Monitored laser shock peening

The present invention relates to surface peening of a metal work piece, and more specifically to laser impact peening of a metal work piece surface.

The fatigue strength of a metal member can be improved by introducing a compressive residual stress on the surface of such a member. This is typically achieved by shot peening the surface with a small metal bullet to plastically deform and compress the metal surface layer. The metal surface must be uniformly peened to ensure the effectiveness of the peening process.

Laser Impact Peening (LSP), a recent development in peening, uses a high peak power laser to generate mechanical shock waves that generate compressive residual stresses on metal surfaces. This process is performed by applying an absorbent material such as black paint or tape onto the metal surface to absorb energy from the laser beam and generate plasma that rapidly expands or explodes. Plasma generates a shock wave that can plastically deform a metal surface to introduce residual compressive stress into the surface.

LSP is greatly improved by locally confining the expanding plasma and concentrating the explosive pressure on the metal surface. This is typically achieved by covering the metal surface with a thin confinement layer of water that flows continuously over the surface and is replenished as the LSP takes place.

The high power of the laser is generated by operating the laser in pulse mode with a suitable repetition rate or number of pulse repetitions. In this way, the energy of each pulse can be maximized to maximize the impact peening effect, and the confined water film can be replenished between continuous laser beam pulses.

The water film is temporarily disrupted by the occurrence of a small explosion of each laser pulse at the peening position. Therefore, in order to efficiently confine continuous pulse shots, the number of iterations of the output laser must be low enough to ensure that a sufficiently thick and smooth water film is regenerated after each peening pulse. If the number of repetitions is excessively large and the water film is not rapidly regenerated, the continuous laser pulses will not be properly confined, thus degrading the quality of the peening process and reducing the efficiency of the entire peening process. Become.

High power pulse mode lasers configured for LSPs are optimized for performance under high average power thermal loads. Such pulsed lasers operate with maximum efficiency at the corresponding pulse repetition rate. However, operating a pulsed laser below its design pulse repetition rate to ensure that the confinement membrane is regenerated will result in reduced laser performance.

There is currently no practical way to monitor the quality of the water film to ensure the effect of the water film on the LSP. Care must be taken in the LSP process to ensure that a proper water film flows over the surface of the work piece and that this water film is properly regenerated after each laser pulse. This is currently achieved by visually observing the water film and limiting the pulse repetition rate to no more than one pulse approximately every 4 seconds to ensure proper confinement water film regeneration. Has been done.<patcit num="1"><text>U.S. Pat. No. 6,570,126</text></patcit><patcit num="2"><text>U.S. Pat. No. 6,559,415</text></patcit><nplcit num="1"><text>W. Koechner, "Solid-State Laser Engineering," 4th Edition, 1996, Springer-Verlag, New York</text></nplcit>

<p> Therefore, in order to increase the repetition rate of the laser pulse and improve the efficiency of LSP processing, it is desirable to provide a laser impact peening system including automatic monitoring of the confinement membrane.</p>

<p> A pulsed laser is configured to project a pulsed laser beam at a target location on a fluid film on the workpiece for laser impact peening of the workpiece. The fluid film is monitored by a probe laser that projects the probe laser beam at the target position and a photodetector that detects the reflection of the probe beam from the target position. The pulsed laser is tuned by the detector to emit a pulsed beam depending on the monitored membrane.</p>

In FIG. 1, laser impact peening according to one exemplary embodiment of the invention configured to perform laser impact peening on one surface of the metalwork 12 to introduce plastic deformation and the resulting compressive residual stress. (LSP) System 10 is shown.

The same system 10 in which the opposite surfaces of the work piece in the preferred embodiment are simultaneously peened to balance the compressive stresses introduced into the work piece is schematically shown in a square frame on the right side of the work piece 12 in FIG. ing. The system can therefore be used alone or with double-sided peening on any surface of the metalwork, as required.

The work piece 12, which is partially enlarged and shown in FIG. 2, can have any conventional configuration in which it is desirable to perform laser impact peening on the outer surface of the work piece. LSP is performed by first providing a light absorbing layer or ablative layer 14 on the exposed surface of the work piece in order to absorb light energy and generate the desired explosive plasma during processing. The absorbent layer 14 can take any conventional form, such as black paint or tape applied on the exposed surface of the work piece.

