Weld bead shape control method, power supply control method, additive manufacturing method, control device, power supply device, welding system, additive manufacturing system, and program

Abstract

To uniformize a shape of a weld bead regardless of a distance between chip base materials without changing an average feeding speed of a welding wire, even if delivery and pull-back of the welding wire are repeated for performing welding.SOLUTION: A control method for a weld bead shape periodically repeats a forward feeding period TP and a reverse feeding period TN of a welding wire as one period, provides an arc period where an arc is generated at a torch tip and a short circuit period in one period, and controls a welding bead shape of a weld bead to be formed. The control method for the weld bead shape performs detection of the short circuit time and control of a peak current value for each period of feeding of the welding wire so that the short circuit time is within a target range determined by characteristic information in which a peak current value and the short circuit time are associated with each other, on the basis of the characteristic information, while keeping an average feeding speed of the welding wire constant.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a weld bead shape control method, a power supply control method, an additive manufacturing method, a control device, a power supply device, a welding system, an additive manufacturing system, and a program. [Background technology]

[0002] Cold Metal Transfer (CMT) welding is known as a method of welding by controlling the advance and retreat of the welding wire and the current flow between the contact tip and the molten pool to generate an intermittent arc. According to this CMT welding, when the welding wire is turned into droplets to form a weld bead, the current is reduced just before a short circuit, the welding wire is pulled back after the short circuit to promote the detachment of the droplets, and the welding current is controlled to a minimum when the arc is re-ignited, thereby realizing droplet transfer with reduced spatter. In addition, the welding current is controlled in synchronization with the advance and retreat of the welding wire, the welding wire is sent toward the molten pool when an arc is generated, and the wire is pulled back immediately after a short circuit is detected to cool the molten pool, thereby reducing heat input.

[0003] Such a CMT welding technique is described, for example, in Patent Document 1. Patent Document 1 describes a power supply control method assuming additive manufacturing, which compensates for deviations in the shape of the weld bead that is formed by adjusting the welding current, free length of the welding wire, the distance between the contact tip and the workpiece (distance between the tip and the base metal), etc. while monitoring the feed speed of the welding wire to keep the welding speed constant. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2021 / 219677 Summary of the Invention [Problem to be solved by the invention]

[0005] The above-mentioned CMT (Cold Metal Transfer) welding is a welding technique particularly suited to joining thin plates, and it achieves low heat input and low spatter by using a constant current waveform pattern to ensure constant penetration, and by reliably executing short-circuiting between the contact tip and the molten pool and re-arcing. However, in this CMT welding, when the tip-to-base metal distance changes, the timing of feeding and pulling back the welding wire is changed, so the average feeding speed of the welding wire changes. Although the change in the average feeding speed is not a problem when welding thin plates, it is not desirable when the process requires high repetitive stability and a constant weld bead shape is desired, such as in additive manufacturing.

[0006] The present invention is intended to solve the above-mentioned problems, and aims to provide a weld bead shape control method, power supply control method, additive manufacturing method, control device, power supply device, welding system, additive manufacturing system, and program that can keep the shape of the weld bead constant in real time regardless of the tip-to-base material distance and without changing the average welding wire feed speed, even when welding is performed by repeatedly feeding and pulling back the welding wire. [Means for solving the problem]

[0007] The present invention comprises the following configurations. (1) A method for controlling a shape of a weld bead in manufacturing an additive manufacturing object by repeatedly stacking weld beads formed by periodically repeating a forward feed period and a reverse feed period of a welding wire as one cycle and providing an arc period in which an arc is generated at a tip of a torch and a short circuit period during the one cycle, the method comprising the steps of: While keeping the average feed speed of the welding wire constant, a peak current value at which the welding current rises from a base current and a short circuit time, which is the length of the short circuit period within one cycle, are associated with characteristic information, and based on the characteristic information, the short circuit time and the peak current value are detected and controlled for each cycle of feeding of the welding wire so that the short circuit time falls within a target range determined by the characteristic information. (2) A power supply control method for controlling a welding power supply based on the weld bead shape control method described in (1). (3) An additive manufacturing method for manufacturing an additive manufactured object by stacking the weld beads formed based on the method for controlling a weld bead shape described in (1). (4) A control device that controls the welding current based on the method for controlling a weld bead shape described in (1). (5) A welding power source equipped with the control device described in (4). (6) A welding system equipped with the welding power source described in (5). (7) An additive manufacturing system comprising the welding system according to (6) and configured to stack the weld beads to form an additive manufacturing object. (8) A program for realizing a function of controlling a shape of a weld bead when manufacturing an additive manufacturing object by repeatedly stacking weld beads formed by periodically repeating a forward feed period and a reverse feed period of a welding wire as one cycle and providing an arc period in which an arc is generated at a tip of a torch and a short circuit period during the one cycle, the program comprising: On the computer, While keeping the average feed speed of the welding wire constant, A program that realizes a function of detecting the short circuit time and controlling the peak current value for each cycle of feeding of the welding wire, based on characteristic information correlating the peak current value at which the welding current rises from the base current with the short circuit time, which is the length of the short circuit period within one cycle, so that the short circuit time falls within a target range determined by the characteristic information. Effect of the Invention

