JPS622153A - Defect inspection by laser irradiation - Google Patents

Abstract

PURPOSE:To detect a defect in a machine or a construction material, by a method wherein the surface of an object to be measured is irradiated with a pulse laser beam to generate a heat impact wave and a fine swell vibration as caused by the reflected wave from the object being measured is detected with a laser speedometer. CONSTITUTION:A laser beam 16 generated with a continuous wave laser unit 15 is split into two laser beams equal in the intensity with a beam splitter 17 and one thereof reaches the position of a pulse laser light spot 5 via mirrors 18 and 19 and a condenser lens 21. The other thereof reaches the position of a spot 5 via the mirror 19 and the condenser lens 21. The two laser beams propagating through the two optical paths forms an interference fringe with the generation of a heat impact wave at the intersection thereof. When the object 1 to be measured is passed through the interference fringe with the surface thereof traversing it, the intensity of the scattered light thereof gives a repetition of a strong and weak pattern. Thus, the cycle T0 of the strong-weak signal with a photoelectric converter 13 and a laser speedometer signal processor 14 is measured to calculate the ratio D/T0 thereof to the interval D of the interference and a defect is detected in the surface of the object being measured for the speed thereof.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to defect inspection of parts and products such as various machines and structures such as steam turbines, boilers, ships, nuclear couplants, aircraft, rockets, and automobiles.

[Conventional technology]

Conventionally, ultrasonic flaw detection has been generally used to inspect defects in various machines and structures, and the conventional technique will be explained with reference to FIG.

01 is the object to be measured, and 02 is its defects such as cracks, voids, and impurities. 03 is a probe using crystal, barium titanate, etc., which generates ultrasonic waves and transmits them into the object to be measured 01, receives reflected waves, exchanges them into electrical signals, and transmits them to the amplifier 07.

04 is a couplant, and oil or water is usually used. A synchronization signal generator 05 generates a pulse voltage and transmits a synchronization signal to the probe driving device 06 and the signal recording device 08. 06
is a probe drive device that sends high-frequency pulses to the probe to generate ultrasonic waves.

An amplifier 07 amplifies the ultrasonic signal detected by the probe 03 and transmits it to the signal recording device 08. Reference numeral 08 denotes a signal recording device which is activated by a synchronization signal transmitted from the synchronization signal generator 05 to record and display the electric signal transmitted from the probe 03.

In this device, a synchronization signal generated by a synchronization signal generator 05 is transmitted to a probe driving device 06 and a signal recording device 08. The probe driving device 06 generates a high frequency pulse synchronized with the synchronization signal and applies the voltage to the probe 03. When a high-frequency pulse voltage is applied to the probe 03, the probe 03 generates an ultrasonic pulse and transmits it to the object to be measured 01 via the couplant material 04.

Note that if there is air in the couplant 04, the intensity of the ultrasonic wave will be significantly attenuated, so it is necessary to apply the couplant 04 appropriately. A piezoelectric element such as crystal or barium titanate is used for the probe, and the size is 5φ to 10 or more.

The ultrasonic waves transmitted from the probe 03 propagate through the object to be measured, are reflected at the end face, and return to the probe 03 via the couplant material 04. If a defect 02 such as a crack, void, or impurity exists inside the probe 02, a portion of the ultrasonic wave is reflected there and returns to the probe 03 via the couplant 04. When the probe 03 receives the reflected waves from the defect 02 and the end face, it generates a voltage proportional to the intensity of the ultrasonic wave and transmits it to the amplifier 07 . The amplifier 07 amplifies the input signal and transmits it to the signal recording device 08. The signal recording device 08 records and displays the signal received by the probe 03 via the amplifier 07 using the synchronization signal transmitted from the synchronization signal generator 05.

An example of the measurement results obtained by this method is shown in FIG. 4(a).

Shown in fbl. In the same figure (al is the case where there is no defect, and only the transmitted ultrasonic signal T and the reflected wave B from the end face of the object to be measured can be seen. In the same figure (bl is the case where there is a defect, and the transmitted ultrasonic signal T
A reflected wave F from the defect appears between the reflected wave B from the end face of the object to be measured.

[Problem that the invention seeks to solve]

However, the conventional method has the following problems.

(b) Since it is necessary to bring the probe into contact with the object to be measured,
Application to rotating objects such as turbine rotors is extremely difficult.

