JPH03180286A - Laser beam machining method - Google Patents

Abstract

PURPOSE:To perform machining such as uniform welding and heat treatment of high quality by scanning an object by a square irradiation spot formed by condensing a laser beam having a square cross section. CONSTITUTION:A laser beam medium 11 of a solid laser beam machine 10 is formed by cutting out into a pillarlike body having a square cross section from an optical crystal and both end faces are ground orthogonally to the axial direction. The slid layer beam machine 10 oscillates the laser beam in a resonant condition in the axial direction to progress in the axial direction of the laser beam medium 11 and the laser beam LB having the same square cross section as the laser beam medium 11 is taken out to the outside of a laser beam resonant system from a partial reflection mirror 15 side. The laser beam LB is directed in the desired direction by a bending mirror 21 and then, condensed on the irradiation spot SP on the object 1 located in the vicinity of the focus by a lens 20. The object 1 is scanned in the scanning direction SD by the irradiation spot SP to perform specified machining.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a laser processing method for processing an object by sweeping it with an irradiation spot obtained by focusing a laser beam emitted from a solid-state laser device.

[Conventional technology]

As is well known, solid-state laser devices that use optical crystals such as YAG as the laser medium have the advantage of being simpler in structure and easier to handle than gas lasers.Moreover, recent advances in excitation lamps and water-cooling structures have made it possible to use a variety of compact devices. It is possible to generate high-output pulse oscillations of several hundred W, which is suitable for various types of processing.

Conventionally, solid-state laser devices for such processing have used a rod of optical crystal with a circular cross section as the laser medium, which is housed together with an excitation light source such as a xenon lamp or krypton lamp in an airtight container with a mirror-finished inner surface, and is cooled under powerful water cooling. Quasi-continuous oscillation is performed using pulse oscillation or a Q switch.

During laser processing, the laser beam from this high-output solid-state laser device is focused using a lens or other means, and usually one
An irradiation spot with a high power density in the range of 0 to 10' W/c is created, and this irradiation spot is normally applied at a sweep speed of about 1 to 100 m/sec depending on the processing content such as welding, heat treatment, cutting, etc. Machining is performed by sweeping the object with .

Furthermore, a so-called slab-type solid-state laser device is known as a high-output laser suitable for processing. This uses a flat plate-shaped optical crystal as a laser medium, and as is well known, the laser beam is generated in a resonant state in which the laser beam is totally reflected between a pair of plate surfaces and travels in a zigzag pattern. However, if the laser beam that is extracted from this has the same flat cross section as the laser medium, it is not very convenient in terms of power processing, so it is usually made into a nearly square cross section using a cylindrical lens, etc., and then focused. to create an irradiation spot for processing. Although the method of creating the irradiation spot is different from that of a solid-state laser device in this way, the processing method is the same as in the conventional case of using a rod-shaped solid-state laser device.

(Problem to be solved by the invention) In the processing method using the above-mentioned rod-shaped solid-state laser device,
Since the irradiation spot where the laser beam is focused is circular, there has been a problem in the past that some non-uniformity tends to occur in processing. This will be explained below with reference to FIG.

Fig. 5 (Al is a circular irradiation spot l-5P that pulses a solid-state laser device and focuses a laser beam for butt welding processing, for example, along the welding line in the direction SD of the figure.
The sweep speed at this time is set according to the pulse oscillation frequency so that adjacent irradiation spots SP overlap as shown by the hatching in the figure. If the overlap is too small, welding defects will occur. , although the overlap ratio is quite high, it is still easy for non-uniformity such as fine irregularities to appear in the weld line, and if the sweep speed is reduced until this non-uniformity is no longer recognized, the welding speed will drop significantly. Put it away.

