Arc welding control method

Abstract

Provided is an arc welding control method. In forward and reverse feed arc welding, even if a shielding gas in which an inert gas is a main component is used, a good welding quality is obtained. A shielding gas containing 60% by volume or more of an inert gas is used, the feed speed (Fw) of a welding wire is alternately switched between forward feed and reverse feed, a short-circuit period and an arc period are repeated, in the arc period, a first arc period (Ta1) in which a first arc current (Ia1) is switched on, a second arc period (Ta2) in which a second arc current (Ia2) is switched on, and a third arc period (Ta3) in which a third arc current (Ia3) is switched on are switched on with the passage of time, control is performed so that Ia1>Ia2>Ia3, in such an arc welding control method, the first arc current Ia1 is set to be equal to or greater than a critical current value, the first arc period (Ta1) is set to be shorter than the time in which a droplet transitions in the period, and the second arc current (Ia2) is set to be less than the critical current value.

Description

TECHNICAL FIELD

[0001] The present application relates to an arc welding control method, using a shielding gas containing 60% by volume or more of inert gas, alternately switching the feeding of a welding wire between forward feeding and reverse feeding, alternately repeating a short-circuit period and an arc period to perform welding. BACKGROUND

[0002] In general consumable electrode arc welding, a consumable electrode, i.e., a welding wire, is fed at a fixed speed, and an arc is generated between the welding wire and a base material to perform welding. In consumable electrode arc welding, the welding state in which the welding wire and the base material alternately repeat a short-circuit period and an arc period is common.

[0003] In order to further improve the welding quality, a forward and reverse feeding arc welding in which the feeding of a welding wire is alternately switched between forward feeding and reverse feeding to perform welding has been proposed (for example, refer to Patent Literature 1). In this forward and reverse feeding arc welding, since the period of repetition of short-circuit and arc can be stabilized compared to the prior art with a fixed feeding speed, reduction in the amount of sputtering, improvement in the appearance of a weld bead, and the like can be sought to improve the welding quality.

[0004] PRIOR ART DOCUMENT

[0005] PATENT LITERATURE

[0006] Patent Literature 1: JP Patent Application Laid-Open No. 2018-1270

[0007] In the forward and reverse feeding arc welding, by suppressing the variation in the period of the short-circuit period and the arc period, the transition of the droplet is surely performed in the short-circuit period, and the welding quality is improved. However, in the case where a shielding gas in which inert gas is the main component is used in the forward and reverse feeding arc welding, if the welding current value in the arc period becomes larger than the critical current value, the droplet transitions in the arc period. In this case, the variation in the period of the short-circuit period and the arc period becomes large, and the transition of the droplet becomes no longer synchronized with the short-circuit period. As a result, there is a problem that the welding quality deteriorates. SUMMARY

[0008] Therefore, in the present application, the object is to provide an arc welding control method that can obtain good welding quality even when a shielding gas in which inert gas is the main component is used in the forward and reverse feeding arc welding.

[0009] In order to solve the above problem, an arc welding control method is provided based on one aspect of the present application. The method has the following steps.

[0010] The feeding of a welding wire is alternately switched between forward feeding and reverse feeding using a shielding gas containing 60% by volume or more of inert gas, and a short-circuit period and an arc period are repeated.

[0011] During the arc period, the first arc period in which the first arc current Ial is switched on, the second arc period in which the second arc current Ia2 is switched on, and the third arc period in which the third arc current Ia3d are controlled so as to become Ial > Ia2 > Ia3 with the passage of time.

[0012] The first arc current Ial is set to be equal to or greater than a critical current value, and the first arc period is set to be a short time length during which a droplet transfer is not caused.

[0013] The second arc current Ia2 is set to be less than the critical current value.

[0014] Preferably, during the first arc period, constant current control is performed.

[0015] Preferably, during the second arc period, constant voltage control is performed.

[0016] Effects of the Invention

[0017] According to the present application, even if a protective gas in which an inert gas is a main component is used in a forward and reverse feed arc welding, a good welding quality can be obtained. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 is a block diagram of a welding power source for implementing an arc welding control method according to an embodiment of the present application.

