Lamination molding method

Abstract

To provide a lamination molding method capable of uniformizing heights of weld beads without stopping molding.SOLUTION: A lamination molding method for laminating molten metal obtained by melting a metal wire 4a using an arc heat source, and molding a molded article 10 performs control to monitor a measured value of any one of current and a voltage of the arc heat source, and to change a command value of the other of the current and the voltage of the arc heat source, according to variations in the measured values.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present invention relates to an additive manufacturing method for manufacturing a model by layering molten metal obtained by melting a metal wire using an arc heat source. [Background technology]

[0002] There is a technology called additive manufacturing. As an example of additive manufacturing, a method for manufacturing a layered structure is known in which layers of synthetic resin, metal, etc. are modeled and the modeled layers are stacked to produce a three-dimensional object.

[0003] 3D printers are a typical example of additive manufacturing technology-based modeling devices that have been put to practical use. Because 3D printers can manufacture structures with complex shapes in a short time, they are attracting attention as a promising technology in advanced technology fields such as the aircraft industry and medicine. 3D printers that use metallic materials use a heat source such as a laser or arc to melt metal powder or metal wire, and then layer the molten metal to create a model.

[0004] For example, Patent Document 1 describes a method for forming a three-dimensional mold material, comprising the steps of generating shape data representing the shape of a mold, dividing the mold into stacked bodies along contour lines based on the generated shape data, and creating a movement path for a welding torch that supplies filler metal based on the shape data of the resulting stacked bodies, and moving the welding torch along the created movement path while melting the filler metal with the welding torch, thereby continuously stacking weld beads made of the molten filler metal.

[0005] Furthermore, for example, Patent Document 2 describes a method for manufacturing an additive manufacturing object by using a welding robot equipped with a welding head having a torch on the tip shaft, and repeatedly stacking weld beads by melting and solidifying a filler metal sent from the welding head while moving the welding head using the welding robot and moving the filler metal. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 3784539 [Patent Document 2] JP 2019-98381 A Summary of the Invention [Problem to be solved by the invention]

[0007] In the above-mentioned additive manufacturing method, when an additive object is manufactured by stacking multiple weld beads formed by melting and solidifying a filler material using an arc heat source, it is necessary to repeatedly form and stack many weld beads.

[0008] In this case, it is unavoidable that the stacking height of the weld bead will fluctuate due to various disturbances, which in turn causes the arc length when forming the next layer of weld bead and the distance between the tip (electrode) and the base material to fluctuate, making the arc unstable. As a result, there are issues such as uneven weld bead height, which can cause the shape of the model to collapse or modeling to stop midway through stacking.

[0009] The present invention has been made in consideration of these problems, and its purpose is to provide an additive manufacturing method that can make the height of a weld bead uniform without stopping the modeling. [Means for solving the problem]

[0010] <1> The additive manufacturing method of the present invention is an additive manufacturing method in which molten metal obtained by melting a metal wire using an arc heat source is layered to form a model, and is characterized in that an actual measured value of either the current or voltage of the arc heat source is monitored, and control is performed to change the command value of the other of the current or voltage of the arc heat source in accordance with fluctuations in the actual measured value.

[0011] <2> The layered manufacturing method of the present invention is <1> In the configuration of claim 1, when the arc heat source has a constant current characteristic, the actual voltage measurement value of the arc heat source is monitored, and a control is performed to change the current command value in accordance with fluctuations in the actual voltage measurement value.

[0012] <3> The layered manufacturing method of the present invention is <1> In the configuration of claim 1, when the arc heat source has a constant voltage characteristic, the actual measured current value of the arc heat source is monitored, and a control is performed to change the voltage command value in accordance with fluctuations in the actual measured current value.

[0013] <4> The layered manufacturing method of the present invention is <2> or <3> In the configuration of the present invention, feedback control including proportional control or integral control is performed.