Fig. 5(b) shows a state in which the laser device is continuously oscillated for heat treatment such as hardening, and a circular irradiation spot SP is continuously swept in the direction SO on the heat treatment surface. In this case, it is shown on the right side of the figure. As shown, the irradiation intensity I is always high at the center of the irradiation spot SP and low at the periphery, resulting in uneven heat treatment.If the spot diameter is increased, the unevenness can be improved, but the maximum irradiation intensity must be below the limit required for heat treatment. cannot be lowered.

For this reason, in actual heat treatment processing, it is common to sweep the heat treatment surface multiple times with the irradiation spot 7) SP while sequentially shifting the range as shown in the figure, but at this time, the distribution of the irradiation intensity I is also made uniform. To do this, it is necessary to overlap the sweep ranges slightly as shown by the hunting in the figure. However, controlling the degree of overlapping is actually difficult; if it is too little, for example, the hardening hardness will become uneven in the surface, and if it is too much, the once hardened area will become dull.

Also, when the processing content is cutting, the laser beam is focused so that the irradiation spot SP is even smaller than in the case of Fig. 5 (a), but since the irradiation spot is circular, fine irregularities are likely to appear on the cutting line. It is.

Furthermore, it is desirable to increase the laser beam output as much as possible for cutting, but when a solid-state laser device is operated at high output, the divergence angle of the laser beam increases due to the so-called thermal lens effect of the laser medium, which causes the beam to be focused on a small irradiation spot. As a result, the width of the cutting groove tends to widen, and the generation of dross increases, resulting in an unsightly cut surface.

Processing methods using slab-type solid-state laser devices have the advantage of reducing the thermal lens effect mentioned above and narrowing the divergence angle of the laser beam, but since the cross section of the laser beam is very flat, the above-mentioned method is not suitable for many processing applications. Since it is necessary to once correct the cross-sectional shape using a means such as a cylindrical lens and then condense the light to create an irradiation spot, the optical means for condensing the light onto the irradiation spot becomes complicated and its adjustment is not easy.

Further, since the process of providing the optical crystal with a beveled end face is complicated and is particularly prone to damage, the solid-state laser device tends to be expensive and difficult to handle at the processing site. Furthermore, there are still many issues that need to be resolved before full-scale practical use, such as the problem of burnout of the thermal insulation provided on the m-plane of the optical crystal.

The main object of the present invention is to provide a laser processing method that can alleviate the problems of the conventional method and improve the uniformity of processing. Furthermore, a further object of the method of the present invention is to enable various types of processing to be performed using the same solid-state laser device.

(Means for solving the i!! problem) According to the method of the present invention, this purpose is to oscillate a solid-state laser device in an axial resonance state within the laser medium by using an optical crystal with a rectangular cross section as the laser medium, The cross section of the laser beam is directed in a predetermined direction with respect to the sweep direction of the irradiation spot where the emitted laser beam of the solid-state laser device is condensed, and the object to be processed is swept with the irradiation spot at a sweep speed that corresponds to the oscillation state of the solid-state laser device. This makes them distant relatives.

Furthermore, in order to be able to carry out various types of processing using the same solid-state laser device, it is advantageous to provide an aperture means that narrows the laser beam to a cross section with a predetermined shape and area before it is focused on the irradiation spot. It is desirable that this aperture means be incorporated into the resonance system of the solid-state laser device, and furthermore, it should be replaceable so that the size and shape of the aperture can be selected depending on the processing content, and the cross section of the laser beam with respect to the sweeping direction of the irradiation spot. It is very advantageous to provide an adjustable mounting angle so that the direction of the mounting angle can be adjusted depending on the processing conditions.

The rectangular cross-section of the optical crystal used as the laser medium of the solid-state laser device for the method of the invention is advantageously rectangular with an aspect ratio of up to 4 for many processing operations. When it is necessary to increase the irradiation intensity of the irradiation spot due to welding or cutting, it is possible to increase the processing speed by concentrating the light on the irradiation spot in the cross-sectional direction of the laser beam with the long side of the rectangular cross section as the sweep direction. It is advantageous to increase In addition, if the processing is heat treatment and the irradiation intensity of the irradiation spot may be low,
It is advantageous to focus the laser beam with the short side of the rectangular cross section in the scanning direction of the irradiation spot in order to perform heat treatment over a wide area.

