Laser processing device

Abstract

A laser processing apparatus according to the present application includes an irradiation device that irradiates a pulsed laser with a prescribed low energy density, processes one or more layers from a workpiece in succession with a pulse width of less than 10 picoseconds, and removes protrusions generated on a surface of the layer with the pulsed laser at a high energy density that is higher than the low energy density, and a control device that includes a switching section that switches the pulsed laser output from the irradiation device between the low energy density and the high energy density based on a switching condition, and a switching condition setting section that sets the switching condition based on a condition of the workpiece.

Description

TECHNICAL FIELD

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

[0002] When a workpiece is irradiated with an ultrashort pulse laser having a pulse width of 1 picosecond or less, the material of the irradiated portion is non-thermally scattered and removed (ablation). Ultrashort pulse laser processing using this phenomenon can achieve atomic-scale fine processing, and since the heat influence on the surroundings of the irradiated portion is small, high-quality processing can be performed on a variety of materials. Patent Document 1 (Japanese Patent No. 6340459) discloses a manufacturing method for a diamond die for a wire electrode used in a wire electrode discharge machining process, which can form a die hole having high surface precision in a short time by processing using a femtosecond laser.

[0003] When a processing target portion of a workpiece is divided into a plurality of processing layers having a prescribed removal amount, and the processing layers are sequentially processed by a method in which an ultrashort pulse laser is irradiated, there are cases in which a protrusion having a substantially elliptical cross section is formed on the surface of the processing layer during the processing. Such a protrusion has been confirmed to be formed in a variety of materials including metals and resins. Once a protrusion is formed, it grows larger as the processing layer is processed, and in the processing of a bottomed hole (particularly a bottomed hole having a relatively deep depth), such a protrusion is a major cause of a decrease in processing quality.

[0004] By irradiating an ultrashort pulse laser using an energy density that is much higher than the lower limit of the energy density required for processing the processing layer (laser ablation threshold), it is possible to suppress the generation of such a protrusion. However, when processing is performed using such a high energy density, the heat influence on the material increases, and there is a risk that the precision of the processed surface will decrease. SUMMARY

[0005] The present application was completed in view of this situation, and has as its object to provide a laser processing apparatus that enables high-precision processing using an ultrashort pulse laser.

[0006] To solve the above-described technical problem, the present application provides a laser processing apparatus that includes an irradiation apparatus that irradiates a pulse laser having a pulse width of 10 picoseconds or less at a prescribed low energy density, sequentially processes one or more processing layers from a workpiece, and removes a protrusion generated on the surface of the processing layer by irradiating the pulse laser at a high energy density that is higher than the low energy density, and a control apparatus that includes a switching section that switches the pulse laser output from the irradiation apparatus between the low energy density and the high energy density based on a switching condition, and a switching condition setting section that sets the switching condition based on a condition of the workpiece.

[0007] Next, various embodiments of the present application will be described by way of example. The embodiments shown below can be combined with each other.

[0008] Preferably, the laser processing apparatus is provided with an imaging device that acquires an image of the processing layer, and an image processing device that analyzes the image and detects the protrusions on the surface of the processing layer, and the switching section switches the pulsed laser between the low energy density and the high energy density based on the detection result of the protrusions.

[0009] Preferably, the image processing device analyzes the image and acquires the number or area of the protrusions on the surface of the processing layer.

[0010] Preferably, the switching condition setting section sets the number of low energy density processing layers and the number of high energy density processing layers as the switching conditions, and the switching section switches the pulsed laser from the low energy density to the high energy density based on the number of low energy density processing layers, and switches the pulsed laser from the high energy density to the low energy density based on the number of high energy density processing layers.

[0011] Preferably, the switching condition setting section sets the low energy density processing depth and the high energy density processing depth as the switching conditions, and the switching section switches the pulsed laser from the low energy density to the high energy density based on the low energy density processing depth, and switches the pulsed laser from the high energy density to the low energy density based on the high energy density processing depth.

[0012] The irradiation device is configured to be able to irradiate the pulsed laser at a first high energy density that is the high energy density, and a second high energy density that is lower than the first high energy density, and the switching section switches the pulsed laser output from the irradiation device between the low energy density, the first high energy density, and the second high energy density based on the switching condition.

[0013] Preferably, the control device is provided with an energy density setting section that sets the values of the high energy density and the low energy density based on a processing condition, the processing condition including the material of the workpiece.

[0014] Preferably, the processing condition further includes the scanning speed and the repetition frequency of the pulsed laser.

[0015] Preferably, the processing layer includes a first region that is a region adjacent to the end portion, and a second region that is a region different from the first region, the pulsed laser irradiated on the first region has a smaller spot diameter than the pulsed laser irradiated on the second region, and the energy density of the pulsed laser irradiated on the first region is equal to the energy density of the pulsed laser irradiated on the second region.

[0016] Preferably, the processing layer is composed of an alloy steel containing inclusions in a base material, and the high energy density is above a laser ablation threshold of the inclusions.

[0017] Preferably, the irradiation device is provided with a laser oscillator, and the laser device switches between the low energy density and the high energy density of the pulsed laser by changing an output pulse energy of the laser oscillator.

[0018] Preferably, the pulsed laser is switched between the low energy density and the high energy density by changing a spot diameter of the pulsed laser.

[0019] A laser processing device according to the present application includes an irradiation device that irradiates a pulsed laser with a low energy density and a control device that switches the pulsed laser output from the irradiation device between the low energy density and a high energy density based on a switching condition. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is a schematic configuration diagram of a laser processing device 1 according to an embodiment of the present application.

[0021] Figure 2 is a schematic configuration diagram of a control device 8 of the laser processing device 1.

[0022] Figure 3A is a plan view of a workpiece 10 that is a processing target of the laser processing device 1.

[0023] Figure 3B is Figure 3A is a cross-sectional view of the workpiece 10 at line A-A in

[0024] Figures 4A to 4C is a cross-sectional view showing how a processing layer of the workpiece 10 is processed by the laser processing device 1.

[0025] Figure 5A and Figure 5B is a cross-sectional view showing how a protrusion 20 on the processing layer Lk is removed by the laser processing device 1.

[0026] Figure 6 is a flowchart of a processing method using the laser processing device 1 according to the present application.

