JP2019136735A - Laser processing method and laser processing device - Google Patents

Abstract

To provide a laser processing method and a laser processing device capable of shortening a processing time while restraining thermal influence received by a workpiece.SOLUTION: A laser processing method comprises an abrasion step and an oxidation layer removal step. The abrasion step forms a second processed surface having a projection part lower than a projection part of a first processed surface by removing the projection part of the first processed surface by irradiating the first processed surface having irregularities with a first pulse laser beam in an oxidative atmosphere that promotes oxidation. The oxidation layer removal step removes an oxidation layer by irradiating the oxidation layer formed on the second processed surface in the abrasion step with a second pulse laser beam different from the first pulse laser beam in an oxidation restraining atmosphere that restrains oxidation after the abrasion step.SELECTED DRAWING: Figure 19

Description

  The present invention relates to a laser processing method and a laser processing apparatus.

  Conventionally, as a laser processing method, for example, there is a method in which a processing surface of a workpiece is melted by laser light and the processing surface is flattened by the action of surface tension. Patent Document 1 discloses a material processing method for forming a recess by removing a processing surface with a laser beam.

JP 2008-119735 A

  By the way, in the conventional laser processing method, for example, when the processing surface is flattened, there is a risk that softening or transformation such as deformation of the workpiece may occur due to thermal effects. When the power is lowered, the processing time tends to increase.

  Therefore, the present invention has been made in view of the above, and it is an object of the present invention to provide a laser processing method and a laser processing apparatus capable of reducing the processing time while suppressing the thermal influence on the workpiece. And

  In order to solve the above-described problems and achieve the object, the laser processing method according to the present invention irradiates the first laser beam onto the first processed surface having irregularities in an oxidizing atmosphere that promotes oxidation, and A removal step of removing a convex portion of one processed surface and forming a second processed surface having a convex portion lower than the convex portion of the first processed surface, and an oxidation that suppresses oxidation after the removing step An oxide layer removal step of removing the oxide layer by irradiating the oxide layer formed on the second processed surface in the removal step with a second laser beam different from the first laser beam in a suppression atmosphere; It is characterized by having.

  In the laser processing method, after the oxide layer removal step, the second laser beam is irradiated with a third laser beam different from the first laser beam and the second laser beam. It is preferable to further have a melting step of forming a processed flat surface by melting the convex portion of the second processed surface and flattening the second processed surface.

  In the laser processing method, in the oxide layer removal step, the oxide layer formed on the second processing surface is removed by the second laser light, and the second processing surface is processed by the second laser light. It is preferable to form a processed flat surface by melting the convex portions of the first flat surface and flattening the second processed surface.

  The laser processing apparatus according to the present invention promotes oxidation by a laser beam irradiation unit that irradiates a first workpiece surface having irregularities with a first laser beam and a second laser beam different from the first laser beam. A gas supply device that supplies an oxidation promoting gas or an oxidation suppression gas that suppresses oxidation, and a control unit that controls the laser light irradiation unit and the gas supply device, wherein the control unit supplies the gas supply In an oxidizing atmosphere formed by the oxidation promoting gas by controlling the apparatus, the laser beam irradiation unit is controlled to irradiate the first laser beam to the first laser beam to form a convex portion of the first workpiece surface. Removing, forming a second workpiece surface having a convex portion lower than the convex portion of the first workpiece surface, and after forming the second workpiece surface, controlling the gas supply device to control the oxidation suppressing gas In the oxidation-inhibiting atmosphere formed by And removing the oxide layer by irradiating a different second laser beam said the first laser beam formed by controlling the light irradiation portion and the second surface to be processed oxide layer.

  A laser processing method and a laser processing apparatus according to the present invention form a second workpiece surface by removing a convex portion of a first workpiece surface of a workpiece by a first laser beam in an oxidizing atmosphere, and in an oxidation-inhibiting atmosphere. Then, the oxide layer formed on the second processed surface at the time of removal is removed by the second laser beam. Thereby, the laser processing method and the laser processing apparatus can suppress the thermal influence which the said workpiece receives by removing a workpiece, and shorten processing time by accelerating removal processing by oxidation reaction heat can do.

FIG. 1 is a block diagram illustrating a configuration example of a laser processing apparatus according to an embodiment. FIG. 2 is a schematic diagram illustrating a configuration example of the gas supply device according to the embodiment. FIG. 3 is an explanatory diagram showing an ablation process according to the embodiment. FIG. 4 is a diagram showing a laser intensity distribution in the ablation process according to the embodiment. FIG. 5 is a schematic diagram illustrating an ablation process according to the embodiment. FIG. 6 is a schematic diagram illustrating an example of forming an oxide layer and oxide debris according to the embodiment. FIG. 7 is an image (top view) showing an example of forming an oxide layer and oxide debris according to the embodiment. FIG. 8 is an image (cross-sectional view) showing an example of forming an oxide layer and oxide debris according to the embodiment. FIG. 9 is a schematic diagram illustrating an oxide layer removing process according to the embodiment. FIG. 10 is a schematic diagram illustrating an example of forming the second processed surface from which the oxide layer and oxide debris according to the embodiment have been removed. FIG. 11 is an image (top view) showing a formation example of the second processed surface from which the oxide layer and oxide debris according to the embodiment have been removed. FIG. 12 is an image (cross-sectional view) showing an example of forming the second processed surface from which the oxide layer and oxide debris according to the embodiment have been removed. FIG. 13 is an explanatory diagram showing a melting step according to the embodiment. FIG. 14 is a diagram showing a laser intensity distribution in the melting step according to the embodiment. FIG. 15 is a schematic diagram illustrating a melting step according to the embodiment. FIG. 16 is a schematic diagram illustrating an example of forming a processed flat surface according to the embodiment. FIG. 17 is an image (top view) showing an example of forming a processed flat surface according to the embodiment. FIG. 18 is an image (cross-sectional view) showing an example of forming a processed flat surface according to the embodiment. FIG. 19 is a flowchart illustrating the laser processing method according to the embodiment. FIG. 20 is a diagram illustrating a processing amount for performing the ablation processing in the oxidation-inhibiting atmosphere according to the comparative example. FIG. 21 is a diagram illustrating a processing amount for performing the ablation processing in the oxidizing atmosphere according to the embodiment.

