JP3357646B2 - Laser processing apparatus and laser processing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to laser processing for irradiating a workpiece with a laser beam to remove the workpiece into a desired shape.

[0002]

2. Description of the Related Art Machining using a laser beam has the advantages that there is no problem of tool wear, there is a high degree of freedom in machining, and there is no need for a mold as in press machining, as compared with machining such as a lathe. Have.

However, since this processing method is a non-contact type processing using light, it has a drawback that the processing position and the processing depth cannot be obtained from the position of the tool unlike the mechanical processing.

As a solution to this drawback, the relationship between the processing conditions and the processing amount such as the frequency of Q switch oscillation, which is one of the laser oscillation types, the focal position of the laser, and the number of times of processing, is determined in advance, and the processing shape In addition, processing has been performed by setting processing conditions (Applied Physics Vol. 5).
7 No11, p. 1789, Japan Society of Precision Engineering, Vol. 60 No3 397 pages 1988
, 1988, 1988 spring meeting of Japan Society for Precision Engineering, etc.).

[0005] However, this method has a problem that a processing error increases when a laser oscillation condition or a state of a processing surface of a workpiece changes during processing.

Further, in order to obtain the actually machined depth, there is a problem that the machining must be interrupted or terminated and actual measurement must be performed, and additional machining or correction machining must be performed as necessary. is there.

On the other hand, as an in-process control method in laser processing, an example in which a change in the processing state during laser processing is detected by utilizing the generation of acoustic emission at a processing point and detecting the change in acoustic emission. There is also.

For example, JP-A-8-47786 and JP-A-8-90261 disclose a laser processing apparatus capable of controlling laser ablation by capturing a change in acoustic emission and performing processing under optimum conditions. ing.

However, the in-process control method using the change in acoustic emission monitors a processing state such as a timing (threshold) at which processing starts to occur or a change between different materials, and uses the result to perform laser processing. Since it controls the processing and does not monitor the depth of the processing, there is a problem that it cannot be applied to the processing of the shape as designed.

[0010] Further, the ultrasonic wave generated from the laser beam irradiation point is detected by the ultrasonic wave receiving element, and the laser irradiation state, the thickness and the surface state of the workpiece are monitored, and the irradiation condition and the processing condition are controlled. A laser processing apparatus capable of performing the above has been disclosed (Japanese Patent Application Laid-Open No. Hei 7-232291).

However, since this processing apparatus detects the ultrasonic wave propagating in the liquid on the laser beam irradiation side, it is difficult to accurately monitor the thickness due to a decrease in detection accuracy due to the attenuation of the signal, and the design shape is increased. There was a problem that it could not be processed with high precision. In addition, there is a problem that the method cannot be applied to general processing in a gas phase.

[0012]

SUMMARY OF THE INVENTION The present invention relates to a machining control device or control method for predicting a machining amount and presetting machining conditions, and an in-process control device or control method in laser machining using acoustic emission. In view of the above problems, it is not necessary to experimentally obtain the correlation between the processing conditions and the processing amount in advance, and the processing depth can be directly monitored, processing can be performed in a short time and at low cost, and laser oscillation during processing is performed. It is an object of the present invention to provide a laser processing apparatus and a laser processing method capable of processing a design shape with high accuracy without increasing a processing error even if a condition or a condition of a processing surface of a workpiece changes.

[0013]

SUMMARY OF THE INVENTION The present invention relates to a laser processing apparatus for processing a workpiece with a laser beam, the laser processing apparatus having laser irradiation means capable of irradiating a laser beam. The acoustic emission measurement sensor installed on the side opposite to the laser irradiation surface with respect to the workpiece, and the processing depth as the amount of change in the thickness of the workpiece at the laser irradiation point from information obtained by the acoustic emission measurement sensor. Calculating means for calculating the position of the workpiece and the irradiation position of the laser beam at the laser irradiation point based on information obtained by the calculating means, according to a predetermined program. And

FIG. 1 is a schematic diagram of this processing apparatus. The laser is irradiated as a laser pulse by the laser oscillator 1. The laser beam is condensed by the lens 7 and is irradiated to one point of the workpiece, and the workpiece 2 is removed in the depth direction by the melting and evaporation phenomenon. At this time, as is well known, acoustic emission occurs from a processing point irradiated with the laser beam. This acoustic emission is detected by the acoustic emission measuring sensor 6 after propagating in the workpiece.

In the present invention, the acoustic emission measurement sensor is not particularly limited, but preferably has a characteristic that it has a high frequency band and can sufficiently attenuate at laser pulse oscillation intervals. This is because the time resolution of the signal measurement of the acoustic emission is increased, and even if the irradiation interval of the laser pulse is shortened, the measurement can be accurately performed without disturbing the signal of the acoustic emission.

The signal detected by the acoustic emission measurement sensor is processed by the signal processing device 3 to calculate a delay time from laser beam irradiation to acoustic emission detection, and from this value the thickness of the workpiece at the laser irradiation point. Is converted to This principle is based on the fact that the delay time is theoretically proportional to the thickness of the workpiece. In addition, as shown in FIG. 2, the results obtained by actual experiments also showed a good proportional relationship between the theoretical value and the thickness of the workpiece.

