Welding device

Abstract

This welding device performs consumable electrode-type arc welding. The welding device comprises: a power supply circuit that has inverter circuits and that supplies, to an arc, welding power which periodically changes; and a control circuit that controls the power supply circuit. The control circuit sets a target effective current or a target effective voltage for one cycle after the present time, so that a current effective value and a voltage effective value of the welding power exist on a characteristic line corresponding to a set external characteristic, and controls an instantaneous welding current or an instantaneous welding voltage in accordance with the set target effective current or target effective voltage.

Description

welding equipment

[0001] The present disclosure relates to welding equipment.

[0002] Conventionally, some welding devices perform consumable electrode arc welding. For example, Patent Document 1 discloses a conventional welding device (welding power source). The welding device described in Patent Document 1 generates a predetermined external characteristic and performs output control according to the generated external characteristic. In this output control, the welding device sets an instantaneous current target value based on the external characteristic and sequentially controls the welding current to the current target value.

[0003] JP 2009-178763 A

[0004] In AC welding, which outputs AC power, the welding current varies, for example, so that its waveform becomes sinusoidal. Therefore, when current is controlled based on an instantaneous current target value, the welding current and welding voltage may deviate from the external characteristic curve. In other words, output control according to the external characteristic may be difficult, and arc stability may be reduced. This is not limited to AC welding, but can also occur in welding that outputs periodically changing welding power (e.g., DC pulse welding).

[0005] The present disclosure has been devised in consideration of the above circumstances, and its purpose is to provide a welding device that can suppress a decrease in arc stability when welding by outputting periodically changing welding power.

[0006] The welding apparatus provided by the present disclosure is a welding apparatus for performing consumable electrode arc welding, and is equipped with a power supply circuit having an inverter circuit and supplying periodically changing welding power to an arc, and a control circuit for controlling the power supply circuit, wherein the control circuit sets a target effective current or target effective voltage for one cycle from the present time so that the effective current value and effective voltage value of the welding power exist on a characteristic line corresponding to a set external characteristic, and controls the instantaneous welding current or instantaneous welding voltage according to the set target effective current or target effective voltage.

[0007] In a preferred embodiment of the welding device, the control circuit sets the target effective current or the target effective voltage for each cycle of the welding power.

[0008] In a preferred embodiment of the welding device, the control circuit calculates the waveform of the welding current from the set target effective current or calculates the waveform of the welding voltage from the set target effective voltage at a calculation period shorter than one cycle of the welding power, and sets the target effective current or the target effective voltage for each calculation period.

[0009] In a preferred embodiment of the welding device, the control circuit calculates a target effective current for a subsequent cycle from the current time point using the effective current value and the effective voltage value for a previous cycle from the current time point, and determines a current waveform for the subsequent cycle from the current time point so that the effective value of the welding current for the subsequent cycle from the current time point becomes the target effective current for the subsequent cycle from the current time point.

[0010] In a preferred embodiment of the welding device, the control circuit uses the target effective current in the previous cycle instead of the effective current value in the previous cycle.

[0011] In a preferred embodiment of the welding device, the control circuit uses the target effective voltage in the previous cycle from the current time point instead of the effective voltage value in the previous cycle from the current time point.

[0012] In a preferred embodiment of the welding device, the control circuit uses the target effective current in the previous cycle instead of the effective current value in the previous cycle, and uses the average value of the instantaneous output voltage in the previous cycle instead of the effective voltage value in the previous cycle.

[0013] In a preferred embodiment of the welding device, the control circuit calculates the target effective current Itgt(n) for one cycle after the current time point by the calculation shown in equation (1) below, where Iset is the set current, Vset is the set voltage, R is the slope of the characteristic line corresponding to the external characteristic that passes through the set current Iset and the set voltage Vset, Δt is the AC period, L is the virtual inductance, Itgt(n-1) is the target effective current for one cycle before the current time point, and Vfb is the effective value of the output voltage for one cycle before the current time point.

[0014] In a preferred embodiment of the welding device, the power supply circuit supplies AC power to the arc as the welding power.

[0015] In a preferred embodiment of the welding device, the welding device further comprises an operation unit capable of specifying parameters of the external characteristics, and the control circuit is switchable between a standard value mode in which a standard value corresponding to information related to welding is set as the setting value of the external characteristics, and a free setting mode in which a specified value specified by the operation unit is set.

[0016] The welding device disclosed herein sets a target effective current or target effective voltage and controls the instantaneous welding current or instantaneous welding voltage so that the effective values ​​of the welding current and welding voltage lie on a characteristic line corresponding to the external characteristics. Therefore, since the welding current and welding voltage are controlled by the effective values ​​rather than by the instantaneous target values, output control according to the external characteristics can be performed even when the welding current varies, for example, sinusoidally or pulse-like. In other words, the welding device disclosed herein can suppress a decrease in arc stability during welding that outputs periodically varying welding power.

[0017] FIG. 1 is a schematic diagram showing an example of the configuration of a welding device according to a first embodiment; FIG. 2 is a diagram showing an example of the configuration of a power supply device of a welding device according to a first embodiment; FIG. 3 is a diagram showing an example of external characteristics set in a power supply device (control circuit) of a welding device according to a first embodiment; FIG. 4 is a flowchart showing an example of current control performed by a power supply device (control circuit) of a welding device according to a second embodiment; FIG. 5 is a diagram showing an example of waveforms of a welding current and a welding voltage for one cycle of an AC period; FIG. 6 is a diagram showing an example of the operation of a welding device according to a fifth embodiment; FIG. 7 is a diagram showing an example of the configuration of a welding device according to a modified embodiment; FIG. 8 is a schematic diagram showing an example of the configuration of a welding device according to a sixth embodiment;

[0018] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the welding device of the present disclosure will be described below with reference to the drawings. In the following, identical or similar components will be designated by the same reference numerals, and redundant description will be omitted.

