Film removal method and film removal system

Abstract

This film removal method comprises, for example, a first step for performing laser light irradiation on the surface of a processing object having a base material and a film covering the base material to form a crack in the film, and a second step for removing the film subdivided by the crack. In the first step, a mesh-like crack may be formed in the film. The method may further include a third step for performing laser light irradiation on the surface of the processing object to form a crack at the boundary between the film and an object to which the film adheres. Furthermore, in the first step, the portion where the film adheres to the object covered with the film may be irradiated with laser light with power greater than that of the portion where the film is separated from the object covered with the film.

Description

Film removal method and film removal system

[0001] This invention relates to a method for removing a coating and a system for removing a coating.

[0002] Conventionally, a method for removing coatings and deposits from the surface of a structure by irradiating it with laser light is known (for example, Patent Document 1).

[0003] Patent No. 5574354

[0004] The inventors had been diligently researching the removal of coatings from base materials by laser irradiation, and as a result, they discovered a novel method that allows for easier and more precise removal of coatings.

[0005] In other words, one of the objectives of the present invention is, for example, to provide an improved and novel method and system for removing coatings.

[0006] The present invention provides a method for removing a coating, comprising, for example, a first step of irradiating the surface of a workpiece having a base material and a coating covering the base material with laser light to cause cracks in the coating, and a second step of removing the coating that has been subdivided by the cracks.

[0007] In the above-mentioned method for removing the coating, a network of cracks may be formed in the coating during the first step.

[0008] The aforementioned coating removal method may include a third step of irradiating the surface of the object to be processed with laser light to cause cracks at the boundary between the coating and the object to which the coating adheres.

[0009] In the above-mentioned film removal method, in the first step, the portion of the film that is attached to the object to be covered by the film may be irradiated with laser light at a greater power than the portion of the film that is separated from the object to be covered by the film.

[0010] In the above-mentioned coating removal method, the laser beam spot may be scanned on the surface of the workpiece in the first step.

[0011] In the aforementioned film removal method, the spot may have a plurality of first spots.

[0012] In the above-mentioned film removal method, in the first step, the plurality of first spots may be scanned while rotating on the surface of the workpiece.

[0013] In the above-mentioned film removal method, the laser beam is divided by a diffractive optical element to form the plurality of first spots on the surface of the workpiece, and the plurality of first spots on the surface of the workpiece may be rotated by rotating the diffractive optical element.

[0014] In the above-mentioned method for removing the coating, the fragmented coating may be blown off by blowing gas in the second step.

[0015] In the aforementioned coating removal method, the base material may be an iron-based material, and the coating may be an oxide film.

[0016] The coating removal system of the present invention comprises, for example, a laser device that outputs laser light, and an optical head that irradiates the laser light output from the laser device toward the surface of a workpiece having a base material and a coating covering the base material, and removes the coating after cracks are formed in the coating by irradiating the surface of the workpiece with laser light.

[0017] The aforementioned coating removal system may include a coating removal mechanism that removes the coating that remains in a fragmented state due to the cracks.

[0018] In the aforementioned coating removal system, the coating removal mechanism may include a blower that blows gas onto the workpiece.

[0019] According to the present invention, for example, it is possible to provide a novel and improved method and system for removing coatings.

[0020] Figure 1 is an exemplary schematic configuration diagram of the coating removal system of the embodiment. Figure 2 is a schematic and exemplary cross-sectional view of an optical head included in the coating removal system of the embodiment. Figure 3 is an explanatory diagram illustrating the concept of the principle of a diffractive optical element included in the coating removal system of the embodiment. Figure 4 is a schematic plan view showing an example of a spot pattern formed on a virtual irradiation surface in the coating removal method of the embodiment. Figure 5 is a flowchart showing an exemplary processing procedure of the coating removal method of the embodiment. Figure 6 is an exemplary cross-sectional view of a location where there is no gap between the base material and the coating before processing by the coating removal method of the embodiment. Figure 7 is an exemplary cross-sectional view showing a state in which cracks have formed in the coating at the location in Figure 6 of the processing object being processed by the coating removal method of the embodiment. Figure 8 is a photographic image of the surface showing a state in which a mesh-like crack has formed in the coating of the processing object irradiated with laser light in the coating removal method of the embodiment. Figure 9 is an exemplary cross-sectional view showing the state of the location in Figure 6 of the processing object being processed by the coating removal method of the embodiment after Figure 7. Figure 10 is an exemplary cross-sectional view of the location in Figure 6 of the processing object being processed by the coating removal method of the embodiment. Figure 11 is an exemplary cross-sectional view showing a state in which cracks have formed in the coating at a location where there is a gap between the base material and the coating being processed by the coating removal method of the embodiment. Figure 12 is an exemplary cross-sectional view showing the state of the location in Figure 11 of the workpiece being processed by the coating removal method of the embodiment after Figure 11. Figure 13 is an exemplary cross-sectional view of the location in Figure 11 of the workpiece being processed by the coating removal method of the embodiment. Figure 14 is an exemplary cross-sectional view showing a state in which cracks have formed in the outermost coating of a part of a workpiece being processed by the coating removal method of the embodiment, where a double coating has been formed on the base material. Figure 15 is an exemplary cross-sectional view showing the state of the location in Figure 14 of the workpiece being processed by the coating removal method of the embodiment after Figure 14. Figure 16 is an exemplary cross-sectional view of the location in Figure 14 of the workpiece after the outermost coating has been removed by the coating removal method of the embodiment. Figure 17 is a schematic plan view showing another example of a spot pattern formed on a virtual irradiation surface in the coating removal method of the embodiment. Figure 18 is a schematic plan view showing an example of the change in the treatment area of ​​the surface of the workpiece due to the coating removal method of the embodiment.