[0014] <5> The layered manufacturing method of the present invention is <2> In the configuration of the present invention, the current command value is changed based on any one of the following calculation formulas (1) to (3) in which a reference voltage value−actual voltage measurement value is set as a voltage value deviation. (1) Current command value = Reference current value + (3~25) × (Voltage value deviation) (2) Current command value = Reference current value + (0.05 to 10.00) x (integral of voltage value deviation) (3) Current command value = Reference current value + (3 to 25) x (Voltage value deviation) + (0.05 to 10.00) x (Integral of voltage value deviation)

[0015] <6> The layered manufacturing method of the present invention is <3> In the configuration of the present invention, the voltage command value is changed based on any one of the following calculation formulas (1) to (3) in which a reference current value−actual current value is set as a current value deviation. (1) Voltage command value = Reference voltage value + (0.03~0.25) × (current value deviation) (2) Voltage command value = Reference voltage value + (0.0005~0.1000) × (integral of current value deviation) (3) Voltage command value = Reference voltage value + (0.03 to 0.25) × (current value deviation) + Reference voltage value + (0.0005 to 0.1000) × (integral of current value deviation) Effect of the Invention

[0016] According to the invention, when a molten metal formed by melting a metal wire using an arc heat source is layered to form a shaped object, even if the height of the shaped object varies during the process, the height of the weld bead can be made uniform without stopping the process. In addition, the arc is prevented from becoming unstable, which can cause the shape of the shaped object to become distorted, and thus the process can be prevented from being stopped midway. As a result, the production efficiency of the shaped object can be improved. Furthermore, since the shape of the shaped object can be prevented from becoming distorted, the number of post-processing steps performed after the shaped object is formed can be reduced.

[0017] In this way, according to the present invention, it is possible to provide an additive manufacturing method that can uniformize the height of the weld bead without stopping the modeling. [Brief description of the drawings]

[0018] [Figure 1] 1 is a diagram showing a schematic configuration of an additive manufacturing apparatus capable of carrying out an additive manufacturing method according to an embodiment of the present invention; [Diagram 2] FIG. 13 is a diagram showing the positional relationship between the object and the welding torch when the arc length is the reference length. [Diagram 3] FIG. 13 is a diagram showing the positional relationship between the object and the welding torch when the arc length is shorter than the reference length. [Figure 4] FIG. 13 is a diagram showing the positional relationship between the object and the welding torch when the arc length is longer than the reference length. [Diagram 5] FIG. 2A is a side view and a perspective view of a standing wall manufactured by the additive manufacturing method of Comparative Example 1, and FIG. 2B is a side view and a perspective view of a standing wall manufactured by the additive manufacturing method of Example 1. [Figure 6] FIG. 11 is a diagram showing changes in a current command value, a target voltage, and a measured voltage value with respect to the number of layers during fabrication when a standing wall is fabricated by the additive fabrication method of Example 1. [Figure 7]1A is a side view and an oblique view of a square pipe manufactured by the additive manufacturing method of Comparative Example 2, and FIG. 1B is a side view and an oblique view of a square pipe manufactured by the additive manufacturing method of Example 2. [Figure 8] FIG. 11 is a diagram showing changes in the current command value, the target voltage, and the measured voltage value with respect to the number of layers during manufacturing when a square pipe is manufactured by the additive manufacturing method of Example 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Hereinafter, an example of an additive manufacturing method according to an embodiment of the present invention will be described in detail with reference to the drawings.

[0020] An additive manufacturing method according to one embodiment of the present invention is an additive manufacturing method in which molten metal obtained by melting a metal wire using an arc heat source is layered to form a model, and is characterized in that an actual measured value of either the current or voltage of the arc heat source is monitored, and control is performed to change the command value of the other of the current or voltage of the arc heat source in accordance with fluctuations in the actual measured value.

[0021] The additive manufacturing method according to the present embodiment can be carried out, for example, by using an additive manufacturing apparatus 1 as shown in FIG.

[0022] The additive manufacturing apparatus 1 includes a base plate 2, a torch 3, a wire supplying device 4, a gas supplying unit 5, a control device 6, and a moving device 7. The basic configuration of this additive manufacturing apparatus 1 is similar to that of an automatic welding machine that performs TIG welding.

