JP2011206794A - Plasma mig welding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain excellent welding quality by preventing any degradation or crack of a structure of a base metal when using the pulse waveform in the welding current conducting both arcs, in a plasma MIG welding method for generating the MIG arc and the plasma arc from one welding torch.SOLUTION: In the plasma MIG welding method, the MIG arc is generated by repeating the conduction of the first peak current Ipm and the conduction of the first base current Ibm as one pulse period Tf; the second peak current Ipp is conducted during a part of the conduction period or the entire period of the first base current Ibm, and the second base current Ibp is conducted during the other period of the pulse period Tf to generate the plasma arc; wherein the second peak current Ipp or its conduction period Tpp is controlled so that the average value of the plasma welding current Iwp to be formed of the second peak current Ipp and the second base current Ibp is equal to the predetermined current set value.

Description

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

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

  The MIG welding current generally uses a DC pulse waveform in order to suppress the generation of spatter and stably supply droplets. Therefore, the MIG welding method is a general MIG pulse welding method. In the consumable electrode type arc welding method including the MIG pulse welding method, it is important to maintain the arc length during welding at an appropriate value, and therefore arc length control is performed. A DC or DC pulse waveform is used for the plasma welding current. Here, a MIG arc is generated by energizing the MIG welding current formed from the first peak current and the first base current, and a plasma arc is generated by energizing the plasma welding current formed from the second peak current and the second base current. In the conventional technique, the second base current is supplied during the first peak current application, and the second peak current is supplied during the first base current application (see Patent Document 2). Is disclosed. In other words, the pulse waveform is used for the MIG welding current and the plasma welding current, and the phases are shifted so that the peak currents do not overlap each other. By doing so, the peak currents overlap each other, so that the heat input to the base material is not excessive, so that the deterioration and cracking of the structure can be prevented in the welding of the aluminum material, and good welding quality can be obtained. Can do. In the following description, when the arc length is simply described, it means the arc length of the MIG arc. Hereinafter, this prior art will be described.

  FIG. 9 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, and (C) shows the plasma welding current Iwp. Since power supply to the MIG arc is performed by constant voltage control, current and voltage waveforms are shown. Since power supply to the plasma arc is performed by constant current control, only current waveforms are shown. Hereinafter, a description will be given with reference to FIG.

  As shown in FIG. 5A, the first peak current Ipm is energized during the peak period Tp from time t1 to t2, and the first base current Ibm is energized during the base period Tb from time t2 to t3. The peak period Tp and the base period Tb are combined to form a pulse period Tf. Then, corresponding to the energization of the MIG welding current Iwm, as shown in FIG. 5B, the first peak voltage Vpm is applied between the welding wire and the base material during the peak period Tp, and the base period Tb. The first base voltage Vbm is applied inside.

  In MIG welding, arc length control is performed to maintain the arc length at an appropriate value in order to obtain good welding quality. Normally, this arc length control uses the fact that the MIG welding voltage Vwm is substantially proportional to the arc length, and controls the pulse cycle so that the average value of the MIG welding voltage Vwm is equal to a predetermined voltage setting value. Is done. 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 frequency modulation control. In this case, the peak period Tp, the first peak current Ipm, and the first base current Ibm are set to predetermined values and become constant pulse parameters. The first peak current Ipm 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 first base current Ibm 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 first base current Ibm are set to appropriate values according to the material, diameter, gas type, etc. of the welding wire. The pulse period Tf is a parameter that is an operation amount in the feedback control, and changes transiently in response to a change in the arc load by the frequency modulation control. When the arc state is in a stable state, the pulse period Tf becomes a steady value having a substantially constant value. When the feed speed of the welding wire changes, in order to maintain an appropriate arc length, the average value of the MIG welding current Iwm needs to change correspondingly. This is because the arc length is determined by the balance between the feeding speed and the melting speed, and the melting speed is proportional to the average value of the MIG welding current Iwm. That is, in the arc length control by frequency modulation control, when the feed speed changes, the voltage setting value is changed to an appropriate value correspondingly, so that the steady value of the pulse period Tf changes. In other words, in frequency modulation control, the pulse period Tf changes according to the feeding speed.

