JP5495758B2 - Plasma MIG welding method - Google Patents

Description

  The present invention relates to a plasma MIG welding method for performing welding by simultaneously generating a MIG arc and a plasma arc using a single welding torch.

  Conventionally, a plasma MIG welding method combining a plasma welding method and a MIG welding method has been proposed (see, for example, Patent Document 1). In this plasma MIG welding method, a MIG arc is generated by applying a MIG welding current between a welding wire fed through a welding torch and a base material. At the same time, a gas such as argon is supplied so as to surround the welding wire, and a plasma arc is generated by passing a plasma welding current between the welding torch and the base material through this gas. The welding wire functions as an electrode for generating a MIG arc, and the tip of the welding wire melts to form a droplet to assist the joining of the base materials. Therefore, the plasma MIG welding method is often used for high-efficiency welding of thick plates, high-speed welding of thin plates, and the like.

  The MIG welding current generally uses a DC pulse waveform in order to suppress the generation of spatter and stably supply droplets. Therefore, the MIG welding method is a general MIG pulse welding method. In the consumable electrode type arc welding method including the MIG pulse welding method, it is important to maintain the arc length during welding at an appropriate value, and therefore arc length control is performed. A DC or DC pulse waveform is used for the plasma welding current. In the following description, when the arc length is simply described, it means the arc length of the MIG arc. Hereinafter, the plasma MIG welding method described above will be described.

  FIG. 7 is a waveform diagram showing a plasma MIG welding method. (A) shows the MIG welding current Iwm, (B) shows the MIG welding voltage Vwm, and (C) shows the plasma welding current Iwp. Hereinafter, a description will be given with reference to FIG.

  As shown in FIG. 6A, during the peak rising period Tup from time t1 to t2, a transition current rising from the base current Ib to the peak current Ip is energized, and then during the peak period Tp from time t2 to t3. The peak current Ip is energized, and subsequently, during the peak fall period Tdw from time t3 to t4, a transition current that decreases from the peak current Ip to the base current Ib is energized. The base current Ib is energized during the base period Tb from t4 to t5. Further, in response to the application of the MIG welding current Iwm, a transition voltage that rises from the base voltage Vb to the peak voltage Vp is applied during the peak rising period Tup as shown in FIG. Subsequently, during the peak period Tp, the peak voltage Vp is applied. Subsequently, during the peak fall period Tdw, a transition voltage that falls from the peak voltage Vp to the base voltage Vb is applied. Subsequently, the base voltage Vb is applied during the base period Tb. The welding is performed by repeating the period from time t1 to t5 as one pulse period Tf.

  In MIG welding, arc length control is performed to maintain the arc length at an appropriate value in order to obtain good welding quality. Normally, this arc length control uses the fact that the MIG welding voltage Vwm is substantially proportional to the arc length, and controls the pulse cycle so that the average value of the MIG welding voltage Vwm is equal to a predetermined voltage setting value. Is done. This arc length control method is called a frequency modulation method. In this case, the peak period Tp, the peak current Ip, and the base current Ib are set to predetermined values and become pulse parameters. The peak current Ip is set to a critical value or more and is called a unit pulse condition in combination with the peak period Tp. This unit pulse condition is set so that one droplet period is one droplet transfer. The base current Ib is set to a small current value of about several tens of A that is less than the critical value. The unit pulse condition and the base current Ib are set to appropriate values according to the welding wire material, diameter, feeding speed, and the like. The arc length control method includes a pulse width modulation method in addition to the above frequency modulation method. In this pulse width modulation method, the pulse period Tf, the peak current Ip, and the base current Ib are set to predetermined values, and the peak period Tp is controlled so that the average value of the MIG welding voltage Vwm is equal to a predetermined voltage setting value. The

  On the other hand, as shown in FIG. 5C, the plasma welding current Iwp is constant-current controlled and becomes a DC waveform having a predetermined constant value. Therefore, the plasma arc is generated by energizing the plasma welding current Iwp with a constant value.

  By the way, in the MIG pulse welding, the cathode spot of the arc has a property of being formed at a position where an oxide film exists on the surface of the base material. Since the oxide film is removed (cleaned) by the arc, the cathode spot moves to the peripheral portion in search of the portion where the oxide film remains. As a result, since the arc is in an unstable state that is constantly moving, a short circuit is likely to occur. When the welding wire and the base metal are short-circuited and the short-circuit is released and the arc is re-ignited, or when a wobbling phenomenon of the arc cathode spot due to non-uniformity of the oxide film on the base metal surface occurs, abnormal voltage Is superimposed on the MIG welding voltage Vwm. Since this abnormal voltage is a voltage that is not proportional to the arc length, it is necessary to remove the abnormal voltage superimposed on the MIG welding voltage Vwm in order to accurately detect the arc length. As a method for this removal, a reference voltage waveform Vc and a fluctuation range ΔVc of a pulse waveform are set, and a portion where the MIG welding voltage Vwm is outside the range of Vc ± ΔVc is cut and limited as an abnormal voltage. Technology has been proposed. Hereafter, this prior art is demonstrated (refer patent document 2 and 3).

