JP2013000783A - Monitoring method for plasma mig welding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an abnormal arc discharge generated between a plasma electrode 1b and a welding wire 1a in a plasma MIG welding method.SOLUTION: A plasma arc 3b is generated between the plasma electrode 1b and a base material 2. A MIG arc 1a is generated between the welding wire 1a and the base material 2. Before starting welding, a torch height Lt which is a distance between an end of the plasma electrode 1b and the base material 2 is set, and a plasma weld voltage Vwp is estimated by an arc characteristic function with the set value of the torch height Lt and a set value Ir of a plasma weld current as input. When a set voltage difference between the estimated value of the plasma weld voltage Vwp and a set value Vr of a MIG weld voltage is higher than a reference voltage value, it is determined that the abnormal arc discharge is generated, and an alarm is generated. The abnormal arc discharge can be prevented by reconsidering the welding condition when the alarm is generated.

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. 6 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, an abnormal arc discharge is prevented from occurring between the plasma electrode and the welding wire, the welding torch is prevented from being damaged, and the welding quality can be maintained well. The purpose is to provide a monitoring method.

In order to solve the above-described 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 preset plasma welding current. Generating a plasma arc, and forming the plasma electrode into a hollow shape, and feeding a welding wire fed through a power feed tip disposed in the plasma electrode through the hollow shape, In the plasma MIG welding method of generating a MIG arc by applying a MIG welding current by applying a MIG welding voltage set in advance between the base material,
Before starting welding, a torch height, which is a distance between the tip of the plasma electrode and the base material, is set, and a predetermined arc is set with the set value of the torch height and the set value of the plasma welding current as inputs. The plasma welding voltage is estimated by a characteristic function, and an abnormal arc discharge occurs when the set voltage difference between the estimated value of the plasma welding voltage and the set value of the MIG welding voltage is larger than a predetermined reference voltage value. Discriminate and issue an alarm,
This is a method for monitoring plasma MIG welding.

The invention of claim 2 calculates and displays a set value of the plasma welding current at which the set voltage difference becomes equal to or less than the reference voltage value when the alarm is issued.
The plasma MIG welding monitoring method according to claim 1, wherein:

The invention of claim 3 calculates and displays a set value of the torch height at which the set voltage difference becomes equal to or less than the reference voltage value when the alarm is issued.
The plasma MIG welding monitoring method according to claim 1 or 2, wherein the plasma MIG welding is monitored.

  According to the present invention, it is possible to determine whether or not an abnormal arc discharge may occur before starting welding, and to issue an alarm when there is a possibility. For this reason, in the present invention, it is possible to prevent an abnormal arc discharge from occurring between the plasma electrode and the welding wire, and by reviewing the welding conditions, the welding torch is prevented from being damaged, Good welding quality can be maintained.

It is a block diagram of the welding apparatus for enforcing the monitoring method of the plasma MIG welding 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 block diagram of monitoring device AM which constitutes the welding device of FIG. FIG. 5 is a diagram for explaining an arc characteristic function built in the abnormal arc discharge determination circuit AR of FIG. 4. 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 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, a plasma welding power source PSP, and a monitoring device AM 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. When the MIG welding voltage Vwm is applied from the MIG welding power source PSM via the power feed tip 4, the welding wire 1a is set to the + side. The MIG welding voltage Vwm is a voltage between the power feed tip 4 and the base material 2, but can be regarded as a voltage between the welding wire 1 a and the base material 2. The MIG welding power source PSM is a power source having a constant voltage characteristic, and is controlled such that the average value of the MIG welding voltage Vwm is equal to the predetermined value of the MIG welding voltage setting signal Vr. The MIG welding voltage setting signal Vr is output to the monitoring device AM. 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 equal to a predetermined value of the plasma welding current setting signal Ir. This plasma welding current setting signal Ir is output to the monitoring device AM. 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.

  The monitoring device AM receives the MIG welding voltage setting signal Vr and the plasma welding current setting signal Ir as described above, and abnormal arc discharge occurs between the plasma electrode 1b and the welding wire 1a as will be described later with reference to FIG. Whether or not there is a possibility of occurrence is determined from welding conditions before welding, and if it is determined that there is a possibility of occurrence, an alarm is issued. In addition, when an alarm is issued, the monitoring device AM displays a welding condition correction method on the display.

  FIG. 2 is a block diagram of the MIG welding power source PSM that constitutes the welding apparatus of 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 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 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 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 MIG welding voltage setting circuit VR outputs a predetermined MIG welding voltage setting signal Vr to the voltage error amplification circuit EV and the monitoring device AM. The voltage error amplification circuit EV amplifies an error between the MIG welding 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 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 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 a constant voltage characteristic 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 MIG welding voltage setting signal Vr.

  FIG. 3 is a block diagram of the plasma welding power source PSP that constitutes the welding apparatus of 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 plasma welding current setting circuit IR outputs a predetermined plasma welding current setting signal Ir to the current error amplification circuit EI and the monitoring device AM. 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 Ir 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. The plasma welding power source PSP described above is controlled so that the plasma welding current Iwp is equal to the value of the plasma welding current setting signal Ir.

