JP5557515B2 - Plasma MIG welding method - Google Patents

Description

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

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

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

  FIG. 5 is a waveform diagram showing a plasma MIG welding method. (A) shows the MIG welding current Iwm, (B) shows the MIG welding voltage Vwm, and (C) shows the plasma welding current Iwp. Hereinafter, a description will be given with reference to FIG.

  As shown in FIG. 6A, a MIG welding current Iwm composed of a peak current Ip during the peak period Tp and a base current Ib during the base period Tb is energized. The peak period Tp and the base period Tb are combined to form a pulse period Tf. Corresponding to the energization of the MIG welding current Iwm, the peak voltage Vp is applied between the welding wire and the base material during the peak period Tp, and during the base period Tb, as shown in FIG. A base voltage Vb is applied.

  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 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.

  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.

JP 2008-229641 A

  In plasma MIG welding, two arcs of MIG arc and plasma arc are generated simultaneously between one welding torch and the base material. The mig arc is generated in a state of being surrounded by a plasma arc. For this reason, the MIG arc welding wire receives heat from the plasma arc. The arc length of the MIG arc is maintained at a predetermined value by balancing the feeding speed and the melting speed. The feeding speed is a constant value. The melting rate is substantially proportional to the average value of the MIG welding current Iwm. In plasma MIG welding, a melting rate approximately proportional to the average value of the plasma welding current Iwp is taken into account. That is, feeding speed = (melting speed based on average value of MIG welding current Iwm) + (melting speed based on average value of plasma welding current Iwp). Since the feed rate is a constant value, the arc length is maintained so that the arc length is kept constant when the melting rate based on the average value of the plasma welding current Iwp is increased, so that the melting rate based on the average value of the MIG welding current Iwm is reduced. Long control works. The average value of the MIG welding current Iwm is inversely proportional to the pulse period Tf, as shown in FIG. As a result, when the average value of plasma welding current Iwp increases, the arc length control acts so that the melting rate by the average value of plasma welding current Iwp increases and the melting rate by the average value of MIG welding current Iwm decreases. The pulse period Tf of the MIG welding current Iwm becomes longer. When the pulse period Tf changes, the size of the droplet that moves every pulse period changes. When the average value of the plasma welding current Iwp becomes large and the pulse period becomes too long, the size of the droplet increases and the droplet transfer state becomes unstable. If it becomes like this, as shown in FIG. 6, it will become the rough bead appearance which has a streak on the bead surface. A numerical example is as follows. Welding wire: Aluminum alloy wire with a diameter of 1.2 mm, feed rate = 9 m / min, peak period Tp = 1.2 ms, peak current Ip = 300 A, base current Ib = 30 A, plasma welding current Iwp = 50 A In this case, the pulse period Tf = 4.5 ms, and when Iwp = 100 A, Tf = 8 ms. Thus, the pulse period Tf is about twice as long.

  Accordingly, an object of the present invention is to provide a plasma MIG welding method that can maintain a stable droplet transfer state even when the set value of the plasma current changes and can obtain a good bead appearance. To do.

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. The MIG arc is generated by energizing the MIG welding current, and the plasma arc is energized by energizing the plasma welding current between the welding torch and the base material via the gas supplied to surround the welding wire. In the plasma MIG welding method for generating
The arc period is controlled by controlling the pulse period so that the MIG welding voltage value becomes equal to a predetermined voltage setting value, and the peak period and the peak current are set according to the average value of the plasma welding current. Change so that becomes a constant value,
This is a plasma MIG welding method.

  According to the present invention, the pulse period can be maintained at a constant value by changing the peak period and the peak current in the MIG welding current according to the average value of the plasma welding current. For this reason, even if the average value of the plasma welding current changes, the droplet size per pulse period becomes substantially constant, so that the droplet transfer state becomes stable. As a result, a smooth and beautiful bead appearance having no streaks on the surface can be obtained.

It is a block diagram of the welding apparatus for enforcing the plasma MIG welding method which concerns on embodiment of this invention. It is a figure which shows the change of the peak period Tp and the peak current Ip with respect to the average value of the plasma welding current Iwp which concerns on embodiment 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. It is a wave form diagram which shows the plasma MIG welding method in a prior art. It is a figure which illustrates the bead appearance by a prior art.

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

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

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

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

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

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

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

  Waveform diagrams of the MIG welding current Iwm, the MIG welding voltage Vwm, and the plasma welding current Iwp are the same as those in FIG. 5 described above. However, a pulse waveform may be used for the plasma welding current Iwp. Therefore, an average value is used instead of an instantaneous value as a parameter of the plasma welding current Iwp. When the plasma welding current Iwp is a direct current, the instantaneous value and the average value coincide with each other. In the present embodiment, the peak period Tp and the peak current Ip, which are unit pulse conditions, vary depending on the average value of the plasma welding current Iwp. This is different from the prior art. Hereinafter, this point will be described.

  FIG. 2 is a diagram showing the relationship between the average value (A) of the plasma welding current Iwp, the peak period Tp (ms) and the peak current Ip (A) which are unit pulse conditions. The horizontal axis of the figure shows the average value (A) of the plasma welding current Iwp, and shows the range of 50 to 150 A that is often used in practice. The vertical axis represents the peak period Tp (ms) and the peak current Ip (A). In the figure, the solid line shows the change in the peak period Tp, and the broken line shows the change in the peak current Ip. As in the numerical example described above, an aluminum alloy wire having a diameter of 1.2 mm is used for the welding wire, and the feed rate is 9 m / min. The base current Ib is a constant value at 30A.

