Submerged arc welding control method and submerged arc welding apparatus

Abstract

In a submerged arc welding control method, the voltage tolerance required to stabilize the welding state is widened, even when the distance between the power supply tip and the base metal is long. [Solution] In a submerged arc welding control method that outputs a welding current Iw and a welding voltage Vw based on a voltage setting value Vs and a current setting value Is, and controls the welding wire feeding speed Fw to a variable speed so that the detected welding voltage Vd is equal to the voltage setting value Vs, the variable speed control is performed based on a value obtained by subtracting a correction value Vc set according to the distance Lr between the power supply tip and the base material from the detected welding voltage Vd.

Description

Technical Field

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

Background Art

[0002] Conventionally, submerged arc welding has been known. Submerged arc welding involves spraying flux on the base material, feeding a welding wire into the flux, and generating an arc between the tip of the welding wire and the base material to perform welding. In submerged arc welding, by passing a large current through a thick welding wire, thick plates can be welded at high efficiency.

[0003] A submerged arc welding method is used in which the feeding speed of the welding wire is variably controlled based on the detected value of the welding voltage to control the arc length (see, for example, Patent Document 1).

[0004] In variable speed control, the feeding speed is feedback-controlled based on the error between the detected value of the welding voltage and the voltage set value, thereby maintaining the welding voltage correlated with the arc length at an appropriate value. In submerged arc welding using a thick wire, since the change in the wire melting speed is small even when the welding current changes, it is difficult to obtain the self-control action of the arc length generally used in consumable electrode arc welding using a constant voltage characteristic welding power source. For this reason, in submerged arc welding, variable speed control is performed using a welding power source with a constant current characteristic to maintain the arc length at an appropriate value.

[0005] In variable speed control, when the detected value of the welding voltage is greater than the voltage set value, the arc length is longer than the desired value, so the feeding speed is accelerated to shorten the arc length and bring it closer to the desired value. Conversely, when the detected value of the welding voltage is smaller than the voltage set value, the arc length is shorter than the desired value, so the feeding speed is decelerated 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 [Overview of the project] [Problems that the invention aims to solve]

[0007] In conventional submerged arc welding methods, when welding is performed with a distance between the power supply tip and the base metal that is 2 to 4 times longer than the standard length (approximately 20 to 30 mm), the arc length can be maintained at an appropriate value by variable speed control, and the wire melting speed can be increased because Joule heat is supplied to the long wire protrusion due to resistance heating, thus warming it up. As a result, thick plates can be welded more efficiently. However, in conventional submerged arc welding methods, when welding is performed with a longer distance between the power supply tip and the base metal, the range of voltage settings (voltage tolerance) in which the welding state is stable becomes narrower, which presents a problem in that setting welding conditions is difficult.

[0008] Therefore, the present invention aims to provide a submerged arc welding control method and a submerged arc welding apparatus that can widen the voltage margin at which the welding state stabilizes, for example, when welding is performed with a long distance between the power supply tip and the base material, thereby facilitating the setting of welding conditions. [Means for solving the problem]

[0009] A submerged arc welding control method provided by a first aspect of the present invention is a submerged arc welding control method that outputs a welding current and a welding voltage based on a voltage set value and a current set value, and controls the feeding speed of the welding wire to a variable speed so that the detected value of the welding voltage is equal to the voltage set value, characterized in that the variable speed control is performed based on a value obtained by subtracting a correction value set according to the distance between the power supply tip and the base material from the detected value of the welding voltage.

[0010] As an example, the submerged arc welding control method of the present invention is characterized in that the correction value is set based on the distance between the power supply tip and the base material, the resistance value per unit length of the welding wire, and the welding current value.

[0011] As an example, the submerged arc welding control method of the present invention is characterized by calculating the distance between the power supply tip and the base material based on the feed rate and the welding current value.

[0012] As an example, the submerged arc welding control method of the present invention is characterized by changing the gain of the variable speed control according to the distance between the power supply tip and the base material.

[0013] As an example, the submerged arc welding control method of the present invention is characterized by setting an external characteristic that passes through the intersection of the current setting value and the voltage setting value and has a negative slope at the intersection, and changing the slope according to the distance between the power supply tip and the base material.

