Submerged arc welding control method and submerged arc welding apparatus

Abstract

In a submerged arc welding control method, the welding current Iw and welding voltage Vw can be output according to the values ​​of the current set value Is and the voltage set value Vs, and the welding wire 1 can be fed quickly and stably even when a relatively small diameter welding wire 1 is used. [Solution] In a submerged arc welding control method that feeds a welding wire and outputs a welding current Iw and welding voltage Vw according to set external characteristics, the diameter of the welding wire 1 is 3.2 mm or less, the output of the feeding motor that feeds the welding wire 1 is 200 W or more, a current setting value Is and a voltage setting value Vs are set, the external characteristics are set to pass through the intersection A of the current setting value Is and the voltage setting value Vs, and the slope at the intersection A is a negative value, and the feeding speed of the welding wire is controlled at a variable speed so that the welding voltage Vw is equal to the voltage setting value Vs, and the operating points of the welding current Iw and welding voltage Vw are converged to the intersection A of the external characteristics.

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 with high efficiency.

[0003] A submerged arc welding method that variably controls the feeding speed of the welding wire based on the welding voltage to control the arc length is used (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 constant current characteristics 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 Initiative] [Problems that the invention aims to solve]

[0007] In variable speed control, when the detected welding voltage is significantly greater than the voltage setpoint, the arc length is significantly longer than the desired value. Therefore, it is desirable to rapidly shorten the arc length by accelerating the feed speed to approach the desired value. Conversely, when the detected welding voltage is significantly less than the voltage setpoint, the arc length is significantly shorter than the desired value. Therefore, it is desirable to rapidly lengthen the arc length by rapidly decelerating the feed speed to approach the desired value. However, in variable speed control, setting a large gain to rapidly accelerate / decelerate the feed speed results in the feed speed fluctuating excessively, leading to an unstable welding state. Thus, in conventional variable speed control, the gain cannot be set very large, resulting in a convergence where an error remains between the detected welding voltage and the voltage setpoint.

[0008] In submerged arc welding, welding conditions are primarily set and managed by the welder by setting the current and voltage settings. Therefore, it is crucial for the welding current to be output according to the current setting and the welding voltage to be output according to the voltage setting, for the sake of setting and managing welding conditions. In conventional variable-speed control, the welding current is controlled at a constant current, so it is always equal to the current setting. On the other hand, as mentioned above, the welding voltage will have an error compared to the voltage setting, which poses a problem for setting and managing welding conditions.

[0009] Furthermore, when welding under high current conditions using welding wire with a relatively small diameter (e.g., 3.2 mm or less), it is necessary to feed the welding wire at high speed. Adjusting the reduction ratio (gear ratio) between the feed motor and the feed roll to enable high-speed feeding reduces the feeding torque. In submerged arc welding, various factors such as the long distance from the wire reel to the tip and the use of heavy wire reels tend to increase the resistance to feeding the welding wire. Therefore, if the feeding torque decreases, it becomes impossible to feed the welding wire stably.

[0010] Therefore, the present invention aims to provide a submerged arc welding control method and a submerged arc welding apparatus that can output welding current and welding voltage according to the current and voltage setting values, and that can feed the welding wire at high speed and stably even when using a welding wire with a relatively small diameter. [Means for solving the problem]

[0011] A submerged arc welding control method provided by a first aspect of the present invention is a submerged arc welding control method that feeds a welding wire and outputs a welding current and welding voltage according to set external characteristics to perform welding, wherein the diameter of the welding wire is 3.2 mm or less, the output of the feeding motor that feeds the welding wire is 200 W or more, a current setting value and a voltage setting value are set, the external characteristics are set to pass through the intersection of the current setting value and the voltage setting value and the slope at the intersection is a negative value, the feeding speed is controlled to be variable so that the welding voltage is equal to the voltage setting value, and the operating points of the welding current and the welding voltage are converged to the intersection of the external characteristics.

