JPH09150267A - Carbon dioxide shield arc welding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a sputter producing amount compared with the case of performing a carbon dioxide pulse arc welding under a low welding condition by controlling to switch the welding condition from the pulse arc welding condition to a short circuiting transfer welding condition. SOLUTION: A wire feeding velocity lower limit setting value, an average welding current lower limit setting value and an average welding voltage lower limit setting value are previously set with respect to the pulse arc welding condition. When at least one of the wire feeding velocity, the average welding current detecting value and the average welding voltage detecting value is less than the respectively corresponding lower limit setting value during welding in the pulse arc welding condition, control for switching the welding condition from the pulse arc welding condition to the short circuiting transfer arc welding condition is performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carbon dioxide shielded arc welding method, and by controlling the welding state to be switched from a pulse arc welding state to a short circuit transition arc welding state, the wire protrusion length at a low wire feeding speed. The present invention relates to a carbon dioxide gas shielded arc welding method capable of reducing the amount of spatter generated as compared with the case of performing pulse arc welding under low welding conditions such as low welding current and low welding voltage due to the increase in thickness.

[0002]

2. Description of the Related Art As is well known, carbon dioxide shield pulse arc welding (hereinafter referred to as carbon dioxide pulse welding) uses carbon dioxide alone or a mixed gas containing carbon dioxide as a main component as a shield gas, as shown in FIG. In addition, between the welding wire and the base material, a pulse current and a base current are alternately and repeatedly supplied as the welding current, and the droplet at the tip of the welding wire is separated by the pinch force in the first half of the pulse period in which the pulse current is passed, Subsequently, the welding wire tip is melted to form droplets in the latter half of the pulse period, and the droplets at the welding wire tip are shaped in the base period in which the base current is flowed. The droplets are allowed to separate / transfer in the first half of the next pulse period. In this way, carbon dioxide gas pulse welding is performed by regularly performing one pulse / one droplet transfer, in which one droplet is separated from the welding wire tip and transferred every pulse cycle, as compared with normal welding in which no pulse current is applied. To reduce the amount of spatter generated. Note that the pulse frequency f in carbon dioxide pulse welding is TP for the pulse period and TB for the base period.
f = 1 / (TP + TB), and the pulse current is I _P ,
If the base current is I _B , the average welding current I _AV is I _AV
= Represented by _{(I P · TP + I B} · TB) / (TP + TB).

[0003]

However, carbon dioxide pulse welding has a drawback that the amount of spatter is significantly increased under low welding conditions.

That is, in carbon dioxide pulse welding, the pulse frequency is lowered in order to reduce the average welding current value as the wire feeding speed is lowered, and there is a wire feeding speed as shown in FIG. Value (7m in Fig. 5
/ Min), the base period becomes too long due to a large decrease in the pulse frequency, and during this base period, the droplet at the tip of the welding wire and the molten pool short-circuit, and the amount of spatter generated increases.

On the other hand, in the carbon dioxide pulse welding in which the welding wire is fed at a constant speed, when the wire protrusion length changes, the Joule heat generation amount at the wire protrusion portion from the current-carrying tip changes, and the wire melting rate changes. Since the arc length changes due to the arc length, arc length control is performed to prevent the arc length from varying due to variations in the wire protrusion length. For example, if the wire protrusion length becomes longer than the set value, the wire melting rate increases due to the increase in the Joule heat generation amount, and the wire easily melts.Therefore, it is necessary to keep the arc length constant by decreasing the average welding current value. I have to. As is well known, the arc length control includes a pulse frequency modulation method and a pulse width modulation method.

When the arc length control of the pulse frequency modulation system is carried out, the pulse period is made constant and the base period is changed to change the pulse frequency, whereby the arc length is kept constant against variations in the wire protrusion length. Since the average welding current value is controlled to increase or decrease as shown in FIG. 6, the wire protrusion length has a certain value as shown in FIG.
30 mm), that is, when the average welding current falls below a certain value (200 A in FIG. 6), the pulse frequency is drastically reduced in order to reduce the current value and the base period becomes too long. The droplet at the tip of the welding wire and the molten pool short-circuit due to contact, and the amount of spatter generated increases.

