JP2020076148A - Surface hardening treatment method for workpiece - Google Patents

Abstract

To provide a surface hardening treatment method in which a sufficient depth of a cured layer is obtained while preventing a tempering layer from being formed on a surface of a shaft-shaped workpiece.SOLUTION: The surface hardening treatment method is a method for irradiating a region to be cured of a rotating shaft-shaped workpiece with laser light, heating the processed region, and then self-cooling. The method includes a first step of applying a laser beam to the cured processing region by setting a rotation speed S of the workpiece to a first rotation speed S1, and a second step of additionally irradiating the cured processing region with the laser beam while accelerating the rotation speed to a second rotation speed S2. The first rotation speed S1 has a low speed such that the irradiated region heated by being irradiated with the laser light becomes equal to or lower than a tempering temperature by self-cooling when the workpiece has been rotated by one turn. The second rotation speed S2 is such that the irradiation region heated by irradiation with the laser light is maintained at a temperature higher than the tempering temperature even when the irradiation region is self-cooled when the workpiece has been rotated by one or more turns.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a surface hardening treatment method for a metal workpiece using an energy beam such as a laser or an electron beam, and more specifically, it has a shaft-like portion in at least a part thereof, and the shaft-like portion has an entire circumferential direction. The present invention relates to a method for surface-hardening a metal work having a region to be hardened which is to be hardened.

  In the following description, a work having a shaft-shaped portion at least in part will be referred to as a shaft-shaped work.

  In addition, the same reference numerals are given to the same parts and the same parts throughout the drawings.

  For example, in the case of shaft-shaped workpieces made of steel, such as camshafts for automobile parts, ball screws for machine tools, and spindles, for the shaft-shaped portion that requires mechanical strength and wear resistance, etc. Surface hardening treatment is generally performed.

  By the way, as one of the surface hardening treatment methods for a steel work, quenching by an energy beam such as a laser or an electron beam can be mentioned. Quenching with an energy beam is performed by irradiating the area to be hardened on the surface of the workpiece such as steel material to be hardened for a short time with the energy beam to heat the irradiation point to a temperature above the transformation point to austenite, The surface layer portion of the work is made to have a quenched structure (martensite structure) by cooling, that is, rapid cooling by heat diffusion inside the work.

  In general, the surface hardening treatment by the energy beam does not require a cooling device or coolant, and it can be applied to parts with complicated shapes and can be applied to small parts, deep grooves, side surfaces of holes, and bottom surfaces of holes. It is advantageous. Further, in the carburizing treatment for heating the entire part to a high temperature, thermal deformation occurs, and machining is required after the hardening treatment, but quenching by the energy beam can locally treat a part of the work surface. There is little deformation, and machining after processing can be minimized. On the other hand, in the case of the surface hardening treatment using the energy beam described above, there is a problem that a sufficient hardened layer depth cannot be secured.

  FIG. 8 shows a steel shaft shape having a shaft-shaped portion (1a) in at least a part thereof, and a region to be hardened (2) to be hardened over the entire circumference in the shaft-shaped portion (1a). An example of a method for performing a surface hardening treatment on a work (1) by using a laser beam (4) as an energy beam is shown. The surface hardening treatment method, above the shaft-shaped work (1), a laser oscillator (3) as an energy beam irradiation source is arranged, for example, the shaft-shaped work (1) the center line (1a) of the shaft-shaped portion (1a). By rotating the workpiece (1) and the laser oscillator (3) relative to each other by rotating around (X), the laser oscillator (3) is moved to the cured region (2) of the shaft portion (1a). Irradiation area (5) of curing area (2) by irradiating laser beam (4) (energy beam) from laser oscillator (3) on the area to be cured (2) while moving relatively in the circumferential direction. Is heated to a temperature equal to or higher than the transformation point to be austenitized, then rapidly cooled by self-cooling, and the hardened region (2) is quenched to form a hardened layer.

  In the method shown in FIG. 8, in order to secure a sufficient depth of the hardened layer, the rotation speed of the work (1) is set to a low speed, and the laser oscillator for the hardening target region (2) of the shaft-shaped part (1a) is set. By irradiating the region (2) to be cured of the shaft-shaped portion (1a) with the laser beam (4) while reducing the relative movement speed of (3), a large amount of heat is applied in the depth direction for quenching. There is a need to do.