[0012] As an example, in the submerged arc welding control method of the present invention, the inclination is set to a range of -1V / 100A or less and -25V / 100A or more.

[0013] As an example, in the submerged arc welding control method of the present invention, the diameter of the welding wire is 2.0 mm or less.

[0014] As an example, in the submerged arc welding control method of the present invention, when the output is AC, the welding current and the welding voltage are set to their effective values ​​or average values.

[0015] A submerged arc welding apparatus provided by a second aspect of the present invention is a submerged arc welding apparatus that feeds a welding wire and outputs a welding current and welding voltage according to set external characteristics to perform welding, wherein the diameter of the welding wire is 3.2 mm or less, and the apparatus is equipped with a feed motor that feeds the welding wire and has an output of 200 W or more, and a current setting value and a voltage setting value are set, the external characteristics are set to pass through the intersection of the current setting value and the voltage setting value and the slope at the intersection is a negative value, the feed speed is variably controlled so that the welding voltage is equal to the voltage setting value, and the operating points of the welding current and the welding voltage are converged to the intersection of the external characteristics. [Effects of the Invention]

[0016] According to the above configuration, for example, with respect to a submerged arc welding control method and a submerged arc welding apparatus, it is possible to output welding current and welding voltage according to the current setting value and voltage setting value, and even when using welding wire with a relatively small diameter, the welding wire can be fed quickly and stably. [Brief explanation of the drawing]

[0017] [Figure 1] This is a block diagram of a 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.

Embodiments for Carrying Out the Invention

[0018] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In this document, the average value means the average value of the absolute value of that value.

[0019] FIG. 1 is a block diagram of a welding apparatus for implementing a submerged arc welding control method according to an embodiment of the present invention. Hereinafter, each block will be described with reference to the same figure.

[0020] The main power circuit PM is connected to a commercial power source (not shown) such as a three-phase 200V power source, and performs inverter control according to the current error amplification signal Ei described later and the polarity switching signal Spn described later, and switches between the electrode positive polarity EP and the electrode negative polarity EN according to the polarity switching signal Spn to output an alternating current or direct current 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 source, a smoothing capacitor for smoothing the rectified direct current, a primary side inverter circuit for converting the smoothed direct current into a high-frequency alternating current, a high-frequency transformer for reducing the high-frequency alternating current to a voltage value suitable for welding, a secondary rectifier for rectifying the reduced high-frequency alternating current into a direct current, a reactor for smoothing the rectified direct current, a secondary side inverter circuit for switching the smoothed direct current between the electrode positive polarity EP and the electrode negative polarity EN according to the polarity switching signal Spn, a modulation circuit for inputting the current error amplification signal Ei and outputting a pulse width modulation signal, and a drive circuit for driving the switching element of the primary side inverter circuit by inputting the pulse width modulation signal.

[0021] In the present invention, the diameter of the welding wire 1 to be used is 3.2 mm or less. It is desirable that the diameter of the welding wire 1 to be used is 2.0 mm or less. The material of the welding wire 1 is not limited.

[0022] The welding wire 1 is fed through the welding torch 4 by the rotation of the feed roll 5 coupled to the feed motor WM of the feeding device, and an arc 3 is generated between 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 a 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.

[0023] The automatic carriage AT mounts the above-mentioned welding torch 4 and the above-mentioned flux feeder 6, and during welding, while spraying the flux from the flux feeder 6, it moves at a predetermined moving speed so that the tip position of the welding torch 4 follows the weld line.

[0024] 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.

[0025] The current setting circuit IS outputs a predetermined current setting signal Is. The voltage setting circuit VS outputs a predetermined voltage setting signal Vs.

[0026] The voltage detection circuit VD detects the instantaneous value of the above-mentioned welding voltage Vw, converts it to an absolute value, and outputs a voltage detection signal Vd.

