JPH08309533A - Mag pulse arc welding method of galvanized steel sheet - Google Patents

Abstract

PURPOSE: To make it possible to extremely lessen the occurrence of blowhole defects, such as pits and blowholes, and to obtain weld beads having good appearance free from sagging down of the beads in difficult position welding, such as vertical welding and three o'clock welding. CONSTITUTION: A solid wire for welding galvanized steel sheets contg. 0.02 to 0.10wt.% C, 0.3 to 0.7wt.% Si and 1.5 to 3.0wt.% Mn as basic alloy components and a shielding gas which consists of a gaseous mixture composed of gaseous argon and gaseous CO2 and has a gaseous CO2 mixing ratio of 50 to 10vol.% are used at the time of subjecting the galvanized steel sheets to MAG pulse arc welding. The galvanized steel sheets are subjected to MAG pulse arc welding by executing globule transfer by short circuit during a base current period by setting the welding voltage in such a manner that the peak current value attains 450 to 600A, the peak current period attains 1.0 to 2.0ms and the value of the short circuit transfer rate (r) attains a range of r=0.7 to 1.0.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mag-pulse arc welding method for galvanized steel sheets, which is capable of extremely reducing the occurrence of pore defects such as pits and blow holes.

[0002]

2. Description of the Related Art As is well known, galvanized steel sheets have corrosion resistance obtained by applying zinc or an alloy containing zinc to the surface of the galvanized steel sheet (hot dipping, galvannealing, electroplating, etc.) to prevent corrosion. It is an excellent steel plate. The main applications of galvanized steel sheets are in the field of thin sheets, and the use of galvanized steel sheets is expanding as automobile body parts in the automobile industry and as lightweight steel frame housing members in the housing industry.

In the case of gas shielded arc welding of galvanized steel sheet, the boiling point (906) is much lower than the melting point of the steel sheet.
(° C) zinc is vaporized by the heat during welding, and the zinc vapor enters the molten pool and remains as defects without being floated or released during the solidification process of molten metal, which causes pits (opening on the bead surface) in the weld metal. Pores), blowholes (pores existing inside the weld metal) and the like frequently occur.

In order to prevent the occurrence of such a pore defect, a groove gap of about 0.5 mm is provided between two members to be welded constituting the lap joint to allow zinc vapor to escape. , A welding wire for galvanized steel plate that obtains a molten metal having a low viscosity and a low surface tension for the purpose of promoting the floatation / release of zinc vapor that has penetrated into the molten metal, and a mixed gas of Ar gas and CO ₂ gas for CO ₂ Gas mixing ratio is 50
Using a shield gas whose volume is less than or equal to
(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 (JP-A 1-3).
09796) has been proposed.

[0005]

However, the method of forming the groove gap described above is not practical because it takes time to manage the groove gap. The method of using a welding wire for galvanized steel sheets, which produces a molten metal with low viscosity and low surface tension, has the drawback that the welding bead tends to droop, especially in difficult position welding such as vertical welding or horizontal welding, and also the pit There is also room for improvement in reducing the occurrence of pore defects such as blowholes.

The present invention makes it possible to extremely reduce the occurrence of pore defects such as pits and blow holes during arc welding of galvanized steel sheets, and to prevent bead dripping even in difficult-position welding such as vertical welding and horizontal welding. An object of the present invention is to provide a method for mag-pulse arc welding of galvanized steel sheet, which can obtain a weld bead having a good appearance without dropping.

[0007]

According to a first aspect of the present invention, when performing galvanized arc welding of a galvanized steel sheet, C:
A solid wire for welding a galvanized steel sheet, which contains 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 shield 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 is 450 to 600 A and a peak current period is 1.0 to 2 0.0 ms and the value of the short-circuit transfer rate r below is r
= 0.7 to 1.0, the welding voltage is set to cause droplet transfer due to a short circuit during the base current period, and the galvanized steel sheet is subjected to mag pulse arc welding. It is a method of mag-pulse arc welding of steel sheets. Short-circuit transfer rate r = (1 pulse per unit time t, the number of pulses in which one short-circuited droplet transfer was performed) / (number of pulses per unit time t)

According to a second aspect of the present invention, in the first aspect of the present invention, the wire further contains Mo: 0.1 to 0.5% by weight. It is an arc welding method.

