JPWO2012029226A1 - AC TIG welding method - Google Patents

Abstract

The present invention is an AC TIG welding method in which welding is performed by alternately repeating a positive polarity period and a reverse polarity period, and the contact between the TIG electrode and the welding object is detected during welding, and the TIG electrode and the welding object are detected. In the case of contact with the other, the commutation from one polarity period to the other polarity period is prohibited, so that the surge voltage generated by switching at the time of polarity reversal does not occur, and the semiconductor element is damaged. Can be prevented.

Description

  The present invention relates to an AC TIG welding method in which arc welding is performed by alternately repeating reverse polarity and positive polarity.

  In recent years, aluminum and magnesium materials, which are lightweight and excellent in recyclability, are frequently used in buildings, vehicles, and the like in consideration of the environment, and AC TIG welding apparatuses are often used when forming such joints. An AC TIG welding apparatus performs arc welding by alternately repeating reverse polarity and positive polarity (see, for example, Patent Document 1).

  In particular, at work sites that produce large buildings, it is necessary to perform work using a large current. In high-current AC welding, particularly when the output cable is extended, the surge voltage generated during switching at the time of polarity reversal of AC welding increases. There is a problem that the semiconductor element constituting the secondary inverter may be damaged due to the magnitude of the surge voltage.

  Therefore, conventionally, in order to protect the semiconductor element, the current is controlled to a low current (for example, 100 A or less) before the polarity is reversed, and switching of the polarity reversal is performed in this low current state, thereby suppressing the generated surge voltage. Measures have been implemented.

  However, when the operator's mistake, workpiece accuracy, or jig accuracy is poor, the TIG electrode may contact the welding object during the welding operation (this case is referred to as “electrode short-circuit” or “short-circuit”). . And during the short circuit, the degree of decrease in the welding current becomes gentler than in the arc. For this reason, if a short circuit occurs, polarity reversal may occur without sufficiently reducing the current before polarity reversal. There has been a problem that a semiconductor element as a constituent element of the secondary inverter constituting the TIG welding apparatus may be damaged by the magnitude of the surge voltage generated at the time of switching at the time of the polarity reversal of the AC welding.

  Next, the operation of an AC TIG welding apparatus conventionally used will be described with reference to FIGS. FIG. 8 is a diagram showing a schematic configuration of a conventional AC TIG welding apparatus, and FIG. 9 is a diagram showing a time change of a welding current waveform in the conventional AC TIG welding apparatus.

  The operation of the AC TIG welding apparatus configured as shown in FIG. 8 will be described with reference to FIG. In the following description, an example using a non-consumable electrode type AC TIG welding apparatus that performs welding by alternately repeating a reverse polarity period and a positive polarity period will be described.

  In FIG. 8, the AC TIG welding apparatus 101 includes a welding output unit 102, a welding control unit 103, a current detection unit 104, a setting unit 107, and a first time measuring unit 108. The AC TIG welding apparatus 101 is electrically connected to a welding torch 110 including an electrode 109 and a base material 112 that is an object to be welded, and by supplying electric power between the electrode 109 and the base material 112. An arc 111 is generated between the electrode 109 and the base material 112.

  Further, in FIG. 9 showing the time change of the welding current waveform, TEN is a positive polarity period, TEP is a reverse polarity period, TP1 is a positive polarity peak period, TB1 is a positive polarity base period, TP2 is a reverse polarity peak period, and TB2 is reverse The polarity base period is shown. In addition, IENP is positive polarity peak current, IEPP is reverse polarity peak current, IENB is positive polarity base current, IEPB is reverse polarity base current, IEN1 is welding current before polarity reversal (current in positive polarity period during short circuit), and IEP1 is The welding current before polarity inversion (current in the reverse polarity period during short circuit) is shown. E1 indicates a time when a short circuit occurs, and E2 indicates a time when an arc is regenerated.

  In FIG. 8, the welding output unit 102 of the AC TIG welding apparatus 101 receives a commercial power source (for example, three-phase 200 V) supplied from the outside. The welding output unit 102 performs a primary inverter operation and a secondary inverter operation (not shown) provided inside the welding output unit 102 based on a control signal from the welding control unit 103, and appropriately sets the positive polarity and the reverse polarity. The welding voltage and welding current suitable for welding are output.

  The primary inverter is normally an IGBT (Insulated Gate Bipolar Transistor) (not shown) driven by a PWM (Pulse Width Modulation) operation or a phase shift operation, or a MOSFET (Metal-Oxide Semiconductor Transistor Transducer 1), not shown. It consists of a secondary rectifier diode, a smoothing electrolytic capacitor, a power conversion transformer, and the like.

  Further, the secondary inverter is usually constituted by a half bridge or a full bridge using an IGBT (not shown), and switches the output polarity.

  Here, the positive polarity means a case where the moving direction of electrons in the arc plasma is a direction from the electrode 109 toward the base material 112, the electrode 109 is negative, and the base material is positive. The reverse polarity means a case where the moving direction of electrons in the arc plasma is a direction from the base material 112 toward the electrode 109, the electrode 109 is positive, and the base material 112 is negative.

  The setting unit 107 including a CPU or the like includes a positive polarity peak period TP1 (for example, 9.5 msec), a positive polarity base period TB1 (for example, 0.5 msec), a reverse polarity peak period TP2 (for example, 3.81 msec), Reverse polarity base period TB2 (eg, 0.47 msec), positive polarity peak current IENP (eg, 400 A), reverse polarity peak current IEPP (eg, −400 A), positive polarity base current IENB (eg, 100 A), reverse polarity base current IEPB (for example, −100 A) is set and output to the welding control unit 103. The parameters may be set by inputting each parameter by the operator, or automatically by a table or formula based on a set current (executed value or average value) or frequency set separately. It may be set.

  The first time measuring unit 108 configured by a CPU or the like measures the time from the start of the positive polarity period and the reverse polarity period, and the current detection unit 104 configured by CT or the like detects a welding current. Is.

  The welding control unit 103 outputs an output command signal to the welding output unit 102 based on the output of the setting unit 107, the elapsed time measured by the first timing unit 108, and the welding current value detected by the current detection unit 104. To do. The welding control unit 103 reverses the positive polarity peak current during the positive polarity peak period, the positive polarity base current lower than the positive polarity peak current during the positive polarity base period, and the reverse polarity peak current during the reverse polarity peak period. During the polarity base period, an output command signal for outputting a reverse polarity base current lower than the reverse polarity peak current (small absolute value) is output to the welding output unit 102.

  The welding output unit 102 operates as a positive polarity period during the positive polarity period by the operation of the secondary inverter based on the output command signal from the welding control unit 103, and outputs in a direction in which electrons move from the electrode 109 to the base material 112. Switch polarity. During the reverse polarity period, it operates as a reverse polarity period and switches the output polarity in the direction in which electrons move from the base material 112 to the electrode 109.

  Further, the welding output unit 102 outputs a positive peak current (for example, 400 A) during the positive peak period and a positive base current (for example, 100 A) during the positive base period by the operation of the primary inverter. Output. The welding output unit 102 outputs a reverse polarity peak current (for example, −400 A) during the reverse polarity peak period, and outputs a reverse polarity base current (for example, −100 A) during the reverse polarity base period.

  The welding current and welding voltage output by the welding output unit 102 are fed to the welding torch 110 connected to the AC TIG welding apparatus 101, and the tip of the electrode 109 which is a TIG electrode made of tungsten or the like and the aluminum material or the like. An arc 111 is generated between the base metal 112, which is a welding object, and AC TIG welding is performed.

  Next, the operation | movement and welding current waveform in the conventional alternating current TIG welding are demonstrated using FIG.

  As shown in FIG. 9, until the time point E1 when the short-circuit occurs, when the positive polarity peak period TP1 is completed and the positive polarity base period TB1 is shifted in the positive polarity period TEN, the welding current is positive. The peak current IENP (eg, 400 A) decreases to a positive base current IENB (eg, 100 A). When the positive polarity base period TB1 ends, the welding current shifts to the reverse polarity period TEP.

  Further, in the reverse polarity period TEP, when the reverse polarity peak period TP2 is completed and the process proceeds to the reverse polarity base period TB2, the welding current is changed from the reverse polarity peak current IEPP (for example, −400 A) to the reverse polarity base current IEEP ( For example, it decreases to −100 A). When the reverse polarity base period TB2 ends, the welding current shifts to the positive polarity period TEN.

  In this way, the surge voltage generated by switching of the secondary inverter at the time of polarity reversal by reducing the welding current to the positive base current IENB and the reverse polarity base current IEPB which are target command values before polarity reversal. Is kept low (for example, about 300V). Thereby, the semiconductor element which comprises the secondary inverter of the welding output part 102 is not damaged.

  Next, the operation of the welding current waveform when a short circuit between the electrode 109 and the base material 112 occurs during conventional AC TIG welding will be described with reference to FIG.

  As shown in FIG. 9, in the positive polarity period TEN in the short circuit after the time point E1 when the short circuit occurs, the welding current is changed to the positive polarity base current when the positive polarity peak period is completed and the positive polarity base period is entered. Assume that a command has been issued to be IENB. However, the welding current cannot be reduced from the positive peak current IENP (for example, 400 A) to the positive base current IENB (for example, 100 A). Then, the welding current decreases only to the welding current IEN1 before polarity inversion (for example, 300A) larger than the positive polarity base current IENB, and shifts to the reverse polarity period in the state of the welding current IEN1 before polarity inversion (for example, 300A). To do. This reason will be described later.

  In addition, when the short circuit between the electrode 109 and the base material 112 continues, when the reverse polarity peak period is completed and the process proceeds to the reverse polarity base period in the reverse polarity period TEP, the welding current is the reverse polarity base current IEPB. Suppose you have been instructed to However, the welding current cannot be reduced from the reverse polarity peak current IEPP (for example, −400 A) to the reverse polarity base current IEPB (for example, −100 A). Then, the welding current decreases only to the welding current IEP1 before polarity reversal (for example, −300 A), which is larger than the reverse polarity base current IEPB, and is positive in the state of the welding current IEP1 before polarity reversal (for example, −300 A). Transition to a period. The reason for this will be described below.

  For example, when the welding current needs to be sharply reduced from the reverse polarity peak current IEPP (for example, −400 A) to the reverse polarity base current IEPP (for example, −100 A), the primary inverter of the welding output unit 102 stops and the welding is stopped. The output unit 102 outputs a voltage output 0V. Therefore, during the arc, the welding current sharply decreases due to the arc resistance. However, during the short circuit in which the electrode 109 and the base material 112 are short-circuited, the arc resistance becomes 0, so that the welding current does not rapidly decrease. Therefore, the welding current before polarity inversion cannot be reduced to the positive base current IENB or the reverse polarity base current IEPB of the target command value.

