Arc welding control method

Abstract

To perform preferable arc start, even when an adhesion state of slag is insufficient, in forward and reverse feed arc welding.SOLUTION: An arc welding control method is provided in which, when starting welding, during an initial period Ti since a feeding start time point of a welding wire until energization of a welding current is started, a feeding speed Fw is alternately switched between a forward feeding period and a reverse feeding period, namely forward and reverse feeding control is performed. In the initial period Ti, when it is determined that, a state in which no slag is removed, is continuous and a determination signal Hd is changed to a high level at a time t5, during the initial period Ti on and after the determination and the change of the determination signal, an amplitude and / or an average value of the feeding speed Fw is increased for making impact of collision of the welding wire and a base material strong. Therefore a slag removal effect can be enhanced. The determination is performed on the basis of a fact that, a lapse time of the initial period Ti becomes a reference time or longer, or torque of the feeding motor becomes the reference torque or more.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an arc welding control method for performing forward and reverse feed control in which the feed speed is alternately switched between a forward feed period and a reverse feed period during an initial period from when welding wire feed starts to when welding current starts to flow when welding starts. [Background technology]

[0002] In general consumable electrode arc welding, a welding wire, which is a consumable electrode, is fed at a constant speed and an arc is generated between the welding wire and the base metal to perform welding. In consumable electrode arc welding, the welding wire and the base metal are often in a welding state in which a short-circuit period and an arc period alternately repeat.

[0003] In order to further improve welding quality, an arc welding control method is used in which forward and reverse feed control is performed in which the welding wire feed speed is alternately switched between a forward feed period and a reverse feed period, thereby generating a short circuit period and an arc period for welding. Here, forward feed means feeding the welding wire in a direction approaching the base metal, and reverse feed means feeding the welding wire in the opposite direction to forward feed (a direction in which the welding wire moves away from the base metal).

[0004] In consumable electrode arc welding, an insulating material called slag may adhere to the tip of the welding wire at the end of welding. Slag is produced by a chemical reaction between components contained in the welding wire. The state of slag adhesion varies depending on welding conditions such as the type of welding wire, average welding current value, and welding position. If the next arc start is performed with slag adhered to the tip of the welding wire, even if the welding wire comes into contact with the base metal, an arc will not be generated because the slag is an insulator, resulting in an arc start failure. The same is true for arc welding with forward / reverse feed control.

[0005] Patent Document 1 discloses a method for improving arc start failures caused by slag in forward / reverse feed controlled arc welding. In the invention of Patent Document 1, forward / reverse feed control is performed even during the initial period from when welding wire feeding begins at the start of welding until welding current is applied. As a result, when slag adheres to the tip of the welding wire and the base metal, the tip of the welding wire repeatedly collides with the base metal when the tip of the welding wire contacts the base metal but no welding current is applied. In the invention of Patent Document 1, the slag at the tip of the welding wire is removed by this repeated collision, generating an arc. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 6593923 Summary of the Invention [Problem to be solved by the invention]

[0007] In the above-described conventional technology, even if slag adheres to the tip of the welding wire, by performing forward / reverse feed control during the initial period, the slag is removed and an arc is generated while the tip of the welding wire and the base metal collide several times. However, if the slag adhesion is severe, an arc may not be generated even if the tip of the welding wire and the base metal collide several times.

[0008] Therefore, an object of the present invention is to provide an arc welding control method that can reliably start an arc even when the slag adhesion state is severe. [Means for solving the problem]

[0009] In order to solve the above-mentioned problems, the present invention provides an arc welding control method that performs forward and reverse feed control to alternately switch the feed speed between a forward feed period and a reverse feed period during an initial period from when welding wire feed starts to when welding current application starts, when starting welding, comprising: If it is determined that the slag has not been removed during the initial period, the amplitude of the feeding speed is reduced during the subsequent initial period. 、 Average , frequency and time ratio of the forward transmission period Increase When the slag is removed by the forward / reverse feed control and the welding current starts to flow during the forward feed period of the feed speed, after a delay period of 1 to 10 ms has elapsed from that point, the feed speed is switched to the reverse feed period to generate an arc. The arc welding control method is characterized by the above.

