Laser processing device

Abstract

This laser processing device is provided with: a light source that emits laser light; an irradiation unit that irradiates an object to be processed with the laser light; a monitor unit that detects thermal radiation light emitted from an irradiation region of the laser light on the object to be processed; and a first optical fiber that propagates the laser light from the monitor unit to the irradiation unit and propagates the thermal radiation light from the irradiation unit to the monitor unit. The monitor unit causes the laser light to be incident on a first end surface of the first optical fiber, and detects the thermal radiation light emitted from the first end surface. When the outer diameter of a core included in the first optical fiber is defined as D1 and the outer diameter of a cladding included in the first optical fiber is defined as D2, the first optical fiber satisfies (D2 - D1) > D1 at least at the first end surface.

Description

Laser Processing Equipment

[0001] The present disclosure relates to a laser processing apparatus.

[0002] A laser processing device is known that guides laser light emitted from a light source to an irradiation unit through an optical fiber and irradiates the laser light from the irradiation unit onto an object to be processed. In such a laser processing device, a malfunction may occur at the end of the optical fiber on the laser light incident side due to heat generated in response to the incidence of the laser light.

[0003] Patent Document 1 describes a configuration in which the outer diameter of the intermediate portion (main portion of the cladding) of the end of the optical fiber on the laser light incident side is larger than the outer diameter of the end face on the laser light incident side, in order to prevent damage to the adhesive material arranged around the intermediate portion (main portion of the cladding) due to heat generated in response to the incidence of laser light.

[0004] International Publication No. 2020 / 184603

[0005] In the laser processing device as described above, in order to measure the temperature of the area irradiated with laser light on the workpiece, the thermal radiation light emitted in the irradiated area may be guided from the irradiation unit by an optical fiber, and the thermal radiation light emitted from the end face of the optical fiber on the laser light incident side may be detected.

[0006] In such cases, it is necessary to accurately detect the thermal radiation light emitted in the laser light irradiation area of ​​the workpiece, but even if the configuration described in Patent Document 1, for example, is adopted, there is a risk that the detection accuracy will decrease due to the heat generated in response to the incidence of the laser light.

[0007] An object of the present disclosure is to provide a laser processing device that can accurately detect thermal radiation light emitted from a region of an object to be processed that is irradiated with laser light.

[0008] A laser processing device according to one aspect of the present disclosure is [1] "a laser processing device comprising: a light source that emits laser light for processing a workpiece; an irradiation unit that irradiates the laser light onto the workpiece; a monitor unit that detects thermal radiation light emitted in an irradiation area of ​​the workpiece with the laser light; and a first optical fiber that propagates the laser light from the monitor unit to the irradiation unit and propagates the thermal radiation light from the irradiation unit to the monitor unit, wherein the first optical fiber has a first end face optically connected to the monitor unit and a second end face optically connected to the irradiation unit, wherein the monitor unit directs the laser light to the first end face and detects the thermal radiation light emitted from the first end face, wherein the first optical fiber satisfies (D2-D1)>D1 at least at the first end face, where D1 is an outer diameter of a core included in the first optical fiber and D2 is an outer diameter of a cladding included in the first optical fiber."

[0009] In the laser processing device, the first optical fiber, which propagates laser light from the monitor unit to the irradiation unit and propagates thermal radiation light from the irradiation unit to the monitor unit, satisfies (D2-D1)>D1 (D1: outer diameter of the core, D2: outer diameter of the cladding) at the first end face optically connected to the monitor unit. This suppresses a temperature rise at the first end face of the monitor unit due to the incidence of laser light, and suppresses the generation of thermal radiation light at the first end face. Therefore, in the monitor unit, thermal radiation light emitted in the laser light irradiation area of ​​the workpiece and emitted from the first end face is less likely to be obscured by thermal radiation light emitted at the first end face due to the incidence of laser light. Therefore, the laser processing device can accurately detect thermal radiation light emitted in the laser light irradiation area of ​​the workpiece.

[0010] A laser processing apparatus according to one aspect of the present disclosure may be [2] "the laser processing apparatus according to [1] above, in which the first optical fiber satisfies (D2-D1)>D1 from the first end face to the second end face." According to this laser processing apparatus, even if the center of the laser light incident region at the first end face is offset from the center of the core, the intensity of the laser light propagating through the clad of the first optical fiber can be prevented from exceeding the processing threshold. In other words, even if the center of the laser light incident region at the first end face is offset from the center of the core, the workpiece can be accurately processed by the laser light propagating through the core of the first optical fiber. Furthermore, since the thermal radiation light emitted in the irradiation region of the laser light on the workpiece can be propagated not only through the core of the first optical fiber but also through the clad of the first optical fiber, which is sufficiently wide and ensured from the second end face to the first end face, the thermal radiation light emitted in the irradiation region can be reliably detected.

[0011] The laser processing device according to one aspect of the present disclosure may be [3] "the laser processing device according to the above [2], wherein the first optical fiber further includes a coating layer covering the clad, and the thermal radiation light propagating from the irradiation unit to the monitor unit is totally reflected at the interface between the clad and the coating layer." According to this laser processing device, the thermal radiation light emitted in the irradiation area of ​​the laser light on the workpiece can be reliably propagated in the clad of the first optical fiber, which is secured to be sufficiently wide from the second end face to the first end face.

