Submerged arc welding control method and submerged arc welding apparatus

Abstract

To improve the setting and management of welding conditions by outputting a welding current Iw and a welding voltage Vw according to a current set value Is and a voltage set value Vs in a submerged arc welding control method.SOLUTION: In the submerged arc welding control method, a current set value Is and a voltage set value Vs are set, the external characteristic is set to a characteristic passing through an intersection point A of the current set value Is and the voltage set value Vs and having a negative gradient at the intersection point A, and a feeding speed of the welding wire is variably controlled so that the welding voltage Vw becomes equal to the voltage set value Vs to converge operation points of the welding current Iw and the welding voltage Vw to the intersection point A of the external characteristic.SELECTED DRAWING: Figure 4

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] A submerged arc welding method is used in which the arc length is controlled by variably controlling the feed speed of the welding wire based on the welding voltage (see, for example, Patent Document 1).

[0004] In variable speed control, the welding voltage, which correlates with the arc length, is maintained at an appropriate value by feedback-controlling the wire feed rate based on the error between the detected welding voltage and the set voltage. In submerged arc welding using a large-diameter wire, the change in wire melting rate is small even when the welding current changes, so it is difficult to achieve the self-regulation of the arc length that is generally used in consumable electrode arc welding using a welding power source with constant voltage characteristics. For this reason, in submerged arc welding, the arc length is maintained at an appropriate value by performing variable speed control using a welding power source with constant current characteristics.

[0005] In variable speed control, when the detected welding voltage is greater than the set voltage, the arc length is longer than the desired value, so the feed speed is accelerated to shorten the arc length and bring it closer to the desired value. Conversely, when the detected welding voltage is less than the set voltage, the arc length is shorter than the desired value, so the feed speed is slowed down to lengthen the arc length and bring it closer to the desired value. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 9-271944 Summary of the Invention [Problem to be solved by the invention]

[0007] In variable speed control, when the detected welding voltage is significantly greater than the set voltage, the arc length is significantly longer than the desired value. Therefore, it is desirable to rapidly shorten the arc length by rapidly accelerating the feed speed to approach the desired value. Conversely, when the detected welding voltage is significantly smaller than the set voltage, the arc length is significantly shorter than the desired value. Therefore, it is desirable to rapidly decelerate the feed speed to quickly lengthen the arc length to approach the desired value. However, in variable speed control, if the gain is set large to rapidly accelerate / decelerate the feed speed, a problem occurs in that the feed speed fluctuates too sensitively, resulting in an unstable welding state. For this reason, in conventional variable speed control, the gain cannot be set too large, resulting in a convergence state in which an error remains between the detected welding voltage and the set voltage.

[0008] In submerged arc welding, the welding operator sets and manages welding conditions mainly by setting the current and voltage settings. Therefore, it is important from the perspective of setting and managing welding conditions that the welding current and welding voltage be output according to the current and voltage settings, respectively. With conventional variable speed control, the welding current is controlled to a constant current, so it is always equal to the current setting. However, as mentioned above, the welding voltage value contains an error compared to the voltage setting, which poses a problem in setting and managing welding conditions.

[0009] Therefore, an object of the present invention is to provide a submerged arc welding control method and submerged arc welding device that can output a welding current and welding voltage according to, for example, a current setting value and a voltage setting value, thereby enabling good setting and management of welding conditions. [Means for solving the problem]

[0010] A submerged arc welding control method provided according to a first aspect of the present invention is a submerged arc welding control method for feeding a welding wire and outputting a welding current and a welding voltage according to set external characteristics for welding, characterized in that a current set value and a voltage set value are set, the external characteristics are set to a characteristic that passes through an intersection of the current set value and the voltage set value and has a negative slope at the intersection, the feed speed is variably controlled so that the welding voltage is equal to the voltage set value, and operating points of the welding current and the welding voltage are converged to the intersection of the external characteristics.

[0011] As an example, the submerged arc welding control method of the present invention is characterized in that the gradient is set in the range of −5 V / 100 A or less and −25 V / 100 A or more.

[0012] As an example, the submerged arc welding control method of the present invention is characterized in that, when the output is AC, the welding current and the welding voltage are set to effective values ​​or average values.

[0013] As an example, the submerged arc welding control method of the present invention is characterized in that the gain of the variable speed control is set so that the absolute value of the error between the convergence value of the welding voltage and the voltage set value is 0.1 V or more and 1 V or less.