  During the short circuit in which the electrode 109 and the base material 112 are short-circuited in this way, the welding current IEN1 before polarity reversal, which is a current higher than the positive base current IENB and the reverse polarity base current IEPB, which are target command values, Polarity reversal occurs in the state of the welding current IEP1 before reversal. Therefore, a surge voltage generated by switching of the secondary inverter becomes high (for example, about 600 V), and there is a possibility that the semiconductor element constituting the secondary inverter is damaged.

  In addition, when an extension cable is connected to the output side of the AC TIG welding apparatus 1 and the cable is extended and used (for example, length 40 m), the inductance of the cable increases. Therefore, the generated surge voltage is further increased, and the risk of damage to the semiconductor element is further increased.

  As described above, in the prior art, if a short circuit occurs between the electrode 109 and the base material 112 during the operation in which a large current of AC TIG welding flows, the welding current cannot be sharply decreased. Cannot be reduced to the target command value positive base current IENB or reverse polarity base current IEPB. Therefore, polarity reversal occurs in the state of the welding current IEN1 before polarity reversal and the welding current IEP1 before polarity reversal that are higher than the positive base current IENB and the reverse polarity base current IEPB that are target command values.

  Therefore, the surge voltage generated by the switching of the secondary inverter becomes high (for example, about 600 V), and there is a problem that the semiconductor element constituting the secondary inverter is damaged.

  As described above, in the conventional AC TIG welding apparatus, when a short circuit occurs between the electrode and the base material during a work in which a large current (for example, a current of 300 A or more and 500 A or less) flows, a sufficient welding current is obtained before the polarity is reversed. Polarity inversion is performed in a state where it cannot be lowered. For this reason, the surge voltage which generate | occur | produces by switching of a secondary inverter becomes high, and there existed a subject that the semiconductor element which comprises a secondary inverter might be damaged.

JP-A-2-235574

  The present invention provides a high-quality AC TIG welding method that suppresses damage to a semiconductor element constituting an inverter even when a short circuit between an electrode and a base material occurs during welding in which a large current flows.

  In order to solve the above-described problem, an AC TIG welding method of the present invention is an AC TIG welding method in which welding is performed by alternately repeating a positive polarity period and a reverse polarity period, and a TIG electrode and a welding object during welding. When the TIG electrode and the welding object are in contact with each other, commutation from one polarity period to the other polarity period is prohibited.

  As described above, according to the present invention, even when the contact between the TIG electrode and the welding object occurs during welding, the polarity reversal is prohibited during the short circuit, thereby causing the switching during the polarity reversal. No surge voltage is generated. Thereby, high quality alternating current TIG welding which can prevent a semiconductor element from being damaged is realizable.

FIG. 1 is a diagram showing a schematic configuration of an AC TIG welding apparatus used in the AC TIG welding method according to Embodiment 1 of the present invention. FIG. 2 is a diagram showing a temporal change in the welding current waveform in the AC TIG welding method according to Embodiment 1 of the present invention. FIG. 3 is a diagram showing a schematic configuration of an AC TIG welding apparatus used in the AC TIG welding method according to Embodiment 2 of the present invention. FIG. 4 is a diagram showing a temporal change in the welding current waveform in the AC TIG welding method according to Embodiment 2 of the present invention. FIG. 5 is a diagram showing a temporal change in the welding current waveform in the AC TIG welding method according to Embodiment 2 of the present invention. FIG. 6 is a diagram showing a schematic configuration of an AC TIG welding apparatus used in the AC TIG welding method according to Embodiment 3 of the present invention. FIG. 7 is a diagram showing a temporal change in the welding current waveform in the AC TIG welding method according to Embodiment 3 of the present invention. FIG. 8 is a diagram showing a schematic configuration of a conventional AC TIG welding apparatus. FIG. 9 is a diagram showing a time change of a welding current waveform in a conventional AC TIG welding apparatus.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following drawings, the same components are denoted by the same reference numerals, and the description thereof may be omitted.

(Embodiment 1)
FIG. 1 is a diagram illustrating a schematic configuration of an AC TIG welding apparatus used in the AC TIG welding method according to the first embodiment, and FIG. 2 is a time change of a welding current waveform in the AC TIG welding method according to the first embodiment. FIG. About the alternating current TIG welding apparatus comprised like FIG. 1, the operation | movement is demonstrated using the time change of the welding current waveform of FIG.

  Hereinafter, a non-consumable electrode type AC TIG welding apparatus that performs welding by alternately repeating a reverse polarity period and a positive polarity period will be described as an example.

  As shown in FIG. 1, the AC TIG welding apparatus 1 includes a welding output unit 2, a welding control unit 3, a current detection unit 4, a voltage detection unit 5, an AS determination unit 6, a setting unit 7, 1 timer unit 8. Here, the welding output part 2 performs welding output. The welding control unit 3 controls the welding output unit 2. The current detection unit 4 detects a welding current. The voltage detector 5 detects the welding voltage. Based on the detection result of the voltage detection unit 5, the AS determination unit 6 is in a short-circuit state in which the electrode 9 and the base material 12 are short-circuited, or an arc is generated between the electrode 9 and the base material 12. It is detected whether the arc state is in progress. The setting unit 7 sets welding conditions and the like. The first time measuring unit 8 measures time.

  The AC TIG welding apparatus 1 is electrically connected to a welding torch 10 including an electrode 9 and a base material 12 that is an object to be welded, and supplies power between the electrode 9 and the base material 12. The arc 11 is generated between the electrode 9 and the base material 12.

  In FIG. 2 showing current waveforms, TEN is a positive polarity period, TEP is a reverse polarity period, TP1 is a positive polarity peak period, TB1 is a positive polarity base period, TP2 is a reverse polarity peak period, TB2 is a reverse polarity base period, TEN1 indicates a period until a short circuit occurs in the positive polarity period.

  IENP is positive polarity peak current, IEPP is reverse polarity peak current, IENB is positive polarity base current, IEPB is reverse polarity base current, IEP2 is welding current (current at the end of reverse polarity period during short circuit), and IEPBABS is reverse The absolute value of the polarity base current, IEPPABS, indicates the absolute value of the reverse polarity peak current.

  E1 indicates a time when a short circuit occurs, E2 indicates a time when arc regeneration is performed, and E6 indicates a time when a reverse polarity period is completed.

  In FIG. 1, the welding output unit 2 of the AC TIG welding apparatus 1 receives a commercial power source (such as three-phase 200 V) supplied from the outside, and the inside of the welding output unit 2 is illustrated based on the output from the welding control unit 3. No primary inverter operation and secondary inverter operation are performed. Thereby, the welding output part 2 switches the positive polarity and reverse polarity appropriately, and outputs the welding voltage and welding current suitable for welding.

  The primary inverter is normally an IGBT (Insulated Gate Bipolar Transistor) (not shown) driven by a PWM (Pulse Width Modulation) operation or a phase shift operation, or a MOSFET (Metal-Oxide Semiconductor Transistor Transducer 1), not shown. It consists of a secondary rectifier diode, a smoothing electrolytic capacitor, a power conversion transformer, and the like.

  Further, the secondary inverter is normally configured as a half bridge or a full bridge using an IGBT (not shown), and switches the output polarity.

  Here, the positive polarity means a case where the moving direction of the electrons in the arc plasma is a direction from the electrode 9 toward the base material 12, the electrode 9 is negative, and the base material is positive. Reverse polarity refers to the case where the moving direction of electrons in the arc plasma is the direction from the base material 12 toward the electrode 9, the electrode 9 is positive, and the base material 12 is negative.

  The setting unit 7 including a CPU or the like includes a positive polarity peak period TP1 (for example, 9.5 msec), a positive polarity base period TB1 (for example, 0.5 msec), a reverse polarity peak period TP2 (for example, 3.81 msec), Reverse polarity base period TB2 (eg, 0.47 msec), positive polarity peak current IENP (eg, 400 A), reverse polarity peak current IEPP (eg, -400 A), positive polarity base current IENB (eg, 100 A), reverse polarity base A current IEPB (for example, −100 A) is set and output to the welding control unit 3. The parameters may be set by inputting each parameter by the operator, or automatically by a table or formula based on a set current (executed value or average value) or frequency set separately. It may be set.

  The 1st time measuring part 8 comprised with CPU etc. time-measures the time from the start of a positive polarity period, and the start of a reverse polarity period. The current detection unit 4 configured by CT or the like detects a welding current.

  Based on the output of the setting unit 7, the elapsed time measured by the first time measuring unit 8, and the welding current value detected by the current detecting unit 4, the welding control unit 3 performs positive polarity peak current during the positive polarity peak period. The positive polarity base current is lower than the positive polarity peak current during the positive polarity base period, the reverse polarity peak current is lower during the reverse polarity peak period, and lower than the reverse polarity peak current during the reverse polarity base period (the absolute value is An output command signal for outputting a (small) reverse polarity base current is output to the welding output unit 2.

  The welding output unit 2 operates as a positive period during the positive period by the operation of the secondary inverter based on the output command signal from the welding control unit 3, and outputs in the direction in which electrons move from the electrode 9 to the base material 12. Switch polarity. During the reverse polarity period, it operates as a reverse polarity period and switches the output polarity in the direction in which electrons move from the base material 12 to the electrode 9.

  Further, the welding output unit 2 outputs a positive peak current (for example, 400 A) during the positive peak period and a positive base current (for example, 100 A) during the positive base period by the operation of the primary inverter. The reverse polarity peak current (for example, −400 A) is output during the reverse polarity peak period, and the reverse polarity base current (for example, −100 A) is output during the reverse polarity base period.

  The welding current and welding voltage output by the welding output unit 2 are fed to the welding torch 10 connected to the AC TIG welding apparatus 1, and the tip of the electrode 9 which is a TIG electrode made of tungsten or the like and the aluminum material or the like. An arc 11 is generated between the base metal 12 which is a welding object and AC TIG welding is performed.

  A voltage detection unit 5 configured by CT or the like and measuring a voltage between output terminals of the AC TIG welding apparatus 1 detects a welding voltage.

  The AS determination unit 6 composed of a CPU or the like inputs the voltage detection signal from the voltage detection unit 5 and calculates the absolute value of the voltage detection signal. A case is considered in which the absolute value of the voltage detection signal reaches (decreases) a preset detection level (for example, 10 V) while it is determined that the arc is in progress. In this case, it is determined that the electrode 9 and the base material 12 that is the welding object are in contact (referred to as an electrode short circuit or short circuit), and the AS signal is determined as a short circuit determination (low level). Further, consider a case where the detection level (for example, 15 V) set in advance is reached (increased) while it is determined that a short circuit is occurring. In this case, it is determined that the contact (short circuit) between the electrode 9 and the base material 12 that is the welding object is released and an arc is generated (referred to as arc regeneration or arcing), and the AS signal is determined as arc determination (high Level).

  The welding control unit 3 that controls the welding output unit 2 inputs an AS signal output from the AS determination unit 6 that indicates whether a short circuit or an arc is being performed. When the AS signal is a short-circuit determination (low level), the welding control unit 3 can perform the commutation from one polarity period to the other polarity period even if it is the timing to perform the commutation from one polarity period to the other polarity period. The welding output unit 2 is controlled so as to prohibit commutation to the. When the short circuit determination (low level) continues as the AS signal, the commutation prohibition is maintained.