Further, when the arc length control of the pulse width modulation system is carried out, the pulse frequency is made constant and the pulse period is changed, whereby the average welding current is adjusted so that the arc length becomes constant against variations in the wire protrusion length. Since the value is controlled to be increased or decreased, if the wire protrusion length becomes long and the welding current falls below a certain value (200 A in FIG. 6), the pulse period becomes too short to reduce the current value,
During the pulse period, the droplets cannot be separated and the droplets cannot be formed after the droplets are separated, and the droplet transfer phenomenon is deviated from the one-pulse / one-droplet transfer, and the amount of spatter is increased.

Regarding the average welding voltage value, as shown in FIG. 7, when the average welding voltage is lower than a certain value (29 V in FIG. 7), the arc length becomes too short, and the droplet at the tip of the welding wire and the molten pool are separated. Contact short-circuiting causes a large amount of spatter.

Therefore, according to the present invention, by controlling the welding state to be switched from the pulse arc welding state to the short-circuit transfer arc welding state, the amount of spatter generation can be reduced as compared with the case of performing pulse arc welding under low welding conditions. An object of the present invention is to provide a carbon dioxide gas shielded arc welding method which can be performed and requires less labor to remove spatter adhered to the welding base material and the welding torch.

[0010]

According to a first aspect of the present invention, carbon dioxide alone or a mixed gas containing carbon dioxide as a main component is used as a shield gas, and the welding wire and the base metal are fed at a constant speed. In the carbon dioxide shielded arc welding method in which an arc is generated to weld the base metal, the wire feed speed lower limit set value, average welding current lower limit set value, and average welding voltage lower limit set value are set in advance for pulse arc welding conditions. If at least one of the wire feeding speed, the average welding current detection value and the average welding voltage detection value falls below the corresponding lower limit setting value during welding in the pulse arc welding state, pulse arc welding is performed. It is characterized in that control is performed to switch the welding state from the state to the short-circuit transfer arc welding state.

According to a second aspect of the present invention, in the carbon dioxide gas shielded arc welding method according to the first aspect, the wire feeding speed lower limit setting value, the average welding current lower limit setting value and the average welding voltage lower limit setting value are hysteresis. It is characterized by having a width. Further, the invention of claim 3 is the carbon dioxide shield arc welding method of claim 1 or 2, wherein the average welding current lower limit setting value and the average welding voltage lower limit setting value increase as the wire feeding speed increases. It is characterized in that it is set as a function of the wire feeding speed having a functional relationship.

In carbon dioxide pulse welding using a welding wire having a diameter of 1.2 mm, which is a typical wire diameter, as a shield gas of carbon dioxide alone, as shown in FIGS. 5 to 7, the wire feeding speed is 7.5 m. When the average welding current is lower than 200 A when the wire protrusion length exceeds 30 mm, the wire welding speed is 10 m
/ Min), and the average welding voltage is lower than 29 V (when the wire feeding speed is 10 m / min), the spatter generation rate becomes larger than about 1 g / min and significantly increases. On the other hand, in the welding condition region where spatter frequently occurs in carbon dioxide pulse welding, as shown in FIG.
As shown in FIG. 7, according to so-called short-circuit transfer arc welding (short arc welding) in which a short circuit period and an arc generating period are alternately repeated, the amount of spatter is significantly smaller than that in carbon dioxide pulse welding.

Therefore, regarding the pulse arc welding conditions, a wire feed speed lower limit setting value, an average welding current lower limit setting value and an average welding voltage lower limit setting value are set in advance, and the wire is not welded during welding in the pulse arc welding state. Control for switching the welding state from the pulse arc welding state to the short-circuit transition arc welding state when at least one of the feed rate, the average welding current detection value, and the average welding voltage detection value falls below the corresponding lower limit setting value. By doing so, it is possible to reduce the amount of spatter generated as compared with the related art.

