Laser processing method, laser processing machine, program, and computer-readable medium

Abstract

This laser processing method includes: a processing step for processing a workpiece by radiating a laser beam from a nozzle; and a standby step for stopping the output of the laser beam. The standby step is started if the cumulative time of the processing step without intervention of the standby step exceeds a predetermined threshold time.

Description

Laser processing method, laser processing machine, program, and computer-readable medium

[0001] The present invention relates to a laser processing method, a laser processing machine, a program, and a computer-readable medium.

[0002] In laser processing, the temperature of the nozzle rises as the laser irradiates, causing the nozzle to thermally expand, which changes the relationship between the distance between the nozzle and the workpiece and the capacitance, which can adversely affect processing. To prevent this, a method has been proposed in which a flow path for cooling water is provided in the nozzle and the cooling water flows during processing to suppress the temperature rise (see, for example, Patent Document 1). Another method has been proposed in which the mount or the underside of the laser focusing lens is plated with a metal (e.g., gold plating or nickel-chrome plating) that has high laser reflectivity to suppress absorption of laser light and suppress the temperature rise (see, for example, Patent Document 2).

[0003] Japanese Utility Model Application Publication No. 02-006185 Japanese Patent No. 4812172

[0004] In recent years, the output of laser light has increased, and even if the above-mentioned method is used, it is difficult to sufficiently suppress the temperature rise of the nozzle, making it difficult to carry out continuous processing stably.

[0005] The purpose of the technology disclosed in this application is to provide a laser processing method, a laser processing machine, a program, and a computer-readable medium that can effectively cool the nozzle even when the laser light is highly powered, and can perform continuous processing stably.

[0006] A laser processing method according to a first aspect of the present disclosure includes a processing step of irradiating a workpiece with laser light from a nozzle and a waiting step of stopping output of the laser light, the waiting step being started when a cumulative time of the processing steps excluding the waiting step exceeds a predetermined threshold time.

[0007] According to a second aspect of the present disclosure, in the laser processing method according to the first aspect, the processing step includes irradiating laser light through a through-hole of a nozzle having a gold-plated surface.

[0008] According to a third aspect of the present disclosure, in the laser processing method according to the first or second aspect, the threshold time is determined based on the output intensity of the laser light and the ratio between the opening diameter at the tip of the nozzle and the diameter at which the power density of the laser light in the nozzle exceeds a predetermined threshold.

[0009] According to a fourth aspect of the present disclosure, in the laser processing method according to any one of the first to third aspects, the waiting step is performed for a waiting time that depends on the degree to which the nozzle is heated in the processing step.

[0010] According to a fifth aspect of the present disclosure, in the laser processing method according to the fourth aspect, the waiting time is determined based on the output intensity of the laser light, the ratio between the opening diameter at the tip of the nozzle and the diameter at which the output density of the laser light in the nozzle exceeds a predetermined threshold, and the accumulated time.

[0011] According to a sixth aspect of the present disclosure, in the laser processing method according to any one of the first to fifth aspects, the standby step further includes storing the position of the nozzle immediately after switching to the standby step as a return target position. The standby step further includes changing the position of the nozzle to a standby position away from the return target position. The processing step further includes returning the position of the nozzle from the standby position to the return target position. Note that the standby position is preferably a position spaced above the return target position, a position spaced horizontally away from the workpiece, or a position spaced above the return target position and spaced horizontally away from the workpiece.

[0012] According to a seventh aspect of the present disclosure, in the laser processing method according to the sixth aspect, the waiting step further includes cooling the nozzle by a cooling device provided at the waiting position.

[0013] According to an eighth aspect of the present disclosure, in the laser processing method according to the sixth or seventh aspect, the processing step further includes, at the start of the processing step, piercing at a restart position deviated from the target return position, and then moving the nozzle to the target return position.

[0014] According to a ninth aspect of the present disclosure, in the laser processing method according to the eighth aspect, the processing step further includes correcting the position of the nozzle based on whether the product portion is present on either the right side or the left side in the direction of movement of the nozzle. The restart position is located on the other side opposite to the one side of the return target position.

[0015] According to a tenth aspect of the present disclosure, in the laser processing method according to the ninth aspect, the one side is determined based on a code for tool radius compensation in the processing program.

[0016] According to an eleventh aspect of the present disclosure, in the laser processing method according to any one of the first to tenth aspects, the processing step includes moving the nozzle for each processing unit set in the processing program to process the workpiece. If the nozzle position is in a switching prohibited area that is a predetermined distance or less from an end point of the processing unit when the cumulative time exceeds a threshold time, the processing step is continued until the nozzle position passes the switching prohibited area, and after the nozzle position passes the switching prohibited area, a waiting step is started.

[0017] According to a twelfth aspect of the present disclosure, in the laser processing method according to any one of the first to eleventh aspects, both the processing step and the waiting step further include cooling the nozzle by at least one of spraying assist gas from the nozzle and flowing a refrigerant through a nozzle cooling circuit provided in the nozzle.

[0018] A laser processing machine according to a thirteenth aspect of the present disclosure comprises a control circuit configured to execute a laser processing method according to any one of the first to twelfth aspects, a laser oscillator configured to output laser light, a nozzle, and a moving mechanism configured to move the nozzle.

[0019] A program according to a fourteenth aspect of the present disclosure includes instructions that, when executed by a control circuit of a laser processing machine, cause the control circuit to execute the laser processing method according to any one of the first to twelfth aspects.

[0020] A computer-readable medium according to a fifteenth aspect of the present disclosure comprises instructions that, when executed by a control circuit of a laser processing machine, cause the control circuit to perform a laser processing method according to any one of the first to twelfth aspects.

[0021] In the laser processing method according to the first aspect, the laser processing machine according to the thirteenth aspect which is equipped with a control circuit configured to execute the laser processing method according to the first aspect, the program according to the fourteenth aspect which is equipped with instructions for causing the control circuit to execute the laser processing method according to the first aspect, and the computer-readable medium according to the fifteenth aspect which is equipped with instructions for causing the control circuit to execute the laser processing method according to the first aspect, the standby step is started when the cumulative time of processing steps which do not have a standby step in between exceeds a predetermined threshold time, so that even in continuous laser processing, the nozzle can be cooled at a timing which prevents the nozzle temperature from rising too much, and stable, high-precision laser processing can be achieved.

[0022] In the laser processing method according to the second aspect, the laser processing machine according to the thirteenth aspect including a control circuit configured to execute the laser processing method according to the second aspect, the program according to the fourteenth aspect including instructions for causing the control circuit to execute the laser processing method according to the second aspect, and the computer-readable medium according to the fifteenth aspect including instructions for causing the control circuit to execute the laser processing method according to the second aspect, the gold plating prevents oxidation of the nozzle material, thereby preventing absorption of the laser light by the nozzle material and allowing the laser to be reflected by the gold plating, so that the laser output does not change even with use over time.

