Laser cutting machine and control method for laser cutting machine

Abstract

By suppressing the dross remaining on the cut surface of the workpiece at the corners, the cutting quality of the cut surface at the corners of the workpiece is improved. [Solution] When the oxygen concentration of the assist gas is less than or equal to the oxygen concentration in the air, the plate thickness is 2.3 mm or more, the angle θ of the corner Cn is 150 degrees or less, and the shape of the corner Cn is a corner or a radius of curvature of 2 mm or less, the control device 60 performs a second output control when accelerating the laser beam to the standard speed after passing the corner Cn, so as to maintain a constant laser peak output with a laser average output that is the same as or lower than the standard average output and a pulse duty cycle higher than the pulse duty cycle during deceleration, or within the range of a laser average output lower than the standard average output, the laser peak output is increased as the cutting speed increases while maintaining a pulse duty cycle higher than the pulse duty cycle during deceleration.

Description

Technical Field

[0001] The present invention relates to a laser cutting machine and a control method for a laser cutting machine.

Background Art

[0002] Laser cutting that cuts a workpiece using the thermal energy of a laser beam is known. In laser cutting, it is known that cutting defects occur at corners where the cutting speed of the laser beam decreases when cutting the workpiece along a cutting path corresponding to the shape of the product. For example, Patent Document 1 discloses a laser cutting method for preventing cutting defects at corners by changing the processing conditions when cutting corners. In Patent Document 1, for example, in a corner section including a corner, it is disclosed that the workpiece is cut based on processing conditions for the corner that have a lower cutting ability than the normal processing conditions applied to paths other than the corner section. The change in the processing conditions between the normal processing conditions and the processing conditions for the corner is performed by changing at least one of the laser output (laser peak output), pulse duty, pulse frequency, assist gas pressure, and cutting speed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, even when the average laser output is controlled by adjusting the laser output, pulse duty cycle, pulse frequency, etc., dross may remain on the cut surface of the workpiece at corners. This is thought to be because, in corner cutting, the volume of the cutting kerf from which the molten metal escapes is small, so the molten metal generated during cutting has nowhere to go and remains on the cut surface of the workpiece. Such dross residue is particularly noticeable on the cut surface of the workpiece when the laser beam reaches the corner, that is, on the side of the workpiece where the cutting speed is reduced. There is a need to improve the cutting quality of the cut surface of the workpiece at corners by suppressing the dross remaining on the cut surface of the workpiece at corners. [Means for solving the problem]

[0005] One embodiment of one or more of these embodiments is a laser cutting machine comprising: a laser oscillator that emits a laser beam; a processing head that cuts a workpiece by irradiating the workpiece with the laser beam emitted from the laser oscillator; a moving mechanism that moves the processing head relative to the workpiece; an assist gas supply device that supplies assist gas to the processing head; and a control device that controls the laser average output of the laser beam by controlling the laser oscillator and moves the laser beam along the cutting path by controlling the moving mechanism. The control device selects a standard average output, which is a standard value of the average laser output, and a standard speed, which is a standard value of the cutting speed of the laser beam, based on the material and thickness of the workpiece, and performs acceleration / deceleration control to decelerate the laser beam to below the standard speed when the laser beam reaches a corner on the cutting path, and accelerate the laser beam to the standard speed when the laser beam leaves the corner, and performs first output control to reduce the average laser output to below the standard average output by controlling the pulse duty cycle and pulse frequency of the laser beam during the execution of acceleration / deceleration control, and the control device controls the oxygen concentration of the assist gas When the oxygen concentration is below that of the air, the plate thickness is 2.3 mm or more, the angle of the corner is 150 degrees or less, and the shape of the corner is a corner or a radius of curvature of 2 mm or less, when accelerating the laser beam to the standard speed, a second output control is performed so that the laser peak output remains constant while maintaining a laser average output that is the same as or lower than the standard average output and a pulse duty cycle higher than the pulse duty cycle during deceleration, or within the range of a laser average output lower than the standard average output, the laser peak output increases as the cutting speed increases while maintaining a pulse duty cycle higher than the pulse duty cycle during deceleration. [Effects of the Invention]

[0006] According to one aspect of the present invention, dross remaining on the cut surface of the workpiece at the corners can be suppressed, thereby improving the cutting quality of the cut surface of the workpiece at the corners. [Brief explanation of the drawing]

[0007] [Figure 1]Figure 1 is a block diagram showing the configuration of the laser cutting machine according to this embodiment. [Figure 2] Figure 2 is a diagram illustrating the concept of laser cutting according to this embodiment. [Figure 3] Figure 3 illustrates the delay on the underside of the cutting front. [Figure 4] Figure 4 shows the cutting front of the corner. [Figure 5] Figure 5 is a block diagram of the control device. [Figure 6] Figure 6 is a flowchart showing the control method for a laser cutting machine according to this embodiment. [Figure 7] Figure 7 is a flowchart showing the control method for a laser cutting machine according to this embodiment. [Figure 8] Figure 8 shows the relationship between cutting speed and average laser power when cutting a normal corner. [Figure 9] Figure 9 shows the relationship between the cutting speed and the average laser power when cutting a corner that satisfies the switching conditions. [Modes for carrying out the invention]

[0008] The laser cutting machine and the control method for the laser cutting machine according to the embodiment will be described below with reference to the drawings.

