Ac arc welding method

Abstract

This AC arc welding method uses an electrode 70, which is a non-consumable electrode, and comprises first to third steps. In the first step, the welding period Tw is set as a plurality of periods including at least an initial welding period Ts and a main welding period Tm, and welding conditions are individually set in each of the plurality of periods. In the second step, the AC frequency f of the welding current Aw and the set current Is are individually set in each of the plurality of periods. In the third step, a base material 200 is welded by controlling the welding current Aw on the basis of the set current Is and the AC frequency f. In the second step, the AC frequency f1 of the initial welding period Ts is set higher than the AC frequency f2 of the main welding period Tm.

Description

AC arc welding method

[0001] The present disclosure relates to AC arc welding methods, and more particularly to AC TIG welding methods.

[0002] AC Tungsten Inert Gas (TIG) welding is a well-known method for arc welding base metals made of aluminum or aluminum alloys. In AC TIG welding, a highly directional arc is generated during the electrode negative period when the electrode is negative, allowing for the formation of a narrow weld bead with a deep penetration. Furthermore, during the electrode positive period when the electrode is positive, a cleaning action occurs on the surface of the base metal, removing any oxide film formed on the surface of the base metal, resulting in a clean surface suitable for welding.

[0003] In AC TIG welding, by appropriately controlling the welding current flowing through the electrode and the AC frequency of the welding current according to the shape and thickness of the base material, the arc pressure directly below the electrode can be changed to obtain the desired weld bead.

[0004] For example, Patent Document 1 discloses an AC arc welding method in which the AC frequency is changed in conjunction with the welding current. In a low-current region where the arc has low directivity and does not concentrate, the AC frequency can be increased to increase the directivity of the arc and concentrate it. On the other hand, in a high-current region where the arc concentrates too much, the AC frequency can be decreased to weaken the arc concentration and prevent the occurrence of undercuts and the like.

[0005] Furthermore, Patent Document 2 discloses an AC arc welding method in which, after setting the welding current, the AC frequency is changed to control the penetration depth. By utilizing the fact that the arc pressure changes in response to the AC output frequency and the penetration depth changes in response to the arc pressure, the penetration depth can be controlled by changing the AC output frequency.

[0006] Patent No. 2718545 Patent No. 2942783

[0007] When fillet welding of base metals made of aluminum or aluminum alloys is performed using an AC TIG welding machine, it is necessary to melt the upper and lower base metal sheets in a short time at the start of welding. To meet this requirement, it is conceivable to increase the heat input to the base metal by increasing the set current and concentrating the arc, or to increase the AC frequency and concentrate the arc, as disclosed in Patent Documents 1 and 2, thereby increasing the melting rate of the base metal.

[0008] However, simply increasing the set current can result in excessive heat input, which can lead to burn-through at the start of welding if the base material is thin. Also, if the AC frequency is uniformly increased over the welding period, the arc noise becomes too loud, putting a strain on the welder.

[0009] In other words, when fillet welding of base metals made of aluminum or aluminum alloys is performed using an AC TIG welding machine, it is difficult to set appropriate welding conditions at the start of welding, which reduces welding workability.

[0010] The present disclosure has been made in consideration of the above points, and its purpose is to provide an AC arc welding method that can improve workability at the start of welding when arc welding base materials made of aluminum or aluminum alloys.

[0011] In order to achieve the above object, an AC arc welding method according to the present disclosure is an AC arc welding method using a non-consumable electrode, comprising at least a first step of setting a welding period as a plurality of periods including at least an initial welding period and a main welding period and enabling welding conditions to be set individually for each of the plurality of periods; a second step of setting an AC frequency of a welding current flowing through the non-consumable electrode and a set current which is a moving average value of the welding current individually for each of the initial welding period and the main welding period; and a third step of controlling the welding current based on the set current and the AC frequency set in the second step and welding a base material, for each of the initial welding period and the main welding period, and characterized in that in the second step, the AC frequency in the initial welding period is set higher than the AC frequency in the main welding period.

[0012] According to the present disclosure, when arc welding a base material made of aluminum or an aluminum alloy, workability at the start of welding can be improved.

