JP2024054700A - Manufacturing method of coil springs - Google Patents

Abstract

[Problem] To provide a manufacturing method of a coil spring capable of reducing the variation in quality of the coil springs. [Solution] The manufacturing method of the coil spring according to the present invention is a manufacturing method of a coil spring by processing a base material made of wire, and includes a cold forming step of cold forming the base material to produce a formed material having a spiral shape, a quenching step of quenching the formed material, and an electric tempering step of tempering the quenched formed material by electric heating, in which a first electric current period is set from the start of heating the formed material to the lapse of a predetermined time, and a second electric current period is set from the lapse of the predetermined time to the end of heating, and the rate of increase in temperature of the formed material during the second electric current period is lower than the rate of increase in temperature of the formed material during the first electric current period. [Selected Figure] Figure 1

Description

The present invention relates to a method for manufacturing a coil spring.

Conventionally, hot forming and cold forming are used in the process of manufacturing coil springs. Of these, hot forming allows for the forming of thick wire rods, but the degree of freedom in the shape of the formed wire rods is small. On the other hand, cold forming allows for a high degree of freedom in the shape of the formed wire rods, but it is difficult to form thick wire rods. As a technology that allows for a high degree of freedom in the shape of the formed wire rods and allows for the forming of thick wire rods, a technology is known in which the wire rods are cold formed and then heat treated, such as quenching and tempering, is performed (see, for example, Patent Document 1). In Patent Document 1, heat treatment is performed by attaching electrodes to both ends of the coil-shaped formed product (workpiece) after cold forming and passing electricity through them.

Patent No. 5574772

However, when attempting to heat a workpiece in a short period of time during heat treatment by passing an electric current through it, the amount of electric power input to the workpiece increases, and even if the current is stopped when the workpiece reaches the target temperature, the temperature of the workpiece may continue to rise. In this case, the heating temperature may vary between workpieces, and the quality of the coil springs produced may also vary.

The present invention has been made in consideration of the above, and aims to provide a method for manufacturing coil springs that can reduce the variation in quality of coil springs.

In order to solve the above-mentioned problems and achieve the object, the manufacturing method of the coil spring according to the present invention is a manufacturing method of a coil spring by processing a base material made of wire, and includes a cold forming step of cold forming the base material to produce a formed material having a spiral shape, a quenching step of quenching the formed material, and an electric tempering step of tempering the quenched formed material by electric heating, and the electric tempering step is characterized in that a first electric period from the start of heating the formed material to the lapse of a predetermined time and a second electric period from the lapse of the predetermined time to the end of heating are set, and the rate of increase in temperature of the formed material during the second electric period is lower than the rate of increase in temperature of the formed material during the first electric period.

The coil spring manufacturing method according to the present invention is characterized in that, in the above invention, the current value or voltage value is controlled during the first and second current-flow periods, and the current-flow tempering step makes the current value/voltage value during the second current-flow period smaller than the current value/voltage value during the first current-flow period.

The manufacturing method of the coil spring according to the present invention is characterized in that, in the above invention, the current tempering step applies current to the formed material in a state where both ends of the formed material are gripped by a first current-carrying member that grips one end of the formed material after quenching and a second current-carrying member that grips the other end of the formed material after quenching, and the first and second current-carrying members are a first gripping member located on the outer periphery of the formed material and a second gripping member located on the inner periphery of the formed material and sandwiching the formed material between the first gripping member, the radius of curvature of the surface that contacts the formed material is smaller than the radius of curvature of the inner periphery of the formed material, and the formed material is gripped by the second gripping member that sandwiches the formed material between the first gripping member.

The method for manufacturing a coil spring according to the present invention is characterized in that, in the above invention, it further includes an electrical heating step that is performed before the quenching step, and that electrically heats the formed material after the cold forming.

The present invention has the effect of reducing the variation in quality of coil springs.

FIG. 1 is a diagram showing the structure of a coil spring produced by a manufacturing method according to an embodiment of the present invention. FIG. 2 is a diagram for explaining a method for manufacturing a coil spring according to an embodiment of the present invention. FIG. 3 is a diagram for explaining the change over time in the current value and the temperature of the formed material during electrical heating. FIG. 4 is a diagram for explaining electrical heating according to the first modification. FIG. 5 is a view seen from the direction of the arrow A shown in FIG. FIG. 6 is a diagram for explaining electrical heating according to the second modification. FIG. 7 is a diagram for explaining electrical heating according to the third modification.

