JP5755942B2 - Plasma MIG welding control 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 plasma arc is generated by passing a plasma welding current between a plasma electrode and a base material arranged in a welding torch. At the same time, the plasma electrode is formed into a hollow shape, and a welding wire fed through a power supply tip disposed in the plasma electrode is fed through the hollow shape, and between the welding wire and the base material. A MIG arc is generated by applying a MIG welding current. Therefore, the MIG arc is wrapped 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.

  In general, a pulse waveform is often used for the MIG welding current in order to suppress the generation of spatter and stably supply droplets. Therefore, the MIG welding method is a general MIG pulse welding method. Of course, a DC MIG welding method can also be used for the MIG 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 direct current or a 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 current / voltage waveform diagram of plasma MIG welding in the prior art. (A) shows the MIG welding current Iwm, (B) shows the MIG welding voltage Vwm, (C) shows the plasma welding current Iwp, and (D) shows the plasma welding voltage Vwp. Show. Hereinafter, a description will be given with reference to FIG.

  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 pulse 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 about 400 to 500 A, which is equal to or higher than the critical value, and is called 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 100 to 180 A, which is less than the critical value. The unit pulse condition and the base current Ib are set to appropriate values according to the welding wire material, diameter, feeding speed, and the like. The value of the peak current Ip is smaller than that of a general single pulse arc welding, and the value of the base current Ib is large. This is because the mig arc is enveloped in the plasma arc, and the welding wire receives heat from the plasma arc, so the droplet transfer state is not stable unless the values of the peak current Ip and the base current Ib are set in this way. is there.

  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. Further, as shown in FIG. 4D, a plasma welding voltage Vwp is applied between the plasma electrode and the base material. Therefore, the plasma arc is generated by energizing the plasma welding current Iwp with a constant value. The plasma welding current Iwp may be a pulse waveform. In this case, the plasma welding voltage Vwp also has a pulse waveform.

JP 2008-229641 A

  As described above, the plasma arc is generated between the plasma electrode and the base material. The mig arc is generated between the welding wire fed through the hollow plasma electrode and the base material. Since the plasma electrode and the welding wire need to be insulated, a cylindrical insulator is provided in the plasma electrode so that the welding wire is passed through the inside. Therefore, since the inside of the plasma electrode and the welding wire are separated by an insulator, they are not in direct contact with each other, and abnormal arc discharge does not occur between the two in the plasma electrode.

  However, the welding wire delivered from the through-hole of the plasma electrode and the tip (lower end) of the plasma electrode are not in contact with each other, but are at a very close distance. For this reason, when the voltage difference between the plasma electrode and the welding wire increases, an abnormal arc discharge may occur between the welding wire and the tip of the plasma electrode. When this abnormal arc discharge occurs, the generation state of the plasma arc and the MIG arc becomes unstable and the welding quality deteriorates. Furthermore, when this abnormal arc discharge occurs, the plasma electrode partially melts and the welding torch is damaged, and welding may not be continued.

  Therefore, in the present invention, plasma MIG welding control that prevents abnormal arc discharge from occurring between the plasma electrode and the welding wire, prevents damage to the welding torch, and maintains good welding quality. It aims to provide a method.

In order to solve the above-mentioned problem, the invention of claim 1 applies a plasma welding voltage between a plasma electrode and a base material arranged in a welding torch and energizes a plasma welding current having a preset value. And generating a plasma arc, forming the plasma electrode in a hollow shape, and feeding a welding wire fed through a power feed tip disposed in the plasma electrode through the hollow shape. In a plasma MIG welding control method for generating a MIG arc by applying a MIG welding voltage between a tip and a base material and energizing a MIG welding current,
When the voltage difference between the average value of the plasma welding voltage and the average value of the MIG welding voltage is larger than a predetermined reference voltage value, the plasma welding current is decreased from a set value to reduce the voltage difference. ,
This is a plasma MIG welding control method.

The invention of claim 2 provides a predetermined lower limit when reducing the plasma welding current,
The plasma MIG welding control method according to claim 1.

