JP3188821B2 - Mag pulse arc welding method for galvanized steel sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of mag-pulse arc welding of a galvanized steel sheet in which occurrence of pore defects such as pits and blow holes can be extremely reduced.

[0002]

2. Description of the Related Art As is well known, a galvanized steel sheet has a corrosion resistance obtained by subjecting its surface to a plating treatment (hot-dip plating, alloyed hot-dip plating, electroplating, etc.) with zinc or an alloy containing zinc. It is an excellent steel plate. The main use of galvanized steel sheet is in the field of thin sheet, and the use of galvanized steel sheet has been expanding as an automobile body member in the automobile industry and as a lightweight steel frame housing member in the housing industry.

When gas-shielded arc welding of a galvanized steel sheet, the boiling point (906) is much lower than the melting point of the steel sheet.
℃) zinc is vaporized by the heat during welding, and the zinc vapor enters the molten pool and remains as a defect without being raised or released in the process of solidifying the molten metal, thereby leaving pits (opening on the bead surface) in the weld metal. Pores such as blown holes) and blowholes (pores existing inside the weld metal).

In order to prevent the occurrence of such pore defects, there is provided a method in which a groove gap of about 0.5 mm is provided between two members to be welded constituting a lap joint in order to allow zinc vapor to escape. , CO ₂ gas mixture of a low viscosity, low surface tension welding wire galvanized steel sheet molten metal is obtained in the purpose of promoting the floating and release of zinc vapor penetrated into the molten metal, and Ar gas and CO ₂ gas Gas mixture ratio is 50
Using a shielding gas having a volume percentage of
tal active gas) welding, or a method of performing mag pulse arc welding in which a peak current and a base current are alternately and repeatedly supplied to a welding wire (Japanese Patent Application Laid-Open No. 1-3).
No. 09796) has been proposed.

[0005]

However, in the above-described method of providing a groove gap, the management of the groove gap is troublesome and not practical. The method using a welding wire for galvanized steel sheet, which can provide a low-viscosity, low-surface-tension molten metal, has the disadvantage that the weld bead tends to sag, especially in difficult-position welding such as vertical welding and horizontal welding. There is also room for improvement in reducing the occurrence of pore defects such as blowholes.

According to the present invention, when arc-welding a galvanized steel sheet, the occurrence of pore defects such as pits and blowholes can be extremely reduced, and bead dripping can also be performed in difficult-position welding such as vertical welding and horizontal welding. It is an object of the present invention to provide a method of mag-pulse arc welding of a galvanized steel sheet that can obtain a weld bead having a good appearance without falling.

[0007]

According to the first aspect of the present invention, when performing galpulse arc welding of a galvanized steel sheet, C:
A solid wire for welding a galvanized steel sheet containing 0.02 to 0.10% by weight, Si: 0.3 to 0.7% by weight, and Mn: 1.5 to 3.0% by weight as a basic alloy component;
Using a shielding gas composed of a mixed gas of r gas and CO ₂ gas and having a CO ₂ gas mixing ratio of 5 to 10% by volume, a peak current value of 450 to 600 A, and a peak current period of 1.0 to 2 0.0 ms, and the following short-circuit transfer rate r during welding:
Is measured, and the value of the short circuit transfer ratio r is r = 0.7 to 1.0.
Magnesium arc welding method for galvanized steel sheets, characterized in that the welding voltage is increased or decreased so as to be within the range, the droplet transfer by short circuit is performed during the base current period, and the galvanized steel sheets are subjected to mag pulse arc welding. is there. Short circuit transfer rate r
= (Number of pulses per pulse per unit time t transferred to one short-circuit droplet) / (number of pulses per unit time t)

According to a second aspect of the present invention, there is provided the mag pulse of the galvanized steel sheet according to the first aspect, wherein the wire further contains Mo: 0.1 to 0.5% by weight. This is an arc welding method.

[0009]

The present inventors first investigated the mechanism of formation of pores (pits, blowholes) by zinc vapor. As a result, the following was found. FIG.
It is a figure for explaining a generation position of zinc vapor which causes a pit and a blow hole. Investigation of the location of zinc vapor, which enters the molten pool and causes porosity, reveals that zinc vapor from the overlapped portion (region a in FIG. 8) adjacent to the weld bead is responsible for the porosity. did. The zinc in region c of FIG. 8 is not heated until it reaches its boiling point and does not cause pores. Also, the zinc in the portion where the weld bead is formed (regions b and d in FIG. 8) is instantaneously evaporated and vaporized by the heat of the welding arc or the heat of the molten metal and does not enter the molten pool. Even if invaded, it will rise and be released immediately.