  Further, when the AS signal is an arc determination (high level), and when it is time to perform a commutation from one polarity period to the other polarity period, the welding control unit 3 starts from one polarity period to the other. The welding output unit 2 is controlled so as to enable commutation to the polarity period. In addition, although details will be described later, in the state where the short circuit determination and the commutation prohibition are maintained, even in the case of an arc determination, the welding control unit 3 performs the commutation from one polarity period to the other polarity period. The welding output unit 2 is controlled so as to be possible.

  Next, with reference to FIG. 2, an operation and a welding current waveform that prohibit commutation from one polarity period to the other polarity period when a short circuit occurs during AC TIG welding will be described.

  In FIG. 2, until the time point E1 at which the short circuit occurs, in the positive polarity period TEN, when the positive polarity peak period TP1 is completed and the positive polarity base period TB1 is entered, the welding current is the positive polarity peak current IENP. (For example, 400 A) decreases to a positive polarity base current IENB (eg, 100 A), and when the positive polarity base period TB1 ends, the period shifts to the reverse polarity period TEP.

  Further, in the reverse polarity period TEP, when the reverse polarity peak period TP2 is completed and the process proceeds to the reverse polarity base period TB2, the welding current is changed from the reverse polarity peak current IEPP (for example, −400 A) to the reverse polarity base current IEEP ( For example, when the reverse polarity base period TB2 ends, the period shifts to the positive polarity period TEN.

  In the short circuit after the time point E1 when the short circuit shown in FIG. 2 occurs, in the positive polarity period TEN, the positive polarity peak period TP1 is completed and the positive current base period TB1 is entered and the welding current is changed to the positive polarity base current IENB. Suppose that you have been commanded to Even in this case, the current cannot be decreased from the positive polarity peak current IENP (for example, 400 A) to the positive polarity base current IENB (for example, 100 A) and is larger than the positive polarity base current IENB, and the welding current IEN2 before polarity inversion (for example, The positive polarity period TEN is completed with a decrease only to 300A). The reason why the current is difficult to decrease during the short circuit between the electrode 9 and the base material 12 is that when the short circuit between the electrode 109 and the base material 112 occurs during the operation in which a large current flows in AC TIG welding, the welding current decreases sharply. This is because it cannot be done. The reason is the same as that described in the background art with reference to FIG.

  And even at the end of the positive polarity period TEN, since the electrode 9 and the base material 12 are continuously short-circuited from the time point E1, the AS determination unit 6 determines a short circuit, and the welding control unit 3 Prohibits commutation to polar periods. In the case of FIG. 2, the commutation of the reverse polarity from the positive polarity is prohibited.

  Thus, since polarity commutation is prohibited, polarity inversion is not performed in a high current state, and a surge voltage generated by switching of the secondary inverter for polarity inversion does not occur. Therefore, there is no possibility that the semiconductor element constituting the secondary inverter is damaged.

  As shown in FIG. 2, the welding command shifts to the reverse polarity period without polarity reversal (the actual current has no polarity reversal). At this time, the absolute value IEPPABS (for example, 400 A) of the reverse polarity peak current is applied to the reverse polarity peak current (no polarity reversal). Further, the absolute value IEPBABS (for example, 100 A) of the reverse polarity base current is applied to the reverse polarity base current (no polarity inversion).

  It is assumed that the welding current when the reverse polarity peak period (no polarity reversal) is completed and the welding current shifts to the reverse polarity base period (no polarity reversal) is commanded to be the reverse polarity base current IEPBABS. Even in this case, the welding current cannot be reduced from the absolute value IEPPABS (for example, 400 A) of the reverse polarity peak current to the absolute value IEPBABS (for example, 100 A) of the reverse polarity base current. Then, the welding current decreases only to the welding current IEP2 before polarity reversal (for example, 300 A) which is a value larger than the absolute value IEPBABS of the reverse polarity base current, and in this state, shifts to the positive polarity period TEN.

  At this time, since the electrode 9 and the base material 12 are continuously short-circuited from the time point E1, the AS determination unit 6 determines a short circuit, and the welding control unit 3 prohibits commutation to the other polarity period. To do.

  Since polarity commutation is prohibited in this way, polarity inversion is not performed in a state where the current is high, and a surge voltage generated by switching of the secondary inverter for polarity inversion does not occur. Therefore, there is no possibility that the semiconductor element constituting the secondary inverter is damaged.

  Next, referring to FIG. 2, when a short circuit occurs during AC TIG welding and commutation is prohibited, and then the short circuit is opened and an arc is generated (arc regeneration), one polarity period An operation and a welding current waveform that enable commutation from one to the other polarity period will be described.

  At the time E2 when the arc regeneration shown in FIG. 2 is performed, the short circuit between the electrode 9 and the base material 12 is released and an arc is generated, so that the AS determination unit 6 determines an arc and enables commutation.

  The welding control unit 3 controls the current so as to obtain a current waveform at a reference timing in which the positive polarity period and the reverse polarity period are repeated at a predetermined timing.

  Here, the reference timing of the next commutation from the positive polarity to the reverse polarity at the time point E2 at which the arc is regenerated is waited, and the welding control is performed so as to commutate from the positive polarity to the reverse polarity at the time point E5 when the positive polarity period TEN is completed. The part 3 performs the commutation by controlling the welding output part 2.

  Note that time E5 is already in the arc, and the current before commutation to the reverse polarity is sufficiently reduced as shown in FIG. 2, so that the problem of surge voltage due to switching of the secondary inverter does not occur.

  If the arc is regenerated at the time point E4 shown in FIG. 2, the commutation is not performed at the time point E6 when the reverse polarity period TEP is completed, and the next reference timing of commutation from the positive polarity to the reverse polarity is awaited. Then, control is performed so as to cause commutation at time point E5 when the positive polarity period TEN is completed.

  As described above, when it is detected that the electrode 9 that is the TIG electrode and the base material 12 that is the welding target are short-circuited during the welding, and the short-circuit is determined, the polarity from the one polarity period to the other polarity is determined. It is prohibited to transfer to the period. As a result, it is possible to prevent polarity reversal in a high current state and to suppress generation of a high surge voltage generated by switching of the secondary inverter at the time of polarity reversal. As a result, the semiconductor element constituting the secondary inverter can be prevented from being damaged.

  In addition, for the purpose of protecting the secondary inverter from damage, when an overvoltage protection circuit is installed in the AC TIG welding apparatus 1, the conventional AC TIG welding apparatus 101 can be switched even when the electrode 109 and the base material 112 are short-circuited. High surge voltage is likely to occur because of the flow. Therefore, the overvoltage protection circuit operates and the AC TIG welding apparatus 101 is easily stopped, and the welding work efficiency is lowered. However, in the alternating current TIG welding apparatus 1 of the first embodiment, commutation is prohibited when the electrode 9 and the base material 12 are short-circuited, so that the occurrence of a high surge voltage can be suppressed. Therefore, it can suppress that an overvoltage protection circuit operate | moves and the alternating current TIG welding apparatus 1 stops, and it can prevent that welding work efficiency falls.

  That is, the AC TIG welding method of the present invention is an AC TIG welding method in which welding is performed by alternately repeating a positive polarity period and a reverse polarity period, and detects contact between a TIG electrode and a welding object during welding. When the TIG electrode and the welding object are in contact (when short-circuited), commutation from one polarity period to the other polarity period is prohibited.

  This method prohibits polarity reversal during a short circuit, thereby preventing a surge voltage generated due to switching during polarity reversal. Thereby, high quality alternating current TIG welding which can prevent a semiconductor element from being damaged is realizable.

  Also, after detecting contact between the TIG electrode and the welding object during welding, until the contact between the TIG electrode and the welding object is released and an arc is generated, the TIG electrode and the welding object are in contact with each other. The current may be maintained as a method.

  By this method, polarity inversion is not performed in a high current state, and a surge voltage generated by switching of the secondary inverter for polarity inversion does not occur. Thereby, there is no possibility that the semiconductor element which comprises a secondary inverter will be damaged.

  Further, when contact between the TIG electrode and the welding object is detected during welding, the current may be reduced to a current value lower than the current value at the time when contact between the TIG electrode and the welding object is detected.

  By this method, polarity inversion is not performed in a high current state, and a surge voltage generated by switching of the secondary inverter for polarity inversion does not occur. Thereby, there is no possibility that the semiconductor element which comprises a secondary inverter will be damaged.

  In addition, after detecting contact between the TIG electrode and the welding object during welding, detecting the release of contact between the TIG electrode and the welding object enables commutation from one polarity period to the other polarity period. It is good also as a method to do.

  By this method, it is possible to prevent polarity reversal in a high current state and to suppress generation of a high surge voltage generated by switching of the secondary inverter at the time of polarity reversal. As a result, the semiconductor element constituting the secondary inverter can be prevented from being damaged.

  In addition, when contact between the TIG electrode and the welding object is detected after the contact between the TIG electrode and the welding object is detected during welding, the reference timing between the predetermined positive polarity period and the reverse polarity period is detected. It is good also as a method of controlling an electric current so that it may become a current waveform.

  By this method, it is possible to prevent polarity reversal in a high current state and to suppress generation of a high surge voltage generated by switching of the secondary inverter at the time of polarity reversal. As a result, the semiconductor element constituting the secondary inverter can be prevented from being damaged.

  In the first embodiment, the case where a short circuit occurs in the positive polarity period has been described as an example. However, the same effect can be obtained by performing the same control when a short circuit occurs in the reverse polarity period. Can do.

(Embodiment 2)
FIG. 3 is a diagram showing a schematic configuration of the AC TIG welding apparatus in the second embodiment of the present invention, FIG. 4 is a diagram showing a time change of the welding current waveform in the second embodiment of the present invention, and FIG. It is a figure which shows the time change of the welding current waveform in Embodiment 2 of this invention.

  In the second embodiment, a non-consumable electrode type AC TIG welding apparatus that performs welding by alternately repeating a reverse polarity period and a positive polarity period will be described as an example. About the alternating current TIG welding apparatus which has a structure as shown in FIG. 3, the operation | movement is demonstrated using the welding current waveform of FIG. 4 and FIG.

  In FIG. 3, the AC TIG welding apparatus 21 includes a short-circuit reduced current setting unit 13 for setting a current when the electrode 9 and the base material 12 are short-circuited. The point provided with the reduced current setting unit 13 during short circuit is different from the AC TIG welding apparatus 1 shown in FIG.

  4 and 5, IS indicates a reduced current during a short circuit, which is a current when the electrode 9 and the base material 12 are short-circuited.

  In FIG. 3, a short circuit reduction current setting unit 13 composed of a CPU or the like inputs an AS signal that is an output of the AS determination unit 6 and a current signal that is an output of the current detection unit 4, and the electrode 9 and the base material 12. The short-circuit reduced current IS, which is a current value lower than the current value at the time when the short circuit is detected, is set.

