JP2011224600A - Laser piercing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser piercing method by which a hole having the diameter of a degree to which drilling is smoothly shiftable to cutting is formed in a short time by irradiating a material to be cut with a laser beam.SOLUTION: In the laser piercing method by which a through-hole 8 in the thickness direction is formed on the material to be cut by irradiating the material B to be cut with the laser beam 7 and also jetting assist gas composed of gaseous oxygen from a laser nozzle A to the material B to be cut, in the state where the focus S of the laser beam 7 is set in a position in the inside direction of a plate thickness of the material B to be cut and where the position is held, the material B to be cut is irradiated from the laser nozzle A with a pulse-like laser beam, the peak output of which is ≥50% of the rated output of a laser oscillator 11 and the duty ratio of which is set to ≥50%, also the assist gas which is set to lower pressure than the pressure of the assistant gas which is suitable to cut the material B to be cut is jetted and shield gas containing the gaseous oxygen is jetted to the outside of the assist gas.

Description

  The present invention relates to a laser piercing method in which a laser beam is irradiated toward a material to be cut to form a through hole, and in particular, the diameter of the through hole can be reduced and the time required for piercing can be shortened. The present invention relates to a method for laser piercing.

  While irradiating a laser beam from a laser nozzle toward a material to be cut made of metal, the laser nozzle is moved along the shape of a target figure and cut. In the case of this laser cutting, first, piercing is performed at a position on the scrap side separated from the target figure in the material to be cut to form a through hole, and cutting is started from this through hole as a starting point. is there.

  When piercing is performed by irradiating a material to be cut with laser light, an assist gas made of oxygen gas is injected along the laser light. In addition, a shield gas made of oxygen gas is injected along the assist gas. The assist gas has a function of burning a material to be cut at a site irradiated with laser light and removing a molten product from the base material. The shield gas has a function of shielding the assist gas from the atmosphere.

  Currently, two methods are generally used as piercing methods. The first method is a method of forming a hole having a diameter of about 1 mm or smaller by using a pulse laser (PW) having a low duty ratio. With this method, small holes can be formed. However, there is a problem that the processing time increases rapidly as the thickness of the material to be cut increases, and there is a problem that the diameter on the back side becomes too small to smoothly shift to cutting. .

  The second method uses a continuous wave laser (CW) and sets the focal point of the laser beam above the surface of the material to be cut to form a hole in a short time. With this method, holes can be formed in a short time. However, there is a problem that the diameter of the formed hole becomes large and the amount of the melt removed from the base material becomes large, and the heat storage amount of the base material increases.

  In order to solve the above problems, a piercing method described in Patent Document 1 has been proposed. In this piercing method, after irradiating the laser beam under the first piercing condition, the laser beam irradiation is stopped for 0.5 seconds or more, and then the laser beam is irradiated under the second piercing condition to complete the piercing process. It is what you do. The first piercing condition is that the laser beam is in a continuous waveform mode or the beam spot diameter is changed. The second piercing condition is that the laser beam is in a continuous waveform mode, the beam spot diameter is changed, or the laser beam is in a pulse waveform mode.

Japanese Patent Laid-Open No. 2007-075878

  In the invention described in Patent Document 1, by providing a beam stop period during the piercing process, the amount of spatter generated during the piercing process can be reduced and the through hole can be formed in a short time. As shown, the hole diameter formed in the workpiece is 6 mm. It can be said that this hole diameter is sufficiently small as compared with the conventional second method. However, in reality, companies that perform laser cutting are required to develop a piercing method for forming smaller holes in a shorter time.

  The through hole formed in the material to be cut by irradiating the laser beam generally has a large diameter on the front surface side and a small diameter on the back surface side, and the cutting is performed with the through hole as a starting point. And when the diameter of the back surface side in the through hole is too small, there is a problem that when the process shifts to cutting, the generated melt is not smoothly removed to the back surface side and causes a cutting failure.

  An object of the present invention is to provide a laser piercing method capable of forming a hole having a diameter that can be smoothly cut by irradiating a material to be cut with a laser beam in a short time.

  The inventors of the present invention conducted various experiments in order to solve the above problems. This experiment was performed by piercing a steel plate with SS400 and a plate thickness of 16 mm using a carbon dioxide laser with a peak output of 4000 W. In order to shorten the piercing time, the time required for piercing the material to be cut was 2 seconds or less, and when it took 2 seconds or more, it was determined that the piercing was unsuccessful and the drilling success rate was calculated. Here, the reason for determining the time required for piercing as a limit of 2 seconds is that there is no significant change in the time required for piercing even when the plate thickness of the material to be cut or the peak output of the laser beam is changed. ing.

