Method for manufacturing spring and cylindrical coil spring

Abstract

This method for manufacturing a spring comprises: a shot peening pretreatment step for applying pretreatment to a wire material before being subjected to shot peening; a first shot peening step (S13) for projecting, onto a coiled wire material (3) subjected to the pretreatment in the shot peening pretreatment step, a first medium (5) formed in a spherical shape and having a diameter value of 1.3 mm or more and hardness of 570 Hv or more at a speed of 70 m / sec or more, thereby performing a first shot peening; and a second shot peening step (S15) for projecting, onto the coiled wire material (3) subjected to the treatment in the first shot peening step (S13), a second medium (7) formed in a spherical shape and having a diameter value smaller than the diameter value of the first medium (5) at a speed lower than the speed in the first shot peening step (S13), thereby performing a second shot peening.

Description

Spring manufacturing method and cylindrical coil spring

[0001] The present invention relates to a method for manufacturing a spring and a cylindrical coil spring.

[0002] Patent Documents 1 and 2 propose manufacturing methods for manufacturing springs with excellent corrosion resistance, etc., by subjecting the wire of the spring to shot peening. In springs manufactured by these manufacturing methods, compressive residual stress is imparted to the wire from the surface to a predetermined depth by the shot peening.

[0003] The application of compressive residual stress can prevent cracks from occurring and progressing during use. By increasing the depth (depth from the surface) to which compressive residual stress is applied, the compressive residual stress remains even if there is thinning due to corrosion. In other words, thinning due to corrosion can cause the wire to be lost up to a certain depth from the surface. However, the compressive residual stress applied to the wire may remain and not disappear. By increasing the depth from the surface to which compressive residual stress is applied, the strength of the spring can be increased.

[0004] JP 2011-663 A JP 2011-149036 A

[0005] In the case of springs, there is a demand to increase the depth from the surface to which the above-mentioned compressive residual stress is imparted, thereby further suppressing the occurrence of cracks even when there is thinning due to corrosion.

[0006] An object of the present invention is to provide a spring manufacturing method and a cylindrical coil spring that can suppress the occurrence and progression of cracks more than conventional methods, even when there is wall thinning due to corrosion.

[0007] A method for manufacturing a spring according to an embodiment of the present invention includes: a shot peening pretreatment step of subjecting a material to pretreatment before shot peening; a first shot peening step of subjecting the material pretreated in the shot peening pretreatment step to first shot peening by projecting first media, which are spherical and have a diameter of 1.3 mm or more and a hardness of 570 Hv or more, at a speed of 70 m / sec or more; and a second shot peening step of subjecting the material treated in the first shot peening step to second shot peening by projecting second media, which are spherical and have a diameter smaller than the diameter of the first media used in the first shot peening step, at a speed slower than the speed in the first shot peening step.

[0008] A manufacturing method of a cylindrical coil spring according to an embodiment of the present invention includes: a shot peening pretreatment step of subjecting wire to pretreatment before shot peening; a first shot peening step of subjecting the coiled wire pretreated in the shot peening pretreatment step to first shot peening by projecting first media, which are spherical and have a diameter of 1.3 mm or more and a hardness of 570 Hv or more, at a speed of 70 m / sec or more; and a second shot peening step of subjecting the coiled wire treated in the first shot peening step to second shot peening by projecting second media, which are spherical and have a diameter smaller than the diameter of the first media used in the first shot peening step, at a speed slower than the speed in the first shot peening step.

[0009] The cylindrical coil spring according to this embodiment of the present invention has a residual stress value of 500 MPa or more at a depth of 0.28 mm from the surface, a maximum stress value of 1300 MPa or more, a maximum hardness value of 570 Hv or more, and is subjected to uniform compressive stress in the circumferential direction.

[0010] According to the above configuration, even when there is a reduction in thickness due to corrosion, the occurrence and progression of cracks can be suppressed more effectively than in the past.

[0011] FIG. 1 is a diagram showing a manufacturing process for a cylindrical coil spring according to an embodiment of the present invention. FIG. 2 is a diagram showing compressive residual stresses in a cylindrical coil spring according to an embodiment of the present invention and a cylindrical coil spring according to a comparative example. FIG. 3A is a diagram showing compressive residual stresses and cracks in a cylindrical coil spring according to an embodiment of the present invention, illustrating a state in which no thinning due to corrosion has occurred. FIG. 3B is a diagram showing compressive residual stresses and cracks in a cylindrical coil spring according to an embodiment of the present invention, illustrating a state in which thinning due to corrosion has occurred. FIG. 4A is a diagram showing compressive residual stresses and cracks in a cylindrical coil spring according to a comparative example, illustrating a state in which no thinning due to corrosion has occurred. FIG. 4B is a diagram showing compressive residual stresses and cracks in a cylindrical coil spring according to a comparative example, illustrating a state in which thinning due to corrosion has occurred.