[0014] As an example, the submerged arc welding control method of the present invention is characterized in that the gain of the variable speed control is set so that the absolute value of the error between the convergence value of the effective value or average value of the welding voltage and the voltage set value is 0.1 V or more and 1 V or less.

[0015] 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 performs welding by outputting a welding current and a welding voltage according to set external characteristics, characterized in that the submerged arc welding apparatus sets a current set value and a voltage set value, sets the external characteristics to characteristics that pass through an intersection of the current set value and the voltage set value and have a negative slope at the intersection, variably controls the feed speed so that the welding voltage is equal to the voltage set value, and converges the operating points of the welding current and the welding voltage to the intersection of the external characteristics. [Effects of the Invention]

[0016] According to the above configuration, for example, in the submerged arc welding control method and submerged arc welding apparatus, the welding current and welding voltage can be output in accordance with the current set value and voltage set value, and the setting and management of welding conditions can be improved. [Brief explanation of the drawings]

[0017] [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] 2 is a timing chart of each signal in the welding device of FIG. 1 in a DC output mode. [Figure 3] 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. [Figure 4] FIG. 2 is a diagram illustrating the relationship between external characteristics and operating points of welding current and welding voltage, for explaining a submerged arc welding control method according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0018] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In this description, the average value means the average value of the absolute values ​​of the values.

[0019] 1 is a block diagram of a welding apparatus 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.

[0020] The power supply main circuit PM is connected to a commercial power supply (not shown) such as a three-phase 200V power supply, and receives as input a current error amplification signal Ei (described later) and a polarity switching signal Spn (described later), 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 an 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.

[0021] 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.

[0022] The automatic carriage AT is equipped with the above-mentioned welding torch 4 and the above-mentioned flux supply device 6, and during welding, moves at a predetermined speed so that the tip position of the welding torch 4 is along the weld line while spraying flux from the flux supply device 6.

[0023] The output mode setting circuit MR outputs an output mode setting signal Mr that is at a high level in the AC output mode and at a low level in the DC output mode.

[0024] The current setting circuit IS outputs a predetermined current setting signal Is, and the voltage setting circuit VS outputs a predetermined voltage setting signal Vs.

[0025] 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.

[0026] The voltage effective value / average value detection circuit VED receives the voltage detection signal Vd as an input, calculates an effective value or an average value from the voltage detection signal Vd, and outputs an effective value / average value detection signal Ved.

[0027] The external characteristic control circuit CC receives the current setting signal Is, the voltage setting signal Vs, the output mode setting signal Mr, the RMS / average voltage detection signal Ved, and the voltage detection signal Vd as inputs, and outputs an RMS / average current setting signal Ier and a 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 Ie is the effective value or average value of the welding current Iw as input and Ve is the effective value or average value of the welding voltage Vw as output. If the function is defined as a straight line with a slope K that passes through the intersection of the current setting signal Is and the voltage setting signal Vs, the following equation is obtained. Ve=K·(Ie-Is)+Vs Here, the slope K is a negative value set in the range of -5 to -25 (V / 100 A). The above equation is rearranged with Ie, and the following equation is obtained by replacing Ie with the current effective value / average value setting signal Ier and Ve with the voltage effective value / average value detection signal Ved. Ier = (Ved - Vs) / K + Is (1) In AC output mode, output control based on external characteristics is performed using 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-Vs) / K+Is (2) In DC output mode, output control based on external characteristics is performed using this formula.

[0028] 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.

[0029] The current effective value / average value detection circuit IED receives the current detection signal Id as an input, calculates an effective value or an average value from the current detection signal Id, and outputs a current effective value / average value detection signal Ied.

[0030] The current amplitude modulation circuit AMC receives the RMS / average current detection signal Ied and the RMS / average 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 or average value of the welding current Iw becomes equal to the value of the RMS / average current setting signal Ier.

[0031] 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.

[0032] The AC current setting circuit IAR 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 processing, and outputs an AC current setting signal Iar having a half-cycle waveform of a sine wave or a square wave (including a trapezoidal wave), 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 waveform of a sine wave or square wave (including trapezoidal wave) with an amplitude set by the current amplitude modulation signal Amc is output as the AC current setting signal Iar. During the electrode positive polarity period Tep, a polarity signal Tpn that is at a high level is output. 2) Subsequently, 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 above-mentioned polarity switching current value, and a half-cycle waveform of a sine wave or square wave (including trapezoidal wave) with an amplitude set by the current amplitude modulation signal Amc is output as the AC current setting signal Iar. 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.

