JP7570565B1 - Additive manufacturing method and device - Google Patents

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 a machining pass 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

The present disclosure relates to an additive manufacturing method and an additive manufacturing apparatus for producing three-dimensional objects.

Additive manufacturing (AM) is one of the known techniques for manufacturing three-dimensional objects. In Directed Energy Deposition (DED), one of the multiple methods in additive manufacturing, a beam is irradiated onto the material and workpiece while supplying the material to a commanded position, forming a bead, which is then stacked in sequence to manufacture the object.

There is a demand for using such additive manufacturing methods to manufacture hollow objects with long holes. The hollow object is used, for example, as a mold, and a coolant is flowed through the circular cross-section cavity 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.

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>

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, raising concerns about a shortened lifespan, and there are problems such as a deterioration in product dimensions and shape due to the accumulation of impurities.

The present disclosure has been made in consideration of the above, and aims to obtain 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.

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 lined up 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.

The additive manufacturing method disclosed herein has the advantage of preventing sagging of the bead at the top of the cavity due to the effects of gravity and thermal distortion.

FIG. 1 is a diagram showing a configuration of an additive manufacturing apparatus according to a first embodiment. 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; FIG. 1 is a perspective view showing a model of a finished product formed by the additive manufacturing apparatus according to a first embodiment; FIG. 1 is a diagram for explaining an intermediate machining path introduced in the additive manufacturing apparatus according to the first embodiment. 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. 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; 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. 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. 1 is a flowchart showing a second example of an overall operation procedure performed by a control device in an additive manufacturing device according to a first embodiment. FIG. 13 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; 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; 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; 1 is a cross-sectional view showing a molding method in a comparative example. FIG. 11 is a cross-sectional view showing a modeling method in an additive manufacturing apparatus according to a second embodiment. 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;

Below, the additive manufacturing method and additive manufacturing apparatus relating to the embodiments are described in detail with reference to the drawings.

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 or an electron beam, etc. 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. A layering method other than the DED method may also be used.

The additive manufacturing device 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. A bead is a solidified product obtained when molten material solidifies on the workpiece. The bead is formed in a molten pool. The molten pool is a pool of molten metal that is created when the workpiece 9 and wire 3 are melted by irradiation with the laser beam L.

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 device 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 during modeling. The object 1 is formed on the substrate 2.

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 considered to be the vertical upward direction. The beads BD are stacked in the positive Z direction. In the first embodiment, for ease 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.

The additive manufacturing device 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).

The 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.

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 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 the processing path, which is the movement path, during the 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 the movement path, is specified by the processing program.

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.

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 at a constant angle to the object 1 on the stage 40.

The head driving device 50 moves the machining head 7 in the X-axis, Y-axis, and Z-axis directions based on instructions from the control device 15.

The object 1 is placed and fixed on the substrate 2 of the stage 40. The stage 40 can rotate around the Z axis or around both the Z axis and the X axis.

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, that is, 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 movement 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 a 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 a height measuring device 8 that can detect height 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 to measure 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.

The control device 15 drives and controls 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. Since the stage 40 below the model 1 is rotatable, it is possible to measure the height and perform additive manufacturing with the model 1 tilted to an appropriate position.

With this configuration, the object 1 rotates 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.

In the first embodiment, if a cavity in the molded object 1 is detected by the height measuring device 8, the machining path is skipped until the cavity is eliminated. If a machining path exists at the 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. The skipped bead portion is then machined, for example, at the original machining position and with the original bead diameter. Machining performed in a skipped machining path is called machining in an intermediate machining path. The details are explained below.

Figure 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 tube 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 create the design model.

Figure 3 is an oblique 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, cavity K is formed by not providing a machining path in a part of the intermediate layer corresponding to cavity K and not performing machining.

Figure 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 Figure 4 show a case where machining corresponding to the model shown in Figure 3 is performed. In Figure 4, each bead BD extends in the Y direction. In the left diagram of Figure 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 in dashed line is the skipped machining path Pskip. In the right diagram of Figure 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 mentioned above.

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 sealing the cavity K, after a bead BD is formed by the end machining path Pn-1, machining is skipped by the machining path Pskip. In the machining path Pe of the opposite end, a bead BD has already been 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 end machining path Pn-1 is performed, and then machining of the machining path that is in contact with the opposite end machining path Pe 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 end machining path Pn-1 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 path Pcn that contacts the machining path 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 lower part.

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 Figure 5. Figure 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 device 100 according to the first embodiment. Figure 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 Figure 5, each bead BD extends in the Y direction perpendicular to the paper surface.

In the upper left diagram of FIG. 5, in the machining path of the top layer for sealing 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 device 8 in the machining path Pn-1 at the end. The path along the Y direction of the height measuring device 8 is the same path as the machining path Pn-1. In this machining path Pn-1, it is determined that the cavity K does not exist, so a bead BD is formed in the machining path 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 device 8 in the machining path Pn. In the machining path Pn, the bottom of the cavity K is measured, so the presence of the cavity K is detected. For this reason, the machining path Pn is skipped. As shown in the upper center diagram of FIG. 5, the presence of the cavity K is also detected in the next machining path Pn+1 by the measurement of the height measuring device 8, and the machining is skipped in the machining path Pn+1.