[0009] Referring to Figure 1, the configuration of the laser cutting machine 1 according to this embodiment will be described. The laser cutting machine 1 is a processing machine that cuts a workpiece W by irradiating it with a laser beam and using the thermal energy of the laser beam. The workpiece W to be processed is a sheet material, typically sheet metal.

[0010] The laser cutting machine 1 comprises a laser oscillator 10, a processing unit 20, an assist gas supply device 40, an operation display unit 50, and a control device 60.

[0011] The laser oscillator 10 generates and emits a laser beam. The laser oscillator 10 is preferably a laser oscillator that amplifies excitation light emitted from a laser diode to emit a laser beam of a predetermined wavelength, or a laser oscillator that directly utilizes the laser beam emitted from a laser diode. Examples of the laser oscillator 10 include a solid-state laser oscillator, a fiber laser oscillator, a disk laser oscillator, and a direct diode laser oscillator (DDL oscillator). The laser oscillator 10 may also be a CO2 laser oscillator.

[0012] The laser oscillator 10 emits a laser beam in the 1 μm band with a wavelength of 900 nm to 1100 nm. Taking a fiber laser oscillator and a DDL oscillator as examples, the fiber laser oscillator emits a laser beam with a wavelength of 1060 nm to 1080 nm, and the DDL oscillator emits a laser beam with a wavelength of 910 nm to 950 nm. The laser beam emitted from the laser oscillator 10 is transmitted to the processing unit 20 by the process fiber 12.

[0013] The processing unit 20 cuts the workpiece W using a laser beam transmitted by the process fiber 12. The processing unit 20 includes a processing table 21 on which the workpiece W is placed, a moving mechanism 22, and a processing head 30.

[0014] The moving mechanism 22 includes a gantry-type X-axis carriage 23 and a Y-axis carriage 24. The X-axis carriage 23 is configured to be movable along the X-axis direction on the machining table 21. The Y-axis carriage 24 is configured to be movable along the Y-axis direction perpendicular to the X-axis on the X-axis carriage 23. The Y-axis carriage 24 is mounted on the X-axis carriage 23, which is movable in the X-axis direction.

[0015] The X-axis carriage 23 and the Y-axis carriage 24 are driven by a drive mechanism such as a servo motor, a rack and pinion mechanism, etc., and move in the X-axis direction and the Y-axis direction. The X-axis carriage 23 and the Y-axis carriage 24 may be driven by a linear motor, and the drive mechanism for driving the X-axis carriage 23 and the Y-axis carriage 24 may vary depending on the model of the laser cutting machine 1. Also, instead of the rack and pinion mechanism, a ball screw and nut mechanism may be used.

[0016] The processing head 30 irradiates the workpiece W with the laser beam transmitted by the process fiber 12. The processing head 30 has a collimator lens 31 into which the laser beam emitted from the emission end of the process fiber 12 is incident, and a bend mirror 33 that reflects the laser beam emitted from the collimator lens 31 downward in the Z-axis direction perpendicular to the X-axis and the Y-axis. The processing head 30 also has a focusing lens 34 that focuses the laser beam reflected by the bend mirror 33. The collimator lens 31, the bend mirror 33, and the focusing lens 34 are arranged in a state where the optical axes are adjusted in advance.

[0017] The processing head 30 has a processing head main body 35. A nozzle 36 for emitting a laser beam is detachably attached to the tip of the processing head main body 35. A circular opening is provided at the tip of the nozzle 36, and the laser beam focused by the focusing lens 34 is irradiated onto the workpiece W from the opening at the tip of the nozzle 36.

[0018] The processing head 30 is fixed to the Y-axis carriage 24 that is movable in the Y-axis direction. Therefore, the processing head 30 can move in the X-axis direction and the Y-axis direction respectively along the surface of the workpiece W by driving the movement mechanism 22.

[0019] Note that the laser cutting machine 1 may be configured to move the work W while fixing the position of the processing head 30 instead of moving the processing head 30 along the surface of the work W. The laser cutting machine 1 only needs to include a moving mechanism for relatively moving the processing head 30 with respect to the surface of the work W. Further, the moving mechanism 22 may be provided with a function of moving the processing head 30 in the Z-axis direction.

