JP2006281406A - Shot peening method, disc spring obtained under this method and shot peening device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a shot peening method most suitable for manufacturing a leaf spring to provide the leaf spring never producing a crack, etc. by lengthening delay breaking time of a spring eye part of an end part of the leaf spring to suspend a car body, etc. <P>SOLUTION: A part of a member to surround a closed space in which a steel ball moves is constituted of a workpiece in shot peening by projecting the steel ball to at least a part of the workpiece, and compression residual stress of more than -300 MPa is given to at least a part of the workpiece by continuously moving the steel ball by supersonic wave vibration in the closed space. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a shot peening method, a plate spring obtained by this method, and a shot peening apparatus, and in particular, by applying a compressive residual stress to a center part of a plate spring end for suspending a vehicle body or a general machine, The present invention relates to a shot peening technique capable of extending the delayed fracture time.

  The heat-treated leaf spring is subjected to shot peening (hereinafter sometimes simply referred to as “SP”) in order to increase fatigue strength (improve durability). However, the predetermined portion of the workpiece to be subjected to SP is limited to the surface portion of the leaf spring, and SP cannot be reliably performed on the inner surface of the end portion. However, when a bush or the like is press-fitted into the inner surface of the eyeball portion, a tensile stress is also generated at a part of the inner surface of the eyeball portion. Therefore, there has been a demand for a technique that can reliably perform SP.

  Conventionally, the effect of SP has been recognized for the inner surface of the eyeball, but as a specific method, a so-called impeller method has been proposed in which an angle is given to the impeller and a shot is projected onto a part of the inner surface of the eyeball. It was only. However, in the impeller method, it is almost impossible to project a shot near the top of the eyeball portion where the stress is most concentrated when the bush is actually pressed into the eyeball portion. Could not be applied.

  On the other hand, an air nozzle method has been proposed as a method of positively applying SP to the inner surface of the center part (see Patent Document 1). This air nozzle system is a system in which an SP device is used, a shot reflecting member is arranged on the downstream side of the shot ejection device, and a shot is projected onto the inner surface of the eyeball portion according to an angle given to the reflecting member. In this method, it is possible to carry out SP aiming at an arbitrary position on the inner surface of the eyeball part, but since the shot projected on the inner surface of the eyeball part is scattered, it is necessary to collect the scattered shot. The work becomes big. Furthermore, in order to accurately perform SP on the inner surface of the eyeball part in the SP device, it is necessary to accurately position the shot ejection device and the reflecting member with respect to the inner surface of the eyeball part. For this reason, the apparatus itself becomes large-scale and is not yet put into practical use.

Japanese Patent Publication No. 7-36982

  In recent years, in response to needs for reducing the weight of leaf springs, increasing the hardness of leaf springs has been attempted. In addition, as the front and rear inputs at the time of braking increase with the increase in the diameter and thickness of the bush attached to the eyeball and the increase in power performance, the stress generated on the inner surface of the eyeball tends to increase. Furthermore, as monotechnology (single spring) is developed as a new technology, early damage countermeasures for the eyeball part are indispensable due to safety problems, and SP construction on the inner surface of the eyeball part is expected to be an essential process. Under such circumstances, in recent years, increasing the delayed fracture time of the eyeball part and increasing the strength have become more and more important issues than before.

  The present invention has been made in view of the circumstances as described above, and provides a leaf spring that increases the delayed fracture time of the center part of the leaf spring end for suspending the vehicle body and the like and does not cause cracks or the like. Accordingly, it is an object of the present invention to provide a shot peening method suitable for manufacturing the leaf spring, a leaf spring obtained by the method, and a shot peening apparatus suitable for manufacturing the leaf spring.

  In the shot peening method of the present invention, when performing shot peening by projecting a steel ball onto at least a part of the workpiece, a part of a member surrounding the closed space in which the steel ball moves is formed by the workpiece, The steel ball is continuously moved by ultrasonic vibration to impart a compressive residual stress of −300 MPa or more to at least a part of the workpiece.

  In such a shot peening method, the steel ball is preferably a hard ground steel ball having a Rockwell C hardness of 65 or more.

  Next, the leaf spring of the present invention is obtained by subjecting a leaf spring comprising at least one leaf to the above shot peening. In order to reduce the weight of the leaf spring, it is desirable to follow the recent trend of monoleafing. However, if it is not possible to meet the strength establishment range, two or more leaf springs can be stacked. It can also be configured.

