Submerged arc welding control method and submerged arc welding apparatus

Abstract

To obtain excellent welding quality by suppressing the occurrence of magnetic blow in submerged arc welding.SOLUTION: In a submerged arc welding control method in which welding is performed by feeding a welding wire and outputting a DC welding voltage and a DC welding current between the welding wire and a base material to generate an arc, welding is performed by outputting the DC welding voltage and the DC welding current in a section from a welding start position Ps to a specific position Pa, and welding is performed by outputting an AC welding voltage and an AC welding current in a section from the specific position Pa to a welding end position Pe. The specific position Pa is a position before the welding end position Pe by a predetermined specific distance.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a submerged arc welding control method and a submerged arc welding apparatus. [Background technology]

[0002] Submerged arc welding has been known for some time. In submerged arc welding, granular flux is dispersed on the base metal, a welding wire is fed into the flux, and an arc is generated between the tip of the welding wire and the base metal to perform welding. In submerged arc welding, a large current is passed through a large-diameter welding wire, allowing for high-efficiency welding of thick plates.

[0003] In consumable electrode arc welding, including submerged arc welding, a magnetic field is formed around the arc by the welding current flowing through the arc and base metal, and the arc may be deflected by the force of this magnetic field. This condition is called magnetic arc blow. Whether magnetic arc blow occurs depends on the shape of the magnetic field formed by the welding current flowing through the base metal. When the welded portion is far from the edge of the base metal, the magnetic field is often formed symmetrically, so the arc is not subjected to a biased force from the magnetic field, and magnetic arc blow is unlikely to occur. On the other hand, when the welded portion is close to the edge of the base metal, the magnetic field is formed asymmetrically, so the arc is subjected to a biased force from the magnetic field, making magnetic arc blow more likely to occur. Therefore, magnetic arc blow is likely to occur at the end of the weld, which is often near the edge of the base metal. Magnetic arc blow deteriorates the weld quality.

[0004] In the invention of Patent Document 1, welding locations where magnetic arc blow does not occur are welded by DC pulse arc welding, and welding locations where magnetic arc blow is likely to occur are welded by AC pulse arc welding. In AC pulse arc welding, the welding current is AC, so the direction of current flow reverses periodically, and the direction of the magnetic field created also reverses accordingly. As a result, the force acting on the arc from the magnetic field is weaker than in DC pulse arc welding. As a result, AC pulse arc welding can suppress the occurrence of magnetic arc blow. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-200735 Summary of the Invention [Problem to be solved by the invention]

[0006] Submerged arc welding involves passing a large current exceeding 800 A, which creates a strong magnetic field. As a result, submerged arc welding has the problem of magnetic arc blow, which deflects the arc and degrades welding quality. As mentioned above, magnetic arc blow is particularly likely to occur at the end of the weld near the edge of the base material, resulting in poor welding quality.

[0007] Therefore, an object of the present invention is to provide a submerged arc welding control method and submerged arc welding apparatus that can suppress the occurrence of magnetic arc blow and obtain good welding quality, for example. [Means for solving the problem]

[0008] A submerged arc welding control method provided according to a first aspect of the present invention is a submerged arc welding control method in which a welding wire is fed and a direct current welding voltage and welding current are output between the welding wire and a base metal to generate an arc and perform welding, characterized in that the welding voltage and welding current are output as alternating currents within a specific distance from a welding end position.

[0009] As an example, the submerged arc welding control method of the present invention is characterized in that it is determined that the welding end position is within the specified distance by being in a crater treatment period.

[0010] As an example, the submerged arc welding control method of the present invention is characterized in that it determines whether the welding end position is within the specific distance based on the elapsed time from the start of welding and the welding speed.

[0011] As an example, the submerged arc welding control method of the present invention is characterized in that an external characteristic is set, and when the DC is output, the output is controlled so that the instantaneous value of the welding current and the instantaneous value of the welding voltage lie on a characteristic line corresponding to the external characteristic, and when the AC is output, the output is controlled so that the effective value of the welding current and the effective value of the welding voltage lie on a characteristic line corresponding to the external characteristic.

[0012] As an example, the method for controlling submerged arc welding of the present invention is characterized in that a feed speed of the welding wire is variably controlled based on the welding voltage.

