Spring wire for producing a helical spring, helical spring and method for producing a helical spring

Abstract

The invention relates to a spring wire (4) for producing helical springs (2), comprising a spring wire core (6) having a martensitic structure and having a lateral surface delimiting the spring wire core (6) with respect to the outside, a carrier layer formed on the entire lateral surface of the spring wire core (6) and having a lateral surface delimiting the carrier layer with respect to the outside, wherein a spring wire anti-corrosion layer (8) is applied to the entire lateral surface of the carrier layer. The invention further relates to a helical spring (2) and to a method for producing a helical spring (2).

Description

[0001] Spring wire for producing a coil spring, coil spring and method for producing a coil spring

[0002] The invention relates to a spring wire for producing coil springs, comprising a spring wire core with a martensitic structure and a jacket surface that outwardly defines the spring wire core, a carrier layer formed over the entire jacket surface of the spring wire core, with a jacket surface that outwardly defines the carrier layer. Furthermore, the invention relates to a coil spring and a method for its production.

[0003] A large number of embodiments of such spring wires, coil springs made of a spring wire and the production of coil springs are already known from the prior art.

[0004] The object of the present invention is to improve a spring wire for producing a coil spring, a coil spring, and a method for producing a coil spring. To achieve this object, the invention, in conjunction with the preamble of patent claim 1, is characterized in that a spring wire corrosion protection layer is applied to the entire surface of the carrier layer. The carrier layer is preferably formed as a diffusion layer consisting of zinc and iron with an intermetallic phase. Furthermore, this object is achieved by a coil spring according to claim 7 and a method according to claim 13.

[0005] The particular advantage of the invention is that a spring wire for producing a coil spring, a coil spring, and a method for producing a coil spring are improved. Due to the inventive design of the spring wire, the coil spring, and the method for producing the coil spring, a coil spring can be produced cost-effectively. This applies in particular to the use of the coil spring according to the invention in the automotive sector, and here in particular to the use of the coil spring according to the invention as a compression spring in a drive for opening and closing a tailgate or the like, wherein corrosion protection of the coil spring, namely of the spring wire used for this purpose, is essential for the correct functioning of the coil spring in the long term.In contrast to conventional methods, the coating of the spring wire core according to the invention is carried out in a much simpler manner in terms of production technology before the production of the helical spring according to the invention from the spring wire formed therefrom.

[0006] In principle, the spring wire can be freely selected within wide, suitable limits in terms of its type, material, dimensions, and geometry, particularly the geometry of its cross-section. For example, the spring wire can be a steel wire. However, this is not mandatory; it depends on the specific application. Furthermore, the application of the spring wire according to the invention is not limited to the use of the spring wire according to the invention on springs, in particular coil springs.

[0007] A particularly advantageous development of the spring wire according to the invention provides that the spring wire core is designed as an alloyed and tempered spring wire core, preferably as a SiCr-alloyed and tempered spring wire core, particularly preferably as a SiCrV-alloyed and tempered spring wire core. In this way, the spring wire core of the spring wire according to the invention is particularly well suited for most applications, in particular in the automotive sector. This applies particularly to the preferred and in particular to the particularly preferred embodiment of this development. The spring wire core has a martensitic structure. Accordingly, this results in a pretreatment of the spring wire core that is known per se to those skilled in the art. SiCr-alloyed stands for an alloy with silicon and chromium; SiCrV-alloyed stands for an alloy with silicon, chromium, and vanadium.A SiCr alloy, particularly a SiCrV alloy, for the spring wire core ensures its very high strength. The SiCr-alloyed and SiCrV-alloyed spring wire core can contain other alloy components in addition to the aforementioned alloy components. Of course, other materials for the spring wire core are also conceivable, for example, with other alloys. Accordingly, the expert can select the appropriate material for the spring wire core depending on the requirements of the individual case. The expert is familiar with the respective pretreatment of the spring wire core.

[0008] Analogous to the spring wire core, the spring wire corrosion protection layer can also be freely selected in terms of type, material, and dimensions within wide, suitable limits. The spring wire corrosion protection layer is advantageously formed as a zinc-aluminum layer, or ZnAl layer for short. Preferably, the zinc-aluminum layer has an aluminum content of up to 15%, preferably from 3% to 7%, for example 5%, or Zn95Al5 layer for short. This results in a particularly suitable selection of the material for the spring wire corrosion protection layer for the production of the coil spring according to the invention and for most applications. This applies in particular to applications in the automotive sector. See the above explanations.

