JP2012030281A - Plasma mig welding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent occurrence of poor weld by change of a plasma arc associated with wear of a plasma electrode, in plasma MIG welding.SOLUTION: Between a weld wire and a base material, a MIG arc is generated by passing a MIG weld current Iwm including a peak current Ip during a peak period Tp and a base current Ib during a base period Tb for one pulse period Tf, and a plasma arc is generated by passing a plasma weld current Iwp as a DC between the plasma electrode arrange to surround the weld wire and the base material. A plasma weld voltage Vwp (an inductive peak voltage Vpp and an inductive base voltage Vbb) during a specific period (a peak period Tp and a base period Tb) of the pulse period Tf is detected at each pulse period Tf, and deviation of the plasma arc is determined depending on continuation for a predetermined period or more of a state where the detected value has increased or a state where the detected value has decreased, thereby issuing an alarm and stopping the welding.

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. A hollow plasma electrode is arranged so as to surround the welding wire, and a plasma such as argon is supplied, and a plasma welding current is passed between the plasma electrode and the base material through this gas to generate plasma. Generate an arc. The MIG arc is generated between the welding wire fed through the axis of the welding torch and the base material, and a plasma arc is generated so as to surround the MIG arc. Therefore, the MIG arc is encased in a plasma arc. 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 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. On the other hand, a constant direct current is often 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. 8 is a waveform diagram showing a conventional plasma MIG welding method. (A) shows the MIG welding current Iwm, (B) shows the MIG welding voltage Vwm, (C) shows the plasma welding current Iwp, and (D) shows the plasma welding voltage Vwp. Show. Hereinafter, a description will be given with reference to FIG.

  In the figure, the period from time t1 to t3 represents the (n-1) th pulse period Tf (n-1), and the period from time t3 to t5 represents the nth pulse period Tf (n). The (n−1) th pulse cycle Tf (n−1) is the (n−1) th peak period Tp (n−1) at times t1 to t2 and the (n−1) th base period Tb at times t2 to t3. (n-1). The n-th pulse period Tf (n) is formed from the n-th peak period Tp (n) from time t3 to t4 and the n-th base period Tb (n) from time t4 to t5.

  As shown in FIG. 9A, in the (n-1) th pulse cycle Tf (n-1), a predetermined peak current Ip is applied during the peak period Tp (n-1) from time t1 to t2. During the base period Tb (n−1) from time t2 to t3, a predetermined base current Ib is energized. Therefore, the MIG welding current Iwm is formed from the peak current Ip and the base current Ib. Then, as shown in FIG. 5B, in the (n-1) th pulse period Tf (n-1), the peak voltage Vp (n-1) proportional to the arc length during the peak period Tp (n-1). ) Is applied between the welding wire and the base metal, and a base voltage Vb (n-1) proportional to the arc length is applied during the base period Tb (n-1). Therefore, the MIG welding voltage Vwm is formed from the peak voltage Vp and the base voltage Vb. The same applies to the nth pulse cycle Tf (n). Here, the peak current Ip and the base current Ib in the n−1th pulse cycle Tf (n−1) have the same values as the peak current Ip and the base current Ib in the nth pulse cycle Tf (n), respectively. Be controlled. On the other hand, when the arc generation state is stable, the peak voltage Vp (n-1) and the base voltage Vb (n-1) in the (n-1) th pulse period Tf (n-1) are nth. The peak voltage Vp (n) and the base voltage Vb (n) in the second pulse period Tf (n) are substantially equal to each other.

  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 approximately proportional to the arc length, and the pulse period Tf is set so that the average value of the MIG welding voltage Vwm becomes equal to a predetermined voltage setting value. Be controlled. The average value of the MIG welding voltage Vwm is generated by passing the MIG welding voltage Vwm through a low-pass filter. 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.

  In addition to frequency modulation control, pulse width modulation control may be used as an arc length control method. In this pulse width modulation control, the pulse period Tf, the peak current Ip, and the base current Ib are set to predetermined values and become pulse parameters. Then, the peak period Tp (pulse width) is controlled so that the average value of the MIG welding voltage Vwm is equal to the voltage setting value.