  On the other hand, the plasma welding current Iwp is synchronized with the MIG welding current Iwm. Here, assuming that the time when the predetermined delay period Td has elapsed from the end time t2 of the peak period Tp is t21, the predetermined second base current Ibp is maintained during the period from time t1 to t21 as shown in FIG. Energized, and a predetermined second peak current Ipp is energized during the period from time t21 to t3. That is, in the waveform of the plasma welding current Iwp, the delay period Td, the second peak current Ipp, and the second base current Ibp, which are predetermined values, are constant pulse parameters, and the cycle thereof is the same as the above-described pulse cycle Tf. By doing in this way, it controls so that electricity supply of the 1st peak current Ipm and electricity supply of the 2nd peak current Ipp may not overlap.

JP 2008-229641 A JP 2008-105039 A

  As described above, in the prior art, the pulse period Tf changes transiently in response to the load fluctuation of the MIG arc when the feed speed is constant. Further, the steady value of the pulse period Tf changes correspondingly when the feeding speed changes. In the MIG arc, when the pulse period Tf changes in this way, the arc length is maintained at an appropriate value, and a stable arc state is obtained. On the other hand, with respect to the plasma welding current Iwp, when the pulse period Tf changes, the average value of the plasma welding current Iwp changes accordingly. This is because, as described above, the delay period Td, the second peak current Ipp, and the second base current Ibp, which are pulse parameters, are predetermined values, so that the average value changes when the period changes. The average value of the plasma welding current Iwp is set so that a good weld bead is formed according to the weld joint of the base material, the plate thickness, the welding speed, and the like. However, as described above, when the pulse period Tf is changed by the frequency modulation control, the average value of the plasma welding current Iwp is also changed forcibly. As a result, the weld bead may be deteriorated.

  Therefore, an object of the present invention is to provide a plasma MIG welding method capable of maintaining the average value of the plasma welding current at a predetermined value even if the pulse period is changed by frequency modulation control of the MIG welding current.

In order to solve the above-described problem, the invention of claim 1 generates a mig arc between the welding wire and the base material by repeating the energization of the first peak current and the energization of the first base current in one pulse cycle. And controlling the arc length of the MIG arc by changing the pulse period by frequency modulation control,
The second peak current is applied during part or all of the first base current supply period, and the second base current is supplied during the other period of the pulse period so as to surround the welding wire. In a plasma MIG welding method for generating a plasma arc between the formed plasma electrode and the base material,
Controlling the waveform parameter of the plasma welding current so that an average value of the plasma welding current formed from the second peak current and the second base current is equal to a predetermined current setting value;
This is a plasma MIG welding method.

In the invention of claim 2, the waveform parameter control sets the energization period of the second base current and the second peak current to a predetermined value, and the average value of the plasma welding current becomes equal to the current set value. As described above, the second peak current is controlled by feedback control.
The plasma MIG welding method according to claim 1.

In the invention of claim 3, the control of the waveform parameter sets the second base current and the second peak current to predetermined values, and the average value of the plasma welding current is equal to the current set value. It is a control that changes the energization period of the second peak current by feedback control.
The plasma MIG welding method according to claim 1.

  According to the present invention, the phase is shifted so that the energization of the first peak current of the MIG welding current and the energization of the second peak current of the plasma welding current do not overlap, and the pulse is controlled by frequency modulation control of the MIG welding current. Control is performed so that the average value of the plasma welding current becomes a predetermined value even if the cycle changes. For this reason, the peak currents do not overlap each other, so that the heat input to the base material does not become excessive, and the heat input from the plasma arc can be set to a predetermined value. Deterioration and cracking can be prevented, and good welding quality can be obtained.

