JP2002144063A - Lap welding method of thin steel plate, and welded thin steel plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lap welding method capable of obtaining sufficient joint strength at high speed by increasing the allowable space in the lap welding of thin steel plates having a space or of a structure formed thereof, and realizing appropriate bead width. SOLUTION: When performing gas metal arc welding after irradiating YAG laser beam at parts to be welded in the lap welding of the thin steel plates, the output of the laser beam, the arc current and the welding speed are adjusted so that the width W of the weld bead satisfies the condition of the formula (1). W>TS×t/(1.9×Hv) (1), where W (mm) is width of weld bead (the bead width between two plates), Hv is the Vickers hardness, t (mm) is thickness of the thin steel plate with smaller value of TS×t out of the two thin steel plates to be lap-welded), and TS (MPa) is tensile strength of the thin steel plate with smaller value of TS×t out of the two thin steel plates to be lap- welded).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a welding method used for lap welding of a thin steel sheet or a structure formed by the thin steel sheet, and a welded thin steel sheet obtained by the method.

[0002]

2. Description of the Related Art Conventionally, an electric resistance spot welding method and an arc welding method have been mainly used for joining a structure formed of a thin steel sheet, but in recent years, a laser welding method has been adopted. Was. This is because when laser welding is used, welding from one side is sufficient, and the bead width is narrow, so the degree of freedom in design of the joint is greater than that of the conventional methods such as resistance spot welding and arc welding. This is because there is an advantage that it is possible to reduce the width of the substrate.

[0003] Laser light has a very strong light-collecting property,
Since it is a concentrated heat source with an extremely high energy density, if it is applied to welding, the penetration depth is deep and high-speed welding can be performed.

However, the laser welding method has the following problems. In laser welding, as a reversal of the feature of good laser light focusing, it is necessary to strictly control the superposition quality of the workpiece. For lap joints,
The allowable amount of the gap between the upper and lower workpieces is about 30% of the plate thickness of the upper workpiece, and if it exceeds this, the molten portion melts down from the upper workpiece and the strength of the lap joint decreases. . In order to satisfy the above conditions, a method of applying laser pressure from above or from both the upper and lower sides of the lap joint to correct the dimension of the gap of the lap joint while performing laser welding is disclosed in These are disclosed in JP-A-59-179284 and JP-A-4-258391.

On the other hand, in the welding of a thin steel sheet closed-section structure, since a pressing force cannot be applied from both the upper and lower sides, a method of applying pressure from only one side is disclosed in Japanese Patent Laid-Open No. Hei 8-90264. When the rigidity of the thin steel plate closed section structure is high, the gap between the plates decreases with the increase of the pressing force,
If the rigidity of the thin steel plate closed section structure is low, the deformation of the entire joint will increase if the pressing force increases beyond a certain value,
On the contrary, there is a problem that the gap becomes large. Therefore, a method for online control of the pressing displacement and the pressing force has been proposed.

As described above, when a structure formed of a thin steel plate is welded by a laser, it is necessary to perform welding under strict pressure in order to strictly manage the gap between the objects to be welded. . However, when the shape of the thin steel plate structure is complicated or when the thickness of the steel plate structure is various, high-precision pressure control becomes difficult, and the joint strength may be reduced. Also,
In the welding of a thin steel sheet closed-section structure, an arc welding method capable of one-side welding may be used. As an arc welding method,
Conventionally, TIG welding, plasma welding, and gas metal arc welding are widely used.
TIG welding is performed in an inert gas atmosphere such as argon.
In this method, an arc is generated between a tungsten electrode and a base material to perform welding. In plasma welding, an electric current is applied between two electrodes in a welding torch to generate an arc, and a working gas, which is a mixture of argon and hydrogen, is sent around the arc. When the working gas is ionized by the heat of the arc, ions and electrons are generated. This is a method of forming a plasma which is a mixed gas body, and welding when the plasma is mature. TIG welding and plasma welding are called non-consumable electrode welding methods. On the other hand, in gas metal arc welding, an arc is generated between the welding wire and the base metal while continuously supplying the welding wire in an atmosphere of an inert gas such as argon, carbon dioxide, or a mixture of these gases. This is a method in which the two are melted and welded together, and is called a consumable electrode type welding method.

