Submerged arc welding control method and submerged arc welding apparatus

Abstract

In a submerged arc welding control method, even when the distance between the power supply tip and the base metal is increased, the control during the transient period from arc start can be stabilized, and the transition to a steady state can be facilitated. [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 feeding speed of the welding wire in a variable speed manner so that the detected value of the welding voltage Vw is equal to the voltage setting value Vs, the voltage setting value Vs is a first voltage Vs1 at the start of the arc, and thereafter is switched to a second voltage Vs2 which is lower than the first voltage Vs1.

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 granular flux onto a 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, a thick plate can be welded at high efficiency by passing a large current through a thick welding wire.

[0003] A submerged arc welding method that controls the arc length by changing the feeding speed of the welding wire based on the welding voltage is used (see, for example, Patent Document 1). Hereinafter, the method of controlling the arc length by changing the feeding speed of the welding wire based on the welding voltage may be described as "feeding variable speed control".

[0004] In feeding variable speed control, the welding voltage correlated with the arc length is maintained at an appropriate value by feedback controlling the feeding speed based on the error between the detected value of the welding voltage and the voltage set 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. Therefore, in submerged arc welding, the arc length is maintained at an appropriate value by performing feeding variable speed control.

[0005] In feeding 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 conventional submerged arc welding methods, a known method involves making the distance between the power supply tip and the base metal 2 to 4 times longer than the standard length (approximately 20 to 30 mm) during welding. This method maintains the arc length at an appropriate value through variable wire feed speed control, and the long wire protrusion is heated by Joule heat due to resistance heating, thereby increasing the wire melting speed. As a result, while keeping the welding current and voltage settings the same, the heat input is limited, and the amount of welded material is increased by 20-40%, enabling efficient welding. However, in this method, it takes time for the welding wire temperature to rise sufficiently due to resistance heating after current is applied. Therefore, there is a transient period of about 5 seconds from arc start until a steady state is reached and the wire feed speed reaches its maximum. During this transient period, because the wire feed speed is increased, the short-circuit release cannot keep up, making long-term short circuits likely. When a long-term short circuit occurs, two control mechanisms coexist: one that increases the wire feeding speed by extending the wire protrusion, and another that decreases the wire feeding speed to increase the voltage by feeding back the low voltage during the short circuit. As a result, the wire feeding speed alternates between increasing and decreasing, leading to unstable control and an inability to transition from a transient state to a steady state.

[0008] Therefore, the present invention aims to provide a submerged arc welding control method and a submerged arc welding apparatus that can stabilize control during the transient period from arc start and facilitate the transition to a steady state, even when the distance between the power supply tip and the base material is increased. [Means for solving the problem]

[0009] A submerged arc welding control method provided by a first aspect of the present invention 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 in a variable speed manner so that the detected value of the welding voltage is equal to the voltage set value, wherein the voltage set value is a first voltage at the start of the arc, and thereafter is switched to a second voltage lower than the first voltage.

[0010] As an example, in the submerged arc welding control method of the present invention, when the distance between the power supply tip and the base material is approximately the standard length, the voltage setting value is set to the second voltage from the start of the arc.

[0011] As an example, in the submerged arc welding control method of the present invention, the period during which the voltage setting value is the first voltage is 1 second or more and 5 seconds or less from the time of arc start.

[0012] As an example, in the submerged arc welding control method of the present invention, the voltage difference between the first voltage and the second voltage is 2V or more and 5V or less.