[0027] Figure 7 FIG. 6 is a view for explaining an irradiation method of the pulsed laser 71 in Modification 4.

[0028] Figure 8A and Figure 8B FIGS. 8 and 9 are images of the machined surface of the blind hole 10a, which are images obtained by photographing the blind hole 10a from above, respectively in Example 1 and Comparative Example 1.

[0029] Figure 9A FIG. 10 is an image of the machined surface of the blind hole 10a, which is an image obtained by photographing the blind hole 10a from above, in Comparative Example 2.

[0030] Figure 9B FIG. 11 is an enlarged view of the region B in FIG. 10. Figure 9A

[0031] Reference Signs:

[0032] 1: laser processing apparatus

[0033] 2: laser oscillator

[0034] 3: optical system

[0035] 4: scanning device

[0036] 8: control device

[0037] 10: workpiece

[0038] 10a: blind hole

[0039] 20: protrusion

[0040] 41: first galvanometer mirror

[0041] 42: second galvanometer mirror

[0042] 51: beam splitter

[0043] 52: condenser lens

[0044] 53: image forming lens

[0045] 71: pulsed laser

[0046] 72: reflected light

[0047] 81: input section

[0048] 82: numerical control section

[0049] 83: irradiation control section

[0050] 84: arithmetic section

[0051] ​85: Storage Department

[0052] 86: Switching Condition Setting Section

[0053] 87: Energy Density Setting Section

[0054] 88: Switching Unit

[0055] 91: Camera device

[0056] 92: Image processing device

[0057] 93: CAD device

[0058] 94: CAM device. Detailed Implementation

[0059] Next, embodiments of the present invention will be described with reference to the accompanying drawings. The various features shown in the following embodiments can be combined with each other. Furthermore, each feature independently constitutes the present invention.

[0060] 1. Laser processing equipment 1

[0061] like Figure 1 As shown, the laser processing apparatus 1 in this embodiment processes the workpiece 10 into a desired shape by irradiating it with a pulsed laser 71 with a pulse width of less than 10 picoseconds, causing material to scatter at the irradiated area. The laser processing apparatus 1 includes a laser oscillator 2, an optical system 3, a scanning device 4, a beam splitter 51, a condenser lens 52, an image forming lens 53, a camera device 91, an image processing device 92, and a control device 8.

[0062] Laser oscillator 2 converts the laser emitted from a laser source (not shown) into pulsed laser 71 with a pulse width of less than 10 picoseconds, and adjusts it to a predetermined pulse energy before outputting it. It should be noted that "pulse width" refers to the duration of each pulse of the pulsed laser 7. Optical system 3, using a built-in lens (not shown), adjusts the beam diameter of the pulsed laser 71 output from laser oscillator 2. Optical system 3 can be configured, for example, using a beam expander.

[0063] In the process of machining using the pulsed laser 71, the machining target portion of the workpiece 10 is divided into one or more machining layers in the depth direction, and the machining layers are machined in order from the upper side, thereby machining the workpiece 10 into a desired shape. The scanning device 4 two-dimensionally scans the pulsed laser 71 for each machining layer. The scanning device 4 is provided with a first galvanometer mirror 41, a second galvanometer mirror 42, and actuators (not shown) that control the operations of the galvanometer mirrors 41, 42, respectively. The pulsed laser 71 output from the optical system 3 is reflected by the first galvanometer mirror 41 and scanned in a first direction in the horizontal 1-axis direction, and is further reflected by the second galvanometer mirror 42 and scanned in a second direction in the horizontal 1-axis direction that is perpendicular to the first direction. Thus, by irradiating the pulsed laser 71 to a prescribed position of the machining layer, the material at the irradiation site can be removed. Note that the scanning method of the pulsed laser 71 by the scanning device 4 is not limited to the above-described galvanometer scanning method. For example, a method of scanning the pulsed laser 71 to the workpiece 10 that moves with a stage by driving the stage on which the workpiece 10 is placed, or a method of scanning the pulsed laser 71 to the workpiece 10 by driving the laser oscillator 2 can be used.

[0064] The beam splitter 51 is configured to reflect the pulsed laser 71 output from the scanning device 4 and to allow the reflected light 72 from the workpiece 10 to pass therethrough. The beam splitter 51 is disposed on the optical path of the pulsed laser 71 output from the scanning device 4 and is disposed at a position between the condenser lens 52 and the image forming lens 53 in the vertical direction. Thus, the pulsed laser 71 output from the scanning device 4 can be reflected by the beam splitter 51 and irradiated onto the workpiece 10 after passing through the condenser lens 52. In addition, the reflected light 72 from the workpiece 10 passes through the beam splitter 51 and reaches the imaging device 91 after passing through the image forming lens 53.

[0065] The condenser lens 52 is disposed below the beam splitter 51 and adjusts the beam diameter of the pulsed laser 71 output from the scanning device 4. The condenser lens 52 can be configured using an objective lens. By adjusting the beam diameters of the optical system 3 and the condenser lens 52, the pulsed laser 71 can be irradiated onto the machining layer with a prescribed spot diameter (beam diameter of the pulsed laser 71 at the irradiation site on the machining layer). The image forming lens 53 is disposed above the beam splitter 51 and condenses the reflected light 72 from the workpiece 10 and forms an image in the imaging device 91.

[0066] In addition, a beam splitting element (not shown) for splitting the pulsed laser 71 into a plurality of sub-beams can be further disposed between the beam splitter 51 and the condenser lens 52 or below the condenser lens 52. The use of the beam splitting element can shorten the total machining time when machining a plurality of prescribed shapes.

[0067] The imaging device 91 acquires an image of the processed layer of the workpiece 10. The imaging device 91 is disposed above the condenser lens 52, so that an image when the processed layer is viewed from above can be acquired. The imaging device 91 can be configured using, for example, a CMOS camera or a CCD camera. When imaging is performed using the imaging device 91, an illuminating device such as an LED light source for illuminating the workpiece 10 can also be used as needed.

