Current control method for ac TIG welding and ac TIG welding apparatus

Abstract

This current control method for AC TIG welding includes: providing, in an electrode negative period, at least an electrode negative rise period and an electrode negative fall period; causing an electrode negative current to rise in a gentle curved manner from zero to a predetermined constant electrode negative peak current value during the electrode negative rise period; causing the electrode negative current to fall in a gentle curved manner from the electrode negative peak current value to zero during the electrode negative fall period; supplying the electrode negative current so that the electrode negative current is constant at the electrode negative peak current value during the period from the end point of the electrode negative rise period to the start point of the electrode negative fall period; and supplying, in the electrode positive period as well, an electrode positive current that has similar portions that change gently in a curved manner and a constant electrode positive peak current value.

Description

Current control method for AC TIG welding and AC TIG welding device

[0001] The present disclosure relates to a current control method for AC TIG welding and an AC TIG welding device.

[0002] AC Tungsten Inert Gas (TIG) welding is a conventional method for arc welding base materials made of aluminum or aluminum alloys. In AC TIG welding, an electrode negative period (EN (Electrode Negative) period) in which the electrode has a negative polarity and the workpiece has a positive polarity is alternated periodically with an electrode positive period (EP (Electrode Positive) period) in which the electrode has a positive polarity and the workpiece has a negative polarity. During the EN period, a highly directional arc is generated, allowing the formation of a narrow bead with a deep penetration depth. Meanwhile, during the EP period, a cleaning action occurs that removes the oxide film covering the surface of the workpiece, resulting in a clean surface suitable for welding.

[0003] Furthermore, AC TIG welding generates a loud arc noise, and a reduction in noise level is required. For example, Patent Document 1 discloses a current control method for AC TIG welding that reduces noise from the arc.

[0004] Japanese Patent Application Publication No. 2005-28383

[0005] The present disclosure has been devised in view of the conventional circumstances, and aims to perform AC TIG welding while achieving both quietness and rigidity of the generated arc.

[0006] The present disclosure relates to a current control method for AC TIG welding in which welding is performed by alternately and repeatedly passing a negative electrode current during a negative electrode period and a positive electrode current during a positive electrode period, wherein the negative electrode period includes at least a negative electrode rise period and a negative electrode fall period, and the negative electrode current rises in a gentle curve from zero to a predetermined constant negative electrode peak current value during the negative electrode rise period, falls in a gentle curve from the negative electrode peak current value to zero during the negative electrode fall period, and continues from the end of the negative electrode rise period to the negative electrode fall period. and a current control method for AC TIG welding, wherein the electrode positive current is kept constant at the electrode negative peak current value from the end of the electrode positive rise period to the start of the electrode positive fall period, the electrode positive period is provided with at least an electrode positive rise period and an electrode positive fall period, the electrode positive current rises in a gentle curve from zero to a predetermined constant electrode positive peak current value during the electrode positive rise period, and falls in a gentle curve from the electrode positive peak current value to zero during the electrode positive fall period, and the electrode positive current is kept constant at the electrode positive peak current value from the end of the electrode positive rise period to the start of the electrode positive fall period.

[0007] The present disclosure also provides an AC TIG welding device for generating an arc between a workpiece and the workpiece to perform AC TIG welding, the device comprising at least a welding torch having an electrode disposed thereon, and a welding power source for supplying a welding current for generating the arc between the tip of the electrode and the workpiece, the welding current being supplied alternately and repeatedly as an electrode negative current during an electrode negative period and an electrode positive current during an electrode positive period, the electrode negative period including at least an electrode negative rising period and an electrode negative falling period, the electrode negative current rising in a gentle curve from zero to a predetermined constant electrode negative peak current value during the electrode negative rising period, and the electrode negative peak current being supplied in a gentle curve from zero to a predetermined constant electrode negative peak current value during the electrode negative falling period. and the electrode positive peak current is kept constant at the electrode negative peak current value from the end of the electrode negative rise period to the start of the electrode negative fall period, and the electrode positive period is at least provided with an electrode positive rise period and an electrode positive fall period, and the electrode positive current is increased in a gentle curve from zero to a predetermined constant electrode positive peak current value during the electrode positive rise period, and is decreased in a gentle curve from the electrode positive peak current value to zero during the electrode positive fall period, and is kept constant at the electrode positive peak current value from the end of the electrode positive rise period to the start of the electrode positive fall period.

[0008] According to the present disclosure, AC TIG welding can be performed while achieving both quietness and rigidity of the arc generated.

[0009] Graph showing an example of a schematic configuration of an AC TIG welding device according to this embodiment; Graph showing an example of an X waveform characteristic; Graph showing an example of an EP peak current ratio; Flowchart showing an example of an operation procedure for adjusting control parameters according to this embodiment in a time series; Graphs showing an example of an evaluation method for arc rigidity, (a) captured image, (b) arc visualization, (c) arc center position, (d) time change of arc center position; Graph showing noise level of X waveform and variation in arc center position; (a) graph showing peak current value at each peak period ratio; (b) graph showing measurement results of noise level at each peak period ratio; (c) graph showing measurement results of variation in arc center position at each peak period ratio; (d) graph showing measurement results of effective range of peak period ratio; (a) graph showing peak current value at each EP peak current ratio; (b) graph showing each E (c) A graph showing the measurement results of noise levels at EP peak current ratios, (d) A graph showing the measurement results of the effective range of the EP peak current ratio, (e) A graph showing the measurement results of the effective range of the peak period ratio and the EP peak current ratio, (f) A graph showing an example of the relationship between the control parameter value and the weldability, (g) A graph showing the overall evaluation criteria for the weldability and an evaluation example for each evaluation item, (h) A graph showing an example of the individual evaluation criteria for the evaluation item shown in (b), (i) A graph showing a schematic diagram of another example of the characteristics of the X waveform, and (j) A graph comparing the characteristics of the X waveform and the waveform of the prior art. (a) A graph showing the measurement results of noise levels at the rise and fall shapes of the X waveform and the waveform of the prior art, (b) A graph showing the measurement results of the variation in the arc center position at the rise and fall shapes of the X waveform and the waveform of the prior art.

[0010] (Background to the present disclosure) In the current control method for AC TIG welding disclosed in Patent Document 1, an electrode positive period includes an electrode positive rise period and an electrode positive fall period. During the electrode positive rise period, the electrode positive current rises sharply to a predetermined electrode positive bending current value and then rises in a gentle curve to a predetermined electrode positive peak current value. During the electrode positive fall period, the electrode positive current falls in a gentle curve from the electrode positive peak current value to the electrode positive bending current value and then falls sharply from the electrode positive bending current value. Furthermore, an electrode negative period includes an electrode negative rise period and an electrode negative fall period. During the electrode negative rise period, the electrode negative current rises sharply to a predetermined electrode negative bending current value and then rises in a gentle curve to a predetermined electrode negative peak current value. During the electrode negative fall period, the electrode negative current falls in a gentle curve from the electrode negative peak current value to the electrode negative bending current value and then falls sharply from the electrode negative bending current value.