  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. Then, as shown in FIG. 4D, in the (n-1) th pulse period Tf (n-1), an induced peak whose voltage value is increased by the influence of mig arc during the peak period Tp (n-1). A voltage Vpp (n-1) is applied between the plasma electrode and the base material, and an induced base voltage Vbb (n-1) whose voltage value is lowered due to the influence of the MIG arc during the base period Tb (n-1). Apply. Therefore, the MIG welding voltage Vwm is formed from the induced peak voltage Vpp and the induced base voltage Vbb. Since the plasma welding current Iwp is a constant value of direct current, the plasma welding voltage Vwp should be essentially a constant value substantially proportional to the arc length. Nevertheless, the reason why the plasma welding voltage Vwp becomes a pulse waveform in synchronization with the peak period Tp and the base period Tb of the MIG arc is as follows. The MIG arc has an expanded shape during the peak period Tp in which the peak current Ip having a large current value is applied, and a contracted shape in the base period Tb in which the base current Ib having a small current value is applied. As described above, the plasma arc is generated so as to wrap around the MIG arc. For this reason, the shape of the plasma arc is also affected by the change in the shape of the MIG arc. Due to the change of the plasma arc, the plasma welding voltage Vwp changes in a pulse shape. Therefore, since the plasma welding voltage Vwp is changed by being induced by the change of the MIG arc, the expressions of induced peak voltage Vpp and induced base voltage Vbb are used. The same applies to the nth pulse cycle Tf (n). In the state where the arc generation state is stable, the induced peak voltage Vpp (n-1) and the induced base voltage Vbb (n-1) in the (n-1) th pulse period Tf (n-1) are nth. The induced peak voltage Vpp (n) and the induced base voltage Vbb (n) in the second pulse period Tf (n) are substantially equal to each other.

JP 2008-229641 A

  As described above, in plasma MIG welding, a plasma arc is generated between a plasma electrode which is a non-consumable electrode and a base material. For this reason, if the welding is repeated many times and the welding time becomes long, the tip of the plasma electrode gradually wears out and the shape of the tip is deformed. When the deformation of the tip shape of the plasma electrode proceeds relatively evenly and the symmetry of the tip shape is maintained, the generation state of the plasma arc does not change abruptly. However, the tip of the plasma electrode may be deformed into a distorted shape. When such distorted deformation proceeds, the plasma arc is suddenly deflected and generated. When the plasma arc is deflected, the state of occurrence of the MIG arc contained in the plasma arc also changes, so that the bead appearance becomes non-uniform. Furthermore, if the plasma arc is deflected, a deviation occurs in the target position to the welding location, which may result in poor welding.

  Accordingly, an object of the present invention is to provide a plasma MIG welding method capable of determining the deflection of the plasma arc accompanying the consumption of the plasma electrode and preventing the occurrence of poor welding due to the deflection of the plasma arc.

In order to solve the above-mentioned problem, the invention of claim 1 is characterized in that a peak current during a peak period and a base current during a base period are defined as one pulse period between a welding wire and a base material fed through a welding torch. A MIG arc is generated by energizing the MIG welding current to be generated, and a plasma arc is generated by energizing a DC plasma welding current between the plasma electrode arranged so as to surround the welding wire and the base material. In the plasma MIG welding method to be performed,
The plasma welding voltage during a specific period of the pulse period is detected for each pulse period, and the state in which the detected value increases or decreases continues for a predetermined period or more to determine the deflection of the plasma arc, and the plasma arc deflection When an error is detected, an alarm is issued.
This is a plasma MIG welding method.

In the invention of claim 2, the plasma welding voltage in the specific period of the pulse period is the plasma welding voltage during the peak period.
The plasma MIG welding method according to claim 1.

In the invention of claim 3, the plasma welding voltage in the specific period of the pulse period is the plasma welding voltage in the base period.
The plasma MIG welding method according to claim 1.

In the invention of claim 4, the plasma welding voltage in the specific period of the pulse period is the plasma welding voltage during the peak period and the plasma welding voltage during the base period.
The plasma MIG welding method according to claim 1.

When the plasma arc deflection is determined, the plasma welding current is increased to correct the plasma arc deflection.
It is a plasma MIG welding method of any one of Claims 1-4 characterized by the above-mentioned.

The invention of claim 6 performs the increase of the plasma welding current for a predetermined increase period.
The plasma MIG welding method according to claim 5.

The invention of claim 7 increases the plasma welding current until the deflection of the plasma arc is corrected.
The plasma MIG welding method according to claim 5.

  According to the present invention, it is possible to determine the deflection of the plasma arc accompanying the consumption of the plasma electrode from the fluctuation of the plasma welding voltage. And if the deflection | deviation of a plasma arc is discriminate | determined, generation | occurrence | production of the welding defect resulting from the deflection | deviation of a plasma arc can be prevented by issuing a warning.

It is a wave form diagram which shows the plasma MIG welding method which concerns on Embodiment 1 of this invention. It is a wave form diagram different from FIG. 1 which shows the plasma MIG welding method which concerns on Embodiment 1 of this invention. It is a block diagram of the welding apparatus for enforcing the plasma MIG welding method which concerns on Embodiment 1 of this invention. It is a block diagram of the MIG welding power supply PSM which comprises the welding apparatus of FIG. It is a block diagram of the plasma welding power supply PSP which comprises the welding apparatus of FIG. It is a wave form diagram which shows the plasma MIG welding method which concerns on Embodiment 2 of this invention. 6 is a block diagram of a plasma welding power source PSP according to Embodiment 2. FIG. It is a wave form diagram which shows the plasma MIG welding method of a prior art.