[0068] The image processing device 92 analyzes the image of the processed layer acquired by the imaging device 91 and detects the protrusions 20 on the surface of the processed layer. The image processing device 92 of the present embodiment is configured in a manner that analyzes the image and acquires the number or area of the protrusions 20 on the surface of the processed layer. Specifically, after the image acquired by the imaging device 91 is appropriately corrected, a binary processing is performed to identify the portion on the surface of the processed layer where the protrusions 20 exist and the other portion (where the protrusions 20 do not exist, and the processed layer itself is exposed). In general, in the image, the portion on the surface of the processed layer where the protrusions 20 exist is displayed brighter than the other portion. By utilizing this difference in brightness on the image, the portion where the protrusions 20 exist and the other portion are identified by the binary processing.

[0069] This binary processing is preferably performed in units of pixel units of the image or unit cells obtained by dividing the image into a lattice shape. For example, the binary processing is performed using the pixel units of the image, and the portion where the protrusions 20 exist is marked in white, and the remaining portion is marked in black. Then, at least a portion of the outer edge of the pixels marked in white, which repeatedly appear, are grouped into one or more regions, and the number of the regions is used as the number of the protrusions 20. Alternatively, the number of pixels marked in white can also be counted, and the area of one pixel is multiplied by the number of pixels, which is used as the area of the portion on the surface of the processed layer where the protrusions 20 exist.

[0070] 2. Control device 8

[0071] The control device 8 controls the above-described constituent elements of the laser processing device 1. Hereinafter, only the control related to the present application among the control operations of the control device 8 will be described. As shown in FIG. 8, the control device 8 is provided with an input unit 81, a numerical control unit 82, and an irradiation control unit 83. Figure 2

[0072] ​It should be noted that each of the following constituent elements can be realized by software or by hardware. When realized by software, each function can be realized by a CPU executing a computer program. The program can be stored in a built-in storage or in a non-transitory computer-readable recording medium. Alternatively, the program stored in an external storage can be read by a so-called cloud computing. When realized by hardware, various circuits such as an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array), or a DRP (Dynamically Reconfigurable Processor) can be used. In the present embodiment, various information or concepts including the same are represented by a height of a signal value in a binary bit set composed of 0 or 1, and then communicated or operated in the above-described software or hardware.

[0073] The control device 8 is externally provided with a CAD device 93 and a CAM device 94. The CAD device 93 generates three-dimensional shape data (CAD data) representing a machining shape and dimensions of the workpiece 10. The CAM device 94 generates action step data (CAM data) of the laser machining device 1 at the time of machining the workpiece 10, based on the CAD data. The CAM data can include, for example, data of irradiation positions of the pulsed laser 71 in each machining layer or data of various settings related to the pulsed laser 71.

[0074] The input section 81 is used for an operator to input information required for various processes in the numerical control section 82. For example, it can be composed of a touch panel, a keyboard, or a mouse. The input information can include, for example, a material of the workpiece 10, a scanning speed of the pulsed laser 71, a repetition frequency (number of pulses generated per unit time) of the pulsed laser 71, and the like. The input information is transmitted to the numerical control section 82.

[0075] The numerical control section 82 generates action instructions for each constituent element of the laser machining device 1 by processing the CAM data and the input information input from the input section 81 using a numerical control program. The numerical control section 82 is provided with an arithmetic section 84 and a storage section 85.

[0076] The arithmetic section 84 generates action instructions for each constituent element of the laser machining device 1 using a numerical control program stored in the storage section 85. The arithmetic section 84 is provided with a switching condition setting section 86, an energy density setting section 87, and a switching section 88.

[0077] The switching condition setting section 86 sets a condition for switching the energy density of the pulsed laser 71 based on the condition of the workpiece 10. In the present embodiment, when the work layer of the workpiece 10 is processed, the pulsed laser 71 is irradiated with a relatively low energy density (low energy density FL), and when the protrusions 20 formed on the surface of the work layer are to be removed, the pulsed laser 71 is irradiated with a higher energy density (high energy density FH) than the low energy density FL. Note that the "energy density (fluence)" refers to the energy per unit area at the irradiation point of the pulsed laser 71. In the present embodiment, the "energy density" refers to the energy density of the pulsed laser 71 at the irradiation site on the work layer. The switching condition setting section 86 sets a condition for switching the pulsed laser 71 between the low energy density FL and the high energy density FH.

[0078] The condition of the workpiece 10 can include, for example, the material of the workpiece 10. The switching condition setting section 86 of the present embodiment sets a threshold value for the number or area of the protrusions 20 formed on the surface of the work layer based on the condition of the workpiece 10. For example, the relationship between the condition of the workpiece 10 and the threshold value can be recorded in the storage section 85 as a database or a numerical control program, and the switching condition setting section 86 can read the corresponding value from the database or the numerical control program and determine the threshold value based on the material of the workpiece 10 included in the input information.

[0079] The energy density setting section 87 sets the values of the low energy density FL and the high energy density FH based on the processing condition. For example, a database or a numerical control program of the optimum low energy density FL and high energy density FH corresponding to the processing condition can be stored in the storage section 85, and the energy density setting section 87 can set the values of the low energy density FL and the high energy density FH by reading the corresponding value from the database or the numerical control program based on the processing condition included in the input information. Alternatively, a function for calculating the values of the low energy density FL and the high energy density FH from the processing condition as a variable can be stored in the storage section 85, and the energy density setting section 87 can set the low energy density FL and the high energy density FH by calculating the values using the function. Note that the details of the setting of the low energy density FL and the high energy density FH by the energy density setting section 87 will be described later.

[0080] The switching section 88 switches the pulsed laser 71 output from the irradiation device between the low energy density FL and the high energy density FH based on the switching condition set by the switching condition setting section 86. The switching section 88 of the present embodiment receives data of the number or area of the protrusions 20 on the surface of the processed layer transmitted from the image processing device 92, and compares the number or area of the protrusions 20 with the threshold value set by the switching condition setting section 86. When it is judged through the comparison that the low energy density FL needs to be switched to the high energy density FH or the high energy density FH needs to be switched to the low energy density FL, the switching section 88 outputs an operation instruction for switching the energy density of the pulsed laser 71 to the irradiation control section 83. Specifically, based on the specific values of the low energy density FL or the high energy density FH set by the energy density setting section 87, the switching section 88 generates an operation instruction using a numerical control program, and outputs it to the irradiation control section 83 so that the energy density of the pulsed laser 71 at the irradiation site is the prescribed value.

