JP4643236B2 - Polarity switching short-circuit arc welding method - Google Patents

Description

  The present invention relates to a polarity switching short-circuit arc welding method for smoothly switching between electrode positive polarity welding and electrode negative polarity welding during welding.

  In the consumable electrode short-circuit arc welding, welding wire as a consumable electrode is fed at a constant speed, and welding is performed while repeating an arc state and a short-circuit state between the welding wire and the base material. Short-circuit arc welding includes CO2 welding, MAG welding, MIG welding in the short-circuit transition region below the middle current region, and CO2 welding, MAG welding, MIG welding in the globule transition region or spray transition region exceeding the middle current region. In short-circuit arc welding, welding is usually performed with an electrode plus polarity EP in which the welding wire serves as an anode and the base material serves as a cathode. However, when the workpiece is a thin plate and the gap is large, there is a case where welding is performed with an electrode negative polarity EN in which the welding wire serves as a cathode and the base material serves as an anode. In the electrode positive polarity welding, it is possible to perform welding with deep penetration and stable over the entire current range. On the other hand, in electrode negative polarity welding, the heat input to the base material can be lowered, and the amount of wire melt can be increased. For this reason, it is possible to obtain a good welding quality for a thin plate with a large gap. A welding power source with constant voltage characteristics is used for both polarities.

  In order to switch the output polarity of the welding power source when welding is stopped, not during welding, it is possible to provide a switching element or a mechanical switch for the output of the welding power source. Since the welding is stopped, the polarity may be switched at an arbitrary timing. On the other hand, in order to switch the polarity during welding, it is necessary to perform various ideas described below. In the case where the joint and plate thickness of the workpiece change along the weld line, better welding quality can be obtained by switching the polarity during welding. Therefore, in such a case, the polarity is switched about several times during one welding. When the polarity is switched during welding, if the switching timing is in an arc state, an arc break occurs during polarity switching, resulting in poor welding. In order to prevent this arc break, it is necessary to apply a high voltage of several hundred volts when switching the polarity. This high voltage application circuit has a problem that it is expensive and large because of its complicated circuit configuration. In order to solve this problem in short-circuit arc welding, the conventional techniques described in Patent Documents 1 and 2 described below are proposed. In this prior art, polarity switching during welding is always performed in a short-circuit state. Since it is not in an arc state, there is no worry of arc breakage. For this reason, the above-described high voltage application circuit is also unnecessary. The prior art will be described below with reference to the drawings.

  FIG. 7 is a voltage / current waveform diagram in the conventional polarity-switching short-circuit arc welding. FIG. 4A shows the polarity switching signal Sa, FIG. 4B shows the polarity switching start signal Sb, and FIG. 4C shows the welding voltage v which is the voltage between the welding wire and the base metal. (D) shows the welding current i for energizing the arc / short-circuit load, and (E) shows the change over time in the wire feed speed Wf of the welding wire. In the figure, EP indicates the positive polarity of the electrode, and EN indicates the negative polarity of the electrode. Hereinafter, a description will be given with reference to FIG.

  During the short-circuit period Ts, the welding voltage v becomes a short-circuit voltage value of about several volts as shown in FIG. 10C, and the welding current i gradually increases as shown in FIG. Subsequently, during the arc period Ta, the welding voltage v has an arc voltage value of about several tens of volts as shown in FIG. 3C, and the welding current i gradually decreases as shown in FIG. The above state is substantially the same for both the electrode positive polarity EP and the electrode negative polarity EN. The wire feed speed Wf is fed at a predetermined constant speed as shown in FIG. At this time, the feeding speed may be set to a different value between the electrode positive polarity EP and the electrode negative polarity EN.

  When the polarity switching signal Sa changes at time t1 and the next short circuit occurs at time t2, as shown in FIG. 9A, a predetermined short circuit until time t3 is performed as shown in FIG. During the initial period Ti, the welding current i is reduced to a predetermined short-circuit initial current Ii having a low value. At the same time, the polarity switching start signal Sb changes as shown in FIG. 5B at time t3. Therefore, the polarity of the welding voltage v shown in FIG. 5C and the welding current i shown in FIG. Switching from positive polarity EP to electrode negative polarity EN. The reason for making the welding current i low by providing the above-mentioned initial short-circuit period Ti is that the short-circuit state between the droplet and the molten pool is made more reliable and the arc suddenly reappears during polarity switching and the arc breaks. This is to prevent the occurrence of the above.