[0011] The characteristics of the electrode positive current and electrode negative current disclosed in Patent Document 1, such as those described above, result in high noise levels in the high welding average current range due to the steep rise in the current, making it difficult to achieve a quiet arc welding work environment. Here, special noise countermeasures are required at work sites where the noise level exceeds 85 dB, and therefore quiet work sites are required. However, simply maintaining quietness at present poses the problem of poor arc rigidity, which adversely affects weldability. Arc rigidity refers to the property of the arc advancing straight along the central axis of the electrode without bending toward the workpiece, even when the welding torch is tilted relative to the workpiece. This can also be expressed as arc straightness. Therefore, current waveform characteristics that enable both quietness and arc rigidity are required in AC TIG welding.

[0012] Therefore, in the following embodiments, an example of a current control method for AC TIG welding and an AC TIG welding device that perform AC TIG welding while achieving both quietness and rigidity of the generated arc will be described.

[0013] Hereinafter, with reference to the drawings as appropriate, embodiments specifically disclosing an AC TIG welding current control method and an AC TIG welding device according to the present disclosure will be described in detail. However, unnecessary detailed description may be omitted. For example, detailed description of well-known matters or redundant description of substantially identical configurations may be omitted. This is to avoid unnecessary redundancy in the following description and to facilitate understanding by those skilled in the art. Note that the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand the present disclosure and are not intended to limit the subject matter recited in the claims.

[0014] 1. Configuration of AC TIG Welding Apparatus First, the hardware configuration of AC TIG welding apparatus 100 according to this embodiment will be described with reference to Fig. 1. Fig. 1 is a diagram showing an example of the schematic configuration of AC TIG welding apparatus 100 according to this embodiment. AC TIG welding apparatus 100 is configured to include at least a welding power source 40 and a welding torch 60.

[0015] 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, which is the material to be welded, thereby welding the base material 200. In other words, AC TIG welding is performed by the AC TIG welding device 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.

[0016] Welding power source 40 has at least welding output unit 10, welding output detection unit 20, control unit 30, and input unit 32. Welding output unit 10 has first rectification unit 11, first switching unit 12, transformer 13, second rectification unit 14, reactor (DCL) 15, and second switching unit 16.

[0017] The first rectifier 11 is composed of rectifying elements such as diodes and rectifies the 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 with an iron core and converts the output of the first switching unit 12 to an output suitable for welding. The second rectifier 14 is, for example, a full-wave rectifier circuit composed of four diode circuits and rectifies the output of the transformer 13. The reactors 15 are connected in series to each of the two output lines of the second rectifier 14 and smooth the output of the second rectifier 14. The second switching unit 16 is, for example, a polarity-inverting circuit composed of two transistors and switches the two transistors at timings according to control commands from the control unit 30 to control the polarity of the output of the welding torch 60.

[0018] In the present 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.

[0019] Welding output detection unit 20 has welding current detection unit 21 and welding voltage detection unit 22. Welding current detection unit 21 detects welding current Aw supplied to electrode 70, and welding voltage detection unit 22 detects 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.

[0020] The control unit 30 is configured with one or more central processing units (CPUs), or one or more micro control units (MCUs), and also includes a drive unit 30A.

[0021] 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 random access memory (RAM) and read-only memory. The memory unit 31 may be configured with a hard disk drive (HDD) or a solid state drive (SSD). The memory unit 31 may be a functional block of the CPU or MCU, that is, a ROM or RAM built into the CPU or MCU. The memory unit 31 stores welding conditions used in arc welding. The memory unit 31 also stores control programs and welding parameters for various devices.

[0022] The control unit 30 controls the switching operations of the first switching unit 12 and the second switching unit 16 based on the welding conditions input from the input unit 32. 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 preset set current is achieved. The drive unit 30A also controls the switching operation of the second switching unit 16 based on the set current and the AC frequency of the welding current Aw input from the input unit 32. The set current refers to the moving average value of the welding current Aw during the welding period. However, as will be described later, in this embodiment, the welding period is made up of a plurality of periods (specifically, an EN time T as an example of an electrode negative period) ｎ , EP time T as an example of the electrode positive period ｐ ) and in each period, a set current (specifically, an EN peak current value I as an example of an electrode negative peak current value) ｎｐ , an EP peak current value I as an example of an electrode positive peak current value ｐｐ ) can be set.

[0023] 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, or a rotary encoder with a switch. If the display device is a touch panel, the input device may be omitted. The input unit 32 is used to input welding conditions for arc welding, such as the aforementioned set current, AC frequency, and cleaning width.

[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, teaching pendant 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] Display unit 34 is configured with a display device such as a liquid crystal display or a touch panel, and displays various welding conditions including the welding conditions input from input unit 32. Furthermore, as will be described later, when the welding period is divided into multiple periods, display unit 34 displays various welding conditions for each of the multiple periods. Display unit 34 may also display the detection results of welding current detection unit 21 and welding voltage detection unit 22. Note that when display unit 34 is configured with a touch panel, display unit 34 may be integrated with input unit 32 and teaching pendant 33.

[0026] The welding torch 60 holds the electrode 70 and is operated by a welding operator while being held in his / her hand. The electrode 70 is a non-consumable electrode made of tungsten containing inorganic additives. With an arc (ARC) generated, the welding torch 60 is moved in the welding direction at a predetermined speed (welding speed) along a weld line (not shown) in the base metal 200 so that the distance between the tip of the electrode 70 and the surface of the base metal 200 is within a predetermined range, thereby arc-welding the base metal 200.

[0027] The welding torch 60 also has a torch switch 61. When the welding operator operates the torch switch 61, a welding current Aw is supplied to the electrode 70, generating an arc ARC. Furthermore, by operating the torch switch 61 at a different timing, the supply of the welding current Aw to the electrode 70 is stopped, and the arc ARC is extinguished. As will be described later, by operating the torch switch 61, the welding period Tw can be divided into multiple periods to weld the base material 200. The welding torch 60 may be held by a robot (not shown). In this case, the robot moves the welding torch 60 at a predetermined speed (welding speed) along the weld line so that the distance between the tip of the electrode 70 and the surface of the base material 200 is within a predetermined range.

[0028] 1, a filler metal 80 may be used when performing arc welding. The filler metal 80 is made of the same metal as the base metal 200, and is melted by the arc ARC to be used as a metal supply source for maintaining the strength and appearance of the welded portion. The filler metal 80 is not essential, and can be omitted depending on the conditions required for the welded portion and the shape of the base metal 200.

[0029] Furthermore, a camera 90, an image processing device 91, a sound level meter 92, and a display 93 are further provided to evaluate quietness and arc rigidity at the work site during welding by AC TIG welding device 100 (e.g., while welding current Aw is being supplied to electrode 70). The camera 90 and image processing device 91, the image processing device 91 and display 93, and the sound level meter 92 and display 93 are connected by wired cables or the like to enable input and output of data signals.

[0030] The camera 90 is placed at a safe position within a viewing angle that allows it to capture an image of the AC TIG welding device while it is generating an arc ARC on the base material 200 and welding, and captures and generates a video that shows the state when the arc ARC is generated. When the camera 90 acquires each captured image (frame) that constitutes the video obtained by capturing, it sends the data of the captured image to an image processing device 91.

