JP2021133385A - Laser peening construction method and laser peening construction system - Google Patents

Abstract

To provide a laser peening construction technology capable of applying laser peening under optimum execution conditions.SOLUTION: A laser peening construction method includes: a step S18 of acquiring test results obtained by applying laser peening to a test piece T under a plurality of construction conditions different from each other in energy of at least a laser 6; a step S20 of identifying the construction conditions in which at least a fatigue life of an object Q serving as a construction object can be extended, on the basis of the acquired test results; and a step S22 of applying the laser peening to the object Q by the energy corresponding to the identified construction conditions.SELECTED DRAWING: Figure 7

Description

An embodiment of the present invention relates to a laser peening construction technique.

Conventionally, as a method for improving the fatigue strength of a metal material or preventing the occurrence of stress corrosion cracking, shot peening, laser shock peening, laser peening, water jet peening, ultrasonic peening, etc. are used to apply compressive residual stress to the surface of the metal material. The technology is known.

Japanese Unexamined Patent Publication No. 2017-35712 Japanese Unexamined Patent Publication No. 2017-177162 JP-A-2019-124135

Laser peening applies compressive residual stress to a metal material by means of a plasma shock wave generated by irradiating the surface of the metal material with which water is in contact with a laser. In particular, in order to apply high compressive residual stress, it is appropriate that the plasma generated by the laser spreads in a spherical shape. However, in laser peening, the shape of the plasma tends to collapse because there is water around the surface of the metal material. Further, if the pulse energy is simply increased in order to apply a large compressive residual stress, the shape of the plasma is disturbed, and a sufficient impact force cannot be applied to the surface of the metal material. There is an optimum value for this pulse energy, and there is a demand for laser peening under the most appropriate construction conditions.

An embodiment of the present invention has been made in consideration of such circumstances, and an object of the present invention is to provide a laser peening construction technique capable of performing laser peening under the most appropriate construction conditions.

The laser peening construction method according to the embodiment of the present invention includes a step of acquiring a test result obtained by performing laser peening on a test piece under a plurality of construction conditions in which laser energies are different from each other, and the acquired test result. Based on this, it includes a step of specifying the construction condition that can extend at least the fatigue life of the object to be constructed, and a step of applying the laser peening to the object with the energy corresponding to the specified construction condition. ..

An embodiment of the present invention provides a laser peening construction technique capable of performing laser peening under the most appropriate construction conditions.

The block diagram which shows the laser peening construction system. A side view showing a laser peening device. Top view showing the surface of an object irradiated with a laser. The graph which shows the relationship between the laser energy and the compressive residual stress. The graph which shows the measurement result of the surface roughness of two construction conditions. The graph which shows the number of repeated fractures of the fatigue test under two construction conditions. A flowchart showing a laser peening construction method.

Hereinafter, the laser peening construction method and the embodiment of the laser peening construction system will be described in detail with reference to the drawings.

Reference numeral 1 in FIG. 1 is the laser peening construction system of the present embodiment. This laser peening construction system 1 can provide optimum construction conditions according to the metal material to be constructed when the construction is performed using the laser peening device 2. For example, the laser peening construction system 1 comprehensively determines the results of compressive residual stress, surface roughness, hardness, etc. generated in a metal material, and determines the construction conditions for laser peening.

As shown in FIG. 2, the laser peening device 2 includes a laser oscillator 3, a light guide unit 4, and a laser irradiation unit 5. The laser peening device 2 irradiates the object Q or the test piece T as a metal material with the laser 6.

The laser oscillator 3 is a device that oscillates a pulsed laser 6. The laser oscillator 3 oscillates, for example, a YAG laser. The YAG laser is a laser 6 that oscillates using yttrium aluminum garnet crystals. Further, in order to suppress the influence of the heat of the plasma 7 generated by the laser 6, the pulse width of the laser 6 is set to 10 nanoseconds (1/100 million second) or less.

The light guide unit 4 guides the laser 6 oscillated by the laser oscillator 3 to the laser irradiation unit 5. The light guide unit 4 has, for example, a light guide member such as an optical fiber. Further, the light guide unit 4 may have a collimator to guide the laser 6 in a state of parallel light (collimated light).