[0023] The base plate 2 is also called a base material, and is formed in a plate shape from a metal material that can pass electricity, such as steel. The object 10 produced by the additive manufacturing method according to this embodiment is produced on the base plate 2. The shape of the base plate 2 can be changed in various ways.

[0024] The torch 3 includes an electrode (power supply tip) 3b formed of a metal such as tungsten inside a cylindrical case 3a. When power is supplied from a control device 6 to the electrode 3b, the torch 3 can generate an arc between the electrode 3b and the base plate 2.

[0025] The wire feeder 4 has a reel 4b around which a metal wire 4a is wound, a guide unit 4c attached to the torch 3, and a feed unit 4d that feeds the metal wire 4a from the reel 4b to the guide unit 4c. The wire feeder 4 supplies the metal wire 4a toward the arc generated between the torch 3 and the base plate 2 at a constant feed speed.

[0026] The gas supply unit 5 is a cylinder that contains an inert gas such as argon gas or helium gas. The gas supply unit 5 is connected to the torch 3 by a pipe 5a, and can supply the inert gas from the tip of the torch 3 toward the arc generated between the torch 3 and the base plate 2. The inert gas supplied toward the arc functions as a shielding gas that covers the molten metal melted by the arc.

[0027] The control device 6 has a power supply unit 6a, a control unit 6c, and a monitoring unit 6b.

[0028] The power supply unit 6a is connected to the base plate 2 by a cable 6d and is also connected to the electrode 3b by a cable 6e. The power supply unit 6a supplies a direct current to the electrode 3b to energize the base plate 2 and the electrode 3b, thereby generating an arc between the base plate 2 and the electrode 3b.

[0029] The monitoring unit 6b constantly monitors the actual measured value of the voltage when the power supply unit 6a supplies a direct current to the electrode 3b, that is, the actual measured voltage value.

[0030] The control unit 6c is composed of, for example, a microcomputer. The control unit 6c can control the power supply unit 6a to supply current between the base plate 2 and the electrode 3b at a predetermined reference current value and a predetermined reference voltage value, with a preset reference current value as a current command value. The control unit 6c can also control the power supply unit 6a to supply current between the base plate 2 and the electrode 3b at a current value changed from the reference current value by changing the current command value. Furthermore, the control unit 6c controls the operation of the moving device 7.

[0031] The moving device 7 is configured, for example, by a robot arm or the like, and can drive the torch 3 in the X-axis, Y-axis, and Z-axis directions to move it to an arbitrary position relative to the base plate 2. The moving device 7 is not limited to a robot arm, and may be configured in various ways.

[0032] In the additive manufacturing apparatus 1 having the above configuration, an arc is generated between the base plate 2 and the electrode 3b by supplying a current from the power supply unit 6a of the control device 6 to the electrode 3b, and the wire feeder 4 supplies a metal wire 4a as a filler material to the arc, and the molten metal melted by the arc is covered with an inert gas supplied from the gas supply unit 5, while the moving device 7 moves the torch 3 along the base plate 2, thereby forming a weld bead 10a formed by solidifying the molten metal wire 4a, i.e., the molten metal, on the base plate 2, and further stacking the weld bead 10a in multiple layers on the formed weld bead 10a, thereby forming a model 10 of a desired shape. In other words, by using the additive manufacturing apparatus 1 having the above configuration, it is possible to carry out the additive manufacturing method according to this embodiment in which the molten metal obtained by melting the metal wire 4a is stacked using the arc generated between the base plate 2 and the electrode 3b as a heat source, i.e., an arc heat source, to form a model 10.

[0033] Here, when many weld beads 10a are repeatedly formed and stacked, the stacking height of the weld beads 10a may vary due to various disturbances, and accordingly, the arc length and the distance between the base plate 2 and the electrode 3b may vary when forming the next layer of weld beads 10a, making the arc unstable. As a result, the height of the weld beads 10a may become non-uniform, causing the shape of the model 10 to collapse, or modeling by the additive manufacturing device 1 to stop midway through stacking.

