15 generates the above-mentioned intermediate machining path Pcn1 between the machining path Pn that was skipped first 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 executes machining at the position of the intermediate machining path Pcn1 (step S110). 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, respectively. 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). Then, the control device 15 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 executes 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 in the machining path Pn+2 overlap by the first overlap amount θ, respectively.

[0044] The control device 15 moves the machining path to the position of the next machining path (step S160). Next, the control device 15 judges 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 process in this flowchart is terminated, and the next process 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). Such processing 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 Fig. 8 and Fig. 9. Fig. 8 is a flowchart showing a first example of an 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. 8, intermediate machining paths are generated in advance.

[0047] Using the CAD of the external computer 16, a molding model shown in FIG. 3 is created from the design model of the finished product shown in FIG. 2 (step S200). Next, using the CAM of the external computer 16, a plurality of machining paths are created to realize the molding model (step S210). Next, a simulation of the machining path is performed using the CAM of the external computer 16, and the presence or absence of a cavity is detected during this simulation (step S220). If a cavity is detected in the molding model, the above-mentioned intermediate machining path is generated using the CAM of the external computer 16 (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 apparatus 100 checks for interference between the machining head 7 and the wire nozzle 4, etc., on the actual machine (step S250). Next, the control device 15 of the additive manufacturing apparatus 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. For this reason, a large amount of calculation time and data communication time is required in the external computer 16 to create an enormous number of intermediate machining paths depending on the shape and size of the cavity, 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, an intermediate machining path is 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, no intermediate machining path is created, and a simulation of the machining path is performed. If a cavity is detected, in step S285, an intermediate machining path is generated during actual machining.

[0051] In this way, in the procedure of Fig. 9, since the intermediate machining path is created during actual machining, the actual machining result can be measured by the height measuring device 8 to create the intermediate machining path, and a more accurate intermediate machining path can be created, thereby reducing machining defects. When machining cannot be performed using the intermediate machining path created in advance as explained in Fig. 8, the actual machining result may be measured using the method shown in Fig. 9 to create the intermediate machining path.

[0052] Thus, according to the first embodiment, when it is detected that there is no bead in the lower layer, the machining passes are skipped until there is a bead 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. This makes it possible to prevent the bead from sagging in the upper part of the cavity due to the effects of gravity and thermal distortion.

[0053] Embodiment 2 In the first embodiment, the cavity shape of the open end is machined, but in the second embodiment, the cavity shape of the closed end, in which the front and rear ends in the Y direction of the cavity are completely covered, is machined. The second embodiment is applicable to a molded object in which a cavity exists at a part of the Y direction in 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 is a cylindrical tube shape with a closed end having a cavity K with a circular cross section 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 of FIG. 10 cut by the line XI-XI, which is a Y direction position 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 does not appear, but in Fig. 12, cavity K appears.

[0054] 11 and 12, attention is focused on the bead BDq of the Nth layer marked with a 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, in the central part in the Y direction, the lower part of the bead BDq contacts the cavity K. The XZ position of the bead BDq of 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 of one bead with a length of Lb. For this reason, in 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 showing a modeling method in the additive manufacturing apparatus 100 according to the second embodiment. In FIG. 14, the Nth layer of the modeling model in FIG. 11 and FIG. 12 is cut along the XZ plane. In the second embodiment, when a bead formed by one machining pass has a part that contacts the cavity K at the bottom, the bead is divided into a first region that contacts the cavity K and a second region that does not contact the cavity K. For this reason, 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 result 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 a height measurement result by the height measuring instrument 8 in the additive manufacturing apparatus 100 according to the second embodiment. In Fig. 15, the horizontal axis is time T, and the vertical axis is the measured height. Fig. 15 shows, for example, the result of measuring the machining path for forming the bead BDq along the Y direction by the height measuring instrument 8. In the region of the machining path for forming the bead BDq2, the height measurement result is smaller than in other regions, and the presence of a cavity K is detected.

[0058] In some regions where the height measuring device 8 detects the presence of a cavity K, the intermediate machining path Pcn1 described in the first embodiment is introduced. In the second embodiment, the machining path for forming the bead BDq2 is divided within the same bead BDq, so that only the machining path for forming the bead BDq2 can be processed with the intermediate machining path Pcn1 with a changed bead cross-sectional area 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 movement speed of the XY axes by the head driving device 50, as described above.

[0059] 15, for the area where the cavity K is detected to exist, the area 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 cavity K is detected to exist corresponds to program number N10 to program number N20, even in the newly selected machining path, among program numbers N1 to N30, only program numbers N10 to N20 are changed to machining by the intermediate machining path Pcn1. As a result, even when a cavity K is contacted in the middle of one bead, machining can be performed by the optimal intermediate machining path by dividing the machining path.

[0060] Thus, according to embodiment 2, when a cavity K exists in a part 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 if a cavity K exists in a part 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 the embodiments may be combined with each other. Also, parts of the configurations may be omitted or modified without departing from the gist of the present disclosure. [Explanation of symbols]

[0062] 1 object, 2 substrate, 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 that is a stack of the bead layers by moving a processing point along a plurality of processing paths 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, comprising: a detection step of detecting whether or not the first bead is present in a lower layer for each processing pass when forming the bead layer; a skipping step of skipping machining in machining passes arranged in the second direction from a first machining pass, which is a first machining pass where it is detected that the first bead does not exist in a lower layer, to a second machining pass, which is a last machining pass where it is detected that the first bead does not exist in a lower layer; a second bead forming step of forming a second bead having a second cross-sectional area on the first machining pass after the position of the first machining pass is corrected; and a third bead forming step of forming the first bead or a third bead having a third cross-sectional area in a machining pass from a machining pass next to the first machining pass after the correction to the second machining pass. An additive manufacturing method comprising:

2. 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.

2. The additive manufacturing method of claim 1.

3. In the second bead forming step, a position on a plane including the second direction and the third direction of a first bead formed by a third machining pass, which is a machining pass immediately before the first machining pass, is detected, and the second bead is formed by correcting the first machining pass so that the second bead overlaps the first bead formed by the third machining pass and the first bead formed by a machining pass next to the first machining pass by a first overlap amount.

3. An additive manufacturing method according to claim 1 or 2.

4. When 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 in which the cavity exists and a second region in which the cavity does not exist, and the detection step, the skip step, the second bead forming step, and the third bead forming step are performed by the machining path corresponding to the first region.

3. An additive manufacturing method according to claim 1 or 2.

5. The first machining path after correction is created during a simulation using a molding model.

2. The additive manufacturing method of claim 1.

6. The first machining path after correction is created during machining.

2. The additive manufacturing method of claim 1.

7. An additive manufacturing apparatus for forming 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 by moving a processing point along a plurality of processing paths extending in a first direction, and stacking the bead layers in a third direction perpendicular to the first direction and the second direction to form a shaped object having a three-dimensional cavity which is a deposit of the bead layers, the additive manufacturing apparatus comprising: a detection device that detects whether or not the first bead is present in a lower layer for each processing pass when the bead layer is formed; a control device that skips machining in machining passes aligned in the second direction from a first machining pass that is the first machining pass at which it is detected that the first bead does not exist in a lower layer to a second machining pass that is the last machining pass at which it is detected that the first bead does not exist in a lower layer, forms a second bead having a second cross-sectional area in the first machining pass after correction in which a position of the first machining pass is corrected, and forms the first bead or a third bead having a third cross-sectional area in a machining pass from a machining pass next to the first machining pass after correction to the second machining pass. An additive manufacturing device characterized by:

8. 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.

8. An additive manufacturing device as claimed in claim 7.