The laser irradiation unit 5 irradiates the laser 6 toward the object Q or the test piece T as the metal material. The laser irradiation unit 5 has a condensing lens that collects the laser 6 guided by the light guide unit 4. Further, the laser irradiation unit 5 may have a focal position changing unit for moving the condenser lens in order to change the focal position of the laser 6.

Laser peening applies compressive residual stress to a metal material by the shock wave of plasma 7 generated by irradiating the surface of the metal material (object Q or test piece T) in contact with water 8 with the laser 6. It is a technology. By performing this laser peening, the strength of the metal material can be improved.

When the surface of a metal material is irradiated with a laser 6 having a large energy, plasma 7 of atoms constituting the metal material is instantaneously generated. Here, in the state where the water 8 is present around the plasma 7, the expansion of the plasma 7 is hindered. Then, a shock wave is generated by the reaction force of the plasma 7. The pressure is several GPa. This shock wave propagates in the metal material and applies compressive residual stress to the metal material. By applying this compressive residual stress to the metal material, there is an effect of preventing stress corrosion cracking or fatigue cracking of the metal material. That is, by applying laser peening, the tensile residual stress that causes stress corrosion cracking of the metal material can be changed to the compressive residual stress.

In the present embodiment, the pulsed laser 6 is irradiated toward the object Q or the test piece T provided in the water 8. The object Q or test piece T to be subjected to laser peening does not necessarily have to be provided in water 8. For example, the laser 6 may be irradiated while flowing water 8 on the surface of the object Q or the test piece T.

As shown in FIG. 3, when performing laser peening, the laser 6 is scanned in the X direction (lateral direction) of the surface of the object Q (test piece T). Then, a plurality of irradiation points 9 arranged along the scanning direction are formed. After scanning over a predetermined distance, the irradiation position is shifted in the Y direction (longitudinal direction) and scanning is performed again. By repeating this, laser peening is applied to a predetermined region 10 on the surface of the object Q (test piece T). In the predetermined region 10, rows of irradiation points 9 arranged in the scanning direction are formed so as to be arranged in the pitch direction.

When the laser irradiation unit 5 is moved relative to the object Q in the scanning direction or the pitch direction, the object Q may be fixed and the laser irradiation unit 5 may be moved, or the laser irradiation unit 5 may be moved. 5 may be fixed and the object Q may be moved. Further, both the laser irradiation unit 5 and the object Q may be moved in different directions.

The laser peening construction system 1 of the present embodiment is the most appropriate construction by controlling the irradiation energy of the laser 6, the irradiation diameter, the moving speed in the scanning direction (X direction), and the moving distance in the pitch direction (Y direction). Laser peening is performed under the conditions.

When performing laser peening, the number of pulses per unit length in the scanning direction or pitch direction and the density of irradiation points 9 per unit area are determined by the frequency of the laser 6, the moving speed in the scanning direction, and the moving distance in the pitch direction. Based on this, it is calculated by the following formula.

(Formula 1)
[Number of pulses per unit length in the scanning direction (pulse / mm)] = [Laser frequency (Hz)] / [Movement speed in the scanning direction (mm / sec)]

(Formula 2)
[Number of pulses per unit length in the pitch direction (pulse / mm)] = 1 / [Movement distance in the pitch direction (mm)]

(Formula 3)
[Density of irradiation points per unit area (number of irradiation points / mm ² )] = [Number of pulses per unit length in scanning direction (pulse / mm)] x [Number of pulses per unit length in pitch direction (pulse / mm)] Pulse / mm)]

Here, the number of irradiation points 9 formed on the surface of the object Q (test piece T) and the number of pulses (number of shots) of the laser 6 irradiated from the laser peening device 2 are the same. By controlling the number of pulses per unit length when the laser 6 moves, the number of irradiation points 9 formed on the surface of the object Q can be adjusted.

Next, it will be specifically described using the test results conducted by the inventors. Refer to the graphs of FIGS. 4 to 6.

First, before the construction of the object Q, the test piece T corresponding to the object Q is prepared. For example, a plurality of test pieces T having the object Q formed of the same metal material are used. Laser peening is applied to each test piece T under a plurality of different construction conditions. Then, a repeated load is applied to the test piece T, and a fatigue test is performed to determine the number of repetitions until the test piece T breaks. Then, the construction conditions of laser peening that maximize the number of repeated breaks are obtained.