[0008] According to the present invention, even when welding is performed by repeatedly feeding and pulling back the welding wire, the shape of the weld bead can be made constant in real time without changing the average feeding speed of the welding wire and regardless of the tip-to-base metal distance. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram showing the overall configuration of an additive manufacturing system. [Diagram 2] FIG. 2 is a block diagram showing a schematic configuration of a power supply control unit in the welding power supply unit. [Diagram 3] FIG. 3 is a timing chart of the welding current, wire feed speed, and welding voltage controlled by the power supply control unit. [Figure 4] FIG. 4 is a graph showing waveforms of the welding current and welding voltage illustrating the first control example. [Diagram 5] FIG. 5 is a flowchart showing a procedure for adjusting the peak current in accordance with the short-circuit duration and the welding voltage. [Figure 6] FIG. 6 is a graph showing waveforms of the welding current and welding voltage illustrating the second control example. [Figure 7] FIG. 7 is a flowchart showing a procedure for setting the peak current depending on the presence or absence of a short circuit. [Figure 8] FIG. 8 is a graph showing waveforms of the welding current, welding voltage, and wire feed speed illustrating the third control example. [Figure 9] FIG. 9 is a flowchart showing a procedure for controlling the welding current and the wire feed speed depending on the presence or absence of a short circuit. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. <Welding equipment configuration> Here, a welding system used for forming an additively shaped object is described. The welding system described here is used when manufacturing an additively shaped object having a three-dimensional shape by stacking weld beads, and the welding system cyclically repeats a period of forward feed and a period of reverse feed of the welding wire as one cycle, and forms a weld bead by providing an arc period during which an arc is generated at the tip of the torch and a short circuit period during one cycle. The welding system controls the shape of the weld bead when manufacturing an additively shaped object by repeatedly stacking such weld beads. The configuration of the welding system described below is one example, and is not limited to this.

[0011] FIG. 1 is a schematic diagram showing the overall configuration of an additive manufacturing system 100. An additive manufacturing system 100 as an example of a welding system includes a manipulator 11, a manipulator control unit 13, a wire supply unit 15, a welding power supply unit 17, and a control device 19.

[0012] The manipulator 11 is, for example, an articulated robot, and a torch 21 provided on a tip shaft is supported so that a welding wire M can be continuously supplied. The torch 21 holds the welding wire M protruding from the tip. The position and posture of the torch 21 can be set arbitrarily in three dimensions within the range of the degrees of freedom of the robot arm constituting the manipulator 11. The manipulator 11 is preferably one having six or more degrees of freedom, and is preferably one in which the position of the heat source at the tip of the torch can be arbitrarily changed in the torch axial direction. The manipulator 11 may be in various forms, such as a four-or-more-axis articulated robot as shown in FIG. 1, or a robot equipped with angle adjustment mechanisms for two or more orthogonal axes.

[0013] The torch 21 has a shield nozzle (not shown), and a shielding gas is supplied from the shielding nozzle. The shielding gas blocks the atmosphere and prevents oxidation and nitridation of the molten metal during welding, thereby suppressing welding defects. The arc welding method used in this configuration may be either a consumable electrode type such as a shielded metal arc welding or a carbon dioxide gas arc welding, or a non-consumable electrode type such as a TIG (Tungsten Inert Gas) welding or a plasma arc welding, and is appropriately selected depending on the additive manufacturing body to be manufactured. Here, gas metal arc welding is taken as an example for explanation. In the case of a consumable electrode type, a contact tip is disposed inside the shield nozzle, and a welding wire M to which a current is supplied is held by the contact tip. The torch 21 generates an arc from the tip of the welding wire M in a shielding gas atmosphere while holding the welding wire M.

[0014] The manipulator control unit 13 mainly controls the operation of the manipulator 11. The manipulator control unit 13 holds teaching data that predetermines the operation pattern, welding start position, welding end position, welding conditions, weaving operation, etc. of the manipulator 11, and controls the operation of the manipulator 11 by instructing the manipulator 11 on these. The manipulator control unit 13 also provides information on welding conditions such as welding current, welding voltage, and feed speed during welding work to the welding power source unit 17 in accordance with the teaching data. A controller (not shown) is connected to the manipulator control unit 13, and an operator can instruct any operation to the manipulator control unit 13 via the controller.

[0015] The wire supply unit 15 supplies the welding wire M toward the torch 21. The wire supply unit 15 includes a reel 15a around which the welding wire M is wound, and a payout mechanism 15b that pays out the welding wire M from the reel 15a. The payout mechanism 15b includes a feed motor and the like that serves as a power for paying out the welding wire M. The welding wire M is fed to the torch 21 while being fed in the forward or reverse direction by the payout mechanism 15b as necessary. That is, at the tip of the torch 21, the welding wire M is fed in the forward or reverse direction, so that the tip position of the welding wire M is changed. The payout mechanism 15b is not limited to a push type that is arranged on the wire supply unit 15 side and pushes out the welding wire M, but may be a pull type or a push-pull type that is arranged on a robot arm or the like.

[0016] The welding power supply unit 17 includes a power supply and a power supply control unit that supplies power required for welding by the manipulator 11. The welding power supply unit 17 adjusts the welding current and welding voltage supplied when forming a bead by melting and solidifying the welding wire M. In addition, the feeding speed of the welding wire M by the wire supply unit 15 is adjusted in conjunction with the welding conditions, such as the welding current and welding voltage, set by the welding power supply unit 17.

[0017] The heat source for melting the welding wire M is not limited to the above-mentioned arc. For example, other types of heat sources may be used, such as a heating method using both an arc and a laser, a heating method using plasma, or a heating method using an electron beam or a laser. When heating with an electron beam or a laser, the amount of heat can be controlled more precisely, and the state of the bead to be formed can be more appropriately maintained, which contributes to further improving the quality of the laminated structure. The material of the welding wire M is also not particularly limited, and the type of welding wire M used may be different depending on the characteristics of the laminated object, such as mild steel, high-tensile steel, aluminum, aluminum alloy, nickel, or nickel-based alloy.