[0013] A submerged arc welding apparatus provided according to a second aspect of the present invention is a submerged arc welding apparatus that feeds a welding wire and outputs a DC welding voltage and welding current between the welding wire and a base metal to generate an arc and perform welding, characterized in that the submerged arc welding apparatus outputs an AC welding voltage and welding current within a specific distance from a welding end position. [Effects of the Invention]

[0014] According to the above configuration, for example, in the submerged arc welding control method and the submerged arc welding apparatus, the occurrence of magnetic arc blow can be suppressed and good welding quality can be obtained. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a block diagram of a welding device for carrying out a submerged arc welding control method according to an embodiment of the present invention. [Figure 2] 1 is a diagram showing the weld lines for the base materials 2a and 2b in which the grooves are provided as straight lines. [Figure 3] 2 is a timing chart of each signal in the welding device of FIG. 1 in a DC output mode. [Figure 4] 2 is a timing chart of each signal in the welding device of FIG. 1 when a welding current having a sine waveform is applied in an AC output mode. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0017] 1 is a block diagram of a welding device for carrying out a submerged arc welding control method according to an embodiment of the present invention. Each block will be described below with reference to the diagram.

[0018] The main power supply circuit PM is connected to a commercial power supply (not shown) such as a three-phase 200V, and receives as input a welding start signal St (described later), a current error amplification signal Ei (described later), and a polarity switching signal Spn (described later).When the welding start signal St is at a high level, the main power supply circuit PM performs inverter control in accordance with the current error amplification signal Ei, switches between electrode positive polarity EP and electrode negative polarity EN in accordance with the polarity switching signal Spn, and outputs AC or DC welding current Iw and welding voltage Vw. Although not shown, this power supply main circuit PM includes a primary rectifier that rectifies the commercial power supply, a smoothing capacitor that smooths the rectified DC, a primary-side inverter circuit 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, a secondary rectifier that rectifies the stepped-down high-frequency AC to DC, a reactor that smooths the rectified DC, a secondary-side inverter circuit that switches the smoothed DC between electrode positive polarity EP and electrode negative polarity EN in accordance with a polarity switching signal Spn, a modulation circuit that receives as input the current error amplified signal Ei and outputs a pulse-width modulated signal, and a drive circuit that receives as input the pulse-width modulated signal to drive the switching elements of the primary-side inverter circuit.

[0019] The welding wire 1 is fed through the welding torch 4 by the rotation of a feed roll 5 connected to a feeder WM, and an arc 3 is generated between the welding wire 1 and the base material 2. A welding voltage Vw is applied between a power feed tip (not shown) of the welding torch 4 and the base material 2, and a welding current Iw flows. A flux feeder 6 supplies flux (not shown) to the arc generation part. The arc generation part is covered with the flux, so the arc 3 cannot be seen from the outside.

[0020] The welding start circuit ST is a circuit that includes a push button, etc., and receives the position determination signal Pd (described later) as input. When the welding operator turns it on, it goes to high level, and outputs a welding start signal St that returns to low level when the position determination signal Pd changes from 3 (crater processing period) to 0.

[0021] The welding length setting circuit LWR outputs the value input by the welding operator after measuring the length of the welding line to be welded as a welding length setting signal Lwr [cm].

[0022] The welding speed setting circuit WSR outputs a predetermined welding speed setting signal Wsr [cm / min].

[0023] The specific distance setting circuit LAR outputs a predetermined specific distance setting signal Lar [cm].

[0024] The current detection circuit CD receives a current detection signal Id (described later) as input, and outputs a current detection signal Cd that goes high when it determines that the welding current Iw is being applied based on the current detection signal Id.