Below, a mode for carrying out the present invention (hereinafter referred to as "embodiment") will be described with reference to the attached drawings. Note that the drawings are schematic, and the relationship between the thickness and width of each part, the thickness ratio of each part, etc. may differ from the actual ones, and the drawings may include parts with different dimensional relationships and ratios.

(Embodiment)
1 is a diagram showing the configuration of a coil spring manufactured by a manufacturing method according to an embodiment of the present invention. The coil spring 1 is manufactured by spirally winding a wire material. The coil spring 1 is manufactured using, for example, a wire material made of a metal or an alloy.

Next, a method for manufacturing the coil spring 1 will be described with reference to Figs. 2 to 4. Fig. 2 is a diagram for explaining a method for manufacturing a coil spring according to one embodiment of the present invention. The coil spring 1 is produced by processing a base material.

First, a wire material 100 (see FIG. 2(a)) is drawn to obtain a drawn wire material 101 (see FIG. 2(b)). At this time, the wire material 100 (drawn wire material 101) is not subjected to heat treatment, and a wire drawing machine is used to reduce the diameter of the wire material, for example by passing it through a die, to obtain a wire material (drawn wire material 101) with a designed diameter.

Then, the drawn wire material 101 is shaped by cold forming (see FIG. 2(c)). Specifically, the drawn wire material 101 is wound using a winding machine 200. This winding machine 200 includes, for example, a winding pin and a cutting tool, and shapes the drawn wire material 101 by contacting it with the winding pin, and cuts the drawn wire material 101 to a predetermined length using the cutting tool.

The formed material 102 obtained by winding and cutting the drawn wire 101 is subjected to electrical heating (see FIG. 2(d)). In electrical heating, a first current-carrying member 211 is attached to one end of the formed material 102, and a second current-carrying member 212 is attached to the other end, and an electric current is passed through the first current-carrying member 211 and the second current-carrying member 212 to pass the electric current through the formed material 102. Heat is generated by this current passage, and the formed material 102 is heated.
The first current-carrying member 211 and the second current-carrying member 212 are controlled by the control device 210 in terms of movement of the members (gripping of the molding material 102) and electrical conduction.

After the formed material 102 is electrically heated, the formed material 102 is quenched (see FIG. 2(e)). The formed material 102 is immersed in a tank 221 containing a water-soluble quenching agent 222. At this time, the temperature and concentration of the water-soluble quenching agent are controlled so as to obtain an appropriate heat treatment quality. By immersing the formed material 102 in the water-soluble quenching agent 222, a quenched formed material 103 is obtained. Note that oil may be used instead of the water-soluble quenching agent 222.

After quenching, the formed material 103 is subjected to electrical heating for tempering (electrical tempering) (see FIG. 2(f)). In electrical tempering, a first electrical member 231 is attached to one end of the formed material 103, and a second electrical member 232 is attached to the other end, and an electric current is passed through the first electrical member 231 and the second electrical member 232 to pass an electric current through the formed material 103. This electrical current generates heat, and the formed material 103 is heated. In electrical tempering, electrical current conditions are set for reheating the formed material 103 to a predetermined hardness.
The first current-carrying member 231 and the second current-carrying member 232 are controlled by the control device 230 in terms of movement of the members (gripping of the molding material 103) and electrical conduction.

Here, the electrical heating performed during electrical tempering (see FIG. 2(f)) will be described with reference to FIG. 3. Note that electrical heating can also be performed in the same way when electrical heating is performed on the formed material 102 before quenching (see FIG. 2(d)).

Figure 3 is a diagram for explaining an example of the change over time in the current value and the temperature of the molding material 103 during electrical heating. In Figure 3, the solid line indicates the current value, and the dashed line indicates the temperature of the molding material 103. Therefore, the slope of the dashed line indicates the rate of temperature rise of the molding material 103.