JP 58-38664 A Japanese Unexamined Patent Publication No. 63-157765

  In the prior art described above with reference to FIG. 7, the polarity switching signal Sa changes when the welding torch reaches the workpiece polarity switching point. Therefore, the polarity switching signal Sa changes regardless of whether the welding state is an arc state or a short circuit state. The actual polarity switching timing is time t3 when the next short circuit occurs at time t2 and the initial short circuit period Ti has elapsed. If this time delay becomes longer and the variation becomes larger, the deviation between the polarity switching point and the polarity switching becomes larger, and the variation in the deviation becomes larger, so that the welding quality is deteriorated. Of the time delay between times t1 and t3, the initial short-circuit period Ti is as short as about 1 ms and has a constant value, so there is no problem. However, the short-circuit waiting period from time t1 to t2 is several tens of milliseconds to several hundreds of milliseconds, particularly in the middle current region or more, and the time delay becomes long. Therefore, there is a greater risk of adversely affecting the welding quality when switching the polarity.

  Then, this invention provides the polarity switching short circuit arc welding method which can solve the subject mentioned above.

In order to solve the above-described problem, the first invention is short-circuit arc welding in which a welding wire is fed at a constant speed and a short-circuit state and an arc state are repeated, and welding is performed according to a predetermined polarity switching signal. In the polarity-switching short-circuit arc welding method in which welding is performed by switching between electrode positive polarity welding and electrode negative polarity welding by switching the output polarity of the power source during welding,
When the polarity switching signal changes, the welding current decreases or the welding voltage decreases or the wire feeding speed increases from the time when the arc period from the previous short circuit cancellation becomes the reference value until the next short circuit occurs. When a short circuit occurs, the welding current is maintained at a low value for a predetermined period, then the output polarity of the welding power source is switched, and then the welding current is increased to reduce the short circuit state. A polarity-switching short-circuit arc welding method characterized by leading to release.

Moreover, 2nd invention sets the reference value of 1st invention description based on the average value of each arc period until the said polarity switching signal changes, The polarity switching short circuit arc welding characterized by the above-mentioned Is the method.

The third invention, the polarity switching signal to switch the polarity by changing when the predetermined start initial period after an arc start has elapsed, the first or second invention, wherein the This is a polarity switching short-circuit arc welding method.

According to the first aspect, when the polarity switching signal changes and the arc period reaches the reference value, the welding current is reduced, the welding voltage is lowered, or the wire feed speed is increased at an early stage. Since a short circuit can be induced, the polarity can be switched smoothly in a short circuit state. For this reason, since the difference between the change point of the polarity switching signal and the actual polarity switching timing is small, the welding quality at the time of polarity switching is improved. Furthermore, in the first invention, since the welding current is reduced only when the arc period is longer than the normal value, the influence on the bead accompanying the reduction in the welding current can be minimized.

Furthermore, according to the second invention , in addition to the above-described effects, the reference value is set based on the average value of each arc period until the polarity switching signal changes, thereby reducing the welding current. Etc. are optimized.

Furthermore, according to the third invention , the polarity can be smoothly switched by the first and second inventions after an arc start and an initial start period elapses. For this reason, the welding quality of a start part becomes favorable.

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

[Embodiment 1]
FIG. 1 is a voltage / current waveform diagram showing a polarity switching short-circuit arc welding method according to Embodiment 1 of the present invention. (A) in the figure shows the polarity switching signal Sa, (B) in the figure shows the polarity switching start signal Sb, (C) shows the welding voltage v, and (D) shows the welding current i. E) shows the time change of the wire feed speed Wf. This figure corresponds to FIG. 7 described above, and the operation before time t1 is the same. Hereinafter, the operation after time t1 will be described with reference to FIG.

  When the polarity switching signal Sa changes at time t1, as shown in FIG. 6A, the welding voltage v is lowered as shown in FIG. Similarly, the welding current i also decreases. At the same time, the wire feed speed Wf is increased as shown in FIG. When the welding voltage v or the welding current i is lowered, the wire melting rate is slowed, so that a short circuit is likely to occur at an early stage. Similarly, when the wire feeding speed is increased, a short circuit is likely to occur at an early stage. As a result, as shown in FIG. 5C, a short circuit is induced early at time t2. The period from time t1 to t2 is a short circuit induction period Td. When a short circuit occurs at time t2, the welding current i is reduced to the short circuit initial current Ii during a predetermined short circuit initial period Ti as shown in FIG. As shown in FIG. 5B, the polarity switching start signal Sb changes when the short-circuit initial period Ti elapses at time t3. In response to this, the operation shifts to the polarity switching operation. As a result, the welding voltage v shown in FIG. 5C and the welding current i shown in FIG. 4D are switched from the electrode positive polarity EP to the electrode negative polarity EN.

