Welding device and laminate molding device

Abstract

To preferably control heat input to a wire and a member to be welded and improve the accuracy of molding.SOLUTION: A laminate molding device (1) includes a wire (2) being a filler material and serving as a positive electrode, and two metal rods (4) serving as negative electrodes. The wire (2) and the two metal rods (4) are arranged such that a molten filler (2b) passes between the distal end portions (4a) of the two metal rods (4), the molten filler being obtained by melting a distal end portion (2a) of the wire (2) by arc discharge between the distal end portion (2a) of the wire (2) and a distal end portion (4a) of the two metal rods (4).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a welding apparatus and an additive manufacturing apparatus. [Background technology]

[0002] The Wire-Arc Additive Manufacturing (WAAM) process is a metal additive manufacturing process based on a welding process (Non-Patent Document 1). In WAAM, an arc plasma is generated between a wire, which is a filler material, and the workpieces to be welded. Alternatively, a wire is placed near the workpieces to be welded, and an arc plasma is generated between a tungsten rod and the workpieces to be welded. This melts the tip of the wire and a part of the workpieces to be welded, and the molten filler at the tip of the wire drips into the molten part of the workpieces to be welded (base material). The molten filler integrates with the molten part and solidifies, thereby completing the weld. By repeating this process, the filler is layered to create a molded object. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] SW Williams, et al., "Wire + Arc Additive Manufacturing", Materials Science and Technology, 2016, Vol. 32, p. 641-647 Summary of the Invention [Problem to be solved by the invention]

[0004] Currently available 3D metal printers use a powder bed fusion (PBF) method, which applies thermal energy using a laser or other device to an area where metal powder is laid, melting and bonding the layers together while removing any unbonded metal powder. However, PBF has problems, such as difficulty in producing large objects and extremely slow printing speed. In contrast, WAAM can produce large objects more efficiently than PBF, but it suffers from poor printing accuracy and also has problems controlling the heat input to the wire and the workpiece.

[0005] An aspect of the present invention aims to effectively control the heat input to the wire and the workpiece, and to improve the accuracy of the shaping. [Means for solving the problem]

[0006] In order to solve the above problems, a welding apparatus according to one embodiment of the present invention comprises a wire that is a filler material and serves as an anode, and a plurality of metal rods that serve as cathodes, and the wire and the plurality of metal rods are arranged so that an arc discharge between the tip of the wire and the tip of the plurality of metal rods causes the molten filler that has melted the tip of the wire to pass between the tip of the plurality of metal rods.

[0007] In the welding apparatus, the number of metal rods may be two, and the wire and the plurality of metal rods may be arranged so that the molten filler passes through the midpoint of a line segment connecting the tips of the two metal rods.

[0008] In the welding apparatus, the number of the metal rods may be three or more, the tips of the metal rods may be located at the vertices of a regular polygon whose number of sides is the same as the number of the metal rods, and the wire and the metal rods may be arranged so that the molten filler passes through the center of the regular polygon.

[0009] In the welding device, the angle formed between the extending direction of the wire and the extending direction of each of the plurality of metal rods may be the same, and the angle may be 30° to 90°, 45° to 75°, or 55° to 65°.

[0010] In the welding apparatus, the plurality of metal rods may be made of tungsten or a tungsten alloy in which at least one of cerium oxide, lanthanum oxide, yttrium oxide, and zirconium oxide is added to tungsten.

[0011] Moreover, an additive manufacturing apparatus according to another aspect of the present invention includes a welding apparatus having the above-described configuration and a stage on which members to be welded are placed, and at least one of the welding apparatus and the stage is movable.

