JP6876083B2 - Method of forming a fracture start part of a metal part - Google Patents

Description

The present invention relates to a method for forming a fracture start portion of a metal part, for example, for forming a fracture start portion of a metal part such as an automobile connecting rod (hereinafter, simply referred to as a “connecting rod”).

It may be used as a pair of products in which metal parts are pulled and broken and the parts divided in half are recombined. An example of such a component is a connecting rod (hereinafter, simply referred to as a "connecting rod") known as an automobile component.

For example, Patent Document 1 includes a step of forming a groove portion by broaching at a portion corresponding to a fracture start portion of a metal part and a step of forming a plurality of recess portions at a predetermined interval from each other at a portion at the bottom of the groove portion. A method for forming a fracture start portion of a metal part having a metal part is disclosed.

For example, in Patent Document 2, the focal point is defocused from the inner peripheral surface of the through hole by a certain amount to irradiate the inner peripheral surface of the through hole, and at the same time, an assist gas is supplied to the laser beam irradiation position to form a recessed portion. While irradiating the inner peripheral surface of the through hole with a constant pulse of laser light, the laser light is linearly moved from one side opening to the other side opening of the through hole inner peripheral surface at a predetermined speed. The method of forming a part is disclosed.

Japanese Patent No. 5340822 Japanese Patent No. 4297341

However, in the method described in Patent Document 1, mechanical (cutting tool) processing such as a brooch is required before laser processing. Further, in the method described in Patent Document 2, an assist gas for blowing off the removed substance during processing is required.

The present invention, on the one hand, has been made in view of such circumstances, and an object of the present invention is to provide a method for forming a fracture start portion of a metal part with a simple configuration.

The present invention employs the following configuration in order to solve the above-mentioned problems.

That is, the method for forming a fracture start portion of a metal part according to one aspect of the present invention is a fracture start portion of a metal part having a predetermined through hole and forming a fracture start portion on the inner peripheral surface of the through hole. It is a forming method, and is a path along the path on the inner peripheral surface of the through hole connecting one opening of the through hole to the other opening, while irradiating the laser beam with a constant pulse at the irradiation position of the laser beam. Including a step of forming a large number of recesses separated by a predetermined distance by moving along.

In the above configuration, even if the metal is liquefied and fume is generated by each laser pulse, the liquefied metal is solidified and the fume is diffused during the period when the output of the laser beam is low. Therefore, the laser pulse can reach the metal part without being blocked by the liquefied metal or fume. Therefore, a fracture starting portion is formed, which is composed of a recessed portion having a sufficient depth and in which a raised portion is not formed in the periphery.

In the method for forming a fracture start portion of a metal part according to the above one side surface, in the step of forming a large number of recessed portions, one recessed portion is formed by irradiating the first portion of the path with a laser beam a predetermined number of times with a constant pulse. After forming the above, another recess may be formed by irradiating the second portion of the path with a laser beam with a constant pulse a predetermined number of times. According to this configuration, since the processing width can be adjusted only by setting a numerical value, it becomes easy to support high-mix production.

In the method for forming a fracture start portion of a metal part according to the above one side surface, the step of forming a large number of dents is within a predetermined range included in the path while irradiating the laser beam with a constant pulse. May include scanning with. According to this configuration, the time for adjusting the focal position of the laser pulse can be shortened.

In the method for forming a break start portion of a metal part according to the one side surface, the laser light may be supplied by a laser marker for printing on the metal. According to this configuration, a fracture start portion can be formed on a metal part by a simple laser beam source called a laser marker.

According to the present invention, it is possible to provide a method for forming a fracture start portion of a metal part with a simple structure.

