JP2019188403A - Laser cutting method - Google Patents

Abstract

To provide a laser cutting method in which occurence of self burning can be suppressed regardless of a condition for cutting a material to be cut.SOLUTION: When cutting a material to be cut made of iron-based metal by irradiating laser light to and jetting assist gas composed mainly of oxygen gas to the material together with the laser light, and further jetting shield gas composed mainly of oxygen gas to the material along the assist gas, the material is cut while decreasing oxygen concentrations of the assist gas and oxygen concentrations of the shield gas to suppress oxidation reaction.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a laser cutting method capable of suppressing the occurrence of self-burning regardless of the cutting conditions of the material to be cut when laser cutting toward the material to be cut made of an iron-based metal. is there.

  A laser that irradiates a laser beam toward a workpiece made of metal, injects an assist gas made of oxygen gas along with the laser beam, and further injects a shield gas along the assist gas to cut the workpiece. The cutting method is widely adopted.

  When the material to be cut is an iron-based metal, a reaction called self-burning, in which the base material melts and oxidizes around the irradiated portion of the laser beam, may occur. When this self-burning occurs, the cutting site is eroded or a deep groove called a notch is formed on the cut surface, leading to a reduction in cutting quality. For this reason, a laser cutting method that prevents the occurrence of self-burning has been proposed (see, for example, Patent Document 1).

  In the invention described in Patent Document 1, a high-concentration gas having a high oxygen concentration is ejected from at least one nozzle port to form an air flow around the laser beam, and a low-concentration gas having a low oxygen concentration is generated from another nozzle port. By adjusting the oxygen concentration distribution in the range of several millimeters from the cutting point with the air flow formed by jetting, a high oxygen concentration is secured near the cutting point, and the oxygen concentration behind the cutting progress direction is lowered from the cutting point. It is a thing. In this invention, the adverse effect on the cut surface due to self-burning can be prevented by reducing the oxygen concentration behind the cutting direction in the cutting direction.

Japanese Patent No. 4183379

  In the invention described in Patent Document 1, self-burning can be prevented. However, there is a problem that the self-burning occurrence point is not necessarily limited to the rear side in the cutting progress direction.

  For example, when cutting steel materials such as rolled steel for welded structures (SM material) and rolled steel for building structures (SN material), for example, a surface state in which rust or oxide film (black skin) exists. When cutting a steel material that has deteriorated, when cutting a steel material with a rust-proof coating on the surface, or when cutting the tilting torch with respect to the steel material, such as groove cutting, the direction of cutting progress Regardless, there is a problem that self-burning occurs.

  An object of the present invention is to provide a laser cutting method capable of suppressing the occurrence of self-burning regardless of the cutting conditions of a material to be cut.

  The inventors have continuously studied self-burning that occurs when laser cutting is performed on a steel sheet, and have developed a method for preventing or suppressing the occurrence of self-burning. As a result, it has been found that the generation situation varies depending on conditions such as the material of the material to be cut, the surface properties, and the thickness.

  For example, when cutting a steel sheet with inferior cutting properties such as SM material or SN material, it is necessary to reduce the cutting speed, and it has been found that self-burning is likely to occur.

  In addition, when a scale such as rust or black skin (hereinafter referred to as “scale”) is present on the surface of the steel plate, the scale peeled off from the base material preferentially causes an oxidation reaction, which causes self-burning. It has been found.

  Also, if the surface is coated with a rust-proof paint such as zinc rich primer, or if the cutting load is large, such as cutting thick plates, the cutting speed will decrease, the assist gas flow will increase, and the laser light output will increase. It is necessary to select a single condition or a plurality of conditions simultaneously. For this reason, the amount of heat input to the material to be cut increases, and it has been found that self-burning is likely to occur due to the vicinity of the laser light irradiation region rising to the combustion temperature.

  In addition, when cutting with a cutting torch inclined as in groove cutting, the laser light irradiation surface becomes elliptical, so the energy absorption rate differs around the laser light irradiation point on the material to be cut. It was found that self-burning is likely to occur.