[0014] A submerged arc welding apparatus provided by a second aspect of the present invention outputs a welding current and a welding voltage based on a voltage setting and a current setting, and performs welding by variable speed control of the welding wire feeding speed so that the detected value of the welding voltage is equal to the voltage setting, characterized in that the variable speed control is performed based on a value obtained by subtracting a correction value set according to the distance between the power supply tip and the base material from the detected value of the welding voltage. [Effects of the Invention]

[0015] According to the above configuration, for example, with respect to a submerged arc welding control method and a submerged arc welding apparatus, when welding is performed with a long distance between the power supply tip and the base material, the voltage margin at which the welding state stabilizes can be widened, making it easier to set welding conditions. [Brief explanation of the drawing]

[0016] [Figure 1]This is a block diagram of a submerged arc welding apparatus for implementing a submerged arc welding control method according to an embodiment of the present invention. [Figure 2] This is a timing chart of each signal in the welding apparatus shown in Figure 1 when in DC output mode. [Figure 3] This is a timing chart of each signal in the welding apparatus shown in Figure 1 when a sinusoidal welding current is applied in AC output mode. [Figure 4] This diagram illustrates the relationship between external characteristics and the operating points of welding current and welding voltage, illustrating a submerged arc welding control method according to an embodiment of the present invention. [Modes for carrying out the invention]

[0017] Embodiments of the present invention will be described below with reference to the drawings. In this paper, the term "average value" refers to the average of the absolute values ​​of the given values.

[0018] Figure 1 is a block diagram of a submerged arc welding apparatus for implementing a submerged arc welding control method according to an embodiment of the present invention. Each block will be described below with reference to the same figure.

[0019] The main power circuit PM is connected to a commercial power supply (not shown) such as three-phase 200V. Taking the current error amplification signal Ei and the polarity switching signal Spn (both to be described later) as inputs, it performs inverter control according to the current error amplification signal Ei, and switches between the electrode positive polarity EP and the electrode negative polarity EN according to the polarity switching signal Spn to output an AC or DC welding current Iw and a welding voltage Vw. Although not shown in the figure, this main power circuit PM includes a primary rectifier for rectifying the commercial power supply, a smoothing capacitor for smoothing the rectified DC, a primary-side inverter circuit for converting the smoothed DC into high-frequency AC, a high-frequency transformer for stepping down the high-frequency AC to a voltage value suitable for welding, a secondary rectifier for rectifying the stepped-down high-frequency AC into DC, a reactor for smoothing the rectified DC, a secondary-side inverter circuit for switching the smoothed DC between the electrode positive polarity EP and the electrode negative polarity EN according to the polarity switching signal Spn, a modulation circuit for taking the current error amplification signal Ei as an input and outputting a pulse-width modulation signal, and a drive circuit for driving the switching elements of the primary-side inverter circuit with the pulse-width modulation signal as an input.

[0020] The welding wire 1 is fed through the welding torch 4 by the rotation of the feeding roll 5 coupled to the 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 the power supply tip (not shown) of the welding torch 4 and the base material 2, and a welding current Iw flows. The flux feeder 6 supplies flux (not shown) to the arc generation part. Since the arc generation part is covered by the flux, the arc 3 cannot be visually recognized from the outside.

[0021] The automatic carriage AT mounts the above-mentioned welding torch 4 and the above-mentioned flux feeder 6, and during welding, it moves at a predetermined moving speed so that the tip position of the welding torch's 4 moves along the welding line while the flux feeder 6 sprays flux.

[0022] The output mode setting circuit MR outputs an output mode setting signal Mr that becomes High level in the AC output mode and Low level in the DC output mode.

[0023] The current setting circuit IS outputs a predetermined current setting signal Is. The voltage setting circuit VS outputs a predetermined voltage setting signal Vs.

[0024] The power supply chip-base material distance setting circuit LR takes the power supply speed modulation signal Fmc and the current detection signal Id (described later) as inputs and outputs a power supply chip-base material distance setting signal Lr set by either method 1) or 2) below. 1) The distance between the power supply tip and the base metal, input by the welder, is output as the power supply tip-to-base metal distance setting signal Lr. 2) The average value of the feed rate modulation signal Fmc and the average value of the current detection signal Id are input into a predetermined function, and the calculated value is output as the feed chip-base material distance setting signal Lr. The function is defined in advance through experiments, etc.