  FIG. 4 is a block diagram of the monitoring device AM constituting the welding device of FIG. 1 described above. Hereinafter, each block will be described with reference to FIG.

  The monitoring device AM is surrounded by a broken line and includes a torch height setting circuit LTR, a reference voltage value setting circuit VTH, an abnormal arc discharge determination circuit AR, a notification circuit HT, and a display DP.

  The torch height setting circuit LTR outputs a predetermined torch height setting signal Ltr. This torch height setting signal Ltr is preset by measuring the distance between the tip of the plasma electrode and the base material. Further, in welding using a welding robot, the torch height data is stored in the robot control device, and therefore may be transmitted from the robot control device. The torch height setting signal Ltr is set in a range of about 15 to 30 mm.

  The reference voltage value setting circuit VTH outputs a predetermined reference voltage value signal Vth. In order to explain how to set this value, the cause of abnormal arc discharge between the plasma electrode and the welding wire will be described. When the torch height increases due to a change in joint shape, weaving, camera shake, or the like, the voltage difference between the plasma welding voltage and the MIG welding voltage increases. This voltage difference is a voltage between the plasma electrode and the welding wire. Further, the plasma welding current Iwp is often set in a range of about 50 to 200 A, but the voltage difference increases as this value increases. The value of the voltage difference that causes an abnormal arc discharge between the plasma electrode and the welding wire depends on the structure of the welding torch, the type of center gas and plasma gas, the time during which the voltage is applied, and the feed Although it depends on the speed, the probability increases when the voltage is 22 to 32 V or higher. When a voltage difference equal to or greater than this value is continuously applied for 2 to 5 seconds or more, abnormal arc discharge often occurs. Therefore, the value of the reference voltage value signal Vth is set to a value that does not cause abnormal arc discharge according to the welding conditions. Specifically, it is set to about 20-30V.

  The abnormal arc discharge discrimination circuit AR includes a plasma welding current setting signal Ir from the plasma welding power source PSP, a MIG welding voltage setting signal Vr from the MIG welding power source PSM, the torch height setting signal Ltr, and the reference voltage value signal Vth. As an input, the following processing described with reference to FIG. 5 is performed to output an alarm signal Ar, a recommended plasma welding current value signal Ips, and a recommended torch height value signal Lts. As will be described later, when the alarm signal Ar is at a high level, an alarm is issued because an abnormal arc discharge may occur.

1) Estimation of Plasma Welding Voltage FIG. 5 is an arc characteristic diagram showing the relationship between the plasma welding current Iwp (A) shown on the horizontal axis and the plasma welding voltage Vwp (V) shown on the vertical axis. The characteristic L1 in the figure is when the torch height Lt = 20 mm, the characteristic L2 is when the torch height Lt = 25 mm, and the characteristic L3 is when the torch height Lt = 30 mm. When the plasma welding current setting signal Ir and the torch height setting signal Ltr are input, the plasma welding voltage Vwp can be estimated using these arc characteristics as a function. A numerical example is shown in FIG. Assuming that the plasma welding current setting signal Ir = 150A and the torch height setting signal Ltr = 30 mm, the point where the plasma welding current Iwp = 150A on the characteristic L3 is the operating point Pa. A numerical value 52V on the vertical axis of the operating point Pa is an estimated value of the plasma welding voltage Vwp.

2) Calculation of set voltage difference The MIG welding voltage setting signal Vr is a signal for setting the average value of the MIG welding voltage Vwm, which is a pulse waveform, as described above with reference to FIG. Set voltage difference = (estimated value of plasma welding voltage) − (Mig welding voltage setting signal Vr) is calculated. Due to the structure of the welding torch, the plasma welding voltage value is larger than the MIG welding voltage value. Therefore, this set voltage difference is a positive value. In the numerical example, if the MIG welding voltage setting signal Vr = 28V, the setting voltage difference = 52−28 = 24V.

3) Determination of the possibility of occurrence of abnormal arc discharge When the set voltage difference is larger than the value of the reference voltage value signal Vth, it is determined that abnormal arc discharge may occur, and the alarm signal Ar is set to High. Output as level. When the set voltage difference is less than or equal to the reference voltage value signal Vth, the alarm signal Ar is set to the low level and output. In the numerical example, if the set voltage difference = 24V and the reference voltage value signal Vth = 20V, in this case, a high level alarm signal Ar is output.