[0012] In the additive manufacturing apparatus, a tip of at least one metal rod in the welding apparatus may be arranged in a direction opposite to a direction in which the workpieces are sequentially placed on the stage. A current flowing through the at least one metal rod may be greater than a current flowing through the remaining metal rods in the welding apparatus. A distance between the tip of the at least one metal rod and the tip of the wire may be greater than a distance between the tip of the remaining metal rods and the tip of the wire. [Effects of the Invention]

[0013] According to one aspect of the present invention, it is possible to effectively control the heat input to the wire and the workpiece, and to improve the accuracy of shaping. [Brief explanation of the drawings]

[0014] [Figure 1] The top diagram is a cross-sectional view showing an outline of the WAAM process of an additive manufacturing apparatus according to one embodiment of the present invention, and the bottom diagram is a cross-sectional view showing an outline of the WAAM process of a conventional additive manufacturing apparatus. [Figure 2] FIG. 2 is a view of the additive manufacturing device, showing the tip of the wire from the molten part of the base material. [Figure 3] FIG. 10 is a view of the tip of the wire as seen from the molten part of the base material in an additive manufacturing apparatus according to another embodiment of the present invention. [Figure 4] FIG. 10 is a diagram showing a modified example of the layered manufacturing apparatus, in which the tip of the wire is viewed from the molten part of the base material. [Figure 5] FIG. 10 is a perspective view showing an overview of an additive manufacturing apparatus according to yet another embodiment of the present invention. [Figure 6] 10 is a photograph showing one state of arc plasma and molten filler in one example of the embodiment. [Figure 7] 6 is a photograph showing another state of the arc plasma and the molten filler. [Figure 8] FIG. 10 is a cross-sectional view showing an overview of the WAAM process of an additive manufacturing apparatus according to yet another embodiment of the present invention. [Figure 9] FIG. 10 is a cross-sectional view showing an overview of the WAAM process of an additive manufacturing apparatus according to yet another embodiment of the present invention. [Figure 10] The upper row is a photograph showing the side surface of a metal shaped object produced by an example of the above embodiment, and the lower row is a photograph showing the side surface of a metal shaped object produced by a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, embodiments of the present invention will be described in detail. For the sake of convenience, the same reference numerals will be used to designate components having the same functions as those in the embodiments, and the description thereof will be omitted where appropriate.

[0016] [Embodiment 1] An embodiment of the present invention will be described with reference to Figures 1 and 2. The additive manufacturing apparatus according to this embodiment is an apparatus that produces a three-dimensional object by welding and laminating metals.

[0017] The upper part of FIG. 1 is a cross-sectional view showing an outline of the WAAM process of the additive manufacturing apparatus 1 (welding apparatus) of this embodiment, and the lower part of FIG. 1 is a cross-sectional view showing an outline of the WAAM process of the conventional additive manufacturing apparatus 101.

[0018] As shown in the lower part of Fig. 1, a conventional additive manufacturing apparatus 101 is configured to include a wire 102, which is a filler material (welding material), and a base material 103 (member to be welded). The additive manufacturing apparatus 101 generates an arc discharge between the wire 102 and the base material 103, thereby generating an arc plasma AP between the wire 102 and the base material 103. The heat of this arc plasma AP melts a tip 102a of the wire 102 and also melts a portion of the base material 103. The molten filler 102b from the tip 102a drips onto a molten portion 103a of the base material 103, whereby the molten filler 102b is welded to the molten portion 103a and is layered in the portion indicated by the dashed dotted line in the lower part of Fig. 1.

[0019] Meanwhile, as shown in the upper part of FIG. 1, the additive manufacturing apparatus 1 of this embodiment is configured to include a wire 2, which is a filler material, a base material 3, and a metal rod 4. The metal rod 4 has a sharp tip 4a to facilitate arc discharge. Furthermore, the metal rod 4 is preferably made of a material that is extremely resistant to wear due to the arc discharge. Examples of such materials include tungsten, or a tungsten alloy in which at least one of cerium oxide, lanthanum oxide, yttrium oxide, and zirconium oxide is added to tungsten. The wire 2 and base material 3 are made of a material appropriately selected depending on the purpose of additive manufacturing.