[0010] The invention of claim 2 is as follows: The determination is made when the elapsed time of the initial period is equal to or longer than a reference time. 2. The arc welding control method according to claim 1, wherein:

[0011] The invention of claim 3 is as follows: The determination is made based on whether the torque of the feed motor during the initial period is equal to or greater than a reference torque. 2. The arc welding control method according to claim 1, wherein: [Effects of the Invention]

[0012] According to the arc welding control method of the present invention, even when the slag adhesion state is severe, the arc can be reliably started. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a block diagram of a welding power source for carrying out an arc welding control method according to a first embodiment of the present invention. [Figure 2] 2 is a timing chart of signals at the start of welding in the welding power source of FIG. 1, illustrating the arc welding control method according to the first embodiment of the present invention. [Figure 3] FIG. 6 is a block diagram of a welding power source for carrying out an arc welding control method according to a second embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0015] [Embodiment 1] 1 is a block diagram of a welding power source for carrying out an arc welding control method according to a first embodiment of the present invention. Each block will be described below with reference to the diagram.

[0016] The main power supply circuit PM receives a commercial power supply (not shown) such as a three-phase 200V power supply as input, performs output control using inverter control or the like in accordance with a drive signal Dv described below, and outputs an output voltage E. Although not shown, the main power supply circuit PM includes a primary rectifier that rectifies the commercial power supply, a smoothing capacitor that smooths the rectified DC, an inverter circuit driven by the drive signal Dv that converts the smoothed DC into high-frequency AC, a high-frequency transformer that steps down the high-frequency AC to a voltage value suitable for welding, and a secondary rectifier that rectifies the stepped-down high-frequency AC into DC.

[0017] The reactor WL smoothes the output voltage E. The inductance value of the reactor WL is, for example, 100 μH.

[0018] The feed motor WM receives a feed control signal Fc (described later) as an input and alternates between a forward feed period and a reverse feed period to feed the welding wire 1 at a feed speed Fw. A motor with good transient characteristics is used for the feed motor WM. In order to increase the rate of change in the feed speed Fw of the welding wire 1 and the reversal of the feed direction, the feed motor WM is sometimes installed near the tip of the welding torch 4. In some cases, two feed motors WM are used to form a push-pull type feed system.

[0019] The welding wire 1 is fed through the welding torch 4 by the rotation of a feed roll 5 coupled to the feed motor WM, and an arc 3 is generated between the welding wire 1 and the base metal 2. A welding voltage Vw is applied between a power feed tip (not shown) in the welding torch 4 and the base metal 2, and a welding current Iw flows between the power feed tip and the base metal 2.

[0020] The output voltage setting circuit ER outputs a predetermined output voltage setting signal Er. The output voltage detection circuit ED detects and smoothes the output voltage E, and outputs an output voltage detection signal Ed.

[0021] The voltage error amplifier circuit EV receives the output voltage setting signal Er and the output voltage detection signal Ed, amplifies the error between the output voltage setting signal Er(+) and the output voltage detection signal Ed(-), and outputs a voltage error amplified signal Ev. This circuit controls the welding power supply to a constant voltage.

[0022] The hot start current setting circuit IHR outputs a predetermined hot start current setting signal Ihr. The current detection circuit ID detects the welding current Iw and outputs a current detection signal Id.

[0023] The current error amplifier circuit EI receives the hot start current setting signal Ihr and the current detection signal Id, amplifies the error between the hot start current setting signal Ihr(+) and the current detection signal Id(-), and outputs a current error amplified signal Ei. This circuit controls the welding power source to a constant current during the period when the hot start current is supplied (hot start period).

[0024] The current flow discrimination circuit CD receives the current detection signal Id as input, and when this value is equal to or greater than a threshold value (approximately 10 A), determines that the welding current Iw is flowing and outputs a high-level current flow discrimination signal Cd.

[0025] The power supply characteristics switching circuit SW receives the current error amplified signal Ei, the voltage error amplified signal Ev, and the current conduction determination signal Cd as inputs, and outputs the current error amplified signal Ei as the error amplified signal Ea during a predetermined hot start period from the time when the current conduction determination signal Cd changes to a high level (conducting), and outputs the voltage error amplified signal Ev as the error amplified signal Ea during other periods.