[0025] The position determination circuit PD receives the welding length setting signal Lwr, the welding speed setting signal Wsr, the specific distance setting signal Lar, and the energization determination signal Cd as inputs, performs the following processing, and outputs a position determination signal Pd. 1) When the energization determination signal Cd is at a low level, the position determination signal Pd=0 is output. 2) When the energization determination signal Cd changes to high level, the position determination signal Pd=1 is output. 3) When the time elapsed since the current detection signal Cd changed to high level is equal to or greater than (Lwr-Lar) / Wsr, it is determined that the tip position of welding torch 4 is within a specific distance from the welding end position, and a position detection signal Pd=2 is output. For example, if Lwr=100 cm, Lar=5 cm, and Wsr=20 cm / min, then (100-5) / 20=4.75 minutes, and Pd=2 is output when 4.75 minutes have passed since the start of welding. 4) When the time elapsed since the current detection signal Cd changed to high level reaches Lwr / Wsr, it is determined that the tip position of the welding torch 4 has reached the welding end position, and a position detection signal Pd = 3 is output. In the above example, 100 / 20 = 5 minutes, and Pd = 3 is output when 5 minutes have passed since the start of welding. 5) When the time elapsed since the position discrimination signal Pd changed to Pd=3 reaches the crater processing period, the position discrimination signal Pd=0 is output.

[0026] The automatic carriage AT is equipped with the welding torch 4 and the flux supply device 6, and receives the position determination signal Pd and the welding speed setting signal Wsr as inputs. When the position determination signal Pd changes from 0 to 1 (start of current flow), the automatic carriage AT moves at the speed set by the welding speed setting signal Wsr so that the tip position of the welding torch 4 follows the weld line while spraying flux from the flux supply device 6, and stops moving when the position determination signal Pd changes to 3 (end of welding position).

[0027] The output mode setting circuit MR receives the position determination signal Pd as an input, performs one of the following processes 1) and 2), and outputs an output mode setting signal Mr. 1) An output mode setting signal Mr is output which is at a low level (DC output mode) when the position determination signal Pd = 0 or 1, and at a high level (AC output mode) when the position determination signal Pd = 2 or 3. In other words, when the tip position of the welding torch 4 is within a specific distance from the welding end position, the AC output mode is selected. 2) An output mode setting signal Mr is output that is low level (DC output mode) when the position determination signal Pd = 0 to 2, and high level (AC output mode) when the position determination signal Pd = 3. That is, when the tip position of the welding torch 4 reaches the welding end position and enters the crater processing period, the AC output mode is entered. In other words, the specific distance is set to 0 cm, and it is determined that the tip is within the specific distance from the welding end position by being in the crater processing period.

[0028] The voltage detection circuit VD detects the instantaneous value of the welding voltage Vw, converts it into an absolute value, and outputs a voltage detection signal Vd.

[0029] The voltage effective value detection circuit VED receives the voltage detection signal Vd, calculates an effective value from the voltage detection signal Vd, and outputs an effective voltage value detection signal Ved.

[0030] The external characteristic control circuit CC receives the output mode setting signal Mr, the voltage effective value detection signal Ved, the voltage detection signal Vd, and the position determination signal Pd as inputs, and outputs the current effective value setting signal Ier and the DC current setting signal Idr calculated based on the following equation (1) or (2): 1) When the output mode setting signal Mr is at High level (AC output mode) The external characteristic is the output characteristic of the welding power source, and can be expressed as a function Ve=f(Ie), where the effective value of the welding current Ie is the input and the effective value Ve of the welding voltage Vw is the output. If the function is defined as a straight line, it becomes the following equation. Ve=K·Ie+V0 Here, K [V / A] is the slope of a predetermined line, and V0 is the predetermined value of Ve when Ie = 0. Rearranging the above equation with Ie, substituting Ie with the current effective value setting signal Ier and Ve with the voltage effective value detection signal Ved, yields the following equation. Ier=(Ved-V0) / K (1) K is set in the range of about -0.1 to -40V / 100A, and V0 is set in the range of about 20 to 50V. The value of V0 is set separately when the position determination signal Pd is 1 or 2 (main welding period) and when it is 3 (crater processing period). In AC output mode, the external characteristics are controlled by this formula. 2) When the output mode setting signal Mr is at low level (DC output mode) In the above equation (1), if Ier is replaced with Idr and Ved with Vd, the following equation is obtained. Idr=(Vd-V0) / K (2) formula The value of V0 is set separately when the position determination signal Pd is 1 or 2 (main welding period) and when it is 3 (crater processing period). In the DC output mode, the external characteristics are controlled by this formula.