  DESCRIPTION OF EMBODIMENTS Embodiments (embodiments) for carrying out the present invention will be described in detail with reference to the drawings. The present invention is not limited by the contents described in the following embodiments. The constituent elements described below include those that can be easily assumed by those skilled in the art and those that are substantially the same. Furthermore, the structures described below can be combined as appropriate. Various omissions, substitutions, or changes in the configuration can be made without departing from the scope of the present invention.

Embodiment
The laser processing method and the laser processing apparatus 1 according to the embodiment will be described. The laser processing method is a method of processing the workpiece surface Wa by irradiating the workpiece surface Wa of the workpiece W with pulsed laser light. The laser processing apparatus 1 is an apparatus for performing a laser processing method, and processes the workpiece W by irradiating the workpiece W with pulsed laser light LB. Here, the workpiece W is formed of, for example, a metal material. The workpiece W is, for example, a layered product by a 3D printer, a metal workpiece on which a tool mark or the like is formed. Hereinafter, the laser processing method and the laser processing apparatus 1 will be described in detail.

  In the following description, the first direction (X direction), the second direction (Y direction), and the third direction (Z direction) are orthogonal directions. The first direction and the second direction are directions orthogonal to each other on a placement surface 81b on which a workpiece W to be described later is placed. The third direction is a direction orthogonal to the placement surface 81b. The first direction and the second direction are typically directions orthogonal to each other on the virtual plane when a plane orthogonal to the thickness direction of the workpiece W is a virtual plane, and the third direction. Is a direction orthogonal to the virtual plane.

  For example, the laser processing apparatus 1 fixes the focal point of the pulsed laser beam LB and focuses the pulsed laser beam LB on the processing surface Wa of the workpiece W for processing. As shown in FIG. 1, the laser processing apparatus 1 includes a laser beam irradiation unit 10, a shutter 20, an attenuator 30, a beam expander 40, a beam transmission optical system 50, an episcopic optical system 60, and an objective lens 70. A drive unit 80, a lamp illumination 90, a camera 100, a gas supply device 110, and a control unit 120.

The laser beam irradiation unit 10 is a laser beam oscillator that oscillates a pulsed output (pulsed laser beam LB) at a constant repetition frequency. The laser beam irradiation unit 10 is, for example, a master oscillator output amplifier (MOPA) using a variable pulse width light source as a seed light source. When the laser beam irradiation unit 10 uses MOPA, an example of output characteristics of the pulsed laser beam LB is as follows. That is, the operating wavelength of the pulse laser beam LB is about 1030 nm ± 1 nm, the repetition frequency is about 5 kHz to 10 MHz, the pulse width is about 50 ps to 1 μs, the output power is 10 W or more, The wave is straight, the beam quality square (M ² ) is less than 1.2, and the roundness is more than 80%. The laser beam irradiation unit 10 outputs (emits) the pulsed laser beam LB to the shutter 20. The pulse width is a time interval between the rise and fall of the pulse at a point that is half the peak power of the pulse laser beam LB. Since the laser beam irradiation unit 10 can change the pulse width by using MOPA, the laser beam irradiation unit 10 can cope with various types of processing and can suppress the processing cost.

  The shutter 20 switches between transmission and blocking of the pulse laser beam LB. The shutter 20 is installed between the laser beam irradiation unit 10 and the attenuator 30, and transmits or blocks the pulse laser beam LB output from the laser beam irradiation unit 10. The shutter 20 outputs the transmitted pulsed laser beam LB to the attenuator 30.

  The attenuator 30 is an attenuator that adjusts the intensity of the pulse laser beam LB. The attenuator 30 is installed between the shutter 20 and the beam expander 40, adjusts the intensity of the pulsed laser light LB output from the shutter 20, and outputs it to the beam expander 40.

  The beam expander 40 widens the beam diameter of the pulse laser beam LB. The beam expander 40 is installed between the attenuator 30 and the beam transmission optical system 50, widens the beam diameter of the pulse laser beam LB output from the attenuator 30, and outputs it to the beam transmission optical system 50.

  The beam transmission optical system 50 is an optical system including a light guide mirror that guides the pulse laser beam LB. The beam transmission optical system 50 is installed between the beam expander 40 and the epi-illumination optical system 60, guides the pulse laser beam LB output from the beam expander 40, and outputs it to the epi-illumination optical system 60.

  The epi-illumination optical system 60 is an optical system including a direction change mirror that changes the direction in which the pulse laser beam LB travels. The epi-illumination optical system 60 is installed between the beam transmission optical system 50 and the objective lens 70, changes the traveling direction of the pulsed laser light LB output from the beam transmission optical system 50, and outputs it to the objective lens 70.

  The objective lens 70 collects the pulse laser beam LB and irradiates the workpiece surface Wa of the workpiece W with the pulse laser beam LB. The objective lens 70 is installed between the epi-illumination optical system 60 and the drive unit 80, collects the pulsed laser light LB output from the epi-illumination optical system 60, and the workpiece W placed on the drive unit 80. The processing surface Wa is irradiated with pulsed laser light LB.