[0019] Figure 2 is a timing chart showing each signal in the welding power source of the arc welding control method according to an embodiment of the present application. Figure 1

[0020] Explanation of Reference Numerals

[0021] 1 welding wire

[0022] 2 base material

[0023] 3 arc

[0024] 4 welding torch

[0025] 5 feed roll

[0026] CM current comparison circuit

[0027] Cm current comparison signal

[0028] DR drive circuit

[0029] Dr drive signal

[0030] E output voltage ​

[0031] Ea error amplification signal

[0032] ED output voltage detection circuit

[0033] Ed output voltage detection signal

[0034] EI current error amplification circuit

[0035] Ei current error amplification signal

[0036] ER output voltage setting circuit

[0037] Er output voltage setting signal

[0038] EV voltage error amplification circuit

[0039] Ev voltage error amplification signal

[0040] FC feed control circuit

[0041] Fc feed control signal

[0042] FR feed speed setting circuit

[0043] Fr feed speed setting signal

[0044] Fw feed speed

[0045] Ia1 first arc current

[0046] IA1R first arc current setting circuit

[0047] Ia1r first arc current setting signal

[0048] Ia2 second arc current

[0049] Ia3 third arc current

[0050] IA3R third arc current setting circuit

[0051] Ia3r third arc current setting signal

[0052] ICR current control setting circuit

[0053] Icr current control setting signal

[0054] ID current detection circuit

[0055] Id current detection signal

[0056] ILR low-level current setting circuit

[0057] Ilr low-level current setting signal

[0058] 1w welding current

[0059] ND neck-down detection circuit

[0060] Nd neck-down detection signal

[0061] PM power main circuit

[0062] R current-limiting resistor

[0063] SD short-circuit discrimination circuit

[0064] Sd short-circuit discrimination signal

[0065] STA1 first arc period circuit

[0066] Sta1 first arc period signal

[0067] STA3 third arc period circuit

[0068] Sta3 third arc period signal

[0069] SW power source characteristic switching circuit

[0070] Tc delay period

[0071] TA1R first arc period setting circuit

[0072] Ta1r first arc period setting signal

[0073] Td current fall time

[0074] TR transistor

[0075] Trd reverse feed deceleration period

[0076] TRDR reverse feed deceleration period setting circuit

[0077] Trdr reverse feed deceleration period setting signal

[0078] Trp reverse feed peak period

[0079] Tru reverse feed acceleration period

[0080] TRUR reverse feed acceleration period setting circuit

[0081] Trur reverse feed acceleration period setting signal

[0082] Tsd forward feed deceleration period

[0083] TSDR forward feed deceleration period setting circuit

[0084] Tsdr forward feed deceleration period setting signal

[0085] Tsp forward feed peak period

[0086] Tsu forward feed acceleration period

[0087] TSUR forward feed acceleration period setting circuit

[0088] Tsur forward feed acceleration period setting signal

[0089] VD voltage detection circuit

[0090] Vd voltage detection signal

[0091] Vw welding voltage

[0092] WL reactor

[0093] WM feed motor

[0094] Wrp reverse feed peak

[0095] WRR reverse feed peak setting circuit

[0096] Wrr reverse feed peak setting signal

[0097] Wsp forward feed peak

[0098] WSR forward feed peak setting circuit

[0099] Wsr forward feed peak setting signal DETAILED DESCRIPTION

[0100] Embodiments of the present application will be described below with reference to the accompanying drawings.

[0101] Figure 1 is a block diagram of a welding power source for implementing an arc welding control method involved in the embodiments of the present application. Each block will be described below with reference to the drawing.

[0102] The power source main circuit PM takes a commercial power source (omitted from the drawing) of 3-phase 200 V or the like as input, performs output control based on an inverter control or the like in accordance with an error amplification signal Ea described later, and outputs an output voltage E. Although the drawing is omitted, the power source main circuit PM is provided with a primary rectifier that rectifies the commercial power source, a smoothing capacitor that smoothes the rectified direct current, an inverter circuit that converts the smoothed direct current into high-frequency alternating current, which is driven by the error amplification signal Ea described above, a high-frequency transformer that steps down the high-frequency alternating current to a voltage value suitable for welding, and a secondary rectifier that rectifies the stepped-down high-frequency alternating current into direct current.

[0103] The reactor WL smoothes the output voltage E described above. The inductance value of the reactor WL is, for example, 100 μH.

