LASER MACHINING APPARATUS AND LASER MACHINING METHOD

A control unit performs: a control of forming a cut groove by running a first laser beam along a machining path in an in-plane direction of an upper surface of the workpiece; a control of stopping irradiation with the first laser beam when an irradiation position of the laser beam reaches a position short of an end point on the machining path; and a control of continuing ejection of gas over a first waiting time. The control unit performs: a control of irradiating the workpiece with a second laser beam that gives less thermal energy to the workpiece per unit time than the first laser beam; and a control of forming a joint portion coupling the product and the offcut by running the second laser beam in an uncut region on the machining path, the joint portion having a thickness smaller than a thickness of the workpiece.

FIELD

The present disclosure relates to a laser machining apparatus and a laser machining method for irradiating a workpiece with a laser beam to cut the workpiece.

BACKGROUND

In conventional cutting of a workpiece using a laser, a plurality of products can be cut out from one plate-like workpiece. For cutting out a plurality of products from one workpiece through laser machining, a cutting method called micro-joint method is used in order to prevent failure in laser machining or collection of products due to movement of the cut-out products. Micro-joint method is a machining method for keeping a workpiece and a product coupled by a fine coupling portion called a joint portion so as not to completely separate the product from the workpiece. Then, by applying an impact to the joint portion at the time when all the cutting processes on the workpiece are completed, the product is separated from the offcut, i.e. portion of the workpiece other than the product.

Patent Literature 1 discloses that a coupling piece is formed between a workpiece and a product in a manner that does not cut entirely through the workpiece by causing the speed of cutting the workpiece higher, and the output of laser light lower, compared with those values for cutting out the product from the workpiece.

CITATION LIST

Patent Literature

Summary of Invention

Problem to be solved by the Invention

However, the adjustment of machining conditions according to the technique of Patent Literature 1, namely increasing the cutting speed and reducing the cutting output, is unsuitable for obtaining a coupling piece having a desired shape. When machining is performed under the conditions of increased cutting speed and reduced cutting output, the laser beam may move before the workpiece positioned above the coupling piece is certainly melted. For this reason, the technique of Patent Literature 1 has a possibility in that a desired shape cannot be stably obtained.

In addition, as the cutting speed is increased, the speed at which the machining gas moves also becomes higher. In this case, there is a possibility in that the discharge of melt by the laser beam from the cut groove with the machining gas cannot keep up with the melting of the workpiece. Therefore, the technique of Patent Literature 1 has a possibility in that, because the discharge of melt cannot keep up with the cutting speed at the time of forming the coupling piece, melt may remain undischarged downward from the cut groove of the workpiece and may blow up to the upper side of the workpiece. The blow-up of melt to the upper side of the workpiece makes it impossible to obtain the coupling piece having a desired shape, and causes the product to be covered with melt, resulting in a machining defect in the whole cutting.

The present disclosure has been made in view of the above, and an object thereof is to obtain a laser machining apparatus capable of reliably forming a coupling piece that has a desired shape and couples the workpiece and the product in laser beam cutting.

Means to Solve the Problem

In order to solve the above-described problems and achieve the object, a laser machining apparatus according to the present disclosure performs cutting to separate a workpiece into a product and an offcut by irradiating the workpiece with a laser beam and ejecting gas to the workpiece. The laser machining apparatus includes: a machining head that irradiates the workpiece with the laser beam; a gas nozzle that ejects gas to the workpiece; a drive unit that moves at least one of the workpiece and the machining head; and a control unit that controls irradiation with the laser beam. The control unit performs: a control of forming a cut groove by running a first laser beam along a predetermined machining path conforming to an outer shape of the product in an in-plane direction of an upper surface of the workpiece that is a surface irradiated with the laser beam; a control of stopping irradiation with the first laser beam when an irradiation position of the laser beam reaches a position short of an end point on the machining path; and a control of continuing ejection of the gas over a predetermined first waiting time while the irradiation with the first laser beam is stopped. The control unit performs: a control of irradiating the workpiece with a second laser beam that gives less thermal energy to the workpiece per unit time than the first laser beam; a control of keeping irradiation of the workpiece with the second laser beam over a predetermined second waiting time; and a control of forming a joint portion coupling the product and the offcut by running the second laser beam in an uncut region where the cut groove is not formed on the machining path, the joint portion having a thickness smaller than a thickness of the workpiece, in a thickness direction of the workpiece.

Effects of the Invention

The present disclosure can achieve the effect of reliably forming a coupling piece that has a desired shape and couples the workpiece and the product in laser beam cutting.

DESCRIPTION OF EMBODIMENTS

Hereinafter, a laser machining apparatus and a laser machining method according to an embodiment will be described in detail based on the drawings.

First Embodiment.

FIG.1is a diagram illustrating a functional configuration of a laser machining apparatus100according to the first embodiment.

The laser machining apparatus100has a function of cutting a plate-like workpiece30by irradiating the workpiece30with a pulsed laser beam1. That is, the laser machining apparatus100is a laser machining apparatus that performs cutting to separate the workpiece30into a product30aand an offcut30bto be described later by irradiating a machining point30con the workpiece30with a laser beam and ejecting a machining gas2to the machining point30c.

The workpiece30in the first embodiment is a plate-like workpiece made of, for example, stainless steel. Note that the material constituting the workpiece30is not limited to stainless steel, and various types of materials can be used.

The laser machining apparatus100includes a laser oscillator11, an optical path12, a machining head13, a drive unit14, a detection unit15, and a control unit16. InFIG.1, the X axis, the Y axis, and the Z axis are three axes perpendicular with each other. The X axis and the Y axis are axes parallel to the horizontal direction, for example. The Z axis is an axis parallel to the vertical direction, for example.

The laser oscillator11generates a laser beam for use in cutting the workpiece30. That is, the laser oscillator11oscillates and emits a laser beam for use in cutting the workpiece30. The laser oscillator11used in the laser machining apparatus100according to the first embodiment is a laser oscillator that emits the pulsed laser beam1. Therefore, the laser beam for use in cutting the workpiece30in the first embodiment is the pulsed laser beam1.

Note that a continuous wave laser beam may be used for cutting. That is, in the cutting of the workpiece30with the laser machining apparatus100, the pulsed laser beam1or a continuous laser beam can be used. In the case of using a continuous wave laser beam for laser beam cutting, the laser machining apparatus100includes the laser oscillator11that emits a pulsed laser beam and the laser oscillator11that emits a continuous wave laser beam. In this case, in the laser machining apparatus100, the continuous wave laser beam is used for cutting the workpiece30, and the pulsed laser beam is used for forming a joint portion.

The pulsed laser beam1emitted from the laser oscillator11is supplied to the machining head13via the optical path12. The optical path12is a path for transmitting the pulsed laser beam1emitted by the laser oscillator11to the machining head13, and may be a path for propagating the pulsed laser beam1in the air or a path for transmitting the pulsed laser beam1through an optical fiber. The optical path12is designed according to the characteristics of the pulsed laser beam1.

The machining head13includes an optical system that focuses the pulsed laser beam1on the workpiece30, and irradiates the machining point30cwith the pulsed laser beam1. The machining head13focuses the supplied pulsed laser beam1to irradiate one surface of the workpiece30, which is a surface to be machined of the workpiece30. The machining head13preferably includes an optical system that has a focal point near the surface of the workpiece30.