FIG. 1 schematically illustrates an example of the configuration of the fracture start portion forming device 1 according to the present embodiment. FIG. 2 schematically illustrates an example of a perspective view showing a fracture start portion of the connecting rod rough material with a part of the through hole of the connecting rod rough material removed. FIG. 3 schematically illustrates an example of a cross-sectional view of the connecting rod rough material at the breaking position shown in FIG. FIG. 4 schematically illustrates an example of a waveform diagram of a laser pulse in the method for forming a fracture start portion according to the present embodiment. FIG. 5 schematically illustrates an example of a cross-sectional view of the recessed portion 500 formed by the laser pulse according to the present embodiment. FIG. 6 schematically illustrates an example of the functional configuration of the laser beam irradiation device 50 according to the present embodiment. FIG. 7 schematically illustrates an example of a waveform diagram of a laser beam of a comparative example. FIG. 8 schematically illustrates an example of a cross-sectional view of the recessed portion 400 formed by the laser beam of the comparative example. FIG. 9 schematically illustrates an example of a graph showing the relationship between the frequency of the laser pulse and the processing depth of the recessed portion under a predetermined condition.

Hereinafter, embodiments according to one aspect of the present invention (hereinafter, also referred to as “the present embodiment”) will be described with reference to the drawings. However, the embodiments described below are merely examples of the present invention in all respects. Needless to say, various improvements and modifications can be made without departing from the scope of the present invention. That is, in carrying out the present invention, a specific configuration according to the embodiment may be appropriately adopted. Although the data appearing in the present embodiment is described in natural language, more specifically, it is specified in a pseudo language, a command, a parameter, a machine language, etc. that can be recognized by a computer.

§1 Application example First, an example of a situation in which the present invention is applied will be described with reference to FIG. FIG. 1 schematically illustrates an example of the configuration of the fracture start portion forming device 1 according to the present embodiment. The fracture start portion forming device 1 has a through hole in a part thereof, applies tensile stress to divide it into two parts from a specific fractured portion to form a half-split portion, and abuts the fracture surface of the half-split portion again. A device for forming a fracture start in a metal part such as that used. The fracture start portion forming device 1 according to the present embodiment includes, for example, a laser light irradiation device 50. The laser light irradiation device 50 is an example of a device having a function of "irradiating a laser beam with a constant pulse" of the present invention. Further, the laser light irradiation device 50 may be an example of the "laser marker for printing on metal" of the present invention. In the method for forming a fracture start portion of a metal part according to the present embodiment, for example, a pulsed laser beam emitted by a laser beam irradiation device 50 is irradiated to a predetermined fracture start portion forming position to start fracture of the metal component. The part can be formed.

FIG. 2 schematically illustrates an example of a perspective view showing a fracture start portion of a connecting rod rough material, which is a raw material of a connecting rod, with a part of a through hole of the connecting rod rough material removed. Here, the connecting rod is an example of the "metal part" of the present invention. "Metal parts" are not limited to connecting rods, but have through holes in some parts, and apply tensile stress to divide them into two parts from a specific fractured part to make a half-split part, and re-create the fracture surface of the half-split part. As long as the parts are used in contact with each other, for example, a bearing or a half-split spacer may be used. In the example of FIG. 2, a fracture start portion is formed at a position extending from one end opening to the other end opening (break start portion forming position) on one side in the radial direction of the inner peripheral surface of the through hole of the connecting rod rough material. That is, at the fracture start portion forming position, a large number of recessed portions are formed as the fracture start portions at a certain distance from each other.

FIG. 3 schematically illustrates an example of a cross-sectional view of the connecting rod rough material at the breaking position. Here, FIG. 3 shows an example of "a large number of recessed portions separated by a predetermined distance" of the present invention. In the example of FIG. 3, the angle between the inner peripheral surface of the through hole of the connecting rod rough material and the irradiation direction of the laser pulse (the direction in which the recess is formed) is about 30 degrees, and the pitch P of the recess is about 0. It is .1 mm, and the depth D of the recessed portion is about 0.2 to 0.5 mm.