[0013] 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, wherein the voltage setting is a first voltage at the start of the arc, and thereafter is switched to a second voltage lower than the first voltage. [Effects of the Invention]

[0014] According to the above configuration, for example, with respect to a submerged arc welding control method and submerged arc welding apparatus, a first voltage higher than the second voltage during steady state is set as the voltage setting value at arc start. At arc start, the arc length is controlled to be longer compared to the steady state, making long-term short circuits less likely to occur. As a result, even when the distance between the power supply tip and the base material is increased, the control during the transient period from arc start can be stabilized, and the transition to a steady state can be facilitated. [Brief explanation of the drawing]

[0015] [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. [Figure 5] This figure shows the experimental results when no initial conditions are used in the submerged arc welding control method according to an embodiment of the present invention. [Figure 6] This figure shows the experimental results when the submerged arc welding control method according to an embodiment of the present invention is implemented. [Modes for carrying out the invention]

[0016] 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.

[0017] 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 figure.

[0018] The main power circuit PM is connected to a commercial power supply (not shown) such as a three-phase 200V power supply. Taking the current error amplification signal Ei described later and the polarity switching signal Spn 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 alternating current or direct current welding current Iw and a welding voltage Vw. Although not shown, this main power circuit PM includes a primary rectifier for rectifying the commercial power supply, 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 voltage of 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.

[0019] The welding wire 1 is fed through the welding torch 4 by the rotation of the feeding roll 5 coupled to the feeding motor WM of the feeding device, and an arc 3 is generated between the welding wire 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 is energized. 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.

[0020] 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 4 follows the welding line while spraying the flux from the flux feeder 6.

[0021] 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.

[0022] The feed tip - base material distance setting circuit LR outputs the feed tip - base material distance input by the welding operator as a feed tip - base material distance setting signal Lr. The feed tip - base material distance is the distance from the tip of the feed tip to the base material, which is the length obtained by adding the so - called wire protrusion length and the arc length. However, since the arc length is much smaller compared to the wire protrusion length and is difficult to measure, in some cases, the wire protrusion length is treated as the feed tip - base material distance. The feed tip - base material distance is usually set to a standard length (for example, about 20 - 30 mm) which is about 8 times the diameter of the welding wire. However, in the case of a welding method that increases the melting amount by using the long wire protrusion part described above, the feed tip - base material distance is set to about 100 mm, which is much larger than the standard length.

[0023] The initial time setting circuit TR outputs a preset initial time as an initial time setting signal Tr. For example, the initial time is set to 2 seconds. Although the initial time is not limited, it is desirable that it be 1 second or more and 5 seconds or less. At least 1 second or more is required until the control stabilizes. On the other hand, since the transient period from the start of the arc until the wire feeding speed rises is about 5 seconds, there is no need to set the initial time to more than 5 seconds.

[0024] The voltage setting circuit VS takes the above-mentioned power supply chip-base material distance setting signal Lr and initial time setting signal Tr as inputs and outputs a voltage setting signal Vs. The voltage setting circuit VS compares the power supply chip-base material distance setting signal Lr with a threshold value to determine whether the set power supply chip-base material distance is sufficiently larger than the standard length. The threshold value is set to a value sufficiently larger than the standard length (for example, about 60 mm). If the power supply chip-base material distance setting signal Lr is greater than or equal to the threshold value (hereinafter, this case may be referred to as "extended mode"), the voltage setting circuit VS outputs a first voltage Vs1 (for example, 38V) as the voltage setting signal Vs at arc start. Then, after the initial time set by the initial time setting signal Tr (for example, 2 seconds) has elapsed, the voltage setting circuit VS outputs a second voltage Vs2 (for example, 30-35V), which is lower than the first voltage Vs1, as the voltage setting signal Vs. In other words, the voltage setting circuit VS outputs a first voltage Vs1 that is higher than the second voltage Vs2 until the initial time has elapsed from the start of the arc (hereinafter, this condition may be referred to as the "initial condition"). Note that the first voltage Vs1 and the second voltage Vs2 are not limited. The first voltage Vs1 is higher than the second voltage Vs2, and the voltage difference between the first voltage Vs1 and the second voltage Vs2 is greater than 0V, 10V or less, and preferably between 2V and 5V. If the voltage difference is less than 2V, control during the transient period is difficult to stabilize, and if it is greater than 5V, the possibility of arc failure increases. On the other hand, if the power supply chip-base material distance setting signal Lr is less than the threshold (hereinafter, this case may be referred to as the "normal mode"), the voltage setting circuit VS outputs the second voltage Vs2 (e.g., 30~35V) as the voltage setting signal Vs from the start of the arc.

