JP2014172082A - High-power laser machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide as a high-power laser machine a machine that can compensate a thermal lens characteristic without the necessity of a special drive mechanism and special control mechanism, can readily perform high-precision laser machining, and can be manufactured at a low cost.SOLUTION: In a high-power laser machine having a scraper 2, which includes a full-reflection film, in a laser optical path, a thermal lens action on a converging side exerted by optical components other than the scraper 2 intervened in the laser optical path is canceled out by a thermal lens action on a diffusing side due to a change in a curvature of a reflection surface 2a derived from thermal expansion of the scraper 2 that has absorbed laser light, and a thermal lens characteristic of the entire laser machine is thus compensated.

Description

  The present invention relates to a high-intensity and high-convergence laser processing machine such as a fiber laser or a disk laser used for laser welding or the like, and more particularly to a high-power laser processing machine in which a scraper having a total reflection film is interposed in a laser beam path.

  Laser welding irradiates the surface of the workpiece with a high-power laser beam focused by the condenser lens of the machining head, and moves the irradiation position along the welding site, thereby allowing the workpiece at the irradiated site to move. The material is continuously melted and solidified, and high-density energy can be concentrated in a minute region, so that deep penetration can be achieved with a narrow weld bead width and high-efficiency welding can be performed with a small heat input. There is an advantage. In such laser welding, a high-intensity and high-convergence laser processing machine for a laser wavelength band of 1 μm, such as a fiber laser or a disk laser, is often used. However, it is generally used as an optical component such as a condenser lens or a collimator lens. In particular, a quartz base material with a non-reflective coating is used.

  However, in laser welding, it is generally recognized that the weld quality tends to decrease with increasing distance from the welding start position. This is because, as a thermal lens phenomenon, an optical component intervening in the laser optical path absorbs the laser light and rises in temperature, causing thermal expansion and a change in refractive index to change the focal length of the laser light (usually the focal lens effect causes a focal point). This is because the distance becomes shorter. The absorption of the laser light that leads to this thermal lens phenomenon occurs to some extent even in the quartz base material of the optical component, but the absorption at the non-reflective coating portion on the surface is large. On the other hand, such a high-power laser processing machine also has a problem of overheating of peripheral components due to laser scattered light inside the processing head.

  Conventionally, several means have been proposed in order to cope with the thermal lens phenomenon in a laser beam machine. One of them is that a rotating automatic stage with two sets of temperature sensors is installed above the condenser lens, and the entire upper surface on the laser beam incident side of the condenser lens is scanned by both temperature sensors. The focal length change amount of the condenser lens is calculated, and the focal lens is moved up and down by the automatic focal length adjustment device based on the calculated value, so that the focal point is always connected to the workpiece. It is a system (patent document 1). The other is a laser processing machine having a processing optical path system including a transmission optical element having a positive temperature change rate of refractive index made of zinc selenide or the like, and a refractive index made of barium fluoride or the like in the middle of the processing optical path. This is a system that cancels out the thermal lens characteristics of a converging system that occurs in a transmissive optical element having a positive refractive index temperature change rate by arranging a transmission type thermal lens correction element having a negative temperature change rate (Patent Document 2). . The other one calculates the amount of change in the focal position at the laser light irradiation position based on the magnitude of the laser light output that changes during laser processing, and controls the position of the processing lens based on this amount of change. Alternatively, a bend mirror having a space on the back side is disposed, and the focus position is corrected by elastically deforming the bend mirror by the fluid supply pressure to the space and controlling the curvature (Patent Document 3). ).

Japanese Patent Laid-Open No. 2003-212359 JP 2007-95936 A International Publication WO2009 / 122758

  However, the method of Patent Document 1 requires two sets of temperature sensors, a rotary automatic stage and its driving mechanism, a vertical lens moving mechanism and its control mechanism, and so on, and the cost of the processing head and incidental equipment is high. At the same time, a great deal of labor is required to construct a thermal analysis means for sequentially calculating the temperature measurement value → the temperature distribution of the entire condenser lens → the amount of thermal deformation → the amount of change in focal length. Further, in the method of Patent Document 2, a transmission type lens that is made of a special material such as zinc selenide, and a transmission type thermal lens correction element made of a special material such as barium fluoride, is manufactured. There is a problem that the material cost and the manufacturing cost are extremely high and the practicality is poor. Furthermore, in the method of Patent Document 3, it is necessary to input many various numerical values to the processing control device as setting information regarding processing conditions and thermal lens information from the laser processing mechanism, and to calculate the amount of change in the focal position from the input information. Therefore, it takes a lot of time to construct the operation and control system, and a very special device and control mechanism for deforming the working lens drive and control mechanism and the bend mirror with fluid pressure are required.