  The welding control unit 3 inputs the AS signal that is the output of the AS determination unit 6 and the output of the reduced current setting unit 13 during short circuit, and during the short circuit between the electrode 9 and the base material 12, the reduced current IS during short circuit is obtained. To control the welding current.

  In AC TIG welding apparatus 21 according to the second embodiment, short-circuit reduced current IS is calculated and set based on the output current from current detector 4 at the time when a short circuit is detected. In addition, you may make it calculate and set the reduction current IS during a short circuit from the welding current command which the welding control part 3 hold | maintains.

  Moreover, you may make it set the lower one of the preset current value (for example, 100A) and the welding current value at the time of detecting a short circuit, and a coefficient smaller than the preset one (for example, 0.5). ) And a welding current value at the time when a short circuit is detected may be set.

  Next, referring to FIG. 4, when a short circuit occurs between the electrode 9 and the base material 12 at the time point E1 during AC TIG welding, an operation for prohibiting commutation from one polarity period to the other polarity period and The welding current waveform will be described.

  At time E1 when the short circuit shown in FIG. 4 occurs, the AS determination unit 6 detects the short circuit between the electrode 9 and the base material 12 and determines the short circuit. The welding control unit 3 prohibits commutation from the polarity period at the time of detecting a short circuit that is one polarity period based on the output of the AS determination unit 6 to the other polarity period. In the example of FIG. 4, commutation from positive polarity to reverse polarity is prohibited.

  During the short circuit between the electrode 9 and the base material 12, the current value is lower than the current value at the time of detecting the short circuit (in the case of FIG. 4, 400A which is the positive peak current IENP), and the reduced current setting unit during the short circuit The welding current is controlled by the welding control unit 3 so as to be reduced to the short-circuit reduced current IS set by 13 (for example, 100 A).

  Next, an operation for allowing commutation and a welding current waveform when an arc is regenerated in a state where a short circuit occurs and commutation is prohibited will be described with reference to FIG.

  At time E2 when the arc shown in FIG. 4 is regenerated, the AS determination unit 6 performs arc determination, commutation is permitted, and a polarity period (reverse polarity) opposite to the polarity period (here, positive polarity period TEN) in which a short circuit is detected. The welding current is controlled by the welding control unit 3 so as to start the current control from the current waveform from the start of the period TEP).

  In addition, regarding the control of the current after the arc regeneration time E2, as shown in FIG. 5, the current from the current waveform from the start of the polarity period (here positive polarity period TEN) in which the short circuit is detected at the arc regeneration time E2. The welding current may be controlled by the welding control unit 3 so as to start the control.

  As described above, according to the present embodiment, when a short circuit is determined during welding, the commutation to the other polarity period is prohibited, and as in the first embodiment, 2 during polarity reversal. Suppresses the occurrence of high surge voltage generated by the switching of the next inverter. Thereby, it can prevent that the semiconductor element which comprises a secondary inverter is damaged.

  Further, during short-circuiting, unnecessary current consumption and damage can be prevented by reducing the current to a short-circuit reduced current IS lower than the current at the time of short-circuit detection.

  In addition, since normal AC welding is started immediately after arc regeneration, the normal welding state is quickly restored and welding defects are less likely to occur.

  That is, the AC TIG welding method of the present invention is an AC TIG welding method in which welding is performed by alternately repeating a positive polarity period and a reverse polarity period, and detects contact between a TIG electrode and a welding object during welding. When the TIG electrode and the welding object are in contact (when short-circuited), the commutation from one polarity period to the other polarity period is prohibited. Then, after detecting the contact between the TIG electrode and the welding object during welding and detecting the release of the contact between the TIG electrode and the welding object, commutation from one polarity period to the other polarity period becomes possible. As a way to do it. Then, after detecting the contact between the TIG electrode and the welding object during welding and detecting the release of the contact between the TIG electrode and the welding object, the start of the polarity period in which the contact between the TIG electrode and the welding object is detected. Alternatively, the current may be controlled such that the current waveform is the same as the current waveform from.

  By this method, generation of a high surge voltage generated by switching of the secondary inverter at the time of polarity inversion is suppressed. Thereby, it can prevent that the semiconductor element which comprises a secondary inverter is damaged.

  In addition, after detecting contact between the TIG electrode and the welding object during welding and then detecting release of contact between the TIG electrode and the welding object, the polarity period in which contact between the TIG electrode and the welding object is detected is The current may be controlled so that the current waveform is the same as the current waveform from the start of the opposite polarity period.

  By this method, generation of a high surge voltage generated by switching of the secondary inverter at the time of polarity inversion is suppressed. Thereby, it can prevent that the semiconductor element which comprises a secondary inverter is damaged.

  In the second embodiment, the case where a short circuit occurs during the positive polarity period has been described as an example. However, the same effect can be obtained by performing the same control even when a short circuit occurs during the reverse polarity period. Can do.

(Embodiment 3)
FIG. 6 is a diagram showing a schematic configuration of the AC TIG welding apparatus in the third embodiment of the present invention, and FIG. 7 is a diagram showing a time change of the welding current waveform in the third embodiment of the present invention.

  In the third embodiment, a non-consumable electrode type AC TIG welding apparatus that performs welding by alternately repeating a reverse polarity period and a positive polarity period will be described as an example. About the alternating current TIG welding apparatus 31 which has a structure as shown in FIG. 6, the operation | movement is demonstrated using the welding current waveform of FIG.

  In FIG. 6, the AC TIG welding apparatus 31 includes a welding output stop time setting unit 14 at the time of occurrence of a short circuit and a second time measuring unit 15 that measures the time after the occurrence of the short circuit. The point that the welding output stop time setting unit 14 and the second timing unit 15 at the time of occurrence of a short circuit are provided is different from the AC TIG welding apparatus 1 shown in FIG. 1 of the first embodiment.

  In FIG. 7, TRES indicates a time for stopping the welding output when a short circuit occurs. E3 indicates a point in time when TRES has elapsed since the occurrence of a short circuit.

  In FIG. 6, the welding output stop time setting unit 14 at the occurrence of a short circuit constituted by a CPU or the like is a threshold value of an elapsed time after the occurrence of the short circuit, and the contact between the electrode 9 and the base material 12 is predetermined during welding. When this period is continued, a welding output stop time TRES at the time of occurrence of a short circuit, which is a predetermined period for stopping the welding output, is set. The second timing unit 15 composed of a CPU or the like measures the time after the occurrence of a short circuit.

  The welding control unit 3 inputs the outputs of the AS determination unit 6, the short-circuit occurrence welding output stop time setting unit 14, and the second timing unit 15. When the contact (short circuit) between the electrode 9 and the base material 12 during welding is continued for a predetermined period during the welding output stop time TRES (for example, 1 sec), the welding control unit 3 The part 2 is controlled to stop the welding output.

  Next, referring to FIG. 7, when a short circuit occurs between the electrode 9 and the base material 12 at the time point E1 during AC TIG welding, an operation for prohibiting commutation from one polarity period to the other polarity period and The welding current waveform will be described.

  At the time E1 when the short circuit shown in FIG. 7 occurs, the AS determination unit 6 detects that the electrode 9 and the base material 12 are short-circuited based on the output of the voltage detection unit 5 and determines the short circuit. Then, the welding control unit 3 prohibits commutation to the other polarity period based on the output of the AS determination unit 6. In the example of FIG. 7, commutation from positive polarity to reverse polarity is prohibited.

  After the short circuit between the electrode 9 and the base material 12 is detected, until the short circuit between the electrode 9 and the base material 12 is opened and an arc is generated, the welding control unit 3 determines the current value at the point E1 when the short circuit occurs. Here, the welding current is controlled so as to maintain the positive peak current IENP value.

  The welding control unit 3 inputs outputs from the AS determination unit 6, the short-circuit occurrence welding output stop time setting unit 14, and the second timing unit 15, and from the point E1 when the short-circuit occurs, the welding output at the occurrence of the short-circuit. If the short circuit continues for the stop time TRES (for example, 1 sec), the welding output is stopped.

  Thus, when a short circuit occurs for a long time, it is determined as abnormal and the welding output is stopped. Thereby, the abnormal short circuit current does not continue to flow and the welding operation can be performed safely.

  As described above, according to the third embodiment, when a short circuit is determined during welding, commutation to the other polarity period is prohibited. Thereby, generation | occurrence | production of the high surge voltage which generate | occur | produces by switching of the secondary inverter in the case of polarity inversion can be prevented, and it can prevent that the semiconductor element which comprises a secondary inverter is damaged.

  That is, the AC TIG welding method of the present invention is an AC TIG welding method in which welding is performed by alternately repeating a positive polarity period and a reverse polarity period, and detects contact between a TIG electrode and a welding object during welding. When the TIG electrode and the welding object are in contact (when short-circuited), the commutation from one polarity period to the other polarity period is prohibited. And it is good also as a method of stopping welding output, when contact with a TIG electrode and a welding target object continues for a predetermined period during welding.

  By this method, an abnormal short-circuit current does not continue to flow and the welding operation can be performed safely.

  Note that the welding output stop time TRES at the occurrence of a short circuit may be a fixed value set in advance or a value based on the output welding current. In the third embodiment, the case where a short circuit occurs in the positive polarity period has been described as an example. However, the same effect can be obtained by performing the same control when a short circuit occurs in the reverse polarity period. Can do.

  As described above, the present invention prohibits output polarity reversal during a short circuit even when contact between an electrode and a welding object occurs during welding with a large current. As a result, surge voltage generated by polarity inversion switching is not generated, and damage to the semiconductor element can be prevented. Therefore, the present invention is industrially useful as an AC TIG welding method in an industry in which production is performed using an aluminum material or a magnesium material, such as an automobile industry or a construction industry that performs AC TIG welding.

1, 21, 31 AC TIG welding equipment 2 Welding output unit 3 Welding control unit 4 Current detection unit 5 Voltage detection unit 6 AS determination unit 7 Setting unit 8 First timing unit 9 Electrode 10 Welding torch 11 Arc 12 Base material 13 Short circuit Medium reduction current setting part 14 Welding output stop time setting part when short-circuit occurs 15 Second timing part

  The present invention relates to an AC TIG welding method in which arc welding is performed by alternately repeating reverse polarity and positive polarity.

  In recent years, aluminum and magnesium materials, which are lightweight and excellent in recyclability, are frequently used in buildings, vehicles, and the like in consideration of the environment, and AC TIG welding apparatuses are often used when forming such joints. An AC TIG welding apparatus performs arc welding by alternately repeating reverse polarity and positive polarity (see, for example, Patent Document 1).

  In particular, at work sites that produce large buildings, it is necessary to perform work using a large current. In high-current AC welding, particularly when the output cable is extended, the surge voltage generated during switching at the time of polarity reversal of AC welding increases. There is a problem that the semiconductor element constituting the secondary inverter may be damaged due to the magnitude of the surge voltage.