[0021] Illustrative embodiments of the present invention are disclosed below. The configurations of the embodiments shown below, as well as the actions and results (effects) brought about by such configurations, are examples only. The present invention can also be realized by configurations other than those disclosed in the following embodiments. Furthermore, according to the present invention, it is possible to obtain at least one of the various effects (including derived effects) that can be obtained by the configuration.

[0022] Furthermore, in this specification, ordinal numbers are assigned for convenience to distinguish items to which they are assigned, and do not indicate priority, order, or limit the number of items.

[0023] In addition, directions are sometimes defined by arrows labeled X, Y, and Z in the diagram. The X, Y, and Z directions intersect and are also orthogonal to each other.

[0024] Furthermore, in the following explanation, in patterns containing multiple spots, unless otherwise specified, the power densities of the multiple spots are assumed to be approximately the same. Also, in each plan view showing the pattern on the virtual illumination surface, the arrangement of the multiple spots is shown in an unrotated state.

[0025] [Coating Removal System] Figure 1 is a diagram showing the schematic configuration of the coating removal system 1 of an embodiment. As shown in Figure 1, the coating removal system 1 comprises a base device 100, an optical head 200, and a cable 300.

[0026] The objects to be processed 10 are diverse, including buildings, structures, architectural materials, steel plates, bridge girders, concrete, and the products, parts, and objects that make them up. The objects to be processed 10 have a base material 11 and a coating 12 that covers the base material 11. The base material 11 is, for example, metal made of iron-based materials, concrete, mortar, etc., but is not limited to these. The coating 12 is, for example, an oxide film such as black rust (mill scale) or red rust, or a paint film, etc., but is not limited to these.

[0027] The base device 100 includes a laser device 101 and a gas supply device 102.

[0028] The laser device 101 is equipped with a laser oscillator and is configured to output laser light with a power of 6000 [W], for example. The laser oscillator is an example of a laser device. The wavelength of the laser light output by the laser oscillator is, for example, 400 [nm] or more and 1200 [nm] or less. The laser oscillator is typically a fiber laser oscillator with a wavelength of 1070 [nm]. However, the laser oscillator may also be a semiconductor laser oscillator with a wavelength of 940 [nm], a semiconductor laser oscillator with a wavelength of 450 [nm], or a disk laser or solid-state laser with a wavelength of 1064 [nm].

[0029] The laser device 101 and the optical head 200 are optically connected via an optical fiber cable 301 (see Figure 2) housed within the cable 300. The optical fiber cable 301 has an optical fiber (not shown) having a core and a cladding surrounding the core. The optical fiber transmits the laser light output from the laser device 101 to the optical head 200.

[0030] To accommodate a workpiece 10 located relatively far from the base device 100 or a relatively large workpiece 10, the length of the optical fiber cable 301 and, by extension, the cable 300 is set to, for example, 5 [m] or more and 300 [m] or less. Because there is a trade-off relationship between optical density and transmittable cable length due to the energy shift caused by stimulated Raman scattering, in order to achieve transmission of laser light over such long distances, the diameter of the optical fiber core is preferably 50 [μm] or more, more preferably 80 [μm] or more, and even more preferably 100 [μm] or more.

[0031] Furthermore, in order to obtain a high-quality processed surface (surface removal surface) with less processing unevenness and high shape accuracy, it is essential to maintain high quality laser light output from the optical fiber to the optical head 200. From this perspective, the optical fiber, in the specifications having the length and diameter described above, has a high M laser light output from the optical fiber. ２ The beam quality is set to below a predetermined value. ２ Beam quality is M ２ It can also be called a factor.

[0032] If the optical fiber is a single-mode optical fiber, M ２ The beam quality is set to 1.5 or less, in which case the laser output is set to between 300 [W] and 5000 [W].