[0009]

The present inventors first investigated the mechanism of formation of pores (pits, blow holes) by zinc vapor. As a result, the following was found. Figure 8
It is a figure for demonstrating the generation position of the zinc vapor which causes a pit and a blow hole. When the location of the zinc vapor that enters the molten pool and causes the pores was investigated, it was found that the zinc vapor from the overlapping portion (area a in FIG. 8) adjacent to the welding bead caused the pores. did. The zinc in the region c in FIG. 8 is not heated to its boiling point and does not cause pores. Further, the zinc in the portion where the weld bead is formed (region b and region d in FIG. 8) does not invade into the molten pool by instantaneous evaporation and vaporization by the heat of the welding arc or the heat of the molten metal. Even if it breaks in, it is immediately levitated and released.

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

From the above survey results, it was found that in order to reduce pits and blow holes, it is necessary to reduce the amount of zinc vapor generated and to suppress the invasion of zinc vapor into the molten pool. . In order to realize the above, the region a can be narrowed by reducing the welding heat input, and as a result, the amount of zinc vapor generated can be reduced. To achieve the above, increase the viscosity of the molten metal,
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, this welding heat input is determined by three factors of welding current, welding voltage, and welding speed. The lower the welding current and welding voltage, and the higher the welding speed, the higher the welding heat input. The value becomes smaller. Among them, the welding speed and the welding current influence the welding bead amount (the amount of deposited metal per unit length) in the welding by the welding power source (wire constant speed feed control type) which has a DC constant voltage characteristic which is generally used. It is a thing. When the welding current is reduced and the welding speed is increased in order to reduce the welding heat input, the welding bead becomes thin and the joint performance of the welded portion deteriorates.

Since low heat input welding is performed, in order to reduce the welding current without reducing the welding bead amount, the wire diameter can be made smaller or the wire protruding length can be made longer to reduce the electric resistance of the wire. It is possible to utilize Joule heat generated by However, using a welding wire with a smaller diameter has the disadvantage that the price of the welding material becomes higher, and increasing the wire protrusion length tends to cause the displacement of the wire target position with respect to the welding line. However, there is a problem that it is difficult to apply to automatic welding by a welding robot or the like.

Therefore, as a result of various studies on arc welding of galvanized steel sheet, the present inventors have found that the welding bead can be obtained by appropriately combining the three factors of the chemical composition of the welding wire, the shielding gas composition and the mag pulse welding condition. The inventors have found that the heat input for welding can be reduced and the viscosity of the molten metal can be increased without reducing the amount, thereby making it possible to extremely reduce the occurrence of pits and blow holes, and arrived at the present invention.

First, the reasons for limiting the basic alloying components of the solid wire for welding 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 has an appropriate value for the base metal. When the content of C is less than 0.02% by weight, the strength of the weld metal is reduced and the arc becomes unstable, which deteriorates the workability of welding. On the other hand, when 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 CO gas generated in the droplets increases and the welding workability deteriorates. .

The Mn content is in the range of 1.5 to 3.0% by weight, and the Si content 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 react with oxygen in the molten metal,
It acts as a deoxidizer for removing excess oxygen as slag outside the molten pool. The viscosity and surface tension of molten metal are
Although it is also affected by the contents of each element of C, Mn, and Si, the greatest effect is exerted by oxygen, and the higher the oxygen content, the higher. In addition to low heat input welding, strengthening the deoxidizing power in the molten metal results in high viscosity and high surface tension, which suppresses zinc vapor intrusion and is effective in reducing pore defects. On the other hand, if a large amount of Mn and Si are added, the deoxidizing power increases, but the hardness of the welding wire itself increases, and wire breakage easily occurs during the wire drawing step during the production of the welding wire, which lowers the productivity. That is, problems such as the strength of the weld metal becoming too high occur.