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

[Embodiment 1]
In the invention according to the first embodiment, the plasma welding voltage during a specific period of the pulse period is detected for each pulse period, and the state in which the detected value increases or decreases continues for a predetermined period or longer to determine the plasma arc deflection. When the deflection of the plasma arc is determined, an alarm is issued. Hereinafter, the first embodiment will be described.

  FIG. 1 is a waveform diagram showing a plasma MIG welding method according to Embodiment 1 of the present invention. (A) shows the MIG welding current Iwm, (B) shows the MIG welding voltage Vwm, (C) shows the plasma welding current Iwp, and (D) shows the plasma welding voltage Vwp. Show. Hereinafter, a description will be given with reference to FIG.

  This figure shows waveforms corresponding to five cycles from the (n-3) th pulse cycle Tf (n-3) to the (n + 1) th pulse cycle Tf (n + 1). The (n-3) th pulse cycle Tf (n-3) is formed from the (n-3) th peak period Tp (n-3) and the base period Tb (n-3). The same applies to other periods. In the figure, the plasma arc is deflected due to the distorted deformation of the plasma electrode in the nth pulse period Tf (n). The current point in the figure is the end point of the nth pulse cycle Tf (n) indicated by time tn.

  As shown in FIG. 5A, the MIG welding current Iwm is formed from a predetermined peak current Ip during the peak period and a predetermined base current Ib during the base period in each period. Since the peak current Ip and the base current Ib are controlled by constant current, they have the same value in each period. The method for setting the peak current Ip and the base current Ib is the same as that in the prior art. The method for setting the peak period Tp and the base period Tb is also the same as in the prior art. That is, when the output control (arc length control) of the welding power source is frequency modulation control, the peak period Tp becomes a predetermined value, and the base period Tb changes every moment by feedback control. On the other hand, in the pulse width modulation control, the pulse period Tf becomes a predetermined value, and the peak period Tp changes every moment by feedback control.

  As shown in FIG. 5B, the MIG welding voltage Vwm in the n-3th pulse period Tf (n-3) is the peak voltage Vp during the n-3th peak period Tp (n-3). (n-3) and the base voltage Vb (n-3) in the (n-3) th base period Tb (n-3). The same applies to other periods. Since the peak voltage and the base voltage in each cycle are values corresponding to the arc length of the MIG arc (arc generation state), each value is a different value. However, when the MIG arc generation state is in a stable steady state, the peak voltage and the base voltage in each period are substantially the same value. As described above, when plasma arc deflection occurs in the n-th pulse period Tf (n), the subsequent peak voltages Vp (n), Vp (n + 1)... And base voltages Vb (n), Vb ( n + 1) ... is affected, but the fluctuation is small.

  As shown in FIG. 5C, the plasma welding current Iwp has a DC current waveform having a predetermined constant value. The plasma welding current Iwp is constant current controlled. The plasma welding current Iwp is set to an appropriate value according to the material of the base material, the plate thickness, the welding speed, and the like.

  As shown in FIG. 4D, the plasma welding voltage Vwp in the n-3th pulse period Tf (n-3) is the induced peak voltage during the n-3th peak period Tp (n-3). It is formed from Vpp (n-3) and the induced base voltage Vbb (n-3) during the (n-3) th base period Tb (n-3). The same applies to other periods. As described above, the induced peak voltage and the induced base voltage in each period are voltages that change in a pulse shape in synchronization with the change in the shape of the MIG arc. In other words, the MIG arc has a shape that is widened by energizing the peak current Ip having a large current value, and a shape that is contracted by energizing the base current having a small current value. Induced by the periodic change in the shape of the MIG arc, the plasma welding voltage Vwp changes in a pulse shape. Therefore, when the MIG arc and the plasma arc are in a stable steady state, the induced peak voltage Vpp and the induced base voltage Vbb have substantially the same value. As described above, when the plasma arc is deflected in the nth pulse period Tf (n), induced peak voltages Vpp (n), Vpp (n + 1)... And induced base voltage Vbb (n), Vbb (n + 1)... Increases together. That is, the plasma welding voltage Vwp after the nth pulse period Tf (n) has a waveform shifted in the increasing direction. The reason for this is as follows. The plasma arc is usually generated in a symmetrical shape in the central axis direction of the welding torch. When the plasma arc is deflected, its shape is shifted from the central axis direction and becomes asymmetric. As a result, since the arc length of the plasma arc becomes longer, the plasma welding voltage Vwp is shifted in the increasing direction. This is the first pattern of plasma arc deflection. The second pattern will be described later with reference to FIG. Once plasma arc deflection occurs, the deflection state is often maintained for at least several hundred ms. In addition, the deflection of the plasma arc may not be eliminated as it is.