The control device 230 changes the current value in two stages, for example, as shown in FIG. 3, to raise the temperature of the molding material 103. In this case, the control period of the control device 230 is roughly divided into a first current-carrying period S1 in which current is passed at a current value I2 from the start of current-carrying until a predetermined time has elapsed, and a second current-carrying period S2 in which current is passed at a current value I1 smaller than that of the first current-carrying period. In FIG. 3, the first current-carrying period is from the start of current-carrying (t0) to time t1, and the second current-carrying period is from time t1 to time t2. In this current-carrying heating, the temperature rise rate in the second current-carrying period is smaller than the temperature rise rate in the first current-carrying period, and the temperature of the molding material 103 rises relatively slowly.

Ｓ：成形材１０３の断面積（ｍｍ²）、ΔＴ：温度差（℃）、ｔ：加熱時間（ｓｅｃ）、α：定数
なお、温度差ΔＴは、加熱開始前の成形材１０３の温度と温度Ｔ１との差、または温度Ｔ１と温度Ｔ２との差を示し、各期間（第１通電期間Ｓ１または第２通電期間Ｓ２）に応じて変わる。具体的には、第１通電期間Ｓ１における温度差ΔＴは、加熱開始前の成形材１０３の温度と温度Ｔ１との差であり、第２通電期間Ｔ２における温度差ΔＴは、温度Ｔ１と温度Ｔ２との差である。 The control device 230 applies a large current during the first current application period to raise the temperature to a preset temperature T1 (for example, a temperature 50°C lower than the heating end temperature) in one go, and then applies a small current (for example, a current value 1 kA lower than the current value during the first current application period) during the second current application period to gradually raise the temperature to the heating end temperature T2, thereby stabilizing the temperature at the end of heating. In Fig. 3, the ratio of the heating time during the first current application period to the heating time during the second current application period is approximately 2:1. The current value and the heating time during each period are determined by the material diameter and the target heating time.
Here, the current value I (A) can be set based on the calculation formula shown in the following formula (1). For example, the current value is determined by the value calculated by formula (1) or based on this value.

S: cross-sectional area of molded material 103 ( ^mm2 ), ΔT: temperature difference (°C), t: heating time (sec), α: constant. Note that the temperature difference ΔT indicates the difference between the temperature of molded material 103 before heating starts and temperature T1, or the difference between temperature T1 and temperature T2, and changes depending on each period (first current-flow period S1 or second current-flow period S2). Specifically, the temperature difference ΔT in the first current-flow period S1 is the difference between the temperature of molded material 103 before heating starts and temperature T1, and the temperature difference ΔT in the second current-flow period T2 is the difference between temperature T1 and temperature T2.

The control device 230 is placed on the forming material 103 at a predetermined position, for example, and grips one end and the other end of the forming material 103 by moving the gripping members of the first current-carrying member 231 and the second current-carrying member 232. The control device 230 then passes a current through the first current-carrying member 231 or the second current-carrying member 232 via the power transmission line. A current flows between the first current-carrying member 231 and the second current-carrying member 232 and the forming material 103 through the contact points. The heat generated at this time heats the forming material 103.

By processing the base material 100 in the above-described manner, the coil spring 1 shown in FIG. 1 is produced.
Here, annealing may be performed before or after the wire drawing process. Also, if the wire diameter is as designed in the base material state, it is possible to perform cold forming on the base material 100 without performing the wire drawing process.

In the embodiment of the present invention described above, when performing heat treatment (here, at least electric tempering), the current value is changed in two stages, and control is performed to reduce the rate of temperature rise as the temperature of the formed material 103 approaches the heating end temperature. By reducing the temperature rise before the heating ends, the temperature rise of the formed material 103 after heating stops is suppressed. According to this embodiment, it is possible to reduce the variation in the quality of the coil spring.

In addition, according to this embodiment, by performing electric tempering, the time required for tempering can be shortened compared to tempering using a furnace, and carbon dioxide emissions can also be reduced.

The temperature control during electrical heating is not limited to the two-stage current value control as in the above-described embodiment. For example, while Fig. 3 shows an example in which the maximum current value is set at the timing of starting electrical current, the current value may be gradually increased from the start of electrical current. Also, when switching the current between the first electrical current period and the second electrical current period, the current value may be decreased in stages. The temperature rise in this case is set in accordance with the tact time of the heating process.
The heating temperature may be adjusted by controlling the current on and off. For example, the on period of the second current supply period is shorter than the first current supply period, or the off period is longer. For the on and off control of the current, the control method disclosed in Japanese Patent No. 6077790 can be adopted.