[0026] The voltage detection circuit VD detects the welding voltage Vw and outputs a voltage detection signal Vd. The short circuit determination circuit SD receives the voltage detection signal Vd and outputs a short circuit determination signal Sd that goes High when the voltage detection signal Vd is less than a short circuit determination value (approximately 10 V) and indicates a short circuit period, and goes Low when the voltage detection signal Vd is equal to or greater than the short circuit determination value and indicates an arc period.

[0027] The welding start circuit ST outputs a welding start signal St that goes high when the welding power source is started. This welding start circuit ST corresponds to a start switch for the welding torch 4, a control device for the welding process, a robot control device when a welding robot is used, etc.

[0028] The drive circuit DV receives the error amplified signal Ea and the welding start signal St as inputs, and when the welding start signal St is at a high level (welding starts), performs PWM modulation control based on the error amplified signal Ea, and outputs a drive signal Dv for driving the inverter circuit in the main power supply circuit PM.

[0029] The initial period timer circuit STI receives the welding start signal St and the current energization determination signal Cd as inputs, and outputs an initial period timer signal Sti that goes to a high level when the welding start signal St changes to a high level (welding starts), and goes to a low level when the current energization determination signal Cd changes to a high level (energization).

[0030] The discrimination circuit HD receives the initial period timer signal Sti as input and outputs a discrimination signal Hd that goes High when the elapsed time from the time when the initial period timer signal Sti changed to High level (initial period) reaches or exceeds a reference time, and goes Low when the initial period timer signal Sti changes to Low level. The reference time is set as the time from the time when the feeding of the welding wire 1 starts (the start of the initial period) until the tip of the welding wire 1 repeatedly collides with the base material 2 multiple times. Therefore, the time when the discrimination signal Hd changes to High level is when the tip of the welding wire 1 repeatedly collides with the base material 2 multiple times but the slag has not yet been removed. The time until the first collision of the welding wire 1 with the base material 2 is, for example, about 0.5 seconds. The time required for 50 repeated collisions is, for example, about 0.5 seconds. In this case, the reference time is set to 0.5 + 0.5 = 1.0 second. In practice, the initial time is set to about 0.5 to 2.0 seconds.

[0031] The steady forward transmission peak value setting circuit FSCR outputs a predetermined steady forward transmission peak value setting signal Fscr, and the steady backward transmission peak value setting circuit FRCR outputs a predetermined steady backward transmission peak value setting signal Frcr.

[0032] The steady-state welding period feed speed setting circuit FCR receives the short-circuit detection signal Sd, the steady-state forward feed peak value setting signal Fscr, and the steady-state reverse feed peak value setting signal Frcr as inputs, switches between a forward feed period and a reverse feed period based on the short-circuit detection signal Sd, and outputs a steady-state welding period feed speed setting signal Fcr of a trapezoidal wave formed from the steady-state forward feed peak value Fsc determined by the steady-state forward feed peak value setting signal Fscr and the steady-state reverse feed peak value Frc determined by the steady-state reverse feed peak value setting signal Frcr. The steady-state welding period feed speed setting signal Fcr will be described in detail with reference to FIG.

[0033] The initial forward feed peak value setting circuit FSIR receives the discrimination signal Hd as input and outputs an initial forward feed peak value setting signal Fsir that is a predetermined standard value when the discrimination signal Hd is at a low level and a predetermined increased value when the discrimination signal Hd is at a high level. The standard value is smaller than the increased value. Therefore, when the signal is switched to the increased value, the value of the initial forward feed peak value setting signal Fsir increases, and the amplitude of the feed speed Fw increases.

[0034] The initial reverse feed peak value setting circuit FRIR receives the discrimination signal Hd as input and outputs an initial reverse feed peak value setting signal Frir, which is a predetermined standard value when the discrimination signal Hd is at a low level and a predetermined increased value when the discrimination signal Hd is at a high level. The standard value is smaller than the increased value. Therefore, when the signal is switched to the increased value, the absolute value of the initial reverse feed peak value setting signal Frir increases, and the amplitude of the feed speed Fw increases.

[0035] The initial frequency setting circuit SIR receives the discrimination signal Hd as input and outputs an initial frequency setting signal Sir that has a predetermined standard value when the discrimination signal Hd is at a low level and a predetermined incremental value when the discrimination signal Hd is at a high level. The initial frequency setting signal Sir is a signal that sets the frequency at which the forward feed period and the reverse feed period are switched during the initial period. The standard value is smaller than the incremental value. Therefore, when the initial frequency setting signal Sir is switched to the incremental value, the value of the initial frequency setting signal Sir increases.