As shown in FIG. 1, a suitable means including one or more discharge nozzles 16 is provided to discharge water 18 onto or on the exposed surface of the workpiece along the light absorption layer 14 during work. To do. If both sides are to be peened at the same time, it may also be necessary to discharge water onto the opposite surface of the work piece, typically in the same manner. The work piece can be oriented vertically such that water simply flows down on the work piece surface in the vertical direction to form a relatively thin film on the work piece surface. The water film 18 forms a liquid confinement layer on the absorption layer 14 in order to locally limit the impact peening plasma generated during the work.

The peening laser 20 generates a pulsed laser beam 22 and projects it at a target position or a working position 24 of the fluid film on the upper part of the workpiece. The peening laser is preferably a high peak power laser that operates in pulse mode to generate high energy laser pulses, the high energy laser pulse as a pulse train forming a periodic laser oriented at target position 24. Be projected. The laser or workpiece can be moved such that the laser beam can traverse the entire exposed surface of the workpiece that requires LSP. Such relative motion between the laser beam and the workpiece can be performed by any conventional method by mounting the laser or workpiece on a carriage that preferably drives it.

The peening laser 20 may be of any conventional configuration, such as a neodymium-doped glass (Nd) laser, operated in Q-switched mode with an exemplary output greater than about 1 gigawatt, for example. it can. For example, the peening laser 20 preferably includes a laser slab or rod 26 made of a suitable gain material that is photoexcited to generate a laser beam.

The laser rod 26 is mounted in a cooling housing that includes an opposing flash lamp 28 in any conventional configuration for photoexciting the laser rod 26. A pair of end mirrors 30 are placed at both ends of the laser rod to create a resonator or oscillator cavity in which the laser beam is generated. Conventional optics containing a polarizer are used in the resonator cavity to generate the laser beam. For example, a Q-switch 32 in the form of a Pockels cell is used in a resonator cavity to generate a high pulse output from the laser.

Q-spoiling or Q-switching in high-power pulsed lasers is conventional, and more details can be found in W. Koechner, Solid-State Laser Engineering, 4th Edition, 1996, Springer-Verlag, New York. Seen in Chapter 8 of the literature, especially about Q-switching.

The peening laser 20 is preferably oriented substantially vertically towards the workpiece 12 at the target position 24. As shown enlarged in FIG. 2, the pulse beam 22 is oriented so as to pass through the thin water film 18 and collide with the underlying light absorbing layer 14, which absorbs the laser beam energy. Then, it explodes momentarily and effectively, and the membrane 18 generates a locally limited plasma.

The exploding plasma plastically deforms the exposed surface of the workpiece under the target position, producing a shock wave that leaves a small surface depression with residual compressive stress. The lower part of the workpiece 12 shown in FIG. 2 is subjected to LSP treatment, where the peening laser beam 22 moves in the vertical direction to continue the vertical LSP treatment and, if desired, the workpiece. It traverses the exposed surface in the transverse direction and forms a uniformly plastically deformed compression layer in the exposed surface of the work piece.

A water film 18 can be formed on the surface of the workpiece exposed by any conventional method to produce a reasonably thin confinement layer, and individual laser pulses explode locally to increase the continuity of the film 18. Divide. Therefore, it is not desirable to discharge the continuous laser pulse until the fluid film is regenerated at the corresponding target position 24. Furthermore, various irregularities on the surface of the work piece itself can cause local fragmentation of the fluid film, so that in any form the quality of the fluid film is inadequate or abnormal. Is not desirable to emit a laser pulse. Thus, the LSP system 10 shown in FIG. 1 includes means in the form of a monitoring device 34 that automatically monitors the quality of the fluid film 18 at the target position 24, which means in the particular LSP process in which the fluid film is in use. It is intended for use in controlling the peening laser 20 when in normal condition with the desired sufficient quality.

