JP2012061477A - Arc start control method for plasma mig welding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce sputter adhering to a plasma electrode from MIG arc during arc start in plasma MIG welding.SOLUTION: A welding wire is fed forward to temporarily come into contact with a base material, then is fed backward to be separated from it, thereby generating initial MIG arc. Then, plasma arc carrying plasma welding current Iwp is generated. Switching to forward re-feeding is performed in response to this, and peak current and base current are carried to switch it to regular MIG arc. An initial period Ts is disposed after a generation point (t4) of the plasma arc. In the initial period Ts, the plasma welding current Iwp is gradually decreased from an initial value Iwps to a steady value Iwpc, and the peak current Ip is gradually increased from an initial value Ips to a steady value Ipc. The peak current value can be decreased by preheating from the plasma arc, so that the adhesion of spatter can be reduced.

Description

  The present invention relates to an arc start control method for plasma MIG welding in which a MIG arc and a plasma arc are simultaneously generated using a single welding torch for welding.

  Conventionally, a plasma MIG welding method combining a plasma welding method and a MIG welding method has been proposed. 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. 7 is a waveform diagram in a steady state of the plasma MIG welding method in the prior art. (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.

  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−1) th 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. Become. 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 (cutoff frequency is about 1 to 10 Hz). 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.

  Since the plasma MIG welding method described above is often used for high quality welding, in addition to arc stability in a steady state, it is also required that arc starting performance is good. For this purpose, a method is employed in which a mig arc is generated by a retract start method, which will be described later, and a plasma arc is induced by the mig arc (see, for example, Patent Documents 1 and 2). Hereinafter, the arc start method of plasma MIG welding of this prior art is demonstrated.

  FIG. 8 is a timing chart showing an arc start control method of plasma MIG welding in the prior art. (A) shows the welding start signal St, (B) shows the welding wire feed speed Fw, (C) shows the MIG welding voltage Vwm, and (D) shows MIG welding. (E) shows the plasma welding voltage Vwp, (F) shows the plasma welding current Iwp, and (G1) to (G5) are schematic diagrams showing the arc generation state at each time. FIG. Hereinafter, a description will be given with reference to FIG.

(1) Forward feeding period (slow-down feeding period) at times t1 to t2
At time t1, as shown in FIG. 6A, when the welding start signal St from the outside becomes a high level (welding start), as shown in FIGS. The value becomes a small positive value, and the welding wire 1a starts forward feeding at a slow slow-down feeding speed Fi of about 1 to 2 m / min. Here, when the feeding speed Fw is a positive value, the welding wire 1a is fed forward in a direction approaching the base material 2, and when the feeding speed Fw is a negative value, the welding wire 1a is a direction away from the base material 2. It shows that it is repatriated to. As shown in FIG. 2C, a no-load voltage is applied between the welding wire 1a and the base material 2, and as shown in FIG. Another no-load voltage is applied.

(2) Reverse feed short circuit period at time t2 to t3 At time t2, as shown in FIG. (G2), when the welding wire 1a contacts (short circuit) with the base material 2 by the above forward feed, As shown in C), the MIG welding voltage Vwm decreases from a no-load voltage to a short-circuit voltage value of about several volts. When a short circuit is determined by this voltage drop, the feed speed Fw is switched to a negative reverse feed speed Fb, and the welding wire 1a moves backward in the direction away from the base material 2, as shown in FIG. Be sent. Further, as shown in FIG. 4D, the MIG welding current Iwm is an initial current Ii that is a constant current of about 20 to 80 A, such that the welding wire is hardly melted by Joule heat.

(3) Reverse feed arc period from time t3 to t4 At time t3, as shown in FIG. 3G3, when the wire tip is separated from the base material 2 by the above reverse feed, an initial mig arc 31a is generated, As shown in FIG. (D), the MIG welding current Iwm is maintained at the initial current Ii. The initial MIG arc 31a is generated by reverse feeding, and the current value for energizing the arc (initial current value Ii) is small, so that almost no sputtering occurs and a reliable arc start can be realized. When the initial MIG arc 31a is generated, the MIG welding voltage Vwm rapidly increases from the short-circuit voltage value to an arc voltage value of about several tens of volts as shown in FIG. Since the reverse feed is continued at the time t3, the arc length of the initial MIG arc 31a is gradually increased as shown in FIG. Since the inside of the initial MIG arc 31a generated between the tip of the welding wire 1a and the base material 2 is a plasma atmosphere, as the arc length increases, the gap between the plasma electrode 1b and the base material 2 is increased. A plasma atmosphere is also formed in the space.