[0036] The initial time ratio setting circuit DIR receives the discrimination signal Hd as input and outputs an initial time ratio setting signal Dir that has a predetermined standard value when the discrimination signal Hd is at a low level and a predetermined incremental value when the discrimination signal Hd is at a high level. The initial time ratio setting signal Dir sets the time ratio between the forward feed period and the reverse feed period during the initial period. Time ratio = (length of forward feed period) / (length of forward feed period + length of reverse feed period). That is, it is the time ratio of the forward feed period in one cycle determined by the reciprocal 1 / Sir of the initial frequency setting signal Sir. Therefore, the length of the forward feed period = Dir / Sir, and the length of the reverse feed period = (1 - Dir) / Sir. In the above, the standard value < the incremental value. As a result, when switched to the incremental value, the ratio of the forward feed period increases, and the average value of the feed speed Fw increases.

[0037] The initial period feed speed setting circuit FIR receives the initial forward feed peak value setting signal Fsir, the initial reverse feed peak value setting signal Frr, the initial frequency setting signal Sir, and the initial time ratio setting signal Dir as inputs, and outputs an initial period feed speed setting signal Fir of a trapezoidal wave in which the forward feed period and the reverse feed period are determined based on the initial frequency setting signal Sir and the initial time ratio setting signal Dir, the initial forward feed peak value Fsi is determined by the initial forward feed peak value setting signal Fsir, and the initial reverse feed peak value Fri is determined by the initial reverse feed peak value setting signal Frr. The initial period feed speed setting signal Fir will be described in detail with reference to FIG.

[0038] The feed speed setting circuit FR receives the steady-state welding period feed speed setting signal Fcr, the initial-period feed speed setting signal Fir, and the initial-period timer signal Sti as inputs, and outputs the initial-period feed speed setting signal Fir as the feed speed setting signal Fr during the initial period when the initial-period timer signal Sti is at a high level, and outputs the steady-state welding period feed speed setting signal Fcr as the feed speed setting signal Fr during the steady-state welding period when the initial-period timer signal Sti is at a low level.

[0039] The feed control circuit FC receives the welding start signal St and the feed speed setting signal Fr as inputs, and outputs a feed control signal Fc to the feed motor WM to feed the welding wire 1 at a feed speed Fw corresponding to the value of the feed speed setting signal Fr when the welding start signal St is at a high level (welding starts).

[0040] 2 is a timing chart of signals at the start of welding in the welding power source of FIG. 1, which illustrates the arc welding control method according to the first embodiment of the present invention. (A) in FIG. 2 shows the change over time in the welding start signal St, (B) in FIG. 2 shows the change over time in the feed rate Fw, (C) in FIG. 2 shows the change over time in the welding current Iw, (D) in FIG. 2 shows the change over time in the welding voltage Vw, (E) in FIG. 2 shows the change over time in the current conduction determination signal Cd, (F) in FIG. 2 shows the change over time in the short-circuit determination signal Sd, (G) in FIG. 2 shows the change over time in the initial period timer signal Sti, (H) in FIG. 2 shows the change over time in the welding wire-tip-to-base metal distance Lw, which is the distance between the welding wire tip and the base metal surface, and (I) in FIG. 2 shows the change over time in the determination signal Hd. The operation of each signal at the start of welding will be described below with reference to FIG.

[0041] As shown in FIG. 1B, the feed speed Fw is in the forward feed period above zero and in the reverse feed period below zero. During the initial period Ti, the feed speed Fw is controlled by the initial period feed speed setting signal Fir in FIG. 1, and the forward feed period and the reverse feed period are switched at a predetermined frequency. On the other hand, during the steady welding period Tc, the feed speed Fw is controlled by the steady welding period feed speed setting signal Fcr in FIG. 1, and the forward feed period and the reverse feed period are switched in synchronization with the short circuit period and the arc period. The feed speed Fw changes in a trapezoidal wave shape. The average value of the feed speed Fw is a positive value, and the welding wire 1 is fed forward on average.

