JPH09206970A - Laser beam machining method and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of built-up and crack of a machining part due to residual stress by supplying plural pulses to a flash lamp within the time required for completing one machining and outputting a laser beam thereby performing machining. SOLUTION: A pulse group P consisting of plural pulses 1, 2,...n is supplied to a flash lamp within the time T required for completing one machining. Within one pulse group P, respective pulse voltages V1 , V2 ,...Vn of the pulses 1, 2,...n are equal to each other. Their pulse widths t1 , t2 ,...Tn and the pulse internals g1 , g2 ,...gn among the pulses 1, 2,...n are selected at a proper value in accordance with various conditions of an object to be machined such as the material, shape, thickness and pulse voltage.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a laser processing method and a laser processing apparatus.

[0002]

2. Description of the Related Art Conventionally, in laser processing, laser light obtained by one pulse in one processing has been used. That is, the laser energy required for one processing was obtained by one pulse. The laser light is generated from a flash lamp, the energy of the laser light, ie the laser energy, depends on the energy of the pulses supplied to the flash lamp. Therefore, 1
One pulse having an energy corresponding to the laser energy required for one processing was supplied to the flash lamp in one processing. The laser energy can be changed to an arbitrary intensity by changing the intensity of the pulse energy, and conventionally, the intensity of the pulse energy is changed by changing the pulse voltage.

By the way, according to the above conventional laser processing method, the following problems often occur. That is,
The surroundings of the machined part are raised or splashes occur on the back side of the machined part, making the appearance of the work piece bad, or secondary processing such as post-processing is required and the processing efficiency is extremely poor. If it is worse, it breaks from the processed part due to the residual stress in the processed part,
In some cases, it was torn.

More specifically, for example, as shown in FIG. 1, a raised portion 23 is formed around the processed portion 21 of the work piece 20, or light passes through the back side of the work piece (in this state). (Indicated by a dotted line in the figure) A splash 24 is generated on the back side of the processed portion, and the dimensional accuracy of the component is deteriorated and the component cannot be used as it is. Further, there is a problem that extra work is required to remove this.

Further, in the case where the raised portion 23 and the splash 24 are formed, the laser energy is mostly supplied excessively, and as a result, the laser energy is rapidly supplied after the laser irradiation and during the cooling. In the case where stress is concentrated in the part where the temperature change is forced and there are cracks on the surface or inside and it is easy to break or rupture, or if it has broken. There was also.

[0006] Such a problem occurs because an excessive laser energy is supplied to the processed portion or a sudden temperature change is forced. On the contrary, the method tends to cause a shortage of total energy, and eventually, in the conventional laser processing method of adjusting the pulse energy by adjusting the pulse voltage, an appropriate amount of laser energy is generated and residual stress is generated. Could not be supplied to the processing section.

As an attempt to solve the above problems, YAG
The following proposal was made as a flash lamp power source for laser excitation. That is, as a flash lamp power source, a direct current power source charges a storage capacitor, and when a control circuit closes a switch in response to a demand signal of a laser pulse, a voltage is applied to the flash lamp through an inductance, and a current flowing through an inductance has an upper limit in advance. The upper limit value of the demand signal set as a value (hereinafter,
When it reaches the HIGH level), this information is transmitted by the current sensor to the control circuit as an electric signal, and in response to this information, the control circuit opens the switch to cut off the electrical connection state and the energy stored in the inductance. Continuously supplies current to the flash lamp through the flywheel diode, and when the energy of the inductance decreases and the current falls below the lower limit value (hereinafter referred to as LOW level) of the demand signal preset as the lower limit value, this information is An electric signal is transmitted to the control circuit by the current sensor, and the control circuit closes the switch again in response to this information.
Power supplies have been proposed that are configured to be repeated during a pulse width demand, with a switching frequency of the order. This power supply method is called a switch mode method (Lumonics method). In the switch mode method, one pulse wavelength is 0.1 msec or more.

A method of controlling the waveform of the pulse supplied to the flash lamp (hereinafter referred to as pulse shaping) using this switch mode power supply has been proposed. In order to distinguish this method from the above-mentioned conventional method, the following second
The conventional method of.