FIG. 8 is a diagram showing a method for setting the reference voltage waveform Vc. First, as will be described later with reference to FIG. 10, a reference peak voltage value Vpc, a reference base voltage value Vbc, and a fluctuation range ΔVc are set. Then, as shown in the figure, the reference voltage waveform Vc is defined by the following equation by the elapsed time t when the start time of the peak rising period Tup is 0 second.
0 ≦ t <Tup
Vc = ((Vpc−Vbc) / Tup) · t + Vbc (11) Expression Tup ≦ t <Tup + Tp
Vc = Vpc (12) Expression Tup + Tp ≦ t <Tup + Tp + Tdw
Vc = ((Vbc−Vpc) / Tdw) · (t−Tup−Tp) + Vpc (13) Expression Tup + Tp + Tdw ≦ t <Tup + Tp + Tdw + Tb
Vc = Vbc (14) Formula

For example, as shown in the figure, it is assumed that the MIG welding voltage detection value at the elapsed time t = ta is Vd1. Since the elapsed time ta is Tup + Tp ≦ ta <Tup + Tp + Tdw, the center value Vc1 of the reference voltage waveform is expressed by the following equation by substituting into the above equation (13).
Vc1 = ((Vbc-Vpc) / Tdw). (Ta-Tup-Tp) + Vpc
Therefore, the MIG welding voltage detection value Vd1 at the elapsed time ta is limited to the fluctuation range Vc1 ± ΔVc. That is, when Vd1 ≧ Vc1 + ΔVc, it is limited to the MIG welding voltage limit value Vft1 = Vc1 + ΔVc, and when Vd1 ≦ Vc1−ΔVc, it is limited to Vft1 = Vc1−ΔVc. The MIG welding voltage limit value Vft calculated in this way is a voltage value that is substantially proportional to the arc length from which the abnormal voltage is substantially eliminated.

  FIG. 9 is a voltage waveform diagram when an abnormal voltage is generated due to arc re-ignition immediately after the short circuit is released. FIG. 4A shows the time change of the MIG welding voltage Vwm, and FIG. 4B shows the time change of the MIG welding voltage limit value Vft after the abnormal voltage is removed by the reference voltage waveform. As shown in FIG. 5B, the MIG welding voltage Vwm is limited within a fluctuation range Vc ± ΔVc having the reference voltage waveform as the center value Vc. As a result, the MIG welding voltage limit value Vft = Vc−ΔVc during the short-circuit period from time t1 to t2 and the MIG welding voltage limit value Vft = Vc + ΔVc during the abnormal voltage generation period from time t2 to t3. Thus, the abnormal voltage can be substantially eliminated.

  FIG. 10 is a diagram showing a time change of the MIG welding voltage limit value Vft for explaining a method of automatically setting the reference voltage waveform Vc described above with reference to FIG. In the figure, the current time is time tn, which is the start time of the nth pulse cycle Tf (n). Further, the average value of the MIG welding voltage limit value only during the peak period in the (n-1) th pulse period Tf (n-1) is the peak voltage limit value Vpf (n-1), and the MIG welding voltage only during the base period. The average value of the limit values is the base voltage limit value Vbf (n-1). Similarly, the average value of the MIG welding voltage limit value only during the peak period in the (n−m) th pulse period Tf (nm) is the peak voltage limit value Vpf (nm), and the MIG welding voltage limit value only during the base period. The average value is the base voltage limit value Vbf (nm).

At time tn, the peak voltage moving average value Vpr (n) is calculated as shown in the following equation using the (n-1) to (nm) -th peak voltage limit value Vpf as an input.
Vpr (n) = (Vpf (n-1) +... + Vpf (nm)) / m Similar to the equation (21), at the time tn, the above (n-1) th to (nm) th base voltage limit Using the value Vbf as an input, the base voltage moving average value Vbr (n) is calculated as in the following equation.
Vbr (n) = (Vbf (n-1) +... + Vbf (nm)) / m (22)

In the equations (11) to (14), the peak voltage moving average value Vpr is substituted for the reference peak voltage value Vpc, and the base voltage moving average value Vbr is substituted for the reference base voltage value Vbc. Then, the reference voltage waveform during the nth pulse period Tf (n) is automatically set as shown in the following equation.
0 ≦ t <Tup
Vc (n) = ((Vpr (n) −Vbr (n)) / Tup) · t + Vbr (n) (31) Expression Tup ≦ t <Tup + Tp
Vc (n) = Vpr (n) (32) Expression Tup + Tp ≦ t <Tup + Tp + Tdw
Vc (n) = ((Vbr (n) −Vpr (n)) / Tdw) · (t−Tup−Tp) + Vpr (n) (33) Expression Tup + Tp + Tdw ≦ t <Tup + Tp + Tdw + Tb
Vc (n) = Vbr (n) (34)