[0013] FIG. 1 is a schematic diagram of an arc welding machine according to an embodiment. FIG. 2 is a flowchart showing an AC arc welding procedure. FIG. 3 is a schematic diagram showing a set current for each period of a welding period. FIG. 4 is a schematic diagram of a welding current waveform. FIG. 5 is a schematic diagram for explaining fillet welding. FIG. 6 is a diagram showing the influence of welding conditions for the initial welding period and the main welding period on welding performance. FIG. 7 is a diagram showing the relationship between the overall evaluation criteria for welding performance and the evaluation results for each evaluation item. FIG. 8 is a diagram showing the individual evaluation criteria for the evaluation items shown in FIG. 7. FIG. 9 is a schematic diagram for explaining arc directionality. FIG. 10 is a diagram showing the relationship between AC frequency and the improvement rate of arc noise and base metal melting rate. FIG. 11 is a diagram showing the relationship between the evaluation results of welding performance and the set current for the main welding period and the AC frequency for the initial welding period.

[0014] 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.

[0015] (Embodiments) [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.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] The control unit 30 is configured with one or more central processing units (CPUs), or one or more micro control units (MCUs). The control unit 30 also has a drive unit 30A.

[0022] In the example shown in FIG. 1 , a storage unit 31 is provided independent of the control unit 30. The storage unit 31 is configured with a semiconductor memory such as a random access memory (RAM) or a read-only memory (ROM). The storage unit 31 may also be configured with a hard disk drive (HDD) or a solid state drive (SSD). The storage 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 storage unit 31 stores welding conditions used in arc welding. The storage unit 31 also stores control programs and welding parameters for various devices.

[0023] 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 from 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 is achieved. The drive unit 30A also controls the switching operation of the second switching unit 16 based on the set current Is and the AC frequency of the welding current Aw input from the input unit 32. The set current Is refers to the moving average value of the welding current Aw during the welding period Tw. However, as will be described later, in this embodiment, the welding period Tw includes multiple periods, and the set current Is can be set for each of the multiple periods.

[0024] 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.

[0025] The input unit 32 is used to input welding conditions during arc welding, such as the set current Is and AC frequency described above, and also the cleaning width, which will be described later.

[0026] 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.

[0027] 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 welding period Tw 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.

[0028] 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.

[0029] 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. When the torch switch 61 is operated at a different time, the supply of the welding current Aw to the electrode 70 is stopped, causing the arc ARC to disappear. As will be described later, by operating the torch switch 61, the base material 200 can also be welded by dividing the welding period Tw into multiple periods.

[0030] 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 the weld line so that the distance between the tip of electrode 70 and the surface of base material 200 is within a preset range.

[0031] 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.

[0032] In this embodiment, the welding period Tw is set as an initial welding period Ts, a main welding period Tm, and a crater treatment period Tc, and welding may be performed without using filler material 80 during the initial welding period Ts, and using filler material 80 during the main welding period Tm and the crater treatment period Tc.

[0033] In addition, when the filler material 80 is supplied during the initial welding period Ts, it is preferable to start welding by relatively increasing the AC frequency during the initial welding period Ts, in order to melt the base material 200 quickly at the start of welding.

[0034] After the arc ARC is generated, the temperature of the base material 200 begins to rise, and when a certain amount of heat input is accumulated, the base material 200 finally melts. Since supplying the filler metal 80 in the early stage before the base material 200 melts will not result in a clean weld, the filler metal 80 is basically supplied to the molten pool 201 of the base material 200 after it has been confirmed, for example, visually, that melting has started.

[0035] The timing for supplying the filler material 80 to the molten pool 201 of the base material 200 after the base material 200 has melted may be either of the following two: First, the filler material 80 is supplied during the initial welding period Ts, and then the welding period is switched to the main welding period Tm; Alternatively, the filler material 80 is supplied after the welding period is switched to the main welding period Tm.

[0036] [Outline of AC Arc Welding Method] Fig. 2 is a flowchart showing an AC arc welding procedure, Fig. 3 is a schematic diagram showing a set current for each period of a welding period, and Fig. 4 is a schematic diagram showing a welding current waveform.

[0037] 2, first, the input unit 32 is operated to set the welding condition setting mode to the individual setting mode (step S1). Specifically, the input unit 32 is operated to read the individual setting mode stored in the memory unit 31 to the control unit 30. In the individual setting mode, the welding period Tw is set as an initial welding period Ts, a main welding period Tm, and a crater treatment period Tc. Furthermore, the welding conditions for each period can be set individually.

