JPH0160355B2 - - Google Patents

Description

[Detailed description of the invention] The present invention melts and welds a consumable welding wire in a shielding gas mainly composed of an inert gas.
This relates to the MIG arc welding method.

In consumable shielded gas arc welding, if a crater occurs at the welding point, it will cause weld cracking. Further, if welding is completed with the tip of the consumable welding wire (hereinafter referred to as wire) having a spherical shape larger than the wire diameter, the next arc start will not be performed smoothly. Therefore, conventionally, these two problems have been individually studied and various improvement techniques have been proposed.
One method for removing the molten ball at the tip of the wire is to gradually reduce the wire feeding speed due to the mechanical inertia of the wire feeding device at the end of welding, that is, to gradually reduce the welding current, and perform welding that is appropriate for the current value. The voltage can be gradually reduced or reduced in stages,
Alternatively, it has been proposed to make the no-load voltage of the welding power source approximately equal to the arc voltage at the end of welding. Although such a method is effective for carbon dioxide arc welding, it cannot be expected to be effective for MIG arc welding, which uses inert gas as the main component. In carbon dioxide arc welding, as the current value increases, the electromagnetic repulsion force increases, and large droplets form at the tip of the wire, causing irregular droplet transfer. Conversely, as the welding current value decreases and the transition form of the molten metal at the wire tip changes from a drop transition to a short circuit transition, the distance between the wire tip and the molten pool decreases, and the electromagnetic repulsion force also decreases. Before the molten metal grows into large particles as when a large current is applied, the molten metal at the tip of the wire and the molten pool easily become short-circuited. When this short circuit occurs, the molten metal at the tip of the wire easily transfers to the molten pool due to the surface tension of the molten pool, so that no molten ball is formed at the tip of the wire. In this way, in carbon dioxide arc welding, as the welding current increases, the molten metal at the tip of the wire becomes larger particles, making it difficult to separate, and conversely, when the current decreases and a short-circuit transition region occurs, the molten metal at the tip of the wire melts. Easier transition to pond.

Therefore, it is effective to gradually reduce the welding current at the end of welding as described above, and to gradually reduce the welding voltage accordingly to shorten the arc length and move it from the drop transition region to the short circuit transition region,
Thereby, it is possible to effectively prevent the formation of molten balls at the tip of the wire at the end of welding. In contrast, in the MIG arc welding method, which uses inert gas as the main component, the pinch force increases as the welding current increases, so the molten metal at the tip of the wire becomes small particles and sprays into the molten pool in an extremely regular manner. However, when the current decreases, on the other hand, the melting speed at the wire tip and the pinching force decrease, causing the molten metal at the wire tip to become large particles and separate.
Furthermore, in the short-circuit transition region of the MIG arc welding method, compared to the short-circuit transition region of carbon dioxide arc welding, even with the same welding current, the potential gradient of the former is smaller than that of the latter. In addition, the heat input is low and the cooling rate of the wire tip and molten pool increases, making it more likely that stagnation will occur. Since it is difficult to maintain, defects at the end of the weld are also likely to occur.

Therefore, in the MIG arc welding method, especially when welding aluminum, the method of reducing the welding voltage in response to the decrease in the welding current as described above may leave a molten ball at the tip of the wire or cause a stagnation. Therefore, a substantially constant effect cannot be obtained as in the case of carbon dioxide arc welding. Therefore, in such MIG arc welding, an output voltage higher than the welding voltage is supplied in pulses between the wire and the workpiece at the end of welding, and the pinch effect of the large current flowing at that time causes the tip of the consumable electrode to A method of forcibly separating the molten sphere and transferring it to the molten pool is also shown. However, the setting of the magnitude and timing of the voltage to be generated in a pulsed manner differs slightly depending on the output voltage of the welding machine or the amount of consumable electrode feeding, making it difficult to select the conditions and the setting may be incorrect. In the perfect case, there remained drawbacks such as sticking and an increase in the diameter of the molten sphere. Furthermore, this method of supplying pulse voltage has the disadvantage that the welding current is applied to obtain a large pinch force at the end of welding, which generates a large arc force and increases the size of the crater. Ta.