The oscillation state of this solid-state laser device is selected depending on the processing content. For example, if the processing content is welding or cutting,
The solid-state laser device is oscillated in pulses so that two areas adjacent to each other in the sweep direction that are successively irradiated with the irradiation spot in a pulsed manner are almost in contact with each other or partially overlap each other.
This processing is performed at a sweep speed of the irradiation spot according to the frequency of this pulse oscillation.

In addition, if the processing content is heat treatment, a Q-switch or the like is usually incorporated into the solid-state laser device to generate quasi-continuous oscillation, and the laser beam is focused on a relatively large irradiation spot with a sweep speed corresponding to the beam output. Heat treatment is performed by sweeping and heating the object.

[Effect]

The method of the present invention focuses on the fact that the problem of non-uniformity in conventional processing is due to the use of a circular irradiation spot, and uses an optical crystal with a rectangular cross section as the laser medium of a solid-state laser device to generate a laser beam. By taking out a rectangular cross section and sweeping and heating the target with a condensed rectangular irradiation spot, the temperature distribution within the target in the sweep direction and in the direction perpendicular to the sweep is made more uniform than before, resulting in uniform processing. It is something that improves. Furthermore, in the present invention, a solid-state laser device using a laser medium with a rectangular cross section is caused to oscillate in a normal axial resonance state, thereby eliminating the various drawbacks of the slab-type laser device mentioned above and increasing the practicality of the solid-state laser device. To improve usability at the processing site.

It is advantageous for various processing contents to have a rectangular cross section of the laser medium or laser beam used in the method of the present invention.
By appropriately selecting the direction of this rectangular cross section to be focused on the irradiation spot, for example, uniform welding can be performed at high speed with the long sides of the rectangle of the irradiation spot aligned with the sweep direction, or by sweeping this long side. With the setting perpendicular to the direction, it becomes possible to perform uniform heat treatment over a larger area than before.

In an advantageous embodiment of the present invention using an aperture means for narrowing the laser beam to a cross-section of a predetermined shape and area before converging it onto the irradiation spot, it is of course possible to shape the irradiation spot to be most convenient for the processing content. In addition, by narrowing down the area of the laser beam during cutting, etc., it is possible to focus the beam onto a smaller irradiation spot than before. This is because the laser beam can be extracted only from the central portion where the thermal lens effect within the cross section of the laser medium has a small divergence angle, and the laser beam can be focused at a spot where the irradiation intensity is very high to perform good cutting.

〔Example〕

Hereinafter, some practical examples of the method of the present invention will be explained with reference to FIGS. 1 to 4. FIG. 1 is a perspective view showing a first embodiment of the present invention. In this example, an engraving 1 is subjected to welding and heat treatment.

The laser medium 11 for the solid-state laser device 10 is, for example, a columnar body with a rectangular cross section cut from an optical crystal such as YAG that uses normal Nd ions as a laser active substance, and the cross section is several to several tens of squares and long. The diameter is from 100 to several 100 squares, the ratio of the vertical and horizontal dimensions of the cross section is selected to be 1 to 4, preferably 2 to 3, and both end surfaces are polished perpendicular to the axial direction. This laser medium 11
The excitation light source 12, which is a flash lamp such as a xenon lamp, is housed in a closed container and cooled by flowing pure water or the like.

As usual, these are placed at the focal points of the elliptical halves 13a and 13b of the closed container 13, whose inner surfaces are mirror-finished, as shown in the cross-sections of FIGS.

are respectively placed at the focal point of a single elliptical vessel IO, such that in each case the excitation light from the excitation light source 12 is focused into the laser medium 11.