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

[0028] The external characteristic control circuit CC takes the above-mentioned current setting signal Is, the above-mentioned voltage setting signal Vs, the above-mentioned output mode setting signal Mr, the above-mentioned voltage effective value / average value detection signal Ved, and the above-mentioned voltage detection signal Vd as inputs, and outputs a current effective value / average value setting signal Ier and a DC current setting signal Idr calculated based on the following formula (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 with a slope K passing through the intersection of the current setting signal Is and the voltage setting signal Vs, then the following equation is obtained. Ve = K·(Ie-Is) + Vs Here, the slope K is a negative value and is set in the range of -1 to -25 (V / 100A). 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) / K + 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) / K + Is (2) In DC output mode, output control is performed based on external characteristics using this formula.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] The gain setting circuit GR outputs a predetermined gain setting signal Gr.

[0038] 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 controls the feed speed Fw to a variable speed 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.

[0039] The feed control circuit FC takes the feed speed modulation signal Fmc as input and outputs a feed control signal Fc to the feed motor WM to control the feed speed Fw of the welding wire 1 to the speed determined by the feed speed modulation signal Fmc.

[0040] The feed motor WM feeds the welding wire 1 according to the above feed control signal Fc. The feed motor WM has an output of 200W or more. Currently, feed motors for feed devices for submerged arc welding that are available on the market are limited to those with an output of around 100W. This is because, within the range of welding conditions that have been widely used in the past, a motor with an output of around 100W can feed the welding wire 1 without any problems. In this invention, a feed motor WM with an output of 200W or more is used to enable welding under high current conditions (for example, around 1000A) using a welding wire 1 with a diameter of 3.2mm or less.

[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 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-based. As shown in Figure (A), the welding current Iw is 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 for 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 feed 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 controls the arc length.

[0044] 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.

[0045] 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.

[0046] 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).

[0047] 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. 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 allows for output control based on external characteristics. For example, Tep = 10 ms, Ten = 10 ms, polarity switching current value = ±200 A, and amplitude ±1000 A.

[0048] As shown in Figure (B), the welding voltage Vw has a waveform similar to a square wave. The RMS value or average value of the welding voltage Vw correlates with the arc length. The feed speed 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.

[0049] The above assumes that the welding current Iw has a sinusoidal waveform, but it can also have a rectangular waveform (including a trapezoidal waveform).

[0050] 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.

[0051] 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 current setting signal 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.

[0052] 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. At operating point C, the welding current Iw2 is smaller than the current setting signal Is at intersection A, so the wire melting speed slows down, and the arc length shortens. Furthermore, at operating point C, the welding voltage Vw2 is larger than the voltage setting signal Vs, so the feed speed is accelerated by the variable speed control, and the arc length shortens. The effects of the external characteristics and variable speed control described above are superimposed, causing 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 the appropriate value.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] In conventional submerged arc welding control methods, the practical upper limit of the welding current was approximately 600A when using a welding wire with a diameter of 2.4mm. In the submerged arc welding control method of this embodiment, when the external characteristic slope K is set to -5V / 100A and a welding wire with a diameter of 2.4mm is used, the welding wire can be fed at high speed and stably even at a welding current of 1200A, enabling stable welding.

[0057] The effects of this embodiment will now be described. 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 variably controlled so that the welding voltage is equal to the voltage set value, causing the operating point of the welding current and welding voltage to converge to the aforementioned 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 become 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 aforementioned intersection, and do not need to be the straight line described above in Figure 4; they may be a broken line, curve, etc., with different slopes for each of the multiple sections of the welding current.