The information of the processing depth obtained as the amount of change in the thickness is fed back to the control device 4, and the workpiece and the irradiation position of the laser beam are relatively moved in accordance with a predetermined program, whereby the workpiece is processed. The object can be processed into a desired shape.

In this laser processing apparatus, the acoustic emission propagates through the workpiece from the laser irradiation, and the acoustic emission measuring sensor 6
The processing depth is calculated as the amount of change in the thickness by measuring the delay time until it is detected in, and it is not necessary to obtain the relationship between the processing depth and the processing conditions in advance by experiments,
As a result, processing can be performed in a short time and at low cost.

Also, instead of monitoring the processing status,
Since the processing depth is monitored, even if the laser oscillation conditions during processing or the condition of the processing surface of the workpiece change, the processing error does not increase, and the design shape can be processed with high precision. it can.

Further, since this processing apparatus relatively moves a workpiece and an irradiation position of a laser beam according to a predetermined program, unlike a simple laser drilling, a desired shape can be precisely formed in a short time. Can be processed in time.

The installation position of the acoustic emission measurement sensor 6 is not particularly limited as long as it is on the side opposite to the laser irradiation surface, but it is particularly preferable that the sensor is coaxial with the laser. This is because the error in the thickness calculated by the signal processing device 3 can be minimized.

The acoustic emission measuring sensor 6 may be fixed to the workpiece using an interposition such as a double-sided tape at a portion which does not affect the measurement, but the workpiece and the acoustic emission measuring sensor are fixed. If the distance is maintained, it is not particularly necessary to fix. In the case where the acoustic emission measurement sensor 6 is not fixed, if only the workpiece is moved, the processing can be performed without being restricted by the size of the processing shape or the processing range.

The laser processing can be performed in the gas phase or the liquid phase. In the case of the gas phase, it is desirable to discharge the processed material by a method such as sending dry air. When a gap exists between the acoustic emission measuring sensor and the workpiece, it is particularly effective to supply a liquid such as water to the gap in order to match the acoustic impedance with the sensor.

The signal processing device 3 is not particularly limited as long as it can determine the delay time of the acoustic emission signal, but a digital oscilloscope, a dedicated circuit using a gate or a timer, or the like can be used.

Further, the present invention is characterized in that a means for periodically moving a laser beam during processing and for synchronizing measurement of acoustic emission and pulse oscillation of the laser with the periodic movement of the laser beam are provided.

With such an apparatus, since additional processing is not performed after measurement of acoustic emission, higher processing accuracy can be obtained as compared with a processing apparatus which does not periodically move a laser beam. . In this case, the type of the periodic movement of the laser beam is not particularly limited, but for example, eccentric rotation can be adopted. FIG. 3 shows a state where the laser beam is eccentrically rotated.

Although there is no particular limitation on the method of periodically moving the laser beam, as shown in FIG. 1, a wedge-shaped plate 9 through which the laser beam is transmitted is placed between the laser pulse generator and the workpiece. It can be performed by installing and rotating this with a motor or the like. Further, a method of eccentrically rotating the condenser lens may be used.

[0028]

Embodiments of the present invention will be described below.

[0029]

Embodiment 1 An Nd: YAG laser was used at a frequency of 1 kHz.
Q switch oscillation with average output 10W, focal length 50mm
The light was collected by the lens. The laser beam was tilted from the optical axis by refraction of a wedge (wedge-shaped plate), and rotated at a focal point so that the radius of rotation became about 0.1 mm and the number of rotations was 600 rotations per minute. The in-process measurement of the depth during processing is performed by synchronizing the rotation of the laser beam and the depth measurement by acoustic emission detection with the slit of the rotating part, and detecting the acoustic emission in a fixed direction (at the end of the processing direction). Was. In addition, the Q switch oscillation of the laser was synchronized with the rotation of the laser beam using a control device and a photoelectric switch, and the number of pulse oscillations was externally controlled by a gate. At each point obtained by dividing the circumference into eight, a pulse group having 1 to 12 pulses was oscillated to control the machining depth.

The work piece is made of silicon nitride having a thickness of 4 mm.
The acoustic emission generated at the laser irradiation point was detected using a broadband transducer for ultrasonic thickness measurement (center frequency: 5 MHz) installed coaxially with the laser on the back surface of the workpiece, and amplified by an ultrasonic receiver.

The processing speed is 0.5 mm / sec, a single groove processing without pitch scanning feed is performed, and the number of processing times is 1
The machining depth was compared by changing to ~ 3 times. The processing range is about 4mm at the center of the acoustic emission measurement sensor.
The measurement was performed in the corner, and the acoustic emission measurement sensor was directly adhered to the back surface of the workpiece with a double-sided tape at two places that did not affect the measurement. Approximately 7 resulting from the thickness of the tape
Water was supplied to the gap of 0 μm in order to match the acoustic impedance with the sensor, and an acoustic emission signal was propagated.