[0033] Furthermore, if the optical fiber is a multimode optical fiber, M ２ The beam quality is set to 10 or less, in which case the laser output is set to between 500 [W] and 20,000 [W].

[0034] The gas supply device 102 includes a pump, tank, valve, etc., for supplying gas to the optical head 200 at a predetermined pressure or flow rate via a gas tube 302 (see Figure 2) housed within the cable 300. The gas is, for example, an inert gas such as nitrogen or air.

[0035] The base device 100 also includes a power supply and a cooling device (not shown). The power supply includes, for example, a battery or a generator, and supplies the power necessary for the electrical components in the optical head 200 to operate via power wiring in an electrical cable 303 (see Figure 2) housed within the cable 300. These electrical components include, for example, actuators such as electric motors and sensors such as temperature sensors. The electrical cable 303 may also house control signal wiring for transmitting control signals from actuators and detection signal wiring for transmitting detection signals from sensors (not shown) provided in the optical head 200. The cooling device includes, for example, a tank for storing refrigerant and a pump for discharging the refrigerant, and supplies refrigerant to the refrigerant passage 201b (see Figure 2) in the optical head 200 via a refrigerant tube 304 (see Figure 2) housed within the cable 300.

[0036] [Optical Head] FIG. 2 is a cross-sectional view showing a schematic configuration of an optical head 200 according to an embodiment. The optical head 200 irradiates a laser beam L onto a surface 10a of a workpiece 10 to be processed. By irradiating the laser beam L under appropriate conditions, a coating 12 covering a base material 11 can be removed at and in the vicinity of a location irradiated with the laser beam L on the surface 10a. Details of the method for removing the coating 12 will be described later.

[0037] The optical head 200 is an optical device for appropriately irradiating a laser beam, which is input from a laser device 101 through an optical fiber cable 301, toward the workpiece 10. The laser beam L output from the optical head 200 is, for example, a continuous wave.

[0038] As shown in FIG. 2, the optical head 200 includes a housing 201, a plurality of optical components 202, a connector 203, a motor 204, a rotation transmission mechanism 205, a slider 206, and the like.

[0039] The housing 201 has a substantially cylindrical shape, and accommodates the plurality of optical components 202 inside thereof. In addition to the plurality of optical components 202, the housing 201 also functions as a support member that supports the connector 203, the motor 204, the rotation transmission mechanism 205, the slider 206, and the like.

[0040] A window member 201a that transmits the output laser beam L is attached to an end of the housing 201. Further, the housing 201 is provided with a passage 201b through which a refrigerant supplied via a refrigerant tube 304 passes. The portion of the housing 201 that constitutes the passage 201b, the refrigerant tube 304, and the cooling device can also be referred to as a cooling mechanism that cools the housing 201 and thus the optical components 202.

[0041] The optical components 202 are, for example, collimating lenses 202a and 202b, a diffractive optical element 202c (hereinafter referred to as DOE 202c, DOE: diffractive optical element), an adjustment lens 202d, and the like.

[0042] The collimating lenses 202a and 202b collimate laser light input via an optical fiber and a connector 203. The collimated laser light becomes parallel light.

[0043] The DOE 202c shapes the beam of laser light that has been converted into parallel light by the collimating lenses 202a and 202b. The DOE 202c may also be referred to as a beam shaper.

[0044] Fig. 3 is an explanatory diagram showing the conceptual principle of the DOE 202c. As conceptually illustrated in Fig. 3, the DOE 202c has, for example, a configuration in which a plurality of diffraction gratings 202c1 with different periods are superimposed. The DOE 202c can shape the beam profile by bending the parallel light in directions affected by each diffraction grating 202c1 and superimposing the light components.

[0045] By including a beam shaper such as the DOE 202c, in the optical head 200, the laser light is split into a plurality of beams whose respective powers are appropriately adjusted. Laser light L having a plurality of beams is output in the Z direction from the optical head 200 toward the surface 10a, and a plurality of spots are formed by the plurality of beams on the surface 10a. The spots may be spaced apart from each other or may be connected to each other. The Z direction is the output direction of the laser light L from the optical head 200, and is an example of a first direction.

[0046] The adjustment lens 202d is a condensing lens or a diffusion lens. The adjustment lens 202d is attached to the housing 201 such that the position thereof along the optical axis Ax can be changed. Specifically, for example, the configuration is such that the position of the adjustment lens 202d can be changed by a manually operable slider 206 outside the housing 201. Note that the position adjustment of the adjustment lens 202d may be performed by an electrically actuated actuator.

[0047] Furthermore, the adjustment lens 202d is replaceably attached to the housing 201. Specifically, for example, a subassembly in which the slider 206 and the adjustment lens 202d are integrated is replaceably attached to the housing 201.

[0048] With this configuration, in this embodiment, the laser beam L output from the optical head 200 can be enlarged or reduced, and consequently, the size of the spot formed on the surface 10a can be adjusted.

