JPH0471796A - Laser beam cutting method - Google Patents

Abstract

PURPOSE:To obtain the same machining speed as at the time of machining continuously even if a laser beam is not emitted continuously and to perform laser beam machining with little streaks by regulating a duty ratio of an output pulse of the laser beam to a specific ratio and setting frequency of the output pulse above specific Hz. CONSTITUTION:The oxidation reaction temperature at a workpiece is raised and the extension region of the oxidation reaction temperature is reduced by regulating the duty ratio of the output pulse of the laser beam to <=70% (except zero) and setting the frequency of the output pulse above 1,000Hz. Accordingly, for instance, a pitch interval of a cut plane is made to <=0.18mm and roughness of the cut plane can be improved and the effect that the need for finish machining is eliminated is obtained. The effect of pulse cutting according to the invention can be also applied to metal and nonmetal in addition to aluminum, stainless steel, titanium, high carbon steel, etc., except mild steel material. In addition, in a pulse oscillator having the same pulse peak value and average value, the power of a power source and the strength of an electrode are increased and the frequency and duty ratio of this invention can be used.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] This invention relates to a laser cutting method, and more particularly to a laser cutting method that improves the roughness of a cut surface by controlling the duty ratio and frequency of a laser beam.

[Conventional technology] In conventional laser processing, when cutting a thick plate of mild steel at high speed, the output form of the laser beam is C, which is emitted continuously over time.
W (continuous wave) cutting is used, and when machining sharp edges or small holes, conversely, low frequency pulse cutting is used to minimize heat input to the workpiece.

In particular, in CW cutting, the interaction between the moving speed of the beam and the propagation speed of the oxidation reaction results in scratches (0.4 mm) on the cut surface.
(above) occurred, making the cut surface rough.

FIG. 6(a) is a diagram illustrating the striations of laser processing by CW processing.

FIG. 6(b) shows the temperature state of the reaction initiation surface due to CW processing.

In the figure, (1) is a laser beam circle, (2) is a streak,
(3) is the reaction initiation plane, and (8) is the laser beam moving speed. VR is the propagation speed of the oxidation reaction; for example, in oxygen acetylene cutting, cutting cannot be performed at a speed of 1.5 m/min or higher, and the dotted line is the minimum temperature required for the reaction.

In addition, the diagrams marked 1-0 in FIGS. 6(a) and (b) indicate the start of the oxidation reaction, and the cutting speed is V R (1.5 s/sin).
) This shows that laser beam heating triggers the oxidation reaction in the low velocity region below.

t-τ1 in Figures 6(a) and (b) indicates the expansion of the oxidation reaction region, and the temperature at the front of the cut surface rises above the oxidation reaction initiation temperature, indicating that the laser beam advances faster than the laser beam. .

t-τ2 in Figures 6(a) and (b) indicates the termination of the oxidation reaction zone, and the temperature of the cutting front gradually decreases as it moves away from the laser heating zone, and when it reaches the minimum temperature required for the reaction, the oxidation reaction stops. This indicates that forward movement has stopped.

t-τ ~ -τ4 in Figures 6(a) and (b) indicates the interruption of the oxidation reaction zone (not completely stopped), and when the laser beam catches up with the cut surface again, the previous oxidation reaction temperature This indicates that one cycle of machining is completed and one streak is formed.

When machining is performed in a cycle like this, the phenomenon from t-0 to τ4 occurs repeatedly, and this repeated interruption of cutting is added to the previous oxidation reaction temperature, expanding the oxidation reaction region to 0.4
This caused unevenness of 1 mm or more.

The pitch of these striations is approximately constant regardless of the cutting speed, and the pitch width increases as the beam diameter increases.

Furthermore, since heat is continuously generated in CW processing, the area of oxidation reaction expands and the cut surface becomes rough.

However, although theoretically VB>VR should result in a cut surface with no streaks, in reality some tendencies remain.

FIGS. 7(a) to (C) are diagrams showing striations on the cut surface when continuous processing is performed.

The figure shows, for example, the roughness of the cut surface when 5S41 having a thickness of 12 mm is cut in the CW direction.