The invention of claim 3 has a slope when reducing the plasma welding current,
The plasma MIG welding control method according to claim 1 or 2, wherein the plasma MIG welding control method is used.

  According to the present invention, when the voltage difference between the average value of the plasma welding voltage applied to the plasma electrode and the average value of the MIG welding voltage applied to the welding wire is larger than the reference voltage value, plasma welding is performed. The voltage difference is reduced by reducing the current. For this reason, it is possible to prevent abnormal arc discharge from occurring between the plasma electrode and the welding wire, prevent damage to the welding torch, and maintain good welding quality.

It is an electric current / voltage waveform diagram which shows the plasma MIG welding control method concerning an embodiment of the invention. It is a block diagram of the welding apparatus for enforcing the plasma MIG welding control method 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 the plasma welding power supply PSP which comprises the welding apparatus of FIG. It is a current and voltage waveform diagram of plasma MIG welding in the prior art.

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

  FIG. 1 is a current / voltage waveform diagram showing a plasma MIG welding control method according to an embodiment of the present invention. (A) shows the time change of the torch height (distance between the tip of the plasma electrode and the base material) Lt (mm), and (B) shows the time change of the average value Ima of the MIG welding current. (C) shows the change over time of the average value Vma of the MIG welding voltage, (D) shows the change over time of the average value Ipa of the plasma welding current, and (E) shows the average of the plasma welding voltage. The time change of the value Vpa is shown. Each average value is generated by passing through a low-pass filter having a cutoff frequency of 1 to 10 Hz. Since the time axis (horizontal axis) in the figure is about 1 second / cm, and FIG. 5 described above is about 1 ms / cm, the waveform in FIG. It has become. Hereinafter, a description will be given with reference to FIG.

  As shown in FIG. 5A, the torch height Lt is L1 (mm) during the period before time t1, and is increased to L2 (mm) during the period from time t1 to t2, and from time t2 to t3. During the period, it further increases to L3 (mm), and returns to L1 (mm) during the period after time t3. Therefore, L1 <L2 <L3. For example, L1 = 20 mm, L2 = 25 mm, and L3 = 30 mm. The welding wire feeding speed is constant throughout the entire period.

(1) Period before time t1 (Lt = L1)
As shown in FIG. 5B, the average value Ima of the MIG welding current becomes an approximately straight line by averaging the pulse waveform described above with reference to FIG. 5A, and the value is determined by the feeding speed and the arc load. (A). As shown in FIG. 5C, the average value Vma of the MIG welding voltage is averaged from the pulse waveform described above with reference to FIG. 5B and becomes a substantially straight line, and the value becomes equal to the voltage setting value, Vma1 ( V). As shown in FIG. 6D, the average value Ipa of the plasma welding current is a straight line because it is not a pulse waveform but a pulse waveform as described above with reference to FIG. 5C, and its value is equal to the current set value. It becomes Ipa1 (A). As shown in FIG. 5E, the average value Vpa of the plasma welding voltage is a straight line because it is not a pulse waveform but a pulse waveform as described above with reference to FIG. (V). Therefore, in the figure, the average value Ipa of the plasma welding current is substantially the same as the plasma welding current Iwp. Similarly, the average value Vpa of the plasma welding voltage is substantially the same as the plasma welding voltage Vwp. For example, Ima1 = 200A, Vma1 = 28V, Ipa1 = 150A, Vpa1 = 40V.

(2) Time period from t1 to t2 (Lt = L2)
As shown in FIG. 5B, the average value Ima of the MIG welding current decreases slightly because the torch height Lt increases and the arc load increases, and becomes Ima2 (A). Ima2 <Ima1. As shown in FIG. 5C, the average value Vma of the MIG welding voltage increases as the torch height Lt increases and the arc load increases, and becomes Vma2 (V). Vma2> Vma1. As shown in FIG. 4D, the average value Ipa of the plasma welding current is a reference voltage value determined by a voltage difference ΔV = Vpa−Vma between the average value Vpa of the plasma welding voltage and the average value Vma of the MIG welding voltage. Since it is Vth or less, Ipa1 (A) equal to the current set value remains unchanged. As shown in FIG. 5E, the average value Vpa of the plasma welding voltage increases as the torch height Lt increases and the arc load increases, and becomes Vpa2 (V). Vpa2> Vpa1. For example, Ima2 = 180A, Vma2 = 29V, Vpa2 = 46V, and reference voltage value Vth = 20V. Therefore, the voltage difference ΔV = Vpa2−Vma2 = 17V, which is smaller than the reference voltage value Vth.

