Method and program for correcting welding current waveform

Abstract

A method for correcting a welding current waveform disclosed herein comprises first to third steps. In the first step, a basic waveform of a welding current Aw is prepared. In the second step, the basic waveform is described by a function using, as variables, a current command value Is, a plate thickness D of a base material 200 that is an object to be welded, and time t. In the third step, the basic waveform is corrected by substituting an actual-use command value Is1 used to weld the base material 200 for the current command value Is in the function described in the second step S2, and substituting an actual-use plate thickness D1 used to weld the base material 200 for the plate thickness D in the function. The corrected basic waveform is acquired as a welding current waveform.

Description

Welding current waveform correction method and program

[0001] The present disclosure relates to a method for correcting a welding current waveform, and more particularly to a method and program for correcting a welding current waveform in AC arc welding.

[0002] Typically, a current command value for the welding current and the like are input to a welding power source to complete the setting of welding conditions, and then arc welding is performed (see, for example, Patent Document 1).

[0003] For example, a basic waveform stored in a memory unit provided in the welding power source is read out, and the current command value is adjusted according to the structure and thickness of the base material to be welded, before arc welding is performed.

[0004] Japanese Patent Application Laid-Open No. 60-064773

[0005] However, in actual arc welding, simply adjusting the current command value to change the welding conditions is sometimes insufficient. For example, when applying a basic waveform set for a medium-thickness base metal to a thin base metal, lowering the current command value reduces the heat input to the base metal. However, depending on the shape of the basic waveform, the heat input to the base metal may become too large, resulting in poor welding, such as burn-through.

[0006] The present disclosure has been made in consideration of these points, and its purpose is to provide a welding current waveform correction method and a welding current waveform correction program that can appropriately correct the welding current waveform in accordance with the plate thickness of the base material and the current command value.

[0007] In order to achieve the above object, a method of correcting a welding current waveform according to the present disclosure is a method of correcting a welding current waveform in AC arc welding, wherein a welding machine that performs AC arc welding has at least a welding output unit, a welding torch, and a control unit, and the control unit has at least a calculation unit and a storage unit, and the method includes a first step of preparing a basic waveform of a welding current, a second step of describing the basic waveform with a function having variables of a current command value, a thickness of a base metal that is an object to be welded, and time, and a second step of substituting an actual use command value used for welding the base metal as the current command value in the function, and substituting the actual use command value used for welding the base metal as the thickness in the function. and a third step of correcting the basic waveform by substituting an actual use plate thickness to be used in the welding process, thereby obtaining the welding current waveform, wherein the current command value is a moving average value of the welding current in a period of the basic waveform, the basic waveform is a waveform obtained by plotting current values ​​of the welding current against times discrete at predetermined time intervals when the current command value is the initial command value and the plate thickness is the initial plate thickness, and the welding current waveform is a waveform obtained by plotting current values ​​of the welding current against times discrete at the time intervals when the current command value is the actual use command value and the plate thickness is the actual use plate thickness.

[0008] The program according to the present disclosure causes one or more processors to execute the welding current waveform correction method.

[0009] According to the present disclosure, the welding current waveform can be appropriately corrected according to the thickness of the base metal and the current command value.

[0010] FIG. 1 is a schematic diagram of an arc welding machine according to a first embodiment. FIG. 2 is a flowchart showing a procedure for correcting a welding current waveform. FIG. 3 is a schematic diagram showing a basic waveform of a welding current. FIG. 4 is an enlarged view of a portion surrounded by a dashed line in FIG. 3. FIG. 5 is a schematic diagram showing a change in the rising portion of the basic waveform when the plate thickness is reduced. FIG. 6 is a schematic diagram showing a change in the rising portion of the basic waveform when the current command value is reduced. FIG. 7 is a flowchart showing a procedure for correcting a welding current waveform according to a second embodiment. FIG. 8 is a conceptual diagram for explaining a procedure for halving the period of the basic waveform. FIG. 9 is a conceptual diagram for explaining a procedure for doubling the period of the basic waveform.