[0012] As shown in FIG. 1, the method for manufacturing a cylindrical coil spring 1 according to the embodiment of the present invention includes a shot peening pretreatment step, a first shot peening step S13, and a second shot peening step S15.

[0013] The shot peening pretreatment step is a step of performing pretreatment before shot peening on a wire rod (e.g., a wire rod made of spring steel) 3. The shot peening pretreatment step includes, for example, a rolling step S1, a heating step S3, a coiling step S5, a heat treatment step (quenching) S7, a heat treatment step (tempering) S9, and a hot setting step S11.

[0014] The rolling process step S1 is a process of rolling the wire rod 3. The cross section of the wire rod 3 rolled in the rolling process step (a cross section taken along a plane perpendicular to the longitudinal direction of the wire rod 3) has, for example, a circular shape.

[0015] The heating step S3 is a step of heating the entire wire rod 3 that has been rolled in the rolling step S1 in order to austenitize it. The coiling step S5 is a step of coiling (for example, by cold working) the wire rod 3 that has been heated in the heating step S3 into a coil shape (spiral shape).

[0016] The heat treatment steps S7 and S9 are steps of heat treating (quenching and tempering) the wire rod 3 formed into a coil shape in the coiling step S5. The hot setting step S11 is a step of hot setting the coil-shaped wire rod 3 heat-treated in the heat treatment steps S7 and S9.

[0017] The first shot peening step S13 is a step of peening the coiled wire 3 that has been pretreated in the shot peening pretreatment step by projecting first media (first shot material) 5 onto the coiled wire 3. The first media 5 are formed in a spherical shape.

[0018] The first medium 5 has a diameter of 1.3 mm or more (1.3 mm to 1.5 mm) and a hardness of 570 Hv or more (570 Hv to 900 Hv). The speed of the first medium 5 when projected is 70 m / sec or more (70 m / sec to 100 m / sec).

[0019] The second shot peening step S15 is a step of peening the coiled wire 3 that has been treated in the first shot peening step S13 by projecting second media (second shot material) 7 onto the coiled wire 3. The second media 7 are also formed into a spherical shape.

[0020] The second media 7 used have a diameter smaller than that of the first media 5 used in the first shot peening step S13 (for example, 0.6 mm to 1.2 mm). The speed of the second media 7 when projected is slower than that of the first media 5 in the first shot peening step S13 (for example, 40 m / sec or more and less than 70 m / sec). The hardness of the second media 7 is also 570 Hv or more (570 Hv or more and 900 Hv or less).

[0021] In the manufacturing method of the cylindrical coil spring 1 according to the embodiment of the present invention, as shown in Fig. 1, in a painting pretreatment step S17, the coiled wire 3 that has been treated in the second shot peening step S15 is subjected to pretreatment such as degreasing for painting. Furthermore, in a painting step S19, the coiled wire 3 that has been pretreated in the painting pretreatment step S17 is painted, thereby obtaining the cylindrical coil spring 1. The cylindrical coil spring 1 is inspected in a load inspection step S21. After the load inspection step S21, the cylindrical coil spring 1 is completed.

[0022] Here, a further description will be given of the cylindrical coil spring 1 manufactured by the manufacturing method of the cylindrical coil spring 1 according to the embodiment of the present invention. The cylindrical coil spring 1 is used, for example, as a compression coil spring such as a suspension coil spring.

[0023] As a result of shot peening, the cylindrical coil spring 1 has numerous (too many to count) small, round, shallow dents formed on the surface 9 (see FIG. 3A) that are almost invisible to the naked eye. The numerous small dents formed on the surface 9 give the surface a matte finish. If the surface is treated with a coating or the like, the dents will be hidden and will not be visible. Note that in FIGS. 3A, 3B, 4A, and 4B, the coating film formed by the coating and the dents are not shown. Also, the arrows DD in FIGS. 3A, 3B, 4A, and 4B indicate the depth direction.

[0024] In the cylindrical coil spring 1, the value (absolute value) of the residual stress (e.g., compressive residual stress) at a depth of 0.28 mm from the surface 9 is 500 MPa or more (e.g., 500 MPa or more and 600 MPa or less). In the cylindrical coil spring 1, the value of the maximum stress (the maximum stress generated when the maximum design force is applied) is 1300 MPa or more (e.g., 1300 MPa or more and 1500 MPa or less).

