Shot-peening device and shot-peening method

Abstract

Provided is a shot-peening device capable of improving fatigue strength of a workpiece by applying compressive residual stress to the inside of the workpiece. The shot-peening device comprises: a hollow housing 2; and a vibration means 3 for vibrating the housing 2. The housing 2A accommodates a workpiece W and shot SH therein. Due to this configuration, the vibration means 3 vibrates the housing 2 with the workpiece W and the shot SH accommodated therein. Accordingly, the fatigue strength of the workpiece W is improved by applying compressive residual stress to the inside of the workpiece W.

Description

Shot peening device and shot peening method

[0001] The present invention relates to a shot peening apparatus and a shot peening method.

[0002] A conventional shot peening apparatus is known, for example, from Patent Document 1. In this shot peening apparatus, a plurality of spherical particles (hereinafter referred to as shot) are transported upward by a bucket elevator and then fed toward a lateral screw. The shot then flows into a guide line from the lateral screw, falls downward along the guide line, and is guided to an impeller. The impeller then projects the shot toward the workpiece.

[0003] To explain this point in more detail with reference to Fig. 6, a conventional shot peening apparatus 100 includes an endless belt 101 that is arc-shaped when viewed from the front. This endless belt 101 moves in the direction of arrow Y100 shown in Fig. 6. A workpiece W (a compression coil spring is shown as an example in Fig. 6) is placed on the endless belt 101. Shots SH are projected onto the workpiece W by an impeller 102. This imparts compressive residual stress to the workpiece W, thereby improving the fatigue strength of the workpiece W.

[0004] Patent No. 6304957

[0005] Incidentally, it is known that compression coil springs, in particular, as workpieces W, have a higher stress on the inside than on the outside. Therefore, compression coil springs often break from the inside. Therefore, in order to improve the fatigue strength of compression coil springs, it is considered to impart compressive residual stress to the inside of the compression coil spring. However, in order to impart compressive residual stress to the inside of the compression coil spring, it is necessary to increase the kinetic energy of the shot SH. As is well known, the kinetic energy is 1 / 2 mv ２Since m is expressed as m = mass, v = velocity, the only way to improve the kinetic energy is to increase the mass and / or velocity of the shot SH. However, if the impeller 102 is used to project the shot SH at high speed, the mass of the shot SH must be reduced. On the other hand, increasing the mass of the shot SH increases the particle size of the shot SH. Therefore, if an attempt is made to impart residual stress to the inner diameter side of the compression coil spring, the only option is to project shot SH with a particle size smaller than the wire pitch of the compression coil spring at high speed. However, projecting shot SH with a small particle size at high speed may cause surface roughness of the compression coil spring, resulting in a decrease in fatigue strength. Therefore, due to the possibility of such problems occurring, the impeller 102 cannot project the shot SH at high speed, and the velocity must be reduced. Therefore, the conventional shot peening apparatus 100 has limitations on the mass and velocity of the shot SH, making it impossible to improve the kinetic energy and ultimately resulting in the inability to impart compressive residual stress to the interior of the compression coil spring.

[0006] In view of the above problems, an object of the present invention is to provide a shot peening apparatus and a shot peening method that can improve the fatigue strength of a workpiece by imparting compressive residual stress to the interior of the workpiece.

[0007] The above object of the present invention can be achieved by the following means: Note that the parentheses indicate reference symbols of embodiments to be described later, but the present invention is not limited to these.

[0008] The shot peening apparatus according to the invention of claim 1 comprises a hollow housing (2) and a vibration means (3) for vibrating the housing (2), wherein a workpiece (W) and shot (SH) are stored in the housing (2), and the vibration means (3) vibrates the housing (2) in a state in which the workpiece (W) and the shot (SH) are stored.

[0009] According to the invention of claim 2, in the shot peening apparatus (1) of claim 1, the shot (SH) is disposed inside the workpiece (W).

[0010] According to a third aspect of the present invention, in the shot peening apparatus (1) of the second aspect, the workpiece (W) is a compression coil spring, and the diameter (H1) of the shot (SH) is formed to be larger than the pitch (H2) of the compression coil spring.

[0011] According to a fourth aspect of the present invention, the shot peening apparatus (1) according to the first aspect further comprises a rotating means for rotating the housing (2).

[0012] According to a fifth aspect of the invention, in the shot peening apparatus (1) of the first aspect, the workpiece (W) is a compression coil spring, the shot (SH) and the compression coil spring are stored in a compressed state in the housing (2), and the vibration means (3) vibrates the compression coil spring in the compressed state and the housing (2) in which the shot (SH) is stored.