[0009] A particularly advantageous development of the spring wire according to the invention provides that the spring wire has a spring wire cross-section that deviates from a circular cross-section over substantially its entire length before the coil spring is manufactured, and preferably that the spring wire does not have opposing and parallel boundary surfaces on the casing side. In this way, it is possible, for example, to specifically design the geometry of the cross-section of the spring wire according to the invention of the coil spring according to the invention even before the actual production of the coil spring according to the invention from this spring wire.For example, the geometry of the cross section of the spring wire according to the invention could be designed before the production of the helical spring in such a way that after the production of the helical spring according to the invention from this spring wire a cross section of the spring wire desired for the helical spring results, for example a substantially circular spring wire cross section of the helical spring.

[0010] It is also conceivable, for example, that the spring wire has a spring wire cross-section over substantially its entire length such that the spring wire of a helical spring made from this spring wire has two opposing and parallel casing-side boundary surfaces. Preferably, the mutually parallel casing-side boundary surfaces of the helical spring made from the spring wire are oriented perpendicularly or substantially perpendicularly to a longitudinal axis of the helical spring.

[0011] When assessing whether a casing-side boundary surface is oriented perpendicular to the longitudinal axis of the coil spring and / or whether two opposing casing-side boundary surfaces are parallel to each other, the typical accuracy of the relevant production steps in the manufacture of such a coil spring, and in particular the accuracy in stamping the spring wire and winding the coil spring, must be taken into account. Typically, a manufacturing tolerance of ± 2 to 3° must be taken into account for the vertical or parallel orientation of the casing-side boundary surfaces.

[0012] For example, the spring wire may have a circular cross-section before the coil spring is manufactured. The coil spring produced from the spring wire then has a cross-section that deviates from the circular geometry, for example, an elliptical one.

[0013] An advantageous development of the helical spring according to the invention provides that the spring wire of the helical spring is ground at at least one end of the helical spring such that, in a position of use of the helical spring, only this ground spring wire forms a support surface of the helical spring for force-transmitting support of the helical spring at this end of the helical spring against an abutment, wherein the support surface extends substantially perpendicular to the longitudinal axis of the helical spring. This enables a very simple construction of the helical spring according to the invention with a minimum of components for the helical spring according to the invention.

[0014] A particularly advantageous development of the aforementioned embodiment of the helical spring according to the invention provides that only a helical spring separation surface created by severing the spring wire and a helical spring grinding surface created by the aforementioned grinding of the spring wire at this front end of the helical spring are coated with a helical spring corrosion protection layer. In this way, on the one hand, the corrosion protection of the helical spring according to the invention, namely the spring wire according to the invention, is ensured, and on the other hand, the complexity of manufacturing the helical spring according to the invention is reduced.After the aforementioned cutting and grinding, the coil spring is not coated again in its entirety with a corrosion protection layer; instead, only the resulting cutting surface and the resulting grinding surface of the coil spring, namely the spring wire, are coated with a corrosion protection layer. For example, the cutting surface and grinding surface can be coated with the same coil spring corrosion protection layer, for example, in a single operation. The coating of the cutting surface and the grinding surface can be carried out in a manner known per se to those skilled in the art. This naturally also applies to the other coating according to the invention.

[0015] According to a further development of the invention, measures are provided to reduce the tendency of the coil spring according to the invention to vibrate. For example, the diameter of the spring wire can be varied to reduce the tendency of the coil spring to vibrate. For example, flocking the outer surface of the spring wire or the coil spring with plastic fibers can be provided. To apply the flocking, it is preferably provided to statically charge the coil spring, apply an adhesive, and then apply the plastic fibers.

[0016] Further advantages, features, and details of the invention can be derived from the further subclaims and the following description. Features mentioned therein may be essential to the invention individually or in any combination. Features and details of the spring wire and the coil spring described according to the invention naturally also apply in connection with the method according to the invention, and vice versa. Thus, the disclosure of the individual aspects of the invention can always be referenced reciprocally. The drawings serve merely as examples to clarify the invention and are not limiting in nature.

