JP2009045670A - Pulse arc welding method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pulse arc welding method by which a stable arc state can be kept even when the shield gas mixing ratio is changed in pulse arc welding. <P>SOLUTION: In the pulse arc welding method, the welding is performed by repeating conduction of a peak current in a peak period Tp and conduction of a base current in a base period as one pulse period Tf, the peak period Tp is formed of a first peak period Tp1 for applying a first peak current Ip1 and a second peak period Tp2 for applying a second peak current Ip2 smaller than the first peak current Ip1. The first peak period Tp1 and the first peak current Ip1 are set to a value such that an arc anode point is formed at the top of the droplet even when the shield gas mixing ratio deviates from a standard ratio. The second peak period Tp2 and the second peak current Ip2 are set to a value such that one droplet is transferred during every pulse period Tf, and beads are formed with no undercuts. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a pulse arc welding method capable of performing stable welding even when the mixing ratio of shielding gas is changed.

  FIG. 5 is an example of a current / voltage waveform diagram of consumable electrode pulse arc welding. FIG. 4A shows the welding current Iw, and FIG. 4B shows the welding voltage Vw. During the peak rising period Tup from time t1 to t2, a transition current that rises from the base current Ib to the peak current Ip is energized as shown in FIG. 9A, and as shown in FIG. A transition voltage increasing from the voltage Vb to the peak voltage Vp is applied between the welding wire and the base material. During the peak period Tp from time t2 to t3, a peak current Ip greater than or equal to the critical current value is energized as shown in FIG. 5A, and a peak voltage Vp is applied as shown in FIG. During the peak fall period Tdw from time t3 to t4, a transition current that decreases from the peak current Ip to the base current Ib is energized, and as shown in FIG. 5B, the peak voltage Vp decreases to the base voltage Vb. A transition voltage is applied. During the base period Tb from time t4 to t5, as shown in FIG. 6A, the base current Ib having a small current value that does not allow the droplet to grow is energized, and as shown in FIG. Is applied. The period from t1 to t5 is the pulse period Tf.

  The peak rising period Tup and the peak falling period Tdw are set to appropriate values according to the base material. In pulse MAG welding in which the base material is a steel material, both values are set to small values, so that the peak current waveform is substantially rectangular. On the other hand, in pulse MIG welding in which the base material is an aluminum material, both values are set to large values, so that the peak current waveform is trapezoidal. In addition, the transition current is not only linearly raised / lowered in order to improve weldability, but may be changed in a curved shape (see, for example, Patent Documents 1 and 3). In some cases, the peak current Ip is increased stepwise (see, for example, Patent Document 2). As the shielding gas, a mixed gas of 80% argon gas + 20% carbon dioxide gas is used in pulse MAG welding, and 100% argon gas is often used in pulse MIG welding.

  In consumable electrode arc welding, it is important to control the arc length to an appropriate value in order to obtain good welding quality. For this purpose, the output of the welding power source is controlled so that the welding voltage average value Vav becomes equal to a predetermined voltage setting value by utilizing the fact that the average value Vav of the welding voltage Vw is substantially proportional to the arc length. Arc length control. Similarly, in the pulse arc welding, the above-described pulse cycle Tf is controlled so that the welding voltage average value Vav becomes equal to the voltage setting value, and output control of the welding power source is performed (frequency modulation control). In addition to this, the output control of the welding power source may be performed by setting the pulse period Tf to a predetermined value and controlling the peak period Tp (pulse width modulation control).

  FIG. 6 is a one-pulse / one-droplet transfer range diagram showing a method of setting the peak period Tp and the peak current Ip. In the figure, the horizontal axis indicates the peak period Tp (ms), and the vertical axis indicates the peak current Ip (A). The hatched portion is a condition range in which one droplet moves in synchronism with the pulse period Tf (so-called one pulse / one droplet transfer). When a combination condition (referred to as a unit pulse condition) between the peak period Tp and the peak current Ip is within the shaded portion, one pulse per droplet transfer occurs. The unit pulse condition is set in such a condition that a good bead shape (no undercut occurs and a beautiful bead appearance) is formed within this one pulse / one droplet transfer range. When the peak current Ip is not a constant value, both values are set so that the current integrated value obtained by integrating the peak current Ip during the peak period Tp falls within the range corresponding to the shaded portion. The unit pulse condition described above needs to be reset according to the one pulse / one droplet transfer range depending on the type of welding wire, the mixing ratio of the shield gas, the wire feed speed, and the like.