[0025] Alternatively, instead of the voltage setting circuit VS determining whether it is in "extended mode" or "normal mode," the welder may input whether it is in "extended mode" or "normal mode." In this case, the welder can input by selecting either "extended mode" or "normal mode," or by selecting "ON" or "OFF" for "extended mode," using an input means not shown in the diagram. Alternatively, the system may automatically set whether it is in "extended mode" or "normal mode" by determining whether the distance between the power supply tip and the base material is the standard length using other methods.

[0026] The current setting circuit IS outputs a predetermined current setting signal Is.

[0027] The tilt setting circuit KS takes the above-mentioned power supply chip-base material distance setting signal Lr as input and outputs a predetermined tilt setting signal Ks, 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. Preferably, the tilt setting signal Ks is set in the range of -5 to -25 (V / 100A). In addition, the tilt setting circuit KS may output a predetermined negative value of the tilt setting signal Ks regardless of the power supply chip-base material distance setting signal Lr.

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

[0029] 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.

[0030] The external characteristic control circuit CC takes the above-mentioned current setting signal Is, voltage setting signal Vs, slope setting signal Ks, 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 we define the function as a straight line passing through the intersection of the current setting signal Is and the voltage setting signal Vs, with a slope equal to the slope setting signal Ks, then we get the following equation. Ve = Ks · (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) / Ks + 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) / Ks + Is (2) In DC output mode, output control is performed based on external characteristics using this formula.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] The current control setting circuit ICR takes the above output mode setting signal Mr, the above AC current setting signal Iar, and the above 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.

[0038] 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.

[0039] 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 power supply chip-base material distance setting signal Lr is than the standard length. Alternatively, the gain setting circuit GR may output a predetermined gain setting signal Gr regardless of the power supply chip-base material distance setting signal Lr.

[0040] 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 feed speed variable 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 feed 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.

[0041] The feed control circuit FC receives 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. The feed motor WM feeds the welding wire 1 according to the feed control signal Fc.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] From the start of the arc until the initial time has elapsed, the first voltage Vs1, which is higher than the steady-state second voltage Vs2, is set as the voltage setting signal Vs, so the welding voltage Vw is high, as shown in Figure (B). Also, the DC current setting signal Idr calculated by equation (2) above becomes smaller, so the welding current Iw becomes smaller, as shown in Figure (A).

[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. 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.

[0050] 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.

[0051] From the start of the arc until the initial time has elapsed, the first voltage Vs1, which is higher than the steady-state second voltage Vs2, is set as the voltage setting signal Vs. As shown in Figure (B), the amplitude of the welding voltage Vw is large. Also, the DC current setting signal Idr calculated by equation (2) above becomes small, so as shown in Figure (A), the amplitude of the welding current Iw becomes small.

[0052] The above assumes that the welding current Iw has a sinusoidal waveform, but it can also have a rectangular waveform (including a trapezoidal waveform).

[0053] Figure 4(a) 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.

[0054] The figure shows the case where the output is DC. The external characteristics shown in the figure are straight lines that slope downward to the right, passing through the intersection point A of the current setting signal Is and the voltage setting signal Vs in Figure 1, and having a negative slope Ks. 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 feed speed control, and the arc length changes in the direction of increasing. The effects of the above external characteristics and the variable feed 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.

[0055] 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 feed speed control, and the arc length shortens. The effects of the external characteristics and the variable feed 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.

[0056] If the output is AC, in Figure 4(a), 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.