[0020] The additive manufacturing apparatus 1 generates an arc discharge between the wire 2 and the metal rod 4, thereby generating an arc plasma AP between the wire 2 and the metal rod 4. The heat of this arc plasma AP melts the tip 2a of the wire 2 and also melts a part of the base material 3 provided near the tip 2a. The molten filler 2b from the tip 2a drips onto the molten portion 3a of the base material 3, whereby the molten filler 2b is welded to the molten portion 3a and laminated in the portion indicated by the dashed line in the upper part of Figure 1.

[0021] 1, in a conventional additive manufacturing device 101, the wire 102 serves as the anode, the base material 103 serves as the cathode, and current flows from the wire 102 to the base material 103. This makes it difficult to separately control the amount of heat input to the tip 102a of the wire 102 and the amount of heat input to the molten portion 103a of the base material 103.

[0022] In contrast, in the additive manufacturing apparatus 1 of this embodiment, the wire 2 serves as the anode, the metal rod 4 serves as the cathode, and current flows from the wire 2 to the metal rod 4. This makes it easy to separately control the amount of heat input to the tip 2a of the wire 2 and the amount of heat input to the molten zone 3a of the base material 3. As a result, the heat input to the wire 2 and the base material 3 can be well controlled. Furthermore, by minimizing the heat input to the molten zone 3a while ensuring sufficient heat input to the tip 2a, it is possible to prevent the molten filler 2b from wetting and spreading on the base material 3.

[0023] FIG. 2 is a view of the tip 2a of the wire 2 as viewed from the molten zone 3a of the base material 3 in the additive manufacturing apparatus 1 of this embodiment. As shown in FIGS. 1 and 2, the additive manufacturing apparatus 1 of this embodiment is provided with two metal rods 4. The two metal rods 4 and the wire 2 are arranged so that the molten filler 2b dripping from the tip 2a into the molten zone 3a passes between the tips 4a of the two metal rods 4. This stabilizes the behavior of the molten filler 2b and reduces variation in the drip position of the molten filler 2b. As a result, the accuracy of modeling using the filler material can be improved.

[0024] In the additive manufacturing apparatus 1 of this embodiment, the two metal rods 4 and the wire 2 may be arranged so that the molten filler 2b passes through or near the midpoint of the line segment connecting the two tip ends 4a. In this case, the two currents flowing through the two metal rods 4 can be made to be approximately the same, which makes it easier to control the paths of the two currents symmetrically and stably with respect to the wire 2.

[0025] Furthermore, since the molten filler 2b passes through positions equidistant from the tips 4a of the two metal rods 4, the force acting on the molten filler 2b is stabilized. This further stabilizes the behavior of the molten filler 2b, further reducing variations in the dripping position of the molten filler 2b. As a result, the accuracy of molding using the filler material can be further improved.

[0026] Furthermore, the molten filler 2b may pass through a position on the line segment connecting the two tip portions 4a that is offset from the midpoint of the line segment. In this case, the drip position of the molten filler 2b will be offset corresponding to the offset from the midpoint, but the likelihood of the variance in the drip position increasing is low, and as a result, it is believed that the stability of the behavior of the molten filler 2b can be maintained. Furthermore, by making the welding direction in the base material 3 the direction along the line segment, the effects of the offset in the drip position can be suppressed.

[0027] [Embodiment 2] Another embodiment of the present invention will be described with reference to Fig. 3. The additive manufacturing apparatus 1 of this embodiment differs from the additive manufacturing apparatus 1 shown in Figs. 1 and 2 in that three metal rods 4 are provided instead of two metal rods 4, but the rest of the configuration is the same.

[0028] FIG. 3 is a view of the additive manufacturing apparatus 1 of this embodiment, similar to FIG. 2, of the tip 2a of the wire 2 viewed from the molten zone 3a of the base material 3. As shown in FIG. 3, in the additive manufacturing apparatus 1 of this embodiment, the three metal rods 4 and the wire 2 are arranged so that the molten filler 2b dripping from the tip 2a into the molten zone 3a passes between the tips 4a of the three metal rods 4, i.e., within a triangle with the three tips 4a as vertices. In this embodiment as well, the behavior of the molten filler 2b is stable, and variation in the drip position of the molten filler 2b can be suppressed. As a result, the accuracy of molding using the filler material can be improved.