[0018] The additive manufacturing system 100 configured as described above operates according to a modeling program created based on a modeling plan for an additive manufacturing object. The modeling program is composed of a large number of command codes, and is created based on an appropriate algorithm according to various conditions such as the shape, material, and heat input of the object. When the supplied welding wire M is melted and solidified while moving the torch 21 according to this modeling program, a linear weld bead B, which is a molten solidified body of the welding wire M, is formed on the base 23. That is, the manipulator control unit 13 drives each unit such as the manipulator 11, the wire supply unit 15, and the welding power supply unit 17 based on a predetermined modeling program provided by the control device 19. The manipulator 11 moves the torch 21 while melting the welding wire M with an arc, according to a command from the manipulator control unit 13, to form a weld bead B. By sequentially forming and stacking the weld beads B in this manner, an additive manufacturing object (workpiece W) having a desired shape is obtained.

[0019] <Functional configuration of welding power source> Next, the functional configuration of welding power supply unit 17 will be described in detail. FIG. 2 is a block diagram showing a schematic configuration of a power supply control section in welding power supply section 17. As shown in FIG. The power supply control section of welding power supply section 17 is implemented, for example, through execution of a program by control device 19 or a computer (not shown). The power supply control unit of the welding power supply unit 17 includes a current setting unit 31. In addition to a function of setting various current values ​​that define the welding current flowing through the welding wire M, the current setting unit 31 in this embodiment has a function of setting a time t1 at which a period during which the current value of the welding current is suppressed by a current suppression period setting unit 31a and a time t2 at which the period ends, a function of detecting a short circuit period by a short circuit period detection unit 31b, and a function of setting a target value of the peak current by a peak current target value setting unit 31c.

[0020] FIG. 3 is a timing chart of the welding current, wire feed speed, and welding voltage controlled by the power supply control unit. In this embodiment, the welding current exhibits a pulse waveform that alternates between welding current in a current non-suppression period and a current suppression period. Current setting unit 31 sets a set current value Ip (hereinafter also referred to as "peak current Ip") for the current non-suppression period and a set current value Ib (hereinafter also referred to as "base current Ib") for the current suppression period. Peak current Ip is set to a waveform that rises from base current Ib and is larger than base current Ib. Current setting unit 31 basically controls the welding current at two values, peak current Ip and base current Ib, based on information on the wire tip position (welding wire feed speed signal).

[0021] The main power supply circuit of welding power supply unit 17 shown in FIG. 2 is composed of a three-phase AC power supply (hereinafter also referred to as the "AC power supply") MC1, a primary side rectifier MC2, a smoothing capacitor MC3, a switching element MC4, a transformer MC5, a secondary side rectifier MC6, and a reactor MC7.

[0022] The AC power input from the AC power source MC1 is full-wave rectified by the primary rectifier MC2, and then smoothed by the smoothing capacitor MC3 to be converted into DC power. Next, the DC power is converted into high-frequency AC power by inverter control using the switching element MC4, and then converted into secondary power via the transformer MC5. The AC output of the transformer MC5 is full-wave rectified by the secondary rectifier MC6, and then smoothed by the reactor MC7. The output current of the reactor MC7 is provided to the welding tip of the torch 21 as an output from the main power supply circuit, and is passed through the welding wire M as a consumable electrode.

[0023] The welding wire M is fed by a feed motor of the feeding mechanism 15b, and an arc 33 is generated between the workpiece (also called base material) W and the feeding mechanism 15b. In this embodiment, the feeding mechanism 15b feeds the welding wire M so that a forward feed period TP (FIG. 2) in which the tip of the welding wire M moves toward the base material W and a reverse feed period TN (FIG. 2) in which the tip of the welding wire M moves in a direction opposite to the direction in which the base material W is located are periodically switched when the forward feed period TP and the reverse feed period TN are one cycle. Hereinafter, the movement of the tip of the welding wire M toward the base material W is also referred to as "forward feed" or "feed out", and the opposite direction is also referred to as "reverse feed" or "pull back". In addition, the "tip of the welding wire" here usually refers to the tip of the wire when the presence of droplets hanging down from the tip of the welding wire M is ignored. In other words, the welding wire M melted by the arc 33 is considered to have been immediately transferred to the base material W.

[0024] The feeding of the welding wire M by the payout mechanism 15b is controlled by a control signal Fc from the feed drive unit 35. The average value of the feeding speed of the welding wire M (average feeding speed) is approximately the same as the melting speed of the welding wire M, and is kept constant in this embodiment.

[0025] A voltage setting signal Vr, which is a target value of the voltage to be applied between the welding tip of the torch 21 and the base metal W, is provided to the current setting unit 31 from the voltage setting unit 37. The voltage setting signal Vr here is also provided to a voltage comparison unit 39, where it is compared with a voltage detection signal Vo detected by a voltage detection unit 41. The voltage detection signal Vo is an actual measurement value. The voltage comparison unit 39 amplifies the difference between the voltage setting signal Vr and the voltage detection signal Vo, and outputs it to the current setting unit 31 as a voltage error amplified signal Va.

[0026] The current setting unit 31 resets the value of the peak current Ip, the value of the base current Ib, the period for which the peak current Ip is provided, or the magnitude of the value of the peak current Ip and the value of the base current Ib based on the voltage setting signal Vr and the voltage error amplification signal Va, and outputs a current setting signal of a current target value Ir according to the reset period or the magnitude of the reset value to the current error amplification unit 43.

[0027] The current error amplifier 43 amplifies the difference between the current setting signal given as the current target value Ir and the current detection signal Io detected by the current detector 45, and outputs it as a current error amplified signal Ed to the inverter driver 47. The inverter driver 47 corrects the drive signal Ec of the switching element MC4 using the current error amplified signal Ed.