[0019] 1 and 2 are configuration diagrams showing a welding apparatus A1 according to a first embodiment. The welding apparatus A1 performs submerged arc welding. As shown in FIG. 1 , the welding apparatus A1 includes a control device 1, a power supply device 2, a carriage 4, a wire feeder 5, a wire reel 6, a sprayer 7, and an electrode 8. The welding apparatus A1 moves the carriage 4 along a weld line of the workpiece W, spraying granular flux stored in a hopper of the sprayer 7 and causing the wire feeder 5 to feed the welding wire into the flux. The welding wire is supplied from the wire reel 6. The power supply device 2 converts AC power supplied from a commercial power source P into power suitable for welding and outputs the power. An arc is generated within the flux between the electrode 8, which is the tip of the welding wire, and the workpiece W. The heat of the arc causes welding. This results in welding along the weld line of the workpiece W. Note that instead of using the carriage 4, the workpiece W may be moved or rotated.

[0020] The control device 1 performs various controls of the welding device A1. The control device 1 may be a general-purpose computer with a program installed to perform various controls of the welding device A1, or it may be a dedicated device for controlling the welding device A1. The control device 1 moves the carriage 4 at a predetermined speed. The speed is set depending on the material and thickness of the workpiece W. The control device 1 instructs the spraying device 7 to spray flux. The control device 1 instructs the wire feeder 5 to start and stop feeding the welding wire. The control device 1 also instructs the welding wire feed speed. The feed speed is set depending on the set welding current, etc. The control device 1 instructs the power supply device 2 to output power. The control device 1 also sets the welding current and welding voltage according to user operation and outputs each set value to the power supply device 2 (control circuit 28 described below). The set values ​​of the welding current and welding voltage are, for example, effective values.

[0021] The power supply device 2 converts AC power supplied from a commercial power source P into AC power of a desired frequency. The power supply device 2 supplies the converted AC power to the arc as welding power. Note that a plurality of power supply devices 2 connected in parallel (specifically, the output terminals a of the power supply devices 2 are connected to each other and connected to the workpiece W, and the output terminals b of the power supply devices 2 are connected to each other and connected to the welding wire) may be used instead of the power supply device 2.

[0022] As shown in FIG. 2, the power supply device 2 includes a power supply circuit 20, a current sensor 26, a voltage sensor 27, and a control circuit 28.

[0023] Power supply circuit 20 converts AC power supplied from commercial power source P into AC power of a desired frequency. Power supply device 2 supplies the converted AC power to the arc as welding power. Power supply circuit 20 includes a rectifying and smoothing circuit 21, an inverter circuit 22, a transformer 23, a rectifying and smoothing circuit 24, and an inverter circuit 25. Note that power supply circuit 20 is not limited to this configuration and may be any circuit that is capable of outputting AC power (welding power).

[0024] The rectifying and smoothing circuit 21 converts AC power input from the commercial power source P into DC power and outputs it. The rectifying and smoothing circuit 21 includes a rectifying circuit that rectifies the AC current and a smoothing capacitor that smoothes the AC current. The configuration of the rectifying and smoothing circuit 21 is not limited.

[0025] The inverter circuit 22 is, for example, a single-phase full-bridge PWM-controlled inverter and includes four switching elements. The inverter circuit 22 converts the DC power input from the rectifying and smoothing circuit 21 into high-frequency power and outputs it by switching the switching elements in response to a drive signal input from the control circuit 28. Note that the inverter circuit 22 may be any circuit that converts DC power into high-frequency power, and may be, for example, a half-bridge type inverter circuit or an inverter circuit with another configuration.

[0026] The transformer 23 transforms the high-frequency voltage output by the inverter circuit 22 and outputs the transformed voltage to the rectifying and smoothing circuit 24. The transformer 23 includes a primary winding 23a and a secondary winding 23b. The input terminals of the primary winding 23a are connected to the output terminals of the inverter circuit 22, respectively. The output terminals of the secondary winding 23b are connected to the input terminals of the rectifying and smoothing circuit 24, respectively. The output voltage of the inverter circuit 22 is transformed according to the turn ratio between the primary winding 23a and the secondary winding 23b and input to the rectifying and smoothing circuit 24. The secondary winding 23b is insulated from the primary winding 23a, thereby preventing current input from the commercial power source P from flowing into the secondary circuit. Furthermore, because the transformer 23 transforms the high-frequency voltage output by the inverter circuit 22, it is smaller and lighter than a transformer that transforms the AC voltage of the commercial power source P.

[0027] The rectifying and smoothing circuit 24 converts the high-frequency power input from the transformer 23 into DC power and outputs it. The rectifying and smoothing circuit 24 includes a rectifying circuit that rectifies the high-frequency current and a DC reactor that smoothes the high-frequency current. Note that the configuration of the rectifying and smoothing circuit 24 is not limited.

[0028] The inverter circuit 25 is, for example, a single-phase full-bridge PWM-controlled inverter and includes four switching elements. The inverter circuit 25 converts the DC power input from the rectifying and smoothing circuit 24 into AC power and outputs it by switching the switching elements in response to a drive signal input from the control circuit 28. Note that the inverter circuit 25 may be any circuit that converts DC power into AC power, and may be, for example, a half-bridge type inverter circuit or an inverter circuit with another configuration.