[0011] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Note that the following description of the preferred embodiments is merely exemplary in nature and is not intended to limit the present disclosure, its applications, or its uses.

[0012] First Embodiment [Configuration of Arc Welding Machine] FIG. 1 shows a schematic configuration diagram of an arc welding machine according to a first embodiment. An arc welding machine 100 includes a welding power source 40 and a welding torch 60.

[0013] The welding power source 40 converts AC power supplied from the three-phase AC power source PS into AC power suitable for arc welding and outputs it to the electrode 70 held by the welding torch 60. In this embodiment, a welding current Aw is supplied from the welding power source 40 to the electrode 70. An arc ARC is generated between the tip of the electrode 70 to which the welding current Aw is supplied and the base material 200, thereby welding the base material 200. In other words, AC TIG welding is performed by the arc welder 100. The output of the welding power source 40 can be changed depending on the type of arc welding. For example, the output of the welding power source 40 may be a welding voltage Vw applied between the base material 200 and the electrode 70.

[0014] The welding power source 40 has at least a welding output unit 10, a welding output detection unit 20, a control unit 30, and an input unit 32, and the welding output unit 10 has a first rectification unit 11, a first switching unit 12, a transformer 13, a second rectification unit 14, a reactor (DCL) 15, and a second switching unit 16.

[0015] The first rectifier 11 is composed of rectifying elements such as diodes and rectifies AC power received from the three-phase AC power source PS. The first switching unit 12 is, for example, an inverter circuit composed of multiple transistors. The first switching unit 12 switches the multiple transistors at timings according to control commands from the control unit 30 to control the output of the first rectifier 11 to an output suitable for welding. The transformer 13 is, for example, a transformer having an iron core and converts the output of the first switching unit 12 to an output suitable for welding. The second rectifier 14 has a configuration similar to that of the first rectifier 11 and rectifies the output of the transformer 13. The reactor 15 is connected in series with the second rectifier 14 and smooths the output of the second rectifier 14. The second switching unit 16 has a configuration similar to that of the first switching unit 12. In other words, the second switching unit 16 is an inverter circuit composed of multiple transistors and switches the multiple transistors at timings according to control commands from the control unit 30 to adjust the output of the reactor 15.

[0016] In this embodiment, the output of second switching unit 16 is the aforementioned welding current Aw, which is supplied to electrode 70 held by welding torch 60 via power cable 51. When the output of second switching unit 16 is welding voltage Vw, a predetermined voltage is applied between electrode 70 and base material 200 via power cables 51 and 52, respectively.

[0017] Welding output detection unit 20 has a welding current detection unit 21 and a welding voltage detection unit 22. Welding current detection unit 21 detects the welding current Aw supplied to electrode 70, and welding voltage detection unit 22 detects the welding voltage Vw applied between electrode 70 and base material 200. The results detected by welding current detection unit 21 and welding voltage detection unit 22 are sent to control unit 30 and used to control the arc welding.

[0018] The control unit 30 is composed of one or more central processing units (CPUs). Alternatively, the control unit 30 is composed of one or more micro control units (MCUs). The control unit 30 also has a calculation unit 30A composed of one or more CPUs. When at least one of a current command value and the thickness of the base material 200, which will be described later, is input, the calculation unit 30A executes a correction process for the welding current waveform. In other words, the calculation unit 30A executes a correction process for the welding current waveform in three patterns: when only the current command value is input, when only the thickness is input, and when both the current command value and the thickness are input.

[0019] In the example shown in FIG. 1 , a memory unit 31 is provided independent of the control unit 30. The memory unit 31 is configured with semiconductor memory such as a random access memory (RAM) or a read-only memory (ROM). The memory unit 31 may also be configured with a hard disk drive (HDD) or a solid state drive (SSD). The memory unit 31 may be a functional block of a CPU or an MCU, i.e., a ROM or RAM built into the CPU or MCU. The memory unit 31 stores control programs and welding parameters for various devices used in arc welding. The memory unit 31 also stores a program describing a welding current waveform correction procedure, which will be described later.

