JPH0819886A - Laser beam welding nozzle - Google Patents

Abstract

PURPOSE:To provide a laser beam welding nozzle capable of welding a thick object to be welded in high quality of no blow hole. CONSTITUTION:In the nozzle, which is provided with a means to irradiate a weld zone 1 of an object to be welded with a converged laser beam 6 and a means to inject a shield gas 13 for protecting weld zone, a means 12, which injects an enert gas or mixed thereof inside the converged laser beam 6 toward the weld zone of object to be welded 1 along its center axis, is provide.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a welding nozzle which uses a focused laser beam as heat energy, and more specifically, a laser welding nozzle for welding a material to be welded having a thickness of 3 mm or more with high quality. It is about.

[0002]

2. Description of the Related Art Laser welding is a technique for focusing a laser beam and effectively utilizing the energy thereof. To irradiate a focused thin laser beam on a material to be welded and colliding it with a welding portion. According to the above, the joint portion is heated to a high temperature and melt-welded.

There are various characteristics of this welding, and for example, the following can be mentioned. High-speed welding is possible, and since welding input is small, welding distortion and welding deformation are small. Since deep penetration welding can be performed, it is suitable for welding thick materials to be welded. Since the width of the weld is narrow and the deterioration of the material due to the influence of heat is small, high quality precision welding is possible. Due to these useful characteristics, laser welding is widely used as a joining method for metallic materials.

FIG. 1 is a diagram for explaining a welding method using a laser welding nozzle of the present invention described later. In this laser welding method, the laser beam 6 having high density energy is penetrated through the material to be welded 1 to form the so-called keyhole 3. However, during welding, welding defects caused by bubbles or the like, particularly thick wall When welding the work piece 1 to be welded, blow holes may occur, which may cause a serious problem in quality.

FIG. 4 is a view for explaining the mechanism of blowhole formation in the laser welded portion, in which the material to be welded 1 moves in the direction of the arrow during welding. In the cavity formed by irradiating the welded portion with the laser beam 6, a plasma gas 18 composed of metal ions in which some of the metal atoms are ionized and gas ions in which the atmospheric gas is ionized is generated, and explosive ejection Happens. The plasma gas 18 melts the material to be welded 1 to generate molten metal 2, forms a molten metal flow 16 on one side of the cavity (advancing side of the material to be welded), and forms a molten metal on the surface near the welded portion. Create a molten pool.

When the material to be welded 1 becomes thicker, higher output laser energy is required, and the amount of plasma gas increases, so that the inner diameter and the depth of the generated cavity are increased and the molten metal 2 is generated. The quantity also increases. When the amount of the molten metal 2 increases in this way, it becomes difficult to hold the molten metal 2 with its surface tension, and the molten metal 2 is retained in the cavity.
Part of the inflow and the cavity is closed. In such a state, a part of the plasma gas 18 is trapped in the molten metal 2 and a blow hole 17 is generated.

In order to prevent blowholes generated by the above mechanism, several methods have been conventionally proposed. For example, there is a so-called twin-beam laser welding method (see JP-A-60-240395). In this welding method, the laser beam to be applied is divided into a first laser beam for welding and a second laser beam for shaping the weld metal, and the base metal material is irradiated with the first laser beam, and the second laser beam is applied. By irradiating the molten metal immediately after the irradiation position of the first laser beam with the beam, the flow of the molten metal is stabilized, and by sufficiently discharging the metal vapor, welding defects are prevented.

As another method, a laser welding method has been proposed in which side gas is injected to the inner wall in front of the keyhole (on the side where the molten metal is present). In this method, the side gas is injected to the inner wall of the molten metal to prevent the weld metal from entering the keyhole and stabilize the flow of the weld metal.

However, the above method has the following problems. That is, in the twin-beam laser welding method, it becomes difficult to completely prevent molten metal from penetrating into the cavity as the amount of molten metal increases, and it is not effective as a countermeasure for a thick welded material. Further, since the first laser beam and the second laser beam are distributed, a part of the laser beam supplied from the laser light source is transmitted and the other laser beam is reflected by a transmission mirror in the device. Since it is necessary to provide a condenser mirror for condensing the laser beam, the equipment cost becomes expensive. Furthermore, it is necessary to adjust the irradiation position and output of the second laser beam as the thickness of the material to be welded changes, but the second laser beam, which has a lower output than the first laser beam, is generated by the first laser beam. However, there is a problem that the irradiation position and the output are not accurately adjusted and the shaping of the weld metal tends to be difficult.