On the other hand, zinc in the region a is vaporized by heat during welding, but there is a slight time delay before it enters the molten pool, and the molten pool cools and solidifies. At the beginning it will penetrate into the weld pool. For this reason,
The molten metal solidifies before the infiltrated zinc vapor floats and discharges, and remains as pits (small holes opened in the bead surface) and blow holes in the weld metal.

From the above investigation results, it was found that in order to reduce pits and blowholes, it is necessary to reduce the amount of zinc vapor generated and to suppress the penetration of zinc vapor into the molten pool. . In order to realize the above, the area a is narrowed by reducing the welding heat input, and as a result, the amount of generated zinc vapor can be reduced. In order to realize the above, the viscosity of the molten metal is increased,
The cooling rate of the molten metal may be increased, and the cooling rate can be increased by reducing the welding heat input.

As is well known, the welding heat input is determined by three factors: welding current, welding voltage, and welding speed. The lower the welding current and welding voltage, and the higher the welding speed, the more the welding heat input. The value decreases. Of these, the welding speed and welding current determine the amount of weld bead (the amount of deposited metal per unit length) in welding with a commonly used DC constant voltage characteristic welding power source (wire constant speed feed control type). Things. If the welding current is reduced and the welding speed is increased in order to reduce the welding heat input, the weld bead becomes thinner and the joint performance of the welded portion decreases.

In order to reduce the welding current without reducing the welding bead amount for performing low heat input welding, the electric resistance of the wire is reduced by making the wire diameter smaller or making the wire protrusion length longer. It is conceivable to use the Joule heat generated by this. However, using a smaller diameter welding wire has the disadvantage of increasing the welding material price, and increasing the wire projection length tends to cause a displacement of the wire target position with respect to the welding line. However, there is a problem that application to automatic welding by a welding robot or the like is difficult.

The inventors of the present invention have conducted various studies on arc welding of galvanized steel sheets. As a result, by properly combining the three components of the chemical composition of the welding wire, the shielding gas composition, and the mag-pulse welding conditions, the welding bead was formed. The inventors have found that it is possible to reduce the welding heat input and increase the viscosity of the molten metal without reducing the amount, thereby making it possible to extremely reduce the occurrence of pits and blowholes, and reached the present invention.

First, the reasons for limiting the basic alloy components of the solid wire for welding a galvanized steel sheet used in the mag pulse arc welding method according to the present invention are as follows.

The content of C is 0.02 to 0.10% by weight.
Range. C is added so that the strength of the weld metal becomes an appropriate value for the base metal. If the content of C is less than 0.02% by weight, the strength of the weld metal decreases, the arc becomes unstable, and welding workability deteriorates. On the other hand, if the content of C exceeds 0.10% by weight, the strength of the weld metal becomes too high, and the amount of spatter generated by the CO gas generated in the droplet increases, resulting in poor welding workability. .

The content of Mn is in the range of 1.5 to 3.0% by weight, and the content of Si is in the range of 0.3 to 0.7% by weight. Mn and Si are elements for adjusting the strength of the weld metal, and also react with oxygen in the molten metal,
Acts as a deoxidizer for removing excess oxygen as slag out of the molten pool. The viscosity and surface tension of the molten metal
It is also affected by the content of each element of C, Mn, and Si, but is most affected by oxygen, and becomes higher as the amount of oxygen decreases. When the deoxidizing power in the molten metal is enhanced in addition to performing the low heat input welding, the molten metal has a high viscosity and a high surface tension, which suppresses penetration of zinc vapor and is effective in reducing pore defects. On the other hand, if a large amount of Mn and Si is added, the deoxidizing power increases, but the hardness of the welding wire itself increases, and wire breakage is likely to occur in the wire drawing process during the production of the welding wire, resulting in a decrease in productivity. And that the strength of the weld metal becomes too high.

