JPS63174793A - Method for cutting alloy steel by laser beam - Google Patents

Abstract

PURPOSE:To improve the squareness and to prevent the dross from sticking by cutting a material to be cut while cooling directly by flowing liquefied gas and enabling cutting a thick plate at high speed by a continuous laser beam and moreover, preventing a cutting plane from roughing. CONSTITUTION:The direct cooling by a liquid is optimum as a cooling method and especially, the utilization of the gasification latent heat is most effective as this method. In short, the liquefied gas like a liquid N2, for instance, which is gasified at the normal temperature and does not produce a harmful product at the time of coming into contact with the material to be cut with the high temperature is most effective for this purpose. Further, in order to improve a cooling effect, the liquefied gas is directly brought into contact with the material to be cut and besides, the liquid and gasified gas which are brought into contact with the material to be cut are made in a flowing state so as not to stangnate there. Furthermore, when the laser beam irradiates on the material 1 to be cut, a cut groove is formed in a tapered shape and the dross 3 is stuck for it, so it is more effective to carry out the cooling from the rear.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention is a book relating to a method for cutting alloy steels, particularly chromium-containing steels such as chromium steel and stainless steel, using a laser beam.

[Conventional technology]

In general, the method of cutting steel with a laser beam is to install a nozzle whose center axis is the laser beam irradiation axis, and to blow oxygen for cutting at high speed as an assist gas from this nozzle. The most commonly used method for cutting is to melt the metal (and the heat of oxidation reaction caused by oxygen) and remove the molten metal using a high-speed oxygen flow.

Cutting alloy steel requires the assistance of oxygen, as in the case of 3. If an inert gas such as argon or helium is used as an assist gas instead of oxygen.

The cutting ability is reduced by several fractions of a second, and the smoothness of the cut surface cannot be obtained. Therefore, the use of this oxygen is essential for cutting alloy steel.

[Problems to be Solved by the Invention] However, when alloy steel, particularly steel containing chromium as an alloy component, is cut using oxygen as an assist gas, the following serious drawbacks occur.

(1) The cutting groove widens in a tapered shape on the side opposite to the laser beam irradiation side, and cannot be cut straight.

(2) Because it is highly resistant to dross adhesion and is strong.

It takes a lot of effort to clean up the dross.

(3) The smoothness of the cut surface is poor, especially when cutting a small diameter circle, etc.
In cases where the density of the cutting lines is high, a rather good cut surface can be obtained for several tens of cods after cutting is started, but after that, it becomes a state of intense combustion and the unevenness becomes severe, making it impossible to obtain a normal cut surface.

The above problem becomes more noticeable as the thickness of the material to be cut increases. Figure 2 is a diagram showing the experimental results of the present inventor's cutting of stainless steel (5us304 material), which is a typical ROM-containing steel, using a conventional method, and the vertical axis shows the cutting speed. , the horizontal axis indicates the thickness of the material to be cut.

The curve (a) in the figure shows the case of straight-line cutting, and in this case, the density per unit area of the cutting line is small, so that even a continuous laser beam can cut at the speed shown.

On the other hand, the curve (b) shows the relationship between the cutting OT capacity and the plate thickness when a circular cutout with a diameter of 50 mm is made with a beam output of 1 kW. In the case of such circular cutting, the density of cutting lines per unit area is 4 times higher than that of straight cutting, so when cutting with a continuous laser beam, the cut surface becomes extremely rough and becomes 1/3 to 1/3 After the second round, a smooth cut surface cannot be obtained. Therefore, in the experiment, the duty ratio was 35%.

The beam was cut as a pulsed beam of 100 Hz and a peak value of 1 kW by reducing the average beam power. In each case, oxygen was used as the assist gas, and the cutting was performed by jetting it out from a nozzle at a pressure of 311/d.