On the other hand, in the method of injecting the side gas onto the inner wall of the keyhole, in order to prevent the invasion of the molten metal and stabilize the flow of the molten metal, the injection flow rate of the side gas, the injection position, the injection angle, etc. The range of appropriate conditions for is extremely narrow,
It is difficult to apply in actual operation. Further, it has been confirmed that the side gas injection effect is not exhibited at all when the laser beam has a large output (10 kW or more).

[0011]

In view of the above-mentioned problems of the prior art, the present invention reliably prevents welding defects (blowholes) that are likely to occur when the material to be welded is thick, and It is an object of the present invention to provide a laser welding nozzle capable of obtaining a quality welded portion.

[0012]

As shown in FIG. 4 described above, at the welded portion irradiated with the laser beam 6 in laser welding, the recoil pressure of metal evaporation of the material to be welded 1 and the vapor pressure of evaporated metal cause The depth of the generated cavity increases, and finally the keyhole 3 is formed through the material to be welded 1. When the keyhole 3 is formed, a flow 16 of the weld metal that flows out from the inner surface of the keyhole 3 mainly to the outer surface side of the material 1 to be welded and partly to the inner surface side is generated. A molten pool is formed near the surface of the.

When the material to be welded 1 is thin, the amount of the molten metal 2 flowing out from the inner surface of the keyhole 3 is small and the molten metal 2 is sufficiently retained by its surface tension. It is in a stable state.

As the material to be welded 1 becomes thicker, the amount of molten metal 2 generated increases accordingly. This is laser welding,
Especially in high-speed laser welding, secondary melting due to the jetting heat energy of the plasma gas 18 is small, so the amount of metal to be melted is almost determined by the wall thickness of the material to be welded.
Therefore, when the material to be welded 1 becomes thick and the molten metal 2 increases and the balance between the surface tension of the molten metal and the amount of molten metal is lost, the molten metal 2 begins to enter the cavity. When the molten metal 2 starts to infiltrate, the solidification rate of the welded portion in laser welding is extremely higher than that of other welding, so the plasma gas is easily trapped in the invaded molten metal 2 and blowholes 17 Remains in the weld.

Blowholes remaining in the welded portion in this way
In order to prevent 17, the molten metal 2 should be directed toward the welded portion of the work material 1 inside the laser beam 6 and along the central axis thereof so that the molten metal 2 does not enter even if the amount of generated molten metal 2 increases. The molten metal 2 is prevented from entering the keyhole 3 and the plasma gas 18
It is effective to provide a means for smoothly discharging.

The laser welding nozzle of the present invention has been completed based on the above findings, and its gist is as follows.

That is, as shown in FIG. 1, means for irradiating the welded portion of the workpiece 1 with the focused laser beam 6 and a shield gas for protecting the laser beam and the welded portion.
A laser welding nozzle comprising means for injecting 13 and injecting an inert gas toward the welded portion of the material to be welded 1 inside the focused laser beam 6 and along the central axis thereof. A laser welding nozzle, characterized in that it comprises means 12 for injecting.

[0018]

The structure of the laser welding nozzle of the present invention will be described with reference to the drawings.

FIG. 1 is a vertical cross-sectional view of a laser welding nozzle of the present invention, and a diagram showing flows of gas and molten metal when laser welding is performed using the nozzle. Further, in order to facilitate understanding of the structure of the laser welding nozzle, FIG. 2 shows a horizontal cross-section of the main part of the laser welding nozzle of the present invention. 2 (a) is a sectional view taken along the line AA in FIG.
Shows a sectional view taken along the line BB in FIG. 1.

In laser welding using the laser welding nozzle of the present invention, a laser beam 6 focused from a laser source (not shown) is irradiated from the injection port of the welding torch 4 onto the welded portion of the workpiece 1. To do. Laser beam 6 here
The irradiation target is the irradiation focus 15 on the central axis of the welding torch 4, that is, the central axis of the laser beam 6. The material 1 to be welded, which is irradiated with the laser beam 6, moves in the direction of the arrow shown in the drawing during the welding operation.

Along with the irradiation of the laser beam 6, a keyhole 3 is formed in the welded portion of the workpiece 1 and the generated molten metal 2 becomes a molten metal flow 16 and the welded portion of the workpiece 1 is welded. Create a molten pool near the. Further, from the welding torch 4, in order to protect the laser beam 6 and prevent the weld from being contaminated by oxidation and nitriding, a shield gas 13 is jetted so as to cover the outer periphery of the laser beam 6 and the surface of the weld. .