[0012] The laser processing device according to one aspect of the present disclosure may be [4] "the laser processing device according to the above [3], in which the refractive index of the cladding material is greater than the refractive index of the coating layer material." With this laser processing device, thermal radiation light emitted from the laser light irradiation area on the workpiece can be reliably propagated in the cladding of the first optical fiber, which is secured to be sufficiently wide from the second end face to the first end face.

[0013] A laser processing apparatus according to one aspect of the present disclosure may be [5] "the laser processing apparatus according to any one of [1] to [4] above, in which the first optical fiber satisfies (D2-D1)≧(D1×1.5) at least at the first end face." According to this laser processing apparatus, the monitor unit can more reliably suppress a temperature rise at the first end face caused by the incidence of laser light, and more reliably suppress the generation of thermal radiation light at the first end face. As a result, thermal radiation light emitted from the irradiated area of ​​the laser light on the workpiece can be detected with higher accuracy.

[0014] The laser processing device according to one aspect of the present disclosure may be [6] "the laser processing device according to any one of [1] to [5] above, in which the outer diameter of the core included in the first optical fiber is 200 μm or less." With this laser processing device, the laser light propagating through the core of the first optical fiber can be focused into a sufficiently small spot, thereby improving the processing accuracy using the laser light.

[0015] The laser processing device according to one aspect of the present disclosure may be [7] "the laser processing device according to any one of the above [1] to [6], further comprising a second optical fiber that propagates the laser light from the light source to the monitor unit, wherein the outer diameter of the core included in the first optical fiber is substantially equal to the outer diameter of the core included in the second optical fiber." According to this laser processing device, the beam diameter of the laser light generated from the light source and propagated through the second optical fiber can be maintained in the first optical fiber, thereby improving the processing accuracy using the laser light.

[0016] The laser processing device according to one aspect of the present disclosure may be [8] "the laser processing device according to any one of the above [1] to [7], wherein the irradiation unit includes an optical scanning unit, and the optical scanning unit reflects the laser light emitted from the second end face to scan the laser light across the workpiece, and reflects the thermal radiation light emitted in the irradiation area of ​​the laser light on the workpiece to cause the thermal radiation light to be incident on the second end face." With this laser processing device, while moving the irradiation area of ​​the laser light relative to the workpiece, it is possible to accurately detect the thermal radiation light emitted in the irradiation area for each position of the irradiation area.

[0017] According to the present disclosure, it is possible to provide a laser processing device that can accurately detect thermal radiation light emitted from an area of ​​an object to be processed that is irradiated with laser light.

[0018] FIG. 1 is a configuration diagram of an example laser processing apparatus. FIG. 2 is a configuration diagram of the laser processing monitor shown in FIG. 1. FIG. 3 is a configuration diagram of the optical unit shown in FIG. 2. FIG. 4 is a schematic diagram of the optical fiber on the light source side and the optical fiber on the irradiation unit side shown in FIG. 3. FIG. 5 is a view of the optical fiber on the irradiation unit side shown in FIG. 4 as seen from the irradiation unit side. FIG. 6 is a schematic diagram showing the intensity profile of laser light emitted from the laser processing apparatus shown in FIG. 1 and the intensity profile of laser light emitted from a laser processing apparatus of a comparative example. FIG. 7 is a diagram showing the intensity profile of laser light emitted from the optical fiber of the example. FIG. 8 is a table showing the detection results of thermal radiation light using the optical fiber of the example.

[0019] Hereinafter, an example of the present disclosure will be described in detail with reference to the drawings. In each drawing, the same or corresponding parts are denoted by the same reference numerals, and duplicated explanations will be omitted. [Configuration of the laser processing device]

[0020] 1, the laser processing apparatus 1 includes a light source 2, two optical fibers 4 and 5, an irradiation unit 6, and a monitor unit 10. The optical fiber 4 is an optical fiber (second optical fiber) having an end face 4a optically connected to the light source 2 and an end face 4b optically connected to the monitor unit 10. The optical fiber 5 is an optical fiber (first optical fiber) having an end face (first end face) 5a optically connected to the monitor unit 10 and an end face (second end face) 5b optically connected to the irradiation unit 6.

[0021] The light source 2 emits laser light L1 for processing the workpiece S and makes the laser light L1 incident on an end face 4a of the optical fiber 4. The light source 2 includes, for example, a laser diode. The optical fiber 4 propagates the laser light L1 from the light source 2 to the monitor unit 10. The monitor unit 10 makes laser light L1a having a first wavelength band, out of the laser light L1 emitted from the end face 4b of the optical fiber 4, incident on an end face 5a of the optical fiber 5. The optical fiber 5 propagates the laser light L1a from the monitor unit 10 to the irradiation unit 6. The irradiation unit 6 irradiates the workpiece S with the laser light L1a emitted from the end face 5b of the optical fiber 5. As a result, the workpiece S is processed in an irradiation area Sa of the workpiece S with the laser light L1a. The type of processing is, for example, cutting, welding, surface treatment, etc.

