JPS63154237A - Manufacture of cold formed high strength spring - Google Patents

Abstract

PURPOSE:To simplify the manufacturing process and to improve the productivity by including a bending back stage in a coiling stage and manufacturing a coil spring having no tensile residual stress without annealing. CONSTITUTION:A spring steel wire 6 is fed by rotation of a feed roller 5 through a wire guide 4 and is bent to be formed into a coil by a 1st coiling pin 1. Then, the wire 6 is bent back by a 2nd coiling pin 2 to be formed into the final spring shape. A member 3 is a pitch tool giving a pitch to the wire 6. Thus, the spring having no tensile residual stress without annealing is obtained by including the bending back stage in the coiling stage.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of manufacturing a high-strength cold-formed coil spring.

[Conventional technology]

Cold-formed coil springs are generally drawn out through a straightener 7 that straightens the spring wire 6 by rotating a feed roller 5 shown in FIG. 3, for example, and fed out through a wire guide 4. This sent-out wire 6 is bent to a predetermined curvature using coiling bins la and lb, and is formed at a predetermined pitch using a pitch tool 3 (Spring, 3rd edition, No. 47
6 pages, Maruzen). Due to this forming, tensile residual stress is generated inside the coil spring, but this tensile residual stress deteriorates fatigue strength and fatigue resistance, so in order to remove the tensile residual stress, the formed coil spring is heated at a low temperature. (380° C. or lower) Annealing [Problem to be Solved by the Invention] However, the above-mentioned low-temperature annealing cannot completely remove the residual stress.

Therefore, in order to completely remove residual stress, it is necessary to perform annealing at a temperature of 500°C or higher, but if annealing is performed at a high temperature of 500°C or higher, the material strength will decrease, and conversely, the strength will weaken and the strength will decrease. There is a problem in that the characteristics deteriorate. In addition, in order to improve the strength, we applied shot peening t-M to the coil springs that have been annealed at this low temperature.
However, there is also the problem that large surface compressive residual stress cannot be obtained. Additionally, since a low-temperature annealing process is required, it takes time to manufacture coil springs.

The present invention is intended to solve the above-mentioned problems, and aims to provide a method for manufacturing a cold-formed coil spring that is free from tensile residual stress and has excellent strength.

[Means for solving problems]

The method for manufacturing a high-strength cold-formed spring of the present invention includes, in the cold coiling process of a coil spring, first bending a wire to a radius of curvature smaller than the final shape of the coil spring;
It is then characterized in that it is bent back in a direction that increases the radius of curvature to form the final shape.

[Effect]

In the cold coiling process of coil springs, after the first bending process, the unbending process generates residual stress in the direction that dissipates the residual stress generated in the first bending process, and as a result, after forming, tensile stress is generated. Almost no stress remains. Then, by bending the material so that the radius of curvature is smaller than the intended final shape by the amount of the unbending process during the first bending process, the desired final shape can be formed by the unbending process.

Even if the degree of this bending is small, the purpose can be sufficiently achieved.

〔Example〕

The present invention will be explained by way of one embodiment with reference to the drawings.

Wire diameter is 9.5mm, tensile strength σB -185Kff/1
A coil spring having the specifications shown in Hori 1 was cold-formed using a 5UP12 spring steel wire that had been oil-tempered to have a diameter of 1.5 m.

To form a coil spring with a spring constant of Table 1, as shown in FIG. 1, the feed roller 5 is rotated to feed the spring steel wire 6 through the wire guide 4. The coil diameter was bent to a coil diameter of 90cm, which is slightly smaller than 100m, and then bent back to the coil diameter shown in Table 1 using the second coil/grip 2 placed inside the coil to form the final spring shape. .

In addition, in the figure, 3 is a pitch tool for adding a pitch.

Next, the coil spring formed above was subjected to shot peening using a 0.6 piece cut wire under the condition of an arc height of 0.5 m.

Comparative Example Using the same wire as in Example 1, it was molded into the same shape as in Example without bending back, and then low-temperature annealing was performed at 380°C, and shot peening was further performed under the same conditions as in Example 1. did.

Test Examples The coil springs of Examples and Comparative Examples were subjected to a fatigue test and a sag test. Fatigue testing was performed by subjecting to a varying stress of 70 ± 45 b f/m′. For the settling test, compress the surface stress to τ110 Kqf/■2 and heat it to 80°C.
This was done by leaving it at ℃ for 96 hours. Test conditions and results for Examples and Comparative Examples are shown in Tables 2 and 3, respectively.

Table 2 Test conditions Table 3 Test results The fatigue life of the coil spring of this example was 1 million times without breaking, which is more than three times the breakage of the comparative example at 324,000 times. residual shear strain) is
Compared to the comparative example, which was 12.5, it was 8.3, which was a decrease of about 35-.

In addition, as shown in Figure 2, the compressive residual stress of the comparative example spring is low because the tensile residual stress due to coiling is not completely removed, whereas the compressive residual stress of the example spring is low. The coil spring has a residual stress up to three times that of the comparative example.

[Effects of the Invention] As described above, the method for manufacturing a high-strength cold-formed spring of the present invention includes an unbending process in the coiling process, so a coiled spring without tensile residual stress can be manufactured without annealing. , and no annealing process is required.
The manufacturing process is simplified and productivity is improved. Furthermore, since the obtained coil spring has no tensile residual stress, it has excellent strength and a long life, and by shot peening, it can be made into a coil spring with even higher strength and a longer life.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of a coil spring manufacturing apparatus according to an embodiment of the present invention, Fig. 2 is a residual stress distribution diagram of a coil spring according to an embodiment of the present invention, and Fig. 3 is a conventional coil spring manufacturing apparatus. Equipment schematic % formula %

Claims (1)

[Claims] In the cold coiling process of coil springs, the wire is
A method for producing a high-strength cold-formed spring, which comprises first bending the spring to have a smaller radius of curvature than the final shape of the coil spring, and then bending it back in a direction that increases the radius of curvature to form the final shape.