In the figure, (a) shows the roughness at a position 0.5 mm from the top of the plate, (b) shows the roughness at the center, and (C) shows the roughness at a position 1 mm from the bottom.

That is, the figure shows that large streaks of 0.4 mm or more are generated, especially in the upper part.

Therefore, if the diameter is 0.4 mm or more, depending on the target sample, a grinder is used after processing, or the cut surface is reprocessed using a Luder or the like.

In addition, if the output of the laser beam is processed by PW processing with a frequency of 200H2° and a duty ratio of 80%, the pitch will be smaller than in CW processing, but the cut surface will be reprocessed using a grinder or Luda etc. as described above. Ta.

Furthermore, Japanese Patent Application Laid-open No. 56-99091 discloses a processing method in which an appropriate beam output format is selected depending on the shape of the plastic material. was 100Hz.

[Problems to be Solved by the Invention] In the conventional laser processing as described above, the oxidation reaction region is located at the oxidation reaction region if the peak value of the laser beam irradiated to the cut surface is the value required for the oxidation reaction temperature. Since the area is determined by the width of the peak value, for example, if the laser beam is continuously irradiated, the width of the peak value will be large, so the oxidation reaction area will expand and the pitch of streaks of 0.4 mm or more will be generated on the cut surface. There was a problem in that the material had to be processed again using a grinder or the like after cutting.

In addition, when pulse processing is performed, the oxidation reaction temperature decreases during the beam OFF time, so although the pitch of the striations generated is smaller than that of continuous striations, the pitch of striations of 0.3 mm or more is generated, and the grinder is used after cutting. There was a problem in that it had to be processed again.

This invention was made to solve this problem, and when processing mild steel materials at high speed with a laser, it is possible to obtain a processing speed similar to that of continuous processing without continuous laser firing, and to achieve a It is an object of the present invention to obtain a laser processing method that produces fewer scratches with an interval of 0.4 mm or less.

[Means for Solving the Problems] A laser cutting method according to the present invention is a laser cutting method in which a workpiece is processed by controlling a laser beam according to the material, thickness, or shape of the workpiece. This is a laser cutting method in which the duty ratio of the beam output pulse is set to 70% or less (excluding 0) and the frequency of the output pulse is set to 1000 Hz or higher.

[Function] In this invention, the duty ratio of the output pulse of the laser beam is set to 70% or less (excluding 0) to increase the oxidation reaction temperature at the workpiece, and the frequency of the output pulse is set to 10%.
By setting the frequency to 00 Hz or higher, the expansion range of the oxidation reaction temperature becomes smaller.

[Example] FIG. 1 is a diagram illustrating the concept of a laser processing apparatus using the present invention.

In the figure, (10) is an input means, and the workpiece (1
When machining 4) at high speed, set the output timing of the discharge current output from the resonance pulse modulation section, which will be described later, so that the laser beam output is CW (continuous).
For example, when machining sharp edges or small holes, the pulse duty ratio of the laser beam output should be 70% or less and the frequency should be 100% to suppress heat input to the workpiece.
The output timing of the discharge current of the resonant pulse modulator is set so as to have a pulse form of 0 Hz or more.

(11) is a resonant pulse modulation section, and input means (10)
A high frequency power source (not shown) is controlled so that a discharge current is output based on the timing of the discharge current set by.

(12) is a laser oscillator, and a resonant pulse modulation section (12) is a laser oscillator.
1) outputs a laser beam corresponding to the tanning of the discharge current outputted from 1), for example, if the output timing of the discharge current is in the form of a pulse with a pulse duty ratio of 70% or less and a frequency of 1000Hz or more, A pulsed laser beam corresponding to the numerical value is output.

Further, in this description, it is assumed that the laser oscillator is capable of outputting a laser beam with a pulse peak value (Pp) of 3 KW and a pulse average value (Pa) of 1.6 KW. This pulse average value (Pa) is roughly expressed as Pa-Pp/D (duty ratio).

(13) is an optical system section that focuses the laser beam from the laser oscillator (12) and irradiates it onto the workpiece (14).

The invention will be explained using a laser processing apparatus configured as described above.