[0023] In the laser processing method according to the third aspect, the laser processing machine according to the thirteenth aspect which is equipped with a control circuit configured to execute the laser processing method according to the third aspect, the program according to the fourteenth aspect which includes instructions for causing the control circuit to execute the laser processing method according to the third aspect, and the computer-readable medium according to the fifteenth aspect which includes instructions for causing the control circuit to execute the laser processing method according to the third aspect, the amount of heat absorbed by the nozzle is determined based on the output intensity of the laser light, the ratio between the diameter of the opening hole at the tip of the nozzle and the diameter at the nozzle at which the output density of the laser light exceeds a predetermined threshold, and the rising temperature of the nozzle, so that the laser processing machine can be controlled so that a standby process is initiated when the temperature of the nozzle exceeds a predetermined temperature.

[0024] In the laser processing method according to the fourth aspect, the laser processing machine according to the thirteenth aspect which is equipped with a control circuit configured to execute the laser processing method according to the fourth aspect, the program according to the fourteenth aspect which has instructions for causing the control circuit to execute the laser processing method according to the fourth aspect, and the computer-readable medium according to the fifteenth aspect which has instructions for causing the control circuit to execute the laser processing method according to the fourth aspect, the nozzle is cooled during a waiting time according to the degree to which the nozzle is heated during the processing step, and the nozzle temperature is cooled until it drops below a predetermined temperature, thereby achieving stable, high-precision laser processing for a long period of time.

[0025] In the laser processing method according to the fifth aspect, the laser processing machine according to the thirteenth aspect which is equipped with a control circuit configured to execute the laser processing method according to the fifth aspect, the program according to the fourteenth aspect which includes instructions for causing the control circuit to execute the laser processing method according to the fifth aspect, and the computer-readable medium according to the fifteenth aspect which includes instructions for causing the control circuit to execute the laser processing method according to the fifth aspect, the rising temperature of the nozzle is determined based on the output intensity of the laser light, the ratio between the diameter of the opening hole at the tip of the nozzle and the diameter at the nozzle at which the output density of the laser light exceeds a predetermined threshold, and the accumulated time, so that a waiting time can be set for the time required to cool the nozzle temperature down to below a predetermined temperature.

[0026] In the laser processing method according to the sixth aspect, the laser processing machine according to the thirteenth aspect including a control circuit configured to execute the laser processing method according to the sixth aspect, the program according to the fourteenth aspect including instructions for causing the control circuit to execute the laser processing method according to the sixth aspect, and the computer-readable medium according to the fifteenth aspect including instructions for causing the control circuit to execute the laser processing method according to the sixth aspect, by changing the position of the nozzle to a standby position away from the return target position in the standby step, it is possible to prevent the nozzle from being exposed to radiant heat caused by heating of the workpiece, thereby increasing the cooling efficiency of the nozzle and shortening the standby time.

[0027] In the laser processing method according to the seventh aspect, the laser processing machine according to the thirteenth aspect which is equipped with a control circuit configured to execute the laser processing method according to the seventh aspect, the program according to the fourteenth aspect which includes instructions for causing the control circuit to execute the laser processing method according to the seventh aspect, and the computer-readable medium according to the fifteenth aspect which includes instructions for causing the control circuit to execute the laser processing method according to the seventh aspect, the waiting time can be shortened by cooling the nozzle with a cooling device.

[0028] In the laser processing method according to the eighth aspect, the laser processing machine according to the thirteenth aspect equipped with a control circuit configured to execute the laser processing method according to the eighth aspect, the program according to the fourteenth aspect equipped with instructions for causing the control circuit to execute the laser processing method according to the eighth aspect, and the computer-readable medium according to the fifteenth aspect equipped with instructions for causing the control circuit to execute the laser processing method according to the eighth aspect, if processing is performed at the return target position at the start of the processing step when the laser output and assist gas pressure are not stable, unnecessary heat will be generated and there is a risk of damaging the product surface. Therefore, the processing quality on the product surface can be improved by piercing at a resume position away from the return target position and then moving the nozzle to the return target position.

[0029] In the laser processing method according to the ninth aspect, the laser processing machine according to the thirteenth aspect having a control circuit configured to perform the laser processing method according to the ninth aspect, the program according to the fourteenth aspect having instructions for causing the control circuit to perform the laser processing method according to the ninth aspect, and the computer-readable medium according to the fifteenth aspect having instructions for causing the control circuit to perform the laser processing method according to the ninth aspect, it is possible to reliably set a restart position outside the product portion.

[0030] The laser processing method according to the tenth aspect, the laser processing machine according to the thirteenth aspect having a control circuit configured to execute the laser processing method according to the tenth aspect, the program according to the fourteenth aspect having instructions for causing the control circuit to execute the laser processing method according to the tenth aspect, and the computer-readable medium according to the fifteenth aspect having instructions for causing the control circuit to execute the laser processing method according to the tenth aspect use EIA / ISO program codes that are widely used, making it easy to apply this laser processing method to many processing programs.

[0031] In the laser processing method according to the eleventh aspect, the laser processing machine according to the thirteenth aspect including a control circuit configured to execute the laser processing method according to the eleventh aspect, the program according to the fourteenth aspect including instructions for causing the control circuit to execute the laser processing method according to the eleventh aspect, and the computer-readable medium according to the fifteenth aspect including instructions for causing the control circuit to execute the laser processing method according to the eleventh aspect, switching between processing steps and standby steps can be performed while avoiding portions near the end points of processing units that are likely to form corners of the product. Corners of a product are prone to heat accumulation, and switching between processing steps and standby steps near the corners can melt the material, resulting in processing defects. By switching between processing steps and standby steps while avoiding portions near the end points of processing units, such processing defects can be prevented.

[0032] In the laser processing method according to the 12th aspect, the laser processing machine according to the 13th aspect having a control circuit configured to execute the laser processing method according to the 12th aspect, the program according to the 14th aspect having instructions for causing the control circuit to execute the laser processing method according to the 12th aspect, and the computer-readable medium according to the 15th aspect having instructions for causing the control circuit to execute the laser processing method according to the 12th aspect, the nozzle can be cooled by an assist gas or a refrigerant even during the processing step, thereby preventing the temperature of the nozzle from rising during processing.

[0033] The technology disclosed in the present application makes it possible to provide a laser processing method, a laser processing machine, a program, and a computer-readable medium that can effectively cool the nozzle and perform continuous processing stably.

