JP2017218669A - Residual stress imparting device and residual stress imparting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device and a method capable of imparting residual stress to a coil spring.SOLUTION: A residual stress imparting device 10 for imparting residual stress to a coil spring 20 is provided that comprises: a circumscribing member 1 which has a radially unexpandable inner circumferential surface 1a having a circular cross section, and in which the coil spring 20 is clearance-fit; an inscribing member 2 which is inserted into the coil spring 20 inside the inner circumferential surface 1a of the circumscribing member 1 and has a radially expandable outer circumferential surface 2a having a circular cross section; and an expansion member 3 for diametrically expanding the outer circumferential surface 2a of the inscribing member 2.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an apparatus and method for applying a residual stress to a coil spring.

  Coil springs are known to experience fatigue failure from the inner portion of the helical structure. Conventionally, in order to prevent fatigue failure of a coil spring, residual stress is applied to the surface of the steel wire by shot peening or the like, or the coil spring is strengthened by surface hardening of the steel wire using nitriding treatment or the like.

  However, there have been reports of cases in which fatigue failure occurs not from the surface of the steel wire that constitutes the coil spring, but from the inside that is slightly closer to the center of the steel wire than the surface. That is, in order to prevent fatigue failure of the coil spring, it is necessary to apply compressive residual stress not only to the surface of the coil spring but also to an internal region of about 0.1 to 0.5 mm from the surface.

  However, in shot peening, although high compressive residual stress can be applied to the surface, tensile residual stress that reduces the fatigue strength is generated in the inner region of about 0.1 to 0.5 mm from the surface. Often.

  For example, Patent Document 1 discloses that a high compressive residual stress layer is formed on a surface of the metal material by applying external force to the surface in a state where tensile stress is applied to the surface of the metal material and then removing the external force. A method for providing a high compressive residual stress layer is disclosed.

  Further, Patent Document 2 discloses an ultrasonic hammering process for a coil spring that can uniformly apply compressive residual stress to the inner peripheral surface of the coil spring and shorten the processing time to improve the fatigue characteristics of the coil spring. An apparatus and an ultrasonic hitting method for a coil spring are disclosed.

  Furthermore, Patent Document 3 discloses a metal surface strengthening treatment method capable of performing a surface strengthening treatment uniformly on the surface of a metal workpiece having a complicated shape.

JP 59-30670 A JP 2012-117119 A Japanese Patent Laid-Open No. 5-148536

  According to the technique described in Patent Document 1, it is said that the surface compressive residual stress value and the fatigue life are greatly improved by hitting the particles in a tensioned state. However, even when tension is applied, compressive residual stress cannot be applied to a sufficient depth by particle hitting such as shot peening.

  According to the technique described in Patent Document 2, by applying ultrasonic vibration to a rod-shaped striking jig inserted inside the coil of the coil spring, the inner peripheral surface of the coil is repeatedly hit and compressed to the inner peripheral surface of the coil. Residual stress is applied. However, this method has a problem that the equipment cost is high, and there is still room for improvement.

  Moreover, according to the technique of patent document 3, regardless of the shape of a metal workpiece, by embedding a metal workpiece in a granular material and compressing a granule by applying pressure from the outside, It is said that the surface can be subjected to a uniform surface strengthening treatment. However, in this method, uniform stress can be applied to all surfaces, but it is impossible to perform control such that more residual stress is applied to the inner portion of the coil spring, for example.

  An object of the present invention is to provide an apparatus and method capable of solving the above-described problems and applying a residual stress to a coil spring.

  The present invention has been made in order to solve the above-described problems, and provides the following residual stress applying apparatus and residual stress applying method.

(1) A device for applying residual stress to a coil spring,
A circumscribing member having a circular inner peripheral surface that cannot be expanded in the radial direction, and the coil spring is fitted in a gap;
An inscribed member having an outer peripheral surface with a circular cross section that is inserted into the coil spring and can be expanded in the radial direction inside the inner peripheral surface of the circumscribed member;
An expansion member that expands the outer peripheral surface of the inscribed member in a radial direction,
Residual stress applying device.

(2) The inscribed member has an inner peripheral surface having a C-shaped cross section,
The expansion member includes an expansion portion having an outer diameter larger than a diameter of the inner peripheral surface of the inscribed member.
The residual stress applying apparatus according to (1) above.

(3) It further includes a deformable member that applies an axial force to the coil spring and elastically deforms the coil spring.
The residual stress applying apparatus according to the above (1) or (2).