  Patent Document 1 describes an example of a surface hardening treatment method capable of sufficiently ensuring the depth of a hardened layer. In the method described in Patent Document 1, the workpiece (1) is preheated by irradiating it with the laser beam (4) while rotating the workpiece (1) at a relatively high speed, and then the workpiece (1) is rotated at a relatively low speed while the shaft-shaped portion (1a This is a method of uniformly heating the entire area (2) to be cured above the transformation point and then rapidly cooling it by self-cooling.

  However, in this case, in the tissue distribution of the cross-section of the shaft-shaped portion (1a) of the work (1) that has been subjected to the surface hardening treatment, although a deep hardened layer (6) is obtained as shown in FIG. A tempered layer (7) is formed in the vicinity of the end point (8). This tempered layer (7) was cooled to the tempering temperature at the point where the hardened layer (6) had already been cooled and formed near the irradiation end point (8) of the laser beam (4) in the work (1). It occurs due to being heated. The tempered layer (7) becomes a problem because it has a lower hardness than the surrounding hardened layer (6). For example, when parts are brought into contact with each other on the tempering layer (7) during the assembly and operation of mechanical parts, damage such as wear, deformation and scratches occurs. These damages impair the dimensions and accuracy of the parts and, in the worst case, impair their function as mechanical parts. For these reasons, preventing or suppressing the occurrence of the tempered layer (7) is important in the surface hardening treatment.

  The methods described in Patent Documents 2 and 3 are known as surface hardening treatment methods for a shaft-shaped work that can prevent the above-mentioned tempering layer (7) from being generated.

  According to the method described in Patent Document 2, in the method shown in FIG. 8, the workpiece (1) is irradiated with a laser beam (4) while being rotated a plurality of times at a relatively high speed, so that the shaft-shaped portion (1a) is cured. This is a method in which the entire region (2) is uniformly heated to the transformation point temperature or higher and then rapidly cooled by self-cooling.

  According to the method described in Patent Document 3, in the method shown in FIG. 8, by irradiating the laser beam (4) while rotating the workpiece (1) a plurality of times at a relatively high speed, the axial portion (1a) to be heated is Among the circumferential portions of the cured region (2), the temperature of the hottest portion exceeds the austenitizing temperature, and the temperature of the coldest portion falls below the austenitizing temperature and the martensite transformation start temperature It is a method in which the material is heated to a temperature higher than the above and then rapidly cooled by self-cooling.

  According to the methods described in Patent Documents 2 and 3, the surface of the region to be cured (2) in the shaft-shaped portion (1a) of the work (1) can be reheated before being self-cooled, and laser light ( It is possible to prevent the vicinity of the irradiation end point (8) of 4) from reaching the tempering temperature and prevent the occurrence of a tempering layer. Then, as shown in FIG. 10, it is possible to obtain a uniform hardened layer (6) having no tempering layer in the vicinity of the irradiation end point (8) of the laser beam (4).

Japanese Patent Laid-Open No. 1-116025 JP-A-57-171618 Japanese Patent No. 5756745

  The methods described in Patent Documents 2 and 3 are useful for obtaining a uniform hardened layer (6) without a tempered layer as shown in FIG. 10, but as an effect of rotating the work (1) at high speed, The amount of heat input in the depth direction decreases, and it becomes difficult to secure a sufficient depth of the hardened layer (6).

  In the methods described in Patent Documents 2 and 3, in order to obtain a deeper hardened layer (6) in the region to be hardened (2) while the work (1) is rotated at a high speed, a laser oscillator (3) is usually used. However, the high-power laser oscillator (3) is expensive and leads to a large increase in equipment cost. Therefore, there is a strong demand for a treatment method that secures the depth of the hardened layer (6) with a small laser output and does not generate a softened layer due to tempering.

  This invention has been made in view of the above problems, and as a surface hardening treatment method for a shaft-shaped workpiece by irradiating an energy beam such as a laser, a tempering layer is prevented from being formed in the vicinity of the irradiation end point. Above, it aims at providing the method of obtaining a hardened layer of sufficient depth.

  The present invention has the following aspects to achieve the above object.