[0058] Furthermore, according to this embodiment, in the submerged arc welding control method, the diameter of the welding wire is 3.2 mm or less, and the output of the feed motor that feeds the welding wire is 200 W or more. When welding under high current conditions using a relatively small diameter welding wire, it is necessary to feed the welding wire at high speed. In this embodiment, by setting the output of the feed motor to 200 W or more, it is possible to maintain a large feed torque while enabling high-speed feeding. This allows for stable and high-speed feeding of the welding wire. Also, as the diameter of the welding wire decreases, the wire feeding speed per unit of current increases, so it is necessary to increase the gain in order to increase the amount of control over the wire feeding speed by variable speed control. In this embodiment, in addition to variable speed control, the self-control effect of the arc length due to external characteristics is also utilized. Furthermore, because the diameter of the welding wire is small, the amount of current change required to change the wire melting speed is small, and the delay time until the current change affects the amount of wire melted is small, so the effect of the self-control effect is relatively large. Therefore, it is not necessary to set a large gain in the variable speed control. This prevents the feed rate from fluctuating too much and causing the welding condition to become unstable, which can occur when the gain is set high.

[0059] More preferably, according to this embodiment, the slope of the external characteristics is set in the range of -1V / 100A or less and -25V / 100A or more. If the slope is greater than -1V / 100A, the change in welding current due to the variation in 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 variation in 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 -1.5V / 100A or less and -15V / 100A or more.

[0060] More preferably, according to this embodiment, the diameter of the welding wire is 2.0 mm or less. The smaller the diameter of the welding wire, the greater the amount of wire welded per unit current, so it is necessary to feed the welding wire at high speed. According to this embodiment, even if the diameter of the welding wire is 2.0 mm or less, the welding wire can be fed at high speed and stably.

[0061] More preferably, according to this embodiment, when the output is AC, the welding current and welding voltage are set to their effective values ​​or average values. In this way, this embodiment can also be applied when the output is AC.

[0062] 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.

[0063] 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.

[0064] 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, the welding wire diameter is 3.2 mm or less, the apparatus is equipped with a feeding motor that feeds the welding wire and has an output of 200 W or more, the current setting value and voltage setting value are set, the external characteristics are set to pass through the intersection of the current setting value and voltage setting value and the slope at the intersection is a negative value, the feeding speed is variably controlled so that the welding voltage is equal to the voltage setting value, and the operating point of the welding current and welding voltage is converged 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]

[0065] 1: Welding wire, 2: Base material, 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: Electric Current RMS / average value detection circuit, Ied: Current RMS / average value detection signal, IS: Current setting circuit, Is: Current setting signal, Iw: Welding current, 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, 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: Feed motor

Claims

1. In a submerged arc welding control method that feeds welding wire and outputs welding current and welding voltage according to set external characteristics, The diameter of the welding wire is 3.2 mm or less. The output of the feeding motor that feeds the welding wire is 200W or more. The current setting value and the voltage setting value are set, the external characteristics are set to pass through the intersection of the current setting value and the voltage setting value and the slope at the intersection is a negative value, the feed speed is variable-speed controlled so that the welding voltage is equal to the voltage setting value, and the operating points of the welding current and the welding voltage are converged to the intersection of the external characteristics. Submerged arc welding control method.

2. The aforementioned slope is set within the range of -1V / 100A or less and -25V / 100A or more. The submerged arc welding control method according to claim 1.

3. The diameter of the welding wire is 2.0 mm or less. The submerged arc welding control method according to claim 1.

4. When the output is AC, the welding current and welding voltage shall be set to their effective values ​​or average values. A submerged arc welding control method according to any one of claims 1 to 3.

5. A submerged arc welding apparatus that feeds welding wire and outputs welding current and welding voltage according to set external characteristics, The diameter of the welding wire is 3.2 mm or less. The device is equipped with a feeding motor that feeds the welding wire and has an output of 200W or more, The current setting value and the voltage setting value are set, the external characteristics are set to pass through the intersection of the current setting value and the voltage setting value and the slope at the intersection is a negative value, the feed speed is variable-speed controlled so that the welding voltage is equal to the voltage setting value, and the operating points of the welding current and the welding voltage are converged to the intersection of the external characteristics. Submerged arc welding equipment.

Images