(b) In addition, when large structures such as boilers and ships are targeted, preparatory work such as setting up scaffolding for the measurer is required, which increases the inspection time.

(c) When targeting mechanical parts with small curvature, such as the roots of gears and the roots of blades, the size of the probe is approximately 5.
It cannot be applied because it is large, φ to 10 trowels.

[Failure to solve the problem]

The present invention was proposed in view of the above circumstances, and by irradiating the object with a laser beam and absorbing the laser beam near the surface, a thermal shock wave is generated. In order to receive thermal shock wave defects and reflected waves from the end face of the measured object, we provide a method for detecting minute bump vibrations of the measured object caused by the reflected waves using a laser velocimeter.

〔Example〕

An embodiment of the method of the invention will be described with reference to FIGS. 1 and 2. FIG. In FIG. 1, 1 is an object to be measured and 2 is a defect. 3 is a pulse laser device, ■Number of IQmJ per pulse
~Several 10 pulsed laser beams with energy of several 100 mJ
It occurs in the frequency range of ~1,000 Hz,
For example, a YAC) laser. This device generates pulsed laser light in synchronization with a signal from a synchronization signal generator 8, which will be described later.

4 is a first condensing lens that condenses the pulsed laser beam into a spot on the surface of the object to be measured. 5 is a pulsed laser beam spot with maximum energy density. 6 is a thermal shock wave,
It is generated by the above-mentioned pulsed laser beam spot. Note that the frequency of this shock wave is proportional to the reciprocal of the pulse width of the pulsed laser beam. Reference numeral 7 indicates a micro-bump vibration, which occurs during irradiation with a pulsed laser beam and when a reflected wave of a thermal shock wave arrives.

Reference numeral 8 denotes a synchronization signal generator, which is controlled by a computer 9 and transmits a synchronization signal to the pulse laser device 3 and the laser speedometer signal processing device 14. 9 is a computer,
The output signal from the laser velocimeter signal processing device 14 is displayed on a display device 10 (described later), controls an XYZ stage controller 11 (described later), and controls the synchronization signal generator 8. A display device 10 displays the output of the computer 9. Reference numeral 11 denotes an XYZ stage controller that drives the XYZ stage under the control of the computer 9. 12 is the XYZ stage, the above XYZ
The object to be measured 1 is driven by the stage controller 11.
move.

A photoelectric converter 13 converts the intensity of the input laser light into an electrical signal. 14 is a laser speed meter signal processing device,
The output signal of the photoelectric converter is converted into a speed signal. 15
is a continuous wave laser device, which is the light source of the laser velocimeter. Note that a Ha-Ne laser is used here. 16 is a continuous wave laser beam. 17 is a beam splitter,
Split the laser beam into two. 18, 19, and 20 are the 1st. The laser beam is reflected by the second and third mirrors. A second condenser lens 21 condenses the laser beam onto the pulsed laser beam spot 5.

22 is scattered light, which has information on the velocity of the surface of the object 1 to be measured. A third condensing lens 23 causes the scattered light 22 to enter the photoelectric converter 13.

To explain the operation of this device, the pulsed laser beam of frequency f generated by the pulsed laser device 3 is passed through the first condensing lens 4.
The pulsed laser beam is focused as a pulsed laser beam spot 5 and irradiated onto the object 1 to be measured. Then, a part of the energy of the pulsed laser beam is absorbed by the object to be measured 1, and a thermal shock wave 6 is generated. Note that since the pulse width of the pulsed laser beam is usually very short, from several tens of microseconds to several hundred microseconds, the frequency of the shock wave is from several tens of KHz to several tens of MHz.

The thermal shock wave 6 propagates through the object to be measured 1 in the normal direction of the pulsed laser beam spot 5. If there is a defect 2 on the way, a part of the shock wave becomes a reflected wave and returns in the opposite direction, that is, in the direction of the position of the pulsed laser beam spot 5.The reflected wave reaches the surface of the object to be measured 1. Then, a minute bump vibration 7 is generated as an elastic vibration.The minute bump vibration 7 is measured by a laser velocimeter as described later, and the presence of a reflected wave can be ascertained.

On the other hand, a portion of the thermal shock wave 6 goes around the defect 2 or passes through it directly, reaches the back surface of the object to be measured 1, and is reflected. The reflected wave from the back surface generates minute vibrations on the surface of the object to be measured 1, similar to the reflected waves from the defects described above.