4) Calculation of recommended plasma welding current value signal Ips and recommended torch height signal Lts When alarm signal Ar is at a high level, recommended plasma welding current value signal Ips and recommended torch height signal Lts are calculated. Calculation is not performed when the alarm signal Ar is at a low level. The method of calculating the recommended plasma welding current value signal Ips is performed as follows with reference to FIG. First, an addition value between the value of the MIG welding voltage setting signal Vr and the value of the reference voltage value signal Vth is calculated as a target voltage value. This target voltage value is the maximum value of the plasma welding voltage at which abnormal arc discharge does not occur. Next, starting from the operating point Pa in FIG. 5, the characteristic L3 is moved in the lower left direction, and the operating point at which the value on the vertical axis becomes the target voltage value is defined as Pb. The value on the horizontal axis of this operating point Pb is the recommended plasma welding current value signal Ips. Similarly, starting from the operating point Pa in FIG. 5, the horizontal axis moves to the same value so that the value on the horizontal axis becomes the same value, and the operating point where the vertical axis value becomes the target voltage value is defined as Pc. The torch height at the operating point Pc is the recommended torch height value signal Lts. In the numerical example, the value on the horizontal axis of the operating point Pb is 50 A, so the plasma welding current recommended value signal Ips = 50 A. Further, since the operating point Pc is on the characteristic L2, the recommended torch height value signal Lts = 25 mm. When the operating point Pc is located in the middle of the characteristics L1 to L3, the torch height of the characteristics L1 to L3 is stored and calculated.

  The notification circuit HT receives the alarm signal Ar described above, and when this signal is at a high level, notifies the abnormality by lighting the indicator lamp, an alarm sound by a buzzer, or the like. Further, the alarm circuit HT may be disconnected to output the alarm signal Ar to the outside of the welding apparatus. In robot welding, you may transmit to a robot control apparatus.

  The display DP receives the plasma welding current recommended value signal Ips and the recommended torch height value signal Lts, and displays these data. The display device DP is, for example, a liquid crystal display. These indications indicate what value the plasma welding current setting signal Ir or torch height setting signal Ltr should be set to prevent abnormal arc discharge from occurring when an alarm is issued. is doing. For this reason, when a warning is issued and it becomes necessary to review the welding conditions, a solution can be presented quickly and accurately. The above-described determination of whether there is a possibility of occurrence of abnormal arc discharge, an alarm, a notification based on the alarm, and a display of a recommended value of the welding condition when the alarm is issued are all performed before the start of welding. Therefore, it is possible to review the welding conditions before abnormal arc discharge occurs during welding and the welding quality deteriorates or the welding torch is damaged.

v
The arc characteristic function based on the arc characteristic diagram described above with reference to FIG. 4 is set in advance by experiments in accordance with the type of welding torch, the type of center gas and plasma gas, the flow rate, and the like. The description so far is the case where the plasma welding current is a direct current waveform. If the plasma current has a pulse waveform, the average value may be processed as a substitute value.

  According to the above-described embodiment, it is possible to determine whether or not there is a possibility of abnormal arc discharge before starting welding, and to issue an alarm when there is a possibility. For this reason, in this embodiment, it is possible to prevent an abnormal arc discharge from occurring between the plasma electrode and the welding wire, and to prevent the welding torch from being damaged by reviewing the welding conditions. At the same time, the welding quality can be maintained well.

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 AM Monitoring device AR Abnormal arc discharge discrimination circuit Ar Alarm Signal DP Indicator EI Current error amplifier circuit Ei Current error amplifier signal EV Voltage error amplifier circuit Ev Voltage error amplifier signal FC Feed control circuit Fc Feed control signal FR Feed speed setting circuit Fr Feed speed setting signal Fw Feed speed 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 Ips Plasma welding current recommended value signal IR Plasma welding current setting circuit Ir Plasma welding Current setting Constant signal IRC Current setting control circuit Irc Current setting control signal Iwm MIG welding current Iwp Plasma welding current HT Notification circuit L1 to L3 Arc characteristic LTR Torch height setting circuit Ltr Torch height setting signal Lts Torch height recommended value signal Pa to Pc Operating point 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 VR MIG welding voltage setting Circuit Vr MIG welding voltage setting signal VTH Reference voltage value setting circuit Vth Reference voltage value signal Vwm MIG welding voltage Vwp Plasma welding voltage WM Feed motor WT Welding torch

Claims (3)

A plasma arc is generated by applying a plasma welding current by applying a plasma welding voltage between a plasma electrode and a base material arranged in the welding torch, 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 preset MIG welding voltage is applied between the feeding tip and the base material. In the plasma MIG welding method for generating a MIG arc by energizing the MIG welding current,
Before starting welding, a torch height, which is a distance between the tip of the plasma electrode and the base material, is set, and a predetermined arc is set with the set value of the torch height and the set value of the plasma welding current as inputs. The plasma welding voltage is estimated by a characteristic function, and an abnormal arc discharge occurs when the set voltage difference between the estimated value of the plasma welding voltage and the set value of the MIG welding voltage is larger than a predetermined reference voltage value. Discriminate and issue an alarm,
A method for monitoring plasma MIG welding. When the alarm is issued, the set value of the plasma welding current is calculated and displayed so that the set voltage difference is equal to or less than the reference voltage value.
The method of monitoring plasma MIG welding according to claim 1. When the alarm is issued, the set value of the torch height at which the set voltage difference is less than or equal to the reference voltage value is calculated and displayed.
3. The method for monitoring plasma MIG welding according to claim 1, wherein the plasma MIG welding is performed.

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