[0104] The feed motor WM, which is inputted with the feed control signal Fc described later, alternately repeats the forward feed and the reverse feed to feed the welding wire 1 at the feed speed Fw. The feed motor WM uses a motor having a fast transient response. In order to accelerate the change rate of the feed speed Fw of the welding wire 1 and the reversal of the feed direction, there is a case where the feed motor WM is disposed in the vicinity of the front end of the welding torch 4. In addition, there is a case where a push-pull type feed system is made using two feed motors WM.

[0105] The welding wire 1 is fed in the welding torch 4 by the rotation of the feed roll 5 combined with the feed motor WM described above, and an arc 3 is generated between the welding wire 1 and the base material 2. The welding voltage Vw is applied between the electrode (not shown) in the welding torch 4 and the base material 2, and the welding current Iw is turned on. The shielding gas (not shown) is ejected from the front end of the welding torch 4. The shielding gas has an inert gas as a main component, and is, for example, argon 100%, argon 80% + carbon dioxide gas 20%, argon 98% + oxygen 2%, and the like.

[0106] The output voltage setting circuit ER outputs a predetermined output voltage setting signal Er. The output voltage detecting circuit ED detects and smoothes the output voltage E described above, and outputs an output voltage detecting signal Ed.

[0107] The voltage error amplification circuit EV, which is inputted with the output voltage setting signal Er described above and the output voltage detecting signal Ed described above, amplifies the error of the output voltage setting signal Er (+) and the output voltage detecting signal Ed (-), and outputs a voltage error amplification signal Ev.

[0108] The current detecting circuit ID detects the welding current Iw described above, and outputs a current detecting signal Id. The voltage detecting circuit VD detects the welding voltage Vw described above, and outputs a voltage detecting signal Vd. The short-circuit discrimination circuit SD, which is inputted with the voltage detecting signal Vd described above, discriminates that it is in the short-circuit period when the value is less than a predetermined short-circuit discrimination value (10 V or so), and outputs a short-circuit discrimination signal Sd which becomes a high level, and discriminates that it is in the arc period when the above is not the case, and outputs a short-circuit discrimination signal Sd which becomes a low level.

[0109] The forward feed acceleration period setting circuit TSUR outputs a predetermined forward feed acceleration period setting signal Tsur.

[0110] The forward feed deceleration period setting circuit TSDR outputs a predetermined forward feed deceleration period setting signal Tsdr.

[0111] The reverse feed acceleration period setting circuit TRUR outputs a predetermined reverse feed acceleration period setting signal Trur during the reverse feed acceleration period.

[0112] The reverse feed deceleration period setting circuit TRDR outputs a predetermined reverse feed deceleration period setting signal Trdr during the reverse feed deceleration period.

[0113] The forward feed peak setting circuit WSR outputs a predetermined forward feed peak setting signal Wsr.

[0114] The reverse feed peak setting circuit WRR outputs a predetermined reverse feed peak setting signal Wrr.

[0115] The feed speed setting circuit FR, which takes as inputs the above-mentioned forward feed acceleration period setting signal Tsur, the above-mentioned forward feed deceleration period setting signal Tsdr, the above-mentioned reverse feed acceleration period setting signal Trur, the above-mentioned reverse feed deceleration period setting signal Trdr, the above-mentioned forward feed peak setting signal Wsr, the above-mentioned reverse feed peak setting signal Wrr, and the above-mentioned short-circuit discrimination signal Sd, outputs a feed speed pattern generated by the following processing as a feed speed setting signal Fr. When the feed speed setting signal Fr is 0 or more, it becomes a forward feed period, and when it is less than 0, it becomes a reverse feed period.

[0116] 1) In the forward feed acceleration period Tsu determined by the forward feed acceleration period setting signal Tsur, the feed speed setting signal Fr is output which accelerates from 0 to a positive value of the forward feed peak value Wsp determined by the forward feed peak setting signal Wsr.

[0117] 2) Next, in the forward feed peak period Tsp, the feed speed setting signal Fr is output which maintains the above-mentioned forward feed peak value Wsp.

[0118] 3) If the short-circuit discrimination signal Sd changes from a low level (arc period) to a high level (short-circuit period), it transitions to the forward feed deceleration period Tsd determined by the forward feed deceleration period setting signal Tsdr, and the feed speed setting signal Fr is output which decelerates from the above-mentioned forward feed peak value Wsp to 0.