FIG. 9 is a diagram showing an example of the relationship between the Si content and the number of blowholes generated when the Mn content is used as a parameter. Blowholes having a size of 1 mm or more as observed in an X-ray transmission photograph were counted. The results shown in FIG. 9 were obtained using various prototype welding wires.
It is obtained by stacking galvanized steel sheets having a thickness of 2.3 mm and a basis weight of 45 g / m ² with a gap of zero, and performing downward facing fillet by mag pulse arc welding. The welding conditions were as follows: wire diameter: 1.2 mm, shielding gas composition: Ar
+ 20% CO ₂ , shield gas flow rate: 20 l / m
in, wire feeding speed: 7 m / min, welding speed: 12
0 cm / min, wire protrusion length: 15 mm, peak current value: 470 A, peak current period: 1.6 ms, short circuit transfer rate r: 0.03 to 0.95.

As shown in FIG. 9, when the content of both Mn and Si is large, the number of blowholes generated is small. When the Mn content is in the range of 1.5% by weight or more, the Si content is smaller than the Mn content. Therefore, even at a low level of 0.3 to 0.7% by weight, the number of blowholes is reduced. The deoxidation rate of the molten metal by Mn and Si depends on the Mn / Si value,
When the Si value is small, it becomes slow. If the deoxidation rate is low, the active oxygen in the molten metal increases, so that the viscosity of the molten metal decreases and the penetration of zinc vapor cannot be suppressed.

Therefore, when the amount of Mn is less than 1.5% by weight and the amount of Si is less than 0.3% by weight, penetration of zinc vapor into the molten metal is suppressed by increasing the viscosity and surface tension of the molten metal. When the effect is not obtained, on the other hand, when the Mn content exceeds 3.0% by weight and the Si content exceeds 0.7% by weight, wire breakage is apt to occur during the production of the welding wire, and the productivity of the welding wire decreases,
In addition, the strength of the weld metal is set to the base material (mainly mild steel
/ Mm ² class high tensile steel).

The solid wire for welding a galvanized steel sheet used in the mag pulse arc welding method according to the present invention is C,
Si and Mn are used as basic alloy components, and the balance is Fe and unavoidable impurities.
It may be contained in the range of 1 to 0.5% by weight. Mo
Is an element that increases the viscosity of the molten metal, and is effective in suppressing the penetration of zinc vapor into the molten metal. However, when the content is 0.1.
If it is less than 1% by weight, there is no effect on increasing the viscosity of the molten metal,
If the content exceeds 0.5% by weight, the strength of the weld metal becomes too high with respect to the base metal.

It is desirable that both P and S contained as unavoidable impurities be 0.05% by weight or less. Both P and S are elements that increase the susceptibility of the weld to cracking, and it is desirable that the P content be as small as possible. Because there is no. Although the same applies to S as described above, S is also an element that lowers the surface tension and viscosity of the molten metal, and one of the aims of the present invention is to increase the viscosity of the molten metal to suppress the penetration of zinc vapor. Therefore, it is desirable that the content of S be small.

Next, the reasons for limiting the composition of the shielding gas will be described.

In gas shielded arc welding of steel, the presence of an oxide having a low ionization voltage is indispensable for stably generating an arc, and a shielding gas containing Ar gas as a main component includes CO ₂ gas or It is necessary to mix O ₂ gas. However, since CO ₂ gas is an active gas, when the shielding gas is a mixed gas of Ar gas and CO ₂ gas, O ₂ gas is generated from the CO ₂ gas by arc heat, and the O ₂ gas is Reduces viscosity and surface tension of molten metal. The point of the present invention as described above, the welding heat input is reduced, increasing the viscosity of the molten metal, since thereby the zinc vapor in point refrains from entering into the molten metal, CO ₂ is the active gas It is necessary to properly define the gas mixture ratio.

FIG. 10 is a diagram showing an example of the relationship between the mixing ratio of CO ₂ gas or O ₂ gas in the shielding gas containing Ar gas as a main component and the blowhole index BH. The blowhole index BH, which is an evaluation value, is proportional to the number of blowholes generated.
It will be described later based on The results shown in FIG. 10 are obtained by stacking galvanized steel sheets having a thickness of 2.3 mm and a basis weight of 45 g / m ² with zero gap using a commercially available wire for MAG welding (JIS YGW-15), This was obtained by performing mag pulse arc welding of fillet. The welding conditions are
Wire diameter: 1.2 mm, wire feeding speed: 7 m / mi
n, welding speed: 120 cm / min, wire protrusion length: 15 mm, peak current value: 470 A, peak current period: 1.6 ms, short circuit transfer rate r: 0 to 0.91.