[0081] The storage section 85 stores the CAM data, the input information sent out by the input section 81, the numerical control program, a database or a function used by the switching condition setting section 86 and the energy density setting section 87, and the like.

[0082] The irradiation control section 83 controls each component of the laser processing device 1 according to the operation instruction transmitted from the numerical control section 82. When the pulsed laser 71 is switched between the low energy density FL and the high energy density FH, it can be adjusted to the desired energy density by changing the output pulse energy of the pulsed laser 71 by controlling the laser oscillator 2, or changing the spot diameter of the pulsed laser 71 by controlling the optical system 3 or the condenser lens 52.

[0083] 3. Setting of Energy Density

[0084] Next, the setting of the energy density by the energy density setting section 87 is described in further detail. The energy density setting section 87 of the present embodiment sets the values of the low energy density FL and the high energy density FH based on prescribed processing conditions. As the processing conditions, the material of the workpiece 10, the scanning speed of the pulsed laser 71, and the repetition frequency of the pulsed laser 71 are exemplified.

[0085] In the present embodiment, the value of the low energy density FL is set to be the lower limit of the energy density required to remove the material constituting the processing layer and above the laser ablation threshold value, based on the material of the workpiece 10. If the energy density is too low, the processing efficiency of the processing layer decreases, and if the energy density is too high, the processing quality deteriorates. Specifically, if the energy density is too high, a small hole is generated in the processing surface due to thermal influence and the surface roughness increases, and changes in material properties such as hardness or material deformation occur, so that the amount of sputtering (particles of the material scattered from the irradiation site of the pulsed laser 71 or its periphery) generated when the pulsed laser 71 is irradiated sometimes increases.

[0086] The value of the low energy density FL is preferably set taking into account the scan speed and the repetition frequency of the pulsed laser 71. Specifically, it is preferable that the processing effect of the value of the low energy density FL set at the time of processing does not change in a manner determined by the spot interval determined by the scan speed and the repetition frequency of the pulsed laser 71. For example, it can be adjusted in such a manner that the value of the low energy density FL is set to be above the laser ablation threshold value of the material constituting the processing layer, and the processing effect of the value of the low energy density FL set at the time of processing does not change with respect to the spot interval determined by the scan speed and the repetition frequency of the pulsed laser 71. Note that the "processing effect" of the present application refers to the energy required to process per unit volume of the pulsed laser 71 irradiated on the region of the processing layer. That is, the "processing effect" of the value of the low energy density FL refers to the energy required to process per unit volume of the pulsed laser 71 irradiated on the region of the processing layer with the low energy density FL.

[0087] The pulsed laser 71 raster scans or vector scans each processing layer in a manner with a prescribed spot interval. Here, the "spot interval" refers to the distance between the centers of two irradiation points adjacent to each other in the scan direction (the direction of travel of the irradiation points on the processing layer) of the pulsed laser 71. The spot interval is determined by the scan speed and the repetition frequency of the pulsed laser 71, and for example, the greater the repetition frequency and the slower the scan speed, the smaller the spot interval, and the larger the overlapping region between adjacent irradiation points. In the region where the irradiation points overlap each other, the processing layer that is the irradiation target of the pulsed laser 71 and the material below the processing layer are subjected to greater thermal influence than in other regions, and thus, the deterioration of the accuracy of the processing surface due to thermal influence is likely to occur. In the above structure, when the spot interval is relatively small (the overlapping region is large), by setting the value of the low energy density FL to be small, the thermal influence received by the overlapping region between the spots can be suppressed.

[0088] On the other hand, when a protrusion 20 is generated on the surface of the processed layer while the processing of the processed layer is being performed, it is difficult to remove by a method of irradiation with the pulsed laser 71 of the low energy density FL suitable for the processing of the processed layer. For example, in the workpiece 10 made of alloy steel, a protrusion 20 of a substantially elliptical cross-sectional shape is generated from an inclusion contained in the alloy steel as a base material, and since the laser ablation threshold of the inclusion is much higher than the laser ablation threshold of the alloy steel, irradiation with the pulsed laser 71 of the low energy density FL suitable for the processing of the processed layer is difficult to remove the protrusion 20. Therefore, once the protrusion 20 is formed, the protrusion 20 grows in the depth direction as the processing of the processed layer is continued. Here, the so-called "inclusion" refers to a trace amount of a non-metallic compound that is inevitably mixed during the manufacturing process of the alloy steel and is difficult to remove. The inclusion of the alloy steel is usually several micrometers (μm) to several tens of micrometers (μm) in size and irregularly distributed in the alloy steel as a base material. As the inclusion, for example, an oxide-type inclusion such as Al2O3, MgO, CaO, a sulfide-type inclusion such as MnS, CaS, a nitride-type inclusion such as TiN, NbN, and the like can be listed.

[0089] The high energy density FH is set to a value higher than the low energy density FL to remove the protrusion 20 formed. When the high energy density FH is a value α times the low energy density FL (i.e., FH = α x FL), for example, 2 ≦ α ≦ 20, specifically, for example, α = 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, or a range between any two of the values exemplified here can be used. Further, in order to be able to simultaneously obtain the removal efficiency of the protrusion 20 and the thermal influence on the material, it is preferable to set the high energy density FH to 7 ≦ α ≦ 15. Further, when the material of the workpiece 10 is alloy steel, in order to effectively remove the protrusion 20 caused by the inclusion, it is preferable to set the high energy density FH to be higher than the laser ablation threshold of the inclusion. In addition, it is preferable to set the value of the high energy density FH so that the processing effect does not change when the spot interval determined by the scanning speed and the repetition frequency of the pulsed laser 71 is processed. It should be noted that the so-called "processing effect of the value of the high energy density FH" refers to the energy required per unit volume of processing by the pulsed laser 71 of the high energy density FH irradiated at a region on the processed layer.

[0090] 4. Method of processing the workpiece 10

[0091] Next, the method of processing the workpiece 10 using the laser processing apparatus 1 according to the present embodiment will be described with reference to Figures 3A to 6 to the processing of the workpiece 10 using the laser processing apparatus 1 according to the present embodiment will be described below. In the following, one example of processing using the laser processing apparatus 1, i.e., in the case of processing the workpiece 10 made of alloy steel, will be described. Figure 3A and Figure 3BThe case where a bottom hole 10a is formed in the workpiece 10 is shown. The material of the workpiece 10 is alloy steel, and the bottom hole 10a to be formed has a rectangular opening portion with a planar dimension of W1 x W2 and a depth of D.

