JPH04253584A - Laser beam cutting method and laser beam machining apparatus - Google Patents

Abstract

PURPOSE:To allow high-speed cutting by changing an optical path length by utilizing the spreading angle of a laser beam introduced to a condenser lens system, thereby varying an incident beam diameter. CONSTITUTION:A material to be cut is cut by introducing the laser beam introduced into a processing head from a laser oscillator while this laser beam is condensed by the condenser lens system in the head. The optical path length of the laser beam introduced into the condenser system is changed by utilizing its spreading angle (diverting angle), by which the incident beam diameter is varied. The incident beam diameter is varied stepless or stepwise. The optical path length from the laser oscillator to the processing head is varied. More preferably the laser beam is set at a focal depth and convergent beam density in this way.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a laser cutting method for cutting a workpiece of a predetermined thickness, such as a metal plate or a plastic plate, into a desired shape using laser light. The present invention relates to a laser cutting method and a laser processing apparatus in which a laser beam guided inside the head is guided onto a material to be cut while being focused by a condensing lens system in the head to cut into a desired shape.

0002

2. Description of the Related Art Conventionally, as shown in FIG. 1, for example, a carbon dioxide laser or other laser beam emitted from a laser oscillator is guided to a processing head while being deflected by a deflection mirror, and a condenser lens in the processing head is used. There is a known laser cutting device that uses a system to focus the beam on the surface of the material to be cut, and cuts the material into a desired shape while ejecting air or oxygen gas from around the beam. . In such a device, for example, Japanese Patent Application Laid-Open No. 63-154285 (Japanese Patent Application No. 61-296684)
As shown in , a meniscus lens or the like is placed in the laser optical path from the laser oscillator to the processing head, and the laser light emitted from the laser oscillator is collimated (parallel rays), so that a constant beam of laser light is always directed to the processing head. However, it is impossible to completely collimate the laser beam, so in conventional devices, the optical path length from the laser oscillator to the condensing lens system is made constant. The laser beam is configured to be focused on the surface of the workpiece with high precision.

0003

[Problem to be Solved by the Invention] In recent years, laser cutting devices have been designed to increase the output of the laser beam and are configured to be able to cut even thick parts. Since the laser beam is configured to be focused on the surface of the workpiece with high accuracy, there is a large difference in the power density of the focused beam between the front surface area and the back surface area of the workpiece.
The thicker the workpiece, the more difficult it becomes to obtain a good cut surface.

For example, when we consider the case of cutting mild steel plates of different thicknesses using oxygen as the cutting gas (assist gas), we find that in cutting thick plates, in addition to reducing the difference in power density in the thickness direction, In order to improve the removal of molten metal by the assist gas, it is required to increase the width of the cutting groove. Particularly when cutting mild steel using oxygen as an assist gas, when the gas pressure is increased to improve the removal of molten metal, the roughness of the cut surface increases and the quality of the cut is significantly degraded. Therefore, as a condition for stabilizing the airflow of the assist gas passing through the cutting groove width up to the lower surface of the cut, it is important to increase the cutting groove width without increasing the airflow. On the other hand, when cutting thin plates, the difference in power density in the thickness direction of the material required for thick plate cutting and the effect of airflow have relatively little effect on cutting quality, and rather the conditions for cutting at high speed are important factors. Become. High-speed cutting is made possible by increasing the power density at the focal point, but if the laser beam output is constant, increasing the power density means decreasing the focal beam diameter at the focal point. This means that the cutting groove width will be made smaller as a result. Therefore, with the conventional method of fixing the beam diameter at the focal point, it is difficult to cut thin to thick materials with optimal quality and speed as long as the same focusing lens is used. be.

SUMMARY OF THE INVENTION In view of the shortcomings of the prior art, it is an object of the present invention to provide a laser cutting method and a laser processing apparatus that make it possible to always obtain a good cut surface depending on the thickness of the member to be cut. .

[0006]

[Means for Solving the Problems] The present invention effectively utilizes spherical aberration caused by the shape of the focusing lens in the processing head and diffraction aberration caused by the beam wavelength, thereby reducing the thickness of the material to be cut. In other words, when cutting a thick plate 20A,
As shown in FIGS. 1 and 3(A), the diameter D of the incident beam guided to the condensing lens system in the head is made small (A) and the thin plate 20B
The depth of focus is increased compared to when processing (see FIG. 3(B)), and as a result, the focused beam diameter d01 becomes larger than d11, and the power density at the focused point decreases, but The change in power density from the upper surface to the lower surface of the cutting (
d01-d02) can be made smaller than (d11-d12). In addition, as the focused beam diameter increases, the cutting groove width increases, and the cutting gas (
The removal of molten metal by the action of assist gas (assist gas) improves the cutting quality.

In addition, in the case of a thin plate, the change in beam power density between the front surface and the back surface of the material to be cut is not as important as in the case of a thick plate, as shown in FIG. 2B. The diameter D is increased (B), specifically, the compound aberration (spherical aberration + diffraction aberration) of the focused beam diameter guided to the surface of the cutting material
It is preferable to change the diameter of the incident beam so that it becomes relatively small, which enables cutting with high power density and high speed cutting.

In this case, the depth of focus F changes in proportion to the lens focal length f, as shown in the following equation, so when the focal length is fixed, the beam diameter changes with respect to the optical path length. The optical path length from the laser oscillator to the processing head is varied by taking advantage of the fact that the laser beam has a divergence angle, and specifically, the optical path length is shortened in the case of a thick plate and lengthened in the case of a thin plate. Good too. F (depth of focus) = f (focal length) / D (incidence beam diameter)
Note that the present invention is not limited only to the thickness of the material to be cut, but must be set in consideration of the material, etc.