[0022] When the workpiece S is processed, thermal radiation light L2 is emitted from the irradiation area Sa. The thermal radiation light L2 includes, for example, infrared light. The irradiation unit 6 makes the thermal radiation light L2 incident on the end face 5b of the optical fiber 5. The optical fiber 5 propagates the thermal radiation light L2 from the irradiation unit 6 to the monitor unit 10. The monitor unit 10 detects the thermal radiation light L2 emitted from the end face 5a of the optical fiber 5. In this way, the temperature of the irradiation area Sa is measured when the workpiece S is processed. [Configuration of the irradiation unit]

[0023] The irradiation unit 6 includes a head unit 61, an optical scanning unit 62, and an fθ lens 63. The laser light L1a emitted from the end face 5b of the optical fiber 5 passes through the head unit 61, the optical scanning unit 62, and the fθ lens 63 in this order, and is irradiated onto the workpiece S. The thermal radiation light L2 emitted in the irradiation area Sa passes through the fθ lens 63, the optical scanning unit 62, and the head unit 61 in this order, and is incident on the end face 5b of the optical fiber 5.

[0024] The head unit 61 includes at least one lens optically connected to the end face 5b of the optical fiber 5. The head unit 61 collimates the laser light L1a emitted from the end face 5b of the optical fiber 5 and makes it incident on the optical scanning unit 62, and also condenses the thermal radiation light L2 emitted from the optical scanning unit 62 and makes it incident on the end face 5b of the optical fiber 5.

[0025] The optical scanning unit 62 includes a pair of galvanometer mirrors that oscillate around a pair of axes that are perpendicular to each other. The optical scanning unit 62 reflects the laser beam L1a emitted from the head unit 61 to make it incident on the fθ lens 63, and also reflects the thermal radiation light L2 emitted from the fθ lens 63 to make it incident on the head unit 61 of the optical fiber 5.

[0026] The fθ lens 63 focuses the laser light L1a emitted from the optical scanning unit 62 and irradiates the workpiece S, and also collimates the thermal radiation light L2 emitted in the irradiation area Sa and makes it incident on the optical scanning unit 62. The fθ lens 63 positions the focusing point of the laser light L1a on a predetermined surface of the workpiece S, regardless of the incident angle of the laser light L1a.

[0027] As described above, the irradiation unit 6 constitutes a two-dimensional galvano system. In the irradiation unit 6, the optical scanning unit 62 reflects the laser light L1a emitted from the end face 5b of the optical fiber 5 to scan the laser light L1a over the workpiece S, and also reflects the thermal radiation light L2 emitted in the irradiation area Sa to make the thermal radiation light L2 incident on the end face 5b of the optical fiber 5. [Configuration of the monitor unit]

[0028] 2 , the monitor unit 10 includes a box 11, a power supply unit 12, a circuit unit 13, and an optical unit 20. The box 11 houses the power supply unit 12, the circuit unit 13, and the optical unit 20. The power supply unit 12 supplies driving power from an external power source to the circuit unit 13. The circuit unit 13 includes, for example, a two-color radiation thermometer or a monochromatic radiation thermometer, and calculates the temperature of the irradiation area Sa based on a detection signal of the thermal radiation light L2 detected by the optical unit 20.

[0029] As shown in FIG. 3, the optical unit 20 includes a pair of optical fiber holding units 21 and 22, a first dichroic mirror 23, a second dichroic mirror 24, a light detecting unit 25, a light absorbing unit 26, and a housing 27.

[0030] The optical fiber holding part 21 has a cylindrical lens holding part 21a and a flange-shaped optical fiber holding part 21b. The lens holding part 21a holds a lens 31. The optical fiber holding part 21b holds the end of the optical fiber 4. The lens 31 collimates the laser light L1 emitted from the end face 4b of the optical fiber 4. The optical fiber holding part 21 is unitized so as to maintain the positional relationship between the end face 4b of the optical fiber 4 and the lens 31 and to cover the optical path formed between the end face 4b of the optical fiber 4 and the lens 31. In the optical fiber holding part 21, the lens 31 functions as a window material, and by inserting the end of the optical fiber 4, a closed space is formed within the optical fiber holding part 21 (between the end face 4b of the optical fiber 4 and the lens 31).

[0031] The optical fiber holding part 22 has a cylindrical lens holding part 22a and a flange-shaped optical fiber holding part 22b. The lens holding part 22a holds a lens 32. The optical fiber holding part 22b holds the end of the optical fiber 5. The lens 32 focuses the laser light L1a onto the end face 5a of the optical fiber 5 and collimates the thermal radiation light L2 emitted from the end face 5a of the optical fiber 5. The optical fiber holding part 22 is unitized to maintain the positional relationship between the end face 5a of the optical fiber 5 and the lens 32 and to cover the optical path formed between the end face 5a of the optical fiber 5 and the lens 32. In the optical fiber holding part 22, the lens 32 functions as a window material, and by inserting the end of the optical fiber 5, a closed space is formed within the optical fiber holding part 22 (between the end face 5a of the optical fiber 5 and the lens 32). Note that the end face 5a of the optical fiber 5 is coated with an AR coating to prevent the laser light L1a from becoming return light.