[0049] In this embodiment, as an example, an adjustment lens 202d as an optical component 202 is shown to be interchangeably (removably) attached to the housing 201. However, other optical components 202, such as a DOE 202c or collimating lenses 202a and 202b, may also be interchangeably (removably) attached to the housing 201.

[0050] Furthermore, the DOE 202c is mounted on the housing 201 so as to be rotatable around a rotation center parallel to the optical axis Ax while the laser beam L is output. In this embodiment, the rotor of the motor 204 rotates due to power supplied via the electrical cable 303, and the rotation of the rotor is transmitted to the DOE 202c via the rotation transmission mechanism 205, thereby causing the DOE 202c to rotate. In this case, the rotation center of the DOE 202c may substantially coincide with the optical axis Ax, or it may be separated from the optical axis Ax. The motor 204 and the rotation transmission mechanism 205 are examples of rotation mechanisms and are also examples of movement mechanisms that move the DOE 202c relative to the housing 201. The rotation transmission mechanism 205 may also be called a reduction mechanism. In this embodiment, the motor 204 is an electric motor, but it is not limited to this and may be an air motor. In this case, the motor 204, which functions as an air motor, is operated by compressed air supplied from an air supply device (not shown) mounted on the base device 100 via an air tube (not shown) housed in the cable 300.

[0051] [Spot Pattern] Due to the rotation of the DOE202c described above, the spot of the laser beam L rotates around the rotation center Ce on the surface 10a and on a virtual irradiation surface Pv that is separated from the optical head 200 in the Z direction and intersects and is orthogonal to the Z direction (see Figure 2).

[0052] Here, the actual surface 10a of the workpiece 10 is not necessarily planar, nor is it necessarily perpendicular to the Z direction. Therefore, it can be difficult to determine the configuration and arrangement of spots on the surface 10a. In this embodiment, the shape and arrangement of the laser beam L spots are determined on a virtual irradiation surface Pv that is perpendicular to the Z direction, i.e., the output direction of the laser beam L, and is located away from the optical head 200. That is, the virtual irradiation surface Pv is a virtual plane for determining the configuration and arrangement of the laser beam L spots, and may also be called an identification plane or a detection plane. In this way, by comparing the configuration and arrangement of spots formed by the laser beam L on the virtual irradiation surface Pv, it is possible to determine the agreement or disagreement between the film removal method of this embodiment and another film removal method regarding the configuration and arrangement of spots. The virtual irradiation surface Pv may be defined, for example, as a plane located at a distance from the optical head 200 that is the center of the design range of the distance between the optical head 200 and the surface 10a, or as a plane located at a position that partially overlaps with the surface 10a.

[0053] According to this embodiment, the DOE202c, acting as a beam shaper, splits the laser beam into multiple beams. By further rotating the DOE202c, spots corresponding to multiple beams can be rotated on the surface 10a, thereby increasing the area of ​​the surface 10a that can be processed simultaneously. Furthermore, the energy density at each position on the surface 10a can be set lower, which has the advantage of mitigating the thermal effects on areas deeper than the surface to be processed. When the target object is metal, the formation of a surface oxide film due to thermal effects can be suppressed simultaneously with the removal of the coating, resulting in the ability to achieve both the required processing speed and quality for coating and rust removal. Moreover, in a pattern containing multiple spots by appropriately setting the DOE202c, the arrangement of the multiple spots and the power of each spot can be appropriately set, thereby suppressing variations in the power density distribution on the surface 10a, and thus suppressing variations and uneven processing on the processed surface. Note that if only a single spot with a single beam is rotated without splitting the beam, it becomes difficult to suppress uneven processing.

[0054] Figure 4 is a plan view illustrating a pattern P21 of spots S formed on a virtual irradiation surface Pv. As shown in Figure 4, the pattern P21 includes multiple spots S of multiple beams of laser light L, each at a different distance from the rotation center Ce. The multiple spots S are arranged in a roughly cross shape in a plan view with respect to the virtual irradiation surface Pv. The power and size of the multiple spots S are the same. Spot S is an example of the first spot.