[0119] 4) Next, in the reverse feed acceleration period Tru determined by the reverse feed acceleration period setting signal Trur, the feed speed setting signal Fr is output which accelerates from 0 to a negative value of the reverse feed peak value Wrp determined by the reverse feed peak setting signal Wrr.

[0120] 5) Next, in the reverse feed peak period Trp, the feed speed setting signal Fr is output which maintains the above-mentioned reverse feed peak value Wrp.

[0121] 6) If the short-circuit discrimination signal Sd changes from the high level (short-circuit period) to the low level (arc period), the transition is made to the reverse feed deceleration period Trd determined by the reverse feed deceleration period setting signal Trdr, and the feed speed setting signal Fr is output from the above-mentioned reverse feed peak value Wrp to 0.

[0122] 7) The feed speed setting signal Fr of the positive and negative trapezoidal wave-shaped change feed pattern is generated by repeating the above-mentioned 1) to 6).

[0123] The feed control circuit FC outputs the above-mentioned feed speed setting signal Fr as an input, and outputs the feed control signal Fc for feeding the welding wire 1 at the feed speed Fw corresponding to the value of the feed speed setting signal Fr to the above-mentioned feed motor WM.

[0124] The current reduction resistor R is inserted between the above-mentioned reactor WL and the welding torch 4. The value of this current reduction resistor R is set to a value (0.5 to 3 Ω) which is 50 times or more larger than that (0.01 to 0.03 Ω) of the short-circuit load. If this current reduction resistor R is inserted into the power circuit, the energy accumulated in the reactor WL and the external cable reactor is rapidly discharged.

[0125] The transistor TR is connected in parallel to the above-mentioned current reduction resistor R, and is turned on or off controlled in accordance with the drive signal D described later.

[0126] The necking detection circuit ND inputs the above-mentioned short-circuit discrimination signal Sd, the above-mentioned voltage detection signal Vd, and the above-mentioned current detection signal Id, and at the time point when the voltage rise value of the voltage detection signal Vd when the short-circuit discrimination signal Sd is at the high level (short-circuit period) reaches the reference value, it discriminates that the formation state of the necking becomes the reference state, and outputs the necking detection signal Nd which becomes the high level. At the time point when the short-circuit discrimination signal Sd changes to the low level (arc period), it outputs the necking detection signal Nd which becomes the low level. In addition, it is also possible to make the necking detection signal Nd change to the high level at the time point when the differential value of the voltage detection signal Vd during the short-circuit period reaches the reference value corresponding thereto. Furthermore, it is also possible to calculate the resistance value of the molten droplet by dividing the value of the voltage detection signal Vd by the value of the current detection signal Id, and to make the necking detection signal Nd change to the high level at the time point when the differential value of the resistance value reaches the reference value corresponding thereto.

[0127] The low-level current setting circuit ILR outputs the low-level current setting signal Ilr which is predetermined. The current comparison circuit CM inputs the low-level current setting signal Ilr and the above-mentioned current detection signal Id, and outputs the current comparison signal Cm which becomes the high level when Id < Ilr, and the current comparison signal Cm which becomes the low level when Id ≥ Ilr.

[0128] The drive circuit DR outputs a drive signal Dr to the base terminal of the transistor TR with the current comparison signal Cm and the necking detection signal Nd as inputs. If the necking detection signal Nd changes to the high level, the drive signal D changes to the low level, and if the current comparison signal Cm changes to the high level thereafter, the drive signal D changes to the high level. Therefore, if necking is detected, the drive signal Dr becomes the low level, the transistor TR becomes the off state, and the current reduction resistor R is inserted into the power circuit, so the welding current Iw connected to the short-circuit load is sharply reduced. Then, if the value of the welding current Iw sharply reduced decreases to the value of the low-level current setting signal Ilr, the drive signal Dr becomes the high level, the transistor TR becomes the on state, and thus the current reduction resistor R is short-circuited to return to the normal state.

[0129] The 1st arc period setting circuit TA1R outputs a predetermined 1st arc period setting signal Ta1r. The 1st arc period setting signal Ta1r is configured to set the time length of the period short in a manner that does not cause droplet transfer in the period determined by the signal.