The machining head13includes a beam nozzle17and a gas nozzle18on the side facing the workpiece30.

The beam nozzle17emits the pulsed laser beam1toward the workpiece30.

The gas nozzle18ejects the machining gas2toward the workpiece30. The gas nozzle18is a gas ejection nozzle that ejects the machining gas2from the machining head13to the machining point30cat which the workpiece30is irradiated with the pulsed laser beam1. Specifically, the gas nozzle18ejects, toward the optical axis la, the machining gas2from outside an optical axis la of the pulsed laser beam1with which the workpiece30is irradiated from the machining head13. As the machining gas2, for example, an inert gas such as nitrogen or oxygen can be used. In the machining head13, the gas nozzle18is provided coaxially with the beam nozzle17on the outer circumferential side of the beam nozzle17in the XY plane, and ejects the machining gas2along the central axis of the pulsed laser beam1emitted from the beam nozzle17. That is, the beam nozzle17and the gas nozzle18are disposed coaxially with each other.

Note that the gas nozzle18may eject the gas in a direction oblique to the Z axis. That is, the gas nozzle18may eject the gas in a direction oblique to the central axis of the pulsed laser beam1emitted from the beam nozzle17. The machining gas2is supplied to the gas nozzle18from a machining gas supply source21such as a gas cylinder provided outside the laser machining apparatus100. Note that the machining gas supply source21may be included in the laser machining apparatus100.

The drive unit14can control and change the relative positional relationship between the machining head13and the workpiece30by changing the position of the machining head13. Note that although the drive unit14of the laser machining apparatus100is configured to change the relative positional relationship between the machining head13and the workpiece30by changing the position of the machining head13, the drive unit14may change the position of the table on which the workpiece30is placed, or change the positions of both the machining head13and the table on which the workpiece30is placed. That is, the drive unit14only needs to have a function of moving the machining head13and/or the workpiece30. The machining head13irradiates the workpiece30with the pulsed laser beam1while the drive unit14changes the relative positional relationship between the machining head13and the workpiece30, so that the workpiece30can be cut.

The detection unit15is a sensor that detects the state of the workpiece30or the state of the laser machining apparatus100. The detection unit15measures, as time-series signals, measurement values of physical quantities such as the position of the workpiece30during machining, the intensity and wavelength of light generated during machining, sound waves, and ultrasonic waves. The detection unit15is, for example, a capacitance sensor, a photodiode, a charge coupled device (CCD) sensor, a complementary metal oxide semiconductor (CMOS) sensor, a spectral spectrometer, an acoustic sensor, an acceleration sensor, a gyro sensor, a distance sensor, a position detector, a temperature sensor, a humidity sensor, and the like. The detection unit15inputs the time-series signals indicating measurement values to the control unit16.

The control unit16controls components including the laser oscillator11and the drive unit14such that the pulsed laser beam1runs a predetermined machining path on the workpiece30according to the set machining conditions and the measurement values sent from the detection unit15.

That is, the control unit16controls on and off of the pulsed laser beam1from the laser oscillator11, output of the pulsed laser beam1from the laser oscillator11, positioning of the drive unit14, pressure of the machining gas2from the machining gas supply source21, on and off of the machining gas2, ejection pressure of the machining gas2, and the like.

The machining conditions include, for example, the material of the workpiece30, the thickness of the workpiece30, and the state of the surface of the workpiece30. The machining conditions further include conditions related to the laser oscillator11, such as laser output intensity, laser output frequency, duty ratio of laser output, mode, waveform, and wavelength. The machining conditions can include the focal position of the pulsed laser beam1, the focus diameter of the pulsed laser beam1, the type of the machining gas2ejected from the gas nozzle18, the gas pressure of the machining gas2, the hole diameter of the gas nozzle18, the machining speed, and the like. The machining conditions can also include measurement values input from the detection unit15, such as the distance between the workpiece30and the machining head13, temperature, and humidity.

Next, the workpiece30in a state in which cutting with the laser machining apparatus100is completed will be described.FIG.2is a plan view illustrating the workpiece30in a state in which cutting with the laser machining apparatus100illustrated inFIG.1is completed. AlthoughFIG.2is a plan view, the product30ainFIG.2is hatched for easy understanding.FIG.3is a perspective view illustrating the product30aand a joint portion J in a state in which cutting with the laser machining apparatus100illustrated inFIG.1is completed.FIG.3is a view featuring the product30aand the joint portion J from the workpiece30in a state in which cutting with the laser machining apparatus100is completed, and does not depict the offcut30b.

Here, the direction of a workpiece thickness T that is the thickness of the workpiece30, i.e. the thickness direction of the workpiece30, can be rephrased as the plate thickness direction of the workpiece30. The plate thickness direction is a direction that is parallel to the height direction of the joint portion J and extends in the Z-axis direction. The in-plane direction of the workpiece30is a direction parallel to the XY plane.

The laser machining apparatus100performs cutting to separate the workpiece30into the product30aand the offcut30bby irradiating the irradiation surface of the workpiece30with the pulsed laser beam1. The irradiation surface is one surface of the workpiece30irradiated with the pulsed laser beam1, and is an upper surface31of the workpiece30. That is, the upper surface31is the surface close to the machining head13among a pair of surfaces of the workpiece30facing each other in the thickness direction of the workpiece30, and is the surface irradiated with the pulsed laser beam1on the workpiece30.

The product30ais used as merchandise or the like after cutting. The offcut30bis an unnecessary portion left after cutting. The position at which the workpiece30is irradiated with the pulsed laser beam1is controlled by the control unit16, and moves along a predetermined machining path.

As illustrated inFIG.2, the workpiece30in a state in which cutting with the laser machining apparatus100is completed still has the product30aconnected to the offcut30bby the joint portion J. A cut groove33is formed between the product30aand the offcut30bas a result of cutting. The cut groove33is a through groove cut entirely through the workpiece30in the direction of the workpiece thickness T, i.e. the thickness of the workpiece30, that is, in the plate thickness direction of the workpiece30.

The cut groove33is composed of a cut groove331which is a cut groove along the X-axis direction, a cut groove332which is a cut groove along the Y-axis direction, a cut groove333which is a cut groove along the X-axis direction, a cut groove334which is a cut groove along the Y-axis direction, and a cut groove335which is a cut groove along the X-axis direction, which are connected in this order. In addition, as will be described later, the offcut30bhas a cut groove34connecting a piercing hole P formed first in the cut groove forming process and the cut groove331.

One joint portion J is formed in a part between the product30aand the offcut30b.The joint portion J is a coupling portion that couples the workpiece30and the product30a,that is, a coupling portion that couples the product30aand the offcut30b.That is, in the workpiece30for which cutting with the laser machining apparatus100has been completed, the product30aand the offcut30bare connected only by one joint portion J. The joint portion J is formed between the cut groove331and the cut groove335in the X-axis direction.

For this reason, the product30acan be collected from the workpiece30in a state in which cutting with the laser machining apparatus100is completed simply by removing one joint portion J, which facilitates the collection of the product30a.

