JPH07116885A - Method for cutting thick plate with high quality by laser beam - Google Patents

Abstract

PURPOSE:To provide a high quality laser beam cutting method for a thick plate by which reduction of cutting accuracy is prevented by evading generation of self-burning phenomenon and cutting is efficiently and economically carried out. CONSTITUTION:When the thick plate is cut by a laser beam, a surface condition of the plate at a position in immediately front of the cutting position is monitored and cutting is carried out alternatively switching cutting gas in accordance with change of the surface condition as when a hot red heated zone 11 is expanding, the cutting gas is switched from an oxygen gas 15 to an inert gas 14 and when the red heated zone 11 is shrinking, the cutting gas is switched from the inert gas 14 to the oxygen gas 15.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-quality laser cutting method for a thick plate which is applied to dismantling and cutting a large-scale thick structure such as a nuclear power plant.

[0002]

2. Description of the Related Art In laser cutting, it is necessary to blow away the melt from the material to be cut by laser heat.
Conventionally, gas is used. As this gas, there is an inert gas or oxygen, and conventionally, when cutting a thick plate, oxygen, which can increase the cutting ability, has been generally widely used as a cutting gas.

[0003]

As described above, when laser cutting a thick plate, oxygen is used as a cutting gas in order to improve the cutting ability. However, when the plate is thicker than 100 mm, the cutting speed becomes slower, so that oxygen diffuses forward from the cutting position. As a result, a self-burning phenomenon occurs in front of the cutting position, and the burning portion is missing, so that there is a problem that the cutting accuracy is significantly deteriorated.

The present invention has been proposed in view of the above circumstances, and provides an efficient and economical high-quality laser cutting method for thick plates that avoids the occurrence of the self-burning phenomenon and prevents the reduction of cutting accuracy. The purpose is to do.

[0005]

To this end, the present invention monitors the surface condition in front of the cutting position during laser cutting of a thick plate, and when the high-temperature red hot zone spreads, the cutting gas is oxygenated. Is switched to an inert gas, and when the red heat range becomes narrower, the cutting gas is alternately switched from the inert gas to oxygen for cutting.

[0006]

According to this structure, when laser cutting a thick plate, oxygen and an inert gas are alternately supplied as a cutting gas to prevent the self-burning phenomenon due to excess oxygen while supplying oxygen. The ability to cut thick plates can be maintained. Although the cutting ability decreases with an inert gas, the self-burning phenomenon does not occur, so the cutting accuracy does not decrease.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is an overall system diagram thereof. In the above figure, the laser beam 2 emitted from the laser oscillator 1 is reflected by mirrors 3, 5
After that, it is converged by the concave mirror 6 near the surface of the material 8 to be cut. Since the cutting gas is supplied through the nozzle 7, it is necessary to surround the reflection mirror 5 and the concave mirror 6, and for that purpose, the transmission window 4 is provided in the mirror box 16.

Here, 9 is a cutting groove of the material 8 to be cut, 11 is a red heat region slightly in front of the cutting groove 9, 10 is an optical fiber for monitoring, 12 is an image analysis device, 13 is a gas switch, and it is inactive. The cutting gas of the gas cylinder 14 is switched to and introduced into the mirror box 16.

In such an apparatus, a cut groove 9 is formed in the material 8 to be cut by the focused laser beam 2, and a red heat zone 11 is generated around the cut groove 9. Therefore, the portion of the red heat region 11 is observed with the monitoring optical fiber 10. Then, the obtained information is sent to the image analysis device 12, where the size of the red heat zone 11 is judged and the signal is sent to the gas switching device 13 to disconnect either the inert gas cylinder 14 or the oxygen cylinder 15. Gas in mirror box 1
6 is fed to the cutting portion of the material 8 to be cut through the nozzle 7. At that time, since self-burning due to excess oxygen is likely to occur on the surface side, the surface condition in front of the cutting position is monitored with an optical fiber, and when the high-temperature red heat region spreads, an inert gas is supplied, and conversely. When it gets narrower, it supplies oxygen.

[0010]

According to such a method, it is possible to significantly reduce the groove width of the laser cutting portion, which has been very wide as a result of the self-burning phenomenon caused by excess oxygen in the past.

In summary, according to the present invention, when the thick plate is laser-cut, the surface condition in front of the cutting position is monitored, and if the high-temperature red hot zone is widened, the cutting gas is changed from oxygen to an inert gas. If the red hot zone becomes narrower by switching, the cutting gas is switched from inert gas to oxygen alternately to cut, thereby avoiding the occurrence of self-burning phenomenon and preventing a decrease in cutting accuracy. The present invention is extremely useful in industry because it provides a high-quality laser cutting method for thick plates which is economical and economical.

[Brief description of drawings]

FIG. 1 is a system diagram showing a laser cutting method according to an embodiment of the present invention.

[Explanation of symbols]

 1 Laser Oscillator 2 Laser Beam 3 Reflecting Mirror 4 Transmission Window 5 Reflecting Mirror 6 Concave Mirror 7 Nozzle 8 Material to be Cut 9 Cutting Groove 10 Optical Fiber 11 Red Heat Zone 12 Image Analysis Device 13 Gas Switch 14 Inert Cylinder 15 Oxygen Cylinder 16 Mirror Box

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Sumio Mohri 2-1-1 Nihama, Arai-cho, Takasago-shi, Hyogo Mitsubishi Heavy Industries Ltd. Takasago Research Institute

Claims (1)

[Claims] 1. When cutting a thick plate by laser, the surface condition in front of the cutting position is monitored, and if the high-temperature red heat zone spreads, the cutting gas is switched from oxygen to an inert gas, and the red heat zone is changed. If the cutting width becomes narrower, the cutting gas is switched from the inert gas to oxygen alternately to cut, and a high-quality laser cutting method for a thick plate.