[0020] The control unit 30 controls the switching operations of the first switching unit 12 and the second switching unit 16 in accordance with a predetermined welding program. Specifically, the control unit 30 controls the switching operation of the second switching unit 16 based on a preset current command value Is and the AC period (hereinafter simply referred to as the period) of the welding current Aw. The control unit 30 also receives the detection result of the welding current detection unit 21 and controls the switching operations of the first switching unit 12 and the second switching unit 16 based on the detection result so that the welding current Aw becomes the preset current command value Is. The current command value Is refers to the moving average value of the welding current Aw during the set welding period Tw.

[0021] The input unit 32 is composed of, for example, a display device such as a liquid crystal display and an input device such as a keyboard, input buttons, a rotary encoder with a switch, etc. If the display device is a touch panel, the input device may be omitted.

[0022] The input unit 32 inputs welding conditions during arc welding, for example, an actual use command value I ｓ１ and the actual thickness D of the base material 200 １ It is used to input

[0023] Welding torch 60 may be held by a robot (not shown). In this case, the robot moves welding torch 60 at a predetermined speed (welding speed) along a predetermined weld line (not shown) so that the distance between the tip of electrode 70 and the surface of base material 200 is within a predetermined range.

[0024] 1, input unit 32 is provided in welding power source 40, but input unit 32 may be provided outside welding power source 40 as long as it is capable of communicating with control unit 30. For example, a teaching pendant (TP) 33 for teaching the robot the movement trajectory of welding torch 60 may be input unit 32. In this case, communication between teaching pendant 33, which is input unit 32, and control unit 30 may be wired or wireless.

[0025] Although not shown, a filler metal may be used when performing arc welding. The filler metal is made of the same metal as the base metal 200, and is melted in the arc ARC to be used as a metal supply source for maintaining the strength and appearance of the welded portion. Note that the filler metal is not essential, and can be omitted depending on the conditions required for the welded portion and the shape of the base metal 200.

[0026] [Procedure for correcting welding current waveform] Normally, when AC TIG welding is performed using the arc welding machine 100, the basic waveform of the welding current Aw (hereinafter simply referred to as the basic waveform) stored in the memory unit 31 is read into the control unit 30, and the current command value is changed to a value suitable for welding the base material 200.

[0027] However, as already mentioned, if the basic waveform is maintained and only the current command value is changed, for example, if the base material 200 is a thin plate, there is a risk of burn-through occurring depending on the shape of the waveform.

[0028] Therefore, in this embodiment, a method is proposed in which the time waveform of the welding current (hereinafter referred to as the welding current waveform) is obtained by modifying the basic waveform in accordance with the plate thickness of the base material 200 and the current command value. This will be further explained below with reference to the drawings.

[0029] Fig. 2 is a flowchart showing the procedure for correcting the welding current waveform, Fig. 3 is a schematic diagram showing the basic waveform of the welding current, and Fig. 4 is an enlarged view of the portion surrounded by the dashed line in Fig. 3.

[0030] As shown in Fig. 2, a basic waveform is prepared (step S1). The basic waveform is stored in the storage unit 31 as described above and is read out by the control unit 30. Note that the basic waveform in this embodiment is a waveform obtained by applying a voltage to the base material 200 during a period T ＥＮ (Electrode negative period T ＥＮ The welding current Aw is a constant positive value I. ＥＮ The period T2 is the period until the welding current Aw reaches a positive constant value I ＥＮ The period T3 is a period in which the welding current Aw is maintained at a constant value I ＥＮ The period T ＥＰ (Electrode positive period T ＥＰ The welding current Aw falls from zero to a constant negative value I ＥＰ The period T5 is the period until the welding current Aw reaches a negative constant value I ＥＰ During the period T6, the welding current Aw is maintained at a constant value I ＥＰ This is the period from when the voltage rises to when it reaches zero.