[0130] The 1st arc period circuit STA1 outputs a 1st arc period signal Sta1 with the short-circuit determination signal Sd and the 1st arc period setting signal Ta1r as inputs. As shown in (E) of FIG. 6, the 1st arc period signal Sta1 becomes the high level at the point in time (t51) at which the short-circuit determination signal Sd changes to the low level (arc period) (t4) and a predetermined delay period Tc (t4-t51) elapses, and maintains this level in the 1st arc period Ta1 predetermined by the 1st arc period setting signal Ta1r. Figure 2

[0131] The 1st arc current setting circuit IA1R outputs a predetermined 1st arc current setting signal Ia1r. The 1st arc current setting signal Ia1r is set to a value equal to or higher than the critical current value.

[0132] The 3rd arc period circuit STA3 outputs a 3rd arc period signal Sta3 with the short-circuit determination signal Sd as an input. The 3rd arc period signal Sta3 becomes the high level at the point in time at which the short-circuit determination signal Sd changes to the low level (arc period) and a predetermined current drop time Td elapses, and becomes the low level if the short-circuit determination signal Sd becomes the high level (short-circuit period) thereafter.

[0133] The 3rd arc current setting circuit IA3R outputs a predetermined 3rd arc current setting signal Ia3r.

[0134] ​The current control setting circuit ICR inputs the short-circuit discrimination signal Sd, the low-level current setting signal Ilr, the necking detection signal Nd, the first arc period signal Sta1, the third arc period signal Sta3, the first arc current setting signal Ialr, and the third arc current setting signal Ia3r, and performs the following processing to output the current control setting signal Icr.

[0135] 1) During a delay period from the time point when the short-circuit discrimination signal Sd changes to the low level (arc period) to the time point when the first arc period signal Sta1 changes to the high level, the current control setting signal Icr is output as the value of the low-level current setting signal Ilr.

[0136] 2) Thereafter, during the time when the first arc period signal Sta1 is at the high level (first arc period), the current control setting signal Icr is output as the first arc current setting signal Ialr.

[0137] 3) During a period (second arc period and third arc period) from the time point when the first arc period signal Sta1 changes to the low level to the time point when the third arc period signal Sta3 changes to the low level, the current control setting signal Icr is output as the third arc current setting signal Ia3r.

[0138] 4) If the short-circuit discrimination signal Sd changes to the high level (short-circuit period), the current control setting signal Icr is output as a predetermined initial current setting value during a predetermined initial period, and thereafter, the current control setting signal Icr is output as a predetermined short-circuit peak setting value with a predetermined short-circuit time slope rise and maintained at the value.

[0139] 5) Thereafter, if the necking detection signal Nd changes to the high level, the current control setting signal Icr is output as the value of the low-level current setting signal Ilr.

[0140] The current error amplification circuit EI inputs the current control setting signal Icr and the current detection signal Id, amplifies the error between the current control setting signal Icr (+) and the current detection signal Id (-), and outputs the current error amplification signal Ei.

[0141] The power source characteristic switching circuit SW inputs the current error amplification signal Ei, the voltage error amplification signal Ev, the first arc period signal Sta1, and the third arc period signal Sta3, performs the following processing, and outputs the error amplification signal Ea.

[0142] 1) In the second arc period Ta2 until the first arc period signal Sta1 changes to the low level and the third arc period signal Sta3 changes to the high level, the voltage error amplification signal Ev is output as the error amplification signal Ea.

[0143] 2) In the period other than this, the current error amplification signal Ei is output as the error amplification signal Ea.

[0144] By this circuit, the characteristic of the welding power source becomes the constant current characteristic in the short circuit period, the delay period, the first arc period Ta1 and the third arc period Ta3, and becomes the constant voltage characteristic in the second arc period Ta2.

[0145] Figure 2 is a timing chart of each signal in the welding power source of the embodiment of the present application. Figure 1 (A) of the drawing shows the time change of the feed speed Fw, (B) of the drawing shows the time change of the welding current Iw, (C) of the drawing shows the time change of the welding voltage Vw, (D) of the drawing shows the time change of the short circuit discrimination signal Sd, (E) of the drawing shows the time change of the first arc period signal Sta1, and (F) of the drawing shows the time change of the third arc period signal Sta3. The operation of each signal will be described below with reference to the drawing.