  FIG. 7 is a schematic diagram of the arc generating portion when the unit pulse condition is in the 1 pulse / one droplet transfer range. An arc 3 is generated between the welding wire 1 delivered from the tip of the welding torch 4 and the base material 2. A molten pool 2 a is formed on the base material 2. The arc anode point 3a is formed on the top of the droplet 1a at the tip of the wire. For this reason, the droplet 1a is encased by the arc 3. On the other hand, the arc cathode spot 3b is formed on the molten pool 2a. Immediately after the peak current Ip ends energization, the detached droplet 1b moves.

JP 2005-28383 A Japanese Patent Laid-Open No. 2005-118872 JP 2006-75890 A

  As described above, the above unit pulse condition is based on the premise that the mixing ratio of the shield gas is the reference ratio, so that a one-pulse / one-droplet transfer range and a good bead shape can be obtained. Is set. For example, in pulse MAG welding of steel materials, a mixed gas of argon gas and carbon dioxide gas is used as the shielding gas. The standard ratio in this case is generally 80% argon gas + 20% carbon dioxide gas in Japan.

  When using a gas cylinder or the like that is precisely adjusted to the above-mentioned reference ratio and filled as a shielding gas supply method, there is almost no variation in the mixing ratio of the shield gas, and welding can be performed while maintaining the reference ratio. it can. However, in a large-scale factory, argon gas and carbon dioxide gas are often stored in separate tanks, mixed in a reference ratio by a mixer, and then supplied to each welding apparatus through a centralized pipe. In such a case, the initial fluctuation often occurs until the mixing ratio of the shield gas is stabilized at the start of the first factory operation in the morning. The fluctuation range varies depending on the shield gas supply equipment, but may be as large as ± 5 to ± 10%. In addition to the initial fluctuation, there is a fluctuation in a steady state, and the fluctuation width is smaller than the initial fluctuation width, but may be about ± 5%. Furthermore, welding may be performed by adjusting the mixing ratio of the shield gas to a more appropriate value from the shape of the workpiece, required quality, and the like. In such high quality welding, the reference ratio of the shielding gas is set by increasing or decreasing the argon gas ratio.

By the way, even if the mixing ratio of the shielding gas is changed in the direction in which the argon gas ratio is increased, the arc state can be substantially maintained in a stable state in many cases. This is because when the argon gas ratio increases, the droplets are easily transferred. Therefore, in many cases, it is not necessary to reset the unit pulse condition for a change in the direction in which the argon gas ratio increases.

  On the other hand, when the argon gas ratio of the shield gas changes in a decreasing direction, as will be described in detail with reference to FIG. 8, the transition of the droplets becomes difficult, and the arc state becomes unstable. Hereinafter, this phenomenon will be described.

  FIGS. 8A to 8C are schematic views of the arc generation portion when the argon gas ratio of the shield gas is reduced from the reference ratio. The same figure (A)-(C) has shown the droplet transfer with progress of time. As shown in FIG. 5A, when the argon ratio of the shielding gas decreases, the arc anode point 3a is formed below the droplet 1a. When the arc anode point 3a is formed below the droplet 1a, the vicinity of the arc anode point 3a becomes extremely high as shown in FIG. Spouts in the direction. As a result, since the droplet 3a receives the force 6 in the direction of being pushed up by the metal vapor 5, the droplet transfer becomes unstable. Then, as shown in FIG. 5C, since the transfer is blocked by the push-up force 6 and the transfer of one pulse / one droplet cannot be performed, the droplet 3a grows large and scatters other than the wire extension line. As a result, a large amount of spatter 7 is generated.