[0031] The current detection circuit ID detects the instantaneous value of the welding current Iw, converts it into an absolute value, and outputs a current detection signal Id.

[0032] The current effective value detection circuit IED receives the current detection signal Id, calculates an effective value from the current detection signal Id, and outputs a current effective value detection signal Ied.

[0033] The current amplitude modulation circuit AMC receives the RMS current detection signal Ied and the RMS current setting signal Ier, performs modulation control based on the error amplification value of both signals, and outputs a current amplitude modulation signal Amc. This circuit changes the amplitude of the welding current Iw so that the RMS value of the welding current Iw becomes equal to the RMS current setting value.

[0034] The electrode positive polarity period setting circuit TPR outputs a predetermined electrode positive polarity period setting signal Tpr, and the electrode negative polarity period setting circuit TNR outputs a predetermined electrode negative polarity period setting signal Tnr.

[0035] The current setting circuit IR receives the electrode positive polarity period setting signal Tpr, the electrode negative polarity period setting signal Tnr, and the current amplitude modulation signal Amc as inputs, performs the following processes 1) to 3), and outputs a current setting signal Ir having a half-cycle waveform of a sine wave or a square wave (including a trapezoidal wave, the same applies below), as well as a polarity signal Tpn. 1) During the electrode positive polarity period Tep set by the electrode positive polarity period setting signal Tpr, the start and end points of the period are set to predetermined polarity switching current values, and a half-cycle sinusoidal waveform with an amplitude set by the current amplitude modulation signal Amc is output as the current setting signal Ir. During the electrode positive polarity period Tep, a polarity signal Tpn that is at a high level is output. 2) During the electrode negative polarity period Ten set by the electrode negative polarity period setting signal Tnr, the start and end points of the period are the polarity switching current value described above, and a half-cycle waveform of a sine wave with an amplitude set by the current amplitude modulation signal Amc is output as the current setting signal Ir. During the electrode negative polarity period Ten, a polarity signal Tpn that is at a low level is output. 3) Repeat steps 1) and 2) above.

[0036] The polarity switching setting circuit SPN receives the output mode setting signal Mr and the polarity signal Tpn as inputs, performs the following processing, and outputs the polarity switching signal Spn. 1) When the output mode setting signal Mr is at a high level (AC output mode) and the polarity signal Tpn is at a high level (electrode positive polarity EP), a polarity switching signal Spn that is at a high level is output. 2) When the output mode setting signal Mr is at a high level (AC output mode) and the polarity signal Tpn is at a low level (electrode negative polarity EN), a polarity switching signal Spn that goes to a low level is output. 3) When the output mode setting signal Mr is at a low level (DC output mode), a polarity switching signal Spn is output at a high level when the electrode positive polarity EP is set, and at a low level when the electrode negative polarity EN is set.

[0037] The current control setting circuit ICR receives the output mode setting signal Mr, the current setting signal Ir, and the DC current setting signal Idr as inputs, performs the following processing, and outputs the current control setting signal Icr. 1) When the output mode setting signal Mr is at a high level (AC output mode), the current setting signal Ir is output as the current control setting signal Icr. 2) When the output mode setting signal Mr is at a low level (DC output mode), the DC current setting signal Idr is output as the current control setting signal Icr.

[0038] The current error amplifier circuit EI receives the current control setting signal Icr and the current detection signal Id, amplifies the difference between the two values, and outputs a current error amplified signal Ei. This circuit controls the welding device to a constant current.

[0039] The voltage setting circuit VR outputs a predetermined voltage setting signal Vr.

[0040] The variable feed speed control circuit FMC receives the RMS voltage detection signal Ved and the voltage setting signal Vr as inputs, performs variable feed speed control using P (proportional) control, PI (proportional-integral) control, or PID (proportional-integral-derivative) control based on the error amplification value of these two values, and outputs a feed speed modulation signal Fmc. This circuit variably controls the feed speed Fw so that the arc length is maintained at an appropriate value. In DC output mode, the voltage detection signal Vd may be used instead of the RMS voltage detection signal Ved.