(4) A method of applying a residual stress to a coil spring using the device according to (1) or (2) above,
An arrangement step of fitting the coil spring into the circumscribed member with a gap and inserting the inscribed member inside the coil spring;
Expanding the outer peripheral surface of the inscribed member in the radial direction,
Residual stress application method.

(5) A method of applying a residual stress to a coil spring using the apparatus described in (3) above,
An arrangement step of fitting the coil spring into the circumscribed member with a gap and inserting the inscribed member inside the coil spring;
Expanding the outer peripheral surface of the inscribed member in the radial direction in a state where the coil spring is elastically deformed by the deformable member,
Residual stress application method.

(6) In the expanding step, the coil spring is sandwiched between the inner peripheral surface of the circumscribed member and the outer peripheral surface of the inscribed member, and the expanded member is brought into contact with the inner peripheral surface of the inscribed member. Expanding the inscribed member by passing it through the inscribed member.
The residual stress imparting method according to the above (4) or (5).

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to give a compression residual stress to an internal area | region at low cost, without significantly deteriorating the surface property with respect to a coil spring.

It is sectional drawing (a) which showed an example of the reference | standard state of the residual stress provision apparatus which concerns on one Embodiment of this invention, and the aa sectional view (b) of the circumscribed member and inscribed member in (a). It is sectional drawing (a) which showed an example of the use condition of the residual stress provision apparatus which concerns on one Embodiment of this invention, and the bb sectional view (b) of the circumscribed member and inscribed member in (a). It is a figure which shows the cross-sectional shape of the expansion member with which the residual stress provision apparatus which concerns on other embodiment of this invention is provided. It is sectional drawing (a) which showed an example of the reference | standard state of the residual stress provision apparatus which concerns on other embodiment of this invention, and the cc line sectional drawing (b) of the circumscribed member and inscribed member in (a). It is sectional drawing (a) which showed an example of the use condition of the residual stress provision apparatus which concerns on other embodiment of this invention, and the dd line sectional drawing (b) of the circumscribed member and inscribed member in (a). It is sectional drawing which showed an example of the reference | standard state of the residual stress provision apparatus which concerns on other embodiment of this invention. FIG. 6 is a cross-sectional view showing an example of a state in which an axial force is applied to a coil spring and contracted in a residual stress applying apparatus according to another embodiment of the present invention. It is sectional drawing which showed an example of the use condition of the residual stress provision apparatus which concerns on other embodiment of this invention. It is sectional drawing which showed an example of the reference | standard state of the residual stress provision apparatus which concerns on other embodiment of this invention. FIG. 6 is a cross-sectional view showing an example of a state in which an axial force is applied to a coil spring and extended in a residual stress applying apparatus according to another embodiment of the present invention. It is sectional drawing which showed an example of the use condition of the residual stress provision apparatus which concerns on other embodiment of this invention. It is a figure for demonstrating the measurement position and measurement direction of a residual stress.

  An embodiment of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1A is a cross-sectional view showing an example of a reference state of a residual stress applying apparatus 10 according to an embodiment of the present invention, and FIG. It is an aa sectional view of a contact member. 2A is a cross-sectional view showing an example of a usage state of the residual stress applying apparatus 10 according to the embodiment of the present invention, and FIG. 2B is a circumscribed member in FIG. FIG. 6 is a cross-sectional view taken along line bb of the inscribed member. In the present invention, a state in which an inscribed member described later is not expanded is referred to as a reference state, and a state in which the inscribed member is expanded in a radial direction is referred to as a use state.

  A residual stress applying apparatus 10 according to an embodiment of the present invention is an apparatus that applies a residual stress to a coil spring 20, and includes a circumscribed member 1, an inscribed member 2, and an expansion member 3. Each component will be described. However, the present invention is not limited to the following embodiments.

  The circumscribed member 1 has a circular inner peripheral surface 1a and is a member into which the coil spring 20 is fitted into a gap. That is, as shown in FIG. 1, the outer portion 20 a of the coil spring 20 and the inner peripheral surface 1 a of the outer member 1 are in contact with each other in a state where the coil spring 20 is disposed inside the outer member 1. And the inner peripheral surface 1a of the circumscribed member 1 cannot be expanded in the radial direction, and restricts the outer portion 20a of the coil spring 20 from being expanded in the radial direction.

  The inscribed member 2 is a cylindrical member having an outer peripheral surface 2 a that is inserted into the coil spring 20 and can be expanded in the radial direction inside the inner peripheral surface 1 a of the circumscribed member 1. Specifically, as shown in FIGS. 1 and 2, the inscribed member 2 has an inner peripheral surface 2b having a C-shaped cross section. In the above configuration, since the inscribed member 2 is partially cut, it can be expanded in the radial direction. In the present invention, the “circular shape” includes a shape obtained by cutting a part of the circle. Further, the “C-shaped cross section” means a shape in which a part of a circle is cut, and the cut one end and the other end may be in contact with each other or may be separated from each other.