The monitoring device 34 preferably includes a probe laser 36 that generates a probe laser beam 38 and projects it onto the target position 24 in order to detect the quality of the fluid film 18. The target position itself may be as small as or reasonably larger than the collision position of the peening beam 22 to ensure the proper quality of the fluid film, confining the explosive plasma with maximum effect. it can. The probe laser 36 can be of any conventional type, such as a helium-neon (HeNe) laser or a diode laser, which emits a continuous wave laser beam 38 that is preferably focused at the target location.

The monitoring device also includes a photodetector 40, such as a photodetector, which is optically aligned with the target position to detect the reflection of the probe beam 38 from the target position. The probe laser 36 and the photodetector 40 typically align with the target position 24 at the same tilt angle A with respect to the plane of the fluid film. On the other hand, the peening laser beam 22 is preferably oriented perpendicular to the plane of the fluid film.

The system 10 further includes means in the form of an electrical control device 42 that produces a pulsed laser beam in response to the monitoring state or quality of the fluid film 18 operatively coupled to the peening laser 20 and the photodetector 40.

The peening laser 20 shown in FIG. 1 generates a pulsed laser beam 22 as a pulse train generated at an appropriate pulse repetition rate. The Q-switch 32 is actuated in a conventional manner to switch the laser during photoexcitation of the laser rod 26 at a fixed pumping rate and corresponding thermal conditions. In this way, the operating efficiency of the pulsed laser 20 can be maximized or optimized at a particular pulse repetition rate desirable to increase the processing speed of the LSP.

In a preferred embodiment, the pulse repetition rate of the peening laser 20 is substantially greater than every 4 seconds per cycle typically seen in conventional LSPs, preferably at least 10 cycles per second (10 Hz). This relatively high repetition rate in high power pulsed lasers is designed for maximum efficiency and heat load conditions and can be linked with LSP processing to maximize the peening area range over time.

For such relatively high pulse repetition rates, the condition of the fluid film 18 is monitored after the corresponding short time interval to ensure that the fluid film is regenerated after each laser pulse, thereby producing the laser pulse. It is important to eliminate the possibility of firing and penetrating an inadequate fluid film, which would waste such pulses and reduce the overall efficiency of the LSP process.

As shown in FIG. 1, the control device 42 is preferably operatively coupled with the Q-switch 32 to emit the peening laser beam 22 in conjunction with the monitoring state of the fluid film.

During normal operation, the Q-switched 32 is controlled to generate the desired laser beam pulses in a periodic sequence. However, by monitoring the condition of the fluid film 18 using the photodetector 40, the controller 42 further selects the Q-switch 32 of the pulsed laser 20 only when the normal film 18 is detected at the target position 24. It can be used to make it switchable.

FIG. 2 schematically illustrates an exemplary method of laser impact peening of workpiece 12 in response to the monitoring state of fluid film 18 with the same reference numerals given to the indicated functions of the apparatus of FIG. .. The water film 18 is relatively smooth (ie, the filmed surface has a sufficiently slow motion cycle and the state of the liquid film can be evaluated using the laser monitoring method described above). For example, it can be formed by any suitable method so as to have a thickness B of about 1.0 mm. The pulsed laser 20 then operates to emit a row of laser pulses 22 at target position 24 as the pulse train moves across the surface of the workpiece. Each laser pulse rapidly heats the light absorption layer 14 to generate explosive plasma, which corresponds to peening the surface of the workpiece.

The fluid film 18 at the target position 24 is continuously monitored by projecting the probe laser beam 38 onto the target position and detecting the reflected light from the probe laser beam 38. In a simple embodiment, the presence of film 18 at target position 24 reflects the largest amount of probe laser light energy to photodetector 40. This maximum magnitude of detected light indicates that the pulsed laser is operating continuously and normally.

For example, if the fluid film is disrupted at the target position 24 by a plasma explosion immediately after the preceding laser pulse, the light from the probe laser 36 will be hardly reflected to the photodetector 40. During this anomalous state of the fluid membrane, the controller 42 is used to disable the Q-switch 32 to discharge the laser pulse until the fluid membrane is properly regenerated and sufficient probe light is reflected back to the detector 40. It can be stopped.