[0041] The feed control circuit FC receives the welding start signal St and the feed speed modulation signal Fmc as inputs, and when the welding start signal St is at a high level, outputs a feed control signal Fc to the feeder WM to control the feed speed Fw of the welding wire 1 to a speed determined by the feed speed modulation signal Fmc.

[0042] FIG. 2 is a diagram showing the weld line as a straight line for base materials 2a and 2b with grooves. The shape of the groove is omitted from the figure. The left end of the weld line indicates the welding start position Ps, and the right end indicates the welding end position Pe. The position a specific distance before the welding end position Pe is the specific position Pa. Below, the operation during submerged arc welding will be explained with reference to the figure.

[0043] When the welder measures the weld line length (Ps-Pe) and inputs it into the weld length setting circuit LWR in Figure 1, the weld length setting signal Lwr is set. The welder sets the welding speed setting signal Wsr using the welding speed setting circuit WSR in Figure 1. The welder sets the specific distance setting signal Lar using the specific distance setting circuit LAR in Figure 1. The welder sets the external characteristics for DC output mode by setting equation (2) in the external characteristics control circuit CC in Figure 1. The welder sets the external characteristics for AC output mode by setting equation (1) in the external characteristics control circuit CC in Figure 1. At this time, the welder sets external characteristics appropriate for the main welding period and the crater treatment period, respectively. The welder sets the voltage setting signal Vr, which is the target value for variable speed control of the feed speed, using the voltage setting circuit VR in Figure 1.

[0044] [Operation of the main welding section between the welding start position Ps and the specific position Pa] When the welding operator turns on the push button of the welding start circuit ST (FIG. 1) with the tip of the welding torch 4 at the welding start position Ps, flux is sprayed from the flux supply device 6 (FIG. 1), followed by the feeding of the welding wire 1. The welding current Iw and welding voltage Vw are output, generating the arc 3. When the welding current Iw is applied, the current-discharge determination signal Cd (FIG. 1) changes to a high level, and the position determination signal Pd (FIG. 1) changes from 0 to 1. In response, the automated carriage AT (FIG. 1) begins moving at the speed set by the welding speed setting signal Wsr. Since the output during the main welding period from the welding start position Ps to the specific position Pa is in DC output mode, DC welding current Iw and welding voltage Vw are output, as described later in FIG. 3, and welding is performed. As described above, the output is controlled based on the external characteristics for the main welding set by Equation (2) so that the instantaneous values ​​of the welding current Iw and welding voltage Vw lie on the characteristic curve corresponding to the external characteristics. The feed speed of the welding wire 1 is variably controlled so that the welding voltage Vw is equal to the voltage setting signal Vr, and the arc length is controlled to an appropriate value.

[0045] [Operation of the main welding section from specific position Pa to welding end position Pe] When the elapsed time from the start of welding when the energization determination signal Cd changes to a high level becomes (Lwr-Lar) / Wsr, it is determined that the tip position of the welding torch 4 has reached the specific position Pa, and the position determination signal Pd changes to 2. In response to this, the output mode is switched to AC output mode. During the main welding period from the specific position Pa to the welding end position Pe, AC welding current Iw and welding voltage Vw are output, as will be described later with reference to FIG. 4, and welding is performed. As described above, the output is controlled based on the external characteristics for main welding set by equation (1) so that the effective values ​​of the welding current Iw and welding voltage Vw lie on the characteristic line corresponding to the external characteristics. The feed speed of the welding wire 1 is variably controlled so that the welding voltage Vw is equal to the voltage setting signal Vr, and the arc length is controlled to an appropriate value. For example, if Lwr = 100 cm, Lar = 5 cm, and Wsr = 20 cm / min, then (Lwr - Lar) / Wsr = 4.75 minutes. Therefore, the tip position of welding torch 4 will reach specific position Pa 4.75 minutes after the start of welding. The section (specific position Pa - welding end position Pe) that is the specific distance Lar before welding end position Pe is close to welding end position Pe, which is the end of base materials 2a and 2b, and is therefore a section where magnetic arc blow is likely to occur. For this reason, the output in this section is set to AC to suppress the occurrence of magnetic arc blow.