[0055] As the DOE202c rotates as described above, pattern P21 rotates on the virtual irradiation surface Pv around the rotation center Ce at a substantially constant angular velocity over time. As a result, multiple beam spots S, each with appropriately adjusted power density by the DOE202c, rotate on the surface 10a. Compared to, for example, a case where a single beam spot without special power density adjustment rotates on the surface 10a, variations in power density depending on location on the surface 10a, and consequently variations in the processing state of the surface 10a depending on location, can be suppressed. Furthermore, pattern P21 forms multiple spots S on the virtual irradiation surface Pv that are far from the rotation center Ce, and does not form any spots that overlap with the rotation center Ce. If pattern P21 included spots S that overlapped with the rotation center Ce, the spots S would intermittently pass through each position in the region far from the rotation center Ce on the surface 10a as pattern P21 rotates, and the laser beam L would be intermittently irradiated. In contrast, the spot S remains near the rotation center Ce, and the laser beam L is continuously irradiated there. As a result, on the surface 10a, the region where the rotation center Ce is located will be processed more rapidly than the region further away from the rotation center Ce, which may lead to a large difference in processing status depending on the location on the surface 10a. In this regard, as in pattern P21 in Figure 4, when there is no spot S overlapping with the rotation center Ce, the continuous irradiation of the laser beam L near the rotation center Ce can be suppressed, and consequently, the large difference in processing status depending on the location on the surface 10a can be suppressed. In reality, however, it is unlikely that the rotation center Ce will remain completely still, so in the case of pattern P21, there will almost never be any localized areas where the laser beam L is not irradiated and the surface is not treated.

[0056] Furthermore, when rotating the spot S pattern on the surface 10a, the pattern may be formed such that the power density per spot S increases as it moves away from the rotation center Ce, or the area of ​​each spot S increases as it moves away from the rotation center Ce. In this case, the difference in power density depending on the distance from the rotation center Ce can be reduced, and variations in power density depending on the location on the surface 10a, and consequently variations in the processing state depending on the location on the surface 10a, can be further suppressed.

[0057] [Surface Removal Method] Figure 5 is a flowchart showing the procedure for the coating removal method of this embodiment. In the coating removal method of this embodiment, first, cracks C are formed in the coating 12 by irradiation with laser light L (S1, see Figure 7). Next, cracks C are formed at the boundary B between the coating 12 and the object to which the coating 12 adheres (hereinafter also referred to as the adhesion boundary) by irradiation with laser light L (S2, see Figure 9). Finally, the coating 12 is removed by blowing gas g or the like (S3, see Figures 9 and 10). The coating removal method shown here is a novel removal method that subdivides the coating 12 in S1 and S2 to make it easier to peel off, and then removes the subdivided coating 12 more easily in S3. S1 is an example of the first step. S2 is an example of the third step. S3 is an example of the second step.

[0058] [Case (1)] Figure 6 is a cross-sectional view of a portion of the workpiece 10 where there is no gap between the base material 11 and the coating 12 (or a portion of the workpiece 10). Laser light L is irradiated onto the surface 10a of this portion, that is, the surface of the coating 12 opposite to the base material 11. In case (1), the object to which the coating 12 adheres, and the object covered by the coating 12, is the base material 11.

[0059] FIG. 7 is a cross-sectional view showing a state where cracks C are formed in the coating film 12 at the location of the workpiece 10 shown in FIG. 6 by irradiation of the laser beam L (S1 in FIG. 5). Further, FIG. 8 is a plan view of the workpiece 10 in which mesh-like cracks C are formed in the coating film 12 by S1 in FIG. 5. As shown in FIGS. 7 and 8, the inventors have found that by irradiating the coating film 12 of the workpiece 10 with a laser beam L under predetermined conditions, mesh-like cracks C as shown in FIG. 7 can be formed over a relatively wide range of the coating film 12. It has been found that the cracks C are formed by irradiation with a power lower than that used when removing the coating film 12 by ablation. The conditions under which suitable cracks C could be formed in the coating film 12 were, for example, as follows. (Object) ・Material of base material: Steel material ・Material of coating film: Black scale (black rust, oxide film) ・Thickness of coating film: 10 to 1000 [μm] (Irradiation conditions) ・Spot pattern: Only one row going radially outward from the rotation center Ce among the four rows constituting the cross of P21 (FIG. 4) ・Diameter of each spot S: 312.5 [μm] (on the virtual irradiation surface Pv) ・Number of spots per row: 5 to 10 ・Rotation speed of the pattern: 1000 to 10000 [rpm] ・Moving speed of each spot S by rotation of the pattern: 1 to 20 [m / s] ・Total output of the laser device: 700 to 20000 [W] ・Power density of each spot S: 10 ５ to 10 ７ [W / cm ２ or more ・Power per unit area on the surface of the workpiece: 50 to 100 [W / cm ２] ・Scanning speed: 5 to 1000 [mm / sec] ・Wavelength: 1070 ± 20 [nm] (infrared laser) ・Number of scans: Performing scans at least once under the above irradiation conditions As a result of diligent research, it was found that when the maximum dimension of the area surrounded by crack C in a plan view relative to the surface is 2 [mm] or less, the coating 12 becomes easier to peel off from the base material 11 and easier to remove. Irradiation under the above irradiation conditions made it possible to reduce the maximum dimension in the irradiated area to 2 [mm] or less. If cracks C with a maximum dimension of 2 [mm] or less do not occur in one scan under the above irradiation conditions, it was found that cracks C with a maximum dimension of 2 [mm] or less will occur by repeating the irradiation under the above irradiation conditions. Intermittent irradiation is performed at appropriate intervals, which generates a heat cycle in the coating 12, and it is presumed that this makes it easier for cracks C to occur in the coating 12. Furthermore, it was found that if the rotation speed of the pattern, the movement speed of each spot S due to the rotation of the pattern, and the scanning speed each fall below the lower limit of the above numerical range by a predetermined amount, the coating 12 melts due to excess energy, and cracks C do not occur. It was also found that if the total output of the laser device, the power density of each spot S, and the power per unit area on the surface of the workpiece each exceed the upper limit of the above numerical range by a predetermined amount, the coating 12 melts due to excess energy, and cracks C do not occur. Furthermore, it was found that if the rotation speed of the pattern, the movement speed of each spot S due to the rotation of the pattern, and the scanning speed each exceed the upper limit of the above numerical range by a predetermined amount, the state in which cracks C occur does not occur due to insufficient energy. Furthermore, it was found that if the total output of the laser device, the power density of each spot S, and the power per unit area on the surface of the workpiece each fall below the lower limit of the above numerical range by a predetermined amount, the state in which cracks C occur does not occur due to insufficient energy. The above irradiation conditions (numerical range) apply to the case where the spot pattern is arranged in a single line radially from the rotation center Ce. If the number of rows of spot patterns extending radially from the rotation center Ce increases by a factor of n (where n is an integer of 2 or more) in the circumferential direction, the rotation speed should be reduced to 1 / n. For example, in the case of the cross-shaped spot pattern in Figure 4, the number of rows of spot patterns increases fourfold, so the rotation speed should be reduced to 1 / 4 under the above irradiation conditions.