The basic idea in adopting pulse shaping is that fine adjustment of the pulse energy can be performed in one machining, and the phase change of the machined portion can be slowly progressed to finely adjust the machining state. In order to reduce the residual stress inside the machined part or the processed part, as shown in FIG. 2, one “multi-stage” having the total energy required for one machining within the time required for one machining This is different from the above-mentioned conventional method in that a "waveform" pulse is supplied to the flash lamp, and the pulse waveform is a pulse having a multi-step waveform rather than a square waveform. However, the point that the change in pulse energy depends on the change in pulse voltage is the same as in the past.

[0010]

However, even in the above-mentioned second conventional method, it is still not possible to finely adjust the energy, and the above-mentioned problems cannot be completely solved. .

The present invention has been made in view of the above points, and by performing a fine adjustment of the laser energy during a single machining, the phase change of the machined portion is allowed to progress slowly to achieve the machining state. SUMMARY OF THE INVENTION It is an object of the present invention to provide a laser processing method capable of finely adjusting the above and reducing residual stress inside the processing section, thereby eliminating the above-mentioned various problems in the processing section, and a laser processing apparatus which enables the method.

[0012]

The present invention is characterized in that (1) a plurality of pulses are supplied to a flash lamp within a time required to complete one processing and a laser is output to perform the processing. And (2) a laser processing apparatus characterized by comprising a switching mechanism for supplying a plurality of pulses to a flash lamp within a time required to complete one processing.

The present invention is a laser processing method capable of adjusting a laser output energy and an output pattern to an optimum state so as to prevent a raised portion or a crack from being generated in a processed portion of a workpiece. There is also a laser processing apparatus provided with a mechanism capable of realizing the processing method.

[0014]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in detail below with reference to the drawings.
Will be described. FIG. 3 shows the pattern of the laser processing method of the present invention.
An example of a loose waveform is the pulse voltage on the vertical axis and time on the horizontal axis.
It is a diagram shown as a graph, and T indicates that one processing is completed.
Time required for machining 1, 2, ... N is one machining time
Multiple pulses delivered to the flashlamp during T
Each pulse in the pulse group P consisting of₁, T_Two...
t_nIs the pulse width of each pulse 1, 2, ... N, g₁, G_Two
... g_nIs the pulse interval of each pulse 1, 2, ... N, v
₁, V_Two... v_nRepresents the pulse voltage, respectively.

In the laser processing method of the present invention, as shown in FIG.
As shown in, a pulse group P including a plurality of pulses 1, 2, ... N is supplied to the flash lamp during a time T required until one machining is completed.

In one pulse group P, the voltages v ₁ , v ₂ ... V _n of each pulse of pulses ₁ , _2, ... N.
Are the same.

The pulse widths t ₁ , t of the pulses ₁ , 2, ...
₂ ... t _n and the pulse intervals g ₁ , g _2, ... G _n between the pulses ₁ , _2, ... _N are the object to be machined (workpiece).
An appropriate value is selected according to various conditions such as the material, shape, thickness, pulse voltage and the like. Usually, the pulse voltage is first set to an appropriate value, and the material, shape, and thickness of the work piece are set so that the set pulse voltage gives a pulse waveform that allows the work piece to be processed in a good state. The pulse width and the pulse interval are adjusted according to the above conditions, and the temporal pattern of the pulse is determined.

In other words, the pulse width and the pulse interval are adjusted under the condition of a predetermined constant voltage, and finally, the workpiece is satisfactorily made to meet the conditions such as the material, shape and thickness of the workpiece. A pulse temporal pattern that can be processed into a state is found, and a pulse waveform having this pattern and having the above-mentioned predetermined voltage is determined. The above-mentioned good condition is, for example, swelling or splash of the processed portion, breakage due to cracks on the surface or inside, or in a situation where it is easy to tear,
Or, it means a state that has not been broken.

The predetermined constant voltage is approximately DC500.
Although it is about V, the voltage does not necessarily have to be about this level, and may be appropriately set according to the material, thickness, shape, thickness, etc. of the workpiece. The pulse voltages v ₁ , v ₂ ... V _n in one pulse group P are constant, but they do not necessarily have to be constant between the pulse groups, and even if the pulse voltages differ from pulse group to pulse group, Or they may be the same.