1) Relative movement of a metal work having at least a part of a shaft-like part and a hardening target region to be hardened along the entire circumference in the shaft-like part, and an energy beam irradiation source By doing so, the energy beam irradiation source is irradiated with an energy beam from the energy beam irradiation source to the curing target region while moving the energy beam irradiation source relatively in the circumferential direction of the curing target region of the shaft-shaped portion. A method for surface hardening treatment of a work, wherein a hardening layer is formed in the hardening target area by heating the hardening target area and then allowing it to self-cool,
The relative movement speed of the energy beam irradiation source with respect to the hardening target area of the shaft-shaped portion is set to a first speed, and the hardening target area is irradiated with an energy beam to heat the hardening target area of the workpiece. And the first step, the relative movement speed is accelerated to a second speed that is faster than the first speed, and an energy beam is overlapped and irradiated on the region to be cured, And a second step of heating
The first speed is the irradiation target area heated by being irradiated with the energy beam from the energy beam irradiation source in the hardening target area, and the energy beam irradiation source is the circumference of the hardening target area of the axial portion. When the relative movement in the direction of one or more turns, the cooling speed is set so that the tempering temperature will be below the tempering temperature due to self-cooling.
The second speed is the irradiation target area heated by the energy beam irradiation from the energy beam irradiation source in the curing processing area, and the energy beam irradiation source is the circumference of the curing processing area of the axial portion. When the relative movement in the direction of 1 or more turns, the high speed is maintained at a temperature higher than the tempering temperature even if it is self-cooled, or the high speed is reduced so that the region of the irradiated region having the tempering temperature or lower is reduced. A surface hardening treatment method for a work, comprising:

  2) The method for hardening the surface of a work according to 1), wherein the acceleration from the first speed to the second speed is performed at a constant acceleration.

  3) Accelerate the relative moving speed from the first speed to the second speed in proportion to time or relative rotation angle of the energy beam irradiation source with respect to the region to be cured of the shaft-shaped portion. The work surface hardening treatment method according to the above 2), which is characterized in that

  4) Upon acceleration from the first speed to the second speed, the acceleration increases with the passage of time, and gradually shifts from the initial low acceleration state to the high acceleration state as it approaches the second speed. The method for surface hardening a work according to the above 1), characterized in that the work is hardened.

  5) The relative speed of the first speed according to a downward convex function whose independent variable is the time or the relative rotation angle of the energy beam irradiation source with respect to the region to be cured of the shaft-shaped portion. To the second speed, the method for hardening a surface of a work according to the above 4).

  6) The surface hardening treatment method for a work according to the above 5), wherein the downward convex function is a downward convex function having an acceleration start point as a minimum value.

  7) The downward convex function is one function selected from the group consisting of an Nth-order function, a trigonometric function, an exponential function and a sigmonide function, or a function combining two or more functions selected from the group. The surface hardening treatment method for a work according to the above 5) or 6).

  According to the methods of 1) to 7) above, the relative movement speed of the energy beam irradiation source with respect to the region to be cured of the shaft portion is set to a first speed, and the region to be cured is irradiated with an energy beam. The first step of heating the area to be cured of the work, and, following the first step, accelerating the relative movement speed to a second speed that is faster than the first speed to perform the hardening. A second step of irradiating a treatment area with an energy beam in an overlapping manner to heat the work, and the energy beam is radiated from the energy beam irradiation source in the curing treatment area at the first speed of the first step. The irradiated area heated by heating the energy beam irradiation source to a low speed such that the energy beam irradiation source becomes below the tempering temperature due to self-cooling when the energy beam irradiation source relatively moves one or more times in the circumferential direction of the cured area of the shaft-shaped portion. Since it is set, the heat input amount in the depth direction of the irradiation portion can be increased and a deep hardened layer can be obtained.

  Further, in the second step, when accelerating the relative moving speed from the first speed to the second speed, the second speed is increased by an energy beam from the energy beam irradiation source in the region to be cured. The temperature of the irradiated area that has been irradiated and heated exceeds the tempering temperature even if it is self-cooled when the energy beam irradiation source relatively moves one or more times in the circumferential direction of the hardening target area of the shaft-shaped portion. Is set to a high speed such that the tempering temperature in the irradiated region is reduced to a temperature equal to or lower than the tempering temperature in the irradiated region. Formation can be prevented or suppressed. Further, in the process of gradually increasing the rotation speed, the formation of the softened layer due to the above-described tempering can be avoided while ensuring the heat input in the depth direction, so that a deep hardened layer can be obtained.

