KR20220094747A - Coil spring, manufacturing method of coil spring and apparatus therefor - Google Patents

Abstract

The present invention relates to a coil spring, and a manufacturing method and a manufacturing device for the same. The coil spring uses a wire material, of which a diameter is 8.0-18.0 mm, has internal strength on a cross-section of the wire material is 540-690 HV, and has a difference between hardness of 0.2 mm from a surface and the hardness of 3.0 mm from the surface is 70-120 HV. Therefore, the present invention secures low surface hardness while maintaining high core hardness of the coil spring to maximize effects of improving corrosion fatigue life and durability, and at the same time, reduces processes to save energy cost and improve productivity.

Description

Coil spring and its manufacturing method and manufacturing apparatus TECHNICAL FIELD

The present invention relates to a coil spring, a method for manufacturing the same, and a manufacturing apparatus, wherein a wire having a diameter of 8.0 to 18.0 mm is used, the internal hardness in the cross section of the wire is 540 to 690 HV, and a hardness of 0.2 mm from the surface and 3.0 from the surface The difference in hardness of mm is 70~120HV, so it maintains the high core hardness of the coil spring and secures low surface hardness to maximize the effect of improving corrosion fatigue life and durability, and at the same time shorten the process to reduce energy costs and improve productivity It relates to a coil spring that can be made, a method for manufacturing the same, and an apparatus for manufacturing the same.

A coil spring used in a vehicle's suspension system is a part that improves riding comfort by absorbing shocks transmitted from the road surface while repeatedly moving up and down while driving.

In recent years, as the demand for low fuel consumption increases, as small and lightweight automobile parts are required, coil springs have also been made light-weight and high-strengthened according to the increase in the load received by the parts.

In order to secure the corrosion life, the impact toughness of the material must be improved. The lower the hardness, the higher the impact toughness and the corrosion life can be secured.

Therefore, as a method capable of improving the corrosion life of the high strength spring, a method of reducing the hardness of only the surface layer is being developed.

However, in the method of reducing the hardness of only the surface layer, the furnace tempering process is performed to remove the stress by reheating after the cooling coiling process. As it rises, there is a limit in securing low surface hardness.

On the other hand, as related prior art, the technology of compression coil spring and its manufacturing method of Korean Patent Registration No. 19300979 and the technology of high strength spring steel wire with excellent hydrogen embrittlement resistance and the manufacturing method of the Korean Patent Registration No. 1768785 are known. .

The present invention was devised to solve the various problems of the prior art, and provides a coil spring capable of improving corrosion fatigue life and durability while maintaining a high core hardness while maintaining a low surface hardness, and a manufacturing method and manufacturing apparatus thereof. There is a technical problem of the present invention to provide.

The coil spring of the present invention for achieving the above object is a coil spring using a wire having a diameter of 8.0 to 18.0 mm. The difference in hardness of 3.0 mm from the surface is 70-120 HV.

The coil spring has a hardness of 0.2 mm from the surface of 550 to 570 HV, a hardness of 0.8 mm from the surface of 600 to 630 HV, and a hardness of 3 mm from the surface is 640 to 660 HV.

The coil spring has a surface compressive residual stress of 750 MPa or more at a depth of 1 to 5 μm, 1100 MPa or more at a depth of 80 to 120 μm, durability characteristics of 350,000 times or more, corrosion resistance characteristics of 120,000 times or more, and permanent deformation of less than 3.0 mm to be.

The surface portion of the coil spring has a grain size of ASTM No.8.5 to 10.

In addition, the method for manufacturing a coil spring of the present invention includes a rolling step (S1) of applying a compressive load to the surface of the coil spring wire, and a coiling step (S2) of inserting the rolled wire into a coiling device and forming at room temperature (S2) and a tempering process (S3) of softening and heat treating the surface through a heat treatment coil immediately after the coiling, and a shot peening process (S4) of applying a residual compressive stress to the surface of the tempered wire rod.

According to the present invention, it has the effect of maximizing the effect of improving corrosion fatigue life and durability by securing low surface hardness while maintaining high core hardness of the coil spring, and at the same time shortening the process, thereby reducing energy cost and improving productivity.

