JP2001138085A - Laser welding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a good quality weld zone by making the penetration deeper and by preventing generation of blow holes. SOLUTION: In a laser welding, a gas in which carbon dioxide is mixed with an inert gas at a ratio of 80-95 vol.% is used as shielding gases, and the generation of blow holes in the weld zone 9 of a material 7 to be welded or the lowering of toughness are prevented.

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 joining steel materials and the like, and more particularly to the prevention of generation of pores in a weld metal.

[0002]

2. Description of the Related Art A laser welding method generally used as high-speed welding or deep penetration welding is to guide a laser beam generated by a laser oscillation device to a welding torch, and to condense the laser beam in a welding torch. In this method, the material to be welded is irradiated, and the material to be welded 7 is heated, melted, and joined by the irradiated beam energy. The laser beam applied to the material to be welded is narrowed down by a condensing lens, so it has a high energy density 1000 times or more that of arc welding. As a result, a hole is formed on the surface of the material to be welded as a vapor reaction force. The reflection loss of the laser beam entering this hole becomes smaller, the hole becomes gradually deeper, and deep penetration welding can be performed. When performing this laser welding, in order to prevent oxidation of the welded part and to prevent scattered matters such as spatter from attaching to the condenser lens, etc.
The shield gas is jetted from the nozzle at the tip of the welding torch. As the shielding gas, an inert gas such as an argon gas or a helium gas is generally used.

[0003]

Normally, in the laser welding method, argon gas or helium gas is used as a shielding gas, and only the material to be welded is melted without using any additional material. Further, the laser welding method is a welding method having a very high energy density like the electron beam welding method, and has a narrow penetration width and a deep penetration depth. However, pores are generated in the weld metal due to deep penetration and a high solidification rate. For example, laser welding was performed on a mild steel plate having a thickness of 12 mm using 100% argon gas as an inert gas as a shielding gas. As a result, a plurality of pores 10 were formed in a welded portion 9 as shown in FIG.

An object of the present invention is to provide a laser welding method capable of improving such disadvantages, deepening the penetration, preventing generation of pores, and obtaining a high-quality weld.

[0005]

A laser welding method according to the present invention is characterized in that a gas obtained by mixing an inert gas with a carbon dioxide gas in a volume ratio of 80% to 95% is used as a shielding gas.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION In the laser welding method of the present invention, carbon dioxide gas is used as a shielding gas in an inert gas at a volume ratio of 90%.
Laser welding is performed using a mixed gas to improve the absorptivity of the molten metal to a laser beam, increase the flowability of the molten metal, greatly reduce the generation of pores, and deepen the penetration.

[0007]

FIG. 1 is a block diagram of a laser welding apparatus according to an embodiment of the present invention. As shown in the figure, the laser welding device
The laser beam 2 generated by the laser oscillation device 1 is guided to the welding torch 5 by the lens 3 and the mirror 4,
The light is condensed by the converging lens 6 in the inside and is irradiated on the material 7 to be welded. When performing the laser welding, a gas obtained by mixing an inert gas with a carbon dioxide gas at a volume ratio of 80% to 95% is ejected from a nozzle 8 at the tip of the welding torch 6 as a shielding gas.

The reason why a gas obtained by mixing 80% to 95% by volume of an inert gas with a carbon dioxide gas as a shielding gas in the laser welding will be described. As a result of observing the pore generation behavior in the molten metal during laser welding using various shield gases with a real-time X-ray transmission observation device, many bubbles are generated when an inert gas is used as the shield gas, and welding is performed. While pores (defects) were solidified in the metal, it was confirmed that when 100% carbon dioxide gas was used as the shielding gas, almost no bubbles and pores were generated in the molten metal. . When the inert gas is used as the shielding gas as described above, bubbles are generated in the molten metal because the laser beam absorption at the tip of the keyhole formed by melting the material to be welded 7 is disturbed,
As a result, it is considered that the flow of the molten metal becomes irregular, and pores are generated, and the penetration depth becomes unstable. Therefore, laser welding was performed using a shielding gas in which carbon dioxide was mixed at various ratios with argon gas. As a result, when a shielding gas in which argon gas was mixed with carbon dioxide at less than 80% was used, pores were also formed in the weld metal. And a good weld was not obtained. On the other hand, when a shielding gas containing more than 95% of carbon dioxide gas was used, the toughness of the welded portion was reduced due to oxygen dissolved in the weld metal. When the carbon dioxide gas was mixed with the argon gas at 80% to 95%, no porosity was generated in the weld metal, and a high quality weld was obtained without reducing the toughness of the weld. Similar results were obtained when helium gas was used as the inert gas.