[0026] From FIG. 10, but also increases blowhole defects as CO ₂ gas mixture ratio is increased, CO ₂ blowhole defects on the contrary gas mixing ratio exceeds 20% by volume is seen to be a tendency to decrease . Also, O ₂ for even gas, O ₂ blowhole defects when gas mixing ratio exceeds 10% by volume it can be seen that tends to decrease. This is because when the O ₂ gas is mixed and used, if the activity is high and the mixing ratio exceeds 10% by volume, the viscosity of the molten metal
The surface tension is reduced, and the zinc vapor invading the molten metal is easily floated and released, thereby reducing the number of blowholes generated. When CO ₂ gas is mixed and used, if the mixing ratio exceeds 20% by volume, the O ₂ gas is used.
As in the case of gas, the number of blowholes was reduced.

However, in the case where the pore defects are reduced by lowering the viscosity and surface tension of the molten metal, as described above, the welding bead drips in a difficult position welding such as a vertical welding or a horizontal welding. There is a disadvantage that it is easy.

[0028] Therefore, in this invention, in order to suppress the penetration of the molten metal in the zinc vapor due to the high viscosity of the molten metal, as the shielding gas consists of a mixture of Ar gas and CO ₂ gas, CO ₂ A shielding gas having a gas mixture ratio of 5 to 10% by volume is used. CO ₂
If the gas mixture ratio exceeds 10% by volume, the effect of increasing the viscosity of the molten metal by the wire component will be reduced,
If it is less than 5% by volume, the arc becomes unstable.

Next, pulse welding conditions used in the mag pulse arc welding method according to the present invention will be described.

In order to reduce the amount of generated zinc vapor itself and to suppress the penetration of zinc vapor into the molten metal, the welding heat input may be reduced. Then, in order to perform welding with low heat input without reducing the welding bead amount, the welding voltage may be reduced. FIG. 11 is a diagram illustrating an example of the relationship between the welding voltage and the blowhole index BH. The results shown in FIG. 11 consist of a solid wire for welding galvanized steel sheet (wire diameter: 1.2 mm) used in the method of the present invention, a mixed gas of 93% of Ar gas and 7% of CO ₂ gas, and a flow rate of 20%.
Liter / min shielding gas, plate thickness 2.3
This is obtained by stacking galvanized steel sheets having a basis weight of 45 g / m ² and a gap of 0 mm, and performing downward lapping fillet by mag pulse arc welding. The welding conditions were as follows: wire feeding speed: 7 m / min, welding speed: 120 cm / mi
n, peak current value: 470 A, peak current period: 1.6
ms, and the short-circuit transfer rate r: 0 to 1.0.

FIG. 11 shows that the lower the welding voltage value, the less the blowhole defects. However, if the welding voltage is excessively lowered to lower the welding voltage, a so-called wire stick (wire stubbing) occurs, in which the unmelted tip of the welding wire is inserted into the molten pool, causing an arc to be cut off and making welding impossible. When setting the welding voltage low, it was not easy to determine the proper welding voltage setting value, because the lower limit welding voltage at which welding can be performed without producing a wire stick varies depending on the material of the welding wire.

Therefore, the present inventors have studied the mag-pulse arc welding of galvanized steel sheets by focusing on the relationship between the droplet transfer phenomenon and the welding voltage. As a result, most of the droplet transfer per one pulse cycle is one-pulse one-short-circuit droplet transfer (see FIG. 5) in which one droplet transfer is performed by a short circuit during the base current period of one pulse period. It has been found that if the welding voltage is set as described above, stable arc welding can be performed without generating a wire stick even if the welding voltage is reduced for low welding heat input. In addition, this makes it possible to determine whether the welding voltage set value is appropriate or not based on the value of the welding voltage itself, not from the droplet transfer state that can be quantified, and that the setting of the appropriate welding voltage value can be easily adjusted. all right.

FIG. 5 is a schematic diagram showing the state of one pulse and one short-circuit droplet transfer in mag pulse arc welding. As shown in the figure, one pulse 1 In short droplet transfer, droplet peak current I _P is formed on the welding wire tip during the peak current period T _P that flows is molten pool during the base current period T _B Once and short-circuited. When a mag pulse arc welding power supply capable of supplying a sufficient short-circuit current at the time of droplet short-circuiting is used, generation of spatter at the time of droplet short-circuiting may be reduced.