[0057] Next, with reference to Figures 5 and 6, experimental results of the submerged arc welding control method according to an embodiment of the present invention will be described. Figure 6 shows the experimental results when the submerged arc welding control method is implemented. On the other hand, Figure 5 is for comparison and shows the experimental results when the initial conditions are not used. The solid lines in Figures 5(a) and 6(a) show the time change of the measured effective current of the welding current Iw (see the vertical axis on the left), and the dashed lines show the time change of the measured effective voltage of the welding voltage Vw (see the vertical axis on the right). Figures 5(b) and 6(b) show the measured wire feeding speed.

[0058] This experiment uses AC output mode, with the AC current waveform set to a square wave. "US-36 φ4.0mm" welding wire and "MF-38" flux were used, and the distance between the power supply tip and the base metal was set to 100mm. The steady-state current setting was 1100A, and the voltage setting (second voltage Vs2) was 30-35V. In the initial conditions of the experiment shown in Figure 6, the current setting was 600A, the voltage setting (first voltage Vs1) was 38V, and the initial time was 2 seconds. Arc start occurs at "0" s on the horizontal axis of each figure.

[0059] As shown in Figure 5, when initial conditions are not used, the wire feed speed alternates between increasing and decreasing, and the welding current Iw and welding voltage Vw also alternate between increasing and decreasing, resulting in unstable control and an inability to transition from a transient state to a steady state. On the other hand, as shown in Figure 6, in the submerged arc welding control method according to an embodiment of the present invention, the wire feed speed increases from the time of arc start (time "0" s in each figure) due to the addition of initial conditions. Then, around time "6" s, the wire feed speed, welding current Iw, and welding voltage Vw stabilize, and the system can transition from a transient state to a steady state.

[0060] The effects of this embodiment will now be described. 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 a voltage setting value and a current setting value, and variable speed control of the welding wire feeding speed so that the detected value of the welding voltage is equal to the voltage setting value, the voltage setting value is a first voltage at the start of the arc, and thereafter it is switched to a second voltage that is lower than the first voltage. In this embodiment, as the voltage setting value, a first voltage that is higher than the second voltage in the steady state is set at the start of the arc. At the start of the arc, the arc length is controlled to be longer compared to the steady state, so that long-term short circuits are less likely to occur. As a result, even when the distance between the power supply tip and the base material is increased, the control during the transient period from the start of the arc is stabilized and the transition to the steady state is made easier.

[0061] More preferably, according to this embodiment, when the distance between the power supply tip and the base material is approximately the standard length, the voltage setting value is set to the second voltage from the time of arc start. In this embodiment, the voltage setting value is switched between being the second voltage (normal mode) or the first voltage (extended mode) at the time of arc start depending on whether the distance between the power supply tip and the base material is approximately the standard length. This makes it possible to use the initial conditions only when the distance between the power supply tip and the base material is large.

[0062] More preferably, according to this embodiment, the period during which the voltage setting value is the first voltage is 1 second or more and 5 seconds or less from the time of arc start. At least 1 second is required for the control to stabilize. On the other hand, since the transient period from the time of arc start until the wire feeding speed has fully increased is about 5 seconds, the initial time does not need to be set to more than 5 seconds. Therefore, by setting the period within the above range, it is possible to stabilize the control during the transient period without waste, even when the distance between the power supply tip and the base material is increased. It is even more preferable that the period be 2 seconds or more and 4 seconds or less from the time of arc start.

[0063] More preferably, according to this embodiment, the voltage difference between the first voltage and the second voltage is 2V or more and 5V or less. If the voltage difference is less than 2V, control during the transient period is difficult to stabilize, and if it is greater than 5V, the possibility of arc failure increases. Therefore, by setting the voltage difference within the above range, it is possible to stabilize control during the transient period while suppressing the occurrence of arc failure, even when the distance between the power supply tip and the base material is increased.

[0064] 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.

[0065] More preferably, according to this embodiment, the gain of the variable feed speed control is changed according to the distance between the power supply tip and the base material. If the gain of the variable feed 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 feed 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.