[0031] The image processing device 91 is configured using, for example, a general-purpose personal computer (PC), and upon acquiring captured image data sent from the camera 90, identifies the center of gravity of the arc ARC in the captured image by performing predetermined image processing (see FIG. 5 ) on the acquired data each time the data is acquired. Although a detailed example of the hardware configuration is not shown, the image processing device 91 is a computer device equipped with a processor and memory. The image processing device 91 generates an image showing the change over time in the center of gravity of the arc ARC (see, for example, FIG. 5( d )), and sends it to the display 93 for display.

[0032] The sound level meter 92 measures the noise level generated at the work site while the AC TIG welding device is generating an arc ARC on the base material 200 to weld it, and sends the measurement results to a display 93.

[0033] The display 93 is configured with a display device such as a liquid crystal display or a touch panel, and displays a display screen showing the image processing results indicating an example of time-dependent changes in the center of gravity position of the arc ARC sent from the image processing device 91, and the noise level measurement results sent from the sound level meter 92. Note that the display 93 may be substituted by the display unit 34, in which case the image processing device 91 and the sound level meter 92 are connected to the display unit 34 so that data signals can be input and output from each of them.

[0034] 2. Characteristics of the X Waveform Next, the characteristics of the X waveform will be described with reference to Fig. 2 and Fig. 3. Fig. 2 is a graph showing a typical example of the characteristics of the X waveform. Fig. 3 is a graph showing a typical example of the EP peak current ratio. As shown in Fig. 2, the welding current Aw supplied during AC TIG welding according to this embodiment is a negative electrode period (EN time T ｎ The electrode negative current during the period T ｐ The current is supplied (supplied) alternately between the positive current and the positive current to the electrode. The waveform of the welding current Aw shown in Fig. 2 will be referred to as the "X waveform" hereinafter. The horizontal axis of Fig. 2 represents time, and the vertical axis of Fig. 2 represents current value. Although Fig. 2 only shows the X waveform of one cycle of the AC welding current Aw, the welding current Aw that satisfies this X waveform is supplied repeatedly during AC TIG welding.

[0035] As shown in FIG. 2, in the X waveform, the EN time T ｎ , EP time T ｐ In this order, EN time T ｎ During this time, an EN current (an example of a negative electrode current) is supplied, and the EP time T ｐ EP current (electrode positive current) is supplied during EN time T ｎ is the EN rising period and EN peak period T ｎｐ During the EN rising period, the EN current increases from zero (A) to the set current (see above), i.e., the EN peak current value I ｎｐ The characteristic rises in a gentle curve until the EN peak period T ｎｐ Then, the EN current is the EN peak current value I ｎｐ This keeps the EN peak period T ｎｐ In this case, the EN current is equal to the EN peak current value I from the end of the EN rising period to the start of the EN falling period. ｎｐ Since the EN current remains constant, the characteristics of the arc ARC supplied to the base metal (for example, noise level and rigidity) are maintained constant. During the EN falling period, the EN current reaches the EN peak current value I ｎｐ The EN peak period T ｎｐ is the period from the first inflection point, which is the end point of the EN rising period, to the second inflection point, which is the start point of the EN falling period.

[0036] EP time T ｐ is the EP rise period and the EP peak period T ｐｐ During the EP rising period, the EP current increases from zero (A) to the set current (see above) to the EP peak current value I ｐｐ The EP peak period T ｐｐ Then, the EP current is the EP peak current value I ｐｐ This keeps the EP peak period T ｐｐ In this case, the EP current is equal to the EP peak current value I from the end of the EP rise period to the start of the EP fall period. ｐｐSince the EP current remains constant, the characteristics of the arc ARC supplied to the base metal (for example, noise level and rigidity) are maintained constant. During the EP falling period, the EP current reaches the EP peak current value I ｐｐ The EP peak period T ｐｐ is the period from the third inflection point, which is the end point of the EP rise period, to the fourth inflection point, which is the start point of the EP fall period.

[0037] Here, the control parameters that indicate the characteristics of the X waveform, (1) "peak period ratio" and (2) "EP peak current ratio", will be explained.

[0038] (1) "Peak period ratio" First, the peak period ratio is a general term for the EN peak period ratio and the EP peak period ratio. Specifically, the peak period ratio is a control parameter for controlling the proportion of the peak current period in the time of each polarity, and is expressed by the following formula. In order to keep the average current value of one AC cycle constant, the peak current value (i.e., the EN peak current value I ｎｐ and EP peak current value I ｐｐ ) is adjusted. The reason for keeping the average current value for one AC cycle constant is as follows. Specifically, first, it is to keep the total amount of heat input to base material 200 constant before and after a change in welding conditions. Second, the items set by the welding operator on welding power source 40 are mainly the average current value related to heat input. If the average current value differs depending on the peak period ratio, which indicates the proportion of the peak period, the amount of heat input will change, which makes setting the welding conditions complicated and undesirable.

[0039] EN peak period ratio = EN peak time T ｎｐ / EN time T ｎ EP peak period ratio = EP peak time T ｐｐ / EP time T ｐ

[0040] (2) "EP Peak Current Ratio" Next, the EP peak current ratio indicates the ratio of the EP peak current value to the reference peak current value (see FIG. 3), as shown in the following formula. The reference peak current value is the "absolute value of the peak current value" when the "absolute value of the EN peak current value" and the "absolute value of the EP peak current value" are equal. In other words, the absolute value of the EN peak current value |I ｎｐ |=Absolute value of EP peak current value |I ｐｐ When |, the reference peak current value I ｂｐ = Absolute value of EP peak current value |I ｐｐ |It becomes.

[0041] EP peak current ratio = EP peak current value |I ｐｐ | / reference peak current value I ｂｐ

[0042] The absolute value of the EP peak current value |I ｐｐ The absolute value of the EN peak current value |I ｎｐ | is determined. By using the EP peak current ratio, it becomes possible to individually control the "absolute value of the EP peak current value" and the "absolute value of the EN peak current value." Experiments have confirmed that this has the effect of improving the arc rigidity.

[0043] For reference, Figure 3 shows schematic waveforms of AC current when the EP peak current ratio is 100%, 120%, and 80%. When the EP peak current ratio is 100%, the absolute value of the EN peak current is equal to the absolute value of the EP peak current. When the EP peak current ratio is greater than 100% (e.g., when the EP peak current ratio is 120%), the EP peak current is greater than the EN peak current, improving arc rigidity compared to when the EP peak current ratio is 100%. When the EP peak current ratio is less than 100% (e.g., when the EP peak current ratio is 80%), the EP peak current is smaller than the EN peak current, reducing arc rigidity compared to when the EP peak current ratio is 100%.

[0044] 3. Current Control Method for AC TIG Welding Next, a current control method for AC TIG welding according to this embodiment will be described with reference to Fig. 4. Fig. 4 is a flowchart showing a time series of an example of the operational procedure for adjusting control parameters according to this embodiment. Through the series of processes shown in Fig. 4, the "peak period ratio" and "EP peak current ratio," which are control parameters for the X waveform, are determined and set in the memory unit 31 of the AC TIG welding apparatus 100 via the input unit 32. When using the X waveform, it is possible to adjust the "peak period ratio" and "EP peak current ratio" within their respective effective ranges, under the constraint that the average current value over one AC cycle remains constant.