[0029] The triangle may be an equilateral triangle. Alternatively, the three metal rods 4 and the wire 2 may be arranged so that the molten filler 2b passes through or near the center of the equilateral triangle. In this case, the three currents flowing through the three metal rods 4 can be made to be approximately the same, which makes it easier to control the paths of the three currents symmetrically and stably with respect to the wire 2.

[0030] Furthermore, since the molten filler 2b passes through positions equidistant from the tips 4a of the three metal rods 4, the force acting on the molten filler 2b is stabilized. This further stabilizes the behavior of the molten filler 2b, and further reduces variation in the drip position of the molten filler 2b. As a result, the accuracy of molding using the filler material can be further improved.

[0031] At least one of the tips 4a of the three metal rods 4 may be offset from the apex of the equilateral triangle. In this case, the dripping position of the molten filler 2b will be shifted corresponding to the deviation from the apex, but it is unlikely that the variation in the dripping position will increase, and as a result, it is thought that the stability of the behavior of the molten filler 2b can be maintained. Furthermore, the molten filler 2b may pass through a position offset from the center of the equilateral triangle. In this case, the dripping position of the molten filler 2b will be shifted corresponding to the deviation from the center, but it is unlikely that the variation in the dripping position will increase, and as a result, it is thought that the stability of the behavior of the molten filler 2b can be maintained.

[0032] (Variation) FIG. 4 is a diagram showing a modified example of the additive manufacturing apparatus 1 of this embodiment, and similarly to FIG. 2, is a view of the tip 2a of the wire 2 from the molten zone 3a of the base material 3. As shown in FIG. 3, in this modified example, four metal rods 4 are provided. Furthermore, the four metal rods 4 and the wire 2 are arranged so that the molten filler 2b dripping from the tip 2a into the molten zone 3a passes between the tips 4a of the four metal rods 4, i.e., within a quadrangle with the four tips 4a as vertices. In this embodiment as well, the behavior of the molten filler 2b is stable, and variation in the drip position of the molten filler 2b can be suppressed. As a result, the accuracy of molding using the filler material can be improved.

[0033] The quadrangle may be a square. Alternatively, the four metal rods 4 and wire 2 may be arranged so that the molten filler 2b passes through or near the center of the square. In this case, the four currents flowing through the four metal rods 4 can be made approximately equal, which makes it easier to control the paths of the four currents symmetrically and stably with respect to the wire 2.

[0034] Furthermore, since the molten filler 2b passes through positions equidistant from the tips 4a of the four metal rods 4, the force acting on the molten filler 2b is stabilized. This further stabilizes the behavior of the molten filler 2b, and further reduces variation in the drip position of the molten filler 2b. As a result, the accuracy of molding using the filler material can be further improved.

[0035] That is, in the additive manufacturing apparatus 1 of this embodiment, when the number of metal rods 4 is three or more, the tip ends 4a of the multiple metal rods 4 are arranged at the vertices of a polygon whose number of sides is the same as the number of metal rods 4. Furthermore, the wire 2 is arranged so that the molten filler 2b passes through the polygon. Furthermore, in the additive manufacturing apparatus 1 of this embodiment, the polygon may be a regular polygon. Furthermore, the multiple metal rods 4 and the wire 2 may be arranged so that the molten filler 2b passes through or near the center of the regular polygon.

[0036] At least one of the tip portions 4a of the multiple metal rods 4 may be offset from a vertex of the regular polygon. In this case, the dripping position of the molten filler 2b will be shifted corresponding to the deviation from the vertex, but it is unlikely that the variation in the dripping position will increase, and as a result, it is thought that the stability of the behavior of the molten filler 2b can be maintained. Furthermore, the molten filler 2b may pass through a position offset from the center of the regular polygon. In this case, the dripping position of the molten filler 2b will be shifted corresponding to the deviation from the center, but it is unlikely that the variation in the dripping position will increase, and as a result, it is thought that the stability of the behavior of the molten filler 2b can be maintained.