  As a result of the above findings, a typical laser cutting method according to the present invention irradiates a workpiece made of an iron-based metal with a laser beam and adds an assist gas containing oxygen gas as a main component along with the laser beam. In addition, when the shielding gas mainly composed of oxygen gas is injected along the assist gas and cut, the oxygen concentration of the assist gas and the oxygen concentration of the shielding gas are reduced to suppress the oxidation reaction. It cut | disconnects, characterizing.

  The laser cutting method according to the present invention reduces the oxygen concentration of the assist gas injected along with the laser beam and the shield gas injected along the assist gas, thereby oxidizing the material to be cut. The reaction can be suppressed. For this reason, the occurrence of self-burning can be suppressed.

It is a figure explaining the structure of the laser nozzle at the time of implementing the laser cutting method which concerns on this invention. It is a figure explaining the structure of the supply system of assist gas and shield gas.

  Hereinafter, the laser cutting method according to the present invention will be described. The laser cutting method according to the present invention irradiates a material to be cut (hereinafter referred to as “steel plate”) made of an iron-based metal with a laser beam and injects an assist gas mainly containing an oxygen gas along with the laser beam, Further, when the shield gas is injected along the assist gas, the oxygen concentration of the assist gas and the shield gas is reduced.

  Thus, it becomes possible to suppress the oxidation reaction of the base material of the steel sheet by reducing the oxygen concentration of the assist gas and the shield gas, and as a result, it is possible to suppress the occurrence of self-burning.

  In the present invention, the wavelength of the laser beam is not limited, and can be applied to a laser beam in a range of 1.070 μm to 10.600 μm that is generally used at present.

  In the present invention, the oxygen concentration range of the assist gas is not limited. That is, the lower limit of the oxygen concentration of the assist gas is a value at which the laser cutting can be stably continued and the quality of the cut surface can be maintained. Further, the limit of the assist gas having a higher oxygen concentration is a value capable of suppressing the occurrence of self-burning.

  The relationship between the frequency of self-burning and the oxygen concentration of the assist gas depends on the cutting conditions such as the material of the steel sheet, the surface condition of the steel sheet, the groove angle when the steel sheet is grooved, and the thickness of the steel sheet. Change. For this reason, it is preferable that the oxygen concentration of the assist gas is appropriately set according to the cutting conditions in the target steel sheet.

  When the inventors conducted a cutting experiment corresponding to each of the above conditions, when the oxygen concentration of the assist gas is lower than 95%, self-burning does not occur, but the cutting speed is reduced, and the cutting surface quality is reduced. Adverse effects such as deterioration occurred. When the oxygen concentration of the assist gas was 99.5%, both the cutting speed and the cut surface quality were substantially good, and the occurrence frequency of self-burning could be suppressed. Further, when the oxygen concentration of the assist gas was 99.7%, self-burning frequently occurred although the cutting speed and the quality of the cut surface were both good.

  From the above results, in order to eliminate the occurrence of self-burning, ensure the cutting speed and ensure the cut surface quality in a substantially good state, the lower limit of the assist gas oxygen concentration is approximately 95%. Further, in order to suppress the occurrence of self-burning to ensure the cutting speed and to ensure a good quality of the cut surface, the limit of the assist gas having a higher oxygen concentration is approximately 99.5%. From these facts, it can be said that the oxygen concentration of the assist gas is in the range of about 95% to about 99.5%.

  In the present invention, the oxygen concentration of the shield gas is lowered while the oxygen concentration of the assist gas is lowered. The shield gas is injected along the assist gas so as to wrap around the assist gas. For this reason, the spray area when the shield gas is sprayed onto the surface of the steel sheet is wider than the assist gas. Therefore, the influence on the scale existing on the surface of the steel plate is increased.

  That is, the scale adhering to the surface of the steel sheet peels from the base material as the cutting progresses. Since the peeled scale existing on the surface of the base material has a small heat capacity, the temperature rises quickly and reaches the ignition point. For this reason, an oxidation reaction is caused by the oxygen gas which is the main component of the shield gas. In this way, the scale existing on the surface of the steel plate becomes the starting point of self-burning.