(Variation 1)
Next, a first modified example of the present embodiment will be described with reference to Figs. 4 and 5. Fig. 4 is a diagram for explaining the electric heating according to the first modified example. Fig. 5 is a diagram seen from the direction of the arrow A shown in Fig. 4. In the first modified example, the configuration of the current-carrying member that performs the electric heating will be described. In the first modified example, the configuration of the current-carrying member is the same as in the embodiment, except for the configuration of the current-carrying member, and therefore the description will be omitted. In Fig. 4, the same components as in the embodiment are denoted by the same reference numerals.

The first current-carrying member 231 has a first gripping member 231 a and a second gripping member 231 b , and is located on one end side of the molding material 103 .
The first gripping member 231a has a rectangular column shape and is located on the outer periphery of the molded material 103. The first gripping member 231a has a flat portion 2311 having a flat surface on the side that contacts the molded material 103. Note that as long as the surface of the first gripping member 231a that contacts the molded material 103 is flat, other portions of the first gripping member 231a may be cylindrical or have another polygonal shape.
The second gripping member 231b is cylindrical and is located on the inner periphery of the molded material 103. The radius of curvature of the side surface 2312 (outer periphery) of the second gripping member 231b is smaller than the radius of curvature of the inner periphery of the molded material 103. Here, the radius of curvature of the inner periphery of the molded material 103 corresponds to the radius of curvature of the inner periphery of the molded material 103 in a plan view (see FIG. 5) seen from the axial direction (winding axial direction) of the molded material 103. By making the radius of curvature of the side surface of the second gripping member 231b smaller than the radius of curvature of the inner periphery of the applicable molded material 103, it can be applied to various types of molded materials 103.

The first gripping member 231a and the second gripping member 231b are supplied with electricity through a power transmission line (not shown) under the control of the control device 230. The first gripping member 231a can be moved toward or away from the second gripping member 231b under the control of the control device 230. The second gripping member 231b can be moved toward or away from the first gripping member 231a under the control of the control device 230. The second gripping member may be configured to be movable toward the first gripping member in order to correspond to the diameter of the turns of the formed material 103, or the first current-carrying member 231 and the second current-carrying member 232 may be configured to be movable toward or away from each other in order to correspond to the number of turns of the formed material 103, etc.

The second current-carrying member 232 has a first gripping member 232 a and a second gripping member 232 b , and is located on the other end side of the molded material 103 .
The first gripping member 232a has a rectangular column shape and is located on the outer periphery of the molded material 103. The first gripping member 232a has a flat portion 2321 having a flat surface on the side that contacts the molded material 103. Note that as long as the surface on the side that contacts the molded material 103 is flat, the other portions of the first gripping member 232a may be cylindrical or have another polygonal shape.
The second gripping member 232b has a cylindrical shape and is located on the inner periphery side of the molded material 103. The radius of curvature of a side surface 2322 (outer periphery) of the second gripping member 232b is smaller than the radius of curvature of the inner periphery of the molded material 103.

The first current-carrying member 231 and the second current-carrying member 232 are controlled by the control device 230 via a power transmission line (not shown). The first gripping member 232a and the second gripping member 232b are movable under the control of the control device 230.

In the above-described first modified example, similar to the embodiment, when performing heat treatment (here, at least electric tempering), the current value is changed in two stages, and the temperature rise rate is controlled to decrease as the temperature of the formed material 103 approaches the heating end temperature, thereby reducing the variation in the quality of the coil spring.

In addition, according to this modified example 1, one side (here, the outer periphery) of the gripping member that grips the formed material 103 is flat and the other side (here, the inner periphery) is curved, and the radius of curvature of the other curved surface is made smaller than the radius of curvature of the inner periphery of the formed material 103, so that the formed material 103 (coil spring 1) can be securely gripped and current can be passed through it regardless of its shape. According to this modified example 1, it is possible to suppress a decrease in productivity when manufacturing coil springs of multiple shapes.

(Variation 2)
Next, a second modified example of the present embodiment will be described with reference to Fig. 6. Fig. 6 is a diagram for explaining the electrical heating according to the second modified example. In the second modified example, the configuration of the current-carrying member that performs the electrical heating is different from that of the current-carrying member according to the embodiment. In the second modified example, the configuration of the current-carrying member is the same as in the embodiment, and therefore the description will be omitted. In Fig. 6, the same components as in the embodiment are denoted by the same reference numerals.