  In view of the above circumstances, the present invention can compensate for thermal lens characteristics without requiring a separate drive mechanism or control mechanism as a high-power laser processing machine used for laser welding or the like, thereby facilitating highly accurate laser processing. Another object of the present invention is to provide a device that can be manufactured at low cost and that can suppress overheating of peripheral components due to laser scattered light inside the processing head.

  If the means for solving the above-mentioned problems are shown with reference numerals in the drawings, the invention of claim 1 is a high-power laser beam machine having a scraper 2 having a total reflection film in the laser beam path. The curvature of the reflecting surface 2a due to the thermal expansion of the scraper 2 that has absorbed the laser light L due to the thermal lens action on the convergence side by the optical components (the condensing lens 4, the collimator lens 5 and the protective glass 6) other than the intervening scraper 2. It is characterized in that it is configured to compensate the thermal lens characteristics of the entire laser processing machine by canceling out by the thermal lens action on the diffusion side due to the change.

  According to a second aspect of the present invention, in the high power laser processing machine according to the first aspect, the total reflection film of the scraper 2 is composed of two or more dielectric layers.

  According to a third aspect of the present invention, in the high-power laser processing machine according to the first or second aspect, a plurality of scrapers 2 having a total reflection film are interposed in the laser optical path, and the diffusion side thermal lens action by the scrapers 2 is used. It is assumed that it is set so as to cancel the thermal lens action on the convergence side.

  According to a fourth aspect of the present invention, in the high-power laser processing machine according to any one of the first to third aspects, the inner surface 10a of the processing head 1 in which an optical component including the condenser lens 4 and at least one scraper 2 is mounted. In addition, blasting and blackening are performed.

  According to a fifth aspect of the present invention, in the high-power laser processing machine according to the fourth aspect, the cooling water passage 7 is provided inside the structural members 11 to 13 of the processing head 1 subjected to the blasting process and the blackening process. The heat energy associated with the laser scattered light absorption of the members 11 to 13 is configured to be exhausted by heat exchange with the cooling water flowing through the cooling water passage 7.

  Next, effects of the present invention will be described with reference numerals in the drawings. First, in the high-power laser processing machine according to the first aspect of the present invention, the thermal lens action on the convergence side by the optical components (the condensing lens 4, the collimator lens 5, and the protective glass 6) other than the scraper 2 interposed in the laser optical path is previously obtained. As a scraper 2 having a total reflection film, a curvature change that causes a thermal lens action on the diffusion side corresponding to the thermal lens action on the converging side to the reflecting surface 2a with thermal expansion due to absorption of the laser light L. By using the one that causes the thermal lens action on the converging side and the diffusing side is canceled. Therefore, according to this high-power laser processing machine, the thermal lens characteristics of the entire laser processing machine can be obtained by simply selecting the scraper 2 having the absorption characteristics that cause the above-described change in curvature without requiring separate drive mechanisms and control mechanisms. Since it is compensated, high-precision laser processing can be easily performed, and the laser processing machine can be manufactured at low cost.

  According to the second aspect of the present invention, since the total reflection film of the scraper 2 is composed of two or more dielectric layers, the scraper 2 having the absorption characteristics can be obtained by setting the number of dielectric layers and the layer thickness profile. Easy to manufacture.

  According to the invention of claim 3, since a plurality of scrapers 2 having a total reflection film are interposed in the laser light path, the thermal lens action on the convergence side is canceled by the thermal lens action on the diffusion side superimposed by these scrapers 2, Even if the thermal lens action on the diffusion side by the individual scraper 2 is small, the necessary thermal lens action on the diffusion side can be secured by the plurality of scrapers 2, and the design and production of the scraper 2 can be facilitated, and the laser processing machine Even if the intensity of the thermal lens action on the convergence side differs depending on the model and the type of optical components other than the scraper 2 to be used, it can be dealt with by appropriately combining the scrapers 2 having different thermal lens actions on the individual diffusion side.