[0033] 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 that is at a high level when welding with electrode positive polarity EP and at a low level when welding with electrode negative polarity EN.

[0034] The current control setting circuit ICR receives the output mode setting signal Mr, the AC current setting signal Iar, 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 AC current setting signal Iar 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.

[0035] The current error amplifier circuit EI receives the current control setting signal Icr and the current detection signal Id, amplifies the error between the two values, and outputs a current error amplification signal Ei.

[0036] The gain setting circuit GR outputs a predetermined gain setting signal Gr.

[0037] The variable speed control circuit FMC receives the output mode setting signal Mr, the RMS / average voltage detection signal Ved, the voltage detection signal Vd, the voltage setting signal Vs, and the gain setting signal Gr as inputs, performs the following processing, 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. 1) When the output mode setting signal Mr is at a high level (AC output mode), the error between the voltage effective value / average value detection signal Ved and the voltage setting signal Vs is amplified by the value of the gain setting signal Gr, and variable speed control is performed using P (proportional) control, PI (proportional-integral) control, or PID (proportional-integral-derivative) control, and the feed speed modulation signal Fmc is output. 2) When the output mode setting signal Mr is at a low level (DC output mode), the error between the voltage detection signal Vd and the voltage setting signal Vs is amplified by the value of the gain setting signal Gr, and variable speed control is performed using P (proportional) control, PI (proportional-integral) control, or PID (proportional-integral-derivative) control, and the feed speed modulation signal Fmc is output.

[0038] The feed control circuit FC receives the feed speed modulation signal Fmc as an input and 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.

[0039] Figure 2 is a timing chart of each signal in the welding device of Figure 1 when in DC output mode. Figure 2(A) shows the change over time in welding current Iw, Figure 2(B) shows the change over time in welding voltage Vw, and Figure 2(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.

[0040] 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.

[0041] 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 output control based on external characteristics. 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 Vs in Figure 1. This allows arc length control.

[0042] 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.

[0043] Figure 3 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 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 the figures.

[0044] 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.

[0045] 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 / average value setting signal Ier in Figure 1 is calculated by inputting the voltage effective value / average value detection signal Ved into equation (1) above. The welding current amplitude is modulated and controlled so that the current effective value / average value detection signal Ied in Figure 1 is equal to the current effective value / average value setting signal Ier. This allows output control based on external characteristics. For example, Tep = 10 ms, Ten = 10 ms, polarity switching current value = ±200 A, and amplitude ±1000 A.

[0046] As shown in Figure 1(B), the welding voltage Vw has a waveform similar to a square wave. The effective or average 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 / average value detection signal Ved is equal to the voltage setting signal Vs in Figure 1. This allows for arc length control.

[0047] The above is the case where the welding current Iw has a sine waveform, but it may also have a rectangular waveform (including a trapezoidal waveform).

[0048] 4 is a diagram illustrating the relationship between external characteristics and the operating points of the welding current and welding voltage, for explaining a submerged arc welding control method according to an embodiment of the present invention. The horizontal axis of the diagram represents the welding current Iw, and the vertical axis represents the welding voltage Vw. The following description will be made with reference to this diagram.

[0049] This figure shows the case of DC output. The external characteristic curve shown in this figure is a straight line with a negative slope K that passes through the intersection A of the current setting signal Is in Figure 1 and the voltage setting signal Vs in Figure 1. The operating point where the welding current Iw = Is and the welding voltage Vw = Vs converges to intersection A, and the arc length is at the appropriate value. If the arc length shortens from this state due to external disturbances such as irregular weld pool movement, fluctuations in the contact tip-workpiece distance, or temporary fluctuations in the feed speed, the welding current Iw changes to Iw1, which is greater than Is, and the welding voltage Vw changes to Vw1, which is less than Vs, and the operating point moves to B on the lower right of the external characteristic curve. Because the welding current Iw1 at operating point B is greater than the welding current Is at intersection A, the wire melting rate increases and the arc length increases. Furthermore, because the welding voltage Vw1 at operating point B is smaller than the voltage setting signal Vs, the feed speed is slowed down by the variable speed control, and the arc length changes in the direction of lengthening. The effects of the above external characteristics and the variable speed control are combined, and the operating points of the welding current Iw and welding voltage Vw quickly return from B to the intersection point A, and the arc length returns to the appropriate value.