The respective lower limit set values, which are reference values for switching the welding state from the pulse arc welding state to the short-circuit transition arc welding state, and vice versa, from the short-circuit transition arc welding state to the original pulse arc welding state are shown in FIG. And, as shown in FIG. 4, it is preferable to have a hysteresis width. Regarding the respective lower limit setting values of the wire feeding speed, the average welding current, and the average welding voltage, the upper side of the hysteresis width is set to the upper lower limit setting value (UL in FIGS. 3 and 4), and the lower side of the hysteresis width is set to the lower lower limit value. Value (denoted by LL in FIGS. 3 and 4). By providing such a hysteresis width, for example, when the average welding current fluctuates slightly with the lower limit setting value having no hysteresis width as a boundary, the pulse arc welding state and the short-circuiting transition arc welding state frequently occur at minute time intervals. It is possible to reliably prevent the welding from becoming unstable due to switching to.

Among the lower limit setting values having the above-mentioned hysteresis width, the average welding current lower limit setting value and the average welding voltage lower limit setting value are such that the appropriate condition range of the pulse arc welding condition is high as the wire feeding speed increases. Since it shifts to the current / high welding voltage side, it may be set as a function of the wire feeding speed having a functional relationship that increases as the wire feeding speed increases.

[0016]

1 is a block diagram showing an example of a consumable electrode type gas shield welding power source for carrying out the welding method according to the present invention.

In FIG. 1, reference numeral 1 is a three-phase AC power supply unit. The alternating current supplied from the three-phase alternating-current power supply unit 1 is rectified into direct current by the first rectifier circuit 2 and smoothed by the smoothing capacitor 3. This direct current is converted into a high frequency alternating current by an inverter 4 using a transistor as a switching element. The transformer 5 steps down the output of the inverter 4 to a welding voltage. The high frequency alternating current from the transformer 5 which has been stepped down for welding is rectified by the second rectifier circuit 6 into a welding direct current. This direct current is supplied between the welding wire 8 and the base material 9 via the smoothing reactor 7 to perform arc welding.

Reference numeral 10 is an average welding voltage detector for detecting an average welding voltage, and 11 is a welding current detector for detecting a welding current (instantaneous value). Average welding voltage detector 10
And the output of the welding current detector 11 is given to the control unit 40 described later. The welding wire 8 is fed toward the base material 9 by the wire feeding roller 27 driven by the wire feeding motor 28, and welding is performed by generating an arc between the welding wire 8 and the base material 9. The wire feeding motor control circuit 29
Wire feed speed signal E from wire feed speed setter 26
The rotation speed of the feed motor 28 is controlled based on _W.

The control section 40 performs welding state switching control based on the presence / absence of a pulse welding command signal PS, which will be described later. In the pulse arc welding state, the base current and the pulse current of the set values flow in the inverter 4. Switching control of the transistor, and in the short-circuit transition arc welding state, the welding power supply output characteristic is set to a constant voltage characteristic, and the transistor of the inverter 4 is switching-controlled so that the set short-circuit transition arc welding voltage is obtained. Is. In this example, the welding power supply output characteristics during pulse arc welding are constant voltage characteristics during the pulse period and constant current characteristics during the base period.

The control unit 40 will be described. Pulse current setting circuit 12 is wire feed speed signal E _W from wire feed rate setting device 26 are input to set the proper pulse current value according to the value of the wire feed speed, setting signal for the pulse current To the output waveform selection circuit 23.

Similarly, the base current setting circuit 13 receives the wire feed speed signal E _W from the wire feed speed setter 26 and receives the wire feed speed signal E _W to maintain the arc according to the value of the wire feed speed. The current is set and the base current setting signal is output to the output waveform selection circuit 23. Further, the pulse period setting circuit 14 receives the wire feeding speed signal E _W from the wire feeding speed setting device 26, sets an appropriate pulse period according to the value of the wire feeding speed, and sets this pulse period. The signal is output to the output waveform selection circuit 23.