[0007] In these arc welding methods, since the convergence of the heat source is inferior to the laser welding method and the welding speed is low, welding heat input to the thin steel plate structure is excessive and burn-through defects occur. And has the problem of reducing joint strength.

On the other hand, although there is no example of application to thin steel sheet welding, a method of simultaneously irradiating a laser and an arc to perform welding has been proposed.

The amount of penetration when laser welding and arc welding are combined is simply larger than the sum of the penetrations of both welding methods. It is considered that this is because the laser irradiation forms a keyhole in the welded portion, so that the arc is heated not only from the surface of the steel material but also from inside the keyhole. In addition, it is pointed out that since the steel material surface is heated by the arc, the absorption rate of laser energy into the steel material is improved.

This welding method is disclosed, for example, in Japanese Patent Application Laid-Open No. 62-26386.
No. 9, Japanese Patent No. 1798896, Japanese Patent Application Laid-Open No. 9-122950 and Japanese Patent Application Laid-Open No. 10-272578. What is common here is that the laser and the TIG arc are combined. Japanese Patent Application Laid-Open No. 10-216979 discloses a welding method in which laser and plasma are combined.

However, the welding technique disclosed herein is not suitable for lapping and fillet welding of thin plate structures having a gap between thin steel plates. That is, by combining laser and TIG arc or plasma, the welding speed can be increased. However, since both TIG arc and plasma welding methods are non-consumable electrode type welding methods, the upper and lower welded portions of the lap joint are welded. This does not contribute to an increase in the allowable amount of the gap between the objects, and cannot solve the problem that the joint strength is reduced due to the burn-through defect.

Research examples of a welding method in which laser welding and gas metal arc welding are combined are described in IIWDoc. XII-1565-99 and the like. The research examples here show welding cases of thick steel plates and aluminum alloys. Regarding the former thick steel plate welding, the welding productivity is improved by changing the groove shape from the V groove to the Y groove, and the laser weld metal is annealed by the heat cycle after arc welding to improve the toughness. It is pointed out that this can be achieved. On the other hand, in the latter case, a research case of butt welding of aluminum alloy sheets is shown. Here, since the aluminum alloy has a high reflectance with respect to laser light, the laser welding efficiency is low. Therefore, it has been pointed out that high-efficiency welding can be performed by heating an aluminum alloy with an arc heat source to increase the absorption rate of laser light.

[0013] However, even in these research cases, it does not contribute to the increase in the allowable amount of the gap between the objects to be welded in the lap welding of the thin steel plate structure, and the joint strength decreases due to the burn-through defect. The challenge of coming cannot be solved.

[0014]

In the above-mentioned prior art, there are the following problems in lap welding of a thin steel plate or a structure formed by the same.

In laser welding, there is a problem that the allowable gap between the objects to be welded is small, and when the gap exceeds the allowable amount, the upper object to be welded is melted off. In addition, when the thickness of the material to be welded is large or the strength is high due to the narrow weld bead width, the strength of the welded portion is lower than that of the base material, and there is a problem that sufficient joint strength cannot be secured. To solve this problem, the bead width may be increased, but there has been no suitable welding technique to achieve this. That is, in laser welding, even if the laser power is increased or the welding speed is reduced in order to increase the bead width, the laser beam penetrates the thin metal plate and the bead width cannot be greatly increased.

In various types of arc welding, when a thin steel plate structure is targeted, there is a problem that the heat input to welding is excessive and the upper and lower workpieces are melted off. Furthermore, in the arc welding method, when the welding speed is increased, the beads hang,
The range in which each parameter can be changed independently, such as the inability to maintain an arc, is narrow, making it difficult to control welding heat input. For this reason, it is difficult to obtain a weld having an appropriate bead width according to the sheet thickness in butt welding of thin steel sheets.

In a combined welding method using a laser and a TIG arc or a plasma, since the welding method is not a welding method in which a welding wire is added, it is not possible to solve the problem that the non-welded material on the upper side is burnt off similarly to the laser welding.

As a welding method for adding a welding wire,
There is a welding method in which laser welding and gas metal arc welding are combined, but there is no welding technique for lap welding of a thin steel plate structure having a gap.

According to the present invention, when combining laser welding and gas metal arc welding, the width of the weld bead is set so as to satisfy a specific condition, thereby providing a thin steel plate having a gap or a structure formed by the same. By providing a lap welding method and a weld-bonded thin steel sheet that can provide sufficient joint strength by increasing the clearance allowance and optimizing the bead width in lap welding of objects, and can perform high-speed welding. is there.