[0031] As shown in FIG. 4, the welding current Aw is ＩＮＶThis is a waveform in which the current value is plotted against discrete time t. Here, the time interval T ＩＮＶ is the control period of the second switching unit 16 by the control unit 30. Furthermore, the basic waveform is the period when the current command value of the welding current Aw is equal to the initial command value I ｓ０ The thickness of the base material 200 is the initial thickness D ０ If the time interval T ＩＮＶ 1 is a waveform obtained by plotting the current value of the welding current Aw against discrete time t.

[0032] Next, the basic waveform is described by a function with variables being the current command value Is, the thickness D of the base material 200, and time t (step S2). This function is a set of multiple subfunctions. In the example shown in FIG. 3, during the period T1 (time 0 to time ta), the welding current Aw is described by the subfunction shown in equation (1).

[0033] Aw = I ＥＮ (1-e （－ｔ／Ａ） ) (1) Furthermore, the sub-function A is written as a function of the plate thickness D in the form shown in equation (2).

[0034] A = α × D / D ０ ...(2) Also, the current value I ＥＮ When viewed as a subfunction of the current command value Is and the plate thickness D, the subfunction I ＥＮ is written in the form shown in equation (3).

[0035] I ＥＮ = β × Is / I ｓ０ × (D / D ０ ) (3) where α and β are positive constants. In the following explanation, D ０ is called the initial plate thickness, and I ｓ０ is called the initial command value.

[0036] During the period T2 (time ta to time tb), the welding current Aw is described in the form shown in equation (3) as a sub-function having at least one of the current command value Is and the plate thickness D as a variable. In other words, during the period T2, the welding current Aw does not depend on the time t.

[0037] During the period T3 (time tb to time tc), the welding current Aw is described by the subfunction shown in equation (4).

[0038] Aw=B×((1 / e)((t−tc) / A)−1)=B×(e((tc−t) / A)−1) (4) Here, B is a coefficient that satisfies the relationship shown in equation (5).

[0039] B=I ＥＮ / ((e((tc-tb) / A))-1) (5) The welding current Aw in period T4 (from time tc to time td) can be described by a transformation of the sub-function represented by the relationship shown in equation (4), and therefore a description thereof will be omitted. Similarly, the welding current Aw in period T5 (from time td to time te) and the welding current Aw in period T6 (from time te to time tn) can be described by a transformation of the sub-function represented by the relationship shown in equations (3) and (1), respectively, and therefore a description thereof will be omitted.

[0040] The subfunction describing the waveform of the welding current Aw is changed as appropriate depending on the shape of the basic waveform. For example, if the time gradient of the current, that is, the rate of increase or decrease of the welding current Aw with respect to time t, is linear, then, for example, Equations (1) and (4) are transformed into the following Equations (1A) and (4A), respectively.

[0041] Aw = I ＥＮ ×a×t...(1A) Aw=I ＥＮ ×b×(tc−t) (4A) where a and b are positive constants and b=1 / (tc−tb). Furthermore, equation (2) may be transformed into equation (2A) shown below.

[0042] A = α1 × ((D - D ０ ) / D ０ ) (2A) where α1 is a positive constant.

[0043] Next, the current command value actually used in welding, that is, the actual use command value I ｓ１ and the actual thickness of the plate used, that is, the actual thickness of the plate used D １ and are substituted into each sub-function shown in step S2 (step S3). For example, according to equation (2), sub-function A is ０ Actual plate thickness D １ The value changes depending on the ratio of the welding current Aw to the actual plate thickness D. １ It changes depending on

[0044] The basic waveform is modified and corrected in accordance with the values ​​substituted in step S3, and the result is obtained as the welding current waveform (step S4).

[0045] As is clear from the above explanation, the basic waveform is such that the current command value of the welding current Aw is equal to the initial command value I ｓ０ The thickness of the base material 200 is the initial thickness D ０ In the case of the aforementioned time interval T ＩＮＶ 1 is a waveform obtained by plotting the current value of the welding current Aw against discrete time t.