  Therefore, conventionally, in order to protect the semiconductor element, the current is controlled to a low current (for example, 100 A or less) before the polarity is reversed, and switching of the polarity reversal is performed in this low current state, thereby suppressing the generated surge voltage. Measures have been implemented.

  However, when the operator's mistake, workpiece accuracy, or jig accuracy is poor, the TIG electrode may contact the welding object during the welding operation (this case is referred to as “electrode short-circuit” or “short-circuit”). . And during the short circuit, the degree of decrease in the welding current becomes gentler than in the arc. For this reason, if a short circuit occurs, polarity reversal may occur without sufficiently reducing the current before polarity reversal. There has been a problem that a semiconductor element as a constituent element of the secondary inverter constituting the TIG welding apparatus may be damaged by the magnitude of the surge voltage generated at the time of switching at the time of the polarity reversal of the AC welding.

  Next, the operation of an AC TIG welding apparatus conventionally used will be described with reference to FIGS. FIG. 8 is a diagram showing a schematic configuration of a conventional AC TIG welding apparatus, and FIG. 9 is a diagram showing a time change of a welding current waveform in the conventional AC TIG welding apparatus.

  The operation of the AC TIG welding apparatus configured as shown in FIG. 8 will be described with reference to FIG. In the following description, an example using a non-consumable electrode type AC TIG welding apparatus that performs welding by alternately repeating a reverse polarity period and a positive polarity period will be described.

  In FIG. 8, the AC TIG welding apparatus 101 includes a welding output unit 102, a welding control unit 103, a current detection unit 104, a setting unit 107, and a first time measuring unit 108. The AC TIG welding apparatus 101 is electrically connected to a welding torch 110 including an electrode 109 and a base material 112 that is an object to be welded, and by supplying electric power between the electrode 109 and the base material 112. An arc 111 is generated between the electrode 109 and the base material 112.

  Further, in FIG. 9 showing the time change of the welding current waveform, TEN is a positive polarity period, TEP is a reverse polarity period, TP1 is a positive polarity peak period, TB1 is a positive polarity base period, TP2 is a reverse polarity peak period, and TB2 is reverse The polarity base period is shown. In addition, IENP is positive polarity peak current, IEPP is reverse polarity peak current, IENB is positive polarity base current, IEPB is reverse polarity base current, IEN1 is welding current before polarity reversal (current in positive polarity period during short circuit), and IEP1 is The welding current before polarity inversion (current in the reverse polarity period during short circuit) is shown. E1 indicates a time when a short circuit occurs, and E2 indicates a time when an arc is regenerated.

  In FIG. 8, the welding output unit 102 of the AC TIG welding apparatus 101 receives a commercial power source (for example, three-phase 200 V) supplied from the outside. The welding output unit 102 performs a primary inverter operation and a secondary inverter operation (not shown) provided inside the welding output unit 102 based on a control signal from the welding control unit 103, and appropriately sets the positive polarity and the reverse polarity. The welding voltage and welding current suitable for welding are output.

  The primary inverter is normally an IGBT (Insulated Gate Bipolar Transistor) (not shown) driven by a PWM (Pulse Width Modulation) operation or a phase shift operation, or a MOSFET (Metal-Oxide Semiconductor Transistor Transducer 1), not shown. It consists of a secondary rectifier diode, a smoothing electrolytic capacitor, a power conversion transformer, and the like.

  Further, the secondary inverter is usually constituted by a half bridge or a full bridge using an IGBT (not shown), and switches the output polarity.

  Here, the positive polarity means a case where the moving direction of electrons in the arc plasma is a direction from the electrode 109 toward the base material 112, the electrode 109 is negative, and the base material is positive. The reverse polarity means a case where the moving direction of electrons in the arc plasma is a direction from the base material 112 toward the electrode 109, the electrode 109 is positive, and the base material 112 is negative.

The setting unit 107 including a CPU or the like includes a positive polarity peak period TP1 (for example, 9.5 msec), a positive polarity base period TB1 (for example, 0.5 msec), a reverse polarity peak period TP2 (for example, 3.81 msec), Reverse polarity base period TB2 (eg, 0.47 msec), positive polarity peak current IENP (eg, 400 A), reverse polarity peak current IEPP (eg, −400 A), positive polarity base current IENB (eg, 100 A), reverse polarity base current IEPB (for example, −100 A) is set and output to the welding control unit 103. The parameters may be set by inputting each parameter by the operator, or automatically by a table or formula based on a separately set current ( effective value or average value) or frequency. It may be set.

  The first time measuring unit 108 configured by a CPU or the like measures the time from the start of the positive polarity period and the reverse polarity period, and the current detection unit 104 configured by CT or the like detects a welding current. Is.

  The welding control unit 103 outputs an output command signal to the welding output unit 102 based on the output of the setting unit 107, the elapsed time measured by the first timing unit 108, and the welding current value detected by the current detection unit 104. To do. The welding control unit 103 reverses the positive polarity peak current during the positive polarity peak period, the positive polarity base current lower than the positive polarity peak current during the positive polarity base period, and the reverse polarity peak current during the reverse polarity peak period. During the polarity base period, an output command signal for outputting a reverse polarity base current lower than the reverse polarity peak current (small absolute value) is output to the welding output unit 102.

  The welding output unit 102 operates as a positive polarity period during the positive polarity period by the operation of the secondary inverter based on the output command signal from the welding control unit 103, and outputs in a direction in which electrons move from the electrode 109 to the base material 112. Switch polarity. During the reverse polarity period, it operates as a reverse polarity period and switches the output polarity in the direction in which electrons move from the base material 112 to the electrode 109.

  Further, the welding output unit 102 outputs a positive peak current (for example, 400 A) during the positive peak period and a positive base current (for example, 100 A) during the positive base period by the operation of the primary inverter. Output. The welding output unit 102 outputs a reverse polarity peak current (for example, −400 A) during the reverse polarity peak period, and outputs a reverse polarity base current (for example, −100 A) during the reverse polarity base period.

  The welding current and welding voltage output by the welding output unit 102 are fed to the welding torch 110 connected to the AC TIG welding apparatus 101, and the tip of the electrode 109 which is a TIG electrode made of tungsten or the like and the aluminum material or the like. An arc 111 is generated between the base metal 112, which is a welding object, and AC TIG welding is performed.

  Next, the operation | movement and welding current waveform in the conventional alternating current TIG welding are demonstrated using FIG.

  As shown in FIG. 9, until the time point E1 when the short-circuit occurs, when the positive polarity peak period TP1 is completed and the positive polarity base period TB1 is shifted in the positive polarity period TEN, the welding current is positive. The peak current IENP (eg, 400 A) decreases to a positive base current IENB (eg, 100 A). When the positive polarity base period TB1 ends, the welding current shifts to the reverse polarity period TEP.

  Further, in the reverse polarity period TEP, when the reverse polarity peak period TP2 is completed and the process proceeds to the reverse polarity base period TB2, the welding current is changed from the reverse polarity peak current IEPP (for example, −400 A) to the reverse polarity base current IEEP ( For example, it decreases to −100 A). When the reverse polarity base period TB2 ends, the welding current shifts to the positive polarity period TEN.

  In this way, the surge voltage generated by switching of the secondary inverter at the time of polarity reversal by reducing the welding current to the positive base current IENB and the reverse polarity base current IEPB which are target command values before polarity reversal. Is kept low (for example, about 300V). Thereby, the semiconductor element which comprises the secondary inverter of the welding output part 102 is not damaged.

  Next, the operation of the welding current waveform when a short circuit between the electrode 109 and the base material 112 occurs during conventional AC TIG welding will be described with reference to FIG.

  As shown in FIG. 9, in the positive polarity period TEN in the short circuit after the time point E1 when the short circuit occurs, the welding current is changed to the positive polarity base current when the positive polarity peak period is completed and the positive polarity base period is entered. Assume that a command has been issued to be IENB. However, the welding current cannot be reduced from the positive peak current IENP (for example, 400 A) to the positive base current IENB (for example, 100 A). Then, the welding current decreases only to the welding current IEN1 before polarity inversion (for example, 300A) larger than the positive polarity base current IENB, and shifts to the reverse polarity period in the state of the welding current IEN1 before polarity inversion (for example, 300A). To do. This reason will be described later.

  In addition, when the short circuit between the electrode 109 and the base material 112 continues, when the reverse polarity peak period is completed and the process proceeds to the reverse polarity base period in the reverse polarity period TEP, the welding current is the reverse polarity base current IEPB. Suppose you have been instructed to However, the welding current cannot be reduced from the reverse polarity peak current IEPP (for example, −400 A) to the reverse polarity base current IEPB (for example, −100 A). Then, the welding current decreases only to the welding current IEP1 before polarity reversal (for example, −300 A), which is larger than the reverse polarity base current IEPB, and is positive in the state of the welding current IEP1 before polarity reversal (for example, −300 A). Transition to a period. The reason for this will be described below.

For example, when the welding current needs to be sharply increased from the reverse polarity peak current IEPP (for example, −400 A) to the reverse polarity base current IEPB (for example, −100 A), the primary inverter of the welding output unit 102 is stopped and welding is performed. The output unit 102 outputs a voltage output 0V. Therefore, during the arc, the welding current sharply increases due to the arc resistance. However, during the short circuit in which the electrode 109 and the base material 112 are short-circuited, the arc resistance becomes 0, so that the welding current does not increase sharply. Therefore, the welding current before polarity reversal cannot increase to the positive base current IENB or the reverse polarity base current IEPB of the target command value.

During the short circuit in which the electrode 109 and the base material 112 are short-circuited in this way, the welding current before polarity reversal, which is a current having an absolute value higher than the positive base current IENB and the reverse polarity base current IEPB that are target command values. Polarity reversal occurs in the state of IEN1 or welding current IEP1 before polarity reversal. Therefore, a surge voltage generated by switching of the secondary inverter becomes high (for example, about 600 V), and there is a possibility that the semiconductor element constituting the secondary inverter is damaged.

In addition, when an extension cable is connected to the output side of the AC TIG welding apparatus 101 and the cable is extended and used (for example, a length of 40 m), the inductance of the cable increases. Therefore, the generated surge voltage is further increased, and the risk of damage to the semiconductor element is further increased.

As described above, in the conventional technique, if a short circuit between the electrode 109 and the base material 112 occurs during the operation in which a large current flows in AC TIG welding, the absolute value of the welding current cannot be sharply decreased. The absolute value of the welding current cannot be reduced to the target command value positive base current IENB or reverse polarity base current IEPB. For this reason, polarity reversal occurs in the state of the welding current IEN1 before polarity reversal or the welding current IEP1 before polarity reversal, which is a current having a higher absolute value than the positive base current IENB or the reverse polarity base current IEPB that is the target command value. .

  Therefore, the surge voltage generated by the switching of the secondary inverter becomes high (for example, about 600 V), and there is a problem that the semiconductor element constituting the secondary inverter is damaged.