[0046] [Operation of the crater processing section at the welding end position Pe] When the elapsed time from the start of welding, when the energization determination signal Cd changes to a high level, reaches (Lwr / Wsr), it is determined that the tip position of the welding torch 4 has reached the welding end position Pe, and the position determination signal Pd changes to 3. In response to this, the automated carriage AT stops moving and transitions to the crater removal period in AC output mode. During the crater removal period at the welding end position Pe, AC welding current Iw and welding voltage Vw are output, as described later in FIG. 4, and welding is performed. As described above, the output is controlled based on the external characteristics for the crater removal period set by equation (1) so that the effective values ​​of the welding current Iw and welding voltage Vw lie on the characteristic curve corresponding to the external characteristics. The feed speed of the welding wire 1 is variably controlled so that the welding voltage Vw is equal to the voltage setting signal Vr, and the arc length is controlled to an appropriate value. In the numerical example described above, (Lwr / Wsr) = 5 minutes. Therefore, five minutes after the start of welding, the tip of welding torch 4 reaches welding end position Pe. Since welding end position Pe is at the end of base materials 2a and 2b, it is a section where magnetic arc blow is likely to occur. For this reason, the output in this section is set to AC to suppress the occurrence of magnetic arc blow.

[0047] [Welding end processing operation at welding end position Pe] When the tip position of welding torch 4 reaches welding end position Pe and the crater processing period ends, position determination signal Pd changes to 0. In response to this, feeding of welding wire 1 and output from the welding power source are stopped, the arc is extinguished, and welding is completed.

[0048] The value of the specific distance setting signal Lar is set in the range of approximately 0 to 10 cm, where magnetic arc blow is likely to occur. When Lar = 0, the specific position Pa coincides with the welding end position Pe. In this case, being within the specific distance from the welding end position Pe is determined by being in the crater treatment period. In the above, whether the tip position of the welding torch 4 is within the specific distance from the welding end position Pe is determined based on the elapsed time from the start of welding and the welding speed. Other determination methods include a CCD camera, optical sensor, mechanical contact sensor, etc. In the above, the start of the crater treatment period and the end of welding are automatically determined based on the elapsed time from the start of welding and the welding speed. These operations may also be performed by the welding operator by operating the push button of the welding start circuit ST in Figure 1.

[0049] Figure 3 is a timing chart of each signal in the welding device of Figure 1 when in DC output mode. Figure 3(A) shows the change over time in welding current Iw, Figure 3(B) shows the change over time in welding voltage Vw, and Figure 3(C) shows the change over time in polarity switching signal Spn. The operation of each signal will be explained below with reference to this figure.

[0050] In the figure, the output mode is DC output mode and the output polarity is electrode positive polarity EP. Therefore, as shown in (C) of the figure, the polarity switching signal Spn is at a high level for the entire period, resulting in electrode positive polarity EP.

[0051] Submerged arc welding is basically performed under welding conditions that prevent short circuits between the welding wire and the base metal, so the entire period is the arc period. As shown in Figure 1(A), the welding current Iw has a DC waveform and is controlled to the value of the DC current setting signal Idr in Figure 1. The DC current setting signal Idr is calculated by inputting the voltage detection signal Vd into equation (2) above. This allows external characteristic control to be performed. As shown in Figure 1(B), the welding voltage Vw has a DC waveform and is a value correlated with the arc length. The welding wire feed speed Fw (not shown) is variably controlled so that the voltage detection signal Vd is equal to the voltage setting signal Vr in Figure 1. This allows arc length control to be performed.

[0052] When the output polarity is the electrode negative polarity EN, the polarity switching signal Spn shown in (C) of the figure is at low level for the entire period, and the welding current Iw and welding voltage Vw have waveforms with negative values.

[0053] Figure 4 is a timing chart of each signal in the welding device of Figure 1 when a sinusoidal welding current is applied in AC output mode. Figure 4(A) shows the change over time in welding current Iw, Figure 4(B) shows the change over time in welding voltage Vw, and Figure 4(C) shows the change over time in polarity switching signal Spn. The operation of each signal will be explained below with reference to the figures.

[0054] In the figure, positive values ​​above 0 A and 0 V indicate positive electrode polarity EP, and negative values ​​below 0 A and 0 V indicate negative electrode polarity EN.