[0013] According to the shot peening method of the invention of claim 6, there is provided a method of imparting compressive residual stress to the workpiece (W) using the shot peening apparatus (1) of claim 1, and then imparting compressive residual stress again to the workpiece (W) to which the compressive residual stress has been imparted using an existing shot peening apparatus (conventional shot peening apparatus (100)).

[0014] According to the shot peening method of the invention of claim 7, an existing shot peening apparatus (conventional shot peening apparatus (100)) is used to impart compressive residual stress to a workpiece (W), and then the shot peening apparatus (1) of claim 1 is used to improve the surface roughness of the workpiece (W).

[0015] Next, the effects of the present invention will be described with reference to the drawings. Note that the reference symbols in parentheses are those of the embodiments described below, but the present invention is not limited to these.

[0016] According to the invention of claim 1, the vibration means (3) vibrates the workpiece (W) and the housing (2) containing the shot (SH), so there are no limitations on the mass or speed of the shot (SH) as in the conventional shot peening device (100). This makes it possible to improve kinetic energy and impart compressive residual stress to the interior of the workpiece (W). Therefore, according to the present invention, by imparting compressive residual stress to the interior of the workpiece (W), the fatigue strength of the workpiece (W) can be improved.

[0017] According to the invention of claim 2, the shot (SH) is arranged inside the workpiece (W), so that compressive residual stress can be reliably imparted to the inside of the workpiece (W).

[0018] According to the invention of claim 3, the diameter (H1) of the shot (SH) is formed to be larger than the pitch (H2) of the compression coil spring, so that it is possible to prevent the shot (SH) from coming into contact with the inside of the workpiece (W) and going outside the workpiece (W).

[0019] According to the invention of claim 4, since a rotation means for rotating the housing (2) is provided, if the workpiece (W) does not rotate freely, the workpiece (W) can be rotated.

[0020] According to the invention of claim 5, the compression coil spring in a compressed state and the housing (2) in a state in which the shot (SH) is stored are vibrated, so that optimal stress peening can be performed.

[0021] According to the sixth aspect of the present invention, after compressive residual stress is imparted to the workpiece (W), an existing shot peening device (conventional shot peening device (100)) is used to impart compressive residual stress again to the workpiece (W) to which compressive residual stress has been imparted. This makes it possible to impart compressive residual stress accurately to the inside and outside of the workpiece (W).

[0022] According to the seventh aspect of the present invention, an existing shot peening device (conventional shot peening device 100) is used to impart compressive residual stress to a workpiece (W), and then the shot peening device 1 is used to improve the surface roughness of the workpiece (W). This makes it possible to effectively improve the surface roughness of the workpiece (W).

[0023] 1 is a perspective view of a shot peening apparatus according to an embodiment of the present invention, as seen from above. (a) is a vertical cross-sectional view of a housing according to the embodiment, and (b) is a partial vertical cross-sectional front view of a portion of the shot peening apparatus according to the embodiment, as seen from the front. (a) is a perspective view of a jig used when compressing a compression coil spring, which is an object to be treated. (a) to (c) are side views of the jig, illustrating a method of compressing a compression coil spring, which is an object to be treated, using the jig shown in FIG. 3. (a) is a vertical cross-sectional view of a state in which shots are stored in the housing according to the embodiment, together with the jig in a state in which the compression coil spring, which is an object to be treated, is compressed. (b) is a partial vertical cross-sectional front view of a portion of the shot peening apparatus according to the embodiment, as seen from the front. (c) is a schematic explanatory view illustrating a conventional shot peening apparatus.

[0024] An embodiment of a shot peening apparatus according to the present invention will be described below in detail with reference to the drawings. In the following description, when directions such as up, down, left, and right are indicated, they refer to up, down, left, and right when viewed from the front of the drawing.

[0025] <Outline of Shot Peening Apparatus> The shot peening apparatus according to this embodiment is capable of improving the fatigue strength of a workpiece by imparting compressive residual stress to the interior of the workpiece. Specifically, as shown in Figures 1 and 2(b), the shot peening apparatus 1 is composed of a housing 2 and a vibration applying means 3. Each component will be described in detail below.

[0026] <Explanation of the Housing> The housing 2 is formed, for example, from an acrylic case etc. As shown in Fig. 2, the housing 2 is formed in a horizontally elongated rectangular shape in cross section and in a cylindrical shape with a hollow interior.