FIG. 9 is a diagram showing an example of the relationship between the Si content and the number of blowholes when the Mn content is used as a parameter. The blowholes counted were 1 mm or more in size as observed on an X-ray transmission photograph. The results shown in FIG. 9 are obtained by using various trial welding wires.
It is obtained by stacking galvanized steel plates having a plate thickness of 2.3 mm and a basis weight of 45 g / m ² with a gap of zero, and performing a downward pulse lap fillet mag pulse arc welding. Welding conditions are wire diameter: 1.2 mm, shield gas composition: Ar
+ 20% CO ₂ , shield gas flow rate: 20 liters / 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 contents of both Mn and Si are large, the number of blowholes generated is small, and when the Mn amount is in the range of 1.5% by weight or more, the Si amount is compared with the Mn amount. Even at a low level of 0.3 to 0.7% by weight, the number of blowholes generated is small. The deoxidation rate in molten metal due to Mn and Si depends on the Mn / Si value, and
If the Si value is small, it becomes slow. When the deoxidation rate is slow, the active oxygen in the molten metal increases, the viscosity of the molten metal decreases, and it becomes impossible to suppress the penetration of zinc vapor.

From the above, when the Mn content is less than 1.5% by weight and the Si content is less than 0.3% by weight, the penetration of zinc vapor into the molten metal is suppressed due to the high viscosity and high surface tension of the molten metal. If the Mn content exceeds 3.0% by weight and the Si content exceeds 0.7% by weight, the wire breakage is likely to occur at the time of manufacturing the welding wire and the productivity of the welding wire is lowered.
In addition, the strength of the weld metal is the base metal (mainly mild steel, 490N
/ Mm ² grade high strength steel) is too high.

The solid wire for welding galvanized steel sheet used in the mag pulse arc welding method according to the present invention is C,
Si and Mn are 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 intrusion of zinc vapor into the molten metal. However, if the content is 0.
If it is less than 1% by weight, there is no effect on increasing the viscosity of the molten metal,
If it exceeds 0.5% by weight, the strength of the weld metal is too high for the base metal.

The content of P and S contained as unavoidable impurities is preferably 0.05% by weight or less. Both P and S are elements that increase the susceptibility to the occurrence of cracks in the weld, and the content of P is desirably as low as possible, but if it is 0.05% by weight or less, it does not impair the quality of the weld. Because there is no. Although S is similar to the above, S is 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 and suppress the invasion of zinc vapor. Therefore, it is desirable that the content of S is small.

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

In gas shielded arc welding of steel, the presence of oxides having a low ionization voltage is essential for stable arc generation, and the shielding gas containing Ar gas as the main component is CO ₂ gas or It is necessary to mix O ₂ gas. However, since CO ₂ gas is an active gas, when the shield gas is composed of a mixed gas of Ar gas and CO ₂ gas, O ₂ gas is generated by arc heat from the CO ₂ gas, and this O ₂ gas is Reduces the 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 specify the gas mixture ratio.

FIG. 10 is a diagram showing an example of the relationship between the blowhole index BH and the mixing ratio of CO ₂ gas or O ₂ gas in the shield gas containing Ar gas as the main component. The blowhole index BH, which is an evaluation value, is proportional to the number of blowholes generated, and its definition is shown in FIG.
It will be described later based on. The results shown in FIG. 10 are obtained by using a commercially available wire for MAG welding (JIS YGW-15), stacking galvanized steel plates having a plate thickness of 2.3 mm and a basis weight of 45 g / m ^{2 with} a zero gap, and stacking them downward. It was obtained by performing mag pulse arc welding of fillet. 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 O ₂ gas is used as a mixture, the activity is high and if the mixing ratio exceeds 10% by volume, the viscosity of molten metal
The surface tension is lowered, zinc vapor that has penetrated into the molten metal is easily floated and released, and the number of blowholes is reduced. When CO ₂ gas is mixed and used, if the mixing ratio exceeds 20% by volume, the O ₂
Similar to the case of gas, the number of blowholes generated is reduced.

However, when the porosity defects are reduced by lowering the viscosity and surface tension of the molten metal, as described above, the welding bead drips in difficult welding such as vertical welding and horizontal welding. It has the drawback of being easy.