[0032] The first dichroic mirror 23 reflects a laser beam L1a having a first wavelength band that is part of the laser beam L1 emitted from the end face 4b of the optical fiber 4 and collimated by the lens 31. On the other hand, the first dichroic mirror 23 transmits a light beam L1b having a second wavelength band that corresponds to the wavelength band of the thermal radiation light L2. The first dichroic mirror 23 is configured by providing a reflective layer 23a made of a dielectric multilayer film that reflects the laser beam L1a and transmits the light beam L1b on the incident surface of the laser beam L1, the reflective layer 23a being made of a material that hardly absorbs the laser beam L1 (e.g., synthetic quartz). The first dichroic mirror 23 has a reflectance of 90% or more for the laser beam L1a and a transmittance of 90% or more for the light beam L1b.

[0033] The second dichroic mirror 24 reflects the laser light L1a reflected by the first dichroic mirror 23. The laser light L1a reflected by the second dichroic mirror 24 is collected by a lens 32 and incident on the end face 5a of the optical fiber 5. On the other hand, the second dichroic mirror 24 transmits the thermal radiation light L2 emitted from the end face 5a of the optical fiber 5 and collimated by the lens 32. The second dichroic mirror 24 is configured by providing a reflective layer 24a made of a dielectric multilayer film that reflects the laser light L1a and transmits the thermal radiation light L2 on the incident surface of the laser light L1a, the reflective layer 24a being made of a material that hardly absorbs the laser light L1 (e.g., synthetic quartz). The second dichroic mirror 24 has a reflectance of 90% or more for the laser light L1a and a transmittance of 90% or more for the thermal radiation light L2.

[0034] The light detection unit 25 has a cylindrical lens holding portion 25a and a flange-shaped photodiode support portion 25b. The lens holding portion 25a holds a lens 33 and a filter 34. The photodiode support portion 25b supports a photodiode 35. The lens 33 focuses the thermal radiation light L2 that has passed through the second dichroic mirror 24 onto the photodiode 35. The filter 34 has the function of transmitting only light having a wavelength band corresponding to the wavelength band of the thermal radiation light L2. The photodiode 35 detects the thermal radiation light L2 that has been focused by the lens 33 and passed through the filter 34. A detection signal of the thermal radiation light L2 detected by the photodiode 35 is sent to the circuit unit 13. The light detection unit 25 is unitized so as to maintain the positional relationship between the lens 33, the filter 34, and the photodiode 35 and to cover the optical path formed between the lens 33 and the photodiode 35.

[0035] The lens 33 is given chromatic aberration so that the focusing position of the thermal radiation light L2 is located on the photodiode 35, while the focusing position of the laser light L1a is shifted from the photodiode 35 (i.e., the laser light L1a is blurred on the photodiode 35). As a result, even if the laser light L1a enters the light detection unit 25 and is focused by the lens 33, it will have almost no effect on the detection of the thermal radiation light L2 by the photodiode 35.

[0036] The light absorbing portion 26 absorbs the light L1b transmitted through the first dichroic mirror 23. The light absorbing portion 26 is a damper that absorbs light and converts it into heat. The light absorbing portion 26 is disposed so that even if the light L1b is reflected by the light absorbing portion 26, the reflected light L1b travels toward a second side wall 29b of the cover 29, which will be described later.

[0037] The housing 27 has a base 28 and a cover 29. The base 28 supports the pair of optical fiber holding units 21, 22, the first dichroic mirror 23, the second dichroic mirror 24, the light detection unit 25, and the light absorbing unit 26. The cover 29 covers the optical path formed between the pair of optical fiber holding units 21, 22, the first dichroic mirror 23, the second dichroic mirror 24, the light detection unit 25, and the light absorbing unit 26.

[0038] The base 28 includes a pair of first side walls 28b. The pair of first side walls 28b face each other in the X-axis direction and are arranged parallel to each other. The cover 29 includes a pair of second side walls 29b. The pair of second side walls 29b face each other in the Y-axis direction and are arranged parallel to each other. The base 28 and cover 29 are combined to form a rectangular box-shaped housing 27. In the base 28, the thickness of each first side wall 28b is greater than the thickness of the bottom wall 28a. In addition, in the cover 29, a light-absorbing treatment is applied to an inner surface 29c of the cover 29, including the inner surfaces of the pair of second side walls 29b. The light-absorbing treatment is, for example, application of black paint.

[0039] A pair of through holes 28c, 28d are formed in one first side wall 28b of the base 28. The optical fiber holding unit 21 is provided on the one first side wall 28b by fixing the optical fiber holding unit 21b to the outer surface of the one first side wall 28b with the lens holding unit 21a inserted into the through hole 28c. The optical fiber holding unit 22 is provided on the one first side wall 28b by fixing the optical fiber holding unit 22b to the outer surface of the one first side wall 28b with the lens holding unit 22a inserted into the through hole 28d. A through hole 28e is formed in the other first side wall 28b of the base 28 so as to face the through hole 28d in the X-axis direction. The light detection unit 25 is provided on the other first side wall 28b by fixing the photodiode support unit 25b to the outer surface of the other first side wall 28b with the lens holding unit 25a inserted into the through hole 28e.

[0040] The inner surface of the bottom wall 28a has recesses formed therein for positioning the first dichroic mirror 23, the second dichroic mirror 24, and the light absorbing portion 26. The first dichroic mirror 23, the second dichroic mirror 24, and the light absorbing portion 26 are attached to the bottom wall 28a while being disposed in the respective recesses. Note that recesses may be formed in the first dichroic mirror 23, the second dichroic mirror 24, and the light absorbing portion 26, and protrusions to be disposed in the respective recesses for positioning them may be formed on the inner surface of the bottom wall 28a.

