Laser beam machining method

Abstract: A laser machining apparatus adapted to apply a laser beam to a work and cut the same. The cutting of a work of a nonferrous metal is done efficiently and stably, and the cutting of even a work of a large thickness is also done. In a point A, a boring process is carried out under a machining condition A to form an arcuate portion (31). The machining condition is then switched to B, and an expansion treatment is carried out to form an expanded bore (32) in an extended form of the original arcuate portion (31). When the expansion treatment has completed in the position B, the stand-off (distance between the front end of a machining nozzle and the surface of the work) is set to a lowest possible level, and the machining condition is switched to C, under which a cutting process is started. Therefore, the cutting process is carried out in substantially the same manner as in a process in which the cutting of a work is started directly from the outer side of an end portion thereof. During the cutting process, the pressure of an assist gas is set high, and the stand-off small, so that the dross scattering effect by the assist gas is displayed more remarkably. Accordingly, a cutting process can be carried out efficiently and stably.

Description: The present invention relates to a laser beam machining method to execute a cutting operation by irradiating a laser beam to a workpiece, and in particular, to a laser beam machining method wherein the material of workpiece is made of aluminum, brass, stainless steel and alloys of those, and an inert gas other than oxygen or an air is used as an assist gas to execute a cutting operation. Background Art Recently, laser beam machines have been widely used for cutting a metal. In the case where the metal is made of nonferrous metals such as aluminum, brass, stainless steel, the machining condition for executing the cutting operation is modified when piercing is executed at the cutting start point, and when the cutting operation after that is executed. For example, an oxygen gas is used as an assist gas in piercing; on the other hand, an inert gas such as nitrogen gas is used as an assist gas in cutting. However, these nonferrous metals are made of materials which are very difficult to be cut for the following reasons. (1) These nonferrous metals have high reflectance with respect to a wavelength 10.6 µm of a carbon-dioxide laser beam; for this reason, piercing is difficult to be executed at the cutting start point. (2) It is difficult to readily remove dross (mass of melted metals) causing at the lower portion of the cutting groove in a cutting operation. (3) An inert gas or an air is used as an assist gas in the cutting operation; for this reason, the depth of the cutting groove becomes narrow. These disadvantages cause problems in that it is impossible to effectively and stably execute a cutting operation of nonferrous metals such as aluminum, and cutting defects occur frequently. For example, in the case where the cutting operation is executed by using a carbon-dioxide laser beam having an output of 3.0 KW, the limiting thickness, at which machining can be stably executed regardless of the kind of material, is about 5 mm. Particularly, the aforesaid cutting defective occurs frequently when the operation is transferred from piercing to cutting at the machining start point. The thicker the material is, the more remarkably the aforesaid tendency appears. This results from the following reasons; an inert gas or an air is mainly used as an assist gas in the cutting operation; for this reason, the cutting groove depth is narrow, and this influence is greatly shown when the operation is transferred from piercing to cutting. On the other hand, in the case where the cutting operation is started directly from the outer-side end of the workpiece without executing a piercing operation at the machining start point, it has been found from experience that a workpiece having considerable thickness can be stably cut. JP-A-230388 discloses a laser beam cutting method with variable machining speed. JP-A-61-219492 discloses a laser beam cutting method. The present invention has been made in view of such a situation. An object of the present invention is to provide a laser beam machining method to effectively and stably execute an operation of cutting nonferrous metals, such as aluminium, having a considerable thickness. To solve the above problems, the present invention provides a laser beam machining method of executing a cutting operation by irradiating a laser beam on a workpiece, the method comprising the steps of: executing a piercing operation at the machining start point of said cutting operation in accordance with a first machining condition: executing enlargement processing for enlarging a depth of a cutting groove directly after said piercing operation is completed in accordance with a second machining condition; and executing a cutting operation after said enlargement processing of said depth of the cutting groove is completed in accordance with a third machining condition. In an apparatus performing the invention, the piercing command means executes a piercing operation at the cutting start point according to the first machining condition. The enlargement processing command means executes the enlargement processing of the depth of the cutting groove directly after the piercing operation is executed, according to the second machining condition. The cutting command means executes the cutting operation after the enlargement processing of the depth of the cutting groove is completed, according to the third machining condition. In other words, the enlargement processing for enlarging the depth of the cutting groove is executed directly after the piercing operation is executed at the machining start point, and the cutting operation is started after the enlargement processing is completed. Therefore, the cutting operation is executed in the substantially same state as that in which a cutting operation is started directly from the outer-side