The present invention uses MIG arc welding, which uses inert gas as the main component, to apply a welding current that allows spray transfer of molten metal at the tip of the wire at the end of welding, and that does not cause large craters. By spray transfer, the wire feeding is stopped and stuck is prevented without generating a molten ball at the tip of the wire, and before the wire burns back (welding with the chip due to burning). MIG that cuts welding current
This proposed an arc welding method.

Hereinafter, the MIG arc welding method of the present invention will be explained with reference to the drawings.

FIGS. 1A to 1D show an embodiment of the MIG arc welding method of the present invention, with the vertical axis representing welding current I and the horizontal axis representing elapsed time t. In the figure D, t ₀ is the time when the welding current Ia is changed to the crater filler current If before the end of the welding operation, and in the figures A to D, t ₁
is the time when the power supply to the welding wire feeding device is cut off at the end of welding, and if the output setting value of the welding device is maintained constant before and after this time, the welding current Id is the wire feeding speed Corresponding to the gradual decrease in , it gradually decreases as shown by the two-dot chain line. t ₂ is the time when the output setting value of the welding device is set to a welding completion processing current value Ie that allows spray transfer and does not increase the crater depression, and t ₃ is the time when the output setting value of the welding device is set at the welding end processing current value Ie that allows spray transfer and does not make the crater depression large. Welding end processing current value
It is time to cut off Ie. Ic indicated by a dashed-dotted line
is the spray transfer critical welding current value (hereinafter referred to as critical current value) determined by the material and diameter of the welding wire and the components of the shielding gas. For example, if the material of the welding wire is pure aluminum and its diameter is 1.2,
100, 130 and 1.6 and 2.4mm respectively
185A, aluminum alloy with diameters of 1.2, 1.6 and
130, 170 and 240A respectively for 2.4mm, 180A and 220A respectively for stainless steel and 1.2 and 1.6mm diameter, and 180A and 220A respectively for nickel alloy.
1.6mm is 240A, and 1.6mm mild steel is 260A. In Figure A, the welding current Ia up to time t ₁ before the end of welding is sufficiently larger than the above-mentioned critical current value Ic at which spray transfer is possible, and the welding current Ia before the end of welding at time t ₁ is sufficiently larger than the critical current value Ic that allows spray transfer. Therefore, the power supply to the wire feeding device is cut off. After time _t1 , the speed of the wire feeding device gradually decreases due to mechanical inertia, and correspondingly, the welding current value I'd gradually decreases and approaches the critical current value Ic. At time t ₂ , by adjusting the output setting device of the welding device, the welding current Id, which would otherwise gradually decrease as shown by the two-dot chain line and become below the critical current value Ic, is reduced. , a current value greater than the critical current value Ic
Keep it in Ie. By doing so, the droplets continue to migrate from the tip of the wire in the form of a spray, so that no molten ball is generated at the tip of the wire. At time _t3 , when the wire feeding has almost stopped and stagnation no longer occurs, and before burnback occurs,
Cut off the output of the welding equipment to finish welding. The above-mentioned welding completion processing current value Ie exceeds the critical current value Ic but is close to the critical current value Ic, so that spray transfer occurs and no molten ball is generated at the wire tip, and the above-mentioned welding process current value Ie is close to the critical current value Ic. Since it is smaller than the current value Ia, it also has the effect of reducing the size of the crater.
In FIG. B, the welding current Ia before the end of welding up to time _t1 is smaller than the critical current value Ic, so the droplet from the tip of the wire short-circuits into the molten pool. At time _t1 , the power supply to the wire feeding device is cut off, and the output setting device of the welding device is adjusted to increase the current value Ie to a critical current value Ic or more. The subsequent steps are the same as in the case of A in the same figure.