  For this reason, in the present invention, in addition to reducing the oxygen concentration of the assist gas, the oxygen concentration of the shield gas is also reduced, thereby suppressing the occurrence of self-burning. The oxygen concentration of the shield gas is not particularly limited, but is preferably lower than the oxygen concentration of the assist gas. That is, when the oxygen concentration of the shield gas is higher than the oxygen concentration of the assist gas, there is a risk that self-burning due to the shield gas may occur despite the fact that the cutting performance is reduced as the oxygen concentration of the assist gas decreases. Will increase.

  In the experiments by the present inventors, the oxygen concentration of the shield gas is in the range of about 50% to about 98%, and is lower than the oxygen concentration of the assist gas. It was possible to suppress the occurrence of self-burning due to gas.

  The type of gas mixed when the oxygen concentration of the assist gas or shield gas is reduced is not limited, and a gas such as nitrogen gas, argon gas, or air can be used. However, other gases may be used. For example, hydrogen gas, helium gas, krypton gas, or the like can be used. In particular, when helium gas is used as the gas for reducing the oxygen concentration, it is possible to reduce the generated fumes.

  In order to reduce the oxygen concentration of the assist gas and the shield gas, it is possible to use one kind of gas selected from the above gases or a gas in which a plurality of gases are mixed. Then, the assist gas and the shield gas can be reduced to the target oxygen concentration by mixing the gas with a high concentration oxygen gas by a predetermined amount.

  Further, the process for producing the assist gas and shield gas with reduced oxygen concentration is not limited. For example, the assist gas and shield gas adjusted to the target oxygen concentration in advance may be supplied to the laser cutting torch. Further, the oxygen concentration may be lowered by the supply system of the assist gas and the shield gas.

  In addition, the assist gas passage and the shield gas passage are communicated inside the laser nozzle, and the shield gas with reduced oxygen concentration is mixed with the assist gas that does not reduce the oxygen concentration, or the shield gas diffuses into the assist gas. By doing so, the oxygen concentration of the assist gas may be lowered. Furthermore, the shield gas passage and the atmosphere may be communicated, and the atmosphere may be mixed with or diffused in the shield gas to reduce the oxygen concentration of the shield gas.

  Next, an example of a laser nozzle that can be used when performing the laser cutting method according to the present invention will be described.

  A laser nozzle A shown in FIG. 1 is attached to a laser head (not shown), irradiates a laser beam oscillated from a laser oscillator toward a material to be cut, and injects an assist gas, and a shield gas along the assist gas. It is comprised so that can be injected.

  The laser nozzle A has an inner nozzle 1 and an outer nozzle 2. The inner nozzle 1 and the outer nozzle 2 are formed integrally, a shield gas passage 3 is formed between the nozzles 1 and 2, and a ring-like injection port 3 a for injecting the shield gas to the tip of the passage 3. Is configured.

  In the center of the inner nozzle 1, an injection hole 4 for injecting laser light and assist gas is formed. A plurality of communication holes 5 are formed in the body portion 1 a of the inner nozzle 1, and the injection holes 4 and the shield gas passages 3 communicate with each other through the communication holes 5.

  By forming the communication hole 5 communicating with the shield gas passage 3 in the inner nozzle 1, the shield gas flowing through the passage 3 diffuses into the assist gas as the assist gas is injected. For this reason, when an assist gas that does not reduce the oxygen concentration and a shield gas with a reduced oxygen concentration are supplied, the shield gas diffuses into the assist gas, thereby reducing the oxygen concentration of the assist gas. It becomes.

  The outer nozzle 2 is formed with a plurality of holes 6 penetrating along the axis, and the shield gas passage of the laser head and the passage 3 can be communicated with each other through the holes 6.