[0042] At the start of welding, time t1, the tip of the welding wire 1 is separated from the surface of the base material 2, so the distance Lw between the tip of the welding wire and the base material is a positive value, as shown in (H) of the figure. The value of Lw at time t1 is approximately 2 to 20 mm. The period from time t1, when the welding start signal St shown in (A) of the figure becomes high level, to time t7, when the current energization determination signal Cd shown in (E) of the figure becomes high level, is the initial period Ti, and the period thereafter is the steady welding period Tc.

[0043] [Operation during the initial period Ti from time t1 to t7] At time t1, as shown in (A) of the figure, when the welding start signal St changes to a high level (welding starts), the initial period timer signal Sti changes to a high level, starting the initial period Ti, as shown in (G) of the figure. At the same time, the welding power source is started, and the welding voltage Vw becomes the no-load voltage value of the maximum output voltage value (approximately 70 V), as shown in (D) of the figure. Because the tip of the welding wire 1 and the surface of the base material 2 are separated, the welding current Iw does not flow, as shown in (C) of the figure. At the same time, feeding of the welding wire 1 begins, as shown in (B) of the figure.

[0044] As shown in Fig. 1B, the feed rate Fw during the initial period Ti is controlled by alternately repeating forward and reverse feed periods at a predetermined initial frequency Si [Hz]. The initial frequency Si is set by the standard value (approximately 100 Hz) of the initial frequency setting signal Sir in Fig. 1. The forward and reverse feed periods during the initial period are set by the standard values ​​(approximately 55%) of the initial frequency setting signal Sir and the initial time ratio setting signal Dir in Fig. 1.

[0045] During the forward feed period from time t1 to t2, the feed speed Fw accelerates from 0 at a predetermined rate of change, and when it reaches a predetermined initial forward feed peak value Fsi, it maintains that value and then decelerates to 0 at a predetermined rate of change after a predetermined period has passed. The initial forward feed peak value Fsi is set by the standard value (approximately 25 m / min) of the initial forward feed peak value setting signal Fsir in Figure 1. During the reverse feed period from time t2 to t3, the feed speed Fw accelerates from 0 at a predetermined rate of change, and when it reaches a predetermined negative initial reverse feed peak value Fri, it maintains that value and then decelerates to 0 at a predetermined rate of change after a predetermined period has passed. The initial reverse feed peak value Fri is set by the standard value (approximately -21 m / min) of the initial reverse feed peak value setting signal Frir in Figure 1. The period from time t1 to t3 constitutes one cycle, which is the reciprocal of the initial frequency Si, 1 / Si.

[0046] As shown in Figure 1(H), the distance Lw between the welding wire tip and the base metal gradually shortens during the forward feed period from time t1 to t2, and gradually lengthens during the reverse feed period from time t2 to t3. However, the value of Lw at time t3 is shorter than the value of Lw at time t1. This is because the waveform parameters are adjusted so that the average value of the feed speed Fw per cycle is a positive value. The same operation as above is repeated in the cycle from time t3 to t4. In Figure 1(H), only two cycles from time t1 to t4 are drawn, but in reality, this period lasts for several tens of cycles until the first collision occurs.

[0047] As shown in FIG. 1B, when the tip of the welding wire 1 comes into contact (collides) with the surface of the base metal 2 at time 41 during the forward feed period from time t4 to t42, the distance Lw between the welding wire tip and the base metal becomes 0, as shown in FIG. 1H. However, because slag adheres to the tip of the welding wire 1, a non-conductive contact state occurs. For this reason, as shown in FIG. 1C, the welding current Iw does not flow, and as shown in FIG. 1D, the welding voltage Vw remains at the no-load voltage value. During the forward feed period from time t41 to t42, the distance Lw between the welding wire tip and the base metal remains 0. During the subsequent reverse feed period from time t42 to t5, the distance Lw between the welding wire tip and the base metal gradually increases from 0. In FIG. 1B, only one cycle from time t4 to t5 is plotted, but in reality, this period spans several tens of cycles. Furthermore, the waveform of the feed speed Fw during this period remains a trapezoidal wave because there is play in the feed path even during the short circuit period between the welding wire 1 and the base metal 2. When there is little or no slag attached, an arc often occurs during the first or several collisions between the welding wire 1 and the base metal 2.