[0029] The current sensor 26 detects the output current (welding current) of the power supply device 2. In this embodiment, the current sensor 26 is disposed on a connecting line connecting one output terminal of the inverter circuit 25 to the output terminal a. The welding current detected by the current sensor 26 is substantially equal to the current flowing through the electrode 8. The current sensor 26 outputs a current value signal corresponding to the detected instantaneous current value to the control circuit 28. The configuration of the current sensor 26 is not limited as long as it detects the current from the connecting line. The location of the current sensor 26 is also not limited. For example, the current sensor 26 may be disposed on a connecting line connecting the other output terminal of the inverter circuit 25 to the output terminal b. The current sensor 26 may also be disposed external to the power supply device 2.

[0030] The voltage sensor 27 detects the output voltage (welding voltage) of the power supply device 2. In this embodiment, the voltage sensor 27 detects the voltage between output terminal a and output terminal b. This voltage is approximately equal to the voltage applied between the workpiece W (base metal) and the tip of the electrode 8 (torch). The voltage sensor 27 outputs a voltage value signal corresponding to the detected instantaneous voltage value to the control circuit 28. The configuration of the voltage sensor 27 is not limited as long as it detects the voltage between output terminal a and output terminal b. The location of the voltage sensor 27 is also not limited. The voltage sensor 27 may be disposed outside the power supply device 2, and may be disposed, for example, in a location that allows it to detect the tip voltage between the workpiece W (base metal) and the electrode 8 (torch).

[0031] The control circuit 28 is a circuit for controlling the power supply device 2, and is realized by, for example, a microcomputer. The control circuit 28 receives a current value signal from the current sensor 26 and a voltage value signal from the voltage sensor 27. The control circuit 28 outputs drive signals to the inverter circuits 22 and 25, respectively.

[0032] The control circuit 28 controls the welding power (AC power) to the arc so that the effective current and effective voltage lie on a characteristic line (hereinafter referred to as the "external characteristic line") corresponding to the desired external characteristic. Hereinafter, this control may be referred to as "external characteristic effective value control." The external characteristic represents the relationship between the welding current and the welding voltage. The external characteristic used in this embodiment is set as the relationship between the effective current and the effective voltage. Furthermore, while the external characteristic in this embodiment is, for example, a constant voltage characteristic, it may also be other characteristics such as a drooping characteristic or a constant current characteristic. The external characteristic is expressed by a function corresponding to the characteristic, and an arithmetic expression based on this function is set in the control circuit 28. For example, FIG. 3 is a diagram showing an example of a constant voltage characteristic. The horizontal axis in this diagram represents the effective welding current, and the vertical axis represents the effective welding voltage. The external characteristic shown in FIG. 3 is a straight line where the voltage is V0 when the current is zero and passes through the point (Ie, Ve) (Ie is the effective current, and Ve is the effective voltage). The external characteristic is not limited to a straight line but may be a curve, and the function according to the external characteristic may be a formula for different cases. In this embodiment, the control circuit 28 controls the welding power by controlling the current, but the control circuit 28 may also control the welding power by controlling the voltage.

[0033] The control circuit 28 sets a target effective current for the nth AC cycle (n is a positive integer) so that the effective current and effective voltage for the nth AC cycle of the AC power lie on a set external characteristic line (see, for example, FIG. 3 ). When the power supply device 2 controls the welding power by current control, the control circuit 28 sets the target effective current. In this case, the control circuit 28 calculates the effective value Ve (effective voltage) of the AC voltage for the n-1th cycle based on the voltage value signal input from the voltage sensor 27. The control circuit 28 then applies the effective voltage for the n-1th cycle to the above-mentioned external characteristic equation to derive the effective value Ie (effective current) of the AC current for the n-1th cycle, and sets the derived effective current Ie for the n-1th cycle as the target effective current for the nth cycle.

[0034] Once the target effective current is set, the control circuit 28 generates a current waveform command signal from the set target effective current. The current waveform command signal is a signal indicating the current waveform for the nth cycle. This current waveform is, for example, a sine wave, but may be another waveform such as a rectangular wave (trapezoidal wave). For example, when a perfect sine wave waveform is applied as the current waveform, the current waveform becomes a sine wave waveform in which the peak current is √2 times the target effective current. The control circuit 28 generates the current waveform command signal at a cycle shorter than one cycle of the welding power (AC welding current). Unlike this configuration, in this embodiment, one cycle of the welding power may be the same as the cycle for generating the current waveform command signal.

[0035] After generating the current waveform command signal, the control circuit 28 generates a drive signal for controlling the switching elements of the inverter circuit 22 based on the current value signal input from the current sensor 26 and the internally generated current waveform command signal, and outputs the drive signal to the inverter circuit 22. Furthermore, based on the current waveform command signal, the control circuit 28 generates a drive signal for controlling the switching elements of the inverter circuit 25 to switch the power supply polarity between electrode positive polarity and electrode negative polarity, and outputs the drive signal to the inverter circuit 25. In other words, the control circuit 28 performs feedback control so that the waveform of the welding current matches the waveform command signal. As a result, the power supply device 2 outputs an AC current corresponding to the current waveform command signal. The generation cycle of the drive signals of the inverter circuits 22 and 25 is, for example, shorter than the generation cycle of the current waveform command signal. Note that the control circuit 28 may generate the drive signal based only on the current waveform command signal, without using the current value signal.