In the first current-carrying member 231A and the second current-carrying member 232A in the second modified example, the movement of the members (grasping of the molding material 103) and the current flow are controlled under the control of the control device 230, as in the embodiment.

The first current-carrying member 231A has a first gripping member 231c and a second gripping member 231b, and is located on one end side of the molding material 103.
The first gripping member 231c has a rectangular column shape and is located on the outer periphery of the formed material 103. The first gripping member 231c has a curved surface 2313 in which a part of the surface on the side that comes into contact with the formed material 103 is curved concavely. It is preferable that the radius of curvature of the wall surface that forms this curved surface 2313 is larger than the wire diameter of the formed material 103.
Moreover, the first gripping member 231c can be moved toward or away from the second gripping member 231b under the control of the control device 230. Note that as long as a portion of the surface of the first gripping member 231c that contacts the molding material 103 is a curved surface that is curved in a convex shape, the other portion may be cylindrical or have another polygonal shape.

The second current-carrying member 232A has a first gripping member 232c and a second gripping member 232b, and is located on one end side of the molded material 103.
The first gripping member 232c has a rectangular column shape and is located on the outer periphery of the formed material 103. The first gripping member 232c has a curved surface 2323 in which a part of the surface on the side that comes into contact with the formed material 103 is curved concavely. It is preferable that the radius of curvature of the wall surface that forms this curved surface 2323 is larger than the wire diameter of the formed material 103.
Moreover, the first gripping member 232c can be moved toward or away from the second gripping member 232b under the control of the control device 230. Note that as long as a portion of the surface of the second gripping member 232c that comes into contact with the molding material 103 is a curved surface that is curved in a convex shape, the other portion may be cylindrical or have another polygonal shape.

The first current-carrying member 231A and the second current-carrying member 232A are controlled by the control device 230 via a power transmission line (not shown).

The control device 230 is placed on the formed material 103 at a predetermined position, and grips one end and the other end of the formed material 103 by moving the gripping members of the first current-carrying member 231A and the second current-carrying member 232A, respectively. The control device 230 then passes a current through the first current-carrying member 231A and the second current-carrying member 232A via the power transmission line. A current flows between the first current-carrying member 231A and the second current-carrying member 232A and the formed material 103 through the contact points. The heat generated at this time heats the formed material 103.

In the second modified example described above, as in the embodiment, when performing heat treatment (here, at least electric tempering), the current value is changed in two stages, and the temperature rise rate is controlled to decrease as the temperature of the formed material 103 approaches the heating end temperature, thereby reducing the variation in the quality of the coil spring.

In addition, according to this modified example 2, the first gripping members 231c, 232c are each formed with a concave curved surface 2313, 2323 on the surface that comes into contact with the molding material 103, and the molding material 103 is gripped by each curved surface, so that the molding material 103 can be gripped more reliably.

(Variation 3)
Next, a third modification of the present embodiment will be described with reference to Fig. 7. Fig. 7 is a diagram for explaining the electric heating according to the third modification. In the third modification, the configuration of the current-carrying member that performs the electric heating is different from that of the current-carrying member according to the embodiment. In the third modification, the configuration of the current-carrying member is the same as in the embodiment, and therefore the description will be omitted. In Fig. 7, the same components as in the embodiment are denoted by the same reference numerals.

In the first current-carrying member 231B and the second current-carrying member 232B in the third modified example, the movement of the members (grasping of the molding material 103) and the flow of electricity are controlled under the control of the control device 230, as in the embodiment.

The first current-carrying member 231B has a first gripping member 231d and a second gripping member 231b, and is located on one end side of the molding material 103.
The first gripping member 231d has a rectangular column shape and is located on the outer periphery of the molding material 103. The first gripping member 231d has a groove portion 2314 in which a part of the surface that contacts the molding material 103 is a V-shaped groove. The formation area (forming width and depth) of the groove portion 2314 is set so that the first gripping member 231d and the second gripping member 231b do not contact each other. Note that the first gripping member 231d may have a cylindrical shape or another polygonal shape as long as a part of the surface that contacts the molding material 103 is a V-shaped groove.
Further, the first gripping member 231d is movable under the control of the control device 230 in a direction toward or away from the second gripping member 231b.