  Furthermore, the shot peening apparatus of the present invention includes a housing that is movable in the vertical direction with respect to the workpiece and that is rotatable about a vertical axis, a reflection member that is disposed at an upper portion in the housing, And a shutter that opens and closes an opening formed on a side of the housing by moving up and down with respect to the housing, and in an engaged state between the housing and the workpiece. Forms a closed space by a work, a housing, a reflecting member, and a vibrator, and a steel ball is continuously projected onto the work by ultrasonic vibration in the closed space, and at least a part of the work has a pressure of −300 MPa or more. Applying compressive residual stress, and housing, reflecting member, vibrator, and shutter in a non-engaged state between the housing and the workpiece To form a more enclosed space, it is characterized by preventing falling off to the outside of the steel ball.

  According to the shot peening method of the present invention, it is possible to provide a leaf spring in which the delayed fracture time of the center part of the spring end is increased and cracks and the like do not occur. In addition, as described above, when a hard ground steel ball having a Rockwell C hardness of 65 or more is used without using a general cut wire to be used, fine scratches are generated at the spot subjected to shot peening. Can be prevented, and uniform surface roughness can be obtained.

Next, the effect of the shot peening apparatus of the present invention will be described.
That is, since the shot peening apparatus of the present invention is an apparatus for suitably carrying out the above shot peening method, according to the present apparatus, as described above, the delayed fracture time of the center part of the spring end is increased. As a matter of course, it is possible to provide a leaf spring which does not cause cracks, but as other effects, the following effects [1] to [6] are exhibited.
[1] Since the SP is performed by realizing the movement of the steel ball in the closed space formed by the workpiece, the housing, the reflecting member, and the vibrator, the SP projection device is compared with the device described in Patent Document 1. It can be made compact. For this reason, SP can be performed also on the inner surface of the eyeball portion which is smaller than the conventional one.
[2] Since the SP projection apparatus is made compact as described above, the apparatus itself can be reduced in weight and the projection positioning can be easily performed as compared with the apparatus described in Patent Document 1. SP can be applied aiming at a portion that requires an effect.
[3] By replacing the attachment (a casing provided in the vicinity of the exit of the opening formed on the side of the housing), shot peening can be performed on the eyeballs of various sizes with simple setup.
[4] The amount of steel balls charged at one time can be made very small (10 g or less), and the steel balls can be directly put into the moving space. Moreover, since the projected steel ball can be continuously used without being collected in the projection apparatus as it is, the steel ball can be repeatedly used without being collected. For this reason, steel ball scattering countermeasures and special steel ball recovery devices are unnecessary, and no large-scale equipment is required.
[5] Since steel balls can be used repeatedly as described above, the amount of steel balls used is very small (10 g or less when steel balls are introduced once a day), and the running cost is low. It is.
[6] By controlling the vibration frequency and amplitude of the vibrator, the size of the steel ball used and the projection time can be appropriately changed. As a result, it is possible to obtain a high compressive residual stress of −800 MPa or more by irradiation in a short time, which is difficult with the air nozzle method.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a view showing a shot peening apparatus 10 according to the present invention and a center part W of a leaf spring. FIG. 1A is a partial sectional view showing a non-engagement state between the apparatus 10 and the center part W. FIG. ) Is a partial cross-sectional view showing an engaged state between the apparatus 10 and the eyeball part W, and FIG. 5C is a plan view of the shot peening apparatus shown in FIGS. As shown in FIG. 1A, the shot peening apparatus 10 includes a housing 11 that can move in the vertical direction with respect to the eyeball portion W and that can rotate around a vertical axis, and an upper portion in the housing 11. The reflection member 12 disposed, the vibrator 13 that is vibrated by the ultrasonic wave disposed below the reflection member 12 in the housing 11, and formed on the side of the housing 11 by moving up and down relative to the housing 11. A shutter 15 that opens and closes the opening 14 is provided.

  As shown in FIG. 1A, the housing 11 includes a small-diameter cylindrical upper portion 11a, a medium-diameter cylindrical middle portion 11b, and a large-diameter cylindrical lower portion 11c, and an opening is formed on the side of the upper portion 11a. 14 is provided. The reflecting member 12 has an upper surface that coincides with the upper surface of the housing 11 and a lower surface that is inclined with respect to the horizontal direction. The reason why the lower surface of the reflecting member 12 is inclined is that the inner surface of the eyeball W is perpendicular to the upper surface of a vibrator 13 described later.

  Further, the vibrator 13 is arranged with its outer peripheral surface maintaining a minute gap with the inner peripheral surface of the housing 11, and vibrates in the vertical direction of FIGS. 1 (a) and 1 (b). Below the vibrator 13, a horn 16 and a piezoelectric element 17 are arranged in that order from above, and the piezoelectric element 17 is connected to a generator 18 via a high-voltage cable c. Under such a configuration, when high-frequency power generated by the generator 18 is input to the piezo element 17, the power is converted into mechanical vibration by the piezoelectric effect of the piezo element 17. Further, the vibration generated by the piezo element 17 is transmitted to the horn 16, and the vibration amplitude is amplified by the horn 16 and transmitted to the vibrator 13.