  As described above, in the conventional AC TIG welding apparatus, when a short circuit occurs between the electrode and the base material during a work in which a large current (for example, a current of 300 A or more and 500 A or less) flows, a sufficient welding current is obtained before the polarity is reversed. Polarity inversion is performed in a state where it cannot be lowered. For this reason, the surge voltage which generate | occur | produces by switching of a secondary inverter becomes high, and there existed a subject that the semiconductor element which comprises a secondary inverter might be damaged.

JP-A-2-235574

  The present invention provides a high-quality AC TIG welding method that suppresses damage to a semiconductor element constituting an inverter even when a short circuit between an electrode and a base material occurs during welding in which a large current flows.

  In order to solve the above-described problem, an AC TIG welding method of the present invention is an AC TIG welding method in which welding is performed by alternately repeating a positive polarity period and a reverse polarity period, and a TIG electrode and a welding object during welding. When the TIG electrode and the welding object are in contact with each other, commutation from one polarity period to the other polarity period is prohibited.

  As described above, according to the present invention, even when the contact between the TIG electrode and the welding object occurs during welding, the polarity reversal is prohibited during the short circuit, thereby causing the switching during the polarity reversal. No surge voltage is generated. Thereby, high quality alternating current TIG welding which can prevent a semiconductor element from being damaged is realizable.

FIG. 1 is a diagram showing a schematic configuration of an AC TIG welding apparatus used in the AC TIG welding method according to Embodiment 1 of the present invention. FIG. 2 is a diagram showing a temporal change in the welding current waveform in the AC TIG welding method according to Embodiment 1 of the present invention. FIG. 3 is a diagram showing a schematic configuration of an AC TIG welding apparatus used in the AC TIG welding method according to Embodiment 2 of the present invention. FIG. 4 is a diagram showing a temporal change in the welding current waveform in the AC TIG welding method according to Embodiment 2 of the present invention. FIG. 5 is a diagram showing a temporal change in the welding current waveform in the AC TIG welding method according to Embodiment 2 of the present invention. FIG. 6 is a diagram showing a schematic configuration of an AC TIG welding apparatus used in the AC TIG welding method according to Embodiment 3 of the present invention. FIG. 7 is a diagram showing a temporal change in the welding current waveform in the AC TIG welding method according to Embodiment 3 of the present invention. FIG. 8 is a diagram showing a schematic configuration of a conventional AC TIG welding apparatus. FIG. 9 is a diagram showing a time change of a welding current waveform in a conventional AC TIG welding apparatus.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following drawings, the same components are denoted by the same reference numerals, and the description thereof may be omitted.

(Embodiment 1)
FIG. 1 is a diagram illustrating a schematic configuration of an AC TIG welding apparatus used in the AC TIG welding method according to the first embodiment, and FIG. 2 is a time change of a welding current waveform in the AC TIG welding method according to the first embodiment. FIG. About the alternating current TIG welding apparatus comprised like FIG. 1, the operation | movement is demonstrated using the time change of the welding current waveform of FIG.

  Hereinafter, a non-consumable electrode type AC TIG welding apparatus that performs welding by alternately repeating a reverse polarity period and a positive polarity period will be described as an example.

  As shown in FIG. 1, the AC TIG welding apparatus 1 includes a welding output unit 2, a welding control unit 3, a current detection unit 4, a voltage detection unit 5, an AS determination unit 6, a setting unit 7, 1 timer unit 8. Here, the welding output part 2 performs welding output. The welding control unit 3 controls the welding output unit 2. The current detection unit 4 detects a welding current. The voltage detector 5 detects the welding voltage. Based on the detection result of the voltage detection unit 5, the AS determination unit 6 is in a short-circuit state in which the electrode 9 and the base material 12 are short-circuited, or an arc is generated between the electrode 9 and the base material 12. It is detected whether the arc state is in progress. The setting unit 7 sets welding conditions and the like. The first time measuring unit 8 measures time.

  The AC TIG welding apparatus 1 is electrically connected to a welding torch 10 including an electrode 9 and a base material 12 that is an object to be welded, and supplies power between the electrode 9 and the base material 12. The arc 11 is generated between the electrode 9 and the base material 12.

  In FIG. 2 showing current waveforms, TEN is a positive polarity period, TEP is a reverse polarity period, TP1 is a positive polarity peak period, TB1 is a positive polarity base period, TP2 is a reverse polarity peak period, TB2 is a reverse polarity base period, TEN1 indicates a period until a short circuit occurs in the positive polarity period.

  IENP is positive polarity peak current, IEPP is reverse polarity peak current, IENB is positive polarity base current, IEPB is reverse polarity base current, IEP2 is welding current (current at the end of reverse polarity period during short circuit), and IEPBABS is reverse The absolute value of the polarity base current, IEPPABS, indicates the absolute value of the reverse polarity peak current.

  E1 indicates a time when a short circuit occurs, E2 indicates a time when arc regeneration is performed, and E6 indicates a time when a reverse polarity period is completed.

  In FIG. 1, the welding output unit 2 of the AC TIG welding apparatus 1 receives a commercial power source (such as three-phase 200 V) supplied from the outside, and the inside of the welding output unit 2 is illustrated based on the output from the welding control unit 3. No primary inverter operation and secondary inverter operation are performed. Thereby, the welding output part 2 switches the positive polarity and reverse polarity appropriately, and outputs the welding voltage and welding current suitable for welding.

  The primary inverter is normally an IGBT (Insulated Gate Bipolar Transistor) (not shown) driven by a PWM (Pulse Width Modulation) operation or a phase shift operation, or a MOSFET (Metal-Oxide Semiconductor Transistor Transducer 1), not shown. It consists of a secondary rectifier diode, a smoothing electrolytic capacitor, a power conversion transformer, and the like.

  Further, the secondary inverter is normally configured as a half bridge or a full bridge using an IGBT (not shown), and switches the output polarity.

  Here, the positive polarity means a case where the moving direction of the electrons in the arc plasma is a direction from the electrode 9 toward the base material 12, the electrode 9 is negative, and the base material is positive. Reverse polarity refers to the case where the moving direction of electrons in the arc plasma is the direction from the base material 12 toward the electrode 9, the electrode 9 is positive, and the base material 12 is negative.

The setting unit 7 including a CPU or the like includes a positive polarity peak period TP1 (for example, 9.5 msec), a positive polarity base period TB1 (for example, 0.5 msec), a reverse polarity peak period TP2 (for example, 3.81 msec), Reverse polarity base period TB2 (eg, 0.47 msec), positive polarity peak current IENP (eg, 400 A), reverse polarity peak current IEPP (eg, -400 A), positive polarity base current IENB (eg, 100 A), reverse polarity base A current IEPB (for example, −100 A) is set and output to the welding control unit 3. The parameters may be set by inputting each parameter by the operator, or automatically by a table or formula based on a separately set current ( effective value or average value) or frequency. It may be set.

  The 1st time measuring part 8 comprised with CPU etc. time-measures the time from the start of a positive polarity period, and the start of a reverse polarity period. The current detection unit 4 configured by CT or the like detects a welding current.

  Based on the output of the setting unit 7, the elapsed time measured by the first time measuring unit 8, and the welding current value detected by the current detecting unit 4, the welding control unit 3 performs positive polarity peak current during the positive polarity peak period. The positive polarity base current is lower than the positive polarity peak current during the positive polarity base period, the reverse polarity peak current is lower during the reverse polarity peak period, and lower than the reverse polarity peak current during the reverse polarity base period (the absolute value is An output command signal for outputting a (small) reverse polarity base current is output to the welding output unit 2.

  The welding output unit 2 operates as a positive period during the positive period by the operation of the secondary inverter based on the output command signal from the welding control unit 3, and outputs in the direction in which electrons move from the electrode 9 to the base material 12. Switch polarity. During the reverse polarity period, it operates as a reverse polarity period and switches the output polarity in the direction in which electrons move from the base material 12 to the electrode 9.

  Further, the welding output unit 2 outputs a positive peak current (for example, 400 A) during the positive peak period and a positive base current (for example, 100 A) during the positive base period by the operation of the primary inverter. The reverse polarity peak current (for example, −400 A) is output during the reverse polarity peak period, and the reverse polarity base current (for example, −100 A) is output during the reverse polarity base period.

  The welding current and welding voltage output by the welding output unit 2 are fed to the welding torch 10 connected to the AC TIG welding apparatus 1, and the tip of the electrode 9 which is a TIG electrode made of tungsten or the like and the aluminum material or the like. An arc 11 is generated between the base metal 12 which is a welding object and AC TIG welding is performed.

  A voltage detection unit 5 configured by CT or the like and measuring a voltage between output terminals of the AC TIG welding apparatus 1 detects a welding voltage.

  The AS determination unit 6 composed of a CPU or the like inputs the voltage detection signal from the voltage detection unit 5 and calculates the absolute value of the voltage detection signal. A case is considered in which the absolute value of the voltage detection signal reaches (decreases) a preset detection level (for example, 10 V) while it is determined that the arc is in progress. In this case, it is determined that the electrode 9 and the base material 12 that is the welding object are in contact (referred to as an electrode short circuit or short circuit), and the AS signal is determined as a short circuit determination (low level). Further, consider a case where the detection level (for example, 15 V) set in advance is reached (increased) while it is determined that a short circuit is occurring. In this case, it is determined that the contact (short circuit) between the electrode 9 and the base material 12 that is the welding object is released and an arc is generated (referred to as arc regeneration or arcing), and the AS signal is determined as arc determination (high Level).

  The welding control unit 3 that controls the welding output unit 2 inputs an AS signal output from the AS determination unit 6 that indicates whether a short circuit or an arc is being performed. When the AS signal is a short-circuit determination (low level), the welding control unit 3 can perform the commutation from one polarity period to the other polarity period even if it is the timing to perform the commutation from one polarity period to the other polarity period. The welding output unit 2 is controlled so as to prohibit commutation to the. When the short circuit determination (low level) continues as the AS signal, the commutation prohibition is maintained.

  Further, when the AS signal is an arc determination (high level), and when it is time to perform a commutation from one polarity period to the other polarity period, the welding control unit 3 starts from one polarity period to the other. The welding output unit 2 is controlled so as to enable commutation to the polarity period. In addition, although details will be described later, in the state where the short circuit determination and the commutation prohibition are maintained, even in the case of an arc determination, the welding control unit 3 performs the commutation from one polarity period to the other polarity period. The welding output unit 2 is controlled so as to be possible.

  Next, with reference to FIG. 2, an operation and a welding current waveform that prohibit commutation from one polarity period to the other polarity period when a short circuit occurs during AC TIG welding will be described.

  In FIG. 2, until the time point E1 at which the short circuit occurs, in the positive polarity period TEN, when the positive polarity peak period TP1 is completed and the positive polarity base period TB1 is entered, the welding current is the positive polarity peak current IENP. (For example, 400 A) decreases to a positive polarity base current IENB (eg, 100 A), and when the positive polarity base period TB1 ends, the period shifts to the reverse polarity period TEP.