The laser welding nozzle of the present invention is characterized in that, in addition to the shield gas (hereinafter referred to as the first gas) 13, a gas is injected inside the laser beam 6 with its central axis directed toward the irradiation focal point 15. (Hereinafter referred to as the second gas) 14 is to be ejected. This second gas must have a small diameter and a relatively high pressure. As a means for ejecting the second gas 14,
A second gas ejection nozzle 12 protected by a nozzle damage prevention member 10 from the upper part of the conventional welding torch 4 is arranged coaxially with the laser beam 6.

The inert gas (eg, He gas, Ar gas, or mixed gas thereof) supplied from the second gas supply port 11 is supplied from the shield gas supply port 5 attached to the welding torch 4. The inside of the laser beam 6 which is covered with one gas 13 and is irradiated is directed toward the irradiation focus 15 to form a second gas.
It becomes 14 and erupts. The reason why the second gas 14 can be ejected coaxially inside the laser beam 6 is that the laser mode is the ring mode (donut type). In addition, the tip of the second gas ejection nozzle 12 prevents diffusion from the tip of the gas nozzle, and irradiates a small-diameter gas flow with an irradiation focus 15
In order to maintain the temperature up to the above, it is desirable to use a convergent type mouth in which the inner diameter of the tip portion is narrowed in two steps.

In order to provide the second gas ejection nozzle 12 on the central axis of the welding torch 4, it is necessary to prevent damage from the thermal energy of the laser beam. As shown in FIG. 1, even if the horizontal insertion position of the second gas ejection nozzle 12 is provided above the welding torch 4 so that the laser beam in the converging stage with low energy density is irradiated, thermal damage to the nozzle surface is caused. Can't be avoided. Therefore, the structure of the second gas ejection nozzle 12 is a double pipe structure capable of water cooling the nozzle. That is, as shown in FIGS. 2 and 3, the nozzle damage prevention member 10 is provided with a cooling water pipe 7 that circulates the cooling water from the cooling water supply port 8 to the drainage port 9.

By using the laser welding nozzle having the above-mentioned structure, the gas flow directly above the keyhole 3 of the welded portion is jetted from the jet port of the welding torch 4 over the laser beam 6 and is jetted at a low pressure. And the center of the welding torch, that is, the flow of the small-diameter, high-pressure second gas 14 which is ejected coaxially with the laser beam 6 toward the irradiation focal point 15.

As described above, during the laser welding, the ejection of the plasma gas and the outflow of the molten metal 2 are continuously performed from the keyhole 3 of the welded portion which is irradiated with the laser beam 6.
However, when the balance between the surface tension of the molten metal 2 and the amount of the molten metal is lost, the intrusion of the molten metal 2 into the keyhole 3 occurs. At this time, the second gas 14 jetted from the laser welding nozzle is jetted as a small-diameter high-pressure gas flow toward the irradiation focal point 15 located on the central axis of the keyhole 3, so that the molten metal 2 entering Is pushed back to the inner wall of the keyhole 3 and is prevented from entering the keyhole 3. However, the effect of preventing the invasion of the molten metal exhibited at this time is remarkable in the case of the small-diameter gas flow.

When the ejection diameter of the second gas 14 becomes large, on the contrary, the molten metal flow 16 in the vicinity of the welded portion may be disturbed to promote the invasion of the molten metal, so that its action is deteriorated. Therefore, the ejection diameter of the second gas 14 is preferably as small as possible, and the guideline is equal to or smaller than the inner diameter of the keyhole.

When welding is performed using the laser welding nozzle having the above structure, the material to be welded 1 transferred in the direction of the arrow is irradiated with the laser beam 6, and the plasma gas is smoothly discharged from the keyhole 3 and the keyhole 3 is discharged. Since a stable molten metal flow 16 is formed toward the rear of the molten metal 3 and welding proceeds, blowholes are prevented from being generated due to trapping of plasma gas in the molten metal 2, and a high quality laser welded portion can be secured. it can.

[0029]

EXAMPLES The effects of using the laser welding nozzle of the present invention will be described based on examples.

FIG. 3 is a view for explaining the structure of the laser welding used in the embodiment, in which the test material 22 having each wall thickness t was arranged on the welding table 21 and the butt welding was performed. He gas was used as the inert gas of the first gas and the second gas, and when the inner surface was shielded as a comparative example, Ar gas was injected from the central portion of the welding table. Each of the test materials 22 is a steel plate having the chemical composition shown in Table 1 and has a wall thickness of 3 mm.
The thick material described above was used.