  FIG. 2 is a waveform diagram different from FIG. 1 showing the plasma MIG welding method according to Embodiment 1 of the present invention. (A) shows the MIG welding current Iwm, (B) shows the MIG welding voltage Vwm, (C) shows the plasma welding current Iwp, and (D) shows the plasma welding voltage Vwp. Show. This figure corresponds to FIG. 1 described above, and only the plasma welding voltage Vwp after the n-th pulse period Tf (n) is different, so the explanation of other points is omitted. Hereinafter, this different point will be described with reference to FIG.

  As in FIG. 1, the figure shows waveforms corresponding to five cycles from the (n-3) th pulse cycle Tf (n-3) to the (n + 1) th pulse cycle Tf (n + 1). In this figure, similarly to FIG. 1, the deflection of the plasma arc due to the distorted deformation of the plasma electrode occurs in the nth pulse period Tf (n). The current point in the figure is the end point of the nth pulse cycle Tf (n) indicated by time tn.

  As shown in FIG. 4D, the plasma welding voltage Vwp in the n-3th pulse period Tf (n-3) is the induced peak voltage during the n-3th peak period Tp (n-3). It is formed from Vpp (n-3) and the induced base voltage Vbb (n-3) during the (n-3) th base period Tb (n-3). The same applies to other periods. As described above, the induced peak voltage and the induced base voltage in each period are voltages that change in a pulse shape in synchronization with the change in the shape of the MIG arc. When the plasma arc is deflected in the nth pulse period Tf (n), induced peak voltages Vpp (n), Vpp (n + 1)... And induced base voltages Vbb (n), Vbb (n +) thereafter. 1) are both reduced from FIG. That is, unlike the case of FIG. 1, the plasma welding voltage Vwp after the nth pulse period Tf (n) has a waveform shifted in a decreasing direction. The reason for this is as follows. The plasma arc is normally generated from the entire circumference of the plasma electrode having a hollow shape. However, if the consumption at the tip of the plasma electrode becomes significant and the plasma arc generation source is biased, the plasma arc contracts and the plasma welding voltage Vwp shifts in a decreasing direction. This is the second pattern of plasma arc deflection.

  1 and 2 described above, it can be seen that when the plasma arc is deflected, the plasma welding voltage Vwp is shifted in the increasing or decreasing direction. Therefore, based on this knowledge, in the present embodiment, the plasma arc deflection is determined by the following three methods. When the plasma arc deflection is determined, an alarm is issued because there is a risk of poor welding. Examples of alarms include lighting of an indicator lamp, sounding of an alarm sound, and output of an alarm signal to an external device.

(1) First deflection determination method A plasma welding voltage during a specific period in the n-th pulse period Tf (n) is detected. The plasma welding voltage for the specific period is the induced peak voltage Vpp (n) during the peak period and the induced base voltage Vbb (n) during the base period. The induced peak voltage Vpp (n) is a steady value or an average value during the peak period. The same applies to the induced base voltage Vbb (n). The moving average value of the detected values is a moving average value of a plurality of m detected values from the previous cycle Tf (n−1) to the previous cycle Tf (nm). Therefore, the moving average value Vppa of the induced peak voltage and the moving average value Vbba of the induced base voltage can be calculated by the following equations.
Vppa = (Vpp (nm) + ... + Vpp (n-1)) / m (1) Formula Vbba = (Vbb (nm) + ... + Vbb (n-1)) / m (2) where m Is an integer of 1 or more.
When | Vpp (n) −Vppa | ≧ Vt and | Vbb (n) −Vbba | ≧ Vt are established, it is determined that the plasma welding voltage has increased or decreased (increased or decreased). When this determination state continues for a predetermined determination period Tt or more, it is determined that plasma arc deflection has occurred. Thereafter, when the above is not established, the increase / decrease state returns to the original state, and it is determined that the change of the plasma arc has been eliminated. Here, the determination value Vt is a value predetermined as a positive value. Therefore, the determination value Vt becomes a threshold value. This determination value Vt is set to an appropriate value by experiment. For example, the determination value Vt is set to about 1 to 5V. The determination value may be set to a different value depending on the induced peak voltage and the induced base voltage. The determination period Tt is set to about 50 to 200 ms, for example. The number m of moving averages is set to, for example, about 50 to 400 so that the engine that performs the moving average is about 5 to 10 times the determination period Tt. The determination value Vt, the determination period Tt, and the moving average number m are set to appropriate values by experiments according to the material, diameter, feed speed, gas type, and the like of the welding wire.