The joint portion J is formed in a quadrangular prism shape. The length of the joint portion J along the X-axis direction is referred to as a joint portion width WJ, i.e. the width of the joint portion J. The X-axis direction is parallel to the extending direction of the cut groove335and is parallel to the joint portion machining direction in which the joint portion J is produced. The length of the joint portion J along the Y-axis direction is referred to as a joint portion depth DJ, i.e. the depth of the joint portion J. The dimension of the joint portion depth DJ is the same as the dimension of the groove width of the cut groove33. The length of the joint portion J in the thickness direction of the workpiece30, that is, the length of the joint portion J along the Z-axis direction, is referred to as a joint portion height HJ, i.e. the height of the joint portion J. The height direction of the joint portion J is parallel to the thickness direction of the workpiece30, that is, the plate thickness direction of the workpiece30. The joint portion height HJ can be rephrased as the joint portion thickness, i.e. the thickness of the joint portion J.

The joint portion J is formed from the position of a lower surface32of the workpiece30to an intermediate position between the upper surface31of the workpiece30and the lower surface32of the workpiece30in the thickness direction of the workpiece30. The lower surface32of the workpiece30faces a direction that is opposite to a direction the irradiation surface faces. That is, the dimension of the joint portion height HJ is smaller than the dimension of the workpiece thickness T. In the thickness direction of the workpiece30, that is, in the height direction of the joint portion J, the height position of an upper surface JI of the joint portion J is lower than the height position of the upper surface31of the workpiece30. The upper surface JI of the joint portion J is the surface on aside of the machining head13and on a side of the upper surface31of the workpiece30among a pair of surfaces of the joint portion J facing each other in the thickness direction of the joint portion J.

Next, a method of cutting the workpiece30with the laser machining apparatus100will be described.FIG.4is a plan view for explaining a method of cutting the workpiece30with the laser machining apparatus100illustrated inFIG.1.FIG.5is a flowchart illustrating a procedure for the method of cutting the workpiece30with the laser machining apparatus100illustrated inFIG.1.FIGS.6to11are schematic cross-sectional views for explaining the method of cutting the workpiece30with the laser machining apparatus100illustrated inFIG.1.FIGS.6to11depict longitudinal sections of the workpiece30passing through the cut groove331and the cut groove335. InFIGS.6and10, arrow A1indicates the machining direction of the workpiece30. The machining direction of the workpiece30can be rephrased as the moving direction of the machining head13and the moving direction of the pulsed laser beam1. InFIGS.6to11, arrows A2indicate directions in which the machining gas2flows.

First, in step S10, as illustrated inFIG.6, a cut groove forming process is performed. The cut groove forming process is a process in which the cut groove33is formed along a predetermined machining path CP so that the workpiece30is cut. Specifically, the control unit16performs control to cause the laser oscillator11to start emitting the pulsed laser beam1under a first pulse condition, and control to start ejection of the machining gas2from the gas nozzle18. Then, the control unit16controls the drive unit14such that the irradiation position of the pulsed laser beam1on the upper surface31of the workpiece30moves along the machining path CP.

The first pulse condition is a pulse condition of the pulsed laser beam1for cut groove formation which is used in the cut groove forming process, and is a first laser beam condition. Hereinafter, the pulsed laser beam1emitted under the first pulse condition may be referred to as the first pulsed laser beam1.

The drive unit14performs control to change the position of the machining head13and/or the workpiece30under the control of the control unit16such that the pulsed laser beam1travels along the machining path CP on the upper surface31of the workpiece30. The first embodiment assumes that the drive unit14performs control such that the pulsed laser beam1travels on the upper surface31of the workpiece30along the machining path CP by moving the machining head13in the in-plane direction of the upper surface31of the workpiece30, with the position of the workpiece30fixed.

The cut groove forming process in step S10includes a piercing process. That is, the piercing hole P is opened by irradiating a predetermined position on the upper surface31of the workpiece30with the first pulsed laser beam1. The piercing hole P is a through hole cut entirely through the workpiece30in the direction of the workpiece thickness T. After the piercing hole P is formed, the cut groove33is formed along the machining path CP. The arrows illustrated inFIG.4indicate the machining direction of the workpiece30during the formation of the cut groove33along the machining path CP. The machining direction of the workpiece30can be rephrased as the moving direction of the machining head13, the moving direction of the pulsed laser beam1, or the cutting direction.

The machining path CP includes a first machining path CP1and a second machining path CP2. The first machining path CP1is a machining path conforming to the outer shape of the product30ain the in-plane direction of the upper surface31of the workpiece30, and is a cutting path conforming to the outer shape of the product30ain the in-plane direction of the upper surface31of the workpiece30. The first machining path CP1is a machining path composed of a machining path CP11which is a machining path along the X-axis direction, a machining path CP12which is a machining path along the Y-axis direction, a machining path CP13which is a machining path along the X-axis direction, a machining path CP14which is a machining path along the Y-axis direction, and a machining path CP15which is a machining path along the X-axis direction, which are coupled in this order. The first machining path CP1is continuously machined.

The second machining path CP2is a cutting path connecting the piercing hole P and the first machining path CP1. The cutting in which the cut groove33is formed along the second machining path CP2from the piercing hole P is successively followed by the cutting in which the cut groove33is formed along the first machining path CP1from the intersection of the first machining path CP1and the second machining path CP2. The cutting along the first machining path CP1is performed in the counterclockwise direction.

Next, in step S20, as illustrated inFIG.7, the irradiation of the irradiation surface of the workpiece30with the first pulsed laser beam1is stopped at a predetermined irradiation stop position SP which is a position just before a machining end point CPe. As illustrated inFIG.4, the machining end point CPe on the machining path CP is the end point of machining on the machining path CP, and is located at the same position as a machining start point CPIs on the first machining path CP1.

The machining end point CPe on the machining path CP is located at the same position as an end Je of the joint portion J in the machining direction on the machining path CP15.

The irradiation stop position SP, which is a position just before the machining end point CPe, is a position immediately before the formation region of the joint portion J in the machining direction along the first machining path CP1, that is, a position adjacent to the formation region of the joint portion J in the cutting direction along the machining path CP15. The position just before the machining end point CPe is in other words a position just before the formation region of the joint portion J in the machining direction on the machining path CP15. In addition, the irradiation stop position SP can be rephrased as a machining condition change position at which the machining conditions for cutting of the workpiece30are changed, and can also be rephrased as a pulse condition change position at which the pulse condition of the pulsed laser beam1is changed. The formation region of the joint portion J is a region where the joint portion J is formed in the in-plane direction of the workpiece30.

Specifically, the control unit16controls the laser oscillator11to stop the emission of the first pulsed laser beam1. In addition, the control unit16controls the drive unit14to stop the movement of the machining head13from a position slightly before the irradiation stop position SP, so as to stop the movement of the machining head13at the irradiation stop position SP.