(4) Generation period of mig arc 3a and plasma arc 3b at time t4 At time t4, as shown in FIG. 5E, no-load voltage has already been applied between the plasma electrode 1b and the base material 2, Further, as described above, since the space between the plasma electrode 1b and the base material 2 is a plasma atmosphere, the plasma arc 3b is induced and generated as shown in FIG. When the plasma arc 3b is generated, the plasma welding voltage Vwp decreases from the no-load voltage to the arc voltage value as shown in FIG. 5E, and the plasma welding current Iwp is determined in advance as shown in FIG. The steady-state plasma welding current value Iwpc is obtained. At the same time, when the plasma arc 3b is generated at time t4, the feed speed Fw is switched from the negative reverse feed speed Fb to the positive steady feed speed Fwc, as shown in FIG. The welding wire 1a is fed forward again. As a result, as shown in FIG. 7D, the MIG welding current Iwm becomes a pulse waveform formed from the peak current Ip and the base current Ib as described above with reference to FIG. 7, and as shown in FIG. The MIG welding voltage Vwm has a pulse waveform formed from the peak voltage Vp and the base voltage Vb as described above with reference to FIG. The average value of the MIG welding current Iwm at time t4 is substantially determined by the steady feeding speed Fwc. Further, the average value of the MIG welding voltage Vwm at time t4 is controlled so as to be substantially equal to the voltage setting value as described above with reference to FIG. 7, and is feedback controlled so that the arc length becomes an appropriate value. Then, after 100 to 700 ms from time t4, the arc length of the MIG arc 3a converges to a steady value and enters a steady state. Thereby, the arc start of plasma arc welding is completed. The plasma arc 3b is generated because the space between the plasma electrode 1b and the base material 2 becomes a plasma atmosphere by the initial MIG arc 31a in a state in which no load voltage is applied. It is random in the range. Therefore, the reverse arc period from time t3 to t4 has some variation.

JP 2007-144509 A JP 2008-229704 A

  Immediately after time t4 in FIG. 8 described above, the arc length of the MIG arc 3a is long, so that the tip of the welding wire 1a is located near the plasma electrode 1b. In this state, droplet transfer of the welding wire 1a is performed in synchronization with the pulse cycle. As a result, a small amount of spatter generated at the time of droplet transfer from the MIG arc 3a adheres to the plasma electrode 1b. When the arc start is repeated a plurality of times, the amount of sputtering adhering to the plasma electrode 1b gradually increases. In this case, since the tip of the plasma electrode 1b has a distorted shape, the plasma arc 3b also has a deformed shape, resulting in poor welding quality. Furthermore, when the tip of the plasma electrode 1b is deformed into a strain, the smooth flow of the center gas flowing inside the plasma electrode 1b and the plasma gas flowing outside the plasma electrode is hindered, resulting in poor welding quality.

  Therefore, an object of the present invention is to provide a plasma MIG welding arc start control method capable of performing high-quality welding by suppressing spatter adhesion from the MIG arc to the plasma electrode at the time of arc starting. .

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 plasma MIG welding,
At the start of welding, a no-load voltage is applied between the plasma electrode and the base material, and the welding wire is fed forward, once brought into contact with the base material, and then retracted and pulled away. The plasma is generated by generating an initial MIG arc that is energized with current, continuing the backward feeding, and gradually increasing the arc length of the initial MIG arc to form a plasma atmosphere in the space between the plasma electrode and the base material. The plasma arc that is energized by the welding current is generated, and when the plasma arc is generated, the welding wire is switched to re-forward feeding, and the MIG welding current formed from the peak current and the base current is energized to generate a steady MIG arc. In the arc start control method of plasma MIG welding,
A predetermined initial period is provided from the time of occurrence of the plasma arc, and during the initial period, the plasma welding current is gradually decreased from an initial plasma welding current value to a steady plasma welding current value, and the peak current is reduced to an initial peak current. Gradually increase from the value to the steady peak current value,
This is an arc start control method for plasma MIG welding.