Further, in the reverse polarity period TEP, when the reverse polarity peak period TP2 is completed and the process proceeds to the reverse polarity base period TB2, the absolute value of the welding current is changed from the reverse polarity peak current IEPP (for example, −400 A) to the reverse polarity base period. When the current IEPB decreases to -100 A (for example, -100 A) and the reverse polarity base period TB2 ends, the period shifts to the positive polarity period TEN.

  In the short circuit after the time point E1 when the short circuit shown in FIG. 2 occurs, in the positive polarity period TEN, the positive polarity peak period TP1 is completed and the positive current base period TB1 is entered and the welding current is changed to the positive polarity base current IENB. Suppose that you have been commanded to Even in this case, the current cannot be decreased from the positive polarity peak current IENP (for example, 400 A) to the positive polarity base current IENB (for example, 100 A) and is larger than the positive polarity base current IENB, and the welding current IEN2 before polarity inversion (for example, The positive polarity period TEN is completed with a decrease only to 300A). The reason why the current is difficult to decrease during the short circuit between the electrode 9 and the base material 12 is that when the short circuit between the electrode 109 and the base material 112 occurs during the operation in which a large current flows in AC TIG welding, the welding current decreases sharply. This is because it cannot be done. The reason is the same as that described in the background art with reference to FIG.

  And even at the end of the positive polarity period TEN, since the electrode 9 and the base material 12 are continuously short-circuited from the time point E1, the AS determination unit 6 determines a short circuit, and the welding control unit 3 Prohibits commutation to polar periods. In the case of FIG. 2, the commutation of the reverse polarity from the positive polarity is prohibited.

  Thus, since polarity commutation is prohibited, polarity inversion is not performed in a high current state, and a surge voltage generated by switching of the secondary inverter for polarity inversion does not occur. Therefore, there is no possibility that the semiconductor element constituting the secondary inverter is damaged.

  As shown in FIG. 2, the welding command shifts to the reverse polarity period without polarity reversal (the actual current has no polarity reversal). At this time, the absolute value IEPPABS (for example, 400 A) of the reverse polarity peak current is applied to the reverse polarity peak current (no polarity reversal). Further, the absolute value IEPBABS (for example, 100 A) of the reverse polarity base current is applied to the reverse polarity base current (no polarity inversion).

  It is assumed that the welding current when the reverse polarity peak period (no polarity reversal) is completed and the welding current shifts to the reverse polarity base period (no polarity reversal) is commanded to be the reverse polarity base current IEPBABS. Even in this case, the welding current cannot be reduced from the absolute value IEPPABS (for example, 400 A) of the reverse polarity peak current to the absolute value IEPBABS (for example, 100 A) of the reverse polarity base current. Then, the welding current decreases only to the welding current IEP2 before polarity reversal (for example, 300 A) which is a value larger than the absolute value IEPBABS of the reverse polarity base current, and in this state, shifts to the positive polarity period TEN.

  At this time, since the electrode 9 and the base material 12 are continuously short-circuited from the time point E1, the AS determination unit 6 determines a short circuit, and the welding control unit 3 prohibits commutation to the other polarity period. To do.

  Since polarity commutation is prohibited in this way, polarity inversion is not performed in a state where the current is high, and a surge voltage generated by switching of the secondary inverter for polarity inversion does not occur. Therefore, there is no possibility that the semiconductor element constituting the secondary inverter is damaged.

  Next, referring to FIG. 2, when a short circuit occurs during AC TIG welding and commutation is prohibited, and then the short circuit is opened and an arc is generated (arc regeneration), one polarity period An operation and a welding current waveform that enable commutation from one to the other polarity period will be described.

  At the time E2 when the arc regeneration shown in FIG. 2 is performed, the short circuit between the electrode 9 and the base material 12 is released and an arc is generated, so that the AS determination unit 6 determines an arc and enables commutation.

  The welding control unit 3 controls the current so as to obtain a current waveform at a reference timing in which the positive polarity period and the reverse polarity period are repeated at a predetermined timing.

  Here, the reference timing of the next commutation from the positive polarity to the reverse polarity at the time point E2 at which the arc is regenerated is waited, and the welding control is performed so as to commutate from the positive polarity to the reverse polarity at the time point E5 when the positive polarity period TEN is completed. The part 3 performs the commutation by controlling the welding output part 2.

  Note that time E5 is already in the arc, and the current before commutation to the reverse polarity is sufficiently reduced as shown in FIG. 2, so that the problem of surge voltage due to switching of the secondary inverter does not occur.

  If the arc is regenerated at the time point E4 shown in FIG. 2, the commutation is not performed at the time point E6 when the reverse polarity period TEP is completed, and the next reference timing of commutation from the positive polarity to the reverse polarity is awaited. Then, control is performed so as to cause commutation at time point E5 when the positive polarity period TEN is completed.

  As described above, when it is detected that the electrode 9 that is the TIG electrode and the base material 12 that is the welding target are short-circuited during the welding, and the short-circuit is determined, the polarity from the one polarity period to the other polarity is determined. It is prohibited to transfer to the period. As a result, it is possible to prevent polarity reversal in a high current state and to suppress generation of a high surge voltage generated by switching of the secondary inverter at the time of polarity reversal. As a result, the semiconductor element constituting the secondary inverter can be prevented from being damaged.

  For the purpose of protecting the secondary inverter from damage, when an overvoltage protection circuit is installed in the AC TIG welding apparatus, the conventional AC TIG welding apparatus 101 commutates even when the electrode 109 and the base material 112 are short-circuited. High surge voltage is likely to occur. Therefore, the overvoltage protection circuit operates and the AC TIG welding apparatus 101 is easily stopped, and the welding work efficiency is lowered. However, in the alternating current TIG welding apparatus 1 of the first embodiment, commutation is prohibited when the electrode 9 and the base material 12 are short-circuited, so that the occurrence of a high surge voltage can be suppressed. Therefore, it can suppress that an overvoltage protection circuit operate | moves and the alternating current TIG welding apparatus 1 stops, and it can prevent that welding work efficiency falls.

  That is, the AC TIG welding method of the present invention is an AC TIG welding method in which welding is performed by alternately repeating a positive polarity period and a reverse polarity period, and detects contact between a TIG electrode and a welding object during welding. When the TIG electrode and the welding object are in contact (when short-circuited), commutation from one polarity period to the other polarity period is prohibited.

  This method prohibits polarity reversal during a short circuit, thereby preventing a surge voltage generated due to switching during polarity reversal. Thereby, high quality alternating current TIG welding which can prevent a semiconductor element from being damaged is realizable.

  Also, after detecting contact between the TIG electrode and the welding object during welding, until the contact between the TIG electrode and the welding object is released and an arc is generated, the TIG electrode and the welding object are in contact with each other. The current may be maintained as a method.

  By this method, polarity inversion is not performed in a high current state, and a surge voltage generated by switching of the secondary inverter for polarity inversion does not occur. Thereby, there is no possibility that the semiconductor element which comprises a secondary inverter will be damaged.

  Further, when contact between the TIG electrode and the welding object is detected during welding, the current may be reduced to a current value lower than the current value at the time when contact between the TIG electrode and the welding object is detected.

  By this method, polarity inversion is not performed in a high current state, and a surge voltage generated by switching of the secondary inverter for polarity inversion does not occur. Thereby, there is no possibility that the semiconductor element which comprises a secondary inverter will be damaged.

  In addition, after detecting contact between the TIG electrode and the welding object during welding, detecting the release of contact between the TIG electrode and the welding object enables commutation from one polarity period to the other polarity period. It is good also as a method to do.

  By this method, it is possible to prevent polarity reversal in a high current state and to suppress generation of a high surge voltage generated by switching of the secondary inverter at the time of polarity reversal. As a result, the semiconductor element constituting the secondary inverter can be prevented from being damaged.

  In addition, when contact between the TIG electrode and the welding object is detected after the contact between the TIG electrode and the welding object is detected during welding, the reference timing between the predetermined positive polarity period and the reverse polarity period is detected. It is good also as a method of controlling an electric current so that it may become a current waveform.

  By this method, it is possible to prevent polarity reversal in a high current state and to suppress generation of a high surge voltage generated by switching of the secondary inverter at the time of polarity reversal. As a result, the semiconductor element constituting the secondary inverter can be prevented from being damaged.

  In the first embodiment, the case where a short circuit occurs in the positive polarity period has been described as an example. However, the same effect can be obtained by performing the same control when a short circuit occurs in the reverse polarity period. Can do.

(Embodiment 2)
FIG. 3 is a diagram showing a schematic configuration of the AC TIG welding apparatus in the second embodiment of the present invention, FIG. 4 is a diagram showing a time change of the welding current waveform in the second embodiment of the present invention, and FIG. It is a figure which shows the time change of the welding current waveform in Embodiment 2 of this invention.

  In the second embodiment, a non-consumable electrode type AC TIG welding apparatus that performs welding by alternately repeating a reverse polarity period and a positive polarity period will be described as an example. About the alternating current TIG welding apparatus which has a structure as shown in FIG. 3, the operation | movement is demonstrated using the welding current waveform of FIG. 4 and FIG.

  In FIG. 3, the AC TIG welding apparatus 21 includes a short-circuit reduced current setting unit 13 for setting a current when the electrode 9 and the base material 12 are short-circuited. The point provided with the reduced current setting unit 13 during short circuit is different from the AC TIG welding apparatus 1 shown in FIG.

  4 and 5, IS indicates a reduced current during a short circuit, which is a current when the electrode 9 and the base material 12 are short-circuited.

  In FIG. 3, a short circuit reduction current setting unit 13 composed of a CPU or the like inputs an AS signal that is an output of the AS determination unit 6 and a current signal that is an output of the current detection unit 4, and the electrode 9 and the base material 12. The short-circuit reduced current IS, which is a current value lower than the current value at the time when the short circuit is detected, is set.

  The welding control unit 3 inputs the AS signal that is the output of the AS determination unit 6 and the output of the reduced current setting unit 13 during short circuit, and during the short circuit between the electrode 9 and the base material 12, the reduced current IS during short circuit is obtained. To control the welding current.

  In AC TIG welding apparatus 21 according to the second embodiment, short-circuit reduced current IS is calculated and set based on the output current from current detector 4 at the time when a short circuit is detected. In addition, you may make it calculate and set the reduction current IS during a short circuit from the welding current command which the welding control part 3 hold | maintains.

  Moreover, you may make it set the lower one of the preset current value (for example, 100A) and the welding current value at the time of detecting a short circuit, and a coefficient smaller than the preset one (for example, 0.5). ) And a welding current value at the time when a short circuit is detected may be set.

  Next, referring to FIG. 4, when a short circuit occurs between the electrode 9 and the base material 12 at the time point E1 during AC TIG welding, an operation for prohibiting commutation from one polarity period to the other polarity period and The welding current waveform will be described.