  According to the invention of claim 4, since the blasting process and the blackening process are performed on the inner surface 10a of the processing head 1, the laser scattered light is efficiently absorbed by the structural members 11 to 13 of the processing head 1, Therefore, overheating of peripheral parts is suppressed.

  According to the invention of claim 5, the cooling water passage 6 is provided inside the structural members 11 to 13 of the processing head 1 subjected to the blasting process and the blackening process, and the structural members 11 to 13 absorb laser scattered light. Since the accompanying heat energy can be efficiently exhausted by heat exchange with the cooling water in the cooling water channel 6, overheating of peripheral components can be more effectively prevented.

It is a vertical side view which shows the process head of the high output laser beam machine which concerns on one Embodiment of this invention. The focal displacement by the thermal lens of a high power laser beam machine is shown, (a) is a schematic longitudinal side view when the scraper has a low absorption rate, and (b) is a schematic longitudinal side view when the absorption rate is high. FIG. 4 shows compensation of thermal lens characteristics in the high-power laser processing machine of the present invention, where (a) is a schematic longitudinal side view in a state where the laser output is low, and (b) is a schematic longitudinal side view in a state where the laser output is high. . It is a radius-displacement amount characteristic view from the reflection center which shows the deformation | transformation condition of the reflective surface at the time of laser beam absorption in an example of the scraper of a quartz base material. It is a schematic diagram of the high output laser beam machine which concerns on other embodiment of this invention.

  The processing head 1 shown in FIG. 1 constitutes a fiber laser welding head for laser welding, and is sequentially provided from the upper side in the figure along a laser beam path in a cylindrical housing 10 bent in a substantially L shape in side view. The collimator lens 5 that converts the laser light L emitted from the emission end 3a of the optical fiber 3 into parallel light is inclined at an angle of 45 °, and the parallel light is totally reflected in different directions (left direction in the drawing) by 90 °. A reflective scraper 2, a condensing lens 4 for converging the reflected light and converging the focal point F near the surface of the workpiece W on the processing table T, and a flat protective glass 6 are arranged.

  The housing 10 is subjected to blasting and blackening treatment on the inner surface 10a, and the structural members 11 and 12 around the collimator lens 5 and the condensing lens 4 and the structural member at the portion where the scraper 2 is disposed. The cooling water channel 6 is provided in each of 13. Further, an observation CCD camera 15 is disposed on the outer side facing the opening 14 provided in the optical axis direction of the focusing lens 4 on the back side of the scraper 2 in the housing 10.

  Here, the condensing lens 4 and the collimator lens 5 and the protective glass 6 are all provided with a non-reflective film on the surface of the quartz base material, and the scraper 2 is provided with a total reflection film on the surface of the quartz base material. . The optical components excluding the scraper 2 interposed in the laser light path, that is, the condensing lens 4, the collimator lens 5, and the protective glass 6 focus the focal point F due to thermal expansion and refractive index change accompanying absorption of the laser light L. Whereas the converging side (positive) thermal lens action is displaced to the side, the scraper 2 has a curvature change in which the reflecting surface 2a is deformed into a convex shape due to thermal expansion accompanying absorption of the laser beam L, as will be described later. Thus, a diffusion side (negative) thermal lens action that cancels out the convergence side (positive) thermal lens action is generated, thereby compensating the thermal lens characteristics of the entire processing head 1.

Next, test results of thermal lens characteristics by a processing head using commercially available reflective scrapers 2A to 2C (diameter 80 mm, thickness 8 mm) will be shown. Each of these scrapers 2A to 2C includes a total reflection film in which dielectric layers of SiO ₂ and TiO ₂ are alternately stacked on the surface of a quartz base material by electron beam evaporation. It has a layer number ratio of the total reflection film (ratio with the scraper 2A as a reference 1). In the test, the focal displacement toward the condenser lens 4 side after 3 minutes from the start of emission of the laser beam L with an output of 10 kW, and the temperature difference between the center (reflection center) of the scraper and the periphery at that time were measured. In Table 1 below, the measurement results are shown as relative values with the scraper 2A as the reference 1, and the situation during the test is schematically shown in FIG. The focus shift is a shift toward the shortening side.