  After switching the polarity at time t3, the welding current i is increased to lead to the release of the short circuit. The timing of this current increase may be at the time of polarity switching or after being delayed until the switching state is stabilized.

  In the above, in order to induce a short circuit at an early stage, it is possible to perform any one or more of a decrease in the welding voltage v, a decrease in the welding current i, or an increase in the wire feed speed Wf. The value after reducing the welding current i is about 10 to 100 A according to the average welding current, and may be set to the same value as the short-circuit initial current Ii.

  FIG. 2 is a block diagram of a welding power source for carrying out the polarity switching short-circuit arc welding method according to Embodiment 1 described above. Hereinafter, each block will be described with reference to FIG.

  The inverter circuit INV rectifies using an AC commercial power supply AC (three-phase 200 V or the like) as an input, and outputs high-frequency AC by inverter control according to a drive signal Dv described later. The high frequency transformer INT outputs a high frequency alternating current obtained by stepping down the high frequency alternating current to a voltage value suitable for arc welding. The secondary side diodes D2a to D2d rectify the stepped-down high-frequency alternating current into direct current. The electrode positive polarity switching element PTR is turned on / off in accordance with an electrode positive polarity drive signal Pd, which will be described later. The electrode negative polarity switching element NTR is turned on / off according to an electrode negative polarity drive signal Nd, which will be described later, and when in the on state, has an electrode negative polarity EN. The reactor WL smoothes the rectified rippled direct current. The welding wire 1 is fed through the welding torch 4 by a feeding roll 5 directly connected to a feeding motor M of the wire feeding device, and an arc 3 is generated between the welding wire 1 and the base material 2.

  The voltage detection circuit VD detects the welding voltage v and outputs a voltage detection signal Vd. The short-circuit / arc discrimination circuit SD determines a short-circuit state based on the value of the voltage detection signal Vd and outputs a short-circuit / arc discrimination signal Sd which becomes a high level and discriminates an arc state. The polarity switching signal circuit SA outputs a polarity switching signal Sa for switching to the polarity according to the welding location. The short-circuit induction period generation circuit TD is a short-circuit induction period signal that becomes a high level during a period from the time when the polarity switching signal Sa changes to the time when the short-circuit / arc determination signal Sd first changes to a high level (short-circuit). Td is output. The polarity switching start signal generation circuit SB is short-circuited to be at a high level during a predetermined short-circuit initial period from the time when the polarity switching signal Sa is changed and the short-circuit / arc determination signal Sd is at a high level (short-circuit). An initial period signal Ti is output. Further, the polarity switching start signal generation circuit SB outputs a polarity switching start signal Sb that changes when the initial short-circuit period elapses. That is, in FIG. 1 described above, the short-circuit induction period signal Td is at a high level from time t1 to t2, and the short-circuit initial period signal Ti is at a high level from time t2 to t3. The voltage drop setting circuit ΔVR has a first predetermined value while the short circuit induction period signal Td is at a high level, and then has a second predetermined value with a larger value while the short circuit initial period signal Ti is at a high level. In other periods, a voltage drop setting signal ΔVr that is zero is output.

  The welding start circuit ON outputs a welding start signal On that changes to a high level when welding is started. The feed control circuit FC starts constant-speed feeding when the welding start signal On changes to the high level, and feed control signal Fc for increasing the speed while the short-circuit induction period signal Td is at the high level. Is output. The feed motor M controls the feed speed by this feed control signal Fc. The voltage setting circuit VR outputs a predetermined voltage setting signal Vr. The subtraction circuit SUB subtracts the voltage drop setting signal ΔVr from the voltage setting signal Vr, and outputs a voltage control setting signal Vcr = Vr−ΔVr. Therefore, the value of the voltage control setting signal Vcr during the short-circuit induction period and the initial short-circuit period is decreased, whereby the welding voltage v can be decreased and the welding current i can be decreased. The error amplifier circuit AMP amplifies an error between the voltage control setting signal Vcr and the voltage detection signal Vd, and outputs an error amplification signal Amp. With this circuit, the welding power source has constant voltage characteristics. The primary side drive circuit DV1 outputs a drive signal Dv for driving the inverter circuit INV in accordance with the error amplification signal Amp when the welding start signal On is at a high level.