The time T for supplying the pulse group P is the time required for one machining. The time T is usually 0.1 to 1
Although it is about (msec), the present invention is not limited to this, and may be a time required for one processing, that is, a time required for one laser irradiation. However, it is not preferable to make the time T too long because the time efficiency of processing is deteriorated. If the time T is too short, the pulse voltage needs to be increased in order to compensate for the shortage of the total amount of pulse energy. As a result, the temporal pattern of the pulse must be made finer, but there is a limit to the fineness. Therefore, after all, it becomes difficult to finely adjust the pulse waveform, which is not preferable.

The time-dependent pattern of each pulse in the pulse group P may be set so as to correspond to the conditions such as the material, shape and thickness of the workpiece under the conditions of the pulse voltage,
The pulse widths t ₁ , t _2, ... Of the pulses ₁ , _2, ...
t _n, and the pulse 1,2, pulse interval g _1, g ₂ ··· g _n between · · · n may take any value as long as it is within the range of the T, it is appropriately selected . t ₁ , t ₂ ·
..T _n may all have the same value or different values. Also, g ₁ , g ₂ ... G _n may all have the same value or different values.

Each t ₁ , t ₂ ... t _n and each g ₁ , g ₂
The value of g _n is usually 0.001 to 0.25
(Msec), but the present invention is not limited to this, and at least [t ₁ + g ₁ + t ₂ + g ₂ ] during T.
May be a value that can be included. That is, the pulse width and the pulse interval may be such that the pulses (pulses 1 and 2) of at least two cycles are included in the time T required for one processing. Each t ₁ , t ₂ ... t _n and each g
The preferable values of ₁ , g ₂ ... G _n are 0.001 to 0.
05 (msec), and more preferably 0.001 to
It is 0.025 (msec).

Typically, two to four pulses are applied during T. That is, one pulse group P is made up of 2 to 4 pulses. From the viewpoint that residual stress in the processed portion can be reduced, it is preferable that the number of pulses constituting one pulse group is large. However, if the number of pulses is too large, the corresponding effect cannot be obtained. The significant effect of increasing the number of pulses is that the number of pulses is 2
This is the case of about four. Of course, in the present invention, the number of pulses is not limited to this, and may be 5 or more.

In each pulse, when the pulse voltage is constant,
The pulse width and the pulse energy are in direct proportion,
When the pulse width is increased, the pulse energy can be increased. Similarly, if the pulse width is reduced, the pulse energy can be reduced. Conventionally, the pulse energy was changed by changing the pulse voltage, but in the present invention, the pulse energy is changed by changing the pulse width instead of keeping the pulse voltage constant. The means for changing the energy are different.

Even when the method of the present invention is compared with the second conventional method, in the second conventional method, the pulse supplied in one machining is a stepped waveform pulse, and each step height is different. Although the pulse energies between the stages are different from each other, the difference in the pulse energies is caused by both the difference in the voltage of each stage and the difference in the width of each stage. Not only due to the difference, but different means for changing the pulse energy.

Further, in the second conventional method, the pulse energy changes stepwise, but continues without breaking within one processing time. That is, in the pulse waveform as shown in FIG. 2, the energy of the pulse waveform is 0 on the way.
(It means that the voltage becomes 0 in this case), and the process continues for the full time required for one machining without passing through the stage. On the other hand, according to the method of the present invention, as shown in FIG. 3, the pulse waveform requires a step in which the energy becomes 0 (meaning that the voltage becomes 0 here) in the middle for one processing. It has been several times in time and here is the difference from the second conventional method.

In applying the laser processing method of the present invention to actual processing, as described above, the temporal pattern of the pulse is changed under the conditions of a predetermined pulse voltage, such as the material, shape, and thickness of the workpiece. Set the waveform of the pulse group so that the waveform corresponds to. The waveform of the pulse group thus obtained may be, for example, one having a pattern as shown in FIG.

In FIG. 4, the solid line represents the waveform of the pulse group. Making the waveform of the pulse group as shown in FIG. 4 is also included in the category of so-called pulse shaping (waveform control). However, as described above, the pulse shaping performed in the method of the present invention is performed with a constant pulse voltage. This is done by changing the pulse width and pulse interval and setting them to appropriate values. When a pulse group (group of a plurality of pulses supplied within the time required for one processing) obtained by shaping by this method is supplied to a flash lamp, a laser beam (laser energy having a waveform corresponding to this) is supplied. ) Is obtained from the flash lamp. And if this laser light is applied to the processed part,
The temperature of the processed portion follows the transition schematically shown by the dotted line in FIG.

