JP2811664B2 - Laser welding method for rustproof steel plate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser welding method for improving the welding quality of a steel sheet whose surface has been rust-proofed by galvanizing or the like.

[0002]

2. Description of the Related Art In recent years, a joining material obtained by butt-welding a thin steel plate with a laser beam has been frequently used as a forming material in an automobile factory. Usually, the allowable amount of the butt gap in laser welding is said to be about 15 to 20% of the plate thickness, and when the welding line is long, it is difficult to maintain the butt gap within the allowable value. Therefore, a technique has been developed in which a filler wire is fed to the butt gap, and the filler wire and the material to be welded are irradiated with laser light to perform welding. As prior art related to this, for example, Japanese Patent Publication No. 63-325
No. 54 is known.

[0003] When oxygen or nitrogen in the atmosphere intrudes into the metal melted by the laser beam irradiation, the properties of the weld metal are hindered. Shielding gas is supplied to shut off. Ar, Ar,
There are He, CO _2, or a mixed gas thereof, which is selected according to the material of the workpiece.

[0004] From the viewpoint of energy saving, automobiles are required to be reduced in weight, and as one of measures to reduce the weight, thin steel plates are often used as a material of a body. Corrosion resistance of thin steel plates poses a problem, and therefore, rust-preventive steel plates whose surfaces have been subjected to a rust-preventive treatment such as galvanization have been widely used for automobile bodies. As a result, the corrosion resistance of the thin steel plate is significantly increased, and the durability of the body is greatly improved.

[0005]

However, in the case of laser welding a rust-preventive steel plate which has been subjected to a rust-preventive treatment such as galvanization, the following problems have occurred. When a rust-proof steel plate is welded by the method described in the above-mentioned publication, zinc having a lower melting point than iron is rapidly heated and evaporated by laser light irradiation, and the evaporated zinc is in a plasma state. To create a plasma wall. Therefore, a phenomenon occurs in which the filler wire is melted by the wall of the plasma just before heading toward the molten pool, and the melting of the filler wire becomes unstable. Therefore, the occurrence of spatter increases, and a spherical bulge is formed in the middle of the weld bead, or the weld bead is formed with a sink bead (concave bead).
There was a problem of becoming.

An object of the present invention is to provide a laser welding method capable of improving the welding quality of a rust-proof steel sheet whose surface has been subjected to a rust-proof treatment such as galvanization.

[0007]

The laser welding method for a rustproof steel plate of the present invention, which achieves the above object, comprises the following method. The end of one rust-proof steel plate and the end of the other rust-proof steel plate are butted, and while the filler wire is being fed into the gap formed at the butted portion, the butted portion is irradiated with laser light, What is claimed is: 1. A laser welding method for a rust-proof steel plate which performs butt welding by supplying a shielding gas to a melting portion, wherein the shielding gas is supplied to both a welding nozzle and a side nozzle of a torch, and a shielding gas and a side nozzle of the welding nozzle are provided. And injecting the shielding gas from the side nozzle from the same direction as the feed direction of the filler wire, while injecting the shielding gas toward the molten portion of the rust-preventive steel sheet. .

[0008]

According to the laser welding method of the present invention, since the shielding gas from the side nozzle is injected from the same direction as the direction in which the filler wire is fed, the laser beam is applied to evaporate zinc and the like. The resulting plasma wall is blown away from the filler wire by the shielding gas. Therefore, the phenomenon that the filler wire is melted just before heading for the molten pool is eliminated, and the melting of the filler wire is maintained in a stable state. In addition, since the shielding gas is injected from both the welding nozzle and the side nozzle of the torch, the injection of the shielding gas from the side nozzle is not too strong, and the occurrence of sink beads is also eliminated. Therefore, a spherical bulge can be formed in the middle of the weld bead, and on the contrary, the occurrence of sink of the weld bead is eliminated,
The quality of the laser weld is improved.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the laser welding method for rustproof steel sheets according to the present invention will be described below with reference to the drawings.

FIGS. 1 to 3 show an embodiment of the present invention, particularly an example applied to a thin steel plate used for a body of an automobile. FIG. 1 shows an outline of a laser welding apparatus for carrying out the present invention. In FIG. 1, reference numeral 1 denotes a rust-preventive steel plate having a surface plated with zinc, and reference numeral 2 denotes a rust-preventive steel plate having a surface coated with zinc. A shear-cut end face of the rustproof steel sheet 1;
The shear-cut end face of the rust-preventive steel plate 2 is butted. A butt gap S is formed between the end face of the rust-proof steel sheet 1 and the end face of the rust-proof steel sheet 2 as shown in FIG.