The frequency setting device 15 receives the wire feeding speed signal E _W from the wire feeding speed setting device 26, sets the pulse frequency at the time of pulse arc welding according to the value of the wire feeding speed, and sets the pulse frequency. The frequency is output to the adder 20.

The short-circuit transition arc welding voltage setting device 16 receives the wire feeding speed signal E _W from the wire feeding speed setting device 26, and an appropriate average during short-circuit transition arc welding is received according to the value of the wire feeding speed. The welding voltage is set and the short-circuit transfer arc welding voltage setting signal is applied to the voltage selection circuit 18. Further, the pulse arc welding voltage setting device 17 receives the wire feeding speed signal E _W from the wire feeding speed setting device 26,
An appropriate average welding voltage at the time of pulse arc welding is set according to the value of the wire feeding speed, and the pulse arc welding voltage setting signal is given to the voltage selection circuit 18.

The voltage selection circuit 18 switches S2 when a pulse welding command signal PS described later is input.
Is turned off and the switch S1 is turned on to output the pulse arc welding voltage setting signal to the error amplifier 19, and when the signal PS is not input, the switch S1 is turned off and the switch S2 is turned on to turn on the switch. The short circuit transfer arc welding voltage setting signal is output to the error amplifier 19.

When the pulse welding command signal PS is input, the error amplifier 19 sets the pulse arc welding voltage set value by the pulse arc welding voltage setter 17 and the welding voltage detected value detected by the average welding voltage detector 10. A voltage deviation signal is output to the adder 20 in order to adjust the pulse frequency set by the frequency setting unit 15 so that and coincide with each other.

The adder 20 adds the output of the error amplifier 19 to the pulse frequency signal from the frequency setting unit 15, and outputs the result to the pulse frequency setting circuit 30. When the pulse welding command signal PS is input in this manner, the pulse frequency is adjusted by adjusting the pulse frequency by the frequency setter 15 based on the difference between the pulse arc welding voltage setting value and the welding voltage detection value. Arc length control is performed. Then, the pulse frequency setting circuit 30
The pulse frequency is determined based on the pulse frequency from the adder 20, and the pulse start signal is output to the output waveform selection circuit 23 every pulse period.

The error amplifier 19 detects the short-circuit transition arc welding voltage set value and the average welding voltage detected by the short-circuit transition arc welding voltage setting device 16 when the pulse welding command signal PS is not input, that is, during short-circuit transition arc welding. The voltage deviation from the welding voltage detection value detected by the instrument 10 is output to the voltage-current conversion circuit 22. Voltage-current conversion circuit 2
2 outputs a welding current value signal for eliminating the voltage deviation from the error amplifier 19 to the output waveform selection circuit 23. As a result, arc length control during short-circuit transfer arc welding is performed.

The output waveform selection circuit 23 outputs a pulse current setting signal to the error amplifier 24 when a pulse start signal is given from the pulse frequency setting circuit 30 when the pulse welding command signal PS is input, and the pulse current setting signal is output. When the pulse period set by the period setting circuit 14 has elapsed, the base current setting signal is output to the error amplifier 24 until the next pulse start signal is input. During short-circuit transfer arc welding,
The welding current value signal from the voltage / current conversion circuit 22 is output to the error amplifier 24.

The error amplifier 24 compares the welding current detection value by the welding current detector 11 with each current setting value from the output waveform selection circuit 23, and outputs the deviation to the output control circuit 25. Then, the output control circuit 25 uses the error amplifier 24.
The inverter 4 is controlled so that the current value flowing through the welding current detector 11 matches each current set value output from the output waveform selection circuit 23, based on the deviation output from.