[0038] Next, the set current Is, AC frequency f, and cleaning width Rc are set for each of the initial welding period Ts, main welding period Tm, and crater treatment period Tc (step S2).

[0039] 3, the current value of the set current Is is set to Is1 during the initial welding period Ts and the crater treatment period Tc, and to Is2 (Is2 > Is1) during the main welding period Tm. However, the current value of the set current Is during the initial welding period Ts is not particularly limited to this, and the current value of the set current Is during the initial welding period Ts may be set to the same as or greater than the current value Is2 of the set current Is during the main welding period Tm.

[0040] The current value of the set current Is during the crater treatment period Tc is set to be smaller than the current value Is2 of the set current Is during the main welding period Tm. However, the current value of the set current Is (Is3) during the crater treatment period Tc may be different from the current value of the set current Is (Is1) during the initial welding period Ts.

[0041] Furthermore, the AC frequency f1 in the initial welding period Ts is set higher than the AC frequency f2 in the main welding period Tm.

[0042] The intervals during which the set current Is increases or decreases during the initial welding period Ts, the main welding period Tm, and the crater treatment period Tc represent the transition period from the initial welding period Ts to the main welding period Tm, or the transition period from the main welding period Tm to the crater treatment period Tc. Specifically, the transition period from the initial welding period Ts to the main welding period Tm is an interval during which the set current Is increases, and the transition period from the main welding period Tm to the crater treatment period Tc is an interval during which the set current Is decreases.

[0043] Here, the AC frequency f during the transition period is the same as the frequency before switching to the transition period, that is, the frequency during the period before the transition period begins.

[0044] For example, if the initial welding period Ts is 200 Hz, the main welding period Tm is 70 Hz, and the crater treatment period Tc is 150 Hz, the AC frequency f during the transition period from the initial welding period Ts to the main welding period Tm is 200 Hz, and the AC frequency f during the transition period from the main welding period Tm to the crater treatment period Tc is 70 Hz. The AC frequency f during the transition period is set to the same as the frequency before switching to the transition period, but it may also be set to the same as the frequency during the period after the transition period ends.

[0045] Furthermore, a cleaning width Rc is set during the main welding period Tm. The definition of the cleaning width Rc will be explained with reference to FIG.

[0046] As shown in FIG. 4, the time waveform of the welding current Aw (hereinafter referred to as the welding current waveform) is ＥＮ and the electrode positive period T ＥＰ The negative electrode period T ＥＮ is a period during which the base material 200 has a positive polarity and the electrode 70 has a negative polarity, and the current value is I ＥＮ The electrode positive period T ＥＰ is a period during which the base material 200 has a negative polarity and the electrode 70 has a positive polarity, and the current value is I ＥＰ is maintained.

[0047] The AC frequency f is the reciprocal of the AC period T. As is clear from this, the AC period T in the initial welding period Ts is set to be shorter than the AC period T in the main welding period Tm. Also, the cleaning width Rc is set to be the ratio of the electrode positive period T to the AC period T. ＥＰ and satisfies the relationship shown in formula (1).

[0048] Rc (%) = 100 x (T ＥＰ / T) (1) The AC frequency f3 in the crater treatment period Tc is set separately to reduce a depression (not shown) at the welding end point. In this embodiment, the cleaning width Rc in the initial welding period Ts and the crater treatment period Tc is set to be the same as the cleaning width Rc in the main welding period Tm, but these may be different from each other.

[0049] Once the welding conditions have been set, when the torch switch 61 is operated, a welding current Aw flows through the electrode 70 based on the welding conditions for the initial welding period Ts set in step S2, and an arc ARC is generated between the tip of the electrode 70 and the surface of the base material 200. The arc ARC is irradiated onto the base material 200, and the initial welding period Ts begins (step S3).

[0050] When the torch switch 61 is operated again after a predetermined period of time has elapsed, the welding conditions are switched to those for the main welding period Tm, and the welding period transitions from the initial welding period Ts to the main welding period Tm (step S4). When the welding of the planned welding points on the base material 200 is completed, the torch switch 61 is operated again. This operation switches the welding conditions to those for the crater treatment period Tc, and the welding period transitions from the main welding period Tm to the crater treatment period Tc (step S5). When the crater treatment is completed, the torch switch 61 is operated again to extinguish the arc ARC, ending the crater treatment period Tc (step S6), and welding of the base material 200 is completed.