[0092] As shown in FIG. 1, the laser processing apparatus 1 includes an input unit 81, a numerical control unit 82, an energy density setting unit 87, a switching condition setting unit 86, an image pickup device 91, an image processing device 92, and an irradiation control unit 83. Figure 6 As shown in FIG. 1, the laser processing apparatus 1 includes an input unit 81, a numerical control unit 82, an energy density setting unit 87, a switching condition setting unit 86, an image pickup device 91, an image processing device 92, and an irradiation control unit 83.

[0093] In the present embodiment, the processing target portion is divided into n processing layers L1, L2, L3,... Ln from the upper surface side of the workpiece 10. n It should be noted that the thickness of each processing layer L1, L2, L3,... Ln can be the same or different from one another. n

[0094] At the start of processing, the laser processing apparatus 1 irradiates the pulsed laser 71 with the low energy density FL and sequentially processes the processing layers L1, L2, L3,... from the workpiece 10 (step S3). Specifically, as shown in FIG. 2, the processing layer L1 is processed by irradiating the pulsed laser 71 with the low energy density FL to the processing layer L1 of the 1st layer (the uppermost layer). Then, as shown in FIG. 3, the processing layer L2 of the 2nd layer located directly below the processing layer L1 is processed by irradiating the pulsed laser 71 with the low energy density FL. The same operation is repeated for the processing layers L3, L4,... of the 3rd layer and the following layers, and the processing layers are sequentially processed in the depth direction. Figure 4A Figure 4B

[0095] Then, the image pickup device 91 acquires an image of the processing layer of the workpiece 10 (step S4). The image processing device 92 analyzes the acquired image and acquires the number N of protrusions 20 on the surface of the processing layer (step S5). It should be noted that the image acquisition of the processing layer by the image pickup device 91 can be performed each time a prescribed number of processing layers are processed, or each time a prescribed thickness of processing layers are processed in the depth direction, or each time the processing by the low energy density FL is performed for a prescribed time.

[0096] ​​​The switching unit 88 compares the number N of protrusions 20 with the threshold TH set by the switching condition setting unit 86 (step S6). When the number N of protrusions 20 is below the threshold TH, the switching unit 88 determines that it is not necessary to switch to high energy density FH, and continues to irradiate the processed layer with low energy density FL. When the number N of protrusions 20 is greater than the threshold TH, the switching unit 88 determines that it is necessary to switch to high energy density FH, and sends an operation command to the irradiation control unit 83 to switch the pulsed laser 71 to high energy density FH.

[0097] After the energy density switch, the laser processing apparatus 1 irradiates the pulsed laser 71 with a high energy density FH to remove the protrusions 20 generated on the surface of the processed layer (step S7). When in such... Figure 5A The processing layer L of the k-th layer is shown. k When a protrusion 20 is generated on the upper layer, it affects the processing layer L. k A pulsed laser 71 with high energy density FH is applied. As a result, the protrusion 20 can be removed along with the processed layer.

[0098] The imaging device 91 acquires an image of the processed layer of the workpiece 10 (step S8). The image processing device 92 analyzes the acquired image and obtains the number N of protrusions 20 on the surface of the processed layer (step S9). It should be noted that the acquisition of the image of the processed layer by the imaging device 91 can be performed each time a predetermined number of processed layers are processed, or each time a processed layer of predetermined thickness is processed in the depth direction, or each time a predetermined time has elapsed during processing by high energy density FH irradiation.

[0099] The switching unit 88 compares the number N of protrusions 20 with the threshold TH set by the switching condition setting unit 86 (step S10). When the number N of protrusions 20 is greater than the threshold TH, the protrusions 20 are removed by high energy density FH irradiation. When the number N of protrusions 20 is less than or equal to the threshold TH, the switching unit 88 determines that it is necessary to switch to low energy density FL and outputs an operation command to the irradiation control unit 83 to switch the pulsed laser 71 to low energy density FL.

[0100] Before switching from low energy density (FL) to low energy density (FL) by switching unit 88, the processing layers with one or more layers are irradiated with a pulsed laser 71 of high energy density (FH). After switching to low energy density (FL), the processing layers are processed sequentially by irradiating the pulsed laser 71 again with low energy density (FL). For example, when processing layers L... k After the m processing layers are irradiated with a high-energy-density pulsed laser 71 (FH) to remove the protrusions 20, when the switching unit 88 switches to a low-energy-density laser (FL), as... Figure 5B As shown, by processing layers L after the (k+m)th layer... k＋m L k＋m＋1... the pulse laser 71 is irradiated with a low energy density FL to sequentially process the processing layers.

[0101] until the nth layer of the processing layers L n is processed. By repeating the above process, a blind hole 10a having a desired depth D as shown in Figure 4C is formed. Note that, in order to improve the accuracy of the processed surface of the blind hole 10a, it is preferable to perform the final processing (processing of a portion of the processing layers L n containing at least the nth layer) using irradiation with a low energy density FL to complete the processing.

[0102] 5. Effects

[0103] The control device 8 of the laser processing device 1 according to the present embodiment is provided with a switching section 88 and a switching condition setting section 86, and the switching section 88 switches the pulse laser 71 between a low energy density FL and a high energy density FH based on a switching condition set by the switching condition setting section 86. When a protrusion 20 is generated on a processing layer while processing the processing layer using irradiation with a low energy density FL, the switching section 88 can be switched to the high energy density FH to remove the protrusion 20. Further, after the protrusion 20 is removed, the switching section 88 can be switched to the low energy density FL to continue processing the processing layer, and thus the processing using the high energy density FH can be minimized, and the decrease in the accuracy of the processed surface due to the thermal influence on the material can be suppressed. Further, since a portion of the processing layer can be processed using irradiation with the pulse laser 71 of the high energy density FH, the total processing time can be shortened compared to the case where the processing is performed using only irradiation with the low energy density FL.