In this case, the output of the laser beam is set to a frequency of 1300H2.
, the case where the workpiece (14) is machined with a duty ratio of 50%, an output power of 1350 W, and a machining speed of 0.8/min will be explained.

FIGS. 2(a) to 2(e) are diagrams illustrating the roughness of the cut surface of the workpiece according to the present invention.

Figure (a) shows the workpiece (1
4) Shows the surface roughness at 0.5 mm from the top, and shows the surface roughness of the conventional C
Compared to the roughness of the surface (FIG. 7(a)) at 0.5 mm from the top of the W-processed workpiece, the surface is smoother.

Figure (b) shows the workpiece (1
4) shows the roughness of the surface at the center, and compares it with the roughness of the surface at the center of the conventional workpiece ((b) in Figure 7).
It has a smoother surface.

Figure (C) shows the workpiece (1
4) The roughness of the surface 1mm from the bottom is shown, and compared to the roughness of the surface 1mm from the bottom of the conventional workpiece ((a) in Figure 7), the surface is smoother. .

FIG. 3 is a diagram explaining CW processing and PW processing according to the present invention, where Z indicates the focal position of the laser beam, and 0 to +4
This is a comparison of the cut surfaces changed to .

In Z-0 to +4, the change in the cutting groove width is larger in CW processing, and the change in cutting groove width is smaller in PW processing in which the laser beam output frequency is 1300H2 and the duty ratio is 50%.

Furthermore, if it is +3 or more, the CW cut surface will be greatly deformed and unstable.

In other words, when performing FW processing with a laser beam output frequency of 1300H7 and a duty ratio of 50%, the conventional P
Compared to W processing, the peak value is higher, cutting grooves can be easily formed due to the strong drilling action, and the frequency of 130
If the duty ratio is set to 0H2 and 50%, the output timing of the laser and the timing of the oxidation reaction will match, and the scratches on the machined surface will become smaller stably.

This means that the output frequency fp1 average power of the laser beam is P
When a is the surface roughness and Pk is the surface roughness, it is expressed by the following local expression.

P k = Pa

In addition, the expanded region of the oxidation reaction is the average output Pa (Pa - P
Since it is determined by the value of p/D), when D is increased, the average power Pa output to the workpiece becomes smaller and does not reach the predetermined oxidation reaction temperature.

However, if D is made smaller, Pa becomes larger, and although the oxidation reaction temperature is sufficiently satisfied, if it is too large, the oxidation reaction expansion region becomes wider and the pitch becomes larger.

Therefore, when the frequency fp is increased, the width of Pa becomes smaller and the oxidation reaction temperature is satisfied, and since the amount of energy is small, the oxidation reaction expansion region becomes smaller and the pitch becomes smaller.

Therefore, in order to make the oxidation reaction temperature sufficient, D should be made small, and the pitch should be made small so that the output timing frequency does not expand the oxidation reaction expansion area.

FIG. 4(a) is a diagram illustrating the relationship between the output frequency of the laser beam and the striations.

In the figure, (17) is a symbol indicating the dispersion of the cut surface, and is the average of about 10 samples of the pitch of the striations on the cut surface, for example.

Further, if the bar (1B) is long, the pitch interval of the striations varies widely, which indicates that the roughness of the cut surface is not stable.

According to the figure, the output frequency of the laser beam is 600Hz.
The pitch of the streaks on the workpiece decreases rapidly from 1300Hz to 1300H2, increases transiently from 1300Hz to 3000Hz, and the pitch of the streaks reaches a maximum of 0618m.
m, and the roughness of the cut surface is from 1000Hz to 200Hz.
It is stable up to 0Hz.

However, even if there are variations in the cut surface, if the pitch interval is as small as 0.18 mm at most, it will serve the purpose.

FIG. 4(b) is a diagram illustrating the relationship between the duty ratio of the laser beam and the striations.

In the figure, (17) and (18) are the same as in FIG.

According to the figure, when the duty ratio is 100%, the pitch of the streaks is maximum (0.4 mm or more), but as the duty ratio is decreased, the pitch of the streaks thereafter becomes smaller.