  In addition, after the piercing is completed, in order to make a smooth transition to cutting, the diameter of the through hole on the back surface side is set to about 1 mm or more, and the diameter of the through hole is made as small as possible on the back surface side. A condition for determining the diameter of the through hole to be about 3 mm or less was set as a standard for determination.

  In particular, in laser cutting, since a series of operations from piercing to cutting is generally automated, a problem arises in terms of workability and operating rate when the drilling success rate is low. Therefore, the drilling success rate is desirably 100%, and preferably at least 90%.

  And if it was the piercing which satisfy | fills the said conditions, it acquired the touch that it can be said that it can fully show an advantage compared with the conventional piercing.

  As a result, in the laser piercing method according to the present invention, a laser beam is irradiated from the laser nozzle toward the material to be cut and an assist gas made of oxygen gas is injected to form a through hole in the thickness direction in the material to be cut. In this laser piercing method, the peak output of the laser beam is directed from the laser nozzle toward the workpiece while the focal point of the laser beam is set at the position in the inner direction of the thickness of the workpiece and the position is maintained. The pressure is set to a pressure lower than the assist gas pressure suitable for cutting the material to be cut while irradiating a pulsed laser beam having a rated output of 50% or more and a duty ratio of 50% or more. The assist gas is injected, and a shield gas containing oxygen gas is injected outside the assist gas.

  In the laser piercing method, it is preferable to apply the laser piercing method described in claim 1 to the prepared hole after forming a prepared hole that does not penetrate in the thickness direction in the material to be cut.

  In the laser piercing method, the pilot hole is set at a position where the focal point of the laser beam is separated from the surface of the material to be cut, and the laser nozzle is directed from the laser nozzle toward the material to be cut in a state where the position is held. More than the pressure of the assist gas suitable for irradiating a pulsed laser beam having a peak output of 50% or more of the rated output of the laser oscillator and a duty ratio of 50% or more and cutting the material to be cut It is preferable to form by injecting an assist gas set at a low pressure and injecting a shield gas containing oxygen gas outside the assist gas.

  In the laser piercing method according to the present invention, a through-hole having a small diameter on the back surface side and no problem in shifting to cutting can be formed in a short time.

  That is, the laser beam irradiated to the material to be cut is set so that the focal point of the laser beam is in the internal direction of the thickness of the material to be cut, the peak output is 50% or more of the rated output of the laser oscillator, and the duty ratio is 50% or more. A pulse laser is used, and the assist gas pressure is set to a pressure lower than the pressure at the time of cutting, and a shielding gas containing oxygen gas is injected outside the assist gas. The base material temperature can be raised, and combustion of the base material of the material to be cut by the assist gas can be suppressed. For this reason, the quantity of a combustion product can be reduced, the discharge amount of a base material can be reduced, and the diameter of a hole can be made small. In particular, the assist gas is shielded from the atmosphere by the shield gas, and the oxygen gas contained in the shield gas can be used as an auxiliary gas of the assist gas whose flow rate is reduced by reducing the pressure.

  In addition, prior to carrying out the laser piercing method, by forming a pilot hole that does not penetrate in the thickness direction in the material to be cut, even when the thickness of the material to be cut increases can do.

  When forming the pilot hole, the focal point of the laser beam is set at a position separated from the surface of the material to be cut, and then the peak output is 50% or more of the rated output of the laser oscillator and the duty ratio is 50% or more. A good pilot hole can be formed by using a pulse laser, setting the pressure of the assist gas to a pressure lower than the pressure at the time of cutting, and injecting a shield gas containing oxygen gas outside the assist gas.

  Therefore, after the pilot hole is formed as described above, the focal position of the laser beam is changed and set in the internal direction of the plate thickness of the material to be cut. In this state, the peak output is 50 of the rated output of the laser oscillator. %, And the duty ratio is 50% or more, the assist gas pressure is set to a pressure lower than the pressure at the time of cutting, and a shield gas containing oxygen gas is injected outside the assist gas. Through holes can be processed continuously. For this reason, smooth and good laser piercing can be performed even when the thickness of the material to be cut increases.

It is a figure which illustrates typically the composition of the device for carrying out the laser piercing method. It is a figure explaining the procedure which implements the laser piercing which concerns on 1st Example. It is a figure which shows the piercing conditions and result in 1st Example. It is a figure which shows the piercing conditions and result in 1st Example. It is a figure explaining the procedure which implements the laser piercing based on 2nd Example. It is a figure which shows the piercing conditions and result in 2nd Example. It is a figure which shows the piercing conditions and result in 2nd Example.