[0020]

According to a first aspect of the present invention, there is provided a laser welding method comprising the steps of irradiating a YAG laser to a portion to be welded in lap welding of a thin steel sheet, and performing gas metal arc welding after the irradiating step. A lap welding method for a thin steel sheet in which a laser output, an arc current and a welding speed are adjusted so that a width W of a weld bead satisfies the condition of the following equation (1) in an irradiation step and an arc welding step. W> TS × t / (1.9 × Hv) (1) where W (mm): weld bead width (bead width between two plates), Hv: Vickers hardness of weld metal, t
(Mm): Plate thickness (T of two thin steel plates to be lap welded)
TS (MPa): Tensile strength (side of two thin steel plates to be lap welded, where TS × t is small). According to a second aspect of the present invention, in the step of irradiating the YAG laser, a target position of the laser is in a range of 0 mm or more and 8 mm or less than a target position of the gas metal arc welding. Lap welding method for steel sheets. According to a third invention, in the gas metal arc welding process, the chemical composition of the welding wire material is C: 0.0010 to 0.030% by mass, Si: 0.02 to 100% by mass.
The first or second invention is characterized in that the first or second invention contains 1.50% and Mn in a range satisfying 0.02 to 1.50%, and the balance substantially includes a component composed of Fe and unavoidable impurities. The lap welding method described. The fourth invention has a thickness of 0.3
A welded steel sheet manufactured by lap welding a steel sheet having a thickness of not less than 6 mm and not more than 6 mm according to any one of the first to third inventions. According to a fifth aspect, in the lap welding method according to any one of the first to third aspects, the chemical component is C: 0.00 in mass%.
10 to 0.030%, Si: 0.02 to 1.50%, M
n: a welding wire material containing 0.02 to 1.50% in a range that satisfies 0.02 to 1.50%, with the balance being substantially composed of Fe and unavoidable impurities.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION The thickness range of a thin steel sheet applicable to the present invention depends on welding conditions such as welding heat input and welding speed, but is generally 0.3 mm or more and 6 mm or less. .

When welding a plurality of members formed by molding the thin steel plate with a mold or a roll or the like, since the thin steel product has a gap in the overlapped portion or the fillet portion due to springback, the molten metal is formed. It is necessary to weld while supplying. The present inventors have found a technique for speeding up welding and greatly reducing welding accuracy in a welding method in which laser welding and gas metal arc welding are combined.

According to the first aspect of the invention, a thin steel sheet having a gap is formed by a welding method in which laser welding and gas metal arc welding for supplying a welding wire are combined (a welding method in which gas metal arc welding is performed after laser welding). The product can be welded without welding defects such as burn-through.

That is, in gas metal arc welding alone, the welding speed is about 2 m / min at the maximum, and when welding a thin steel plate structure, the welding heat input becomes excessive and burn-through defects tend to occur.

On the other hand, in the present invention, gas metal arc welding is performed after laser irradiation. This allows
The steel material irradiated with the laser melts and evaporates, and a part thereof is ionized to become plasma. In this high temperature region, in addition to the high metal vapor density and metal ion density due to laser irradiation, thermionic emission energy from steel material or thermionic absorption energy into steel material also significantly decreases,
If the arc is irradiated here, it will easily become the anode or cathode point of the arc, stabilizing the generation and maintenance of the arc,
Arcs are concentrated. Further, since the YAG laser is not absorbed by the plasma generated by the arc, it can be irradiated during the arc. However, since the carbon dioxide gas laser is absorbed by the plasma generated by the arc, the laser irradiation position must be separated from the arc welding position, and the combined effect of the laser and the arc cannot be obtained.

Therefore, according to the present invention, by combining with laser welding, the gas metal arc is stabilized, and welding can be performed even at a welding speed exceeding 6 m / min.
As described above, since high-speed welding is enabled, welding heat input is 30% or less as compared with gas metal arc alone welding, and burn-through defects do not occur. In addition, in gas metal arc welding, welding is performed while melting a welding wire to fill a gap in a thin steel plate structure, so that the allowable gap can be greatly increased.

In the present invention, the proper welding bead width W
Is defined so as to satisfy the expression (1).

