JPS63121813A - Optical system for laser cutting - Google Patents

Abstract

PURPOSE:To enable cutting with good cutting quality by providing a mode conversion optical system which converts the mode of incident laser light so that the maximum energy density is distributed to the outer periphery of laser luminous flux and an energy compression optical system which compresses the energy of the luminous flux. CONSTITUTION:This optical system consists of the mode conversion optical system 10 and energy compression optical system 30. The mode conversion optical system 10 consists of a splitting optical system 1, an optical path conversion optical system 20, and a composition optical system 12. Composite laser light L2 is variable in energy density distribution and shape by adjusting the position of a reflecting mirror 12. For example, when the reflecting mirror 12 is moved to left, the energy density distribution and the section of the luminous flux vary. Namely, the size of the luminous flux can be adjusted regardless of the energy compression optical system 30, so the adjustment of the width of the luminous flux is facilitate greatly. Consequently, a material to be worked on a cut surface is vaporized sufficiently and to fused body sticks on the cut surface of the workpiece 40, so that the cutting with good cutting quality is enabled.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical system used in a laser cutting device that cuts a workpiece using a laser source.

2. Description of the Related Art In a conventional laser cutting optical system, as shown in FIG. 12, a single-mode laser beam (!1), which is a parallel beam of light emitted from a light source (not shown), is incident from the left in the figure. However, the energy of the light beam is compressed by the condensing lens (60) and becomes a laser beam (!2).

Then, the laser beam (!2) is applied to the workpiece (40) placed near the focal point of the lens (60), and the workpiece (40) is cut by evaporating the workpiece. Note that a single mode laser beam is a laser beam whose energy density forms a Gaussian distribution in the cross section of its light beam.

Problem 1 to be solved by the invention By the way, the laser beam (AI) used for cutting, (7
Since 2) is a single mode, the maximum energy density is distributed at the center of the luminous flux, and the energy density is low at the outer periphery of the luminous flux. Such laser light (71), (
72), the energy density of the outer periphery of the laser beam (!2) in contact with the cut surface of the workpiece (40) is low, so it does not evaporate the workpiece on the cut surface, and the heat The molten material may adhere to the cut surface of the workpiece (40), resulting in a dull cutting process.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to provide an optical system for a laser cutting device that can cut a workpiece with good sharpness without causing melt to adhere to the cut surface of the workpiece.

In order to achieve the above object, the optical system for laser cutting of the present invention includes a mode conversion optical system that converts the mode of the incident laser beam so that the maximum energy density is distributed around the outer periphery of the laser beam, and a mode conversion optical system that converts the mode of the incident laser beam so that the maximum energy density is distributed around the outer periphery of the laser beam. It consists of an energy compression optical system that compresses energy.

Effect By adopting the above configuration, the maximum energy density is distributed in the outer periphery of the laser beam that comes into contact with the cut surface of the workpiece, so the workpiece on the cut surface can be sufficiently evaporated and melted. Materials do not stick to the cut surface of the workpiece, allowing for sharp cutting.

EXAMPLES Hereinafter, examples of the optical system for laser cutting of the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a plan view showing an embodiment of the laser cutting optical system of the present invention. As shown in the figure, this optical system includes a mode conversion optical system (10) and an energy compression optical system (30).
). The mode conversion optical system (10) includes a splitting optical system (11), an optical path conversion optical system (20), and a combining optical system (1
It is composed of three optical systems (2). Split optical system (1
1) and the combining optical system (12) are each composed of a triangular prism-shaped reflecting mirror having an isosceles triangular cross section, and the optical path conversion optical system (20) is (21).

(23), (26), (28) and (22), (
It consists of a total of eight mirrors, two sets each of four mirrors: 24), (25), and (27). Energy compression optical system (
30) may be of a prism element system as shown in the figure, which will be described in detail later, or may be a condensing lens as shown in the conventional example (FIG. 12).

A single-mode laser beam (≠1), which is a parallel light beam emitted from a light source (not shown), enters from the left side = 5- in the figure, and is reflected by the reflecting mirror (11) into two directions in the upper and lower directions in the figure. Divided, one side has mirrors (21), (23),
(26) and (28) to convert the reflection into a reflector (
12), and the other mirror (22), (24),
(25) and (27) repeat the reflection to form a reflecting mirror (
12). Then, the two divided beams are combined by a reflecting mirror (12), and the laser beam (-#2) is
The energy of the light beam is directed toward the energy compression optical system (3o), and enters the prism (31) perpendicularly, and the energy of the light beam is compressed in a direction parallel to the plane of the paper and perpendicular to the direction of light propagation in the figure, resulting in a laser beam. Similarly, in the prism (32), the energy of the light beam is compressed in the direction perpendicular to the plane of the paper and becomes a laser beam ($4), which cuts the workpiece (40). .