[0025] The correction value setting circuit VC takes the above-mentioned power supply chip-base material distance setting signal Lr and the current detection signal Id (described later) as inputs and outputs a correction value signal Vc calculated by either method 1) or 2) below. 1) The correction value signal Vc is calculated by inputting the value of the power supply chip-base material distance setting signal Lr into a predetermined function. An example of the function is shown below: Vc = Lr / standard length. Here, the standard length is the standard distance between the power supply chip and the base material, and if it is 30 mm, then when Lr = 60 mm, Vc = 2 V, and when Lr = 120 mm, Vc = 4 V. 2) The correction value signal Vc is calculated from (power supply chip-base material distance setting signal Lr) × (average value of current detection signal Id) × (predetermined resistance value per unit length of welding wire).

[0026] The voltage detection circuit VD takes the correction value signal Vc as input, detects the instantaneous value of the welding voltage Vw, converts it to an absolute value, subtracts the value of the correction value signal Vc from the result, and outputs the voltage detection signal Vd.

[0027] The voltage RMS / average value detection circuit VED takes the above-mentioned voltage detection signal Vd as input, calculates the RMS value or average value from that value, and outputs the voltage RMS / average value detection signal Ved.

[0028] The tilt setting circuit KR takes the above-mentioned power supply chip-base material distance setting signal Lr as input and outputs a predetermined tilt setting signal Kr, which is a negative value whose absolute value becomes smaller the longer the power supply chip-base material distance setting signal Lr is than the standard length. It is preferable to set the tilt setting signal Kr in the range of -5 to -25 (V / 100A).

[0029] The external characteristic control circuit CC takes the above-mentioned slope setting signal Kr, current setting signal Is, voltage setting signal Vs, output mode setting signal Mr, voltage RMS / average value detection signal Ved, and voltage detection signal Vd as inputs and outputs the current RMS / average value setting signal Ier and DC current setting signal Idr, which are calculated based on the following equation (1) or (2). 1) When the output mode setting signal Mr = High level (AC output mode) The external characteristics are the output characteristics of the welding power supply and can be expressed as a function Ve=f(Ie) that takes the effective value or average value Ie of the welding current Iw as input and outputs the effective value or average value Ve of the welding voltage Vw. If the function is defined as a straight line of the slope setting signal Kr passing through the intersection of the current setting signal Is and the voltage setting signal Vs, then the following equation is obtained. Ve = Kr·(Ie-Is)+Vs Rearranging the above equation in terms of Ie, replacing Ie with the current RMS value / average value setting signal Ier, and replacing Ve with the voltage RMS value / average value detection signal Ved, we obtain the following equation. Ier = (Ved - Vs) / Kr + Is (1) In AC output mode, output control is performed based on external characteristics using this formula. 2) When the output mode setting signal Mr = Low level (DC output mode) In equation (1) above, substituting Ier with Idr and Ved with Vd results in the following equation. Idr = (Vd - Vs) / Kr + Is (2) In DC output mode, output control is performed based on external characteristics using this formula.

[0030] The current detection circuit ID detects the instantaneous value of the welding current Iw mentioned above, converts it to an absolute value, and outputs a current detection signal Id.

[0031] The current RMS / average value detection circuit IED takes the above-mentioned current detection signal Id as input, calculates the RMS value or average value from that value, and outputs the current RMS / average value detection signal Ied.

[0032] The current amplitude modulation circuit (AMC) takes the above-mentioned RMS / average value detection signal Ied and the above-mentioned RMS / average value setting signal Ier as inputs, performs modulation control based on the error amplification value of both values, and outputs a current amplitude modulation signal Amc. This circuit changes the amplitude of the welding current so that the RMS or average value of the welding current Iw becomes equal to the value of the current RMS / average value setting signal Ier.

[0033] The electrode positive polarity period setting circuit TPR outputs a predetermined electrode positive polarity period setting signal Tpr. The electrode negative polarity period setting circuit TNR outputs a predetermined electrode negative polarity period setting signal Tnr.

[0034] The AC current setting circuit IAR takes the above-mentioned electrode positive polarity period setting signal Tpr, electrode negative polarity period setting signal Tnr, and current amplitude modulation signal Amc as inputs, performs the following processing, and outputs an AC current setting signal Iar in the form of a half-period waveform of a sine wave or 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 become predetermined polarity switching current values, and a half-period 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 high-level polarity signal Tpn 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 will be the above polarity switching current values, and a half-period waveform of a sine wave or square wave (including trapezoidal wave) with an amplitude set by the current amplitude modulation signal Amc will be output as the AC current setting signal Iar. During the electrode negative polarity period Ten, a low-level polarity signal Tpn will be output. 3) Repeat steps 1) and 2) above.