The second current-carrying member 232B has a first gripping member 232d and a second gripping member 232b, and is located on one end side of the molded material 103.
The first gripping member 232d has a rectangular column shape and is located on the outer periphery of the molded material 103. The first gripping member 232d has a groove portion 2324 in which a part of the surface on the side that contacts the molded material 103 is a V-shaped groove. The formation area (forming width and depth) of this groove portion 2324 is set so that the first gripping member 232d and the second gripping member 232b do not contact each other. Note that the first gripping member 232d may have other parts that are cylindrical or polygonal as long as the surface that contacts the molded material 103 is flat.
Further, the first gripping member 232d is movable under the control of the control device 230 in a direction toward or away from the second gripping member 232b.

The current supply to the first current-carrying member 231B and the second current-carrying member 232B is controlled via a power transmission line (not shown) under the control of the control device 230.

The control device 230 is placed on the formed material 103 at a predetermined position, for example, and grips one end and the other end of the formed material 103 by moving the gripping members of the first current-carrying member 231B and the second current-carrying member 232B. The control device 230 then passes current through the first current-carrying member 231B and the second current-carrying member 232B via the power transmission line. Current flows through the contact points between the first current-carrying member 231B and the second current-carrying member 232B and the formed material 103. The heat generated at this time heats the formed material 103.

In the third modified example described above, as in the embodiment, when performing heat treatment (here, at least electric tempering), the current value is changed in two stages, and the temperature rise rate is controlled to decrease as the temperature of the formed material 103 approaches the heating end temperature, thereby reducing the variation in the quality of the coil spring.

In addition, according to this modified example 3, grooves 2314, 2324 are formed on the surfaces of the first gripping members 231d, 232d that come into contact with the molding material 103, respectively, and the molding material 103 is gripped in each groove, so that the molding material 103 can be gripped more reliably.

So far, we have explained the form for implementing the present invention, but the present invention should not be limited to only the above-mentioned embodiment.

As such, the present invention may include various embodiments not described here, and various design changes may be made without departing from the technical ideas specified in the claims.

As described above, the manufacturing method of the coil spring according to the present invention is suitable for reducing the variation in the quality of the coil spring.

REFERENCE SIGNS LIST 1 Coil spring 100 Base material 101 Drawn wire material 102, 103 Formed material 200 Winding machine 210, 230 Control device 211, 231, 231A, 231B First current-carrying member 212, 232, 232A, 232B Second current-carrying member 221 Tank 222 Water-soluble quenching agent 231a, 231c, 231d, 232a, 232c, 232d First gripping member 231b, 232b Second gripping member 2311, 2321 Planar portion 2312, 2322 Side surface 2313, 2323 Curved surface 2314, 2324 Groove portion

Claims (4)

A method for manufacturing a coil spring by treating a base material made of a wire, comprising the steps of:
a cold forming step of cold forming the base material to produce a spirally formed material;
a quenching step of quenching the formed material;
a current tempering step of tempering the quenched formed material by current heating;
Including,
The electric tempering step includes:
A first current application period from the start of heating the molding material to the lapse of a predetermined time, and a second current application period from the lapse of the predetermined time to the end of heating are set,
A rate of increase in temperature of the molding material during the second current supply period is lower than a rate of increase in temperature of the molding material during the first current supply period.
A method for manufacturing a coil spring comprising the steps of: In the current tempering step, a current value in the second current supply period is set to be smaller than a current value in the first current supply period.
2. The method for manufacturing a coil spring according to claim 1. The electric tempering step includes:
a first current-carrying member that holds one end of the formed material after quenching and a second current-carrying member that holds the other end of the formed material after quenching, and a current is applied to the formed material while both ends of the formed material are held by the first current-carrying member that holds one end of the formed material after quenching,
The first and second current-carrying members are a first gripping member located on the outer periphery of the formed material, and a second gripping member located on the inner periphery of the formed material and sandwiching the formed material between the first gripping member, and the radius of curvature of the surface that contacts the formed material is smaller than the radius of curvature of the inner periphery of the formed material, and the second gripping member that sandwiches the formed material between the first gripping member and the formed material is gripped by the first gripping member.
The method for manufacturing a coil spring according to claim 1 . an electric current heating step, which is performed before the quenching step, for electrically heating the cold-formed material;
The method for manufacturing a coil spring according to claim 1, further comprising:

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