[0036] Unlike the above example, when controlling welding power by voltage control, the control circuit 28 executes the following process. First, the control circuit 28 sets a target effective voltage. In this case, the control circuit 28 calculates the effective value Ie (effective current) of the AC current for the n-1th cycle based on the current value signal input from the current sensor 26. Then, the control circuit 28 applies the effective current value Ie for the n-1th cycle to the above-described formula for the external characteristics to derive the effective value Ve (effective voltage) of the AC voltage for the n-1th cycle, and sets the derived effective voltage value Ve for the n-1th cycle as the target effective voltage for the nth cycle. After setting the target effective voltage, the control circuit 28 generates a voltage waveform command signal from the set target effective voltage. The voltage waveform command signal is a signal indicating the voltage waveform for the nth cycle. This voltage waveform is, for example, a sine wave, but may also be another waveform such as a rectangular wave (trapezoidal wave). When control circuit 28 generates the voltage waveform command signal, it generates a drive signal for controlling the switching elements of each inverter circuit 22, 25 based on the voltage value signal input from voltage sensor 27 and the waveform command signal generated internally, and outputs the drive signal to the corresponding inverter circuit 22, 25. In other words, control circuit 28 performs feedback control so that the waveform of the welding voltage matches the waveform commanded by the voltage waveform command signal. As a result, power supply device 2 outputs an AC voltage according to the voltage waveform command signal.

[0037] Fig. 4 is a flowchart showing the current control of the welding power performed by the control circuit 28 in the welding device A1. In the flowchart shown in Fig. 4, the case where the control circuit 28 controls the welding power by controlling the current is described, but the welding power may also be controlled by controlling the voltage. In this case, the "voltage" and "current" in Fig. 4 may be interchanged.

[0038] First, the control circuit 28 calculates the effective voltage value of the previous AC cycle based on the voltage value signal input from the voltage sensor 27 (S101). The method for calculating the effective value is not limited. Immediately after the start of the output of welding power, there is no voltage value signal for the previous AC cycle, so the set voltage may be used as the effective voltage value for the previous AC cycle.

[0039] Next, the effective voltage value of the previous cycle is applied to the function of the external characteristic to derive the effective current value of the previous AC cycle (S102). This provides the effective voltage value and the effective current value of the previous AC cycle. At this time, since the effective current value is derived using the function of the external characteristic, the effective voltage value and the effective current value exist on the external characteristic line.

[0040] Next, the calculated effective current value of the previous AC cycle is set as the target effective current of the current AC cycle (S103).

[0041] Next, a current waveform command signal is generated so that the effective current value of the current AC cycle becomes the set target effective current (S104). For example, the waveform commanded by the generated current waveform command signal is a sine wave.

[0042] Next, the instantaneous welding current is controlled so that the current value signal input from the current sensor 26 has a waveform commanded by the current waveform command signal (S105).

[0043] While the welding device A1 is outputting welding power, the welding device A1 repeatedly performs the current control from step S101 to step S105 for each AC cycle. In the above control example, the previous cycle and the current cycle may be separated based on a certain point in the AC cycle of the welding power (for example, the timing when the current switches from negative to positive), or may be separated based on the current time point and the period one AC cycle before and one AC cycle after the current time point.

[0044] In the welding device A1, a target effective current is set to control the instantaneous current so that the effective values ​​(effective current and effective voltage) of the welding current and welding voltage lie on the external characteristic curve. This configuration controls the instantaneous current based on a target for the effective value, enabling output control according to external characteristics in welding that outputs AC welding power. This applies not only to welding that outputs welding power by current control, but also to welding that outputs welding power by voltage control. In other words, by setting a target effective voltage instead of a target effective current and controlling the instantaneous voltage, output control according to external characteristics in welding that outputs AC welding power can be achieved. Therefore, the welding device A1 can suppress a decrease in arc stability in welding that outputs AC power (whether current control or voltage control). The welding device A1 can suppress a decrease in arc stability not only in welding that outputs AC power, but also in welding that outputs periodically changing welding power (e.g., DC pulse welding).

[0045] Next, a welding device A2 according to a second embodiment will be described. The welding device A2 differs from the welding device A1 in the method of calculating the target effective current in welding power control. The configuration of the welding device A2 is the same as the configuration of the welding device A1 (see FIG. 1).

[0046] Control circuit 28 of welding device A2 sets a target effective current for the nth AC cycle so that the effective current and effective voltage for the nth AC cycle of the AC power lie on the set external characteristic line as follows: Let Iset be the set current, Vset be the set voltage, and the external characteristic line be a straight line on the IV plane that passes through point (Iset, Vset) and has a slope of R. Also, let Δt be the AC cycle, L be the virtual inductance, Ifb be the effective value of the welding current for the (n-1)th cycle, and Vfb be the effective value of the welding voltage for the (n-1)th cycle, and control circuit 28 calculates target effective current Itgt(n) for the nth AC cycle using the following equation (2):

[0047] The above equation (2) is derived from the following equation (3) described in Patent Document 1 (Equation (3) in Patent Document 1) as follows: In the following equation (3), Irc is the welding current control set value, which is the instantaneous command current at that time. Also, in the following equation (3), Lr is the inductance set value, v is the welding voltage, and i is the welding current. Irc = ∫ ((Er(i) - v) / Lr) dt (3) In the above equation (3), the relational expression v = Er(i) represents the external characteristic. Here, in the above equation (3), if Er is the output voltage set value (corresponding to the above set voltage Vset) and Ir is the output current set value (corresponding to the above set current Iset), Patent Document 1 gives the external characteristic as a straight line that passes through the point (0, Er) and has a slope of Rr, and the function of the external characteristic is given by the following equation (4). In contrast, for welding device A2, the external characteristic is given as a straight line that passes through point (Ir, Er) and has a slope of Rr, and the function of the external characteristic is given by the following equation (5): Er(i)=Er-Rr·i (4) Er(i)=Er-Rr·(i-Ir) (5) Substituting this equation (5) into the above equation (3) gives Irc=∫((Er-Rr·(i-Ir)-v) / Lr)dt, and differentiating both sides of this equation with respect to t gives the following equation (6). dIrc / dt=(Er-Rr(i-Ir)-v) / Lr (6) If the effective value of the output current in the nth cycle is Itgt(n) and the feedback current (effective value of the output current in the (n-1)th cycle) is Ifb, then the left side of equation (6) above becomes dIrc / dt≈(Itgt(n)-Ifb) / Δt. Furthermore, since the welding current is controlled so that i=Itgt(n), the right side of equation (6) above becomes (Er-Rr(Itgt(n)-Ir)-v) / Lr. Solving this for Itgt(n) gives the following equation (7).Itgt(n) = {Lr · Ifb + Δt (Er + Rr · Ir - v)} / ​​(Lr + Rr · Δt) (7) Here, in each symbol in equation (7), the output voltage set value Er corresponds to the set voltage Vset at the welding device A2, the output current set value Ir corresponds to the set current Iset at the welding device A2, the inductance set value Lr corresponds to the virtual inductance L at the welding device A2, the slope Rr corresponds to the slope R at the external characteristic line at the welding device A2, and the welding voltage v corresponds to the feedback voltage Vfb (effective value of the welding voltage in the (n-1)th cycle) at the welding device A2. Therefore, by substituting Er → Vset, Ir → Iset, Lr → L, Rr → R, and v → Vfb, the equation becomes equation (2). In this way, while the equation in Patent Document 1 is an equation in which the target value is an instantaneous value, it is expanded and used in the welding device A2 to an equation in which the target value is an effective value.