[0027] On the other hand, as shown in FIG. 1, the housing 2 formed as described above has rod-shaped support portions 2a attached and fixed to the left and right side surfaces.

[0028] 1 and 2, a single workpiece W (a compression coil spring is shown as an example) is stored inside the housing 2 configured as described above. As shown in Fig. 2, the left and right ends of the workpiece W are rotatably supported by supports 2a that protrude inward into the housing 2. As a result, the workpiece W is maintained in its storage position inside the housing 2 at a predetermined distance (e.g., distance D1) from the upper and lower inner wall surfaces 2b and 2c of the housing 2, as shown in Fig. 2(a).

[0029] 2, a plurality of shots SH are arranged inside the workpiece W, i.e., on the inner diameter side. As the shots SH, for example, steel balls for bearings having excellent wear resistance are used.

[0030] <Explanation of the Vibration Means> As shown in Fig. 1, the vibration means 3 includes a circular base 30. As shown in Fig. 1, a pair of mounting bases 31 are attached and fixed to the left and right side surfaces of an upper surface 30a of the base 30 using bolts B. As shown in Fig. 1, the mounting bases 31 are arranged opposite each other and are formed in a substantially semicircular shape. The support portions 2a of the housing 2 are attached and fixed to the pair of mounting bases 31, respectively.

[0031] 2(b), a rod-shaped piston rod 32 is attached and fixed to the center of the lower surface 30b of the base 30. The piston rod 32 is movable in the vertical direction (in the direction of arrow Y1 in FIG. 2(b)) by hydraulic pressure or the like (not shown).

[0032] Thus, the shot peening apparatus 1 is configured as described above.

[0033] <Explanation of an Example of Use of Shot Peening Apparatus> Next, an example of use of the shot peening apparatus 1 configured as above will be described.

[0034] First, before moving the piston rod 32 shown in FIG. 2(b) in the vertical direction, the workpiece W (shown as a compression coil spring) is stored in the housing 2 as shown in FIGS. 1 and 2(a), and further, a plurality of shots SH are placed inside the workpiece W, i.e., on the inner diameter side.

[0035] In this state, when the piston rod 32 shown in Fig. 2(b) is moved up and down, the base 30 also moves up and down, and further, the pair of mounting bases 31 also move up and down. As a result, the housing 2 also moves up and down. Therefore, the housing 2 is vibrated.

[0036] Thus, when the housing 2 is vibrated in this manner, the workpiece W and shot SH housed within the housing 2 are also vibrated. Accordingly, the shot SH moves irregularly up and down inside the workpiece W, i.e., on the inner diameter side, as shown by the arrow in FIG. 2(b). Furthermore, since the workpiece W in this embodiment is a compression coil spring and is formed in a spiral shape, it moves up and down, i.e., freely rotates around the support portion 2a as it is vibrated. Therefore, the shot SH comes into contact with the entire inner diameter of the workpiece W. This makes it possible to impart compressive residual stress to the interior of the workpiece W, i.e., the inner diameter. Therefore, the fatigue strength of the workpiece W can be improved.

[0037] To explain this in more detail, as explained above, the kinetic energy is 1 / 2 mv ２ (m: mass, v: velocity). In this case, unlike the conventional shot peening apparatus 100, the shot peening apparatus 1 according to this embodiment does not need to project the shots SH at high speed, and a plurality of shots SH are arranged in advance inside the workpiece W, i.e., on the inner diameter side. Therefore, the size (diameter) of the shot SH can be made larger (e.g., 6 mm) than that used in the conventional shot peening apparatus 100 (e.g., 3 mm). Furthermore, the vibration speed can be increased by increasing the speed of movement in the vertical direction.

[0038] Therefore, the shot peening apparatus 1 according to this embodiment is capable of improving kinetic energy because there are no limitations on the mass or velocity of the shot SH, as in the conventional shot peening apparatus 100. Therefore, the shot peening apparatus 1 according to this embodiment is capable of imparting compressive residual stress to the interior of the workpiece W. Therefore, according to this embodiment, by imparting compressive residual stress to the interior of the workpiece W, the fatigue strength of the workpiece W can be improved.