[0028] A short circuit detection signal Drl, which is a signal indicating that a short circuit in the welding current has been detected, is also input to the current setting unit 31. The short circuit detection signal Drl is output from a short circuit detection unit 49. The short circuit detection unit 49 monitors a change in the voltage detection signal Vo output by the voltage detection unit 41, and detects a short circuit in the welding current from the change.

[0029] The short circuit detector 49 detects a short circuit by, for example, comparing the value of the voltage detection signal Vo with a detection threshold value that is stored in advance in a storage unit (not shown).

[0030] An average feed speed Fave of the welding wire M to be fed is also provided to the current setting unit 31. The average feed speed Fave is output by the average feed speed setting unit 51 based on teaching data stored in a storage unit (not shown). Based on the provided average feed speed Fave, the current setting unit 31 determines various parameters such as the current values ​​of the peak current Ip and the base current Ib, the time t1 at which the supply of the peak current Ip starts, and the time t2 at which the supply of the base current Ib ends.

[0031] The average feed speed Fave is given to the amplitude feed speed setting unit 53. The amplitude feed speed setting unit 53 here determines the values ​​of the amplitude Wf ​​and the period Tf based on the input average feed speed Fave. The amplitude feed refers to a feeding method in which a forward feed period, which is a period in which the feed speed is higher than the average feed speed Fave, and a reverse feed period, which is a period in which the feed speed is lower than the average feed speed Fave, alternately appear. The period in which the feed speed is lower than the average feed speed Fave refers to a period less than the average feed speed Fave, and includes a negative feed speed, that is, a speed at which the wire tip moves in the opposite direction to the position where the base material W is located. The amplitude Wf ​​gives the change width for the average feed speed Fave, and the period Tf gives the time of the amplitude change, which is a repetition unit. The amplitude feed speed setting unit 53 generates an amplitude feed speed Ff according to the determined amplitude Wf ​​and period Tf or frequency f, and outputs it to the feed speed setting unit 55.

[0032] The feed speed setting unit 55 outputs a feed speed target value signal Fr based on the amplitude feed speed Ff and the average feed speed Fave. In this embodiment, the feed speed target value signal Fr is expressed by the following equation. Fr = Ff + Fave (1)

[0033] The feed speed target value signal Fr is output to a phase shift detection unit 57 , a feed error amplification unit 59 , and a current setting unit 31 . The feed error amplifier 59 amplifies the difference between the feed speed target value signal Fr, which is information on the target speed, and the feed speed detection signal Fo, which is the actual measurement of the feed speed of the welding wire M by the payout mechanism 15b, and outputs a speed error amplified signal Fd, which has been corrected for the error, to the feed drive unit 35. The feed drive unit 35 generates a control signal Fc based on the speed error amplified signal Fd and provides the control signal Fc to the feed mechanism 15b. The feed speed conversion unit 61 here converts the amount of rotation of the drive motor of the feed mechanism 15b, etc., into a feed speed detection signal Fo of the welding wire M. The phase shift detector 57 in this embodiment compares the feed speed target value signal Fr with the feed speed detection signal Fo, which is a measured value, and outputs the phase shift time Tθd. The phase shift detector 57 may obtain the phase shift time Tθd by measuring the feed operation of the payout mechanism 15b when parameters that define the amplitude feed, such as the period Tf and the amplitude Wf, are varied.

[0034] The phase shift time Tθd is provided to the current setting unit 31. Based on the feed speed target value signal Fr and the phase shift time Tθd, the current setting unit 31 corrects an error in the feed amount of the welding wire M. The above are the basic functions of the power supply control unit.

[0035] <Welding current control> Next, the control of the welding current using the above-mentioned power supply control unit will be described. As shown in Fig. 3, in this embodiment, the welding wire is fed to the torch tip at a sinusoidal feed / retract speed centered on the average feed speed Fave, and the welding current is changed in accordance with the feeding operation of the welding wire. Here, the arc length, which is the key to reducing heat input, can be controlled by the amount of retraction of the welding wire M and the timing of outputting the peak current Ip. This control is performed based on speed control rather than position control of the welding wire M. The feed and retract amounts of the welding wire M are found by integrating the feeding speed of the welding wire with respect to time.

[0036] In the basic control example shown here, the welding current is increased when the welding wire M starts to be fed from the top end position P1 of the feeding amplitude, and is reduced at the maximum speed reaching point (wire midpoint P2) to prepare for a short circuit. Then, a short circuit occurs when the wire approaches the lowest point P3, and after passing the lowest point P3 and the welding wire starts to be pulled back, the short circuit is released and the arc is re-ignited. It is preferable that the timing to increase the welding current is determined from the command value of the wire feeding speed, and the maximum speed reaching point is determined from the detected value of the wire feeding speed, but this is not limited to this. The wire feeding speed may be measured by a known means, such as using an encoder that detects the rotation of the motor of the payout mechanism 15b.

[0037] In this process, the welding wire M has a constant average feed speed Fave, and operates at the set forward / reverse frequency and amplitude of wire feed. Therefore, the peak value of the welding current becomes the control manipulated variable. Specifically, the average welding voltage during arcing and the short circuit time are fed back, and the peak current Ip is controlled (e.g., PI control) using the deviation from the target values ​​so that the arc length is within a predetermined range. By using this control method, welding can be stably performed with a welding wire feed speed of about 3 mpm or more. However, if the feed speed falls below 3 mpm, it becomes difficult to maintain the melting balance of the welding wire, and long periods of non-short circuit or short circuit states occur frequently, making it difficult to form a stable bead.