  The secondary drive circuit DV2 outputs the electrode positive polarity drive signal Pd when the polarity switching start signal Sb is at a high level, and outputs the electrode negative polarity drive signal Nd when the polarity switch start signal Sb is at a low level. In the above description, the case where the welding current i is reduced by reducing the voltage control setting signal Vcr during the short-circuit induction period and the short-circuit initial period has been described. In addition to this, the welding current i may be reduced by controlling the welding power source to constant current characteristics only during both periods and setting the current setting signal to a low value.

[Embodiment 2]
FIG. 3 is a voltage / current waveform diagram showing a polarity switching short-circuit arc welding method according to Embodiment 2 of the present invention. (A) in the figure shows the polarity switching signal Sa, (B) in the figure shows the polarity switching start signal Sb, (C) shows the welding voltage v, and (D) shows the welding current i. E) shows the time change of the wire feed speed Wf. In the figure, the operations other than the period from time ta to tb are the same as those in FIG. The operation during the period from time ta to tb will be described below with reference to FIG.

  At the time tb when the polarity switching signal Sa changes at the time t1 and the arc period from the time ta when the previous short circuit is released reaches the reference value Tt, the short circuit induction period Td is started. In response to this, the welding voltage v shown in FIG. 10C decreases, the welding current i shown in FIG. 10D also decreases, and the wire feed speed Wf shown in FIG. Induces the next short circuit early. Since the operation after time tb is the same as that in FIG.

  The reference value is set to a period slightly longer than the average value of one arc period from the start of welding until the polarity switching signal Sa changes. Under welding conditions in which the average value of the arc period is about several tens of ms, the period from when the polarity switching signal Sa changes until a short circuit occurs is not so long as to affect the welding quality. For this reason, it is better to wait for the short circuit to occur naturally in the average arc period than to decrease the welding current i or the like immediately in conjunction with the polarity switching signal Sa and to affect the bead. is there. However, sometimes a short circuit may occur after much longer than the average arc period. In such a case, a short circuit induction period Td is provided to induce a short circuit at an early stage.

  FIG. 4 is a block diagram of a welding power source for carrying out the polarity switching short-circuit arc welding method according to the second embodiment described above. In the figure, the same blocks as those in FIG. 2 described above are denoted by the same reference numerals, and description thereof is omitted. Hereinafter, blocks indicated by dotted lines different from those in FIG. 2 will be described with reference to FIG.

  The second short circuit induction period generation circuit TD2 is configured to perform the above short circuit / arc from the time when the reference value Tt has elapsed from the time when the polarity switching signal Sa is changed and the short circuit / arc determination signal Sd is changed to the previous low level (arc). A short circuit induction period signal Td is output that is at a high level for a period until the determination signal Sd changes to a high level (short circuit). That is, the short-circuit induction period signal Td is at a high level during the period from time tb to t2 in FIG. 3 described above.

[Embodiment 3]
FIG. 5 is a voltage / current waveform diagram showing a polarity switching short-circuit arc welding method according to Embodiment 3 of the present invention. (A) in the figure shows the polarity switching signal Sa, (B) in the figure shows the polarity switching start signal Sb, (C) shows the welding voltage v, and (D) shows the welding current i. E) shows the wire feed speed Wf, and FIG. 5F shows the time change of the welding start signal On. This figure is a waveform diagram at the start of welding, and the operation after time t1 when a predetermined initial start period Tai has elapsed from the arc start is the same as that in FIG. Hereinafter, the operation before time t1 will be described with reference to FIG.

  At time tc, when the welding start signal On changes to a high level (welding start) as shown in FIG. 5F, the feeding of the welding wire is started as shown in FIG. As shown in (C), the welding voltage v is output. When the welding wire reaches and contacts the base metal at time td, the welding voltage v becomes a short-circuit voltage value as shown in FIG. 10C, and the welding current i is energized as shown in FIG. Starts and arc starts. At time t1 when a predetermined start initial period Tai has elapsed from this time point, the polarity switching signal Sa changes as shown in FIG. The subsequent operations are the same as those in FIG. In the drawing, the electrode positive polarity EP is used during the start initial period Tai and the electrode negative polarity EN is used thereafter, but the reverse is also possible. The reason for switching the polarity at the time of arc start is that the polarity at which the quality of the arc start portion is good may be determined depending on the type of welding wire, the type of shield gas, the material of the workpiece, the plate thickness, the joint, and the like. Therefore, the start initial period Tai is set to an appropriate value according to these various welding conditions.