[0051] [Effects of welding conditions during the initial welding period and the main welding period on welding workability] Fig. 5 is a schematic diagram for explaining fillet welding. Fig. 6 is a diagram showing the effects of welding conditions during the initial welding period and the main welding period on welding workability.

[0052] Fig. 7 is a diagram showing the relationship between the overall evaluation criteria for welding workability and the evaluation results for each evaluation item. Fig. 8 is a diagram showing the individual evaluation criteria for the evaluation items shown in Fig. 7. Fig. 9 is a schematic diagram for explaining the directionality of the arc. Fig. 10 is a diagram showing the relationship between the AC frequency and the improvement rate of the arc noise and the melting rate of the base metal.

[0053] The inventors of the present application performed arc welding using a base material 200 having the structure shown in Fig. 5, and investigated the effects of the welding conditions for the initial welding period Ts and the main welding period Tm on welding workability. The base material 200 shown in Fig. 5 is a T-joint in which the side of the upper plate 210 abuts against the top surface of the lower plate 220, and arc welding is performed along the weld line (boundary line) between the upper plate 210 and the lower plate 220. In other words, the upper plate 210 and the lower plate 220 of the base material 200 are joined by fillet welding.

[0054] 5, the AC frequency f2 during the main welding period Tm was fixed to 70 Hz, and the cleaning width Rc was fixed in the range of 20% to 40%.

[0055] Under these conditions, the conditions were varied using the set current Is2 in the main welding period Tm and the AC frequency f1 in the initial welding period Ts as parameters, and the base material 200 was welded to evaluate the welding workability. Note that, since the heat input to the base material 200 increases as the set current Is2 increases, the plate thicknesses of the upper plate 210 and the lower plate 220 were also increased as the set current Is2 increased.

[0056] As shown in FIG. 7 , the welding operability was evaluated comprehensively, taking into consideration factors related to shortening the welding time in the initial stage of welding (directivity of the arc ARC and melting rate of the base metal 200) and the physical burden on the welding operator (arc noise). That is, both the directivity of the arc ARC and the melting rate of the base metal 200 were evaluated using values ​​during the initial welding period Ts. As shown in FIG. 7 , the welding operability was evaluated using a five-level scale: Excellent (⊚), Very Good (○), Average (▲), Poor (×), and Unacceptable (XX). As shown in FIG. 8 , the three evaluation items that determine the welding operability (directivity of the arc ARC, melting rate of the base metal 200, and arc noise) were evaluated using two or three levels out of four levels: Very Good (○), Good (△), Average (▲), and Poor (×).

[0057] The directivity of the arc ARC indicates the degree of spread of the arc ARC, and it was determined that the smaller the spread, the better the directivity. As shown in Figure 9, when the AC frequency f1 during the initial welding period Ts was higher than the AC frequency f2 of 70 Hz during the main welding period Tm, the diameter D2 of the arc ARC when welding at the AC frequency f1 was smaller than the diameter D1 of the arc ARC when welding at the AC frequency f2 of 70 Hz. In other words, the spread of the arc ARC was suppressed, and the directivity of the arc ARC was improved.

[0058] Specifically, if the diameter D2 of the arc ARC when welding at an AC frequency f1 is 20% or more smaller than the diameter D1 of the arc ARC when welding at an AC frequency f2 of 70 Hz, it was judged as ○. Also, if the variation in diameter D2 with respect to diameter D1 is less than 20%, it was judged as ▲, as the directivity of the arc ARC is equivalent.

[0059] The melting rate of the base material 200 was evaluated as the time from when the arc ARC was applied until the upper plate 210 and the lower plate 220 melted. Specifically, compared to the time (approximately 2 seconds) until the upper plate 210 and the lower plate 220 of the base material melted when welding was performed at an AC frequency f2 of 70 Hz during the main welding period Tm, if the time until melting was 0.5 seconds or more faster when welding was performed at an AC frequency f1 during the initial welding period Ts, it was evaluated as △, and if it was 1 second or more faster, it was evaluated as ○.

[0060] When the arc noise was less than 95 dB, it was judged as "○" (low), when it was 95 dB or more but less than 100 dB, it was judged as "△" (medium), and when it was 100 dB or more, it was judged as "×" (high).

