LASER MACHINING APPARATUS

Abstract: A laser machining apparatus adapted to carry out a cutting process by applying a laser beam to a work. During the cutting of a work with a laser beam applied thereto, a corner portion is cut stably and reliably under actually effective machining conditions. The machining route (path) according to a program which is being executed currently is judged for its conformity with a corner portion, i.e. a point B (step S1), and, if it conforms, a cutting operation is carried out in a stepped manner in accordance with a machining condition M stored in a RAM 3 in advance (step S2). When the machining condition has reached the corner portion, i.e. the point B, it is set to a lower level or a level of zero, and then increased in a stepped manner up to normal machining conditions Mo with the machining position (time). When the cutting operation at the corner portion in the point B is completed, a normal cutting operation is carried out under the constant machining condition Mo (step S3). Accordingly, the cutting of the corner portion in the point B can be done stably and reliably under actually effective machining conditions.

Description: Technical Field The present invention relates to a laser beam machine for irradiating a laser beam onto a workpiece to cut the same, and more particularly, to a laser beam machine for cutting corners under predetermined machining conditions. Background Art When cutting a cornered shape by means of a laser beam, situations are likely to arise where a corner is melted and thus lost due to heat. To avoid such situations, various methods for achieving stable corner cutting have been proposed and implemented. FIGS. 5(a) and 5(b) illustrate conventional corner cutting methods, wherein FIG. 5(a) shows a cutting path, and FIGS. 5(b), 5(c) and 5(d) each show a machining condition pattern. As shown in FIG. 5(a), the machining path extends from a point A to a point C via a corner B, and corner cutting is carried out at the point B. In FIGS. 5(b), 5(c) and 5(d), the axis of ordinate indicates machining condition M1, and the axis of abscissa indicates machining position or machining time. The machining condition M1 comprises a cutting speed F, and laser beam output command values including a peak output S, a frequency P and a duty factor Q. In the machining method shown in FIG. 5(b), the machining condition M1 is changed at the corner B through a feedback of an actual movement of a workpiece, i.e., an actual speed at which a table is actuated. In this method, the time constant of actual acceleration/deceleration of the table is set to a value small enough to improve the shaping accuracy, and even if the machining condition M1 is controlled only for a time period involving the cutting of the corner B, there is almost no difference between the controlled machining and the uncontrolled machining. Thus, no practical effects are obtained. In the machining method shown in FIG. 5(c), the laser output is interrupted at the corner B, in order to reduce the influence of heat at the corner B, and after a natural or forced cooling for a fixed period of time, the subsequent machining is started. In this method, the laser output must be stopped for a considerably long time to achieve sufficient cooling at the corner B. The machining method shown in FIG. 5(d) is a combination of the methods shown in FIGS. 5(b) and 5(c), and has the problems associated with these methods (b) and (c). As described above, the prior art methods fail to provide a stable and reliable technique for machining corners. This is because the prior art techniques are focused on optimum machining condition settings for the cutting speed (FIGS. 5(b) and 5(d)) or on the elimination of concentration of heat (FIGS. 5(c) and 5(d)), and are unable to provide practical effects or require an excessively long machining time. JP-A-61-189893 discloses a laser beam machine according to the preamble of claim 1, with corner detection and compensation. The present invention was created in view of the above circumstances, and an object thereof is to provide a laser beam machine capable of carrying out stable and reliable corner cutting under machining conditions that provide practical effects. To achieve the above object, the present invention provides a laser beam machine for irradiating a laser beam onto a workpiece, to cut the same, the machine comprising: machining shape determining means for reading a machining program and determining whether a shape to be machined is a corner; and machining command means for instructing a stepwise machining condition which includes a cutting speed, to cut the workpiece according to the stepwise machining condition after the corner is cut, characterized in that said machining command means for instructing the stepwise machining condition which includes the cutting speed, includes also a peak output, a duty factor and a frequency for the laser beam, and a distance or time of continuance of the machining condition when the shape to be machined is the corner, to cut the workpiece according to the stepwise machining condition on and after the corner is cut. When cutting a workpiece along a machining path having a corner, the cutting process for a path portion following the corner is carried out in accordance with a machining condition which varies stepwise. According to this stepwise-varying machining condition, the machining condition is not modified in a region where practical effects are not obtained, e.g., before the corner is reached, and is modified only in a region where practical effects are obtained, i.e., after the corner is passed. Accordingly, dissipation and concentration of heat can be optimized at the corner where the influence of heat is great. That is, it is possible to carry out stable and reliable cutting of corners according to the machining condition that provides practical effects. Brief Description of the Drawings FIG. 1 is a flowchart illustrating a cutting process executed according to the present invention; FIG. 2 is a block diagram of a laser beam machine according to the present invention; FIGS. 3(a) and 3(b) illustrate a machining condition for corner cutting according to the present invention, wherein FIG. 3(a) shows a machining path, and FIG. 3(b) shows a machining condition pattern; FIG. 4 is a chart illustrating machining conditions; and FIGS. 5(a), 5(b), 5(c) and 5(d) illustrate