In the invention of claim 2, during the initial period, the peak period is gradually increased from the initial peak period to the steady peak period.
The arc start control method of plasma MIG welding according to claim 1.

In the invention of claim 3, during the initial period, the feeding speed of the re-forward feeding is gradually accelerated from the initial feeding speed to the steady feeding speed.
The arc start control method of plasma MIG welding according to claim 1 or 2, wherein

  According to the present invention, during the initial period from the time when the plasma arc is generated, the peak current or the peak current and the peak period are gradually increased to a steady value, and the plasma welding current is gradually decreased to a steady value. As a result, the force acting on the droplets can be reduced while maintaining the one-pulse cycle and one droplet transfer state, so that the occurrence of spatter accompanying the droplet transfer can be reduced. For this reason, in the state where the arc length of the MIG arc is long, the amount of sputtering adhering to the plasma electrode from the MIG arc can be suppressed, so that a good welding state can be maintained.

It is a timing chart which shows the arc start control method of the plasma MIG welding which concerns on Embodiment 1 of this invention. It is a block diagram of the welding apparatus for enforcing the arc start control method of the plasma MIG welding 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 timing chart which shows the arc start control method of the plasma MIG welding which concerns on Embodiment 2 of this invention. 6 is a block diagram of a MIG welding power source PSM according to Embodiment 2. FIG. It is a wave form diagram in the steady state of the plasma MIG welding method in a prior art. It is a timing chart which shows the arc start control method of plasma MIG welding in a prior art.

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

[Embodiment 1]
The invention according to the first embodiment provides a predetermined initial period Ts from the time of occurrence of the plasma arc, and during this initial period Ts, the plasma welding current Iwp is changed from the initial plasma welding current value Iwps to the steady plasma welding current value Iwpc. The peak current Ip that forms the MIG welding current Iwm is gradually increased from the initial peak current value Ips to the steady peak current value Ipc, and the peak period Tp that forms the MIG welding current Iwm is changed from the initial peak period Tps to the steady peak period. It gradually increases up to Tpc. Hereinafter, this embodiment will be described.

  FIG. 1 is a timing chart showing an arc start control method of plasma MIG welding according to Embodiment 1 of the present invention. FIG. 4A shows the change over time of the welding wire feeding speed Fw, FIG. 4B shows the change over time of the MIG welding current Iwm, and FIG. 4C shows the change over time of the plasma welding current Iwp. FIG. 4D shows the time change of the arc length La of the MIG arc. This figure shows changes in each signal after time t4 when the plasma arc is generated in FIG. 8 described above. Since the operation up to the time t4 is the same as that in FIG. 8, the period before the time t4 is omitted in order to explain the operation in the period that is a feature of the present invention in detail. Hereinafter, a description will be given with reference to FIG.

  As described above, when a plasma arc is generated at time t4, a predetermined initial period Ts from this time to time t5 is set. The initial period Ts from time t4 to t5 is a transient period until the arc length La of the MIG arc gradually decreases from a long state and converges to a steady arc length, as will be described later. And after time t5 becomes a stationary period.