Both end faces of the laser medium 111 are exposed outward from the end face of the sealed container 13, and a total reflection mirror 14 is placed opposite to them.
9 solid-state laser device 2 used in the method of the present invention, in which a partial reflection mirror 15 and a partial reflection mirror 15 are respectively arranged to drive the laser resonant system t#I.
10, unlike in the case of a slab type, the excitation light Ll is oscillated in an axial resonance state in which it always travels in the axial direction of the laser medium 11, and the laser beam LB having the same rectangular cross section as the laser medium 10 is generated as usual. The light is taken out of the laser resonant system from the partial reflection mirror 15 side. This laser beam LB
is directed in a desired direction, usually vertically, by a pendor mirror 21, and then focused by a lens 20 onto an irradiation spora (SP) on the object 1 located near its focal point.

This irradiation spot SP is set to a size according to the processing content by finely adjusting the distance between the condenser lens 2o and the object 1. In addition, by moving the object 1 with respect to the irradiation spot SP (normally, the irradiation spot SP), the specified processing is performed by sweeping the irradiation spot SP in the sweep direction SD shown in the figure. This shows the process of processing.

FIG. 3(a) shows the case of welding, in which the solid-state laser device 10 is turned on by pulsed lighting of the excitation light source 12.
Laser beam LB with a rectangular cross section is oscillated at a repetition frequency of several tens to 200 pulses per second.
The light is focused to an irradiation intensity of about 0' W/cj to form a small rectangular irradiation spora 1-3P of about 1x2 to 4 lines, and the light is focused so that the long side of the rectangle faces the sweep direction SD as shown in the figure. .

The sweep speed of this irradiation spot SP is of course set according to the pulse oscillation frequency of the solid-state laser device IO, but the irradiation intensity within the irradiation spot usually has an elliptical distribution and is low at both ends of the long side of the rectangle. Become! Also in the method of the present invention, the sweep speed is set so that irradiation spots that are sequentially adjacent in the sweep direction are slightly shaped. However, in the case of the present invention, since the irradiated spora) SP is rectangular, the degree of overlap may be smaller than that of the conventional method, and the spot area is usually 10%.
It may be the following. Such a sweep speed is the irradiation spot SP.
The length of the long side varies depending on the length of the long side, but it is usually set in a range of several tens of mm/sec.

As can be seen by comparing FIG. 3(a) with the conventional method shown in FIG. 5(a), since the method of the present invention uses a rectangular irradiation spot, there is little unevenness in heating and good welding can be performed without unevenness on the bead. Furthermore, by orienting the long side of the rectangle of the irradiation spot in the sweeping direction, it is possible to narrow the weld bead and increase the welding speed by at least twice with the same laser output as in the past.

Figure 3 (bl shows the case of heat treatment such as quenching,
In this case, the solid-state laser device lo is customary.

Use a switch to turn the laser beam into a high-frequency oscillation or quasi-continuous oscillation state of 10"'t4/c4.
The irradiation intensity is several to several tens of decimal degrees irradiation spora) focused on the SP and swept at a high speed of usually more than LoomIl/see. In the case of this heat treatment, by using the rectangular irradiation spot according to the present invention, it is possible to perform more uniform heat treatment than in the past, and by making the irradiation spot rectangular and orienting the long side at right angles to the 11 direction, one sweep can be performed. Heat treatment can be applied to a wide area. Furthermore, even in the case of multiple sweeps as shown in the figure, there is no need to overlap the sweep ranges as in the conventional case of Fig. 5).

In FIG. 3(C), the solid-state laser device is oscillated in pulses as in FIG. 3(a), but the sweep speed of the rectangular irradiation spot (SP) is set so that adjacent spots do not overlap and are almost in contact with each other. This mode is suitable when it is desired to increase the processing speed by sweeping a relatively large spot with a lower irradiation intensity than that shown in FIG. 4(a) at high speed.