[0041] In the optical unit 20 configured as described above, the laser light L1 propagating from the light source 2 through the optical fiber 4 is emitted from the end face 4b of the optical fiber 4 in the optical fiber holding unit 21, collimated by the lens 31, and travels along the X-axis direction toward the first dichroic mirror 23. Of the laser light L1 traveling toward the first dichroic mirror 23, laser light L1a having the first wavelength band is reflected by the first dichroic mirror 23 and travels along the Y-axis direction toward the second dichroic mirror 24.

[0042] Of the laser light L1 that has traveled toward the first dichroic mirror 23, light L1b having a second wavelength band corresponding to the wavelength band of the thermal radiation light L2 is transmitted through the first dichroic mirror 23 and travels along the X-axis direction toward the light absorbing section 26. The light L1b that has traveled toward the light absorbing section 26 is absorbed by the light absorbing section 26. Even if part of the light L1b is reflected by the light absorbing section 26 without being absorbed by the light absorbing section 26, part of the light L1b will travel toward the second side wall 29b of the housing 27 and be absorbed by the inner surface 29c of the second side wall 29b that has been subjected to the light absorption treatment.

[0043] The laser light L1a, which is reflected by the first dichroic mirror 23 and travels toward the second dichroic mirror 24, is reflected by the second dichroic mirror 24 and travels along the X-axis direction toward the optical fiber holding unit 22. The laser light L1a that travels toward the optical fiber holding unit 22 is collected by the lens 32 in the optical fiber holding unit 22, enters the end face 5a of the optical fiber 5, and propagates through the optical fiber 5 to the head unit 61. Even if part of the light L1b travels toward the second dichroic mirror 24 without passing through the first dichroic mirror 23, part of the light L1b passes through the second dichroic mirror 24 and travels toward the second side wall 29b of the housing 27, and is absorbed by the inner surface 29c of the second side wall 29b, which has been subjected to a light-absorbing treatment.

[0044] The thermal radiation light L2 propagating from the irradiation area Sa through the optical fiber 5 is emitted from the end face 5a of the optical fiber 5 in the optical fiber holding unit 22, collimated by the lens 32, and travels along the X-axis direction toward the second dichroic mirror 24. The thermal radiation light L2 traveling toward the second dichroic mirror 24 passes through the second dichroic mirror 24 and travels along the X-axis direction toward the photodetector 25. The thermal radiation light L2 traveling toward the photodetector 25 is collected by the lens 33 in the photodetector 25, passes through the filter 34, and is detected by the photodiode 35. [Configuration of Optical Fiber]

[0045] Fig. 4 is a schematic diagram of the two optical fibers 4 and 5, and Fig. 5 is a view of the optical fiber 5 as seen from the side of the irradiation unit 6. In Fig. 4, the two optical fibers 4 and 5 are shown on the same straight line to facilitate comparison between the optical fiber 4 and the optical fiber 5.

[0046] 4, the optical fiber 4 includes a core 41, a cladding 42 covering the core 41, and a coating layer 43 covering the cladding 42. The laser light L1 propagating from the light source 2 to the monitor unit 10 propagates through the core 41. As an example, the core 41 is made of pure quartz, the cladding 42 is made of low-refractive-index quartz, and the coating layer 43 is made of silicone resin. As an example, the outer diameter of the core 41 is 100 μm, the outer diameter of the cladding 42 is 200 μm, and the thickness of the coating layer 43 is 100 μm.

[0047] The optical fiber 5 includes a core 51, a cladding 52 covering the core 51, and a coating layer 53 covering the cladding 52. The laser light L1a propagating from the monitor unit 10 to the irradiation unit 6 propagates through the core 51. The thermal radiation light L2 propagating from the irradiation unit 6 to the monitor unit 10 propagates not only through the core 51 but also through the cladding 52 and is totally reflected at the interface between the cladding 52 and the coating layer 53. In the optical fiber 5, the refractive index of the material of the cladding 52 is greater than the refractive index of the material of the coating layer 53. For example, the material of the core 51 is pure quartz, the material of the cladding 52 is low-refractive-index quartz, and the material of the coating layer 53 is silicone resin. For example, the outer diameter of the core 51 is 100 μm, the outer diameter of the cladding 52 is 500 μm, and the thickness of the coating layer 53 is 100 μm.

