JPH0768397A - Method for decompression laser beam machining - Google Patents

Abstract

PURPOSE:To eliminate the defect of porosity or the like of a weld zone by reducing the pressure of the atmosphere of a part to be irradiated with the laser beam to the prescribed pressure or less, and feeding the shield gas to deepen the penetration of the laser beam welding. CONSTITUTION:A work 5 is set on a machining table 7 of a decompression chamber 6, and the laser beam 1 is made incident from the top of the decompression chamber 6 and shut off from the atmosphere by a converging lens 4. The decompression chamber 6 is evacuated to the pressure of <=50Torr by a rotary pump or the like, and the inert gas of He, Ar or the like is flowed as a small amount of shield gas to form the inert gas atmosphere in the decompression chamber. Penetration is generated in the part irradiated with the laser beam in the work 5, and the laser beam plasma is generated in the penetration zone. When the pressure is <=50Torr, the penetration 1.5 times that in the atmosphere is obtained, and generation of the porosity can be suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low pressure laser processing method.

[0002]

2. Description of the Related Art In conventional laser welding and heat treatment, processing is performed in the atmosphere or under an atmospheric pressure gas environment such as a shield gas.

[0003]

However, such a conventional method has the following problems. (1) Since the laser processing is performed in the atmosphere, a large laser plasma is generated directly above the welded portion and the heat-treated portion, and this plasma refracts and absorbs the laser beam, limiting the penetration and heat input of the processed portion. This makes deep penetration and welding difficult. (2) Since the formation of the laser plasma is unstable, the quality of the processed portion becomes unstable, defects such as blow holes are likely to occur in the welded portion, and the depth of the heat treatment tends to vary. (3) In the case of an active metal, the shield gas is disturbed due to the instability of the laser plasma, the molten portion is oxidized, and the construction becomes impossible. (4) As a method of solving this, when a vacuum is applied,
Atmospheric pressure is applied to the laser optical parts, the reproducibility of the working conditions is difficult, and a lot of time is required for vacuuming, so that there is no merit for electron beam processing.

The present invention has been proposed in view of the above circumstances, and an object thereof is to provide a low-pressure laser processing method which has good deep penetration even with an active metal, has few defects in the welded portion, and has a high processing speed. And

[0005]

Therefore, according to the present invention, in laser processing, the atmosphere of the laser irradiation portion is set to 50 Torr.
Laser processing is performed in a reduced pressure inert gas atmosphere by supplying a shielding gas such as He or Ar while reducing the pressure to r or less.

[0006]

In the present invention, in order to reduce the laser plasma that deteriorates the quality of laser processing to a level that does not affect the processing, laser processing is performed under a low pressure shield gas.
Also, when selecting the laser gas pressure, since the laser beam can be transmitted in the atmosphere, the high vacuum required for electron beam transmission is not required. Therefore, in welding, select a low pressure value that stabilizes and improves the penetration characteristics. The vacuum pump shall be a low-pressure value that can be supported by a vacuum pump such as a rotary pump. Furthermore, because of the low pressure, impurities may be mixed depending on the workpiece, so as a countermeasure against this, a shield gas (Ar, H
e, N ₂ etc.) to form a low pressure atmosphere. According to such a method of the present invention, the laser beam energy enters the base metal without being consumed and a deep-penetration welded portion is obtained. In addition, since the amount of laser beam energy incident on the base metal becomes constant due to the reduction in plasma, the penetration depth is stable, and a weld portion having no defects can be obtained. Furthermore, because of the low-pressure gas shield, the effect of oxidation of the weld metal is small, and even if it is an especially active metal, the use of a low-pressure inert gas (inert gas) makes it possible to obtain a weld with excellent mechanical properties. can get.

[0007]

1 is a longitudinal sectional view showing a first embodiment of the present invention, FIG. 2 is a vertical sectional view showing a second embodiment thereof, and FIG. FIG. 2 shows the laser processing head in FIG. 2, (A) is a horizontal sectional view, (B) is a vertical sectional view, and FIG. 4 shows the atmospheric pressure and the size of laser plasma in the laser processing shown in FIGS. FIG. 5 is a diagram showing the relationship, and FIG. 5 is a diagram showing the relationship between the atmospheric pressure and the penetration depth in the laser processing according to FIGS.