  At time t4, as shown in FIG. 5A, the feed speed Fw is switched from the negative value reverse feed speed Fb to the positive value steady feed speed Fwc. At the same time, as shown in FIG. 5B, the MIG welding current Iwm becomes a pulse current having a plurality of periods from the first pulse period Tf (1) to the last pulse period Tf (n) of the initial period Ts. . The first pulse period after time t5 is the (n + 1) th pulse period Tf (n + 1), and the second is the (n + 2) th pulse period Tf (n + 2). During the first pulse period Tf (1), the initial peak current Ips during the initial peak period Tps and the base current Ib during the base period Tb are applied. Here, as described above, the initial peak period Tps, the initial peak current Ips, and the base current Ib are parameters set to predetermined values. Since the pulse period is determined by feedback control (arc length control), the base period Tb is also fed back. It depends on the control. Therefore, the base period Tb in each pulse period has a different value. Similarly, during the second pulse period Tf (2), the peak current Ip (2) during the peak period Tp (2) and the base current Ib during the base period Tb are applied. Similarly, during the n-th pulse period Tf (n), the peak current Ip (n) during the peak period Tp (n) and the base current Ib during the base period Tb are applied. Similarly, during the (n + 1) th pulse cycle Tf (n + 1), the steady peak current Ipc during the steady peak period Tpc and the base current Ib during the base period Tb are energized. Similarly, during the (n + 2) th pulse cycle Tf (n + 2), the steady peak current Ipc during the steady peak period Tpc and the base current Ib during the base period Tb are energized. The base current Ib has the same value in all pulse periods. The peak current Ip gradually increases from the initial peak current value Ips to the steady peak current value Ipc during the initial period Ts, and becomes the steady peak current value Ipc during the steady period after time t5. Therefore, Ips <Ip (2) <... <Ip (n) <Ipc. The peak period Tp gradually increases from the initial peak period Tps to the steady peak period Tpc during the initial period Ts, and becomes the steady peak period Tpc during the steady period after time t5. Therefore, Tps <Tp (2) <... <Tp (n) <Tpc.

  On the other hand, as shown in FIG. 5C, the plasma welding current Iwp gradually decreases from the initial plasma welding current value Iwps to the steady plasma welding current value Iwpc during the initial period Ts, and is steady during the steady period after time t5. The plasma welding current value is Iwpc. Therefore, Iwps> Iwpc. Further, as shown in FIG. 4D, the arc length La becomes the longest at the time t4, gradually decreases during the initial period Ts, and converges to the steady arc length before and after the time t5.

  The above-mentioned steady peak current value Ipc and steady peak period Tpc are appropriately determined by experiments according to the diameter, material, feeding speed, etc. of the welding wire so as to achieve a stable droplet transfer state of one droplet period and one droplet transfer. Set to a value. The steady plasma welding current value Iwpc is set to an appropriate value by experiment so as to obtain a bead appearance required according to the thickness of the base material, the joint shape, the welding speed, and the like. The initial peak current value Ips, the initial peak period Tps, and the initial plasma welding current value Iwps are set as follows. By energizing the initial plasma welding current Iwps having a value larger than the steady value from the start of the initial period Ts, the heat radiation from the plasma arc to the welding wire is increased to increase the temperature rise of the welding wire. Since the temperature of the welding wire has risen, even if the initial peak current value Ips and the initial peak period Tps are smaller than the steady values, it is possible to maintain the one-pulse cycle 1 droplet transfer state. When the initial peak current value Ips and the initial peak period Tps are reduced, the electromagnetic pinch force acting on the droplet is reduced, so that spatter is reduced when the droplet is detached from the welding wire. As a result, spatter adhering to the plasma electrode is also reduced. Therefore, the initial peak current value Ips, the initial peak period Tps, and the plasma welding current value Iwps are set by experiment so that one droplet period is in one droplet transfer state and spatter generation at the time of droplet transfer is reduced. These values are set to appropriate values according to the steady peak current value Ipc, the steady peak period Tpc, the steady plasma welding current value Iwpc, the shape of the plasma electrode, the torch height, and the like. As the time during the initial period Ts elapses, the arc length of the MIG arc gradually decreases and approaches a steady value, so that the peak current Ip and the peak period Tp are gradually increased and the plasma welding current Iwp is gradually decreased. The initial period Ts is set by experiment so that the arc length of the MIG arc is substantially equal to the time for the convergence from the long state at time t4 to the short steady state. This initial period Ts is set in a range of about 100 to 700 ms. This initial period Ts is set to an appropriate value according to the shape of the plasma electrode, the torch height, the response speed of the feeding motor, the diameter of the welding wire, the material, and the like. Since the response speed of the feed motor affects the time until convergence to a steady value when the reverse feed speed Fb is switched to the steady feed speed Fwc at time t4, it affects the convergence time of the arc length. become. The initial period Ts includes a pulse cycle of about 10 to 70 times. Therefore, the above n is about 10 to 70. In the figure, the case where both the peak current Ip and the peak period Tp are increased during the initial period Ts has been described. However, even if only the peak current Ip is increased during the initial period Ts, the above-described effects can be obtained.