  At time E1 when the short circuit shown in FIG. 4 occurs, the AS determination unit 6 detects the short circuit between the electrode 9 and the base material 12 and determines the short circuit. The welding control unit 3 prohibits commutation from the polarity period at the time of detecting a short circuit that is one polarity period based on the output of the AS determination unit 6 to the other polarity period. In the example of FIG. 4, commutation from positive polarity to reverse polarity is prohibited.

  During the short circuit between the electrode 9 and the base material 12, the current value is lower than the current value at the time of detecting the short circuit (in the case of FIG. 4, 400A which is the positive peak current IENP), and the reduced current setting unit during the short circuit The welding current is controlled by the welding control unit 3 so as to be reduced to the short-circuit reduced current IS set by 13 (for example, 100 A).

  Next, an operation for allowing commutation and a welding current waveform when an arc is regenerated in a state where a short circuit occurs and commutation is prohibited will be described with reference to FIG.

  At time E2 when the arc shown in FIG. 4 is regenerated, the AS determination unit 6 performs arc determination, commutation is permitted, and a polarity period (reverse polarity) opposite to the polarity period (here, positive polarity period TEN) in which a short circuit is detected. The welding current is controlled by the welding control unit 3 so as to start the current control from the current waveform from the start of the period TEP).

  In addition, regarding the control of the current after the arc regeneration time E2, as shown in FIG. 5, the current from the current waveform from the start of the polarity period (here positive polarity period TEN) in which the short circuit is detected at the arc regeneration time E2. The welding current may be controlled by the welding control unit 3 so as to start the control.

  As described above, according to the present embodiment, when a short circuit is determined during welding, the commutation to the other polarity period is prohibited, and as in the first embodiment, 2 during polarity reversal. Suppresses the occurrence of high surge voltage generated by the switching of the next inverter. Thereby, it can prevent that the semiconductor element which comprises a secondary inverter is damaged.

  Further, during short-circuiting, unnecessary current consumption and damage can be prevented by reducing the current to a short-circuit reduced current IS lower than the current at the time of short-circuit detection.

  In addition, since normal AC welding is started immediately after arc regeneration, the normal welding state is quickly restored and welding defects are less likely to occur.

  That is, the AC TIG welding method of the present invention is an AC TIG welding method in which welding is performed by alternately repeating a positive polarity period and a reverse polarity period, and detects contact between a TIG electrode and a welding object during welding. When the TIG electrode and the welding object are in contact (when short-circuited), the commutation from one polarity period to the other polarity period is prohibited. Then, after detecting the contact between the TIG electrode and the welding object during welding and detecting the release of the contact between the TIG electrode and the welding object, commutation from one polarity period to the other polarity period becomes possible. As a way to do it. Then, after detecting the contact between the TIG electrode and the welding object during welding and detecting the release of the contact between the TIG electrode and the welding object, the start of the polarity period in which the contact between the TIG electrode and the welding object is detected. Alternatively, the current may be controlled such that the current waveform is the same as the current waveform from.

  By this method, generation of a high surge voltage generated by switching of the secondary inverter at the time of polarity inversion is suppressed. Thereby, it can prevent that the semiconductor element which comprises a secondary inverter is damaged.

  In addition, after detecting contact between the TIG electrode and the welding object during welding and then detecting release of contact between the TIG electrode and the welding object, the polarity period in which contact between the TIG electrode and the welding object is detected is The current may be controlled so that the current waveform is the same as the current waveform from the start of the opposite polarity period.

  By this method, generation of a high surge voltage generated by switching of the secondary inverter at the time of polarity inversion is suppressed. Thereby, it can prevent that the semiconductor element which comprises a secondary inverter is damaged.

  In the second embodiment, the case where a short circuit occurs during the positive polarity period has been described as an example. However, the same effect can be obtained by performing the same control even when a short circuit occurs during the reverse polarity period. Can do.

(Embodiment 3)
FIG. 6 is a diagram showing a schematic configuration of the AC TIG welding apparatus in the third embodiment of the present invention, and FIG. 7 is a diagram showing a time change of the welding current waveform in the third embodiment of the present invention.

  In the third embodiment, a non-consumable electrode type AC TIG welding apparatus that performs welding by alternately repeating a reverse polarity period and a positive polarity period will be described as an example. About the alternating current TIG welding apparatus 31 which has a structure as shown in FIG. 6, the operation | movement is demonstrated using the welding current waveform of FIG.

  In FIG. 6, the AC TIG welding apparatus 31 includes a welding output stop time setting unit 14 at the time of occurrence of a short circuit and a second time measuring unit 15 that measures the time after the occurrence of the short circuit. The point that the welding output stop time setting unit 14 and the second timing unit 15 at the time of occurrence of a short circuit are provided is different from the AC TIG welding apparatus 1 shown in FIG. 1 of the first embodiment.

  In FIG. 7, TRES indicates a time for stopping the welding output when a short circuit occurs. E3 indicates a point in time when TRES has elapsed since the occurrence of a short circuit.

  In FIG. 6, the welding output stop time setting unit 14 at the occurrence of a short circuit constituted by a CPU or the like is a threshold value of an elapsed time after the occurrence of the short circuit, and the contact between the electrode 9 and the base material 12 is predetermined during welding. When this period is continued, a welding output stop time TRES at the time of occurrence of a short circuit, which is a predetermined period for stopping the welding output, is set. The second timing unit 15 composed of a CPU or the like measures the time after the occurrence of a short circuit.

  The welding control unit 3 inputs the outputs of the AS determination unit 6, the short-circuit occurrence welding output stop time setting unit 14, and the second timing unit 15. When the contact (short circuit) between the electrode 9 and the base material 12 during welding is continued for a predetermined period during the welding output stop time TRES (for example, 1 sec), the welding control unit 3 The part 2 is controlled to stop the welding output.

  Next, referring to FIG. 7, when a short circuit occurs between the electrode 9 and the base material 12 at the time point E1 during AC TIG welding, an operation for prohibiting commutation from one polarity period to the other polarity period and The welding current waveform will be described.

  At the time E1 when the short circuit shown in FIG. 7 occurs, the AS determination unit 6 detects that the electrode 9 and the base material 12 are short-circuited based on the output of the voltage detection unit 5 and determines the short circuit. Then, the welding control unit 3 prohibits commutation to the other polarity period based on the output of the AS determination unit 6. In the example of FIG. 7, commutation from positive polarity to reverse polarity is prohibited.

  After the short circuit between the electrode 9 and the base material 12 is detected, until the short circuit between the electrode 9 and the base material 12 is opened and an arc is generated, the welding control unit 3 determines the current value at the point E1 when the short circuit occurs. Here, the welding current is controlled so as to maintain the positive peak current IENP value.

  The welding control unit 3 inputs outputs from the AS determination unit 6, the short-circuit occurrence welding output stop time setting unit 14, and the second timing unit 15, and from the point E1 when the short-circuit occurs, the welding output at the occurrence of the short-circuit. If the short circuit continues for the stop time TRES (for example, 1 sec), the welding output is stopped.

  Thus, when a short circuit occurs for a long time, it is determined as abnormal and the welding output is stopped. Thereby, the abnormal short circuit current does not continue to flow and the welding operation can be performed safely.

  As described above, according to the third embodiment, when a short circuit is determined during welding, commutation to the other polarity period is prohibited. Thereby, generation | occurrence | production of the high surge voltage which generate | occur | produces by switching of the secondary inverter in the case of polarity inversion can be prevented, and it can prevent that the semiconductor element which comprises a secondary inverter is damaged.

  That is, the AC TIG welding method of the present invention is an AC TIG welding method in which welding is performed by alternately repeating a positive polarity period and a reverse polarity period, and detects contact between a TIG electrode and a welding object during welding. When the TIG electrode and the welding object are in contact (when short-circuited), the commutation from one polarity period to the other polarity period is prohibited. And it is good also as a method of stopping welding output, when contact with a TIG electrode and a welding target object continues for a predetermined period during welding.

  By this method, an abnormal short-circuit current does not continue to flow and the welding operation can be performed safely.

  Note that the welding output stop time TRES at the occurrence of a short circuit may be a fixed value set in advance or a value based on the output welding current. In the third embodiment, the case where a short circuit occurs in the positive polarity period has been described as an example. However, the same effect can be obtained by performing the same control when a short circuit occurs in the reverse polarity period. Can do.

  As described above, the present invention prohibits output polarity reversal during a short circuit even when contact between an electrode and a welding object occurs during welding with a large current. As a result, surge voltage generated by polarity inversion switching is not generated, and damage to the semiconductor element can be prevented. Therefore, the present invention is industrially useful as an AC TIG welding method in an industry in which production is performed using an aluminum material or a magnesium material, such as an automobile industry or a construction industry that performs AC TIG welding.

1, 21, 31 AC TIG welding equipment 2 Welding output unit 3 Welding control unit 4 Current detection unit 5 Voltage detection unit 6 AS determination unit 7 Setting unit 8 First timing unit 9 Electrode 10 Welding torch 11 Arc 12 Base material 13 Short circuit Medium reduction current setting part 14 Welding output stop time setting part when short-circuit occurs 15 Second timing part

Claims (8)

An AC TIG welding method in which welding is performed by alternately repeating a positive polarity period and a reverse polarity period,
Detects contact between the TIG electrode and the welding object during welding,
An alternating current TIG welding method for prohibiting commutation from one polarity period to the other polarity period when the TIG electrode and the welding object are in contact with each other. After detecting contact between the TIG electrode and the welding object during welding, until the contact between the TIG electrode and the welding object is released and an arc is generated, the TIG electrode and the welding object are The alternating current TIG welding method according to claim 1, wherein the current at the time of contact is maintained. The current is reduced to a current value lower than a current value at the time when contact between the TIG electrode and the welding object is detected when contact between the TIG electrode and the welding object is detected during welding. AC TIG welding method. After detecting contact between the TIG electrode and the object to be welded during welding, detecting a release of contact between the TIG electrode and the object to be welded causes commutation from one polarity period to the other polarity period. The AC TIG welding method according to claim 1, wherein the AC TIG welding method is enabled. After detecting contact between the TIG electrode and the welding object during welding and detecting contact release between the TIG electrode and the welding object, contact between the TIG electrode and the welding object is detected. The AC TIG welding method according to claim 4, wherein the current is controlled so that the current waveform is the same as the current waveform from the start of the polarity period. After detecting contact between the TIG electrode and the welding object during welding and detecting contact release between the TIG electrode and the welding object, contact between the TIG electrode and the welding object is detected. The AC TIG welding method according to claim 4, wherein the current is controlled so that the current waveform is the same as the current waveform from the start of the polarity period opposite to the polarity period. After detecting the contact between the TIG electrode and the welding object during welding and detecting the release of the contact between the TIG electrode and the welding object, a reference for a predetermined positive polarity period and reverse polarity period is determined. The AC TIG welding method according to claim 4, wherein the current is controlled so as to obtain a timing current waveform. The alternating current TIG welding method according to any one of claims 1 to 7, wherein the welding output is stopped when the contact between the TIG electrode and the welding object continues for a predetermined period during welding.

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