  As shown in Table 1, in the processing head using the reflective scrapers 2A and 2C, the action of the thermal lens toward the convergence side is strong and the focus shift is large. The temperature difference between the center and the periphery of the scrapers 2A and 2C is slight. This is because the scraper 2A, 2C has a low absorptance of the laser light L, and as a result, the reflecting surface 2a is kept flat as shown in FIG. 2A. As a result, the condenser lens 4 excluding these scrapers 2A, 2C, etc. The converging (positive) thermal lens action due to the thermal expansion and refractive index change accompanying the absorption of the laser beam L of the optical component appears as it is, and a large focal shift Δf1 in which the focal position moves from the original F0 to F1 is generated. It can be said. On the other hand, in the processing head using the reflective scraper 2B, the thermal lens action toward the convergence side is weak and the focus shift is small, but the temperature difference between the center and the periphery of the scraper 2B is the scraper 2A, 2C. It is larger than 6 times. In this case, since the absorptivity of the laser beam L is large in the scraper 2B, the reflection surface 2a is deformed into a convex shape as shown in FIG. 2B due to thermal expansion, and the laser beam L is reflected by the convex surface and diffused. Side (negative) thermal lens action is generated, and as a result, the convergence side (positive) thermal lens action by the optical components such as the condenser lens 4 excluding the scraper 2B is diminished, so that the focal position is changed from the original F0 to F2. It is assumed that the focal point shift Δf2 is small enough to move to.

  From the knowledge based on the above test results, the present invention measures in advance the thermal lens action on the convergence side by an optical component other than the scraper 2 (condensing lens 4, collimator lens 5, protective glass 6, etc.) interposed in the laser optical path. In addition, by using a scraper 2 that causes a change in curvature that causes a thermal lens action on the diffusion side corresponding to the thermal lens action on the convergence side on the reflecting surface 2a as the laser light is absorbed, the convergence side and the diffusion side It has been found that the thermal lens function of the laser processing machine as a whole can be compensated by canceling out the thermal lens action.

  That is, in the high-power laser processing machine of the present invention, as shown in FIG. 3A, when the load applied to each optical component is low with a low laser output, the heat of the optical components such as the condenser lens 4 other than the scraper 2 is reduced. The convergence (positive) thermal lens action due to expansion and refractive index change is small, but the scraper 2 also has a slight thermal expansion, so that the convex curvature change of the reflecting surface 2a is small, and the diffusion side (negative) heat due to the curvature change. The lens action and the convergent (positive) thermal lens action cancel each other, and the original focal position F0 is maintained. As shown in FIG. 3B, when the load applied to each optical component is high with high laser output, the thermal lens action on the convergence side (positive) due to the thermal expansion and refractive index change of the optical components other than the scraper 2 is Although the scraper 2 also has a large thermal expansion, the curvature change of the convex shape of the reflecting surface 2a becomes large, and the diffusion side (negative) thermal lens action and the convergence side (positive) thermal lens action due to the curvature change Canceling each other, the original focal position F0 is maintained. Therefore, according to this high-power laser processing machine, high-precision laser processing can be performed at a constant focal position at all times without requiring separate drive mechanisms and control mechanisms for compensating the thermal lens characteristics.

Incidentally, when the surface transition of the reflective surface 2a in the region from the reflection center to the radius of 10 mm was measured for the reflective scraper 2B at the time of the test, the result shown in FIG. 4 was obtained. As shown in the figure, this surface transition draws a substantially arc-shaped curve that is higher toward the center side, and the transition curve substantially corresponds to a radius of curvature R = 26.5 m. Therefore, the absorption characteristic, that is, the thermal expansion characteristic of the reflective scraper 2 to be used can be arbitrarily set according to the type of dielectric used for the total reflection film, the number of layers, and the layer thickness profile. Corresponding to thermal lens characteristics on the converging side (positive) by other optical components such as the condensing lens 4, collimator lens 5, protective glass 6, etc. Just choose. The material of the scraper 2 is not particularly limited, but a quartz base material is preferable from the viewpoint of optical characteristics and material cost, and SiO ₂ and TiO ₂ are preferable as the dielectric constituting the total reflection film. Various thin film forming methods can be used as a means for forming the total reflection film, but the electron beam evaporation method or the ion beam evaporation method is particularly recommended because it can easily form a dielectric layer having a uniform thickness. .