[0034] FIG. 1 is a diagram showing the external configuration of a laser processing machine according to an embodiment. FIG. 2 is a cross-sectional view of a laser head of the laser processing machine according to an embodiment. FIG. 3 is a cross-sectional view taken along the line III-III' in FIG. 2. FIG. 4 is a diagram showing the internal configuration of an optical fiber according to an embodiment. FIG. 5 shows an example of laser light output according to an embodiment. FIG. 6 is a schematic diagram of laser light from a torch according to an embodiment. FIG. 7 is an example of setting data. FIG. 8 is an example of a processing program for laser processing. FIG. 9 is a flowchart of a laser processing method according to a first embodiment. FIG. 10 shows an example of a nozzle movement trajectory according to the first embodiment as viewed from the Z direction. FIG. 11 shows an example of a nozzle movement trajectory according to the first embodiment as viewed from the X direction. FIG. 12 shows a modified example of the nozzle movement trajectory according to the first embodiment as viewed from the X direction. FIG. 13 is a flowchart of a laser processing method according to a second embodiment. FIG. 14 shows an example of a nozzle movement trajectory according to the second embodiment as viewed from the Z direction. FIG. 15 shows an example of a nozzle movement trajectory according to the second embodiment as viewed from the Y direction.

[0035] The present invention will be described in detail below with reference to the drawings illustrating embodiments thereof. Note that the same reference numerals in the drawings indicate corresponding or substantially identical components. <First Embodiment> <Configuration of Laser Processing Machine 1> FIG. 1 is a schematic diagram illustrating the external configuration of a laser processing machine 1 according to an embodiment of the present invention. The X-axis in FIG. 1 corresponds to the depth direction of the laser processing machine 1, the Y-axis corresponds to the width direction of the laser processing machine 1, and the Z-axis corresponds to the height direction of the laser processing machine 1. Hereinafter, the directions along the X-axis, Y-axis, and Z-axis will be referred to as the X-direction, the Y-direction, and the Z-direction, respectively. As shown in FIG. 1, the laser processing machine 1 includes a base 10, a first guide rail 11, a column 12, a second guide rail 13, a saddle 14, an oil nozzle 15, a first valve 16, a laser head 20, a laser oscillator 40, an optical fiber 45, and a numerical control apparatus 6. The laser processing machine 1 is a device for processing a metal plate MP on a base 10. The metal plate MP is preferably made of mild steel, but may also be made of stainless steel, aluminum steel, brass, or copper. The thickness of the metal plate MP is preferably 16 mm to 60 mm, but is not limited to this size. The metal plate MP may also be referred to as a workpiece W. The base 10 may have multiple elongated projections. A pair of first guide rails 11 extending along the X direction are attached to both ends of the base 10 in the Y direction. A column 12 is attached to the first guide rails 11 so as to be freely movable on the first guide rails 11. The column 12 moves on the first guide rails 11 by a driving force from a driving device D1, such as a motor, provided on either the first guide rail 11 or the column 12.

[0036] A second guide rail 13 is provided on the column 12 along a Y-axis perpendicular to the X-axis, and a saddle 14 is attached thereto so as to be movable in the Y-direction. The saddle 14 moves on the second guide rail 13, for example, by a driving force from a driving device D2, such as a motor, provided on either the second guide rail 13 or the saddle 14. Although not shown, the column 12 may be covered with a bellows-shaped cover. A laser head 20 is attached to the saddle 14 so as to be movable in the Z-direction along a Z-axis perpendicular to the X-axis and Y-axis. The laser head 20 moves on the saddle 14 by a driving force from a driving device D3, such as a motor, provided on either the saddle 14 or the laser head 20. The laser head 20 is configured to process the sheet metal MP on the base 10. The laser head 20 includes an optical system into which laser light emitted from a laser oscillator 40 is introduced. The optical system includes a collimation unit (not shown) for converting the laser light into a parallel beam. The laser head 20 includes a laser nozzle 28 for laser processing. The laser nozzle 28 may be simply referred to as a nozzle.

[0037] The oil nozzle 15 is configured to spray oil onto the workpiece W during piercing, which will be described later. The oil is stored in an oil tank (not shown). The first valve 16 is configured to adjust the amount of oil sent to the oil nozzle 15 from a pump (not shown). In FIG. 1 , the oil nozzle 15 and the first valve 16 are shown attached to the saddle 14, but they may also be attached to the base 10. The laser oscillator 40 is configured to output laser light for processing the sheet metal MP. The optical fiber 45 retractably connects the laser oscillator 40 and the laser head 20 to supply the laser light output from the laser oscillator 40 to the laser head 20. The optical fiber 45 has a first end 45a that receives the laser light from the laser oscillator 40 and a second end 45b opposite the first end 45a. The numerical control device 6 has a control circuit 7 including a hardware processor, memory, etc. The control circuit 7 is configured to execute the control program 8 and the machining program 9 and control the laser oscillator 40, the drive devices D1 to D3, the first valve 16, and the second valve 17 and third valve 37 (described later) to machine the metal sheet MP. For example, the machining program 9 is written in EIA / ISO program code, and the control program 8 is a program that analyzes the program code of the machining program 9 and generates control signals for controlling the laser oscillator 40, the drive devices D1 to D3, the first valve 16, and the second valve 17 and third valve 37 (described later) while referencing setting data 8a. The setting data 8a describes outputs to the laser oscillator 40, the drive devices D1 to D3, the first valve 16, and the second valve 17 and third valve 37 (described later) corresponding to each parameter in the code of the machining program 9. The control program 8 is, for example, a library. In the following embodiments, the drive devices D1 to D3 are collectively referred to as a transfer mechanism TM. The moving mechanism TM is configured to move the laser nozzle 28 .

[0038] FIG. 2 is a cross-sectional view of the laser head 20 of the laser processing machine 1 according to the embodiment. To explain the optical system of the laser head 20, FIG. 2 shows a cross-sectional view of the laser head 20 taken along a cutting plane passing through the optical axis Ax3 of the laser light emitted from the laser nozzle 28. Referring to FIG. 2, the laser head 20 has a head main body 21, an upper unit 22, and a lower unit 23. The upper unit 22 is attached to the head main body 21. The upper unit 22 includes a connector 25. The connector 25 is used to attach the second end 45b of the optical fiber 45 to the laser head 20.

[0039] The lower unit 23 is attached to the head main body 21. The lower unit 23 is provided opposite the second end 45b of the optical fiber 45 and includes a lens 24 configured to focus the laser light that passes through the optical fiber 45 toward the workpiece W. In other words, the laser processing machine 1 includes the lens 24. Although not shown in FIG. 2 , a separate lens for focusing the light emitted from the second end 45b of the optical fiber 45 may be provided between the connector 25 and the lens 24. A laser nozzle 28 is attached to the tip of the lower unit 23. An optical path 27 for passing the laser light is provided in the upper unit 22, the head main body 21, the lower unit 23, and the laser nozzle 28.