[0104] The laser processing device 1 according to the present embodiment is provided with an imaging device 91 that acquires an image of the processing layer and an image processing device 92 that analyzes the image and detects the protrusion 20, and the switching section 88 switches the pulse laser 71 between the low energy density FL and the high energy density FH based on the detection result of the protrusion 20. Since the generation of the protrusion 20 can be monitored in real time, the switching section 88 can be switched to the high energy density FH to remove the protrusion 20 immediately when the protrusion 20 is generated, and thus the growth of the protrusion 20 can be avoided. By being switched to the low energy density FL immediately after the removal of the protrusion 20 is completed, the thermal influence on the material can be suppressed.

[0105] 6. Other Embodiments

[0106] The present application can also be implemented in the following manner.

[0107] <Modified Example 1 and Modified Example 2>

[0108] In the above-described embodiment, the configuration is such that the image of the processed layer is acquired by the imaging device 91, the image is analyzed by the image processing device 92 and the protrusions 20 are detected, and the energy density of the pulsed laser 71 is switched by the switching unit 88 by comparing the detection result of the protrusions 20 with the threshold value set by the switching condition setting unit 86. However, the configuration of the switching unit 88 and the switching condition setting unit 86 is not limited to this, and other configurations can also be used.

[0109] As a modification example 1, the switching condition setting unit 86 can be configured to set the number of processed layers NL at a low energy density and the number of processed layers NH at a high energy density as the switching conditions, and the switching unit 88 can be configured to switch the pulsed laser 71 from the low energy density FL to the high energy density FH based on the number of processed layers NL at the low energy density, and from the high energy density FH to the low energy density FL based on the number of processed layers NH at the high energy density. Specifically, after the laser processing device 1 starts processing the processed layers by irradiating the pulsed laser 71 at the low energy density FL, when NL layers of the processed layers are processed, the switching unit 88 switches the pulsed laser 71 from the low energy density FL to the high energy density FH. When the laser processing device 1 finishes processing the processed layers of NH layers by irradiating the pulsed laser 71 at the high energy density FH, the switching unit 88 switches the pulsed laser 71 from the high energy density FH to the low energy density FL. Thereafter, the processing of the processed layers of NL layers by irradiation at the low energy density FL and the processing of the processed layers of NH layers by irradiation at the high energy density FH are repeated until the bottomed hole 10a having the desired depth is formed.

[0110] As a modification example 2, the switching condition setting unit 86 can be configured to set the processing depth DL at a low energy density and the processing depth DF at a high energy density as the switching conditions, and the switching unit 88 can be configured to switch the pulsed laser 71 from the low energy density FL to the high energy density FH based on the processing depth DL at the low energy density, and from the high energy density FH to the low energy density FL based on the processing depth DF at the high energy density. Specifically, after the laser processing device 1 starts processing the processed layers by irradiating the pulsed laser 71 at the low energy density FL, when the processed layers to the depth DL are processed, the switching unit 88 switches the pulsed laser 71 from the low energy density FL to the high energy density FH. Further, when the laser processing device 1 processes the processed layers to the depth DF by irradiating the pulsed laser 71 at the high energy density FH, the switching unit 88 switches the pulsed laser 71 from the high energy density FH to the low energy density FL. Thereafter, the processing of the processed layers to the depth DL by irradiation at the low energy density FL and the processing of the processed layers to the depth DH by irradiation at the high energy density FH are repeated until the bottomed hole 10a having the desired depth is formed.

[0111] The origin of the protrusion 20 is generated at each time of processing the processing layer of the prescribed depth, and the distribution of the origin in the depth direction differs depending on the material of the workpiece 10 as a condition of the workpiece 10. Therefore, the most appropriate number of low-energy-density processing layers NL and the number of high-energy-density processing layers NH, or the low-energy-density processing depth DL and the high-energy-density processing depth DF in the case where the processing can be performed while removing the protrusion 20 can be determined by previously investigating various materials and then performing trial processing to grasp the origin distribution. In the above example, the most appropriate number of low-energy-density processing layers NL and the number of high-energy-density processing layers NH, or the low-energy-density processing depth DL and the high-energy-density processing depth DF for each material can be stored in the storage section 85 as a database or a numerical control program, and the number of low-energy-density processing layers NL and the number of high-energy-density processing layers NH, or the low-energy-density processing depth DL and the high-energy-density processing depth DF can be set by the switching condition setting section 86 reading the corresponding values corresponding to the material of the workpiece 10 included in the input information.

[0112] In Modification Example 1 and Modification Example 2, the switching of the energy density is performed based on the number of low-energy-density processing layers NL and the number of high-energy-density processing layers NH, or the low-energy-density processing depth DL and the high-energy-density processing depth DF. Even in such a structure, the generated protrusion 20 can be removed at a relatively early stage, and thus the growth of the protrusion 20 can be avoided, and the reduction in the precision of the processed surface due to the thermal influence on the material can be suppressed. Further, in the above example, monitoring by the imaging device 91 and the image processing device 92 is not required at the time of actual processing.

[0113] <Modification Example 3>

[0114] In the above embodiment, the values of the low-energy-density FL and the high-energy-density FH are respectively set to one fixed value in the processing for forming the bottomed hole 10a. The setting of the low-energy-density FL and the high-energy-density FH is not limited to this, and the low-energy-density FL and the high-energy-density FH can be respectively set to two or more energy densities. For example, the irradiation device can be configured to irradiate the pulsed laser 71 in a manner that the first high-energy-density FH1 as the high-energy-density FH and the second high-energy-density FH2 lower than the first high-energy-density FH1 are switched, and the switching section 88 can be configured to switch the pulsed laser 71 emitted from the irradiation device between the low-energy-density FL, the first high-energy-density FH1, and the second high-energy-density FH2 based on the switching condition.

[0115] Specifically, in order to remove the protrusion 20, when switching from a low energy density FL, the switching unit 88 switches the pulsed laser 71 to a first high energy density FH1. After irradiating the pulsed laser 71 with the first high energy density FH1 and removing at least a portion of the protrusion 20, the pulsed laser 71 is switched to a second high energy density FH2, which is lower than the first high energy density FH1. By irradiating with the second high energy density FH2, the protrusion 20 can be completely removed. It should be noted that the switching from the first high energy density FH1 to the second high energy density FH2 can be based on setting the switching conditions based on the number or area of ​​the protrusions 20 generated on the surface of the processed layer, and executed based on these switching conditions. Alternatively, the first high energy density FH1 can be used, and when a processed layer of a predetermined number of layers or processing depth has been processed, the switch can be made to the second high energy density FH2.