[0009]

[Effects of the Invention] As is clear from the above description, the present invention does not always make the optical path length constant as in the prior art, or in other words, does not make the depth of focus or the focused beam density constant. It is characterized in that the most preferable depth of focus and focused beam density are set by varying the optical path length and incident beam diameter in accordance with the thickness of the material.

[0010] As a result, when cutting a thin plate, the focused beam density is increased to enable high-speed cutting, while when cutting a thick plate, the depth of focus is effectively utilized to adjust the depth of focus to the above-mentioned target. By increasing the size according to the thickness of the material to be cut, it is possible to improve cutting quality. Therefore, in the present invention, when cutting a thick plate, emphasis is placed on the quality of the cut surface in consideration of overall quality, but when cutting a thin plate, the quality of the cut surface is extremely poor even if the depth of focus is made shallow, depending on the thickness. In order to avoid deterioration, machining performance (cutting speed) is emphasized.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail by way of example with reference to the drawings. However, the dimensions, materials, shapes, relative positions, etc. of the structural parts described in this example are merely illustrative examples, and are not intended to limit the scope of the present invention, unless otherwise specified. It's nothing more than that. 1st
The figure is a plan configuration diagram of a laser processing apparatus according to an embodiment of the present invention, in which a pair of Y-axis rails 13 and 14 are arranged in parallel, a main frame 11 and a main frame 11 are installed movably between the Y-axis rails 13 and 14. A processing machine main body 10 consisting of a girder 12, a laser oscillator 18 mounted on the main frame 11, Y
A reversing mirror block 15 for optical path length adjustment is mounted on the main frame 11 so as to be movable in the axial direction. Mounted deflection mirror 16
It consists of a processing head 22 that can reciprocate along the X-axis rail 17 attached to the girder 12, and a reversing mirror block 25 for fixing the optical path length.

[0012]The first reversing mirror block 15
is a servo (not shown) that can be displaced in the Y-axis direction in accordance with the optimum optical path length set by an arithmetic circuit (not shown) using input information such as the thickness of the material to be cut, the material, and the focal length of the lens used. A motor etc. are attached. On the other hand, the second mirror block 25 is configured to be movable in the X-axis direction together with the processing head 22.
1/ for the amount of movement of the processing head 22 during cutting operation.
The moving amount of 2, in other words, the moving speed is set to 1/2, so that the optical path length from the oscillator 18 to the processing head 22 is always constant no matter where the processing head 22 moves in the X-axis direction. It seems like it's under control.

As is well known, the processing head 22 incorporates a deflection mirror and a focusing lens (not shown), and can focus the incident beam guided into the head 22 and form an image on the surface of the material to be cut 20. It is composed of

Next, the operation of this embodiment will be briefly explained. First, during the setup operation, in accordance with the thickness of the material to be cut, if the material to be cut 20 is thick, the diameter of the incident beam guided to the condensing lens system in the head 22 is adjusted as shown in FIG. D is (
After the first mirror block 15 is slightly shifted up and down in the figure so that it is located at A), the process proceeds to the cutting process described below.

On the other hand, when processing a thin plate, the incident beam diameter D
After the first mirror block 15 is slightly shifted upward in the figure so that it is located at the position shown in (B), the process proceeds to the cutting process described below. In this case, the movement of the mirror block may be set in two steps or in a plurality of steps, or may be controlled steplessly.

In this state, by oscillating a laser beam from the laser oscillator 21, the oscillator 18 mounted on the main frame 11, the first mirror block 15, and the deflection mirror 16 are all positioned during the cutting operation. It is fixed, so the beam length until it is guided to the deflection mirror does not change. In this state, the second mirror block 25 is moved to 1/2 of the moving speed of the processing head 22.
By following the movement in the X-axis direction at a moving speed of , the optical path length from the oscillator 18 to the processing head 22 is always constant, which enables stable cutting during cutting of the same workpiece 20.

It should be noted that the optical path length changing means may be a method of changing the set distance between the mirror block 25 and the processing head 22 without using the first mirror block 15.

[Brief explanation of the drawing]

FIG. 1 is an aberration graph diagram showing the incident beam diameter and the focused beam diameter on the horizontal and vertical axes, respectively, for explaining the present invention.

FIG. 2 is a configuration plan view of a laser processing apparatus according to an embodiment of the present invention.

FIG. 3 is a basic configuration diagram of the present invention, showing the relationship between the wall thickness of the material to be cut and the beam diameter, where (A) is for thick plate processing, (B)
shows the case of thin plate processing.

[Explanation of symbols]

15 First inversion mirror body 18 Laser oscillator 25 Second inversion mirror body 22 Processing head

Claims (4)

[Claims] 1. A laser cutting method in which a laser beam guided from a laser oscillator into a processing head is guided onto a material to be cut while being focused by a condensing lens system in the head to cut a desired shape, comprising: Based on a variable corresponding to at least the thickness of the material to be cut, the angle of divergence of the laser beam guided to the condensing lens system in the head is used to change the optical path length. Laser cutting method characterized by variable beam diameter [Claim 2]
Claim characterized in that the diameter of the incident beam is varied steplessly or stepwise by changing the optical path length using a divergence angle (divergence angle) of the laser beam in substantially inverse proportion to the wall thickness. Laser cutting method described in 1. 3. A processing device for cutting a desired shape by guiding a laser beam guided into a processing head from a laser oscillator onto a material to be cut while being focused by a condensing lens system within the head. A laser processing device characterized in that the optical path length from the laser oscillator to the processing head is varied based on a variable corresponding to at least the thickness of the material to be cut. 4. The laser processing apparatus according to claim 3, wherein the optical path length is varied steplessly or stepwise in substantially inverse proportion to the wall thickness.