  The laser piercing method according to the present invention (hereinafter simply referred to as “piercing method”) will be described below. In the piercing method according to the present invention, when the through hole is formed in the material to be cut, the focal position of the laser beam is set in the internal direction of the thickness of the material to be cut, and the peak output of the laser beam is the rating of the laser oscillator. 50% or more of the output and the duty ratio are set to 50% or more, and the assist gas is set to a pressure lower than the pressure suitable for cutting the material to be cut, and oxygen gas is included outside the assist gas. By injecting the shielding gas, a through hole having a small diameter and capable of smoothly shifting to cutting is formed in a short time.

  When piercing is performed by irradiating the workpiece with laser light, the peak output of the laser oscillator and the thickness of the workpiece are correlated, and piercing can be performed within a predetermined time when the peak output is set. The thickness of the material to be cut is automatically set. For this reason, although the thickness of the material that can be pierced increases as the peak output of the laser oscillator increases, it is extremely difficult to pierce the material that exceeds the maximum plate thickness that can be pierced.

  This means that when the peak output of the laser oscillator is set, the maximum plate thickness that can be pierced with this peak output is set, and when piercing a workpiece that is thinner than the maximum plate thickness, This means that it is possible to pierce with a small output.

  Therefore, by setting the peak output to 50% or more of the rated output of the laser oscillator, it is possible to perform piercing up to the maximum plate thickness that can be pierced when the peak output laser beam is emitted from the laser oscillator. .

  In addition, a pilot hole is formed in advance by irradiating a laser beam at a position where a through hole is to be formed in the material to be cut, and after this pilot hole is formed, piercing is performed at the position of the pilot hole under the above-described conditions. By doing so, it is possible to reliably form a through-hole having a small diameter even when the material to be cut becomes thick.

  That is, as described above, when the peak output of the laser oscillator is set, the maximum plate thickness that can be pierced by this laser oscillator is set. For this reason, it is possible to expand the range of the plate thickness that can be pierced by the laser oscillator in which the peak output is set by forming the pilot holes in advance.

  In addition, when forming the pilot hole, the focal point of the laser beam is set at a position separated from the material to be cut, and the conditions consisting of the nature of the laser beam, the assist gas pressure, and the shield gas pressure are different from the cutting conditions. It is possible to form a pilot hole in the material to be cut by irradiating the laser beam with setting.

  That is, the range of the maximum plate thickness that can be pierced even when using a laser oscillator in which the maximum plate thickness that can be pierced according to the set peak output is determined by forming the pilot hole by irradiating laser light Can be expanded.

  First, the configuration of an apparatus for carrying out the piercing method according to the present invention will be briefly described with reference to FIG.

  The laser nozzle A is provided with a nozzle 1 that emits laser light at the tip and jets assist gas, and a lens 2 is disposed at a predetermined position inside. Reference numeral 3 denotes an optical axis of the laser beam, which is set by connecting the center of the nozzle 1 and the center of the lens 2. A shield gas nozzle 4 for injecting a shield gas is provided around the nozzle 1.

  A laser oscillator 11 is connected to the laser nozzle A. The laser oscillator 11 is disposed on an extension line of the optical axis 3, and laser light emitted from the laser oscillator 11 is collected by the lens 2, emitted from the nozzle 1, and focused on the optical axis 3. To converge.

  Further, an assist gas supply device 12 is connected to the laser nozzle A, and the assist gas supplied from the assist gas supply device 12 is a chamber formed between the nozzle 1 and the lens 2 via a hose 12a. 5 is injected from the nozzle 1 toward the workpiece B through the chamber 5.

  The assist gas supply device 12 adjusts a supply facility such as an oxygen cylinder for supplying oxygen gas constituting the assist gas or an oxygen pipe in the factory, and a primary pressure supplied by the supply facility to a pressure used as the assist gas. The pressure adjusting device is configured. In particular, it is preferable to provide two systems as pressure adjusting devices so that the pressure supplied to the chamber 5 during piercing and the pressure supplied to the chamber 5 during cutting can be easily switched.

  Further, a shield gas supply device 13 is connected to the laser nozzle A, and the shield gas supplied from the shield gas supply device 13 flows into the chamber 6 through the hose 13a, and passes through the chamber 6 to provide the shield gas nozzle 4. To the cut material B.

  The shield gas supply device 13 includes an oxygen gas supply device that supplies oxygen gas that constitutes the shield gas, another gas that constitutes the shield gas, such as a supply device that supplies nitrogen gas, and a mixer that mixes these gases. And is configured.

  In this embodiment, since compressed air is used as the shielding gas, the shielding gas supply device 13 includes an air compressor, a dehumidifier, and a pressure regulator.

  Reference numeral 14 denotes a focal position adjusting device having a function of adjusting the position of the focal point S to a desired position by changing the distance of the lens 2 from the material B to be cut. The focus position adjusting device 14 may be any device that can exhibit the above function. For this reason, it is possible to change the distance of the lens 2 from the workpiece B by changing the position of the laser nozzle A itself. Further, the lens 2 has a structure capable of changing the position independently, and the distance from the material to be cut B is changed only by the lens 2 regardless of the distance between the laser nozzle A and the material B to be cut. It is also possible to configure as described above.