FIG. 4 schematically illustrates an example of a waveform diagram of a laser pulse in the method for forming a fracture start portion according to the present embodiment. In FIG. 4, the horizontal axis represents time and the vertical axis represents output. The laser pulse shown in FIG. 4 is an example of the "constant pulse" of the present invention. In the method for forming a fracture start portion according to the present embodiment, for example, as shown in FIG. 4, a fracture start portion is formed by irradiating a metal part with a laser beam (laser pulse) composed of a plurality of pulses. Various parameters of "constant pulse" (output of laser pulse, repetition frequency of laser pulse, pulse width of laser pulse, etc.) are not particularly limited, but in the example shown in FIG. 4, for example, the interval between laser pulses is about 15 ns. The repetition frequency is about 30 kHz, and the processing point output is about 16 W.

FIG. 5 schematically illustrates an example of the recessed portion 500 formed by the laser pulse according to the present embodiment. In the example of the recessed portion 500 shown in FIG. 5, the recessed portion 500 has a sufficient depth and no raised portion is formed in the periphery. This is due to the following reasons. That is, when the laser pulse is irradiated, a part of the metal on the surface of the metal part is liquefied and a fume is generated. Here, in the laser pulse according to the present embodiment, a period in which the output of the laser beam is low (including a period in which the output of the laser beam is 0) occurs between the individual laser pulses. Even if the metal is liquefied and fume is generated by each laser pulse, the liquefied metal solidifies and the fume diffuses during the period when the output of the laser beam is low. The next laser pulse can reach the bottom of the recess 500 without being blocked by the liquefied metal or fume. Therefore, a recessed portion 500 having a sufficient depth and having no raised portion formed around the recessed portion 500 is formed.

As described above, the method for forming the fracture start portion according to the present embodiment has higher accuracy in processing the recessed portion and is also excellent in energy efficiency as compared with the method for forming the fracture start portion in the comparative example.

§2 Configuration example <Break start part forming device>
In the example shown in FIG. 1, the break start portion forming device 1 includes a bed (base) 10 made of an elongated rectangular thick plate and an X-axis table device 20 provided with a slider 25 that can move in the longitudinal direction of the bed 10. , A Y-axis table device 30 provided with a slider 35 vertically installed on the upper surface of the bed 10 and movable in the vertical direction, and a conrod rough material support portion 40 attached to the slider 25 of the X-axis table device 20. , The laser light irradiation device 50 and the like attached to the slider 35 of the Y-axis table device 30 are provided.

The X-axis table device 20 includes a box-shaped housing 21, a servomotor 22 attached to one end of the housing 21, and two guide rails 23a and 23b attached to the upper surface of the housing 21 over the entire longitudinal direction of the housing. A slider 25 that can move on the guide rail, a ball screw (not shown) that is provided inside the housing and that moves the slider 25 in the X-axis direction according to the rotation of the servomotor 22 and the like are provided.

Further, the Y-axis table device 30 is attached to the housing 31 having a side view trapezoidal shape, the servomotor 32 attached to the upper surface of the housing 31, perpendicular to the upper surface of the bed 10 and parallel to each other. It is built into two guide rails 33a and 33b, a slider 35 that moves on the guide rail in the Y-axis direction, and a housing 31 that is provided inside the housing and moves the slider 35 in the Y-axis direction according to the rotation of the servomotor 32. It is equipped with a ball screw (not shown).

The connecting rod rough material support portion 40 is separated from the bracket portion 41 attached to the slider 25 of the X-axis table device 20 at intervals corresponding to the large end portion and the small end portion of the connecting rod rough material above the bracket portion 41. The arranged plates 42, 43, a pressing portion 44 that presses the small end of the connecting rod rough material, an air cylinder 45 that presses the pressing portion 44 of the connecting rod rough material toward the small end of the connecting rod rough material, and a connecting rod rough material. It is provided with a restraint portion (not shown) that restrains a predetermined portion around the large end portion. The plates 42, 43 of the connecting rod rough material support portion 40 are provided with seat surfaces (spacers) 42a, 43a having a constant thickness for arranging the connecting rod rough material in parallel with the upper surface of the bed 10.