[0048] At time t5, when the elapsed time from the start of the initial period Ti at time t1 exceeds a predetermined reference time, as shown in FIG. 1(I), it is determined that the slag has not been removed, and the discrimination signal Hd changes to a high level. In response to this, as shown in FIG. 1(B), the waveform parameters of the feed speed Fw change as follows, with the amplitude and / or average value increasing by approximately 1.2 to 1.5 times: the initial forward feed peak value Fsi increases as the initial forward feed peak value setting signal Fsir of FIG. 1 increases; the initial reverse feed peak value Fri increases as the initial reverse feed peak value setting signal Frir of FIG. 1 increases; the initial frequency Si increases as the initial frequency setting signal Sir of FIG. 1 increases; and the initial time ratio Di increases as the initial time ratio setting signal Dir of FIG. 1 increases. It is not necessary for all of these waveform parameters to increase; it is sufficient that at least one of them increases, resulting in an increase in the amplitude and / or average value of the feed speed Fw. As shown in FIG. 1B, when the tip of the welding wire 1 comes into contact (collides) with the surface of the base metal 2 at time 51 during the forward feed period from time t5 to t52, the distance Lw between the welding wire tip and the base metal becomes 0 as shown in FIG. 1H. However, because slag adheres to the tip of the welding wire 1, a non-conductive contact state continues. For this reason, as shown in FIG. 1C, the welding current Iw does not flow, and as shown in FIG. 1D, the welding voltage Vw remains at the no-load voltage value. During the forward feed period from time t51 to t52, the distance Lw between the welding wire tip and the base metal remains 0. During the subsequent reverse feed period from time t52 to t6, the distance Lw between the welding wire tip and the base metal gradually increases from 0. Although only one cycle from time t5 to t6 is plotted in FIG. 1B, in reality, this period lasts for several to several tens of cycles until an arc is generated. During this period, the amplitude and / or average value of the feed speed Fw increases, increasing the impact when the tip of the welding wire 1 collides with the base material 2, and enhancing the slag removal effect. As a result, even if the slag is heavily attached, it can be effectively removed. However, doing so may increase the stress on the feed motor WM shown in FIG. 1, which may shorten its lifespan. For this reason, the amplitude and / or average value of the feed speed Fw are not increased from the beginning, but are increased only after the reference time has elapsed.If the slag adhesion is not severe, an arc is often generated by multiple collisions before the reference time has elapsed.

[0049] As shown in FIG. 1B, at time t7 during the forward feed period from time t6, the tip of the welding wire 1 again contacts (collides with) the surface of the base metal 2. As shown in FIG. 1H, the distance Lw between the welding wire tip and the base metal becomes 0. Because the slag adhering to the tip of the welding wire 1 was scraped off and removed by the collisions in the previous cycle, the current contact results in a conductive contact (short-circuit state). As a result, as shown in FIG. 1C, the welding current Iw begins to flow. As shown in FIG. 1D, the welding voltage Vw drops from the no-load voltage value to a short-circuit voltage value of several volts. In response to this, at time t7, as shown in FIG. 1E, the current flow discrimination signal Cd goes high (current flow). As shown in FIG. 1G, the initial period timer signal Sti goes low, ending the initial period Ti. At the same time, as shown in FIG. 1I, the discrimination signal Hd also goes low. At time t7, as shown in (F) of the figure, the short circuit determination signal Sd becomes high level (short circuit).

[0050] [Operation during steady welding period Tc after time t7] When a short circuit occurs at time t7, as shown in (C) of the figure, a welding current Iw of a predetermined hot start current value (approximately 200 to 500 A) is supplied. The hot start current is supplied during a predetermined hot start period from time t7 to t91.

[0051] At time t8, when a predetermined delay period has elapsed since the current application determination signal Cd changed to a high level at time t7, the feed speed Fw is switched from forward feed to reverse feed, and is rapidly accelerated to a predetermined steady-state reverse feed peak value Frc, and maintained at that value, as shown in FIG. 1B. The delay period is set to approximately 1 to 10 ms. The delay period may be set to 0, thereby eliminating the delay. This delay is provided to smoothly generate an initial arc when the welding wire 1 contacts the base material 2.