A torch 12 having a condensing lens 11 is located immediately above the butted portion of the rust-proof steel plate 1 and the rust-proof steel plate 2. Laser light L output from a laser oscillator (not shown) is converged by a condenser lens 11 and its focal point is adjusted so as to come to an abutting portion. During welding,
The filler wire 3 is automatically fed into a butt gap S between the rust-preventive steel plate 1 and the rust-preventive steel plate 2. The torch 12 having the condensing lens 11 and the wire feeding nozzle 16 for feeding the filler wire 3 move integrally in the welding direction. The filler wire 3 is fed from a wire feed nozzle 16 to a butt portion via a wire feed tube 13 attached along the torch 12. The feeding direction of the filler wire 3 is set to be opposite to the welding traveling direction A.

At the lower end of the torch 12, a welding nozzle 14 is located. Below the condenser lens 11 of the torch 12, so that the shielding gas G ₁ from the shielding gas supply pipe 15 is guided. The shielding gas G ₁ introduced into the torch 12 is blown out from the tip of the welding nozzle 14 toward the molten portions of the rust-proof steel plates 1 and 2. Shield gas G ejected from welding nozzle 14
₁ plays a function for mainly blocking the melted portion of the rustproof steel sheet 1 from the atmosphere.

The shield gas G from the shield gas supply pipe 15 is divided into the shield gas G ₁ guided into the torch 12 and the shield gas G guided into the side nozzle 17.
It is diverted into _two . The shielding gas G ₂ guided into the side nozzle 17 feeds the wire from the tip of the side nozzle 17 located immediately above the feed nozzle 16 to the rust-proof steel plates 1, 2.
Is spouted toward the melted portion of. The flow rate of the shield gas G ₂ is, is adjustable by the flow rate regulating valve 18 provided in the branch portion of the shield gas supply pipe 15. Shield gas G ₂ from side nozzle 17
Is set in the same direction as the feed direction of the filler wire 3. The shield gas G ₂ from the side nozzle 17 has a function of blowing off the wall of the plasma P formed by the evaporation of zinc on the surfaces of the rust-proof steel plates 1 and 2 by the irradiation of the laser beam L.

Next, a specific example of a method for laser welding a rustproof steel plate will be described. As shown in FIG. 1, when the thin rust-preventive steel plate 1 and the thin rust-preventive steel plate 2 are set at predetermined positions, laser light L is output from the laser oscillator, and the laser light L passes through the condenser lens 11. Then, it is irradiated to the butted portion with the rust-proof steel plates 1 and 2. At the same time, the filler wire 3 is automatically fed to the portion irradiated with the laser beam L. In this state, the movement of the torch 12 having the condensing lens 11 and the wire feeding nozzle 16 in the welding progress direction is started. When the irradiation of the laser beam L is started, the butted portions of the rust-proof steel plates 1 and 2 are heated and melted, and the filler wire 3 is heated and melted. At the time of welding, the molten metal due to the melting of the filler wire 3 forms a butt gap S between the rust-proof steel plates 1 and 2.
And the butting gap S is filled with the molten metal.

When a rust-preventive steel sheet having a galvanized surface is laser-welded, zinc having a melting point lower than that of iron is rapidly heated by the irradiation of the laser beam L to evaporate, as described in the prior art. Then, the evaporated zinc becomes a plasma state and generates a plasma wall. For this reason, the phenomenon that the filler wire is melted by the plasma wall just before heading for the molten pool occurs, the melting of the filler wire becomes unstable, a spherical bulge is formed in the middle of the weld bead, or the weld bead is concave. Hike beads occur.

[0016] In the present embodiment, as shown in FIG. 2, with jetting shielding gas G ₁ from the welding nozzle 14 of the torch 12, shield gas G ₂ from the side nozzles 17
The above problem is solved by ejecting the filler wire in the same direction as the feeding direction of the filler wire 3. That is,
By injecting the shielding gas G ₂ in the same direction as the feed direction of the filler wire 3, the wall of the plasma P can be blown away by the shielding gas G ₂ in a direction away from the filler wire 3, and the filler wire 3 is melted. The phenomenon that the plasma P is melted by the wall just before going to 25 is eliminated. Further, by ejecting the shielding gas from both the welding nozzle 14 and the side nozzles 17 of the torch 12 to shield ejection strength of the gas G ₂ from the side nozzles 17 can have a suitable value, from the side nozzles 17 the occurrence of sink marks of the weld bead due to the shielding gas G ₂ is too high can be suppressed.

FIG. 4 shows how the flow rate adjusting valve 18 provided at the branch of the shield gas supply pipe 15 is adjusted so that the shield gas (main shield gas) G ₁ from the welding nozzle 14 is adjusted.
And flow rate, indicating the quality of the welded portion in a case where the shielding gas (side shield gas) to change the ratio between the flow rate of G ₂ from the side nozzles 17. In the welding quality tests (a) to (e) of FIG. 4, the total supply amount of the shielding gas to the melting part was fixed at 30 l / min, and each welding quality test was performed ten times.