The laser light irradiation device 50 is attached to both ends of the laser light emitting unit 51, the laser light guiding unit 52 that guides the laser light excited by the laser light transmitting unit 51 through a predetermined optical path, and the laser light guiding unit 52. It is composed of two laser light irradiation units 55 and 56 attached to the laser light guidance unit 52 in a state of being formed at a constant angle with each other. The laser beam irradiating portions 55 and 56 are attached to the side surfaces of the laser beam guiding portion 52, and the tip portions 55a and 56a that irradiate the laser beam so that the laser beams radiated by the laser beam irradiating portions 55 and 56 intersect with each other. They are arranged at a certain angle.

<Laser light irradiation device>
Next, an example of the functional configuration of the laser beam irradiation device 50 according to the present embodiment will be described with reference to FIG. FIG. 6 schematically illustrates an example of the functional configuration of the laser beam irradiation device 50 according to the present embodiment. The laser light irradiation device 50 according to the present embodiment may have a function as a laser marker for printing on metal. That is, as described below, according to the method for forming a fracture start portion of a metal part according to the present embodiment, even a simple laser light irradiation device 50 used as a laser marker does not require other incidental equipment or the like. With a simple structure, it is possible to form a fracture start portion on a metal part.

The laser light irradiation device 50 includes a controller 201 and a marker head 202. The controller 201 and the marker head 202 correspond to the above-mentioned laser light transmitting unit 51, the laser light guiding unit 52, the laser light irradiating units 55, 56, and the like.

The laser light irradiation device 50 typically includes a MOPA (Master Oscillator and Power Amplifier) type fiber amplifier. In this embodiment, the laser light irradiation device 50 includes a two-stage fiber amplifier. More specifically, the controller 201 includes an optical amplification fiber 210, a seed laser diode (LD) 202, an excitation laser diode 203, 207, an isolator 204, 206, a combiner 205, 208, and a drive circuit 221. , 222 and a control unit 220.

The marker head 202 includes an optical amplification fiber 209, an optical coupler 216, an isolator 211, a beam expander 212, a Z-axis scanning lens 213, and galvano scanners 214 and 215. In the following description, the laser diode may be simply referred to as "LD".

The optical amplification fiber 210, the LD202 for seeding, and the LD203 for excitation are basic components of a MOPA type fiber amplifier. The optical amplification fiber 210 includes a core to which a rare earth element which is an optical amplification component is added, and a clad provided around the core. Like the optical amplification fiber 210, the optical amplification fiber 209 includes a core to which a rare earth element which is an optical amplification component is added, and a clad provided around the core.

The type of rare earth element added to the cores of the optical amplifier fibers 210 and 209 is not particularly limited, and for example, Yb (ytterbium), Er (erbium), Nd (neodymium) and the like can be used. In the present embodiment, a case where an optical amplifier fiber to which Yb is added as a rare earth element is used will be illustrated. The optical amplifier fibers 210 and 209 may be, for example, a single clad fiber having a single layer of clad around the core, or a double clad fiber having two layers of clad around the core.

The optical amplification fiber 210 amplifies the seed light from the seed LD 202 by the excitation light from the excitation LD 203. That is, in the MOPA type fiber amplifier, the excitation light from the excitation LD203 and the pulsed seed light from the seed LD202 are given to the optical amplification fiber 210. The excitation light incident on the optical amplification fiber 210 is absorbed by the atoms of the rare earth element contained in the core, and the atoms are excited. When the seed light propagates through the core of the optical amplification fiber 210 in a state where the atoms are excited, the atoms excited by the seed light cause stimulated emission, so that the seed light is amplified. In this way, the optical amplification fiber 210 amplifies the seed light by using the excitation light.

The seed LD202 is a laser light source and is a seed light source that generates seed light. The wavelength of the seed light is selected, for example, from the range of 1000 to 1100 nm. The drive circuit 21 pulse-drives the seed LD202 by repeatedly applying a pulsed current to the seed LD202 in accordance with a command from the control unit 220. That is, the seed LD202 emits pulsed seed light.