  As described above, the peak voltage moving average value Vpr and the base voltage moving average value Vbr are calculated for each start point of the pulse period, and the reference voltage waveform is automatically set by the above equations (31) to (34). The In the above, when calculating the peak voltage moving average value Vpr, the peak voltage limit value Vpf may be calculated by weighted moving average. Similarly, when calculating the base voltage moving average value Vbr, the base voltage limit value Vbf may be calculated by weighted moving average. Further, the length of the moving average period (predetermined period) is set to the past several cycles to several tens of cycles. This predetermined period is set to an appropriate value by experiment according to the welding wire material, diameter, feed speed, welding speed, welding joint, and other welding conditions. The peak voltage moving average value Vpr and the base voltage moving average value Vbr cannot be calculated based on the equations (21) and (22) until m pulse periods Tf have elapsed from the arc start. . Therefore, during this period, the peak voltage initial value and the base voltage initial value are preset and used as the peak voltage moving average value Vpr and the base voltage moving average value Vbr.

JP 2008-229641 A Japanese Patent No. 4263886 JP 2007-307564 A

  As described above, the MIG welding voltage Vwm includes voltage fluctuations due to fluctuations in the arc length caused by fluctuations in feed speed, fluctuations in torch height, fluctuations in the molten pool state, and movement of the cathode spot. The resulting abnormal voltage is superimposed. The voltage fluctuation accompanying the fluctuation of the arc length needs to be accurately detected in order to perform the arc length control. On the other hand, it is desirable to remove as much as possible the abnormal voltage that is not related to the fluctuation of the arc length in order to perform precise arc length control. In the abnormal voltage removal method using the reference waveform Vc and the fluctuation range ΔVc described above, if the fluctuation range ΔVc is reduced, the removal rate of the abnormal voltage is improved, but on the other hand, the voltage fluctuation accompanying the fluctuation of the arc length can be removed at the same time. Increases nature. On the contrary, when the fluctuation range ΔVc is increased, the abnormal voltage removal rate decreases, but the voltage fluctuation accompanying the fluctuation of the arc length can be detected without being removed. Consider the balance between the removal rate of abnormal voltage and the detection rate of voltage fluctuation accompanying the fluctuation of arc length according to the welding conditions such as the condition of the participation coating of the base metal, the material of the welded joint and welding wire, diameter, welding speed, etc. Thus, the variation range ΔVc is set by experiment. In plasma MIG welding, the abnormal voltage generation state changes due to the influence of the plasma arc. Therefore, in order to perform precise arc length control, it is necessary to optimize the fluctuation range ΔVc according to the state of the plasma arc.

  Accordingly, the present invention provides a plasma MIG welding method capable of improving the stability of MIG arc arc length control by optimizing the fluctuation range ΔVc for removing abnormal voltage according to the state of the plasma arc. Objective.

In order to solve the above-described problems, the invention of claim 1 generates a MIG arc by applying a MIG welding voltage between a welding wire fed through a welding torch and a base material and applying a MIG welding current. Let
A transition current rising from the base current to the peak current is applied during the peak rising period, the peak current is applied during the subsequent peak period, and the peak current is decreased from the peak current during the subsequent peak falling period. Energize the transition current, energize the base current during the subsequent base period, energize the MIG welding current by repeating these energization as one pulse period,
The MIG welding voltage is detected, and the MIG welding voltage limit value is calculated by using the MIG welding voltage detection value as an input and limiting the reference voltage waveform within a predetermined fluctuation range with the center voltage value as a center voltage value. Perform the arc length control of the MIG arc by changing the pulse period or the peak period based on the value,
The MIG welding voltage limit value during the peak period is moving averaged over the past predetermined period to calculate a peak voltage moving average value, and the MIG welding voltage limit value during the base period is averaged over the past predetermined period. The base voltage moving average value is calculated, and the reference voltage waveform is set to a transition voltage that rises from the base voltage moving average value to the peak voltage moving average value during the peak rising period, and during the subsequent peak period, Set to the peak voltage moving average value, set to a transition voltage falling from the peak voltage moving average value to the base voltage moving average value during the subsequent peak falling period, and then to the base voltage during the subsequent base period Set to moving average value,
In the plasma MIG welding method of generating a plasma arc by energizing a plasma welding current between the welding torch and the base material through a gas supplied so as to surround the welding wire,
Changing the fluctuation range according to the value of the plasma welding current;
This is a plasma MIG welding method.

The invention of claim 2 sets the fluctuation range to a first fluctuation range when the value of the MIG welding current is equal to or greater than a reference current value, and when the value of the MIG welding current is less than the reference current value. The plasma when the second fluctuation range is set, the first fluctuation range and the second fluctuation range are changed according to the value of the plasma welding current, and the value of the MIG welding current is equal to or greater than the reference current value. When the value of the welding current and the value of the plasma welding current when the value of the MIG welding current is less than the reference current value are the same value, the first fluctuation range is larger than the second fluctuation range. Set to
The plasma MIG welding method according to claim 1.