W> TS × t / (1.9 × Hv) (1) where W (mm): weld bead width (bead width between two plates), Hv: Vickers hardness of weld metal, t
(Mm): Thickness (T of two thin steel plates to be vertically welded)
The side with the smaller value of S × t), TS (MPa): the tensile strength (the side with the smaller value of TS × t of the two thin steel plates to be lap welded).

In the conventional lap welding using a laser, the bead width is almost constant irrespective of the plate thickness, and it is difficult to make an appropriate bead width according to the plate thickness of two steel plates to be lap welded. . On the other hand, according to the method of the present invention, by combining laser welding and arc welding, the arc is stabilized, the range in which the arc current and the welding speed can be taken is wide, and the adjustment of welding heat input can be easily performed. . This makes it possible to obtain an appropriate welding bead width according to the thickness and strength of the material to be welded.

The bead width is defined by the bead width between two steel plates as in the following equation (1). The reason will be described with reference to the drawings. FIG. 1 shows a cross section of a welded portion when two thin steel plates are overlap-welded. The tensile strength Tw (N / mm) of the weld metal per unit width of the welded joint shown in FIG. 1 is determined by the Vickers hardness Hv of the weld metal and the bead width W (m) between the two steel plates.
m) is expressed as follows. Tw = 1.9 × Hv × W The tensile strength TB (N / mm) per unit width of the base material is expressed as follows from the tensile strength TS (MPa) of the material and the plate thickness t (mm). You. TB = TS × t In order for the strength of the weld metal to exceed the strength of the base material and cause the joint to break at the base material, 1.9 × Hv × W> TS × t, ie, W> TS × t / ( 1.9 × Hv). Since the hardness Hv of the weld metal depends on the welding conditions and the compositions of the base metal and the welding wire, the weld bead width W may be determined by actual measurement.

Since the gas metal arc welding apparatus is intended for welding thin steel sheets, the welding wire has a diameter of 1.
It is desirable to use a small diameter wire of 2 mm or less. It is desirable to use an inert gas such as an argon gas as the shielding gas in order to simultaneously achieve the stability of the arc and the oxidation prevention of the weld metal.
A gas in which hydrogen gas or helium gas is mixed in a range of 2 to 20% in a gas mixed in a range of 0 to 100% and an argon gas can also be used.

In the present invention, the laser beam axis is
It is preferable to set the irradiation angle of the gas metal arc torch to 5 degrees or more and 50 degrees or less.

When the irradiation angle of the gas metal arc torch is set to less than 5 degrees with respect to the laser optical axis, the molten metal supplied by the gas metal arc welding crushes the evaporation holes formed by the laser welding. At the same time, the molten metal is irradiated with a laser to induce the generation of spatter, which causes a problem of deteriorating the quality of the welded joint.

On the other hand, when the irradiation angle of the gas metal arc torch is set to be more than 50 degrees with respect to the laser beam bow, the vapor metal holes formed coaxially with the laser beam axis by the laser irradiation are subjected to gas metal arc welding. Since the supply angle of the molten metal from the metal becomes steep, the molten metal cannot be supplied stably to the laser welded portion, and welding defects such as blow holes and humping beads are likely to occur. For this reason, the irradiation angle of the gas metal arc torch is preferably set to 5 to 50 degrees.

The optical system preferably has an optical system in which a reflecting mirror for deflection and several positive and negative focusing lenses are combined, but the laser light is emitted only by a combination of a concave mirror and a convex mirror without using a lens system. You may make it converge.

Next, according to the second aspect of the present invention, the target position of the laser is set to be ahead of the target position of gas metal arc welding by 0 to 8 mm with respect to the welding line direction.

When the distance between the target position of the laser and the target position of the gas metal arc welding is set to be more than 8 mm, the distance between the two is too large, and the stabilization of the arc and the concentration effect by the laser irradiation are performed. Cannot be expected. In addition, even if the aiming position of the laser is shifted in the direction perpendicular to the welding line direction, the aiming position of the gas metal arc welding is shifted within ± 2 mm if the aiming position of the gas metal arc welding is set within ± 2 mm. A concentration effect is recognized, which is preferable.

In the third invention, when performing the lap welding according to the present invention, the chemical composition of the welding wire material is expressed as C: 0.0 in mass%.
010-0.030%, Si: 0.02-1.50m
%, Mn: 0.02 to 1.50%, with the balance being substantially composed of iron and inevitable impurities. In the method of the present invention, since the welding heat input is small, the weld metal is rapidly cooled and hardened. When the weld is hardened, the formability of the joining member decreases. Therefore, the components of the welding wire are specified as described above. The reason for defining each component in this manner will be described below.