[0037] In addition, if the number of metal rods 4 is large, it becomes difficult to align the current supplied to each metal rod 4, and the current flowing through each metal rod becomes small, making it difficult to stabilize the arc plasma, which may result in a decrease in molding accuracy. Therefore, it is desirable that the number of metal rods 4 be between 2 and 6.

[0038] [Embodiment 3] Yet another embodiment of the present invention will now be described with reference to FIG.

[0039] Fig. 5 is a perspective view showing an overview of the additive manufacturing apparatus 1 according to this embodiment. As shown in Fig. 5, the additive manufacturing apparatus 1 according to this embodiment includes a three-axis stage 11 (stage), a holding plate 12, an adjustment mechanism 13, a nozzle 14, and a contact tip 15, in addition to the wire 2, the base material 3, and the two metal rods 4 shown in Figs. 1 and 2.

[0040] 1, 2, and 5, the two metal rods 4 are arranged symmetrically with respect to the wire 2. In addition, in the additive manufacturing apparatus 1 shown in FIGS. 1 and 2, the angle between the extension direction of the wire 2 and the extension direction of each of the two metal rods 4 is the same, 90°. On the other hand, in the additive manufacturing apparatus 1 shown in FIG. 5, the angle between the extension direction of the wire 2 and the extension direction of each of the two metal rods 4 is the same, 60°.

[0041] The base material 3 is placed on a three-axis stage 11. The three-axis stage 11 is movable in three axial directions.

[0042] The holding plate 12 is a plate-like member for holding the two adjustment mechanisms 13 and the nozzle 14, and is fixed to a frame (not shown) of the additive manufacturing apparatus 1. The adjustment mechanism 13 holds the metal rod 4 and adjusts the position and angle of the metal rod 4.

[0043] The nozzle 14 supplies a shielding gas to the space where the arc plasma AP is generated. The shielding gas is an inert gas such as argon gas or helium gas. A contact tip 15 is provided inside the nozzle 14. The contact tip 15 is a cylindrical conductor that guides the wire 2 and supplies current to the wire 2. The wire 2 protrudes from the tip of the contact tip 15.

[0044] The nozzle 14 and the contact tip 15 extend in a direction perpendicular to the surface of the triaxial stage 11. Therefore, the wire 2 guided by the contact tip 15 also extends in a direction perpendicular to the surface of the triaxial stage 11. Furthermore, if the surface of the triaxial stage 11 is a horizontal plane, the wire 2, the nozzle 14, and the contact tip 15 will extend in the vertical direction.

[0045] An actual additive manufacturing apparatus 1 includes a device for feeding out the wire 2, a device for supplying shielding gas to the nozzle 14, a device for applying voltage to the metal rod 4 and the contact tip 15 (wire 2), a device for driving the three-axis stage 11, etc. However, since these devices can be well-known devices, their description will be omitted.

[0046] If the distance between the tip ends 4a of the two metal rods 4 is too long, it becomes difficult to stabilize the arc discharge. On the other hand, if the distance is too short, the tip ends 4a of the metal rods 4 are more likely to wear. Therefore, it is desirable that the distance be approximately 4 to 8 mm.

[0047] Furthermore, if the distance between the tip 4a and the surface of the base material 3 is long, the heat input to the base material 3 will be small, which may make it difficult to weld the molten part 3a of the base material 3 and the molten filler 2b. On the other hand, if the distance is short, some measure will be required to prevent the tip 4a from coming into contact with the laminate of the base material 3. Therefore, the distance is preferably about 3 to 5 mm.

[0048] In the additive manufacturing apparatus 1 configured as described above, the arc plasma AP generated between the wire 2 and the metal rod 4 causes the molten filler 2b on the tip 2a of the wire 2 to drip onto the molten portion 3a of the base material 3, where it is welded and layered. As the wire 2 is successively supplied, the molten filler 2b on the tip 2a of the wire 2 is successively dripped onto the molten portion 3a of the base material 3, where it is welded and layered, while the three-axis stage 11 is driven in three axial directions. This allows a three-dimensional metal object to be produced.