  The drive unit 80 holds the workpiece W and moves the workpiece W relative to the optical system including the objective lens 70 and the like. The drive unit 80 includes an XY axis drive unit 81 and a Z axis drive unit 82. The XY axis drive unit 81 includes a plate-like mounting table 81a, a fixing unit (not shown), and an XY axis drive mechanism (not shown) configured by a ball screw or the like. The XY axis driving unit 81 fixes the workpiece W to the mounting surface 81b of the mounting table 81a by the fixing unit, and the X or Y axis driving mechanism moves the workpiece W to the optical system such as the objective lens 70 in the X direction or Move relative to Y direction. The Z-axis drive unit 82 includes a Z-axis drive mechanism (not shown) configured by a ball screw or the like, and moves the workpiece W relative to the optical system such as the objective lens 70 in the Z direction by the Z-axis drive mechanism. .

  The lamp illumination 90 illuminates the workpiece W with illumination. The lamp illumination 90 is installed, for example, facing the placement surface 81b of the drive unit 80, and illuminates the workpiece W placed on the placement surface 81b.

  The camera 100 images the workpiece W. The camera 100 is installed to face the mounting surface 81b of the drive unit 80, and images the unevenness of the processing surface Wa of the workpiece W mounted on the mounting surface 81b. The camera 100 outputs the captured image to the control unit 120.

  The gas supply device 110 supplies gas. For example, as shown in FIG. 2, the gas supply device 110 includes an air pipe 111, a gas pipe 112, a branch connector 113, a mixed gas pipe 114, a first flow rate adjustment unit 115, and a second flow rate adjustment unit 116. And a dust collector 117.

  The air pipe 111 is a pipe capable of supplying air (atmosphere) as an oxidation promoting gas (a support gas). The air pipe 111 has one end connected to an air supply unit (not shown) and the other end connected to the branch connector 113. The air pipe 111 flows the air supplied from the air supply unit toward the branch connector 113.

  The gas pipe 112 is a pipe capable of supplying an inert gas (for example, argon, nitrogen gas, etc.) as an oxidation suppression gas. The gas pipe 112 has one end connected to an inert gas supply unit (not shown) and the other end connected to the branch connector 113. The gas pipe 112 flows the inert gas supplied from the inert gas supply unit toward the branch connector 113.

  The branch connector 113 is a connector that branches or mixes the fluid. The branch connector 113 is a so-called T-type branch connector, and has a first inlet 113a, a second inlet 113b, and an outlet 113c. The branch connector 113 has a first inlet 113 a connected to the air pipe 111, a second inlet 113 b connected to the gas pipe 112, and an outlet 113 c connected to the mixed gas pipe 114. The branch connector 113 mixes, for example, air flowing through the air pipe 111 and inert gas flowing through the gas pipe 112. And the branch connector 113 flows the mixed gas which mixed air and an inert gas toward the mixed gas piping 114. FIG.

  The mixed gas pipe 114 is a pipe through which air, inert gas, or mixed gas can flow. One end of the mixed gas pipe 114 is connected to the branch connector 113, and a nozzle 114a is provided at the other end. In the mixed gas pipe 114, the nozzle 114 a is directed to the workpiece W. The mixed gas pipe 114 injects air, inert gas, or mixed gas flowing out from the branch connector 113 onto the workpiece surface Wa of the workpiece W from the nozzle 114a.

  The first flow rate adjusting unit 115 is a measuring instrument that adjusts and measures the flow rate of the fluid. The first flow rate adjustment unit 115 includes a first adjustment valve 115a and a first flow meter 115b. The first adjustment valve 115a and the first flow meter 115b are provided in the air pipe 111 and are connected to the control unit 120, respectively. The first adjustment valve 115 a adjusts the flow rate of air flowing through the air pipe 111 based on a control signal output from the control unit 120. The first flow meter 115 b measures the flow rate of air flowing through the air pipe 111 and outputs the measured flow rate of air to the control unit 120.

  The second flow rate adjusting unit 116 is a measuring instrument that adjusts and measures the flow rate of the fluid. The second flow rate adjustment unit 116 includes a second adjustment valve 116a and a second flow meter 116b. The second adjustment valve 116a and the second flow meter 116b are provided in the gas pipe 112 and are connected to the control unit 120, respectively. The second adjustment valve 116 a adjusts the flow rate of the inert gas flowing through the gas pipe 112 based on the control signal output from the control unit 120. The second flow meter 116 b measures the flow rate of the inert gas flowing through the gas pipe 112 and outputs the measured flow rate of the inert gas to the control unit 120.

  The control unit 120 controls the laser processing apparatus 1. The control unit 120 includes an electronic circuit mainly composed of a well-known microcomputer including a CPU, a ROM that constitutes a storage unit, a RAM, and an interface. The control unit 120 controls the optical system such as the laser beam irradiation unit 10 and the shutter 20 to adjust the output of the pulsed laser beam LB. Further, the control unit 120 outputs a control signal based on the air flow rate output from the first flow meter 115b to control the first adjustment valve 115a. Further, the control unit 120 outputs a control signal based on the flow rate of the inert gas output from the second flow meter 116b to control the second adjustment valve 116a.

  The dust collector 117 is a device that collects dust. The dust collector 117 has a collection tube 117 a that collects dust, and one end of the collection tube 117 a is directed to the workpiece W. The dust collector 117 collects oxidized debris D (dust) generated when the workpiece W is processed through the collection tube 117a.