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 plasma welding power supply PSP which comprises the welding apparatus of FIG. In Embodiment 1, it is a timing chart of each signal of the MIG welding power source PSM and the plasma welding power source PSP when the feeding speed is low. In Embodiment 1, it is a timing chart of each signal of the MIG welding power source PSM and the plasma welding power source PSP when the feeding speed is high. It is a block diagram of the plasma welding power supply PSP which concerns on Embodiment 2 of this invention. In Embodiment 2, it is a timing chart of each signal of the MIG welding power supply PSM and the plasma welding power supply PSP when the feeding speed is low. In Embodiment 2, it is a timing chart of each signal of the MIG welding power supply PSM and the plasma welding power supply PSP when the feeding speed is high. It is a wave form diagram which shows the plasma MIG welding method in a prior art.

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

[Embodiment 1]
In the first embodiment of the present invention, when the pulse period is changed by frequency modulation control with respect to the MIG welding current, the average value of the plasma welding current formed from the second peak current and the second base current is a predetermined current setting. The second peak current value is feedback controlled so as to be equal to the value.

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

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

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

  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 such that the second peak current and the second base current that form the plasma welding current Iwp become predetermined values.

  FIG. 2 is a block diagram of the MIG welding power source PSM constituting the above-described 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 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. 1, and is shown here in a simplified manner.

  The voltage detection circuit VD detects the MIG welding voltage Vwm having a pulse waveform 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. This average value is calculated by passing through a low-pass filter.

  The feeding speed setting circuit FR outputs a predetermined feeding speed setting signal Fr. The feed control circuit FC outputs a feed control signal Fc for feeding the welding wire 1a at the feed speed Fw determined by the feed speed setting signal Fr 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 Tfs having a frequency corresponding to the value of the voltage error amplification signal Ev. The pulse cycle signal Tfs is a trigger signal that becomes High level for a short time every pulse cycle.

  The peak period setting circuit TPR outputs a predetermined peak period setting signal Tpr. The peak period timer circuit TPS supplies a peak period timer signal Tps, which becomes a high level for a period determined by the value of the peak period setting signal Tpr to the current setting control circuit IRC, which will be described later, when the pulse period signal Tfs becomes a high level. Output to the plasma welding power source PSP. The peak period is the peak period when the peak period timer signal Tps is at the high level, and the base period is when the peak period timer signal Tps is at the low level.

  The first base current setting circuit IBMR outputs a predetermined first base current setting signal Ibmr. The first peak current setting circuit IPMR outputs a predetermined first peak current setting signal Ipmr. The current setting control circuit IRC outputs the first base current setting signal Ibmr as the current setting control signal Irc when the peak period timer signal Tps is at the low level, and the first peak current when the peak period timer signal Tps is at the high level. The setting signal Ipmr is output as the current setting control signal Irc.

  The current detection circuit ID detects the MIG welding current Iwm having a pulse waveform 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 power source PSM described above is a power source having a constant voltage characteristic because the pulse period is changed and the frequency modulation control is performed so that the average value of the MIG welding voltage Vwm becomes equal to the value of the voltage setting signal Vr.

  FIG. 3 is a block diagram of the plasma welding power source PSP that constitutes FIG. 1 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 200V as 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. The plasma welding current Iwp is energized through the plasma electrode 1b, the plasma arc 3b, and the base material 2. The structure of the welding torch is as shown in FIG. 1 described above, but is shown here in a simplified manner.

  The logic inversion circuit NOT receives the peak period timer signal Tps from the MIG welding power supply PSM as described above, inverts the logic thereof, and outputs a logic inversion signal Not. This logic inversion signal Not is a signal that is at a low level during the peak period of the MIG welding current Iwm and that is at a high level during the base period. The on-delay circuit OD receives this logic inverted signal Not and outputs an on-delay signal Od that is delayed by a predetermined on-delay period Tod before the signal becomes a high level. The second peak current conduction period setting circuit TPPR outputs a predetermined second peak current conduction period setting signal Tppr. The second peak current conduction period timer circuit TPPS receives the logical inversion signal Not, the on-delay signal Od and the second peak current conduction period setting signal Tppr as input, and the time when the on-delay signal Od changes to the high level. A signal which becomes High level only for a period determined by the second peak current conduction period setting signal Tppr is generated, and a logical product of this signal and the logic inversion signal Not is obtained to output a second peak current conduction period timer signal Tpps. When the second peak current energizing period timer signal Tpps is at a high level, the second peak current is energized. When the timer signal Tpps is at a low level, the second base current is energized. The period during which the second peak current energization period timer signal Tpps is at the High level is a signal obtained by ANDing the logic inversion signal Not and is limited to the base period of the MIG welding current Iwm. .