Next, the mode conversion optical system (1o) will be explained in more detail. The mode conversion optical system (1o) has a first division optical system (11) and a luminous flux optical system (1o) whose maximum energy density is
12).

In the same figure, a splitting optical system (11) and a compression optical system (12) are shown.
) are each composed of a single reflecting mirror with an isosceles triangular cross section, but are not limited to this; for example, each mirror is composed of two plate-shaped mirrors. may be arranged to form two equal sides of an isosceles triangle.

As mentioned earlier, the optical path conversion optical system (20) is composed of (21
).

(23), (26), (28) and (22)
) , (24) , (25) , (Mirror (23) consists of 2 sets of 8 mirrors, 4 mirrors of 27 mm.

The two beams of light reflected at (24) are each mirrored at (26)
, (25), the optical path is reversed. Optical path conversion optical system (20)
is not limited to such a configuration consisting of two sets of mirrors, each with an even number of mirrors, whose optical paths intersect an odd number of times along the way, but also with an odd number of mirrors, as shown in Figure 2. The optical path may be reversed by intersecting the optical path an even number of times (0 times in the figure) on the way.

In Fig. 2, mirrors (24), (25), (26) are used so that the optical paths of the two divided light beams are equal.
), but if the optical path difference is not a problem (for example, if the optical path difference is an integral multiple of the wavelength of the laser light used and the two lights do not weaken each other), a mirror ( 24) at the position (24') shown by the broken line in the figure, remove the mirrors (25) and (26), and place the mirror (24').
The light beam may be directed directly to the combining optical system (12).

In addition, if you want to emit the laser beam (dk2) in the same direction as the incident laser beam (≠1), three mirrors (13), (14), and (15) are used to emit the laser beam (dk2) in the same direction as the incident laser beam (≠1). What is necessary is to reflect the light (t).

Since the incident laser beam (41)U is a single mode, the energy density distribution of the luminous flux has a Gaussian distribution, as shown in Figure 3(a), and the maximum energy density is distributed at the center of the luminous flux. There is. The thick lines in Figures 1 and 2 indicate the area where the maximum energy density is distributed, and as is clear from the figures, the mode conversion optical system (10) causes the maximum energy density to be distributed around the outer periphery of the light beam. . Therefore, the laser beam (t2) whose mode has been converted by the mode conversion optical system (10) is as shown in FIG. 3(b).
It will have an energy density distribution as shown in . Note that the circles or semicircles drawn next to the energy density distribution diagrams in Figure 3 (a) and (+)) are, respectively,
It represents the cross section of the beam of one laser beam (+1), (42).

In addition, the combined laser beam (Member 2, Reflector (12
) can change the energy density distribution and the shape of the luminous flux. For example, the first
When the reflecting mirror (12) is moved to the left from the state shown in the figure or upward from the state shown in FIG. 2, the energy density distribution and the cross section of the light beam become as shown in FIG. 3(C). This allows the thickness of the light beam to be adjusted regardless of the energy compression optical system (30), making it very easy to adjust the width of the light beam.

In this way, the laser beam (≠2) that has passed through the mode conversion optics=#-(10) has a maximum energy density distributed in the outer periphery of the light beam that is in contact with the cut surface of the workpiece (40).

Therefore, compared to the case shown in Fig. 12 in which the energy of the laser beam (τ1) from the light source is directly compressed to cut the workpiece, the laser beam (f2) =
9- It is better to cut by compressing the energy, the workpiece on the cut surface evaporates sufficiently, the molten material does not adhere to the cut surface of the workpiece (40), and it is possible to cut with good sharpness. becomes.

In addition, between the mode conversion optical system (10) and the energy compression optical system (30) in FIG. By arranging another mode conversion optical system in which the system (10) is rotated by 90 degrees, the laser beam (≠2) is further divided into two in the direction perpendicular to the plane of the paper in the figure and combined, and the luminous flux is The laser beam can have a cross section as shown in FIG. In other words, split optical system (
11) and the synthetic optical system (12) are composed of a regular square pyramid reflecting mirror or four triangular plate-shaped mirrors connected in a pyramid shape, and the laser beam (mistake 1) is directed into two directions perpendicular to each other.
direction, for example, by arranging the same optical path conversion optical system (20) = 10- shown in the same figure in the direction perpendicular to the plane of the paper in the same figure, consisting of a first mirror. , the cross section of the light beam is the fourth
The laser beam can be shaped as shown in the figure. As a result, the maximum energy density is distributed at the four corners of the light flux, so no matter what direction the workpiece (40) is cut, the part where the maximum energy density of the light flux is distributed will always be at the four corners of the workpiece (40). 40), and therefore the cutting surface always has good sharpness. In other words, when using a laser beam that is divided into two parts and combined, when cutting in the direction shown in Figure 5(a) (cutting in the direction of the arrow), the part where the maximum energy density of the luminous flux is distributed (black circle) ) are the cut surfaces (41) and (4) of the workpiece (40).
2), but when cutting in the direction shown in FIG. I end up.