  A through hole 7 penetrating through the wall surface of the cylindrical portion 2a is formed in the cylindrical portion 2a formed on the lower end side of the outer nozzle 2. The through hole 7 is formed close to the lower end side of the outer nozzle 2. By forming the through hole 7 in such a part, when the laser gas is cut to the steel plate, the shield gas is supplied from the passage 3 when the shield gas does not pass to the back side of the steel plate for some reason. Shielding gas can be simultaneously injected from the injection port 3a and the through hole 7 to prevent spattering.

  Further, when the shield gas is supplied to the shield gas passage 3, a suction effect is generated in the through hole 7, and the atmosphere is sucked from the through hole 7 and injected from the injection port 3 a together with the shield gas. For this reason, even if a shielding gas that does not lower the oxygen concentration is supplied, the shielding gas has a reduced oxygen concentration.

  The laser cutting method according to the present invention is not limited to using the laser nozzle A configured as described above. That is, the laser cutting method according to the present invention can be applied to a laser nozzle that is capable of injecting an assist gas in addition to a laser beam that is generally used at present and injecting a shield gas along the assist gas. Is possible.

  Next, an example of a supply system that reduces the oxygen concentration of the assist gas and the shield gas that can be used when the laser cutting method according to the present invention is performed will be described.

  As shown in the figure, oxygen gas pipes 11a and 12a and, for example, nitrogen gas pipes 11b and 12b for reducing the oxygen concentration are connected to the assist gas supply pipe 11 and the shield gas supply pipe 12, respectively. . Mass flow controllers 13a and 14a and check valves 15a and 16a are arranged in the oxygen gas pipes 11a and 12a, respectively, and an oxygen supply source 17 such as an oxygen gas cylinder or a factory pipe is connected thereto. Further, mass flow controllers 13b and 14b and check valves 15b and 16ba are arranged in the nitrogen gas pipes 11b and 12b, respectively, and a nitrogen supply source 18 such as a nitrogen gas cylinder or a factory pipe is connected thereto.

  In the supply system configured as described above, the flow rate of oxygen gas corresponding to the oxygen concentration of the assist gas and the oxygen concentration of the shield gas set in advance corresponding to the cutting conditions of the steel plate is set in each mass flow controller 13a, 14a. At the same time, the flow rate of nitrogen gas is set in each mass flow controller 13b, 14b.

  And by supplying oxygen gas and nitrogen gas from the oxygen supply source 17 and the nitrogen supply source 18, each gas is the assist gas piping 11 and shield gas piping by the flow volume set to each mass flow controller 13a, 14a, 13b, 14b. 12 is supplied. And the assist gas with which oxygen concentration fell is injected from the injection hole 4 of the laser nozzle A, and the shield gas of oxygen concentration lower than the oxygen concentration of assist gas is injected from the injection port 3a.

  By using the gas supply system configured as described above, it is possible to obtain the assist gas and shield gas having the optimum oxygen concentration corresponding to the cutting conditions of the steel sheet when cutting the target steel sheet. . However, it is natural that the laser cutting method according to the present invention is not limited to using the gas supply system described above.

  In the laser cutting method according to the present invention, it is possible to suppress the occurrence of self-burning in accordance with the cutting conditions such as the material and the surface state, which is advantageous when used for cutting a steel sheet.

A Laser nozzle 1 Inner nozzle 2 Outer nozzle 3 Passage 3a Injection port 4 Injection hole 5 Communication hole 6 Hole 7 Through hole 11, 12 Supply piping 11a, 12a Oxygen gas piping 11b, 12b Nitrogen gas piping 13a, 13b, 14a, 14b
Mass flow controller 15a, 15b, 16a, 16b
Check valve 17 Oxygen source 18 Nitrogen source

Claims (2)

  A material to be cut made of an iron-based metal is irradiated with laser light, an assist gas mainly containing oxygen gas is injected along with the laser light, and oxygen gas is mainly contained along the assist gas. A laser cutting method characterized in that when the shielding gas to be cut is injected and cut, the oxygen concentration of the assist gas and the oxygen concentration of the shielding gas are lowered to cut while suppressing the oxidation reaction.   The laser cutting method according to claim 1, wherein the oxygen concentration of the shielding gas is lower than the oxygen concentration of the assist gas.

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