[0034] To address such problems, a method is known for stabilizing the arc in TIG welding by using a position tracking device (AVC device). In this method, the actual measured value of the arc voltage is constantly monitored in order to monitor the change in the arc voltage during welding. Since TIG welding uses a current-controlled welding machine with a constant current setting, the change in the arc voltage is proportional to the change in the arc length. Therefore, if a reference voltage value is set before the forming process, the difference between the actual measured value of the current arc voltage and the reference voltage value represents the magnitude of deviation of the actual arc length from the set arc length. In the position tracking device, the control device instructs the moving device to correct the torch position so that this deviation is reduced. The moving speed at this time is instructed to be slow if the deviation is small, and to be fast if the deviation is large.

[0035] However, in the method using the above-mentioned position tracking device, the torch is moved vertically in accordance with changes in the height of the weld bead, so while the stability of the arc can be maintained, it is not possible to eliminate variations in the height of the weld bead.

[0036] Therefore, in the additive manufacturing method according to this embodiment, the actual voltage value of the arc heat source is monitored while the object 10 is being manufactured, and when the actual voltage value monitored by the monitoring unit 6b fluctuates, the current command value is changed in accordance with the fluctuation in the actual voltage value, and control is performed to supply current based on the changed current command value.

[0037] To explain more specifically the case where the additive manufacturing apparatus 1 having the above configuration is used, when the actual voltage measurement value of the arc heat source monitored by the monitoring unit 6b is equal to the reference voltage value, the control unit 6c determines that the length of the arc 20 between the base plate 2 and the electrode 3b, i.e., the arc length, is equal to the set value, as shown in Fig. 2, and maintains the current command value at a preset reference current value. This allows an arc to be formed at a predetermined reference current value and reference voltage value, and a weld bead 10a of a set height and width can be formed.

[0038] Furthermore, when the actual voltage measurement value of the arc heat source monitored by the monitoring unit 6b decreases from the reference voltage value (when the monitoring unit 6b detects that the actual voltage measurement value of the arc 20 has decreased from the reference voltage value), the control unit 6c determines that the height of the weld bead 10a has become higher than the set height and the arc length of the arc 20 between the base plate 2 and the electrode 3b has decreased, as shown in Fig. 3, and changes the current command value to increase. This allows the arc to be formed at a current value higher than a predetermined reference current value and a voltage value lower than the reference voltage value, thereby widening the width of the weld bead 10a and decreasing the height of the weld bead 10a.

[0039] Furthermore, when the actual voltage measurement value of the arc heat source monitored by the monitoring unit 6b increases from the reference voltage value (when the monitoring unit 6b detects that the actual voltage measurement value of the arc 20 has increased from the reference voltage value), the control unit 6c determines that the height of the weld bead 10a has become lower than the set height and the arc length of the arc 20 between the base plate 2 and the electrode 3b has increased, as shown in Fig. 4, and changes the current command value to decrease. This allows the arc to be formed at a current value smaller than a predetermined reference current value and a voltage value larger than the reference voltage value, thereby narrowing the width of the weld bead 10a and increasing the height of the weld bead 10a.

[0040] In addition, in the additive manufacturing method of this embodiment, the feed speed of the metal wire 4a during manufacturing is kept constant, so if the current command value is corrected to increase the height of the weld bead 10a, the width of the weld bead 10a will be narrower, and if the current command value is corrected to decrease the height of the weld bead 10a, the width of the weld bead 10a will be wider.

[0041] In this way, in the additive manufacturing method according to this embodiment, in the case where the arc 20 is generated with a constant current command value (when the arc heat source has constant current characteristics), the actual voltage measurement value of the arc heat source is monitored, and even if a fluctuation in the actual voltage measurement value of the arc heat source is detected, the position of the torch 3 in the height direction is not corrected, but the current command value is changed according to the detected fluctuation in the actual voltage measurement value. This makes it possible to eliminate variations in the height of the weld bead 10a while maintaining the stability of the arc 20 during the modeling of the model 10. Therefore, according to the additive manufacturing method according to this embodiment, it is possible to uniform the height of the weld bead 10a and accurately model the model 10 into a desired shape while preventing the arc 20 from becoming unstable and modeling being stopped.