[0066] More preferably, according to this embodiment, current and voltage setpoints are set, the external characteristics are set to pass through the intersection of the current and voltage setpoints 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 setpoint, causing the operating points 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 feed 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 and voltage setpoints, thus improving the setting and management of welding conditions. 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.

[0067] 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.

[0068] More preferably, according to this embodiment, an external characteristic is set that 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. 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.

[0069] Furthermore, according to this embodiment, in a submerged arc welding apparatus that outputs welding current and welding voltage based on a voltage setting value and a current setting value, 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 value, the voltage setting value is a first voltage at the start of the arc, and thereafter it is switched to a second voltage lower than the first voltage. The submerged arc welding apparatus according to this embodiment can achieve the above-mentioned effects.

[0070] In this embodiment, the case in which the tilt setting circuit KS outputs a fixed tilt setting signal Ks according to the power supply chip-base material distance setting signal Lr has been described, but it is not limited to this. The tilt setting circuit KS may switch the tilt setting signal Ks midway through the process. A modified example in which the tilt setting circuit KS switches the tilt setting signal Ks midway through the process will be described below.

[0071] In the modified configuration, the inclination setting circuit KS outputs a first inclination Ks1 (e.g., -5V / 100A) at arc start. After a predetermined time T1 (e.g., 3 seconds) has elapsed, it outputs a second inclination Ks2 (e.g., -15V / 100A). The second inclination Ks2 is set to a value less than -10V / 100A. The first inclination Ks1 is set to a value with a smaller absolute value than the second inclination Ks2, and is set to a value between -1V / 100A and -10V / 100A. Furthermore, it is desirable that the first inclination Ks1 be between 1 / 2 and 1 / 4 of the second inclination Ks2, with about 1 / 3 being more desirable. If it is less than 1 / 2, the self-regulating effect of the arc length does not work well, so the convergence of the arc length does not improve easily. On the other hand, if it is greater than 1 / 4, the increase and decrease in current becomes too large, which may cause welding to become unstable. Furthermore, it is desirable that the predetermined time T1 be between 0.2 seconds and 5 seconds. If the time is less than 0.2 seconds, even if the first slope Ks1 is set to a small absolute value, there is insufficient time for convergence, and a sufficient effect cannot be obtained. If it exceeds 5 seconds, the period during which the current increases and decreases becomes longer, which begins to negatively affect welding.

[0072] In this modified example, as shown in Figure 4(b), the external characteristics are switched between external characteristics X1 (slope of the first slope Ks1) at arc start and external characteristics X2 (slope of the second slope Ks2) at steady state (after a predetermined time T1 has elapsed since arc start). External characteristics X1 at arc start are closer to constant voltage characteristics, allowing for relatively effective self-regulation of arc length. On the other hand, external characteristics X2 at steady state are closer to constant current characteristics, making it relatively difficult for the self-regulation of arc length to work, and thus making it difficult for the current to increase or decrease.

[0073] In this modified version, the slope of the external characteristics is a first slope at arc start, and then switches to a second slope with a larger absolute value than the first slope. In this modified version, the first slope, which has a smaller absolute value than the second slope in steady state, is used as the slope of the external characteristics at arc start. Therefore, at arc start, the self-regulating effect of the arc length is more active compared to steady state, improving the convergence of the arc length. This improves the stability of welding. Also, in steady state, the self-regulating effect of the arc length is relatively less active, and the current is less likely to increase or decrease, thus suppressing welding instability due to increases or decreases in current.

[0074] More preferably, according to this modification, the period during which the slope is at the first slope is 0.2 seconds or more and 5 seconds or less from the start of the arc. If this period is less than 0.2 seconds, even if the first slope Ks1 is set to a small absolute value, there is insufficient time to converge, and a sufficient effect cannot be obtained. Also, if this period exceeds 5 seconds, the period during which the current increases and decreases becomes longer, which begins to adversely affect the welding. Therefore, by setting this period within the above range, a sufficient effect can be obtained and adverse effects on welding can be suppressed. It is even more preferable that this period be 1 second or more and 4 seconds or less from the start of the arc.