[0038] Therefore, in this control method, a specific process is added to ensure that the specified short circuit period is obtained, and if the short circuit period is inappropriate, a short circuit is generated for a necessary and sufficient period or a short circuit is forcibly generated, thereby making it possible to form a stable bead shape even with a welding wire feed speed of 1 mpm. Note that in each control example described below, the average wire feed speed (value per unit time or per unit cycle) is set constant as a premise. Therefore, according to this control method, the bead shape is stable, and additive manufacturing objects with high shape accuracy can be stably manufactured in real time.

[0039] <First control example> FIG. 4 is a graph showing waveforms of the welding current and welding voltage illustrating the first control example. In the first control example, the length of the short circuit period (short circuit time) is measured, and the obtained short circuit time is compared with a predetermined short circuit target time. If the short circuit time is too larger or too smaller than the short circuit target time, the welding current is adjusted so that the short circuit time becomes the short circuit target time. The short circuit target time does not have to be a single point, and may be set to a specific time range. When a specific time range is set, the welding current is adjusted so that the short circuit time falls within that specific time range. In this control example, the average welding wire feed speed Fave is set to 1.5 mpm.

[0040] As shown in Figure 3, when the welding current is reduced from the peak current Ip to the base current Ib during the forward feed period TP of the welding wire, the tip of the forward-feeding welding wire shorts out to the base metal, causing a sudden drop in the welding voltage. Then, when the tip of the welding wire leaves the base metal during the reverse feed period TN of the welding wire and enters the arc period, the welding voltage increases again. This period of decrease in the welding voltage corresponds to the short-circuit period St. The short-circuit period St can be identified from the waveform of the welding voltage.

[0041] Specifically, voltage detection unit 41 shown in Fig. 2 detects the voltage waveform (voltage detection signal Vo) of the welding voltage, and short circuit detection unit 49 detects the short circuit period St from the voltage detection signal Vo of the welding voltage shown in Fig. 4 and outputs short circuit detection signal Dril to current setting unit 31. Short circuit detection unit 49 compares, for example, the voltage value of voltage detection signal Vo with a predetermined short circuit discrimination voltage Vth, and determines a period in which voltage detection signal Vo exceeds short circuit discrimination voltage Vth (Vo>Vth) to be an arc period, and determines a period in which the voltage signal is equal to or lower than the short circuit discrimination voltage Vth (Vo≦Vth) to be a short circuit period. This makes it possible to accurately detect the short circuit period.

[0042] The short circuit detection unit 49 outputs this determination result as a short circuit detection signal Drl to the current setting unit 31. The short circuit duration detection unit 31b of the current setting unit 31 detects the time length of the short circuit period St, that is, the short circuit duration Δt(i) (i is an integer), based on the input short circuit detection signal Drl and voltage detection signal Vo, and outputs the short circuit duration Δt(i) to the peak current target value setting unit 31c.

[0043] The peak current target value setting unit 31c adjusts the current target value Ir(i+1) of the peak current Ip(i+1) in the forward transmission period TP in the next cycle Tf (Figure 3) using the correction value ΔI as shown in equation (2) in accordance with the obtained short circuit time Δt(i). Ir(i+1)=Ip(i)+ΔI...Equation (2)

[0044] For example, if it is determined that the short circuit time Δt(1) is shorter than the short circuit target time range, the current target value Ir(2) of the peak current Ip(2) in the next period is corrected by adding a negative correction value ΔI to the peak current Ip(1). Similarly, in the next short circuit period St, the short circuit time Δt(2) is detected, and if it is determined that the short circuit time Δt(2) is longer than the short circuit target time range, the current target value Ir(3) of the peak current Ip(3) in the next period is corrected by adding a positive correction value ΔI to the peak current Ip(2). Each correction value ΔI is set according to the length of the short circuit time. In this way, for each short circuit period St, the peak current Ip(i+1) in the next period Tf is adjusted according to the respective short circuit times Δt(i), so that the short circuit period St is always within the short circuit target time range.

[0045] The correction value ΔI is set based on characteristic information relating the peak current value and the short circuit time. This characteristic information may be a predetermined calculation formula or a table value obtained experimentally or analytically, and is stored in a storage unit (not shown) as a database.

[0046] Peak current target value setting unit 31c may set a target value of peak current Ip according to the short circuit duration and the welding voltage. 5 is a flowchart showing a procedure for adjusting the peak current Ip in accordance with the short circuit duration and the welding voltage. In this case, a voltage target value Vref(i) and a short circuit duration target value st_ref in each short circuit period St are set in advance.

[0047] First, as shown in equation (3), the difference between the target voltage value Vref(i) and the voltage value of the voltage detection signal Vo is calculated as the voltage error ev(i) (step S11, hereinafter referred to as S11). ev(i)=Vref(i)-Vo(i)...Equation (3)

[0048] Moreover, as shown in the formula (4), the difference between the short circuit duration target value st_ref(i) and the short circuit duration detection value st(i) is obtained as the short circuit duration error e_st(i) (S12). e_st(i)=st_ref-st(i)...Equation (4)

[0049] Next, the current target value Ir(i+1) of the peak current in the next cycle Tf is calculated by using the determined voltage error ev(i) and short circuit time error e_st(i) according to equation (5) (S13). Ir(i+1)=Io(i)+Kvp×ev(i)-Kstp×e_st(i)...Equation (5) where Kvp is the voltage error gain and Kstp is the time error gain.

[0050] The peak current target value Ir(i+1) obtained by equation (5) is output to the current error amplifier 43 (S14). This changes the current value of the peak current Ip to the current target value Ir. As a result, the short circuit time is set more appropriately, and the effect of keeping the arc length constant is improved.