[0020] The assist gas supply device 40 supplies nitrogen, oxygen, a mixture of nitrogen and oxygen, or air as the assist gas to the processing head 30. During the processing of the work W, the assist gas is discharged from the opening of the nozzle 36 and blown onto the work W. The assist gas discharges the molten metal in the cutting kerf where the work W is melted, and cools the work W, the cutting kerf, the cutting front, and the molten metal.

[0021] The operation display unit 50 is integrally configured with an operation unit that the user operates to input information to the control device 60 and a display unit that displays information output from the control device 60. The user can input various information to the control device 60 by operating the operation display unit 50. Further, the user can grasp processing conditions and the like from the information displayed on the operation display unit 50.

[0022] The operation display unit 50 may be configured such that the operation unit and the display unit are separate. Further, the operation unit may be configured to input predetermined data generated by a separately installed computer (not shown) to the control device 60 via communication.

[0023] The control device 60 is a device that controls each part of the laser cutting machine 1. The control device 60 is a computer such as an NC (Numerical Control) device. The computer is mainly composed of a hardware processor such as a CPU (Central Processing Unit), a memory, and various interfaces. The memory and various interfaces are connected to the hardware processor via a bus.

[0024] The computer has a predetermined computer program installed. The hardware processor executes the computer program, allowing the computer to function as one of the multiple information processing circuits provided by the control unit 60, as described later.

[0025] Referring to Figure 2, the concept of laser cutting according to this embodiment will be explained before describing the control method of the laser cutting machine 1. Laser cutting cuts the workpiece W by irradiating it with a laser beam, using the thermal energy of the laser beam. In laser cutting, by moving the laser beam relative to the workpiece W along the cutting path, a product of the required shape can be cut out from the workpiece W. In the following description, it is assumed that a corner Cn is included in part of the product, as shown in Figure 2. The cutting path for cutting the corner Cn includes a cutting path that cuts a straight line Ra, changes direction at the corner Cn where the straight line Ra and the straight line Rb are combined at an angle θ, and then cuts the straight line Rb. The corner Cn is the point where the straight line Ra and the straight line Rb intersect, and is typically a specific angle (acute, right, or obtuse), but also includes an R shape (circular arc shape) with a predetermined radius of curvature. When considering the R shape, the angle may be treated as having a radius of curvature of zero.

[0026] The explanation of cutting the corner Cn assumes that the outside of the corner Cn is being cut. Normally, the laser beam emitted from the processing head 30 moves at a standard speed, which is the cutting speed defined in the processing conditions. When the laser beam reaches the corner Cn on the cutting path, the laser beam decelerates to a minimum speed. Then, after reaching the corner Cn, the laser beam accelerates back to the standard speed. The deceleration start position where the laser beam begins to decelerate and the acceleration end position where the laser beam ends are determined by the distance required for the processing head 30 to accelerate and decelerate, which is determined by the standard value of the acceleration / deceleration degree set in the moving mechanism 22, the standard speed, and the minimum speed of the processing head 30 at the corner Cn. The minimum speed of the processing head 30 at the corner Cn can basically be treated as zero.

[0027] As the laser beam passes before and after the corner Cn, the processing head 30 decelerates and accelerates, causing the amount of heat input to the workpiece W relative to the corner Cn to deviate from the optimal value. In other words, during normal cutting, the energy of the laser beam or the energy of the oxidation-reduction reaction accumulates as heat in the material on both sides of the cutting kerf, and this is transferred to the surrounding material by heat conduction. The location of the energy input to the workpiece W and the location of heat conduction move with the normal cutting speed, but during acceleration and deceleration that deviates from the normal cutting speed, the balance of heat input, heat storage, and heat dissipation in the workpiece W changes. Furthermore, from the moment the corner Cn is bent, the volume of metal that is subjected to heat conduction inside the corner Cn decreases. If the amount of heat input to the workpiece W is not suppressed, more heat than the energy required for cutting will accumulate in the workpiece W. An imbalance between the amount of heat input to the workpiece W and the amount of heat stored in the workpiece W is considered to be a cause of processing defects such as excessive melting of the workpiece W, dross formation, and burning of the cut surface.

[0028] Therefore, in order to control the amount of heat input, an output control method has been proposed in which the average laser output is reduced to a standard average output defined in the processing conditions during deceleration and acceleration of the processing head 30. In this output control method, the average laser output is reduced by pulse control. Here, pulse control is a control that reduces the laser beam irradiation time and non-irradiation time per unit time on the workpiece W (pulse duty cycle), and the number of laser beam irradiations per unit time (pulse frequency) from the standard pulse duty cycle and standard pulse frequency without changing the laser peak output. According to this method, the amount of heat input to the workpiece W when cutting the corner Cn can be controlled, and it is an effective solution for suppressing the occurrence of processing defects. An example of such an output control method is disclosed, for example, in Japanese Patent Application Publication No. 2024-063768.