[0042] Furthermore, in additive manufacturing methods, it is common to perform a post-process to modify the shape of object 10 after the object 10 has been manufactured. However, according to the additive manufacturing method of this embodiment, as described above, object 10 can be manufactured into the desired shape with high precision, thereby reducing the labor required for the post-process.

[0043] In the additive manufacturing method according to this embodiment, it is preferable to configure the control for changing the above-mentioned current command value to perform feedback control including proportional control or integral control.

[0044] For example, in the case of a configuration in which feedback control including proportional control is performed, the reference voltage value-actual voltage value is set as the voltage value deviation, and the current command value during the modeling of the object 10 can be changed based on the formula "current command value=reference current value+coefficient×voltage value deviation." In this case, the coefficient multiplied by the voltage value deviation is in the range of 3 to 25, and more preferably in the range of 7 to 15. Proportional control (P control) is a feedback control that performs an operation of outputting a current command value proportional to the voltage value deviation.

[0045] In addition, when a feedback control including integral control is performed, the reference voltage value-actual voltage measurement value is set as the voltage value deviation, and the current command value during the modeling of the object 10 can be changed based on the formula "current command value=reference current value+coefficient×integral of voltage value deviation" (I control). In this case, the coefficient multiplied by the integral of the voltage value deviation is in the range of 0.05 to 10.00, and more preferably in the range of 0.20 to 2.00. Note that the integral control (I control) is a feedback control that performs an operation of outputting a current command value proportional to the integral of the voltage value deviation.

[0046] Furthermore, the feedback control may include both proportional control and integral control. In this case, the reference voltage value-actual voltage measurement value is set as the voltage value deviation, and the current command value during the modeling of the object 10 is changed based on the formula "current command value=reference current value+coefficient 1×voltage value deviation+coefficient 2×integral of voltage value deviation" (PI control). In this case, coefficient 1 multiplied by the voltage value deviation is in the range of 3 to 25, and more preferably in the range of 7 to 15. Moreover, coefficient 2 multiplied by the integral of the voltage value deviation is in the range of 0.05 to 10.00, and more preferably in the range of 0.20 to 2.00.

[0047] In the above feedback control, if the coefficients (coefficient 1, coefficient 2) are smaller than the lower limit, the amount of change in the current command value is insufficient, and the effect of the change or correction cannot be fully achieved. On the other hand, if the coefficients (coefficient 1, coefficient 2) are larger than the upper limit, the amount of change in the current command value becomes extremely large, which may cause poor fusion of the metal wire 4a (if the current command value is reduced too much) or sagging of the weld bead 10a (if the current command value is increased too much). For this reason, an upper limit is set for the coefficients to gradually improve the situation.

[0048] In this way, in the additive manufacturing method according to the present embodiment, when the actual voltage value of the arc heat source is monitored during the manufacturing of the object 10, and the current command value is changed in accordance with the fluctuation of the detected actual voltage value, if the control is performed by feedback control including proportional control or integral control, the current command value changes more significantly with respect to the reference current value as the difference between the actual voltage value and the reference voltage value increases, so that the height of the weld bead 10a can be corrected more quickly and continuously by changing the current command value. Therefore, the height of the weld bead 10a can be made more uniform, and the object 10 can be manufactured into a desired shape with greater accuracy.

[0049] The additive manufacturing method according to the present embodiment uses an additive manufacturing device 1 having a configuration similar to that of an automatic welding machine that performs TIG welding, and the arc heat source is configured to have a constant current characteristic, but it is also possible to use an additive manufacturing device 1 having a configuration similar to that of an automatic welding machine that performs MIG welding, and the arc heat source is configured to have a constant voltage characteristic.