[0046] The welding current waveform acquired in step S4 is determined such that the current command value of the welding current Aw is the actual use command value I ｓ１ The thickness of the base material 200 is the actual thickness D １ In the case of the aforementioned time interval T ＩＮＶ The welding current waveform obtained in step S4 is at least temporarily stored in the memory unit 31, and the current command value is set to the actual use command value I ｓ１ The thickness of the base material 200 is the actual thickness D １ This is used as the basic waveform when welding.

[0047] [Effects, etc.] As described above, the method for correcting a welding current waveform in AC arc welding according to this embodiment performs the first to third steps described below using arc welder 100 having at least welding output unit 10, welding torch 60, and control unit 30. Control unit 30 has at least calculation unit 30A and memory unit 31.

[0048] In the first step, a basic waveform of the welding current Aw is prepared (step S1 in FIG. 2).

[0049] In the second step, the basic waveform is described by a function having variables of the current command value Is, the thickness D of the base metal 200 to be welded, and time t (step S2 in FIG. 2).

[0050] In the third step, the actual use command value I used for welding the base material 200 is used as the current command value Is in the function described in step S2. ｓ１is substituted, and the plate thickness D in the function is the actual plate thickness D used for welding the base material 200. １ The basic waveform is corrected by substituting the above formula: The corrected basic waveform is obtained as the welding current waveform (steps S3 and S4 in FIG. 2).

[0051] The current command value Is is a moving average value of the welding current Aw in the period T of the basic waveform. ｓ０ The thickness of the base material 200 is the initial thickness D ０ If the predetermined time interval T ＩＮＶ The welding current waveform is a plot of the current value of the welding current Aw against discrete time t. The welding current waveform is obtained by plotting the current command value of the welding current Aw against the actual use command value I ｓ１ The thickness of the base material 200 is the actual thickness D １ In the case of the aforementioned time interval T ＩＮＶ 1 is a waveform obtained by plotting the current value of the welding current Aw against discrete time t.

[0052] As described above, the preset initial plate thickness D ０ and the initial command value Is ０ Using the basic waveform corresponding to the initial plate thickness D ０ The actual thickness D is significantly thinner than １ When welding the base material 200, depending on the shape of the basic waveform, burn-through of the base material 200 may occur.

[0053] On the other hand, according to this embodiment, the basic waveform is described as a function having variables of the current command value Is, the plate thickness D of the base material 200 to be welded, and time t, specifically, as a set of multiple sub-functions, and the actual use command value I ｓ１ and actual plate thickness D １ In this way, the waveform of the welding current Aw used in actual welding can be obtained simply and appropriately. This will be further explained.

[0054] 5 is a schematic diagram showing the change in the rising portion of the basic waveform when the plate thickness is reduced. １ When the welding current Aw is reduced, the welding current Aw becomes constant. ＥＮDuring the rising period T1a until the thickness of the base material 200 reaches the initial thickness D ０ As is clear from the formula (2), this is because the value of the subfunction A increases. １ is the initial plate thickness D ０ If the welding current Aw is reduced to a constant value I ＥＮ By lengthening the rise time T1a until the temperature reaches 100° C., the heat input to the base material 200 can be made gentler, and burn-through of the base material 200 can be suppressed.

[0055] As is clear from the equation (3), the constant value I of the welding current Aw ＥＮ is the initial command value I ｓ０ Actual use command value I ｓ１ The value changes depending on the ratio of

[0056] 6 is a schematic diagram showing the change in the rising portion of the fundamental waveform when the current command value is reduced. As shown in FIG. 6, the actual use command value I ｓ１ When decreasing, the constant value I ＥＮ is a constant value I ＥＮ１ As is clear from equation (3), the subfunction I ＥＮ This is because the value of decreases. ＥＮ１ The rise time T1 until the welding current Aw reaches a constant value I ＥＮ From I ＥＮ１ Therefore, the time gradient of the welding current Aw in the period T1 is such that the current command value of the welding current Aw decreases to the initial command value I ｓ０ is lower than in the case of

[0057] In this case, the heat input to the base material 200 can be reduced, and at the beginning of welding, the heat input to the base material 200 is gentle, so burn-through of the base material 200 can be suppressed.