[0055] During the period from time t1 to t2, as shown in FIG. 1C, the polarity switching signal Spn is at a high level, resulting in electrode positive polarity EP. As shown in FIG. 1A, during the electrode positive polarity period Tep from time t1 to t2, the welding current Iw is at a positive polarity switching current value at the start point t1 and end point t2 of the period, and forms a positive half-cycle waveform of a sine wave with an amplitude set by the current amplitude modulation signal Amc. During the period from time t2 to t3, as shown in FIG. 1C, the polarity switching signal Spn is at a low level, resulting in electrode negative polarity EN. As shown in FIG. 1A, during the electrode negative polarity period Ten from time t2 to t3, the welding current Iw is at a negative polarity switching current value at the start point t2 and end point t3 of the period, and forms a negative half-cycle waveform of a sine wave with an amplitude set by the current amplitude modulation signal Amc. Thereafter, the cycle from time t1 to t3 is repeated. The electrode positive polarity period Tep is set by the electrode positive polarity period setting signal Tpr in Figure 1. The electrode negative polarity period Ten is set by the electrode negative polarity period setting signal Tnr in Figure 1. The current effective value setting signal Ier in Figure 1 is calculated by inputting the voltage effective value detection signal Ved into equation (1) above. The welding current amplitude is modulated and controlled so that the current effective value detection signal Ied in Figure 1 is equal to the current effective value setting signal Ier. This allows external characteristic control. The external characteristics set by equation (1) are set to characteristics appropriate for the main welding period and the crater treatment period, respectively. For example, Tep = 10 ms, Ten = 10 ms, polarity switching current value = ±200 A, and amplitude ±1000 A.

[0056] As shown in Figure 1(B), the welding voltage Vw has a waveform similar to a square wave. The effective value of the welding voltage Vw is a value correlated with the arc length. The feed speed Fw in Figure 1 is variably controlled so that the voltage effective value detection signal Ved is equal to the voltage setting signal Vr in Figure 1. This allows arc length control.

[0057] The above is the case where the welding current Iw has a sine waveform, but it may also have a square waveform.

[0058] The effects of this embodiment are described below. According to this embodiment, in a submerged arc welding control method in which a welding wire is fed and a DC welding voltage and welding current are output between the welding wire and a base metal to generate an arc for welding, AC welding voltage and welding current are output within a specific distance from the welding end position. When welding a position close to the welding end position, which is often the end of the base metal, the arc is subjected to a force from an asymmetrically formed magnetic field, which is likely to cause magnetic arc blow. In this embodiment, a position close to the end of the base metal is determined by being within a specific distance from the welding end position, and welding is performed by switching the output from DC to AC in that section. When the output is switched to AC, the direction of the welding current is periodically reversed, and the direction of the magnetic field formed is also reversed accordingly. As a result, the force acting on the arc from the magnetic field is weaker than when DC output is used. As a result, in this embodiment, by switching to AC output when welding within a specific distance from the welding end position, magnetic arc blow can be suppressed and weld quality can be improved.

[0059] More preferably, according to this embodiment, being within a specific distance from the welding end position is determined by being in the crater treatment period. The crater treatment period is usually performed at the welding end position. Therefore, if the specific distance is set to 0 cm, this becomes the welding end position. As described above, the welding end position is often located near the edge of the base material, so magnetic arc blow is likely to occur during the crater treatment period. Therefore, in this embodiment, during the crater treatment period, the output is switched from DC to AC to suppress the occurrence of magnetic arc blow, thereby improving the welding quality.

[0060] More preferably, according to this embodiment, whether the welding is within a specific distance from the welding end position is determined based on the elapsed time from the start of welding and the welding speed. In this way, whether the welding is within the specific distance can be determined by simple means without adding a sensor or the like. As a result, the configuration of the welding device can be simplified and the price can be reduced.

[0061] More preferably, according to this embodiment, external characteristics are set, and when DC is output, the output is controlled so that the instantaneous values ​​of the welding current and the welding voltage lie on characteristic lines corresponding to the external characteristics, and when AC is output, the output is controlled so that the effective values ​​of the welding current and the welding voltage lie on characteristic lines corresponding to the external characteristics. In this way, the output can be controlled by forming external characteristics appropriate for each output, whether DC or AC, thereby stabilizing the welding state. As a result, in this embodiment, even if the output is switched from DC to AC during welding, the welding state can be maintained stable and good welding quality can be achieved.