  Next, a method for piercing the material to be cut B using the laser nozzle A configured as described above will be described.

  This embodiment is a piercing method that is advantageous when applied to a case where the material to be cut B is relatively thin. In the present embodiment, as the material to be cut B, a steel plate of material: SS400, thickness: 16 mm is used. As the laser oscillator 11, a carbon dioxide laser having a peak output of 4000 W is used.

  Cutting conditions for performing normal cutting of the material to be cut B are as follows: laser light conditions: peak output: 4000 W, frequency: 1000 Hz, duty ratio: 45%, focal position: surface of the material to be cut, and gas conditions as assist Gas pressure: 0.035 MPa, shielding gas: oxygen gas pressure: 0.03 MPa, cutting speed: 800 mm / min. This cutting condition is capable of reliably cutting the material to be cut B in a stable state while maintaining the quality of the cut surface.

  The standard positional relationship between the two when the workpiece B is pierced by the laser nozzle A will be described with reference to FIG. As shown in the figure, the laser nozzle A is set at a position separated by a height H from the surface of the material to be cut B. At this time, the position of the focal point S enters Dmm in the internal direction in the thickness of the material to be cut B. Set to the position. In this state, the laser beam 7 is irradiated from the laser nozzle A toward the material to be cut B, and piercing is performed by injecting an assist gas and a shield gas to form the through hole 8 in the material to be cut B.

  In this embodiment, the standard piercing conditions for piercing the workpiece B as described above are as follows: peak output: 4000 W, frequency: 100 Hz, duty ratio: 60%, focal position: thickness of the workpiece The gas conditions are set as assist gas pressure: 0.02 MPa, shield gas: air pressure 0.25 MPa.

  Then, a piercing experiment was performed in a state where any one of the piercing conditions was changed and the other conditions were fixed.

  In each experiment, whether or not the piercing was performed successfully was judged based on the time required for the piercing being 2 seconds or less. If the piercing was not completed within the time, the piercing was successful and the drilling was successful. The rate was calculated.

  As described above, in laser cutting, it is common to automate a series of operations from piercing to cutting. Therefore, if the drilling success rate is low, it is reliable even if other conditions are satisfied. In view of problems, it is desirable that the drilling success rate is 100%, and preferably at least 90%. Therefore, when the drilling success rate was less than 90, it was determined that the piercing was not good.

  Moreover, when the time required for piercing was within 2 seconds, the diameter of the back surface side of the formed through-hole was measured. And when the diameter of the back surface side of a through-hole exists in the range of about 1 mm or more and about 3 mm or less, it determined with it being favorable piercing.

  Moreover, the average diameter and height when the product (dross) generated in the process of piercing adhered to the surface of the material B to be cut were measured. The average diameter of dross was determined with a standard of about 1/2 of the plate thickness. This criterion is generally performed at the site of a company that uses a laser cutting device. Further, when the dross adhesion height increases, there is a risk of contact when the laser nozzle is lowered toward the surface of the material to be cut when shifting from piercing to cutting. For this reason, the height of the dross was determined based on 1 mm or less.

  Prior to describing the experimental results according to the present embodiment, the maximum piercable plate thickness of a laser oscillator having a peak output of 4000 W will be described. When piercing is performed by irradiating a steel plate of SS400 with a laser beam having a peak output of 4000 W, it has been confirmed that the maximum plate thickness that can be pierced is 16 mm.

  For this reason, the drilling success rate was 65% at the maximum when the cut material B was irradiated with a laser beam having a peak output set to 4000 W or less (3000 W, 3500 W). Moreover, when piercing was performed by irradiating a steel plate with a plate thickness of 12 mm with SS400 and irradiating a laser beam with a peak output of 3000 W or 3500 W, the drilling success rate was 100%, and the diameter on the back side in the through hole Was about 1.5 mm. And in the case of this piercing, it was possible to shift to cutting smoothly.

  Next, the conditions and results of the experiment will be described with reference to FIGS.

  FIG. 3A shows that when piercing is performed, when the focus S of the laser beam 7 is set at any position with respect to the material B to be cut, a favorable piercing operation can be performed and a good through hole is formed. The result of having conducted the experiment for judging whether it can form is shown.

  As described in the background art section, when the position of the focal point S of the laser beam 7 is separated from the surface of the workpiece B, the diameter of the through hole formed in the workpiece B may be increased. ing. For this reason, an experiment was performed in which the dimension (D in FIG. 2A) that entered the internal direction in the thickness of the material B to be cut at the focal point S of the laser beam 7 was changed.