  Therefore, it is possible to form a hardened layer having a relatively uniform hardness in the circumferential direction, which is less affected by tempering to the vicinity of the end point of the energy beam irradiation, while ensuring the depth. Further, as a result, it is possible to suppress the output of the energy beam while ensuring the depth of the hardened layer, and thus it is possible to suppress the equipment cost for the surface hardening treatment.

  According to the methods 4) to 7), in the second step, tempering in the depth direction can be reduced in the process of accelerating the relative moving speed from the first speed to the second speed. This makes it possible to keep the depth of the hardened layer formed in the first step constant. Therefore, as compared with the case of making one round in the circumferential direction at the first speed, a deep hardened layer which is relatively uniform in the circumferential direction in the vicinity of the end point of irradiation of the energy beam is less affected by the softening layer. Obtainable.

  In a work requiring hardening such as a shaft-shaped work, the items required for the hardened layer include surface hardness and hardened layer depth. Surface hardness is necessary to suppress scratches and wear caused by contact between parts during assembly of parts and machine operation, and a certain hardened layer depth to prevent internal deformation due to load load via the contact surface. Is required. The surface hardness is desired to be uniform over the entire surface in order to fulfill the above functions. In addition, it is usually difficult to calculate the load applied to the contact surface, and it is not efficient to reset and recondition each work, so the hardened layer depth should be set larger than it should be. It is often done. Therefore, the ability to obtain a deep hardened layer that is relatively uniform in the circumferential direction satisfies the items required for the work.

It is a block diagram which shows the structure of the apparatus which implements the surface hardening treatment method of the workpiece | work by this invention. It is a flow chart which shows an embodiment of a surface hardening treatment method of a work according to the present invention. It is a schematic diagram which shows the cross-section change of the to-be-processed location of the workpiece | work which the surface hardening process is performed by the method of this invention in process order. It is a graph which shows an example of the relationship between the elapsed time at the time of accelerating rotation speed from a 1st rotation speed to a 2nd rotation speed, and the rotation speed of a workpiece | work in step N5 of the flowchart of FIG. 9 is a graph showing a modification of the relationship between the elapsed time and the rotation speed of the work when the rotation speed is accelerated from the first rotation speed to the second rotation speed in step N5 of the flowchart of FIG. 2. FIG. 6 is a schematic diagram showing, in the order of steps, a cross-sectional change in a treated portion of a work which is surface-hardened by the method of FIG. 2 including accelerating the rotation speed of the work based on the graph shown in FIG. 5. It is a graph which shows the result of Examples 1 and 2 by the method of this invention, and the result of the comparative example by the conventional method. It is a front view showing an example of a surface hardening processing method which performs surface hardening processing on a shaft-shaped work using a laser beam as an energy beam. It is a schematic diagram which shows the cross section of the to-be-processed location of the workpiece which surface-hardened by the method of patent document 1. It is a schematic diagram which shows the cross section of the to-be-processed location of the workpiece which surface-hardened by the method of patent document 2 and 3.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS. This embodiment uses laser light as an energy beam. However, the energy beam used is not limited to laser light, and can be changed to an electron beam or the like as appropriate.

  The structure of the work (1) and the arrangement of the work (1) and the laser oscillator (3) are the same as those of the device shown in FIG. In the embodiment of the present invention, the rotation drive source (11) and the laser oscillator (3) for rotating the work (1) around the center line (X) of the shaft-like portion (1a) are the control device (10 )It is connected to the. The laser oscillator (3) used preferably has a rectangular energy distribution with respect to the axial direction of the work (1) (see the shaded irradiated area (5) in FIG. 8). ..

  The control device (10) includes a timer (12) for measuring the time from when the shaft-like portion (1a) of the work (1) starts rotating around the center line (X), and the work (1). A sensor (13) for detecting the rotation speed around the center line (X) of the shaft-like portion (1a) is connected. Further, the control device (10) has a relatively low first rotation speed S1 (rev / min) and a time T1 (sec) for one rotation of the work (1) at the first rotation speed S1 (rev / min). And a second rotation speed S2 (rev / min) higher than the first rotation speed S1 (rev / min), and a second rotation speed S2 from the start of rotation of the work (1) and the start of irradiation of the laser light (4). The time T2 (sec) to reach is set.