[0075] Note that the predetermined time T1 and the initial time may be the same. In this case, the slope setting circuit KS may use the initial time setting signal Tr output from the initial time setting circuit TR as the predetermined time T1.

[0076] In this modified example, the case in which the tilt setting circuit KS switches immediately from the first tilt Ks1 to the second tilt Ks2 after a predetermined time T1 has elapsed since arc start has been described, but it is not limited to this. The tilt setting circuit KS may change from the first tilt Ks1 to the second tilt Ks2 linearly, for example, during a predetermined change period T2 (for example, 3 seconds). However, it may also be a change other than a linear change. The change period T2 is preferably 0 seconds or more and 5 seconds or less. Note that a change period T2 of 0 seconds means switching immediately from the first tilt Ks1 to the second tilt Ks2, which is the change in the modified example described above. If the change period T2 exceeds 5 seconds, the period during which the current increases or decreases becomes longer, which begins to adversely affect welding. When the slope changes linearly from the first slope Ks1 to the second slope Ks2 during a predetermined change period T2, the external characteristics can be prevented from switching immediately because the slope switches instantly from the first slope Ks1 to the second slope Ks2.

[0077] Furthermore, the tilt setting circuit KS may change in steps from the first tilt Ks1 to the second tilt Ks2. For example, the tilt setting circuit KS may switch from the first tilt Ks1 to the third tilt Ks3 (Ks1>Ks3>Ks2), and then switch from the third tilt Ks3 to the second tilt Ks2. Note that multiple tilts may be introduced before switching from the first tilt Ks1 to the second tilt Ks2.

[0078] In this modified example, the gain setting circuit GR may further switch the gain setting signal Gr after a predetermined time T1 has elapsed since the arc start. In this case, when the variable speed control circuit FMC performs PI (proportional-integral) control, the gain setting circuit GR sets the proportional gain to a larger value and the integral gain to a smaller value at arc start compared to the steady state. By increasing the proportional gain at arc start, the feed speed can be accelerated and decelerated more rapidly, improving the convergence of the arc length. On the other hand, by decreasing the proportional gain at steady state, it is possible to suppress excessive fluctuations in the feed speed that would cause the welding state to become unstable. Also, by setting the integral gain to a smaller value at arc start, it is possible to suppress control vibrations. When the variable speed control circuit FMC performs P (proportional) control, the gain setting circuit GR sets the proportional gain to a larger value at arc start compared to the steady state. The gain setting circuit GR may switch the gain setting signal Gr after a predetermined time T1 has elapsed since the arc start, and the slope setting circuit KS may not switch the slope setting signal Ks. [Explanation of symbols]

[0079] 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: 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, I s: Current setting signal, Iw: Welding current, KS: Tilt setting circuit, Ks: 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, TR: Initial time setting circuit, Tr: Initial time 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: Power supply motor

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, The voltage setting is a first voltage at arc start, and is subsequently switched to a second voltage lower than the first voltage. Submerged arc welding control method.

2. When the distance between the power supply tip and the base material is approximately the standard length, the voltage setting value is set to the second voltage from the time of arc start. The submerged arc welding control method according to claim 1.

3. The period during which the voltage setting value is the first voltage is 1 second or more and 5 seconds or less from the time of arc start. The submerged arc welding control method according to claim 1 or 2.

4. The voltage difference between the first voltage and the second voltage is 2V or more and 5V or less. The submerged arc welding control method according to claim 1 or 2.

5. 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, The voltage setting is a first voltage at arc start, and is subsequently switched to a second voltage lower than the first voltage. Submerged arc welding equipment.

Images