[0035] The polarity switching setting circuit SPN takes the above output mode setting signal Mr and the above 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 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 at 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, which is at a high level when welding with the positive electrode polarity EP, and at a low level when welding with the negative electrode polarity EN.

[0036] The current control setting circuit ICR takes the above-mentioned output mode setting signal Mr, the above-mentioned AC current setting signal Iar, and the above-mentioned 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.

[0037] The current error amplification circuit EI takes the above-mentioned current control setting signal Icr and the above-mentioned current detection signal Id as inputs, amplifies the error between the two values, and outputs a current error amplification signal Ei.

[0038] The gain setting circuit GR takes the above-mentioned power supply chip-base material distance setting signal Lr as input and outputs a predetermined gain setting signal Gr, which becomes smaller the longer the value of the power supply chip-base material distance setting signal Lr is compared to the standard length.

[0039] The variable speed control circuit FMC takes the above-mentioned output mode setting signal Mr, the above-mentioned RMS / average voltage detection signal Ved, the above-mentioned voltage detection signal Vd, the above-mentioned voltage setting signal Vs, and the above-mentioned 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 RMS / 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 by 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 by P (proportional) control, PI (proportional-integral) control, or PID (proportional-integral-derivative) control, and the feed speed modulation signal Fmc is output.

[0040] The feed control circuit FC takes the feed speed modulation signal Fmc as 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.

[0041] Figure 2 shows the timing charts for each signal in the welding apparatus shown in Figure 1 when in DC output mode. Figure (A) shows the time variation of the welding current Iw, Figure (B) shows the time variation of the welding voltage Vw, and Figure (C) shows the time variation of the polarity switching signal Spn. The operation of each signal will be explained below with reference to the same figure.

[0042] The figure shows the case where the output mode is DC output mode and the output polarity is positive electrode polarity EP. Therefore, as shown in the figure (C), the polarity switching signal Spn is at a high level for the entire period, resulting in positive electrode polarity EP.

[0043] Submerged arc welding is basically performed under welding conditions that prevent short circuits between the welding wire and the base metal, so the entire welding period is arc-driven. As shown in Figure (A), the welding current Iw is a DC waveform and is controlled by the value of the DC current setting signal Idr in Figure 1.

[0044] In this embodiment, welding is performed with the distance between the power supply tip and the base metal being 2 to 4 times longer than the standard length (approximately 20 to 30 mm). As a result, Joule heat is supplied to the long wire protrusion due to resistance heating, increasing the wire melting speed. This allows for more efficient welding of thick plates. To achieve good welding, it is necessary to control the arc length to an appropriate value. For this purpose, the arc length is detected by the welding voltage Vw and controlled to an appropriate value. The detected value of the welding voltage Vw is the sum of the voltage value due to the arc length and the voltage value at the wire protrusion. When the distance between the power supply tip and the base metal is the standard length, the influence of the voltage value at the wire protrusion is small, so the arc length can be properly controlled even if it is detected by the welding voltage Vw. However, when the distance between the power supply tip and the base metal is significantly longer than the standard length, the influence of the voltage value at the wire protrusion cannot be ignored. Therefore, if the arc length is controlled by the detected value of the welding voltage Vw, a problem arises in that the voltage margin at which the welding state is stable becomes narrow. Therefore, in this embodiment, the arc length is accurately detected by subtracting a correction value set according to the distance between the power supply tip and the base material from the detected welding voltage Vw to obtain the voltage detection signal Vd. The correction value corresponds to the voltage value of the wire protrusion. As a result, by correcting the detected welding voltage Vw and controlling the arc length, the voltage tolerance can be widened even when the distance between the power supply tip and the base material is long, making it easier to set welding conditions.

[0045] The DC current setting signal Idr is calculated by inputting the voltage detection signal Vd into equation (2) above. This enables output control based on external characteristics. As shown in Figure (B), the welding voltage Vw is a DC waveform and is correlated with the arc length. The welding wire feeding speed Fw (not shown) is variable-speed controlled so that the voltage detection signal Vd is equal to the voltage setting signal Vs in Figure 1. This enables arc length control.