[0058] In AC TIG welding, the electrode negative period T ＥＮ In the electrode positive period T, a highly directional arc ARC is generated, so that a weld bead having a narrow width and a deep penetration depth can be formed. ＥＰIn the electrode positive period T ＥＰ In this state, a cleaning action occurs on the surface of the base material 200. As a result, for example, in the case of an aluminum-based base material 200, an oxide film formed on the surface can be removed, and a clean surface suitable for welding can be obtained.

[0059] On the other hand, according to this embodiment, the basic waveform of the welding current Aw, which is an AC waveform, is corrected in the above-described procedure. ＥＮ In this case, by describing the current rising period, falling period, and period in which the current value is constant using appropriate sub-functions, it is possible to appropriately control the generation and growth of the arc ARC. ｓ１ and actual plate thickness D １ In accordance with the electrode positive period T ＥＰ Similarly, by describing the rising period, falling period, and period in which the current value is constant with appropriate sub-functions, the cleaning action on the surface of the base material 200 can be appropriately controlled.

[0060] The subfunction describing the rising period of the welding current Aw in the basic waveform is preferably an increasing function of both the time t and the plate thickness D. In this way, the time gradient of the welding current Aw can be made smaller as the plate thickness D decreases, and burn-through can be suppressed in the thin plate base material 200.

[0061] In the second step, periods in which the time gradient of the welding current Aw in the basic waveform is different may be described by different subfunctions. For example, it is preferable to use different forms of subfunctions for the rising period and the falling period of the current. ＥＮFor example, during the current rising period, an arc ARC is generated and grown to a desired arc length. During the current falling period, the arc ARC is reduced so that it does not disappear. In this way, during periods with different effects on the arc ARC, different sub-functions describing the welding current Aw may be used to appropriately exert the respective effects.

[0062] The welding output unit 10 in the arc welding machine 100 has a second switching unit 16 which is an inverter that controls the time variation of the welding current Aw. ＩＮＶ is the control period of the inverter. ＩＮＶ In other words, the control frequency of the inverter is a fixed value.

[0063] Time interval T ＩＮＶ By setting the time interval T in this way, the period change process of the basic waveform, which will be described later, can be easily performed. If the frequency of the basic waveform is 10 Hz, the period T is 100 msec. ＩＮＶ If the time is 12.5 μsec, the fundamental waveform will be data consisting of 8000 points.

[0064] It is preferable to further include a fifth step of at least temporarily storing the welding current waveform obtained in the third step in the memory unit 31. By doing so, when welding the same type of base material 200 again after a period of time, the corrected welding current waveform can be used as is, simplifying the work of setting welding conditions. Note that if multiple patterns of each sub-function are stored in the memory unit 31, there is no need to store the corrected welding current waveform in the memory unit 31 for a long period of time. This is because the desired welding current waveform can be obtained by modifying the basic waveform using each sub-function.

[0065] The program according to this embodiment causes one or more CPUs (processors) to execute the welding current waveform correction method described above.

[0066] By programming the welding current waveform modification procedure in this way, the basic waveform can be easily modified to obtain a desired welding current waveform.

[0067] (Embodiment 2) Fig. 7 is a flowchart showing a procedure for correcting a welding current waveform according to embodiment 2. Fig. 8 is a conceptual diagram for explaining the procedure for halving the period of the basic waveform. Fig. 9 is a conceptual diagram for explaining the procedure for doubling the period of the basic waveform. For ease of explanation, in Figs. 7 to 9, the same reference numerals are used to designate the same parts as in embodiment 1, and detailed explanations thereof will be omitted.