  As shown in the figure, the position of the focal point S was changed in increments of 2 mm from −1 mm to −11 mm in the depth direction (here, −1 mm means D = 1 mm). As a result, the drilling success rate was 0 when the focal position was -1 mm and -11 mm, and 65% when the focal position was -3 mm. In the range of −5 mm to −9 mm, the success rate of drilling was 100%.

  Further, the hole diameter in the range of −3 mm to −9 mm (the hole diameter on the back surface side of the through hole 8 formed in the workpiece B shown in FIG. 2B) is 1.4 mm to 1.7 mm. Each of the dimensions was such that it could smoothly transition from piercing to cutting. Moreover, the diameter of the dross was in the range of 6 mm to 7.5 mm, and the height was in the range of 0.4 mm to 0.6 mm.

  Accordingly, the position of the focal point S of the laser beam 7 needs to be set at a position where it enters 3 mm to 9 mm in the inner direction in the thickness of the material B to be cut, and is preferably in the range of 5 mm to 9 mm. .

  FIG. 3B shows the result of an experiment in which the average output is changed by setting the output of the laser oscillator 11 to 100% of the rated output and changing the duty ratio in the range of 40% to 100%. . As shown in the figure, the drilling success rate was 0% when the duty ratio was 40%, and 65% when the duty ratio was 100%. When the duty ratio was 50% and 98%, the drilling success rate was 90%, and when the duty ratio was in the range of 60% to 95%, 100% drilling success rate was obtained.

  The hole diameter was 1.3 mm to 2.9 mm when the duty ratio was in the range of 50% to 90%, and 3 mm when the duty ratio was 100%. Further, it was 3.7 mm when the duty ratio was 95%, and 4.1 mm when the duty ratio was 98%.

  As a result of this experiment, it can be said that the laser beam 7 is preferably in the pulse mode rather than oscillating in the continuous oscillation mode. When the laser beam 7 is set to the pulse mode, the duty ratio may be 50% or more in order to perform reliable piercing. However, in order to obtain a through hole with a small diameter, the duty ratio is preferably in the range of 50% to 90%, and more preferably in the range of 60% to 90%.

  FIG. 4A shows the result of an experiment in which the assist gas pressure injected from the nozzle 1 is changed. Since the assist gas injected along the laser beam 7 is composed of oxygen gas, it has a function of oxidizing and burning the base material melted by the irradiation of the laser beam 7. Since the amount of the molten product increases as piercing progresses, an excessive amount of oxygen gas may be supplied when assist gas having the same pressure as that during cutting is injected during piercing. For this reason, this experiment determines how much it is preferable to lower the assist gas pressure at the time of piercing than the assist gas pressure at the time of cutting.

  As shown in the figure, the drilling success rate was 90% when the assist gas pressure was 0.01 MPa, and the drilling success rate was 100% in the range of 0.015 MPa to 0.055 MPa. The hole diameter was 1.5 mm to 2.9 mm in the range of 0.01 MPa to 0.045 MPa, and 3.5 mm when 0.055 MPa.

  As a result of this experiment, piercing can be performed if the assist gas pressure is in the range of 0.01 MPa to 0.055 MPa. However, in order to obtain a through hole having a small hole diameter, the assist gas pressure is preferably in the range of 0.01 MPa to 0.03 MPa, more preferably in the range of 0.015 MPa to 0.025 MPa. Therefore, it can be said that the assist gas pressure at the time of piercing is preferably lower than the assist gas pressure at the time of cutting.

  FIG. 4B shows the result of an experiment in which the shield air pressure injected from the shield gas nozzle 4 is changed. When laser cutting is performed on the material to be cut B, it is common to inject a shield gas made of oxygen gas along the assist gas. However, it has been found that if oxygen gas is injected as a shielding gas during piercing, an excessive amount of oxygen gas is supplied, and the diameter of the through-hole is increased as a whole. For this reason, a gas with reduced oxygen purity (air of about 21% oxygen in this experiment) was injected along the assist gas as a shielding gas, and the shielding gas pressure suitable for piercing was determined.

  As shown in the figure, the drilling success rate was 100% in the range where the shield gas was not injected and the shield gas pressure was 0.4 MPa. When the shield gas pressure was 0.45 MPa, the drilling success rate was 80%. . The hole diameter was 1.3 mm to 2 mm when the shield gas pressure was in the range of 0.1 MPa to 0.45 MPa, and when the shield gas was not injected, it was 3.5 mm and 3.4 mm when 0.05 MPa. .