  The expansion member 3 is a member that expands the inscribed member 2 in the radial direction. Specifically, as shown in FIGS. 1 and 2, the expansion member 3 has a spherical shape, and has an expansion portion 3a having an outer diameter larger than the diameter of the inner peripheral surface 2b of the inscribed member 2 in the reference state. Contains. The expansion member 3 is preferably made of a material harder than the inscribed member 2 so as not to be plastically deformed when the inscribed member 2 is expanded.

  Next, an example of a method for applying a residual stress to a coil spring using a residual stress applying apparatus according to an embodiment of the present invention will be described with reference to FIGS.

  First, the coil spring 20 is fitted into the outer member 1 with a gap, and the inner member 2 is inserted inside the coil spring 20 (arrangement step). Thereafter, the inscribed member 2 is expanded in the radial direction (expansion step). In the arrangement step, either the step of fitting the coil spring 20 into the circumscribed member 1 or the step of inserting the inscribed member 2 inside the coil spring 20 may be performed first or simultaneously. You may go. In the arrangement step, the inscribed member 2 is preferably fitted into the coil spring 20 with a gap.

  In the expansion step, as shown in FIG. 1, first, the expansion member 3 is brought into contact with one end side of the inscribed member 2, and then the expansion member 3 is pushed in. As shown in FIG. 2, in the state where the coil spring 20 is sandwiched between the inner peripheral surface 1 a of the circumscribed member 1 and the outer peripheral surface 2 a of the inscribed member 2, the expanded portion 3 a is the inner peripheral surface 2 b of the inscribed member 2. To pass through the inscribed member 2 so as to come into contact. As described above, the outer diameter of the expansion portion 3 a of the expansion member 3 is larger than the diameter of the inner peripheral surface 2 b of the inscribed member 2. Therefore, when the expansion member 3 passes through the inscribed member 2, the inscribed member 2 is expanded and expanded in the radial direction.

  Then, in a state where the outer portion 20a of the coil spring 20 is fixed by the inner peripheral surface 1a of the circumscribed member 1, the inner portion 20b of the coil spring 20 is expanded to apply stress to the coil spring 20 and cause plastic deformation. Is possible. Thereafter, when the stress applied to the coil spring 20 is unloaded, a residual compressive stress is generated in the coil spring 20.

  When shot peening is used, the pressure applied to the coil spring is shocking. On the other hand, when the method according to the present invention is used, pressure is applied to the coil spring 20 on the inner peripheral surface 1a of the circumscribed member 1 and the outer peripheral surface 2a of the inscribed member 2, so that a quasi-static pressure is applied. It becomes possible to apply compressive residual stress to the deep region of the coil spring 20.

  Further, the coil spring 20 does not come into contact with the expansion member 3, and only the radial stress is applied from the inscribed member 2. For this reason, it is possible to prevent the surface of the coil spring 20 from being scratched when the expansion member 3 passes through the inscribed member 2.

  The present invention is not limited to the above-described embodiment. For example, in the above-described example, the expansion member 3 has a spherical shape. However, as shown in FIG. 3, the tip may be a hemispherical or conical rod.

  In the above-described embodiment, the inscribed member 2 has a cylindrical shape having an outer peripheral surface 2a and an inner peripheral surface 2b having a C-shaped cross section, but may be configured as shown in FIGS. 4 and 5, for example. . That is, the inscribed member 2 has an outer peripheral surface 2a having a circular cross section and an inner peripheral surface 2b having a square cross section, and is divided into four. Then, the inscribed member 2 is expanded in the radial direction by pushing the rod-shaped expansion member 3 having a trapezoidal vertical section and a square horizontal section so as to contact the inner peripheral surface 2b of the inscribed member 2.

  Furthermore, in the above-described example, the inscribed member 2 is expanded in the radial direction by pushing the expanding member 3 which is a spherical or rod-shaped instrument into the inside of the inscribed member 2, but the present invention is not limited thereto. For example, the inscribed member 2 may be expanded by water pressure or hydraulic pressure.