  The current detection circuit ID detects a plasma welding current Iwp having a pulse waveform and outputs a current detection signal Id. The current average value calculation circuit IAV receives the current detection signal Id as an input, calculates the average value, and outputs it as a current average value signal Iav. The current setting circuit IAR outputs a predetermined current setting signal Iar for setting an average value of the plasma welding current Iwp. The current error integration circuit SI receives the current setting signal Iar and the current average value signal Iav, and outputs the second peak current setting signal Ippr = Ipp0 + ∫ (Iar−Iav) · dt. Here, Ipp0 is a predetermined initial value of the second peak current. Integration takes place during welding. The second base current setting circuit IBPR outputs a predetermined second base current setting signal Ibpr. The current setting control circuit IRC receives the second peak current conduction period timer signal Tpps, the second peak current setting signal Ippr and the second base current setting signal Ibpr as inputs, and receives a second peak current conduction period timer signal. When Tpps is High level, the second peak current setting signal Ippr is output as the current setting control signal Irc, and when Tpps is Low level, the second base current setting signal Ibpr is output as the current setting control signal Irc. 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. By performing output control of the welding power source according to the current error amplification signal Ei, the plasma welding current Iwp formed from the second peak current and the second base current is energized.

  4 and 5 are timing charts of the signals of the MIG welding power source PSM and the plasma welding power source PSP described above. FIG. 4 shows a case where the feeding speed is set to be lower than that in FIG. 5, and a case where the pulse period Tf becomes longer than that in FIG. 5 by frequency modulation control. On the other hand, FIG. 5 shows a case where the feeding speed is set to be higher than that in FIG. 4, and a case where the pulse period Tf becomes shorter than that in FIG. 4 by frequency modulation control. The operation will be described below with reference to both figures.

  FIG. 4 is a timing chart of each signal of the MIG welding power source PSM and the plasma welding power source PSP when the feeding speed is low. (A) shows the MIG welding current Iwm, (B) shows the plasma welding current Iwp, (C) shows the pulse period signal Tfs, and (D) shows the peak period timer signal Tps. FIG. 4E shows the second peak current conduction period timer signal Tpps. This figure shows a case where the time ratio between the peak period Tp and the pulse period Tf is about 1: 5 by frequency modulation control. The operation will be described below with reference to FIG.

  As shown in FIG. 3C, the pulse period signal Tfs is a trigger signal that becomes High level for a short time at time t1 and time t3. The period from time t1 to time t3 is the pulse period Tf1. This pulse period Tf1 is determined by frequency modulation control so that the average value of the MIG welding voltage becomes equal to the value of the voltage setting signal Vr. As shown in FIG. 4D, the peak period timer signal Tps is a period (time t1 to t2) determined by the peak period setting signal Tpr from the time (time t1 and t3) when the pulse period signal Tfs changes to the high level. ) Only becomes a high level signal. Therefore, as shown in FIG. 4D, the peak period timer signal Tps is at the high level during the peak period Tp from time t1 to t2, and is at the low level during the base period Tb from time t2 to t3. As shown in FIG. 5A, the MIG welding current Iwm is supplied with the first peak current Ipm during the peak period Tp when the peak period timer signal Tps is at the high level, and the first base during the low level base period Tb. The current Ibm is energized.

  As shown in FIG. 6E, the second peak current conduction period timer signal Tpps has a predetermined on-delay period Tod from time t2 when the peak period timer signal Tps shown in FIG. The high level is reached at the time t21 when it has elapsed, and the low level is reached at the time t22 when the time determined by the second peak current conduction period setting signal Tppr has elapsed since that time. Therefore, as shown in FIG. 5E, the second peak current conduction period timer signal Tpps is at a high level only during the period from time t21 to t22. As shown in FIG. 5B, the plasma welding current Iwp is equal to the second peak current Ipp during the period from time t21 to time t22 when the second peak current conduction period timer signal Tpps shown in FIG. Is energized and the second base current Ibp is energized during the period from time t1 to t21 and time t22 to t3 when the signal becomes low level.