[0040] As shown in FIG. 2 , the laser processing machine 1 includes a second valve 17 on the head body 21. The second valve 17 is configured to send gas to the laser nozzle 28. The control circuit 7 is configured to control the second valve 17. This gas is preferably oxygen gas for promoting melting of the workpiece W, but may also be air, nitrogen gas, or argon gas. In the following embodiments, the gas sent from the second valve 17 is referred to as an assist gas AG. The assist gas AG is stored in a gas storage 18 (see FIG. 1 ) and sent to the laser nozzle 28 via a gas supply path 19 by a pump (not shown). The laser nozzle 28 has a through-hole 28h through which the light focused by the lens 24 and the gas to be sprayed onto the workpiece W pass. Preferably, the laser nozzle 28 is made of copper. Preferably, the surface of the laser nozzle 28 that forms the through-hole 28h is gold-plated 28m. Nickel plating between the gold plating 28m and the copper surface is more preferable to prevent diffusion between the copper and gold. Preferably, the remaining surface of the laser nozzle 28 is chrome-plated. This prevents oxidation of the laser nozzle 28 and reduces the likelihood of laser light being absorbed by the laser nozzle 28. Furthermore, gold plating 28m is even more desirable because it has a high reflectivity for laser light and therefore reduces loss of laser energy. Note that the material of the laser nozzle 28 may be a metal other than copper, and the surface of the laser nozzle 28 does not need to be plated.

[0041] Further, referring to FIG. 2 , the laser nozzle 28 has a tip 28e, and the through-hole 28h forms an opening 28p at the tip 28e. FIG. 3 is a cross-sectional view taken along the line III-III′ in FIG. 2 . As shown in FIGS. 2 and 3 , the laser processing machine 1 includes a third valve 37 on the head body 21. The third valve 37 is configured to adjust the amount of coolant sent from the pump to the laser nozzle 28. The control circuit 7 is configured to control the third valve 37. The coolant is preferably outside air. The coolant is taken in through an outside air intake (not shown) and sent to the laser nozzle 28 via a coolant supply path 38. The laser nozzle 28 includes a nozzle cooling circuit 33 through which the coolant passes. The nozzle cooling circuit 33 includes a primary annular path 34, multiple linear discharge paths 35, and a secondary annular path 36. The coolant flowing in from the coolant supply path 38 is sent to the primary annular path 34, which surrounds the through-hole 28h. The coolant is then sent from the primary annular passage 34 toward the primary discharge port 35e via the discharge path 35. The primary discharge port 35e is connected to the secondary annular passage 36, and the coolant is discharged from the secondary annular passage 36 through a discharge path 36e extending radially with respect to the optical axis Ax3 of the laser beam. That is, the coolant is discharged to the side of the laser nozzle 28. Note that the secondary annular passage 36 and the discharge path 36e may be omitted as long as the coolant is discharged in a direction substantially radially with respect to the optical axis Ax3 of the laser beam. For example, the discharge path 36e may have a recessed structure so that it is provided over the entire outer portion of the secondary annular passage 36. The shape of the nozzle cooling circuit 33 is not limited to the shape shown in FIGS. 2 and 3. A circulating nozzle cooling circuit as disclosed in Japanese Utility Model Laid-Open Publication No. 02-006185 may also be used. In this case, the coolant may be a liquid, such as cooling water.

[0042] FIG. 4 is a diagram illustrating the internal configuration of an optical fiber 45 according to an embodiment. The optical fiber 45 includes a transmitting portion 47 and a reflector 49. The transmitting portion 47 is cylindrical and configured to transmit laser light. The reflector 49 is a tubular member that covers the outer periphery of the transmitting portion 47 and is configured to reflect the laser light at the interface with the transmitting portion 47. FIG. 5 illustrates an example of the output of laser light RL when the optical axis Ax1 of the laser light RL is aligned with the central axis Ax2 of the optical fiber 45. FIG. 5 shows the magnitude of the laser power density on the right side of the diagram of the optical fiber 45. In FIG. 5, the laser power density increases as the line on the graph moves further to the right. FIG. 5 illustrates an example in which the laser power density is distributed according to a Gaussian distribution. As shown in FIG. 5, the laser power density is highest near the central axis Ax2 of the optical fiber 45 and then gradually decreases.

[0043] FIG. 6 is a schematic diagram of the laser beam RL extending from the laser nozzle 28 according to an embodiment. As shown in FIG. 6, the laser beam RL is most focused at the focal position FP and is incident on the surface of the workpiece W in a slightly broadened state. Typically, the focal position FP is located slightly outside the nozzle tip 28e. Here, the portion of the opening 28p of the nozzle tip 28e where the laser power density is equal to or greater than a predetermined threshold is referred to as the irradiated portion RP, and the remaining portion is referred to as the peripheral portion PP. The diameter DCC of the irradiated portion RP can be, for example, the value D4σ specified in the ISO 11446 specification. D4σ defines the range exceeding a power density threshold that is set to encompass an intensity distribution that is four times the standard deviation σ of the intensity distribution of the laser beam RL. This diameter DCC can be determined by measuring with a measuring instrument or using optical analysis software. 6, the diameter of the peripheral portion PP is shown as DBC (hereinafter, DBC will be referred to as the opening diameter), and the opening diameter DBC is determined by the specifications of the laser nozzle 28. The peripheral portion PP surrounds the irradiation portion RP in the radial direction relative to the optical axis Ax3 of the laser beam RL. Note that, as shown in FIG. 6, the assist gas AG is injected from the laser nozzle 28 so as to reach both the irradiation portion RP and the peripheral portion PP.

[0044] In the following embodiments, the ratio of the opening diameter DBC of the nozzle tip 28e to the diameter DCC at which the power density of the laser beam RL in the laser nozzle 28 exceeds a predetermined threshold value (threshold value defined by D4σ) is referred to as the area occupancy AOR [%]. If the output intensity of the laser beam RL output from the laser oscillator 40 is P [W] and the laser power density follows a Gaussian distribution, the amount of heat P applied to the laser nozzle 28 by the laser beam RL per unit time is Ｈ [W] can be calculated using the following formula (1): Ｈ = P × (1.82 × AOR - 100) / 100 (Equation 1) This 1.82 times is based on the size of the beam diameter that contains 99% of the energy. Note that if the laser power density follows a distribution other than a Gaussian distribution, or if a different threshold value (full width at half maximum, 1 / e ２ When using a width (knife edge width) or the like, the magnification by which the area occupancy rate AOR is multiplied should be determined so as to be the size of the beam diameter that contains 99% or more of the energy.