The control unit16performs control to stop the emission of the first pulsed laser beam1at the end of the cut groove forming process, that is, at the time when the irradiation position of the first pulsed laser beam1on the upper surface31of the workpiece30reaches the irradiation stop position SP on the first machining path CP1. The laser oscillator11stops the emission of the first pulsed laser beam1under the control of the control unit16. The drive unit14stops the movement of the machining head13under the control of the control unit16. Consequently, at the time when the irradiation position of the first pulsed laser beam1on the upper surface31of the workpiece30reaches the irradiation stop position SP on the first machining path CP1, the movement of the machining head13is stopped, and the irradiation of the irradiation surface with the first pulsed laser beam1is stopped.

On the other hand, in step S20, the ejection onto the irradiation surface of the machining gas2onto the irradiation surface is not stopped. That is, the control unit16does not perform control to stop the ejection of the machining gas2from the gas nozzle18onto the irradiation surface. Therefore, the machining gas2is continuously ejected onto the upper surface31of the workpiece30even after the irradiation of the upper surface31of the workpiece30with the first pulsed laser beam1is stopped.

The laser machining of the workpiece30with the pulsed laser beam1proceeds mainly in two phenomena: a melting phenomenon in which the material of the workpiece30is melted by the pulsed laser beam1; and a discharge phenomenon in which the melted material is discharged by the machining gas2. When oxygen is used as the machining gas2, the material of the workpiece30also undergoes an oxidation combustion reaction. The machining phenomena on the workpiece30with the pulsed laser beam1will be described.FIG.12is a cross-sectional view for explaining the concept of machining phenomena on the workpiece30with the pulsed laser beam1.

FIG.12schematically depicts a situation in which the workpiece30is melted and discharged by running the pulsed laser beam1on the upper surface31of the workpiece30. By irradiating the upper surface31of the workpiece30with the pulsed laser beam1, the workpiece30is melted from around the upper surface31. The material located below the portion around the upper surface31melted by the irradiation of the workpiece30with the pulsed laser beam1is melted by the energy of the pulsed laser beam1and the heat of the melt of the upper-portion material melted earlier. Consequently, a melt30W1in which the workpiece30is melted is formed. A part of the melt30W1is immediately blown off downward from the workpiece30, that is, toward the lower surface32of the workpiece30, by the machining gas2ejected onto the upper surface31of the workpiece30, and is discharged from the workpiece30.

Another part of the melt30W1flows toward the lower surface32of the workpiece30inside the cut groove33, that is, flows toward the bottom of the cut groove33, and becomes a melt30W2. Then, the melt30W2is also blown off toward the lower surface32of the workpiece30by the machining gas2ejected onto the upper surface31of the workpiece30, and is discharged from the workpiece30. Such machining phenomena occur with the movement of the pulsed laser beam1, whereby the cut groove33, which is a through groove cut entirely through the workpiece30in the plate thickness direction, is formed with the movement of the pulsed laser beam1, and the workpiece30is cut.

Next, in step S30, a first waiting process is performed over a predetermined first waiting time WT1. The first waiting process is a process of stopping the irradiation of the irradiation surface with the first pulsed laser beam1and waiting. The first waiting time WT1is a waiting time for which the first waiting process is continued. Specifically, the control unit16continues the control performed in step S20. That is, in the first waiting process, the stop state of the emission of the first pulsed laser beam1and the movement stop state of the machining head13controlled in step S20are continued, and the irradiation stop state of the first pulsed laser beam1on the irradiation surface is maintained. On the other hand, in the first waiting process, the ejection state of the machining gas2from the gas nozzle18onto the irradiation surface controlled in step S10is maintained. That is, in steps S20and S30, changes in the emission state of the first pulsed laser beam1and the movement state of the machining head13are controlled.

Therefore, in step S30, the phenomenon in which the material of the workpiece30is melted by the first pulsed laser beam1to form the cut groove33, does not occur. On the other hand, in step S30, the phenomenon in which the material melted by the machining gas2is discharged from the workpiece30, continuously occurs. That is, in step S30, with no further melting of the workpiece30, the melt30W2that is a melted material of the workpiece30is discharged downward from the workpiece30by the machining gas2as illustrated inFIG.7.

There is a slight time lag between the melting phenomenon and the discharge phenomenon described above. This means that immediately after the irradiation of the upper surface31of the workpiece30with the pulsed laser beam1is stopped, the melting phenomenon is completed but the discharge phenomenon is not completed for the material of the workpiece30melted by the time immediately before the irradiation of the pulsed laser beam1is stopped. Thus, in the laser machining apparatus100, the first waiting process is performed over the predetermined first waiting time WT1, whereby the discharge phenomenon can be reliably completed for the material of the workpiece30melted by the time immediately before the irradiation of the irradiation surface with the first pulsed laser beam1is stopped, as illustrated inFIG.8. Consequently, the cut groove33formed at the position immediately before the formation region of the joint portion J in the machining direction along the first machining path CP1, that is, the irradiation stop position SP of the first pulsed laser beam1, is prevented from being blocked by the melt.

That is, in the laser machining apparatus100, the first waiting process is performed over the predetermined first waiting time WT1. Therefore, the melt30W2, which has been melted by the time immediately before the irradiation with the first pulsed laser beam1is stopped and has flowed toward the lower surface32of the workpiece30, can be discharged downward from the workpiece30, thereby the cutting machining path along the first machining path CP1can be cut completely through the workpiece30in the thickness direction. Consequently, in the laser machining apparatus100, the cut groove33can be formed at a desired position along the first machining path CP1in the workpiece30, and the region irradiated with the first pulsed laser beam1on the first machining path CP1can be reliably cut out. In other words, the first waiting process is performed in order to completely end the removal, from the workpiece30, of the material of the workpiece30melted by the time immediately before the irradiation of the irradiation surface with the first pulsed laser beam1is stopped.

As described above, in the laser machining apparatus100, by appropriately discharging melt from the cut groove33with the machining gas2, it is possible to prevent blow-up of spatter scattering from the molten portion of the workpiece30. If the discharge of melt from the cut groove33with the machining gas2is not appropriately performed and the machining proceeds to the formation of the joint portion J, there is a possibility that contamination or damage due to blow-up of spatter may occur in the optical system including the machining lens and the protective glass provided in the machining head13, and in the nozzles such as the beam nozzle17and the gas nozzle18. In the laser machining apparatus100, by appropriately discharging melt from the cut groove33with the machining gas2, it is possible to prevent blow-up of spatter scattering from the molten portion of the workpiece30. Then, in the laser machining apparatus100, it is possible to prevent machining defects in the workpiece30to be cut next due to contamination or damage of components caused by blow-up of spatter.

In contrast, if the first waiting process is not performed, the melt that has been melted immediately before the irradiation with the first pulsed laser beam1is stopped and has flowed toward the lower surface32of the workpiece30inside the cut groove33, cannot be completely discharged from the cut groove33. That is, the melt30W2illustrated inFIG.7, which has flowed toward the bottom of the cut groove33inside the cut groove33, cannot be completely discharged from the cut groove33.

With the melt30W2left in the cut groove33, if the formation of the joint portion J is started by radiating the second pulsed laser beam1as described later, the second pulsed laser beam1is reflected by the melt30W2. A part of the reflected second pulsed laser beam1hits a side surface35of the workpiece30facing the machining path CP15in the machining direction on the machining path CP15. In this case, because the side surface35of the workpiece30hit by the reflected second pulsed laser beam1is scratched, the periphery of the side surface35cannot be melted in a manner consistent with the setting at the time of forming the joint portion J, and the balance between melting and melt discharge is lost.