(2) Second deflection discrimination method A plasma welding voltage during a specific period in the n-th pulse period Tf (n) is detected. The plasma welding voltage for a specific period is the induced peak voltage Vpp (n) during the peak period. The induced peak voltage Vpp (n) is a steady value or an average value during the peak period. When | Vpp (n) −Vppa | ≧ Vt is established, it is determined that the plasma welding voltage has been increased or decreased (increased or decreased), and this determined state continues for the determination period Tt or more. If so, it is determined that plasma arc deflection has occurred. Thereafter, when the above is not established, the increase / decrease state returns to the original state, and it is determined that the change of the plasma arc has been eliminated. The moving average value Vppa of the induced peak voltage is calculated by the above-described equation (1). The setting of the determination value Vt, the determination period Tt, and the moving average count m is the same as described above.

(3) Third deflection determination method A plasma welding voltage during a specific period in the n-th pulse cycle Tf (n) is detected. The plasma welding voltage for the specific period is the induced base voltage Vbb (n) during the base period. The induced base voltage Vbb (n) is a steady value or an average value during the base period. When | Vbb (n) −Vbba | ≧ Vt is established, it is determined that the plasma welding voltage has increased or decreased (increased or decreased), and this determined state continues for the determination period Tt or more. If so, it is determined that plasma arc deflection has occurred. Thereafter, when the above is not established, the increase / decrease state returns to the original state, and it is determined that the change of the plasma arc has been eliminated. The moving average value Vbba of the induced base voltage is calculated by the above equation (2). The setting of the determination value Vt, the determination period Tt, and the moving average count m is the same as described above.

  In the above-described deflection determination method, the plasma welding voltage in a specific period of the pulse period is detected for each pulse period, and it is determined whether the plasma welding voltage is in an increased state or a decreased state from fluctuations in the time series data. ing. The reason why the voltage value of the specific period of the pulse cycle is detected is that the plasma welding voltage is a waveform that changes in a pulse shape, and thus it is necessary to process and compare the voltage of the same period as time-series data. . It is also conceivable to use an average value of the plasma welding voltage (such as a low-pass filter processing value of the welding voltage, a smooth value) as the detection value. However, the ratio between the peak period and the base period forming the pulse period changes every moment by frequency modulation control for the MIG arc. That is, this ratio changes in order to maintain the MIG arc length at an appropriate value regardless of the plasma arc deflection. As a result, the average value of the plasma welding voltage varies regardless of the plasma arc deflection. Therefore, it is difficult to determine the deflection of the plasma arc based on the average value of the plasma welding voltage.

  FIG. 3 is a configuration diagram of a welding apparatus for performing the 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. These three systems of gas may be collectively expressed simply as gas.

  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. For this reason, the plasma arc 3b has the effect | action which restrains that the shape of the mig arc 3a spreads.

  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. This MIG welding current Iwm is formed from a peak current during the peak period and a base current during the base period, as shown in FIG. 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). The average value of the MIG welding current Iwm is determined by the feed speed of the welding wire 1a. Further, as will be described later with reference to FIG. 4, the MIG welding power source PSM outputs to the plasma welding power source PSP a peak period signal Tp that becomes High level during the peak period and Low level during the base engine.

  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. As will be described later with reference to FIG. 5, the plasma welding power source PSP has a built-in circuit for determining the occurrence of plasma arc deflection, and issues a warning when a deflection determination signal is output.

  FIG. 4 is a block diagram of the MIG welding power source PSM that constitutes the welding apparatus of FIG. 3 described above. Hereinafter, each block will be described with reference to FIG.

  The power supply main circuit PM receives a commercial power supply (not shown) such as three-phase 200V, performs output control such as inverter control according to a current error amplification signal Ei described later, and outputs a MIG welding voltage Vwm and a MIG welding current Iwm. To do. 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. 3 and is shown here in a simplified manner.

  The voltage detection circuit VD detects the MIG welding voltage Vwm and outputs a voltage detection signal Vd. The voltage average value calculation circuit VAV calculates an average value of the voltage detection signal Vd and outputs a voltage average value signal Vav.

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. The voltage setting circuit VR outputs a predetermined voltage setting signal Vr. The voltage error amplification circuit EV amplifies an error between the voltage setting signal Vr and the voltage average value signal Vav, and outputs a voltage error amplification signal Ev. The voltage / frequency conversion circuit VF outputs a pulse period signal Tf having a frequency corresponding to the value of the voltage error amplification signal Ev. The pulse period signal Tf is a trigger signal that becomes High level for a short time every pulse period.