(3) Period from time t2 to t3 (Lt = L3)
As shown in FIG. 5B, the average value Ima of the MIG welding current is further reduced because the torch height Lt is further increased and the arc load is further increased to become Ima3 (A). Ima3 <Ima2 <Ima1. As shown in FIG. 5C, the average value Vma of the MIG welding voltage is further increased because the torch height Lt is further increased and the arc load is further increased, and becomes Vma3 (V). Vma3>Vma2> Vma1. As shown in FIG. 4D, the average value Ipa of the plasma welding current is such that the voltage difference ΔV = Vpa−Vma between the average value Vpa of the plasma welding voltage and the average value Vma of the MIG welding voltage exceeds the reference voltage value Vth. Therefore, it becomes Ipa3 (A) which is smaller than the current set value by the voltage difference correction control described later. Ipa3 <Ipa1. As shown in FIG. 5E, the average value Vpa of the plasma welding voltage further increases because the torch height Lt is further increased and the arc load is further increased. However, when the voltage difference ΔV becomes the reference voltage value Vth length, the average value Ipa of the plasma welding current is reduced by the voltage difference correction control described later. Therefore, the average value Vpa of the plasma welding voltage is equal to the reference voltage value Vth. And a value Vpa3 (V) that is substantially equal to Vpa3>Vpa2> Vpa1. For example, Ima3 = 160A, Vma3 = 30V, Ipa3 = 100A, Vpa3 = about 50V, and reference voltage value Vth = 20V. Therefore, the voltage difference ΔV = Vpa3−Vma3 = about 20V, which is substantially equal to the reference voltage value Vth.

The voltage difference correction control will be described. The voltage difference correction control includes the following steps.
1) The plasma welding voltage Vwp during welding is detected and passed through a low-pass filter to calculate an average value Vpa of the plasma welding voltage. At the same time, the MIG welding voltage Vwm during welding is detected and passed through a low-pass filter to calculate the average value Vma of the MIG welding voltage. In plasma MIG welding, the average value Vpa of the plasma welding voltage is larger than the average value Vma of the MIG welding voltage because of the structure of the welding torch. The cutoff frequency of the low-pass filter is about 1 to 10 Hz. The cut-off frequency of the MIG welding voltage may be set lower than the plasma welding voltage. This is because the MIG welding voltage is a pulse waveform, so that the DC voltage is substantially DC. Instead of passing through a low-pass filter, smoothing may be performed by an RC circuit. Furthermore, both voltage values may be sampled every minute period (10 to 100 μs) and converted into digital values, and the time-series sampling values may be averaged by moving average.
2) The voltage difference ΔV = Vpa−Vma is calculated by subtracting the average value Vma of the MIG welding voltage from the average value Vpa of the plasma welding voltage.
3) When the voltage difference ΔV is equal to or less than a predetermined reference voltage value Vth, the plasma welding current Iwp is constant-current controlled to a value equal to the current set value.
4) When the voltage difference ΔV exceeds the reference voltage value Vth, the current correction amount ΔIr = G · (ΔV−Vth) is calculated. G is a predetermined amplification factor and takes a negative value. For example, G = −100. Here, since ΔV−Vth is a positive value, the current correction amount ΔIr is a negative value. The plasma welding current Iwp is constant-current controlled to a value obtained by correcting (decreasing) the current set value by the current correction amount ΔIr. As a result, the plasma welding current Iwp decreases, and the average value Vpa of the plasma welding voltage is controlled so that the voltage difference ΔV becomes substantially equal to the reference voltage value Vth.
5) The above 1) to 4) are repeated.