[0029] However, even with output control, in certain machining configurations, dross D may remain on the cut surface of the corner Cn, as shown in Figure 2. This is thought to be because, in corner Cn cutting, the volume of the cutting kerf through which the molten metal escapes becomes smaller when the corner Cn is bent. As a result, the molten metal generated during cutting has nowhere to go and remains on the cut surface of the workpiece. The remaining dross D appears on the cut surface of the workpiece on the side where the laser beam decelerates towards the corner Cn, specifically on the inner corner side of the cutting path.

[0030] After thorough investigation by the inventor, it was discovered that when the oxygen concentration of the assist gas is less than or equal to the oxygen concentration in air, the plate thickness of the workpiece W is 2.3 mm or more, the angle θ of the corner Cn is 150 degrees or less, and the shape of the corner Cn is a corner or an arc with a distance radius of 2 mm or less, the phenomenon of dross remaining on the cut surface of the workpiece corner Cn occurs significantly.

[0031] During deceleration of the processing head 30, output control of the laser beam is pulsed, with pulse duty cycle and pulse frequency reduced compared to standard pulse duty cycle and standard pulse frequency. Because heat input is intermittent in pulsed control, a lag tends to occur on the underside of the cutting front when the laser beam is accelerated, as shown in Figure 3. Since the molten metal flows down the cutting front and is discharged, the lag on the underside of the cutting front makes it difficult for the molten metal to flow along the cutting front. As a result, the molten metal tends to remain on the cut surface of the corner Cn. This lag at the cutting front occurs similarly in both nitrogen cutting, which uses nitrogen as the assist gas, and oxygen cutting, which uses oxygen as the assist gas. However, in oxygen cutting, there is an excess of heat due to the heat of the oxidation reaction, causing the dross to melt and fall off. Therefore, in the case of nitrogen cutting, it is more susceptible to the effects of the lag on the underside of the cutting front. Furthermore, not only in nitrogen cutting, but in any cutting method where oxidation reaction heat is unlikely to occur, specifically in cutting methods that use a mixed gas with a high nitrogen content and oxygen, or air, as an assist gas, the cutting is susceptible to the effects of lag on the lower surface of the cutting front. In other words, when the oxygen concentration of the assist gas is lower than the oxygen concentration of the air, the cutting is susceptible to the effects of lag on the lower surface of the cutting front. The oxygen concentration of the air is approximately 21% at standard atmospheric pressure.

[0032] At the corner of the Cn, the cutting front is curved, making it difficult for the molten metal to flow along the cutting front. Furthermore, the smaller the radius of curvature of the corner of the Cn, the more abruptly the curve of the cutting front changes. As a result, it becomes even more difficult for the molten metal to flow along the cutting front. More preferably, this phenomenon is more pronounced when the shape of the corner of the Cn is a corner or has a radius of curvature of 2 mm or less. Furthermore, the smaller the angle (interior angle) of the corner of the Cn, the more abruptly the curve of the cutting front changes. As a result, it becomes even more difficult for the molten metal to flow along the cutting front. More preferably, this phenomenon is more pronounced when the angle of the corner of the Cn is 150 degrees or less.

[0033] As the plate thickness increases, the cutting front becomes longer, which increases the delay on the underside of the cutting front and increases the amount of molten metal. As a result, the molten metal becomes less able to flow along the cutting front. This phenomenon is more pronounced when the plate thickness is 2.3 mm or more.

[0034] Thus, output control (pulse control) during acceleration and deceleration is suitable for controlling the heat input to reduce the dross height at the cut surface of corner Cn. However, for the reasons mentioned above, when the conditions are met—the oxygen concentration of the assist gas is below the oxygen concentration in air, the plate thickness is 2.3 mm or more, the shape is a corner or R shape with a radius of curvature of 2 mm or less, and the angle is 150 degrees or less—pulse control is insufficient to completely discharge the molten metal, resulting in dross remaining at the cut surface of corner Cn.

[0035] Based on these findings, further investigation revealed that, under the conditions described above, setting a pulse duty cycle higher than the pulse duty cycle during deceleration when accelerating the laser beam from the corner Cn to the standard speed improves the dross remaining on the cut surface of the corner Cn. Here, "a pulse duty cycle higher than the pulse duty cycle during deceleration" means that, under the condition that the speed ratio (the ratio of the cutting speed to the standard speed) is the same during acceleration and deceleration, the pulse duty cycle during acceleration is higher than the pulse duty cycle during deceleration. For example, if the speed ratio at a certain point during acceleration is 30%, then the pulse duty cycle at this time is higher than the pulse duty cycle when the speed ratio is 30% during deceleration. Furthermore, performing CW control with a pulse duty cycle of 100% resulted in an even greater improvement in the dross remaining on the cut surface of the corner Cn.