  The first rotation speed S1 (rev / min) depends on the material of the work (1), the outer diameter of the shaft-shaped portion (1a) having the region (2) to be surface-hardened, and the hardened layer (6) to be obtained. ), The output of the laser oscillator (3), the size of the irradiation range where the laser beam (4) is irradiated from the laser oscillator (3), etc., the laser oscillator (3 ) Is irradiated with the laser beam (4) to heat the irradiated area (5) (see FIG. 3 (a)) at one place, and the shaft-like part (1a) of the work (1) makes one revolution or more. In addition, here, the speed is such that the temperature becomes equal to or lower than the tempering temperature due to self-cooling after one rotation.

  The second rotation speed S2 is determined by the material of the work (1), the outer diameter of the shaft-shaped portion (1a) having the region to be cured (2) to be surface-hardened, the depth of the hardened layer (6) to be obtained, Depending on the output of the laser oscillator (3), the size of the irradiation range where the laser light (4) is emitted from the laser oscillator (3), etc., the laser light from the laser oscillator (3) in the cured region (2) (3) ( One irradiated area (5) (see Fig. 3 (c)) heated by being irradiated with 4) is self-cooled when the shaft-like part (1a) of the work (1) makes one revolution or more. Even so, the speed is such that the temperature is maintained above the tempering temperature, or the area of the irradiated region (5) that is below the tempering temperature is significantly reduced. The both rotation speeds S1 and S2 and both times T1 and T2 are the material of the work (1), the outer diameter of the shaft-shaped portion (1a) having the region to be cured (2) to be cured, and the cured layer to be obtained. Based on the depth of (6), the output of the laser oscillator (3), the size of the irradiation range where the laser light (4) is irradiated from the laser oscillator (3), etc., is calculated in the control device (10), Alternatively, it is experimentally obtained and input to the control device (10).

  Surface hardening treatment method according to the present invention, first, the relative movement speed of the laser oscillator (3) with respect to the region to be cured (2) of the shaft-shaped portion (1a) of the work (1), that is, the shaft-shaped portion of the work (1). While the rotation speed around the center line (X) of (1a) is set to the first rotation speed S1, the region to be cured (2) is irradiated with the laser beam (4) to cure the region to be cured (2). The first step of increasing the amount of heat input in the depth direction and then self-cooling to obtain a deep hardened layer (6), and following the first step, the center of the shaft-like part (1a) of the work (1) Accelerate the rotation speed around the line (X) to the second rotation speed S2 according to a predetermined function, and irradiate the region to be cured (2) with the laser beam (4) from the laser oscillator (3) in an overlapping manner. Thus, the second step of reheating the work (1) before it is self-cooled, or in a state in which the region of the tempering temperature is significantly reduced, and then self-cooling is included.

  Therefore, when the irradiation of the laser beam (4) is stopped, the vicinity of the irradiation end point can be prevented from being reheated to the tempering temperature, or the region at the tempering temperature can be significantly reduced. Further, in the process of gradually increasing the rotation speed, the above-mentioned treatment is performed while ensuring the heat input in the depth direction, so that an effective hardened layer (6) without tempering in the radial direction can be deeply obtained. As a result, the rotation speed around the center line (X) of the shaft-like part (1a) of the work (1) at the time of irradiation with the laser light (4) is initially low, and then accelerated to quench the temper. It is possible to obtain a deep hardened layer (6) while avoiding or greatly suppressing it.

  Next, with reference to FIG. 2 showing a flow chart, FIG. 3 showing a change in cross-sectional structure of the work which has been subjected to the surface hardening treatment, and FIG. 4 showing a relationship between the elapsed time of the surface hardening treatment and the rotation speed of the work, A specific example of subjecting the work (1) having a cylindrical shape with a diameter of Dmm to the whole surface by the method of the present invention will be described.

  The control device (10) uses the rotary drive source (11) so that the rotation speed (S) around the center line (X) becomes the first rotation speed S1. ) Is started (step N1), and the laser beam (4) is supplied from the laser oscillator (3) to the workpiece (1) while rotating the workpiece (1) around the center line (X) at the first rotation speed S1. The outer periphery of the region (2) to be cured in the shaft-shaped portion (1a) is irradiated (step N2).

  When the irradiation of the laser light (4) from the laser oscillator (3) is started, the control device (10) uses the timer (12) to acquire the elapsed time T from the start of the irradiation of the laser light (4). It is started (step N3), and it is checked whether or not the elapsed time T from the start of irradiation with the laser light (4) has passed the time T1 for one rotation of the work (1) (step N4). If the elapsed time T has not passed the time T1 for one rotation of the work (1) in step N4, step N4 is repeated.