  The peak period setting circuit TPR outputs a predetermined peak period setting signal Tpr. The peak period timer circuit TP generates a peak period signal Tp that is at a high level for a period determined by the value of the peak period setting signal Tpr when the pulse period signal Tf is at a high level. Output to PSP. The peak period is when the peak period signal Tp is at a high level, and the base period is when the peak period signal Tp is at a low level.

  The base current setting circuit IBR outputs a predetermined base current setting signal Ibr. The peak current setting circuit IPR outputs a predetermined peak current setting signal Ipr. The current setting control circuit IRC outputs the base current setting signal Ibr as the current setting control signal Irc when the peak period signal Tp is at the low level, and outputs the peak current setting signal Ipr as the current when the peak period signal Tp is at the high level. It is output as a setting control 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 setting control signal Irc and the current detection signal Id, and outputs a current error amplification signal Ei. The MIG welding current Iwm described above with reference to FIGS. 1 and 2 is energized by controlling the output of the welding power source in accordance with the current error amplification signal Ei. The MIG welding power source PSM described above is output controlled (frequency modulation control) with the pulse period changed so that the average value of the MIG welding voltage Vwm is equal to the value of the voltage setting signal Vr. Become. As described above, output control may be performed by pulse width modulation control so that the average value of the MIG welding voltage Vwm is equal to the value of the voltage setting signal Vr.

  FIG. 5 is a block diagram of the plasma welding power source PSP that constitutes the welding apparatus of FIG. 3 described above. Hereinafter, each block will be described with reference to FIG.

  The power supply main circuit PM receives a commercial power supply (not shown) such as a three-phase 200 V input, performs output control such as inverter control according to a current error amplification signal Ei described later, and outputs a plasma welding current Iwp and a plasma welding voltage Vwp. . 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. 3 described above, but is simplified here.

  The plasma welding current setting circuit IWPR outputs a plasma welding current setting signal Iwpr having a predetermined steady value. The plasma welding current detection circuit IDP detects the plasma welding current Iwp and outputs a plasma welding current detection signal Idp. The current error amplification circuit EI amplifies an error between the plasma welding current setting signal Iwpr and the plasma welding current detection signal Idp and outputs a current error amplification signal Ei. By controlling the output of the welding power source in accordance with the current error amplification signal Ei, a constant value (steady value) of plasma welding current Iwp is energized as described above with reference to FIGS. Therefore, the plasma welding power source PSP is controlled so that the plasma welding current Iwp is equal to the value of the plasma welding current setting signal Iwpr, and thus becomes a power source with constant current characteristics.

  The plasma welding voltage detection circuit VDP detects the plasma welding voltage Vwp and outputs a plasma welding voltage detection signal Vdp. The voltage moving average calculation circuit VRA receives the plasma welding voltage detection signal Vdp and the peak period signal Tp from the MIG welding power source PSM as input, and based on the above-described equations (1) and (2), the induced peak voltage moving average The signal Vppa and the induced base voltage moving average signal Vbba are calculated and output. The deflection determination circuit AR receives the plasma welding voltage detection signal Vdp, the induced peak voltage moving average signal Vppa, and the induced base voltage moving average signal Vbba as input, and performs the above-described first to third deflection determination methods. One is selected, the deflection of the plasma arc is determined, and a deflection determination signal Ar which becomes High level is output. Therefore, the deflection determination signal Ar is a signal that is at a high level when the plasma arc is deflected and is at a low level when the plasma arc is not deflected. The alarm circuit KH receives the deflection determination signal Ar and turns on the indicator lamp when the deflection determination signal Ar is at a high level. The indicator lamp is provided on the front panel of the plasma welding power source PSP. Further, when the deflection determination signal Ar is at a high level, an alarm sound may be produced using a buzzer or the like. Further, the deflection determination signal Ar may be output outside the welding power source. When the robot welding apparatus is used, the deflection determination signal Ar may be input to the robot control apparatus, and the welding may be interrupted when the deflection determination signal Ar becomes High level. In this way, welding can be stopped before welding failure occurs due to plasma arc deflection.

  According to the first embodiment described above, it is possible to determine the deflection of the plasma arc accompanying the consumption of the plasma electrode from the fluctuation of the plasma welding voltage. Then, when the plasma arc deflection is determined, an alarm is issued, so that it is possible to prevent the occurrence of welding failure due to the plasma arc deflection.

[Embodiment 2]
In the invention according to the second embodiment, when the plasma arc deflection is determined by the method of the first embodiment, the plasma welding current iWP is increased to correct the plasma arc deflection. The plasma welding current iWP is increased until a predetermined increase period or the plasma arc deflection is corrected. Hereinafter, the second embodiment will be described.