[0046] When the output polarity is the negative electrode polarity EN, the polarity switching signal Spn shown in Figure (C) will be at a low level for the entire period. The welding current Iw and welding voltage Vw will then exhibit negative waveforms.

[0047] Figure 3 shows the timing charts for each signal in the welding apparatus shown in Figure 1 when a sinusoidal welding current is applied in AC output mode. Figure (A) shows the time variation of the welding current Iw, Figure (B) shows the time variation of the welding voltage Vw, and Figure (C) shows the time variation of the polarity switching signal Spn. The operation of each signal will be explained below with reference to the figure.

[0048] In the figure, positive values ​​above 0A and 0V indicate the electrode is positively polarized (EP), while negative values ​​below 0A and 0V indicate the electrode is negatively polarized (EN).

[0049] During the period from time t1 to t2, as shown in Figure (C), the polarity switching signal Spn is at a high level, resulting in a positive electrode polarity EP. As shown in Figure (A), during the positive electrode polarity period Tep from time t1 to t2, the welding current Iw has a positive polarity switching current value at the start and end points t1 and t2 of the period, and is a positive half-period waveform of a sine wave with amplitude set by the current amplitude modulation signal Amc. During the period from time t2 to t3, as shown in Figure (C), the polarity switching signal Spn is at a low level, resulting in a negative electrode polarity EN. As shown in Figure (A), during the negative electrode polarity period Ten from time t2 to t3, the welding current Iw has a negative polarity switching current value at the start and end points t2 and t3 of the period, and is a negative half-period waveform of a sine wave with amplitude set by the current amplitude modulation signal Amc. From here on, 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.

[0050] In this embodiment, welding is performed with the distance between the power supply tip and the base metal being 2 to 4 times longer than the standard length (approximately 20 to 30 mm). As a result, Joule heat is supplied to the long wire protrusion due to resistance heating, increasing the wire melting speed. This allows for more efficient welding of thick plates. To achieve good welding, it is necessary to control the arc length to an appropriate value. For this purpose, since the output is AC, the arc length is detected by the effective value or average value of the welding voltage Vw and controlled to an appropriate value. The effective value or average value of the welding voltage Vw is the sum of the voltage value due to the arc length and the voltage value at the wire protrusion. When the distance between the power supply tip and the base metal is the standard length, the influence of the voltage value at the wire protrusion is small, so the arc length can be properly controlled even if it is detected by the effective value or average value of the welding voltage Vw. However, when the distance between the power supply tip and the base metal is significantly longer than the standard length, the influence of the voltage value at the wire protrusion cannot be ignored. Therefore, if arc length control is performed using the effective value or average value of the welding voltage Vw, a problem arises in that the voltage margin at which the welding state is stable becomes narrow. In this embodiment, the arc length is accurately detected by calculating the effective value or average value from the voltage detection signal Vd, which is obtained by subtracting a correction value set according to the distance between the power supply tip and the base metal from the detected value of the welding voltage Vw, and using this as the effective value / average value detection signal Ved in Figure 1. As a result, by correcting the effective value or average value of the welding voltage Vw and performing arc length control, the voltage margin can be widened even when the distance between the power supply tip and the base metal is long, making it easier to set welding conditions.

[0051] The current RMS / average value setting signal Ier in Figure 1 is calculated by inputting the voltage RMS / average value detection signal Ved into equation (1) above. The amplitude of the welding current is modulated and controlled so that the current RMS / average value detection signal Ied in Figure 1 is equal to the current RMS / average value setting signal Ier. This enables output control based on external characteristics. For example, Tep = 10 ms, Ten = 10 ms, polarity switching current value = ±200 A, and amplitude ±1000 A.

[0052] As shown in Figure (B), the welding voltage Vw has a waveform similar to a square wave.

[0053] The feed rate Fw in Figure 1 is variable-speed controlled so that the RMS / average voltage detection signal Ved is equal to the voltage setting signal Vs in Figure 1. This controls the arc length.

[0054] The above assumes that the welding current Iw has a sinusoidal waveform, but it can also have a rectangular waveform (including a trapezoidal waveform).

[0055] Figure 4 is a diagram illustrating the relationship between external characteristics and the operating points of 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 figure represents the welding current Iw, and the vertical axis represents the welding voltage Vw. The following explanation will refer to this figure.

