JPH10328861A - Laser lap welding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a lap joint having the same mechanical characteristics, coating suitability, etc., as a butt joint by properly setting a lap margin and a laser beam irradiation position. SOLUTION: In laser lap welding in which two steel plates 1, 2 are superposed on each other at their end, with the superposed part 3 of the plates irradiated by a laser beam 5 as a welding heat source; the lap margin x of these plates 1, 2 is set to the size or below of either smaller one of the 40% of the sum of the thicknesses d1 , d2 of the two plates 1, 2 or the diameter ϕ of the beam spot in the laser irradiation part 4; and the welding is carried out in the manner that the center P of the laser beam 5 spot is positioned within the superposed part of the ends of the two plates 1, 2 in the view from the plate thickness direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for welding metal plates using a laser beam, and more particularly to a method for welding lap welding between thin plates, which can provide joint characteristics equivalent to butt welding. .

[0002]

2. Description of the Related Art Laser welding uses a heat source having a high energy density, and therefore has the advantage that high-quality welding with little heat effect can be performed at a high speed. It is known that the requirements for the butt end face accuracy are strict.

[0003] In particular, the accuracy of the butt end face of the material to be welded is affected not only by macro precision such as linearity and parallelism at the time of cutting, but also by microscopic shape such as burrs and burr of the end face at the time of shear cutting. This may cause defects when performing laser welding.

In order to solve this problem, a method of grinding an end face of a material to be welded as disclosed in Japanese Patent Application Laid-Open No. 3-169483, and a method disclosed in
No. 52788, a method for weaving a laser beam, or Japanese Patent Publication No. 63-3 / 1988.
As described in US Pat. No. 2,554, a method has been proposed in which a filler wire is added to reduce the butting accuracy.

[0005] However, these methods all require special equipment in actual application or have a problem that the welding speed is reduced to lower the productivity, which causes an increase in the cost of the welding operation. .

On the other hand, when lap welding is employed, unlike the butt welding, the requirements for the end face accuracy of the base material and the material to be welded are not strict.

[0007]

However, in the conventional laser lap welding of a metal plate, as shown in FIGS. 5, 6 and 7, at one of the overlapping portions 52 of the two metal plates 50, 51, Both ends 51a, 50a remain as notches in the joint without melting. For this reason, conventional lap welding has a problem that mechanical properties such as tensile strength, fatigue strength and formability are inferior to butt joints.

In the case where painting or surface treatment is performed after welding for the purpose of corrosion prevention and rust prevention, the ends 51a and 50a which are not melted as described above are present as notches. There is a problem that untreated portions are easily left during the surface coating treatment, and it is inevitable that the corrosion resistance and rust resistance of the joint are inferior to those of the butt joint.

For this reason, the application to which lap welding can be applied is limited in the past. on the other hand,
In the butt welding, as described above, the required accuracy of the end face shape of the metal plate butt surface is strict, and there is a problem that a welding defect is apt to occur particularly when welding a material having a small thickness.

The present invention has been made in view of such a problem, and in lap welding of a thin metal plate using a laser beam as a heat source, the lap welding and the irradiation position of the laser beam are appropriately set so that the butt joint is performed. It is an object of the present invention to provide a laser lap welding method capable of obtaining a joint having the same mechanical properties and paintability as a joint.

[0011]

According to a first aspect of the present invention, there is provided a laser lap welding method according to the first aspect of the present invention, wherein two metal plates are overlapped with each other, and a laser beam is used as a welding heat source. Is a laser lap welding method of irradiating the overlap portion of the plate and performing fusion welding, wherein the laser lap welding is performed in a state where the ends of the two plates are pressed against each other in the thickness direction, and the lap welding is performed at the time of melting. It is characterized in that all parts are melted.

According to the present invention, the two plates are welded by laser welding in a state where the ends of the two plates are pressed against each other in the plate thickness direction so that there is no overlapped portion that does not melt during welding. The end of the plate moves in the direction in which the positions in the plate thickness direction coincide with each other by the pressing, and the joint shape after welding becomes equal to the joint shape in butt welding.

