Electric heating – Metal heating – By arc
Patent
1989-09-06
1991-04-30
Albritton, C. L.
Electric heating
Metal heating
By arc
36447408, B23K 2600
Patent
active
050120697
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a power control method in a CNC (computerized numerical control) laser machining system, and more particularly to such a method in which an improvement is made in the machining of a corner portion.
BACKGROUND ART
Laser machining apparatuses are extensively used in conjuction with a numerical control apparatus, because a workpiece can be machined thereby to form a complex shape at a high speed. In a conventional laser machining apparatus, a direction in which a laser beam is moved must be reversed while temporarily making a speed of the laser beam relative to the workpiece zero when the workpiece is machined to form a corner portion or an acute angle edge portion. That is, when machining the corner portion, the moving speed of the laser beam is decelerated, stopped, and then accelerated.
FIG. 5 illustrates a workpiece 40 machined by the laser beam to form a groove 41. To form the groove as illustrated, the laser beam is moved relative to the workpiece 40 in the direction indicated by an arrow A. Before reaching a corner portion 42, the speed at which the laser beam is moved is decelerated, the beam is temporarily stopped at the corner portion 42, and the beam is then accelerated after passing the corner portion 42. In this manner, the speed of the laser beam relative to the workpiece 40 is reduced when the laser beam passes through the corner portion 42. Therefore, a defective melting occurs in the corner portion due to a storage of thermal energy and excessive heat absorption when the machining is performed under not only a CW beam condition but also a pulsed beam condition. Thus the cutting accuracy and the quality of the final product are greatly reduced.
FIG. 6 is an enlargement of the corner portion shown in FIG. 5, in which the corner portion of the groove machined by the laser beam is illustrated in detail. Portions B and C indicated by oblique lines alongside of the corner portion are melted down due to the lowering of the relative speed of the laser beam, whereby the machining accuracy is lowered. Further, the thermally influenced regions are extended to portions D and E, to thereby exert adverse influence upon the material of the workpiece and increase the surface roughness of the engraved surface.
As a solution, the machining of the corner portion can be controlled in such a manner that a pulse duty ratio is lowered in accordance with to the lowering of the speed at which the laser beam is moved, to thereby reduce the laser output. This method is not satisfactory, however, in that a dross-free machining cannot be accomplished over an extensive region.
SUMMARY OF THE INVENTION
The present invention has been created in view of the foregoing circumstances, and an object of the invention is to provide a power control method in a CNC laser machining system in which an improvement is made in the machining of a corner portion.
To achieve the above and other objects, there is provided a power control method in a CNC laser machining system including a CNC apparatus and a laser machining apparatus for machining a workpiece, the method comprising the step of: lowering an output power of a laser beam by reducing both a pulse duty ratio and a pulse frequency when the machining velocity is lowered.
As will be described later, when machining a corner portion, the regions in which an excessive melting loss does not occur are limited, even if the pulse duty ratio is reduced in accordance with to the lowering of the machining velocity. Experimental results have proved that such regions are enlarged if the pulse frequency is varied. Therefore, according to the method of the present invention, not only the pulse duty ratio but also the pulse frequency is reduced in accordance with to the lowering of the machining velocity, whereby desirable machining results can be obtained over the entire region along which the machining velocity is varied.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram showing a CNC laser machining apparatus used in the presen
REFERENCES:
patent: 4638145 (1987-01-01), Sakuma et al.
patent: 4758705 (1988-07-01), Hertzel et al.
patent: 4937422 (1990-06-01), Nagamine et al.
Albritton C. L.
Fanuc Ltd.
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