Reference numeral 31 is an average welding current detector. The average welding current detection signal E _I from the detector 31, the average welding voltage signal E _V from the average welding voltage detector 10, and the wire feeding speed signal E _W from the wire feeding speed setting device 26 are It is adapted to be input to a pulse welding command signal generating circuit for switching a welding state which will be described later.

FIG. 2 is a circuit diagram of a pulse welding command signal generating circuit provided in the welding power source shown in FIG.

Referring to FIG. 2, first, a configuration will be described in which the wire feeding speed is compared with the wire feeding speed lower limit setting value having a hysteresis width, and the welding state is switched from the comparison result.

Numeral 51 designates the wire feeding speed setting device 26.
Wire feed speed signal E_WAnd a hysteresis width is provided
Reference voltage E_WRIs a comparator with hysteresis that compares
The reference voltage E_WRThe variable resistor VR that determines the value of
Comparator dedicated operational amplifier IC₁And determine the hysteresis width
Resistance R₁, R_TwoIt consists of. This hysteresis
According to the built-in comparator 51, the hysteresis of the wire feeding speed is
Upper limit corresponding to the upper and lower limit set value (for example, 8 m / min)
Side lower limit setting signal E_WRThe value of U is E_WRU = E_WR+ (V_OH−
E_WR) × (R₁/ (R₁+ R_Two)) Also wire
Hysteresis lower limit lower limit setting value (eg 7m /
min) lower lower limit setting signal E corresponding to _WRThe value of L is E
_WRL = E_WR-E_WR× (R₁/ (R₁+ R_Two))
Note that V _OH≈5V.

In order to facilitate understanding, the operation will be described below. In order to facilitate understanding, pulse arc welding is in progress, and the wire feeding speed, the average welding current, and the average welding voltage are higher than the respective lower limit set values. 3-input AND gate I
It is assumed that the first to third input terminals of C ₇ are all at the H level (high level), and as a result, the 3-input AND gate IC ₇ outputs the pulse welding command signal PS as the H level signal. .

Now, as shown in FIG. 3, when the wire feed speed is lowered during pulse arc welding and the wire feed speed signal E _W falls below the value of the lower lower limit setting signal E _WR L, the operational amplifier The output of IC ₁ becomes H level (about 5 V), which is inverted by the inverter gate IC ₄ and the first input terminal of the 3-input AND gate IC ₇ becomes L level. As a result, the output of the 3-input AND gate IC ₇ becomes L level, the pulse welding command signal PS that has been output until then is turned off, and the pulse arc welding state is switched to the short-circuiting transition arc welding state.

When the wire feeding speed is increased during the short-circuit transfer arc welding, and the wire feeding speed signal E _W exceeds the upper and lower limit setting signal E _WR U, as shown in FIG. 3, The output of the operational amplifier IC ₁ changes from the H level to the L level (about zero volt), which is the inverter gate I.
It is inverted at C ₄ and the first input terminal of the 3-input AND gate IC ₇ becomes H level. As a result, the output of the 3-input AND gate IC ₇ becomes H level, the pulse welding command signal PS is output again, and the short circuit transition arc welding state is switched to the original pulse arc welding state.

Next, a structure for comparing the average welding current detection value and the average welding current lower limit setting value having a hysteresis width and switching the welding state from the comparison result will be described.

Reference numeral 52 is an amplifier for setting a reference voltage E _IR proportional to the magnitude of the wire feeding speed signal E _W from the wire feeding speed setting device 26. This amplifier 52
Is an operational amplifier IC ₈ and resistors R ₅ and R that determine the amplification factor.
1st stage amplifier composed of ₆ and operational amplifier IC
₉ and resistors R ₈ and R ₉ , and an amplification factor of 1 (R ₈ =
R ₉ ) and a second-stage amplifier for inverting the sign of the output of the first-stage amplifier to obtain a positive output, and the magnitude of the wire feeding speed signal E _W. The proportional reference voltage E _IR (E _IR = (R ₆ / R ₅ ) × E _W ) is output.