The seed light emitted from the seed LD202 passes through the isolator 204 and then enters the optical amplification fiber 210. The isolator 204 has a function of passing light in only one direction and blocking light incident in the opposite direction. The isolator 204 allows the seed light from the seed LD202 to pass through and blocks the return light from the optical amplification fiber 210. As a result, it is possible to prevent the return light from the optical amplification fiber 210 from entering the seed LD202. This is because if the return light from the optical amplification fiber 210 is incident on the seed LD202, the seed LD202 may be damaged.

The excitation LD203 is a laser light source, and is an excitation light source that generates excitation light for exciting the atoms of rare earth elements added to the core of the optical amplification fiber 210. When Yb is added as a rare earth element, the wavelength of the excitation light is set to, for example, 915 ± 10 nm. The excitation LD203 is driven by the drive circuit 222.

The seed light from the seed LD202 and the excitation light from the excitation LD203 are combined by the combiner 205 and incident on the optical amplification fiber 210. When the optical amplification fiber 210 is a single clad fiber, both the seed light and the excitation light are incident on the core. On the other hand, when the optical amplification fiber 210 is a double clad fiber, the seed light is incident on the core and the excitation light is incident on the first clad. The first clad of the double clad fiber functions as a waveguide for excitation light. In the process of the excitation light incident on the first clad propagating through the first clad, the rare earth element in the core is excited by the mode of passing through the core.

The laser light amplified by the optical amplification fiber 210 passes through the isolator 206 and is combined with the excitation light from the excitation LD207 in the combiner 208. The excitation LD207 generates excitation light for exciting the atoms of the rare earth element added to the core of the optical amplifier fiber 209. The excitation LD207 is driven by a drive circuit 222.

The optical amplification fiber 209 is optically coupled to the fiber from the controller 201 by the optical coupler 216. The laser light amplified by the optical amplification fiber 210 is further amplified by the excitation light from the excitation LD207 inside the optical amplification fiber 209.

The laser beam emitted from the optical amplification fiber 209 passes through the isolator 211. The isolator 211 passes the laser beam amplified by the optical amplifier fiber 209 and emitted from the optical amplifier fiber 209, and blocks the laser beam returning to the optical amplifier fiber 209.

The beam diameter of the laser beam that has passed through the isolator 211 is expanded by the beam expander 212. The Z-axis scanning lens 213 scans the laser beam in the Z-axis direction (that is, in the vertical direction). The galvano scanners 214 and 215 scan the laser beam in the X-axis direction and the Y-axis direction, respectively. As a result, the laser beam is scanned in the two-dimensional direction on the surface of the object to be processed 250 such as the connecting rod rough material. Although not shown, the marker head 202 may include other optical components such as an fθ lens for condensing laser light.

By scanning the laser beam, that is, the laser pulse from the optical amplifier in the two-dimensional direction on the surface of the object to be processed 250, the surface of the object to be processed 250 made of resin, metal or the like is processed.

In the present embodiment, the optical amplifier is configured to increase the excitation light in the first stage amplification (optical amplification in the controller 201). However, it is not always necessary for the marker head 202 to perform optical amplification. That is, the optical amplifier fiber 209 may be omitted from the marker head 202.

The control unit 220 mainly controls the generation of light by the seed LD202 (seed light source) and the excitation LD203 (excitation light source). More specifically, the control unit 220 receives a command required for scanning the laser beam from the host device 300. Further, the control unit 220 receives a setting from the user via the setting device 301. The control unit 220 controls the drive circuits 221,222 and the galvano scanners 214, 215 and the like according to the user operation from the setting device 301.

The control unit 220 may use any hardware as long as it is configured to give a control command. For example, the control unit 220 may be implemented by using a computer that executes a predetermined program. As the setting device 301, for example, a personal computer can be used. The personal computer may be provided with a mouse, a keyboard, a touch panel, or the like as an input unit.

The characteristics of optical elements such as the seed LD202, the excitation LD203,7, and the isolators 204, 6, 11 can change depending on the temperature. Therefore, it is more preferable to provide the laser beam irradiation device 50 with a temperature controller for keeping the temperature of these optical elements constant.