[0146] The feed speed Fw shown in (A) of the drawing is controlled at the value of the feed speed set signal Fr output from the feed speed setting circuit FR of Figure 1 The feed speed Fw includes the forward feed acceleration period Tsu determined by the forward feed acceleration period setting signal Tsur of Figure 1 the forward feed peak period Tsp until the short circuit occurs, the forward feed peak value Wsp determined by the forward feed peak value setting signal Wsr of Figure 1 the forward feed deceleration period Tsd determined by the forward feed deceleration period setting signal Tsdr of Figure 1 the reverse feed acceleration period Tru determined by the reverse feed acceleration period setting signal Trur of Figure 1 the reverse feed peak period Trp until the arc is generated, and the reverse feed deceleration period Trd determined by the reverse feed deceleration period setting signal Trdr of Figure 1 Furthermore, the forward feed peak value Wsp is determined by the forward feed peak value setting signal Wsr of Figure 1 the reverse feed peak value Wrp is determined by the reverse feed peak value setting signal Wrr of As a result, the feed speed set signal Fr becomes a feed pattern of roughly trapezoidal wave shape in which the positive and negative values change.

[0147] [Operation in the short circuit period of time t1 to t4]

[0148] If a short circuit occurs at time tl in the forward feeding peak period Tsp, as shown in (C) of the figure, the welding voltage Vw sharply decreases to a short-circuit voltage value of several V, and thus, as shown in (D) of the figure, the short-circuit discrimination signal Sd changes to a high level (short-circuit period). In response to this, a predetermined forward feeding deceleration period Tsd from time tl to t2 is entered, and the feeding speed Fw decelerates from the above-mentioned forward feeding peak value Wsp to 0, as shown in (A) of the figure. The forward feeding deceleration period Tsd is set to 1 ms, for example.

[0149] The feeding speed Fw enters a predetermined reverse feeding acceleration period Tru from time t2 to t3, and accelerates from 0 to the above-mentioned reverse feeding peak value Wrp, as shown in (A) of the figure. The short-circuit period continues during this period. The reverse feeding acceleration period Tru is set to 1 ms, for example.

[0150] If the reverse feeding acceleration period Tru ends at time t3, the process enters a reverse feeding peak period Trp, and the feeding speed Fw becomes the above-mentioned reverse feeding peak value Wrp, as shown in (A) of the figure. The reverse feeding peak period Trp continues until the arc is generated at time t4. Thus, the period from time tl to t4 becomes the short-circuit period. The reverse feeding peak period Trp is not a given value, but is about 3 ms. Further, the reverse feeding peak value Wrp is set to -20 to -50 m / min, for example.

[0151] The welding current Iw in the short-circuit period from time tl to t4 becomes a predetermined initial current value in a predetermined initial period, as shown in (B) of the figure. Thereafter, the welding current Iw rises at a predetermined short-circuit time inclination, and if it reaches a predetermined short-circuit time peak value, it is maintained at this value.

[0152] The welding voltage Vw rises from the vicinity of the point at which the welding current Iw becomes the short-circuit time peak value, as shown in (C) of the figure. This is because the molten drop at the front end of the welding wire 1 gradually forms a neck by the effect of the pinch force caused by the reverse feeding of the welding wire 1 and the welding current Iw.

[0153] If the voltage rise value of the welding voltage Vw thereafter reaches a reference value, it is discriminated that the formation state of the neck becomes the reference state, and thus, the neck detection signal Nd changes to a high level. Figure 1

[0154] In response to the neck detection signal Nd becoming the high level, Figure 1 the drive signal Dr becomes a low level, and thus Figure 1 the transistor TR becomes an off state, Figure 1 the current-reducing resistor R is inserted into the power supply circuit. At the same time, Figure 1 ​the current control setting signal Icr to the value of the low-level current setting signal Ilr. To do this, as shown in (B) of the figure, the welding current Iw is sharply reduced from the short-circuit peak value to the low-level current value. Then, since the drive signal Dr returns to the high level if the welding current Iw is reduced to the low-level current value, the transistor TR becomes the on state, and the current reduction resistor R is short-circuited. As shown in (B) of the figure, since the current control setting signal Icr remains in the state of the low-level current setting signal Ilr, the welding current Iw is maintained at the low-level current value from the arc re-ignition to the lapse of the predetermined delay period Tc. Therefore, the transistor TR becomes the off state only during the period from the time point at which the necking detection signal Nd changes to the high level to the time at which the welding current Iw is reduced to the low-level current value. As shown in (C) of the figure, the welding voltage Vw sharply rises after being once reduced due to the reduction of the welding current Iw. The above-described parameters are set to the following values, for example. Initial current = 40 A, initial period = 0.5 ms, short-circuit-time slope = 180 A / ms, short-circuit-time peak value = 400 A, low-level current value = 50 A, delay period Tc = 0.5 ms.