[0051] As described above, in this control, while the average welding wire feed speed is kept fixed during welding bead building, the short circuit time is detected and an adjustment amount is added to the peak current value for each welding wire feed cycle based on the relationship between the peak current value of the welding current and the short circuit time so that the short circuit time falls within a target range. Such adjustment of the welding current is performed by real-time feedback (FB) control. Therefore, by performing real-time FB control for each pulse in the current waveform (or for each cycle Tf of forward and reverse wire feed), the welding wire melting cycle can be stabilized even under low heat input conditions such as a welding wire feed speed of 1 mpm to 3 mpm.

[0052] <Second control example> In the cycle of melting, welding, and detachment of the welding wire, there are cases where the wire tip is not short-circuited even when it is fed to the bottom of the amplitude feed. This is because the tip-to-base metal distance is longer than expected due to a reduction in the amount of welding wire fed by an external force, etc. In this control, therefore, the welding wire is detected as being short-circuited or not short-circuited in accordance with the forward and reverse feed cycles, and if no short circuit occurs during the reverse feed period TN, the welding current is suppressed so that the welding current in the next cycle Tf is not passed at the peak current Ip. This prevents the formation of droplets on the welding wire, and as a result, the generation of spatter is suppressed. This suppression of the peak current Ip is performed for each cycle Tf of the welding wire feed as real-time FB control.

[0053] Fig. 6 is a graph showing waveforms of the welding current and welding voltage showing control example 2. Fig. 7 is a flowchart showing a procedure for setting the peak current Ip depending on the presence or absence of a short circuit. In the second control example, short circuit detection unit 49 shown in Fig. 2 detects the presence or absence of a short circuit from a voltage detection signal Vo of the welding voltage for each cycle Tf of the feeding of the welding wire. As in the first control example, the presence or absence of a short circuit is determined from the waveform of the welding voltage (voltage detection signal Vo), and the result is output to current setting unit 31 as a short circuit detection signal Drl (S21). If the input short circuit detection signal Drl indicates the presence of a short circuit (St(i)>0), current setting unit 31 sets a current target value Ir that generates a peak current Ip in the welding current in the next cycle Tf (S22). On the other hand, if there is no short circuit, the current setting unit 31 sets a current target value Ir that maintains the base current Ib without generating a peak current Ip in the next cycle Tf (S23).

[0054] According to this control example, if no short circuit occurs within one cycle Tf, in the next cycle Tf, the peak current Ip is not generated during the forward feed period TP of the welding wire, and the application of the peak current Ip is temporarily suppressed to maintain the base current Ib. This makes it possible to prevent the scattering of droplets from the wire tip, which would occur if a peak current were generated in the next cycle Tf. As a result, it is possible to suppress the generation of spatter and changes in the shape of the weld bead. In this control example, it is preferable to adjust the peak current Ip of the next cycle Tf according to the short circuit time, as in the first control example.

[0055] <Third control example> Fig. 8 is a graph showing waveforms of the welding current, welding voltage, and wire feed speed showing control example 3. Fig. 9 is a flowchart showing a procedure for controlling the welding current and wire feed speed depending on the presence or absence of a short circuit.

[0056] As described above, in the cycle of melting, welding, and detachment of the welding wire, even if the tip of the wire is fed to the lowest end of the amplitude feed, a short circuit does not occur, and the tip-to-base metal distance may be longer than expected. Therefore, in this control, if a short circuit does not occur within the cycle Tf of forward and reverse feeding of the welding wire, the welding wire is not fed in the reverse direction, and the welding wire continues to be fed in the forward direction until a short circuit occurs. In this way, the tip of the welding wire is brought closer to the base metal, forcing a short circuit to occur. This promotes the continuous formation of a weld bead.

[0057] Time ta0 in the welding voltage waveform shown in Figure 8 is when the wire tip reaches the average feed speed Fave, which is immediately before the lowest point of amplitude feed, and indicates that a short circuit has occurred in the welding voltage. However, at time ta when the average feed speed Fave is reached when transitioning from the forward feed period TP to the reverse feed period TN of the next cycle Tf, the welding voltage remains in a non-short-circuited state. In this case, this control does not pull back the welding wire, but continues to feed the welding wire forward at the average feed speed Fave. Then, at time tb when the short circuit occurs, pulling back the welding wire begins.

[0058] Specifically, similarly to the second control example, short circuit detection unit 49 shown in Fig. 2 detects the presence or absence of a short circuit from the voltage detection signal Vo of the welding voltage for each welding wire feed cycle Tf (S31). The presence or absence of a short circuit here is determined by comparing the waveform of the welding voltage (voltage detection signal Vo) with the short circuit discrimination voltage Vth, similarly to the first control example.

[0059] In addition, the current setting unit 31 detects the time ta at which the average feed speed Fave is reached when the forward feed period TP transitions to the reverse feed period TN. If a short circuit occurs when the current setting unit 31 detects the time ta, the cycle returns to the normal cycle, and the welding current for the next period Tf is set to the peak current Ip described above (S32). On the other hand, if no short circuit occurs, the welding current for the current period Tf remains at the base current Ib (S33), and the feed speed setting unit 55 stops amplitude feed (Ff=0), and outputs a control signal to feed the welding wire in the forward direction at the average feed speed Fave (S34). Then, the feed speed setting unit 55 outputs a feed speed target value signal Fr (Fr=Fave) that sets the average feed speed Fave as the target speed, and sets the feed speed of the welding wire M by the payout mechanism 15b to the average feed speed Fave.

[0060] Then, the welding wire M continues to be fed in the forward direction at the average feed speed Fave (period Tfd). If the short circuit detection unit 49 detects a short circuit in this state (S35), the current setting unit 31 outputs a feed speed target value signal Fr that restarts amplitude feed and causes the feed speed setting unit 55 to start reverse feed (S36). This returns the welding wire M to a normal cycle, and in S32 the welding current for the next cycle Tf is set to the peak current Ip described above.