[0061] According to the noise tolerance standards established by the Japan Society for Occupational Health from the standpoint of hearing protection, if the permissible noise level is 100 dB, the permissible daily exposure time is 15 minutes or less. As mentioned above, when arc welding is performed by moving the welding torch 60 using a robot, there is usually no welding worker near the base material 200, so even if the arc noise exceeds 100 dB, it is acceptable. Similarly, when a welding worker takes soundproofing measures such as wearing earplugs and holds the welding torch 60 in his or her hand to arc weld the base material 200, even if the arc noise exceeds 100 dB, it is acceptable for the work. However, in reality, if the arc noise exceeds 95 dB, the environmental noise in the welding work area becomes large, reducing workability.

[0062] 10, the arc noise increases as the AC frequency f1 increases. Meanwhile, as compared to when the AC frequency is 70 Hz, the melting rate of the base material 200 also increases as the AC frequency f1 increases. However, when the AC frequency f1 becomes higher than 120 Hz, the improvement rate of the melting rate of the base material 200 compared to when the AC frequency is 70 Hz is saturated at 50%.

[0063] 11 is a diagram showing the relationship between the evaluation results of welding performance and the set current in the main welding period and the AC frequency in the initial welding period. Specifically, Fig. 11 shows the evaluation results shown in Fig. 6 organized by the set current Is2 in the main welding period Tm and the AC frequency f1 in the initial welding period Ts.

[0064] If the evaluation result of welding workability is ⊚ or ◯, which is considered to be an improvement in welding workability, it was found that welding workability was improved (◯ to ⊚) when the set current Is2 was greater than 80 A but not greater than 180 A and the AC frequency f1 was greater than 100 Hz but not greater than 250 Hz, as shown in Figure 11. In particular, welding workability was best (⊚) when the AC frequency f1 was greater than 120 Hz but not greater than 200 Hz. Note that when the set current Is2 was greater than 80 A but not greater than 180 A, the plate thicknesses of the upper plate 210 and the lower plate 220 suitable for AC TIG welding were in the range of 1.5 mm or more and 4.0 mm or less, respectively.

[0065] 6 and 11 , when the set current Is2 was set in the range of greater than 80 A and less than or equal to 180 A, the arc noise was reduced to less than 95 dB when the AC frequency f1 during the initial welding period Ts was set to 100 Hz or less, which was equivalent to the level of the arc noise during the main welding period Tm. The directivity of the arc ARC was also equivalent to that during the main welding period Tm when the AC frequency f2 was 70 Hz. Meanwhile, the melting rate of the base metal 200 was also equivalent to that during the main welding period Tm when the AC frequency f2 was 70 Hz. In other words, when the AC frequency f1 was set to 100 Hz or less, the welding workability was equivalent to that during the main welding period Tm when the AC frequency f2 was 70 Hz, and no particular improvement was observed.

[0066] On the other hand, when the AC frequency f1 is increased above 250 Hz during the initial welding period Ts, the arc noise becomes loud (x), reaching 100 dB or more, making it uncomfortable and unbearable for the welding operator even during a short welding period. In this case, the melting rate of the base material 200 is improved compared to when the AC frequency f1 is the same as the AC frequency f2, i.e., 70 Hz. However, it was determined that this is an undesirable condition from the standpoint of noise when actually performing welding work. In other words, when the AC frequency f1 is increased above 250 Hz, the arc noise becomes loud (x), and welding workability deteriorates compared to when the AC frequency f2 is 70 Hz during the main welding period Tm.

[0067] It was also found that welding workability improved when the set current Is2 was greater than 180 A and equal to or less than 300 A and the AC frequency f1 was greater than 100 Hz and equal to or less than 200 Hz. When the set current Is2 was greater than 180 A and equal to or less than 300 A, the plate thicknesses of the upper plate 210 and the lower plate 220 suitable for AC TIG welding were in the range of 4.0 mm or more and 9.0 mm or less, respectively.

[0068] Even when the set current Is2 was set in the range of more than 180 A and not more than 300 A, if the AC frequency f1 was set to 100 Hz or less, the welding workability was the same as that in the case of the main welding period Tm, and no particular improvement was observed. On the other hand, if the AC frequency f1 was set to more than 200 Hz, the arc noise became louder, exceeding 100 dB, which was determined to be an unfavorable condition from the viewpoint of noise, as mentioned above, and the welding workability was reduced compared to the case of the main welding period Tm.