[0039] In this embodiment, the diameter H1 (e.g., 6 mm) of the shot SH shown in FIG. 2B is larger than the pitch H2 (e.g., 4.5 mm) of the workpiece W. This prevents the shot SH from coming into contact with the inner diameter side (inside) of the workpiece W and falling outside the workpiece W. In other words, if the shot SH falls outside the workpiece W, it may become trapped between the pitch H2 of the workpiece W. If this occurs, the workpiece W may not rotate freely, and compressive residual stress may not be imparted to the interior of the workpiece W. Therefore, in this embodiment, the diameter H1 (e.g., 6 mm) of the shot SH shown in FIG. 2B is larger than the pitch H2 (e.g., 4.5 mm) of the workpiece W.

[0040] <Explanation of Modifications> The shapes and the like shown in the present embodiment are merely examples, and various modifications and changes are possible within the scope of the gist of the present invention as described in the claims. For example, the housing 2 and the vibration means 3 described in the present embodiment may have any shape or configuration as long as they have the same functions as those described above.

[0041] In addition, in this embodiment, no compressive residual stress is imparted to the outside of the compression coil spring as the workpiece W, but this need not be done if it is not necessary. As explained above, compression coil springs often break from the inside, so if compressive residual stress is imparted to the inside of the compression coil spring, the fatigue strength of the compression coil spring can be improved and breakage from the inside can be prevented.

[0042] On the other hand, when compressive residual stress is applied to the outside of a compression coil spring as the workpiece W, multiple shots SH may be arranged outside the workpiece W housed in the housing 2.

[0043] On the other hand, it is also possible to use the shot peening apparatus 1 according to this embodiment to impart compressive residual stress to the inside of the workpiece W, and then use a conventional shot peening apparatus 100 to impart compressive residual stress to the outside of the workpiece W. In this way, when manufacturing the shot peening apparatus 1, it is possible to reduce the manufacturing cost to a minimum shot peening apparatus 1 that only imparts compressive residual stress to the inside of the workpiece W. Furthermore, it is possible to impart compressive residual stress accurately to the inside and outside of the workpiece W.

[0044] On the other hand, after compressive residual stress is imparted to the workpiece W using the conventional shot peening apparatus 100, the shot peening apparatus 1 according to this embodiment may be used to improve the surface roughness inside the workpiece W. In this way, the surface roughness inside the workpiece W can be effectively improved.

[0045] Furthermore, in this embodiment, the storage position of the workpiece W within the housing 2 is set to a position (e.g., distance D1) away from the upper inner wall surface 2b and the lower inner wall surface 2c of the housing 2. However, the workpiece W does not have to be set to a position (e.g., distance D1) away from the upper inner wall surface 2b and the lower inner wall surface 2c of the housing 2. However, if the workpiece W is not set to a position (e.g., distance D1) away from the upper inner wall surface 2b and the lower inner wall surface 2c of the housing 2, the workpiece W may come into contact with the upper inner wall surface 2b and the lower inner wall surface 2c of the housing 2, preventing it from moving vertically, i.e., from freely rotating around the support portion 2a as a base point due to vibration. Therefore, it is preferable to set the storage position of the workpiece W within the housing 2 to a position (e.g., distance D1) away from the upper inner wall surface 2b and the lower inner wall surface 2c of the housing 2. However, if the workpiece W does not rotate freely, the workpiece W may be rotated by rotating the support portion 2a using a motor or the like, thereby rotating the housing 2 itself.

[0046] Furthermore, in this embodiment, an example is shown in which a single (one) workpiece W is stored in the housing 2, but the housing 2 itself may be elongated, for example, so that multiple workpieces W can be stored therein.

[0047] Furthermore, in this embodiment, a compression coil spring is used as an example of the workpiece W, but the present invention is not limited to this and can be applied to any part that requires the application of compressive residual stress, such as a welded pipe.

[0048] In addition, in this embodiment, an example has been shown in which a compression coil spring, which is the workpiece W, is simply stored, but the present invention is not limited to this, and the compression coil spring may be stored in a compressed state and subjected to so-called stress peening. This point will be described in detail below.

[0049] First, a jig 4 as shown in Fig. 3 is used to compress a compression coil spring, which is the workpiece W. As shown in Fig. 3, this jig 4 has a thick, circular first support plate 40 and a second support plate 41 having the same shape as the first support plate 40, which are arranged at a fixed interval in the vertical direction. As shown in Fig. 3, this first support plate 40 has a U-shaped left cutout 40b on the left side facing toward the center, and further has a U-shaped right cutout 40c on the right side facing toward the center.

[0050] 3, the first support plate 40 has a circular front through-hole 40d extending vertically through its front end surface, and a circular rear through-hole 40e extending vertically through its rear end surface.