  FIG. 2 is a configuration diagram of a welding apparatus for performing the arc start control method of plasma MIG welding according to Embodiment 1 of the present invention described above with reference to FIG. 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. Moreover, the welding wire 1a receives heat radiation from the plasma arc 3b.

  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. As shown in FIG. 7A, the MIG welding current Iwm is formed from a peak current during the peak period and a base current during the base period. A feed control signal Fc is sent from the MIG welding power source PSM to the feed motor WM, and the feed direction and feed speed Fw of the welding wire 1a are 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 source PSM is a power source having a constant voltage characteristic except for a certain period at the time of arc start as will be described later, and the MIG welding voltage Vwm is equal to a predetermined voltage setting signal Vr (not shown). To be controlled. The average value of the MIG welding current Iwm is determined by the steady feeding speed of the welding wire 1a. Further, as will be described later with reference to FIG. 3, the MIG welding power source PSM receives a plasma arc generation determination signal Ad that becomes a high level when the plasma arc 3b is generated at the time of arc start (time t4 in FIG. 1). Input from PSP.

  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. 4, the plasma welding power source PSP is provided with a circuit for determining the generation of the plasma arc 3b, and outputs the plasma arc generation determination signal Ad to the MIG welding power source PSM.

  The welding start circuit ST installed outside both power supplies outputs a welding start signal St to the MIG welding power source PSM and the plasma welding power source PSP. When this welding start signal St is input, both welding power sources are activated. The welding start circuit ST is provided in the robot controller for robot welding.

  FIG. 3 is a block diagram of the MIG welding power source PSM constituting the above-described welding apparatus of FIG. 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 drive signal Dv described later, and outputs a MIG welding voltage Vwm and a MIG welding current Iwm. 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 Is composed of 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, and a reactor that smoothes the rectified direct current. 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. 2 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 average value is calculated by passing through a low-pass filter as described above. 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 receives a plasma arc generation determination signal Ad from the plasma welding power source PSP, and when the plasma generation determination signal Ad changes to a high level (arc generation), the peak period setting circuit TPR is set in advance during a predetermined initial period Ts. It increases from the initial peak period Tps to a predetermined steady peak period Tpc, and thereafter, a peak period setting signal Tpr for maintaining the steady peak period Tpc is output. The peak period timer circuit TP outputs a peak period signal Tp that is at a high level only during a period determined by the value of the peak period setting signal Tpr when the pulse period signal Tf is at a high level. The peak period is the peak period when the peak period signal Tp is at the high level, and the base period is when the peak period signal Tp is at the low level.

  The base current setting circuit IBR outputs a predetermined base current setting signal Ibr. The peak current setting circuit IPR receives the plasma arc generation determination signal Ad from the plasma welding power source PSP, and when the plasma generation determination signal Ad changes to a high level (arc generation), the initial value set in advance during the initial period Ts. It increases from the peak current value Ips to a predetermined steady peak current value Ipc, and thereafter, a peak current setting signal Ipr that maintains the steady peak current value Ipc is output. The pulse current setting switching circuit SWP outputs the base current setting signal Ibr as the pulse current setting signal Irc when the peak period signal Tp is at the low level, and outputs the peak current setting signal Ipr when the peak period signal Tp is at the high level. It is output as a pulse current setting signal Irc.

  The initial current setting circuit IIR outputs a predetermined initial current setting signal Iir. The current setting switching circuit SWI receives a welding start signal St from the external welding start circuit ST, a plasma arc occurrence determination signal Ad from the plasma welding power source PSP, the pulse current setting signal Irc and the initial current setting signal Iir. When the welding start signal St changes to the high level (welding start), the initial current setting signal Iir is output as the current setting signal Ir, and when the plasma arc generation determination signal Ad changes to the high level (arc generation), the pulse current setting signal Irc is output as the current setting signal Ir. Therefore, the current setting signal Ir becomes the initial current setting signal Iir during the period from time t1 to t4 in FIG. 8, and after the time t4 in FIG. 1, the pulse current setting signal Irc (the peak current setting signal Ipr or the base current setting signal). Ibr).