[0061] In the above-mentioned feeding period Tfd during which the welding wire is fed in the forward direction from time ta to time tb, the feeding speed is set to a preset average feeding speed Fave from the viewpoint of keeping the welding speed constant. This prevents the average feeding speed Fave from fluctuating throughout the entire process, and makes it easier to maintain a constant shape of the weld bead.

[0062] The above-mentioned feeding speed of the welding wire may be controlled, for example, by switching the torque value generated by the feeding motor of the payout mechanism 15b. In this control example, it is preferable to adjust the peak current Ip of the next cycle Tf in accordance with the short circuit time, as in the first control example.

[0063] As such, the present invention is not limited to the above-described embodiments, and the present invention also contemplates mutual combinations of the various components of the embodiments, as well as modifications and applications by those skilled in the art based on the descriptions in the specification and well-known techniques, and these are included in the scope of the protection sought. Although each of the above control examples is mainly implemented by a power supply control unit of welding power supply unit 17, each control example may be implemented by control device 19, or may be controlled from another computer via a line such as a network. Also, welding power supply unit 17 may be configured as a welding power supply including control device 19.

[0064] As described above, the present specification discloses the following: (1) A method for controlling a shape of a weld bead in manufacturing an additive manufacturing object by repeatedly stacking weld beads formed by periodically repeating a forward feed period and a reverse feed period of a welding wire as one cycle and providing an arc period in which an arc is generated at a tip of a torch and a short circuit period during the one cycle, the method comprising the steps of: While keeping the average feed speed of the welding wire constant, a peak current value at which the welding current rises from a base current and a short circuit time, which is the length of the short circuit period within one cycle, are associated with characteristic information, and based on the characteristic information, the short circuit time and the peak current value are detected and controlled for each cycle of feeding of the welding wire so that the short circuit time falls within a target range determined by the characteristic information. According to this method for controlling the shape of a weld bead, by providing a short circuit period of an appropriate length, a weld bead can be stably formed in real time.

[0065] (2) The method for controlling a weld bead shape described in (1), wherein the adjustment of the peak current value is performed by decreasing the peak current value when the short circuit time is smaller than the target range, and by increasing the peak current value when the short circuit time is greater than the target range. According to this method for controlling the shape of a weld bead, the cycle of melting, deposition, and detachment of the welding wire can be stabilized by precisely adjusting the short circuit time.

[0066] (3) The method for controlling a weld bead shape according to (1) or (2), wherein the short circuit time is a period during which the welding voltage is equal to or lower than a predetermined short circuit determination voltage. According to this method for controlling the weld bead shape, the short circuit period can be accurately detected in accordance with the short circuit determination voltage.

[0067] (4) determining an average value of the welding voltage during a period in which current is applied at the peak current value; The method for controlling a weld bead shape according to (3), wherein the target value of the peak current value is determined in accordance with the short circuit time and an average value of the welding voltage. According to this method for controlling the weld bead shape, it becomes possible to more appropriately adjust the short circuit time.

[0068] (5) The method for controlling a weld bead shape according to any one of (1) to (4), further comprising temporarily suppressing passage of current at the peak current value when there is no transition to a short circuit period after an arc period within one cycle of feeding of the welding wire. According to this method for controlling the weld bead shape, scattering of droplets from the wire tip can be prevented, and the occurrence of spatter and changes in the shape of the weld bead can be suppressed.

[0069] (6) The method for controlling a weld bead shape described in (5), wherein, after current is passed at the peak current value during the forward feed period of one cycle, if there is no transition from the arc period to the short circuit period within the one cycle, current is not passed at the peak current value during the next cycle following the one cycle, and a base current lower than the peak current value is maintained. According to this method of controlling the weld bead shape, scattering of droplets from the wire tip, which occurs when a peak current is generated in the next cycle Tf, can be prevented, and the occurrence of spatter and changes in the shape of the weld bead can be suppressed.

[0070] (7) A method for controlling a weld bead shape according to any one of (1) to (4), wherein, when the welding wire feed speed is reduced to reach the average feed speed and a transition from an arc period to a short circuit period has not occurred, the welding wire is fed while maintaining the welding wire feed speed at the average feed speed until a transition occurs to the short circuit period. According to this method for controlling the shape of a weld bead, the tip of the welding wire is brought close to the base metal to forcibly cause a short circuit, thereby promoting the continuous formation of a weld bead.

[0071] (8) A power supply control method for controlling a welding power supply based on the method for controlling a weld bead shape according to any one of (1) to (7). According to this power supply control method, the shape of the weld bead is stabilized by power supply control, and good welding can be performed.

[0072] (9) An additive manufacturing method for manufacturing an additive manufactured object by stacking the weld beads formed based on the method for controlling a weld bead shape according to any one of (1) to (7). According to this additive manufacturing method, the bead shape is stable, so that an additive manufactured object having a highly accurate laminated shape can be manufactured.

[0073] (10) A control device that controls the welding current based on the method for controlling a weld bead shape according to any one of (1) to (7). This control device allows stable formation of a weld bead by controlling the welding current.

[0074] (11) A welding power source equipped with the control device described in (10). According to this welding power source, the welding power source itself controls each part, such as adjusting the short circuit period, so that a good weld bead with high shape accuracy can be easily formed.

[0075] (12) A welding system comprising the welding power source described in (11). This welding system allows welding to be performed with high shape accuracy.

[0076] (13) An additive manufacturing system comprising the welding system according to (12) and configured to stack the weld beads to form an additive manufacturing object. This additive manufacturing system can manufacture additively manufactured objects with high shape accuracy.