The conditions for maximizing the number of repeated fractures differ depending on the metal material. For example, there are those having the largest effect of surface residual stress, those having a large effect of surface roughness, and those having a large effect of compressive residual stress. Alternatively, the combined effect of these determines the number of repeated fractures.

In this embodiment, for example, an experiment was conducted on a test piece T of an aluminum alloy. Then, the construction conditions were examined by paying attention to the magnitude of the compressive residual stress on the surface.

The graph of FIG. 4 is a graph showing the relationship between the energy of the irradiated laser 6 and the compressive residual stress generated in the test piece T.

With the irradiation diameter of the laser 6 being constant, laser peening was performed by changing the energy under three conditions in which the densities of the irradiation points 9 were small, medium, and large. In this graph, the triangular marks indicate the test results of the test piece T having a low density at the irradiation point 9, the diamond marks indicate the test results of the test piece T having a medium density at the irradiation point 9, and the square marks indicate the test results of the test piece T having a medium density. The test result of the test piece T having a high density of is shown.

After laser peening was applied to the test piece T, the compressive residual stress on the surface of each test piece T was measured by using an X-ray diffraction method. Since the compressive residual stress is generally indicated by a minus sign, the lower part of the vertical axis represents the larger compressive residual stress.

As shown in this graph, at any of the densities of the irradiation points 9, when the energy of the laser 6 is increased, the compressive residual stress gradually increases, but after showing the maximum value, it tends to decrease again. From these test results, the construction conditions of the two test results R having a large compressive residual stress and a relatively small energy (the density of the irradiation point 9 is medium and large) were selected.

The graph of FIG. 5 shows the result of measuring the surface roughness of the test piece T corresponding to the two construction conditions selected from the graph of FIG. As a result, the surface roughness under the construction conditions where the density of the irradiation points 9 was medium was smaller.

Then, four test pieces T were prepared, and laser peening was performed on two of the test pieces under construction conditions such that the density of the irradiation point 9 was medium. Further, laser peening was performed under construction conditions such that the density of the irradiation point 9 was increased with respect to the remaining two test pieces T. The graph of FIG. 6 shows the results of fatigue testing of these four test pieces T under the same test conditions.

The graph of FIG. 6 shows the number of repeated breaks. Each corresponds to two test results. As a result, as shown in this graph, it was found that the number of repeated breaks of the test piece T under the construction condition where the density of the irradiation point 9 was medium was large. That is, it can be seen that not only the number of fracture repetitions is increased by simply increasing the density of the irradiation point 9, but also an appropriate density of the irradiation point 9 exists.

Based on these results, it was decided to perform laser peening on the object Q. Since the part to be actually constructed has a curvature so that the stress to be applied is concentrated, it is preferable to hit the minimum necessary area only on the necessary part in order to improve the construction efficiency. In that case, it is preferable to hit the laser 6 with at least 5 pulses or more in the scanning direction and 5 pulses or more in the pitch direction.

In the above test results, the construction conditions were selected by focusing on the compressive residual stress on the surface, but even if the surface roughness and surface residual stress are the same, the deeper the compressive residual stress, the larger the number of fracture repetitions. May be obtained. In that case, it is preferable to select appropriate construction conditions according to the material to be selected.

Furthermore, although laser peening was actually performed and measurements or tests were carried out for confirmation, there may be data that has already been obtained depending on the metal material. It may also be calculated. Therefore, it is possible to select the optimum construction conditions even if the examination is conducted using those data.

In the present embodiment, the construction conditions are specified based on at least one of the residual stress, hardness, and surface roughness generated in the test piece T. In this way, the extension of the fatigue life corresponds to at least one of residual stress, hardness, and surface roughness, so that the most appropriate construction conditions for extending the fatigue life can be specified.

The construction conditions include the number of repeated fractures obtained by repeatedly applying a load until the test piece T breaks, the crack growth time until the test piece T breaks, and the cracks that occur in the test piece T per unit time. It is specified based on at least one of the crack growth rates, which is the amount of growth. In this way, the extension of the fatigue life corresponds to at least one of the number of fracture repetitions, the crack growth time, and the crack growth rate, so that the most appropriate construction conditions for extending the fatigue life can be specified. can.