[0045] The effects of the "peak period ratio" and "EP peak current ratio" on arc noise and arc rigidity are as follows: Increasing the peak period ratio → Arc noise increases and arc rigidity increases. Increasing the EP peak current ratio → Arc rigidity increases.

[0046] 4, AC TIG welding is performed on a base material 200 using current arbitrary control parameters (St1). During this AC TIG welding, it is determined whether the image processing results by an image processing device 91 based on an image captured by a camera 90 and the noise level measurement results by a sound level meter 92 satisfy predetermined conditions (i.e., conditions under which both the arc sound and the arc rigidity are good) (St2). The quantitative content of the predetermined conditions will be described later with reference to FIG. 7. If it is determined that the image processing results and the measurement results satisfy the predetermined conditions (St2, YES), the control parameters are set to the current values ​​used during welding in step St1, and the series of processes shown in FIG. 4 ends.

[0047] On the other hand, if it is determined that the image processing results and the measurement results do not satisfy the predetermined conditions (St2, YES), it is determined whether the arc sound is loud (St3). If it is determined that the arc sound is loud (St3, YES), the peak period ratio, which is one of the control parameters, is adjusted to decrease from its current value during AC TIG welding performed in step St1 (St4). On the other hand, if it is determined that the arc sound is not loud (in other words, the predetermined conditions regarding the arc sound are satisfied) (St3, NO), the peak period ratio, which is one of the control parameters, is not changed from its current value during AC TIG welding performed in step St1, and the process proceeds to step St5.

[0048] After step St4 or if it is determined that the arc sound is not loud (St3, NO), it is determined whether the arc rigidity is poor (St5). If it is determined that the arc rigidity is poor (St5, YES), the EP peak current ratio, which is one of the control parameters, is adjusted to be higher than the current value during AC TIG welding performed in step St1 (St6). After step St6, the process returns to step St1, and AC TIG welding is performed again using the adjusted control parameters. On the other hand, if it is determined that the arc rigidity is not poor (in other words, the predetermined condition regarding the arc rigidity is satisfied) (St5, NO), the EP peak current ratio, which is one of the control parameters, is not changed from the current value during AC TIG welding performed in step St1, and the process proceeds to step St5. In this way, at least one of the control parameters, the peak period ratio and the EP peak current ratio, is repeatedly adjusted until the arc sound and the arc rigidity satisfy the predetermined conditions.

[0049] 4. Method for verifying the effect of the X waveform Next, a method for verifying the effect of the current characteristics of the X waveform will be described with reference to Figures 5 and 6. Figure 5 is a diagram schematically showing an example of a method for evaluating arc rigidity, where Figure 5(a) shows an example of a captured image, Figure 5(b) shows an example of a visualized arc ARC, Figure 5(c) shows an example of the arc center position, and Figure 5(d) shows an example of the change in the arc center position over time. Figure 6 is a graph showing the noise level of the X waveform and the variation in the arc center position.

[0050] (1) Noise level of arc sound: For the X-waveform current characteristics, the noise level of the arc sound during discharge of the arc ARC generated during AC TIG welding is obtained from the measurement results using the sound level meter 92.

[0051] (2) Arc rigidity: The appearance of the arc ARC during AC TIG welding is captured by a camera 90, and the shape of the arc ARC is visualized by image processing by an image processing device 91. This visualization allows the arc rigidity to be quantitatively evaluated by measuring the change over time in the position indicating the center of gravity of the arc ARC (arc center of gravity position).

[0052] The captured image IMG1 in FIG. 5( a) shows the arc ARC generated during AC TIG welding (e.g., see step St1 in FIG. 4 ) captured by the camera 90 at a certain moment. In other words, the image shows the arc ARC being discharged from the electrode 70 toward the base metal 200, which is the material to be welded. After acquiring the data of the captured image IMG1 from the camera 90, the image processing device 91 performs predetermined image processing (e.g., image binarization processing) on ​​the captured image IMG1 to generate a binarized image IMG2 (see FIG. 5( b)). This results in a binarized image IMG2 showing the binarized arc ARC1, which clearly shows the outline of the arc ARC in FIG. 5( a). Based on the binarized image IMG2, the image processing device 91 calculates the position indicating the center of gravity of the arc ARC1 (arc center of gravity position C) (see FIG. 5( c)). Furthermore, the image processing device 91 calculates the position of the arc centroid C based on a certain period of time (in other words, a certain number of captured images of FIG. 5( a)), and generates an image IMG3 showing the change over time in the arc centroid position corresponding to each captured image (frame) (see FIG. 5( d)). In FIG. 5( d), the tip position of the electrode 70 is set as the origin, and the arc centroid C is plotted. Here, the horizontal direction is the X coordinate, and the vertical direction is the Z coordinate.

[0053] By generating the image IMG3, the image processing device 91 can quantitatively calculate the change over time in the arc gravity center position C for a certain period of time (in other words, the degree of wobble of the arc ARC). In order to quantitatively evaluate the degree of wobble of the arc ARC, an index shown in the following formula is introduced. σａｒｃ indicates the variation of the arc center of gravity position, and σ ｘ denotes the standard deviation of the X-direction displacement of the arc center of gravity, and σ ｚ indicates the standard deviation of the Z-direction displacement of the arc center of gravity position.

[0054] σ ａｒｃ =√(σ ｘ ２ +σ ｚ ２ )

[0055] The effects of the X waveform (silence and arc rigidity) were examined by comparing it with a sine wave and a square wave. Both the sine wave and the square wave are examples of conventional waveforms with current characteristics different from those of the X waveform, and serve as comparative examples. The common conditions for the comparison were as follows: average current value of 150 A, EP ratio (i.e., the proportion of EP time in one AC cycle) of 30%, and AC frequency of 100 Hz. Meanwhile, the control parameters for the X waveform were as follows: peak period ratio of 20% and EP peak current ratio of 110%.

[0056] The horizontal axis of Fig. 6 represents the type of current waveform (sine wave and square wave as comparative examples) and the X waveform of this embodiment, and the vertical axis of Fig. 6 represents the noise level of the arc ARC generated by the current flow of each current waveform and the variation in the arc gravity center position. As shown in Fig. 6, the noise level was 88.6 (dB) when the current waveform was square wave, 79.9 (dB) when the current waveform was sine wave, and 80.7 (dB) when the current waveform was X waveform. The noise level was about 1 (%) higher with the X waveform than with the sine wave, but about 11 (%) lower than with the square wave.

[0057] As shown in Figure 6, the variation in the arc center position when the current waveform was a sine wave was 0.5, while the variation in the arc center position when the current waveform was a square wave was 0.13, and the variation in the arc center position when the current waveform was an X waveform was 0.18. Note that the smaller the variation in the arc center position, the better the arc rigidity. With the X waveform, the arc rigidity was about 40% lower than with the square wave, but was about 170% better than with the sine wave.