  As a countermeasure against the above-described problem, there is a method of increasing the value of the peak current Ip in order to move the arc anode point 3a formed below the droplet 1a upward. However, when the peak current value Ip is increased, the arc anode point 3a is formed on the top of the droplet 1a. However, since the arc 3 spreads and the arc force increases, undercut is likely to occur. For this reason, it becomes difficult to obtain a good bead shape. Furthermore, spatter accompanying an increase in arc force also increases.

  Then, an object of this invention is to provide the pulse arc welding method which can maintain the stable arc state even if the mixing ratio of shield gas changes.

In order to solve the above-described problem, the first invention
The welding wire is fed at a wire feed speed corresponding to a predetermined welding current average set value, and the arc current is repeatedly supplied with a peak current during the peak period and a base current during the base period as one pulse period. In the pulse arc welding method in which welding is performed by transferring droplets from the welding wire by this arc,
The peak period is formed from a first peak period in which a first peak current is passed and a second peak period in which a second peak current having a smaller value than the first peak current is passed,
The first peak period and the first peak current are set to values at which the arc anode point is formed on the top of the droplet even when the mixing ratio of the shield gas changes within a predetermined range from the reference ratio,
The second peak period and the second peak current are set to values at which one droplet moves for each pulse period and a bead shape without undercut is formed.
It is the pulse arc welding method characterized by this.

  A second invention is the pulse arc welding method according to the first invention, wherein the values of the first peak period and the first peak current are changed according to the change of the reference ratio.

  According to a third aspect of the present invention, the difference between the first peak current value and the second peak current value is changed so as to decrease as the welding current average set value increases. Or it is the pulse arc welding method of 2nd invention description.

  4th invention WHEREIN: When the said welding current average setting value is more than a critical current value, according to the said welding current average setting value becoming large, between the said 1st peak current value and the said 2nd peak current value The pulse arc welding method according to the first or second invention, wherein the difference is changed so as to be small.

  According to the first aspect of the present invention, the arc anode point can be formed on the top of the droplet even when the mixing ratio of the shielding gas changes within a predetermined range from the reference ratio, and the arc shape is widened and the arc force is increased. Can be suppressed. For this reason, since 1 pulse per 1 droplet transfer can be performed and the occurrence of undercut can be suppressed, a stable arc state can be maintained and good welding quality can be obtained.

  Furthermore, according to the second aspect of the present invention, even when the mixing ratio of the shielding gas changes greatly by optimizing the first peak period and the first peak current according to the reference ratio of the shielding gas, There is an effect.

  Furthermore, according to the third and fourth inventions, by changing the difference between the first peak current value and the second peak current value as the welding current average set value increases, An excessive arc force acting on the molten pool in a large current region can be weakened, and the occurrence of welding defects such as melting and humping can be suppressed. In particular, when the welding current average set value is equal to or higher than the critical current value, this effect becomes remarkable.

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

  FIG. 1 is a waveform diagram of a welding current Iw in a pulse arc welding method according to an embodiment of the present invention. As shown in the figure, the peak period Tp is formed from a first peak period Tp1 and a second peak period Tp2. The first peak current Ip1 is supplied during the first peak period Tp1, and the second peak current Ip2 having a value smaller than the first peak current Ip1 is supplied during the second peak period Tp2. Therefore, the peak current waveform has a step shape with a lower right.

  In the figure, as indicated by the dotted line, the conventional peak current is a constant value Ip. The first peak current Ip1 is set to a value larger than this constant value Ip. During the first peak period Tp1, the first peak current Ip1 is energized by applying a current larger than the conventional peak current value Ip, so that the arc anode point is dropped even if the mixing ratio of the shield gas changes. It is to be formed on the top. Since the first peak current value Ip1 is larger than the conventional peak current value Ip, the arc anode point can be formed on the top of the droplet even if the argon ratio of the shield gas is reduced. In order to form the arc anode point, a first peak period Tp1 of about 0.2 to 1.0 ms is required. Therefore, the first peak current Ip1 during the first peak period Tp1 is preferably a constant value, and is preferably not a waveform that falls in a slope shape.