  Next, ablation processing by the laser processing apparatus 1 will be described. Here, the ablation processing is removal processing performed by instantaneously evaporating and scattering a portion irradiated with the pulse laser beam LB. Ablation processing is non-thermal processing in which the processing portion is instantly evaporated, scattered and removed, so that the thermal influence on the periphery of the processing portion is small and thermal damage is small. In the ablation processing, the laser processing apparatus 1 uses the first pulse laser beam LB1 (first laser beam) whose pulse width is a short pulse width on the order of picoseconds or less. The first pulse laser beam LB1 has a higher peak value of laser intensity than a second pulse laser beam LB2 (second laser beam) and a third pulse laser beam LB3 (third laser beam) described later (FIGS. 4 and 14). See) and the pulse width is short. The first pulse laser beam LB1 can obtain a machining depth at which the peak value of the laser intensity corresponds to the maximum height (for example, a height exceeding 10 μm) of the convex portion P1 of the first workpiece surface W1. Light energy density. The convex portion P1 of the first workpiece surface W1 is a portion protruding along the Z direction when the deepest portion of the first workpiece surface W1 (the bottom of the recess Q) is used as a reference position (see FIG. 3). ). The first pulse laser beam LB1 has a spot diameter r1 that is the diameter of the portion irradiated to the first workpiece surface W1 smaller than the spot diameter r2 of the third pulse laser beam LB3 (see FIGS. 3 and 13).

  In the case of the ablation process, the laser processing apparatus 1 forms an oxidizing atmosphere that promotes oxidation of the workpiece W (generation of the oxide layer V). Here, the oxidizing atmosphere includes an oxidizing atmosphere under the atmosphere and an oxidizing atmosphere that is intentionally formed. The oxidizing atmosphere under the atmosphere is formed by the atmosphere (air). Further, the oxidizing atmosphere that is intentionally formed is formed by a mixed gas in which a gas that promotes oxidation (for example, oxygen or the like) is intentionally mixed. When the ablation process is performed in an oxidizing atmosphere under the atmosphere, it is not necessary to adjust the atmosphere so as to intentionally form an oxidizing atmosphere, so the work load can be reduced. In the present embodiment, the laser processing apparatus 1 forms an oxidizing atmosphere under the atmosphere by injecting air (atmosphere) to the workpiece W by the gas supply device 110. The laser processing apparatus 1 transmits, for example, a control signal for supplying air by the control unit 120 to the first adjustment valve 115a, and an air passage state in which air can pass through the air pipe 111 by the first adjustment valve 115a. And In addition, the laser processing apparatus 1 transmits a control signal for stopping the supply of the inert gas to the second adjustment valve 116a by the control unit 120, and the inert gas passes through the gas pipe 112 by the second adjustment valve 116a. The gas stop state is disabled. The laser processing apparatus 1 injects air toward the workpiece W by setting the air passage state and the gas stop state, thereby forming an oxidizing atmosphere that promotes oxidation (generation of the oxide layer V) of the workpiece W. To do. As shown in FIG. 5, the laser processing apparatus 1 irradiates the first processing surface W1 with the first pulse laser beam LB1 in this oxidizing atmosphere to select the surface layer of the first processing surface W1, particularly the convex portion P1. To remove. And the laser processing apparatus 1 forms the 2nd to-be-processed surface W2 which has the convex part P2 lower than the convex part P1 of the 1st to-be-processed surface W1, as shown in FIG. That is, the laser processing apparatus 1 irradiates the first pulsed laser beam LB1 onto the first processing surface W1 and selectively instantly evaporates and scatters the surface layer of the first processing surface W1, particularly the convex portion P1. The convex part P1 of the one work surface W1 is removed to form a second work surface W2. The laser processing apparatus 1 forms the second processed surface W2 by reducing the surface roughness (unevenness) Ra of the first processed surface W1 to, for example, about 0.5 μm to 0.8 μm by ablation processing. For example, the laser processing apparatus 1 removes the fine convex portion P1 of the first processing surface W1 by relatively reducing the processing influence range, and the second processing surface W2 reduced to about 0.5 μm. Can be formed. Here, the surface roughness Ra is a value obtained by a known mathematical formula, and is an arithmetic average roughness as an example, but may be other than this. Since the laser processing apparatus 1 performs ablation processing in an oxidizing atmosphere, the ablation processing is performed by oxidation reaction heat as compared with the case of performing the ablation processing in an oxidation-inhibiting atmosphere that suppresses oxidation of the workpiece W (generation of the oxidized layer V). Can be promoted. At this time, as shown in FIGS. 6, 7, and 8, the laser processing apparatus 1 includes an oxide layer V in which the surface of the second processed surface W <b> 2 is oxidized by the first pulse laser beam LB <b> 1 irradiated in an oxidizing atmosphere. Oxide debris D, which is formed and formed by bonding the vaporized portions of the oxide layer V, is deposited on the oxide layer V. Here, FIG. 6 is a schematic view showing an example of forming the oxide layer V and the oxide debris D. FIG. 7 is an image (top view) showing an example of forming the oxide layer V and the oxide debris D. FIG. 8 is an image (cross-sectional view) showing a formation example of the oxide layer V and the oxide debris D. Although the laser processing apparatus 1 blows off and removes the oxidized debris D by the air jetted from the nozzle 114a of the mixed gas pipe 114, it cannot completely remove the oxidized debris D.

  In the oxide layer removal processing, the laser processing apparatus 1 removes the oxide layer V and the oxide debris D formed on the second processed surface W2. The laser processing apparatus 1 uses the second pulse laser beam LB2 (second laser beam) to remove the oxide layer V and the oxidized debris D formed on the second processing surface W2, and the second processing surface. The convex part P2 of W2 is not melted as much as possible. For example, the second pulse laser beam LB2 has a pulse width of the order of nanoseconds to microseconds. The second pulse laser beam LB2 has a laser intensity peak value lower than that of the first pulse laser beam LB1, and has a laser intensity peak value higher than that of a third pulse laser beam LB3 (third laser beam) used in melt processing described later. The value is low. The second pulse laser beam LB2 has, for example, a peak value of the laser intensity that can remove the oxide layer V and the oxidized debris D on the second processed surface W2, and processes the second processed surface W2 as much as possible. Not light energy density. The second pulse laser beam LB2 has a pulse width wider than that of the first pulse laser beam LB1, and the pulse width is equal to that of the third pulse laser beam LB3.