In the embodiment shown in FIG. 1, the control device 42 enables Q-switching when the fluid membrane 18 is in a normal state, i.e. smooth and unblocked at the target position, as well as when the fluid membrane is in an abnormal state i.e. It is specifically configured to logically couple the pulsed laser 20 with the photodetector 40 of the monitoring device 34 so that Q-switching is disabled when the target position is fragmented or discontinuous as determined by the monitoring device 34. ing. As used herein, expressions such as "configured" and "fitted" are digital or analog devices (programmable computers) that operate according to algorithms or methods that process input data to provide the desired output signal. , For application-specific integrated mounts, or similar).

In the embodiment shown in FIG. 1, the control device 42 generates a periodic clock signal or a sequence of relatively high voltage values and low voltage values to cause the pulse laser 20 to perform a desired pulse repetition rate. Including 44. The pulsed laser system further includes a conventional electrical driver 46 for Q-switch 32, which would otherwise work with the master clock 44 to generate the laser beam pulse at the desired repetition rate in the prior art. .. However, in the embodiment of FIG. 1, the control device 42 enables the Q-switched driver 46 when the detector detects that the membrane is normal, and the driver 46 when the detector detects that the membrane is abnormal. Changed to work with photodetector 40 to disable.

The control device is preferably configured according to the features of the present invention so that the output signal of the monitoring device 34 is synchronized with the pulse repetition rate of the pulse laser when controlled by the driver 46. This is preferably done by introducing an electrical signal regulator 48 to maximally discriminate between the high voltage signal and the reduced pressure signal generated by the photodetector 40 when monitoring the light from the target position 24. The regulator can include an amplifier and a bias remover suitable for improving the electrical signal generated by the photodetector 40. For example, if the film 18 is smooth, the detector 40 will generate a maximum voltage output due to the light reflected there. When the membrane is disrupted by the laser pulse that produces the explosive plasma, the reflection of the probe laser beam 38 is interrupted and the detector 40 produces a corresponding lower voltage output. This low voltage output will rise to its maximum as the smooth film is regenerated.

The logic converter 50 has a relatively high voltage output signal that corresponds to a normal fluid membrane and represents a logical TRUE state, or a relatively low value that corresponds to an abnormal fluid membrane and represents the opposite FALSE logical value. It is operably coupled to the signal regulator 48 to generate the signal of. In this way, the logic converter 50 generates either a high signal or a low output signal corresponding to the high signal and the low signal from the photodetector 40 corresponding to the normal and abnormal fluid flow states.

The control device 42 cooperates with the logic AND circuit 52 operatively coupled to the photodetector 40 by the signal regulator 48 and the logic converter 50. This AND circuit is operably coupled to the Q-switched driver 46 and the master clock 44. In this way, the Q-switched driver 46 is enabled to generate pulses at the desired number of pulse repetitions corresponding to the clock pulse of the master clock 44 in the conventional manner, but the introduction of the AND circuit 52 is cooperative. Synchronize the Q-switched driver 46 with the operation of the photodetector 40 via a working logic converter 50.

When the photodetector 40 generates a relatively high output voltage corresponding to the normal fluid film state, the logic converter 50 generates a correspondingly high or TRUE value, which is the master in the AND circuit 52. Combined with the signal from clock 44, it enables the Q switch driver 46 when the high peak of the signal from logic converter 50 matches the corresponding high peak of the master clock signal. However, when the photodetector 40 generates a low output voltage corresponding to the abnormal fluid film state, the logic converter 50 generates a low or FALSE state, which causes the AND circuit 52 to Q-switch regardless of the signal from the master clock. Disable switch driver 46.

Therefore, with the introduction of the monitoring device 34 and the AND circuit 52 that cooperates with it, the Q-switched driver 46 is enabled only when permitted by the monitoring device. In this way, the pulsed laser 20 is designed and configured to achieve maximum efficiency at the desired number of pulse repetitions, and can operate at that number of pulse repetitions, and the pulse beam 22 is in a normal state. It is blocked by disabling the Q-switched driver 46 only when necessary to ensure the formation of (ie, a film sufficient to accommodate the laser peening process described above).