[0052] When arc 3 is generated by the application of the hot start current at time t9, as shown in (D) of the figure, the welding voltage Vw rises sharply to an arc voltage value of several tens of volts. In response to this, as shown in (F) of the figure, the short-circuit determination signal Sd changes to a low level (arc). When the short-circuit determination signal Sd changes to a low level (arc) during the reverse feed peak period, as shown in (B) of the figure, the feed speed Fw begins to transition to the forward feed period. The feed speed Fw is decelerated at a predetermined rate from time t9 and becomes zero at time t10. At time t91 during the reverse feed deceleration period, as shown in (C) of the figure, the welding current Iw decreases from the hot start current value to an arc current value that changes depending on the arc load. As described above, the hot start period from time t7 to t91 is a predetermined value, so it is uncertain what period the feed speed Fw will be at when the hot start period ends. The period from time t9 to t11 is the arc period.

[0053] At time t10, the forward feed period begins, and the welding voltage Vw accelerates from 0 at a predetermined rate of change. When the predetermined steady-state forward feed peak value Fsc is reached, the value is maintained. If a short circuit occurs at time t11 during the forward feed peak period, as shown in (D) of the figure, the welding voltage Vw suddenly decreases to a short-circuit voltage value of several volts, and as shown in (F) of the figure, the short-circuit detection signal Sd changes to a high level (short circuit). In response to this, as shown in (B) of the figure, the feed speed Fw begins to transition to the reverse feed period. The feed speed Fw decelerates at a predetermined rate of change during the period from time t11 to t12 and becomes 0. As shown in (C) of the figure, the welding current Iw gradually increases during the short-circuit period from time t11 to t13.

[0054] At time t12, the reverse feed period begins, and the welding current accelerates from 0 at a predetermined rate of change. When the predetermined steady-state reverse feed peak value Frc is reached, the value is maintained. At time t13, an arc is generated by the reverse feed. As shown in (D) of the figure, the welding voltage Vw rapidly increases to an arc voltage value of several tens of volts. As shown in (F) of the figure, the short circuit detection signal Sd changes to a low level (arc). In response to this, as shown in (B) of the figure, the feed speed Fw begins to transition to the forward feed period. During the period from time t13 to t14, the feed speed Fw decelerates at a predetermined rate of change and reaches 0. As shown in (C) of the figure, the welding current Iw gradually decreases during the arc period.

[0055] The change in the distance Lw between the welding wire tip and the base metal is as follows. From time t7, when the welding wire first enters a conductive state (short circuit state), to time t9, when the arc is generated, Lw = 0. During the reverse feed deceleration period from time t9 to t10, the value of Lw gradually increases from 0. During the forward feed period from time t10 to t11, the value of Lw gradually decreases to 0. During the period from time t11 to t13, the value of Lw remains 0. During the reverse feed deceleration period from time t13 to t14, the value of Lw gradually increases.

[0056] According to the first embodiment, if it is determined that the slag has not been removed during the initial period, the amplitude and / or average value of the feed rate is increased for the remainder of the initial period. This determination is made when the elapsed time of the initial period is equal to or exceeds a reference time. There are cases where an arc does not occur even after multiple collisions between the welding wire and the base metal due to severe slag adhesion. In this embodiment, when such a state is determined, the amplitude and / or average value of the feed rate is increased to increase the impact of the collision and enhance the slag removal effect. As a result, in this embodiment, an arc can be reliably started even when the slag adhesion is severe.

[0057] [Embodiment 2] In the invention of the second embodiment, the timing for increasing the amplitude and / or average value of the feed speed during the initial period is determined based on when the torque of the feed motor becomes equal to or greater than the reference torque.

[0058] 3 is a block diagram of a welding power source for carrying out an arc welding control method according to a second embodiment of the present invention. This figure corresponds to the above-mentioned FIG. 1, and the same blocks are designated by the same reference numerals and their description will not be repeated. This figure is obtained by adding a motor current detection circuit IMD to FIG. 1 and replacing the discrimination circuit HD of FIG. 1 with a second discrimination circuit HD2. These blocks will be described below with reference to this figure.

[0059] The motor current detection circuit IMD detects the motor current of the feed motor WM and outputs a motor current detection signal Imd. This motor current detection signal Imd is proportional to the torque of the feed motor WM, so it can be said to detect torque.