Therefore, in the present invention, in order to suppress the invasion of zinc vapor into the molten metal due to the increase in viscosity of the molten metal, the shield gas is composed of a mixed gas of Ar gas and CO ₂ gas, and CO ₂ A shield gas having a gas mixture ratio of 5 to 10% by volume is used. CO ₂
If the gas mixing ratio exceeds 10% by volume, the effect of increasing the viscosity of the molten metal due to the wire component will be reduced.
If it is less than 5% by volume, the arc becomes unstable.

Next, the 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 zinc vapor generated itself and suppress the invasion 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 lowered. FIG. 11 is a diagram showing an example of the relationship between the welding voltage and the blowhole index BH. The results shown in FIG. 11 are obtained by using 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% Ar gas and 7% CO ₂ gas, and a flow rate of 20%.
A shield gas of liter / min is used and the plate thickness is 2.3.
It was obtained by stacking galvanized steel sheets having a unit weight of 45 mm / m ^{2 and} having a unit weight of 45 g / m ² with a gap of zero, and performing a mag-pulse arc welding of the downwardly stacked fillet. Welding conditions are wire feeding speed: 7 m / min, welding speed: 120 cm / mi
n, peak current value: 470 A, peak current period: 1.6
ms, short circuit transfer rate r: 0 to 1.0.

From FIG. 11, it can be seen that blowhole defects decrease as the welding voltage value decreases. However, if the welding voltage is lowered too much in order to lower it, the unmelted tip of the welding wire plunges into the molten pool, causing an arc breakage, so that welding is impossible, so-called wire sticking (wire stubbing) occurs. Since the lower limit welding voltage at which welding is possible without causing this wire stick varies depending on the material of the welding wire, it is not easy to determine the appropriate welding voltage setting value when setting the welding voltage low.

Therefore, the present inventors have studied the mag-pulse arc welding of galvanized steel sheet, focusing on the relationship between the droplet transfer phenomenon and the welding voltage. As a result, most of the droplet transfer for each pulse cycle is one pulse / one short-circuited droplet transfer (see FIG. 5), which is one droplet transfer due to a short circuit during the base current period of one pulse cycle. It was found that by setting the welding voltage in this manner, stable arc welding can be performed without causing wire stick even if the welding voltage is lowered to lower the welding heat input. Further, this makes it possible to judge whether the welding voltage setting value is appropriate or not, not by the value of the welding voltage itself, but by the quantifiable droplet transfer state, and it is possible to easily adjust the setting of the appropriate welding voltage value. all right.

FIG. 5 is a schematic diagram showing a state of transfer of one pulse and one short-circuited droplet in mag pulse arc welding. As shown in the figure, in the 1-pulse 1-short-circuit droplet transfer, the droplets formed at the tip of the welding wire during the peak current period T _P in which the peak current I _P is flowed are the molten pool during the base current period T _B. It makes a short-circuiting contact once and moves. If a mag-pulse arc welding power source that can supply a sufficient short-circuit current when the droplet is short-circuited, the generation of spatter when the droplet is short-circuited can be reduced.

FIG. 6 is an explanatory diagram for explaining the relationship between the welding voltage and the short-circuit transfer rate r in mag pulse arc welding. Here, if the short-circuit transfer rate r is defined as r = (pulse per unit time t, the number of pulses for short-circuited droplet transfer) / (the number of pulses per unit time t), the short-circuit transfer rate r = 1 .0 indicates that one pulse and one short-circuited droplet transfer occur in all pulse periods in each pulse period in unit time t (for example, 1 second). Then, the welding voltage value at the time of 1 pulse 1 short-circuited droplet transfer per 1 pulse cycle, that is, the welding voltage value at the short-circuit transfer rate r = 1.0, is used for welding to reduce welding heat input. This is the lower limit and the optimum voltage value that enables stable arc welding without causing wire sticking even if the voltage is lowered.