Further, the construction conditions include at least one of the irradiation diameter of the laser 6, the density of the irradiation point 9 of the laser 6 per unit area, and the density of the irradiation points 9 in the scanning direction and the pitch direction of the laser 6. In this way, the compressive residual stress applied by the laser 6 corresponds to at least one of the irradiation diameter, the density of the irradiation point 9 per unit area, and the density of the irradiation point 9 in the scanning direction and the pitch direction. Therefore, the most appropriate construction conditions for extending the fatigue life can be specified.

In the present embodiment, the scanning direction and the pitch direction of the laser 6 are set to appropriate directions with respect to the surface of the object Q. Then, based on the acquired test results, the density of the irradiation point 9 of the laser 6 in the scanning direction and the density of the irradiation point 9 in the pitch direction are set. In this way, a high compressive residual stress can be applied to either the scanning direction or the pitch direction of the laser 6. Even if the density of the irradiation points 9 is lowered as a whole, the compressive residual stress can be increased in only one of the directions by changing the density ratio of the irradiation points 9 in the scanning direction and the pitch direction.

For example, as shown in FIG. 3, it is necessary to apply a high compressive residual stress in the Y direction, but it is not necessary to apply a compressive residual stress in the X direction, depending on the intended use or shape of the object Q. In some cases. In that case, the density of the irradiation points 9 per unit length in the pitch direction is increased, and the density of the irradiation points 9 per unit length in the scanning direction is set to be small. Then, while applying a high compressive residual stress in the Y direction, the total number of irradiation points 9 can be reduced, and the laser peening construction time can be shortened.

Next, the system configuration of the laser peening construction system 1 will be described with reference to the block diagram shown in FIG.

The laser peening construction system 1 includes a test result acquisition unit 11, a construction condition specifying unit 12, a device control unit 13, an information input unit 14, a display output unit 15, and a main control unit 16. These are realized by executing the program stored in the memory or the HDD by the CPU.

Further, the laser peening construction system 1 includes a test result database 17. These are a collection of information that is stored in memory or HDD and organized so that it can be searched or stored.

The laser peening construction system 1 of the present embodiment has hardware resources such as a CPU, ROM, RAM, and HDD, and when the CPU executes various programs, information processing by software is realized using the hardware resources. It consists of a computer. Further, the laser peening construction method of the present embodiment is realized by causing a computer to execute various programs.

Each configuration of the laser peening construction system 1 does not necessarily have to be provided in one computer. For example, one laser peening construction system 1 may be realized by using a plurality of computers connected to each other by a network. For example, the construction condition specifying unit 12 and the device control unit 13 may be provided in individual computers.

The test result acquisition unit 11 acquires the test result using the test piece T. For example, the test result acquisition unit 11 acquires the test results obtained by performing laser peening on the test piece T under a plurality of construction conditions in which the energies of the laser 6 are at least different from each other.

The test result may be a test actually carried out using the test piece T or a test result obtained by a simulation using a computer.

Further, the test result acquisition unit 11 stores the obtained test results in the test result database 17. The test result database 17 stores test results when various metal materials are subjected to laser peening under various construction conditions. The test result acquisition unit 11 may acquire the test results already accumulated in the test result database 17 as well as the mode of acquiring the test results from the outside.

Based on the test results acquired by the test result acquisition unit 11, the construction condition specifying unit 12 specifies construction conditions that can extend at least the fatigue life of the object Q to be constructed. The construction condition specifying unit 12 includes an energy setting unit 18, an irradiation diameter setting unit 19, a density setting unit 20, an aspect ratio setting unit 21, and a direction setting unit 22.

The energy setting unit 18 sets the energy of the laser 6 when performing laser peening.

The irradiation diameter setting unit 19 sets the irradiation diameter of the laser 6 when performing laser peening.

The density setting unit 20 sets the density of the irradiation point 9 formed by the laser 6 when laser peening is performed.

The aspect ratio setting unit 21 sets the density of the irradiation points 9 in the scanning direction of the laser 6 or the density of the irradiation points 9 in the pitch direction of the laser 6 when performing laser peening.