The pulsed laser 20 also includes a conventional flash lamp driver 54 coupled to operate in synchronization with the master clock 44. However, in order to achieve the maximum efficiency of a laser that is photoexcited at a fixed excitation rate and thermal state, it is preferable to use a Q-switched driver 46 instead of the flash lamp driver 54 to control the pulsed laser 20.

In the basic embodiment shown in FIG. 1, the control device 42 controls the operation of the pulsed laser 20 in response to the relative intensity or magnitude of the reflected probe beam 38 sensed by the detector 40. It is composed of. The smooth water surface at the target location will best reflect the probe beam and be received by the detector 40, with correspondingly high reflection measurements associated with normal or smooth membranes. On the other hand, for example, an abnormal film fragmented by a preceding laser pulse hardly reflects when there is even one probe beam directed at the detector 40, and the detector measures a relatively low value of reflected light. It will be.

The performance of the photodetector 40 can be enhanced by introducing a focusing lens 56 that is optically aligned between the detector 40 and the target position 24 to collect the reflected light and focus it on the detector. A pinhole opening 58 is optically aligned and placed between the detector 40 and the lens 56 to provide highly collimated specular reflection of the probe beam at the target position and fragmentation immediately after the laser pulse explosion during LSP processing. It is possible to discriminate from the dispersed or diffused beam light from the target position.

A narrowband optical filter 60 is placed optically aligned between the detector 40 and the aperture 58 to reduce or eliminate unwanted background light such as broadband light emitted by the explosive plasma itself. The filter 60 preferably has a passing wavelength centered on the wavelength of the probe laser beam 38 so as to reliably detect the probe laser light and not detect unwanted background light.

As shown above, the signal regulator 48 results from the photodetector 40 by discriminating between the relative high and low values of the signal corresponding to the normal and abnormal smoothness of the water film 18. Adjust the resulting signal appropriately. The tuned signal is converted to a logical TRUE or FALSE voltage level in the logic converter 50 and coupled with the signal from the master clock 44 in the logical AND circuit 52, and the TRUE or normal signal is detected by the photodetector 40. Only then will the Q switch driver 46 be enabled. Conversely, the driver 46 is disabled if the detector 40 emits a FALSE or anomaly signal indicating that the membrane is temporarily inadequate for efficient LSP processing.

In the basic embodiments shown in FIGS. 1 and 2, the quality of the water film 18 detected is the relative smoothness of the water film that allows the detectable reflection of the probe beam 38 on the photodetector 40. Can only be. In order to further improve the LSP treatment, it is desirable to measure the actual thickness of the water film 18, which should be larger than, for example, about 0.5 mm, in real time. However, the thickness measurement of the film 18 needs to be achieved on the spot in real time and without breaking the film itself. Typically, an ultrasonic device is often used to measure the thickness of a solid member, but when this is applied to the thickness measurement of water, the ultrasonic device is intrusive and the water film to be measured It will be divided.

Therefore, FIG. 3 shows a partial modification of the LSP system 10 shown in FIG. 1 to include a light monitoring device 34A specially configured to measure the thickness B of the water film 18 at the target position 24. A minimum thickness B of about 0.5 mm can be sufficient to correspond to the desired normal thickness for film 18, and smaller or inadequate thicknesses are typically immediately after the laser pulse explosion at the target location. Corresponds to the abnormal membrane that occurs in.

As shown in FIG. 2, the probe beam 38 is oriented to the target position 24 at a suitable tilted angle of incidence A that produces two reflections at the target position. The first reflection is a simple specular reflection from the surface of the water film. The second reflection is the result of the refraction of the incident beam into the water film, the reflection from the interface with the workpiece, and the refraction from the film surface to the outside, which is approximately parallel to specular reflection, but there. Generates a beam separated by the displacement C from.

The film thickness B can be obtained by conventional optical analysis by measuring the displacement interval C. Specifically, the distance C between the two reflections is the incident angle A divided by the square root of the difference between the film thickness B and the square of the refractive index n (n = 1.33) of water and the square of the sinus of the incident angle. Is equal to the product of twice the sine. That is, C = Bsin2A / (n²-sin²A)^1/2Is.