According to the laser lap welding method of the present invention, the ends of two metal plates are overlapped with each other, and a laser beam as a welding heat source is applied to the overlapped portions of the plates to perform fusion welding. A laser lap welding method, wherein the overlap margin of the plates is set to 40% of the total thickness of the two plates and the beam spot diameter at the laser irradiation part, whichever is smaller, and The center of the spot of the laser beam is located in the overlapping portion between the ends of the two plates when viewed from the plate thickness direction.

According to the present invention, by forming a lap joint with an appropriate lap allowance, it becomes possible to perform welding by irradiating a laser beam so that there is no overlapped portion that does not melt. Also, there is no need to perform any special treatment on each end face of the metal plate to be joined, and joint characteristics equivalent to butt welding can be obtained.

Next, the limitation of the overlapping margin will be described. When two metal plates are overlapped and welded, the penetration depth is, of course, within the range of the sum of the plate thicknesses of both plates (through plate thickness).

In laser welding, in penetration welding in which the sum of the thicknesses of the two plates becomes the penetration depth, for example, the penetration width (penetration plate thickness) is 2 mm and the fusion width is 1 mm or less. The aspect ratio (penetration depth / melt width) is 2 or more.

In general, the melting width of the laser welded portion is the largest on the laser irradiation side surface, and becomes narrower from the surface in the thickness direction. Approximately 50 of the total thickness of the sheets
% In many cases.

Actually, as shown in the embodiment described later, in a range where the total thickness of the two plates to be joined is 40% smaller than the beam spot diameter at the laser irradiation part, the overlapping is not performed. By setting the margin to 40% or less of the total thickness, it is possible to melt the entire overlapped portion at the time of laser welding and not to leave the overlapped portion that does not melt after welding.

When the thickness of the plate to be joined is large and 40% of the total thickness is larger than the beam spot diameter at the laser irradiation part, there is a possibility that an overlapped portion which does not melt after welding may remain. The overlap margin was set to a range smaller than the beam spot diameter at the laser irradiation part.

Incidentally, many experiments were actually conducted, and it was concluded that laser welding for completely melting the overlapped portion was possible by setting the overlap margin within the range of the present invention. As described above, in the lap joint in which the entire lap portion between the metal plates is melted (fused), mechanical properties such as strength and formability equivalent to those of the butt joint can be obtained. There is no problem that unprocessed portions remain.

Next, the irradiation position of the laser beam will be described. As described above, the irradiating position of the laser beam is also an important parameter for performing lap welding in which no lap portion remains.

As the irradiation position of the laser beam, the center of the overlapping portion of the metal plate is considered to be an ideal position.
The inventors have repeated experiments on the allowable range of the laser beam irradiation position in various joints. As a result, when the beam spot center is located between the end faces of the two superposed metal plates, that is, the laser beam spot center Is set in the overlapped portion between the ends of the two plates viewed from the plate thickness direction, the overlapped portion is completely melted (fusion welding) by adjusting conditions such as laser output and welding speed. ) Was concluded that welding was possible.

For this reason, it is required that the center of the laser beam spot is positioned in the overlapping portion between the ends of the two plates when viewed from the plate thickness direction, and the laser beam is irradiated. Next, according to a third aspect of the present invention, in the configuration of the second aspect, the welding is performed in a state where the joining ends of the two plates are pressed against each other in a plate thickness direction. It is characterized by the following.

By pressing the ends to be joined together in the thickness direction, defects can be reduced and reliability can be increased. That is, when the ends to be joined are pressed in the thickness direction, the relationship between the ends of the respective plates constituting the overlapped portion becomes closer to the abutting state at the time of melting, so that further improvement in characteristics can be expected. .