  On the other hand, the value of the second peak current Ip2 during the second peak period Tp2 is set to a value smaller than the conventional peak current value Ip and the first peak current value Ip1. The formation position of the arc anode point remains the upper portion of the droplet even when the second peak period Tp2 is reached. This is because once the arc anode point is formed, it is stabilized at that position, so that it does not move even if the current value becomes small. In addition, since the second peak current value Ip2 is set to a small value, the average value of the entire peak period Tp is substantially the same as the conventional one. For this reason, the arc shape and the arc force are substantially the same as the conventional one, and a good bead shape without undercut can be obtained.

The setting method of each parameter is as follows.
(1) The first peak period Tp1 and the first peak current Ip1 are set so that the arc anode point is formed above the droplet even when the mixing ratio of the shielding gas changes within a predetermined range.
(2) The second peak period Tp2 and the second peak current Ip2 are set to values at which droplet transfer becomes one pulse / one droplet transfer and a good bead shape without undercut is obtained.

  FIG. 2 is a schematic diagram of an arc generating portion when the stepped peak current described above with reference to FIG. 1 is applied. As shown in the figure, the arc anode point 3a is formed on the top of the droplet 1a even if the mixing ratio of the shielding gas is changed. For this reason, the pushing force 6 described above with reference to FIG. 8B does not act on the droplet 1a, so that one droplet transfer is one pulse one droplet transfer. As a result, a small amount of spatter is generated and a good bead shape can be obtained.

  FIG. 3 is a block diagram of a welding power source according to the embodiment of the present invention. Hereinafter, each block will be described with reference to FIG.

  The power supply main circuit PM receives a commercial power supply such as a three-phase 200 V input, performs output control such as inverter control in accordance with a current error amplification signal ΔI described later, and outputs a welding voltage Vw and a welding current Iw. The power source main circuit PM includes, for example, a primary rectifier that rectifies commercial power, a smoothing capacitor that smoothes the rectified direct current, an inverter circuit that converts the smoothed direct current to high frequency alternating current, and a voltage suitable for arc welding of the high frequency alternating current A high-frequency transformer that steps down the voltage, a secondary rectifier that rectifies the stepped-down high-frequency alternating current, a reactor that smoothes the rectified direct current, a modulation circuit that performs pulse width modulation control using the current error amplification signal ΔI as an input, and pulse width modulated And a drive circuit for driving the inverter circuit based on the received signal. The welding current average setting circuit IAR outputs a predetermined welding current average setting signal Iar. The feed speed setting circuit FR outputs a wire feed speed setting signal Fr corresponding to the welding current average setting signal Iar. The wire feeder WF feeds the welding wire 1 at a wire feeding speed conceived by the wire feeding speed setting signal Fr. The welding wire 1 is fed through the welding torch 4 by the wire feeder WF, and an arc 3 is generated between the welding wire 1 and the base material 2 to perform welding.

  The voltage detection circuit VD detects the welding voltage Vw, calculates an average value thereof, and outputs a voltage detection signal Vav. The voltage setting circuit VR outputs a predetermined voltage setting signal Vr. The voltage error amplification circuit EV amplifies the error between the voltage setting signal Vr and the voltage detection signal Vav and outputs a voltage error amplification signal ΔV. The voltage / frequency conversion circuit VF converts the frequency into a frequency corresponding to the voltage error amplification signal ΔV, and outputs a pulse period signal Tfs that changes to a high level for a short time every pulse period Tf described in FIG.

  The peak period timer circuit TP outputs a peak period signal Tps that becomes High level only during a predetermined peak period Tp from when the pulse period signal Tfs changes to High level. Accordingly, the peak period signal Tps is at a high level during the peak period Tp in FIG. The base current setting circuit IBR outputs a predetermined base current setting signal Ibr. When the peak period signal Tps is at a high level (peak period), the first switching circuit SW1 switches to the a side and outputs a peak current setting signal Ipr, which will be described later, as a current setting signal Ir, and has a low level (base period). At that time, the base current setting signal Ibr is output as the current setting signal Ir.