In order to obtain the waveform of the pulse group shown in FIG. 3 or 4, a switching mechanism capable of repeating electrical connection and disconnection at such a cycle is used. A conventionally known one can be applied as the switching mechanism.

According to the processing method of the present invention, an effect which cannot be obtained by the second conventional method, that is, a swelling portion, a crack or the like does not occur in the processed portion of the workpiece, and a residual which causes a crack is generated. The effect is that the stress can also be made extremely small.

The difference between the case where the processing method of the present invention is used and the case where the conventional method (second conventional method) is used is that the laser beam applied to the workpiece is continuous during one processing time. The point is that it is not done and is intermittent. It is considered that this difference is due to the difference in effect between the processing method of the present invention and the second conventional method.

In the laser processing, the phase change of the processed portion during the processing progresses remarkably even in a very short time (unit: μsec), so that the phase change cannot be progressed if a constant heat energy is taken for a long time. After all, after the pulse is interrupted and the thermal energy is interrupted, the temperature is suddenly changed over a wide temperature range, and the internal stress that leads to future fracture or the like remains in the processed portion. In the conventional method, the laser energy is continuous although it is stepwise, so it cannot be said that it is constant heat energy, but it is still continuous energy for a long time, and the heat energy is the same as the processing part. Therefore, the width of the temperature change can be reduced after the pulse and the thermal energy are interrupted. Did not can be realized by slowing some broad phase change speed of the processing member is forced to change in temperature of the temperature range.

In the method of the present invention, by supplying a plurality of pulses to the flash lamp within the time required for one machining, the laser energy is intermittently supplied to the machining section within the time required for one machining. I did it. It is considered that, as a result, it becomes possible to apply thermal energy controlled to the temperature of the processed portion such that the phase change of the processed portion can proceed slowly.

This will be described in more detail with an example. When the processed portion is first irradiated with a laser having strong energy, the temperature of the processed portion rises and the processed portion melts. In this state, fusing, fusing, perforation and the like are performed. Next, the processing part in the molten state needs to be cooled, but if the supply of laser energy is suddenly stopped here, the processing part will be cooled rapidly,
Problems such as residual stress occur. Cooling must be done gradually so that no stress remains. On the contrary, if the time required for cooling is too long, the processing efficiency will be deteriorated. Even if a weak energy is supplied for a long time from the beginning, the processed portion does not melt and cannot be processed. Splash occurs when the energy supplied at the beginning is too strong. Therefore, it is impossible to solve the problem of residual stress by strengthening or weakening the energy to be initially supplied, and the energy to be initially supplied is determined to some extent. In solving the problem of residual stress, it is important how to cool the machined part which is heated by the energy supplied first.

In the second conventional method, the energy is changed stepwise, but the laser energy is applied to the processed portion only continuously. This means that energy is always supplied to the processing section. As shown in FIG. 2, in the second conventional method, it seems that the temperature change (temperature drop) of the machined part is controlled very slowly, and as a result, the phase change of the machined part is also delayed. Regardless of the number of stages, the phase change seems to proceed slowly at any stage.

However, in reality, the phase change of the processed portion does not proceed so slowly. This is because the laser energy is continuous without any ruptures, so the temperature of the processing part accumulates thermal energy without cooling, so that the last stage is over and within one processing time. At the end of the pulse, the temperature of the machined part is still quite high. Despite this, the supply of energy is stopped, so at this stage a sudden wide range of temperature changes is forced, and the speed cannot keep up with the phase change. The temperature of the machined part is still quite high at the end of the pulse because the steps are continuous.