  According to the present invention, by changing the fluctuation range according to the value of the plasma welding current, it is possible to suppress the abnormal voltage from being superimposed on the MIG welding voltage, and to reduce the voltage fluctuation accompanying the fluctuation of the arc length. It can be detected accurately. For this reason, precise arc length control can be performed and good welding quality can be obtained.

It is a block diagram of the welding apparatus for enforcing the plasma welding method which concerns on Embodiment 1 of this invention. It is a figure which shows the relationship between the plasma welding current Iwp which concerns on Embodiment 1 of this invention, and the fluctuation range (DELTA) Vc. It is a block diagram of the MIG welding power supply PSM which comprises FIG. It is a block diagram of the plasma welding power supply PSP which comprises FIG. It is a figure which shows the relationship between the plasma welding current Iwp which concerns on Embodiment 2 of this invention, 1st fluctuation | variation range (DELTA) Vc1, and 2nd fluctuation | variation range (DELTA) Vc2. It is a block diagram of the MIG welding power supply PSM which concerns on Embodiment 2 of this invention. It is a wave form diagram which shows the plasma MIG welding method of a prior art. It is a figure which shows the setting method of the reference voltage waveform Vc used in order to remove an abnormal voltage in a prior art. In prior art, it is a voltage waveform figure at the time of the abnormal voltage generation | occurrence | production accompanying the arc re-ignition immediately after short circuit cancellation | release. In prior art, it is a figure which shows the time change of the MIG welding voltage limiting value Vft for demonstrating the method to set automatically the reference voltage waveform Vc mentioned above in FIG.

  Embodiments of the present invention will be described below with reference to the drawings.

[Embodiment 1]
FIG. 1 is a configuration diagram of a welding apparatus for performing a plasma MIG welding method according to Embodiment 1 of the present invention. Hereinafter, each component will be described with reference to FIG.

  This welding apparatus includes a welding torch WT, a MIG welding power source PSM, and a plasma welding power source PSP surrounded by a broken line. The welding torch WT has a structure in which a plasma nozzle 51, a plasma electrode 1b, and a power feed tip 4 are arranged on a concentric axis in a shield gas nozzle 52. From the gap between the shield gas nozzle 52 and the plasma nozzle 51, for example, a shield gas 63 such as argon gas or a mixed gas of argon gas and carbon dioxide gas is supplied. A plasma gas 62 such as argon gas or a mixed gas of argon gas and carbon dioxide gas is supplied between the plasma nozzle 51 and the plasma electrode 1b. A center gas 61 such as argon gas or a mixed gas of argon gas and carbon dioxide gas is supplied between the plasma electrode 1 b and the power feed tip 4.

  A welding wire 1 a is fed from a through hole provided in the power feed tip 4. The power feed tip 4 is electrically connected to the welding wire 1a. The welding wire 1a is fed by the rotation of the feed roll 7 using the feed motor WM as a drive source. The plasma electrode 1b is made of, for example, copper or a copper alloy, and is indirectly water-cooled by cooling water passing through a path outside the figure. The plasma nozzle 51 is made of, for example, copper or a copper alloy, and is directly cooled by forming a flow path through which cooling water passes. The welding torch WT is moved relative to the base material 2 while being held by a normal robot (not shown). A mig arc 3 a is generated between the tip of the welding wire 1 a and the base material 2. Between the plasma electrode 1 b and the base material 2, a plasma arc 3 b thermally generated by the plasma gas 62 is generated. Therefore, the MIG arc 3a is in a state of being surrounded by the plasma arc 3b. Therefore, the plasma arc 3b has an action of restraining the shape of the MIG arc 3a from spreading.

  The MIG welding power source PSM is a power source for energizing the MIG welding current Iwm by applying the MIG welding voltage Vwm between the welding wire 1 a and the base material 2 via the power supply tip 4. A feed control signal Fc is sent from the MIG welding power source PSM to the feed motor WM, and the feed speed of the welding wire 1a is controlled. When the MIG welding voltage Vwm is applied from the MIG welding power source PSM, the welding wire 1a is set to the + side. The MIG welding power supply PSM is a power supply having a constant voltage characteristic, and is controlled so that the MIG welding voltage Vwm is equal to a predetermined voltage setting signal Vr (not shown). Further, the value of the MIG welding current Iwm is determined by the feeding speed of the welding wire 1a.

  The plasma welding power source PSP is a power source for energizing the plasma welding current Iwp by applying a plasma welding voltage Vwp between the plasma electrode 1b and the base material 2. When the plasma welding voltage Vwp is applied from the plasma welding power source PSP, the plasma electrode 1b is set to the + side. The plasma welding power source PSP is a power source having a constant current characteristic, and is controlled so that the plasma welding current Iwp becomes a predetermined value.

  The plasma welding current setting circuit IWPR outputs a predetermined plasma welding current setting signal Iwpr to the MIG welding power source PSM and the plasma welding power source PSP. The plasma welding current setting signal Iwpr is a signal for setting the plasma welding current Iwp. The plasma welding current setting circuit IWPR is provided in the robot controller for robot welding.