(4) Period after time t3 (Lt = L1)
Since the torch height Lt returns to L1 and decreases, the operation returns to the same operation as the above item (1). As shown in FIG. 5B, the average value Ima of the MIG welding current increases as the torch height Lt returns to L1, and becomes Ima1 (A). As shown in FIG. 5C, the average value Vma of the MIG welding voltage decreases as the torch height Lt returns to L1, and becomes Vma1 (V). As shown in FIG. 4D, the average value Ipa of the plasma welding current is such that the voltage difference ΔV = Vpa−Vma between the average value Vpa of the plasma welding voltage and the average value Vma of the MIG welding voltage is less than the reference voltage value Vth. Therefore, it increases to Ipa1 (A) equal to the current set value. As shown in FIG. 5E, the average value Vpa of the plasma welding voltage decreases as the torch height Lt returns to L1, and becomes Vpa1 (V). The voltage difference ΔV is equal to or less than the reference voltage value Vth.

  The voltage difference ΔV between the average value Vpa of the plasma welding voltage and the average value Vma of the MIG welding voltage increases as shown in the figure because the torch height Lt increases due to changes in joint shape, weaving, camera shake, etc. This is the case. The plasma welding current Iwp is often set in the range of about 50 to 150 A, but the voltage difference ΔV increases as this value increases. The value of the voltage difference ΔV that causes abnormal arc discharge between the plasma electrode and the welding wire depends on the structure of the welding torch, the types of the center gas and plasma gas, the time during which the voltage is applied, and the feed rate. Although it depends on the feeding speed and the like, the probability increases when it is 22 to 32 V or more. When a voltage difference ΔV greater than this value is continuously applied for 2 to 5 seconds or more, abnormal arc discharge often occurs. Therefore, by the voltage difference correction control described above, the voltage difference ΔV is controlled to be smaller than a value that is likely to cause abnormal arc discharge. For this reason, in this Embodiment, abnormal arc discharge can be prevented. Here, the reference voltage value Vth is set to a value that does not cause an abnormal arc discharge in the range of about 20 to 30V. It is desirable to optimize the reference voltage value Vth according to the structure of the welding torch, the types of center gas and plasma gas, the feeding speed, and the like.

  Further, when the plasma welding current Iwp is decreased by the voltage difference correction control described above, a predetermined lower limit value may be provided. This is because the generation state of the plasma arc becomes unstable if the value at which the plasma welding current Iwp is reduced becomes too small. The lower limit is set to about 20-40A.

  Also, as shown at time t2 in FIG. 4D, when the plasma welding current Iwp is decreased, it is not decreased sharply as shown in FIG. Also good. Similarly, as shown at time t3 in FIG. 4D, when the plasma welding current Iwp is increased, it is not increased sharply as shown in FIG. May be. These inclinations are set to about 1 to 10 A / ms. The reason why the slope is provided is that the state in which the plasma arc is generated can be more stably maintained when the current is gradually changed.

  The figure shows the case where the plasma welding current Iwp is not a pulse waveform but a direct current waveform as described above. When the plasma welding current Iwp is a pulse waveform, it is reduced as follows by voltage difference correction control. When the plasma welding current Iwp is formed from the peak current and the base current, only the peak current may be reduced or both the peak current and the base current may be reduced.

  FIG. 2 is a configuration diagram of a welding apparatus for performing the plasma MIG welding method according to the above-described 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.

  The plasma electrode 1b is formed in a hollow shape. The power feeding chip 4 is insulated and disposed in the hollow shape of the plasma electrode 1b. And the welding wire 1a is fed from the through-hole provided in this electric power feeding chip | tip 4. FIG. The power feed tip 4 is electrically connected to the welding wire 1a. However, the welding wire 1a is insulated from the plasma electrode 1b through the cylindrical insulator 8. The insulator 8 is made of, for example, ceramics. 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). Of course, the welding operator may manually operate the welding torch WT. In this case, since the welding torch WT is larger and heavier than a normal welding torch, camera shake is likely to occur. 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. As shown in the figure, the distance between the tip of the plasma electrode 1b and the base material 2 is the torch height Lt (mm).