The direction setting unit 22 sets the scanning direction and the pitch direction of the laser 6 with respect to the surface of the object Q when performing laser peening.

The device control unit 13 controls the laser peening device 2. The device control unit 13 adjusts at least the energy of the laser 6 so as to correspond to the construction conditions specified by the construction condition specifying unit 12. Based on the construction conditions, the device control unit 13 determines the irradiation diameter of the laser 6 specified by the construction condition specifying unit 12, the density of the irradiation point 9 of the laser 6 per unit area, or the scanning direction of the laser 6. The density of the irradiation points 9 in the pitch direction may be adjusted.

The information input unit 14 inputs predetermined information according to the operation of the user who uses the laser peening construction system 1. The information input unit 14 includes an input device such as a mouse or a keyboard. That is, predetermined information is input to the information input unit 14 according to the operation of these input devices.

The laser peening construction system 1 of the present embodiment includes a display device such as a display that outputs analysis results. The display output unit 15 controls the image displayed on the display. The display may be separate from the computer body or may be integrated. Further, the display output unit 15 may control the image displayed on the display of another computer connected via the network.

In this embodiment, a display is illustrated as a display device, but other embodiments may be used. For example, a printer that prints information on a paper medium may be used instead of the display. That is, a printer may be included as a target controlled by the display output unit 15.

The main control unit 16 comprehensively controls the laser peening construction system 1.

Next, the laser peening construction method will be described with reference to the flowchart of FIG. The above drawings will be referred to as appropriate.

As shown in FIG. 7, first, in step S11, the user of the laser peening construction system 1 sets necessary conditions such as the metal material used for the object Q and the fatigue life. The user also sets the number of tests to be performed (the number of test pieces T).

In the next step S12, the construction condition specifying unit 12 selects the construction conditions for laser peening.

In the next step S13, the energy setting unit 18 sets the energy of the laser 6 when performing laser peening.

In the next step S14, the irradiation diameter setting unit 19 sets the irradiation diameter of the laser 6 when performing laser peening.

In the next step S15, the density setting unit 20 sets the density of the irradiation point 9 formed by the laser 6 when laser peening is performed.

In the next step S16, the aspect ratio setting unit 21 sets the density of the irradiation point 9 in the scanning direction of the laser 6 or the density of the irradiation point 9 in the pitch direction of the laser 6 when performing laser peening.

In the next step S17, the user performs a test using the test piece T corresponding to the object Q. The test performed using the test piece T may include not only a fatigue test but also other tests.

In the next step S18, the test result acquisition unit 11 acquires the test result using the test piece T. Here, the test result acquisition unit 11 stores the obtained test results in the test result database 17.

In the next step S19, the test result acquisition unit 11 determines whether or not all the fatigue tests have been completed. Here, if all the fatigue tests have not been completed (NO in step S19), the process returns to step S12. Then, the test result acquisition unit 11 acquires the test results obtained by performing laser peening on the test piece T under a plurality of different construction conditions. On the other hand, when all the fatigue tests are completed (YES in step S19), the process proceeds to step S20.

In the next step S20, the construction condition specifying unit 12 specifies the construction conditions that can extend at least the fatigue life of the object Q to be constructed based on the test result acquired by the test result acquisition unit 11. Here, the construction condition specifying unit 12 comprehensively determines the results such as the compressive residual stress, the surface roughness, and the hardness of the test piece T, and determines the construction conditions for laser peening.

If there is no test piece T having a good test result, that is, if there is no test piece T that satisfies the necessary conditions such as fatigue life, the process may return to step S12. Then, steps S12 to S18 may be repeated until a test piece T having a good test result is obtained.

In the next step S21, the direction setting unit 22 sets the scanning direction and the pitch direction of the laser 6 with respect to the surface of the object Q when performing laser peening.

In the next step S22, the device control unit 13 controls the laser peening device 2 under the construction conditions specified by the construction condition specifying unit 12. That is, the device control unit 13 controls the object Q to perform laser peening according to the energy and irradiation diameter of the laser 6 and the density of the irradiation point 9 corresponding to the construction conditions specified by the construction condition specifying unit 12.