Waveform diagrams of the MIG welding current Iwm, the MIG welding voltage Vwm, and the plasma welding current Iwp are the same as those in FIG. However, a pulse waveform may be used for the plasma welding current Iwp.
In the present embodiment, the fluctuation range ΔVc for removing the abnormal voltage varies depending on the value of the plasma welding current Iwp. This is different from the prior art. Hereinafter, this point will be described.

  FIG. 2 is a diagram showing the relationship between the plasma welding current Iwp and the fluctuation range ΔVc. The horizontal axis of the figure shows the plasma welding current Iwp (A), and shows a range of 50 to 150 A that is often used in practice. The vertical axis represents the fluctuation range ΔVc (V). In this case, an aluminum alloy wire having a diameter of 1.2 mm is used as the welding wire. Further, the peak current Ip = 280 A, the base current Ib = 30 A, the peak rising period Tup = 0.4 ms, the peak period Tp = 0.8 ms, and the peak falling period Tdw = 0.8 ms.

  As shown in the figure, when the plasma welding current Iwp = 50A, the variation range ΔVc = 1.0V, when Iwp = 100A, ΔVc = 1.5V, and when Iwp = 150A, ΔVc = 2.0V. That is, as the plasma welding current Iwp increases, the fluctuation range ΔVc also increases. The reason for this will be described later. Although not shown, when the plasma welding current Iwp = 0 A, that is, in the same manner as the normal MIG pulse welding in which no plasma arc is generated and only the MIG arc is generated, the fluctuation range ΔVc = 0.5V. And the minimum value. The fluctuation range calculation function shown in the figure is desirably set to an appropriate value by experiment according to the welding conditions such as the state of the participation coating of the base material, the material of the welded joint and the welding wire, the diameter, and the welding speed.

  The reason why the fluctuation range is increased in proportion to the value of the plasma welding current Iwp is as follows. As described above, in plasma MIG welding, the MIG arc is encased in the plasma arc, and the MIG arc is constrained from the plasma arc. For this reason, even if the oxide film on the surface of the base material immediately below the welding wire is removed by the cleaning action of the MIG arc, the range in which the cathode spot of the MIG arc moves in search of the oxide film on the periphery thereof is limited. As a result, the movement range of the cathode spot of the MIG arc is limited by the restraining force from the plasma arc, so that the magnitude and frequency of occurrence of the abnormal voltage are reduced. Further, the restraining force of the plasma arc is proportional to the value of the plasma welding current Iwp. That is, as the value of the plasma welding current Iwp increases, the force of the plasma arc restraining the MIG arc becomes stronger. As a result, the movement range of the cathode spot of the MIG arc is further limited, and the magnitude of the abnormal voltage is increased. And the frequency of occurrence is further reduced. In addition to this, when the value of the plasma welding current Iwp increases, the average value of the MIG welding current Iwm is often set to a large value. For this reason, the voltage fluctuation accompanying the fluctuation | variation of the arc length mentioned above also becomes large. Therefore, by increasing the fluctuation range ΔVc as the value of the plasma welding current Iwp is increased, the voltage fluctuation accompanying the fluctuation of the arc length can be accurately detected under the condition that the influence of the abnormal voltage is small. become.

  FIG. 3 is a block diagram of the MIG welding power source PSM constituting the above-described FIG. 1 in the first embodiment. Hereinafter, each block will be described with reference to FIG.

  The power supply main circuit PM receives an award power supply (not shown) such as a three-phase 200V and performs output control such as inverter control in accordance with a current error amplification signal Ei described later to obtain the MIG welding voltage Vwm and the MIG welding current Iwm. Output. Although not shown, the power supply main circuit PM includes a primary rectifier circuit that rectifies commercial power, a capacitor that smoothes the rectified direct current, an inverter circuit that converts the smoothed direct current into high frequency alternating current, and high frequency alternating current PWM modulation control according to an inverter transformer that steps down the voltage to a voltage value suitable for arc welding, a secondary rectifier circuit that rectifies the stepped-down high-frequency alternating current, a reactor that smoothes the rectified direct current, and a current error amplification signal Ei described later And a drive circuit for driving the inverter circuit based on the result. The welding wire 1 a is fed through the power feed tip 4 by a feed roll 7 coupled to a feed motor WM, and a mig arc 3 a is generated between the welding wire 1 a and the base material 2. The structure of the welding torch is as shown in FIG. 1, and is shown here in a simplified manner.