[0056] The figure shows the case where the output is DC. The external characteristics shown in the figure are straight lines that slope downwards to the right, passing through the intersection point A of the current setting signal Is and the voltage setting signal Vs in Figure 1, with a negative slope K. The operating point where the welding current Iw=Is and welding voltage Vw=Vs converges to the intersection point A, and the arc length is at an appropriate value. From this state, if the arc length shortens due to disturbances such as irregular movement of the molten pool, fluctuations in the distance between the power supply tip and the base metal, and temporary fluctuations in the feed speed, the welding current Iw changes to Iw1, which is a value greater than Is, and the welding voltage Vw changes to Vw1, which is a value less than Vs, and the operating point moves to B in the lower right on the external characteristics. Since the welding current Iw1 at operating point B is greater than the welding current Is at intersection point A, the wire melting speed increases, and the arc length changes in the direction of increasing. Furthermore, since the welding voltage Vw1 at operating point B is smaller than the voltage setting signal Vs, the feed speed is reduced by the variable speed control, and the arc length changes in the direction of increasing. The effects of the above external characteristics and the variable speed control are superimposed, causing the operating points of the welding current Iw and welding voltage Vw to quickly return from B to intersection A, and the arc length returns to an appropriate value.

[0057] When the arc length increases due to disturbances while the operating point is at intersection A, the welding current Iw changes to Iw2, which is smaller than Is, and the welding voltage Vw changes to Vw2, which is larger than Vs. The operating point then moves to C in the upper left of the external characteristics. Since the welding current Iw2 at operating point C is smaller than the welding current Is at intersection A, the wire melting speed slows down, and the arc length changes to shorten. Furthermore, since the welding voltage Vw2 at operating point C is larger than the voltage setting signal Vs, the feed speed is accelerated by the variable speed control, and the arc length changes to shorten. The effects of the external characteristics and the variable speed control described above are superimposed, and the operating points of the welding current Iw and welding voltage Vw quickly return from C to intersection A, and the arc length returns to the appropriate value.

[0058] In conventional technology, the welding current Iw is controlled at a constant current, so the wire melting speed remains constant. Therefore, if the arc length fluctuates, the feed speed is variable-speed controlled to restore the arc length to an appropriate value. As mentioned above, if the gain of the variable speed control is increased at this time, the change in feed speed becomes overly sensitive, and the welding state becomes unstable, so the gain cannot be set to a large value. As a result, in conventional technology, the convergence value of the welding voltage Vw contains an error with the value of the voltage setting signal Vs, and the steady-state error becomes large. In other words, in conventional technology, the arc length control is characterized by a large steady-state error and slow transient response.

[0059] In contrast, in this embodiment, the effects of external characteristics and variable speed control are superimposed, so even without increasing the gain of the variable speed control, the steady-state error of the arc length control can be reduced and the transient response can be improved. 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 the voltage setting signal Vs, thus improving the setting and management of welding conditions.

[0060] If the output is AC, the horizontal axis should be the RMS or average value of the welding current Iw, and the vertical axis should be the RMS or average value of the welding voltage Vw.

[0061] The effects of this embodiment will be explained below. According to this embodiment, in a submerged arc welding control method in which welding is performed by outputting welding current and welding voltage based on voltage setting value and current setting value and variable speed control of the welding wire feeding speed so that the detected value of welding voltage is equal to the voltage setting value, variable speed control is performed based on a value obtained by subtracting a correction value set according to the distance between the power supply tip and the base material from the detected value of welding voltage. In the submerged arc welding method, when welding is performed with the distance between the power supply tip and the base material made about 2 to 4 times longer than the standard length (about 20 to 30 mm), Joule heat due to resistance heating is supplied to the long wire protrusion and it is heated, so the wire melting speed can be increased. As a result, thick plates can be welded more efficiently. In addition, in order to perform good welding, it is necessary to control the arc length to an appropriate value. For this purpose, the arc length is detected by the welding voltage and controlled to an appropriate value. The detected value of welding voltage is the sum of the voltage value due to the arc length and the voltage value of the wire protrusion. When the distance between the power supply tip and the base metal is the standard length, the influence of the voltage value at the wire protrusion is small, so the arc length can be properly controlled even if it is detected by the welding voltage. However, when the distance between the power supply tip and the base metal is significantly longer than the standard length, the influence of the voltage value at the wire protrusion cannot be ignored, and if the arc length is controlled by the detected welding voltage, a problem arises in that the voltage margin at which the welding state is stable becomes narrow. Therefore, in this embodiment, the arc length is accurately detected by subtracting a correction value set according to the distance between the power supply tip and the base metal from the detected welding voltage. The correction value corresponds to the voltage value at the wire protrusion. As a result, by correcting the detected welding voltage and controlling the arc length, the voltage margin can be widened even when the distance between the power supply tip and the base metal is long, making it easier to set welding conditions.