  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. The MIG welding voltage average value signal Vma described later with reference to FIG. 3 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). 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. The MIG welding voltage average value signal Vma is input from the MIG welding power source PSM to the plasma welding power source PSP. A circuit (described later with reference to FIG. 4) for performing the above-described voltage difference correction control is provided in the plasma welding power source PSP. 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 waveform diagrams of the MIG welding current Iwm, the MIG welding voltage Vwm, the plasma welding current Iwp, and the plasma welding voltage Vwp are the same as those in FIG.

  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 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. 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 MIG welding voltage average value calculation circuit VMA averages (smooths) the voltage detection signal Vd by passing it through a low-pass filter (cutoff frequency of about 1 to 10 Hz), and outputs a MIG welding voltage average value signal Vma. . The MIG welding voltage average value signal Vma is also output to the plasma welding power source PSP as described above.

  The feeding speed setting circuit FR outputs a predetermined feeding speed setting signal Fr. The feed control circuit FC inputs the feed speed setting signal Fr and feeds a feed control signal Fc for feeding the welding wire 1a at a feed speed Fw determined by the value of the feed speed setting signal Fr. Output to 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 MIG welding voltage average value signal Vma, and outputs a voltage error amplification signal Ev. The voltage / frequency conversion circuit VF outputs a pulse period signal Tf having a frequency corresponding to the value of the voltage error amplification signal Ev. The pulse period signal Tf is a trigger signal that becomes High level for a short time every pulse period.

  The peak period setting circuit TPR outputs a predetermined peak period setting signal Tpr. The peak period timer circuit TP 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 when the peak period signal Tp is at a high level, and the base period is when the peak period signal Tp is at a low level.

  The base current setting circuit IBR outputs a predetermined base current setting signal Ibr. The peak current setting circuit IPR outputs a predetermined peak current setting signal Ipr. The current setting control circuit IRC outputs the base current setting signal Ibr as the current setting control signal Irc when the peak period signal Tp is at the low level, and outputs the peak current setting signal Ipr as the current when the peak period signal Tp is at the high level. It is output as a setting control signal Irc.

  The current detection circuit ID detects the MIG welding current Iwm and outputs a current detection signal Id. The current error amplification circuit EI amplifies an error between the current setting control signal Irc and the current detection signal Id, and outputs a current error amplification signal Ei. 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.

  FIG. 4 is a block diagram of the plasma welding power source PSP constituting the above-described FIG. As described above, the MIG welding voltage average value signal Vma is input from the MIG welding power source PSM to the plasma welding power source PSP. The above-described voltage difference correction control is performed by the plasma welding power source PSP. 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. 2 described above, but is simplified here.

  The current detection circuit ID detects the plasma welding current Iwp and outputs a current detection signal Id. The voltage detection circuit VD detects the plasma welding voltage Vwp and outputs a voltage detection signal Vd. The plasma welding voltage average value calculation circuit VPA averages (smooths) the voltage detection signal Vd by passing it through a low-pass filter (cutoff frequency of about 1 to 10 Hz), and outputs a plasma welding voltage average value signal Vpa. .

The reference voltage value setting circuit VTH outputs a predetermined reference voltage value signal Vth. The voltage difference calculation circuit DV receives the plasma welding voltage average value signal Vpa and the MIG welding voltage average value signal Vma from the MIG welding power source PSM, and calculates and outputs a voltage difference signal ΔV = Vpa−Vma. The current correction amount calculation circuit DIR receives the voltage difference signal ΔV and the reference voltage value signal Vth as described above, performs the following processing described above with reference to FIG. 1, and outputs a current correction amount signal ΔIr.
1) When ΔV ≦ Vth, ΔIr = 0 is output.
2) When ΔV> Vth, ΔIr = G · ΔV is calculated and output. However, G is a predetermined amplification factor and is a negative value. Therefore, ΔIr <0.