[0116] In Modification 3, the high energy density FH is set to two levels. After at least a portion of the protrusion 20 is removed, it switches to a relatively lower second high energy density FH2. In this way, the protrusion 20 can be effectively removed, and the thermal effects on the workpiece 10 can be further effectively suppressed.

[0117] <Variation Example 4>

[0118] When the same processing layer is irradiated by pulsed laser 71, the spot diameter of pulsed laser 71 can be changed. As a variation 4, for example... Figure 7 The processing layer L shown k The irradiation method of the pulsed laser 71 in the process will be explained. Processing layer L k It includes a first region R1, which is a region adjacent to the end, and a second region R2, which is a region different from the first region R1. Specifically, it will be along the processing layer L k The outer edge region is designated as region 1 R1, and the region further inward than region 1 R1 is designated as region 2 R2. When the pulsed laser 71 irradiates in a low energy density (FL) or high energy density (FH) mode, the control device 8 controls the laser processing apparatus 1 so that the spot diameter H1 of the pulsed laser 71 irradiating point SP1 in region 1 R1 is smaller than the spot diameter H2 of the pulsed laser 71 irradiating point SP2 in region 2 R2. Here, regardless of whether it is high energy density (FH) or low energy density (FL) irradiation, the energy density of the pulsed laser 71 irradiating region 1 R1 is set to be the same as the energy density of the pulsed laser 71 irradiating region 2 R2. Alternatively, the laser processing apparatus 1 can be controlled so that the irradiation points SP1 and SP2 of the pulsed laser 71 overlap at the boundary between region 1 R1 and region 2 R2.

[0119] For example, when the first region R1 is irradiated with the pulsed laser 71 at a low energy density FL, the control device 8 can adjust the pulsed laser 71 to the desired spot diameter H1 in a manner of adjusting the beam diameter by controlling the optical system 3 or the condenser lens 52, and adjust the pulsed laser 71 to the low energy density FL in a manner of adjusting the output pulse energy by controlling the laser oscillator 2. Further, when the second region R2 is irradiated with the pulsed laser 71 at a low energy density FL, the control device 8 can adjust the pulsed laser 71 to the desired spot diameter H1 in a manner of adjusting the beam diameter by controlling the optical system 3 or the condenser lens 52, and adjust the pulsed laser 71 to the low energy density FL in a manner of adjusting the output pulse energy by controlling the laser oscillator 2.

[0120] In Modification 4, the pulsed laser 71 is irradiated with a relatively small spot diameter H1 at the first region R1 adjacent to the end portion, so that the end portion (particularly, the corner portion) of the machined layer L k is machined to a high-precision shape. On the other hand, the pulsed laser 71 is irradiated with a relatively large spot diameter H2 at the second region R2 different from the first region R1, so that the machining efficiency can be improved. Further, in the first region R1 and the second region R2, since the pulsed laser 71 is irradiated at the same energy density, the precision of the machined surface within the same machined layer L k can be maintained to be substantially constant.

[0121] <Others>

[0122] In the above-described embodiments, although the case where the bottomed hole is formed is described as an example, the machined shape of the machining object to which the laser machining method of the present application is applied is not limited thereto. The laser machining method of the present application can be applied to, for example, formation of a groove shape or surface finishing, and the like. Here, the "groove shape" means a shape in which at least one side surface of four side surfaces of a recess is open (opened).

[0123] In the above-described embodiments, although the machined object 10 made of alloy steel is described as the machining object, the material of the machined object 10 to which the laser machining method of the present application is applied is not limited thereto. The laser machining method of the present application can be applied to, for example, other metal materials such as carbon steel or resin materials, and the like.

[0124] In the above-described embodiment, the energy density of the pulsed laser 71 emitted from the one laser oscillator 2 is switched between the low energy density FL and the high energy density FH by changing the output pulse energy or the spot diameter, but the manner of switching the energy density is not limited thereto. For example, two irradiation devices each composed of the laser oscillator 2, the optical system 3, and the scanning device 4 can be provided. In this case, the first pulsed laser output from one of the irradiation devices can be set to the low energy density FL, the second pulsed laser output from the other irradiation device can be set to the high energy density FH, and then the two irradiation devices can be switched by the irradiation control section 83, thereby achieving the switching of the energy density.

[0125] EXAMPLE

[0126] Next, the detailed contents of the present application will be described using examples, but the present application is not limited to the following examples.

[0127] The bottomed hole 10a was formed by the ultrashort pulsed laser processing of the workpiece 10 using the laser processing device 1, and the processed surface of the bottomed hole 10a was observed. In Example 1, the workpiece 10 made of SUS304 was irradiated with the pulsed laser 71 (wavelength: 515 [nm]; frequency: 200 [kHz]) having a pulse width of 410 [fs], and raster scanning was performed under the conditions of a scanning speed of 500 [mm / s], a spot diameter of 9 [μm], a spot interval of 2.5 [μm], and a line interval of 2.5 [μm]. Here, the "line interval" refers to the distance between the centers of two irradiation points adjacent to each other in the horizontal 1-axis direction perpendicular to the scanning direction of the pulsed laser 71 during the raster scanning.

[0128] The low energy density FL was set to 0.63 [J / cm 2 ], and the processing depth of each layer of the processed layer 1 was set to 0.36 [μm] under the irradiation of the pulsed laser 71 at the low energy density FL, and the processed layer was sequentially processed. Further, the high energy density FH was set to 6.3 [J / cm 2], the processing depth of 1 layer of each layer was set to 1.5 [μm] under the high energy density FH irradiation, the pulsed laser 71 was irradiated, and the protrusions 20 on the processing layer were removed with the processing layer. The number of low energy density processing layers NL was set to 50 layers, the number of high energy density processing layers NH was set to 5 layers, the pulsed laser 71 was switched between the low energy density FL and the high energy density FH based on the number of low energy density processing layers NL and the number of high energy density processing layers NH by the switching section 88, and the processing of the processing layer was repeatedly performed. The processing was ended after 50 layers constituting the lowermost portion of the bottomed hole 10a were processed by the irradiation of the low energy density FL, and thus a substantially square opening portion having a planar size of 1000 x 1000 [μm] and a bottomed hole 10a having a depth of 481 [μm] were obtained.