  In the waveform of the MIG welding current Iwm shown in FIG. 5A, the first peak current Ipm, the first base current Ibm, and the peak period Tp are predetermined values, and the pulse period Tf is changed by frequency modulation control. The base period Tb also changes. On the other hand, in the waveform of the plasma welding current Iwp shown in FIG. 5B, the second base current Ibp and the second peak current conduction period Tpp are predetermined values. Then, even if the pulse period Tf is changed by frequency modulation control of the MIG welding current Iwm, the value of the second peak current Ipp is controlled so that the average value of the plasma welding current Iwp becomes the set value. This control is referred to as current modulation control. In the figure, the second peak current Ipp = Ipp1.

  FIG. 5 is a timing chart of each signal of the MIG welding power source PSM and the plasma welding power source PSP when the feeding speed is high. (A) shows the MIG welding current Iwm, (B) shows the plasma welding current Iwp, (C) shows the pulse period signal Tfs, and (D) shows the peak period timer signal Tps. FIG. 4E shows the second peak current conduction period timer signal Tpps. This figure shows a case where the time ratio between the peak period Tp and the pulse period Tf is about 1: 2 by frequency modulation control. This figure corresponds to FIG. 4, the description of the same operation is omitted, and different points will be described.

  In the waveform of the MIG welding current Iwm shown in FIG. 4A, the first peak current Ipm, the first base current Ibm, and the peak period Tp are the same values as in FIG. 4, and the pulse period Tf is changed by frequency modulation control. Along with this, the base period Tb also changes. In FIG. 4, the pulse cycle Tf = Tf1, and in FIG. 4, the pulse cycle Tf = Tf2. Tf1> Tf2. On the other hand, in the waveform of the plasma welding current Iwp shown in FIG. 4B, the second base current Ibp and the second peak current conduction period Tpp have the same values as in FIG. Then, even if the pulse period Tf is changed by frequency modulation control of the MIG welding current Iwm, the value of the second peak current Ipp is controlled so that the average value of the plasma welding current Iwp becomes the current set value. In FIG. 4, the second peak current Ipp = Ipp1, and in FIG. 4, the second peak current Ipp = Ipp2. Ipp1> Ipp2. This is because the pulse period Tf is shorter in the figure, and the second peak current Ipp can be reduced in order to obtain the same average value.

  A numerical example will be described with reference to FIG. It is assumed that the waveform parameters of the MIG welding current Iwm are the first peak current Ipm = 450 A, the first base current Ibm = 50 A, the peak period Tp = 2 ms, and the pulse period Tf1 = 10 ms. On the other hand, the waveform parameters of the plasma welding current Iwp are the on-delay period Tod = 0, the second base current Ibp = 50 A, the second peak current conduction period Tpp = 2 ms, and the second peak current Ipp = 50 to 450 A by current modulation control. The average value of the plasma welding current Iwp can be set in the range of 50 to 130A. At this time, the average value of the MIG welding current Iwm is 130A. Since the average value of the plasma welding current Iwp is practically often set below the average value of the MIG welding current Iwm, the above setting range is not a problem. In the case of FIG. 5, if the pulse period Tf2 = 4 ms, the average value of the plasma welding current Iwp can be set in the range of 50 to 250A. At this time, the average value of the MIG welding current Iwm is 250A. This setting range is the same as described above.

  The reason for providing the on-delay period Tod is as follows. When the on-delay period Tod = 0, the first peak current Ipm falls and the second peak current Ipp rises at time t2 in FIGS. In the actual current waveform, there is a slope at the falling and rising due to the influence of the reactor inside the welding power source and the reactor due to the routing of the external cable. For this reason, by providing the on-delay period Tod, it is possible to prevent the current from overlapping in the period in which the falling and the rising intersect, and to suppress overheating of the base material.