53 is the comparator with hysteresis 51
A comparator with hysteresis having the same configuration as the above, which compares the average welding current detection signal E _I from the detector 31 with the reference voltage E _IR output from the amplifier 52 and provided with a hysteresis width, Comparator dedicated operational amplifier IC
₂ and resistors R ₁₁ and R ₁₂ that determine the hysteresis width. According to the comparator with hysteresis 53, the value of the upper and lower limit setting signal E _IR U corresponding to the hysteresis upper and lower limit setting value of the average welding current (for example, 210 A when the wire feeding speed is 10 m / min) is E _IR U = E _IR
+ And become _{(V OH -E IR) × (} R 11 / (R 11 + R 12)).
In addition, the lower limit setting value of the lower limit of the wire feed speed hysteresis (for example, 190 A when the wire feed speed is 10 m / min)
The lower lower limit setting signal E _IR L corresponding to is E _IR L = E
The _{IR -E IR × (R 11 /} (R 11 + R 12)).

In order to facilitate understanding, the operation will be described below. In order to facilitate understanding, pulse arc welding is now in progress, and the average welding current, the wire feeding speed and the average welding voltage are also higher than the respective lower limit set values. 3-input AND gate I
It is assumed that all the input terminals of C ₇ are H level, and the pulse welding command signal PS as an H level signal is output from the 3-input AND gate IC ₇ .

Now, during the pulse arc welding, the wire protrusion length becomes longer than the reference value and the average welding current decreases, and as shown in FIG. 3, the average welding current detection signal E _I is the lower lower limit setting signal E. _{Below the IR} L value, the operational amplifier IC ₂
Output becomes H level (about 5V), and this is inverted by the inverter gate IC ₅ and the first input terminal of the 3-input AND gate IC ₇ becomes L level. As a result, the output of the 3-input AND gate IC ₇ becomes L level, the pulse welding command signal PS that has been output until then is turned off, and the pulse arc welding state is switched to the short-circuiting transition arc welding state.

The average welding current is increased by returning the wire protrusion length to the reference value during this short-circuit transfer arc welding. As shown in FIG. 3, the average welding current detection signal E _I is set to the upper / lower limit setting signal. When the E _IR U value is exceeded, the output of the operational amplifier IC ₂ goes from H level to L level (about zero volt).
And this is inverted by the inverter gate IC ₅ to 3
The first input terminal of the input AND gate IC ₇ becomes H level. As a result, the output of the 3-input AND gate IC ₇ becomes H level, the pulse welding command signal PS is output again, and the short circuit transition arc welding state is switched to the original pulse arc welding state.

Next, the structure for comparing the average welding voltage detection value and the average welding voltage lower limit setting value having a hysteresis width and switching the welding state from the comparison result will be described.

Reference numeral 54 is an amplifier for setting the reference voltage E _VR proportional to the magnitude of the wire feeding speed signal E _W from the wire feeding speed setting device 26. This amplifier 54
, Said a same configuration as the amplifier 52, the wire feed speed signal E _W of the reference voltage is proportional to the magnitude _{E VR (E VR = (R} 16
/ R ₁₅ ) × E _W ) is output.

55 is a comparator 53 with hysteresis.
A comparator with hysteresis having the same configuration as the above, which compares the average welding voltage signal E _V from the average welding voltage detector 10 with the reference voltage E _VR output from the amplifier 54 and having a hysteresis width. , A comparator-dedicated operational amplifier IC ₃ and resistors R ₂₁ and R ₂₂ that determine the hysteresis width. According to the comparator with hysteresis 55, the value of the upper and lower limit setting signal E _VR U corresponding to the hysteresis upper and lower limit setting value of the average welding voltage (for example, 30 V when the wire feeding speed is 10 m / min) is E _VR U = E _VR
+ Become _{(V OH -E VR) × (} R 21 / (R 21 + R 22)).
Further, the value of the lower lower limit setting signal E _VR L corresponding to the hysteresis lower lower limit setting value of the wire feeding speed (for example, 28 V when the wire feeding speed is 10 m / min) is E _VR L = E _VR
−E _VR × (R ₂₁ / (R ₂₁ + R ₂₂ )). The operation of the amplifier 54 and the comparator with hysteresis 53 is the same as that for the above-mentioned average welding current, and therefore its explanation is omitted.