[0049] In this embodiment, the holding plate 12 is fixed and the three-axis stage 11 is moved, but this is not limiting. The holding plate 12 may be moved in three axial directions and the three-axis stage 11 may be fixed, or both the holding plate 12 and the three-axis stage 11 may be moved.

[0050] Example 1 An example of the above embodiment will be described with reference to FIGS.

[0051] In this example, the current flowing from the wire 2 to the metal rod 4 was 220 A, the feed speed of the wire 2 was 108 mm / s, and the movement speed of the three-axis stage 11 was 10 mm / s. The wire 2 was a mild steel wire with a diameter of 1.2 mm. The two metal rods 4 were made of tungsten, with the distance between the metal rods 4 being 6.9 mm and the distance between the metal rods 4 and the base material 3 being 5 mm.

[0052] 6 and 7 are photographs showing the state of the arc plasma AP and the molten filler 2b in the above example. In the example of Fig. 6, the angle between the extension direction of the wire 2 and the extension direction of the metal rod 4 was set to 90°, as in Figs. 1 and 2. On the other hand, in the example of Fig. 7, the angle between the extension direction of the wire 2 and the extension direction of the metal rod 4 was set to 60°, as in Fig. 5.

[0053] 6 and 7, it can be seen that an arc plasma AP is formed between the tip 2a and molten filler 2b of the wire 2 and the two metal rods 4, and the molten filler 2b flows and drips stably between the two metal rods 4. Furthermore, when the angle is 60°, the dripping of the molten filler 2b is stable and the contact state between the arc plasma AP and the base material 3 is stable, resulting in the best molding accuracy and speed.

[0054] It is not desirable to make the angle between the wire 2 and the metal rod 4 greater than 90°, as this may result in the metal rod 4 and adjustment mechanism 13 colliding with the base material 3 or the three-axis stage 11. Furthermore, if the angle between the wire 2 and the metal rod 4 is made smaller than 30°, the arc plasma AP generated between the wire 2 and one of the metal rods 4 splits into an arc plasma AP generated between the wire 2 and the other metal rod 4, reducing the molding accuracy.

[0055] Therefore, the angle formed by the wire 2 and the metal rod 4 is preferably 30° or more and 90° or less, more preferably 45° or more and 75° or less, and even more preferably 55° or more and 65° or less.

[0056] 6 and 7, the arc plasma AP is also generated on the wire 2 side (upper side in FIGS. 6 and 7) from between the tip ends 4a of the two metal rods 4. Therefore, even if the tip end 2a of the wire 2 is provided between the tip ends 4a of the two metal rods 4, the wire 2 melts from the position where the arc plasma AP is generated, and the molten filler 2b passes between the tip ends 4a of the two metal rods 4.

[0057] [Embodiment 4] Yet another embodiment of the present invention will now be described with reference to FIG.

[0058] 8 is a cross-sectional view showing an overview of the WAAM process of the additive manufacturing apparatus according to this embodiment. As shown in Fig. 8, the additive manufacturing apparatus 1 of this embodiment is configured such that, compared to the additive manufacturing apparatus 1 shown in Fig. 5, the tip 4a of the metal rod 4 is positioned in the direction PD (hereinafter referred to as the "placing direction PD") in which the molten filler 2b at the tip 2a of the wire 2 is successively dropped and placed in the molten portion 3a of the base material 3, and in the opposite direction. For this reason, at least one of the three-axis stage 11 and the holding plate 12 may be configured to be rotationally driven in a direction perpendicular to the surface of the three-axis stage 11.

