JP2957304B2 - Welding method of galvanized steel sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for welding galvanized steel sheets.

[0002]

2. Description of the Related Art Conventionally, for example, many parts of automobile body structural parts have a welded structure of a galvanized steel sheet formed by press forming, and spot welding is mainly used for joining the parts. Lap welding by carbon dioxide laser welding is employed as a construction method. As is well known, this carbon dioxide laser welding excites the free electrons of a metal by irradiating a laser beam to increase the energy density, raise the temperature of that part, and weld the base metal. Since welding can be performed in a non-contact manner, the dimensional restriction of the joint portion is reduced, the welding operation time can be reduced, and the joining strength can be increased. For example, as shown in FIG. 6, when a work 1 formed of a galvanized steel sheet and a work 4 are overlapped and their joints 1a, 4a are joined by carbon dioxide laser welding, a laser beam is set at a predetermined welding position. Irradiate 5a,
The base materials 1c and 4c are welded by the energy. At this time, the base materials 1c and 4c heated by the laser beam 5a are melted to form a molten pool 7, but the heat is transmitted to the nearby plating layers 1b and 4b. And the melting point of iron (153
Since the boiling point (906 ° C.) of zinc is lower than 6.5 ° C.), zinc in the plating layers 1b and 4b around the molten pool 7 evaporates. At this time, since the joint portion 1a and the joint portion 4a are in close contact with each other, the zinc vapor mainly passes through the molten pool 7 and is radiated to the outside.
Molten metal is splashed off. FIG. 7 shows a cross section of the welded portion in this state. FIG. 3 shows the cross section of the welded portion when continuous welding is performed in the direction of the arrow in the figure, and the plating layers 1b, 4b
As a result, the molten metal in the molten pool 7 is repelled by the zinc vapor from which the zinc has evaporated, leaving a cavity 10 in the welded portion 9 of the base materials 1c and 4c, resulting in welding defects.

In order to eliminate the adverse effect of the zinc vapor on the molten pool 7, as shown in FIG.
And then carbon dioxide laser welding of the edge portion 4d of the work 4 is considered. In this case, as compared with the above-described example, the overlapping surface of the joint portion 1a is formed only on one side of the welded portion, so that the adverse effect of the zinc vapor on the molten pool 6 can be reduced. However, since the penetration is reduced, the joining strength is reduced as compared with the lap welding described above. Furthermore, in order to weld the end face of the thin plate, the joint 1a
High precision is required for the shape of the laser beam and the positioning of the laser beam 5a, and the processing cost is increased as compared with the above-described lap welding.

[0004]

In the conventional method of lap welding galvanized steel sheet by carbon dioxide laser welding, welding defects such as cavities are apt to occur in the welded portion due to the effect of zinc vapor, and the joining strength is reduced. In addition, there is a problem that the quality of the product is deteriorated in terms of rust prevention and appearance. Therefore, in order to solve the above problems, in the present invention, when lap welding of galvanized steel sheet by, for example, carbon dioxide laser welding, it is necessary to prevent the zinc vapor evaporated from the plating layer from affecting the molten pool of the base material. It is a technical problem to be solved.

[0005]

A technical means for solving the above-mentioned problem is that a joint which is formed by laminating galvanized steel sheets is sandwiched between a wax which evaporates at a temperature lower than the boiling point of zinc when heated. It is welding after wearing.

[0006]

According to the method of welding a galvanized steel sheet according to the present invention, wax is first vaporized at a predetermined temperature lower than the boiling point of zinc on the overlapped surface of the joint portion by heating during welding, and the vapor is radiated to the outside. Therefore, a gap is formed on the overlapping surface. When the zinc in the plating layer near the molten pool formed on the base material reaches the boiling point, the zinc vapor is diffused to the outside through the gap. Therefore, zinc vapor is prevented from adversely affecting the molten pool of the base material.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 shows a state in which a work 1 on which a galvanized steel plate is press-formed is placed on a jig 2a. At this time, the joint 1a formed on the outer edge of the work 1 has
A wax 3 (also referred to as a vaporizing member), which vaporizes at a predetermined temperature lower than the boiling point of zinc when heated, is applied.
Since this wax is applied in a liquefied state to improve workability, it is dried and solidified after application. Then, as shown in FIG.
a and the joint portion 4a are aligned, the work 1 and the work 4 are fixed by the clamp 2b, and then the laser beam 5a is irradiated from the carbon dioxide laser welding device 5.