[0025]

Next, embodiments of the present invention will be described with reference to the drawings. First, as shown in FIG. 1, the ends of the steel plates 1 and 2 to be welded are vertically overlapped. At this time,
The end of the upper steel plate 1 is pressed toward the lower steel plate 2.

Here, for example, the two steel plates 1,
2 are 0.7 mm, the sum of the thicknesses of the two plates 1 and 2 is D = 1.4 mm. Therefore, the overlap allowance x is 1.4 × 0. 4 = 0.56 mm or less. It is assumed that the diameter φ of the beam spot at the laser irradiation unit 4 is larger than 0.56 mm.

Next, the center of the spot of the laser beam 5 is set at the position of the overlapping portion 3 when viewed from above (in the thickness direction). 3 is melted and welded.

Thus, the two steel plates 1 and 2 are joined,
The joint as shown in FIG. 2 is formed. Thus, only by setting the overlap margin x and the irradiation position of the laser beam 5,
The entire overlapping portion 3 is melted and the two steel plates 1 and 2 are joined.

For this reason, in the laser welding according to the present embodiment, the entire lap portion 3 between the metal plates is melted (fused), and a lap joint in which the unmelted lap portion does not remain as in the related art is obtained. As a result, even if a lap joint having good welding workability is adopted, mechanical properties such as strength and formability equivalent to those of a butt joint can be obtained based on the present invention, and an untreated portion can be formed even when coating. There is no problem of remaining.

It is preferable to perform welding while pressing the upper steel plate 1 against the lower steel plate 2. For example, as shown in FIG. 3, the lower steel plate 2 and the upper steel plate 1 are
And press the upper steel plate 2 in the direction of arrow A to perform laser welding.

In this case, as shown in FIG. 4, as the material is melted, the upper steel plate 1 descends, and a welding state close to butt welding is obtained. The pressing force of the upper steel sheet 1 is not particularly limited. However, in the case of laser welding of a thin steel sheet having a thickness of 2 mm or less to which the present invention has a great effect, the distance (L in FIG. 3) from the welding line to the pressing position is set. It is preferable that the pressing force per unit width be 1 kg / cm or more.

Although the above embodiments have been described assuming that the plate thicknesses d1 and d2 of the two metal plates 1 and 2 to be welded are equal, the same applies to the case where the plate thicknesses d1 and d2 are different from each other.

[0033]

Next, examples of the present invention will be described. The test material (metal plate) and welding conditions were as follows, and welding was performed by changing the overlap margin x and the beam irradiation position according to the plate thickness d and the beam spot diameter φ.

Material: Low carbon steel sheet SPCC (thickness 0.7-
2.0 mm) Laser output: 4-5 kW Welding speed: 4-6 m / min, Shielding gas: Ar (20 l / min) Condensing optical system: Parabolic mirror (focal length: 10 inches) Defocus distance: +1 0.5 mm Beam spot diameter on the steel sheet surface: 0.62 mm The results are shown in Tables 1 and 2 below.

[0035]

[Table 1]

[0036]

[Table 2]

Here, the joint after welding was evaluated by observing the bead appearance and cross-section, and conducting a tensile test (JISZ2201,
No. 5 test piece) and Erichsen test (JISZ2247,
No. 2 test piece).

The test pieces of both steel sheets to be joined have the same shape,
That is, the thicknesses of both steel plates were equal, and a weld bead was arranged at the center of the parallel portion on the overlapped portion in the joint tensile test, and a weld bead was arranged at the center of the overhang portion in the joint Erichsen test.

In Tables 1 and 2, a value of 90% or more of the base material of the tensile strength was evaluated as ○. Further, in Tables 1 and 2, the Erichsen value was evaluated as ７０ when the value was 70% or more of the base material. Here, since the beam spot diameter φ is 0.62 mm in the present embodiment, when the plate thickness is 0.775 mm or more, the beam spot diameter φ is smaller than 40% of the total thickness of the two plates to be joined. Becomes

As shown in Examples 1 to 11 in Table 1, the overlap margin x is set to 40% of the total thickness D or the beam spot diameter φ (0.62 mm), whichever is smaller. And the spot center P of the laser beam 5
When the beam irradiation position is adjusted so that it is located between the end of the steel plate 1 stacked on the upper side and the end of the steel plate 2 stacked on the lower side,
It can be seen that a joint having excellent properties with high tensile strength and Erichsen value without overlapping margins and welding defects in the overlapping portion 3 is obtained.