  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 signal Ir and the current detection signal Id, and outputs a current error amplification signal Ei. The drive circuit DV receives the welding start signal St from the external welding start circuit ST and the current error amplification signal Ei described above, and performs PWM according to the current error amplification signal Ei when the welding start signal St is at a high level (welding start). Modulation control is performed and a drive signal Dv is output, and when it is at a low level (welding stop), the drive signal Dv is not output.

  The short circuit determination circuit SD receives the voltage detection signal Vd as described above, and determines a short circuit between the welding wire 1a and the base material 2 based on the value, and outputs a short circuit determination signal Sd that becomes a high level. The feed speed setting circuit FR receives the welding start signal St from the external welding start circuit ST, the short-circuit determination signal Sd and the plasma arc generation determination signal Ad from the plasma welding power source PSP as inputs, and starts the welding start signal St. Changes to the high level (welding start) and becomes a predetermined slow-down feed speed setting value, and when the short circuit determination signal Sd changes to the high level (short circuit), the predetermined reverse feed speed setting value becomes and the plasma arc occurrence determination When the signal Ad changes to a high level (arc generation), a feed speed setting signal Fr that becomes a predetermined steady feed speed set value is output. Accordingly, the feed speed setting signal Fr becomes a slow-down feed speed set value during the period from time t1 to t2 in FIG. 8, and becomes a reverse feed speed set value during the period from time t2 to t4. During the period after t4, the constant feed speed setting value is set. The feed control circuit FC receives the welding start signal St and the feed speed setting signal Fr as described above, and corresponds to the value of the feed speed setting signal Fr when the welding start signal St becomes a high level (welding start). A feed control signal Fc for feeding the welding wire 1a at the feed speed is output to the feed motor WM.

  With the above circuit configuration, the MIG welding current Iwm, the MIG welding voltage Vwm, and the feed speed Fw as shown in FIGS. 8 and 1 are controlled.

  FIG. 4 is a block diagram of the plasma welding power source PSP that constitutes the welding apparatus of FIG. 2 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 as input, performs output control such as inverter control according to a drive signal Dv 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. 2 described above, but is simplified here.

  The plasma welding current setting circuit IWPR receives a plasma arc generation determination signal Ad, which will be described later, and when the plasma generation determination signal Ad changes to a high level (arc generation), a predetermined initial plasma welding is performed during a predetermined initial period Ts. The current value Iwps is decreased to a predetermined steady plasma welding current value Iwpc, and thereafter a plasma welding current setting signal Iwpr for maintaining the steady plasma welding current value Iwpc is output. 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. The drive circuit DV receives the welding start signal St from the external welding start circuit ST and the current error amplification signal Ei described above, and performs PWM according to the current error amplification signal Ei when the welding start signal St is at a high level (welding start). Modulation control is performed and a drive signal Dv is output, and when it is at a low level (welding stop), the drive signal Dv is not output. By performing the output control of the welding power source according to the drive signal Dv, the plasma welding current Iwp as described above with reference to FIG. 1 is energized. 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 arc occurrence discriminating circuit AD receives the plasma welding current detection signal Idp as described above, and determines that a plasma arc has occurred when the value exceeds a threshold value and becomes a high level. Ad is output to the plasma welding current setting circuit IWPR and the MIG welding power source PSM. For example, the threshold value is set to about 5A.

  According to the first embodiment described above, during the initial period from the time when the plasma arc is generated, the peak current or the peak current and the peak period are gradually increased to the steady value, and the plasma welding current is gradually decreased to the steady value. Yes. As a result, the force acting on the droplets can be reduced while maintaining the one-pulse cycle and one droplet transfer state, so that the occurrence of spatter accompanying the droplet transfer can be reduced. For this reason, in the state where the arc length of the MIG arc is long, the amount of sputtering adhering to the plasma electrode from the MIG arc can be suppressed, so that a good welding state can be maintained.