Further, as shown by the broken line number ζ in the figure, when the plate thickness exceeds 54 mm in both straight cutting and circular cutting, the cutting groove becomes tapered, the straightness deteriorates, and the surface side becomes wider. As the squareness of the cutting groove becomes wider, the amount of dross that adheres to the rough edges also increases, and the rough edges become stronger, requiring finishing with a grinder.

Figure 3 is a cross-sectional view showing this situation, and 1 in the figure
．． 1 is a broken material, 2 is a laser beam, and 3 is dross that is resistant to adhesion. As shown in the figure, the dross resistance 11]1 increases by the amount of the tapered shape.

The above tendency becomes even more pronounced when the density of the cutting lines becomes large, such as when cutting complex shapes other than a single circle or when cutting multiple pieces from a single plate in succession, and it is almost impossible to put it into practical use. It becomes something that cannot become.

The cause of the above phenomenon is not clear, but it is thought to be due to the influence of chromium, one of the components contained in alloy steel.

The molten chromium oxide produced when chromium reacts with oxygen used as an assist gas has a viscosity and lacks fluidity, so it forms t%N on the cut surface, and the heat emitted from this stagnant chromium oxide It is conceivable that the adjacent portion of the cut surface may be melted. This is because the above phenomenon does not occur with steel, and when cutting small diameter circles, rectangles, or complex shapes where the density per unit area of the cutting line is low, the above phenomenon strongly appears. It is also presumed that if the amount of oxygen used as an assist gas is reduced, it will be weakened.

Therefore, the present inventor attempted a method of reducing the amount of oxygen in the assist gas, reducing the duty ratio of the irradiated laser beam by pulse-forming it, and thereby reducing the heat input per unit length of the cutting line. Although the quality of the cut portion could be improved, the cutting speed was extremely slow in both cases, making them impractical. Although this can be improved by increasing the output of the laser beam and reducing the amount of assist gas, the efficiency deteriorates significantly and is not practical.

[Means for solving problems]

Based on the above considerations and experimental results, the inventor of the present invention came up with the idea that the problem could be solved by powerfully cooling the wave-cut object during cutting, and conducted various experiments and studies on cooling methods. The results are shown below.

(1) Required conditions for the cooling method are (a) high cooling efficiency and (b) rapid cooling, but what is suitable for these requirements?

Direct cooling with a liquid is optimal, and it is considered most effective to utilize the latent heat of vaporization of the liquid.

Therefore, the liquid that can be used is other than water.

Liquefied carbon dioxide, liquid oxygen, liquid hydrogen, liquid nitrogen.

Liquefied gases such as liquid argon and liquid helium can be considered.

(2) The conditions required for the cooling material are (a) Absorption even if it enters the laser beam path.

No attenuation.

fo+ Do not adversely affect the optical system for laser beam irradiation and other mechanical parts 1.

(c) The processed product shall not have any negative impact.

) There should be no safety issues.

(e) Easy to obtain and easy to extract.

(to) Be inexpensive.

is possible.

Among the liquids mentioned above, carbon dioxide gas absorbs the laser beam as much as nitrogen, causing a slight decrease in efficiency. When water comes into contact with a hot cutting object, it evaporates into water vapor, and this water vapor exposes the optical system, especially the focusing lens, and damages the expensive optical system. Furthermore, not all of the water evaporates, but most of the water flows down and corrodes mechanical parts such as the workpiece placement table and its driving part. Oxygen tends to promote the shadow of the assist gas, but it can be used as long as the cooling effect can compensate for this. Hydrogen not only poses a fire risk, but also produces water by combining with oxygen in the assist gas, which has the same negative effects on optical systems and other parts as when water itself is used. Argon, helium, and nitrogen are all more suitable than the above-mentioned materials, but among these, argon and helium are expensive, and helium has an extremely low boiling point of around 3°, making it inconvenient to handle. From the above, liquid nitrogen is most suitable as the liquid used in the present invention, but liquid argon, liquid helium, liquid oxygen and liquefied carbon dioxide are also suitable although they generate some low efficiency F.