Therefore, without the first waiting process, the second pulsed laser beam1that has hit the melt30W2is reflected to hit the side surface35of the workpiece30, which adversely affects the formation of the joint portion J and results in an uneven balance between melting and melt discharge.

In step S40, it is determined whether the first waiting time WT1has elapsed. Specifically, the control unit16determines whether the first waiting time WT1has elapsed. The control unit16determines whether the first waiting time WT1has elapsed using the timer function provided in the control unit16.

When it is determined that the first waiting time WT1has not elapsed, the determination in step S40becomes No and step S40is repeated. When it is determined that the first waiting time WT1has elapsed, the determination in step S40becomes Yes and the procedure proceeds to step S50.

In step S50, as illustrated inFIG.9, the workpiece30is irradiated with the pulsed laser beam1under a second pulse condition replacing the pulse condition of the pulsed laser beam1in the cut groove forming process.

The second pulse condition is a pulse condition of the pulsed laser beam1for forming the joint portion J which is used in the joint portion forming process, and is a second laser beam condition. The second pulse condition is a pulse condition of the pulsed laser beam1replacing the pulse condition of the first pulsed laser beam1, which is the first pulse condition The second pulse condition is different from the first pulse condition. Hereinafter, the pulsed laser beam1emitted under the second pulse condition may be referred to as the second pulsed laser beam1.

The second pulse condition differs from the first pulse condition in the output of the pulsed laser beam1, the frequency of the pulsed laser beam1, and the duty ratio of the pulsed laser beam1. Other pulse conditions in the second pulse condition are the same as those in the first pulse condition. In the second pulse condition, the output of the pulsed laser beam1, the frequency of the pulsed laser beam1, and the duty ratio of the pulsed laser beam1are all set to be lower than those in the first pulse condition. Therefore, the second pulsed laser beam1gives less thermal energy to the workpiece30per unit time than the first pulsed laser beam1.

Specifically, the control unit16performs control to cause the laser oscillator11to start emitting the pulsed laser beam1under the second pulse condition that is different from the first pulse condition of the pulsed laser beam1in the cut groove forming process. At this time, because the control unit16does not control the drive unit14, the machining head13does not move. The ejection of the machining gas2from the gas nozzle18is continued.

Therefore, the emission of the second pulsed laser beam1under the second pulse condition is started while the machining gas2is not ejected and the machining head13is not moved. At this point, the second pulsed laser beam1is radiated to the irradiation stop position SP at which the irradiation with the first pulsed laser beam1stopped in step S20, that is, radiated to a part near the end inside the cut groove33, and thus does not hit the upper surface31of the workpiece30.

Next, in step S60, a second waiting process is performed over a predetermined second waiting time WT2. The second waiting process is a process of waiting until the second pulsed laser beam1is stably emitted from the laser oscillator11under the set second pulse condition and radiated to the workpiece30. Thus, the second waiting process is in other words a process of stabilizing the second pulsed laser beam1. The second waiting time WT2is a waiting time for which the second waiting process is continued, and is in other words a time for stabilization of the second pulsed laser beam1.

Specifically, the control unit16continues the control performed in step S50. That is, in the second waiting process, the irradiation state of the second pulsed laser beam1controlled in step S50is maintained. On the other hand, in the second waiting process, the control of starting the ejection of the machining gas2from the gas nozzle18and the control of the drive unit14are not performed. Therefore, in the second waiting process, the irradiation state of the second pulsed laser beam1is maintained while the machining gas2is ejected and the machining head13is not moved.

Immediately after the pulsed laser beam1is radiated from the laser oscillator11that has been in a stop state, there is a transition period that lasts until the state of the pulsed laser beam1is stabilized under the set pulse condition. In the transition period, the state of the pulsed laser beam1is not stable in the set pulse condition; for example, the output of the pulsed laser beam1has not yet increased to the set value, or the pulse waveform of the pulsed laser beam1is not consistent with the setting.

If the joint portion J is formed using the pulsed laser beam1in this transition period, the melting of the material of the workpiece30is not stabilized at the formation start portion of the joint portion J in the formation region of the joint portion J. Consequently, the failure occurs in that, in the formation region of the joint portion J, the melting length from the upper surface31of the workpiece30that is a joint portion melting length LM, cannot be obtained so as to fall within required dimension consistent with the setting. That is, forming the joint portion J using the pulsed laser beam1in the transition period results in the failure in that the joint portion J having a shape consistent with the setting cannot be obtained.

The joint portion melting length LM is the depth by which the workpiece30is melted from the upper surface31of the workpiece30during the formation of the joint portion J in the direction of the workpiece thickness T, and is the melting depth of the workpiece30from the upper surface31of the workpiece30. That is, the joint portion melting length LM is the length, in the thickness direction of the workpiece30, of the portion where the workpiece30is melted and removed during the formation of the joint portion J. As illustrated inFIG.3, the joint portion melting length LM is the length from the upper surface31of the workpiece30to the upper surface J1of the joint portion J in the thickness direction of the workpiece30.

Therefore, in the laser machining apparatus100, in order to avoid the occurrence of the above failure, the second waiting process is provided immediately after the pulsed laser beam1is radiated from the laser oscillator11that has been in a stop state, and after the pulsed laser beam1is stabilized under the second pulse condition, machining to form the joint portion J is performed.

In step S70, it is determined whether the second waiting time WT2has elapsed. Specifically, the control unit16determines whether the second waiting time WT2has elapsed. The control unit16determines whether the second waiting time WT2has elapsed using the timer function provided in the control unit16.

When it is determined that the second waiting time WT2has not elapsed, to the determination becomes No in step S70and step S70is repeated. When it is determined that the second waiting time WT2has elapsed, to the determination becomes Yes in step S70and the procedure proceeds to step S80.

In step S80, as illustrated inFIG.10, the joint portion J is formed. Specifically, the control unit16controls the drive unit14such that the irradiation position of the second pulsed laser beam1on the upper surface31of the workpiece30moves along the machining path CP15.

Then, at the time when the irradiation position

of the second pulsed laser beam1reaches the position of the machining end point CPe, which is the machining end point on the machining path CP, the control unit16performs control to stop the emission of the second pulsed laser beam1and stop the irradiation of the upper surface31of the workpiece30with the second pulsed laser beam1. That is, the control unit16performs control to cause the second pulsed laser beam1to run from the irradiation stop position SP, which is a position just before the machining end point CPe on the first machining path CP1described above, to the position of the machining end point CPe. The region from the irradiation stop position SP to the position of the machining end point CPe on the first machining path CP1, which is the region of the workpiece30in which the second pulsed laser beam1runs, is an uncut region where the cut groove33is not formed on the machining path CP. The uncut region can be rephrased as the region from the irradiation stop position SP, which is a position short of the machining end point CPe on the first machining path CP1, to the start point of the first machining path CP1. The start point of the first machining path CP1is the start point of the first machining path CP1, which is a machining path conforming to the outer shape of the product30ain the in-plane direction of the upper surface31of the workpiece30, and is different from the start point of the machining path CP including the second machining path CP2.