FIG. 6 is an explanatory diagram for explaining the relationship between the welding voltage and the short circuit transfer rate r in the mag pulse arc welding. Here, if the short circuit transfer rate r is defined as r = (the number of pulses in which one pulse per unit time t has transferred one short circuit droplet) / (the number of pulses per unit time t), the short circuit transfer rate r = 1 .0 indicates that, in each pulse cycle in a unit time t (for example, 1 second), one pulse and one short-circuit droplet shift in all the pulse cycles. The welding voltage value at the time of one pulse and one short-circuit droplet transfer per one pulse period, that is, the welding voltage value at the time of the short-circuit transfer rate r = 1.0, is reduced by welding for low welding heat input. Even if the voltage is lowered, the voltage is a lower limit and an optimum voltage value at which stable arc welding can be performed without generating a wire stick.

As shown in FIG. 6, as the welding voltage is gradually increased, the short-circuit transfer rate r becomes smaller than 1.0, and the short-circuit transfer rate r becomes 1 at every two or three pulses.
Pulse 1 short-circuit droplet transfer is performed. When further increase the welding voltage, short circuit transfer rate r is zero, droplet transfer is not performed due to the short circuit, a droplet formed in the welding wire tip during the peak current time period T _P is the base current period T
Withdrawing without short-circuit contact during _B , one pulse per droplet transfer (spray transfer) is performed. Therefore, in order to perform stable arc welding without generating a wire stick even if the welding voltage is reduced for low welding heat input, r is set to be in a range of 0.7 to 1.0. May be set to the welding voltage. If the welding voltage is lower than the value when the short-circuit transfer rate r = 1.0, a wire stick is generated, and the welding voltage is increased to reduce the short-circuit transfer rate to r.
This is because if it is smaller than 0.7, it is not possible to achieve low heat input.

Whether or not the droplet transfer mode is one-pulse / one-short-circuit droplet transfer can be known as follows. FIG. 7 shows a waveform of a welding current / voltage waveform in a transition state of one pulse and one short-circuit droplet in mag pulse arc welding, which is recorded by a waveform recorder, and traced. Due to the influence of noise, the waveform during the peak period is recorded in a band shape due to large noise, but the waveform is basically the same as that shown in the schematic diagram of FIG.

As understood from FIG. 7, the welding voltage is
When the droplet short-circuits into the molten pool during the base current period, it rapidly decreases to almost zero, and then rises sharply when the arc re-occurs, so that the short-circuit state and the non-short-circuit state can be clearly distinguished, and the short circuit during the base current period Can be easily known. For example, a short circuit / non-short circuit can be determined by setting a threshold value (for example, 10 V) and comparing this threshold value with a welding voltage detection value. In this way, the droplet transfer mode is one pulse 1
It is possible to detect whether or not the transfer is a short-circuit droplet transfer. Then, based on this, the short circuit transfer rate r during welding is automatically obtained by a short circuit transfer rate measuring instrument described later, and while the short circuit transfer rate value detected and displayed by the short circuit transfer rate measuring instrument is used, r = 0. By manually adjusting or automatically adjusting the welding voltage so as to fall within a range of 0.7 to 1.0, a welding voltage suitable for suppressing pore defects can be set.

As described above, as the solid wire for welding a galvanized steel sheet and the shielding gas used in the mag-pulse arc welding method according to the present invention, those having a high viscosity and high surface tension in the molten metal are selected. ing. Therefore, the pulse waveform parameter needs to be a value capable of stably transferring a droplet having high viscosity and high surface tension. Therefore, the peak current value is 450-600A,
The peak current period is preferably in the range of 1.0 to 2.0 ms. If the peak current value is lower than 450 A, the droplet cannot be grown to a size large enough to cause the droplet to shift to a short circuit. On the other hand, if the peak current value exceeds 600 A, the heat input during the peak current period becomes too large, and it is impossible to achieve low welding heat input. On the other hand, if the peak current period is less than 1.0 ms, the droplet cannot be grown to a size large enough to cause a transition to a short circuit, and the unmelted wire tends to plunge into the molten pool during a short circuit. On the other hand, when the peak current period exceeds 2.0 ms, the droplet comes off during the peak period,
During the base period, unmelted wire will plunge into the weld pool.

[0039]

Embodiments of the present invention will be described below.
FIG. 1 is a block diagram showing a configuration of a mag-pulse arc welding power supply equipped with a short circuit transfer rate measuring device used for carrying out the method according to the present invention.