[0058] From the above, it was found that the X waveform achieved arc quietness equivalent to that of a sine wave, but arc rigidity more than twice that of a sine wave. Therefore, it was found that the use of the X waveform makes it possible to achieve both quietness and arc rigidity.

[0059] 5. Investigation and Consideration of Effective Ranges of Control Parameters Next, with reference to Figures 7 to 10, investigation and consideration of the effective ranges of control parameters characterizing the X waveform will be described. Figure 7(a) is a graph showing peak current values ​​at each peak period ratio, Figure 7(b) is a graph showing measurement results of noise levels at each peak period ratio, Figure 7(c) is a graph showing measurement results of variations in arc center position at each peak period ratio, and Figure 7(d) is a graph showing measurement results of the effective ranges of peak period ratios. Figure 8(a) is a graph showing peak current values ​​at each EP peak current ratio, Figure 8(b) is a graph showing measurement results of noise levels at each EP peak current ratio, Figure 8(c) is a graph showing measurement results of variations in arc center position at each EP peak current ratio, and Figure 8(d) is a graph showing measurement results of the effective ranges of EP peak current ratios. Figure 9 is a graph showing measurement results of the peak period ratio and the effective ranges of the EP peak current ratio. FIG. 10( a) is a diagram showing an example of the relationship between control parameter values ​​and weldability, FIG. 10( b) is a diagram showing the overall evaluation criteria for weldability and evaluation examples for each evaluation item, and FIG. 10( c) is a diagram showing examples of individual evaluation criteria for the evaluation items shown in FIG. 10( b).

[0060] As control parameters that can achieve both quietness and arc rigidity, the effective ranges of the peak duration ratio and the EP peak current ratio were investigated. Achieving both quietness and arc rigidity means that the following target values ​​for quietness and arc rigidity are both satisfied. These target values ​​are examples of the above-mentioned predetermined conditions (see step St2 in FIG. 4).

[0061] Target value for quietness: Increase in noise level by 2% or less compared to the characteristics (shape) of the sinusoidal current waveform. In other words, 81.5 (dB) (= 79.9 (dB) x 1.02) or less Target value for arc rigidity: Increase in arc rigidity by more than two times compared to the characteristics (shape) of the sinusoidal current waveform. In other words, increase in the variation of the arc center of gravity position σ compared to the characteristics (shape) of the sinusoidal current waveform. ａｒｃ is reduced to 50% or less. Therefore, σ ａｒｃ is 0.25 (= 0.50 x 0.5) or less

[0062] To select an effective range for the peak period ratio, the peak period ratio was varied from 0% to 100% in 20% increments, and the noise level of the arc ARC was measured and the arc rigidity was evaluated for each peak period ratio. The common conditions for the measurements and evaluations performed while varying the peak period ratio were as follows: the average current was 150A, the EP ratio (i.e., the proportion of EP time in one AC cycle) was 30%, the AC frequency was 100Hz, and the EP peak current ratio was 110%. When the peak period ratio was 0%, the current waveform was sinusoidal, while when the peak period ratio was 100%, the current waveform was rectangular.

[0063] 7A shows the EN peak current value and EP peak current value when each peak period ratio is set. The average current value is shown as an absolute value. The smaller the peak period ratio, the larger the absolute value of the EN peak current value and the absolute value of the EP peak current value.

[0064] Figure 7(b) shows the noise level measurement results when various peak period ratios were set. The noise level was 79.9 dB when the peak period ratio was 0%, 80.0 dB when the peak period ratio was 20%, 81.0 dB when the peak period ratio was 40%, 83.5 dB when the peak period ratio was 60%, 86.4 dB when the peak period ratio was 80%, and 88.6 dB when the peak period ratio was 100%. In other words, the noise level of the arc ARC tended to increase as the peak period ratio increased. Therefore, as shown in Figure 7(b), it was found that the range of peak period ratios that achieved the target quietness value for the arc ARC was a peak period ratio of 0% or more but less than 50%.

[0065] FIG. 7( c ) shows the results of calculations of the arc center position variation calculated by image processing using the image processing device 91 when each peak period ratio was set. When the peak period ratio was 0%, the arc center position variation was 0.50. When the peak period ratio was 20%, the arc center position variation was 0.24, when the peak period ratio was 40%, the arc center position variation was 0.25, when the peak period ratio was 60%, the arc center position variation was 0.21, when the peak period ratio was 80%, the arc center position variation was 0.16, and when the peak period ratio was 100%, the arc center position variation was 0.13. Smaller arc center position variation indicates better arc rigidity. In other words, it was quantitatively confirmed that arc rigidity improves with increasing peak period ratio. It was found that the range of peak period ratios that achieves the target arc rigidity value is a peak period ratio of 20% or more.

[0066] Summarizing FIGS. 7( a) to 7(c) collectively, as shown in FIG. 7(d), it is shown that the effective range of the peak period ratio in which the effects of noise reduction and improvement of arc rigidity can both be obtained is equal to or greater than 20(%) and less than 50(%).

[0067] To select the effective range of the EP peak current ratio, the EP peak current ratio was varied from 80% to 120% in 10% increments, and the arc ARC noise level was measured and the arc rigidity was evaluated for each EP peak current ratio. The common conditions for the measurements and evaluations while varying the EP peak current ratio were as follows: average current value 150A, EP ratio (proportion of EP time in one AC cycle) 30%, AC frequency 100Hz, and peak period ratio 20%.

[0068] The reason why the range for changing the EP peak current ratio is set to 80% to 120% is as follows. Specifically, if the EP peak current value is too large, the amount of wear on the electrode 70 increases, and the penetration depth into the base metal 200, which is the material to be welded, becomes shallow. On the other hand, if the EP peak current value is too small, the cleaning width for the base metal 200 becomes small, which can be a cause of welding defects. For reference, Figure 8(a) shows the EN peak current value and the EP peak current value when each EP peak current ratio is set. The average current value in Figure 8(a) is an absolute value.

[0069] 8(b) shows the measurement results of the noise level of the arc ARC for each EP peak current ratio. The noise level was 79.5 dB when the EP peak current ratio was 80%, 79.9 dB when it was 90%, 80.0 dB when it was 100%, 80.7 dB when it was 110%, and 82.2 dB when it was 120%. In other words, a tendency for the noise level to increase as the EP peak current ratio increased was confirmed.

[0070] The following considerations are made regarding these results. Specifically, the increase in noise level with an increase in the EP peak current ratio is believed to be due to the fact that the EP ratio was set at 30% as a common condition and the EP time per AC cycle was shorter than the EN time. As the EP peak current value increases, the EP current value changes more abruptly during the EP time, resulting in an increase in noise level. On the other hand, as the EN peak current value increases, the EN current value changes more abruptly during the EN time. However, because the EN time is longer than the EP time, the current value changes more gradually than during the EP period. Therefore, when the EP peak current ratio is low, i.e., when the EN peak current value is large and the EP peak current value is small, the effect of reducing the noise generated by the arc ARC during welding is believed to be ensured. Based on the above, it was found that the EP peak current ratio range required to achieve the target value for reducing the noise generated by the arc ARC is 80% or more and less than 115%.