In the case of B in the same figure, the welding current Ia is in the short circuit transition region, so no large crater is generated, and the welding end processing current value Ie immediately changes from the current value Ia during welding. Therefore, the time t ₁ at which the power supply to the wire feeding device is cut off and the time t ₂ at which the welding end processing current value Ie is set.
becomes at the same time. In Figure C, the welding current value Ia before the end of welding up to time _t1 is a value slightly larger than the critical current value Ic, so the droplets from the tip of the wire are transferred to the spray. By cutting off the power supply to the wire feeding device at time t ₁ and adjusting the output setting device of the welding device, it is possible to reduce the amount of power that would otherwise gradually decrease as the wire feeding speed gradually decreases. Welding current Id,
Maintain the current value Ie higher than the critical current value Ic. From then on,
This is the same as the case shown in FIG. In figure D,
The welding current value Ia up to time t ₀ is sufficiently larger than the critical current value Ic, so the droplets from the wire tip are transferred to the spray, but the large current value causes a large crater. is occurring. Therefore, at time _t0 , the welding current value is changed from Ia to crater filler current If, which is smaller than the critical current value Ic. At time _t2 , the output setting device of the welding device is adjusted to increase the welding completion processing current value Ie, which exceeds the critical current value Ic again. in this case,
Since the crater filler current If is sufficiently smaller than the critical current value Ic, the wire feeding speed is low, and the mechanical inertia is also small, the welding current value is increased from If to Ie at time t ₂ , and then at time t ₁ . In,
The power supply to the wire feeder is cut off.
In Figure A mentioned above, the welding current value Ia is considerably larger than the critical current value Ie, so a large crater has occurred, and the welding current is reduced by using the gradual reduction by the wire feeding device. Since active crater treatment is not performed, the welding end treatment current value Ie should be set to a value as small as possible, although it exceeds the critical current value Ic, and the duration of this current (t ₃ - t ₂ ) should be lengthened. For example, by setting the time to 50 msec, the crater is made smaller. On the other hand, in the case of short-circuit transition type welding as shown in Figure B, or when the crater is reduced by active crater treatment as shown in Figure D, the welding completion processing current value Ie is equal to the critical current value. By making it sufficiently larger than Ic, the generation of molten balls at the tip of the wire can be more effectively prevented. However, in this case, the output voltage of the welding device has been increased in order to increase the welding end processing current value Ie, and the wire feeding speed has already decreased. The duration time (t ₃ −t ₂ ) of the processing current value Ie is shortened, for example, to 10 msec. If an attempt is made to remove the molten ball at the tip of the wire during this duration of less than 10 msec, the final welding current value Ie will become excessive and the crater will become larger. FIGS. 2A to 2C show the back electromotive force Em of the electric motor of the wire feeding device, respectively, when the MIG arc welding method of the present invention shown in FIG. 1D is carried out.
FIG. 3 is a diagram showing the time course of welding voltage V and welding current I. The welding conditions are argon as the shielding gas, aluminum alloy as the welding wire (JISZ3232 A5183WY), diameter 1.6mm, crater filler current If 120A, crater filler voltage 21V, welding final processing current value Ie 270A, final The welding voltage is 23V, and the duration of the final welding current Ie ( _t3 - _t2 ) is 50msec. As mentioned above, the critical current value of an aluminum alloy wire with a diameter of 1.6 mm is
Since it is 170A, the crater filler current value If is
Since the current is 120A and is less than the critical current value, as shown in the waveform from time t ₀ to t ₂ in Figure B, it is in the short circuit transition region and short circuits are repeated, but the welding completion processing current value Ie is Since the current is 270A, which is larger than the critical current value, the short circuit phenomenon is no longer observed as shown in the waveform between time t ₂ and t ₃ , which indicates that spray transfer has occurred. There is.