C: 0.0010 to 0.030% C is an element which enhances the hardenability of steel and hardens the weld metal. Therefore, the content is set to 0.030% or less. But,
If the C concentration is too low, the grain boundary strength decreases and secondary processing cracks easily occur.

Si: 0.02 to 1.50% Si is used as a deoxidizing element and is also used for solid solution strengthening of steel. Si is added at 0.02% or more in order to prevent oxygen from being mixed into the weld metal from air or a shielding gas during welding and reacting with C in steel to become CO and cause blowholes. However, excessive addition increases the hardenability of the steel and causes the weld metal to harden,
0% or less.

Mn: 0.02 to 1.50% Mn is also added as a deoxidizing element and is used for solid solution strengthening of steel. 0.02% or more is added for the deoxidation of the weld metal, but it is made 1.50% or less in order to enhance the hardenability of the excessively added steel and bring about the hardening of the weld metal.

The balance substantially consists of iron and unavoidable impurities, but may contain trace elements other than the unavoidable impurities as long as the effects of the present invention are not impaired. A fourth invention is a welded thin steel plate obtained by lap welding of the present invention. A fifth invention is a welding wire material used in the lap welding of the present invention.

[0043]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will now be described in detail by way of example.

Example 1 Thin steel plates having upper and lower plate thicknesses of 0.8 mm and 1.2 mm, respectively, were subjected to lap welding. Each of the thin steel sheets is a 450 MPa class cold rolled steel sheet.
Table 1 shows the mechanical properties. As a lap joint, a test piece in which the gap between the upper and lower steel plates was changed from 0.25 mm to 2.0 mm was prepared. Welding was performed using only the YAG laser welding method, only the gas metal arc welding method, and the welding method of the present invention in which YAG laser welding and gas metal arc welding were combined. Table 2 shows the welding conditions of each welding method. Further, in the gas metal arc welding of the method of the present invention in which the gas metal arc welding alone and the YAG laser welding and the gas metal arc welding were combined, a welding wire having a diameter of 0.8 mm was used. Table 3 shows the composition of the welding wire.

Table 4 (and the continuation of Table 4) shows the test results. The evaluation of the welding test was performed as follows. A case where there was no burn-through and a welded part with sufficient joint strength was obtained was rated "〇". In addition, "◎" indicates that a uniform bead was formed without sputter adhesion, with little variation in bead width due to humping, and with a uniform bead. In addition, “△” indicates that the quality of the welded joint is slightly reduced due to a slight decrease in the penetration depth but no penetration occurs, and “×” indicates that the welded part has burned off. Also, when the upper and lower steel plates are not connected, the joint strength is zero, so "×"
And In particular, in the gas metal arc welding method, when the welding speed is increased, the arc becomes unstable and a welded portion cannot be formed. Also in this case, "x" was set.

In the YAG laser welding method, when the welding speed is as low as 0.5 m / min, the allowable amount of the steel plate gap is 0.5 mm. The permissible amount becomes as narrow as 0.25 mm. This is because the welding width of the YAG laser is as narrow as about 1 mm, the amount of molten metal is small, and even if there is a steel sheet gap of at most 0.5 mm, the upper and lower steel sheets are not connected.

In the gas metal arc welding method, when the welding speed is as low as 0.5 m / min, the welding heat input becomes excessive, so that the welding is performed. At a welding speed of 1.0 m / min,
The welding heat input is appropriate, and a sound weld is obtained up to a gap of 0.75 mm. However, if the gap of the steel sheet exceeds 0.75 mm, the upper steel sheet is burnt off and the upper and lower steel sheets are not connected. If the welding speed exceeds 1.0 m / min, the arc becomes unstable and a sound weld cannot be formed.

In the laser-arc combined welding method of the present invention, even when the welding speed is as low as 0.5 m / min, the arc concentrates on the laser-irradiated portion, and the width of the welded portion is smaller than that of the gas metal arc welding method. Therefore, no burn-through occurs. Further, the allowable amount of the steel plate gap exceeds 2.0 mm. Furthermore, since the arc is stabilized by laser irradiation, a sound weld without burn-through can be obtained even when the welding speed is 1.0 m / min or more, and the allowable amount of the steel plate gap is over 2.0 mm.