[0060] Figure 9 is a cross-sectional view showing the state of the location in Figure 6 after Figure 7. It was found that after the state in Figure 7, further irradiation with laser light L may result in the state shown in Figure 9. In the state shown in Figure 9, the crack C formed in the coating 12 at S1 becomes a larger gap G1, and furthermore, crack C is also formed at the boundary B between the base material 11 and the coating 12 (S2 in Figure 5). Due to the formation of such gap G1 and crack C, the coating 12 becomes even easier to peel off from the base material 11.

[0061] Furthermore, once the gap G1 and crack C have formed, gas g is blown from the blower 102a toward the coating 12, as shown in Figure 9. The gas g is supplied from the gas supply device 102 via the gas tube 302. By blowing gas g, the coating 12 can be removed from the base material 11 (S3 in Figure 5). Figure 10 is a cross-sectional view showing the state of the location in Figure 6 after Figure 9. The gas supply device 102, gas tube 302, and blower 102a are an example of a coating removal mechanism. Note that the coating removal mechanism is not limited to the example of this embodiment, and may be other mechanisms such as a brush mechanism that vibrates, oscillates, or rotates.

[0062] As explained above, the inventors have discovered a novel method for removing a coating that allows for easier, faster, and cleaner removal of the coating 12 by forming cracks C in the coating 12 and subdividing the coating 12. It can be presumed that these cracks C are formed by the difference in thermal expansion coefficients between the coating 12 and the object to which the coating 12 adheres (or the object it covers, in case (1), the base material 11). Therefore, the laser light L may be irradiated under conditions in which the area near the coating 12 of the object to which the coating 12 adheres (in case (1), the base material 11) is heated along with the coating 12, or under conditions in which the coating 12 is mainly heated. Furthermore, a cooling step may be added after heating in step S1, or a cooling step may be added after heating in step S2. In addition, under certain conditions, the coating 12 could be removed by blowing gas g in the state shown in Figure 7, which does not result in the state shown in Figure 9. Furthermore, in S3, the subdivided coating 12 may be removed individually, or multiple subdivided coatings 12 may be removed as a certain mass.

[0063] [Case (2)] Figure 11 is a cross-sectional view of a location (or part of the object to be processed 10) where there is a gap G2 between the base material 11 and the coating 12, and shows a state in which cracks C have been formed in the coating 12 by irradiation with laser light L (S1 in Figure 5). In this case, the laser light L is irradiated under conditions that mainly heat the coating 12. That is, in case (2), at S1, the laser light L is irradiated with less power than in case (1). In other words, at S1, the laser light L is irradiated with greater power in areas where the coating 12 is attached to the base material 11 (the object to be covered by the coating 12) than in areas where the coating 12 is far from the base material 11 (the object to be covered by the coating 12).

[0064] Figure 12 is a cross-sectional view showing the state of the location in Figure 11 after Figure 11. It was found that after the state in Figure 11, further irradiation with laser light L may result in the state shown in Figure 12. In the state shown in Figure 12, the crack C formed in the coating 12 in S1 has become a larger gap G1. The formation of such a gap G1 makes the coating 12 even easier to peel off from the base material 11. In case (2), since there is originally a gap G2 between the coating 12 and the base material 11 (the object covered by the coating 12), S2 in Figure 5 is not performed.