Consequently, as illustrated inFIG.11, the workpiece30is machined by melting only a part of the formation region of the joint portion J of the workpiece30from the upper surface31of the workpiece30in the thickness direction of the workpiece30, whereby the joint portion J can be formed. That is, here, the portion of the workpiece30irradiated with the second pulsed laser beam1is not entirely melted in the direction of the workpiece thickness T. In addition, the control unit16performs control to stop the ejection of the machining gas2at the time when the irradiation position of the second pulsed laser beam1reaches the position of the machining end point CPe, which is the machining end point on the machining path CP. That is, the control unit16performs control to stop the ejection of the machining gas2at the same timing as the timing of performing control to stop the ejection of the second pulsed laser beam1. Note that after the control unit16performs control to stop the ejection of the machining gas2, there is a time lag until the ejection of the machining gas2completely stops. According to such control, the melt melted by the

time immediately before the irradiation of the second pulsed laser beam1is stopped, can be completely discharged from the cut groove33and the upper surface J1of the joint portion J, and the cut groove33and the joint portion J having the designed shapes are formed. Then, by performing machining with the second pulsed laser beam1until reaching the machining end point CPe, the joint portion J is formed such that the thickness of the joint portion J is smaller than the plate thickness of the workpiece30in the thickness direction of the workpiece30.

Here, in the second pulse condition, the output of the pulsed laser beam1, the frequency of the pulsed laser beam1, and the duty ratio of the pulsed laser beam1are all set to be lower than those in the first pulse condition. Therefore, the energy supplied per unit area of the upper surface31of the workpiece30by the pulsed laser beam1under the second pulse condition at the time of forming the joint portion J is lower than the energy supplied per unit area of the upper surface31of the workpiece30by the pulsed laser beam1under the first pulse condition in the cut groove forming process. That is, the second pulsed laser beam1gives less thermal energy to the workpiece30per unit time than the first pulsed laser beam1.

The output of the pulsed laser beam1, the frequency of the pulsed laser beam1, and the duty ratio of the pulsed laser beam1are reduced at the time of forming the joint portion J. Given this situation, the moving speed of the machining head13, that is, the moving speed of the pulsed laser beam1, is also made lower than that in the cut groove forming process that uses the pulsed laser beam1under the first pulse condition, in order to reliably supply the energy required for melting the workpiece30to the workpiece30. Consequently, the joint portion J can be precisely formed with a thickness in the thickness direction of the workpiece30that is smaller than the plate thickness of the workpiece30.

Therefore, under the second pulse condition, the control of making the output of the pulsed laser beam1, the frequency of the pulsed laser beam1, and the duty ratio of the pulsed laser beam1lower than those in the first pulse condition and making the moving speed of the machining head13lower than that in the cut groove forming process is performed. It can be said that this control is control that enables precise and reliable formation of the joint portion J having a desired shape.

Here, while the output of the pulsed laser beam1, the frequency of the pulsed laser beam1, and the duty ratio of the pulsed laser beam1are reduced, the gas pressure of the machining gas2is not reduced.

FIG.13is a time chart for the cutting of the workpiece30with the laser machining apparatus100illustrated inFIG.1. The horizontal axis inFIG.13indicates time. The vertical axis inFIG.13indicates the magnitude of each machining condition. Solid line41ainFIG.13indicates the output of the pulsed laser beam1, the frequency of the pulsed laser beam1, and the duty ratio of the pulsed laser beam1in the first pulse condition of the pulsed laser beam1at the time of cutting the workpiece30. Solid line41binFIG.13indicates the output of the pulsed laser beam1, the frequency of the pulsed laser beam1, and the duty ratio of the pulsed laser beam1in the second pulse condition of the pulsed laser beam1.

In the cutting of the workpiece30, the output of the pulsed laser beam1, the frequency of the pulsed laser beam1, and the duty ratio of the pulsed laser beam1change as indicated by solid line41aor solid line41binFIG.13. That is, in the cutting of the workpiece30, the output of the pulsed laser beam1, the frequency of the pulsed laser beam1, and the duty ratio of the pulsed laser beam1are all set to mutually different conditions in the cut groove forming process and the joint portion forming process, such that the set values in the joint portion forming process are smaller than the set values in the cut groove forming process.

Dashed-dotted line42inFIG.13indicates the gas pressure of the machining gas2, among the machining conditions at the time of cutting the workpiece30. The gas pressure of the machining gas2in the cutting of the workpiece30is set to a predetermined constant value from the start of cutting until the end of cutting, and is not changed during the cutting.

Broken line43ainFIG.13indicates the moving speed of the machining head13in the cut groove forming process, that is, the moving speed of the pulsed laser beam1in the cut groove forming process, among the machining conditions at the time of cutting the workpiece30.

Broken line43binFIG.13indicates the moving speed of the machining head13in the joint portion forming process, that is, the moving speed of the pulsed laser beam1in the joint portion forming process, among the machining conditions at the time of cutting the workpiece30.

In the cutting of the workpiece30with the laser machining apparatus100, step S10is started at time to as illustrated inFIG.13. Steps S20and S30are started at time t1. Steps S50and S60are performed at time t2. Step S80is performed at time t3. Then, the cutting of the workpiece30ends at time t4.

Here, a specific length of the first waiting time WT1will be described. In the first embodiment, the first waiting time WT1is 0.1 seconds or more. The inventors conducted an experiment in which a plurality of workpieces30were cut by changing only the first waiting time WT1among the machining conditions, and examined which time is suitable as the first waiting time WT1.

As a result of the experiment, the inventors have found that with the first waiting time WT1of 0 seconds, that is, without the first waiting time WT1, the material of the workpiece30cannot be reliably melted as designed around the formation start portion of the joint portion J, and the required joint portion melting length LM cannot be obtained. That is, the inventors have found that the required joint portion height HJ cannot be obtained with the first waiting time WT1of 0 seconds.

This is because the melt30W2remains at the bottom of the cut groove33at the start of formation of the joint portion J, and thus, as described above, a part of the second pulsed laser beam1reflected by the melt30W2hits the side surface35of the workpiece30. Here, “around the formation start portion of the joint portion J” means “around the side surface35of the workpiece30”.

In addition, the inventors have found that even with the first waiting time WT1of 0.05 seconds, the material of the workpiece30cannot be reliably melted as designed around the formation start portion of the joint portion J, and the required joint portion melting length LM cannot be obtained. That is, the inventors have found that the required joint portion height HJ cannot be obtained even with the first waiting time WT1of 0.05 seconds.

This is because the discharge of the melt30W2from the bottom of the cut groove33is insufficient at the start of formation of the joint portion J, and thus, as described above, a part of the second pulsed laser beam1reflected by the melt30W2hits the side surface35of the workpiece30. However, with the first waiting time WT1of 0.05 seconds, the joint portion J has a shape closer to the design shape than with the first waiting time WT1of 0 seconds.

In addition, the inventors have found that with the first waiting time WT1of 0.1 seconds, the material of the workpiece30can be reliably melted as designed around the formation start portion of the joint portion J, and the required joint portion melting length LM can be obtained. That is, the inventors have found that with the first waiting time WT1of 0.1 seconds, the required joint portion height HJ is obtained, and the joint portion J having the designed shape is obtained.