[0048] 5 is a flowchart showing the current control of welding power performed by control circuit 28 in welding device A2. Compared to the current control of welding power in welding device A1, the current control of welding power in welding device A2 performs steps S201 and S202 instead of steps S101 to S103.

[0049] First, the control circuit 28 calculates the effective voltage value of the previous AC cycle from the voltage value signal input from the voltage sensor 27, and calculates the effective current value of the previous AC cycle from the current value signal input from the current sensor 26 (S201). The method for calculating the effective values ​​is not limited. Immediately after the start of welding power output, there are no voltage value signals or current value signals for the previous AC cycle, so the set voltage and set current may be used as the effective voltage and current values ​​for the previous AC cycle.

[0050] Next, the control circuit 28 calculates the target effective current Itgt(n) for the current AC cycle using an equation corresponding to the external characteristics, i.e., the above equation (2) (S202). Since the above equation (2) is an equation corresponding to the external characteristics, if the target effective current Itgt(n) is calculated using this equation, the effective values ​​of the welding current and welding voltage for the current AC cycle will lie on the external characteristic line. This can be understood from the fact that the above equation (2) is derived by substituting the instantaneous value for the effective value in equation (3) described in Patent Document 1. The control circuit 28 then sets the target effective current Itgt(n) to the calculated value.

[0051] Thereafter, control circuit 28 generates the current waveform command signal (step S104) and controls the instantaneous welding current (step S105) in the same manner as control circuit 28 in welding device A1.

[0052] Like the welding device A1, the welding device A2 controls the instantaneous current by setting a target effective current so that the effective values ​​(effective current and effective voltage) of the welding current and welding voltage lie on the external characteristic line. Therefore, like the welding device A1, the welding device A2 controls the instantaneous current based on a target for the effective value, allowing for output control according to the external characteristic in welding that outputs AC power. In other words, the welding device A2 can suppress a decrease in arc stability in welding that outputs AC welding power.

[0053] Next, a welding device A3 according to a third embodiment will be described. The welding device A3 differs from the welding device A2 in the formula for calculating the target effective current Itgt(n). The configuration of the welding device A3 is the same as the configuration of the welding device A2 (i.e., the configuration of the welding device A1; see FIG. 1).

[0054] The control circuit 28 of the welding device A3 uses the target effective current Itgt(n-1) in the n-1th AC cycle instead of the effective value Ifb of the welding current in the n-1th cycle in the above equation (2). That is, the control circuit 28 of the welding device A3 calculates the target effective current Itgt(n) in the nth AC cycle by calculating the following equation (8). In particular, in submerged arc welding, sudden load fluctuations in the secondary load due to short circuits and the like are unlikely to occur, so the effective value Ifb of the welding current in the n-1th cycle is generally close to the target effective current Itgt(n-1). That is, the target effective current Itgt(n-1) can be used instead of the effective current Ifb. The control circuit 28 of the welding device A3 simply changes the calculation equation used in the process of step S202 from the control circuit 28 of the welding device A2 to the following equation (8).

[0055] Like the welding device A2, the welding device A3 sets a target effective current and controls the instantaneous current so that the effective values ​​(effective current and effective voltage) of the welding current and welding voltage lie on the external characteristic line, thereby suppressing a decrease in arc stability during welding that outputs AC welding power. Furthermore, compared to the welding device A2, the welding device A3 does not require the calculation of the current effective value Ifb. Therefore, the welding device A3 can reduce the calculation load compared to the welding device A2.

[0056] Next, a welding device A4 according to a fourth embodiment will be described. The welding device A4 differs from the welding device A3 in the calculation formula for the target effective current Itgt(n). The configuration of the welding device A4 is the same as the configuration of the welding device A3 (i.e., the configuration of the welding device A1; see FIG. 1).

[0057] The control circuit 28 of the welding device A4 uses the average value Vavg(n-1) of the welding voltage in the n-1th cycle instead of the effective value Vfb of the welding voltage in the n-1th cycle in the above equation (8). That is, the control circuit 28 of the welding device A4 calculates the target effective current Itgt(n) in the nth AC cycle by calculating the following equation (9). The welding current varies (controls) in various ways, such as the sinusoidal waveform described above. However, the welding voltage does not necessarily have a shape similar to the welding current, as shown in FIG. 6 , but rather exhibits a rectangular wave-like appearance. This is because a certain voltage is required to maintain the arc. With such a rectangular waveform, the difference between the effective value and the average value is small, so the effective value Vfb of the welding voltage in the n-1th cycle can be approximated by the average value Vavg(n-1). Control circuit 28 in welding device A4 may be configured by changing the calculation formula used in the process of step S202 in control circuit 28 in welding device A2 to the following formula (9).