  As a result of this experiment, when air of about 21% oxygen is used as the shielding gas, it can be said that the pressure is preferably in the range of 0.1 MPa to 0.4 MPa. Further, when oxygen gas and nitrogen gas are mixed in a mixer so that a gas in which oxygen gas is mixed at a desired ratio is used as a shielding gas, it is preferable that the pressure is decreased when the oxygen gas mixing ratio is increased. When the oxygen gas mixing ratio is lowered, it is preferable to increase the pressure.

  As shown in FIG. 3B, when piercing is performed, the laser beam 7 irradiated to the material to be cut B has obtained an experimental result in which the pulse mode is preferable to the continuous oscillation mode. For this reason, the experiment shown in FIG. 4C shows an experimental result when the piercing is performed by irradiating the pulsed laser beam 7 with the frequency changed.

  As shown in the figure, the drilling success rate was 60% when the frequency was 10 Hz and 1600 Hz, and the drilling success rate was 80% when the frequency was 25 Hz, 50 Hz, and 800 Hz. In the range of 100 Hz to 600 Hz, the drilling success rate was 100%. Moreover, the hole diameter was 1.2 mm-1.5 mm in the range of 10 Hz-1600 Hz.

  As a result of this experiment, it can be said that the frequency is preferably in the range of 100 Hz to 600 Hz.

  Based on the results of a series of experiments as described above, the focal point S of the laser beam 7 is set at a position in the inner direction of the plate thickness of the material B to be cut, and the laser nozzle A applies a target while maintaining this position. To irradiate the cutting material B with a pulsed laser beam having a peak output of 50% or more of the rated output of the laser oscillator 11 and a duty ratio of 50% or more, and to cut the material B to be cut. The through-hole 8 can be formed by performing good piercing by injecting an assist gas set to a pressure lower than a suitable assist gas pressure and injecting a shield gas containing oxygen gas outside the assist gas. It becomes possible.

  And in the through-hole 8 formed as mentioned above, the diameter of the back surface side of the material to be cut B has a dimension required for continuous cutting, and smoothly shifts to cutting. It is possible.

  Next, a piercing method according to the second embodiment will be described. In the piercing method according to the present embodiment, when the thickness of the material to be cut is larger than the thickness that can be pierced according to the peak output of the laser oscillator, the material to be cut is pierced in a good state.

  As described above, when the peak output of the laser oscillator is set, there is an upper limit in the thickness of the material B to be pierced by this peak output. For this reason, in this embodiment, a pilot hole that does not penetrate through the material to be cut is formed in advance, and the thickness from the bottom to the rear surface of the pilot hole is set to a dimension that can be pierced by the peak output of the laser oscillator.

  The method of forming the pilot hole is not particularly limited, and may be a method of forming using a drilling tool such as a drill. However, from the viewpoint of workability and the simplicity of equipment, it is preferable to form the pilot hole using a laser oscillator used for piercing.

  In this embodiment, a pilot hole is formed using a laser oscillator 11 for piercing, and then a through hole is formed by the same laser oscillator 11. A piercing method according to the present embodiment will be described with reference to FIG.

  As shown in FIG. 5A, when forming the pilot hole in the workpiece B, the laser nozzle A is opposed to the workpiece B, and the focal point S is separated from the surface of the workpiece B by a distance L. It is set so that it becomes the position (height H of the laser nozzle A). While maintaining this position, the laser beam 7 is irradiated under the conditions obtained in the later-described experiment, and the assist gas and the shield gas are injected. As a result, the pilot hole 9 is formed as shown in FIG.

  Thereafter, as shown in FIG. 3C, the laser nozzle A is moved close to (to be lowered) the material to be cut B, and the focal point S of the laser light 7 is moved from the bottom of the pilot hole 9 to the back side (the thickness of the material to be cut B). (Inward direction) is set to a position where the distance D enters, and the laser beam 7 is irradiated under the same conditions as in the first embodiment, and the assist gas and the shield gas are injected, so that FIG. As shown, a through hole 8 continuous with the pilot hole 9 is formed in the thickness direction of the material B to be cut.

  By the above procedure, it is possible to pierce the workpiece B having a thickness that cannot be pierced at the peak output of the laser oscillator 11.

  Next, experimental results for setting conditions for forming the pilot holes 9 in the workpiece B will be described with reference to FIGS. In the present embodiment, a material: SS400, a thickness: 19 mm steel plate is used as the material to be cut B, and a carbon dioxide gas laser having a peak output of 4000 W is used as the laser oscillator 11.

  After the pilot hole 9 is formed, piercing is continuously performed starting from the bottom. For this reason, it is not always necessary to have the same shape as the through-hole 8 formed at the time of piercing. The diameter of the surface B of the material to be cut B is large, and the diameter decreases as it enters the thickness in the inner direction. Preferably there is. The diameter of the bottom may be sufficiently larger than the diameter of the back surface side in the through hole 8.