[0065] Furthermore, once the gap G1 is formed, gas g is blown from the blower 102a toward the coating 12, as shown in Figure 12. By blowing this gas g, the coating 12 can be removed from the base material 11 (S3).

[0066] Figure 13 is a cross-sectional view showing the state of the location in Figure 11 after Figure 12. As shown in Figure 13, in the location of case (2) of the workpiece 10, or in the workpiece 10 itself, cracks C are formed in the coating 12 and the coating 12 is subdivided, making it possible to remove the coating 12 more easily, more quickly, or more cleanly. In case (2), in S3, each subdivided piece of coating 12 may be removed individually, or multiple subdivided pieces of coating 12 may be removed as a certain mass.

[0067] [Case (3)] Figure 14 is a cross-sectional view of a part of a workpiece 10 in which a double layer of coatings 12 (12-1, 12-1) is formed on the base material 11, and shows a state in which cracks have been formed in the outermost coating 12-1 due to irradiation with laser light L (S1 in Figure 5). In this case, the laser light L may be irradiated under conditions in which, for example, the area near coating 12-2 (the object to which coating 12-1 is attached, the object covered by coating 12-1) is heated together with coating 12-1, or it may be irradiated under conditions in which coating 12-1 is mainly heated.

[0068] Figure 15 is a cross-sectional view showing the state of the location in Figure 14 after the state in Figure 14. It was found that after the state in Figure 14, further irradiation with laser light L may result in the state shown in Figure 15. In the state in Figure 15, the crack C formed in the coating 12 at S1 becomes a larger gap G1, and furthermore, a crack C is formed at the boundary B between coating 12-1 and coating 12-2 (S2 in Figure 5). Due to the formation of such gap G1 and crack C, coating 12-1 becomes even easier to peel off from coating 12-2.

[0069] Furthermore, once the gap G1 is formed, gas g is blown from the blower 102a toward the coating 12, as shown in Figure 15. By blowing gas g, the fragmented coating 12-1 can be removed from the coating 12-2 (S3).

[0070] Figure 16 is a cross-sectional view showing the state of the area in Figure 14 after Figure 15. As shown in Figure 16, by forming cracks C in the coating 12-1 and subdividing it, the coating 12-1 could be removed more easily, more quickly, and more cleanly, even in the area of ​​case (2) of the workpiece 10 or in the workpiece 10 itself. Subsequently, the coating 12-2 (12) can be removed from the base material 11 by performing the same procedure as in case (1) on the area shown in Figure 16 where the base material 11 is covered with coating 12-2 (12). If multiple coatings 12-1 and 12-2 are formed, if possible, these multiple coatings 12-1 and 12-2 may be removed simultaneously using the procedure in case (1).

[0071] [Variations of Spot Patterns] Figure 17 is a plan view illustrating a spot pattern P22 formed on a virtual irradiation surface Pv. Pattern P22 includes multiple spots S that rotate around a rotation center Ce, as well as multiple spots S at different distances from the rotation center Ce. In pattern P22, adjacent spots S are arranged such that the spacing i between them is greater than or equal to a predetermined distance, and the difference in distance dr (i.e., difference in radius) from the rotation center Ce is less than a predetermined distance. The spacing i is the distance between the centers (geometric centers) of the spots S. If the spacing i between adjacent spots S in a plurality of spots S arranged radially along the rotation center Ce is too short, the power density may become excessively high, potentially causing melting or damage to areas deeper than the surface to be treated. If the spacing i is increased as a countermeasure, variations in the power density distribution in the radial direction may occur, potentially resulting in a situation where sufficiently treated areas and insufficiently treated areas alternate in a concentric pattern. Another approach is to reduce the power of each spot S without changing the spacing i between adjacent spots S. However, this may result in insufficient power for surface treatment or an increased time required to complete the required surface treatment. In this regard, pattern P22 is designed such that adjacent spots S are arranged such that the spacing i between them is greater than a predetermined distance, and the difference in distance dr from the rotation center Ce is smaller than the spacing i. This suppresses excessive energy density between adjacent spots S and allows for setting an appropriate power density while suppressing variations in the radial power density distribution. In other words, pattern P22 reduces uneven processing and shortens the time required for processing. Furthermore, in the example shown in Figure 17, since the spacing i between adjacent spots S is set to a constant (approximately the same) distance, the multiple spots S are arranged approximately along a spiral curve Cs where the angular difference with respect to the radial direction increases as the radial direction moves outward. Furthermore, pattern P22 includes multiple groups of spots S aligned along the curve Cs.In this case, the processing time can be reduced compared to the case where there is only one group of spots S aligned along the curve Cs.