In FIG. 1, reference numeral 51 denotes an inverter-type mag-pulse arc welding power source. Reference numeral 52 denotes a remote control box of the welding power source 51, which manually sets a welding current including a peak current and a base current, a welding voltage, and the like. It is for adjusting. 53 is a wire feed motor for feeding the welding wire SW toward the base material WP, 54 is a welding voltage detector,
55 is a welding current detector. Reference numeral 60 denotes a short circuit transfer rate measuring device which measures the above short circuit transfer rate r based on output signals from the welding voltage detector 54 and the welding current detector 55 and numerically displays the measured value.

The short-circuit time measuring device 61 constituting the short-circuit transfer rate measuring device 60 compares an output signal from the welding voltage detector 54 with a threshold value to determine whether or not a short circuit is occurring. Is output to the comparator 62, that is, a short-circuit time signal. The comparator 62 compares the short-circuit time signal provided from the short-circuit time measuring device 61 with the reference short-circuit time signal from the reference short-circuit time setting device 63, and determines that the short-circuit time signal is within the range of the magnitude of the reference short-circuit time signal. If so, it is determined to be normal, and the base period short-circuit determination device 64
Sends a short-circuit occurrence signal to the The comparison operation includes an abnormal short-circuit such as a short-time short-circuit without the transfer of a droplet, an abnormally long-time short-circuit such as a penetration of a welding wire SW into the base material WP, and a stable short-circuit droplet transfer. Perform to distinguish.

On the other hand, the peak / base period determination unit 65
If it is the base current period based on the output signal from the welding current detector 55, the base period signal is sent to the base period short-circuit determination unit 64. Then, based on the short-circuit occurrence signal and the base period signal, the base-period short-circuit determiner 64 determines that the droplet transfer due to the short-circuit has been performed during the base current period. A drop transfer generation signal is output.

The counting / arithmetic circuit 66 calculates the short-circuit droplet transfer generation signal from the base-period short-circuit judging device 64 and the peak / short signal
The signal indicating the number of pulses from the base period determiner 65 is counted, and the number of pulses per unit time and the number of short circuits per unit time (the number of pulses in which one pulse is transferred to one short circuit droplet) are determined based on the number of pulses. The transition rate r is calculated and obtained, and the value is numerically displayed on the display 67.

The welder manually adjusts the welding voltage by the remote control box 52 so as to be in the range of r = 0.7 to 1.0 while watching the short circuit transfer rate r displayed on the display 67. Mag pulse arc welding is performed.

FIG. 2 is a block diagram showing a configuration of a mag-pulse arc welding power source having a short-circuit transfer rate measuring function and a welding voltage automatic adjusting function used in carrying out the method according to the present invention.

In FIG. 2, reference numeral 1 denotes a three-phase AC power supply unit. The AC current supplied from the three-phase AC power supply unit 1 is rectified into DC by the first rectifier circuit 2 and smoothed by the smoothing capacitor 3. This DC current is supplied to the inverter 4
Is converted into a high-frequency AC current. The transformer 5 reduces the output of the inverter 4 to a welding voltage. Transformer 5
The high-frequency AC current stepped down for welding from is rectified by the second rectifier circuit 6 into a DC current for welding. This DC current is supplied between the welding wire SW and the base material WP via the smoothing reactor 7 to perform arc welding.

Reference numeral 10 is a welding voltage detector, and 11 is a welding current detector. The welding wire SW is fed toward the base material WP by a wire feeding roller 14 driven by a wire feeding motor 13, and an arc is generated between the welding wire SW and the base material WP to perform welding. The wire feed motor control circuit 12 controls the rotation speed of the feed motor 13 based on a feed speed setting signal from a wire feed speed setting device (not shown).

The control unit 30 controls the inverter 4 to
This is for performing control such as alternately and repeatedly supplying a predetermined value of a peak current and a base current between the welding wire SW and the base material WP. The pulse waveform selection circuit 28 of the control unit 30 receives the setting signals from the base period setting circuit 24, the base current setting circuit 25, the peak period setting circuit 26, and the peak current setting circuit 27, and converts these setting signals into An inverter control signal based on the signal is supplied to the power control circuit 29. The power control circuit 29 controls the inverter 4 so as to output a peak current and a base current of predetermined values while feeding back an output signal from the welding current detector 11.