  In addition, the shutter 15 moves up and down with respect to the housing 11 by an elevating member 19 positioned below the shutter 15. Here, when the shape of the housing 11 described above is added, when the SP device 10 rises with respect to the held eyeball portion W, the shutter 15 pushed by the collar portion of the eyeball portion W starts to descend, and the space 21 becomes the eyeball. Open to the inner surface. Further, when the SP device 10 starts to descend, the shutter 15 keeps the state in which the shutter 15 is always in contact with the collar portion of the eyeball portion W by the elevating member 19, thereby preventing the hard abrasive steel balls thrown into the interior from falling. Thus, the semi-cylindrical shape according to the external shape of the housing 11 and the external shape of the eyeball part W is made.

  Under such a configuration, when using the shot peening apparatus 10, the shutter 15 is moved downward with respect to the housing 11 by the elevating member 19 from the state of FIG. A plurality of steel balls 20 are introduced into the space 21 from the opening 14. Next, the shutter 15 is moved upward with respect to the housing 11 by the elevating member 19, and the opening 14 is closed so as to return to the state shown in FIG.

  Further, as shown in FIG. 1B, the eyeball W is pushed down, or the housing is moved upward by a lifting device (not shown) and closed by the eyeball W, the housing 11, the reflecting member 12, and the vibrator 13. A space 22 is formed. Then, the vibrator 13 is vibrated by the ultrasonic vibration as described above, and thereby, the plurality of steel balls 20 disposed above the vibrator 13 are continuously reciprocated between the vibrator 13 and the eyeball portion W. Then, shot peening is performed in the closed space 22. As described above, the lower surface of the reflecting member 12 is inclined because the inner surface of the eyeball portion W and the upper surface of the vibrator 13 are perpendicular to each other. The degree of this inclination is at the SP construction position of the eyeball portion W. It can be changed accordingly. Further, at the time of SP construction, the housing 11 is moved in the vertical direction with respect to the eyeball portion W, or the housing 11 is rotated around the vertical axis line with the eyeball portion W fixed, so that any position of the eyeball portion W is set. Can also be SP.

  FIG. 1C is a plan view showing the relationship between the reflecting member 12 and the shutter 15, and elevating members 19 a to 19 c (elastic bodies) are attached to the shutter 15 at three equal intervals. Thus, stable vertical movement of the shutter 15 by the elevating member 19 is realized.

  According to the shot peening method using the apparatus of the present invention as described above, the ultrasonic ball is used to stably project a steel ball on a predetermined portion of the center part of the leaf spring, and compressive residual stress is applied to the portion. Accordingly, it is possible to provide a leaf spring in which the delayed fracture time of the eyeball portion is lengthened and cracks and the like do not occur.

  2A and 2B are perspective views showing an example of the shot peening apparatus of the present invention described above. FIG. 2A is a view when the shutter 15 is released, and FIG. 2B is a view when the shutter 15 is closed. According to such an apparatus, as described above, since the steel ball can be moved in the closed space formed by the work, the housing, the reflecting member, and the vibrator, SP can be performed. As compared with the apparatus described in (1), the SP projection apparatus itself can be made compact. For this reason, it is possible to perform SP on the inner surface of the eyeball portion which is smaller than the conventional one, and it is possible to reduce the weight.

Next, the present invention will be described in detail with reference to examples.
The effect when ultrasonic SP was applied to the inner surface of the center part of the leaf spring was investigated. As a sample, an eyeball portion having a thickness of 14 mm, a width of 80 mm, and an inner diameter of 42 mm was used. Moreover, the ultrasonic SP used the shot peening apparatus shown in FIG. 2, and used the steel ball A (SUJ2: diameter 2.0mm) and the steel ball B (SUJ2: diameter 2.5mm) as a projection material. In addition, in the eyeball part of the leaf spring, the part where the ultrasonic wave SP is actually applied (near the top part of the eyeball part where SP is considered effective against delayed fracture) is indicated by the hatched portion in FIG.