[0025] The maximum hardness of the cylindrical coil spring 1 is 570 Hv or more (for example, 570 Hv or more and 900 Hv or less). Assuming that the above-described shot peening steps S13 and S15 are performed on a test piece (not shown) of the cylindrical coil spring 1, the arc height will be about 0.65 mmA.

[0026] In the cylindrical coil spring 1, a uniform compressive stress (residual compressive stress) is applied in the circumferential direction. Because the uniform residual compressive stress is applied in the circumferential direction, the residual compressive stress applied to the wire of the cylindrical coil spring 1 is generally uniform in the circumferential direction of the wire. To explain further, for example, the value of the residual compressive stress applied to the wire at a depth of 0.1 mm from the surface of the wire is generally uniform at every point in the circumferential direction of the wire. However, it is not completely uniform. It varies slightly depending on the point in the circumferential direction of the wire, and there is some variation. For example, the difference between the maximum value of the residual compressive stress in the circumferential direction of the wire and the minimum value of the residual compressive stress in the circumferential direction of the wire divided by the minimum value of the residual compressive stress in the circumferential direction of the wire is within 10%.

[0027] The manufacturing method of the cylindrical coil spring 1 according to the embodiment of the present invention includes a first shot peening step S13 and a second shot peening step S15. In the first shot peening step S13, first shots 5 are projected onto the coiled wire 3 at a speed of 70 m / sec or more. The first shots 5 are spherical, have a diameter of 1.3 mm or more, and a hardness of 570 Hv or more.

[0028] In the second shot peening process S15, the coiled wire 3 that has been treated in the first shot peening process S13 is blasted with second shots 7 at a speed slower than that in the first shot peening process S13. The second shots 7 are spherical and have a diameter of approximately 0.6 mm, which is smaller than the diameter of the first shots 5. The second shots 7 have a hardness of 570 Hv or more.

[0029] In the first shot peening step S13, the first shots 5 having a larger diameter than conventional shots are used, and therefore the mass of the first shots 5 is larger than conventional shots. As a result, the first shots 5 have large kinetic energy. As a result, the value of the collision energy when the first shots 5 collide with the coiled wire 3 is large.

[0030] The increased collision energy value allows the depth from the surface of the cylindrical coil spring 1 to which compressive residual stress of a predetermined magnitude or greater is imparted to be greater than in the conventional case. Even when wall thickness reduction 11 (see FIG. 3B ) occurs due to corrosion, the portion to which compressive residual stress of a predetermined magnitude or greater is imparted remains, making it possible to suppress the occurrence and propagation of cracks more effectively than in the conventional case.

[0031] In the second shot peening process S15, second shots 7 having a diameter smaller than that of the first shots 5 are projected at a speed slower than that in the first shot peening process S13. This results in a smaller kinetic energy of the second shots 7 than that of the first shots 5. This reduces the surface irregularities of the coiled wire 3 formed by the first shot peening process S13 while leaving deep compressive residual stresses of a predetermined magnitude or greater imparted in the first shot peening process S13. This minimizes the formation of breakage origins (starting points for crack initiation) due to the irregularities. Furthermore, by performing the second shot peening process S15, the compressive residual stress value of the coiled wire 3 can be adjusted while maintaining the predetermined magnitude or greater.

[0032] Here, the surface and depth from the surface of the wire (element wire) of the cylindrical coil spring 1, and the compressive residual stress will be described with reference to Fig. 2. The horizontal axis of Fig. 2 represents the depth from the surface of the wire of the cylindrical coil spring 1, with the depth increasing toward the right in Fig. 2. The vertical axis of Fig. 2 represents the compressive residual stress, with the absolute value of the compressive residual stress increasing toward the top of Fig. 2.

[0033] The curve indicated by reference sign L1 in Fig. 2 is for the cylindrical coil spring 1 according to the embodiment of the present invention, and the curve indicated by reference sign L2 in Fig. 2 is for the cylindrical coil spring 17 according to the comparative example. As can be seen from Fig. 2, the maximum absolute value of the compressive residual stress of the cylindrical coil spring 1 according to the embodiment of the present invention is greater than the maximum absolute value of the compressive residual stress of the cylindrical coil spring 17 according to the comparative example. With regard to the depth from the surface, the value of the depth at which a certain value of compressive residual stress is imparted is greater for the cylindrical coil spring 1 than for the cylindrical coil spring 17, being about twice as great.

[0034] The compressive residual stress and the occurrence of cracks when there is thinning due to corrosion will now be described. Fig. 3A shows a cylindrical coil spring 1 according to an embodiment of the present invention in a state where there is no thinning 11 due to corrosion. In Fig. 3A, compressive residual stress indicated by arrow A1 is imparted. The compressive residual stress indicated by arrow A1 is imparted deep from the surface of the wire material of the cylindrical coil spring 1. Therefore, cracks indicated by reference numeral 13 are less likely to occur.