Next, a configuration for measuring the short circuit transfer rate r and automatically adjusting and setting the welding voltage will be described. The short-circuit time measuring device 15 determines whether or not a short circuit is occurring by comparing the output signal from the welding voltage detector 10 with a threshold value, and outputs a signal indicating that a short circuit is occurring, that is, a short-circuit time signal. 1 is output to the comparator 17. The comparator 17 compares the short-circuit time signal from the short-circuit time measuring device 15 with the reference short-circuit time signal from the reference short-circuit time setting device 16, and determines whether the short-circuit time signal is within the range of the magnitude of the reference short-circuit time signal. If it is normal, a short-circuit occurrence signal is sent to the base period short-circuit determiner 18. The comparison operation includes an abnormal short-circuit such as a short-time short-circuit without the transfer of a droplet, an abnormally long-time short-circuit such as a penetration of a welding wire SW into the base material WP, and a stable short-circuit droplet transfer. Is performed to distinguish between

The base-period short-circuit judging unit 18 judges, based on the base-period signal from the pulse waveform selection circuit 28 and the short-circuit occurrence signal, that droplet transfer due to a short-circuit has occurred during the base current period, and counts. Output a short-circuit droplet transfer generation signal to the arithmetic circuit 19. The counting / arithmetic circuit 19 counts the short-circuit droplet transfer occurrence signal and the signal indicating the number of pulses from the pulse waveform selection circuit 28, and counts the number of pulses per unit time and the number of short-circuits per unit time (1 pulse). 1
The short-circuit transfer rate r is calculated and calculated from the number of pulses that have been transferred to the short-circuit droplets, and is output to the second comparator 21.

The second comparator 21 calculates the short-circuit transfer rate from the counting / arithmetic circuit 19 and the short-circuit transfer rate from the short-circuit transfer rate setter 20 which can be set in the range of r = 0.7 to 1.0. When the measured value is greater than the set value, a welding voltage increase signal corresponding to the difference is provided to the adder 23, and the increase signal is added to the output of the welding voltage setter 22, Conversely, when the measured value <the set value, the welding voltage decrease signal corresponding to the difference is given to the adder 23 so that the decrease signal is subtracted from the output of the welding voltage setter 22. Then, the base period setting circuit 24 adjusts the wire melting energy by increasing or decreasing the base period based on the output signal from the adder 23 and increasing or decreasing the pulse frequency. Thereby, the welding voltage is automatically adjusted so as to have the short-circuiting transfer rate set value set in the range of 0.7 to 1.0.

Using the above welding power source, mag pulse arc welding of a galvanized steel sheet was carried out under the welding wires and welding conditions shown in Tables 1 and 2, and the occurrence of blowholes was examined. For the welding, fillet welding was performed according to the welding procedure shown in FIG. 3 (downward position, lap joint, zero gap). Common welding conditions are: power supply polarity: DCRP, welding wire diameter: 1.
2mm, wire feeding speed: 7m / min, welding speed: 1
20 cm / min, wire protrusion length: 15 mm. For the test steel sheet, the basis weight of zinc was 45 g /
m ² , thickness 2.3 mm, width 75 mm, length 500 mm
A galvannealed steel sheet was used. The occurrence of blowholes was evaluated by a blowhole index BH shown in FIG. The results are shown in Tables 1 and 2.

In Tables 1 and 2, No. 1 to
In No. 4, the value of the short circuit transfer rate r is obtained by analyzing the welding voltage waveform recorded on the recording paper by the waveform recorder. N
o. In Nos. 27 to 34, an inverter type mag pulse arc welding power source equipped with the short circuit transfer rate measuring device 60 shown in FIG. 1 was used. In addition, No. 5 to 26, the mag pulse arc welding power source provided with the short-circuit transfer rate measuring function and the welding voltage automatic adjusting function shown in FIG. 2 was used.

[0054]

[Table 1]

[0055]

[Table 2]

As understood from Tables 1 and 2, according to the mag-pulse arc welding method according to the present invention, the blow hole index is as low as 50 or less, and the occurrence of pore defects such as pits and blow holes is extremely reduced. Could be reduced. Further, according to the mag pulse arc welding method according to the present invention, as one of means for suppressing the penetration of zinc vapor into the molten pool, the viscosity of the molten metal is increased, so that difficult position welding such as vertical welding or horizontal welding is performed. As a result, a weld bead having a good appearance without bead dripping could be obtained.