  On the other hand, in the processing head 1 of the high-power laser processing machine of the above embodiment, the inner surface is subjected to blasting and blackening processing, so that internal laser scattered light is emitted by the structural members 11 to 13 of the processing head 1. In addition to being efficiently absorbed, the structural members 11 to 13 have the cooling water channels 6, so that the thermal energy associated with the absorption of the laser scattered light of the structural members 11 to 13 is converted into heat from the cooling water in the cooling water channels 6. By exchanging, there is an advantage that heat can be exhausted efficiently, and overheating of peripheral parts such as the infrared sensor 9 and the CCD camera 15 can be effectively prevented. The blasting process increases the absorption rate by reflecting the laser scattered light multiple times at the fine irregularities caused by the roughening, and the blackening process improves the light absorption by blackening by black alumite processing. It is something to enhance.

  In the high-power laser processing machine of the above embodiment, the laser beam path in the processing head 1 changes its direction by 90 ° by reflection by one scraper 2 as the most basic configuration, but is limited to the processing head 1. Instead, a plurality of reflective scrapers 2 may be interposed in the laser beam path of the entire processing machine, and the scraper 2 may change the direction of the laser beam in a plurality of stages. For example, in the high-power laser beam machine according to another embodiment shown in FIG. 5, the laser light L emitted from the laser oscillator 9 is reflected by the first and second scrapers 2 and 2 and sequentially directed by 90 °. Then, the light passes through the collimator lens 5, is further reflected by the third scraper 2, changes the direction of 90 ° to enter the condenser lens 4, is converged by the condenser lens 4, and is irradiated onto the workpiece W. It is like that.

  When a plurality of reflective scrapers 2 are interposed in the laser light path as described above, a converging-side thermal lens formed by optical components intervening in the laser light path other than the scraper 2 due to the diffusion-side thermal lens action caused by the overlap of the scrapers 2. What is necessary is just to set so that an effect | action may be canceled and the thermal lens characteristic of the whole laser beam machine may be compensated. In this case, even if the thermal lens action on the diffusion side by each scraper 2 is small, the necessary thermal lens action on the diffusion side can be ensured by the plurality of scrapers 2, so that the large diffusion side thermal lens action can be achieved with only the single scraper 2. The scraper 2 can be designed and manufactured more easily than in the case of exhibiting. In addition, depending on the type of laser processing machine and the type of optical components other than the scraper 2 to be used, even if there is a difference in the strength of the thermal lens action on the convergence side, the scraper 2 with different thermal lens action on the individual diffusion side is appropriately selected. It becomes possible to respond by combining.

  In the present invention, together with the reflective scraper 2, a transmissive scraper having a non-reflective film, that is, a scraper that generates a converging-side thermal lens function may be interposed in the laser light path as necessary. Further, in the present invention, various design changes other than the embodiment can be made for the detailed configuration such as the arrangement position and number of other optical components such as the condenser lens 4 and the collimator lens 5 and the types and arrangement configurations of the peripheral components. .

DESCRIPTION OF SYMBOLS 1 Processing head 2 Scraper 2a Reflecting surface 4 Condensing lens (other optical components)
5 Collimator lens (other optical components)
6 Protective glass (other optical components)
7 Cooling channel 10a Inner surface 11-13 Processing head component L Laser beam F Focus

Claims (5)

  In a high-power laser processing machine in which a scraper having a total reflection film is interposed in the laser beam path, the thermal lens action on the convergence side by optical components other than the scraper interposed in the laser beam path is used for the thermal expansion of the scraper that has absorbed the laser beam. A high-power laser processing machine configured to compensate for the thermal lens characteristics of the entire laser processing machine by canceling out with the thermal lens action on the diffusion side caused by the change in curvature of the reflecting surface.   The high-power laser processing machine according to claim 1, wherein the total reflection film of the scraper includes two or more dielectric layers.   3. A plurality of scrapers having a total reflection film are interposed in a laser beam path, and are set so as to cancel out the convergence-side thermal lens action by the overlapping diffusion-side thermal lens action by these scrapers. High power laser processing machine.   The high-power laser according to any one of claims 1 to 3, wherein an inner surface of a processing head in which an optical component including a condensing lens and at least one scraper is mounted is blasted and blackened. Processing machine.   A cooling water passage is provided inside the structural member of the processing head that has been subjected to the blasting and blackening treatment, and the heat energy associated with the absorption of the laser scattered light of the structural member is exchanged with the cooling water flowing through the cooling water passage. The high-power laser beam machine according to claim 4, wherein the high-power laser beam machine is configured to exhaust heat.

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