For the laser beam irradiation device 50 according to the present embodiment, the user can set various parameters as processing conditions independently of each other. The parameters are not limited, but are, for example, the shape of the laser pulse, the output of the laser pulse, the repetition frequency of the laser pulse, the pulse width of the laser pulse, the laser pulse irradiation time in one recess, and the correction values (X correction) of various parameters. A value, a Y correction value, a Z correction value, a θX correction value, a θY correction value, a θZ correction value, etc.) may be included.

§3 Example of a method for forming a break start portion of a metal part Next, a method for forming a break start portion of a metal part according to the present embodiment will be described. Hereinafter, a method for forming a fracture start portion of a metal part will be described by taking the case of using the above-mentioned fracture start portion forming device 1 as an example.
(S1) Installation of Connecting Rod Rough Material First, the breaking start portion is formed by locating the slider 25 of the X-axis table device 20 of the breaking start portion forming device 1 at one side end of the guide rails 23a and 23b. The connecting rod rough material is attached to a predetermined attachment portion of the connecting rod rough material support portion 40. Then, the X-axis table device 20 is driven to move the connecting rod rough material support portion 40 to the lower vicinity of the laser beam irradiation portions 55 and 56.

(S2) Matching the Height of the Center of the Machining Surface and the Laser Light Focus Next, one of the laser light irradiation parts 55 and 56 is placed in the radial direction of one of the inner peripheral surfaces of the through holes of the rough material of the conrod. Position it to the side. At this time, the laser beam of the laser beam irradiation portions 55 and 56 is adjusted so that the focus of the laser beam is aligned with the inner peripheral surface of the through hole of the connecting rod rough material.

(S3) Setting of Machining Conditions Next, various machining conditions are set by operating the setting device 301. The processing conditions are, for example, as described above, the shape of the laser pulse, the output of the laser pulse, the repetition frequency of the laser pulse, the pulse width of the laser pulse, the laser pulse irradiation time in one recess, and the correction values (X correction value) of various parameters. , Y correction value, Z correction value, θX correction value, θY correction value, θZ correction value, etc.) and the like may be included.

(S4) Formation of Breaking Start Part Next, the laser light emitting unit 51 emits the laser light to coarsely control the laser light by the laser light emitting unit (for example, the laser light emitting unit 55) with a predetermined pulse set as described above. Irradiate the inner peripheral surface of the through hole of the material. At this time, for example, one recess may be irradiated with a laser pulse a predetermined number of times, and then the next recess may be irradiated with a laser pulse to form the recesses in sequence. More specifically, when the irradiation of the laser pulse for a specified number of times (for example, 900 times in this example) for one recess forming position is completed, the focal position of the laser light irradiation portion is located at the adjacent recess forming position. After adjusting the positions of the rough material of the conrod and the laser beam irradiation portion as described above, irradiation of the laser pulse to the adjacent recessed portion forming position is executed a predetermined number of times. In this way, on one side in the radial direction of the inner peripheral surface of the through hole of the connecting rod rough material, a large number of recesses (for example, FIG. 2 etc.) are formed at the fracture start portion forming position (for example, FIG. 2) extending from one end opening to the other end opening. , Fig. 3 etc.) are formed at a certain distance from each other as a fracture start portion.

§4 Effect Next, the effect of the fracture start portion forming method according to the present embodiment will be described with reference to FIGS. 7 and 8.

FIG. 7 schematically illustrates an example of a waveform diagram of a laser beam of a comparative example. In FIG. 7, the horizontal axis represents time and the vertical axis represents output. In the example of FIG. 7, the waveform diagram of the laser beam of the comparative example does not repeat the increase and decrease as in the laser pulse according to the present embodiment, and the output increases from 0 to the peak value over a predetermined period. After that, it drops from the peak value to 0 over a predetermined period.

FIG. 8 schematically illustrates an example of a cross-sectional view of the recessed portion 400 formed by the laser beam of the comparative example, and FIG. 8 is a cross-sectional view of the recessed portion 400 formed by the laser pulse according to the present embodiment. An example is schematically illustrated.