When the gap between the steel sheets is 1.0 mm or less, there is almost no variation in the bead width, and a uniform bead is formed. When the gap between the steel sheets exceeds 1.0 mm and is equal to or less than 2.0 mm, the penetration depth varies slightly, but the penetration depth does not decrease. When the steel plate gap is 2.0 mm,
The penetration depth is slightly reduced. Therefore, according to the method of the present invention, it is possible to simultaneously increase the speed of welding and significantly reduce welding accuracy.

[0050]

[Table 1]

[0051]

[Table 2]

[0052]

[Table 3]

[0053]

[Table 4]

[0054]

[Table 5]

Example 2 The effect of the irradiation angle of the gas metal arc torch with respect to the laser optical axis on the quality of the weld was investigated. In the welding experiment, the present invention combines YAG laser welding and gas metal arc welding using lap specimens having upper and lower plate thicknesses of 1.2 mm and 1.6 mm, respectively, and a gap of 0.5 mm. The welding was performed. The welding conditions were such that the irradiation angle of the gas metal arc torch with respect to the laser optical axis was changed from 5 degrees to 70 degrees. Other conditions are the same as those shown in Table 2. The quality evaluation of the welded joint was performed in the same manner as the evaluation method performed in Example 1. Each of the steel sheets is a 450 MPa class cold-rolled steel sheet similar to that used in Example 1.

Table 5 shows the results of the welding test. When the irradiation angle of the gas metal arc torch with respect to the laser optical axis was less than 5 degrees, the occurrence of spatter was large and the penetration depth was slightly reduced. On the other hand, when the irradiation angle of the gas metal arc torch is set to be more than 50 degrees with respect to the laser optical axis, the supply of molten metal from the gas metal arc welding to the laser welded portion is slightly inferior, resulting in a hump bead. . Therefore, preferably, the irradiation angle of the gas metal arc torch with respect to the laser optical axis is 5 degrees or more,
It can be seen that by setting the angle to 50 degrees or less, a sound weld can be reliably obtained. Further, when the irradiation angle of the gas metal arc with respect to the laser optical axis is set to be not less than 10 degrees and not more than 30 degrees, the adhesion of spatter is greatly reduced,
Since there is almost no variation in bead width due to humping, it is more preferable to set the irradiation angle of the gas metal arc torch to 10 degrees or more and 30 degrees or less with respect to the laser optical axis.

[0057]

[Table 6]

Example 3 The influence of the target position of the laser and the target position of gas metal arc welding on the weld quality was investigated. In the welding experiment, the present invention combines YAG laser welding and gas metal arc welding using lap specimens having upper and lower plate thicknesses of 1.2 mm and 1.6 mm, respectively, and a gap of 0.5 mm. The welding was performed. The welding conditions varied the target position of the laser and the target position of the gas metal arc welding from 0 mm to 12 mm. Other conditions are the same as those shown in Table 2. The quality evaluation of the welded joint was performed by the same method as the evaluation method performed in Example 1. Each of the steel sheets is a 450 MPa class cold-rolled steel sheet similar to that used in Example 1. Table 6 shows the results of the welding test.

When the distance between the target position of the laser and the target position of the gas metal arc welding is set to be more than 8 mm, the distance between the two is too large, so that the stabilization and concentration effect of the arc by the laser irradiation are reduced. And the penetration depth is slightly reduced. Therefore, the distance between the target position of the laser and the target position of the gas metal arc welding is set to 0 mm or more and 8 mm or less, which can reliably obtain a healthy weld.
More preferably, it is desirable to set it to 6 mm or less.

When the distance between the target position of the laser and the target position of the gas metal arc welding is set to 0 mm or more and 2 mm or less, the effect of the laser irradiation part on the stability and concentration of the arc becomes more apparent, so that the penetration depth becomes uniform. Increase,
Since the occurrence of spatter can also be suppressed, it is more preferable to set the distance between the target position of the laser and the target position of gas metal arc welding to be 0 mm or more and 2 mm or less.

[0061]

[Table 7]

Example 4 Lap welding of thin steel sheets was performed by the laser-arc joining welding method of the present invention and, for comparison, laser welding (single) and gas metal arc welding (single).