  In the case of the oxide layer removal process, the laser processing apparatus 1 supplies an inert gas to the workpiece W by the gas supply apparatus 110. For example, the laser processing apparatus 1 transmits a control signal for stopping supply of air to the first adjustment valve 115a by the control unit 120, and the air stop in which air cannot pass through the air pipe 111 by the first adjustment valve 115a. State. Further, the laser processing apparatus 1 transmits a control signal for supplying an inert gas by the control unit 120 to the second adjustment valve 116a, and the inert gas can pass through the gas pipe 112 by the second adjustment valve 116a. A certain gas passage state is assumed. The laser processing apparatus 1 injects an inert gas toward the workpiece W by setting the air stopped state and the gas passage state, and suppresses oxidation to suppress oxidation (generation of the oxide layer V) of the workpiece W. An atmosphere (inert gas atmosphere) is formed. As shown in FIG. 9, the laser processing apparatus 1 irradiates the oxidized layer V and oxidized debris D on the second processed surface W2 with the second pulsed laser beam LB2 in this oxidation-suppressed atmosphere, thereby oxidizing the oxidized layer V and oxidized debris. Remove D. Here, for example, the light absorptance at a light wavelength of 1 μm is 35% for iron non-oxide and 85% for iron oxide, and the oxide has higher light absorptance than the non-oxide. Therefore, the oxide layer V is heated and vaporized by the second pulse laser beam LB2, or is removed by promoting a reduction reaction at a high temperature. And the laser processing apparatus 1 forms the 2nd to-be-processed surface W2 from which the oxide layer V and the oxidation debris D were removed, as shown in FIG.10, FIG.11, FIG.12. Here, FIG. 10 is a schematic diagram showing an example of forming the second processed surface W2 from which the oxide layer V and the oxide debris D have been removed. FIG. 11 is an image (top view) showing an example of forming the second processed surface W2 from which the oxide layer V and the oxidized debris D have been removed. FIG. 12 is an image (sectional view) showing an example of forming the second processed surface W2 from which the oxide layer V and the oxidized debris D have been removed.

  The laser processing apparatus 1 selectively melts and flattens the surface layer of the second processed surface W2 from which the oxide layer V and the oxidized debris D have been removed, particularly the projection P2. In the melt processing, the laser processing apparatus 1 uses, for example, a third pulse laser beam LB3 (third laser beam) having a pulse width on the order of nanoseconds to microseconds. The third pulse laser beam LB3 has a lower laser intensity peak value than the first pulse laser beam LB1, and a higher laser intensity peak value than the second pulse laser beam LB2 used in the oxide layer removal step. In the third pulse laser beam LB3, the peak value of the laser intensity has a processing effect in the processing depth direction (Z direction) smaller than that of the first pulse laser beam LB1, and the convex portion P2 of the second processed surface W2 is melted. Is the light energy density possible. The second pulse laser beam LB2 has a wider pulse width than the first pulse laser beam LB1, and has the same pulse width as the third pulse laser beam LB3. The spot diameter r2 of the third pulse laser beam LB3 is larger than the spot diameter r1 of the first pulse laser beam LB1. Moreover, it is preferable that the spot diameter r2 of the third pulse laser beam LB3 is larger than the interval between the adjacent convex portions P2 of the second workpiece surface W2. This can reduce the processing time and obtain surface tension by the processing spot of the third pulse laser beam LB3 reaching the adjacent convex portion P2 of the second workpiece surface W2 and the concave portion between the convex portions P2. Since waviness can be easily removed, smoothing can be efficiently performed on long-period uneven components.

  In the melting process, the laser processing apparatus 1 supplies the workpiece W with a mixed gas obtained by mixing a trace amount of air with an inert gas by the gas supply apparatus 110. For example, the laser processing apparatus 1 transmits a control signal for supplying a minute amount of air to the first adjustment valve 115a by the control unit 120, and the minute amount of air can pass through the air pipe 111 by the first adjustment valve 115a. A certain minute air passage state is assumed. Further, the laser processing apparatus 1 transmits a control signal for supplying an inert gas by the control unit 120 to the second adjustment valve 116a, and the inert gas can pass through the gas pipe 112 by the second adjustment valve 116a. A certain gas passage state is assumed. The laser processing apparatus 1 injects a mixed gas toward the workpiece W by setting a minute air passage state and a gas passage state, and suppresses changes in physical properties such as hardness reduction due to significant oxidation of the workpiece W. At the same time, a mixed gas atmosphere that promotes melt processing is formed by oxidation heat generated by an oxidation reaction that occurs in a very small amount of air. As shown in FIG. 15, the laser processing apparatus 1 irradiates the second processed surface W2 from which the oxide layer V has been removed with the third pulsed laser beam LB3, and particularly the surface layer of the second processed surface W2, particularly the convex portion. P2 is selectively melted. And the laser processing apparatus 1 forms the process flat surface W3 which planarized the 2nd to-be-processed surface W2, as shown in FIG.16, FIG.17, FIG.18. In other words, the laser processing apparatus 1 irradiates the second processed surface W2 with the third pulse laser beam LB3, melts and liquefies in particular the convex portion P2 of the second processed surface W2 (pole surface), and generates the first by surface tension. A processed flat surface W3 is formed by flattening the two processed surfaces W2. Here, FIG. 16 is a schematic diagram illustrating an example of forming the processed flat surface W3. FIG. 17 is an image (top view) showing an example of forming the processed flat surface W3. FIG. 18 is an image (sectional view) showing an example of forming the processed flat surface W3. The laser processing apparatus 1 reduces the surface roughness (unevenness) Ra of the second processed surface W2 to 0.1 μm or less and performs planarization by melt processing. Note that the laser processing apparatus 1 gradually increases the mixing ratio of air to an inert gas (for example, argon) within a range of, for example, 0% to 9.4%, thereby increasing the heat of oxidation due to the oxidation reaction and performing melt processing. It turns out to promote. Further, in the laser processing apparatus 1, the laser beam irradiation unit 10 has about 30% of the case where the melt processing is performed in the mixed gas atmosphere as compared with the case where the melt processing is performed in the oxidation-inhibited atmosphere using an inert gas (eg, argon). Melt processing was possible with low laser power.