end of the workpiece. Thus, the cutting operation can be executed effectively and stably, and workpieces having a considerable thickness can be readily cut, thereby a desired cutting being performed. In the drawings: Fig. 1 is a view showing a state in which the depth of a cutting groove is changed; Fig. 2 is a block diagram schematically showing a configuration of a laser beam machine according to the present invention; Fig. 3 is a view showing the procedures of cutting operation according to the present invention; Fig. 4 is a flowchart for executing the cutting operation according to the present invention; and Fig. 5 is a table showing machining conditions. Best Mode for Carrying Out the Invention One embodiment of the present invention will be described below with reference to the drawings. Fig. 2 is a block diagram schematically showing a configuration of a laser beam machine according to the present invention. In the figure, the laser beam machine comprises a CNC (Numerical Control Device) 1 and a machine body 2. The CNC 1, which is constituted as a processor being a main part, gives piercing, enlargement processing and cutting commands to the machine body 2, and controls an operation of the machine body 2. The details thereof will be described hereinafter. In the machine body 2, a laser beam 20 is emitted from a laser oscillator (not shown) in accordance with the command from the CNC 1. The laser beam 20 is irradiated to a workpiece 30 from a machining nozzle 22 through a machining head 21. An assist gas 23 from a gas bomb (not shown) is guided into the machining head 21 through a gas guiding inlet 24, and is then supplied from the machining nozzle 22 to the workpiece 30. On the surface of the workpiece 30, a thermal and chemical reaction is caused by the laser beam 20 and the assist gas 23, thereby a cutting operation on the workpiece 30 being performed. In this case, the workpiece 30 is made of nonferrous metals (such as aluminum, brass, stainless steel and alloys of those). Fig. 3 is a view showing the procedures of the cutting operation according to the present invention. In order to cut the workpiece 30, piercing is, first, executed at the a machining start point, namely a point A. Then, the enlargement processing is executed between the points A and B. The standoff L (distance from the tip of the machining nozzle 22 to the surface of the workpiece 30) at this point A and between the points A and B, is set to relatively long distance L1 (for example, 2 mm). On the other hand, standoff L at the point B is modified to a short distance L2 (for example, 0.5 mm) as much as possible, thus a cutting operation being started in a state in which the standoff L2 is kept. The aforesaid piercing at the point A, enlargement processing between the points A and B, and cutting after the point B are executed according to machining conditions A, B and C, respectively. The details of these machining conditions will be described hereinafter. Fig. 1 is a view showing a state in which the depth of the cutting groove is changed. In the figure, a cutting groove 300 is a machining groove viewing the workpiece 30 from the top. At the point A, piercing is executed according to the machining condition A, thus forming an arc-shaped portion 31. After this piercing is completed, the machining condition is changed to the machining condition B, and the enlargement processing is executed. As a result, an enlarged cutting groove 32, which has a shape such that the arc-shaped portion 31 is extended as it is, is formed. After the enlargement processing is completed at the point B, the standoff L is set to the shortest possible distance L2 while the machining condition is changed to the machining condition C, thus the cutting operation being started. At that time, the depth of a cutting groove 33 is decreased from the enlargement processing groove 32, and is kept constant. Fig. 4 shows a flowchart for executing the cutting operation according to the present invention. In the figure, numerals next to S denote step numbers. [S1] Piercing is executed at the point A. This piercing operation is executed according to the machining condition A previously stored in a memory 11. [S2] The piercing at the point A completes. The completion of the piercing is detected by counting time set in the machining condition A. Or, a sensor for detecting reflecting light is located at the point A, and the completion is detected according to a piercing completion signal fetched by means of the aforesaid sensor. [S3] The machining condition A is modified to the machining condition B at the point A. Incidentally, the machining condition B is previously stored in the memory 11 like the aforesaid machining condition A. [S4] The enlargement processing is executed according to the machining condition B as the machining head is moved from the point A to the point B. [S5] The enlargement processing is completed at the point B, and the machining condition B is modified to the machining condition C. Incidentally, the machining condition C is previously stored in the memory 11 like the aforesaid machining conditions A and B. [S6] The cutting operation is executed according to the machining condition C as the machining head is moved from the point B to the point C. Fig. 5 is a table showing machining conditions. In the table, the machining conditions A, B and C are set for every material and thickness of the workpiece 30. The machining condition A is composed of items such as a peak output S, frequency P and duty ratio Q, which are regarded as an output command value of laser beam, standoff L, assist gas pressure GP, kinds of assist gases GA and piercing preset time R. The machining condition B is composed of items such as a peak output S, frequency P and duty ratio Q, which are regarded as an output command value of laser beam, standoff L, assist gas pressure GP, kinds of assist gases GA, cutting speed F, and continuation distance or time H of enlargement processing. The machining condition C is composed of items such as a peak output S, frequency P and