  When the average value of the plasma welding current Iwp is 50 A, the peak period Tp = 1.2 ms and the peak current Ip = 300 A are set. The pulse period Tf at this time is 4.5 ms. As the average value of the plasma welding current Iwp increases, both the peak period Tp and the peak current Ip decrease. When the average value of the plasma welding current Iwp reaches 100 A, the peak period Tp = 0.8 ms and the peak current Ip = 270 A are set. At this time, the pulse period Tf has substantially the same value as described above. When the average value of the plasma welding current Iwp is 150 A, the peak period Tp = 0.6 ms and the peak current Ip = 260 A. The pulse period Tf at this time is also substantially the same value as above. Here, the reason why the pulse period Tf is substantially the same value is that, as described above, the pulse period Tf is determined by feedback control so that the average value of the MIG welding voltage Vwm is equal to the predetermined voltage setting value. , They are not exactly the same value. It becomes the same value in the range of ± 10%.

  When the average value of the plasma welding current Iwp increases, as described above, the contribution of the MIG arc to the melting rate of the welding wire increases. For this reason, the average value of the MIG welding current Iwm necessary for maintaining the arc length at a constant value becomes small. At this time, as shown in the figure, when the peak period Tp and the peak current Ip which are unit pulse conditions become small, the average value becomes small in a state where the pulse period Tf does not change. Therefore, if the unit pulse condition is reduced as the average value of the plasma welding current Iwp is increased, the pulse period Tf can be maintained at a constant value.

  The change of the peak period Tp with respect to the average value of the plasma welding current Iwp shown in the figure is called a peak period calculation function. Further, the change of the peak current Ip with respect to the average value of the plasma welding current Iwp is referred to as a peak current calculation function. These functions are set to appropriate values according to the material, diameter, feed speed, etc. of the welding wire. This setting is performed by experiment.

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

  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.

  As described above with reference to FIG. 1, the plasma welding current setting circuit IWPR provided outside the MIG welding power source PSM outputs a predetermined plasma welding current setting signal Iwpr. The plasma welding current average value calculation circuit IWPA receives the plasma welding current setting signal Iwpr, calculates an average value of the values, and outputs a plasma welding current average value signal Iwpa. The feed control circuit FC outputs a feed control signal Fc for feeding the welding wire 1a at a preset feed speed set value to the feed motor WM.

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

  The peak period setting circuit TPR receives the above-mentioned plasma welding current average value signal Iwpa and outputs a peak period setting signal Tpr based on a predetermined peak period calculation function as described above with reference to FIG. 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 welding current average value signal Iwpa and outputs a peak current setting signal Ipr based on the peak current calculation function as described above with reference to FIG. The current setting control circuit IRC outputs the base current setting signal Ibr as the current setting control signal Irc when the peak period signal Tp is at the low level, and outputs the peak current setting signal Ipr as the current when the peak period signal Tp is at the high level. It is output as a setting control signal Irc.

  The current detection circuit ID detects the MIG welding current Iwm and outputs a current detection signal Id. The current error amplification circuit EI amplifies an error between the current setting control signal Irc and the current detection signal Id, and outputs a current error amplification signal Ei. By performing output control of the welding power source in accordance with the current error amplification signal Ei, the MIG welding current Iwm described above with reference to FIG. The above-described MIG welding power source PSM is a power source having constant voltage characteristics because the output is controlled by changing the pulse period so that the average value of the MIG welding voltage Vwm becomes equal to the value of the voltage setting signal Vr. Even when the plasma welding current setting signal Iwpr has a pulse waveform, the plasma welding current average value calculation circuit IWPA calculates the average value Iwpa of the plasma welding current setting signal Iwpr. Then, a peak period Tp and a peak current Ip corresponding to the average value Iwpa are set.

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

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

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

  According to the above-described embodiment, the pulse period can be maintained at a constant value by changing the peak period and the peak current in the MIG welding current according to the average value of the plasma welding current. For this reason, even if the average value of the plasma welding current changes, the droplet size per pulse period becomes substantially constant, so that the droplet transfer state becomes stable. As a result, a smooth and beautiful bead appearance having no streaks on the surface can be obtained.

DESCRIPTION OF SYMBOLS 1a Welding wire 1b Plasma electrode 2 Base material 3a Mig arc 3b Plasma arc 4 Feed tip 51 Plasma nozzle 52 Shield gas nozzle 61 Center gas 62 Plasma gas 63 Shield gas 7 Feeding roll EI Current error amplification circuit Ei Current error amplification signal EV Voltage error amplification Circuit Ev Voltage error amplification signal FC Feed control circuit Fc Feed control signal Ib Base current IBR Base current setting circuit Ibr Base current setting signal ID Current detection circuit Id Current detection signal Ip Peak current IPR Peak current setting circuit Ipr Peak current setting signal IRC Current setting control circuit Irc Current setting control signal Iwm MIG welding current Iwp Plasma welding current IWPA Plasma welding current average value calculation circuit Iwpa Plasma welding current average value signal IWPR Plasma welding current setting circuit Iwpr Plasma welding current setting No. PM main power source circuit PSM MIG welding power supply PSP plasma welding power Tb base period Tf pulse cycle (signal)
TP Peak period timer circuit Tp Peak period (signal)
TPR Peak period setting circuit Tpr Peak period setting signal 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 (1)

A MIG arc is generated by passing a MIG welding current having a peak current during a peak period and a base current during a base period as one pulse period between a welding wire and a base material fed through a welding torch, and In a plasma MIG welding method for generating a plasma arc by energizing a plasma welding current between the welding torch and the base material via a gas supplied so as to surround a welding wire,
The arc period is controlled by controlling the pulse period so that the MIG welding voltage value becomes equal to a predetermined voltage setting value, and the peak period and the peak current are set according to the average value of the plasma welding current. Change so that becomes a constant value,
The plasma MIG welding method characterized by the above-mentioned.

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