[0048] As shown in FIG. 5 , when the outer diameter of the core 51 is D1 and the outer diameter of the cladding 52 is D2, the optical fiber 5 satisfies (D2-D1)>D1 from the end face 5a to the end face 5b. In the laser processing apparatus 1, the optical fiber 5 satisfies (D2-D1)≧(D1×1.5) from the end face 5a to the end face 5b. The outer diameter of the core 51 of the optical fiber 5 is 200 μm or less and is substantially equal to the outer diameter of the core 41 of the optical fiber 4. As an example, the outer diameter of the core 51 of the optical fiber 5 is 90% to 110% of the outer diameter of the core 41 of the optical fiber 4. Here, if the outer shape of the core 51 in the cross section perpendicular to the optical axis of the optical fiber 5 is circular, the outer diameter of the core 51 is the diameter of the circle. However, if the outer shape of the core 51 in the cross section perpendicular to the optical axis of the optical fiber 5 is a shape other than a circle, the outer diameter of the core 51 refers to the diameter of a circle inscribed in the shape. Furthermore, when the outer shape of the cladding 52 in the cross section perpendicular to the optical axis of the optical fiber 5 is circular, the outer diameter of the cladding 52 is the diameter of the circle, but when the outer shape of the cladding 52 in the cross section perpendicular to the optical axis of the optical fiber 5 is a shape other than circular, the outer diameter of the cladding 52 means the diameter of a circle inscribed in the shape. From the viewpoint of ensuring the flexibility of the optical fiber 5, the outer diameter of the cladding 52 is preferably 1.5 mm or less. From the viewpoint of increasing the amount of propagating thermal radiation light L2 while ensuring the flexibility of the optical fiber 5, the outer diameter of the core 51 is preferably 400 μm or less. [Action and Effect]

[0049] In the laser processing apparatus 1, the optical fiber 5, which propagates the laser light L1a from the monitor unit 10 to the irradiation unit 6 and propagates the thermal radiation light L2 from the irradiation unit 6 to the monitor unit 10, satisfies (D2-D1)>D1 (D1: outer diameter of the core 51, D2: outer diameter of the cladding 52) at the end face 5a optically connected to the monitor unit 10. This increases the heat capacity of the portion of the monitor unit 10 consisting of the core 51 and the cladding 52, making it difficult for heat to concentrate even when generated. As a result, the temperature rise of the end face 5a due to the incidence of the laser light L1a is suppressed, and the generation of thermal radiation light at the end face 5a is suppressed. Therefore, in the monitor unit 10, the thermal radiation light L2 emitted in the irradiation area Sa and output from the end face 5a is less likely to be obscured by the thermal radiation light (hereinafter referred to as "noise light") emitted at the end face 5a due to the incidence of the laser light L1a. Therefore, the laser processing device 1 can accurately detect the thermal radiation light L2 emitted from the irradiation area Sa.

[0050] Furthermore, since the optical fiber 5 satisfies (D2-D1)>D1 (D1: outer diameter of the core 51, D2: outer diameter of the cladding 52) at the end face 5a, the temperature rise at the end face 5a caused by the incidence of the laser light L1a is suppressed, and therefore damage to the end face 5a due to the incidence of the laser light L1a can be suppressed.

[0051] In the laser processing device 1, the optical fiber 5 satisfies (D2-D1)>D1 (D1: outer diameter of the core 51, D2: outer diameter of the cladding 52) from the end face 5a to the end face 5b. As a result, even if the center of the incidence region of the laser light L1a at the end face 5a is displaced from the center of the core 51, the intensity of the laser light L1a propagating through the cladding 52 of the optical fiber 5 can be prevented from exceeding the processing threshold. In other words, even if the center of the incidence region of the laser light L1a at the end face 5a is displaced from the center of the core 51, the laser light L1a propagating through the core 51 of the optical fiber 5 can accurately process the workpiece S. In the optical fiber 5, because the outer diameter of the cladding 52 is large, even if the laser light L1a leaks from the core 51 to the cladding 52, the emission area of ​​the component of the laser light L1a propagating through the cladding 52 is wide, and the component is diluted to a negligible level. Therefore, even if the laser light L1a leaks from the core 51 to the cladding 52, the beam profile of the laser light L1a is unlikely to be deformed.

[0052] 6A is an intensity profile of the laser beam L1a emitted from the laser processing apparatus 1 described above, and FIG. 6B is a schematic diagram showing the intensity profile of the laser beam L1a emitted from a laser processing apparatus of a comparative example. As shown in FIG. 6A, when the optical fiber 5 satisfies (D2-D1)>D1 (D1: outer diameter of the core 51, D2: outer diameter of the cladding 52) from the end face 5a to the end face 5b, if the center of the incidence area of ​​the laser beam L1a at the end face 5a is shifted from the center of the core 51, the intensity of the component of the laser beam L1a incident on the core 51 exceeds the processing threshold, while the intensity of the component of the laser beam L1a incident on the cladding 52 is less likely to exceed the processing threshold. 6(b), when the optical fiber 5 satisfies (D2-D1)≦D1 (D1: outer diameter of the core 51, D2: outer diameter of the cladding 52) from the end face 5a to the end face 5b, when the center of the incidence area of ​​the laser light L1a at the end face 5a is shifted from the center of the core 51, not only does the intensity of the component of the laser light L1a that is incident on the core 51 exceed the processing threshold, but the intensity of the component of the laser light L1a that is incident on the cladding 52 also tends to exceed the processing threshold. In FIG. 6(b), the intensity of the component that is incident on the cladding 52 tends to exceed the processing threshold, whereas in FIG. 6(a), the intensity of the component that is incident on the cladding 52 tends to exceed the processing threshold because the cross-sectional area of ​​the cladding 52 becomes larger and the component that is incident on the cladding 52 is diffused in the cladding 52. From the above findings, the laser processing device 1 improves the tolerance for assembly errors of the optical fiber 5 in the monitor unit 10, improves the tolerance for positional deviation due to vibrations, etc., and also has the effect of making it possible to match the outer diameter of the core 51 of the optical fiber 5 with the outer diameter of the core 41 of the optical fiber 4.