[0062] More preferably, according to this embodiment, the correction value is set based on the distance between the power supply tip and the base material, the resistance value per unit length of the welding wire, and the welding current value. By calculating the correction value by multiplying these parameters, the arc length can be accurately detected according to the diameter of the welding wire, the material of the welding wire, and the welding current value. As a result, in this embodiment, arc length control can be stabilized more effectively under various welding conditions, and the voltage margin can be further widened when the distance between the power supply tip and the base material is long.

[0063] More preferably, according to this embodiment, the distance between the power supply tip and the base metal is calculated based on the feed rate and welding current values. The distance between the power supply tip and the base metal can be calculated by inputting the feed rate and welding current values ​​into a function predetermined by experiment. In this way, the distance between the power supply tip and the base metal can be automatically set to an accurate value. As a result, in this embodiment, the arc length can be detected more precisely even when the distance between the power supply tip and the base metal is long, thus widening the voltage margin.

[0064] More preferably, according to this embodiment, the gain of the variable speed control is changed according to the distance between the power supply tip and the base material. If the gain of the variable speed control is large when the distance between the power supply tip and the base material is long, the welding state tends to become unstable. Therefore, in this embodiment, by optimizing the gain of the variable speed control according to the distance between the power supply tip and the base material, the welding state can be kept stable at all times.

[0065] More preferably, according to this embodiment, an external characteristic is set such that the slope at the intersection point passing through the intersection of the current setting value and the voltage setting value is a negative value, and the slope is changed according to the distance between the power supply tip and the base material. If the absolute value of the slope of the external characteristic is small when the distance between the power supply tip and the base material is long, the welding state tends to become unstable. Therefore, in this embodiment, the welding state can be kept stable at all times by optimizing the slope of the external characteristic according to the distance between the power supply tip and the base material.

[0066] Furthermore, according to this embodiment, in a submerged arc welding apparatus that outputs welding current and welding voltage based on voltage and current setting values, and controls the feeding speed of the welding wire in a variable speed manner so that the detected welding voltage is equal to the voltage setting value, variable speed control is performed based on a value obtained by subtracting a correction value set according to the distance between the power supply tip and the base material from the detected welding voltage. The submerged arc welding apparatus according to this embodiment achieves the above-mentioned effects.

[0067] More preferably, according to this embodiment, in the submerged arc welding control method, a current set value and a voltage set value are set, the external characteristics are set to pass through the intersection of the current set value and the voltage set value and have a negative slope at the intersection, and the feed speed is variable-speed controlled so that the welding voltage is equal to the voltage set value, and the operating point of the welding current and welding voltage is converged to the intersection of the external characteristics. In this embodiment, the effects of the external characteristics and the effects of variable speed control are superimposed, so the steady-state error of arc length control can be reduced and transient response can be improved. As a result, in this embodiment, the convergence values ​​of the welding current and welding voltage are equal to the current set value and the voltage set value, so setting and managing welding conditions becomes easier. The external characteristics only need to have a negative slope at the intersection, and do not need to be the straight line described above in Figure 4, but may be a broken line, curve, etc., with different slopes for each of the multiple sections of welding current.

[0068] More preferably, according to this embodiment, the slope of the external characteristics is set in the range of -5V / 100A or less and -25V / 100A or more. If the slope is greater than -5V / 100A, the change in welding current due to the fluctuation of arc length becomes overly sensitive, which can lead to an unstable welding state. If the slope is less than -25V / 100A, the change in welding current due to the fluctuation of arc length becomes smaller, and the effect of returning the arc length to an appropriate value becomes smaller. For this reason, by setting the slope within the above range, the effect of returning the arc length to an appropriate value can be greatly increased while maintaining a stable welding state. It is even more preferable to set the slope setting range to -10V / 100A or less and -20V / 100A or more.