[0155] [Operation during the arc period from time t4 to t7]

[0156] If the arc is generated by the necking progression due to the pinch force caused by the reverse feeding of the welding wire and the turning on of the welding current Iw at time t4, as shown in (C) of the figure, the welding voltage Vw sharply increases to the arc voltage value of several tens of V, and thus, as shown in (D) of the figure, the short-circuit discrimination signal Sd changes to the low level (arc period). In response to this, the process transitions to the predetermined reverse feeding deceleration period Trd from time t4 to t5, and as shown in (A) of the figure, the feeding speed Fw is decelerated from the above-described reverse feeding peak value Wrp to 0. The reverse feeding deceleration period Trd is set to 1 ms, for example.

[0157] If the reverse feeding deceleration period Trd ends at time t5, the process transitions to the predetermined forward feeding acceleration period Tsu from time t5 to t6. In the forward feeding acceleration period Tsu, as shown in (A) of the figure, the feeding speed Fw is accelerated from 0 to the above-described forward feeding peak value Wsp. During this period, the arc period continues. The forward feeding acceleration period Tsu is set to 1 ms, for example.

[0158] If Tsu ends during the forward feed acceleration period Tsu at time t6, the process proceeds to the forward feed peak period Tsp as shown in (A) of the figure, and the feed speed Fw becomes the above-mentioned forward feed peak value Wsp. During this period, the arc period also continues. The forward feed peak period Tsp continues until a short circuit occurs at time t7. Therefore, the period from time t4 to time t7 becomes the arc period. Then, if a short circuit occurs, the operation returns to that at time tl. The forward feed peak period Tsp is not a given value, but becomes about 5 ms. Also, for example, the forward feed peak value Wsp is set to 30 to 60 m / min.

[0159] If an arc occurs at time t4, the welding voltage Vw jumps to an arc voltage value of several tens of V as shown in (C) of the figure. On the other hand, the welding current Iw continues a low-level current value between time t4 and a delay period Tc as shown in (B) of the figure. This is because, if the current value is raised immediately after an arc occurs, the reverse feed of the welding wire and the melting of the welding wire by the welding current are added, the arc length rapidly becomes long, and there is a case where the welding state becomes unstable.

[0160] If the delay period Tc ends at time t51 during the forward feed acceleration period Tsu, the 1st arc period signal Stal changes to the high level as shown in (E) of the figure, and transitions to a predetermined 1st arc period Ta1 from time t51 to t61. Constant current control continues in this 1st arc period Ta1, and the given 1st arc current Ial determined by the 1st arc current setting signal Ialr is turned on as shown in (B) of the figure. The welding voltage Vw becomes a value determined by the current value and the arc load, and becomes a large value as shown in (C) of the figure. Figure 1

[0161] If a predetermined current drop time Td elapses from the arc generation time point t4 at time t62, the 3rd arc period signal Stal changes to the high level as shown in (F) of the figure. The period from time t61 to t62 becomes a 2nd arc period Ta2. In this 2nd arc period Ta2, constant voltage control is performed. The 2nd arc current Ia2, although it varies depending on the arc load, is a value smaller than the 1st arc current Ial and becomes a value larger than the 3rd arc current Ia3 as shown in (B) of the figure. That is, output control is performed so as to become Ial > Ia2 > Ia3. The welding voltage Vw is controlled to a given value by the constant voltage control, and becomes an intermediate value of the voltage value of the 1st arc period Ta1 and the voltage value of the 3rd arc period Ta3 as shown in (C) of the figure. The 2nd arc period Ta2 is not a given value, but is about 3 to 6 ms.