In this way, when at least one of the wire feeding speed, the average welding current detection value and the average welding voltage detection value falls below the corresponding lower limit set value during welding in the pulse arc welding state, Control is performed to switch the welding state from the pulse arc welding state to the short-circuit transition arc welding state.

[0047]

Example A test plate (base material) was welded by a bead-on-plate using the welding power source having the above-mentioned configuration, and the amount of spatter generated was measured. Basic welding conditions are shielding gas: carbon dioxide gas, welding wire: MG-50 (JIS, manufactured by Kobe Steel)
YGW-11 equivalent), wire diameter 1.2 mm, base material: SM400, welding speed: 30 cm / min. The results are shown in Tables 2 to 4.

In Examples 1 to 3, the upper and lower limits of the wire feeding speed are set to 8 m / min, the lower and lower limits of the hysteresis are set to 7 m / min, and the lower limits of the average welding current and the average welding voltage are set. For setting values,
As described with reference to FIG. 2, the value is set in proportion to the wire feeding speed, as shown in Table 1.

[0049]

[Table 1]

[0050]

[Table 2]

[0051]

[Table 3]

[0052]

[Table 4]

As shown in Table 2, in Example 1, the wire feeding speed was gradually reduced from 14 m / min to 4 m / min, and then gradually increased to 12 m / min so as to restore the original value. During the carbon dioxide pulse welding, the welding state switching control was performed so that the arc welding state was temporarily changed to the short circuit. In the welding method according to the present invention, the wire feeding speed is 4 to 6 as shown in (5) to (7) of the first embodiment.
In the low range such as m / min, since the short-circuit transfer arc welding state was set, the spatter generation amount could be reduced as compared with the normal carbon dioxide pulse welding shown in Comparative Example 1. The wire feeding speed of (8) in Example 1 is strictly 8
It is a value slightly exceeding m / min, and by this, the upper and lower limit set value of wire feeding speed of 8 m / min was exceeded, and the state was switched to the carbon dioxide pulse welding state.

As shown in Table 3, in the second embodiment, the wire feeding speed is constant (10 m / min) and the wire protrusion length is gradually increased from 15 mm to 40 mm to reduce the average welding current. And then the original 15
The average welding current was made to increase by gradually shortening to mm, and the welding state switching control was performed to temporarily set the arc welding state to the short circuit during the carbon dioxide pulse welding. In the welding method according to the present invention, as shown in (5) to (7) of the second embodiment, the short-circuit transfer arc welding state occurs in the low range where the wire protrusion length is long and the average welding current is 160 to 180A. Therefore, the amount of spatter generated could be reduced as compared with the normal carbon dioxide gas pulse welding shown in Comparative Example 2.

As shown in Table 4, in Example 3, the wire feeding speed was kept constant (10 m / min), the average welding voltage was gradually reduced from 36 V to 26 V, and then, up to 34 V so as to restore it. Welding state switching control was performed in which the welding current was gradually increased and a short-circuit transfer arc welding state was temporarily obtained during carbon dioxide pulse welding. In the welding method according to the present invention, as shown in (5) to (7) of Example 3, the short-circuit transfer arc welding state was set in the low range where the average welding voltage was 26 to 28 V, and therefore, it is shown in Comparative Example 3. The amount of spatter generated was able to be reduced compared to normal carbon dioxide pulse welding. The average welding voltage of (5) of Example 3 was
Strictly speaking, it is a value slightly smaller than 28V, and by this, the value is below the lower limit lower limit setting value 28V of the average welding voltage and is switched to the short-circuit transfer arc welding state.