[0058] Like the welding devices A2 and A3, the welding device A4 sets a target effective current and controls the instantaneous current so that the effective values ​​(effective current and effective voltage) of the welding current and welding voltage lie on the external characteristic line. This prevents a decrease in arc stability during welding that outputs AC welding power. Furthermore, compared to the welding device A3, the welding device A4 does not require calculation of the effective voltage value Vfb. Therefore, the welding device A4 can reduce the calculation load compared to the welding device A3. In other words, compared to the welding device A2, the welding device A4 does not require calculation of both the effective current value and the effective voltage value, thereby significantly reducing the calculation load compared to the welding device A2.

[0059] In the second to fourth embodiments, the power supply device 2 controls the welding power by current control, but this is not limiting. The power supply device 2 may control the welding power by voltage control. In this case, the above formulas (2), (8), and (9) can be replaced with arithmetic expressions corresponding to the external characteristics, with the target effective voltage of the nth cycle of the welding power as the left-hand side. Details of these arithmetic expressions will be omitted.

[0060] Next, a welding device A5 according to a fifth embodiment will be described. The welding device A5 differs from the welding device A1 in the calculation cycle of the target effective current (or target effective voltage). Specifically, in the welding device A1, the control circuit 28 calculates the target effective current (or target effective voltage) for each AC cycle of the AC power (welding power). However, in the welding device A5, the control circuit 28 calculates the target effective current (or target effective voltage) for each generation cycle of the current waveform command signal (or voltage waveform command signal). Hereinafter, an example in which the target effective current is calculated (set) to control the welding current (AC current) will be described. However, the same applies to the case in which the target effective voltage is calculated (set) to control the welding voltage (AC voltage).

[0061] Similar to the control circuit 28 of the welding device A1, the control circuit 28 of the welding device A5 generates a current waveform command signal from a set target effective current. The generation of this current waveform command signal is shorter than one cycle of the AC welding power (e.g., welding current). This is also true for the control circuit 28 of the welding device A1. That is, the control circuit 28 generates the current waveform command signal at a calculation period shorter than one AC cycle of the AC welding power (welding current). For example, one cycle of the AC welding power (welding current) is 20 msec (the welding power frequency is 50 Hz), and the calculation period of the current waveform command signal is 50 μsec. Note that the period of the AC welding power (welding current) and the calculation period of the current waveform command signal are not limited to this example. In relation to this AC power period and the calculation period of the current waveform command signal, the control circuit 28 of the welding device A5 calculates (sets) the target effective current at the timing of generating the current waveform command signal. That is, in the control circuit 28 of the welding device A5, the start of the calculation cycle of the current waveform command signal is set as the start of the nth calculation cycle of the target RMS current, and the target RMS current for the nth calculation cycle is set for each calculation cycle of the current waveform command signal. Therefore, the cycle for calculating (setting) the target RMS current is shorter in the welding device A5 than in the welding device A1. Note that the control circuit 28 of the welding device A5 may use any of the methods used in the welding devices A1 to A4 to calculate the target RMS current. In this embodiment, the nth cycle is the period from the current time to one cycle of welding power (AC power) later, and the (n-1)th cycle is the period from the current time to one cycle of welding power (AC power) earlier.

[0062] Fig. 7 is a diagram illustrating an example of the operation of welding device A5, showing the waveform of the welding current. In Fig. 7, T1 represents one AC period of the welding power (AC current), and T2 represents the calculation period of the current waveform command signal. In the illustrated example, T2 is 1 / 8 times T1, but the ratio of T1 to T2 is not particularly limited. It is also assumed that the effective value of the welding current does not change during the period shown in Fig. 7.

[0063] At time t1, control circuit 28 calculates and sets a target effective current using information from time t1 to one cycle T1 before. As described above, the calculation of this target effective current may be performed using any of the methods used by welding devices A1 to A4. Control circuit 28 then generates a current waveform command signal for a current waveform from time t1 to one cycle T1 after, based on the target effective current set at time t1.

[0064] Next, at time t2 (= t1 + T2), which is the calculation period T2 after time t1, the control circuit 28 calculates and sets the target effective current using information from the period from time t2 to one period T1 before. Then, based on the target effective current set at time t2, the control circuit 28 generates a current waveform command signal for the current waveform from time t2 to one period T1 after. Thereafter, the same process is performed at time t3 (= t2 + T2).

[0065] As can be seen from the above-described operation example, in the control circuit 28 of the welding device A5, the target effective current is updated for each calculation period T2 of the current waveform command signal. Then, a current waveform command signal is generated in accordance with the updated target effective current, and the welding current is controlled.

[0066] In the welding device A5, the target effective current is updated at a shorter cycle (the calculation cycle of the current waveform command signal) than in the welding devices A1 to A4. During welding, the welding voltage changes depending on the arc length. In the welding device A5, the current responsiveness to the voltage fluctuation of the welding voltage can be improved.

[0067] In the first to fifth embodiments, the control circuit 28 controls the welding power so that it lies on a characteristic line corresponding to a preset external characteristic. Alternatively, the external characteristic may be adjustable. FIG. 8 shows a welding device according to such a modification. While FIG. 8 shows the control circuit 28 and the control device 1, the other configurations are the same as those shown in FIGS. 1 and 2.