On the other hand, when the laser beam is divided into four parts and combined, the fifth
As shown in Figures (C), (d), and (e), no matter what direction the workpiece (40) is cut, the part (black circle) where the maximum energy density of the light beam is distributed is always the workpiece. Cut surfaces (41) and (42) of (40)
Since the cutting edge is in contact with the cutting edge, sharp cutting is always possible.

Alternatively, as shown in FIG. 6, the synthetic optical system (12) may be configured with a condensing lens to condense the divided laser beams to cut the workpiece. That is,
The combining optical system and the energy compression optical system may be configured to be the same. With such a configuration, there is no need to separately provide an optical system for compressing energy, and the device can be made smaller. However, in this case, the optical path conversion optical system (
20), if it is composed of an even number of mirrors, the optical path will cross an even number of times, and if it is composed of an odd number of mirrors, it will illuminate an odd number of times. When cutting a workpiece using laser light,
The energy density of the laser beam needs to be about 10'W/Crn2, and therefore an energy compression optical system is required. By the way, when a condensing lens is used in an energy compression optical system as shown in the conventional example (FIG. 12), there are various failure points as shown below. That is, when the laser beam (!1) is condensed by the condensing lens (60), the laser beam (!2) that hits the workpiece is not a parallel beam, as is clear from FIG. When cutting the workpiece (40), it is limited by the depth, making it difficult to cut the workpiece with an even width in the thickness direction. In addition, the workpiece (40
), the relative distance between the lens (60) and the workpiece (40) must be considered, and focusing becomes complicated. Therefore, in this embodiment, in order to eliminate these drawbacks, the energy compression optical system (30) is
It consists of two prisms (31) and (32).

When the energy of the light beam is compressed by a prism, as shown below, the energy of the parallel light beam is compressed while it remains a parallel light beam, so even when cutting a thick workpiece, it is not limited by the depth, and the energy is reduced in the thickness direction. In addition, since a lens is not used, there is no need to consider the relative distance between the workpiece and the lens. This corresponds to the prisms (31) and (32) in the figure. The apex angle of the prism (50) is α, and the ratio m is, as is well known, mHd7d=5−”rr:/cosα (1
). Moreover, as is clear from the figure, if the incident light beam is a parallel light beam, the exit light beam is also a parallel light beam. Note that β is the refraction angle of the emitted light.

In FIG. 7, when the cross-sectional shape of the incident light beam is circular,
The shapes of the cross sections of the incident light flux and the exit light flux are shown in Fig. 8 (
a) and (b). Therefore, in Fig. 7, if the energy of the emitted light flux is compressed by a prism placed so as to compress the energy of the light flux in the direction perpendicular to the plane of the paper (see Fig. 10), the cross section of the light flux of pressure (≠4) The shapes of (a), (t)) and (C
)become that way.

By the way, according to formula (1), the larger the apex angle α of the prism, the smaller the reduction magnification m becomes. However, if the apex angle α is increased due to critical conditions, etc., the transmission efficiency decreases, so it is not recommended to increase the apex angle α too much. Therefore, in order to obtain a small reduction magnification, we used prisms (31) and (32
) is used to configure an energy compression optical system (30). For example, as shown in FIG. 11, only four sets of energy compression optical systems (30) and prisms that compress the energy of the light beam in eight directions are depicted. In the figure, the angle formed by the prisms is set to be equal to the refraction angle β of the laser beam, so that the laser beam is incident perpendicularly to the incident surface of each prism. With this configuration, the reduction magnification of each prism is expressed by equation (1), so generally, when one prism that compresses the luminous flux in one direction is used, the reduction magnification m' in that direction is m '=mJ'=
(1-n”5in2α)A/2/CO8!α (
2). For example, in the case of Figure 11,! = 4, so m' = m' = (1-n2sin2a)"/c
os' a.

YAG L/- laser (wavelength 10106
When using 0n, each prism of the energy compression optical system (30) should be made of a commonly used material such as BK-7, and the transmittance for the CO2 laser wavelength should be A prism made of material such as KCJL, which has a relatively good resistance, is used.