duty ratio Q, standoff L, assist gas pressure GP, kinds of assist gases GA, and cutting speed F. Here, the standoff L, assist gas pressure GP and kinds of assist gases GA of these items will be described below. The standoff L (in the machining conditions A and B) in piercing and enlargement processing, is set to a relatively long distance (2 mm), as described above. Oxygen is used as the assist gas 23, and its gas pressure GP is set to a low value (2 Kg/cm 2 ). As is clear from the above explanation, an oxygen gas is used in piercing and enlargement processing operations, so that the workpiece 30 can be readily melted. As a result, piercing and enlargement processing operations can be readily executed. In addition, the standoff L is made long, so that reflecting light and spatters (scattering melted metals) can be prevented from flowing into the machining head 21 from the machining nozzle 22, thereby a condensing lens located in the machining head 21 being protected. On the other hand, the standoff L (in the machining condition C) in the cutting operation is set to the shortest possible distance (0.5 mm). An inert gas such as nitrogen, or an air is used as the assist gas 23, and its gas pressure GP is set to a high pressure (6.0 to 9.9 Kg/cm 2 ). As described above, the assist gas pressure GP is highly set, and the standoff L is made short as much as possible, thereby an assist gas having sufficient amount and pressure being supplied to the cutting groove 33 on the workpiece 30. Therefore, dross caused in the cutting groove 33 in the cutting operation is scattered by the assist gas 23, so that machining quality on a cut section of the workpiece can be greatly improved. Such a dross scattering effect appears more remarkably because the assist gas pressure GP is set to a high value, and the standoff L is made short. As described above, in the case where a cutting operation is executed on nonferrous metals such as aluminum, the cutting operation is not executed at once after piercing at the machining start point (point A) is executed, but an enlargement processing for enlarging the depth of the cutting groove is once executed, and the cutting operation is started after the enlargement processing is completed. Therefore, the cutting operation is executed in the substantially same state as that in which a cutting operation is started directly from the outer-side end of the workpiece. In addition, in the case where the cutting operation is executed, the assist gas pressure GP is set to a high value, and the standoff L is set to a short value, so that a dross scattering effect by the assist gas appears more remarkably. Thus, the cutting operation can be executed effectively and stably. As a result, in the case where the cutting speed F is set to 250 mm/min, the allowable thickness of the workpiece 30, which is capable of executing machining operations from piercing to cutting without causing disadvantages, is 10 mm for aluminum, 8 mm for brass and 8 mm for stainless steel. Therefore, the cutting operation can be stably performed beyond the conventional limiting thickness 5 mm. As described above, according to the present invention, in the case where a cutting operation is executed on nonferrous metals such as aluminum, an enlargement processing for enlarging the depth of the cutting groove is executed directly after the piercing operation is executed at the machining start point, and the cutting operation is started after the enlargement processing is completed. Therefore, the cutting operation is executed in the substantially same state as that in which a cutting operation is started directly from the outer side of the end of workpiece. Thus, the cutting operation can be executed effectively and stably, and workpieces having a considerable thickness can be readily cut, thereby a desired cutting being performed.

Claims: A laser beam machining method of executing a cutting operation by irradiating a laser beam (20) on a workpiece (30), the method comprising the steps of: executing a piercing operation at the machining start point of said cutting operation in accordance with a first machining condition; executing enlargement processing for enlarging a depth of a cutting groove directly after said piercing operation is completed in accordance with a second machining condition; and executing a cutting operation after said enlargement processing of said depth of the cutting groove is completed in accordance with a third machining condition. A laser beam machining method according to claim 1, wherein said first machining condition is composed of output command values of said laser beam, standoff (L), the distance from the tip end (22) of a machining nozzle to the surface of said workpiece (30), kinds and pressure of assist gases (23), and a preset time. A laser beam machining method according to claim 1 or claim 2, wherein said second machining condition is composed of output command values for a laser beam standoff (L), kinds and pressure of assist gases (23), a cutting speed, and a position or preset time at which said second machining condition is modified to said third machining condition. A laser beam machining method according to claim 1, 2 or 3, wherein said third machining condition is composed of output command values of said laser beam, standoff (L), kinds and pressure of assist gases (23), and cutting speed. A laser beam machining method according to claim 4, wherein the standoff (L) in said third machining condition is set to a value smaller than the standoff in said first and second machining conditions. A laser beam machining method according to claim 4 or 5, wherein the assist gas (23) used in said first and second machining conditions is oxygen, and the assist gas used in said third machining condition is an inert gas or air.

Inventors: MORI ATSUSHI, NAKATA YOSHINORI, MORI, ATSUSHI, NAKATA, YOSHINORI, MORI, ATSUSHI FANUC DAI-3 VIRA-KARAMATSU, NAKATA, YOSHINORI FANUC MANSION HARIMOMI 4-206
Applicants: FANUC LTD, FANUC LTD.
Application year: 1993
Main classification: B23K26
IPC codes: B23K26