[0056]

As described above, according to the carbon dioxide gas shielded arc welding method of the present invention, at least one of the wire feeding speed, the average welding current detection value and the average welding voltage detection value is pulsed during pulse arc welding. If the lower limit value set in advance for arc welding is below, the welding state is controlled so as to switch from the pulse arc welding state to the short-circuit transition arc welding state.
Compared to pulse arc welding under low welding conditions such as low wire feeding speed, low welding current due to increase in wire protrusion length, low welding voltage, etc., spatter generation can be reduced. By doing so, a welded product with less spatter is obtained, and the labor for removing the spatter adhering to the welding base metal and the welding torch is small.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an example of a consumable electrode type gas shield welding power source for carrying out the welding method of the present invention.

FIG. 2 is a circuit diagram of a pulse welding command signal generation circuit provided in the welding power source shown in FIG.

FIG. 3 is an explanatory diagram of a lower limit set value having a hysteresis width according to the welding method of the present invention.

FIG. 4 is a diagram for explaining the welding method of the present invention by taking an average welding voltage as an example.

FIG. 5 is a diagram showing a relationship between a wire feeding speed and a spatter generation amount in carbon dioxide pulse welding and short-circuit transfer arc welding.

FIG. 6 is a diagram showing a relationship between an average welding current (wire protruding length) and a spatter generation amount in carbon dioxide pulse welding and short-circuit transfer arc welding.

FIG. 7 is a diagram showing a relationship between an average welding voltage and a spatter generation amount in carbon dioxide pulse welding and short-circuit transfer arc welding.

FIG. 8 is a diagram for explaining carbon dioxide pulse welding.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... 3-phase alternating current power supply part 2 ... 1st rectification circuit 4 ... Inverter 5 ... Transformer 6 ... 2nd rectification circuit 8 ... Welding wire 9 ... Base material 10 ...
Average welding voltage detector 11 ... Welding current detector 12 ... Pulse current setting circuit 1
3 ... Base current setting circuit 14 ... Pulse period setting circuit 15 ... Frequency setter 16
… Short circuit transition arc welding voltage setting device 17… Pulse arc welding voltage setting device 18… Voltage selection circuit 19… Error amplifier 20… Adder 22… Voltage / current conversion circuit 23… Output waveform selection circuit 24… Error amplifier 25… Output control circuit 26 ... Wire feeding speed setting device 29 ... Wire feeding motor control circuit 3
0 ... Pulse frequency setting circuit 31 ... Average welding current detector 40 ... Control unit 51, 53, 55 ... Hysteresis comparator 52, 54 ... Amplifier PS ... Pulse welding command signal

Claims (3)

[Claims] 1. A base metal is welded by using a carbon dioxide gas alone or a mixed gas containing carbon dioxide as a main component as a shield gas to generate an arc between a welding wire and a base metal fed at a constant speed. In the carbon dioxide gas shielded arc welding method, set the wire feed speed lower limit setting value, average welding current lower limit setting value and average welding voltage lower limit setting value in advance for pulse arc welding conditions, and perform welding in the pulse arc welding state. When at least one of the wire feeding speed, the average welding current detection value and the average welding voltage detection value falls below the corresponding lower limit setting value, the welding state is changed from the pulse arc welding state to the short-circuit transition arc welding state. A carbon dioxide shield arc welding method characterized by performing switching control. 2. The carbon dioxide gas according to claim 1, wherein the wire feeding speed lower limit setting value, the average welding current lower limit setting value and the average welding voltage lower limit setting value have a hysteresis width. Shield arc welding method. 3. The average welding current lower limit setting value and the average welding voltage lower limit setting value are set as a function of the wire feeding speed having a functional relationship that increases as the wire feeding speed increases. The carbon dioxide shielded arc welding method according to claim 1 or 2.