Although the flowchart of the present embodiment illustrates a mode in which each step is executed in series, the context of each step is not necessarily fixed, and even if the context of some steps is exchanged. good. Also, some steps may be executed in parallel with other steps.

The system of this embodiment includes a control device in which a dedicated chip, a controller such as an FPGA (Field Programmable Gate Array), a GPU (Graphics Processing Unit), or a CPU (Central Processing Unit) is highly integrated, and a ROM (Read Only). A storage device such as Memory or RAM (Random Access Memory), an external storage device such as HDD (Hard Disk Drive) or SSD (Solid State Drive), a display device such as a display, and an input device such as a mouse or keyboard. , With a communication interface. This system can be realized by a hardware configuration using a normal computer.

The program executed by the system of the present embodiment is provided by being incorporated in a ROM or the like in advance. Alternatively, the program may be a computer-readable, non-transient storage medium such as a CD-ROM, CD-R, memory card, DVD, or flexible disk (FD) that is a file in an installable or executable format. It may be stored and provided in.

Further, the program executed by this system may be stored on a computer connected to a network such as the Internet, and may be downloaded and provided via the network. In addition, this system can also be configured by connecting separate modules that independently perform the functions of the components to each other via a network or a dedicated line, and combining them.

In this embodiment, the laser peening construction method is executed by using the laser peening construction system 1, but other embodiments may be used. For example, the laser peening construction method may be manually executed. In particular, the processing performed by the test result acquisition unit 11 and the construction condition specifying unit 12 may be manually executed.

According to the embodiment described above, laser peening is performed under the most appropriate construction conditions by including a step of specifying construction conditions that can extend at least the fatigue life of the object to be constructed based on the acquired test results. be able to.

Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, changes, and combinations can be made without departing from the gist of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, as well as in the scope of the invention described in the claims and the equivalent scope thereof.

1 ... Laser peening construction system, 2 ... Laser peening device, 3 ... Laser oscillator, 4 ... Light guide unit, 5 ... Laser irradiation unit, 6 ... Laser, 7 ... Plasma, 8 ... Water, 9 ... Irradiation point, 10 ... Region , 11 ... Test result acquisition unit, 12 ... Construction condition identification unit, 13 ... Device control unit, 14 ... Information input unit, 15 ... Display output unit, 16 ... Main control unit, 17 ... Test result database, 18 ... Energy setting unit , 19 ... Irradiation diameter setting unit, 20 ... Density setting unit, 21 ... Aspect ratio setting unit, 22 ... Direction setting unit, Q ... Object, R ... Test result, T ... Test piece.

Claims (6)

At least the step of applying laser peening to the test piece under multiple construction conditions with different laser energies and acquiring the test results obtained.
Based on the acquired test results, a step of specifying the construction conditions that can extend at least the fatigue life of the object to be constructed, and
A step of applying the laser peening to the object with the energy corresponding to the specified construction conditions, and
including,
Laser peening construction method. The construction conditions are specified based on at least one of the residual stress, hardness, and surface roughness generated in the test piece.
The laser peening construction method according to claim 1. The construction conditions include the number of repeated fractures obtained by repeatedly applying a load until the test piece breaks, the crack growth time until the test piece breaks, and the crack growth per unit time of the cracks generated in the test piece. Identified based on at least one of the quantities of crack growth rate,
The laser peening construction method according to claim 1 or 2. The construction conditions include at least one of the irradiation diameter of the laser, the density of the irradiation points of the laser per unit area, and the density of the irradiation points in the scanning direction and the pitch direction of the laser.
The laser peening construction method according to any one of claims 1 to 3. A step of setting the scanning direction and the pitch direction of the laser with respect to the surface of the object,
Based on the acquired test results, a step of setting the density of the irradiation points of the laser in the scanning direction and the density of the irradiation points in the pitch direction, and
including,
The laser peening construction method according to any one of claims 1 to 4. A test result acquisition unit that acquires test results obtained by applying laser peening to test pieces under multiple construction conditions with at least different laser energies.
Based on the acquired test results, a construction condition specifying part that specifies the construction conditions that can extend at least the fatigue life of the object to be constructed, and
A device control unit that applies the laser peening to the object with the energy corresponding to the specified construction conditions.
To prepare
Laser peening construction system.

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