[0068] In the flowchart shown in Fig. 7, steps S11 and S13 to S15 are the same as steps S1 to S4 in the flowchart shown in Fig. 2, and therefore description thereof will be omitted. The flowchart shown in Fig. 7 differs from the flowchart shown in Fig. 2 in that a fundamental waveform period change process shown in step S12 is added.

[0069] Step S12 (fourth step) is executed between step S11 (first step) and step S13 (second step). Specifically, in step S12, the basic waveform is corrected in accordance with the cycle (hereinafter referred to as the actual use cycle) of the welding current Aw used to weld the base material 200. This will be further explained.

[0070] In the basic waveform, a fundamental period T (hereinafter simply referred to as period T) is predetermined. As described above, period T is a time interval T ＩＮＶ is an integer multiple of

[0071] T = n × T ＩＮＶ ...(6) where n is an integer, and the period T is the time interval T ＩＮＶ This is the value divided by .

[0072] Therefore, the period T is the time interval T ＩＮＶ By utilizing the fact that the period T is n times the period T, it is possible to easily change the period T. In step S12, the period of the fundamental waveform is changed in the following procedure.

[0073] When the actual use period is half the period T of the fundamental waveform, data is thinned out from the fundamental waveform as shown in FIG. ＩＮＶ After extracting the current value of the welding current Aw at every double of time, the extracted multiple current values ​​are arranged on the time axis at time intervals T ＩＮＶBy placing it every time, the basic waveform is modified.

[0074] When the actual use period is twice the period T of the fundamental waveform, as shown in FIG. 9, the first time point and the time interval T ＩＮＶ After interpolating the current value of one welding current Aw between the first time point and the second time point after the time interval T, the interpolated current values ​​are arranged on the time axis at time intervals T ＩＮＶ By placing it every time, the basic waveform is modified.

[0075] In AC TIG welding, it may be desirable to change the period of the welding current waveform, in other words, the frequency. Increasing the frequency improves the directionality and concentration of the arc ARC, making it possible to form a weld bead with a narrow width and deep penetration. On the other hand, decreasing the frequency makes it possible to widen the cleaning width, which is the width of the surface of the base material 200 cleaned, in a direction intersecting the welding direction. Therefore, it is preferable to change the frequency of the welding current waveform, taking into consideration the material of the base material 200 and the aesthetic appearance of the weld bead, etc.

[0076] According to this embodiment, the period T of the basic waveform, and therefore the frequency of the corrected welding current waveform, can be easily changed by simple data processing.

[0077] In the welding current waveform correction method according to this embodiment, the fourth step can be expanded as follows.

[0078] If the actual use period is 1 / m times the period T of the fundamental waveform (m is an integer of 2 or more), the time interval T ＩＮＶ The current value of the welding current Aw extracted every m times is plotted on the time axis at time intervals T ＩＮＶ By placing it every time, the basic waveform is modified.

[0079] When the actual use period is m times the period T of the fundamental waveform, the first time point and the time interval T from the first time point are ＩＮＶ (m-1) current values ​​of the welding current Aw are interpolated between the second point in time after the time interval T ＩＮＶ By placing it every time, the basic waveform is modified.

[0080] In the example shown in FIG. 7 , the period T is changed by directly thinning or interpolating data from the basic waveform. However, when extending the period T by a factor of m, it may be better to change the period T by interpolating data from the basic waveform after the second step, in other words, after it has been described as a set of multiple subfunctions. This allows one or more pieces of data to be interpolated between the first and second time points to be closer to the actual waveform, so that the shape of the basic waveform after the period T is changed can be made similar to the original basic waveform. In other words, this prevents the shape of the basic waveform from being deformed into an unintended shape, which disrupts the heat input balance to the base material 200 and causes burn-through or other problems.

[0081] Note that the period T can be set to any value by combining the process of changing the period T by (1 / i) times (i is an integer greater than or equal to 2) with the process of changing the period (T / i) by j times (j is an integer greater than or equal to 2). For example, if T = 100 msec and i = 100, the changed period will be 1 msec. If the period is then multiplied by j (= 33), the changed period will be 33 msec. When the period T is 100 msec, the frequency of the fundamental waveform is 10 Hz, and after the two-stage change process, the frequency of the fundamental waveform will be approximately 30 Hz.