  In Step N4, the first rotation speed S1 (rev / min) is the irradiation target area heated by being irradiated with the laser beam (4) from the laser oscillator (3) in the curing processing area (2) of the work (1). (5) is a relatively low speed such that when the shaft-shaped part (1a) of the work (1) makes one rotation, the temperature becomes lower than the tempering temperature due to self-cooling, so the work (1) rotating at the first rotation speed S1 ( The outer peripheral portion of the hardened region (2) of the work (1) is heated by irradiation of the laser light (4) to the hardened region (2) of the shaft-shaped part (1a) of 1) and rapidly cooled by self-cooling. A deep quench hardened layer (6) is formed on the surface (see FIG. 3 (a)). At this time, in order to obtain a deeper hardened layer (6), the surface temperature of the irradiated region (5) exceeds the austenitizing temperature and is in a heating state such that it is equal to or higher than the melting point.

  In step N4, if the elapsed time T has passed the time T1 for one rotation of the work (1), the control device (10) waits until the time T2 from the start of irradiation of the laser beam (4). In the meantime, while accelerating the rotation speed of the work (1) to the second rotation speed S2 according to a predetermined function, the laser beam (4) is irradiated onto the region to be cured (2) in a superimposed manner (step N5).

The acceleration of the rotation speed S in step N5 in the surface hardening treatment method of this embodiment is, for example, S = (S2-S1) * (T-T1) / (T2-T1) + S1
According to the equation (a), the first rotation speed S1 is accelerated to the second rotation speed S2 in proportion to the elapsed time T. The relationship between the elapsed time T and the rotation speed S of the work (1) at this time is as shown in FIG.

  In step N5, the rotation speed of the work (1) may be accelerated from the first rotation speed S1 to the second rotation speed S2 in proportion to the rotation angle of the work (1).

  Next, the control device (10) checks whether or not the elapsed time T from the start of irradiation of the laser light (4) has exceeded the preset irradiation time T2 of the laser light (4) (step N6). .. If the elapsed time T has not passed the laser light (4) irradiation time T2 in step N6, the process returns to step N5.

  When the elapsed time T has passed the preset irradiation time T2 of the laser light (4) in step N6, the control device (10) stops the irradiation of the laser light (4) (step N7), The rotation of the work (1) is stopped (step N8). Thus, the surface hardening treatment of the work (1) is completed.

  In step N5, while the rotation speed S is being accelerated from the first rotation speed S1 to the second rotation speed S2, reheating is performed at a temperature above the tempering temperature in the vicinity of the portion where the laser beam (4) is repeatedly irradiated. Then, a tempered layer (7) is generated from the vicinity of the irradiated region (5) to the inner peripheral portion of the hardened layer (6) (see FIG. 3 (b)). However, the second rotation speed S2 is such that the irradiated area (5) heated by being irradiated with the laser beam (4) from the laser oscillator (3) in the cured area (2) of the workpiece (1) is When the shaft-shaped part (1a) of 1) makes one rotation or more, it is possible to significantly reduce the high speed or the tempering temperature range where the temperature exceeds the tempering temperature even if it is self-cooled. Since the speed is high, until the elapsed time T reaches the time T2, the irradiated area (5) of the work (1) is reheated faster than it is self-cooled and the entire circumference of the cured area (2) is processed. It is possible to maintain the surface temperature of the workpiece above the tempering temperature or to significantly reduce the area of the tempering temperature near the surface, and when the irradiation of the laser beam (4) is stopped in step N7, the work (1) The surface of the work (1) is not hardened by the tempering process or the softening layer is not formed on the surface of the hardened area (2) of the work (1) as shown in Fig. 3 (c). A hardened layer (6) is obtained with a significantly reduced layer area. The tempered layer (7) exists only on the inner peripheral portion of the hardened layer (6).

  The function of changing the rotation speed S of the work (1) in step N5 (step N5) may be performed plural times by changing the function.