  As described above with reference to FIG. 1, the plasma welding current setting circuit IWPR provided outside the MIG welding power source PSM outputs a predetermined plasma welding current setting signal Iwpr. The voltage detection circuit VD detects the MIG welding voltage Vwm and outputs a MIG welding voltage detection signal Vd. The fluctuation range setting circuit ΔVC outputs the fluctuation range setting signal ΔVc based on a predetermined fluctuation range calculation function as described above with reference to FIG. 2 with the plasma welding current setting signal Iwpr as an input. The MIG welding voltage limit value calculation circuit FT limits the MIG welding voltage detection signal Vd to a fluctuation range Vc ± ΔVc determined by a reference voltage waveform signal Vc, which will be described later, and the fluctuation range setting signal ΔVc. The limit value signal Vft is output. The voltage moving average value calculation circuit VRA receives the MIG welding voltage limit value signal Vft and calculates the peak voltage moving average value signal Vpr and the base voltage moving average value signal Vbr as described above with reference to FIG. These calculation methods are performed based on the above-described equations (21) and (22). The reference voltage waveform setting circuit VC receives the peak voltage moving average value signal Vpr and the base voltage moving average value signal Vbr, and outputs the reference voltage waveform signal Vc as described above with reference to FIG. The setting of the reference voltage waveform signal Vc is performed by the above-described equations (31) to (34).

  The voltage integration circuit SV integrates the MIG welding voltage limit value signal Vft from the start of each pulse period (1 / t) ∫Vft · dt, and outputs a voltage integration value signal Sv. Here, t is the elapsed time (seconds) from the start time of each pulse period. Therefore, the value of the voltage integral value signal Sv is calculated as the average value of the MIG welding voltage limit value signal Vft. The voltage setting circuit VR outputs a predetermined voltage setting signal Vr. The comparison circuit CM compares the voltage integrated value signal Sv and the voltage setting signal Vr, and outputs a pulse period signal Tf that is at a high level for a short time in order to end the pulse period at the same time. Output. Sv = Vr means that the average value of the MIG welding voltage limit value signal Vft in each pulse period is equal to the value of the voltage setting signal Vr. In this way, the arc length control described above is performed. Therefore, the interval at which the pulse period signal Tf changes to the high level for a short time is the length of each pulse period.

  The elapsed time measuring circuit ST measures the elapsed time from the time when the pulse period signal Tf changes to the high level (the start time of each pulse period), and outputs the elapsed time signal St. The peak current setting circuit IPR outputs a predetermined peak current setting signal Ipr. The base current setting circuit IBR outputs a predetermined base current setting signal Ibr. The current control setting circuit IRC receives the elapsed time signal St and receives a current control setting signal that rises from the value of the base current setting signal Ibr to the value of the peak current setting signal Ipr during the peak rising period Tup. Irc is output, the value of the peak current setting signal Ipr is output as the current control setting signal Irc during the subsequent peak period Tp, and the value of the peak current setting signal Ipr is output during the subsequent peak falling period Tdw. The current control setting signal Irc that falls to the value of the base current setting signal Ibr is output, and during the subsequent base period Tb, the value of the base current setting signal Ibr is output as the current control setting signal Irc. The current detection circuit ID detects the MIG welding current Iwm and outputs a current detection signal Id. The current error amplification circuit EI amplifies an error between the current control setting signal Irc and the current detection signal Id and outputs a current error amplification signal Ei. The feed control circuit FC outputs a feed control signal Fc for feeding the welding wire 1a at a preset feed speed set value to the feed motor WM. By these blocks, the MIG welding current Iwm as described above with reference to FIG. 7 corresponding to the current control setting signal Irc is applied.

  FIG. 4 is a block diagram of plasma welding power supply PSP constituting the above-described FIG. 1 in the first embodiment. Hereinafter, each block will be described with reference to FIG.

  The power supply main circuit PM receives an award power supply (not shown) such as three-phase 200V as an input, performs output control such as inverter control in accordance with a current error amplification signal Ei described later, and outputs a plasma welding current Iwp. The plasma welding current Iwp is energized through the plasma electrode 1b, the plasma arc 3b, and the base material 2. The structure of the welding torch is as shown in FIG. 1 described above, but is shown here in a simplified manner.

  As described above with reference to FIG. 1, the plasma welding current setting circuit IWPR provided outside the plasma welding power source PSP outputs a predetermined plasma welding current setting signal Iwpr. The current detection circuit ID detects the plasma welding current Iwp and outputs a current detection signal Id. The current error amplification circuit EI amplifies an error between the plasma welding current setting signal Iwpr and the current detection signal Id and outputs a current error amplification signal Ei. By performing output control of the welding power source according to the current error amplification signal Ei, the DC plasma welding current Iwp described above with reference to FIG. Since the plasma welding power source PSP described above is output-controlled so that the plasma welding current Iwp is equal to the value of the plasma welding current setting signal Iwpr, it is a power source with constant current characteristics. When the plasma welding current setting signal Iwpr is changed to a pulse wave shape, the plasma welding current Iwp has a pulse waveform. In this case, the fluctuation range ΔVc changes according to each value of the plasma welding current Iwp of the pulse waveform.