[0062] More preferably, according to this embodiment, the welding wire feed speed is variably controlled based on the welding voltage, so that the arc length, which correlates with the welding voltage, becomes an appropriate value, thereby improving the welding quality.

[0063] Furthermore, according to this embodiment, in a submerged arc welding apparatus that feeds a welding wire and outputs a DC welding voltage and welding current between the welding wire and a base metal to generate an arc for welding, the submerged arc welding apparatus outputs an AC welding voltage and welding current within a specific distance from the welding end position. This submerged arc welding apparatus achieves the above-mentioned effects. [Explanation of symbols]

[0064] 1: welding wire, 2: base material, 3: arc, 4: welding torch, 5: feed roll, 6: flux feeder, AMC: current amplitude modulation circuit, Amc: current amplitude modulation signal, AT: automatic trolley, CC: external characteristic control circuit, CD: current discrimination circuit, Cd: current discrimination signal, EI: current error amplifier circuit, Ei: current error amplifier signal, EN: electrode negative polarity, EP: electrode positive polarity, FC: feed control circuit, Fc: feed control signal, FMC: feed variable speed control circuit, Fmc: feed speed modulation signal, Fw: feed speed, ICR: current control setting circuit, Icr: current control setting signal, ID: current detection circuit, Id: current detection signal, Idr: DC current setting signal, IED: current effective value detection circuit, Ied: current effective value detection signal, IR: current setting circuit, Ir: current setting signal, Iw: welding current, LAR: specific distance setting circuit, Lar: specific distance setting signal signal, LWR: welding length setting circuit, Lwr: welding length setting signal, MR: output mode setting circuit, Mr: output mode setting signal, Pa: specific position, Pe: welding end position, PM: main power supply circuit, Ps: welding start position, SPN: polarity switching setting circuit, Spn: polarity switching signal, ST: welding start circuit, St: welding start signal, Ten: electrode negative polarity period, Tep: electrode positive polarity period, TNR: electrode negative polarity period setting circuit, Tnr: electrode negative polarity period setting signal, Tpn: polarity signal, TPR: electrode positive polarity period setting circuit, Tpr: electrode positive polarity period setting signal, VD: voltage detection circuit, Vd: voltage detection signal, VED: voltage effective value detection circuit, Ved: voltage effective value detection signal, VR: voltage setting circuit, Vr: voltage setting signal, Vw: welding voltage, WM: wire feeder, WSR: welding speed setting circuit, Wsr: welding speed setting signal

Claims

1. 1. A submerged arc welding control method for feeding a welding wire and outputting a direct current welding voltage and welding current between the welding wire and a base metal to generate an arc for welding, comprising: A submerged arc welding control method, characterized in that welding is performed by outputting the welding voltage and welding current as AC within a specific distance from a welding end position.

2. 2. The method for controlling submerged arc welding according to claim 1, wherein the presence of the specified distance from the welding end position is determined by the presence of a crater treatment period.

3. 2. The method for controlling submerged arc welding according to claim 1, wherein the determination of whether the welding is within the specified distance from the welding end position is based on the elapsed time from the start of welding and the welding speed.

4. 4. The submerged arc welding control method according to claim 1, wherein an external characteristic is set, and when the direct current is being output, the output is controlled so that the instantaneous value of the welding current and the instantaneous value of the welding voltage lie on a characteristic line corresponding to the external characteristic, and when the alternating current is being output, the output is controlled so that the effective value of the welding current and the effective value of the welding voltage lie on a characteristic line corresponding to the external characteristic.

5. 4. The method for controlling submerged arc welding according to claim 1, wherein a feed speed of the welding wire is variably controlled based on the welding voltage.

6. A submerged arc welding apparatus that feeds a welding wire and outputs a direct current welding voltage and welding current between the welding wire and a base metal to generate an arc for welding, The submerged arc welding apparatus is characterized in that it performs welding by outputting the welding voltage and the welding current which are AC within a specific distance from a welding end position.

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