  The first peak period timer circuit TP1 outputs a first peak period signal Tps1 that is at a high level only during a predetermined first peak period Tp1 after the peak period signal Tps changes to a high level (peak period). To do. The first peak current setting circuit IPR1 outputs a predetermined first peak current setting signal Ipr1. The second peak current setting circuit IPR2 outputs a predetermined second peak current setting signal Ipr2. The second switching circuit SW2 switches the first peak period signal Tps1 to the a side when the first peak period signal Tps1 is High level (first peak period), and outputs the first peak current setting signal Ipr1 as the peak current setting signal Ipr. During the level (second peak period), the second peak current setting signal Ipr2 is output as the peak current setting signal Ipr.

  The current detection circuit ID detects the welding current Iw and outputs a current detection signal Id. The current error amplification circuit EI amplifies an error between the current setting signal Ir and the current detection signal Id, and outputs a current error amplification signal ΔI. By these circuit blocks, the welding current Iw described above with reference to FIG.

  In the above-described embodiment, as shown in FIG. 1, the case where the peak rising period Tup and the peak falling period Tdw are small values is exemplified, but the same applies when both values are large values. Further, as described above, in pulse MAG welding of steel materials, the reference ratio of shield gas is usually 80% argon gas + 20% carbon dioxide gas. In the present embodiment, even if the mixing ratio of the shielding gas changes within a predetermined range from the reference ratio, the arc stability is maintained. However, when the reference ratio of the shielding gas changes greatly, it is desirable to change the values of the first peak period Tp1 and the first peak current Ip1. In this embodiment, arc stability is ensured even when the mixing ratio of the shielding gas changes within a predetermined range assumed with the reference ratio as the center value, but if the reference ratio changes, This is because a larger change in the mixing ratio can be accommodated by resetting the first peak period Tp1 and the first peak current Ip1 so as to match. Furthermore, in the present embodiment, DC pulse arc welding is exemplified, but it can also be applied to AC pulse arc welding. Further, in the present embodiment, the case of frequency modulation control in which the pulse period is feedback controlled for arc length control is illustrated, but the present invention can also be applied to pulse width modulation control.

  FIG. 4 is a relationship diagram between the welding current average set value Iar and the peak current difference ΔIp. As described above, the welding current average set value Iar is a signal for setting the average value of the welding current Iw, and the welding wire is fed at a wire feeding speed corresponding to this value. The difference ΔIp in the peak current represents the difference Ip1−Ip2 between the first peak current value Ip1 and the second peak current value Ip2. Hereinafter, a description will be given with reference to FIG.

  As shown in the figure, the peak current difference ΔIp decreases as the welding current average set value Iar increases. In particular, the peak current difference ΔIp decreases rapidly above the critical current value It at which the droplet transfer form changes to the spray transfer form. As shown in the figure, by setting the first peak current value Ip1 and the second peak current value Ip2 so that the difference ΔIp in peak current is reduced according to the welding current average set value Iar, the following welding quality is obtained. Can be improved.

  In the large current region, when the difference ΔIp in the peak current is large, the arc force acting on the molten pool becomes too strong as the average value of the welding current increases, so that the welding failure such as humping is likely to occur. . In particular, this phenomenon may become prominent when the welding current average value is equal to or greater than the critical current value It. On the other hand, when the peak current difference ΔIp is set to become smaller as the welding current average value becomes larger, the anode spot is formed at the upper part of the droplet even if the mixing ratio of the shielding gas changes. . In particular, when the welding current average value is equal to or greater than the critical current value, the anode point is formed at the upper part of the droplet even if the difference ΔIp in the peak current is considerably small. Therefore, by setting the peak current difference ΔIp to be small as the welding current average value is increased, an excessive point acting on the molten pool is maintained while maintaining the action of forming the anode spot on the upper part of the droplet. The arc force can be weakened, and poor welding such as melting and humping can be suppressed. As described above, the welding failure is likely to occur when the average value of the welding current becomes equal to or higher than the critical current value. Therefore, the difference ΔIp of the welding peak current may be set as follows. That is, when the welding current average value is equal to or greater than the critical current value, the peak current difference ΔIp is set to be small as the welding current average value is increased.