  According to the first embodiment described above, by changing the fluctuation range ΔVc according to the value of the plasma welding current Iwp, it is possible to suppress the abnormal voltage from being superimposed on the MIG welding voltage, and to increase the arc length. It is possible to accurately detect voltage fluctuations accompanying fluctuations. For this reason, precise arc length control can be performed and good welding quality can be obtained.

[Embodiment 2]
In the plasma MIG welding method according to Embodiment 2 of the present invention, when the value of the MIG welding current Iwm is greater than or equal to the reference current value Ith, the variation range is set to the first variation range ΔVc1 and is less than the reference current value Ith. Is set to the second fluctuation range ΔVc2. Thus, the point which changes the value of a fluctuation range according to the value of the MIG welding current Iwm is different from Embodiment 1 mentioned above. Hereinafter, the second embodiment will be described.

  The block diagram of the welding apparatus for implementing Embodiment 2 is the same as FIG. 1 mentioned above. However, the figure which shows the change of the fluctuation range with respect to the plasma welding current Iwp corresponding to FIG. 2 is different. Further, some of the blocks of the MIG welding power source PSM described above with reference to FIG. 3 are different. The block diagram of the plasma welding power source PSP described above with reference to FIG. 4 is the same. Hereinafter, differences from the first embodiment will be described.

  FIG. 5 is a diagram showing the relationship between the plasma welding current Iwp and the first variation range ΔVc1 and the second variation range ΔVc2. The horizontal axis of the figure shows the plasma welding current Iwp (A), and shows a range of 50 to 150 A that is often used in practice. The vertical axis represents the variation range ΔVc (V), practice indicates the change in the first variation range ΔVc1, and the broken line indicates the change in the second variation range ΔVc2. When the value of the MIG welding current Iwm is equal to or greater than the reference current value Ith, the first variation range ΔVc1 is used, and when it is less than the second variation range ΔVc2. The welding conditions are the same as those in FIG. That is, the case where an aluminum alloy wire having a diameter of 1.2 mm is used as the welding wire. Further, the peak current Ip = 280 A, the base current Ib = 30 A, the peak rising period Tup = 0.4 ms, the peak period Tp = 0.8 ms, and the peak falling period Tdw = 0.8 ms. The reference current value Ith is set to 155A, which is an intermediate value between the peak current Ip and the base current Ib.

  As shown in the figure, when the plasma welding current Iwp = 50A, the first fluctuation range ΔVc1 = 1.5V and the second fluctuation range ΔVc2 = 1.0V, and when Iwp = 100A, ΔVc1 = 2.0V and ΔVc2 = 1. .5V, and when Iwp = 150A, ΔVc1 = 2.5V and ΔVc2 = 2.0V. That is, as the plasma welding current Iwp increases, the first fluctuation range ΔVc1 and the second fluctuation range ΔVc2 both increase, and when the values of the plasma welding current Iwp are the same, the first fluctuation range ΔVc1. Is larger than the second variation range ΔVc2. The reason for this will be described later. The first variation range calculation function and the second variation range calculation function shown in the figure are appropriate values by experiments according to welding conditions such as the state of the participation coating of the base material, the material of the welded joint, the welding wire, the diameter, and the welding speed. It is desirable to be set to.

  As described above, as the value of the plasma welding current Iwp increases, the force with which the plasma arc restrains the MIG arc increases. Therefore, by increasing the fluctuation range, the voltage fluctuation accompanying the fluctuation of the arc length is further increased. It can be detected accurately. As the value of the MIG welding current Iwm increases, the rigidity of the MIG arc itself increases. This is because the force for contracting the MIG arc increases in proportion to the value of the MIG welding current Iwm. In other words, when the value of the MIG welding current Iwm increases, the force with which the MIG arc restrains itself increases. For this reason, when the value of the MIG welding current Iwm is equal to or greater than the reference current value Ith, the value of the fluctuation range is increased to suppress the superposition of abnormal voltage, and only the voltage fluctuation accompanying the fluctuation of the arc length is more increased. More accurate detection is possible. Therefore, when the value of the MIG welding current Iwm is equal to or greater than the reference current value Ith, the value of the fluctuation range is set larger than that when it is less than the reference current value Ith, and is set to the first fluctuation range ΔVc1. The reference current value Ith is set to an intermediate value Ith = (Ip + Ib) / 2 between the peak current Ip and the base current Ib, for example. This reference current value Ith is set to an appropriate value by experiment.

  FIG. 6 is a block diagram of the MIG welding power source PSM according to the second embodiment. In the figure, the same blocks as those in FIG. 3 described above are denoted by the same reference numerals, and description thereof is omitted. In the figure, the fluctuation range setting circuit ΔVC in FIG. 3 is replaced with a current value interlocking fluctuation range setting circuit ΔVCI indicated by a broken line. Hereinafter, this block will be described with reference to FIG.

  The current value interlocking fluctuation range setting circuit ΔVCI receives the plasma welding current setting signal Iwpr and the current control setting signal Irc as input, and when the current control setting signal Irc is greater than or equal to the reference current value Ith as described above with reference to FIG. A fluctuation range setting signal ΔVc is output based on the determined first fluctuation range calculation function, and when the current control setting signal Irc is less than the reference current value Ith, the fluctuation range is set based on the predetermined second fluctuation range calculation function. The signal ΔVc is output.

