JPS6128437B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a laser processing method that prevents craters from occurring at the end of laser melting processing.

FIG. 1 shows a conventional laser processing device. In the figure, 1 is a controller for controlling laser output, 2 is a power supply, 3 is a laser oscillator, 4 is a laser beam, 5 is a total reflection mirror that changes the direction of the laser beam 4, 6 is a condenser lens, and 7 is a processing head. , 8 is a workpiece, and 9 is a processing table that supports and moves the workpiece 8.

Next, the operation will be explained. A laser beam 4 emitted from a laser oscillator 3 is bent by a total reflection mirror 5 and enters a condenser lens 6 perpendicularly. The beam focused by the condenser lens 6 passes through the processing head 7 and is irradiated onto the surface of the workpiece 8. at the same time,
A shielding gas is introduced into the processing head 7 and is emitted coaxially with the beam to perform processing. At the end of the irradiation with the laser beam 4, that is, at the end of the laser melting process, the controller 1 controls the power supply 2 to gradually lower the laser output. Although this had the effect of suppressing the remaining craters to some extent, it had the drawback that it could not completely eliminate them.

This phenomenon will be explained in detail with reference to FIGS. 2 and 3. The second is a characteristic diagram of the laser processing apparatus shown in FIG. 1, with the laser output plotted on the horizontal axis and the melting depth plotted on the vertical axis. As is clear from this figure, even if processing is performed by continuously decreasing the laser output, the melting depth does not become linear, but suddenly changes at a certain output, resulting in a transition point A. The reason for this is that when the power is greater than the point at which the transition point A occurs, melting proceeds in a perforation manner, whereas as the power becomes smaller, melting proceeds in a heat conduction manner. Therefore, when welding is performed by reducing only the laser output at the end of the welding, the state of the workpiece 8 will be as shown in FIGS. 3a and 3b. Figure 3a is a welded cross-sectional view of the workpiece, Figure 3b
shows a surface view of the welded part of the workpiece, and as is clear from this figure, even if processing is performed by continuously decreasing only the laser output, the fusion depth changes suddenly at the transition point A, resulting in a crater. C had occurred.

On the other hand, when the laser output is kept constant and only the focus position of the laser output is changed, the relationship between the focus position and the melting depth is shown in the characteristic diagram shown in Figure 4. It was found that transition point A occurs when Therefore, when melt processing is performed by changing only the focus position of the laser output at the end of processing, the state of the workpiece is as follows.
It will look like Figures a and b. Figure 5a is a welded sectional view of the workpiece, Figure 5b is a surface view of the welded part of the workpiece,
FIG. 5c is a diagram showing the relationship between the focal position of the laser output and the processed surface. As is clear from Fig. 5, even if processing is performed by keeping the laser output constant and changing only the focal point position, the melt depth will suddenly change at the transition point A, resulting in the formation of a crater C. .

This invention eliminates the drawbacks of the above,
At the end of processing, the laser beam output on the workpiece surface is continuously reduced and the beam is continuously defocused, so that the melting depth gradually and stably becomes shallower to prevent craters from forming. The purpose of the present invention is to provide a laser processing device with

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 6, reference numeral 10 denotes a drive mechanism that incorporates a condensing lens 6 and drives the processing head 7 along an axis (Z-axis) perpendicular to the workpiece 8 and the processing table 9. The processing head and condensing lens are driven by a pulse motor using control signals from 11 controllers. Other structures are the same as before. When the melting process is completed, this drive mechanism operates according to instructions from the controller 11, and the distance between the focal position of the laser beam and the surface of the workpiece is gradually changed, and when the power density has sufficiently decreased, the drive mechanism is activated. The laser beam is stopped by operating the power source 2.

The operation at the end of irradiation with the laser beam 4 in the above configuration, that is, at the end of the laser melting process will be described with reference to FIG. At the end of processing, the laser output is continuously and gradually reduced by controlling the power supply 2 by the controller 11 as in the conventional case. In this case, the beam power may be reduced continuously in the stabilization region. As the laser output decreases, the melting depth gradually becomes shallower linearly up to region a, as shown by the solid line. However, if the laser output continues to decrease, a transition point A will occur at the melting depth as shown by the broken line as explained in Figure 2, but in this invention, the beam output is still large before the transition point occurs. At the same time, the laser beam is continuously defocused to lower the power intensity. Therefore, in region b where a reduction in laser output and defocusing are used together, the power density (power intensity) on the workpiece surface is lower than when no defocusing is used, and the fusion depth is shallower than before. Therefore, even in a region where the laser output is small, the shape becomes a straight line as shown by the solid line, and the melting depth at the end of processing becomes a single straight line as a whole.

In the above explanation, the beam defocus point is defined as the moment when the beam output is reduced to a certain extent just before the transition point occurs, but even if the defocus starts at the same time as the beam output starts to decrease, that is, the whole areas a and b Even after defocusing, the melting depth remains in the same straight line.

Also, when the beam is defocused, the cross-sectional area of the beam becomes wider, so the heat-affected zone on the workpiece 8 may also become wider, but when the beam is defocused, the power supply control reduces the beam output. The impact is small.

FIG. 8 shows the state of the workpiece 8 when melt-processed by the method of the present invention, and FIG.
8b shows a welded cross-sectional view of the workpiece, and FIG. 8b shows a surface view of the welded part of the workpiece. As is clear from this figure, when reducing the laser output and changing the focal position, there is no transition point in the middle at the end of welding, so the fusion depth is continuous and smooth, and no craters occur. confirmed.

As described above, in the present invention, the laser beam output is continuously decreased at the end of processing, and the focal position of the laser beam and the relative position of the surface of the workpiece are continuously moved away from each other. Therefore, it is possible to perform high-quality machining without creating a crater at the end of machining.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram showing a conventional laser processing device.
Figure 2 is a processing characteristic diagram of the apparatus shown in Figure 1, Figures 3a and b are welded cross-sectional views and welded part surface views of the workpiece processed by the apparatus shown in Figure 1, and Figure 4. 5 is a processing characteristic diagram when only the focal position of the laser output is changed, and FIGS. FIG. 3 is a partial surface view and a relationship diagram between the focal position and the processed surface. FIG. 6 is a block diagram of a laser processing device according to an embodiment of the present invention, FIG. 7 is a processing characteristic diagram of the device shown in FIG. 6, and FIGS. 8a and b
7 is a welded cross-sectional view and a welded part surface view of a workpiece processed by the apparatus shown in FIG. 6. FIG. In the figure, 1 is a controller that controls laser output, 2 is a power supply, 3 is a laser oscillator,
4 is a laser beam, 5 is a total reflection mirror, 6 is a condenser lens, 7 is a processing head, 8 is a workpiece, 9 is a processing table, 10 is a drive mechanism for the processing head or lens (with built-in pulse motor), 11 is a This is a controller that controls the laser output and drive mechanisms such as the processing head. In addition, in the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. In processing in which a workpiece is irradiated with a laser beam and melted, the laser beam output is continuously decreased when the laser beam irradiation is stopped, and the relative position of the focus position of the laser beam and the surface of the workpiece is A laser processing method characterized by moving the position in a continuous direction.