  FIG. 6 is a waveform diagram showing a plasma MIG welding method according to Embodiment 2 of the present invention. (A) shows the MIG welding current Iwm, (B) shows the MIG welding voltage Vwm, (C) shows the plasma welding current Iwp, and (D) shows the plasma welding voltage Vwp. FIG. 3E shows a plasma arc deflection determination signal Ar. This figure is basically the same waveform as in FIG. 1 described above, but the time scale on the horizontal axis is several times longer than that in FIG. As in FIG. 1, this figure shows a case where the plasma arc is deflected due to the deformation accompanying the consumption of the plasma electrode and the plasma welding voltage Vwp is shifted in the increasing direction. Hereinafter, a description will be given with reference to FIG.

  This figure shows a case where the plasma arc is deflected and the plasma welding voltage Vwp is shifted in the increasing direction at time t1. During the steady period before time t1, the MIG welding current Iwm has a pulse waveform formed from the peak current and the base current, as shown in FIG. Similarly, as shown in FIG. 5B, the MIG welding voltage Vwm has a pulse waveform formed from the peak voltage and the base voltage. As shown in FIG. 5C, the plasma welding current Iwp has a constant steady-state DC waveform. As shown in FIG. 4D, the plasma welding voltage Vwp has a pulse waveform formed from the induced peak voltage and the induced base voltage. As shown in FIG. 5E, the deflection determination signal Ar remains at the low level.

  When plasma arc deflection occurs at time t1, the plasma welding voltage Vwp (induced peak voltage and induced base voltage) has a waveform shifted in an increasing direction, as shown in FIG. By one deflection determination method selected from the first to third deflection determination methods described above, the increase or decrease in the plasma welding voltage Vwp is monitored from before time t1. It is determined by the selected deflection determination method that the plasma welding voltage Vwp has shifted in the increasing direction at time t1. As shown in FIG. 4D, since the increased state of the plasma welding voltage Vwp continues for the determination period Tt from time t1 to time t2, as shown in FIG. At time t2, the level changes to High level. In response to this, as shown in FIG. 5C, the plasma welding current Iwp increases from the steady value by an increase value ΔI.

  When the plasma welding current Iwp increases, the deflection of the plasma arc is corrected to a normal state at time t3. This is because when the current value for energizing the plasma arc is increased, the arc stiffness is increased, and the deflection state is corrected. Further, when the increased plasma welding current Iwp is energized, distorted deformation of the plasma electrode is also corrected. When it is determined at time t3 that the increased state of the plasma welding voltage Vwp has been canceled by the selected deflection determination method and the steady state is returned to the same state as before time t1, the deflection determination is performed as shown in FIG. The signal Ar changes to the low level. In response to this, as shown in FIG. 5C, the plasma welding current Iwp returns to the steady value before time t2. Even if the value of the plasma welding current Iwp returns to the original value, as described above, since the distortion deformation of the plasma electrode is corrected, there is no possibility that the plasma arc is deflected again.

  This figure is the case where the plasma welding voltage Vwp is shifted in the increasing direction due to the deflection of the plasma arc, as in FIG. 1 described above, but the same is true for the case of shifting in the decreasing direction as in FIG. It is. As for the method of determining the plasma arc deflection, one of the above-described first to third deflection determining methods can be selected. Said increase value (DELTA) I is about 100-200A. If this value is small, the deflection of the plasma arc cannot be corrected, and if it is large, the welding state becomes unstable. This value is set to an appropriate value by experiment according to the steady value of the plasma welding current Iwp, the shape of the plasma electrode, and the like.

  In the above, as shown in FIG. 6C, the plasma welding current Iwp increases from the time t2 when the deflection determination signal Ar becomes the high level, and returns to the original value at the time t3 when the deflection determination signal Ar becomes the low level. The timing for returning the plasma welding current Iwp to the original value may be after a predetermined increase period has elapsed since time t2. The increase period is set to about 10 to 70 ms. This increase period is set as a time slightly longer than the time during which the plasma arc deflection is corrected. This increase period is set to an appropriate value by experiment according to the stationary position of the plasma welding current Iwp, the increase value ΔI, the shape of the plasma electrode, and the like.

  The structure of the welding apparatus for implementing the plasma MIG welding method according to Embodiment 2 is the same as that in FIG. 3 described above. However, the block diagram of the plasma welding power source PSP constituting the welding apparatus is partially different from the above-described FIG. The block diagram of the MIG welding power source PSM is the same as FIG. 4 described above. Hereinafter, a block diagram of the plasma welding power source PSP according to the second embodiment will be described.