[0045] The heating time of the laser nozzle 28 is t [seconds], and the temperature of the laser nozzle 28 before heating is T ０ [°C], the specific heat of the laser nozzle 28 is c [kJ / (kg·°C)], the density of the laser nozzle 28 is ρ [kg / m ３ ], and the volume of the laser nozzle 28 is V [m ３ ], the temperature T [°C] of the laser nozzle 28 after heating can be calculated by the following (Equation 2): T-T ０ = (P Ｈ -P ＯＦＦ ) × t / 0.278cρV (Equation 2) P in (Equation 2) ＯＦＦ is the amount of heat radiation per unit time taking into account the convection heat radiation from the atmosphere, refrigerant, and assist gas AG. ＯＦＦ is determined empirically.

[0046] Highly accurate laser processing is achieved by adjusting the distance LW between the nozzle tip 28e and the workpiece W. The control circuit 7 can adjust the distance LW by controlling the capacitance between the nozzle tip 28e and the workpiece W, such as the method disclosed in U.S. Publication No. 2004-159643. When the laser nozzle 28 is heated and expanded by the laser light RL, the relationship between the distance LW and the above-mentioned capacitance changes. Therefore, by preventing the laser nozzle 28 from being heated by the laser light RL, processing can be performed with stable accuracy even during long-term laser processing.

[0047] 7 is an example of the setting data 8a. The setting data 8a indicates the output intensity P of the laser beam RL in the case of piercing for each combination of the material of the workpiece W, the thickness of the workpiece W, and the assist gas AG. Ｐ [W], the output intensity P of the laser light RL in the case of laser cutting Ｒ [W] is set. For example, in the EIA / ISO program format, this combination is set by calling the M622 code. As shown in FIG. 7, the output intensity P of the laser beam RL in the case of piercing is set. Ｐ [W], the output intensity P of the laser light RL in the case of laser cutting Ｒ [W] may be set to a plurality of levels. These levels are called cutting conditions. Figure 7 shows an example in which 10 cutting conditions are set.

[0048] FIG. 8 is an example of a laser processing program 9. FIG. 9 is a flowchart of the laser processing method according to the first embodiment. FIG. 10 shows an example of the movement trajectory of the laser nozzle 28 according to the first embodiment. In FIG. 8, "line number:" is added to the left of the processing program 9 for ease of reference. The control circuit 7, which executes the control program 8 that analyzes the processing program 9, performs the following processing. In other words, the control circuit 7 is configured to execute the laser processing method according to the embodiment. Line number 1 indicates the start of the program, and line number 2 indicates the program number. By the code in line number 3, the control circuit 7 executing the control program 8 reads from the M622 code the settings that the workpiece W is made of mild steel, the thickness of the workpiece W is 25.0 mm, and the assist gas AG is oxygen gas, and selects the corresponding setting data 8a. By the codes in lines 4 to 6, the control circuit 7 executing the control program 8 performs initial settings such as determining coordinates. In step ST1 of FIG. 8, the control circuit 7 executing the control program 8 starts the laser oscillator 40 by executing line number 7. Specifically, the control circuit 7 that executes the control program 8 determines the strength P Ｐ 1 [W]. At this time, the control circuit 7 executing the control program 8 causes oil to be sprayed from the first valve 16 toward the workpiece W. Furthermore, the control circuit 7 executing the control program 8 opens the second valve 17 and the third valve 37, and starts cooling the laser nozzle 28 by spraying the assist gas AG from the laser nozzle 28 and by flowing a refrigerant through the nozzle cooling circuit 33 provided in the laser nozzle 28.

[0049] The control circuit 7 executing the control program 8 sets the laser cutting conditions according to the code in line number 8. At the same time, in step ST2, the control circuit 7 executing the control program 8 sets the threshold time t ｔｈ The G602 code in line 8 omits the argument of the cutting conditions. In this case, the control circuit 7 that executes the control program 8 takes over the cutting conditions S1 of the G600 code and sets the strength P specified by the cutting conditions S1 of the G602 code.Ｒ 1 [W] is calculated from the setting data 8a, and the intensity P Ｒ The laser oscillator 40 is controlled so that cutting is performed at 1 [W]. The output intensity P Ｒ 1 [W] and the temperature T of the laser nozzle 28 at which cooling should be started. ｔｈ The temperature T of the laser nozzle 28 at which cooling should start is read. ｔｈ is set in advance and stored in the memory of the control circuit 7. In addition, the area occupancy rate AOR [%] is previously calculated from the opening diameter DBC of the nozzle tip 28e and the diameter DCC calculated in advance by a measuring instrument or optical analysis software. Therefore, the control circuit 7 that executes the control program 8 calculates the amount of heat P applied to the laser nozzle 28 per unit time as Ｈ [W] can be calculated by (Equation 1). The temperature of the laser nozzle 28 at which cooling should start is T ｔｈ Then, the control circuit 7 that executes the control program 8 determines the threshold time t ｔｈ can be calculated by the following (Equation 3): ｔｈ =0.278cρV(T ｔｈ -T ０ ) / (P Ｈ -P ＯＦＦ ) (Equation 3) This T ｔｈ is a value obtained by subtracting a certain offset from the temperature at which the capacitance may change due to deformation of the laser nozzle 28 caused by heating. As can be seen from (Equation 3), the threshold time t ｔｈ is determined based on the output intensity P of the laser light RL and the ratio (area occupancy rate AOR) between the opening diameter DBC of the tip 28e of the laser nozzle 28 and the diameter DCC at which the output density of the laser light RL in the laser nozzle 28 exceeds a predetermined threshold.

[0050] In step ST3, the control circuit 7 executing the control program 8 executes a machining process in which the workpiece W is machined by irradiating the laser beam RL from the laser nozzle 28. Specifically, the control circuit 7 executing the control program 8 performs tool diameter correction according to the code in line number 9 and moves the laser nozzle 28 to the position (-0.1, 0, 0). The control circuit 7 executing the control program 8 moves the laser nozzle 28 according to the code in lines 10 to 13. In other words, the machining process includes irradiating the laser beam RL through the through-hole 28h of the laser nozzle 28, the surface of which is gold-plated 28m. Furthermore, because the second valve 17 and the third valve 37 have already been opened, the machining process further includes spraying the assist gas AG from the laser nozzle 28 and cooling the laser nozzle 28 by flowing a refrigerant through the nozzle cooling circuit 33 provided in the laser nozzle 28. Note that either or both of the spraying of the assist gas AG and the flow of the refrigerant through the nozzle cooling circuit 33 may be omitted in the machining process. During the execution of the machining process, the control circuit 7 that executes the control program 8 counts the cumulative time t ａｃｍ In this embodiment and the following embodiments, machining performed by moving the laser nozzle 28 in response to one command is called a machining unit. In the case of a machining program written in the EIA / ISO program format such as the machining program 9, one command is defined for each line, and therefore a machining unit is defined for each line. In other words, the machining process includes moving the laser nozzle 28 for each machining unit set in the machining program 9 and machining the workpiece W.