FIG. 4 shows a second embodiment of the present invention. In this embodiment, an aperture means 16 is used to focus the laser beam LB to be focused on the irradiation spot SP into a cross section with a predetermined shape and area. The aperture means 16 shown in FIG. 3A is, for example, a metal plate having a thickness of several plates, and provided with an opening or aperture 16a having an appropriate shape such as circular, rectangular, or elliptical. Although such aperture means 16 may be inserted into the laser beam LB output from the solid-state laser device 10, it is preferable to insert it into the laser resonant system of the solid-state laser device 10 as shown in the figure.

As can be easily seen, only the laser light passing through the aperture means 16 contributes to laser resonance, so that the solid-state laser device 10 outputs a laser beam LB having the same cross section as the aperture 16a.

This aperture means 16 is replaceable so that an aperture 16a with a shape and area suitable for various processing contents can be selected, and when the shape of the aperture 16a is rectangular or elliptical, the cross section of the laser beam LB focused on the irradiation spot is In order to select the direction of Irradiation spot SP
The procedure for condensing light is the same as in the first embodiment.

In this second embodiment, by selecting the shape and adjusting the angle of the aperture 16a, the irradiation spot SP has an optimal shape and direction for the processing content without being restricted by the cross section of the laser medium 11.
Another important advantage of this embodiment is that the irradiation spot SP can be narrowed down to a much smaller size than the conventional one during cutting or the like. This is because by making the size of the aperture 16a slightly smaller than the cross section of the laser medium 11, the spread angle of the laser beam LB can be made smaller than before.

FIGS. 4(b) and 4(C) are for this explanation. If the cross-sectional dimensions of the laser medium 1r11 are 21x and 21y in the X and y directions, respectively, as shown in the same figure, then the laser medium l
The laser beam LB due to the so-called thermal lens effect within l
The spread angle θ is as shown in FIG. The spread angle θX in the X direction is considerably larger than the spread angle θy in the X direction.

Of course, such a spread angle is not corrected by the optical system such as the lens 20, so that the irradiation spot SP is condensed.
The diameter increases according to the maximum spread angle in the cross section of the laser beam LB. If the laser beam is narrowed down by the aperture 16a in this embodiment, the maximum divergence angle will of course become smaller, but for simplicity, if the aperture is made circular, θX = θy = θ, and the diameter d of the irradiation spot SP is the focal point of the lens 20. It can be expressed by the following equation, where the distance is r.

d−f·θ Therefore, the aperture 16a of this embodiment makes it possible to reduce the spread angle θ and narrow down the diameter d of the irradiation spot. However, if the size of the aperture 16a is made too small, the output of the laser beam LB will decrease, and the spread angle θ will not decrease much as shown in FIG. 4(C). The diameter 2'' of the aperture 16a has an optimum value within a range smaller than the narrower dimension 21y of the cross section of the laser medium 11, depending on the type of processing such as cutting and the material to be processed. The optimal size of the aperture is determined. Under conditions where the aperture size is optimized, the size of the irradiation spot is less than half that of a case without an aperture, and the irradiation intensity is also improved several times.

In this second embodiment, by optimizing the size of the aperture 16a and performing the cutting process by sweeping the object 1 with a well-focused irradiation spot SP, the cutting line is thinner than before and the cut surface is smooth. High-quality cutting is possible, and it is also possible to cut materials that were previously impossible to cut.

〔Effect of the invention〕

As described above, in the method of the present invention, an optical crystal with a rectangular cross section is used as a laser medium to cause a solid-state laser device to oscillate in an axial resonance state within the laser medium, and the cross-section of a laser beam emitted from this solid-state laser device is The light is focused on the irradiation spot while facing in a predetermined direction with respect to the sweep direction of the irradiation spot, and the target is swept at a sweep speed corresponding to the oscillation state of the solid-state laser device at this origin/spot to apply a predetermined force U process. By applying this, the following effects can be obtained.

fa) By sweeping the target with a rectangular irradiation spot made by concentrating a laser beam with a rectangular cross section, the temperature distribution of the spot in the target in the sweep direction and in the direction perpendicular to it is made uniform,
It is possible to perform processes such as welding and heat treatment that are much more uniform and of higher quality than conventional methods.