[0069] More preferably, according to this embodiment, when the output is AC, the welding current and welding voltage are set to their RMS values ​​or average values. In this way, this embodiment can also be applied when the output is AC.

[0070] 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 setpoint is 0.1V or more and 1V or less. If the gain of the variable speed control is set so that the absolute value of the error is less than 0.1V, the change in feed speed becomes overly sensitive, which may cause the welding condition to become unstable. If the gain of the variable speed control is set so that the absolute value of the error is greater than 1V, the steady-state deviation from the voltage setpoint becomes large, which adversely affects the setting and management of welding conditions. By setting the gain of the variable speed control within the above range, it is possible to maintain a stable welding condition while ensuring that the steady-state deviation does not adversely affect the setting and management of welding conditions. It is even more preferable to set the gain of the variable speed control so that the absolute value of the error is 0.3V or more and 0.8V or less.

[0071] 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 converged effective value or average value of the welding voltage and the voltage setting value is 0.1V or more and 1V or less. Even when the output is AC, setting the gain of the variable speed control within the above range makes it possible to maintain a stable welding state without the steady-state deviation adversely affecting the setting and management of welding conditions. [Explanation of Symbols]

[0072] 1: Welding wire, 2: Base metal, 3: Arc, 4: Welding torch, 5: Feeding roll, 6: Flux feeder, AMC: Current amplitude modulation circuit, Amc: Current amplitude modulation signal, AT: Automatic trolley, CC: External characteristic control circuit, EI: Current error amplification circuit, Ei: Current error amplification signal, EN: Electrode negative polarity, EP: Electrode positive polarity, FC: Feeding control circuit, Fc: Feeding control signal, FMC: Feeding variable speed control circuit, Fmc: Feeding speed modulation signal, Fw: Feeding 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: Current RMS / average value detection circuit, Ied: Current RMS / average value detection signal, IS: Current setting circuit, Is: Current setting Signal, Iw: Welding current, KR: Tilt setting circuit, Kr: Tilt setting signal, LR: Power supply tip-base material distance setting circuit, Lr: Power supply tip-base material distance setting signal, MR: Output mode setting circuit, Mr: Output mode setting signal, PM: Power supply main circuit, SPN: Polarity switching setting circuit, Spn: Polarity switching signal, t: Time, 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, VC: Correction value setting circuit, Vc: Correction value signal, VD: Voltage detection circuit, Vd: Voltage detection signal, VED: Voltage RMS / average value detection circuit, Ved: Voltage RMS / average value detection signal, VS: Voltage setting circuit, Vs: Voltage setting signal, Vw: Welding voltage, WM: Feeder

Claims

1. In a submerged arc welding control method that outputs a welding current and a welding voltage based on a voltage setting and a current setting, and controls the feeding speed of the welding wire in a variable speed manner so that the detected value of the welding voltage is equal to the voltage setting, A submerged arc welding control method characterized by performing the variable speed control based on a value obtained by subtracting a correction value set according to the distance between the power supply tip and the base material from the detected value of the welding voltage.

2. The submerged arc welding control method according to claim 1, characterized in that the correction value is set based on the distance between the power supply tip and the base material, the resistance value per unit length of the welding wire, and the value of the welding current.

3. The submerged arc welding control method according to claim 1 or 2, characterized in that the distance between the power supply tip and the base material is calculated based on the power supply speed and the welding current value.

4. The submerged arc welding control method according to claim 1 or 2, characterized in that the gain of the variable speed control is changed according to the distance between the power supply tip and the base material.

5. A submerged arc welding control method according to claim 1 or 2, characterized in that an external characteristic is set such that it passes through the intersection of the current setting value and the voltage setting value and the slope at the intersection is a negative value, and the slope is changed according to the distance between the power supply tip and the base material.

6. In a submerged arc welding apparatus that outputs welding current and welding voltage based on a voltage setting and a current setting, and controls the feeding speed of the welding wire in a variable speed manner so that the detected value of the welding voltage is equal to the voltage setting, A submerged arc welding apparatus characterized in that it performs variable speed control based on a welding voltage correction value obtained by subtracting a correction value set according to the distance between the power supply tip and the base material from the detected welding voltage.

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