The graph of this relationship shows that the spacing C is always smaller than the film thickness B, which makes it more difficult to measure small films in the range of hundreds of microns to about 1.0 mm thick. Suitable probe lasers of the conventional HeNe type have a beam diameter of about 1.0 mm, which is approximately equal to or greater than the desired thickness of the film.

Furthermore, although the surface of the water shown in FIG. 2 is flat, it may actually contain ripples, which focus or diverge the two reflections in response to the ripples, increasing the magnitude of the projected displacement interval C. Change. In addition to this, the surface of a typical workpiece is relatively rough, and the components of the probe beam reflected from the surface of the workpiece are reduced in proportion to the roughness compared to the probe beam specularly reflected from the surface of the water. Has a size. However, these difficulties are present in the present invention as shown in FIG. 3 in which a plurality of photodetectors in the form of a two-dimensional flat array 40A are arranged optically aligned with the target position 24 to detect the reflected image. It can be overcome by the embodiment. Collaborative imaging lenses 62 are placed optically aligned between the detector array 40A and the target position 24 to focus the image of the target position on the detector array. In order to invert and focus the image of the target position on the detector array 40A, the imaging lens 62 includes a plurality of cooperating lenses. For example, a group of four lenses taken from a conventional copier was used in one test embodiment to relay the image of the target position to the detector array. The detector array can be in the form of a conventional charge-coupled device (CCD), typically used in video cameras for capturing images.

The focusing lens 64 is optically aligned and placed between the probe laser 36 and the target position 24 to focus the probe laser beam at the target position. For example, a HeNe laser beam with a diameter of 1.0 mm initially should be focused to about 0.05 mm to improve the discrimination of both reflected beams at the target position for the purpose of measuring the distance C between the two reflected beams. Can be done.

As shown by the broken line in FIG. 3, although the ripple of the water film 18 occurs during the operation of focusing or diverging the two reflected beams, an accurate image of the reflection source can still be obtained. In this way, accurate imaging of the two laterally offset reflected beams can be obtained and appropriately measured.

During operation, the focusing lens 64 focuses the probe beam 38 at the target position 24, and the focal length of the lens is preferably exactly equal to the distance between the lens and the target position on the surface of the water. The focused beam is reflected from the surface of the water and the interface with the workpiece, and the two reflected beams are captured by the imaging lens 62 that relays the image to the detector array 40A. The image from this array is then appropriately processed by the controller 42 to determine the beam spacing C and further the film thickness B.

The imaging lens 62 relays images of reflected spots from the water surface and the surface of the work piece onto the detector array with a corresponding spacing D between the two reflected images that are substantially unaffected by the ripples in the water film. To do. The spacing D of the reflection spots imaged on the array 40A is related to the spacing C measured in air, where the spots are generated at the target position by the corresponding magnification used in the imaging lens 62. Will be done. In this way, using the above formula, the film thickness B can be easily obtained from the interval C of the reflection spots detected on the array 40A and the corresponding interval D.

The controller 42 is therefore operably coupled to the detector array 40A and is configured to have suitable software for measuring, for example, the interval D, which in turn reflects the probe beam from the surface of the water film. Represents the distance C between and the reflection from the surface of the workpiece under the film at the target position.

Conventional software for analyzing the image can be used to identify the two reflection spots sensed by the detector array 40A and accurately measure the distance between them.

Therefore, the control device 42 further obtains the thickness B of the water film 18 at the target position from the separation distance D obtained by the relationship between the above equation and the above-mentioned distances C and D and the magnification of the imaging lens 62. It can be configured by adding software to calculate. The controller then compares the measured thickness B of the film with a memorized reference value, such as 0.5 mm, to determine if the film thickness is sufficient or inadequate for the LSP treatment. Can be done.

Similar to the description in the embodiment of FIG. 1, the control device 42 includes a logic converter 50 that activates the Q-switched driver 46 when a sufficient film thickness is measured, and an AND circuit 52 that cooperates with the logic converter 50. The converter 50 can be similarly configured to give the AND circuit 52 a logical TRUE value. When insufficient thickness is measured, the logic converter 50 generates a FALSE value for the AND circuit 52 to disable the Q-switched driver. In this way, the pulsed laser 20 can be operated in the same manner as described above and with similar advantages and is controlled by the thickness of the water film 18 measured using the modified form of the monitoring device 34A. can do.