In the machining method of the present invention, since each pulse in the pulse group is discontinuous in energy, no heat energy is applied to the machining portion during the break of this energy, and the heat energy is accumulated. Not done. Therefore, during this period, the temperature of the processed portion surely drops, and the phase change of the processed portion progresses. However, this phase change is suppressed by the thermal energy of the laser applied by the supply of the next pulse immediately following. That is, the laser energy is supplied by the next pulse supply immediately before the phase change progresses so much that the temperature drop of the processed part is kept within a short time and within a narrow temperature range. The phase change of the part progresses only slightly. Then, the laser energy based on the next pulse may suppress the temperature of the processed portion from dropping to a certain temperature or lower, or may raise the temperature once again from the once lowered temperature. Then, when the temperature rises slightly again, the processed portion is slightly remelted by this, leveling of the raised portion occurs, the residual internal strain is eliminated, and the internal stress is relaxed.

The phase change associated with the temperature change is repeated while the pulse is supplied. By gradually reducing the pulse energy after supplying the first pulse, it is possible to eliminate the raised portion around the processed portion and to extremely reduce the residual stress. At the same time, the laser energy is cut off after the last pulse is finished, and the processing part temperature continues to drop after this, but the processing part temperature is already quite low if the last laser energy is small. However, since the cooling temperature width is small even when the temperature drops to room temperature, the phase change progresses slowly, and as a result, internal stress does not remain in the processed part.

As an embodiment of the method of the present invention, first, a large amount of energy is supplied for a predetermined time, and then the temporary supply is stopped,
There is a pulse group pattern in which a small amount of energy is then supplied for a predetermined period of time, then the temporary supply is stopped, and then a smaller amount of energy is supplied for a predetermined period of time to complete one machining. It is considered that the stress is removed by the second and subsequent supply, and the leveling of the raised portion around the processed portion is promoted to remove it.

The idea of finely adjusting the pulse energy of each pulse by using a plurality of pulses for one machining and changing the width and interval of each pulse has not been found in this field. It is a thing. Heretofore, it has been common to change the pulse energy by changing the voltage, and this method is a kind of common sense in this field, which hinders other ideas.

As a laser processing apparatus used for carrying out the laser processing method of the present invention, a YAG laser,
In addition to a laser processing apparatus using each laser such as CO ₂ laser and excimer laser, all those generally used for processing can be applied to the present invention.

Next, the laser processing apparatus of the present invention will be described. The laser processing apparatus of the present invention is a laser processing apparatus that is advantageous for carrying out the above-described laser processing method, and is a switching apparatus that supplies a plurality of pulses to a flash lamp within a time required to complete one processing. It is equipped with a mechanism.

In the above laser processing apparatus, as the portion other than the switching mechanism, a conventionally known laser processing apparatus can be applied. That is, in addition to a laser processing apparatus using each laser such as a conventionally known YAG laser, CO ₂ laser, and excimer laser, all those generally used for processing can be applied.

In the present invention, as a switching mechanism for closing the flash lamp power supply circuit and supplying the pulses to the flash lamp, a pulse composed of a plurality of pulses within the time required to complete the above-mentioned one machining A group having a function of supplying a group to a flash lamp is used, and further another switch is provided to operate the switching mechanism. The other switch, that is, the switch for operating the flash lamp power source for each machining, is electrically connected to the switching mechanism, and normally, the switching mechanism functions while the switch is closed. Then, the pulse group consisting of a plurality of pulses is continuously supplied to the flash lamp, and the supply can be stopped by opening the switch.

In addition, the above-mentioned switch stops the supply after the switching mechanism functions for a predetermined fixed time to supply a pulse group consisting of a plurality of pulses to the flash lamp when the switch is closed. It may be configured to be able to. A foot switch or the like is generally used as the switch, but the switch is not limited to this.

Here, as the flash lamp power supply circuit, a pulse shaping circuit [PFN (Pulse Forming Network) is used.
ork)] type basic circuit, partial discharge type basic circuit, switch mode type (Lumonics type) basic circuit, or any other conventionally known power supply circuit can be used.

The above-mentioned switching mechanism is usually provided in place of the conventional switch provided in the flash lamp power supply circuit, and the conventional switch is an electric switch that is used as a switch used to operate or stop this switching mechanism. Connected. Therefore, the switch is usually provided so as to be outside the unit of the laser processing apparatus, but the switching mechanism is usually integrated with the flash lamp power supply unit or, if not integrated, inside the laser processing apparatus unit. It is provided in the form built in.