[0069] The AC frequency f2 during the main welding period Tm was set to 70 Hz for the following reasons. When the AC frequency f2 is equal to the commercial frequency, i.e., 50 Hz or 60 Hz, the arc pressure is reduced. Therefore, when the shape of the welding area is recessed rather than flat, such as in fillet welding, the arc ARC is less likely to concentrate at the intended welding area. As a result, the width of the weld bead (not shown) gradually increases during welding. On the other hand, when the AC frequency f2 is increased, the arc pressure increases, making it easier for the arc ARC to concentrate at the intended welding area. Therefore, even in fillet welding, a weld bead with a uniform width can be formed. However, in this case, as the AC frequency f2 increases, the arc noise becomes louder and higher-pitched, which increases the strain on the welder's ears during welding and reduces workability. In consideration of the above, in the study shown in this embodiment, the AC frequency f2 was set to 70 Hz, which can suppress the spread of the arc ARC and reduce the arc noise to less than 95 dB, a level that is gentle on the welder's ears.

[0070] [Effects, etc.] As described above, the AC arc welding method according to this embodiment is an AC arc welding method using electrode 70, which is a non-consumable electrode, and includes at least the following first to third steps.

[0071] In the first step (step S1 in FIG. 2), the welding condition setting mode is switched to the individual setting mode. Specifically, the welding period Tw is set as a plurality of periods including at least an initial welding period Ts and a main welding period Tm, and the welding conditions can be set individually for each of the plurality of periods.

[0072] In the second step (step S2 in FIG. 2), the AC frequency f of the welding current Aw flowing through the electrode 70 and the set current Is, which is the moving average value of the welding current Aw, are individually set for each of the initial welding period Ts and the main welding period Tm.

[0073] In the third step (steps S3 and S4 in Figure 2), during each of the initial welding period Ts and the main welding period Tm, the welding current Aw is controlled based on the set current Is and AC frequency f set in the second step, and the base material 200 is welded.

[0074] In the second step, the AC frequency f1 in the initial welding period Ts is set higher than the AC frequency f2 in the main welding period Tm.

[0075] In this embodiment, the base material 200 is made of aluminum or an aluminum alloy. The base material 200 has a structure in which two plates are overlapped, and in this embodiment, it has a fillet welded structure as shown in FIG.

[0076] According to this embodiment, the directivity of the arc ARC at the start of welding can be improved by setting the AC frequency f1 during the initial welding period Ts higher than the AC frequency f2 during the main welding period Tm, thereby improving the melting rate of the base material 200, which is the T-joint between the upper plate 210 and the lower plate 220, for example.

[0077] Aluminum and aluminum alloys have good thermal conductivity, and stable welding cannot be performed unless the oxide film formed on the surface of the base material 200 is removed during welding. Therefore, immediately after the start of welding, a large amount of heat must be input until the base material 200 melts, which takes time under normal conditions. In particular, when the base material 200 has a fillet-welded structure as shown in this embodiment, the two plates do not melt easily unless heat is input evenly to the upper plate 210 and the lower plate 220. Therefore, a long welding time is required at the start of welding, which reduces welding workability.

[0078] On the other hand, according to this embodiment, the set current Is is set to a constant Is1 during the initial welding period Ts, and set to a constant Is2 during the main welding period Tm. Furthermore, by setting the AC frequency f1 during the initial welding period Ts higher than the AC frequency f2 during the main welding period Tm, the arc pressure can be increased and the directionality of the arc ARC can be improved. As a result, heat can be input locally and concentratedly to the welding start portion, thereby improving the melting rate of the base material 200. As a result, the welding time at the start of welding can be reduced, and welding workability can be improved.

[0079] Furthermore, suppose that the AC frequency f2 during the main welding period Tm is set to the same value as the AC frequency f1 during the initial welding period Ts, and that the AC frequencies f1 and f2 are set to be higher than 70 Hz, for example, approximately 250 Hz. In this case, the directivity of the arc ARC becomes high during the initial welding period Ts, and the melting rate of the base material 200 increases. However, if arc welding is continued at the same AC frequency f2 (= f1) during the main welding period Tm, the high directivity of the arc ARC may make it difficult for the weld bead to widen, and the end and periphery of the weld bead may not fit well with the base material 200.