1 is a flowchart of a method for manufacturing a coil spring of the present invention;
2 is a block diagram of a coil spring manufacturing apparatus for manufacturing a coil spring of the present invention;
3 is a photographic view of a heat treatment coil of a coil spring manufacturing apparatus for manufacturing a coil spring of the present invention.

Hereinafter, a coil spring of the present invention and a manufacturing method and manufacturing apparatus thereof will be described in detail with reference to the drawings.

However, the disclosed drawings are provided as examples to sufficiently convey the spirit of the present invention to those skilled in the art. Accordingly, the present invention is not limited to the drawings presented below and may be embodied in other aspects.

In addition, unless there is another definition in the terms used in the present invention, those of ordinary skill in the art to which the present invention pertains have the meaning commonly understood, and in the following description and accompanying drawings, the gist of the present invention Detailed descriptions of well-known functions and configurations that may be unnecessarily obscure will be omitted.

1 is a flowchart of a method for manufacturing a coil spring of the present invention.

Referring to the drawings, in the method for manufacturing a coil spring of the present invention, a rolling process (S1) of applying a compressive load to the surface of a coil spring wire, and a coiling process of forming the rolled wire into a coiling device at room temperature (S2), a tempering process (S3) of softening the surface through a heat treatment coil immediately after the coiling, and a shot peening process (S4) of applying a residual compressive stress to the surface of the tempered wire rod.

In the rolling process, it is preferable to perform quenching and tempering of the raw material using a high frequency for the wire rod.

In addition, the wire rod input in the rolling process has a reduction in area of 12 to 23%, and when the reduction in area is less than 12%, the effect of refining the surface texture and improving corrosion durability is insufficient, and when it exceeds 23%, wire cracks and disconnection occur. . Preferably, the wire rod input in the rolling process has a reduction ratio of 15-20%.

After rolling the wire rod in the coiling process, adding a high-frequency coil in a cold coiling device, and performing a high-frequency tempering process of softening heat treatment by reheating only the surface through the high-frequency coil immediately after coiling to keep the surface hardness of the coil spring lower and , the core hardness can be further increased.

2 is a block diagram of an apparatus for manufacturing a coil spring according to the present invention.

Referring to the drawings, the apparatus for manufacturing a coil spring of the present invention is used in the coiling process (S2) and the tempering process (S3).

The apparatus for manufacturing a coil spring of the present invention has a configuration in which a heat treatment coil 7 for heat-treating the surface of the wire rod is added to the wire rod immediately after coiling the wire rod in the conventional cold coiling apparatus.

Specifically, the coiling apparatus of the present invention includes a feed roller 1 (feed roller) for continuously supplying a wire rod, and a pitch tool for giving a pitch of the coil while pushing the coil to the outside ( 2), a cutter 3 that cuts the end of the coil when the coil spring is formed, an arbor 4 that forms a contact point that makes a coil shape when the wire is wound as a half-moon-shaped pin, and the arbor A first coiling tool 6 that forms a first contact point for winding the wire that has passed through (4) and gives a bend to the wire to make a coil shape, the arbor 4 and the first coiling tool 6 ) to form a second contact point for winding the wire that has passed through, and a second coiling tool 5 that creates a coil shape by giving the wire a bend, and is installed at the end of the second coiling tool 5 and a heat treatment coil 7 for performing heat treatment by heating the surface of the wire rod immediately after coiling.

The heat treatment coil 7 of the embodiment of the present invention is a coil that performs heat treatment by high frequency, and preferably, as shown in the photograph of FIG. 3 , the heat treatment coil 7 has a shape having one turn. consist of.

In addition, the heat treatment coil 7 of the embodiment of the present invention performs heat treatment in a heating temperature range of 630 to 670° C. using a high frequency frequency band of 200 kHz.

Accordingly, the apparatus for manufacturing a coil spring of the present invention performs the above-described coiling process (S2) and tempering process (S3) by performing tempering for heating the surface of the wire rod by the heat treatment coil 7 immediately after coiling. can be processed continuously.