The steel plate used for welding is a 1.6 mm thick 59 steel plate.
It is a 0 MPa class hot rolled steel sheet. Table 7 shows the chemical components and general mechanical properties.

[0064]

[Table 8]

Table 8 shows the welding conditions.

[0066]

[Table 9]

Table 9 shows the composition of the welding wire used for the gas metal arc.

[0068]

[Table 10]

FIG. 2 shows the shape of the shear tensile test piece used for evaluation of the lap welded joint. A steel bead having a width of 10 mm is overlapped, and a weld bead is placed perpendicular to the tensile direction.

Table 10 shows the evaluation results of the lap welded joint.
In the case of laser (single) welding, since the bead width is narrow, the strength of the welded portion is lower than that of the base material, and all joints are broken at the welded portion. In gas metal arc welding (alone), the bead width increases and the weld strength increases, but the heat input is excessive and the heat-affected zone softens. Tensile strength (about 9800
N). In gas metal arc welding, if the welding speed is increased in order to reduce the heat input, the beads hum and the beads cannot be formed stably.

On the other hand, in the laser-arc combined welding method, an appropriate bead width and heat input can be obtained by adjusting the laser output, arc current, and welding speed. For this reason, no softening of the heat-affected zone has occurred, and when the bead width W is set within the range of the present invention (W> TS · t / 1.9 Hv), the joint breaks at the base material, Of the original strength.

From this table, it is apparent that the welding method of the present invention can obtain a higher welding speed than the laser (single) and the gas metal arc (single).

[0073]

[Table 11]

[0074]

As described above, when laser welding and gas metal arc welding are combined, the weld bead width is adjusted according to the tensile strength of the thin steel plate, the plate thickness, and the Vickers hardness of the weld metal. According to the laser-arc combined welding method of the present invention, the following effects can be obtained.

(1) The allowable gap amount of the lap welding can be greatly increased as compared with the welding with the laser alone and the arc alone.

(2) The speed of the hat can be increased as compared with single arc welding, and high-speed welding comparable to laser welding can be performed.

(3) Sufficient joint strength can be obtained because an appropriate bead width can be obtained by suppressing heat input.

[Brief description of the drawings]

FIG. 1 is a sectional view of a lap welding joint.

FIG. 2 is an explanatory view of a shear tensile strength test piece of a lap welded joint.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B23K 35/30 320 B23K 35/30 320A // B23K 103: 04 103: 04 (72) Inventor Akihide Yoshitake 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Inventor Yoshihiro Hosoya 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. F-term (reference) 4E068 AJ04 BC01 CA02 CA09 DA14 DB01 4E081 AA13 AA14 BA36 CA07 DA06

Claims (5)

[Claims] A step of irradiating a YAG laser to a portion to be welded in lap welding of a thin steel sheet; and a step of performing gas metal arc welding after the irradiation step, wherein a welding bead is formed in the laser irradiation step and the arc welding step. A lap welding method for a thin steel sheet in which a laser output, an arc current and a welding speed are adjusted so that the width W satisfies the condition of the following equation (1). W> TS × t / (1.9 × Hv) (1) where W (mm): weld bead width (bead width between two plates), Hv: Vickers hardness of weld metal, t
(Mm): Plate thickness (T of two thin steel plates to be lap welded)
TS (MPa): Tensile strength (side of two thin steel plates to be lap welded, where TS × t is small). 2. The thin steel sheet according to claim 1, wherein, in the step of irradiating the YAG laser, a target position of the laser is in a range of 0 mm or more and 8 mm or less than a target position of gas metal arc welding. Lap welding method. 3. In the gas metal arc welding process, the chemical composition of the welding wire material is C: 0.0010 to 10% by mass.
0.030%, Si: 0.02 to 1.50%, Mn:
The lap welding method according to claim 1, wherein the lap welding method includes a content in a range satisfying 0.02 to 1.50%, and a balance substantially including a component composed of Fe and unavoidable impurities. 4. A welded steel sheet produced by lap welding thin steel sheets having a thickness of 0.3 mm or more and 6 mm or less according to any one of claims 1 to 3. 5. The chemical composition used in the lap welding method according to claim 1, wherein C is 0.0010 to 10% by mass.
0.030%, Si: 0.02 to 1.50%, Mn:
A welding wire material containing 0.02 to 1.50% in a range that satisfies 0.02 to 1.50%, with the balance being substantially composed of Fe and unavoidable impurities.