[0036] As described above, pulse control results in intermittent heat input, causing a delay on the underside of the cutting front. On the other hand, by setting a pulse duty cycle higher than that used during deceleration, the heat input becomes continuous compared to deceleration, thus increasing the heat input to the workpiece W. In particular, with CW control, the continuous heat input further increases the heat input to the workpiece W. As a result, as shown in Figure 4, the delay on the underside of the cutting front can be suppressed, making it easier to discharge the molten metal. Hereafter, for convenience, CW control will be used as an example to explain the output control during acceleration.

[0037] Furthermore, dross residue occurs on the cut surface on the inner corner side of the cutting path. Therefore, if the product is located inside the cutting path, it will affect the quality of the product. For this reason, in addition to the above conditions, CW control may be performed if the condition that the product is located inside the cutting path is also met.

[0038] Furthermore, when performing CW control as output control during acceleration, the laser peak output may be controlled to be constant at a laser average output that is the same as or lower than the standard average output, or it may be controlled to increase the laser peak output as the cutting speed increases within a range of laser average outputs lower than the standard average output.

[0039] Referring to Figure 5, the control device 60 that realizes the laser cutting method described above will be explained. Various databases are connected to the control device 60.

[0040] The machining program database (machining program DB) 71 stores machining programs necessary for machining various workpieces W.

[0041] The processing condition database (processing condition DB) 72 stores processing conditions for processing workpiece W for each material and thickness of workpiece W. The processing conditions include the cutting speed of the processing head 30 when cutting workpiece W with a laser beam, and the average laser output of the laser beam irradiated from the processing head 30 onto workpiece W. The cutting speed and average laser output selected by the processing condition selection unit 62 correspond to the standard speed, which is the standard value of the cutting speed, and the standard average output, which is the standard value of the average laser output. The average laser output is composed of the laser peak output, pulse frequency, and pulse duty cycle of the laser oscillator 10, and the standard average output is also composed of the standard laser peak output, standard pulse frequency, and standard pulse duty cycle. In addition to the cutting speed and average laser output, the processing conditions also include the type and pressure of the assist gas, the focal length of the focusing lens 34, etc.

[0042] The output control table database (output control table DB) 74 stores the output control tables. The output control tables include an output control table for pulse control and an output control table for CW control.

[0043] The output control table for pulse control is a table that defines the correspondence between cutting speed, pulse frequency, and pulse duty cycle. The cutting speed described in the output control table is expressed as a ratio (speed ratio) of the standard speed, where the cutting speed is reduced by a predetermined percentage A (A < 100%) relative to the standard speed. Similarly, the pulse frequency and pulse duty cycle described in the output control table are expressed as a ratio (output ratio) of the standard pulse frequency and pulse duty cycle, where the pulse frequency and pulse duty cycle are reduced by a predetermined percentage B (B < 100%) relative to the standard pulse frequency and standard pulse duty cycle. The output control table for pulse control is an output control table for performing pulse control, and is configured such that the pulse frequency and pulse duty cycle become smaller than the standard pulse frequency and standard pulse duty cycle as the speed ratio decreases. One or more output control tables for pulse control are provided and are associated with the material and plate thickness of the workpiece W.

[0044] The output control table for CW control, like the output control table for pulse control, is a table that defines the relationship between cutting speed and pulse duty cycle. The output control table for CW control is an output control table for performing CW control, and is configured so that the pulse duty cycle is 100% at any speed ratio. However, the output control table for CW control may be set so that the pulse duty cycle increases to 100% at a constant rate during the initial short period when the laser beam is accelerating from the corner Cn.

[0045] When performing CW control, the pulse frequency and laser peak output can be those specified in the processing conditions (standard pulse frequency and standard laser peak output). However, the output control table for CW control may also specify the pulse frequency and laser peak output in relation to the cutting speed, in addition to the pulse duty cycle. This makes it possible to control the laser peak output to be constant at a laser average output lower than the standard average output, or to control the laser peak output to increase as the cutting speed increases within the range of laser average outputs lower than the standard average output.

[0046] The control device 60 includes a processing program selection unit 61, a processing condition selection unit 62, a parameter determination unit 63, a speed control unit 64, an output control unit 65, and an assist gas control unit 66 as multiple information processing circuits.

[0047] The machining program selection unit 61 selects the machining program required for machining the workpiece W from the machining program DB71.