A particular advantage of using the imaging lens 62 is that the measured value of film thickness B is relatively unaffected by the particular tilting characteristics of the rippled water surface. The two reflection spots at the target location are accurately imaged on the focal plane of the detector array 40A and have a corresponding spacing regardless of the presence and magnitude of ripples on the water surface, and the spacing between the reflection spots is It will be determined only by the magnification of the imaging lens 62.

Another advantage of this monitoring device is that some of the light that is about to be scattered will always pass through the imaging lens 62 and be imaged and detected on the detector array, regardless of the surface roughness or scattering of the workpiece. Is Rukoto. Therefore, even a non-mirror surface, that is, a rough surface, can be treated and monitored in this way.

The sensitivity of the monitoring device 34A can be varied and scaled by selecting a specific imaging lens 62 and the distance between the workpiece and the detector array 40A. Increasing the sensitivity and accuracy of film thickness measurement can be easily achieved by increasing the focal length of the imaging lens 62 accordingly and increasing the distance between the workpiece and the detector array 40A accordingly. It is said.

An additional advantage is obtained by incorporating an optically aligned adjustable aperture 66 between the detector array 40A and the imaging lens 62. This aperture can be used to adjust the relative brightness of the beam component reflected by the water surface and the beam component reflected by the workpiece on the array. Specular reflections from the water surface are typically significantly brighter than reflections from workpieces, the relative brightness of which can be adjusted by openings 66 to improve discrimination between the two reflections and the spacing measurement between the two reflections. If desired, the brightness of any of the reflection spots can be attenuated by interposing a conventional dimming filter between the desired reflection spot and the lens 62.

In yet another embodiment, a telecentric lens can be used to replace the imaging lens 62. Lenses that are telecentric in image space do not change the image spacing in the detector array 40A as a function of focal length. Thus, the distance measurement between two spots detected on the detector array 40A is not sensitive to the focal position. By utilizing this advantage, it is possible to reduce the fluctuation of the measured value due to the error in the construction of the monitoring device setting.

Testing of monitoring equipment configured to fit Figure 3 accurately measured the thickness of the water layer in the range of about 0.1 mm to about 1.5 mm despite water ripple. Therefore, such a monitoring device enables and disables the Q-switched driver 46 to control the operation of the pulsed laser 20, thereby ensuring an appropriate film thickness during real-time LSP processing and optimizing the performance of the pulsed laser itself. It can be effectively incorporated into the LSP system shown in Fig. 1 so as to substantially increase the processing speed.

Although only certain preferred features of the present invention have been illustrated and described, those skilled in the art will be able to make many modifications and modifications. It should be noted that the reference numerals described in the claims are for the sake of comprehension and do not limit the technical scope of the invention to the examples.

<figref num="1">Schematic of a laser impact peening system according to one exemplary embodiment of the present invention.</figref><figref num="2">An enlarged view of a workpiece being laser impact peened in FIG. 1 showing an exemplary method of peening work.</figref><figref num="3">FIG. 6 is a schematic view of the laser impact peening system of FIG. 1 according to another embodiment of the present invention.</figref>

Code description

10 Laser Impact Peening (LSP) System 12 Metalwork 14 Light absorption layer 16 Discharge nozzle 18 Water, water film, fluid film 20 peening laser 22 Pulsed laser beam, laser beam, peening laser beam 24 Target position 26 Laser slab, laser rod 28 flash lamp 30 End mirror 32 Q switch 34 Monitoring device 34A Optical monitoring device 36 probe laser 38 Continuous wave laser beam, probe laser beam 40 photodetector 40A detector array 42 Control unit 44 master clock 46 Q-switched driver 48 Electrical signal regulator 50 logic converter 52 Logical AND circuit 54 Flash lamp driver 56 Condenser lens 58 pinhole opening 60 Narrow band optical filter 62 Imaging lens 64 Condenser lens 66 Adjustable opening