  FIG. 7 is a block diagram of a plasma welding power source PSP according to the second embodiment. In the figure, the same blocks as those in FIG. 5 described above are denoted by the same reference numerals, and description thereof is omitted. In the figure, the plasma welding current setting circuit IWPR in FIG. 5 is replaced with a second plasma welding current setting circuit IWPR2 indicated by a broken line. Hereinafter, this block will be described with reference to FIG.

  The second plasma welding current setting circuit IWPR2 receives the deflection determination signal Ar and takes a predetermined steady value when the deflection determination signal Ar is at a low level (normal), and a steady value when the deflection determination signal Ar is at a high level (during deflection). Is output a plasma welding current setting signal Iwpr which is a value obtained by adding a predetermined increase value ΔI. Alternatively, the second plasma welding current setting circuit IWPR2 receives the deflection determination signal Ar as an input, and maintains a predetermined steady value during a predetermined increase period from the time when the deflection determination signal Ar changes to the high level (during deflection). A plasma welding current setting signal Iwpr that is a value obtained by adding a predetermined increase value ΔI and that is a steady value during the other period is output.

  According to the second embodiment described above, in addition to the effects of the first embodiment, when the change of the plasma arc is determined, the plasma welding current is increased. Thereby, the deflection of the plasma arc can be corrected to the original normal state. For this reason, generation | occurrence | production of the welding defect resulting from the deflection | deviation of a plasma arc can be prevented.

1a Welding wire 1b Plasma electrode
2 Base material 3a Mig arc 3b Plasma arc
4 Power supply chip
51 Plasma nozzle
52 Shield gas nozzle
61 Center gas
62 Plasma gas
63 Shielding gas
7 Feed roll AR Deflection discrimination circuit Ar Deflection discrimination signal EI Current error amplification circuit Ei Current error amplification signal EV Voltage error amplification circuit Ev Voltage error amplification signal FC Feed control circuit Fc Feed control signal KH Alarm circuit Ib Base current IBR Base Current setting circuit Ibr Base current setting signal ID Current detection circuit Id Current detection signal IDP Plasma welding current detection circuit Idp Plasma welding current detection signal Ip Peak current IPR Peak current setting circuit Ipr Peak current setting signal IRC Current setting control circuit Irc Current setting control Signal Iwm MIG welding current Iwp Plasma welding current IWPR Plasma welding current setting circuit Iwpr Plasma welding current setting signal IWPR2 Second plasma welding current setting circuit m Number of moving averages PM Power supply main circuit PSM Mig welding power supply PSP Plasma welding power supply Tb Base period Tf Pulse circumference Period (signal)
tn Current TP Peak period timer circuit Tp Peak period (signal)
TPR Peak period setting circuit Tpr Peak period setting signal Tt Determination period VAV Voltage average value calculation circuit Vav Voltage average value signal Vb Base voltage Vbb Induced base voltage Vbba Induced base voltage moving average signal VD Voltage detection circuit Vd Voltage detection signal VDP Plasma welding voltage Detection circuit Vdp Plasma welding voltage detection signal VF Voltage / frequency conversion circuit Vp Peak voltage Vpp Induced peak voltage Vppa Induced peak voltage moving average signal VR Voltage setting circuit Vr Voltage setting signal VRA Voltage moving average calculation circuit Vt Determination value Vwm Mig welding voltage Vwp Plasma welding voltage WM Feed motor WT Welding torch ΔI Increased value

Claims (7)

A MIG arc is generated by passing a MIG welding current having a peak current during a peak period and a base current during a base period as one pulse period between a welding wire and a base material fed through a welding torch, and In a plasma MIG welding method for generating a plasma arc by passing a DC plasma welding current between a plasma electrode and a base material arranged so as to surround a welding wire,
The plasma welding voltage during a specific period of the pulse period is detected for each pulse period, and the state in which the detected value increases or decreases continues for a predetermined period or more to determine the deflection of the plasma arc, and the plasma arc deflection When an error is detected, an alarm is issued.
The plasma MIG welding method characterized by the above-mentioned. The plasma welding voltage in a specific period of the pulse period is the plasma welding voltage during the peak period,
The plasma MIG welding method according to claim 1. The plasma welding voltage in a specific period of the pulse period is the plasma welding voltage during the base period;
The plasma MIG welding method according to claim 1. The plasma welding voltage in a specific period of the pulse period is the plasma welding voltage during the peak period and the plasma welding voltage during the base period.
The plasma MIG welding method according to claim 1. When the plasma arc deflection is determined, the plasma welding current is increased to correct the plasma arc deflection.
The plasma MIG welding method according to any one of claims 1 to 4, wherein: An increase in the plasma welding current is performed for a predetermined increase period;
The plasma MIG welding method according to claim 5, wherein: Increasing the plasma welding current until the deflection of the plasma arc is corrected;
The plasma MIG welding method according to claim 5, wherein:

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