In the example of FIG. 8, the recessed portion 400 formed by the laser beam of the comparative example does not have a sufficient depth of 400D, and a raised portion 401 is formed in the periphery. This is due to the following reasons. That is, when the laser beam is irradiated, a part of the metal on the surface of the metal part is liquefied and fume is generated. Here, as described above, the laser beam of the comparative example shows a continuous change that is not pulsed. Therefore, after the metal on the surface of the metal part is liquefied and fume is generated, a part of the laser beam irradiated to the metal part is further blocked by the fume or the liquefied metal, so that the metal part is further blocked. Cannot reach the solid part of. Therefore, the energy of the laser beam is not sufficiently applied to the metal part, and the recessed portion 400 does not have a sufficient depth. Further, the liquefied metal is pushed away to the periphery of the recess 400 by being irradiated with the laser beam. Therefore, the liquefied and pushed-out metal is extruded around the recessed portion 400, and is eventually cooled and solidified to form a raised portion 401.

On the other hand, as described above using the example shown in FIG. 4, in the recessed portion 500 formed by the laser pulse according to the present embodiment, the liquefied metal solidifies and fume during the period between the individual laser pulses. Has a sufficient depth and a raised portion is not formed in the periphery because the swelling portion is diffused.

As described above, the method for forming the fracture start portion according to the present embodiment has higher accuracy in processing the recessed portion and is also excellent in energy efficiency as compared with the method for forming the fracture start portion in the comparative example.

FIG. 9 schematically illustrates an example of a graph showing the relationship between the frequency of the laser pulse and the processing depth of the recessed portion under a predetermined condition. Under the predetermined conditions, the laser power is 80%, the pitch of the recessed portion is 0.1 mm, and the number of laser pulses irradiating the recessed portion is 900.

In the graph shown in FIG. 9, in the frequency range of 0 to about 30 kHz, the processing depth increases as the frequency increases, and when the frequency is about 30 kHz, the processing depth is about 0.5 mm. Further, in the frequency range of about 30 to about 50 kHz, the higher the frequency, the smaller the machining depth, and when the frequency is about 50 kHz, the machining depth is about 0.1 mm. Further, in the frequency range of about 50 kHz or more, the processing depth gradually decreases as the frequency increases.

The reason why the graph shown in FIG. 9 shows the above-described aspect can be explained as follows. That is, when the laser pulse is applied to the metal part, the energy of the laser pulse is given to the metal part. This creates a fume and warms the metal, some of which reaches its melting point and liquefies. Here, in the high frequency region, the residual amount of fume and liquefied metal generated by the previous laser pulse increases, which increases the proportion of the laser pulse that prevents it from reaching the bottom of the recess. As a result, in the high frequency region, the machining depth decreases as the frequency increases. On the other hand, in the low frequency region, the metal is cooled for a relatively long time. Therefore, for example, a metal that is below the melting point but has been warmed to near the melting point is sufficiently cooled during the period between the laser pulses, and the case where the metal does not reach the melting point even if the laser pulse is repeatedly irradiated increases. As a result, in the low frequency region, the machining depth decreases as the frequency decreases.

In the example of FIG. 9, in order to increase the processing depth under the above-mentioned conditions, the frequency is preferably in the range of 10 to 50 kHz, more preferably in the range of 10 to 40 kHz, and more preferably in the range of 20 to 35 kHz.

§5 Modification example In the above-described embodiment, the laser pulse irradiation is moved so as to sequentially form the recessed portions. That is, at the fracture start portion forming position of the conrod rough material, a recessed portion is formed by irradiating one location with a laser pulse a predetermined number of times, and then the laser pulse irradiation position is moved to another location. A dented portion is formed by irradiating the other portion with a laser pulse a predetermined number of times. However, the present invention is not limited to this, and a large number of recessed portions may be formed by scanning the irradiation position of the laser pulse within the fracture start portion forming position of the connecting rod rough material, for example. As a result, the processing width can be adjusted simply by setting a numerical value, which facilitates support for high-mix production. Alternatively, the position where the breaking start portion of the connecting rod rough material is formed is divided into a plurality of sections, and then the irradiation position of the laser pulse is scanned in each section, so that the recessed portion is sequentially formed for each section. It may be formed. As a result, the time for adjusting the focal position of the laser pulse can be shortened.