[0051] In step ST4, the control circuit 7 executing the control program 8 determines whether the machining process has ended. If the machining process has not ended (No in step ST4), the process proceeds to step ST5. In step ST5, the control circuit 7 executing the control program 8 determines the cumulative time t of the machining process excluding the waiting process described later. ａｃｍ is a predetermined threshold time t ｔｈ It is determined whether the cumulative time t ａｃｍ is a predetermined threshold time t ｔｈIf the cumulative time t does not exceed the predetermined value (No in step ST5), the process returns to step ST3. ａｃｍ is a predetermined threshold time t ｔｈ (Yes in step ST5), in step ST6, the control circuit 7 executing the control program 8 starts a standby process of stopping the output of the laser beam RL. ａｃｍ is a predetermined threshold time t ｔｈ The standby process is initiated when the oxygen concentration exceeds 0.5%. Because the third valve 37 is not closed during the standby process, the standby process further includes cooling the laser nozzle 28 by flowing a coolant through the nozzle cooling circuit 33 provided in the laser nozzle 28. Note that assist gas AG may also be sprayed during the standby process. Spraying assist gas AG during the standby process prevents air from being mixed into the piping, reducing the possibility of poor oxygen purity and resulting in machining defects when machining is resumed. Furthermore, during the standby process, it is not necessary to flow a coolant through the nozzle cooling circuit 33. Furthermore, in step ST6, the control circuit 7 executing the control program 8 stops the movement of the laser nozzle 28.

[0052] FIG. 10 shows an example of the movement trajectory of the laser nozzle 28 according to the first embodiment as viewed from the Z direction. FIG. 11 shows an example of the movement trajectory of the laser nozzle 28 according to the first embodiment as viewed from the X direction. In FIGS. 10 and 11, the nozzle movement path corresponding to each line number of the program code in FIG. 8 is indicated by R_<line number>. In FIG. 10, the initial position of the laser nozzle 28 indicated on line number 9 is indicated as P_ST, and the position of the laser nozzle 28 at which the standby process starts is indicated as P_RT. In the example of FIGS. 10 and 11, the standby process starts when the code indicated on line number 11 is executed, but the standby process may start during the execution of any of the code on lines 10 to 13.

[0053] After step ST6, in step ST7, the control circuit 7 executing the control program 8 stores the position (stop position) of the laser nozzle 28 immediately after switching to the standby process as the return target position P_RT. The standby process further includes storing the position (stop position) of the laser nozzle 28 immediately after switching to the standby process as the return target position P_RT. In step ST8, the control circuit 7 executing the control program 8 stores a standby time t ｓｕｓ This waiting time t ｓｕｓ is calculated based on the following (Equation 4) based on (Equation 3): ｓｕｓ = (T ｈｅｔ -T ０ )×0.278cρV / P ＯＦＦ (Equation 4) where T ｈｅｔ is a temperature corresponding to the degree to which the laser nozzle 28 is heated during the processing step. ｈｅｔ is T ｔｈ Therefore, by using (Equation 2), (Equation 4) can be expressed as (Equation 5) below. ｓｕｓ ≒ (P Ｈ -P ＯＦＦ ) x t ａｃｍ / P ＯＦＦ (Equation 5) As is clear from (Equation 5), the waiting time t ｓｕｓ is the output intensity P of the laser beam RL, the ratio (area occupancy AOR) of the opening diameter DBC of the tip 28e of the laser nozzle 28 to the diameter DCC at which the output density of the laser beam RL exceeds a predetermined threshold value in the laser nozzle 28, and the cumulative time t ａｃｍ In this embodiment, the cumulative time t ａｃｍ is the threshold time t ｔｈ is roughly equal to

[0054] In step ST9, as shown in Fig. 11 , the control circuit 7 executing the control program 8 changes the position of the laser nozzle 28 to a standby position P_SB away from the return target position P_RT. That is, the standby process further includes changing the position of the laser nozzle 28 to a standby position P_SB away from the return target position P_RT. In the example of Fig. 11 , the standby position P_SB is a position shifted in the Z direction from the return target position P_RT by a height H away from the workpiece W. This height H is a height sufficient to prevent the laser nozzle 28 from receiving radiant heat caused by heating the workpiece W.

[0055] In step ST10, the control circuit 7 that executes the control program 8 determines whether the elapsed time t ｅｌｐ is the waiting time t ｓｕｓ It is determined whether the elapsed time t from the start of the standby process is equal to or greater than the predetermined time t. ｅｌｐ is the waiting time t ｓｕｓ If the time t is less than the predetermined time (No in step ST10), step ST10 is repeated. ｅｌｐ is the waiting time t ｓｕｓ If the above is the case (Yes in step ST10), the control circuit 7 executing the control program 8 resumes the processing step in step ST11. Therefore, the standby step is performed for a standby time t ｓｕｓ The laser nozzle 28 is then moved to the return target position P_RT in step ST11. That is, the machining process further includes returning the laser nozzle 28 from the standby position P_SB to the return target position P_RT. After the laser nozzle 28 is moved to the return target position P_RT, the control circuit 7 executing the control program 8 preferably opens the first valve 16 to inject oil onto the workpiece W. At this time, in step ST12, the control circuit 7 executing the control program 8 restarts the laser oscillator 40 to perform piercing. At this time, the cutting conditions are preferably set to S1 based on the previous G600 code, and piercing is performed. After step ST12 is completed, the process returns to step ST3.