  The depth of the pilot hole 9 is set corresponding to the maximum piercing thickness set according to the peak output of the laser oscillator 11. For example, when the peak output of the laser oscillator 11 is 4000 W, the maximum thickness that can be pierced is about 16 mm. Therefore, when the workpiece B having a thickness of 19 mm is pierced using the laser oscillator 11 having a peak output of 4000 W, the depth of the pilot hole 9 needs to be 3 mm or more.

  FIG. 6A shows a state in which the focal point S of the laser beam 7 is set at any position with respect to the material to be cut B when forming the prepared hole 9 that does not penetrate the material to be cut B in the thickness direction. The result of having conducted the experiment for determining whether the pilot hole 9 with a favorable shape can be formed is shown.

  As shown in the figure, the position of the focal point S was changed in increments of 1 mm from +7 mm to +1 mm in the direction away from the surface of the workpiece B and from −1 mm to −4 mm in the depth direction on the surface. As a result, the depth of the pilot hole 9 was in the range of 4.5 mm to 8.1 mm. In the case of the pilot hole 9 having such a depth, the dimension (apparent plate thickness) from the bottom to the back surface of the material B to be cut is 14.5 mm to 10.9 mm, and the laser oscillator 11 having a peak output of 4000 W is used. It is a dimension that can be reliably pierced.

  Further, the pilot hole diameter is in the range of 3.1 mm to 2 mm when the position of the focus S is in the range of +7 mm to +1 mm, 1.8 mm when the focus S is on the surface, and the focus S is from −1 mm to In the case of -4 mm, it was in the range of 1.8 mm to 1.5 mm. As described above, the diameter of the pilot hole 9 is not preferably too small because piercing is performed in the next step, and is preferably at least larger than 1.5 mm.

  Therefore, the position of the focal point S of the laser beam 7 when forming the pilot hole 9 is preferably in the range of −2 mm to +7 mm, and more preferably set in a direction away from the surface of the material B to be cut. , +5 mm is desirable.

  FIG. 6B shows the result of an experiment in which the average output is changed by setting the output of the laser oscillator 11 to 100% of the rated output and changing the duty ratio in the range of 30% to 100%. . As shown in the figure, a pilot hole 9 having a depth of 5.3 mm to 7.3 mm was obtained in a duty ratio range of 30% to 100%.

  The pilot hole diameter was 0.8 mm and 1.2 mm when the duty ratio was 30% and 40%, and 3 mm when the duty ratio was 100%. Further, when the duty ratio was 50% or more, it was 1.5 mm to 2.8 mm.

  The height of the dross was 0.7 mm when the duty ratio was 80%, 0.9 mm when the duty ratio was 90%, 1 mm when 95% and 98%, and 1.3 mm when 100%.

  As a result of this experiment, when the pilot hole 9 is formed, the laser light 7 may be in a CW mode and a pulse mode with a duty ratio of 50% or more in view of the depth and diameter of the pilot hole 9. However, from the state of dross attached to the surface of the workpiece B, it is preferable that the pulse mode is a pulse mode lower than 90%. Therefore, the duty ratio of the laser beam 7 used when forming the pilot hole 9 is preferably 50% or more, and more preferably in the range of 50% to 90%. Furthermore, it is desirable that it is in the range of 70% to 90%.

  FIG. 7A shows the result of an experiment in which the assist gas pressure injected from the nozzle 1 is changed. As shown in the figure, the depth of the pilot hole 9 is 6.9 mm to 8.5 mm when the assist gas pressure is in the range of 0.01 MPa to 0.05 MPa, and can sufficiently exhibit the function as the pilot hole. Is possible.

  The diameter of the pilot hole was in the range of 1.5 mm to 2.5 mm when the assist gas pressure was in the range of 0.01 MPa to 0.04 MPa, and 4.5 mm when 0.05 MPa. Further, the height of the dross attached to the surface of the material B to be cut was 1 mm when the assist gas pressure was in the range of 0.03 MPa to 0.04 MPa, and 1.5 mm when 0.05 MPa.

  As a result of this experiment, when the pilot hole 9 is formed, the assist gas pressure may be in the range of 0.01 MPa to 0.05 MPa in view of the depth and diameter of the pilot hole 9. However, in terms of dross adhesion, it is preferably lower than 0.025 MPa.

  FIG. 7B shows a result of an experiment in which the shield air pressure injected from the shield gas nozzle 4 is changed. In the present embodiment, air of about 21% oxygen is injected along the assist gas as the shielding gas, as in the first embodiment.

  As shown in the figure, the depth of the pilot hole 9 obtained in the range where the shield gas pressure is 0.4 MPa from the state where the shield gas is not injected is in the range of 6.2 mm to 9.6 mm. It can be preferably used.