The welding conditions for performing the welding quality test shown in FIG. 4 were set as follows. Steel plate to be welded Galvanized steel plate Plate thickness 0.8mm Filler wire diameter 0.8mm Lens focal length 7.5 "Focus position + 1.0mm Laser output 3500w Welding speed 3.5m / min Filler wire feeding speed 1.2m / min Filler Wire feeding angle 10-30 °

As shown in FIG. 4, the main shield gas G
₁ 30l / min, if the side shield gas G ₂ 0 and the testing of (i) a plurality of poor weld part weld length 100mm within as ,, Figure 5 and 6 occurs. FIG.
Fig. 6 shows a state where three or more defective welding locations W have occurred within a welding length of 100 mm, and Fig. 6 shows a case where less than three defective welding locations W have occurred within a welding length of 100 mm. As shown in FIG. 7, the welding bead 21 in FIG. 5 and FIG. 6 has the weld bead 21 raised significantly from the surface of the steel plate. As shown in Test (b), the main shield gas G ₁ 2
5 l / min, side shield gas G ₂ at 5 l / min
In the case of setting to, the welding was sometimes good, but the poor welding W shown in FIGS. 5 and 6 still occurred frequently.

Main shield gas G ₁ is 23 l / mi
n, in the case of the side shield gas G ₂ 7l / min and the test (iii), the main shield gas G ₁ 20l /
min, in the case of side shield gas G ₂ to 10l / min and the test (d), it was observed weld bead 22 in all tests as shown in FIG. 8 is good. As shown in Test (e), the main shield gas G ₁ 17l / min, the side shield gas G ₂ 13
When set to 1 / min, sometimes welding is good,
By the side shield gas G ₂ is too strong, as shown in FIG. 9, Hikebido 23 occurred frequently in the weld bead.

[0021] Thus, by optimizing the ratio between the flow rate of the shielding gas G ₂ from the shield gas G ₁ of the flow and side nozzles 17 from the welding nozzle 14, the effect of blocking the molten pool 25 from the atmosphere The effect of blowing off the wall of the plasma P can be reliably maintained, and a good weld bead can be obtained. In the present embodiment, galvanized steel sheets are used as the rust-preventive steel sheets 1 and 2, but the same effect can be obtained in the case of other rust-preventive steel sheets.

[0022]

According to the present invention, since the shielding gas is ejected from the side nozzle in the same direction as the feed direction of the filler wire, the plasma wall formed by evaporation of the rust preventive material by the irradiation of the laser beam is removed. The shielding gas can be blown away from the filler wire, eliminating the phenomenon that the filler wire is melted by the plasma wall just before heading to the molten pool.Maintains stable melting of the filler wire by the laser beam be able to. In addition, since the shield gas is ejected from both the side nozzle and the welding nozzle of the torch, it is possible to prevent the ejection of the shield gas from the side nozzle from being too strong, and it is possible to suppress the occurrence of sink beads.
Therefore, the formation of a spherical bulge in the middle of the weld bead or the formation of a sink bead on the contrary can be suppressed, and the quality of the laser welded portion can be improved.

[Brief description of the drawings]

FIG. 1 is a front view of a laser welding apparatus used to carry out the present invention.

FIG. 2 is a partially enlarged view of FIG.

FIG. 3 is a partial side view of the apparatus of FIG. 1;

FIG. 4 is a characteristic diagram showing welding quality when the ratio of the flow rate of the shield gas from the welding nozzle to the flow rate of the shield gas from the side nozzle in the apparatus of FIG. 1 is changed.

FIG. 5 is a plan view showing an example of a defective weld bead.

FIG. 6 is a plan view showing another example of a defective weld bead.

FIG. 7 is a cross-sectional view of a weld bead at a defective welding portion in FIGS. 5 and 6;

FIG. 8 is a cross-sectional view of a good quality weld bead.

FIG. 9 is a sectional view showing an example of a fillet bead.

[Explanation of symbols]

1, 2 anti-corrosion steel plate 1a, 2a zinc as anti-corrosion material 3 filler wire 11 condensing lens 12 torch 14 welding nozzle 17 side nozzle L laser beam G ₁ shielding gas from welding nozzle G ₂ shielding gas from side nozzle P plasma

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-59-70487 (JP, A) JP-A-59-206190 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B23K 26/00-26/18

Claims (1)

(57) [Claims] An end of one rust-proof steel plate and an end of the other rust-proof steel plate are butted, and a laser beam is applied to the butted portion while feeding a filler wire into a gap formed at the butted portion. A method of laser welding a rust-proof steel plate, which performs a butt welding by supplying a shielding gas to a melting portion of the butt portion, wherein the shielding gas is supplied to both a welding nozzle and a side nozzle of a torch, and Rust prevention, characterized by injecting a shielding gas and a shielding gas of a side nozzle toward a molten portion of a rust-preventive steel plate, and injecting a shielding gas from the side nozzle from the same direction as a feeding direction of the filler wire. Laser welding method for steel sheet.