  The current setting circuit IR outputs a predetermined current setting signal Ir. The adder AD receives the current setting signal Ir and the current correction amount signal ΔIr, adds both values, and outputs a current addition setting signal Iar. The current control setting circuit ICR receives the current addition setting signal Iar as an input, sets the lower limit value when the value of this signal is equal to or lower than a predetermined lower limit value, and sets a predetermined slope when the value of this signal changes. And the current control setting signal Icr is output. With this circuit, a lower limit value is provided for the value of the current control setting signal Icr. Also, with this circuit, when the current correction amount signal ΔIr changes from 0 to a negative value or from a negative value to 0 in a stepwise manner, the change in the current control setting signal Icr can be inclined. it can. If this slope is set to 0, the change of the current control setting signal Icr becomes steep.

  The current error amplification circuit EI amplifies an error between the current control setting signal Icr 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 current control setting signal Icr, it is a power source having a constant current characteristic. In the plasma welding power source PSP, as described above with reference to FIGS. 1D and 1E, voltage difference correction control is performed.

  According to the above-described embodiment, when the voltage difference between the average value of the plasma welding voltage applied to the plasma electrode and the average value of the MIG welding voltage applied to the welding wire is larger than the reference voltage value. The voltage difference is reduced by reducing the plasma welding current. For this reason, it is possible to prevent abnormal arc discharge from occurring between the plasma electrode and the welding wire, prevent damage to the welding torch, and maintain good welding quality.

DESCRIPTION OF SYMBOLS 1a Welding wire 1b Plasma electrode 2 Base material 3a Mig arc 3b Plasma arc 4 Feed tip 51 Plasma nozzle 52 Shield gas nozzle 61 Center gas 62 Plasma gas 63 Shield gas 7 Feed roll 8 Insulator AD Adder circuit DIR Current correction amount calculation circuit DV Voltage Difference calculation circuit 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 FR Feed speed setting circuit Fr Feed speed setting signal Fw Feed speed Iar Current addition setting signal Ib Base current IBR Base current setting circuit Ibr Base current setting signal ICR Current control setting circuit Icr Current control setting signal ID Current detection circuit Id Current detection signal Ima Mig welding current average value Ip Peak current Ipa Plasma welding current Average value IPR Peak current setting Circuit Ipr Peak current setting signal IR Current setting circuit Ir Current setting signal IRC Current setting control circuit Irc Current setting control signal Iwm MIG welding current Iwp Plasma welding current PM Power supply main circuit PSM MIG welding power supply PSP Plasma welding power supply Tb Base period Tf Pulse period (signal)
TP Peak period timer circuit Tp Peak period (signal)
TPR peak period setting circuit Tpr peak period setting signal Vb base voltage VD voltage detection circuit Vd voltage detection signal VF voltage / frequency conversion circuit VMA MIG welding voltage average value calculation circuit Vma MIG welding voltage average value (signal)
Vp Peak voltage VPA Plasma welding voltage average value calculation circuit Vpa Plasma welding voltage average value (signal)
VR voltage setting circuit Vr voltage setting signal VTH reference voltage value setting circuit Vth reference voltage value (signal)
Vwm MIG welding voltage Vwp Plasma welding voltage WM Feeding motor WT Welding torch ΔIr Current correction amount (signal)
ΔV Voltage difference (signal)

Claims (3)

A plasma arc is generated by applying a plasma welding current between a plasma electrode disposed in the welding torch and a base material and applying a plasma welding current of a preset value, and the plasma electrode is hollow. A welding wire fed through a feeding tip disposed in the plasma electrode is fed through the hollow shape, and a MIG welding voltage is applied between the feeding tip and a base material to In a plasma MIG welding control method for generating a MIG arc by energizing a welding current,
When the voltage difference between the average value of the plasma welding voltage and the average value of the MIG welding voltage is larger than a predetermined reference voltage value, the plasma welding current is decreased from a set value to reduce the voltage difference. ,
The plasma MIG welding control method characterized by the above-mentioned. Providing a predetermined lower limit when reducing the plasma welding current,
The plasma MIG welding control method according to claim 1. Having a slope when reducing the plasma welding current,
The plasma MIG welding control method according to claim 1 or 2, characterized by the above.

Images