  According to the above-described embodiment, even if the mixing ratio of the shielding gas changes within a predetermined range from the reference ratio, the arc anode point can be formed on the top of the droplet, and the arc shape spread and the arc force increase. Can be suppressed. For this reason, since 1 pulse per 1 droplet transfer can be performed and the occurrence of undercut can be suppressed, a stable arc state can be maintained and good welding quality can be obtained. Furthermore, by optimizing the first peak period and the first peak current according to the reference ratio of the shielding gas, the above effect can be achieved even when the mixing ratio of the shielding gas changes greatly. Furthermore, by setting so that the difference in peak current decreases as the welding current average value increases, it is possible to weaken the arc force that acts excessively on the molten pool, and it will melt, hump, etc. The occurrence of poor welding can be suppressed. This effect becomes significant when the welding current average value is equal to or greater than the critical current value.

It is a wave form diagram of welding current Iw in a pulse arc welding method concerning an embodiment of the invention. It is a schematic diagram of an arc generation part when the welding current Iw of FIG. 1 is energized. 1 is a block diagram of a welding power source according to an embodiment of the present invention. FIG. 6 is a relationship diagram between a welding current average set value Iar and a peak current value difference ΔIp according to an embodiment of the present invention. It is a current and voltage waveform diagram in the pulse arc welding method of the prior art. It is a unit pulse condition figure which shows the 1 pulse 1 droplet transfer range. It is a schematic diagram of the arc generation part in the pulse arc welding method of a prior art. It is a schematic diagram of an arc generation part when the mixture ratio of the shielding gas for demonstrating a subject changes.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Welding wire 1a Droplet 1b Separation droplet 2 Base material 2a Molten pool 3 Arc 3a Arc anode point 3b Arc cathode point 4 Welding torch 5 Metal vapor 6 Pushing force 7 Sputter EI Current error amplification circuit EV Voltage error amplification circuit FR Feeding Speed setting circuit Fr Wire feed speed setting signal IAR Welding current average setting circuit Iar Welding current average setting (value / signal)
Ib Base current IBR Base current setting circuit Ibr Base current setting signal ID Current detection circuit Id Current detection signal Ip Peak current Ip1 First peak current Ip2 Second peak current Ipr Peak current setting signal IPR1 First peak current setting circuit Ipr1 First peak Current setting signal IPR2 Second peak current setting circuit Ipr2 Second peak current setting signal Ir Current setting signal Iw Welding current PM Power main circuit SW1 First switching circuit SW2 Second switching circuit Tb Base period Tdw Peak falling period Tf Pulse period Tfs Pulse period signal TP Peak period timer circuit Tp Peak period TP1 First peak period timer circuit Tp1 First peak period Tp2 Second peak period Tps Peak period signal Tps1 First peak period signal Tup Peak rising period Vav Voltage detection signal (welding voltage average) value)
Vb Base voltage VD Voltage detection circuit VF Voltage / frequency conversion circuit Vp Peak voltage VR Voltage setting circuit Vr Voltage setting signal Vw Welding voltage WF Wire feeder ΔI Current error amplification signal ΔIp Peak current difference (Ip1-Ip2)
ΔV Voltage error amplification signal

Claims (4)

The welding wire is fed at a wire feed speed corresponding to a predetermined welding current average set value, and the arc current is repeatedly supplied with a peak current during the peak period and a base current during the base period as one pulse period. In the pulse arc welding method in which welding is performed by transferring droplets from the welding wire by this arc,
The peak period is formed from a first peak period in which a first peak current is passed and a second peak period in which a second peak current having a smaller value than the first peak current is passed,
The first peak period and the first peak current are set to values at which the arc anode point is formed on the top of the droplet even when the mixing ratio of the shield gas changes within a predetermined range from the reference ratio,
The second peak period and the second peak current are set to values at which one droplet moves for each pulse period and a bead shape without undercut is formed.
A pulse arc welding method characterized by that.   2. The pulse arc welding method according to claim 1, wherein values of the first peak period and the first peak current are changed in accordance with a change in the reference ratio.   3. The pulse according to claim 1, wherein a difference between the first peak current value and the second peak current value is changed so as to decrease as the welding current average set value increases. 4. Arc welding method.   When the welding current average set value is equal to or greater than the critical current value, the difference between the first peak current value and the second peak current value is reduced as the welding current average set value is increased. 3. The pulse arc welding method according to claim 1, wherein the pulse arc welding method is changed.

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