In particular, when the duty ratio is 70%, the pitch of the streaks is 0.18 mm or less, and the variation in the cut surface is also stable, as shown in FIG.

FIG. 5 is a diagram for explaining the present invention in detail, in which the horizontal axis shows the frequency f, the duty ratio D1, and the vertical axis shows the pitch interval.

According to the same figure, the duty ratio is 7 at a frequency of 1000Hz.
When it is set to 0%, the pitch of the striations is 0.18 mm from the relationship shown in Figure 4 (a) and (b), and the duty ratio is at a frequency of 1500 Hz.When it is set to 60%, the pitch is 0.11 mm, and the duty ratio is at a frequency of 2000 Hz. If the ratio is 50%, the pitch is 0. It will be 1mm.

In other words, the frequency is 1000Hz or more, and the duty ratio is 70%.
By using the laser beam as below, the oxidation reaction temperature is higher when it is ON (the time when the laser beam is output), and the area where the oxidation reaction is transmitted becomes smaller.
When it is turned off, the oxidation reaction is stopped and then turned on, so the pitch of the streaks can be maintained at 0.18 mm or less, and the roughness of the cut surface is more stable than with conventional CW processing, so it is necessary to use the grinder again. There is no need to perform such processing.

However, the limits of a frequency of 1000 Hz or more and a duty ratio of 70% or less depend on the performance of the laser oscillator.

In addition, in the above example, the effect of pulse cutting on improving the surface roughness of a thick plate of mild steel material was shown using the numerical values of the invention. Furthermore, it is also possible for metallic and non-metallic materials.

Further, in a pulse oscillator in which the pulse peak value and the average value are the same, the frequency and duty ratio of the present invention may be used by increasing the power of the power source and the strength of the electrodes so that the pulse peak value becomes higher.

[Effects of the Invention] As described above, according to the present invention, by setting the duty ratio of the output pulse of the laser beam to 70% or less (excluding 0) and setting the frequency of the output pulse to 1000 Hz or more, the workpiece can be processed. By increasing the oxidation reaction temperature on the material and reducing the expansion area of the oxidation reaction temperature, for example, the pitch interval of the cut surface can be reduced to 0.18 mm or less, improving the roughness of the cut surface and improving the finish. This has the effect of eliminating the need for processing.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining the concept of a laser processing apparatus using the present invention, FIGS. 2(a) to (C) are diagrams for explaining the roughness of the cut surface of a workpiece according to the present invention, and FIG. A diagram explaining CW processing and PW processing according to the present invention, FIG. 4(a) is a diagram explaining the relationship between the output frequency of the laser beam and the striations, and FIG. 4(b) shows the duty ratio of the laser beam and the striations. FIG. 5 is a diagram explaining the details of the present invention, FIG. 6(a) is a diagram explaining the conventional laser processing scratches,
FIG. 6(b) is a diagram showing the temperature state of the reaction initiation surface, and FIGS. 7(a) to (c) are diagrams showing the striations on the cut surface when continuous processing is performed. In the figure, (1) is a laser beam circle, (2) is a streak,
(3) is the reaction initiation plane, VB is the laser beam moving speed, V
R is the propagation speed of the oxidation reaction, (10) is the input means, (11
) is a resonant pulse modulation section, (12) is a laser oscillator, (1
3) is an optical system part, and (17) is a symbol indicating variation in the cut surface. Note that the same reference numerals in the figures indicate the same or equivalent parts. Agent Patent Attorney Muneharu Sasaki (a) (b) Figure 4 - Q t=τ1 [1 (b) -r2 Kaede r3 t-[4 (Q ) Seal r2 (b) Figure 6 is drawn r3 t=r4 Procedural amendment (spontaneous) Indication Patent Application No. 2-181612 2゜ Title of invention Laser cutting method 3 Case made by the person making the amendment Relationship address name 4, agent address

Claims (1)

[Scope of Claims] A laser cutting method for processing a workpiece by controlling a laser beam according to the material, thickness, or shape of the workpiece, wherein the duty ratio of the output pulse of the laser beam is 70%.
or less (excluding 0), and the frequency of the output pulse is set to 1000 Hz or more.