Then, as shown in FIG. 6, as the welding voltage is gradually increased, the short-circuit transfer rate r becomes smaller than 1.0 and becomes 1 at a rate of once every two or three pulses.
Pulse 1 short-circuit droplet transfer will occur. When the welding voltage is further increased, the short-circuit transfer rate r becomes zero, the droplet transfer due to the short circuit is not performed, and the droplet formed at the tip of the welding wire during the peak current period T _P is the base current period T _{P.
During B} , the droplets are separated without making short-circuit contact, and 1 pulse 1 droplet transfer (spray transfer) is performed. Therefore, in order to achieve stable arc welding without causing wire sticking even if the welding voltage is lowered to lower the welding heat input, the range of r = 0.7 to 1.0 is set. Set the welding voltage to. When the welding voltage is lower than the value when the short circuit transfer rate r = 1.0, wire sticking occurs 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, low heat input for welding cannot be achieved.

Whether or not the droplet transfer form is one pulse / one short-circuited droplet transfer can be known as follows. FIG. 7 shows a waveform of a welding current / voltage waveform recorded in a 1-pulse 1-short-circuited droplet transfer state in a mag pulse arc welding, which is traced. The waveform is basically the same as that shown in the schematic diagram of FIG. 5, although it is affected by noise, and the waveform in the peak period is recorded as a band due to large noise.

As can be seen from FIG. 7, the welding voltage is
If the droplet short-circuits to the molten pool during the base current period, it drops rapidly to almost zero, and then rises sharply when the arc re-occurs.Therefore, it is possible to clearly distinguish between the short-circuited state and the non-short-circuited state. You can easily know the presence or absence of. For example, by setting a threshold value (for example, 10 V) and comparing the threshold value with the welding voltage detection value, it is possible to determine short circuit / non-short circuit. In this way, the droplet transfer mode is 1 pulse 1
It is possible to detect whether or not there is a short-circuited droplet transfer. Then, based on this, the short-circuit transfer rate measuring device described later automatically obtains the short-circuit transfer ratio r during welding, and while observing the short-circuit transfer ratio value detected and displayed by the short-circuit transfer ratio measuring device, r = 0 The welding voltage suitable for suppressing the pore defect can be set by manually adjusting the welding voltage or automatically adjusting it so as to be in the range of 0.7 to 1.0.

As described above, the solid wire for welding galvanized steel sheet and the shield gas used in the mag pulse arc welding method according to the present invention are selected such that the molten metal has high viscosity and high surface tension. ing. Therefore, the pulse waveform parameter needs to be a value that can stably transfer droplets having high viscosity and high surface tension. Therefore, the peak current value is 450 to 600A,
The peak current period is preferably in the range of 1.0 to 2.0 ms. If the peak current value is less than 450 A, the droplet cannot be grown to a size large enough to cause a short circuit transfer. On the other hand, when the peak current value exceeds 600 A, the heat input during the peak current period becomes too large, and the low welding heat input cannot be achieved. Further, if the peak current period is less than 1.0 ms, the droplet cannot be grown to a size large enough to transfer to a short circuit, and the unmelted wire easily rushes into the molten pool at the time of short circuit. On the other hand, if the peak current period exceeds 2.0 ms, the droplets will come off during the peak period,
Unmelted wire will plunge into the molten pool during the base period.

[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 source equipped with a short-circuit transfer rate measuring device, which is used for carrying out the method according to the present invention.

In FIG. 1, reference numeral 51 is an inverter type mag pulse arc welding power source, 52 is a remote control box of the welding power source 51, and a welding current consisting of a peak current and a base current, a welding voltage and the like are manually set. It is for adjustment. 53 is a wire feeding 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-mentioned short-circuit transfer rate r based on the output signals of the welding voltage detector 54 and the welding current detector 55, and displays the measured value as a numerical value.

The short-circuit time measuring device 61, which constitutes the short-circuit transfer rate measuring device 60, judges whether or not it is short-circuited by comparing the output signal from the welding voltage detector 54 with the threshold value. A signal indicating that, that is, a short circuit time signal is output to the comparator 62. The comparator 62 compares the short circuit time signal given from the short circuit time measuring device 61 and the reference short circuit time signal from the standard short circuit time setting device 63, and the short circuit time signal is within the range of the magnitude of the standard short circuit time signal. If it is normal, the base period short circuit determination unit 64
Send a short circuit occurrence signal to. This comparison operation is a short-time short-circuit that does not involve the transfer of droplets, an abnormal short-circuit such as an abnormally long short-circuit such as the welding wire SW plunging into the base metal WP, and stable short-circuit droplet transfer. To distinguish.