[0048] The processing condition selection unit 62 selects processing conditions corresponding to the material and thickness of the workpiece W from the processing condition DB 72, according to the information described in the processing program selected by the processing program selection unit 61. Through this selection of processing conditions, the standard average output, which is the standard value of the average laser output, and the standard speed, which is the standard value of the cutting speed of the processing head 30 are selected.

[0049] The parameter determination unit 63 selects an output control table to be used for machining the workpiece W based on the machining conditions.

[0050] The speed control unit 64 controls the moving mechanism 22 based on the processing program selected by the processing program selection unit 61 and the processing conditions selected by the processing condition selection unit 62. By controlling the moving mechanism 22, the speed control unit 64 moves the laser beam along the cutting path and controls the cutting speed of the laser beam. In this embodiment, the speed control unit 64 performs acceleration / deceleration control, which decelerates the processing head 30 from the standard cutting speed to the minimum speed (zero) when the processing head 30 reaches the corner Cn on the cutting path, and then accelerates the processing head 30 back to the standard speed after reaching the corner Cn.

[0051] The output control unit 65 controls the average laser output of the laser beam irradiated onto the workpiece W from the processing head 30 by controlling the laser oscillator 10. In relation to this embodiment, the output control unit 65 performs a first output control that reduces the average laser output from the standard average output during acceleration and deceleration control. That is, when the laser beam passes through a corner Cn, the output control unit 65 performs pulse control (first output control) that reduces the pulse frequency and pulse duty cycle from the standard pulse frequency and standard pulse duty cycle according to the output control table. However, if the oxygen concentration of the assist gas is less than or equal to the oxygen concentration in air, the plate thickness is 2.3 mm or more, the angle of the corner Cn is 150 degrees or less, and the shape of the corner of Cn is a corner or a radius of curvature of 2 mm or less, the output control unit 65 performs CW control (second output control) that sets the pulse duty cycle to 100% when accelerating the laser beam to the standard speed. An example of pulse control is disclosed, for example, in Japanese Patent Publication No. 2024-063768, but the pulse control method is not limited to this if the average laser output of the laser beam is less than the standard average output. Furthermore, if the condition that the product is located inside the corner Cn is also met, the output control unit 65 may perform CW control when accelerating the laser beam to the standard speed.

[0052] The assist gas control unit 66 controls the assist gas supply device 40 based on the machining program selected by the machining program selection unit 61 and the machining conditions selected by the machining condition selection unit 62. By controlling the assist gas supply device 40, the assist gas control unit 66 controls the pressure of the assist gas supplied to the machining head 30.

[0053] Figures 6 and 7 are flowcharts showing the control method for the laser cutting machine according to this embodiment. The processes shown in these flowcharts are executed by the control device 60.

[0054] In step S10, the machining program selection unit 61 selects the machining program required for machining the workpiece W from the machining program DB71.

[0055] In step S11, the machining condition selection unit 62 selects machining conditions from the machining condition DB 72 that correspond to the material and thickness of the workpiece W, based on the information described in the machining program selected by the machining program selection unit 61.

[0056] In step S12, the machining condition selection unit 62 selects the standard average output and standard speed based on the selected machining conditions. The parameter determination unit 63 searches the output control table DB74 and selects the output control table for pulse control associated with the machining conditions. Similarly, the parameter determination unit 63 searches the output control table DB74 and selects the output control table for CW control.

[0057] In step S13, when processing begins, the assist gas control unit 66 supplies the assist gas specified in the processing conditions. The speed control unit 64 controls the movement mechanism 22 to move the laser beam along the cutting path and controls the cutting speed of the laser beam. When cutting a cutting path other than the corner Cn, the speed control unit 64 controls the movement mechanism 22 so that the cutting speed of the laser beam becomes the standard speed. At this time, the output control unit 65 controls the laser oscillator 10 to control the average laser output of the laser beam irradiated from the processing head 30 onto the workpiece W. The output control unit 65 controls the laser oscillator 10 so that the average laser beam output becomes the standard average output (step S14).

[0058] On the other hand, when the laser beam passes through the corner Cn, the speed control unit 64 performs acceleration and deceleration control. Specifically, the speed control unit 64 performs acceleration and deceleration control by decelerating the processing head 30 from the standard speed to the minimum speed when the processing head 30 reaches the corner Cn on the cutting path, and then accelerating the processing head 30 from the minimum speed to the standard speed after reaching the corner Cn. At this time, the output control unit 65 performs pulse control (first output control) by controlling the laser oscillator 10 to reduce the average laser output from the standard average output. The average laser output control is performed according to the output control table for pulse control.

[0059] Specifically, the output control unit 65 determines whether or not the deceleration of the laser beam has started due to acceleration / deceleration control (S15). If the deceleration of the laser beam has not started (S15: NO), the process proceeds to step S21. If the deceleration of the laser beam has started (S15: YES), the output control unit 65 executes the output control table for pulse control and performs pulse control during the deceleration of the laser beam (S16).