[0059] With the above configuration, the placement direction PD, i.e., the direction in which welding progresses in the base material 3, is the direction along the line segment connecting the two tip ends 4a, so that the influence of deviation in the position where the molten filler 2b drips can be suppressed, as described above. Note that, as shown in Figures 3 and 4, when there are three or more metal rods 4, the additive manufacturing device 1 can be configured so that the tip end 4a of any one of the metal rods 40 is located in the opposite direction from the placement direction PD, and the placement direction PD is the direction along the line connecting the tip end 4a of the metal rod 40 and the molten filler 2b.

[0060] At this time, the molten filler 2b is located within a polygon having the tip 4a of the metal rod 4 as its vertex, so at least one of the tip 4a of the remaining metal rods 4 is disposed on the side of the molten filler 2b in the placing direction PD. One of the tip 4a of the remaining metal rods 4 may be disposed on the side of the molten filler 2b in the placing direction PD and on the above-mentioned straight line. Furthermore, at least one pair of tip 4a of the remaining metal rods 4 may be disposed on the side of the molten filler 2b in the placing direction PD and symmetrically disposed with respect to the above-mentioned straight line.

[0061] Furthermore, compared to the additive manufacturing apparatus 1 shown in FIG. 5 , the additive manufacturing apparatus 1 of this embodiment shown in FIG. 8 is newly provided with a power supply for passing a current from the wire 2 to the metal rod 40 located in the opposite direction to the placement direction PD. The power supply is configured so that the current flowing from the wire 2 to the metal rod 40 is larger than the current flowing from the wire 2 to the remaining metal rods 4. This causes an asymmetry in the current flow from the wire 2 to the metal rods 4, and this asymmetry changes the balance of electromagnetic forces, allowing the molten filler 2b to be injected at an angle toward the placement direction PD. As a result, the molten portion 3a of the base material 3 can be prevented from flowing in the opposite direction to the placement direction PD, and the shape of the three-dimensional metal object can be stabilized.

[0062] In this embodiment, the control of making the current flowing from the wire 2 to the metal rod 40 larger than the current flowing from the wire 2 to the remaining metal rods 4 is achieved by providing a new power source, but the present invention is not limited to this. For example, the control may be achieved by making the resistance value of the circuit connected to the metal rod 40 smaller than the resistance value of the circuit connected to the remaining metal rods 4. The control may also be achieved by making the material of the metal rod 40 smaller in resistivity than the material of the remaining metal rods 4. The optimal method for the control can be selected as appropriate depending on the configuration of the additive manufacturing apparatus 1.

[0063] [Embodiment 5] Yet another embodiment of the present invention will now be described with reference to FIG.

[0064] FIG. 9 is a cross-sectional view showing an overview of the WAAM process of the additive manufacturing apparatus according to this embodiment. As shown in FIG. 9, the additive manufacturing apparatus 1 according to this embodiment is configured, compared to the additive manufacturing apparatus 1 shown in FIG. 8, so that the distance between the tip 4a of the metal rod 40 located on the opposite side of the placement direction PD and the tip 2a of the wire 2 is longer than the distance between the tip 4a of the remaining metal rod 4 and the tip 2a of the wire 2. This configuration expands the area of ​​contact between the molten portion 3a of the base material 3 and the arc plasma AP in the opposite direction of the placement direction PD. As a result, the shape of the three-dimensional metal object can be further stabilized.

[0065] (Additional notes) The additive manufacturing apparatus 1 may supply a current from the wire 2 to the metal rod 4 as a pulse current that alternates between a base current and a peak current. In this case, it is possible to easily control the shape of the three-dimensional metal object. Furthermore, the additive manufacturing apparatus 1 may control the pulse current by adjusting the value and duration of the peak current so that one drop of molten filler 2b is injected during one peak current period. This makes it possible to stably manufacture metal objects.

[0066] Example 2 An example of the above embodiment will be described with reference to FIG.

[0067] Photograph G1 in the upper part of Fig. 10 is a side view of the metal structure 20 produced according to this example. Photograph G100 in the lower part of Fig. 10 is a side view of the metal structure 200 produced according to a comparative example. In this example and the comparative example, the wire 2 was a mild steel wire with a diameter of 1.2 mm, and the two metal rods 4 were made of tungsten.