[0060] The second determination circuit HD2 receives the initial period timer signal Sti and the motor current detection signal Imd as inputs, performs either the following process 1) or 2), and outputs a determination signal Hd. 1) When the initial period timer signal Sti is at a high level, the value of the motor current detection signal Imd changes to a reference current value (reference torque) or more, thereby determining a collision between the welding wire 1 and the base material 2. Then, when a predetermined time (about 0.5 to 1.5 seconds) has elapsed since the initial collision was determined, a determination signal Hd is output, which goes to a high level and goes to a low level when the initial period timer signal Sti changes to a low level. 2) When the initial period timer signal Sti is at a high level, the value of the motor current detection signal Imd changes to a reference current value (reference torque) or more to determine a collision between the welding wire 1 and the base material 2. Then, when the number of collision detections reaches a predetermined number (approximately 50 to 150 times), a determination signal Hd is output which goes to a high level, and goes to a low level when the initial period timer signal Sti changes to a low level.

[0061] The timing chart of each signal in Fig. 3 is the same as that in Fig. 2, and therefore will not be described here, except that the timing at which the discrimination signal Hd goes high at time t5 is determined by the second discrimination circuit HD2.

[0062] According to the second embodiment described above, the timing for increasing the amplitude and / or average value of the feed speed is determined based on whether the torque of the feed motor has reached or exceeded the reference torque during the initial period. In this way, the amplitude and / or average value of the feed speed is increased when no arc is generated even after a predetermined number of collisions between the welding wire and the base metal. This allows stress on the feed motor to be minimized. Furthermore, since the time to the first collision is not affected by variations in the distance between the welding wire tip and the base metal at the start of feeding, the time required for arc start can be shortened, thereby improving productivity. [Explanation of symbols]

[0063] 1 welding wire 2 Base material 3. Arc 4 welding torches 5 Feeding roll CD current determination circuit Cd Current discrimination signal DIR Initial time ratio setting circuit Dir Initial time ratio setting signal DV drive circuit Dv drive signal E Output voltage Ea Error amplification signal ED output voltage detection circuit Ed output voltage detection signal EI current error amplifier circuit Ei Current error amplification signal ER output voltage setting circuit Er Output voltage setting signal EV voltage error amplifier circuit Ev Voltage error amplified signal FC feed control circuit Fc feed control signal FCR steady welding period feed speed setting circuit Fcr Steady welding period feed speed setting signal FIR initial period feed speed setting circuit Fir Initial period feed speed setting signal FR feed speed setting circuit Fr feed speed setting signal Frc Steady-state reverse feed peak value FRCR Steady-state reverse peak value setting circuit Frcr Steady-state reverse peak value setting signal Fri Initial Backward Peak Value FRIR Initial reverse peak value setting circuit Frir Initial reverse peak value setting signal Fsc steady-state forward peak value FSCR Steady forward peak value setting circuit Fscr Steady forward peak value setting signal Fsi Initial forward peak value FSIR Initial forward peak value setting circuit Fsir Initial forward peak value setting signal FW feed speed HD discrimination circuit HD discrimination signal HD2 Second discrimination circuit ID current detection circuit Id Current detection signal IHR Hot start current setting circuit Ihr Hot start current setting signal IMD motor current detection circuit Imd Motor current detection signal Iw Welding current Lw: Distance between welding wire tip and base metal PM power supply main circuit SD short circuit detection circuit Sd Short circuit detection signal Si initial frequency SIR initial frequency setting circuit Sir Initial frequency setting signal ST Welding Start Circuit St Welding start signal STI Initial Period Timer Circuit Sti Initial period timer signal SW Power supply characteristic switching circuit Tc Steady welding period Ti initial period VD voltage detection circuit Vd Voltage detection signal Vw welding voltage WL reactor WM feed motor

Claims

1. 1. An arc welding control method for performing forward / reverse feed control in which a feed speed is alternately switched between a forward feed period and a reverse feed period during an initial period from when welding wire feed starts to when welding current application starts, When it is determined that the slag has not been removed during the initial period, the amplitude, average value, frequency and time ratio of the forward feed period of the feeding speed are increased during the subsequent initial period; When the slag is removed by the forward / reverse feed control and the welding current starts to flow during the forward feed period of the feed speed, after a delay period of 1 to 10 ms has elapsed from that point, the feed speed is switched to the reverse feed period to generate an arc.

1. An arc welding control method comprising:

2. The determination is made when the elapsed time of the initial period is equal to or longer than a reference time.

2. The method for controlling arc welding according to claim 1.

3. The determination is made based on whether the torque of the feed motor during the initial period is equal to or greater than a reference torque.

2. The method for controlling arc welding according to claim 1.

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