[0051] Thus, the first support plate 40 and the second support plate 41 formed in this manner are formed to have the same shape. Specifically, as shown in Fig. 3, the second support plate 41 has a U-shaped left cutout 41b formed on the left side surface thereof toward the center, and a U-shaped right cutout 41c formed on the right side surface thereof toward the center. Furthermore, as shown in Fig. 3, the second support plate 41 has a circular front through-hole 41d formed on the front end surface thereof so as to penetrate in the vertical direction, and a circular rear through-hole 41e formed on the rear end surface thereof so as to penetrate in the vertical direction.

[0052] Thus, as shown in Fig. 3, a compression coil spring, which is the workpiece W, is placed between the first support plate 40 and the second support plate 41 formed in this manner. As a result, the compression coil spring, which is the workpiece W, is sandwiched between the first support plate 40 and the second support plate 41. Therefore, if the distance between the first support plate 40 and the second support plate 41 is reduced, the compression coil spring, which is the workpiece W, is compressed by the first support plate 40 and the second support plate 41. Note that Fig. 3 shows a state in which the compression coil spring, which is the workpiece W, is compressed by reducing the distance between the first support plate 40 and the second support plate 41. 3, in order to maintain the distance between the first support plate 40 and the second support plate 41, a first support rod 42 is inserted into the left notch 40b of the first support plate 40 and the left notch 41b of the second support plate 41, and its position is fixed by a pair of first support nuts 42a (see also FIG. 4(c)). Furthermore, as shown in FIG. 3, a second support rod 43 is inserted into the right notch 40c of the first support plate 40 and the right notch 41c of the second support plate 41, and its position is fixed by a pair of second support nuts 43a (see also FIG. 4(c)). In this way, the distance between the first support plate 40 and the second support plate 41 is maintained.

[0053] Here, a method for compressing a compression coil spring, which is the workpiece W, using the jig 4 will be described in more detail. As shown in FIG. 4( a), the compression coil spring, which is the workpiece W, is placed between a first support plate 40 and a second support plate 41. At this time, as shown in FIG. 4( a), a first set rod 44 is inserted into the front through-hole 40d of the first support plate 40 and the front through-hole 41d of the second support plate 41, and its position is fixed by a left first set nut 44a located on the first support plate 40 side and a right first set nut 44b located on the second support plate 41 side. Furthermore, as shown in FIG. 4( a), a second set rod 45 is inserted into the rear through-hole 40e of the first support plate 40 and the rear through-hole 41e of the second support plate 41, and its position is fixed by a left second set nut 45a located on the first support plate 40 side and a right second set nut 45b located on the second support plate 41 side.

[0054] In this state, when the right first set nut 44b and the right second set nut 45b shown in Fig. 4(a) are tightened, the second support plate 41 moves to the left in the figure, guided by the first set rod 44 and the second set rod 45. As a result, as shown in Fig. 4(b), the second support plate 41 moves closer to the first support plate 40, reducing the distance between the first support plate 40 and the second support plate 41, and the compression coil spring, which is the workpiece W sandwiched between the first support plate 40 and the second support plate 41, is compressed.

[0055] As will be described later, the jig 4 is stored in the housing 2. Therefore, in this state, as shown in FIG. 4B, there is a possibility that the jig 4 cannot be stored in the housing 2 due to the excess length on the right side of the first setting rod 44 and the second setting rod 45.

[0056] In this embodiment, after compressing the compression coil spring, which is the workpiece W, the distance between the first support plate 40 and the second support plate 41 is maintained at that position by inserting a second support rod 43 into the right notch 40c of the first support plate 40 and the right notch 41c of the second support plate 41, and fixing the position with a pair of second support nuts 43a, as shown in Fig. 4(b). Furthermore, as shown in Fig. 4(c), the first support rod 42 is inserted into the left notch 40b of the first support plate 40 and the left notch 41b of the second support plate 41, and fixing the position with a pair of first support nuts 42a. After maintaining the distance between the first support plate 40 and the second support plate 41 at the position shown in FIG. 4( b), the left first set nut 44a and the right first set nut 44b shown in FIG. 4( b) are loosened to remove the first set rod 44 from the front through-hole 40d of the first support plate 40 and the front through-hole 41d of the second support plate 41. Then, the left second set nut 45a and the right second set nut 45b shown in FIG. 4( b) are loosened to remove the second set rod 45 from the rear through-hole 40e of the first support plate 40 and the rear through-hole 41e of the second support plate 41. This results in the state shown in FIG. 4( c). This eliminates the possibility that the jig 4 cannot be stored in the housing 2 due to the excess length of the first set rod 44 and the second set rod 45 on the right side in the figure.