First, in the first embodiment shown in FIG.
The workpiece 5 is a processing table 7 in a decompression chamber 6 which is a vacuum container.
The laser beam 1 is set on the upper side, is incident from the top plate of the decompression chamber 6, and is blocked from the atmospheric pressure by the focusing lens 4. The decompression chamber 6 is decompressed to 50 Torr or less by a rotary pump or the like, and a small amount of inert gas is caused to flow as a shield gas to form a low-pressure inert gas atmosphere in the decompression chamber 6. A machining table 7 is movable in X, Y and Z directions.

Next, a second embodiment shown in FIG. 2 shows a local decompression laser processing apparatus, in which the workpiece 5 is placed in the atmosphere,
By locally depressurizing only the laser processing part, restrictions due to the shape of the workpiece are reduced. The laser processing head 3 has a vacuum exhaust pipe 10 and a shield gas pipe 11
Are connected to each other and are sealed from the workpiece 5 with a sealing material such as rubber. The laser processing head 3 can be moved along the surface of the workpiece 5, and the seal portion can be pressed with an appropriate force to secure the seal during the movement. Further, an inert gas is shielded between the first-stage sealing portion and the second-stage sealing portion so that atmospheric air (oxygen, nitrogen) is not mixed. Reference numeral 9 is a back seal that seals the lower surface of the processed portion of the workpiece 5.

According to the above first and second embodiments, FIG.
As shown in (A), (B) and (C) of the same figure, the work piece 5 is melted at the portion irradiated with the laser, and the laser plasma 2 is generated at the melted portion. FIG. 4 qualitatively shows the relationship between the size of the laser plasma and the atmospheric pressure at that time, and FIG. 5 shows the atmospheric pressure, the penetration depth, and the porosity generation state at a laser output of 5 Kw.
According to the figure, when the pressure is 50 Torr or less, the penetration is 1.5 times or more as compared with the atmospheric pressure, and the generation of porosity (welding defects, that is, bubbles) is suppressed.

[0011]

According to such a low-pressure laser processing method, the following effects can be obtained. (1) The low pressure (about 50 Torr) of the laser welding atmosphere suppresses the plasma formation immediately above the laser welding, deepens the laser welding penetration, and removes defects such as porosity in the laser welding portion. (2) Taking advantage of the fact that laser welding can be used in the atmosphere, the level under low pressure is about 50 Torr or less, and EB
High vacuum 10 ^-2 to 10 ^-4 T like W (electron beam welding)
A relatively simple equipment can be used without being restricted by equipment such as a diffusion pump and a cryopump for obtaining the orr, a vacuuming time, and the surroundings of the welded portion. (3) Even in future high-power laser (10 Kw or more) welding, the low-pressure gas shield method is effective because the laser plasma according to the method of the present invention increases as the laser output increases.

In short, according to the present invention, in laser processing, the atmosphere of the laser irradiation portion is depressurized to 50 Torr or less, and a shield gas such as He or Ar is supplied to perform laser processing as a depressurized inert gas atmosphere. As a result, a low-pressure laser processing method that has good deep penetration even with an active metal, has few defects in the welded portion, and has a high processing speed can be obtained. Therefore, the present invention is extremely useful industrially.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing a first embodiment of the present invention.

FIG. 2 is a vertical sectional view showing a second embodiment of the present invention.

FIG. 3 shows a laser processing head of the processing machine in FIGS. 1 and 2, where FIG. 3A is a horizontal sectional view, FIG. 3B is a vertical sectional view, and FIG. It is an enlarged view which shows the C section of.

FIG. 4 is a diagram showing the relationship between the atmospheric pressure and the size of laser plasma in the laser processing shown in FIGS.

FIG. 5 is a diagram showing a relationship between an atmospheric pressure and a penetration depth in the laser processing shown in FIGS.

[Explanation of symbols]

 1 Laser Light 2 Laser Plasma 3 Laser Processing Head 4 Focusing Lens 5 Workpiece 6 Decompression Chamber 7 Processing Table 8 Sealing Material 9 Back Seal 10 Vacuum Exhaust Pipe 11 Shield Gas Pipe 12 Shield Gas

Claims (1)

[Claims] 1. In laser processing, the atmosphere of a laser irradiation portion is depressurized to 50 Torr or less, and He, A
A low-pressure laser processing method, wherein laser processing is performed in a low-pressure inert gas atmosphere by supplying a shield gas such as r.