Next, FIG. 1 is an enlarged view of the welded portion. In the figure, at a joint portion 1a, 4a of a work 1 and a work 4, a predetermined welding position is irradiated with a laser beam 5a, and the base material 1c, 4c is melted by the energy, thereby forming a molten pool 7. The wax 3 in the vicinity is already vaporized and radiated to the outside, and the gap 6 is formed.

Next, the welding process of the galvanized steel sheet at the joints 1a and 4a will be described with reference to FIG. FIG. 7A shows a state in which the joint portion 4a is irradiated with the laser beam 5a to heat the base material 4c, and a part of the base material 4c has begun to melt.
Then, the heat is transferred from the high temperature portion, and the wax 3 near the melting portion is formed.
Is heated to a predetermined temperature lower than the boiling point of zinc, the wax 3 in that portion is vaporized and diffused to the outside to form a gap 6. Next, FIG. 2B shows a state in which the laser beams 5a are further irradiated, the base materials 4c and 1c are melted, and the molten pool 7 is formed. At this time, the boiling point of zinc is lower than the melting point of iron.
The zinc in the plating layers 1b and 4b around the evaporator evaporates, but the evaporated zinc vapor hardly passes through the molten pool 7.
Dissipated from the gap 6 to the outside. FIG. 3C shows a state in which the base materials 1c and 4c are welded after further irradiation with the laser beam 5a. Thus, the lap welding of the galvanized steel sheet by the carbon dioxide laser welding is completed.

In the above embodiment, the work 1 and the work 4 are welded on the jig 2a. However, as shown in FIG. 5, the work 8 is assembled into a sub-assembly.
Can also be used in the additional punching step of welding. In this case, it is sufficient to apply the wax 3 to the joint portion 8a in advance and then assemble it. As in the above-described embodiment, the quality of the welded portion is improved compared to the conventional example and the occurrence of poor welding is prevented. Can be.

[0011]

As described above, in the lap welding method for a galvanized steel sheet according to the present invention, a vaporizing member that vaporizes at a temperature lower than the boiling point of zinc when heated is provided on a joint formed by laminating the galvanized steel sheets. By welding after being sandwiched, a gap is formed by vaporization of the vaporizing member,
Thereafter, the evaporating zinc vapor is radiated to the outside from the gap, and is prevented from passing through the molten pool. For this reason, there is an effect that zinc vapor does not affect the molten pool of the base material, and the occurrence of poor welding can be eliminated.

[0012]

[Brief description of the drawings]

FIG. 1 is a sectional view showing a lap welding method according to an embodiment of the present invention.

FIG. 2 is a sectional view of a work according to the embodiment of the present invention.

FIG. 3 is a cross-sectional view illustrating a method for welding a workpiece according to an embodiment of the present invention.

FIG. 4 is a sectional view illustrating a lap welding method according to an embodiment of the present invention.

FIG. 5 is a sectional view showing another embodiment of the present invention.

FIG. 6 is a cross-sectional view showing a conventional lap welding method.

FIG. 7 is a cross-sectional view showing a conventional welded portion.

FIG. 8 is a sectional view showing a conventional welding method.

[Explanation of symbols]

 1,4 Work 1a, 4a Joint 1b, 4b Plating layer 3 Wax 5a Laser beam

Claims (1)

(57) [Claims] 1. A method for welding galvanized steel sheets, comprising: inserting a wax that evaporates at a temperature lower than the boiling point of zinc when heated into a joint formed by laminating galvanized steel sheets; Method.