Note that in the past, it was necessary to set a large overlap between the emission spots during pulse oscillation in order to make the processing uniform in the sweep direction, but with the method of the present invention, such overlap is not necessary or can be done with a small amount. I can do it.

(b) Conventionally, in order to make the machining uniform in the direction perpendicular to the sweep, the output spot was often vibrated at high speed with a vibrating mirror, but in the method of the present invention, such a vibrating mirror is completely unnecessary, and therefore the output spot The optical system for use can be simplified.

(C) The cross section of the laser beam is rectangular, and the long side of the focused irradiation spot is directed in the direction of the sweep, and welding or cutting is performed at a higher speed than before, or the long side is directed in the direction perpendicular to the sweep direction. Uniform heat treatment can be performed over a larger area than before.

(The solid-state laser device used in the method of the present invention uses a laser medium with a rectangular cross section, but unlike the slab type, it oscillates in an axial resonance state, so it is simple in construction, inexpensive, and practical like the conventional mouth-to-throat type. It is expensive and easy to handle at the processing site.

In addition, according to an advantageous embodiment of the method of the present invention, in which an aperture means is incorporated into the solid-state laser device and the laser beam to be focused on the irradiation spot is narrowed down to a cross-section with a desired shape and area, the following effects can be achieved: can be raised.

(e) By appropriately selecting the shape and area of the aperture or adjusting its angle, the irradiation spot can be given the optimal shape and direction for various processing without being restricted by the cross section of the laser medium, such as processing such as welding. The speed can be improved and heat treatment such as hardening can be applied to a wide area.

(f) By oscillating a solid-state laser device at the center of the cross section of the laser medium and extracting a laser beam with a small spread angle, it is possible to focus the light onto an irradiation spot with a very small diameter and high irradiation intensity. By sweeping the spot 7), it is possible to achieve high-quality cutting with a thin cutting line and no unevenness on the cut surface, and the range of application of the cutting process can be expanded to materials that could not be cut in the past.

The method of the present invention can be easily implemented using a solid-state laser device with a simple and practical configuration similar to the conventional rod-type laser device and an optical system for converging light onto the irradiation spot, and can be used for the various processing described above. Through its unique advantages to the content, it can contribute to the further development and popularization of laser processing technology in the future.

[Brief explanation of drawings]

FIGS. 1 to 4 relate to the present invention, with FIG. 1 being a perspective view of a processing device showing a first embodiment of the laser processing method according to the present invention, and FIG. 2 showing some structural details of the solid-state laser device. FIG. 3 is a diagram showing an irradiation spot and its sweeping procedure showing some application examples of the first embodiment, and FIG. 4 is a perspective view of a processing device showing a second embodiment of the method of the present invention. FIG. 2 is a diagram for explaining the spread angle of a laser beam. FIG. 5 is a diagram of the irradiation spot and its sweep procedure in the conventional method. In FIG.
X laser beam, SD: sweep direction of irradiation spot, SP
: Irradiation spot, θ: Laser beam spread angle, l2 // 2nd Qu Ping 3 Figure 4 Qu 5th month

Claims (1)

[Claims] 1) A method for processing an object by sweeping it with an irradiation spot focused on an emitted laser beam of a solid-state laser device, which method uses an optical crystal with a rectangular cross section as a laser medium to process the solid-state laser device. The laser beam is oscillated in an axial resonance state within the laser medium, and the cross section of the laser beam focused on the irradiation spot is directed in a predetermined direction with respect to the sweep direction of the irradiation spot, and the laser beam is aimed at the target at a sweep speed that corresponds to the oscillation state of the solid-state laser device. A laser processing method characterized by performing predetermined processing. 2) A laser processing method according to claim 1, using an aperture means for focusing the laser beam to be focused on the irradiation spot into a cross section with a predetermined shape and area.