  Next, an operation example of the laser processing apparatus 1 will be described with reference to FIG. In the laser processing apparatus 1, processing conditions are set in advance by an operator (step S1). Here, the processing conditions are, for example, the energy density of the pulse laser beam LB, the overlapping of spot diameters r1 and r2 during scanning, the number of repeated irradiations, the processing time, and the like. These processing conditions are obtained in advance by experiments or the like based on the material of the workpiece W, the roughness of the unevenness of the processing surface Wa, and the like.

  The laser processing apparatus 1 performs an ablation process after the processing conditions are set (step S2). The laser processing apparatus 1 fixes the workpiece W mounted on the mounting table 81a of the driving unit 80 to the driving unit 80, and moves the workpiece W in the X direction or the Y direction by the XY axis driving unit 81. Further, the workpiece W is moved in the Z direction by the Z-axis drive unit 82 to move the workpiece W to the machining start position. The laser processing apparatus 1 causes the gas supply apparatus 110 to be in an air passage state and a gas stop state, thereby injecting air toward the workpiece W to form an oxidizing atmosphere. Then, the laser processing apparatus 1 irradiates the first pulse laser beam LB1 on the convex portion P1 of the first workpiece surface W1 while imaging the first workpiece surface W1 of the workpiece W by the camera 100. The laser processing apparatus 1 moves the workpiece W in the X direction or the Y direction by the XY axis driving unit 81 in a state where the first pulse laser beam LB1 is irradiated, so that the first processing surface W1 is While scanning with the one-pulse laser beam LB1, the surface layer of the first workpiece surface W1, particularly the projection P1, is selectively removed. The laser processing apparatus 1 can suppress the thermal influence on the periphery of the processed portion of the workpiece W by performing ablation processing that is non-thermal processing. Further, the laser processing apparatus 1 can promote the ablation processing by the oxidation reaction heat by performing the ablation processing in the oxidizing atmosphere.

  Next, the laser processing apparatus 1 determines whether or not the ablation process for performing the ablation process over the entire area of the first workpiece surface W1 is completed (step S3). When the laser processing apparatus 1 determines that the ablation process is completed (step S3; Yes), the laser processing apparatus 1 performs an oxide layer removal process (step S4). In the oxide layer removing step, the laser processing apparatus 1 causes the gas supply device 110 to be in an air stop state and a gas passage state, thereby injecting an inert gas toward the workpiece W to form an oxidation suppression atmosphere. The laser processing apparatus 1 moves the workpiece W in the Z direction by the Z-axis drive unit 82 based on the image obtained by imaging the oxide layer V and the oxide debris D on the second workpiece surface W2 by the camera 100. The object W is set to a desired height. Then, the laser processing apparatus 1 irradiates the oxide layer V and the oxide debris D with the second pulse laser beam LB2 while imaging the oxide layer V and the oxide debris D with the camera 100. The laser processing apparatus 1 moves the workpiece W in the X direction or the Y direction by the XY axis driving unit 81 in a state where the second pulse laser beam LB2 is irradiated, so that the oxide layer V and the oxide debris D are moved. The oxide layer V and the oxidized debris D are removed while scanning with the second pulse laser beam LB2. The laser processing apparatus 1 can remove the oxide layer V and the oxidized debris D while suppressing the oxidation of the second workpiece surface W2 by performing the oxide layer removal process in the oxidation-inhibited atmosphere. Next, the laser processing apparatus 1 determines whether or not the oxide layer removal process for removing the oxide layer V and the oxide debris D over the entire second workpiece surface W2 is completed (step S5). When the laser processing apparatus 1 determines that the oxide layer removal process has been completed (step S5; Yes), the laser processing apparatus 1 performs a melting process (step S6).

  In the melting step, the laser processing apparatus 1 injects the mixed gas toward the workpiece W by setting the gas supply device 110 in a minute air passing state and a gas passing state to form a mixed gas atmosphere. The laser processing apparatus 1 moves the workpiece W to the desired height by moving the workpiece W in the Z direction by the Z-axis drive unit 82 based on an image obtained by imaging the second workpiece surface W2 with the camera 100. Set. And the laser processing apparatus 1 irradiates the convex part P2 of the 2nd to-be-processed surface W2 with the 3rd pulse laser beam LB3, imaging the 2nd to-be-processed surface W2 with the camera 100. FIG. The laser processing apparatus 1 moves the workpiece W in the X direction or the Y direction by the XY axis driving unit 81 in a state where the third pulse laser beam LB3 is irradiated, so that the second processing surface W2 is moved to the second processing surface W2. The convex part P2 of the second workpiece surface W2 is melted while scanning the three-pulse laser beam LB3. The laser processing apparatus 1 can suppress changes in physical properties such as a significant decrease in hardness due to significant oxidation by performing melt processing in a mixed gas atmosphere, and can promote melt processing by heat of oxidation due to an oxidation reaction that occurs in a small amount of air. . Next, the laser processing apparatus 1 determines whether the melting process which performs a melt process over the whole area of the 2nd to-be-processed surface W2 was complete | finished (step S7). When the laser processing apparatus 1 determines that the melting process has ended (step S7; Yes), the processing process ends.