[0077] (14) A program for realizing a function of controlling a shape of a weld bead when manufacturing an additive manufacturing object by repeatedly stacking weld beads formed by periodically repeating a forward feed period and a reverse feed period of a welding wire as one cycle and providing an arc period in which an arc is generated at a tip of a torch and a short circuit period during the one cycle, the program comprising: On the computer, While keeping the average feed speed of the welding wire constant, A program that realizes a function of detecting the short circuit time and controlling the peak current value for each cycle of feeding of the welding wire, based on characteristic information correlating the peak current value at which the welding current rises from the base current with the short circuit time, which is the length of the short circuit period within one cycle, so that the short circuit time falls within a target range determined by the characteristic information. According to this program, by setting an appropriate short circuit period, a weld bead can be formed stably in real time. [Explanation of symbols]

[0078] 11 Manipulator 13 Manipulator control section 15 Wire supply unit 15a Reel 15b Payout mechanism 17 Welding power supply unit 19 Control device 21 Torch 23 Base 31 Current setting section 31a Current suppression period setting section 31b Short circuit time detection section 31c Peak current target value setting unit 33 Arc 35 Feeding drive unit 37 Voltage setting section 39 Voltage comparison section 41 Voltage detection section 43 Current error amplifier 45 Current detection section 47 Inverter drive unit 49 Short circuit detection section 51 Average feed speed setting section 53 Amplitude feed speed setting section 55 Feed speed setting section 57 Phase shift detector 59 Feed error amplifier 61 Feeding speed conversion unit 100 Additive Manufacturing System B Weld bead Drl Short circuit detection signal Ec drive signal Ed Current error amplified signal f frequency Fave Average feed speed Fc control signal Fd Speed ​​error amplification signal Ff Amplitude feeding speed Fr Feed speed target value signal Fo Feed speed detection signal Ib Base current Ip Peak current Io Current detection signal Ir Current setting signal M welding wire MC1 Three-phase AC power supply (AC power supply) MC2 primary rectifier MC3 smoothing capacitor MC4 switching element MC5 transformer MC6 Secondary rectifier MC7 Reactor P1 Top position P2 Wire midpoint P3 Wire lowest point TP forwarding period TN reverse transfer period Tf period Tθd Phase shift time Tfd delivery period Va Voltage error amplified signal Vo voltage detection signal Vr Voltage setting signal W Work (Layered Modeling) Wf amplitude ΔI correction value

Claims

1. A method for controlling a weld bead shape in manufacturing an additive manufacturing object by repeatedly stacking weld beads formed by periodically repeating a forward feed period and a reverse feed period of a welding wire as one cycle and providing an arc period in which an arc is generated at a torch tip and a short circuit period during the one cycle, the method comprising: While keeping the average feed speed of the welding wire constant, a peak current value at which the welding current rises from a base current and a short circuit time, which is the length of the short circuit period within one cycle, are associated with characteristic information, and based on the characteristic information, the short circuit time and the peak current value are detected and controlled for each cycle of feeding of the welding wire so that the short circuit time falls within a target range determined by the characteristic information.

2. The adjustment of the peak current value is performed by decreasing the peak current value when the short circuit time is smaller than the target range, and by increasing the peak current value when the short circuit time is larger than the target range. The method for controlling a weld bead shape according to claim 1 .

3. The short circuit time is a period during which the welding voltage is equal to or lower than a predetermined short circuit determination voltage. The method for controlling a weld bead shape according to claim 1 .

4. An average value of the welding voltage during a period in which current is applied at the peak current value is obtained; determining a target value of the peak current value in accordance with the short circuit time and an average value of the welding voltage; The method for controlling a weld bead shape according to claim 3.

5. when the arc period does not transition to a short circuit period within one cycle of feeding of the welding wire, energization at the peak current value is temporarily suppressed. The method for controlling a weld bead shape according to claim 1 .

6. If, after current is passed at the peak current value during the forward transmission period of the one cycle, there is no transition from the arc period to the short circuit period within the one cycle, current is not passed at the peak current value during the next cycle following the one cycle, and a base current lower than the peak current value is maintained. The method for controlling a weld bead shape according to claim 5.

7. if the arc period has not yet transitioned to the short circuit period when the feed speed of the welding wire is reduced and reaches the average feed speed, the welding wire is fed out while maintaining the feed speed of the welding wire at the average feed speed until the short circuit period transitions to the short circuit period. The method for controlling a weld bead shape according to claim 1 .

8. A power supply control method for controlling a welding power supply based on the method for controlling a weld bead shape according to any one of claims 1 to 7.

9. 8. An additive manufacturing method for manufacturing an additive manufactured object by stacking the weld beads formed based on the method for controlling a weld bead shape according to any one of claims 1 to 7.

10. A control device that controls the welding current based on the method for controlling a weld bead shape according to any one of claims 1 to 7.

11. A welding power source comprising the control device according to claim 10.

12. A welding system comprising the welding power supply according to claim 11.

13. An additive manufacturing system comprising the welding system according to claim 12, which is configured to laminate the weld beads to form an additive manufactured object.

14. A program for controlling a weld bead shape when manufacturing an additive manufacturing object by repeatedly stacking weld beads formed by periodically repeating a forward feed period and a reverse feed period of a welding wire as one cycle and providing an arc period in which an arc is generated at a tip of a torch and a short circuit period during the one cycle, the program comprising: On the computer, While keeping the average feed speed of the welding wire constant, A program that realizes a function of detecting the short circuit time and controlling the peak current value for each cycle of feeding of the welding wire, based on characteristic information correlating the peak current value at which the welding current rises from the base current with the short circuit time, which is the length of the short circuit period within one cycle, so that the short circuit time falls within a target range determined by the characteristic information.

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