[0031]

[Table 1]

In this embodiment, the laser has a rated output of 25 kW.
Carbon dioxide gas laser oscillator was used, and all welding was welding to penetrate the keyhole. In addition, as a method of evaluating welds, a method was adopted in which 20 micro-sections were taken from a weld length of 500 mm and the total number of blowholes was compared by micro-observation.

As an example of the present invention which meets the requirements of the present invention,
Test Nos. 1 to 11 were prepared. Of these, Nos. 1 to 4 affected the thickness of the material to be welded, Nos. 5 to 8 affected the welding speed, and Nos. 9 to 11
Is for investigating the influence of the diameter of the second gas ejection nozzle of the method of the present invention.

To compare with the effect of the present invention, test No. 12
~ 23 comparative examples were prepared. The breakdowns are No. 12 to 15 for the effect of the wall thickness of the material to be welded, No. 16 to 19 for the effect of welding speed, and No. 20 to 23 for the case where the side gas used in the past was used. The effect of welding speed was confirmed.

FIG. 5 is a diagram for explaining the structure in which side gas is injected to the inner wall of the keyhole. In the embodiment, in order to reduce the influence of the He gas injection on the molten metal 2, the side gas nozzle The diameter was 1.0 mmφ.

Table 2 shows the welding conditions and the evaluation results of the welded portion of the present invention, and Table 3 shows the welding conditions and the evaluation results of the welded portion of the comparative example.

[0037]

[Table 2]

[0038]

[Table 3]

As is clear from Tables 2 and 3, in Test Nos. 12 to 15 of the comparative examples, the amount of molten metal generated increases as the wall thickness of the material to be welded increases, so the number of blowholes generated increases. It has increased. On the other hand, in Test Nos. 16 to 19, the welding speed was increased and the generation of blowholes was suppressed, but it was not zero. In addition, in Test Nos. 20 to 23, the welding speed was changed while using the side gas, but compared to Test Nos. 16 to 19, the use of side gas reduced the occurrence of blowholes, but it was 0. did not become.

In the comparative example, blowholes were generated under all conditions, whereas in the example of the present invention, the second gas was supplied at a flow rate of 3.0 to 6.0 liters / min with the injection nozzle having a diameter of 0.8 to 1.6 mm. Then, the thickness of the material to be welded and the welding speed were changed, but no blowhole was generated in the welded portion under any of the conditions. Further, it was confirmed by visual observation that the weld beads were all good. Therefore, by using the laser welding nozzle of the present invention, the discharge of the plasma gas and the flow of the molten metal are made smooth by the action of the small-diameter high-pressure gas flow of the second gas inside the laser beam, and the generation of blow holes is prevented. It turns out that a missing weld can be obtained.

[0041]

EFFECTS OF THE INVENTION By using the laser welding nozzle of the present invention, it is possible to obtain a high quality laser welded portion having a good weld bead appearance and no blowholes, even with a thick material to be welded. Moreover, since the structure is simple, the laser welding nozzle can be manufactured and modified inexpensively.

[Brief description of drawings]

FIG. 1 is a view showing a longitudinal section of a laser welding nozzle of the present invention and an example of a case where laser welding is performed using the same.

FIG. 2 is a view showing a horizontal cross section of a main part of the laser welding nozzle of the present invention shown in FIG. 1, in which (a) is a cross sectional view taken along the line AA and (b) is a cross sectional view taken along the line BB. A cross-sectional view is shown.

FIG. 3 is a diagram illustrating a mode of laser welding used in an example.

FIG. 4 is a diagram illustrating a mechanism in which blow holes are generated in a laser welded portion.

FIG. 5 is a diagram illustrating a configuration when side gas is injected to an inner surface wall of a keyhole in an embodiment.

[Explanation of symbols]

1 ... Material to be welded, 2 ... Molten metal, 3 ... Keyhole,
4 ... Welding torch 5 ... Shield gas (first gas) supply port, 6 ... Laser beam 7 ... Cooling water pipe, 8 ... Cooling water supply port, 9 ... Cooling drainage port 10 ... Damage prevention member, 11 ... Second gas supply port , 12 ... Second gas ejection nozzle 13 ... Shield gas (first gas), 14 ... Second gas, 15
… Irradiation focus 16… Molten metal flow, 17… Blowhole, 18… Plasma gas 21… Welding table, 22… Test material

Claims (1)

[Claims] 1. A laser welding nozzle comprising means for irradiating a welded portion of a material to be welded with a focused laser beam and means for injecting a shield gas for protecting the laser beam and the welded portion. A laser welding nozzle comprising means for injecting an inert gas toward the welded portion of the material to be welded inside the focused laser beam and along the central axis thereof.