[0068] In this example, the distance between the tip 4a of the metal rod 40 located on the opposite side of the placement direction PD and the tip 2a of the wire 2 was 3.5 mm, and the distance between the tip 4a of the remaining metal rod 4 and the tip 2a of the wire 2 was 1.7 mm. The current value from the wire 2 to the metal rod 40 was 147 A, and the current value from the wire 2 to the remaining metal rod 4 was 73 A. The formation speed of the metal object 20 was 40 mm / min.

[0069] On the other hand, in the comparative example, the distance between the tip 4a of the metal rod 40 located on the opposite side of the placement direction PD and the tip 2a of the wire 2 was 2.6 mm, and the distance between the tip 4a of the remaining metal rod 4 and the tip 2a of the wire 2 was 2.6 mm. The current value from the wire 2 to the metal rod 40 was 110 A, and the current value from the wire 2 to the remaining metal rod 4 was 110 A. The formation speed of the metal object 200 was 20 mm / min.

[0070] Comparing photographs G1 and G100 in FIG. 10, it can be seen that the present embodiment can achieve stabilization of the shape of the metal object 20 compared to the comparative example, even when the formation speed is increased.

[0071] (Additional notes) In the above embodiment, the present invention is applied to the additive manufacturing apparatus 1, but is not limited to this. For example, the present invention can also be applied to a normal welding apparatus that joins two metal bodies.

[0072] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. [Explanation of symbols]

[0073] 1 Additive manufacturing equipment 2 wire 2a Tip 2b Melt filler 3 Base material 3a Welded part 4, 40 metal rods 4a Tip 11 3-axis stage 12 Holding plate 13 Adjustment mechanism 14 nozzles 15 Contact Tip 20 Metal objects

Claims

1. a wire that is a filler material and an anode; a plurality of metal rods serving as cathodes; A welding device in which the wire and the plurality of metal rods are arranged so that arc discharge between the tip of the wire and the tip of the plurality of metal rods causes molten filler that has melted the tip of the wire to pass between the tip of the plurality of metal rods.

2. The number of the metal rods is two, and The welding device according to claim 1 , wherein the wire and the plurality of metal rods are arranged so that the molten filler passes through a midpoint of a line segment connecting the tips of the two metal rods.

3. The number of the metal rods is three or more, The tip ends of the plurality of metal rods are located at vertices of a regular polygon whose number of sides is the same as the number of the plurality of metal rods, and The welding apparatus of claim 1 , wherein the wire and the plurality of metal rods are arranged so that the molten filler passes through the center of the regular polygon.

4. 2. The welding device according to claim 1, wherein the extending direction of the wire and the extending direction of each of the plurality of metal rods form the same angle.

5. The welding device according to claim 4 , wherein the angle is equal to or greater than 30° and equal to or less than 90°.

6. The welding device according to claim 5 , wherein the angle is equal to or greater than 45° and equal to or less than 75°.

7. The welding device according to claim 6 , wherein the angle is equal to or greater than 55° and equal to or less than 65°.

8. 2. The welding apparatus of claim 1, wherein the plurality of metal rods are made of tungsten or a tungsten alloy containing tungsten and at least one of cerium oxide, lanthanum oxide, yttrium oxide, and zirconium oxide.

9. A welding device according to any one of claims 1 to 8; a stage on which the workpieces to be welded are placed, An additive manufacturing apparatus, wherein at least one of the welding device and the stage is movable.

10. The additive manufacturing apparatus according to claim 9 , wherein a tip end of at least one metal rod in the welding device is arranged in a direction opposite to a direction in which the workpieces are successively placed on the stage.

11. The additive manufacturing apparatus of claim 10 , wherein the current flowing through the at least one metal rod is greater than the current flowing through the remaining metal rods in the welding apparatus.

12. The additive manufacturing apparatus according to claim 11 , wherein a distance between a tip of the at least one metal rod and a tip of the wire is longer than a distance between a tip of the remaining metal rods and a tip of the wire.

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