[0050] In this case, although not shown in detail, the metal wire 4a supplied from the wire feeder 4 penetrates the electrode 3b and is unwound from the tip of the electrode 3b, and the current supplied from the power supply unit 6a to the electrode 3b flows through the metal wire 4a and the arc to the base plate 2, which is the base material, and at that time the metal wire 4a is heated by the arc heat source, i.e. Joule heat. Since the amount of Joule heat increases as the electrical resistance increases, when the protruding length of the metal wire 4a from the electrode 3b increases, the electrical resistance of the protruding part increases and the amount of heat of the metal wire 4a due to Joule heat increases, and the metal wire 4a melts. In other words, in a configuration in which the current is set to a constant value, the longer the protruding length of the metal wire 4a from the electrode 3b, the greater the amount of melting of the metal wire 4a when the current value is the same.

[0051] Therefore, in the additive manufacturing method according to this embodiment, when the arc heat source is configured to have constant current characteristics, the monitoring unit 6b of the control device 6 is configured to monitor the actual current value of the arc heat source during modeling, and the control unit 6c is configured to change the voltage command value in accordance with the fluctuation of the actual current value when the actual current value monitored by the monitoring unit 6b fluctuates, and to control the power supply unit 6a based on the changed voltage command value. At this time, the supply speed of the metal wire 4a, the movement speed of the torch 3, and the height (Z pitch (G code)) of the torch 3 from the top surface of the model 10 to be layered from the top surface are fixed values.

[0052] More specifically, when the actual current value of the arc heat source monitored by the monitoring unit 6b is equal to the reference current value, the control unit 6c determines that the protruding length of the metal wire 4a from the electrode 3b is equal to the set value, and maintains the voltage command value at a preset reference voltage value. This allows the arc 20 or Joule heat to be generated at a predetermined reference current value and reference voltage value, thereby forming a weld bead 10a of a set height and width.

[0053] Furthermore, when the actual current value of the arc heat source monitored by the monitoring unit 6b increases from the reference current value (when the monitoring unit 6b detects that the actual current value has increased from the reference current value), the control unit 6c determines that the height of the weld bead 10a has become higher than the set height and the protruding length of the metal wire 4a from the electrode 3b has decreased from the reference length, and changes the voltage command value to increase. This allows the arc 20 or Joule heat to be generated at a voltage value higher than the predetermined reference voltage value and a current value higher than the reference current value, thereby widening the width of the weld bead 10a and decreasing the height of the weld bead 10a.

[0054] Furthermore, when the actual current value of the arc heat source monitored by the monitoring unit 6b decreases from the reference current value (when the monitoring unit 6b detects that the actual current value has decreased from the reference current value), the control unit 6c determines that the height of the weld bead 10a has become lower than the set height and the protruding length of the metal wire 4a from the electrode 3b has increased from the reference length, and changes the voltage command value to decrease. This makes it possible to generate the arc 20 or Joule heat at a voltage value smaller than the predetermined reference voltage value and a current value smaller than the reference current value, thereby narrowing the width of the weld bead 10a and increasing the height of the weld bead 10a.

[0055] In this way, in the additive manufacturing method according to the present embodiment, when the arc heat source is configured to have a constant current characteristic, the actual current measurement value of the arc heat source is monitored, and even if a fluctuation in the actual current measurement value is detected, the position of the torch 3 in the height direction is not corrected, and the voltage command value is changed according to the detected fluctuation in the actual current value. As a result, even when the arc heat source is configured to have a constant current characteristic, it is possible to eliminate variations in the height of the weld bead 10a while maintaining the stability of the arc 20 during the modeling of the model 10. Therefore, according to the additive manufacturing method according to the present embodiment, even when the arc heat source is configured to have a constant current characteristic, it is possible to uniform the height of the weld bead 10a while preventing the arc 20 from becoming unstable and stopping the modeling, and to accurately model the model 10 into a desired shape.

[0056] In the additive manufacturing method according to this embodiment, even when the arc heat source is configured to have constant voltage characteristics, it is preferable to configure it to perform feedback control including proportional control or integral control.

[0057] For example, in the case where the arc heat source is configured to have constant voltage characteristics and feedback control including proportional control is performed, the reference current value-actual current value is set as the current value deviation, and the voltage command value during modeling of the object 10 is changed based on the formula "voltage command value=reference voltage value+coefficient×current value deviation" (P control). In this case, the coefficient multiplied by the current value deviation is in the range of 0.03 to 0.25, and more preferably in the range of 0.07 to 0.15.