[0162] ​The period from the time t62 when the signal Sta3 changes to the high level to the time t7 when the short circuit occurs is the 3rd arc period Ta3. In this 3rd arc period Ta3, constant current control is performed. As shown in (B) of the figure, the given 3rd arc current Ia3 determined by the 3rd arc current setting signal Ia3r is turned on. As shown in (C) of the figure, the welding voltage Vw becomes a value determined by the current value and the arc load. For example, the 3rd arc current Ia3 = 60 A is set. The 3rd arc period Ta3 is not a given value, but is about 1 to 2 ms. Figure 1

[0163] In the present embodiment, a shielding gas containing 60% by volume or more of inert gas is used. In the case of using an inert gas, 60% by volume or more is mixed in order to stabilize the welding state in practice. As the inert gas, argon, helium, or the like is used.

[0164] As described above, according to the present embodiment, in the arc period, the 1st arc period in which the 1st arc current Ia1 is turned on, the 2nd arc period in which the 2nd arc current Ia2 is turned on, and the 3rd arc period in which the 3rd arc current Ia3 is turned on are switched with the passage of time, and control is performed so as to become Ia1 > Ia2 > Ia3. The 1st arc current Ia1 is set to be equal to or more than the critical current value at which the droplet becomes the spray transfer state (i.e., if the application period of this current is long enough, the droplet becomes equal to or more than the critical current value at which the spray transfer state is reached). On the other hand, the 1st arc period is set to be a short time length in which the droplet transition does not occur in the period. The output voltage setting signal Er of the power supply 10 is adjusted so as to set the 2nd arc current Ia2 to be less than the critical current value described above. ​

[0165] In the prior art forward and reverse feed arc welding, in the case of using a shielding gas in which an inert gas is the main component, if the welding current value in the arc period becomes large, becomes equal to or more than the critical current value, and the droplet transitions in the arc period. In this way, the variation in the cycle of the short circuit period and the arc period becomes large, and the transition of the droplet becomes no longer synchronized with the short circuit period. As a result, the welding quality deteriorates.

[0166] ​​On the other hand, in the present embodiment, the first arc current Ial is set to be higher than a critical current value at which a droplet becomes a jet transition state, the first arc period is set to be a short time period during which a droplet transition does not occur, and the second arc current Ia2 is set to be lower than the critical current value. For this reason, a droplet becomes difficult to transition during the arc period, and a droplet transitions in synchronization with the short circuit period. As a result, the repeating cycle of the short circuit period and the arc period is stabilized, and thus the welding quality becomes good. Furthermore, in the present embodiment, by turning on the first arc current Ial of a high current value within a range in which a droplet does not transition, the heat input to the base material can be increased, and thus the bead appearance becomes good.

[0167] Furthermore, according to the present embodiment, during the first arc period, constant current control is performed. Thus, in the present embodiment, it is possible to precisely control so that a droplet does not transition during the first arc period. In addition, it is possible to precisely control the heat input during the first arc period. As a result, it is possible to make the welding quality even higher.

[0168] Furthermore, according to the present embodiment, during the second arc period, constant voltage control is performed. Thus, in the present embodiment, it is possible to control the average arc length to a suitable value. As a result, it is possible to make the welding state even more stable.

Claims

1. An arc welding control method wherein, using a shielding gas containing 60% by volume or more of an inert gas, feeding of a welding wire is switched between forward feeding and reverse feeding, and a short-circuit period and an arc period are repeated, in the arc period, a first arc period in which a first arc current Ial is turned on, a second arc period in which a second arc current Ia2 is turned on, and a third arc period in which a third arc current Ia3 is turned on are switched in time series, and control is performed so that Ial > Ia2 > Ia3, the arc welding control method is characterized in that, the first arc current Ial is set to be equal to or more than a critical current value at which a droplet becomes a jet transition state, the first arc period is set to be a short time length in which a droplet transition is not caused, the second arc current Ia2 is set to be less than the critical current value, and a droplet is caused to transition in synchronization with the short-circuit period, an output voltage setting signal predetermined in advance is adjusted to set the second arc current Ia2 to be less than the critical current value.

2. The arc welding control method according to claim 1, characterized in that, in the first arc period, constant current control is performed.

3. The arc welding control method according to claim 1, characterized in that, in the second arc period, constant voltage control is performed.

4. The arc welding control method according to claim 2, characterized in that, in the second arc period, constant voltage control is performed.

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