[0056] Thereafter, in step ST3, the control circuit 7 executing the control program 8 executes the remaining machining steps. At this time, it is desirable that the cutting conditions are set to S1 based on the previous G602 code, and the machining steps are carried out. ａｃｍ is the threshold time t ｔｈ If the processing step is completed before the cumulative time t of the processing step is exceeded (Yes in step ST4), the laser processing method according to this embodiment is terminated. This is because the control circuit 7 executing the control program 8 determines that the processing step is completed at the point in time when it identifies the code for turning off laser irradiation in line number 14. <Features and effects of the laser processing method according to this embodiment> The laser processing method according to the first embodiment, the control program 8 including instructions for causing the control circuit 7 to execute the laser processing method, and the laser processing machine 1 are ａｃｍ is the threshold time t ｔｈ , the laser nozzle 28 is effectively cooled, enabling continuous machining to be performed stably. <Modification of the First Embodiment> In the above-described embodiment, the standby position P_SB is a position shifted from the return target position P_RT in the direction away from the workpiece W by the height H, but it may be a different position. Furthermore, a cooling device 30 for cooling the laser nozzle 28 may be separately provided at the standby position P_SB. FIG. 12 shows a modification of the movement trajectory of the laser nozzle 28 according to the first embodiment as viewed from the X direction. Referring to FIG. 12, the standby position P_SB is a position shifted in the Y direction from the return target position P_RT, and the cooling device 30 includes an insertion opening 31 for inserting the laser nozzle 28 and a coolant supply path 32 for supplying coolant to the insertion opening 31. When the laser nozzle 28 is cooled by the cooling device 30 in the standby step, the denominator P ＯＦＦ Since the value of can be increased, the waiting time t ｓｕｓThis can shorten the overall processing time and improve processing efficiency. Second Embodiment In the first embodiment, laser processing is resumed by piercing at the return target position P_RT. However, because the laser output and the assist gas AG output are unstable at the start of laser processing, it is more desirable to resume laser processing by piercing at a resume position P_RS that is off the return target position P_RT in order to improve processing quality. The laser processing method according to the second embodiment includes such a method of moving the laser nozzle 28. FIG. 13 is a flowchart of the laser processing method according to the second embodiment. FIG. 14 shows an example of the movement trajectory of the laser nozzle 28 according to the second embodiment as viewed from the Z direction. FIG. 15 shows an example of the movement trajectory of the laser nozzle 28 according to the second embodiment as viewed from the Y direction.

[0057] In FIG. 13 , the same processes as those in the first embodiment are denoted by the same reference numerals, and their description will be omitted. After step ST2 is completed, in step ST21, the control circuit 7 executing the control program 8 sets the tool radius compensation using the code in line number 9. Line number 9 contains the G41 code, which instructs the correction to shift the nozzle tip 28e to the left in the direction of movement of the laser nozzle 28. Note that if the G42 code is included in the machining program 9, the correction would be to shift the nozzle tip 28e to the right in the direction of travel of the laser nozzle 28. In step ST3A, the control circuit 7 executing the control program 8 performs the tool radius compensation set in step ST21 in addition to the processing in step ST3. That is, the machining process includes correcting the position of the laser nozzle 28 based on whether the product portion is located on either the right or left side in the direction of movement of the laser nozzle 28. This side is determined based on the tool radius compensation code (G41 code or G42 code) in the machining program 9.

[0058] Cumulative time t ａｃｍ is a predetermined threshold time t ｔｈIf the cumulative time t does not exceed the cumulative time t (No in step ST5), the control circuit 7 executing the control program 8 returns to step ST21 and executes step ST21 again. ａｃｍ is a predetermined threshold time t ｔｈ If the distance exceeds the predetermined distance (Yes in step ST5), in step ST22, the control circuit 7 executing the control program 8 determines whether the position of the laser nozzle 28 is within a switching prohibited area SPR, which is a predetermined distance or less from the end point of the processing unit. This end point of the processing unit includes both the start point and the end point of the processing unit. In FIG. 14, the switching prohibited area SPR is shown as an area surrounded by a dotted line. The switching prohibited area SPR is an area close to the corner of the product, where heat is likely to accumulate. Therefore, waiting and resuming processing in the switching prohibited area SPR is likely to result in processing defects. For this reason, the control circuit 7 executing the control program 8 does not wait when the position of the laser nozzle 28 is within the switching prohibited area SPR, but continues laser processing.

[0059] Therefore, when the position of the laser nozzle 28 is in the switching prohibited area SPR, which is a predetermined distance or less from the end point of the machining unit (Yes in step ST22), the control circuit 7 executing the control program 8 returns to step ST21 and executes step ST21 again. When the position of the laser nozzle 28 is not in the switching prohibited area SPR, which is a predetermined distance or less from the end point of the machining unit (No in step ST22), the control circuit 7 executing the control program 8 executes step ST6. In other words, in the laser machining method according to this embodiment, the cumulative time t ａｃｍ is the threshold time t ｔｈ If the position of the laser nozzle 28 is in a switching prohibited area SPR that is a predetermined distance or less from the end point of the processing unit when the time exceeds the predetermined distance, the processing process is continued until the position of the laser nozzle 28 passes the switching prohibited area SPR, and after the position of the laser nozzle 28 passes the switching prohibited area SPR, a waiting process is started.

[0060] After step ST6, in step ST7A, in addition to the processing of step ST7, a restart position P_RS is determined. This restart position P_RS is located on the opposite side of the return target position P_RT. In other words, when the tool radius compensation code is G41 code, the control circuit 7 executing the control program 8 sets the restart position P_RS to the left of the return target position P_RT in the movement direction of the laser nozzle 28. When the tool radius compensation code is G42 code, the control circuit 7 executing the control program 8 sets the restart position P_RS to the right of the return target position P_RT in the movement direction of the laser nozzle 28. The distance between the restart position P_RS and the return target position P_RT is set to a value that empirically improves machining accuracy.

[0061] Thereafter, in step ST8A, the control circuit 7 executing the control program 8 waits for a waiting time t ｓｕｓ is set based on (Equation 5). In the first embodiment, the cumulative time t ａｃｍ is the threshold time t ｔｈ However, in this embodiment, the cumulative time t ａｃｍ is the threshold time t ｔｈ This waiting time t ｓｕｓ is the cumulative time t ａｃｍ The standby position P_SB is set according to the length of the workpiece W. In step ST9A, the control circuit 7 executing the control program 8 changes the position of the laser nozzle 28 to a standby position P_SB determined based on the restart position P_RS. FIG. 15 shows the standby position P_SB according to this embodiment. This standby position P_SB is a position shifted in the Z direction from the restart position P_RS by a height H away from the workpiece W. In the second embodiment, the standby position P_SB may also be the same position as in the first embodiment.