  Under such conditions, the compressive residual stress distribution after ultrasonic SP was investigated. The result is shown in FIG. According to FIG. 4, when the steel ball A was used, a large residual stress could be obtained at any measured location as compared with the case where SP was not applied. In addition, when the steel ball A was used, it was confirmed that a compressive residual stress of about −400 MPa was generated at a position where the distance from the surface was 30 μm or more. Further, when the steel ball B is used, the compressive residual stress is further increased as compared with the case where the steel ball A is used, and at a position where the distance from the surface is 30 μm or more, a compressive residual of −800 MPa or more. It was also confirmed that stress was generated. Therefore, it can be inferred from these results that when the apparatus of the present invention is used, a high residual stress can be obtained, so that the delayed fracture time can be made longer than before.

  For the sample in which the ultrasonic SP is not applied to the center part of the leaf spring and the sample to which the ultrasonic SP is applied, each bush in which various stresses (about 1100 MPa) are generated in the eye part when the bush is press-fitted is prepared. When the bush was press-fitted into the eyeball part of each sample and SP was applied into the eyeball part, an investigation was made as to whether or not the delayed fracture time would be longer. In addition, in the center part of a leaf | plate spring, the location where ultrasonic wave SP was actually implemented is the same as the location shown in Example 1 (refer FIG. 3).

  Under these conditions, for the six samples shown in Table 1 (the size of the eyeball portion is the same as that of the eyeball portion shown in FIG. 3), the press-fitting stress of the bush is variously changed. The state of the inner surface of the eyeball part after 96 hours and 1 month was investigated. The results are also shown in Table 1.

  According to Table 1, Sample No. with SP on the inner surface of the eyeball part. As for 1, 3 and 5, generally, excellent results were shown. Sample No. About 3, although the crack produced, since this crack was produced in places other than SP construction position, it is thought that SP implementation effect is played.

  On the other hand, Sample No. in which SP was not applied to the inner surface of the center part. For Nos. 2, 4, and 6, cracks and the like occurred at the time of press-fitting, immediately after press-fitting, and after 24 hours. For 4 and 6, damage to the eyeball was confirmed. Therefore, from this experimental result, it is considered that SP on the inner surface of the eyeball part is sufficiently effective for delayed fracture of the eyeball part. In addition, it is presumed that by changing the SP irradiation position, the same effect can be obtained for eyeball damage caused by horizontal front-and-rear direction input that occurs when the vehicle stops suddenly.

  As described above, according to the present invention, in recent years, there has been a demand for higher hardness accompanying weight reduction of a leaf spring, thickening of a bush attached to the centerpiece, etc. Even if the generated stress increases or even if monoleafing is advanced as a new technology, it is possible to sufficiently meet the above requirements by performing SP construction as an early damage countermeasure for the eyeball part. Therefore, the present invention is promising in that a compressive residual stress can be applied to the center part of a leaf spring end for suspending a vehicle body or a general machine, and the delayed fracture time can be extended.

It is a figure which shows the shot peening apparatus 10 and the eyeball part W of a leaf | plate spring of this invention, (a) is a fragmentary sectional view which shows the non-engagement state of the apparatus 10 and the eyeball part W, (b) is the apparatus 10 and The fragmentary sectional view which shows an engagement state with the eyeball part W, (c) is a top view of the shot peening apparatus shown to Fig. (A), (b). It is a perspective view which shows the shot peening apparatus of this invention, (a) shows the time of shutter release, (b) shows the time of shutter closing. It is a top view which shows the predetermined location which actually implemented ultrasonic wave SP in the eyeball part of a leaf | plate spring. It is a graph which shows the investigation result about compression residual stress distribution after ultrasonic SP implementation.

Claims (4)

  When shot peening is performed by projecting a steel ball onto at least a part of the workpiece, a part of a member surrounding the closed space in which the steel ball moves is configured by the workpiece, and the steel ball is formed by ultrasonic vibration in the closed space. A shot peening method characterized by continuously moving and applying a compressive residual stress of −300 MPa or more to at least a part of a workpiece.   The shot peening method according to claim 1, wherein the steel balls are hard polished steel balls having a Rockwell C hardness of 65 or more.   A leaf spring comprising at least one leaf, wherein the shot peening according to claim 1 or 2 is performed.   A housing that is movable in the vertical direction with respect to the workpiece and that can rotate around a vertical axis, a reflective member that is disposed at an upper portion of the housing, and a vibration that is disposed below the reflective member in the housing. In a shot peening apparatus comprising a child and a shutter that opens and closes an opening formed on a side of the housing by moving up and down with respect to the housing, the work, the housing, A closed space is formed by the reflecting member and the vibrator, and a steel ball is continuously projected onto the workpiece by ultrasonic vibration in the closed space to give a compressive residual stress of −300 MPa or more to at least a part of the workpiece. When the housing and workpiece are not engaged, they are closed by the housing, reflecting member, vibrator, and shutter Forming between shot peening apparatus, characterized in that to prevent the falling to the outside of the steel ball.

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