The coil spring heat-treated through the heat treatment coil 7 is cut by the cutter 3 when the coil spring is formed, and transferred to the post-process shot peening process S4.

Preferably, the heat treatment coil 7 is disposed so as to be concentric with the wire rod on the movement path of the wire rod so that a uniform heat treatment can be performed.

However, when the line spacing of the coil spring is narrow, interference may occur between the leading wire and the following wire. Considering that, Ø50 or less is preferable.

The reason that the coil spring manufacturing apparatus of the present invention heat-treats the wire by attaching a separate heat treatment coil 7 is that the coil spring itself has a complex curved shape, so the curved shape of the coil spring using a general heat treatment device It is difficult to uniformly perform surface heat treatment along Since the surface treatment of the wire rod is continuously performed along the curved shape of the coil spring while passing through the interior, it is possible to perform uniform surface heat treatment.

Accordingly, in the coil spring manufactured by the apparatus for manufacturing a coil spring of the present invention, it is possible to obtain uniform hardness by minimizing the surface hardness deviation through continuous surface heat treatment immediately after coiling as described above.

In addition, in the coil spring of the present invention manufactured as described above, the energy accumulated by surface reduction, rolling and coiling is removed by surface softening heat treatment in the high frequency tempering step, and nucleation and recrystallization are formed. The effect of refining the surface texture can be obtained.

In addition, as the coil spring of the present invention is tempered by the heat treatment coil 7 immediately after coiling, the surface hardness of the coil spring is maintained lower and the core hardness can be higher, thereby eliminating the conventional furnace tempering. Both the surface and the core of the coil spring are uniformly reheated, so that the surface hardness increases and the core hardness decreases, thereby solving the limitation in securing the difference in hardness between the surface and the core, and the effect of improving corrosion fatigue life and durability was maximized.

The coil spring of the present invention uses a wire having a diameter of 8.0 to 18.0 mm, and an internal hardness of 540 to 690 HV in an arbitrary cross section of the wire, and the difference between the hardness of 0.2 mm from the surface and the hardness of 3.0 mm from the surface is 70 to It is preferable that it is 120HV.

In addition, in the coil spring of the present invention, the hardness of 0.2 mm from the surface is 550 to 570 HV, the hardness of 0.8 mm from the surface is 600 to 630 HV, and the hardness of 3 mm from the surface is 640 to 660 HV.

This is because the lower the surface hardness is, the better the corrosion durability is, but if it is too low, the durability is lowered.

In addition, in the coil spring of the present invention, the surface portion of the coil spring has a softened layer lower than the average hardness, and it is preferable to have a finer structure having a grain size of ASTM No. 8.5 to 10.

In addition, the coil spring of the present invention has a surface compressive residual stress of 750 MPa or more at a depth of 1 to 5 μm, and 1100 MPa or more at a depth of 80 to 120 μm, in order to improve durability characteristics, durability characteristics of 350,000 times or more, corrosion resistance It is preferable that the characteristic is 120,000 times or more and the permanent deformation is less than 3.0 mm.

In addition, in the coil spring of the present invention, the reduction ratio of the wire rod constituting the coil spring is preferably 12-23%, and when the reduction ratio exceeds 23%, wire cracks and disconnection occur, and when the reduction ratio is less than 12%, the surface structure is refined and The effect of improving corrosion durability is insufficient. Preferably, the reduction ratio of the wire rod constituting the coil spring is 15-20%.

Hereinafter, a coil spring and a manufacturing method of the present invention will be described through examples.

< Example 1 >

Using a wire having a reduction in area of 15% that has undergone a rolling process of heating at a temperature of 950 ℃, cooling with water, and reheating to a temperature of 400 ℃, is put into the coil spring manufacturing apparatus of the present invention shown in FIG. After coiling, the wire passing through the second coiling tool 5 is cut by high frequency heat treatment at a temperature of 630 to 670° C. using a heat treatment coil 7 having a frequency of 200 KHz, and then shot peening to the coil spring of the first embodiment. was prepared.