  FIG. 6 is a cross-sectional view showing an example of a reference state of the residual stress applying apparatus 10 according to another embodiment of the present invention. FIG. 7 is a cross-sectional view showing an example of a state in which the axial force is applied to the coil spring 20 and contracted in the residual stress applying apparatus 10 according to another embodiment of the present invention. Further, FIG. 8 is a cross-sectional view showing an example of a usage state of the residual stress applying apparatus 10 according to another embodiment of the present invention.

  The residual stress applying apparatus 10 according to another embodiment of the present invention further includes a deformable member 4 in addition to the above-described circumscribed member 1, inscribed member 2, and expansion member 3. The deformable member 4 is a member that applies an axial force to the coil spring 20 to be elastically deformed. 6 to 8, the deformable member 4 is a cylindrical member, and the outer diameter is smaller than the inner diameter of the circumscribed member 1, and the inner diameter is larger than the outer diameter of the inscribed member 2.

  In the case where the residual stress is applied to the coil spring 20 using the residual stress applying device 10 provided with the deformable member 4, in the above-described expansion process, first, as shown in FIG. Apply direction force to shrink. Then, the inscribed member 2 is expanded in the radial direction while the coil spring 20 is elastically deformed.

  It is possible to apply compressive residual stress to a deeper region of the coil spring 20 by plastically deforming the coil spring 20 by applying pressure in the radial direction in a state where the coil spring 20 is elastically deformed by applying an axial force. .

  In the configuration shown in FIGS. 6 to 8 described above, pressure is applied in the radial direction with the coil spring 20 contracted, but as shown in FIGS. 9 to 11, the radial direction is applied with the coil spring 20 extended. Pressure may be applied to the.

  EXAMPLES Hereinafter, although an Example demonstrates this invention more concretely, this invention is not limited to these Examples.

  A JIS SWOSC-V steel spring manufactured by Daytona (reinforced by shot peening, super clutch center spring 74040, free height: 100 mm, average coil diameter: 53 mm, wire diameter: 4 mm) was used as the coil spring. The total number of turns of the spring used was 5, and the effective number of turns was 3. The coil spring was annealed for 30 minutes at a temperature of 400 ° C. for the purpose of removing residual stress.

  After the residual stress removal annealing, the residual stress was applied using the method according to the present invention. Specifically, first, after fitting a coil spring into a pipe-shaped circumscribed member having an outer diameter of 70 mm, an inner diameter of 57 mm (+0.05 to 0), and a length of 100 mm, an outer diameter of 49 mm (0 to −0. 02), a cylindrical inscribed member having an inner diameter of 31.25 mm ± 0.02 and a length of 100 mm and having a C-shaped inner peripheral surface was inserted into the coil spring. Thereafter, the expansion member, which is a hard sphere having a diameter of 31.75 mm, was passed through the inscribed member and pushed to expand, thereby expanding the inner diameter of the coil spring by 1% (the inner diameter was expanded by 0.5 mm with respect to the coil inner diameter of 49 mm).

  State in which the above shot peening was performed (test No. 1), state in which annealing treatment was performed after shot peening (test No. 2), and state in which residual stress was further applied by the method of the present invention after annealing (test no. .3) Residual stress was measured for the coil springs in the three states. For the measurement of residual stress, an X-ray stress measurement device (PSPC-RSF manufactured by Rigaku Corporation) was used. As shown in FIG. 12, the measurement position and direction of the residual stress, each coil spring is cut in a 90 ° cycle of a circular arc, and a wire element in which one turn is divided into four equal parts is targeted for a range of 3 mm in diameter. Electrolytic polishing was performed, and after removing the surface layer from the inner surface side to a predetermined depth, measurement was performed. The residual stress was measured at three locations on the surface, a depth of 0.15 mm position and a depth of 0.5 mm position.

  The residual stress measurement results are shown in Table 1. Test No. reinforced by shot peening In the spring No. 1, the compressive residual stress decreases as the measurement position becomes deeper at 0.15 mm and 0.5 mm, and tensile residual stress is generated at a depth of 0.5 mm. In addition, Test No. after low temperature tempering. As a result, although the residual stress was not completely removed for the spring No. 2, the compressive residual stress was lower than that of the spring after shot peening.

  In contrast to these, test Nos. Processed by the method of the present invention. It can be seen that compression residual stress is applied to the spring No. 3 at depths of 0.15 mm and 0.5 mm. In particular, at a depth of 0.15 mm, a high compressive residual stress similar to the surface layer was applied. Moreover, it turns out that the high compressive residual stress equivalent to the spring surface after shot peening has generate | occur | produced also in the outer surface part. From the above, it was found that high and deep compressive residual stress can be applied by using the method according to the present invention.