Next, an apparatus for carrying out the welding method of the present invention will be explained.

FIGS. 3A to 3C are a block diagram, a sequence circuit diagram, and a sequence explanatory diagram of a first embodiment of an apparatus for carrying out the welding method of the present invention, respectively. In each figure, 1 is a three-phase AC power source for welding equipment, 2 is a wire, 3 is a workpiece to be welded, T1 is a transformer for a welding power source,
4 is an output control circuit, such as a thyristor.
A circuit constituted by SCR, M is a wire feeding device, M1 is a control circuit for the wire feeding device, and 5a is a first reference signal circuit, which is the output of the welding device before the end of welding, that is, welding This is a circuit that sets voltage Va and welding current Ia. 5b is a second reference signal circuit, which outputs the output signal Vrb of this circuit and the first reference signal circuit.
The output of the welding device at the end of welding, that is, the final welding voltage Ve or the welding end processing current value, is determined by the sum signal or difference signal from the output signal Vra of the reference signal circuit.
Set up Ie. A feedback circuit 7 feeds back a signal Vf corresponding to the welding voltage or welding current to a comparison circuit 6, which will be described later. Reference numeral 6 denotes a comparison circuit which outputs the first reference signal Vra and the feedback signal Vf.
or the difference between the signal Vra±Vrb, which is a composite signal of the first reference signal Vra and the second reference signal Vrb, and the feedback signal Vf is supplied to the output control circuit 4 through the amplifier circuit AMP. 8 is a sequence circuit, TS is a torch switch, and TSa is a self-holding circuit that closes when the torch switch TS is first pressed to start welding and detects the output of the welding device.
This is a contact that opens when the torch switch TS is pressed again to complete welding. CR1 is a contact
Relay coil energized by TSa, CR1
a and CR1b are a normally open contact and a normally closed contact, respectively, which are opened and closed by excitation of relay coil CR1. CR2 is the relay coil excited by contact TSa, CR2a and CR2b are the rectifier DR
1. Normally open contact of relay CR2 with delayed return by resistor R1 and capacitor C1. Next, the operation will be explained. When you press the torch switch TS to start welding, the relay contact TSa
is closed, relays CR1 and CR2 are energized and contact CR1a is closed as shown in FIG. Vra is supplied to the comparison circuit 6, and its output signal Vra-Vf is supplied to the output control circuit 4 through the amplifier circuit AMP to maintain the welding voltage at a substantially constant value of Va or the welding current at a substantially constant value of Ia. welding continues. Upon completion of welding, the torch switch TS is turned on at time _t1 .
When is pressed again, the contact TSa and therefore the contact CR1a open, and the contact CR1b closes, cutting off the power supply to the wire feeding device M and reducing the wire feeding speed as shown by M in Figure 3C. gradually decreases.
However, until the contacts CR2a and CR2b are delayed, the comparator circuit 6 is supplied with the first reference signal Vra, the second reference signal Vrb, and the feedback signal Vf, and when the signal polarity is Vra+Vrb+Vf, the Or, as shown in I, the output voltage or output current of the welding device increases, and when Vra-Vrb-Vf, the output of the welding device decreases as shown in the dotted line in the figure. Contact CR at time t ₃ after the delay time has elapsed
2a and CR2b are opened and the welding device output is cut off. The output signal Vrb of the second reference circuit is set so that the output current of the welding device within the above-described delay time exceeds the critical current value Ic. In the above configuration, the first reference signal is used during welding.
It is also possible to supply Vra to the comparator circuit 6, cut off the signal Vra at the end of welding, and supply the second reference signal Vrb. At this time, the second reference signal
Vrb may be fixed to a predetermined constant value. Further, the adjustment of the first reference signal circuit 5a and the adjustment of the second reference signal circuit 5b may be mechanically or electrically linked to adjust the first reference signal so that the output current value during welding is increased, for example. When the signal Vra is set to a large value, the second reference signal Vrb is set to a small value so that the signal Vra + Vrb, which is the sum of the reference signals at the end of welding, exceeds the critical current value Ic and does not increase the depression of the crater. The welding completion processing current value Ie may be applied. Further, a crater filler control circuit may be provided in the above configuration.