< Example 2 >

Using a wire with a reduction in area of 20% that has been heated at a temperature of 950 ° C, cooled by water, and then reheated to a temperature of 400 ° C., is put into the coil spring manufacturing apparatus of the present invention shown in FIG. 1 and coiled After coiling, the wire passing through the second coiling tool 5 is cut by high-frequency heat treatment at a temperature of 630 to 670° C. The coil springs of the examples were prepared.

< Comparative Example 1 >

A wire rod with a reduction in area of 10%, which was heated at a temperature of 950°C, cooled with water, and then reheated to a temperature of 450°C, was coiled using a cold coil spring manufacturing device, and then fired at 400°C for 10 minutes. A coil spring was manufactured by performing tempering (furnace tempering) and short peening.

< Comparative Example 2 >

A wire rod with a reduction in area of 10%, which was heated at a temperature of 950°C, cooled with water, and then reheated to a temperature of 400°C, was coiled using a cold coil spring manufacturing device, and then fired at 400°C for 10 minutes. A coil spring was manufactured by performing tempering (furnace tempering) and short peening.

< Comparative Example 3 >

Using a wire with a reduction in area of 25% that has been subjected to a rolling process of heating at a temperature of 950 ° C, cooling with water, and reheating to a temperature of 400 ° C, is put into the coil spring manufacturing apparatus of the present invention shown in FIG. After coiling, the wire passing through the second coiling tool 5 is cut by high frequency heat treatment at a temperature of 630 to 670° C. using a heat treatment coil 7 having a frequency of 200 KHz, and then shot peening to the coil spring of the first embodiment. was prepared.

The coil springs of Examples 1 and 2 and the coil springs of Comparative Examples 1 to 3 prepared as described above were evaluated for physical properties in the following manner, and the results are shown in Tables 1 and 2 below.

At this time, the hardness of the cross-section was measured using a Burkers hardness tester with a load of 5 kg, and the corrosion endurance test of the coil spring was evaluated with the i-ABG CSTM equipment and CCT corrosion chamber according to ES 54630-04.

division residual stress durability characteristics Corrosion durability characteristics permanent deformation 1-5 μm 100 μm Example 1 780 1180 370 thousand times 150,000 times 2.6mm Example 2 800 1200 400,000 times 170,000 times 2.4mm Comparative Example 1 850 1280 450,000 times 100,000 times 1.5mm Comparative Example 2 820 1230 400,000 times 120,000 times 2.3mm Comparative Example 3 820 1200 400,000 times 170,000 times 2.4mm

Referring to Tables 1 and 2 above, the coil springs of Examples 1 and 2 manufactured by the coil manufacturing apparatus of the present invention had a surface hardness of 0.2 mm from the surface and a hardness of 3.0 mm from the surface. Since the difference in core hardness is 80HV and 90HV, respectively, it is within the range of 70 to 120HV, which is the difference between the above-described preferred surface hardness and core hardness.

In addition, in the coil springs of Examples 1 and 2 manufactured by the coil manufacturing apparatus of the present invention, the surface portion of the coil spring has a softening layer lower than the average hardness, and the grain size is ASTM No.8.7 and ASTM No. As 9.4, it has a refined structure at the level of ASTM No.8.5 to 10, which is the preferred grain size described above.

In addition, the coil springs of Examples 1 and 2 manufactured by the coil manufacturing apparatus of the present invention have a surface compressive residual stress of 780 MPa at a depth of 1 to 5 μm in Example 1, and 1180 MPa at a depth of 100 μm, In Example 2, 800 MPa at a depth of 1 to 5 μm and 1200 MPa at a depth of 100 μm, the above-described preferred compressive residual stress satisfies 750 MPa or more at a depth of 1 to 5 μm, and 1100 MPa or more at a depth of 80 to 120 μm.

In addition, the coil springs of Examples 1 and 2 manufactured by the coil manufacturing apparatus of the present invention exhibited corrosion resistance characteristics of 150,000 and 170,000 cycles, respectively, respectively, compared to 100,000 cycles of Comparative Example 1 and 120,000 cycles of Comparative Example 2 It can be seen that it has excellent corrosion resistance characteristics.