In the flowchart shown in FIG. 2, instead of performing the acceleration of the rotation speed S in step N5 in the surface hardening treatment method of this embodiment according to the equation (a),
S = (S2-S1) x (T-T1) ² / (T2-T1) ² + S1
According to equation (b), which is a downwardly convex quadratic function with the elapsed time T as an independent variable and the acceleration start point as the minimum value, the acceleration increases with the passage of time and Alternatively, the acceleration may be performed so as to gradually transition to the high acceleration state as the rotation speed approaches the two rotation speed S2. The relationship between the elapsed time T and the rotation speed S of the work (1) at this time is as shown in FIG. 5, and the change in the sectional structure of the work subjected to the surface hardening treatment is as shown in FIG.

  In this case as well, the sectional structure of the work (1) before performing step N5 is the same as that in FIG. 3A, as shown in FIG. 6A. Further, in step N5, the rotation speed of the work (1) is determined as a function of the rotation angle of the work (1) as an independent variable and the acceleration start point is set to the minimum value according to a downward convex function, It may be performed by accelerating so as to increase with the passage of time and gradually transition from the initial low acceleration state to the high acceleration state as the second rotational speed S2 approaches.

  Generally, under the same laser output, the tempering temperature region due to the irradiation of the laser beam (4) becomes smaller as the rotation speed S increases. If the acceleration of the rotation speed S is performed according to the above-described equation (b) which is a quadratic function, the rotation speed sharply accelerates from the first rotation speed S1 to the second rotation speed S2 immediately before the irradiation end point, and therefore the irradiation end The tempering temperature region near the location becomes smaller as the rotation speed increases, the occurrence of the tempering layer (7) can be suppressed, and the region of the tempering layer (7) that has occurred can be greatly reduced (see FIG. 6 (b)). ). In addition, with respect to the rotation speed increase by the "convex downward function", the rotation time at a rotation speed of about the first rotation speed S1 is relatively long as compared with the rotation speed increase proportional to time. Therefore, heat easily propagates deep into the work (1), the temperature of the whole work (1) rises even during the second step, and as a result, the cooling rate during self-cooling becomes slower, and the self-cooling reduces the temperature below the tempering temperature. You can extend the time to reach. Therefore, before the self-cooling is completed, the irradiated area (5) is rotated once and reheated, the occurrence of the tempering layer (7) is prevented or suppressed, and only the inner peripheral portion of the hardened layer (6) is prevented. The area of the existing tempering layer (7) is greatly reduced (see FIG. 6 (c)).

  The acceleration from the first rotation speed S1 to the second rotation speed S2 is a quadratic function if it is performed according to a downward convex function with the elapsed time T as an independent variable and the acceleration start point as the minimum value. In addition to the formula (b), one function selected from the group consisting of N-order functions such as quartic function, trigonometric function, exponential function and sigmonide function, or a combination of two or more functions selected from the group You may go according to a function. Further, the function of changing the rotation speed S of the work (1) (step N5) may be performed plural times by changing the function.

  Finally, the results of Examples 1 and 2 of the method of the present invention are shown in FIG. 7 together with the results of the comparative example.

  Example 1 is a result of measuring the hardness of the surface of the shaft-shaped work (1) obtained by performing the acceleration of the rotation speed S in the second step in the surface hardening treatment method of the present invention according to the above formula (a). In Example 2, the hardness measurement of the surface of the shaft-shaped workpiece (1) obtained by accelerating the rotation speed S in the second step in the surface hardening treatment method of the present invention according to the above formula (B) The result. In the comparative example, the rotation speed of the shaft-shaped work (1) was changed when the irradiated area (5) heated by being irradiated with the laser beam (4) from the laser oscillator was rotated once or more by the work (1). It is the result of measuring the hardness of the surface of the shaft-shaped work which has been subjected to the surface hardening treatment while being maintained at the high third rotation speed such that the temperature exceeds the tempering temperature even if it is self-cooled. The laser outputs of the laser oscillators in both Examples and Comparative Examples are the same. The third rotation speed of the comparative example may be the same as or different from the second rotation speed.

  From the results shown in FIG. 7, it can be seen that the depth of the hardened layer (6) obtained in Examples 1 and 2 is deeper than the depth of the hardened layer obtained in the Comparative Example and is almost doubled. ..

  Further, the depth of the hardened layer (6) obtained in Example 2 is deeper than the depth of the hardened layer (6) obtained in Example 1, and the reason is as follows. Conceivable.