[0060] In step S17, the output control unit 65 determines whether the corner Cn reached by the laser beam satisfies the switching conditions. These switching conditions are that the assist gas is nitrogen, the plate thickness of the workpiece W is 2.3 mm or more, the angle of the corner Cn is 150 degrees or less, and the shape of the corner Cn is a corner or a radius of curvature of 2 mm or less. The switching conditions may also include the further condition that the product is located inside the corner Cn.

[0061] If the corner Cn reached by the laser beam is not a corner Cn that satisfies the switching condition (S17: NO), the output control unit 65 maintains the output control table for pulse control and performs pulse control when accelerating the laser beam (S18). Therefore, when accelerating the laser beam, the output control unit 65 controls the pulse duty cycle and pulse frequency according to the output control table for pulse control. The relationship between the distance from the corner Cn, the cutting speed, and the average laser output is shown, for example, in Figure 8. In Figure 8, when the laser beam is decelerating and approaching the corner Cn, the distance from the corner is shown as a negative value, and when the laser beam is accelerating and moving away from the corner Cn, the distance from the corner is shown as a positive value. In the example shown in Figure 8, output control by pulse control (first output control) is performed on both the deceleration side and the acceleration side of the laser beam. Furthermore, pulse control only needs to be performed while acceleration / deceleration control is in operation. The start timing of pulse control may be the same as or later than the start timing of acceleration / deceleration control, and the end timing of pulse control may be the same as or earlier than the end timing of acceleration / deceleration control.

[0062] On the other hand, if the corner Cn reached by the laser beam satisfies the switching condition (S17: YES), the output control unit 65 switches to the output control table for CW control and performs CW control when accelerating the laser beam (S19). By switching the output control table, when accelerating the laser beam, the output control unit 65 controls the pulse duty cycle according to the output control table for CW control. The relationship between the distance from the corner Cn, the cutting speed, and the average laser output is shown, for example, in Figure 9. In Figure 9, when the laser beam is decelerating and reaching the corner Cn, the distance from the corner is shown as a negative value, and when the laser beam is accelerating and moving away from the corner Cn, the distance from the corner is shown as a positive value. In the example shown in Figure 9, on the deceleration side of the laser beam, output control by pulse control (first output control) is performed, and on the acceleration side of the laser beam, output control by CW control (second output control) is performed. In the example shown in Figure 9, in CW control, the laser peak output is controlled to be constant at the same average laser output as the standard average output.

[0063] In step S20, the output control unit 65 determines whether the cutting speed of the laser beam has returned to the standard speed. That is, the output control unit 65 determines whether the acceleration of the laser beam by acceleration / deceleration control has finished. If the cutting speed of the laser beam has not returned to the standard speed (S20: NO), the output control unit 65 repeats the process in step S15. If the cutting speed of the laser beam has returned to the standard speed (S20: YES), the output control unit 65 controls the laser oscillator 10 so that the average output of the laser beam becomes the standard average output (step S21).

[0064] In step S22, the output control unit 65 determines whether or not to terminate the machining process. If the machining process is not terminated (S22: NO), the output control unit 65 repeats the process in step S14. If the machining process is terminated (S22: YES), the output control unit 65 terminates this process.

[0065] In the laser cutting machine 1 of this embodiment, the control device 60 selects a standard average output, which is a standard value of the average laser output, and a standard speed, which is a standard value of the cutting speed of the laser beam, based on the material and thickness of the workpiece W. It performs acceleration and deceleration control to decelerate the laser beam from the standard speed when the laser beam reaches a corner Cn on the cutting path, and to accelerate the laser beam to the standard speed when the processing head leaves the corner Cn. During the execution of acceleration and deceleration control, it performs first output control to reduce the average laser output to below the standard average output. When the oxygen concentration of the assist gas is less than or equal to the oxygen concentration in the air, the plate thickness is 2.3 mm or more, the angle θ of the corner Cn is 150 degrees or less, and the shape of the corner Cn is a corner or a radius of curvature of 2 mm or less, the control device 60 accelerates the laser beam to the standard speed after passing the corner Cn by controlling the laser peak output to a constant level with a pulse duty cycle of 100% at a laser average output that is the same as or lower than the standard average output, or by increasing the laser peak output as the cutting speed increases, while maintaining a pulse duty cycle of 100% within the range of laser average outputs lower than the standard average output.

[0066] With this configuration, by performing CW control with a pulse duty cycle of 100%, the heat input to the workpiece W becomes continuous, thus increasing the amount of heat input to the workpiece W. This suppresses the lag on the underside of the cutting front, making it easier to discharge molten metal. This suppresses the dross remaining on the cut surface of the corner Cn workpiece, thereby improving the cutting quality of the cut surface of the corner Cn workpiece.