On the other hand, the peak / base period determiner 65 is
When 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, the base period short circuit determination unit 64 determines that the droplet transfer due to the short circuit has occurred during the base current period based on the short circuit occurrence signal and the base period signal, and causes the counting / arithmetic circuit 66 to perform the short circuit dissolution. Outputs a drop transfer generation signal.

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

While watching the short-circuit transfer rate r displayed on the display 67, the welder manually adjusts the welding voltage by the remote control box 52 so that r = 0.7 to 1.0, Performs mag pulse arc welding.

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, which is used for carrying out the method according to the present invention.

In FIG. 2, 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 DC current is the inverter 4
Is converted into high frequency alternating current by. The transformer 5 steps down the output of the inverter 4 to a welding voltage. Transformer 5
The high-frequency alternating current that has been stepped down for welding is rectified by the second rectifier circuit 6 into welding direct current. This DC current is supplied between the welding wire SW and the base metal 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 the wire feeding roller 14 driven by the wire feeding motor 13, and welding is performed by generating an arc between the welding wire SW and the base material WP. The wire feeding motor control circuit 12 controls the rotation speed of the feeding motor 13 based on a feeding speed setting signal from a wire feeding speed setting device (not shown).

The control unit 30 controls the inverter 4 to
This is for performing control such that a peak current of a predetermined value and a base current are alternately and repeatedly supplied 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 outputs them to the respective setting signals. Based on the inverter control signal, the power control circuit 29 is provided. The power control circuit 29 controls the inverter 4 so that the peak current and the base current having a predetermined value are output while feeding back the output signal from the welding current detector 11.

Next, a structure 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 there is a short circuit by comparing the output signal from the welding voltage detector 10 with a threshold value, and outputs a signal indicating that the short circuit is occurring, that is, a short circuit time signal. 1 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 if 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 determination unit 18. This comparison operation is a short-time short-circuit that does not involve the transfer of droplets, an abnormal short-circuit such as an abnormally long short-circuit such as the welding wire SW plunging into the base metal WP, and stable short-circuit droplet transfer. This is done to distinguish between.

Based on the base period signal from the pulse waveform selection circuit 28 and the short circuit occurrence signal, the base period short circuit judging unit 18 judges that the droplet transfer due to the short circuit has occurred during the base current period and counts. A short-circuit droplet transfer occurrence signal is output to the arithmetic circuit 19. The counting / arithmetic circuit 19 counts this short-circuited droplet transfer generation signal and the signal representing the number of pulses from the pulse waveform selection circuit 28, and determines 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 obtained from the pulse number of the short-circuit droplet transfer), and this is output to the second comparator 21.

The second comparator 21 uses the measured value of 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 within the range of r = 0.7 to 1.0. When the measured value> the set value is compared with the set value, a welding voltage increase signal corresponding to the difference is given to the adder 23 so that the increase signal is added to the output of the welding voltage setter 22. On the contrary, 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 increases / decreases the wire melting energy by increasing / decreasing the base period and increasing / decreasing the pulse frequency based on the output signal from the adder 23. Thereby, the welding voltage is automatically adjusted so that the short-circuit transfer rate setting value set in the range of 0.7 to 1.0 is obtained.

Using the above welding power source, galvanized steel sheets were subjected to mag pulse arc welding under the welding wires and welding conditions shown in Tables 1 and 2, and the occurrence of blowholes was examined. For the welding, lap fillet welding was performed according to the welding procedure shown in FIG. 3 (downward posture, lap joint, zero gap). Common welding conditions are power supply polarity: DCRP, welding wire diameter: 1.
2 mm, wire feeding speed: 7 m / min, welding speed: 1
20 cm / min, wire protrusion length: 15 mm. As the test steel sheet, the weight per unit area of zinc is 45 g / each on both sides.
m ² , plate thickness 2.3 mm, plate width 75 mm, length 500 mm
The alloyed hot-dip galvanized steel sheet of was used. The state of blowhole generation was evaluated by the blowhole index BH shown in FIG. 4 by an X-ray transmission photograph of the welded portion. The results are shown in Tables 1 and 2.