[0053] 7A and 7B are diagrams showing the intensity profile of the laser light L1a emitted from the optical fiber 5 of the example. Fig. 7A is a diagram showing the intensity profile of the laser light L1a in one direction including the optical axis of the optical fiber 5 of the example, and Fig. 7B is a diagram showing the intensity profile of the laser light L1a in a direction including the optical axis of the optical fiber 5 of the example and perpendicular to the one direction. In the optical fiber 5 of the example, the outer diameter of the core 51 was 100 μm, and the outer diameter of the cladding 52 was 500 μm. As shown in Fig. 7A and 7B, it was confirmed that a beam diameter of about 100 μm was achieved at FWHM, and that no strong light distribution appeared outside of that.

[0054] Furthermore, since the optical fiber 5 satisfies (D2-D1)>D1 (D1: outer diameter of the core 51, D2: outer diameter of the cladding 52) from the end face 5a to the end face 5b, the thermal radiation light L2 emitted in the irradiation area Sa can be propagated not only in the core 51 of the optical fiber 5 but also in the cladding 52 of the optical fiber 5, which is secured to be sufficiently wide from the end face 5b to the end face 5a, so that the thermal radiation light L2 emitted in the irradiation area Sa can be reliably detected. More specifically, since the temperature of the irradiation area Sa is low, even when the intensity of the thermal radiation light L2 emitted in the irradiation area Sa is low, the amount of the thermal radiation light L2 detected by the monitor unit 10 can be increased, so that the thermal radiation light L2 is less likely to be buried in noise light in the monitor unit 10. In other words, the lower limit of the measurement range in which the temperature of the irradiation area Sa can be measured can be lowered.

[0055] FIG. 8 is a table showing the results of detecting thermal radiation light L2 using an optical fiber 5 according to the example. In the optical fiber 5 according to the example, the core 51 had an outer diameter of 100 μm, and the cladding 52 had an outer diameter of 500 μm. In FIG. 8 , "dark" indicates the count value obtained when the end face 5 b of the optical fiber 5 was shielded from light, "dark and signal" indicates the count value obtained when thermal radiation light was incident on the end face 5 b of the optical fiber 5 from a blackbody furnace at a predetermined temperature, and "signal" indicates the count value obtained by subtracting "dark" from "dark and signal." Although "dark" is excluded by calculation when calculating the temperature of the irradiation area Sa, since the temperature fluctuated between 73.4 and 65.1 in this experiment, it is believed that there was a fluctuation of about 10 counts in "dark." Therefore, the S / N ratio when the blackbody furnace temperature was 150°C was 10.4, and the S / N ratio when the blackbody furnace temperature was 250°C was 71.8. From the above, it can be determined that if the temperature of the irradiation area Sa is 200° C. or higher, the temperature of the irradiation area Sa can be measured with high accuracy.

[0056] In the laser processing device 1, the thermal radiation light L2 propagating from the irradiation unit 6 to the monitor unit 10 is totally reflected at the interface between the cladding 52 and the coating layer 53. This allows the thermal radiation light L2 emitted in the irradiation area Sa to be reliably propagated in the cladding 52 of the optical fiber 5, which is secured to be sufficiently wide from the end face 5b to the end face 5a.

[0057] In the laser processing device 1, the refractive index of the material of the cladding 52 is greater than the refractive index of the material of the coating layer 53. This allows the thermal radiation light L2 emitted in the irradiation area Sa to be reliably propagated in the cladding 52 of the optical fiber 5, which is secured to be sufficiently wide from the end face 5b to the end face 5a.

[0058] In the laser processing device 1, the outer diameter of the core 51 of the optical fiber 5 is 200 μm or less. This allows the laser light L1a propagating through the core 51 of the optical fiber 5 to be focused into a sufficiently small spot, thereby improving the processing accuracy using the laser light L1a. Note that, as the outer diameter of the core 51 of the optical fiber 5 becomes smaller, the focused diameter of the laser light L1a incident on the end face 5a needs to be smaller. In such cases, it is particularly important that the optical fiber 5 satisfies (D2-D1)>D1 (D1: outer diameter of the core 51, D2: outer diameter of the cladding 52) at the end face 5a.

[0059] In the laser processing device 1, the outer diameter of the core 51 of the optical fiber 5 is substantially equal to the outer diameter of the core 41 of the optical fiber 4. This allows the beam diameter of the laser light L1 generated from the light source 2 and propagated through the optical fiber 4 to be maintained in the optical fiber 5, thereby improving the processing accuracy using the laser light L1a.

[0060] In the laser processing apparatus 1, the optical scanning unit 62 reflects the laser light L1a emitted from the end face 5b of the optical fiber 5 to scan the laser light L1a over the workpiece S, and also reflects the thermal radiation light L2 emitted in the irradiation area Sa to cause the thermal radiation light L2 to be incident on the end face 5b of the optical fiber 5. This makes it possible to accurately detect the thermal radiation light L2 emitted in the irradiation area Sa for each position of the irradiation area Sa while moving the irradiation area Sa relative to the workpiece S. In particular, in the laser processing apparatus 1, the optical fiber 5 satisfies (D2-D1)>D1 (D1: outer diameter of the core 51, D2: outer diameter of the cladding 52) from the end face 5a to the end face 5b. Therefore, even if the amount of the thermal radiation light L2 incident on the end face 5b of the optical fiber 5 is reduced as the thermal radiation light L2 passes through the optical scanning unit 62, the thermal radiation light L2 emitted in the irradiation area Sa can be reliably detected, as described above.