[0058] Furthermore, in the case where the arc heat source is configured to have constant voltage characteristics and feedback control including integral control is performed, the voltage command value during modeling of the object 10 can be changed based on the current value deviation (reference current value-actual current value) and the formula "voltage command value=reference voltage value+coefficient×integral of current value deviation" (I control). In this case, the coefficient multiplied by the integral of the current value deviation is in the range of 0.0005 to 0.1000, and more preferably in the range of 0.0020 to 0.0200.

[0059] Furthermore, in the case where the arc heat source is configured to have a constant voltage characteristic, the feedback control may include both proportional control and integral control. In this case, the reference current value-actual current value is set as the current value deviation, and the voltage command value during the modeling of the object 10 is changed based on the formula "voltage command value=reference voltage value+coefficient 1×current value deviation+coefficient 2×integral of current value deviation" (PI control). In this case, coefficient 1 multiplied by the current value deviation is in the range of 0.03 to 0.25, and more preferably in the range of 0.07 to 0.15. Moreover, coefficient 2 multiplied by the integral of the current value deviation is in the range of 0.0005 to 0.1000, and more preferably in the range of 0.0020 to 0.0200.

[0060] In this way, in the additive manufacturing method according to this embodiment, when the actual current value of the arc heat source is monitored during the manufacturing of the object 10, and the voltage command value is changed in accordance with the fluctuation of the detected actual current value, even if the control is performed by feedback control including proportional control or integral control, the voltage command value changes more significantly with respect to the reference voltage value as the difference between the actual current value and the reference current value increases, so that the height of the weld bead 10a can be corrected more quickly and continuously by changing the voltage command value. Therefore, the height of the weld bead 10a can be made more uniform, and the object 10 can be manufactured into a desired shape with greater accuracy.

[0061] In the above feedback control, if the coefficients (coefficient 1, coefficient 2) are smaller than the lower limit, the amount of change in the voltage command value is insufficient, and the effect of the change or correction cannot be fully achieved. On the other hand, if the coefficients (coefficient 1, coefficient 2) are larger than the upper limit, the amount of change in the voltage command value becomes extremely large, which may cause poor fusion of the metal wire 4a (if the voltage command value is reduced too much) or sagging of the weld bead 10a (if the voltage command value is increased too much). For this reason, the coefficients are set at upper limits to allow for gradual improvement.

[0062] In order to confirm the effects of the present invention, tests were conducted to manufacture objects under the following conditions for the additive manufacturing methods of Examples 1 and 2, in which the actual voltage measurement value of the arc heat source is monitored during the manufacture of an object and the current command value is changed in accordance with fluctuations in the actual voltage measurement value, and the additive manufacturing methods of Comparative Examples 1 and 2, in which such control is not performed.

[0063] (1) Shape of the object Example 1 and Comparative Example 1: Vertical wall of length 80 mm x height 70 mm x thickness t mm Example 2 and Comparative Example 2: Square pipe with length 50 mm x width 30 mm x height 70 mm x thickness t (wall thickness t) mm

[0064] (2) Modeling conditions Base plate (base material) material: SUS304 Metal wire material: JIS YS308L Metal wire diameter: 1.2mm Welding machine: Daihen T500P Welding mode: DC (direct current) Electrode rotation speed: 360 rpm Torch: Rotating electrode TIG torch described in Patent No. 6963699 Reference current value: 150A Metal wire feed speed: 2.0m / min Torch movement speed: 200mm / min Shielding gas: Argon (Ar) (purity 99.99%) Shielding gas flow rate: 40L / min

[0065] As shown in Fig. 5(a), in the additive manufacturing method of Comparative Example 1, when the weld bead of the 13th layer was being formed, the arc length became excessive, the arc became unstable, and the manufacturing process stopped. The height of the manufactured object (standing wall) at this time was 14 mm.