[0068] 8 includes an operation unit 91 and a display unit 92. In the illustrated example, the operation unit 91 and the display unit 92 are provided in the control device 1. Alternatively, the operation unit 91 and the display unit 92 may be provided in the power supply device 2. In this case, the operation unit 91 and the display unit 92 are connected to the control circuit 28.

[0069] The operation unit 91 accepts user operations. The operation unit 91 inputs values ​​of each parameter of the external characteristic through user operations. Each parameter of the external characteristic includes the type of external characteristic (constant voltage characteristic, constant current characteristic, or drooping characteristic) and the slope of the external characteristic line. The parameters of the external characteristic are not limited to these two. For example, the operation unit 91 can specify the slope of the external characteristic line within a range of −0.5 V / 100 A to 40 V / 100 A. Note that the values ​​that can be specified for the slope of the external characteristic line are not limited to this range. For example, by specifying 0 (e.g., 0 V / 100 A) as the slope of the external characteristic line, a completely constant current characteristic (current remains constant even when voltage changes) or a completely constant voltage characteristic (voltage remains constant even when current changes) can be specified in combination with the type of external characteristic. The control device 1 outputs the values ​​of each parameter of the external characteristic specified through the operation unit 91 to the power supply device 2 (control circuit 28).

[0070] Display unit 92 is configured with, for example, a liquid crystal display, an OEL (organic electro-luminescence) display, a segment display, etc. Display unit 92 displays various information about the welding device. For example, when each parameter of the external characteristics is specified by operation unit 91, display unit 92 displays the value of each parameter.

[0071] The control circuit 28 includes an external characteristic setting unit 281. The external characteristic setting unit 281 switches between a standard value mode and a free setting mode. The standard value mode is a mode in which standard values ​​are set as external characteristics to be set according to information related to welding. The welding information includes, for example, the welding polarity (AC, DC negative, or DC positive), the control method (constant voltage control mode (constant feed rate control mode), constant current control mode (variable feed rate control mode)), and the set values ​​of the welding current and welding voltage. The welding information is not limited to these. The standard values ​​are recommended values ​​for this welding information. The free setting mode is a mode in which specified values ​​specified (input) by the operation unit 91 are set as external characteristics to be set. The external characteristic setting unit 281 switches to the free setting mode when the values ​​of the parameters of the external characteristics are specified by operating the operation unit 91, i.e., when the values ​​of the parameters of the external characteristics specified by the operation unit 91 are input. On the other hand, if the value of each parameter of the external characteristics is not specified by operating the operation unit 91, that is, if the value of each parameter of the external characteristics specified from the operation unit 91 is not input, the standard value mode is selected.

[0072] In the standard value mode, the control circuit 28 uses the recommended standard value as the external characteristic to perform the external characteristic effective value control shown in the first to fifth embodiments. On the other hand, in the free setting mode, the control circuit 28 uses the specified value specified by the operation unit 91 as the external characteristic to perform the external characteristic effective value control shown in the first to fifth embodiments.

[0073] In the welding apparatus according to the modified example shown in Fig. 8, the user can easily adjust the parameters of the external characteristics (type of external characteristic and slope of the external characteristic line) to suit the welding object, welding material, feed control method, welding wire extension length, and other welding conditions. For example, for a worker with low welding proficiency, the standard value mode can be used to use standard (recommended) external characteristics, thereby preventing a decrease in welding quality. On the other hand, for a worker with high welding proficiency, the free setting mode can be used to adjust the parameters of the external characteristics according to the above-mentioned welding conditions, thereby improving welding quality.

[0074] The above-described function of adjusting the external characteristics (parameters) is not limited to welding devices that perform AC welding. For example, it can be applied to welding devices that perform DC pulse welding, and further, it can be applied to welding devices that perform DC welding.

[0075] Next, a welding apparatus A6 according to a sixth embodiment will be described. The welding apparatus A6 differs from the welding apparatus A1 in the following respects. The control device 1 feedback-controls the output voltage (effective value) of the power supply device 2 using variable wire feed speed control, which adjusts the welding wire feed speed. For example, the power supply device 2 controls the arc length using constant voltage characteristics in external characteristic effective value control. When a thin welding wire with a diameter of 1.6 mm or less is used, the arc length is appropriately controlled using constant voltage characteristics. However, in submerged arc welding, thick welding wires with diameters of, for example, 2.4 mm, 3.2 mm, 4.0 mm, 4.8 mm, or 6.4 mm are used. Note that the diameter of the welding wire used in the welding apparatus of the present disclosure is not limited to these. When a thick welding wire is used, it is difficult to effectively control the wire melting amount by changing the current. The welding apparatus A6 of this embodiment uses both constant voltage characteristics and variable wire feed speed control to control the arc length. For this reason, the control device 1 includes a speed setting unit 11 and a speed correction unit 12 as functional components for variable wire feed speed control, as shown in FIG.

[0076] The speed setting unit 11 has a function of setting a reference speed, which is a standard wire feed speed according to the welding conditions. The speed setting unit 11 stores a reference speed corresponding to the set voltage Vset, and outputs the reference speed according to the set set voltage Vset to the speed correction unit 12. The reference speed is not limited to, but is equal to or less than 10 m / min.

[0077] The speed correction unit 12 has a functional configuration that sets a set speed by correcting the reference speed input from the speed setting unit 11. The speed correction unit 12 calculates the deviation between the set voltage Vset and the effective voltage Ve (the effective value Ve of the AC voltage for n-1 cycles) calculated by the control circuit 28. The speed correction unit 12 performs an operation, for example, by integral control on the calculated deviation to calculate a calculated value. The speed correction unit 12 then calculates the set speed by adding the calculated value by integral control to the reference speed input from the speed setting unit 11. When the effective voltage Ve is smaller than the set voltage Vset, the speed correction unit 12 adds a calculated value corresponding to the negative deviation to set a set speed for the wire feeder 5 that is smaller (slower) than the reference speed. This slows the welding wire feed speed, increases the arc length, and increases the welding voltage. On the other hand, when the effective voltage value Ve is greater than the set voltage Vset, the speed correction unit 12 adds a calculated value corresponding to the positive deviation to set a set speed that is greater (faster) than the reference speed for the wire feeder 5. This increases the welding wire feed speed, shortens the arc length, and reduces the welding voltage.