As shown in the upper right diagram of Figure 5, in processing path Pe, a bead BD has already been formed in the previous layer. Processing path Pn, which is the first processing path at which it is detected that there is no bead BD in the lower layer, corresponds to the first processing path, and processing path Pn-1, which is the last processing path at which it is detected that there is no bead BD in the lower layer, corresponds to the second processing path.

Next, return 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 being skipped, an intermediate machining path Pcn1 is generated as the 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 bottom. A normal bead BD that does not contact the cavity K at the bottom 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.

After that, 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. As will be described later, a third bead having a third cross-sectional area larger than the first cross-sectional area may be formed in the machining path Pn+1 by changing the position of the machining path and the cross-sectional area of the bead BD.

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

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 in this state, 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 will occur, 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.

Therefore, as shown in the lower left diagram of FIG. 6, when forming the next bead BDn, the original machining path Pn is corrected, and an intermediate machining path Pcn, which is the machining path after 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 axes by the head driving device 50. The XZ position of the intermediate machining path Pcn is on the circumference of a circle centered on the center C, the same as that of the original machining path Pn. Then, a bead BDn of radius R is formed on the derived intermediate machining path Pcn.

6, for the next intermediate machining path Pcn+1, a bead BDn+1 having the same cross-sectional area as the original machining path Pn+1 is formed in the original machining path 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 so that the bead BDn overlaps with the bead BDe in the already formed machining path Pe by the first overlap amount θ, and machining may be performed.

In Figure 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, calculations are not limited to those based on the circumference and may also be calculated based on a polygon or an arbitrary curve.

Figure 7 is a flowchart for explaining the machining path skip procedure and intermediate machining path formation procedure performed by the control device 15 in the additive manufacturing device 100 according to the first embodiment. The control device 15 determines whether the current machining path is in contact with the cavity K (step S10). The flowchart shown in Figure 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 is not in contact with 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.

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.

If 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 if no machining path exists in the layer, it moves 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 first 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 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.

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 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 in the machining path Pn+2 overlap by the first overlap amount θ.

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.

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.

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 an 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.

Using the CAD of the external computer 16, the 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, multiple 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 aforementioned 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 the interference between the machining head 7 and the wire nozzle 4, etc. are confirmed on the CAM (step S240).

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).

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, depending on the shape and size of the cavity, a large amount of calculation time and data communication time are required in the external computer 16 to create a huge number of intermediate machining paths, but this calculation time and data communication time can be eliminated, shortening the machining time.

Figure 9 is a flowchart showing a second example of the overall operating procedure performed by the control device 15 in the additive manufacturing device 100 according to the first embodiment. In the flowchart of Figure 9, intermediate machining paths are formed during actual machining. In Figure 9, steps S200, S210, and S240 to S270 are similar to those in Figure 8, and duplicated explanations will be omitted. In step S225, no intermediate machining paths are created, but 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.

In this way, in the procedure of Fig. 9, 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, allowing intermediate machining paths with higher accuracy to be created and machining defects to be reduced. Note that when machining cannot be performed using the intermediate machining paths created in advance as described in Fig. 8, the actual machining results may be measured using the method shown in Fig. 9 to create intermediate machining paths.

Thus, according to the first embodiment, when it is detected that there is no bead 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. 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.

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 where 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 taken along the line XI-XI in FIG. 10, 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 is not visible, but in Fig. 12, cavity K is visible.

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 center 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.

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

Figure 14 is a cross-sectional view showing a modeling method in the additive manufacturing apparatus 100 according to the second embodiment. In Figure 14, the Nth layer of the modeling model in Figures 11 and 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. 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 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.

Figure 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 Figure 15, the horizontal axis is time T and the vertical axis is the measured height. Figure 15 shows, for example, the results of the height measuring device 8 measuring the machining path for forming bead BDq along the Y direction. 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.

In some areas 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 XY axis movement speed of the head drive device 50, as described above.

As shown in Figure 15, for the area where the presence of cavity K is detected, the area is identified, for example, by 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 cavity 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 by 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.

Thus, according to embodiment 2, 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 at the top of the cavity due to the effects of gravity and thermal distortion can be prevented.

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, or parts of the configurations may be omitted or modified without departing from the gist of the present disclosure.

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 (8)

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 process for forming the first bead or a third bead having a third cross-sectional area in a machining path from the next machining path of the first machining path after the correction to the second machining path. 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. The additive manufacturing method according to claim 1 or 2, characterized in that in the second bead forming process, a position on a plane including the second direction and the third direction of a first bead after formation formed by a third processing pass, which is a 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 a processing pass next to the first processing pass by a first overlap amount. The additive manufacturing method according to claim 1 or 2, characterized in that, when the cavity is present in a portion of the bead layer in the first direction, a machining path extending in the first direction is divided into a first region in which the cavity is present and a second region in which the cavity is not present, and the detection process, the skip process, the second bead formation process, and the third bead formation process are performed in the machining path corresponding to the first region. The additive manufacturing method according to claim 1 , wherein the first machining path after correction is created during a simulation using a model. The additive manufacturing method of claim 1 , wherein the first machining path after correction is created during machining. 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 arranged in the second direction from a first machining pass, which is the first machining pass where it is detected that the first bead is not present in a lower layer, to a second machining pass, which is the last machining pass where it is detected that the first bead is not present in a lower layer, forms a second bead having a second cross-sectional area in the first machining pass after correction in which the 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 the next machining pass of the first machining pass after correction to the second machining pass. 8. The additive manufacturing device of claim 7, 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.

Images