[0066] In contrast, the additive manufacturing method of Example 1 was able to form a 68 mm tall object (standing wall) with 40 weld bead layers. The changes in the current command value, target voltage, and actual voltage measurement value versus the number of layers while the object was being manufactured by the additive manufacturing method of Example 1 are shown in Fig. 6. It can be seen from the results shown in Fig. 6 that the current command value is controlled to increase as the actual voltage measurement value decreases, and to decrease as the actual voltage measurement value increases.

[0067] As shown in Fig. 7(a), in the additive manufacturing method of Comparative Example 2, when the weld bead of the 13th layer was being formed, the arc length became excessive, the arc became unstable, and the manufacturing process stopped. The height of the manufactured object (square pipe) at this time was 21 mm.

[0068] In contrast, the additive manufacturing method of Example 2 was able to form a 75 mm tall object (square pipe) with 40 weld bead layers. The changes in the current command value, target voltage, and actual voltage measurement value versus the number of layers while the object was being manufactured by the additive manufacturing method of Example 2 are shown in Figure 8. It can be seen from the results in Figure 8 that the current command value is controlled so that it increases when the actual voltage measurement value decreases, and decreases when the actual voltage measurement value increases.

[0069] The present invention is not limited to the above-described embodiment, and it goes without saying that various modifications can be made without departing from the spirit and scope of the present invention.

[0070] For example, the additive manufacturing apparatus for carrying out the additive manufacturing method according to this embodiment is not limited to the configuration shown in FIG. 1, and various configurations can be used.

[0071] Furthermore, in the additive manufacturing method according to this embodiment, the feedback control is not limited to the above-described method, and may be performed by various methods. [Explanation of symbols]

[0072] 1 Additive manufacturing equipment 2 Base plate 3. Torch 3a Case 3b electrode 4 Wire feeder 4a Metal Wire 4b Reel 4c Guide section 4d Feeding section 5 Gas supply section 5a Piping 6. Control device 6a Power supply section 6b Surveillance Department 6c Control section 6d Power cable 6e Power Cable 7. Mobile Devices 10 Sculptures 10a Weld bead 20 Arc

Claims

1. 1. An additive manufacturing method for manufacturing a model by laminating molten metal obtained by melting a metal wire using an arc heat source, comprising the steps of: monitoring an actual measurement of either a current or a voltage of the arc heat source; An additive manufacturing method, characterized in that control is performed to change the command value of either the current or the voltage of the arc heat source in accordance with fluctuations in the actual measured value.

2. The additive manufacturing method according to claim 1, characterized in that, when the arc heat source has a constant current characteristic, an actual voltage measurement value of the arc heat source is monitored, and a control is performed to change the current command value in accordance with fluctuations in the actual voltage measurement value.

3. The additive manufacturing method according to claim 1, characterized in that, when the arc heat source has a constant voltage characteristic, an actual measured current value of the arc heat source is monitored, and a control is performed to change the voltage command value in accordance with fluctuations in the actual measured current value.

4. The additive manufacturing method according to claim 2 or 3, characterized in that feedback control including proportional control or integral control is performed.

5. The additive manufacturing method according to claim 2, characterized in that the current command value is changed based on any one of the following calculation formulas (1) to (3), in which a reference voltage value - an actual voltage measurement value is defined as a voltage value deviation. (1) Current command value = Reference current value + (3 to 25) x (Voltage value deviation) (2) Current command value = Reference current value + (0.05 to 10.00) x (integral of voltage value deviation) (3) Current command value = Reference current value + (3 to 25) x (Voltage value deviation) + (0.05 to 10.00) x (Integral of voltage value deviation)

6. The additive manufacturing method according to claim 3, wherein the voltage command value is changed based on any one of the following calculation formulas (1) to (3), in which a reference current value - an actual current value is defined as a current value deviation. (1) Voltage command value = Reference voltage value + (0.03 to 0.25) x (current value deviation) (2) Voltage command value = Reference voltage value + (0.0005 to 0.1000) x (integral of current value deviation) (3) Voltage command value = Reference voltage value + (0.03 to 0.25) x (current value deviation) + Reference voltage value + (0.0005 to 0.1000) x (integral of current value deviation)

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