Can be used. In short, any material may be used as long as it is a liquid droplet of gas that evaporates at room temperature and does not generate any harmful products when it comes into contact with a hot object to be cut.

Next, as a method of supplying the cooling liquid, it is brought into direct contact with the wave cutting material in order to improve the cooling effect.

It is necessary to keep the liquid 1r in a fluid state so that the contacting liquid 1r vaporized gas does not stagnate. Therefore, it is preferable to flow the liquid from a liquid discharge nozzle to the vicinity of the cutting part, to lower the liquid a, or to spray it in the form of a mist.

Further, as previously suggested, since the back side of the cut surface (the side opposite to the laser beam irradiation) is heated more and the tapered G is fused, it is more effective to cool the cut surface from the long side.

〔Example〕

In order to confirm the effects of the present invention, Table 1 shows the results of cutting stainless steel 'A' (5us304 material) with a plate thickness of 6wx using the conventional method and the method of the present invention.

In the experiment, only in the method of the present invention, liquid nitrogen was dropped concentrically around the laser beam irradiation position from the beam irradiation side for about 0.117 min.

Table 1 Continuation of Table 1 It was Noh.

Figure 1 shows similar actual tests for other plate thicknesses (diameter 50W).
It is a diagram showing the results of circular cutting), and similarly to Figure @2, the vertical axis shows the cutting speed and the horizontal axis shows the plate thickness, and shows a curve of the speed at which good cutting is possible. As shown in the figure, a good cut surface can be obtained on a thick plate of 5 f1 or more at almost the same speed as the conventional method for straight cutting.

In addition to this, we conducted experiments with a laser beam output of 1.4 kW, and the cutting speed was approximately 1.4 to 1.
．． It was found that Kuruko is even more effective when using a high-power laser beam, as it was possible to increase the number of laser beams by five times.

Note that the cooling liquefied gas can be supplied not only by dropping it concentrically with the laser beam as in the above embodiment, but also in a direction along the cutting line, so it is suitable for devices where the direction of movement of the laser beam head is limited. may be either front or rear or @ or rear in the direction of travel of the head.

The liquid nitrogen used in the experiment has a boiling point of approximately 77'K (-19
6°C), and does not remain in the cut area but immediately vaporizes. Therefore, the cooling effect is extremely strong due to the direct cooling by the extremely low temperature liquid and the latent heat during vaporization, and the absorption of laser beams is also small, and the vaporized nitrogen gas does not damage the optical system or mechanical parts at all, so this invention is suitable for the present invention. can be said to be an ideal material.

However, as mentioned above, the liquid that can be used is any gas that is liquefied from a gas that is a gas at room temperature and does not generate any harmful products.

In addition, the alloy steel to which the present invention is applied is not limited to general stainless steel, but can be applied to alloy steels developed for heat resistance, low temperature use, etc., and is particularly effective for preventing scratches.

〔Effect of the invention〕

According to the method of the present invention, a thick plate can be cut at high speed with a continuous beam without using a pulsed beam, and the cut surface is not rough, the perpendicularity is good, and there is almost no dross adhesion. Therefore, extremely high quality cutting can be performed with high efficiency = T efficiency. Furthermore, if the supply of the cooling liquefied gas is increased, it becomes possible to use a laser beam with a larger capacity, so it becomes possible to cut a board with a roughness of 1≠.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between plate thickness and cutting speed when using the method of the present invention, FIG. 2 is a diagram showing the same relationship as FIG. 1 when using the conventional method, and FIG. FIG. 3 is a sectional view showing the state of cutting along the broken line in FIG. 2.

Claims (1)

[Claims] 1. A method for cutting alloy steel using a laser beam, in which the material to be cut is directly cooled by flowing liquefied gas. 2. The method for cutting alloy steel according to claim 1, in which liquid nitrogen is used as the liquefied gas. 3. The method for cutting alloy steel according to claim 1 or 2, wherein the liquefied gas is brought into contact with the back surface of the material to be cut.