This is because, with the first waiting time WT1of 0.1 seconds, the melt30W2at the bottom of the cut groove33is completely discharged from the cut groove33, and no adverse effect occurs due to a part of the second pulsed laser beam1reflected by the melt30W2and hitting the side surface35of the workpiece30. In addition, with the first waiting time WT1longer than 0.1 seconds, the same result was obtained as with the first waiting time WT1of 0.1 seconds.

Given the above, in order to completely discharge the melt30W2at the bottom of the cut groove33from the cut groove33to obtain the joint portion J having the designed shape, it is necessary to set the first waiting time WT1to 0.1 seconds or more.

Next, a specific length of the second waiting time WT2will be described. In the first embodiment, the second waiting time WT2is 0.1 seconds or more. The inventors conducted an experiment in which a plurality of workpieces30were cut by changing only the second waiting time WT2among the machining conditions, and examined which time is suitable as the second waiting time WT2.

As a result of the experiment, the inventors have found that with the second waiting time WT2of 0 seconds, that is, without the second waiting time WT2, the joint portion J chips around the formation start portion of the joint portion J, and the required joint portion width WJ cannot be obtained. That is, the inventors have found that the joint portion J having the required shape cannot be obtained with the second waiting time WT2of 0 seconds.

This is because the second pulsed laser beam1is not stably emitted from the laser oscillator11under the set second pulse condition at the start of formation of the joint portion J.

In addition, the inventors have found that even

with the second waiting time WT2of 0.05 seconds, the joint portion J chips around the formation start portion of the joint portion J, and the required joint portion width WJ cannot be obtained. That is, the inventors have found that the joint portion J having the required shape cannot be obtained with the second waiting time WT2of 0.05 seconds.

This is because the second pulsed laser beam1is not stably emitted from the laser oscillator11under the set second pulse condition at the start of formation of the joint portion J.

In addition, the inventors have found that with the second waiting time WT2of 0.1 seconds, the joint portion J does not chip around the formation start portion of the joint portion J, and the required joint portion width WJ can be obtained. That is, the inventors have found that the joint portion J having the designed shape can be obtained with the second waiting time WT2of 0.1 seconds.

This is because, with the second waiting time WT2of 0.1 seconds, the second pulsed laser beam1is stably emitted from the laser oscillator11under the set second pulse condition at the start of formation of the joint portion J. In addition, with the second waiting time WT2longer than 0.1 seconds, the same result was obtained as with the second waiting time WT2of 0.1 seconds.

Given the above, in order to obtain the joint portion J having the designed shape without generating a chip in the joint portion J around the formation start portion of the joint portion J, it is necessary to set the second waiting time WT2to 0.1 seconds or more.

FIG.14is a diagram illustrating examples of dimensions of the joint portion J formed in the cutting of the workpiece30with the laser machining apparatus100illustrated inFIG.1.FIG.14illustrates the dimensions of the joint portion J suitable for keeping the product30aand the offcut30bcoupled when given the workpiece thickness T of 12 mm. Here, the material of the workpiece30is SS400, a kind of rolled steel sheet for general structure. The weight of the product30ais 0.5 kg.

From the viewpoint of preventing the product30afrom being detached from the offcut30b,the joint portion J needs to have a certain size in order to keep the product30acoupled to the offcut30b.Meanwhile, the joint portion J that is too large is not preferable for finally breaking the joint portion J and removing the product30afrom the offcut30b.

According to the inventors' knowledge, when using a general joint portion, the joint portion height HJ of which is equal to the workpiece thickness T, it is preferable to set the joint portion width WJ that is about 1.5 to 2.5 times larger than the groove width of the cut groove33in order to prevent the product30afrom being detached from the offcut30b.In this case, for example, given the workpiece thickness T of 12 mm and the groove width of the cut groove33of 0.4 mm, it is preferable to set the joint portion width WJ to 0.6 mm to 1.0 mm. For these dimensional conditions, because the joint portion height HJ is equal to the workpiece thickness T, namely 12 mm, a joint portion area HA is 7.2 mm2to 12 mm2.

The joint portion area HA is the area of a longitudinal section of the joint portion J along the joint portion width WJ and the joint portion height HJ. The joint portion area HA can be calculated by the calculation formula “joint portion width WJ×joint portion height HJ”. The joint portion area HA corresponds to the area of the hatched portion inFIG.3and corresponds to the area of a cross section of the joint portion J along the XZ plane.

On the other hand, in the example of the joint portion J according to the first embodiment, the joint portion width WJ is fixed to 1.5 mm as shown inFIG.14.

For obtaining the joint portion J according to the first embodiment to have the same joint portion area HA and the same mechanical strength as those of a general joint portion having the joint portion height HJ that is equal to the workpiece thickness T and the joint portion width WJ of 0.6 mm, the joint portion height HJ should be 40% or more of the workpiece thickness T. That is, in the laser machining method according to the first embodiment, the joint portion melting length LM should be 60% or less of the workpiece thickness T.

In addition, by setting the joint portion height HJ to 60% or less of the workpiece thickness T, the joint portion J according to the first embodiment has a slightly smaller joint portion area HA and achieves a slightly smaller mechanical strength than a general joint portion with the joint portion height HJ equal to the workpiece thickness T and the joint portion width WJ of 1.0 mm.

That is, by setting the joint portion height HJ to 40% or more of the workpiece thickness T, the joint portion J according to the first embodiment can secure the minimum joint portion area HA of a general joint portion with the joint portion height HJ equal to the workpiece thickness T, and thus can prevent the product30afrom falling off the offcut30b.

In addition, by setting the joint portion height HJ to 60% or less of the workpiece thickness T, the joint portion J according to the first embodiment achieves the joint portion area HA slightly smaller than the maximum joint portion area HA of a general joint portion with the joint portion height HJ equal to the workpiece thickness T, which facilitates the post-processing of finally breaking the joint portion and removing the product30afrom the offcut30b.

FIG.15is a diagram illustrating examples of machining conditions and dimensions of the joint portion J in the cutting of the workpiece30with the laser machining apparatus100illustrated inFIG.1. InFIG.15, “plate thickness” indicates the thickness of the workpiece30, namely the workpiece thickness T. “Gas type” indicates the type of the machining gas2. “Output” indicates the output of the pulsed laser beam1. “Frequency” indicates the frequency of the pulsed laser beam1. “Duty ratio” indicates the duty ratio of the pulsed laser beam1. “Speed” indicates the moving speed of the machining head13, i.e. the moving speed of the pulsed laser beam1. “Joint portion melting amount (%)” is the ratio of the joint portion melting length LM to the plate thickness. “Joint portion height (%)” is the ratio of the joint portion height HJ to the plate thickness. Note that the conditions shown inFIG.15are also based on the premise that the groove width of the cut groove33is 0.4 mm.

FIG.16is a diagram illustrating detailed machining conditions for cutting under conditions (2), (4), and (5) in the examples illustrated inFIG.15. InFIG.16, “gas pressure” indicates the pressure of the machining gas2. “Nozzle height” indicates the height of the beam nozzle17and the gas nozzle18from the upper surface31of the workpiece30.