  According to the second embodiment described above, in addition to the effects of the first embodiment, when the value of the MIG welding current is greater than or equal to the reference current value, the first variation range is set, and when it is less, the second variation. By setting the range, it is possible to more accurately detect the voltage fluctuation accompanying the fluctuation of the arc length without being affected by the abnormal voltage. For this reason, more precise arc length control can be performed.

  In the first and second embodiments, the case where the arc length control is performed by the frequency modulation method is illustrated, but as described above, the pulse width modulation method may be used. In this case, the peak period Tp is feedback controlled.

DESCRIPTION OF SYMBOLS 1a Welding wire 1b Plasma electrode 2 Base material 3a Mig arc 3b Plasma arc 4 Feed tip 51 Plasma nozzle 52 Shield gas nozzle 61 Center gas 62 Plasma gas 63 Shield gas 7 Feed roll CM Comparison circuit EI Current error amplification circuit Ei Current error amplification signal FC Feed control circuit Fc Feed control signal FT MIG welding voltage limit value calculation circuit Ib Base current IBR Base current setting circuit Ibr Base current setting signal ID Current detection circuit Id Current detection signal Ip Peak current IPR Peak current setting circuit Ipr Peak current setting Signal IRC Current control setting circuit Irc Current control setting signal Ith Reference current value Iwm Mig welding current Iwp Plasma welding current IWPR Plasma welding current setting circuit Iwpr Plasma welding current setting signal PM Power supply main circuit PSM Mig welding power supply PSP Plasma melting Power ST elapsed time measuring circuit St elapsed time signal SV voltage integrating circuit Sv voltage integral value signal t elapsed time ta elapsed time Tb base period Tdw peak falling period Tf pulse cycle (signal)
Tp Peak period Tup Peak rising period Vb Base voltage Vbc Reference base voltage value Vbf Base voltage limit value Vbr Base voltage moving average value (signal)
VC Reference voltage waveform setting circuit Vc Reference voltage waveform (signal)
VD voltage detection circuit Vd MIG welding voltage detection signal Vft MIG welding voltage limit value (signal)
Vp Peak voltage Vpc Reference peak voltage value Vpf Peak voltage limit value Vpr Peak voltage moving average value (signal)
VR voltage setting circuit Vr voltage setting signal VRA voltage moving average value calculation circuit Vwm MIG welding voltage Vwp plasma welding voltage WM feed motor WT welding torch ΔVC fluctuation range setting circuit ΔVc fluctuation range (setting signal)
ΔVc1 First variation range ΔVc2 Second variation range ΔVCI Current value interlocking variation range setting circuit

Claims (2)

A MIG arc is generated by applying a MIG welding voltage between the welding wire and the base metal fed through the welding torch and energizing the MIG welding current.
A transition current rising from the base current to the peak current is applied during the peak rising period, the peak current is applied during the subsequent peak period, and the peak current is decreased from the peak current during the subsequent peak falling period. Energize the transition current, energize the base current during the subsequent base period, energize the MIG welding current by repeating these energization as one pulse period,
The MIG welding voltage is detected, and the MIG welding voltage limit value is calculated by using the MIG welding voltage detection value as an input and limiting the reference voltage waveform within a predetermined fluctuation range with the center voltage value as a center voltage value. Perform the arc length control of the MIG arc by changing the pulse period or the peak period based on the value,
The MIG welding voltage limit value during the peak period is moving averaged over the past predetermined period to calculate a peak voltage moving average value, and the MIG welding voltage limit value during the base period is averaged over the past predetermined period. The base voltage moving average value is calculated, and the reference voltage waveform is set to a transition voltage that rises from the base voltage moving average value to the peak voltage moving average value during the peak rising period, and during the subsequent peak period, Set to the peak voltage moving average value, set to a transition voltage falling from the peak voltage moving average value to the base voltage moving average value during the subsequent peak falling period, and then to the base voltage during the subsequent base period Set to moving average value,
In the plasma MIG welding method of generating a plasma arc by energizing a plasma welding current between the welding torch and the base material through a gas supplied so as to surround the welding wire,
Changing the fluctuation range according to the value of the plasma welding current;
The plasma MIG welding method characterized by the above-mentioned. The fluctuation range is set to the first fluctuation range when the value of the MIG welding current is greater than or equal to the reference current value, and is set to the second fluctuation range when the value of the MIG welding current is less than the reference current value. The first fluctuation range and the second fluctuation range are changed according to the value of the plasma welding current, and the value of the plasma welding current and the MIG when the value of the MIG welding current is equal to or greater than the reference current value. When the value of the welding current is less than the reference current value and the value of the plasma welding current is the same value, the first fluctuation range is set to a value larger than the second fluctuation range,
The plasma MIG welding method according to claim 1.

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