  According to Embodiment 1 described above, the phase is shifted so that the energization of the first peak current of the MIG welding current and the energization of the second peak current of the plasma welding current do not overlap, and the frequency of the MIG welding current Even if the pulse period is changed by modulation control, the average value of the plasma welding current is controlled to be a predetermined value. For this reason, the peak currents do not overlap each other, so that the heat input to the base material does not become excessive, and the heat input from the plasma arc can be set to a predetermined value. Deterioration and cracking can be prevented, and good welding quality can be obtained. Furthermore, in this embodiment, since the average value of the plasma welding current is always controlled to a predetermined value, the preheating from the plasma arc to the welding wire becomes constant, the droplet transfer of the welding wire is stabilized, and the welding fume is stabilized. In addition, the generation of spatter can be reduced.

[Embodiment 2]
In the second embodiment of the present invention, when the pulse period is changed by frequency modulation control with respect to the MIG welding current, the average value of the plasma welding current formed from the second peak current and the second base current is a predetermined current setting. The energization period of the second peak current is feedback controlled so as to be equal to the value.

  A welding apparatus for carrying out the plasma MIG welding method according to Embodiment 2 is the same as that shown in FIG. Further, the block diagram of the MIG welding power source PSM constituting the welding apparatus is also the same as FIG. 2 described above. However, since the block diagram of the plasma welding power source PSP constituting the welding apparatus is partially different from the above-described FIG. 3, this point will be described below.

  FIG. 6 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. 3 described above are denoted by the same reference numerals, and description thereof is omitted. The figure shows that the second peak current conduction period setting circuit TPPR in FIG. 3 is deleted, the current error integration circuit SI in FIG. 3 is replaced with a second current error integration circuit SI2 indicated by a broken line, and a second peak current indicated by a broken line is obtained. A setting circuit IPPR is added. Hereinafter, these blocks will be described with reference to FIG.

  The second current error integration circuit SI2 receives the current setting signal Iar and the current average value signal Iav and outputs the second peak current conduction period setting signal Tppr = Tpp0 + ∫ (Iar−Iav) · dt. Here, Tpp0 is a predetermined initial value of the second peak current conduction period. Integration takes place during welding. The second peak current setting circuit IPPR outputs a predetermined second peak current setting signal Ippr.

  7 and 8 are timing charts of respective signals of the MIG welding power source PSM and the plasma welding power source PSP according to the second embodiment. FIG. 7 corresponds to FIG. 4 described above, and is a case where the feeding speed is set to be lower than that of FIG. 8, and is a case where the pulse period Tf becomes longer than that of FIG. 8 by frequency modulation control. On the other hand, FIG. 8 corresponds to FIG. 5 described above, and shows a case where the feeding speed is set higher than that in FIG. 7, and a case where the pulse period Tf becomes shorter than FIG. 7 by frequency modulation control. is there. The operation will be described below with reference to both figures.

  FIG. 7 is a timing chart of each signal of the MIG welding power source PSM and the plasma welding power source PSP when the feeding speed is low. (A) shows the MIG welding current Iwm, (B) shows the plasma welding current Iwp, (C) shows the pulse period signal Tfs, and (D) shows the peak period timer signal Tps. FIG. 4E shows the second peak current conduction period timer signal Tpps. This figure shows a case where the time ratio between the peak period Tp and the pulse period Tf is about 1: 5 by frequency modulation control. The operation will be described below with reference to FIG.

  As shown in FIG. 3C, the pulse period signal Tfs is a trigger signal that becomes High level for a short time at time t1 and time t3. The period from time t1 to time t3 is the pulse period Tf1. This pulse period Tf1 is determined by frequency modulation control so that the average value of the MIG welding voltage becomes equal to the value of the voltage setting signal Vr. As shown in FIG. 4D, the peak period timer signal Tps is a period (time t1 to t2) determined by the peak period setting signal Tpr from the time (time t1 and t3) when the pulse period signal Tfs changes to the high level. ) Only becomes a high level signal. Therefore, as shown in FIG. 4D, the peak period timer signal Tps is at the high level during the peak period Tp from time t1 to t2, and is at the low level during the base period Tb from time t2 to t3. As shown in FIG. 5A, the MIG welding current Iwm is supplied with the first peak current Ipm during the peak period Tp when the peak period timer signal Tps is at the high level, and the first base during the low level base period Tb. The current Ibm is energized.