[0071] Figure 8(c) shows the calculated results of the arc center position variation for each EP peak current ratio. When the EP peak current ratio was 80%, the arc center position variation was 0.70. When the EP peak current ratio was 90%, the arc center position variation was 0.38. When the EP peak current ratio was 100%, the arc center position variation was 0.24. When the EP peak current ratio was 110%, the arc center position variation was 0.18. When the EP peak current ratio was 120%, the arc center position variation was 0.18. In other words, when the EP peak current ratio was 100% or higher, the arc rigidity was significantly improved by more than 2.5 times compared to when the EP peak current ratio was 80%. From the above, it was found that the EP peak current ratio range for achieving the target arc rigidity value is 95% or higher and less than 120%.

[0072] Consideration of the reason why arc rigidity improves when the EP peak current ratio is large: Arc rigidity decreases when the EP peak current value is small. Arc rigidity is lower during the EP time than during the EN time. Therefore, when the EP peak current ratio is small, i.e., when the EP current value during the EP time is small, it is thought that the effects on the deterioration of arc rigidity are compounded, causing a significant deterioration in arc rigidity. On the other hand, when the EP peak current ratio is increased, the variation in the arc center position during the EP time can be compensated for by the magnitude of the EP current value. Therefore, it is thought that arc rigidity improves when the EP peak current ratio increases.

[0073] Here, the reason for the statement that "arc rigidity decreases as the EP peak current value decreases" is presumed to be based on the following. Specifically, arc plasma is an electromagnetic fluid, and an electromagnetic force acts on the arc plasma in a direction that causes it to contract due to the influence of the magnetic field created by the current that constitutes the arc plasma. The magnitude of the pressure generated by this electromagnetic force is greater directly below the electrode 70 than directly above the welded material due to differences in the shapes of the electrode 70 and the welded material (base metal 200). This pressure difference generates a high-speed airflow in the arc plasma from the electrode 70 toward the welded material, and this airflow causes arc rigidity. For this reason, in the case of AC TIG welding, when the current value is small, the electromagnetic force becomes smaller, weakening the airflow and tending to result in poor arc rigidity.

[0074] The reason why "arc rigidity is lower during the EP time than during the EN time" is presumed to be based on the following. Specifically, during the EN time, electrons, which are the origin of the arc ARC, are emitted stably from the tip of the electrode 70, which is in a high-temperature state, and the shape of the arc ARC is also likely to be stable. On the other hand, during the EP time, electrons are emitted preferentially from the oxide film present on the surface of the material to be welded (base metal 200), but the oxide film is destroyed as the electrons are emitted. As a result, the location of electron emission moves in search of a new oxide film, and the shape of the arc ARC is likely to change. Therefore, the arc ARC is more likely to fluctuate during the EP time than during the EN time (in other words, the variation in the arc center of gravity position is more likely to change).

[0075] From the above, it was found that the effective range of the EP peak current ratio for obtaining both the effects of reducing arc noise and improving arc rigidity is an EP peak current ratio of 95% or more and less than 115% as shown in FIG. 8(d). Furthermore, it was found that the effective range of the peak period ratio and EP peak current ratio for obtaining both the effects of reducing arc noise and improving arc rigidity is a peak period ratio of 20% or more and less than 50% and an EP peak current ratio of 95% or more and less than 115% as shown in FIG. 9. This is because when the peak period ratio is less than 20%, arc rigidity is insufficient, and when it is 50% or more, quietness is insufficient. Furthermore, when the EP peak current ratio is less than 95%, arc rigidity is insufficient, and when it is 115% or more, penetration depth is insufficient.

[0076] 10(a) to 10(c) show the results of summarizing the weldability (in other words, the arc sound, the arc rigidity, and the penetration depth) when the control parameters, the peak period ratio and the EP peak current ratio, take various values. In other words, it was found that the weldability (see above) is best when the peak period ratio is 20% or more and less than 50% and the EP peak current ratio is 95% or more and less than 115%.

[0077] The current characteristics (shape) of the X waveform according to this embodiment are not limited to those shown in FIG. 2 . FIG. 11 is a graph schematically illustrating another example of the X waveform characteristics. Specifically, the X waveform in FIG. 2 is formed as a gentle curve in each of the EN rise period, EN fall period, EP rise period, and EP fall period. However, the curved portion in each of these periods may have a linear portion (see FIG. 11 ). Specifically, as shown in FIG. 11 , an inflection point where the linear portion intersects with the curved portion is provided in each of the EN rise period, EN fall period, EP rise period, and EP fall period. This inflection point is located in a current range less than 50% of the EN peak current value or the EP peak current value. Furthermore, when the EN peak current value or the EP peak current value, which are set currents, are equal to or greater than a predetermined value, the position of the inflection point is relatively closer to zero (A) as the set current value increases. As a result, it was found that the noise reduction effect of the arc ARC was sufficiently obtained, similar to the X waveform in FIG.

[0078] Fig. 12 is a graph comparing the characteristics of the X waveform and the waveform of the prior art. Fig. 13(a) is a graph showing the measurement results of the noise level for each rising and falling shape of the X waveform and the waveform of the prior art, and Fig. 13(b) is a graph showing the measurement results of the variation in the arc gravity center position for each rising and falling shape of the X waveform and the waveform of the prior art.

[0079] In the X waveform according to this embodiment, the current waveform is curved throughout the entire rise and fall periods in both the EN time (= EN rise period + EN peak period + EN fall period) and the EP time (= EP rise period + EP peak period + EP fall period). Note that, as explained with reference to FIG. 11 , this curved portion may have a linear portion. In contrast, in the waveform disclosed in Patent Document 1, which is a conventional technique, the current changes sharply in a linear manner during both the rise and fall periods, and then changes to a curved shape near the peak current value.

[0080] Therefore, in order to investigate the effect of making the rise and fall periods curved throughout, the current waveforms in the rise and fall periods were linear up to 80% of the peak current value and then curved thereafter (hereinafter, this may be referred to as the "prior art" as a comparative example), and the noise level of the arc sound and the arc rigidity were compared with those of the X waveform (see FIG. 12 ). In this case, the peak period ratio was set to 20% and the EP peak current ratio was set to 100%, which were common values.

[0081] Figure 13(a) shows the measurement results of the noise level of the arc for each waveform. At all current values, the X waveform had a lower noise level than the conventional technology. Furthermore, the difference in noise level was particularly noticeable when the average current value was large, with the X waveform having a noise level approximately 5% lower than the conventional technology. With the X waveform, the noise level was within the target range for all current values ​​up to 200 A, whereas with the conventional technology, it was outside the target range for current values ​​of 150 A or higher.

[0082] Figure 13(b) shows the calculation results of the variation in the arc center position for each waveform. Although the X waveform had arc rigidity approximately 6% lower than the conventional technology, all waveforms were well within the target range. From the above results, the X waveform was superior in terms of arc quietness. Furthermore, although the conventional technology was superior in terms of arc rigidity, all waveforms were within the target range. In this embodiment, the X waveform, which is curved throughout the entire rise and fall periods, was adopted for the following two reasons.