[0078] As described above, the control device 1 of the welding device A6 controls the output voltage of the power supply device 2 to the set voltage Vset by adjusting the welding wire feed speed. The internal configuration of the control device 1 is not limited to that described above. The control device 1 may control the output voltage (effective value) of the power supply device 2 to the set voltage Vset by adjusting the welding wire feed speed. In the above example, the control circuit 28 calculates the target effective current Itgt(n) and the control device 1 controls the output voltage (effective value) of the power supply device 2 to the set voltage Vset using the variable wire feed speed control. However, if the target effective voltage is set in the control circuit 28, the control device 1 may control the output current (effective value) of the power supply device 2 to the set current Iset using the variable wire feed speed control.

[0079] In the welding device A6, the power supply device 2 controls the arc length using the constant voltage characteristic in the external characteristic effective value control. Furthermore, the wire feeder 5 controls the arc length by adjusting the feed speed so that the output voltage (effective voltage value) of the power supply device 2 becomes the set voltage Vset. Even when a thick welding wire is used and the effect of arc length control using the constant voltage characteristic is difficult to obtain, the welding device A6 can appropriately control the arc length by adding the control of the arc length by changing the feed speed. As a result, the welding device A6 can suppress instability in welding even when the external characteristic is set to the constant voltage characteristic.

[0080] In the first to sixth embodiments (and the modifications thereof), the functions of either the control circuit 28 or the control device 1 may be incorporated into the other of the control circuit 28 or the control device 1.

[0081] Although the above first to sixth embodiments (including modifications) have been described using AC welding (welding that outputs AC power) as an example, the welding device of the present disclosure can be applied to welding that outputs periodically changing welding power (e.g., DC pulse welding that outputs power with a DC pulse waveform). In other words, the welding device of the present disclosure can suppress a decrease in arc stability not only in AC welding but also in welding that outputs periodically changing welding power (e.g., DC pulse welding).

[0082] In the above first to sixth embodiments (including the modified examples), a welding device that performs submerged arc welding has been described as an example, but the welding device of the present disclosure may be one that performs consumable electrode arc welding (e.g., GMA (Gas Metal Arc) welding, etc.).

[0083] The welding device according to the present disclosure is not limited to the above-described embodiment, and the specific configuration of each part of the welding device according to the present disclosure can be freely modified in various ways.

[0084] A1 to A6: welding device, 1: control device, 2: power supply device, 20: power supply circuit, 22, 25: inverter circuit, 28: control circuit, 281: external characteristic setting unit, 91: operation unit

Claims

1. A welding device for performing consumable electrode arc welding, comprising: a power supply circuit having an inverter circuit and supplying a periodically changing welding power to an arc; and a control circuit for controlling said power supply circuit, wherein said control circuit sets a target effective current or target effective voltage for one cycle from the present time so that the effective current value and effective voltage value of said welding power are on a characteristic line corresponding to a set external characteristic, and controls the instantaneous welding current or instantaneous welding voltage according to the set target effective current or target effective voltage.

2. The welding device according to claim 1, wherein the control circuit sets the target effective current or the target effective voltage for each cycle of the welding power.

3. The welding device according to claim 1, wherein the control circuit calculates the waveform of the welding current from the set target effective current or calculates the waveform of the welding voltage from the set target effective voltage at a calculation period shorter than one cycle of the welding power, and sets the target effective current or the target effective voltage for each calculation period.

4. A welding device as described in claim 2 or 3, wherein the control circuit calculates a target effective current for one cycle after the current time point using the effective current value and the effective voltage value for one cycle before the current time point, and determines a current waveform for one cycle after the current time point so that the effective value of the welding current for one cycle after the current time point becomes the target effective current for one cycle after the current time point.

5. The welding device according to claim 4, wherein the control circuit uses the target effective current in the previous cycle from the current time point instead of the effective current value in the previous cycle from the current time point.

6. The welding device according to claim 4, wherein the control circuit uses the target effective voltage in the previous cycle from the current time point instead of the effective voltage value in the previous cycle from the current time point.

7. The welding device of claim 4, wherein the control circuit uses the target effective current in the previous cycle before the current time instead of the effective current value in the previous cycle, and uses an average value of the instantaneous output voltage in the previous cycle before the current time instead of the effective voltage value in the previous cycle before the current time.

8. The welding device according to claim 5, wherein the control circuit calculates a target effective current Itgt(n) for one cycle following the current time point by the calculation shown in the following formula (1): Iset is a set current, Vset is a set voltage, R is a slope of a characteristic line corresponding to the external characteristic that passes through the set current Iset and the set voltage Vset, Δt is an AC period, L is a virtual inductance, Itgt(n-1) is a target effective current for one cycle preceding the current time point, and Vfb is an effective value of the output voltage for one cycle preceding the current time point.

9. The welding device according to any one of claims 1 to 3, wherein the power supply circuit supplies AC power to the arc as the welding power.

10. A welding device as described in any one of claims 1 to 3, further comprising an operation unit capable of specifying parameters of the external characteristics, and the control circuit is switchable between a standard value mode in which a standard value corresponding to information relating to welding is set as the setting value of the external characteristics, and a free setting mode in which a specified value specified by the operation unit is set.

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