[0129] In Comparative Example 1, the pulsed laser 71 was irradiated and processed only in the low energy density FL without using the high energy density FH. The low energy density FL was set to 0.63 [J / cm 2 ], the processing depth of each layer was set to 0.36 [μm], and the processing layer was sequentially processed by the irradiation of the pulsed laser 71. The other conditions were the same as in Example 1. A substantially square opening portion having a planar size of 1000 x 1000 [μm] and a bottomed hole 10a having a depth of 477 [μm] were obtained.

[0130] In Comparative Example 2, the pulsed laser 71 was irradiated and processed only in the high energy density FH without using the low energy density FL. The high energy density FH was set to 6.3 [J / cm 2 ], the processing depth of each layer was set to 1.5 [μm], and the processing layer was sequentially processed by the irradiation of the pulsed laser 71. The other conditions were the same as in Example 1. A substantially square opening portion having a planar size of 1000 x 1000 [μm] and a bottomed hole 10a having a depth of 468 [μm] were obtained.

[0131] Figure 8A and Figure 8B are images of the processing surface of the bottomed hole 10a formed in Example 1 and Comparative Example 1, respectively, and are images taken from above the bottomed hole 10a. A plurality of protrusions 20 were observed on the bottom surface and the side surface of the bottomed hole 10a in Example 1 only, the arithmetic average roughness Ra as an index of the surface roughness was about 0.13 μm, and the processing surface had relatively high precision. Note that the arithmetic average roughness Ra was measured in accordance with JIS B0601-2001. On the other hand, a plurality of protrusions 20 were observed on the bottom surface and the side surface of the bottomed hole 10a in Comparative Example 1, and the arithmetic average roughness Ra was about 2.0 μm.

[0132] Figure 9Ais an image of the machined surface of the blind hole 10a formed in Comparative Example 2, which is an image taken from above of the blind hole 10a. Figure 9B is an image of the region B in Figure 9A enlarged. The bottom surface and the side surface of the blind hole 10a of Comparative Example 2 have almost no protrusions 20 observed. On the other hand, a large number of micro-holes generated due to thermal effects are confirmed on the machined surface, and the arithmetic average roughness Ra thereof is about 0.26 μm.

[0133] The above description is merely illustrative of the various embodiments of the present application and does not limit the scope of the application. The novel embodiments can be implemented in other ways, and various omissions, substitutions, and changes can be made without departing from the spirit of the application. The embodiments and their modifications are included within the scope and spirit of the application, and are included within the scope of the application and its equivalent substitutions as recited in the claims.

Claims

1. A laser processing apparatus characterized by comprising: The laser processing device includes an irradiation device and a control device, The irradiation device is configured to irradiate a pulsed laser with a predetermined low energy density, to process one or more layers from a workpiece containing inclusions in a base material, and to remove protrusions grown in a depth direction by irradiation with the low energy density by irradiating the pulsed laser with a high energy density higher than the low energy density, and to continue processing the layers with the low energy density after removing the protrusions, The control device includes a switching unit and a switching condition setting unit, The switching unit switches the pulsed laser output from the irradiation device between the low energy density and the high energy density based on a switching condition, The switching condition setting unit sets the switching condition based on a condition of the workpiece, The switching condition setting unit sets a number of low energy density processing layers and a number of high energy density processing layers as the switching condition, The switching unit switches the pulsed laser from the low energy density to the high energy density based on the number of low energy density processing layers, and switches the pulsed laser from the high energy density to the low energy density based on the number of high energy density processing layers.

2. The laser processing apparatus according to claim 1, characterized by The control device performs final processing by irradiation with the low energy density, thereby completing processing.

3. The laser processing apparatus according to claim 1, characterized by The laser processing device includes an imaging device that acquires an image of the layers, and an image processing device that analyzes the image and detects the protrusions on the surface of the layers, The switching unit switches the pulsed laser between the low energy density and the high energy density based on a detection result of the protrusions.

4. The laser processing device according to claim 3, wherein The image processing device analyzes the image and acquires a number or an area of the protrusions on the surface of the layers.

5. The laser processing device according to any one of claims 1 to 4, wherein The irradiation device is configured to be capable of irradiating the pulsed laser with a first high energy density as the high energy density and a second high energy density lower than the first high energy density, The switching unit switches the pulsed laser output from the irradiation device between the low energy density, the first high energy density, and the second high energy density based on the switching condition.

6. The laser processing device according to any one of claims 1 to 4, wherein The control device includes an energy density setting unit, The energy density setting unit sets values of the high energy density and the low energy density based on a processing condition, The processing condition includes a material of the workpiece.

7. The laser processing device according to claim 6, wherein The processing condition further includes a scan speed and a repetition frequency of the pulsed laser.

8. The laser processing device according to any one of claims 1 to 4, wherein The layers include a first region that is a region adjacent to an end portion and a second region that is a region different from the first region, A spot diameter of the pulsed laser irradiated in the first region is smaller than a spot diameter of the pulsed laser irradiated in the second region, The energy density of the pulsed laser irradiated on the first region is equal to the energy density of the pulsed laser irradiated on the second region.

9. The laser processing apparatus according to any one of claims 1 to 4, characterized by, wherein, The processing layer is composed of an alloy steel containing inclusions in a base material, The high energy density is above a laser ablation threshold value of the inclusions.

10. The laser processing apparatus according to any one of claims 1 to 4, characterized by, wherein, The irradiation device is provided with a laser oscillator, The laser processing device switches between the low energy density and the high energy density of the pulsed laser by changing the output pulse energy of the laser oscillator.

11. The laser processing device according to any one of claims 1 to 4, wherein The low energy density and the high energy density of the pulsed laser are switched by changing a spot diameter of the pulsed laser.

12. The laser processing device according to any one of claims 1 to 4, wherein The high energy density is a value that is α times the low energy density, 2 ≦ α ≦ 20.

13. The laser processing device according to any one of claims 1 to 4, wherein The high energy density is a value that is α times the low energy density, 7 ≦ α ≦ 15.

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