On the other hand, the coil springs of Examples 1 and 2 manufactured by the coil manufacturing apparatus of the present invention have durability characteristics of 370,000 times and 400,000 times, respectively, and permanent deformations of 2.6mm and 2.4mm, respectively. It satisfies the conditions of more than 350,000 cycles and a permanent deformation of less than 3.0 mm.

One; feed roller
2; pitch tool
3; cutter
4; arbor
5; 2nd coiling tool
6; 1st coiling tool
7; heat treatment coil

Claims (14)

In the coil spring,
The diameter of the wire is 8.0 to 18.0 mm,
The internal hardness in the cross section of the wire is 540 to 690 HV,
A coil spring, characterized in that the difference between the hardness of 0.2 mm from the surface and the hardness of 3.0 mm from the surface is 70 to 120 HV.
The method of claim 1,
The hardness of 0.2 mm from the surface is 550 to 570 HV,
The hardness of 0.8 mm from the surface is 600-630 HV,
A coil spring, characterized in that the hardness of 3 mm from the surface is 640 to 660 HV.
3. The method of claim 1 or 2,
A coil spring, characterized in that the surface compressive residual stress is 750 MPa or more at a depth of 1 to 5 μm, and 1100 MPa or more at a depth of 80 to 120 μm.
3. The method of claim 1 or 2,
A coil spring with a durability of more than 350,000 cycles, a corrosion resistance of more than 120,000 cycles, and a permanent deformation of less than 3.0 mm.
3. The method of claim 1 or 2,
Coil spring, characterized in that the grain size of the surface part is ASTM No.8.5-10.
3. The method of claim 1 or 2,
A coil spring, characterized in that the reduction rate of the wire rod constituting the coil spring is 12-23%.
In the method for manufacturing a coil spring,
A rolling process of applying a compressive load to the surface of the coil spring wire (S1);
a coiling process (S2) of inserting the rolled wire into a coiling device to form a coil;
a tempering process (S3) of softening and heat treating the surface through a heat treatment coil immediately after the coiling;
A method of manufacturing a coil spring, characterized in that it comprises a.
8. The method of claim 7,
The method of manufacturing a coil spring, characterized in that the wire rod input to the rolling process (S1) has a reduction in area of 12 to 23%.
The method according to claim 7, wherein the heat treatment coil in the tempering step (S3) is a coil that is heat treated by high frequency.
The method of claim 9, wherein the tempering process (S3),
The heat treatment coil is a method of manufacturing a coil spring, characterized in that the heat treatment is performed in the heating temperature range of 630 ~ 670 ℃ using a high frequency band of frequency 200 kHz.
According to claim 7, wherein the tempering process (S3),
The method of manufacturing a coil spring, characterized in that the heat treatment is continuously performed on the surface of the wire while the wire coiled in the coiling step (S2) passes through the inside of the heat treatment coil.
In the apparatus for manufacturing a coil spring,
A feed roller (1) (feed roller) for continuously supplying the wire rod;
A pitch tool (2) for giving a pitch of the coil while pushing the coil outward;
A cutter (3) for cutting the end of the coil when the coil spring is formed;
An arbor (4) forming a contact point that makes a coil shape when winding a wire rod (4);
A first coiling tool (6) which forms a first contact point for winding the wire that has passed through the arbor (4) and gives a bend to the wire to make a coil shape;
A second coiling tool 5 which forms a second contact point for winding the wire that has passed through the arbor 4 and the first coiling tool 6 and gives the wire a bend to form a coil shape;
and a heat treatment coil (7) installed at the end of the second coiling tool (5) and performing heat treatment by heating the surface of the wire rod immediately after coiling.
13. The method of claim 12,
The heat treatment coil (7) is a coil spring manufacturing apparatus, characterized in that the heat treatment is performed by a high frequency coil.
14. The method of claim 13,
The heat treatment coil 7 is an apparatus for manufacturing a coil spring, characterized in that the heat treatment is performed in a heating temperature range of 630 to 670° C. using a high frequency band of 200 kHz.

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