[0083] Reason 1: In the case of conventional waveforms, the noise level is high in the large current range, and the likelihood of welding conditions where the noise level is 85 (dB) or less is small.Reason 2: When the entire rise and fall periods are curved (for example, X waveform), there is a disadvantage that the arc rigidity is poor, but by increasing the EP peak current ratio, which is another characteristic of the X waveform, it is possible to improve the arc rigidity and eliminate the disadvantage.

[0084] The reason why the rise and fall periods are curved is believed to be the reason why noise is reduced even in the high-current range. Specifically, arc noise occurs during AC TIG welding because the arc repeatedly expands and contracts due to changes in current value associated with the AC cycle, causing air vibrations. This air vibration generates the noise. Therefore, the volume of the arc noise is due to the current change gradient (the amount of change in current value over a certain period of time). In the prior art disclosed in Patent Document 1, the current value is changed sharply from 70% to 95% of the peak current value during both the rise and fall periods. In the low-current range, the current change gradient is relatively small, resulting in a noise reduction effect. However, in the high-current range, the current change gradient becomes larger, resulting in a louder arc noise. Therefore, to achieve a noise reduction effect even in the high-current range, it is important to curve both the rise and fall periods throughout the entire range, as in the X waveform of this embodiment.

[0085] <Technology of the Present Disclosure> As described above, the present disclosure discloses the following technical ideas.

[0086] (Item 1) Electrode negative period (T ｎ ) and the electrode negative current during the electrode positive period (T ｐ ) in the electrode negative period, at least an electrode negative rise period and an electrode negative fall period are provided, and the electrode negative current is changed from zero to a predetermined constant electrode negative peak current value (I ｎｐ ) rises in a gentle curve until the negative electrode current falls, and during the negative electrode current fall period, it falls from the negative electrode current peak value to zero in a gentle curve, and from the end of the negative electrode current rise period to the start of the negative electrode current fall period (T ｎｐ ) is constant at the electrode negative peak current value, and in the electrode positive period, at least an electrode positive rise period and an electrode positive fall period are provided, and the electrode positive current is changed from zero to a predetermined constant electrode positive peak current value (Iｐｐ ) rises in a gentle curve, and during the electrode positive falling period, falls in a gentle curve from the electrode positive peak current value to zero, and from the end of the electrode positive rising period to the start of the electrode positive falling period (T ｐｐ This current control method for AC TIG welding maintains the electrode positive peak current constant. This current control method for AC TIG welding achieves both quieter arc noise and improved arc rigidity by controlling the current waveform to be curved during the rise and fall periods of the electrode negative and positive electrode periods and flat during the peak periods. Compared to the sinusoidal waveform, which has traditionally been considered quieter, the X-shaped waveform has a noise level approximately 1% higher, but improves arc rigidity by approximately 170%. This reduces the burden on the welding operator and nearby workers due to arc noise, while also reducing arc wobble, even under conditions where the joint shape of the welded materials is prone to arc wobble, such as lap and fillet joints, allowing for efficient heat transfer to the welded materials. Furthermore, the high arc rigidity prevents the arc from being pulled toward the filler rod, facilitating its insertion into the molten pool.

[0087] (Item 2) The current control method for AC TIG welding according to Item 1, wherein the electrode negative peak period ratio, which indicates the proportion of the period during which the electrode negative peak current value is maintained to the electrode negative period, is 20% or more and less than 50%, and the electrode positive peak period ratio, which indicates the proportion of the period during which the electrode positive peak current value is maintained to the electrode positive period, is 20% or more and less than 50%. Thus, according to this current control method for AC TIG welding, by controlling the peak period ratio for each polarity within this effective range, both the effects of reducing arc noise and improving arc rigidity are achieved. Note that when the peak period ratio for each polarity is less than 20%, arc rigidity is poor, resulting in poor weldability under conditions where the arc is prone to wobble, such as lap welding and fillet welding, and when inserting a filler rod. When the peak period ratio for each polarity is 50% or more, the arc noise becomes louder, increasing the burden on the operator. Note that the EN peak period ratio and the EP peak period ratio do not need to be the same.

[0088] (Item 3) The current control method for AC TIG welding according to Item 1 or 2, wherein, when the absolute value of the electrode negative peak current value and the electrode positive peak current value is equal, the absolute value is defined as a reference peak current value, and the absolute value of the electrode positive peak current value is controlled within a range of 95% to 115% of the reference peak current value. Thus, according to this current control method for AC TIG welding, by controlling the EP peak current value within this effective range, not only can the effects of silencing the arc noise and improving arc rigidity be achieved, but the penetration depth of AC TIG welding is also ensured. When the absolute value of the EP peak current value is less than 95% of the reference peak current value, the arc rigidity is poor. When the absolute value of the EP peak current value is 115% or more of the reference peak current value, the effects of silencing the arc noise and improving arc rigidity are achieved, but the current value during the EN time is small, resulting in a decrease in penetration depth, which is one of the causes of reduced welding quality.

[0089] (Item 4) The current control method for AC TIG welding according to any one of Items 1 to 3, wherein, when the absolute values ​​of the electrode negative peak current value and the electrode positive peak current value are equal, the absolute value is taken as a reference peak current value. The period ratio (EN peak period ratio) at which the electrode negative peak current value occurs, the period ratio (EP peak period ratio) at which the electrode positive peak current value occurs, and the electrode positive peak current ratio (EP peak current ratio), which indicates the ratio of the electrode positive peak current value to the reference peak current value, are determined based on at least one of the thickness of the workpiece to be welded and the joint shape. This current control method for AC TIG welding allows for control of arc quietness and arc rigidity according to the thickness of the workpiece to be welded and the joint shape. Specifically, for thin plates (thickness 0.5 to 2.0 mm), reducing the peak period ratio and increasing the EP peak current ratio are effective in preventing the molten zone from reaching the back of the plate. Under conditions where the arc is prone to fluctuating, such as when making a lap joint or inserting a filler rod, it is effective to increase the peak period ratio and the EP peak current ratio.

[0090] Furthermore, decreasing the peak period ratio weakens the concentration of the arc, reducing the heat input density to the material to be welded. Furthermore, increasing the EP peak current ratio increases the current value during the EP time and decreases the current value during the EN time, resulting in a shallower penetration depth. Therefore, in the case of thin plates, it is effective to decrease the peak period ratio and increase the EP peak current ratio. Increasing the peak period ratio improves arc rigidity. Increasing the EP peak current ratio also improves arc rigidity. Therefore, in the case of lap joints or inserting filler rods, it is effective to increase the peak period ratio and the EP peak current ratio.

[0091] (Item 5) The current control method for AC TIG welding according to any one of Items 1 to 4, wherein, during the electrode negative period, the characteristic from zero to the electrode negative peak current value further includes a linear portion during the electrode negative rise period and the electrode negative fall period, and during the electrode positive period, the characteristic from zero to the electrode positive peak current value further includes a linear portion during the electrode positive rise period and the electrode positive fall period. Thus, according to this current control method for AC TIG welding, when the set current value is small, such as less than 100 (A), a sufficient noise reduction effect can be achieved even if the linear ranges included in each of the rise period and fall period are large. On the other hand, when the set current value is large, such as 150 (A) or more, a large linear range included in the rise period and fall period causes noise, so the position of the inflection point needs to be closer to zero (A).