In Tables 1 and 2, No. 1 to
In 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 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. In Nos. 5 to 26, the mag pulse arc welding power source having the function of measuring the short circuit migration rate and the function of automatically adjusting the welding voltage shown in FIG. 2 was used.

[0054]

[Table 1]

[0055]

[Table 2]

As can be understood from Tables 1 and 2, according to the mag pulse arc welding method according to the present invention, the blowhole index is as low as 50 or less, and the occurrence of pore defects such as pits and blowholes is extremely high. I was able to reduce it. Further, according to the mag pulse arc welding method of the present invention, since the viscosity of the molten metal is increased as one of the means for suppressing the invasion of zinc vapor into the molten pool, it is difficult to perform vertical welding or horizontal welding. Also, in the case of, it was possible to obtain a weld bead with a good appearance without bead dripping.

[0057]

As described above, according to the method of magpulse arc welding of a galvanized steel sheet according to the present invention, when welding the galvanized steel sheet, the chemical composition of the welding wire,
Appropriate combination of shield gas composition and mag pulse welding conditions to reduce welding heat input without increasing welding bead amount and increase viscosity of molten metal to reduce zinc vapor generation amount and zinc vapor melting Since it is designed to prevent entry into the pond, it is possible to extremely reduce the occurrence of pore defects such as pits and blowholes, and bead dripping even in difficult position welding such as vertical welding and horizontal welding. It is possible to obtain a weld bead having a good appearance and to contribute to expanding the application of the galvanized steel sheet by welding assembly.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a mag pulse arc welding power source equipped with a short-circuit transfer rate measuring device, which is used for carrying out the 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 migration rate measuring function and a welding voltage automatic adjusting function, which is 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 diagram showing a state of 1 pulse 1 short-circuited 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 mag pulse arc welding.

FIG. 7 is a graph showing the welding current and voltage waveforms recorded in a 1-pulse 1-short-circuit droplet transfer state in a mag pulse arc welding, recorded by a waveform recorder and traced.

FIG. 8 is a diagram for explaining a generation position of zinc vapor that causes a pit and a blow hole.

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

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

FIG. 11 is a diagram showing 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 ... Reference short-circuit time setting device 1
7 ... 1st comparator 18 ... Base period short circuit judging device 19 ...
Counting / arithmetic circuit 20 ... Short-circuit transfer 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 material ZM ... Zinc plating layer WB ... Welding bead WT ... Welding torch

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location B23K 35/30 320 B23K 35/30 320A H02M 9/00 H02M 9/00 B

Claims (2)

[Claims] 1. When performing galvanized arc welding of a galvanized steel sheet, C: 0.02 to 0.10% by weight, Si:
0.3-0.7 wt% and Mn: 1.5-3.0 wt%
Using a solid wire for welding galvanized steel sheet containing as a basic alloy component, and a shield gas composed of a mixed gas of Ar gas and CO ₂ gas and having a CO ₂ gas mixing ratio of 5 to 10% by volume. Current value is 450 to 600
A, the peak current period is set to 1.0 to 2.0 ms, the welding voltage is set so that the value of the following short-circuit transfer rate r falls within the range of r = 0.7 to 1.0, and short circuit occurs during the base current period. A method for performing magpulse arc welding of a galvanized steel sheet, which is characterized in that the galvanized steel sheet is subjected to magpulse arc welding by performing droplet transfer by means of. Short-circuit transfer rate r = (1 pulse per unit time t, the number of pulses in which one short-circuited droplet transfer was performed) / (number of pulses per unit time t) 2. The wire further comprises Mo: 0.1
The method of mag pulse arc welding of a galvanized steel sheet according to claim 1, which contains 0.5% by weight.