[Embodiment 2]
In the invention according to the second embodiment, in addition to the first embodiment, during the initial period Ts, the feeding speed of re-forward feeding is gradually accelerated from the initial feeding speed Fs to the above-described steady feeding speed Fwc. It is. That is, in the second embodiment, the peak current Ip, the peak period Tp, the plasma welding current Iwp, and the feeding speed Fw are gradually changed to the steady state until the initial period Ts elapses after the plasma arc is generated. It is a thing. Hereinafter, this embodiment will be described.

  FIG. 5 is a timing chart showing an arc start control method of plasma MIG welding according to Embodiment 2 of the present invention. FIG. 4A shows the change over time of the welding wire feeding speed Fw, FIG. 4B shows the change over time of the MIG welding current Iwm, and FIG. 4C shows the change over time of the plasma welding current Iwp. FIG. 4D shows the time change of the arc length La of the MIG arc. This figure corresponds to FIG. 1 described above, and the operations of signals other than the feeding speed Fw shown in FIG. As in FIG. 1, FIG. 8 shows changes in signals after time t4 when the plasma arc is generated in FIG. 8 described above. Since the operation up to the time t4 is the same as that in FIG. 8, the period before the time t4 is omitted in order to explain the operation in the period that is a feature of the present invention in detail. Hereinafter, a description will be given with reference to FIG.

  Similar to FIG. 1, when a plasma arc is generated at time t4, a predetermined initial period Ts from this time to time t5 is set. During the initial period Ts from time t4 to time t5, as described above, a transition period in which the arc length La of the MIG arc gradually decreases. And after time t5 becomes a stationary period.

  At time t4, the feed speed Fw is switched from the negative reverse feed speed Fb to the positive initial feed speed Fs, as shown in FIG. Therefore, the welding wire is switched from backward feed to re-forward feed. Then, during the initial period Ts, the vehicle gradually accelerates from a predetermined initial feeding speed Fs to a predetermined steady feeding speed Fwc, and becomes a steady feeding speed Fwc during a steady period after time t5. Therefore, Fs <Fwc. The MIG welding current Iwm shown in FIG. 1B, the plasma welding current Iwp shown in FIG. 1C and the arc length La shown in FIG. 1D are the same as those in FIG.

  The initial feeding speed Fs is set to about 0 to 2 m / min. The setting of the initial period Ts and the steady feeding speed Fwc is as described above. By gradually accelerating the feeding speed Fw for re-forward feeding, the arc stability in the transition period from the initial MIG arc at time t4 to the steady MIG arc at time t5 is improved. This is because, during the initial period Ts corresponding to the transition period, the peak current and the peak period for forming the MIG welding current Iwm gradually increase, so that the feeding speed Fw is accelerated so as to be synchronized with this. This is because the balance between the feed rate and the feeding speed is improved, and the arc stability is improved.

  The welding apparatus for carrying out the arc start control method of plasma MIG welding according to the second embodiment described above is the same as that shown in FIG. However, since the block diagram of the MIG welding power source PSM constituting the welding apparatus of FIG. 2 is different, it will be described later with reference to FIG. The block diagram of the plasma welding power source PSP is the same as FIG. 4 described above.

  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 feeding speed setting circuit FR in FIG. 3 is replaced with a second feeding speed setting circuit FR2 indicated by a broken line. Hereinafter, this block will be described with reference to FIG.

  The second feed speed setting circuit FR2 receives the welding start signal St from the external welding start circuit ST, the short circuit determination signal Sd, and the plasma arc generation determination signal Ad from the plasma welding power source PSP as inputs, and starts welding. When the signal St changes to High level (welding start), a predetermined slow-down feed speed setting value is obtained, and when the short circuit determination signal Sd changes to High level (short circuit), a predetermined reverse feed speed setting value is obtained. When the generation determination signal Ad changes to a high level (arc generation), the predetermined feed speed set value increases from the preset initial feed speed set value during the initial period Ts, and thereafter the steady feed speed. A feed speed setting signal Fr that maintains the set value is output. Accordingly, the feed speed setting signal Fr becomes a slow-down feed speed set value during the period from time t1 to t2 in FIG. 8, and becomes a reverse feed speed set value during the period from time t2 to t4. During the initial period Ts from t4 to t5, the initial feed speed setting value increases from the steady feed speed set value, and during the steady period of time t5, the steady feed speed set value is reached.