[0050] If the arc length increases due to an external disturbance while the operating point is at intersection A, the welding current Iw changes to Iw2, a value smaller than Is, and the welding voltage Vw changes to Vw2, a value larger than Vs, causing the operating point to move to C in the upper left corner of the external characteristic curve. Because the welding current Iw2 at operating point C is smaller than the welding current Is at intersection A, the wire melting rate slows and the arc length decreases. Furthermore, because the welding voltage Vw2 at operating point C is greater than the voltage setting signal Vs, the variable speed control accelerates the wire feed speed, causing the arc length to decrease. The effects of the external characteristic and variable speed control combine to cause the operating points of the welding current Iw and welding voltage Vw to quickly return from C to intersection A, and the arc length returns to its appropriate value.

[0051] In the prior art, the welding current Iw is controlled to a constant current, so the wire melting rate is constant. Therefore, if the arc length fluctuates, the wire feed speed is controlled to be variable to restore the arc length to an appropriate value. As mentioned above, if the gain of the variable speed control is increased, the wire feed speed becomes too sensitive to changes and the welding state becomes unstable, so the gain cannot be set to a large value. As a result, in the prior art, the convergence value of the welding voltage Vw includes an error from the value of the voltage setting signal Vs, resulting in a large steady-state deviation. In other words, in the prior art, the arc length control results in a large steady-state deviation and slow transient response.

[0052] In contrast, in this embodiment, the effects of the external characteristics and the variable speed control are superimposed, so that the steady-state deviation of the arc length control can be reduced and the transient response can be made faster without increasing the gain of the variable speed control. As a result, in this embodiment, the convergence values ​​of the welding current Iw and welding voltage Vw become equal to the current setting signal Is and voltage setting signal Vs, making it easier to set and manage the welding conditions.

[0053] When the output is AC, the horizontal axis may be the effective or average value of the welding current Iw, and the vertical axis may be the effective or average value of the welding voltage Vw.

[0054] The effects of this embodiment are described below. According to this embodiment, in a submerged arc welding control method, a current setpoint and a voltage setpoint are set, an external characteristic is set to a characteristic that passes through an intersection of the current setpoint and the voltage setpoint and has a negative slope at the intersection, and the feed rate is controlled variably so that the welding voltage is equal to the voltage setpoint, and the operating points of the welding current and welding voltage converge to the intersection of the external characteristic. In this embodiment, the effects of the external characteristic and the variable speed control are superimposed, thereby reducing the steady-state deviation of the arc length control and accelerating transient response. As a result, in this embodiment, the convergence values ​​of the welding current and welding voltage are equal to the current setpoint and voltage setpoint, thereby improving the setting and management of welding conditions. The external characteristic need only have a negative slope at the intersection. It need not be a straight line as shown in FIG. 4 , but may be a broken line, curve, or the like, with different slopes for multiple sections of the welding current.

[0055] More preferably, according to this embodiment, the slope of the external characteristic is set in the range of -5 V / 100 A or less and -25 V / 100 A or more. If the slope is greater than -5 V / 100 A, the change in welding current due to arc length fluctuations becomes too sensitive, which may result in an unstable welding state. If the slope is less than -25 V / 100 A, the change in welding current due to arc length fluctuations becomes small, which reduces the effect of restoring the arc length to the appropriate value. Therefore, by setting the slope in the above range, the effect of restoring the arc length to the appropriate value can be enhanced while maintaining a stable welding state. More preferably, the slope is set in the range of -10 V / 100 A or less and -20 V / 100 A or more.

[0056] More preferably, according to this embodiment, when the output is AC, the welding current and welding voltage are set to effective values ​​or average values, so that this embodiment can be applied even when the output is AC.

[0057] More preferably, according to this embodiment, the gain of the variable speed control is set so that the absolute value of the error between the convergence value of the welding voltage and the voltage set value is 0.1 V or more and 1 V or less. If the gain of the variable speed control is set so that the absolute value of the error is smaller than 0.1 V, the feed speed may be too sensitive to changes, resulting in an unstable welding state. If the gain of the variable speed control is set so that the absolute value of the error is larger than 1 V, the steady-state deviation from the voltage set value increases, adversely affecting the setting and management of welding conditions. By setting the gain of the variable speed control within the above range, the steady-state deviation can be prevented from adversely affecting the setting and management of welding conditions while maintaining a stable welding state. More preferably, the gain of the variable speed control is set so that the absolute value of the error is 0.3 V or more and 0.8 V or less.