During processing, dry air was blown to the processing portion coaxially with the laser in order to discharge the processed material. The laser pulse oscillation partially reflected the laser immediately before the condenser lens, detected by a PIN photodiode, and used as a trigger. The delay time from the laser irradiation to the acoustic emission detection was determined by a measurement function of a digital oscilloscope used as a signal processing device.

As a result, it was found that the in-process measurement of the machining depth was possible by detecting the acoustic emission. According to this method, the processing depth can be directly monitored without experimentally obtaining the correlation between the processing condition and the processing amount in advance.

[0034]

Embodiment 2 The laser beam again approaches the depth measurement point by the acoustic emission detection, and the processing speed is 0.5 mm / sec and the pitch scanning feed amount is 0.25 mm without additional processing. In-process measurement of laser processing depth and Q based on the measured value
Perform feedback control of switch oscillation, width 4m
A step-like shape having a length of m, a depth of 3 mm and a depth of about 1 mm was processed by six pitch scans.

Except for the above processing conditions, the same procedure as in Example 1 was carried out.

FIG. 6 shows a comparison between a design shape, an actual measurement value by a shape measuring device, and a machining depth obtained by acoustic emission detection at the time of final pitch scanning machining. By simply inputting the design dimensions from this diagram, the machining depth is measured and confirmed during machining, and the
It was found that shape processing could be performed automatically with a precision of within.

[0037]

[Embodiment 3] Before machining, the center of the workpiece is 0.23 m
Laser beam processing was performed in the same manner as in Example 2 except that grooves of m and 0.44 mm were provided. As a result, despite the provision of the grooves, a workpiece having the same shape as in FIG. 6 could be machined with the same level of accuracy without being affected by the surface shape.

[Brief description of the drawings]

FIG. 1 shows a configuration diagram of a laser processing apparatus according to the present invention.

FIG. 2 shows the relationship between the propagation time of acoustic emission in a workpiece and the thickness of the workpiece.

FIG. 3 shows a state of a laser beam rotated eccentrically.

FIG. 4 shows a voltage versus time of a laser detection signal and an acoustic emission detection signal.

FIG. 5 is a diagram comparing a measured value of the depth of the bottom of the processed groove in Example 1 with a depth value obtained by acoustic emission detection.

FIG. 6 shows a comparison between measured values of a cross-sectional shape processed in Example 2, depth values obtained by acoustic emission detection, and a design shape.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Laser oscillator 2 ... Workpiece 3 ... Signal processing device 4 ... Control device 5 ... Mounting table 6 ... Acoustic emission measurement sensor 7 ... Condensing lens 8 ... PIN photodiode 9 ... Rotating part using a wedge-shaped plate 10 …Photoelectric switch

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI H01S 3/00 H01S 3/00 B (56) References JP-A-63-60087 (JP, A) JP-A-11-156579 ( JP, A) JP-A-57-149087 (JP, A) US Patent 5,045,669 (US, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B23K 26/00-26/42

Claims (6)

(57) [Claims] 1. A laser processing apparatus having a laser irradiation means capable of irradiating a laser beam and processing a workpiece with the laser beam, comprising: a laser oscillator; Acoustic emission measurement sensor installed on the opposite side, and calculation means for calculating the processing depth as the amount of change in the thickness of the workpiece at the laser irradiation point from information obtained by the acoustic emission measurement sensor,
Moving means for relatively moving the workpiece and the irradiation position of the laser beam from information obtained by the calculating means according to a predetermined program; and means for periodically moving the laser beam during processing. Means for synchronizing the acoustic emission measurement and the laser oscillation with the periodic movement of the laser beam. 2. The means for periodically moving a laser beam during processing comprises a light-transmitting refraction plate provided on the optical path of the laser beam, and a driving device for rotating the refraction plate. The laser processing apparatus according to claim 1, wherein: 3. The laser processing apparatus according to claim 1, wherein the acoustic emission measurement sensor does not move integrally with the workpiece. 4. A laser processing method for irradiating a laser beam and processing a workpiece with the laser beam, wherein the laser beam is oscillated by a laser oscillator, and the laser beam is set on a side opposite to a laser irradiation surface with respect to the workpiece. The acoustic emission is measured by the acoustic emission measurement sensor, and the processing depth is calculated as the amount of change in the thickness of the workpiece at the laser irradiation point from information obtained by measuring the acoustic emission,
From the information obtained by the calculation, the workpiece and the irradiation position of the laser pulse beam are relatively moved according to a predetermined program, and the laser beam is periodically moved during the processing to measure the acoustic emission. And a method of synchronizing laser oscillation with movement of the laser beam. 5. The periodic movement of a laser beam is characterized in that a light-transmissive refraction plate is provided on an optical path of the laser beam, and the laser beam is periodically moved by rotating the refraction plate. The laser processing method according to claim 4, wherein 6. The laser processing method according to claim 4, wherein the acoustic emission measurement sensor does not move integrally with the workpiece.