  As shown in FIG. 6E, the second peak current conduction period timer signal Tpps has a predetermined on-delay period Tod from time t2 when the peak period timer signal Tps shown in FIG. The high level is reached at the time t21 when it has elapsed, and the low level is reached at the time t22 when the time determined by the second peak current conduction period setting signal Tppr has elapsed since that time. Therefore, as shown in FIG. 5E, the second peak current conduction period timer signal Tpps is at a high level only during the period from time t21 to t22. As shown in FIG. 5B, the plasma welding current Iwp is equal to the second peak current Ipp during the period from time t21 to time t22 when the second peak current conduction period timer signal Tpps shown in FIG. Is energized and the second base current Ibp is energized during the period from time t1 to t21 and time t22 to t3 when the signal becomes low.

  In the waveform of the MIG welding current Iwm shown in FIG. 5A, the first peak current Ipm, the first base current Ibm, and the peak period Tp are predetermined values, and the pulse period Tf is changed by frequency modulation control. The base period Tb also changes. On the other hand, in the waveform of the plasma welding current Iwp shown in FIG. 5B, the second base current Ibp and the second peak current Ipp are predetermined values. Then, even if the pulse period Tf is changed by the frequency modulation control of the MIG welding current Iwm, the second peak current conduction period Tpp is controlled so that the average value of the plasma welding current Iwp becomes the current set value. This control will be referred to as period modulation control. In the figure, the second peak current conduction period Tpp = Tpp1.

  FIG. 8 is a timing chart of each signal of the MIG welding power source PSM and the plasma welding power source PSP when the feeding speed is high. (A) shows the MIG welding current Iwm, (B) shows the plasma welding current Iwp, (C) shows the pulse period signal Tfs, and (D) shows the peak period timer signal Tps. FIG. 4E shows the second peak current conduction period timer signal Tpps. This figure shows a case where the time ratio between the peak period Tp and the pulse period Tf is about 1: 2 by frequency modulation control. This figure corresponds to FIG. 7, and the description of the same operation will be omitted, and different points will be described.

  In the waveform of the MIG welding current Iwm shown in FIG. 4A, the first peak current Ipm, the first base current Ibm, and the peak period Tp are the same values as in FIG. 4, and the pulse period Tf is changed by frequency modulation control. Along with this, the base period Tb also changes. In FIG. 7, the pulse cycle Tf = Tf1, and in FIG. 7, the pulse cycle Tf = Tf2. Tf1> Tf2. On the other hand, in the waveform of the plasma welding current Iwp shown in FIG. 5B, the second base current Ibp and the second peak current Ipp have the same values as in FIG. Then, even if the pulse period Tf is changed by the frequency modulation control of the MIG welding current Iwm, the time length of the second peak current conduction period Tpp is controlled so that the average value of the plasma welding current Iwp becomes the current set value. . In FIG. 7, the second peak current energization period Tpp = Tpp1, and in FIG. 7, the second peak current energization period Tpp = Tpp2. Tpp1> Tpp2. This is because the pulse period Tf is shorter in the figure, and the second peak current conduction period Tpp is shortened in order to obtain the same average value.

  A numerical example will be described with reference to FIG. It is assumed that the waveform parameters of the MIG welding current Iwm are the first peak current Ipm = 450 A, the first base current Ibm = 50 A, the peak period Tp = 2 ms, and the pulse period Tf1 = 10 ms. On the other hand, the waveform parameters of the plasma welding current Iwp are the on-delay period Tod = 0, the second base current Ibp = 50 A, the second peak current Ipp = 450 A, and the second peak current energization period Tpp = 0-8 ms by period modulation control. The average value of the plasma welding current Iwp can be set in the range of 50 to 370A. The average value of the MIG welding current Iwm at this time is 130A. In the case of FIG. 8, if the pulse period Tf2 = 4 ms, the average value of the plasma welding current Iwp can be set in the range of 50 to 250A. At this time, the average value of the MIG welding current Iwm is 250A.