As shown inFIG.16, the output of the pulsed laser beam1, the frequency of the pulsed laser beam1, and the duty ratio of the pulsed laser beam1for producing the joint portion J are lower than the output of the pulsed laser beam1, the frequency of the pulsed laser beam1, and the duty ratio of the pulsed laser beam1for producing the cut groove33. The first waiting time WT1and the second waiting time WT2are each 0.1 seconds.

As shown inFIG.15, in the joint portion J, the joint portion melting length LM is 40% to 60% of the workpiece thickness T, and the joint portion height HJ is 40% to 60% of the workpiece thickness T. The joint portion J formed under such conditions can prevent the product30afrom being detached from the offcut30b,and facilitates the post-processing of finally breaking the joint portion and removing the product30afrom the offcut30b.

FIG.17is a diagram illustrating a hardware configuration for implementing the functions of the control unit16illustrated inFIG.1. As illustrated inFIG.17, the functions of the control unit16of the laser machining apparatus100are implemented by a control device including a central processing unit (CPU)201, a memory202, a storage device203, a display device204, and an input device205. The functions that are executed by the control unit16are implemented by software, firmware, or a combination of software and firmware. Software or firmware is described as computer programs and stored in the storage device203. The CPU201implements the functions of the control unit16by reading software or firmware stored in the storage device203into the memory202and executing the software or firmware. That is, the computer system includes the storage device203for storing programs that result in execution of the step of performing the operation of the control unit16described in the first embodiment when the functions of the control unit16are executed by the CPU201. It can also be said that these programs cause a computer to execute the processes that the functions of the control unit16implement. The memory202is a volatile storage area such as a random access memory (RAM). The storage device203is a nonvolatile or volatile semiconductor memory such as a read only memory (ROM) or a flash memory, or a magnetic disk. Specific examples of the display device204include a monitor and a display. Specific examples of the input device205include a keyboard, a mouse, and a touch panel.

The laser machining apparatus100according to the first embodiment described above forms only one joint portion J when cutting the workpiece30along the contour of the product30a.Consequently, in the laser machining apparatus100, as compared with the case of forming a plurality of joint portions J, cutting is easily controlled by the control unit16, and machining path programs can be easily created for use in the control of cutting by the control unit16. In the cutting of the workpiece30with the laser machining apparatus100, in which only one joint portion J is formed, the post-processing of finally breaking the joint portion J and removing the product30afrom the offcut30bis facilitated, and the production efficiency of the cutting of the workpiece30is improved.

For forming a plurality of joint portions in the cutting of one product30a,heat is gradually accumulated in the workpiece30as the cutting progresses, and a plurality of joint portions formed under the same machining conditions cannot have the same shape. For this reason, for forming a plurality of joint portions in the cutting of one product30a,it is difficult to set appropriate machining conditions.

On the other hand, in the laser machining apparatus100, in which only one joint portion J is formed when the workpiece30is cut, it is easy to set appropriate machining conditions.

In addition, in the laser machining apparatus100, in the thickness direction of the workpiece30, that is, in the height direction of the joint portion J, the joint portion J is formed with the height position of the upper surface J1of the joint portion J lower than the height position of the upper surface31of the workpiece30, and with the thickness of the joint portion J in the thickness direction of the workpiece30smaller than the plate thickness of the workpiece30. Consequently, in the cutting of the workpiece30with the laser machining apparatus100, the post-processing of finally breaking the joint portion J and removing the product30afrom the offcut30bis facilitated, and the production efficiency of the cutting of the workpiece30is improved. That is, the laser machining apparatus100can form the joint portion J that facilitates the removal of the product30ain the post-process after cutting.

In addition, in the laser machining apparatus100, at the end of the cut groove forming process, the irradiation of the irradiation surface of the workpiece30with the first pulsed laser beam1and the movement of the machining head13are temporarily stopped. Then, after the end of the cut groove forming process, the first waiting process is performed over the first waiting time WT1. In the first waiting process, the machining gas2is ejected onto the irradiation surface while the ejection of the first pulsed laser beam1and the movement of the machining head13are stopped. Therefore, in the first waiting process, with no further melting of the material of the workpiece30, the melt30W2that has been melted by the time immediately before the irradiation with the first pulsed laser beam1is stopped and has flowed toward the lower surface32of the workpiece30inside the cut groove33, is discharged from the cut groove33by the machining gas2. Consequently, the laser machining apparatus100can discharge, from the cut groove33, all the material of the workpiece30melted by the time immediately before the irradiation of the irradiation surface of the workpiece30with the first pulsed laser beam1is stopped.

Therefore, the laser machining apparatus100can prevent an adverse effect on the formation of the joint portion J, the adverse effect being caused due to the second pulsed laser beam1reflected by the melt30W2remaining inside the cut groove33at the start of formation of the joint portion J and hitting the side surface35of the workpiece30. Consequently, in the laser machining apparatus100, the joint portion width WJ and the joint portion melting length LM can be obtained as designed, and the joint portion J having the designed shape can be obtained.

In addition, in the laser machining apparatus100, by appropriately discharging melt from the cut groove33with the machining gas2, it is possible to prevent blow-up of spatter scattering from the molten portion of the workpiece30. Therefore, it is possible to prevent contamination or damage due to blow-up of spatter in the optical system including the machining lens and the protective glass provided in the machining head13, and in the nozzles such as the beam nozzle17and the gas nozzle18. Consequently, it is possible to prevent machining defects in the workpiece30to be cut next.

In addition, in the laser machining apparatus100, the second waiting process is performed over the second waiting time WT2at the start of emission of the second pulsed laser beam1. Consequently, in the laser machining apparatus100, at the start of formation of the joint portion J, the workpiece30can be stably melted by the second pulsed laser beam1stably emitted from the laser oscillator11under the second pulse condition, so that the joint portion width WJ and the joint portion melting length LM can be obtained as designed, and the joint portion J having the designed shape can be obtained.

In addition, in the laser machining apparatus100, the formation of the joint portion J is controlled by combining the discharge of melt from the cut groove33in the first waiting process, the stabilization of the emission state of the second pulsed laser beam1in the second waiting process, the pulse condition of the second pulsed laser beam1, and the movement state of the machining head13, so that the joint portion J having the designed shape can be obtained. That is, in the laser machining apparatus100, by appropriately controlling the discharge of melt from the cut groove33, the emission state of the second pulsed laser beam1, the pulse condition of the second pulsed laser beam1, and the movement and stop of the machining head13, it is possible to appropriately control the joint portion melting length LM and prevent machining defects in the joint portion J.

As described above, in the laser machining apparatus100, the joint portion width WJ and the joint portion melting length LM can be obtained as designed, the joint portion J having the designed shape can be obtained, and the joint portion J having the designed quality can be stably produced throughout continuously repeated cutting of a plurality of workpieces30.

Therefore, the laser machining apparatus100according to the first embodiment can achieve the effect of reliably forming a coupling piece that has a desired shape and couples the offcut30band the product30aof the workpiece30in laser beam cutting.

The configurations described in the above-mentioned embodiment indicate examples. The configurations can be combined with another well-known technique, and some of the configurations can be omitted or changed in a range not departing from the gist.

REFERENCE SIGNS LIST