FIGS. 4A to 4C are a configuration diagram, a sequence circuit diagram, and a sequence explanatory diagram of a second embodiment of an apparatus for carrying out the welding method of the present invention, respectively. In each figure, codes 1 to 4, 6, T1, M, M1,
AMP, TS, TSa, CR1 and CR1a have the same symbols as shown in FIGS. 1A to 1C. 5 is a reference signal circuit for determining the output current Ia of the welding device, 7a is a first feedback circuit for determining the output current Ia during welding, and 7b is a welding end processing current value Ie at the end of welding. This is a second feedback circuit for determining . CR1 and CR1d are relay coil CR
It is a normally open contact that is opened and closed by 1. TDR is the delayed return timer coil and normally closed contact CR1b
TDRb is excited by the closed circuit of timer TDR
It is a normally closed contact. CR3 is a normally closed contact CR1b
A coil is excited by the closing of TDRb and CR3a, and CR3a and CR3c are its normally open contacts. Next, the operation will be explained. When the torch switch Ts is pressed to start welding, the contact TSa is closed, and as shown in Figure 4C, the relay CR1 is energized and the contact CR1a is closed, and power is supplied to the wire feeding device M to feed the wire. On the other hand, by closing the contact CR1c, the feedback signal Vf is supplied to the comparator circuit 6 through the first feedback circuit 7a, and its output signal _Vf1 is supplied to the comparator circuit 6.
Vr-Vf ₁ is supplied to the output control circuit 4 through the amplifier circuit AMP, and welding is continued by maintaining the welding voltage at a substantially constant value of Va or the welding current at a substantially constant value of Ia. During this welding, contact CR1b is open, so voltage is not supplied to timer TDR and relay coil CR3, and contact CR3a is open. Upon completion of welding, when the torch switch TS is pressed again at time _t1 , the contact TSa opens the contacts CR1a, CR1c, and CR1d, and the contact CR1b closes, supplying voltage to the timer TDR and relay coil CR3, causing the contacts CR3a and CR3c is closed. By closing this contact CR3a, the feedback signal Vf is passed through the second feedback circuit 7b, and its output signal _Vf2 is supplied to the comparator circuit 6, and the output signal Vr- _Vf2 is supplied to the amplifier circuit AMP.
It is supplied to the output control circuit 4 through. When the feedback signal is Vf ₁ > Vf ₂ , the output voltage or output current of the welding device increases as shown in Figure 4C, and when Vf ₁ < Vf ₂ , the output of the welding device decreases as shown by the dotted line in the same figure. do. At time _t3 after the delay time has elapsed, the contact TDRb is opened, thereby opening the contact CR3c and cutting off the output of the welding device. The output signal Vf ₂ of the second feedback circuit 7b is set so that the output current of the welding device within the above-described delay time exceeds the critical current value Ic. In the embodiment shown in FIGS. 4A and 4B above, the adjustment of the reference signal circuit 5 and the second feedback circuit 7b
For example, by mechanically or electrically interlocking the adjustment of the reference signal to increase the output current value during welding.
When Vr is set to a large value, the second feedback signal Vf ₂ is set to a large value, and the output signal Vr−Vf ₂ of the comparator circuit 6 at the end of welding exceeds the critical current value Ic and greatly reduces the depression of the crater. Welding completion processing current value that does not cause
Ie may be energized. Furthermore, a crater filler control circuit may be provided by adding a second reference signal circuit and its control circuit to the above configuration.
In addition to the above first and second embodiments, an amplifier circuit
AMP amplification, output control circuit thyristor SCR
By controlling the constants of the ignition circuit, etc., it is possible to apply a welding current such that the welding completion processing current value Ie exceeds the critical current value Ic and the welding current does not increase the size of the crater depression.

As described above, according to the MIG arc welding method of the present invention, the properties of the shielding gas mainly composed of inert gas are used to spray the molten metal at the tip of the wire at the end of welding, and to greatly reduce the depression of the crater. It is possible to stop the wire feeding without generating a molten ball at the tip of the wire by applying a welding current that does not exceed Stakes do not occur. In addition, since a pulse current is not supplied at the end of welding as in conventional methods, it is easy to set the magnitude of the welding end processing current value and its duration to an appropriate value, making the crater depression smaller. Moreover, burnback can be prevented and various problems can be solved at the same time.

[Brief explanation of drawings]

1A to 1D are diagrams showing an embodiment of the MIG welding method of the present invention, and FIGS. 2A to 2C are diagrams showing the electric motor of the wire feeding device when the welding method of the present invention shown in FIG. 1D is implemented. Figures 3A to 3C are diagrams showing the time course of back electromotive force, welding voltage, and welding current, and Figures 3A to 3C are a block diagram, a sequence circuit diagram, and a sequence diagram of a first embodiment of an apparatus for carrying out the welding method of the present invention, respectively. The explanatory diagram and FIGS. 4A to 4C are a configuration diagram, a sequence circuit diagram, and a sequence explanatory diagram of the second embodiment, respectively. 2...Consumable welding electrode, 3...Work to be welded, M...Wire feeding device, Ic...Spray transfer critical welding current.

Claims (1)

[Claims] 1 In a MIG arc welding method in which an arc is generated between a consumable welding wire and a workpiece in a shielding gas containing an inert gas as a main component, and welding is performed by transferring droplets from the tip of the wire, Upon completion of welding, the wire is detached from the tip of the wire sometime between before the power supply to the wire feeding device is cut off and after the power supply is cut off and the welding current Id is gradually decreasing. Applying a preset welding completion processing current Ie that allows spray transfer of droplets and not enlarging the crater depression, and cutting off the welding completion processing current when the wire feeding device almost stops. MIG arc welding method.