[0080] On the other hand, according to this embodiment, the AC frequency f can be switched during the welding period Tw by operating the torch switch 61, so that it is possible to achieve optimal welding required for both the initial welding period Ts and the main welding period Tm. Similarly, it is also possible to achieve optimal welding required for the crater treatment period Tc.

[0081] Furthermore, according to this embodiment, by operating the torch switch 61, the initial welding period Ts can be transitioned to the main welding period Tm and then to the crater treatment period Tc. During this transition, the welding conditions can also be switched. That is, by operating the torch switch 61, the AC frequency can be switched from f1 during the initial welding period Ts to f2 during the main welding period Tm, thereby making the arc noise lower and quieter during the main welding period Tm. This reduces the physical burden on the welder caused by the arc noise, even when the main welding period Tm is long, such as when the welding distance is long.

[0082] In the second step, it is preferable to further individually set the cleaning width Rc for each of the initial welding period Ts, the main welding period Tm, and the crater treatment period Tc. The cleaning width Rc is set during the electrode positive period T, during which the electrode 70 has a positive polarity with respect to the AC period T of the welding current Aw. ＥＰ As described above, in this embodiment, the cleaning width Rc for each period is set to the same value, but the values ​​may be changed individually.

[0083] According to this embodiment, the AC frequency f and cleaning width Rc can be changed in conjunction with the set current Is during each of the initial welding period Ts, main welding period Tm, and crater treatment period Tc. Furthermore, by appropriately setting the cleaning width Rc during each period, it is possible to reliably remove, for example, an oxide film on the surface of the base material 200, thereby performing stable welding. Furthermore, it is possible to prevent smut from adhering to the vicinity of the weld bead. Smut is a black, soot-like substance that adheres to the surface of the base material 200 when aluminum vapor oxidizes.

[0084] In the second step, it is preferable to set the set current Is2 during the main welding period Tm in the range of more than 80 A and not more than 180 A, and to set the AC frequency f1 during the initial welding period Ts in the range of more than 100 Hz and not more than 250 Hz. It is also preferable to set the cleaning width Rc during the main welding period Tm in the range of not less than 20% and not more than 40%.

[0085] By setting the set current Is2 and the AC frequency f1 within the aforementioned ranges, it is possible to increase the directivity of the arc ARC during the initial welding period Ts and improve the melting rate of the base material 200. Furthermore, by setting the cleaning width Rc within the aforementioned ranges, it is possible to reliably remove the oxide film on the surface of the base material 200 and perform stable welding. These factors further improve the welding workability.

[0086] Furthermore, when the set current Is2 is set to be greater than 80 A and equal to or less than 180 A, the thicknesses of the upper plate 210 and the lower plate 220 in the base material 200 are preferably in the range of 1.5 mm or more and 4.0 mm or less, respectively.

[0087] Furthermore, when the set current Is2 is set in the range of more than 80 A and not more than 180 A, it is more preferable to set the AC frequency f1 in the range of more than 120 Hz and not more than 200 Hz. In this way, the directivity of the arc ARC is increased during the initial welding period Ts, the melting rate of the base material 200 is improved, and the arc noise is suppressed to less than 95 dB, thereby further reducing the physical burden on the welding operator.

[0088] In the second step, the set current Is2 during the main welding period Tm may be set in the range of more than 180 A and not more than 300 A, and the AC frequency f1 during the initial welding period Ts may be set in the range of more than 100 Hz and not more than 200 Hz. In this case, it is also preferable to set the cleaning width Rc in the range of not less than 20% and not more than 40%.

[0089] By setting the set current Is2 and the AC frequency f1 within the aforementioned ranges, it is possible to increase the directivity of the arc ARC during the initial welding period Ts and improve the melting rate of the base material 200. Furthermore, by setting the cleaning width Rc within the aforementioned ranges, it is possible to reliably remove the oxide film on the surface of the base material 200 and perform stable welding. These factors further improve the welding workability.

[0090] Furthermore, when the set current Is2 is set to be greater than 180 A and equal to or less than 300 A, the thicknesses of the upper plate 210 and the lower plate 220 in the base material 200 are preferably in the range of 4.0 mm or more and 9.0 mm or less, respectively.