[0062] The elapsed time t from the start of the standby process ｅｌｐ is the waiting time t ｓｕｓIf the above is the case (Yes in step ST10), in step ST23, the control circuit 7 executing the control program 8 resumes the machining process. Specifically, the control circuit 7 executing the control program 8 moves the laser nozzle 28 to the restart position P_RS. After moving to the restart position P_RS, the control circuit 7 executing the control program 8 preferably causes the first valve 16 to inject oil onto the workpiece W. Thereafter, in step ST12, the control circuit 7 executing the control program 8 restarts the laser oscillator 40 and performs piercing. At this time, it is preferable that the cutting conditions be set to S1 based on the previous G600 code, and piercing is performed. In step ST24, the control circuit 7 executing the control program 8 moves the laser nozzle 28 to the return target position P_RT while irradiating the laser beam RL. In other words, the machining process further includes, at the start of the machining process, piercing at the restart position P_RS, which is off the return target position P_RT, and then moving the laser nozzle 28 to the return target position P_RT. At this time, it is desirable to set the cutting conditions to S1 based on the previous G602 code, and move the laser nozzle 28 to the return target position P_RT while irradiating the laser beam RL. After completing step ST24, the control circuit 7 executing the control program 8 returns to step ST21 and executes step ST21 again. <Features and Effects of the Laser Processing Method in This Embodiment> The laser processing method according to the second embodiment, the control program 8 including instructions for causing the control circuit 7 to execute the laser processing method, and the laser processing machine 1 pierce at a restart position P_RS slightly offset from the return target position P_RT and resume laser processing. This results in processing with a stable laser beam RL, thereby improving processing quality. <Modifications of All Embodiments> Step ST22 may be added to the first embodiment, and step ST8A of the second embodiment may be performed instead of step ST8. Alternatively, step ST22 may be omitted from the second embodiment, and step ST8 of the first embodiment may be performed instead of step ST8A.Furthermore, although the above-described embodiment does not show an example of a case where cutting conditions are changed by the G603 code, if the intensity P of the laser light RL is changed by the G603 code during the processing process, step ST2 is executed at that timing, and the threshold time t is set based on the changed intensity P. ｔｈ should be recalculated.

[0063] In the above embodiment, the setting data 8a is set for each combination of the material of the workpiece W, the thickness of the workpiece W, and the assist gas AG. The corresponding setting data 8a is selected by setting the combination of the material of the workpiece W, the thickness of the workpiece W, and the assist gas AG as an argument of the M622 code. However, the setting data 8a may be prepared in a form distinguishable by an arbitrary identifier, and the M622 code may include the identifier as an argument to select a set of cutting conditions such as those shown in FIG. 7 . Furthermore, while the laser processing machine 1 for processing sheet metal MP has been described, the present invention may also be applied to laser processing machines for processing pipes, etc. In this case, the laser head 20 may be rotatable around rotation axes parallel to the X-axis and Y-axis to enable three-dimensional processing. Furthermore, the laser beam of the laser processing machine 1 according to the present application does not need to be high-power.

[0064] A part or all of the functions of the logic of the control program 8 described above may be realized by a dedicated processor or integrated circuit. The control program 8 described above may be stored not only in a memory built into the control circuit 7 but also in a storage medium that is removable from a computer such as the numerical control device 6 and readable by the computer such as the numerical control device 6, such as a disk such as a floppy disk, optical disk, CD-ROM or magnetic disk, an SD card, a USB memory, or an external hard disk.

[0065] In this application, the term "comprises" and its derivatives are open-ended terms that describe the presence of elements and do not exclude the presence of other elements not listed. This also applies to the terms "have," "include," and their derivatives.

[0066] The terms "member," "part," "element," "body," and "structure" may have multiple meanings, such as a single part or multiple parts.

[0067] Ordinal numbers such as "first" and "second" are merely terms for identifying components and do not have any other meaning (e.g., a particular order). For example, the presence of a "first element" does not imply the presence of a "second element," and the presence of a "second element" does not imply the presence of a "first element."

[0068] Words expressing degrees, such as "substantially," "about," and "approximately," can mean a reasonable deviation that does not significantly change the final result, unless otherwise specified in the embodiment. All numerical values ​​described in this application can be interpreted to include words such as "substantially," "about," and "approximately."

[0069] In this application, the phrase "at least one of A and B" should be interpreted to include A only, B only, and both A and B.

[0070] It is apparent that various changes and modifications of the present invention are possible in light of the above disclosure, and therefore, the present invention may be practiced otherwise than as specifically disclosed herein without departing from the spirit of the present invention.

Claims

1. A laser processing method including a processing step of irradiating a workpiece with laser light from a nozzle and a standby step of stopping the output of the laser light, wherein the standby step is started when the cumulative time of the processing step that does not sandwich the standby step exceeds a predetermined threshold time.

2. The laser processing method according to claim 1, wherein the processing step includes irradiating the laser light through a through hole of the nozzle having gold plating on its surface.

3. The laser processing method according to claim 1 or 2, wherein the threshold time is determined based on the output intensity of the laser light and the ratio of the opening diameter of the tip of the nozzle to the diameter at which the output density of the laser light in the nozzle exceeds a predetermined threshold.

4. The laser processing method according to any one of claims 1 to 3, wherein the standby step is performed during a standby time corresponding to the degree of heating of the nozzle in the processing step.

5. The laser processing method according to claim 4, wherein the standby time is determined based on the output intensity of the laser light, the ratio of the opening diameter of the tip of the nozzle to the diameter at which the output density of the laser light in the nozzle exceeds a predetermined threshold, and the cumulative time.

6. The laser processing method according to any one of claims 1 to 5, wherein the standby step further includes storing the position of the nozzle immediately after switching to the standby step as a return target position, the standby step further includes changing the position of the nozzle from the return target position to a standby position away from the return target position, and the processing step further includes returning the position of the nozzle from the standby position to the return target position.

7. The laser processing method according to claim 6, wherein the standby step further includes cooling the nozzle by a cooling device provided at the standby position.

8. The laser processing method according to claim 6 or 7, wherein the processing step further includes moving the nozzle to the return target position after piercing at a restart position deviated from the return target position at the start of the processing step.

9. The laser processing method according to claim 8, wherein the processing step further includes correcting the position of the nozzle based on the presence of a product portion on either the right side or the left side in the moving direction of the nozzle, and the restart position is located on the other side opposite to the one side with respect to the return target position.

10. The laser processing method according to claim 9, wherein the one side is determined based on the code for tool diameter compensation in the processing program.

11. The processing step includes moving the nozzle for each processing unit set in the processing program to process the workpiece. When the cumulative time exceeds the threshold time and the position of the nozzle is in a switching prohibited area within a predetermined distance from the end point of the processing unit, the processing step is continued until the position of the nozzle passes through the switching prohibited area. After the position of the nozzle passes through the switching prohibited area, the standby step is started. The laser processing method according to any one of claims 1 to 10.

12. The laser processing method according to any one of claims 1 to 11, further including cooling the nozzle by at least one of injecting assist gas from the nozzle and flowing a refrigerant through a nozzle cooling circuit provided in the nozzle, both in the processing step and the standby step.

13. A laser processing machine comprising: a control circuit configured to execute the laser processing method according to any one of claims 1 to 12; a laser oscillator configured to output the laser beam; the nozzle; and a moving mechanism configured to move the nozzle.

14. A program including an instruction to cause the control circuit to execute the laser processing method according to any one of claims 1 to 12 when executed by the control circuit of the laser processing machine.

15. A computer-readable medium including an instruction to cause the control circuit to execute the laser processing method according to any one of claims 1 to 12 when executed by the control circuit of the laser processing machine.

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