[Specific Example 1] As the material 7 to be welded, a plate thickness of 12
mm soft steel plate, and YAG
Using a laser oscillator and a laser having an output of 3.5 kW, a method of moving the workpiece 7 to perform the downward posture, beat-on-plate welding. The moving speed of the workpiece 7 is 5
mm / sec, 95% carbon dioxide gas in argon gas
The mixed shield gas was jetted at a flow rate of 30 L / min. After the welding, pores were observed by X-ray inspection. As a result, no pores were found in the welded portion. In addition, as a result of observing the penetration with a macro test piece of cross section, as shown in FIG. 2, a high-quality welded portion 9 free of pores was obtained.

[Specific Example 2] As the material 7 to be welded, a sheet thickness of 9 m
As shown in FIG. 3, laser welding was performed using a mild steel plate having a thickness of 80% and a shielding gas obtained by mixing 80% of carbon dioxide gas with argon gas under the same conditions as in Example 1. As a result, as shown in FIG. This resulted in penetration welding that melted to the back surface. In addition, it was confirmed by X-ray inspection that almost no pores were observed, although this was due to penetration welding.

[Comparative Example] As the material 7 to be welded,
As a result of performing laser welding using a mild steel plate having a thickness of 100 mm and using 100% argon gas as a shielding gas under the same conditions as in Example 2, partial penetration welding was performed as shown in FIG. Pores 10 were generated. As a result, it was confirmed that the penetration was deepened by mixing 80% to 95% of the carbon dioxide gas into the argon gas as compared with the case where the shielding gas of 100% argon gas was used. This means that the volume ratio of carbon dioxide gas in argon gas is 80% to 95%.
By using the mixed gas as a shielding gas, the absorption rate of the laser beam of the molten metal is improved, the fluidity of the molten metal is increased, the generation of pores is greatly reduced, and the penetration is thought to be deeper. Can be

[0012]

According to the present invention, as described above, pores are generated by using a gas obtained by mixing 80% to 95% by volume of carbon dioxide gas with an inert gas as a shielding gas when performing laser welding. It is possible to obtain a high-quality welded part without lowering the toughness.

In addition, since the penetration of the weld can be deepened, the applicable range of laser welding can be expanded and the quality of the structure can be improved.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a laser welding apparatus according to an embodiment of the present invention.

FIG. 2 is a sectional view of a welded portion obtained by laser-welding a mild steel plate having a thickness of 12 mm in an example.

FIG. 3 is a sectional view of a welded portion obtained by laser welding a mild steel plate having a thickness of 9 mm in an example.

FIG. 4 is a sectional view of a welded portion obtained by laser welding a mild steel plate having a thickness of 9 mm using a shielding gas of 100% argon gas.

FIG. 5 is a sectional view of a welded portion obtained by laser-welding a mild steel plate having a thickness of 12 mm using a shielding gas of 100% argon gas.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Laser oscillation apparatus 2 Laser beam 5 Welding torch 6 Condensing lens 7 Material to be welded 9 Welded part 10 Pore

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Seiji Katayama 2-9, A2-402, Yamada Nishi, Suita-shi, Osaka F-term (reference) 4E001 AA03 CA01 DD02 DD04 DD09 4E068 BA00 CH08 CJ01 CJ06 DA14 DB01

Claims (1)

[Claims] 1. A laser welding method using a gas obtained by mixing an inert gas with a carbon dioxide gas in a volume ratio of 80% to 95% as a shielding gas.