[0067] Furthermore, in this embodiment, if the condition that the product is located inside the corner Cn is also met, the control device 60 may perform a second output control when accelerating the laser beam to the standard speed.

[0068] This configuration allows for the suppression of dross remaining in the product, thereby improving product quality.

[0069] Furthermore, the control method of the laser cutting machine 1, which is executed by the control device 60 of the laser cutting machine 1, can suppress the dross remaining on the cut surface of the corner Cn workpiece, thereby improving the cutting quality of the corner Cn workpiece cut surface.

[0070] In this embodiment, CW control with a pulse duty cycle of 100% was exemplified as output control during acceleration under specific conditions. However, the pulse duty cycle during acceleration only needs to be higher than the pulse duty cycle during deceleration, and is not limited to 100%.

[0071] As described above, embodiments of the present invention have been presented, but the statements and drawings that constitute part of this disclosure should not be understood as limiting the invention. Various alternative embodiments, examples, and operational techniques will become apparent to those skilled in the art from this disclosure. [Explanation of Symbols]

[0072] 1. Laser cutting machine 10. Laser Oscillator 20 processing units 22 Moving mechanism 30 Machining Heads 60 Control device

Claims

1. A laser oscillator that emits a laser beam, A processing head that cuts a workpiece by irradiating it with a laser beam emitted from the laser oscillator, A moving mechanism for moving the machining head relative to the workpiece, An assist gas supply device that supplies assist gas to the processing head, The control device controls the average laser output of the laser beam by controlling the laser oscillator and moves the laser beam along the cutting path by controlling the moving mechanism, The control device is Based on the material and thickness of the workpiece, a standard average output, which is a standard value of the average laser output, and a standard speed, which is a standard value of the cutting speed of the laser beam, are selected. Acceleration and deceleration control is performed to decelerate the laser beam to below the standard speed when it reaches a corner on the cutting path, and to accelerate the laser beam to the standard speed when it moves away from the corner. During the execution of the acceleration / deceleration control, a first output control is performed to reduce the average laser output to a standard average output by controlling the pulse duty cycle and pulse frequency of the laser beam. The control device is If the oxygen concentration of the assist gas is less than or equal to the oxygen concentration in air, the plate thickness is 2.3 mm or more, the angle of the corner is 150 degrees or less, and the shape of the corner is a corner or a radius of curvature of 2 mm or less, When accelerating the laser beam to the standard speed, The second output control is performed such that the laser peak output remains constant while maintaining a pulse duty cycle higher than the pulse duty cycle during deceleration, at a laser average output that is the same as or lower than the standard average output, or such that the laser peak output increases as the cutting speed increases, at a range of laser average outputs lower than the standard average output, while maintaining a pulse duty cycle higher than the pulse duty cycle during deceleration. Laser cutting machine.

2. The control device is If the condition that the product is located inside the aforementioned corner is further met, the second output control is performed when accelerating the laser beam to the standard speed. The laser cutting machine according to claim 1.

3. A laser oscillator that emits a laser beam, A processing head that cuts a workpiece by irradiating it with a laser beam emitted from the laser oscillator, A moving mechanism for moving the machining head relative to the workpiece, A control method for controlling a laser cutting machine, which includes an assist gas supply device that supplies assist gas to the processing head, The control device Based on the material and thickness of the workpiece, a standard average output, which is a standard value of the average laser output of the laser beam, and a standard speed, which is a standard value of the cutting speed of the laser beam, are selected. Acceleration and deceleration control is performed to decelerate the laser beam to below the standard speed when it reaches a corner on the cutting path, and to accelerate the laser beam to the standard speed when it moves away from the corner. During the execution of the acceleration / deceleration control, a first output control is performed to reduce the average laser output to a standard average output by controlling the pulse duty cycle and pulse frequency of the laser beam. The control device is If the oxygen concentration of the assist gas is less than or equal to the oxygen concentration in air, the plate thickness is 2.3 mm or more, the angle of the corner is 150 degrees or less, and the shape of the corner is a corner or a radius of curvature of 2 mm or less, When accelerating the laser beam to the standard speed, The second output control is performed such that the laser peak output remains constant while maintaining a pulse duty cycle higher than the pulse duty cycle during deceleration, at a laser average output that is the same as or lower than the standard average output, or such that the laser peak output increases as the cutting speed increases, at a range of laser average outputs lower than the standard average output, while maintaining a pulse duty cycle higher than the pulse duty cycle during deceleration. A control method for a laser cutting machine.

4. The control device is If the condition that the product is located inside the aforementioned corner is further met, the second output control is performed when accelerating the laser beam to the standard speed. A control method for a laser cutting machine according to claim 3.

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