Here, the beam irradiation position is a distance from the end face e of the upper plate 1 to the spot center P in FIG. 1 and a value in which the distance from the end face e to the overlapping portion 3 side is positive. .

On the other hand, Comparative Examples 12, 14, 16, and
As shown in FIG. 18, when the beam irradiation position is not appropriate, that is, since the center P of the beam spot is not in the overlapped portion 3 between the steel plate ends, even if the thickness of the two plates joining the overlap allowance x is large. 40% of total value or beam spot diameter φ
It can be seen that even if the dimension is smaller than (0.62 mm), the burn-through or the overlapped portion remains, and the tensile strength and Erichsen value are lower than those of the base material.

In Table 2, Comparative Examples 13, 15, 17,
As shown in FIG. 19, even if the overlap allowance x is set to be larger than the range of the present application, burn-through or an overlap portion remains,
It can be seen that the tensile strength and the Erichsen value are lower than those of the base material.

For example, as shown in Comparative Examples 17 and 19,
Even if the overlap allowance x is within 40% of the total thickness, if it is set to be larger than the beam spot diameter φ, an unfused overlap portion remains.

Similarly, as shown in Comparative Example 10, even if the overlap margin x is smaller than the beam spot diameter φ, if the overlap margin is larger than 40% of the total thickness, an unfused overlap portion may occur. I understand.

[0046]

As described above, according to the present invention, even when lap welding having better workability and the like than butt welding using a laser is employed, the thickness of the metal plate to be joined and the laser beam can be reduced. By simply setting the overlap margin and the laser beam irradiation position in accordance with the spot diameter, it is possible to obtain a lap joint having excellent mechanical properties without an unfused (unfused) overlap portion. There is.

[Brief description of the drawings]

FIG. 1 is a diagram showing conditions during laser lap welding according to an embodiment of the present invention.

FIG. 2 is a diagram showing a state after laser lap welding according to the embodiment of the present invention.

FIG. 3 is a diagram showing conditions during laser lap welding according to the embodiment of the present invention.

FIG. 4 is a diagram showing a state after laser lap welding according to the embodiment of the present invention.

FIG. 5 is a diagram showing a state after lap welding in the related art.

FIG. 6 is a view showing another state after the conventional lap welding.

FIG. 7 is a view showing another state after the conventional lap welding.

[Explanation of symbols]

 1, steel plate (metal plate) 3 overlapping part 4 laser irradiation part 5 laser beam 6 pedestal 7 pedestal x overlapping margin φ laser spot diameter P spot center of laser beam d1, d2 sheet thickness

Claims (3)

[Claims] 1. A laser lap welding method in which ends of two metal plates are overlapped with each other, and a laser beam as a welding heat source is applied to the overlap portions of the plates to perform fusion welding. A laser lap welding method, wherein the laser lap welding is performed in a state where the laser lap welding is performed in a state in which the laser lap welding is performed, and all of the overlapped portions are melted at the time of melting. 2. A laser lap welding method in which ends of two metal plates are overlapped with each other, and a laser beam as a welding heat source is applied to the overlapped portions of the plates to perform fusion welding. The beam spot diameter at the laser irradiation part is set to 40% or less of the total thickness of the two plates, whichever is smaller, and the center of the spot of the laser beam is viewed from the plate thickness direction. A laser lap welding method characterized in that the laser lap welding method is positioned within a lap portion between the end portions of the laser beam. 3. The laser lap welding method according to claim 2, wherein the welding is performed in a state in which ends of the two plates to be joined are pressed against each other in a plate thickness direction.