  If the laser processing apparatus 1 determines that the ablation process is not completed in step S3 described above (step S3; No), the laser processing apparatus 1 returns to step S2 and continues to remove the convex portion P1 on the first workpiece surface W1. To do. If the laser processing apparatus 1 determines in step S5 described above that the oxide layer removal process has not been completed (step S5; No), the process returns to step S4 and continues to remove the oxide layer V and the oxide debris D. . In Step S7 described above, when the laser processing apparatus 1 determines that the melting process has not ended (Step S7; No), the laser processing apparatus 1 returns to Step S6 and continues to melt the convex portion P2 of the second workpiece surface W2. To do.

  As described above, the laser processing method according to the embodiment includes the ablation process and the oxide layer removal process. In the ablation step, the first processed surface W1 having unevenness is irradiated with the first pulsed laser beam LB1 in an oxidizing atmosphere that promotes oxidation to remove the convex portion P1 of the first processed surface W1, and the first processed surface A second processed surface W2 having a convex portion P2 lower than the convex portion P1 of the surface W1 is formed. In the oxide layer removing step, a second pulse laser different from the first pulse laser beam LB1 is formed on the oxide layer V formed on the second workpiece surface W2 in the ablation step in an oxidation suppression atmosphere that suppresses oxidation after the ablation step. The oxide layer V is removed by irradiation with the light LB2.

  As a result, the laser processing method ablates the first workpiece surface W1, so that the first workpiece surface W1 is given to the first workpiece surface W1 as compared with the conventional case where the first workpiece surface W1 is melted and flattened. The influence of heat can be suppressed, and softening and transformation such as deformation, undulation, alteration, and discoloration of the first workpiece surface W1 can be suppressed. Since the laser processing method performs ablation processing in an oxidizing atmosphere, the ablation processing can be promoted by oxidation reaction heat as compared with the case where ablation processing is performed in an oxidation-inhibiting atmosphere (see FIGS. 20 and 21). Here, FIG. 20 is a diagram showing a processing amount for performing the ablation processing in the oxidation-inhibiting atmosphere according to the comparative example. FIG. 21 is a diagram illustrating a processing amount for performing the ablation processing in the oxidizing atmosphere according to the embodiment. The ablation processing according to the comparative example is processed using the first pulse laser beam LB1 under the same conditions as the ablation processing according to the embodiment. The ablation processing according to the comparative example has a processing amount of about 1 μm as shown in FIG. On the other hand, the ablation processing according to the embodiment has a processing amount of about 3 μm as shown in FIG. As described above, since the ablation processing according to the embodiment is performed in an oxidation atmosphere, the amount of processing can be increased by about three times by the oxidation reaction heat as compared with the case of ablation processing in an oxidation-inhibited atmosphere, and energy efficiency Can be improved. As a result, the laser processing method can reduce the processing time while suppressing the thermal influence on the workpiece W. Further, since the laser processing method removes the oxide layer V formed on the second workpiece surface W2 in the ablation process, the oxide layer V causes the main body of the workpiece W to be cracked or cracked. Can be prevented.

  The laser processing method further includes a melting step. In the melting step, after the oxide layer removing step, the second pulsed laser beam LB3 different from the first pulse laser beam LB1 and the second pulse laser beam LB2 is applied to the second processed surface W2 from which the oxide layer V has been removed. Then, the convex portion P2 of the second processed surface W2 is melted to form a processed flat surface W3 obtained by flattening the second processed surface W2. As a result, the laser processing method smoothes the surface to some extent in the ablation process after the surface is smoothed to some extent as compared with the conventional case where the surface is flattened only by the melt processing. Can be suppressed. Accordingly, the laser processing method can suppress softening and transformation such as deformation, undulation, alteration, and discoloration of the processing flat surface W3 due to thermal effects. For example, as shown in FIG. 18, the laser processing method can prevent voids (cavities) due to the crystal structure and re-solidification on the processed flat surface W <b> 3, and suppress the influence of oxidation and thermal influence on the depth direction. I was able to. Further, the laser processing method can automatically reduce the surface roughness (unevenness) Ra to 0.1 μm or less without performing manual polishing as in the prior art. Thereby, the laser processing method can perform mirror surface processing by flattening the processing surface Wa. In addition, the laser processing method can perform a flattening process that suppresses a low-frequency swell component even in a workpiece W having a wide interval between adjacent convex portions P1.

  The laser processing apparatus 1 according to the embodiment includes a laser light irradiation unit 10 and a control unit 120. The laser beam irradiation unit 10 irradiates the first processed surface W1 having irregularities with the first pulse laser beam LB1 and the second pulse laser beam LB2 different from the first pulse laser beam LB1. The gas supply device 110 supplies air for forming an oxidizing atmosphere that promotes oxidation or an inert gas for forming an oxidation-inhibiting atmosphere that suppresses oxidation. The control unit 120 controls the laser beam irradiation unit 10 and the gas supply device 110. The control unit 120 controls the gas supply device 110 to form an oxidizing atmosphere in which air is supplied, controls the laser beam irradiation unit 10, and irradiates the first pulsed laser beam LB1 on the first workpiece surface W1. The convex part P1 of the processed surface W1 is removed, and a second processed surface W2 having a convex part P2 lower than the convex part P1 of the first processed surface W1 is formed. After forming the second processed surface W2, the control unit 120 controls the gas supply device 110 to form an oxidation-suppressed atmosphere supplied with an inert gas, and controls the laser beam irradiation unit 10 to form the second processed surface W2. The formed oxide layer V is irradiated with a second pulsed laser beam LB2 different from the first pulsed laser beam LB1, and the oxidized layer V is removed. With this configuration, the laser processing apparatus 1 can achieve the same effects as the laser processing method described above.