  According to the second embodiment described above, the feeding speed of re-forward feeding during the initial period is gradually accelerated from the initial feeding speed to the steady feeding speed. Thereby, in addition to the effect of Embodiment 1, the stability of the MIG arc during the intended period can be improved.

  In the first and second embodiments described above, the initial period for increasing the peak current and the peak period, the initial period for decreasing the plasma welding current, and the initial period for accelerating the feed rate are all the same period. However, these three initial periods may be finely adjusted to different values in consideration of MIG arc stability and spatter generation. Further, the base current may be gradually changed during the initial period.

1a Welding wire 1b Plasma electrode 2 Base material 3a MIG arc
31a Initial 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 AD Plasma arc occurrence discriminating circuit Ad Plasma arc occurrence discriminating signal DV Drive circuit Dv Drive signal EI Current error amplification Circuit Ei Current error amplification signal EV Voltage error amplification circuit Ev Voltage error amplification signal Fb Reverse feed speed FC Feed control circuit Fc Feed control signal Fi Slow down feed speed FR Feed speed setting circuit Fr Feed speed setting signal FR2 Second feed speed setting circuit Fs Initial feed speed Fw Feed speed Fwc Steady feed speed 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 I Initial current IIR Initial current setting circuit Iir Initial current setting signal Ip Peak current Ipc Steady peak current IPR Peak current setting circuit Ipr Peak current setting signal Ips Initial peak current Ir Current setting signal Irc Pulse current setting signal Iwm Mig welding current Iwp Plasma welding current Iwpc Steady plasma welding current IWPR Plasma welding current setting circuit Iwpr Plasma welding current setting signal Iwps Initial plasma welding current La Mig arc length PM Power source main circuit PSM Mig welding power source PSP Plasma welding power source SD Short circuit discrimination circuit Sd Short circuit discrimination signal ST Welding start Circuit St Welding start signal SWI Current setting switching circuit SWP Pulse current setting switching circuit Tb Base period Tf Pulse period (signal)
TP Peak period timer circuit Tp Peak period (signal)
Tpc steady peak period TPR peak period setting circuit Tpr peak period setting signal Tps initial peak period Ts initial period VAV voltage average value calculation circuit Vav voltage average value signal Vb base voltage VD voltage detection circuit Vd voltage detection signal VF voltage / frequency conversion circuit Vp Peak voltage VR Voltage setting circuit Vr Voltage setting signal Vwm Mig welding voltage Vwp Plasma welding voltage WM Feed motor WT Welding torch

Claims (3)

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 plasma MIG welding that generates 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,
At the start of welding, a no-load voltage is applied between the plasma electrode and the base material, and the welding wire is fed forward, once brought into contact with the base material, and then retracted and pulled away. The plasma is generated by generating an initial MIG arc that is energized with current, continuing the backward feeding, and gradually increasing the arc length of the initial MIG arc to form a plasma atmosphere in the space between the plasma electrode and the base material. The plasma arc that is energized by the welding current is generated, and when the plasma arc is generated, the welding wire is switched to re-forward feeding, and the MIG welding current formed from the peak current and the base current is energized to generate a steady MIG arc. In the arc start control method of plasma MIG welding,
A predetermined initial period is provided from the time of occurrence of the plasma arc, and during the initial period, the plasma welding current is gradually decreased from an initial plasma welding current value to a steady plasma welding current value, and the peak current is reduced to an initial peak current. Gradually increase from the value to the steady peak current value,
An arc start control method of plasma MIG welding characterized by the above. During the initial period, the peak period is gradually increased from the initial peak period to the steady peak period.
The arc start control method of plasma MIG welding according to claim 1. During the initial period, the feeding speed of the re-forward feeding is gradually accelerated from the initial feeding speed to the steady feeding speed.
The arc start control method of plasma MIG welding according to claim 1 or 2, wherein

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