[0061] In the laser processing device 1, the optical fiber 5 satisfies (D2-D1)>(D1×1.5) (D1: outer diameter of the core 51, D2: outer diameter of the cladding 52) from the end face 5a to the end face 5b. This makes the effect of satisfying (D2-D1)>D1 more pronounced. [Modification]

[0062] The present disclosure is not limited to the above example. For example, from the viewpoint of preventing the thermal radiation light L2 emitted from the end face 5a from being buried in noise light, it is sufficient that the optical fiber 5 satisfies (D2-D1)>D1 at least at the end face 5a. Furthermore, the outer diameter of the core 51 of the optical fiber 5 may be greater than 200 μm.

[0063] The irradiation unit 6 may be configured to include an fθ lens 63 and have the optical scanning unit 62 include one galvanometer mirror, thereby constituting a one-dimensional galvanometer system. Alternatively, the irradiation unit 6 may be configured not to include an fθ lens 63 and have the head unit 61 focus the laser light L1a and move along the optical axis of the laser light L1a, thereby constituting a three-dimensional galvanometer system.

[0064] The light source 2 may be a fiber laser. In this case, the light source 2 includes a semiconductor laser for excitation and an optical fiber for amplification, and the end face 4 a of the optical fiber 4 is connected to the light-emitting end face of the optical fiber for amplification.

[0065] Furthermore, even if the optical fiber 5 does not satisfy (D2-D1)>D1 (D1: outer diameter of the core 51, D2: outer diameter of the cladding 52) from the end face 5a to the end face 5b, by using a configuration in which the thermal radiation light L2 emitted in the irradiation area Sa is propagated not only through the core 51 of the optical fiber 5 but also through the cladding 52 of the optical fiber 5, the thermal radiation light L2 emitted in the irradiation area Sa can be reliably detected.

[0066] Furthermore, if the optical fiber 5 satisfies (D2-D1)≧D1 (D1: outer diameter of the core 51, D2: outer diameter of the cladding 52) at the end face 5a, the thermal radiation light L2 emitted in the irradiation area Sa can be detected with higher accuracy than in a configuration in which the optical fiber 5 satisfies (D2-D1)<D1 at the end face 5a.

[0067] 1...laser processing device, 2...light source, 4...optical fiber (second optical fiber), 5...optical fiber (first optical fiber), 5a...end face (first end face), 5b...end face (second end face), 6...irradiation unit, 10...monitor unit, 41...core, 51...core, 52...clad, 53...coating layer, 62...light scanning unit, L1, L1a...laser light, L2...thermal radiation light, S...object to be processed, Sa...irradiation area.

Claims

1. A laser processing device comprising: a light source that emits laser light for processing a workpiece; an irradiation unit that irradiates the laser light onto the workpiece; a monitor unit that detects thermal radiation light emitted in an area of ​​the workpiece that is irradiated with the laser light; and a first optical fiber that propagates the laser light from the monitor unit to the irradiation unit and propagates the thermal radiation light from the irradiation unit to the monitor unit, wherein the first optical fiber has a first end face optically connected to the monitor unit and a second end face optically connected to the irradiation unit, and the monitor unit directs the laser light to be incident on the first end face and detects the thermal radiation light emitted from the first end face, wherein the first optical fiber satisfies (D2 - D1) > D1 at least at the first end face, where D1 is the outer diameter of a core contained in the first optical fiber and D2 is the outer diameter of a cladding contained in the first optical fiber.

2. The laser processing device according to claim 1, wherein the first optical fiber satisfies (D2-D1)>D1 from the first end face to the second end face.

3. The laser processing device according to claim 2, wherein the first optical fiber further includes a coating layer covering the clad, and the thermal radiation light propagating from the irradiation unit to the monitor unit is totally reflected at the interface between the clad and the coating layer.

4. The laser processing device according to claim 3, wherein the refractive index of the material of the cladding is greater than the refractive index of the material of the coating layer.

5. A laser processing device according to any one of claims 1 to 4, wherein the first optical fiber satisfies (D2 - D1) ≥ (D1 x 1.5) at least at the first end face.

6. A laser processing device according to any one of claims 1 to 5, wherein the outer diameter of the core included in the first optical fiber is 200 μm or less.

7. A laser processing device according to any one of claims 1 to 6, further comprising a second optical fiber that propagates the laser light from the light source to the monitor unit, wherein the outer diameter of the core included in the first optical fiber is substantially equal to the outer diameter of the core included in the second optical fiber.

8. A laser processing device according to any one of claims 1 to 7, wherein the irradiation unit includes an optical scanning unit that reflects the laser light emitted from the second end face to scan the laser light across the workpiece, and reflects the thermal radiation light emitted in the irradiation area of ​​the laser light on the workpiece to cause the thermal radiation light to be incident on the second end face.

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