[0092] (Item 6) An AC TIG welding device (100) for performing AC TIG welding by generating an arc (ARC) between a workpiece (base metal 200) and the workpiece, comprising at least a welding torch (60) having an electrode (70) disposed thereon, and a welding power source (40) for supplying a welding current (Aw) for generating the arc between the tip of the electrode and the workpiece, wherein the welding current is supplied alternately and repeatedly as an electrode negative current during an electrode negative period and an electrode positive current during an electrode positive period, and wherein at least an electrode negative rise period and an electrode negative fall period are provided during the electrode negative period, and the electrode negative current is increased from zero to a predetermined constant electrode negative peak current value (I) during the electrode negative rise period. ｎｐ ) rises in a gentle curve until the negative electrode current falls, and during the negative electrode current fall period, it falls from the negative electrode current peak value to zero in a gentle curve, and from the end of the negative electrode current rise period to the start of the negative electrode current fall period (T ｎｐ ) is constant at the electrode negative peak current value, and in the electrode positive period, at least an electrode positive rise period and an electrode positive fall period are provided, and the electrode positive current is changed from zero to a predetermined constant electrode positive peak current value (I ｐｐ ) rises in a gentle curve, and during the electrode positive falling period, falls in a gentle curve from the electrode positive peak current value to zero, and from the end of the electrode positive rising period to the start of the electrode positive falling period (T ｐｐ) is constant at the electrode positive peak current value. This AC TIG welding device allows for AC TIG welding by creating a current waveform with a curved rise and fall times during the electrode negative and electrode positive periods, and a flat peak time during the period, thereby achieving both quieter arc noise and improved arc rigidity. Compared to the sinusoidal waveform, which has traditionally been considered quieter, the X waveform has a noise level approximately 1% higher, but improves arc rigidity by approximately 170%. This reduces the burden on the welding operator and nearby workers due to arc noise, while also reducing arc wobble even under conditions where the joint shape of the welded materials is prone to arc wobble, such as lap and fillet joints, allowing for efficient heat transfer to the welded materials. Furthermore, the high arc rigidity of the arc prevents the arc from being pulled toward the filler rod, making it easier to insert the filler rod into the molten pool.

[0093] Although various embodiments have been described above with reference to the drawings, it goes without saying that the present disclosure is not limited to such examples. It is clear that a person skilled in the art can conceive of various modifications, alterations, substitutions, additions, deletions, and equivalents within the scope of the claims, and it is understood that these also naturally fall within the technical scope of the present disclosure. Furthermore, the components of the various embodiments described above may be combined in any manner without departing from the spirit of the invention.

[0094] This application is based on a Japanese patent application (Patent Application No. 2024-131158) filed on August 7, 2024, the contents of which are incorporated herein by reference.

[0095] INDUSTRIAL APPLICABILITY The present disclosure is useful as a current control method for AC TIG welding and an AC TIG welding apparatus that perform AC TIG welding while achieving both quietness and rigidity of the generated arc.

[0096] 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 Drive unit 31 Memory unit 32 Input unit 33 Teaching pendant 34 Display unit 40 Welding power source 51 Power cable 52 Power cable 60 Welding torch 61 Torch switch 70 Electrode 80 Filler metal 90 Camera 91 Image processing device 92 Sound level meter 93 Display 100 AC TIG welding device 200 Base metal Aw Welding current PS Three-phase AC power supply

Claims

1. A current control method for AC TIG welding in which welding is performed by repeatedly and alternately passing a negative electrode current during a negative electrode period and a positive electrode current during a positive electrode period, wherein at least a negative electrode rise period and a negative electrode fall period are provided during the negative electrode period, the negative electrode current rises in a gentle curve from zero to a predetermined constant negative electrode peak current value during the negative electrode rise period, falls in a gentle curve from the negative electrode peak current value to zero during the negative electrode fall period, and is constant at the negative electrode peak current value from the end of the negative electrode rise period to the start of the negative electrode fall period, and the positive electrode current is set to be constant at the negative electrode peak current value, and the positive electrode period is set to be constant at the positive electrode peak current value a current control method for AC TIG welding, wherein the electrode positive current rises from zero to a predetermined constant electrode positive peak current value in a gentle curve during the electrode positive rise period, falls from the electrode positive peak current value to zero in a gentle curve during the electrode positive fall period, and is kept constant at the electrode positive peak current value from the end of the electrode positive rise period to the start of the electrode positive fall period.

2. The current control method for AC TIG welding according to claim 1, wherein an electrode negative peak period ratio indicating the proportion of the period during which the electrode negative peak current value is maintained in the electrode negative period is 20% or more and less than 50%, and an electrode positive peak period ratio indicating the proportion of the period during which the electrode positive peak current value is maintained in the electrode positive period is 20% or more and less than 50%.

3. A current control method for AC TIG welding according to claim 1, wherein, when the absolute value of the electrode negative peak current value and the electrode positive peak current value is equal, the absolute value of the electrode positive peak current value is set to a reference peak current value, and the absolute value of the electrode positive peak current value is controlled within a range of 95% or more and less than 115% of the reference peak current value.

4. A current control method for AC TIG welding according to claim 1, wherein, when the absolute value when the absolute values ​​of the electrode negative peak current value and the electrode positive peak current value are equal is taken as a reference peak current value, the period ratio at which the electrode negative peak current value is achieved, the period ratio at which the electrode positive peak current value is achieved, and the electrode positive peak current rate indicating the rate of the electrode positive peak current value to the reference peak current value are determined based on at least one of the plate thickness and joint shape of the materials to be welded in the AC TIG welding.

5. A current control method for AC TIG welding according to claim 1, wherein, during the electrode negative period, the characteristic from zero to the electrode negative peak current value further has a linear portion during the electrode negative rising period and the electrode negative falling period, and during the electrode positive period, the characteristic from zero to the electrode positive peak current value further has a linear portion during the electrode positive rising period and the electrode positive falling period.

6. An AC TIG welding device for performing AC TIG welding by generating an arc between the tip of the electrode and the material to be welded, comprising at least a welding torch on which an electrode is disposed, and a welding power source for supplying a welding current for generating the arc between the tip of the electrode and the material to be welded, wherein the welding current is supplied alternately and repeatedly as a negative electrode current during a negative electrode period and a positive electrode current during a positive electrode period, wherein at least a negative electrode rise period and a negative electrode fall period are provided during the negative electrode period, wherein the negative electrode current rises in a gentle curve from zero to a predetermined constant negative electrode peak current value during the negative electrode rise period, and falls in a gentle curve from the negative electrode peak current value to zero during the negative electrode fall period, and is constant at the negative electrode peak current value from the end of the negative electrode rise period to the start of the negative electrode fall period, wherein at least a positive electrode rise period and a positive electrode fall period are provided during the positive electrode period, the electrode positive current rises in a gentle curve from zero to a predetermined constant electrode positive peak current value during the electrode positive rise period, falls in a gentle curve from the electrode positive peak current value to zero during the electrode positive fall period, and is kept constant at the electrode positive peak current value from the end of the electrode positive rise period to the start of the electrode positive fall period.

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