The embodiments described above are for facilitating the understanding of the present invention, and are not for limiting and interpreting the present invention. Each element included in the embodiment and its arrangement, material, condition, shape, size, and the like are not limited to those exemplified, and can be changed as appropriate. In addition, the configurations shown in different embodiments can be partially replaced or combined.

[Appendix 1]
A method for forming a fracture start portion of a metal part having a predetermined through hole by forming a fracture start portion on the inner peripheral surface of the through hole.
To move the irradiation position of the laser beam along the path along the path on the inner peripheral surface of the through hole connecting one opening of the through hole to the other opening while irradiating the laser beam with a constant pulse. A method for forming a fracture start portion of a metal part, comprising step S4 for forming a large number of recessed portions (500) separated by a predetermined distance.
[Appendix 2]
In the step (S4) of forming a large number of recesses (500), one recess (500) is formed by irradiating the first portion of the path with a laser beam a predetermined number of times with a constant pulse, and then the path (S4) is formed. The method for forming a break start portion of a metal part according to Appendix 1, which comprises forming another recessed portion by irradiating the second portion with a laser beam a predetermined number of times with a constant pulse.
[Appendix 3]
The step (S4) of forming a large number of recesses (500) includes scanning the irradiation position of the laser beam within a predetermined range included in the path while irradiating the laser beam with a constant pulse. The method for forming a fracture start portion of a metal part according to the above.
[Appendix 4]
The method for forming a fracture start portion of a metal part according to any one of Appendix 1 to 3, wherein the laser beam is supplied by a laser marker (50) for printing on a metal.

1 ... Break start portion forming device 10 ... Bed 20 ... X-axis table device 21 ... Housing 22 ... Servo motors 23a, 23b ... Guide rail 25 ... Slider 30 ... Y-axis table device 31 ... Housing 32 ... Servo motors 33a, 33b ... Guide Rail 35 ... Slider 40 ... Conrod rough material support 41 ... Bracket parts 42, 43 ... Plates 42a, 43a ... Seat surface (spacer)
44 ... Pressing unit 45 ... Air cylinder 50 ... Laser light irradiation device 51 ... Laser light transmitting unit 52 ... Laser light guiding unit 55, 56 ... Laser light irradiation unit 55a, 56a ... Tip unit 201 ... Controller 202 ... Marker head 203, 207 ... Laser diode for excitation 204, 206, 211 ... Isolator 205, 208 ... Combiner 209, 210 ... Optical amplification fiber 216 ... Optical coupler 212 ... Beam expander 213 ... Z-axis scanning lens 214, 215 ... Galvano scanner 220 ... Control unit 221 , 222 ... Drive circuit 250 ... Machining object 300 ... Higher-level device 301 ... Setting device 400 ... Recessed part 401 ... Swelling part 500 ... Recessed part

Claims (2)

A method for forming a fracture start portion of a metal part having a predetermined through hole by forming a fracture start portion on the inner peripheral surface of the through hole.
Seed light having a wavelength of 1000 to 1100 nm and excitation light having a wavelength of 905 to 925 nm are combined along a path on the inner peripheral surface of the through hole connecting one opening of the through hole to the other opening. The laser light that has been amplified and supplied by the laser marker for printing on metal is a triangular wave pulse waveform that includes a period with a repetition frequency of 10 to 50 kHz and an output of 0 for each recess. A method for forming a break start portion of a metal part, which comprises a step of forming a large number of recessed portions separated by a predetermined distance by moving the irradiation position of the laser beam along the path while irradiating the laser beam 900 times or more. In the step of forming the large number of recesses, the laser beam is irradiated to the first portion of the path a predetermined number of times with a constant pulse to form one recess, and then the second portion of the path is formed. The method for forming a break start portion of a metal part according to claim 1, wherein the other recessed portion is formed by irradiating the laser beam with a constant pulse a predetermined number of times.

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