  The diameter of the pilot hole was in the range of 5 mm to 6 mm when the shield gas pressure was 0.15 MPa from the state where no shield gas was injected, and was 2 mm to 2.5 mm within the range of 0.2 MPa to 0.4 MPa. Further, the height of the dross is 1.5 mm to 5 mm in a range where the shield gas pressure is 0.15 MPa from the state where the shield gas is not injected, 0.9 mm at 0.2 MPa, and 0.25 MPa to 0.00 mm. It was 0.5 mm to 0.6 mm in the range of 4 MPa.

  As a result of this experiment, when air of about 21% oxygen is used as the shielding gas, the pressure is preferably in the range of 0.2 MPa to 0.4 MPa in view of the pilot hole diameter and the attached state of dross. A range of 25 MPa to 0.4 MPa is more preferable. Further, the pressure is preferably lowered when the concentration of oxygen gas is increased, and the pressure is preferably increased when the concentration of oxygen gas is decreased.

  When forming the pilot hole 9, the laser light 7 irradiated to the material B to be cut has obtained an experimental result in which the PW mode is preferable to the CW mode (see FIG. 6B). For this reason, the experiment shown in FIG. 7C shows an experimental result when the pilot hole 9 is formed by irradiating the pulsed laser beam 7 with the frequency changed.

  As shown in the figure, when the frequency is 10 Hz and 1600 Hz, the pilot hole depth is in the range of 5.5 mm to 7.3 mm, and the pilot hole diameter is in the range of 1.6 mm to 2.3 mm. The height of the dross is in the range of 0.5 mm to 0.7 mm.

  As a result of this experiment, it can be said that the frequency is preferably in the range of 10 Hz to 1600 Hz.

  Based on the results of a series of experiments as described above, the focal point S of the laser beam 7 is set at a position separated from the surface of the material to be cut B, and the laser nozzle A is moved to the material B to be cut while this position is maintained. Toward this, an assist suitable for irradiating pulsed laser light 7 having a peak output of 50% or more of the rated output of the laser oscillator 11 and a duty ratio of 50% or more and cutting the material B to be cut. By injecting the assist gas set to a pressure lower than the gas pressure and injecting the shield gas containing oxygen gas outside the assist gas, it is possible to form the pilot hole 9 having a good shape. .

  Then, after forming the pilot hole 9 as described above, the lens 2 is brought closer to the workpiece B, so that the position of the focal point S is changed from the bottom of the pilot hole 9 to the internal direction of the thickness of the workpiece B. It is possible to form the through-hole 8 continuously with the bottom of the pilot hole 9 by carrying out the piercing method according to the first embodiment while maintaining this state.

  And in the through-hole 8 formed as mentioned above, the diameter of the back surface side of the material to be cut B has a dimension required for continuous cutting, and smoothly shifts to cutting. It is possible.

  The laser cutting method of the present invention configured as described above is advantageous in that it is possible to prevent the occurrence of burning and perform smooth and stable cutting without actually measuring the temperature of the material to be cut.

A Laser nozzle B Material to be cut S Focus D, L Position of focus S Height of laser nozzle from the surface of the material to be cut 1 Nozzle 2 Lens 3 Optical axis 4 Shield gas nozzle 5, 6 Chamber 7 Laser light 8 Through hole 9 Pilot hole 11 Laser oscillator 12 Assist gas supply device 12a, 13a Hose 13 Shield gas supply device 14 Focus position adjustment device

Claims (3)

A laser piercing method in which a laser beam is irradiated from a laser nozzle toward a material to be cut and an assist gas made of oxygen gas is injected to form a through-hole in the thickness direction in the material to be cut. Is set to a position in the inner direction of the plate thickness of the material to be cut, and with this position held, the peak output is 50% or more of the rated output of the laser oscillator and the duty ratio from the laser nozzle toward the material to be cut Is irradiated with a pulsed laser beam set at 50% or more, and an assist gas set to a pressure lower than the pressure of the assist gas suitable for cutting the material to be cut is injected, and the outside of the assist gas A laser piercing method characterized by injecting a shielding gas containing oxygen gas into the substrate. A laser piercing method according to claim 1, wherein the laser piercing method according to claim 1 is applied to the prepared hole after forming a prepared hole that does not penetrate in the thickness direction in the workpiece. The pilot hole is set at a position where the focal point of the laser beam is separated from the surface of the material to be cut, and the peak output from the laser nozzle toward the material to be cut is maintained at this position. The assist gas set at a pressure lower than the pressure of the assist gas suitable for cutting the material to be cut is applied while irradiating the pulsed laser beam with the duty ratio set to 50% or more and 50% or more. 3. The laser piercing method according to claim 2, wherein the laser piercing method is formed by injecting a shielding gas containing oxygen gas outside the assist gas.

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