[0091] Furthermore, in the second step, the AC frequency f2 during the main welding period Tm can be set in the range of 70 Hz or more and 120 Hz or less. If the base material 200 melts during the initial welding period Ts, the base material 200 can be continuously melted by irradiating the arc ARC during the main welding period Tm, in which the set current Is2 is equal to or greater than the set current Is1 of the initial welding period Ts. Therefore, in this case, the range of the AC frequency f2 during the main welding period Tm is set with emphasis on reducing the influence of arc noise rather than on the melting rate.

[0092] Typically, the main welding period Tm is set longer than the initial welding period Ts. Because the initial welding period Ts is short, even if the arc noise is evaluated as medium (△), the impact on the human body is not significant. However, the main welding period Tm may place a significant physical burden on the welding worker. By setting the upper limit of the AC frequency f2 during the main welding period Tm to 120 Hz or less, the arc noise can be kept below 95 dB throughout the entire allowable range of the AC frequency f2. This reduces the physical burden on the welding worker and prevents a decrease in welding workability.

[0093] In this embodiment, the base material 200 has a fillet welded structure such as a T-joint structure, but is not limited to this. The base material 200 may be a single plate material. Also, the base material 200 may have a structure in which two plate materials are stacked in the thickness direction.

[0094] The AC arc welding control method of the present disclosure is useful because it can improve workability at the start of welding when arc welding base materials made of aluminum or aluminum alloys.

[0095] 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 (input unit) 40 Welding power source 51 Power cable 52 Power cable 60 Welding torch 61 Torch switch 70 Electrode 80 Filler metal 100 Arc welding machine 200 Base metal 210 Upper plate 220 Lower plate ARC Arc PS Three-phase AC power supply

Claims

1. An AC arc welding method using a non-consumable electrode, comprising at least a first step of setting a welding period as a plurality of periods including at least an initial welding period and a main welding period, and enabling welding conditions to be set individually for each of the plurality of periods; a second step of setting individually, for each of the initial welding period and the main welding period, an AC frequency of the welding current flowing through the non-consumable electrode and a set current which is a moving average value of the welding current; and a third step of controlling, for each of the initial welding period and the main welding period, the welding current based on the set current and the AC frequency set in the second step, and welding the base material, wherein, in the second step, the AC frequency in the initial welding period is set higher than the AC frequency in the main welding period.

2. An AC arc welding method according to claim 1, characterized in that the base metal has a structure in which two plates are superimposed on each other.

3. An AC arc welding method according to claim 2, characterized in that the base material has a fillet weld structure.

4. An AC arc welding method as claimed in claim 2, wherein in the second step, a cleaning width is further set separately for each of the initial welding period and the main welding period, and the cleaning width is the ratio of the period during which the non-consumable electrode has a positive polarity to the AC cycle of the welding current.

5. An AC arc welding method as claimed in claim 4, wherein in the second step, the set current during the main welding period is set in the range of more than 80 A and not more than 180 A, the cleaning width during the main welding period is set in the range of not less than 20% and not more than 40%, and the AC frequency during the initial welding period is set in the range of more than 100 Hz and not more than 250 Hz.

6. An AC arc welding method according to claim 5, wherein the AC frequency during the initial welding period is set in the range of more than 120 Hz and not more than 200 Hz.

7. An AC arc welding method as set forth in claim 5, wherein in the second step, the AC frequency during the main welding period is set in the range of 70 Hz or more and 200 Hz or less.

8. An AC arc welding method as claimed in claim 4, wherein in the second step, the set current during the main welding period is set in the range of more than 180 A and not more than 300 A, the cleaning width during the main welding period is set in the range of not less than 20% and not more than 40%, and the AC frequency during the initial welding period is set in the range of more than 100 Hz and not more than 200 Hz.

9. An AC arc welding method as set forth in claim 8, wherein in the second step, the AC frequency during the main welding period is set in the range of 70 Hz or more and 120 Hz or less.

10. An AC arc welding method according to claim 5, wherein the thickness of the plate material is 1.5 mm or more and 4.0 mm or less.

11. An AC arc welding method according to claim 8, wherein the thickness of the plate material is 4.0 mm or more and 9.0 mm or less.

12. An AC arc welding method according to any one of claims 1 to 11, characterized in that the base metal is made of aluminum or an aluminum alloy.

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