  That is, in Example 1, in the second step of the surface hardening treatment method of the present invention, the rotation speed S is accelerated in proportion to the elapsed time T, but in this case, the acceleration becomes constant and the rotation speed S becomes Since the temperature gradually rises, the amount of heat input in each phase in the region to be cured (2) tends to be uniform, and the depth of the cured layer (6) also tends to be uniform with respect to the phase. However, when the rotation speed S is changed in proportion to the time, the rotation speed gradually increases over a relatively long period of time before transitioning to the high-speed rotation capable of reducing tempering. Therefore, in the first step The formed deep hardened layer (6) is tempered in the depth direction each time the orbit is repeated, and the hardened layer (6) finally obtained is compared with the hardened layer (6) obtained in the first step. It is thought that the depth of) will become small.

  From the above results, according to the surface hardening treatment method of the present embodiment, even with the same laser output, a deeper hardened layer can be obtained as compared with the conventional method, and the desired mechanical strength and wear resistance for the workpiece can be obtained. Etc. can be added, and a product having excellent performance can be obtained.

  INDUSTRIAL APPLICABILITY The present invention is suitably used as a means for surface-hardening a metal shaft-shaped work such as a cam shaft of an automobile part, a ball screw of a machine tool, and a spindle.

(1): Work
(1a): Shaft
(2): Cured area
(3): Laser oscillator
(4): Laser light
(5): Irradiated area
(6): Hardened layer
(7): Tempered layer
S1: First rotation speed of work
S2: Second rotation speed of work
T1: Time for the work to rotate once at the first rotation speed S1
T2: Time from the start of laser irradiation to the end of irradiation

Claims (7)

To relatively move an energy beam irradiation source and a metal work having a shaft-shaped portion in at least a part thereof and having a region to be hardened to be hardened over the entire circumference in the shaft-shaped portion. Thereby, the energy beam irradiation source is irradiated with an energy beam from the energy beam irradiation source while the energy beam irradiation source is relatively moved in the circumferential direction of the curing target area of the shaft-shaped portion, and the curing target is processed. By heating the area, and then by self-cooling, a method of surface hardening treatment of a work for forming a hardened layer in the hardened area,
The relative movement speed of the energy beam irradiation source with respect to the hardening target area of the shaft-shaped portion is set to a first speed, and the hardening target area is irradiated with an energy beam to heat the hardening target area of the workpiece. And the first step, the relative movement speed is accelerated to a second speed that is faster than the first speed, and the energy beam is overlapped and irradiated on the region to be cured, And a second step of heating
The first speed is the irradiation target area heated by the energy beam irradiation from the energy beam irradiation source in the hardening target area, and the energy beam irradiation source is the circumference of the hardening target area of the shaft-shaped portion. When the relative movement in the direction of one or more turns, the cooling speed is set so that the tempering temperature will be below the tempering temperature due to self-cooling.
The second speed is the irradiation target area heated by the irradiation of the energy beam from the energy beam irradiation source in the hardening target area, and the energy beam irradiation source is the circumference of the hardening target area of the shaft-shaped portion. When relatively moving in one direction or more in the direction, a high speed is maintained such that the temperature exceeds the tempering temperature even if it is self-cooled, or a high speed that reduces the region of the irradiated region that is below the tempering temperature. A surface hardening treatment method for a work, comprising:   The surface hardening treatment method for a work according to claim 1, wherein the acceleration from the first speed to the second speed is performed at a constant acceleration.   Accelerating the relative movement speed from the first speed to the second speed in proportion to time or relative rotation angle of the energy beam irradiation source with respect to the region to be cured of the shaft-shaped portion. The surface hardening treatment method for a work according to claim 2, which is characterized in that.   Upon acceleration from the first speed to the second speed, the acceleration increases with time, and the acceleration gradually changes from the initial low acceleration state to the high acceleration state as the second speed approaches. The surface hardening treatment method for a work according to claim 1, wherein the method is accelerated.   The relative movement speed is changed from the first speed to the first speed according to a downward convex function whose independent variable is a relative rotation angle of the energy beam irradiation source with respect to the hardening target region of the shaft-shaped portion. The surface hardening treatment method for a workpiece according to claim 4, wherein the method is accelerated to a second speed.   The surface hardening treatment method for a work according to claim 5, wherein the downward convex function is a downward convex function having an acceleration start point as a minimum value. The downward convex function is one function selected from the group consisting of an Nth-order function, a trigonometric function, an exponential function and a sigmonide function, or a function in which two or more functions selected from the group are combined. 5. The method for surface hardening treatment of a work according to 5 or 6.

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