Considering an example in which a YAG laser is used and BK-7 (refractive index n = 1.5069) is used as the prism material, if 6 sets of prisms are used to compress the luminous flux to 1150 in one direction, (2 ) Find the prism apex angle α from the formula, α=
3q, 13°. Also, the angle formed by the prism, that is, the refraction angle β, is sin β': n5in from Snell's law.
α,, β: 6S, 4S.

becomes.

In this case, the reflectance increases and the proportion of light that passes through the prism decreases, but by applying a reduction coating etc. to the prism, the proportion of light that passes through the prism can be increased. be able to.

Effects of the Invention As described in detail above, the optical system for laser cutting of the present invention includes a mode conversion optical system that converts the mode of the incident laser beam so that the maximum energy density is distributed around the outer periphery of the laser beam. Because the cut surface of the workpiece is in contact with the part where the maximum energy density of the light beam is distributed, the workpiece on the cut surface is completely evaporated and the molten material does not adhere to the cut surface of the workpiece. , enables sharp cutting.

According to embodiments, the shape of the laser beam can be changed by adjusting the position of the coupling optics, so that
The size of the luminous flux can be adjusted independently of the energy compression optical system, making it extremely easy to adjust the luminous flux width.

Furthermore, since the incident laser beam is divided into four parts and combined, the maximum energy density is distributed at the four corners of the laser beam, and no matter what direction the workpiece is cut, it is always possible to cut the workpiece with good sharpness.

Furthermore, since the energy compression optical system is a prism optical system, even thick workpieces can be processed uniformly in the thickness direction. Furthermore, since no condensing lens is used, there is no need to consider the relative distance between the workpiece and the lens, and no complicated focusing is required, making the operation simple.

[Brief explanation of the drawing]

FIG. 1 is a plan view of a laser cutting optical system embodying the present invention. FIG. 2 is a plan view of a modification of the embodiment of the mode conversion optical system. FIG. 3 is a diagram showing the energy density distribution and the shape of the cross section of the beam of laser light in the cross section; (a) shows the laser beam emitted from the light source;
(b) shows a laser beam that is split into two parts by the mode conversion source optical system and is combined, and (C) shows a laser beam whose shape of the light beam is changed by changing the position of the combining optical system. FIG. 4 is a cross-sectional view of a beam of laser light that has been cut into quarters by the mode conversion optical system and combined. Figure 5 shows the direction in which the workpiece is cut. (a) and (b) are the laser beams that are split into two by the mode conversion optical system and combined, and (c) and (d)
. (e) is a diagram showing a case where cutting is performed using a laser beam that is divided into four parts and combined. FIG. 6 is a plan view of another embodiment of the invention. FIG. 7 is a diagram for explaining the principle of an energy compression optical system composed of prisms. Figures 8 and 9 are diagrams showing how the light flux deforms as the energy of the light flux is compressed by the prism. Figure 8 is a circular parallel light flux, and Figure 9 is divided into two by a mode conversion optical system. FIG. FIG. 10 is a perspective view of the energy compression optical system. FIG. 11 is a plan view depicting only the prisms that compress the energy of a luminous flux in one direction in an energy compression optical system composed of 4 sets of 8 prisms. FIG. 12 is a plan view showing a conventional example of an optical system for laser cutting. 10... Mode conversion optical system, 30... Energy compression optical system, Ll... Incident laser beam. Applicant Minolta Camera Co., Ltd. Figure 7 Army Figure 8 Figure q

Claims (1)

[Claims] 1. A laser comprising a mode conversion optical system that converts the mode of an incident laser beam so that the maximum energy density is distributed around the outer periphery of the laser beam, and an energy compression optical system that compresses the energy of the laser beam. Optical system for cutting. 2. The mode conversion optical system includes: a splitting optical system that splits the light beam into at least two parts at a portion having the maximum energy density of the incident laser beam; and an optical path conversion system that reverses the optical path so that the maximum energy density reaches the periphery of the light beam. The optical system for laser cutting according to claim 1, comprising: an optical system; and a combining optical system that combines the divided and inverted light beams. 3. The optical system for laser cutting according to claim 2, wherein the dividing optical system divides the light beam into four parts. 4. The optical system for laser cutting according to claim 2, wherein the combining optical system is movably arranged and has a beam width adjustment function for adjusting the size of the beam. 5. The optical system for laser cutting according to claim 1, wherein the energy compression optical system is a prism optical system. 6. Laser cutting according to claim 5, wherein the prism optical system includes at least one set of a prism that compresses the energy of the light beam in one direction and a prism that compresses the energy of the light beam in a direction perpendicular to that direction. optical system.