  According to the second embodiment described above, even if the pulse period is changed by frequency modulation control of the MIG welding current, the average value of the plasma welding current is set to a predetermined value by controlling the second peak current conduction period of the plasma welding current. Can be. For this reason, the same effects as those of the first embodiment are obtained. Furthermore, the setting range of the average value of the plasma welding current can be made wider than that in the first embodiment.

  As another embodiment, the second base current value may be feedback controlled so that the average value of the plasma welding current is equal to the current set value. Furthermore, feedback control may be performed by combining at least two of the second peak current value, the second base current value, and the second peak current energizing period so that the average value of the plasma welding current becomes equal to the current setting value. In the frequency modulation control for the MIG arc, the instantaneous value or the average value of the first peak voltage Vpm may be used instead of the average value of the MIG welding voltage Vwm. This is because when the aluminum material is used as the base material, the arc length can be detected more accurately by the instantaneous value or the average value of the first peak voltage Vpm than the average value of the MIG welding voltage Vwm. It is.

DESCRIPTION OF SYMBOLS 1a Welding wire 1b Plasma electrode 2 Base material 3a Mig arc 3b Plasma arc 4 Feed tip 7 Feed roll 51 Plasma nozzle 52 Shield gas nozzle 61 Center gas 62 Plasma gas 63 Shield gas EI Current error amplification circuit Ei Current error amplification signal EV Voltage error amplification Circuit Ev Voltage error amplification signal FC Feeding control circuit Fc Feeding control signal FR Feeding speed setting circuit Fr Feeding speed setting signal Fw Feeding speed IAR Current setting circuit Iar Current setting signal IAV Current average value calculation circuit Iav Current average value Signal Ibm first base current IBMR first base current setting circuit Ibmr first base current setting signal Ibp second base current IBPR second base current setting circuit Ibpr second base current setting signal ID current detection circuit Id current detection signal Ipm first Peak current IPMR First peak current setting times Ipmr first peak current setting signal Ipp second peak current IPPR second peak current setting circuit Ippr second peak current setting signal IRC current setting control circuit Irc current setting control signal Iwm MIG welding current Iwp plasma welding current NOT logic inversion circuit Not logic Inversion signal OD On-delay circuit Od On-delay signal PM Power supply main circuit PSM Mig welding power supply PSP Plasma welding power supply SI Current error integration circuit SI2 Second current error integration circuit Tb Base period Td Delay period Tf Pulse period Tfs Pulse period signal Tod On-delay Period Tp Peak period Tpp Second peak current conduction period TPPR Second peak current conduction period setting circuit Tppr Second peak current conduction period setting signal TPPS Second peak current conduction period timer circuit Tpps Second peak current conduction period timer signal TPR Peak period Setting circuit Tpr Period setting signal TPS Peak period timer circuit Tps Peak period timer signal VAV Voltage average value calculation circuit Vav Voltage average value signal Vbm First base voltage VD Voltage detection circuit Vd Voltage detection signal VF Voltage / frequency conversion circuit Vpm First 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)

The MIG arc is generated between the welding wire and the base material by repeating the energization of the first peak current and the energization of the first base current as one pulse period, and the pulse period is changed by frequency modulation control. Control the arc length,
The second peak current is applied during part or all of the first base current supply period, and the second base current is supplied during the other period of the pulse period so as to surround the welding wire. In a plasma MIG welding method for generating a plasma arc between the formed plasma electrode and the base material,
Controlling the waveform parameter of the plasma welding current so that an average value of the plasma welding current formed from the second peak current and the second base current is equal to a predetermined current setting value;
The plasma MIG welding method characterized by the above-mentioned. The waveform parameter control sets the energization period of the second base current and the second peak current to a predetermined value, and the second peak current so that an average value of the plasma welding current is equal to the current set value. Is a control that changes the feedback control,
The plasma MIG welding method according to claim 1. The waveform parameter control sets the second base current and the second peak current to predetermined values, and the energization period of the second peak current so that an average value of the plasma welding current is equal to the current setting value. Is a control that changes the feedback control,
The plasma MIG welding method according to claim 1.

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