[0057]

As described above, according to the method of mag-pulse arc welding of galvanized steel sheet according to the present invention, when welding galvanized steel sheet, the chemical composition of the welding wire,
Appropriate combination of the shielding gas composition and the mag pulse welding conditions reduces welding heat input without increasing the amount of weld bead, increases the viscosity of the molten metal, reduces the amount of zinc vapor generated, and melts zinc vapor. Because it is designed to suppress intrusion into the pond, the occurrence of pore defects such as pits and blowholes can be extremely reduced, and bead dripping in difficult position welding such as vertical welding and sideways welding. It is possible to obtain a weld bead having a good appearance without cracks and to contribute to expanding the application of galvanized steel sheets by welding and assembling.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a mag-pulse arc welding power supply provided with a short-circuit transfer rate measuring device used for carrying out a method according to the present invention.

FIG. 2 is a block diagram showing a configuration of a mag-pulse arc welding power source having a short-circuit transfer rate measuring function and a welding voltage automatic adjusting function used for carrying out the method according to the present invention.

FIG. 3 is an explanatory diagram showing a welding procedure in the embodiment of the present invention.

FIG. 4 is an explanatory diagram of a blowhole index.

FIG. 5 is a schematic view showing a state in which one pulse and one short-circuit droplet transfer in mag pulse arc welding.

FIG. 6 is an explanatory diagram for explaining a relationship between a welding voltage and a short circuit transfer rate r in the mag pulse arc welding.

FIG. 7 shows waveforms of a welding current and a voltage in a transition state of one pulse and one short-circuit droplet in a mag pulse arc welding, which are recorded by a waveform recorder, and traced.

FIG. 8 is a diagram for explaining positions where zinc vapor causing pits and blowholes is generated.

FIG. 9 is a diagram showing an example of the relationship between the Si content and the number of blowholes generated when the Mn content is used as a parameter.

FIG. 10 is a diagram showing an example of a relationship between a mixing ratio of a CO ₂ gas or an O ₂ gas in a shielding gas containing Ar gas as a main component and a blowhole index.

FIG. 11 is a diagram illustrating an example of a relationship between a welding voltage and a blowhole index.

[Explanation of symbols]

4. Inverter 10, 54 ... Welding voltage detector 11,
55 ... welding current detector 15 ... short circuit time measuring device 16 ... standard short circuit time setting device 1
7 first comparator 18 base period short circuit detector 19
Counting / arithmetic circuit 20: short-circuit transition rate setting device 21: second
Comparator 22 ... Welding voltage setting device 23 ... Adder 24 ...
Base period setting circuit 25 Base current setting circuit 26
... peak period setting circuit 27 ... peak current setting circuit 2
8 ... Pulse waveform selection circuit 29 ... Power control circuit 30 ...
Control unit 51: Inverter type mag pulse arc welding power source 52 ...
Remote control box 60 ... Short circuit transfer rate measuring device SW ... Welding wire WP ... Base metal ZM ... Zinc plating layer WB ... Weld bead WT ... Welding torch

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁷ Identification code FI B23K 35/30 320 B23K 35/30 320A H02M 9/00 H02M 9/00 B (56) References JP-A-4-135088 (JP) JP-A-1-202394 (JP, A) JP-A-6-328253 (JP, A) JP-A-2-290674 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB B23K 9/073 B23K 9/09 B23K 9/16 B23K 9/173 B23K 9/23 B23K 35/30 H02M 9/00

Claims (2)

(57) [Claims] When a galvanized steel sheet is subjected to mag pulse arc welding, C: 0.02 to 0.10% by weight, Si:
0.3 to 0.7% by weight and Mn: 1.5 to 3.0% by weight
Using a solid wire for galvanized steel sheet welding containing as a basic alloying component, and a shielding gas composed of a mixed gas of Ar gas and CO ₂ gas and having a CO ₂ gas mixture ratio of 5 to 10% by volume. Current value 450-600
A, peak current period is 1.0-2.0ms, during welding
The following short circuit transfer rate r is measured, and the value of the short circuit transfer rate r is r
= Adjust the welding voltage to be in the range of 0.7 to 1.0
A method for making a droplet transfer by a short circuit during a base current period and performing a mag pulse arc welding of a galvanized steel sheet. Short circuit transfer rate r = (number of pulses in which one pulse per unit time t transferred one short circuit droplet) / (number of pulses per unit time t) 2. The method according to claim 1, wherein the wire further comprises Mo: 0.1 to
The method according to claim 1, wherein the method comprises 0.5% by weight.