The switching mechanism is provided with or electrically connected to an adjusting mechanism section capable of arbitrarily adjusting the pulse width and pulse interval of each pulse in the pulse group. Further, when the switch is closed, the switching mechanism functions for a predetermined certain period of time to supply a pulse group consisting of a series of a plurality of pulses to the flash lamp and then stop the supply. In this case, the supply time of one pulse group can be arbitrarily set.

The voltage adjusting mechanism for adjusting the pulse voltage may be provided as a part of the above switching mechanism by being directly electrically connected to the switching mechanism, or in the flash lamp power supply circuit separately from the switching mechanism. Either of them may be provided so as to be electrically connected to that part.

Therefore, in the laser processing apparatus of the present invention, the voltage of the laser pulse can be set to a constant arbitrary value for each pulse group, and the pulse width and the pulse interval can be set for each pulse group. It can be set to an arbitrary value for each pulse in each pulse group, and by adjusting the width of each pulse in the group in each pulse group, the magnitude of the pulse energy of each pulse can be adjusted freely. , By adjusting the combination of the width and interval of each pulse in the group, it is possible to freely adjust the temporal pattern of the magnitude of the pulse energy in each pulse group.

An example of the operation procedure for performing laser processing using the laser processing apparatus of the present invention will be described below. First, by operating the adjustment mechanism of the switching mechanism, the pulse width and pulse interval of each pulse in the pulse group can be changed depending on the material, shape, thickness, type of processing (welding, fusing, drilling, etc.) of the workpiece. It is set accordingly (this set value is a value known in advance by experiments or the like). In addition, the pulse voltage is also set by operating the voltage adjustment mechanism according to the material, shape, thickness, type of processing (welding, fusing, drilling, etc.) of the work piece (this set value is also to some extent. It is a value within a range that has been previously determined to be appropriate by experiments, etc.).

Then, the object to be processed is placed on the laser irradiation site. Then, a switch such as a foot switch is operated to operate the laser processing device. When the switch is closed as a switch operation necessary for one machining, the switching mechanism operates in the flash lamp power supply, and a single pulse group consisting of a plurality of pulses is supplied to the flash lamp within a predetermined time. Accordingly, a laser beam corresponding to the waveform of the pulse group is applied to the workpiece, the workpiece is processed, and one-time processing is completed.

In the present invention, since the above-mentioned switching mechanism is electrically interposed between the conventional switch and the flash lamp power supply circuit, a pulse group consisting of a plurality of pulses is automatically formed only by turning on the switch. Can be generated and supplied to a flash lamp, and the above-described processing method of the present invention can be easily carried out.

[0054]

As described above, according to the laser processing method of the present invention, a plurality of pulses are supplied to the flash lamp within the time required to complete one processing and the laser is output to perform the processing. Therefore, when each pulse voltage is set to an arbitrary predetermined value, the pulse width and the pulse interval of each pulse are the pulse voltage and the material of the workpiece,
When set to an appropriate value according to conditions such as shape and thickness, the effect of being able to almost completely eliminate problems such as swelling and splash around the processed part, and generation of cracks due to residual stress Play.

Since the laser processing apparatus of the present invention is equipped with a switching mechanism for supplying a plurality of pulses to the flash lamp within the time required to complete one processing, the laser processing of the present invention described above. The effect that the method can be easily implemented is exhibited.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a processing defect when a conventional laser processing method is used.

FIG. 2 is a diagram showing a pulse waveform according to a second conventional method.

FIG. 3 is a diagram showing an example of a pulse waveform supplied to a flash lamp in one processing in the laser processing method of the present invention.

FIG. 4 is a diagram schematically showing another example of the pulse waveform according to the present invention and the transition of the transition of the temperature of the processed portion that transitions corresponding to this.

[Explanation of symbols]

P pulse group T time required for one machining ₁ , 2 ... n each pulse t ₁ , t ₂ ... t _n pulse width of each pulse g ₁ , g ₂ ... g _n interval between each pulse v ₁ , v ₂ ... V _n Pulse voltage of each pulse

Claims (2)

[Claims] 1. A laser processing method characterized in that a plurality of pulses are supplied to a flash lamp and a laser is output to perform processing within a time required to complete one processing. 2. A laser processing apparatus comprising a switching mechanism for supplying a plurality of pulses to a flash lamp within a time required to complete one processing.