  FIG. 6 is a block diagram of a welding power source for carrying out the polarity switching short-circuit arc welding method according to the third embodiment described above. In the figure, the same blocks as those in FIG. 2 described above are denoted by the same reference numerals, and description thereof is omitted. Hereinafter, blocks indicated by dotted lines different from those in FIG. 2 will be described.

  The current detection circuit ID determines the energization of the welding current i and outputs a current detection signal Id that becomes a high level. The start initial period setting circuit TAI outputs a predetermined start initial period setting signal Tai. The second polarity switching signal circuit SA2 changes when the welding start signal On becomes High level and the current detection signal Id changes to High level, and when the period determined by the start initial period setting signal Tai elapses. The polarity switching signal Sa to be output is output.

  The above is a case where the polarity switching signal Sa is changed at the time when the start start period Tai has elapsed after the arc start in the first embodiment. The same applies to the case where this function is added to the second embodiment.

It is a voltage / current waveform diagram showing a polarity switching short-circuit arc welding method according to Embodiment 1 of the present invention. It is a block diagram of the welding power supply which concerns on Embodiment 1 of this invention. It is a voltage and electric current waveform diagram which shows the polarity switching short circuit arc welding method which concerns on Embodiment 2 of this invention. It is a block diagram of the welding power supply which concerns on Embodiment 2 of this invention. It is a voltage / current waveform diagram showing a polarity switching short-circuit arc welding method according to Embodiment 3 of the present invention. It is a block diagram of the welding power supply which concerns on Embodiment 3 of this invention. It is a voltage / current waveform diagram showing a polarity switching short-circuit arc welding method of the prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Welding wire 2 Base material 3 Arc 4 Welding torch 5 Feed roll AC Commercial power supply AMP Error amplification circuit Amp Error amplification signal D2a-D2d Secondary side diode Dv Drive signal DV1 Primary side drive circuit DV2 Secondary side drive circuit EN Electrode Negative polarity EP Electrode plus polarity FC Feed control circuit Fc Feed control signal i Welding current Ii Short-circuit initial current ID Current detection circuit Id Current detection signal INT High frequency transformer INV Inverter circuit M Feed motor Nd Electrode negative polarity drive signal NTR Electrode minus Polarity switching element ON Welding start circuit On Welding start signal Pd Electrode plus polarity drive signal PTR Electrode plus polarity switching element SA Polarity switching signal circuit Sa Polarity switching signal SA2 Second polarity switching signal circuit SB Polarity switching start signal generation circuit Sb Polarity switching start Signal SD Short / arc Discrimination circuit Sd Short circuit / arc discrimination signal SUB Subtraction circuit Ta Arc period TAI Start initial period setting circuit Tai Start initial period (setting signal)
TD short circuit induction period generation circuit Td short circuit induction period (signal)
TD2 Second short circuit induction period generation circuit Ti Short circuit initial period (signal)
Ts Short-circuit period v Welding voltage Vcr Voltage control setting signal VD Voltage detection circuit Vd Voltage detection signal VR Voltage setting circuit Vr Voltage setting signal WL Reactor ΔVR Voltage drop setting circuit ΔVr Voltage drop setting signal

Claims (3)

In the short-circuit arc welding, which feeds the welding wire at a constant speed and repeats the short-circuit state and the arc state, the electrode positive polarity welding is performed by switching the output polarity of the welding power source during welding in accordance with a predetermined polarity switching signal. In the polarity switching short-circuit arc welding method in which welding is performed by switching between electrode negative polarity welding and
When the polarity switching signal changes, the welding current decreases or the welding voltage decreases or the wire feeding speed increases from the time when the arc period from the previous short circuit cancellation becomes the reference value until the next short circuit occurs. When a short circuit occurs, the welding current is maintained at a low value for a predetermined period, then the output polarity of the welding power source is switched, and then the welding current is increased to reduce the short circuit state. A polarity-switching short-circuit arc welding method, characterized by leading to release. The reference value according to claim 1, wherein the reference value is set based on an average value of each arc period until the polarity switching signal changes. 3. The polarity-switching short-circuit arc welding method according to claim 1, wherein the polarity is switched by changing the polarity switching signal when a predetermined start initial period after the arc start elapses.

Images