[0058] More preferably, according to this embodiment, the gain of the variable speed control is set so that the absolute value of the error between the convergence value of the effective value or average value of the welding voltage and the voltage setting value is 0.1 V or more and 1 V or less. Even when the output is AC, if the gain of the variable speed control is set within the above range, the welding state can be maintained stable and the steady-state deviation can be set to a state that does not adversely affect the setting and management of welding conditions.

[0059] Furthermore, according to this embodiment, in a submerged arc welding apparatus that feeds a welding wire and outputs a welding current and welding voltage according to set external characteristics for welding, the submerged arc welding apparatus sets a current set value and a voltage set value, sets the external characteristics to characteristics that pass through an intersection of the current set value and the voltage set value and have a negative slope at the intersection, and variably controls the wire feed speed so that the welding voltage is equal to the voltage set value, thereby converging the operating points of the welding current and welding voltage to the intersection of the external characteristics. The submerged arc welding apparatus according to this embodiment can achieve the above-mentioned effects. [Explanation of symbols]

[0060] 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 carriage, CC: external characteristic control circuit, 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, GR: gain setting circuit, Gr: gain setting signal, IAR: AC current setting circuit, Iar: AC current setting signal, ICR: current control setting circuit, Icr: current control setting signal, ID: current detection circuit, Id: current detection signal, Idr: DC current setting signal, IED: RMS / average current detection Output circuit, Ied: RMS / average current detection signal, IS: Current setting circuit, Is: Current setting signal, Iw: Welding current, MR: Output mode setting circuit, Mr: Output mode setting signal, PM: Main power supply circuit, SPN: Polarity switching setting circuit, Spn: Polarity switching signal, t: Time, Ten: Negative electrode polarity period, Tep: Positive electrode polarity period, TNR: Negative electrode polarity period setting circuit, Tnr: Negative electrode polarity period setting signal, Tpn: Polarity signal, TPR: Positive electrode polarity period setting circuit, Tpr: Positive electrode polarity period setting signal, VD: Voltage detection circuit, Vd: Voltage detection signal, VED: RMS / average voltage detection circuit, Ved: RMS / average voltage detection signal, VS: Voltage setting circuit, Vs: Voltage setting signal, Vw: Welding voltage, WM: Feeder

Claims

1. 1. A submerged arc welding control method for feeding a welding wire and outputting a welding current and a welding voltage according to preset external characteristics, comprising: a current set value and a voltage set value are set, the external characteristic is set to a characteristic that passes through an intersection of the current set value and the voltage set value and has a negative slope at the intersection, and a feed speed is variably controlled so that the welding voltage is equal to the voltage set value, and operating points of the welding current and the welding voltage are caused to converge to the intersection of the external characteristic.

2. 2. The method for controlling submerged arc welding according to claim 1, wherein the slope is set in a range of −5 V / 100 A or less and −25 V / 100 A or more.

3. 3. The method for controlling submerged arc welding according to claim 1, wherein when the output is AC, the welding current and the welding voltage are set to effective values ​​or average values.

4. 3. The submerged arc welding control method according to claim 1, wherein a gain of the variable speed control is set so that an absolute value of an error between the convergence value of the welding voltage and the voltage setting value is 0.1 V or more and 1 V or less.

5. 4. The submerged arc welding control method according to claim 3, wherein a gain of the variable speed control is set so that an absolute value of an error between a convergence value of the effective value or average value of the welding voltage and the voltage set value is 0.1 V or more and 1 V or less.

6. A submerged arc welding device that feeds a welding wire and outputs a welding current and a welding voltage according to preset external characteristics, The submerged arc welding apparatus is characterized in that it sets a current set value and a voltage set value, sets the external characteristic to a characteristic that passes through an intersection of the current set value and the voltage set value and has a negative slope at the intersection, and variably controls the feed speed so that the welding voltage is equal to the voltage set value, and causes operating points of the welding current and the welding voltage to converge to the intersection of the external characteristic.

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