The presence or absence of the vibration is detected by a laser velocimeter as described below.

Next, detection of surface bump vibrations of the object to be measured 1 using a laser velocimeter will be described. A laser beam 16 generated by a continuous wave laser device 15 is divided into two laser beams of equal intensity by a beam splitter 17, one of which is connected to a first mirror 18, a second mirror 19, and a second condensing beam. lens 2
1, and reaches the position of the pulsed laser beam spot 5.

The other laser beam passes through the second mirror 19 and the second condensing lens 21 and reaches the pulsed laser beam spot 5.
reach the position. The two laser beams propagating along this dual path form interference fringes at their intersection points. Note that the interval between the interference fringes is the wavelength of the laser beam, and θ is the intersection angle of the two laser beams.

When the surface of the object to be measured passes through these interference fringes, the intensity of the scattered light repeats its strength and weakness. Therefore, the photoelectric converter 13 and the laser velocimeter signal processing device 1
4, the period TO of the strength signal is measured and the following calculation, ie, D/To, is performed to obtain the velocity of the surface of the object to be measured. However, the velocity means a velocity component in a direction perpendicular to the bisector of the intersection angle of the two laser beams.

FIG. 2 shows an example of measuring reflected waves of thermal shock waves using a laser velocimeter, ie, an example of application for defect inspection. The same figure (al is the case where there is no defect, the thermal shock wave generation is the waveform T at time 1 (0), and the reflected wave from the back side is the waveform B at time t (Bl)
It is. In the same figure, (bl is the case where there is a reflected wave from the defect, which appears as waveform F at time t, (Fl. This shows almost the same results as the above, but it shows that laser irradiation can do the same thing as ultrasonic flaw detection.

Incidentally, the measurement point can be moved by moving the entire optical system related to the pulsed laser beam irradiation and the laser velocimeter, but in this example, the object to be measured 1 was moved. That is, XYZ controlled by computer 9
This is performed by a stage controller 11 and an XYZ stage 12. Note that the diameter of the pulsed laser beam spot 5 is 0.
．． Good results were obtained when the diameter was 5φ or less.

In this example, a YAG rape is used as the pulse laser device, but a ruby laser, an excimer laser, and a C
It goes without saying that the same thing can be done with an O2 laser. Metals, ceramics, and composite materials can also be used as long as the material of the object to be measured absorbs light.

〔Effect of the invention〕

The present invention has made it possible to inspect products and parts for defects in various machines and structures, such as steam turbines, boilers, ships, and aircraft, in a non-contact manner.

Therefore, it can be applied to rotating objects such as turbine rotors, and it can also be applied to defect inspections of large structures such as boilers and ships using the so-called remote sensing method, without requiring heavy scaffolding as in conventional methods. This makes it possible to apply it to mechanical parts with small curvature, such as the teeth of gears and the roots of blades such as steam turbines.

[BRIEF DESCRIPTION OF THE DRAWINGS] Fig. 1 is a schematic diagram of an embodiment of the method of the present invention, Fig. 2 is an explanatory diagram of its measurement results, Fig. 3 is a schematic diagram of the conventional method, and Fig. 4 is its measurement results. FIG. 1: Object to be measured, 2: Defect, 3: Pulse laser device, 4:
First condensing lens, 5: Pulse laser beam spot,
6: Thermal shock wave, 7: Minute bump vibration, 8: Synchronous signal generator, 9: Computer, 13: Photoelectric converter, 14: Laser velocimeter signal processing device, 15: Continuous wave laser device, 16
: Laser beam, 17: Beam splitter, 18: First
mirror, 19: second mirror, 20: third mirror,
21: Second condensing lens, 22: Scattered light, 23: Third condensing lens once

Claims (1)

[Claims] Pulsed laser light from a pulse laser device that repeatedly generates pulsed laser light is irradiated onto the surface of the object to be measured, generating ultrasonic waves due to thermal shock near the irradiated part, and the ultrasonic waves are transmitted into the object to be measured. A defect inspection method using laser irradiation, characterized in that the presence or absence of a defect is determined by detecting the reflected wave obtained by transmitting the pulsed laser beam and irradiating it to a defect existing inside using a laser velocimeter at the portion irradiated with the pulsed laser beam.