[0035] Fig. 3B shows a state in which corrosion-induced thinning 11 has occurred in the cylindrical coil spring 1 according to the embodiment of the present invention. In Fig. 3B, the portion indicated by reference numeral 11 has been lost due to corrosion, and a new surface 15 has been formed. However, in Fig. 3B, compressive residual stress indicated by arrow A1 remains, making it difficult for cracks indicated by reference numeral 13 to occur.

[0036] Fig. 4A shows a state in which no thinning due to corrosion has occurred in a cylindrical coil spring 17 according to a comparative example. In Fig. 4A, a compressive residual stress indicated by arrow A1 is also imparted. The compressive residual stress indicated by arrow A2 is imparted only to a shallow portion from the surface 9 of the wire material of the cylindrical coil spring 17. However, because the compressive residual stress indicated by arrow A1 is imparted, cracks indicated by reference numeral 13 are less likely to occur.

[0037] Fig. 4B shows a state in which corrosion-induced thinning 11 has occurred in a cylindrical coil spring 17 according to a comparative example. In Fig. 4B, the portion indicated by reference numeral 11 has been lost due to corrosion, and a new surface 15 has been formed. As a result, the compressive residual stress indicated by arrow A1 in Fig. 4A has disappeared in Fig. 4B. This makes it easier for cracks indicated by reference numeral 13 to occur.

[0038] In the cylindrical coil spring 1, the absolute value of the residual stress at a depth of 0.28 mm from the surface is 500 MPa or more, and the maximum stress value is 1300 MPa or more. Furthermore, in the cylindrical coil spring 1, the maximum hardness is 570 Hv or more, and a uniform compressive stress is applied in the circumferential direction. As a result, even if there is a reduction in thickness 11 due to corrosion, there will remain a portion where a compressive residual stress of a predetermined magnitude or more is applied, and the occurrence and propagation of cracks can be suppressed more than before.

[0039] The above manufacturing method may be used to manufacture coil springs such as conical coil springs, and other springs such as leaf springs. That is, the processing target of the first shot peening step S13 and the second shot peening step S15 is not limited to the coiled wire rod 3.

[0040] That is, the above-described manufacturing method may be understood as a spring manufacturing method including: a shot peening pretreatment step of subjecting a material to pretreatment before shot peening; a first shot peening step of subjecting the material pretreated in the shot peening pretreatment step to first shot peening by projecting first media, which are spherical and have a diameter of 1.3 mm or more and a hardness of 570 Hv or more, at a speed of 70 m / sec or more; and a second shot peening step of subjecting the material treated in the first shot peening step to second shot peening by projecting second media, which are spherical and have a diameter smaller than the diameter of the first media used in the first shot peening, at a speed slower than the speed in the first shot peening step.

[0041] Although the embodiments of the present invention have been described above, the descriptions and drawings that form part of this disclosure should not be understood to limit the present invention. Various alternative embodiments, examples, and operating techniques will become apparent to those skilled in the art from this disclosure.

[0042] The entire contents of Japanese Patent Application No. 2024-055942 (filing date: March 29, 2024) are incorporated herein by reference.

Claims

1. A method for manufacturing a spring, comprising: a shot peening pretreatment step of subjecting a material to pretreatment prior to shot peening; a first shot peening step of projecting first media, which are spherical and have a diameter of 1.3 mm or more and a hardness of 570 Hv or more, at a speed of 70 m / sec or more onto the material pretreated in the shot peening pretreatment step, to perform first shot peening; and a second shot peening step of projecting second media, which are spherical and have a diameter smaller than the diameter of the first media used in the first shot peening step, at a speed slower than the speed in the first shot peening step, to perform second shot peening onto the material treated in the first shot peening step.

2. A method for manufacturing a cylindrical coil spring, comprising: a shot peening pretreatment step of subjecting wire to pretreatment prior to shot peening; a first shot peening step of projecting first media, which are spherical and have a diameter of 1.3 mm or more and a hardness of 570 Hv or more, at a speed of 70 m / sec or more onto the coiled wire pretreated in the shot peening pretreatment step, to perform first shot peening; and a second shot peening step of projecting second media, which are spherical and have a diameter smaller than the diameter of the first media used in the first shot peening step, at a speed slower than the speed in the first shot peening step, to perform second shot peening onto the coiled wire treated in the first shot peening step.

3. A cylindrical coil spring having a residual stress value of 500 MPa or more at a depth of 0.28 mm from the surface, a maximum stress value of 1300 MPa or more, a maximum hardness value of 570 Hv or more, and having uniform compressive stress applied in the circumferential direction.

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