conventional corner cutting methods, wherein FIG. 5(a) shows a machining path, and FIGS. 5(b), 5(c) and 5(d) each show a machining condition pattern. Best Mode of Carrying Out the Invention An embodiment of the present invention will be now described with reference to the drawings. FIG. 2 is a block diagram of a laser beam machine according to the present invention. A processor 1 reads a machining program stored in a RAM 3, in accordance with a control program stored in a ROM 2, and globally controls the operation of the laser beam machine. An I/O unit 4 converts control signals from the processor 1 and supplies the converted signals to a laser oscillator 5. The laser oscillator 5 emits a pulsed laser beam 6 in accordance with the converted control signals. The laser beam 6 is reflected at a bending mirror 7 and enters a machine body 8. The machine body 8 comprises a table 10 on which a workpiece 9 is fixed, and a machining head 11 for irradiating the laser beam onto the workpiece 9. The laser beam 6 introduced into the machining head 11 is converged by a nozzle 11a and is irradiated onto the workpiece 9. The machine body 8 is also provided with servomotors 12 and 13 for moving the table 10 in directions along X and Y axes. The servomotors 12 and 13 are connected to servo amplifiers 15 and 16, respectively, and their rotations are controlled in accordance with axis control signals from the processor 1. The machining position of the workpiece 9 and a cutting speed F are controlled through the rotation control of the servomotors. A machining condition for a cutting process executed by the laser beam machine constructed as above will be now described. FIG. 3 illustrates the machining condition for a corner cutting according to the present invention, wherein FIG. 3(a) shows a machining path, and FIG. 3(b) shows a machining condition pattern. As shown in FIG. 3(a), the machining path extends from a point A to a point C via a corner B, and corner cutting is effected at the point B. In FIG. 3(b), the axis of ordinate indicates a machining condition M, and the axis of abscissa indicates the machining position or machining time. The machining condition M comprises the cutting speed F, laser beam output command values including a peak output S, a frequency P and a duty factor Q, and a distance or time K of continuance of the machining condition. As shown in FIG. 3(b), the machining condition M composed of these factors is maintained at a normal machining condition M 0 before the corner B is reached, and is once reduced to a low level or "0" when the corner B is reached. After the corner B is passed, the machining condition is increased stepwise up to the normal machining condition M 0 with distance from the point B (with lapse of time). FIG. 1 is a flowchart of a cutting process according to the present invention, and in the figure, numbers following "S" represent step numbers. [S1] It is determined whether the machining (cutting) along the path according to a currently executed machining program has advanced to the corner B. If the corner B is reached, the program proceeds to Step S2, and if not, the program proceeds to Step S3. This determination is made based on machining program path data D stored in the RAM 3. [S2] Cutting is carried out in accordance with the stepwise-varying machining condition previously stored in the RAM 3. Specifically, the machining condition is once reduced to a low level or "0" when the corner B is reached, and is thereafter increased stepwise up to the normal machining condition M 0 with distance from the point B (with time). [S3] Normal cutting is carried out in accordance with the machining condition M 0 . FIG. 4 illustrates machining conditions. As illustrated, a plurality of machining conditions M are set according to machining condition numbers, i.e., the material or thickness of a workpiece. As mentioned above, each machining condition M is composed of the cutting speed F, the output command values for the laser beam 6 including the peak output S, frequency P and duty factor Q, and the distance or time K of continuance of the machining condition (the distance or time of continuance of each step), and these factors increase stepwise from step 1 to step n. In the embodiment described above, when the workpiece 9 is cut along the machining path having the corner B, the cutting process for a path portion following the corner B is carried out in accordance with the machining condition M which increases stepwise. According to this stepwise-increasing machining condition M, the machining condition is not modified in a region where practical effects are not obtained, e.g. before the corner B is reached, and is modified only in a region where practical effects are obtained, i.e., after the corner B is passed. Accordingly, dissipation and concentration of heat can be optimized at the corner B where the influence of heat is great. In other words, it is possible to carry out stable and reliable cutting of the corner B according to the machining condition that provides practical effects.

Claims: A laser beam machine for irradiating a laser beam (6) onto a workpiece (9), to cut the same, the machine comprising: machining shape determining means (1) for reading a machining program and determining whether a shape to be machined is a corner; and machining command means (1) for instructing a stepwise machining condition which includes a cutting speed, to cut the workpiece (9) according to the stepwise machining condition after the corner is cut, characterized in that said machining command means (1) for instructing the stepwise machining condition which includes the cutting speed, includes also a peak output, a duty factor and a frequency for the laser beam (6), and a distance or time of continuance of the machining condition when the shape to be machined is the corner, to cut the workpiece (9) according to the stepwise machining condition on and after the corner is cut. The laser beam machine according to claim 1, wherein the stepwise machining condition is reduced to a low level or zero when the corner is reached, and is thereafter increased stepwise.

Inventors: NAKATA YOSHINORI, OHARA KAZUKI, NAKATA, YOSHINORI, OHARA, KAZUKI, NAKATA, YOSHINORI FANUC MANSION HARIMOMI 4-206, OHARA, Kazuki Fanuc Dai-3 Villa-karamatsu
Applicants: FANUC LTD, FANUC LTD.
Application year: 1993
Main classification: B23K26
IPC codes: B23K26