[0072] [Removal Area] Figure 18 is a plan view showing an example of the change in the processing area on the surface 10a by the optical head 200. In Figure 18, Ar indicates the irradiation area formed by the rotation of DOE 202c, and As and A indicate the change in the processing area due to the relative movement of the optical head 200 with respect to the workpiece 10, i.e., the expansion of the processed area. The white arrows indicate the direction of movement of the irradiation area As. For simplicity of explanation, in the example of Figure 18, the irradiation area Ar moves linearly, but it is not limited to this, and the irradiation area Ar can move along any path, including a curved path.

[0073] As shown in Figure 18, the relative movement of the optical head 200 allows for an expansion of the irradiation area Ar formed by the rotation of the DOE 202c, making it easier to expand the irradiation areas As and A compared to when the optical head 200 does not move relative to it. Furthermore, if a laser scanner is provided on the optical head 200, at least one of the irradiation areas Ar and As may move due to the operation of the laser scanner alone, or due to the operation of the laser scanner and the relative movement of the optical head 200. Such processing allows for a further expansion of the processing range.

[0074] Although embodiments of the present invention have been illustrated above, these embodiments are merely examples and are not intended to limit the scope of the invention. The above embodiments can be implemented in various other forms, and various omissions, substitutions, combinations, and modifications can be made without departing from the spirit of the invention. Furthermore, each configuration, shape, and other specifications (structure, type, orientation, model, size, length, width, thickness, height, number, arrangement, position, material, etc.) can be modified as appropriate.

[0075] 1…Coating removal system 10…Object to be processed 10a…Surface 11…Base material (object to which the coating adheres, object covered by the coating) 12, 12-1…Coating 12-2…Coating (object to which the coating adheres, object covered by the coating) 100…Base device 101…Laser device 102…Gas supply device 102a…Blower 200…Optical head 201…Housing 201a…Window member 201b…Passage 202…Optical components 202a, 202b…Collimating lens 202c…DOE (diffractive optical element) 202c1…Diffraction grating 202d…Adjustment lens 203…Connector 204…Motor (electric motor, air motor, rotation mechanism, moving mechanism) 205…Rotation transmission mechanism (rotation mechanism, moving mechanism) 206…Slider 300…Cable 301…Optical fiber cable 302...Gas tube 303...Electrical cable 304...Refrigerant tube A...Irradiation area Ar...Irradiation area As...Irradiation area Ax...Optical axis B...Boundary C...Crack Ce...Center of rotation Cs...Curve dr...Difference G1, G2...Gap g...Gas i...Spacing L...Laser beam P21, P22...Pattern Pv...Virtual irradiation surface S...Spot (first spot) S1...Process (first process) S2...Process (third process) S3...Process (second process) Z...Direction

Claims

1. A method for removing a coating, comprising: a first step of irradiating the surface of a workpiece having a base material and a coating covering the base material with laser light to cause cracks in the coating; and a second step of removing the coating that has been subdivided by the cracks.

2. The method for removing a coating according to claim 1, wherein a network of cracks is formed in the coating in the first step.

3. The method for removing a coating according to claim 1, further comprising a third step of irradiating the surface of the object to be processed with laser light to cause cracks at the boundary between the coating and the object to which the coating adheres.

4. The method for removing a coating according to claim 1, wherein in the first step, the portion of the coating that is attached to the object to be covered by the coating is irradiated with laser light at a greater power than the portion of the coating that is separated from the object to be covered by the coating.

5. The method for removing a coating according to claim 1, wherein in the first step, a spot of laser light is scanned on the surface of the object to be processed.

6. The method for removing a coating according to claim 5, wherein the spot has a plurality of first spots.

7. The method for removing a coating according to claim 6, wherein in the first step, the plurality of first spots are scanned on the surface of the workpiece while rotating.

8. The method for removing a coating according to claim 7, wherein a diffractive optical element divides a beam of laser light to form a plurality of first spots on the surface of the workpiece, and the diffractive optical element is rotated to rotate the plurality of first spots on the surface of the workpiece.

9. The method for removing a film according to claim 1, wherein in the second step, the fragmented film is blown away by blowing gas.

10. The method for removing a coating according to claim 1, wherein the base material is an iron-based material and the coating is an oxide film.

11. A coating removal system comprising: a laser device that outputs laser light; and an optical head that irradiates the surface of a workpiece having a base material and a coating covering the base material with the laser light output from the laser device, wherein the system removes the coating after forming cracks in it by irradiating the surface of the workpiece with laser light.

12. The coating removal system according to claim 11, further comprising a coating removal mechanism for removing the coating that remains in a fragmented state due to the cracks.

13. The coating removal system according to claim 12, wherein the coating removal mechanism has a blower for blowing gas onto the workpiece.

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