[0082] The program according to this embodiment also causes one or more CPUs (processors) to execute the welding current waveform correction method including the fourth step.

[0083] By programming the procedure for correcting the welding current waveform in this way, it is possible to easily change the period T of the basic waveform and correct the basic waveform to obtain a desired welding current waveform.

[0084] (Other Embodiments) In the present specification, AC TIG welding has been described as an example, but the present invention is not limited to this and can be applied to consumable electrode AC arc welding, such as AC MIG welding and AC MAG welding.

[0085] The welding current waveform correction method of the present disclosure is useful in AC arc welding because it can appropriately correct the welding current waveform depending on the plate thickness of the base metal and the current command value.

[0086] REFERENCE SIGNS LIST 10 Welding output unit 11 First rectifier unit 12 First switching unit 13 Transformer 14 Second rectifier unit 15 Reactor 16 Second switching unit 20 Welding output detection unit 21 Welding current detection unit 22 Welding voltage detection unit 30 Control unit 30A Calculation unit 31 Memory unit 32 Input unit 33 Teaching pendant (input unit) 40 Welding power source 51 Power cable 52 Power cable 60 Welding torch 70 Electrode 100 Arc welding machine 200 Base material ARC Arc PS Three-phase AC power supply

Claims

1. A method for correcting a welding current waveform in AC arc welding, wherein a welding machine for performing AC arc welding has at least a welding output unit, a welding torch, and a control unit, and the control unit has at least a calculation unit and a memory unit, and the method comprises at least the following steps: a first step of preparing a basic waveform of a welding current; a second step of describing the basic waveform with a function having a current command value, a thickness of a base metal that is an object to be welded, and time as variables; and a third step of substituting an actual use command value to be used for welding the base metal as the current command value in the function and substituting an actual use plate thickness to be used for welding the base metal as the plate thickness in the function to correct the basic waveform and obtain the welding current waveform, wherein the current command value is a moving average value of the welding current in a period of the basic waveform, and the basic waveform is a waveform obtained by plotting the current value of the welding current against discrete times at predetermined time intervals when the current command value is an initial command value and the plate thickness is the initial plate thickness, a welding current waveform correction method characterized in that the welding current waveform is a waveform obtained by plotting the current value of the welding current against the time discrete at the time intervals when the current command value is the actual use command value and the plate thickness is the actual use plate thickness.

2. A welding current waveform correction method as set forth in claim 1, characterized in that in the second step, periods in which the time gradient of the welding current in the basic waveform is different are described by different sub-functions.

3. A welding current waveform correction method according to claim 2, characterized in that the sub-function describing the rising period of the welding current in the basic waveform is an increasing function of both the time and the plate thickness.

4. A method for correcting a welding current waveform as set forth in claim 1, further comprising, after execution of said first step or said second step, a fourth step of correcting said basic waveform in accordance with an actual use cycle of said welding current used to weld said base metal, wherein said fourth step, if said actual use cycle is 1 / m times (m is an integer of 2 or more) the cycle of said basic waveform, corrects said basic waveform by arranging on the time axis for each of said time intervals said current values ​​of said welding current extracted from said basic waveform at each of said m times the time interval; and if said actual use cycle is m times the cycle of said basic waveform, corrects said basic waveform by interpolating with respect to said basic waveform (m-1) current values ​​of said welding current between a first time point and a second time point which is the elapsed time interval from said first time point, and then arranging on said time axis for each of said time intervals said interpolated current values.

5. A welding current waveform correction method as set forth in claim 1, further comprising a fifth step of at least temporarily storing the welding current waveform obtained in the third step in the memory unit.

6. A program for causing one or more processors to execute the welding current waveform correction method according to any one of claims 1 to 5.

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