[Modification]
Next, a modification of the embodiment will be described. In the laser processing method, the oxide layer V and the oxide debris D are removed by the second pulse laser beam LB2, and the convex portion P2 of the second workpiece surface W2 is melted by the third pulse laser beam LB3. Although the example which performs separately the melting process which forms the process flat surface W3 which planarized the two to-be-processed surfaces W2 was demonstrated, it is not limited to this. In the laser processing method, for example, the removal of the oxide layer V and the oxide debris D and the formation of the processed flat surface W3 may be performed simultaneously. In this case, the second pulse laser beam LB2 has, for example, a peak value of the laser intensity that can remove the oxide layer V and the oxidized debris D on the second processing surface W2, and the convexity of the second processing surface W2. This is the light energy density that can melt the portion P2. In the laser processing method, for example, in the oxide layer removal melting step as the oxide layer removal step, the oxide layer V and the oxide debris D formed on the second processed surface W2 are removed by the second pulse laser beam LB2, and The convex portion P2 of the second processed surface W2 is melted by the second pulse laser beam LB2, and a processed flat surface W3 is formed by flattening the second processed surface W2. As a result, the laser processing method can simultaneously remove the oxide layer V and oxide debris D and form the processed flat surface W3, so that the processing time can be further shortened. The removal of the oxide layer V and the oxide debris D and the formation of the processed flat surface W3 may be performed at the same time, and then the melt processing may be performed thereafter to further improve the flatness.

  In addition to air, oxygen, ozone, nitrous oxide, nitric oxide, nitrogen dioxide, fluorine, chlorine, chlorine dioxide, nitrogen trifluoride, chlorine trifluoride, silicon tetrachloride, There are oxygen fluoride, perchloryl fluoride, etc., and these mixed gases are also included.

  The first to third pulse laser beams LB1, LB2, and LB3 may form a beam to be irradiated in a line shape. As a result, the first to third pulse laser beams LB1, LB2, and LB3 can be irradiated over a wide range compared to the point beam, so that the processing time (tact time) can be reduced.

  Although the laser processing apparatus 1 demonstrated the example which melt-processes in the mixed gas atmosphere which mixed trace amount air with the inert gas, it is not limited to this. For example, the laser processing apparatus 1 may perform melt processing in the above-described oxidation-suppressed atmosphere.

  The laser processing apparatus 1 has been described with respect to the example in which the position of the optical system including the objective lens 70 and the like is fixed and the workpiece W is processed by being relatively moved in the X direction, the Y direction, or the Z direction. It is not limited. For example, the laser processing apparatus 1 fixes the position of the workpiece W and relatively moves the optical system including the objective lens 70 in the X direction, the Y direction, or the Z direction to process the workpiece W. A scanner or the like may be used.

  Although the laser beam irradiation unit 10 has been described as an example of a master oscillator output amplifier (MOPA) using a pulse width variable light source as a seed light source, the present invention is not limited to this. For example, the laser light irradiation unit 10 may use another laser light source for each pulse width. In this case, a femtosecond laser or a picosecond laser is used as the first pulse laser beam LB1. As the second and third pulse laser beams LB2 and LB3, nanosecond, microsecond, and millisecond pulse lasers are used. The second and third pulse laser beams LB2 and LB3 may be continuous wave laser beams (CW (Continuous Wave) laser beams) that continuously oscillate a constant output.

DESCRIPTION OF SYMBOLS 1 Laser processing apparatus 10 Laser beam irradiation part 110 Gas supply apparatus 120 Control part LB1 1st pulse laser beam (1st laser beam)
LB2 Second pulse laser beam (second laser beam)
LB3 Third pulse laser beam (third laser beam)
P1, P2 Convex part W1 First processed surface W2 Second processed surface W3 Processed flat surface V Oxide layer

Claims (4)

In an oxidizing atmosphere that promotes oxidation, the first processed surface having irregularities is irradiated with a first laser beam to remove the convex portion of the first processed surface, and is lower than the convex portion of the first processed surface. A removal step of forming a second workpiece surface having a convex portion;
After the removing step, in an oxidation-inhibiting atmosphere that suppresses oxidation, the oxidation layer formed on the second processed surface in the removing step is irradiated with a second laser beam different from the first laser beam, and the oxidation is performed. An oxide layer removal step for removing the layer;
A laser processing method comprising:   After the oxide layer removing step, the second processed surface is irradiated with a third laser beam different from the first laser beam and the second laser beam on the second processed surface from which the oxide layer has been removed. The laser processing method according to claim 1, further comprising a melting step of forming a processed flat surface obtained by melting the convex portion of the first flat surface and flattening the second processed surface.   In the oxide layer removing step, the oxide layer formed on the second processed surface is removed by the second laser light, and a convex portion of the second processed surface is melted by the second laser light. The laser processing method according to claim 1, wherein a processing flat surface is formed by flattening the second processing surface. A laser beam irradiation unit that irradiates a first laser beam and a second laser beam different from the first laser beam on a first workpiece surface having irregularities;
A gas supply device for supplying an oxidation promoting gas for promoting oxidation or an oxidation inhibiting gas for suppressing oxidation;
A control unit for controlling the laser beam irradiation unit and the gas supply device,
The control unit controls the laser supply unit and controls the laser beam irradiation unit to irradiate the first laser beam to the first laser beam in an oxidizing atmosphere formed by the oxidation promoting gas by controlling the gas supply device. Removing the convex portion of one workpiece surface, forming a second workpiece surface having a convex portion lower than the convex portion of the first workpiece surface;
After forming the second work surface, the oxide layer formed on the second work surface by controlling the laser beam irradiation unit in an oxidation-suppressed atmosphere formed by controlling the gas supply device and using the oxidation-suppressing gas. And irradiating a second laser beam different from the first laser beam to remove the oxide layer.