[0057] Next, the jig 4 in the state shown in FIG. 4(c) is placed inside the housing 2 as shown in FIG. 5(a). At this time, the jig 4 in the state shown in FIG. 4(c) is placed inside the housing 2 at a position (e.g., distance D1) away from the upper inner wall surface 2b and the lower inner wall surface 2c of the housing 2. At this time, as shown in FIG. 5(a), multiple shots SH are placed inside the workpiece W, i.e., on the inner diameter side. In this state, as shown in FIG. 5(b), the support portions 2a of the housing 2 are attached and fixed to the pair of mounting bases 31, respectively, and the piston rod 32 shown in FIG. 5(b) is moved up and down (in the direction of arrow Y2). This causes the base 30 to move up and down, and further, the pair of mounting bases 31 also move up and down, causing the housing 2 to move up and down. This causes the housing 2 to vibrate.

[0058] Thus, when the housing 2 is vibrated in this manner, the workpiece W and shot SH contained within the housing 2 are also vibrated. Accordingly, the shot SH moves irregularly up and down inside the workpiece W, i.e., on the inner diameter side, as shown by the arrow in FIG. 5(b). Furthermore, as shown in FIG. 5(a), the jig 4, as shown in FIG. 4(c), is positioned at a predetermined distance (e.g., distance D1) from the upper inner wall surface 2b and the lower inner wall surface 2c of the housing 2. Therefore, there is a difference (e.g., distance D1 × 2) between the circumference of the housing 2 and the circumference of the jig 4 (first support plate 40 and second support plate 41). This difference causes vertical movement, i.e., rotation of the jig 4 around the support portion 2a as vibration occurs. Therefore, the shot SH comes into contact with the entire inner diameter of the workpiece W. This makes it possible to impart compressive residual stress to the inside of the workpiece W, which is a compressed compression coil spring, i.e., to the inner diameter, thereby improving the fatigue strength of the workpiece W.

[0059] As explained above in the section on the problem to be solved by the invention, the conventional shot peening apparatus 100 has a problem in that it is not possible to impart compressive residual stress to the interior of a compression coil spring. This problem becomes even more pronounced when stress peening is performed. That is, when attempting to impart compressive residual stress to the interior of a compressed compression coil spring, the inter-wire gap becomes smaller compared to an uncompressed compression coil spring, making it more difficult for shot SH to penetrate into the inner diameter side of the compression coil spring. Therefore, this problem becomes even more pronounced when stress peening is performed.

[0060] However, by employing the method of the present embodiment described above, such problems can be solved. Therefore, by employing the method of the present embodiment described above, optimal stress peening can be performed.

[0061] In the above explanation, an example has been given in which the jig 4 is used to compress the compression coil spring, which is the workpiece W, but this is not limiting, and any method may be used as long as the compression coil spring, which is the workpiece W, can be stored in the housing 2 in a compressed state.

[0062] 1 Shot peening device 2 Housing 3 Vibration means 4 Jig W Workpiece SH Shot H1 (Shot) diameter H2 (Compression coil spring) pitch 100 Conventional shot peening device (existing shot peening device)

Claims

1. A shot peening apparatus comprising: a hollow housing; and a vibration means for vibrating the housing, wherein a workpiece and shot are stored within the housing, and the vibration means vibrates the housing in which the workpiece and the shot are stored.

2. A shot peening apparatus as set forth in claim 1, wherein the shots are disposed inside the workpiece.

3. A shot peening device according to claim 2, wherein the object to be treated is a compression coil spring, and the diameter of the shot is formed to be larger than the pitch of the compression coil spring.

4. The shot peening apparatus according to claim 1, further comprising a rotating means for rotating said housing.

5. A shot peening apparatus as described in claim 1, wherein the object to be treated is a compression coil spring, the shot and the compression coil spring are stored in a compressed state within the casing, and the vibration means vibrates the compression coil spring in the compressed state and the casing in which the shot is stored.

6. A shot peening method comprising: using the shot peening apparatus according to claim 1 to impart compressive residual stress to the workpiece; and then using an existing shot peening apparatus to impart compressive residual stress again to the workpiece to which the compressive residual stress has been imparted.

7. A shot peening method comprising the steps of: applying compressive residual stress to a workpiece using an existing shot peening device; and then improving the surface roughness of the workpiece using the shot peening device according to claim 1.

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