  The same coil spring as in Example 1 was subjected to an annealing treatment for 30 minutes at a temperature of 450 ° C. for the purpose of removing residual stress. After the residual stress removal annealing, the residual stress was applied using the method according to the present invention.

  Specifically, first, after fitting a coil spring into a pipe-shaped circumscribed member having an outer diameter of 70 mm, an inner diameter of 57 mm (+0.05 to 0), and a length of 100 mm, an outer diameter of 49 mm (0 to −0. 02), a cylindrical inscribed member having an inner diameter of 31.25 mm ± 0.02 and a length of 100 mm and having a C-shaped inner peripheral surface was inserted into the coil spring.

  Thereafter, the coil spring was contracted by 25.5 mm in the axial direction using a pipe-shaped deformable member having an outer diameter of 57 mm and an inner diameter of 50 mm. At this time, the shear stress applied to the outer surface of the coil spring is approximately 500 MPa. With this level of stress, yielding does not occur on the outer surface of the spring, but only elastic deformation. Then, the expansion member, which is a hard sphere having a diameter of 31.75 mm, was passed through the inscribed member and expanded to expand the inner diameter of the coil spring by 1% (the inner diameter was expanded by 0.5 mm with respect to the coil inner diameter of 49 mm).

  State subjected to the above shot peening (Test No. 4), state subjected to annealing treatment after shot peening (Test No. 5), and state subjected to residual stress by the method of the present invention after annealing (Test No. 5) .6) Residual stress was measured for the coil springs in the three states. The residual stress was measured in the same manner as in Example 1.

  Table 2 shows the results of residual stress measurement. Similar to Example 1, the test No. 1 after low temperature tempering. Regarding the spring No. 5, the residual stress was not completely removed, but the compressive residual stress was lower than that of the spring after shot peening. In this example, since the tempering temperature was higher than that in Example 1, the test No. Compared to test No. 2, test no. The compressive residual stress at the surface of 5 was lower.

  In addition, test No. 1 in which pressure was applied in the radial direction in an elastically deformed state. In the spring No. 6, the test No. 1 was expanded in the radial direction without being elastically deformed. Compared with the spring No. 3, the compressive residual stress from the surface to a depth of 0.15 mm was equivalent, whereas the compressive residual stress was remarkably increased at a depth of 0.5 mm. From this, it was found that compressive residual stress can be applied to a deeper region by applying pressure in the radial direction and plastically deforming the spring in an elastically deformed state.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to give a compression residual stress to an internal area | region at low cost, without significantly deteriorating the surface property with respect to a coil spring.

1. Circumscribed member 1a. 1. Inner peripheral surface Inscribed member 2a. Outer peripheral surface 2b. 2. Inner peripheral surface Expansion member 3a. Expansion unit 4. Deformation member 10. Residual stress applying device 20. Coil spring 20a. Outer part 20b. Inner part

Claims (6)

A device for applying residual stress to a coil spring,
A circumscribing member having a circular inner peripheral surface that cannot be expanded in the radial direction, and the coil spring is fitted in a gap;
An inscribed member having an outer peripheral surface with a circular cross section that is inserted into the coil spring and can be expanded in the radial direction inside the inner peripheral surface of the circumscribed member;
An expansion member that expands the outer peripheral surface of the inscribed member in a radial direction,
Residual stress applying device. The inscribed member has an inner peripheral surface having a C-shaped cross section,
The expansion member includes an expansion portion having an outer diameter larger than a diameter of the inner peripheral surface of the inscribed member.
The residual stress applying apparatus according to claim 1. A deformation member that elastically deforms by applying an axial force to the coil spring;
The residual stress applying apparatus according to claim 1 or 2. A method of applying a residual stress to a coil spring using the apparatus according to claim 1 or 2,
An arrangement step of fitting the coil spring into the circumscribed member with a gap and inserting the inscribed member inside the coil spring;
Expanding the outer peripheral surface of the inscribed member in the radial direction,
Residual stress application method. A method of applying a residual stress to a coil spring using the apparatus according to claim 3,
An arrangement step of fitting the coil spring into the circumscribed member with a gap and inserting the inscribed member inside the coil spring;
Expanding the outer peripheral surface of the inscribed member in a radial direction in a state in which the coil spring is elastically deformed by the deformable member,
Residual stress application method. In the expanding step, the coil spring is sandwiched between the inner peripheral surface of the circumscribed member and the outer peripheral surface of the inscribed member, and the inner member is in contact with the inner peripheral surface of the inscribed member. Expanding the inscribed member by passing it through the inscribed member;
The method for imparting residual stress according to claim 4 or 5.

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