[0017] They show:

[0018] Fig. 1a shows an embodiment of the coil spring according to the invention made from the spring wire according to the invention in a perspective view of the coil spring blank,

[0019] Fig. 1b shows the embodiment in a representation analogous to Fig. 1a, with the coil spring blank after grinding one end of the coil spring,

[0020] Fig. 1c shows the embodiment in a representation analogous to Fig. 1b, with the coil spring blank after coating the separating and grinding surfaces,

[0021] Fig. 2a the embodiment in a plan view of the aforementioned frontal coil spring end after its grinding and

[0022] Fig. 2b shows the embodiment in a representation analogous to Fig. 2a, after coating the separation surface created by the separation and the grinding surface created by the grinding. Figs. 1a to 2b show an embodiment of the helical spring according to the invention purely as an example.

[0023] The coil spring 2 is designed for use in the automotive sector, namely as a compression spring in a drive for opening and closing a tailgate of a motor vehicle. The motor vehicle with the tailgate and drive is not explicitly shown.

[0024] The coil spring 2 is made of a spring wire 4, wherein the spring wire 4 comprises a spring wire core 6 with a martensitic structure and with a jacket surface that outwardly delimits the spring wire core 6, as well as a carrier layer formed on the entire jacket surface of the spring wire core 6 and with a jacket surface that outwardly delimits the carrier layer. According to the invention, a spring wire corrosion protection layer 8 is applied to the entire jacket surface of the carrier layer. The carrier layer is not shown individually in Fig. 1b, but only together with the spring wire corrosion protection layer 8 as a unit 9. The carrier layer is formed as a diffusion layer consisting of zinc and iron and having an intermetallic phase.

[0025] In the present embodiment, the spring wire core 6 is designed as an alloyed and tempered spring wire core 6, namely as a SiCrV-alloyed and tempered spring wire core 6.

[0026] The spring wire corrosion protection layer 8 applied to the outer surface of the carrier layer is formed as a zinc-aluminum layer, with the zinc-aluminum layer here having an aluminum content of approximately 5%. In principle, the aluminum content can be up to 15%, preferably between 3% and 7%.

[0027] Furthermore, in the present embodiment, the spring wire 4 has a cross-section that deviates from a circular cross-section over substantially its entire length, namely such that the spring wire 4 has no opposing and parallel boundary surfaces on the casing side. This cross-section of the spring wire 4, which deviates from a circular cross-section, is not apparent from Figs. 1a to 2b. The cross-section of the spring wire 4 is shown in simplified form as a circular cross-section in the aforementioned figures.

[0028] For the purpose of producing the helical spring 2, the spring wire 4 of the helical spring 2 is ground at least at one end 10 of the helical spring 2 in such a way that in a position of use of the helical spring 2, i.e. after installation of the helical spring 2 in the motor vehicle (not shown), only this ground spring wire 4 forms a support surface of the helical spring 2 for force-transmitting support of the helical spring 2 at this end 10 of the helical spring 2 against an abutment of the motor vehicle (likewise not shown), wherein the support surface extends essentially perpendicular to a longitudinal axis of the helical spring 2. The longitudinal axis of the helical spring 2 runs in the image planes of Fig. 2a and 2b perpendicular to the respective image plane. In the image planes of Fig. 2a and 2b, the longitudinal axis is symbolized by a cross 12. The aforementioned support surface of the helical spring 2 is located in the image plane of Fig. 2b.Figure 2a corresponds to Figure 1b, and Figure 2b corresponds to Figure 1c. In principle, it is conceivable that only one of the two end faces of the coil spring according to the invention is machined in the aforementioned manner. However, it is also possible for both end faces of the coil spring according to the invention to be treated in the aforementioned manner.

[0029] In the present embodiment, only a separating surface 5 of the coil spring 2, created by severing the spring wire 4, and a grinding surface 14 of the coil spring 2, created by the aforementioned grinding of the spring wire 4 of the front end 10 of the coil spring 2, are coated with a coil spring corrosion protection layer 16. For the sake of clarity, the coil spring corrosion protection layer 16 is arranged in the image plane of Fig. 1b above the separating surface 5 and the grinding surface 14. As already explained in the introduction to the description, this coating, like the other coatings of the present embodiment, can be applied in any suitable and expedient manner known to those skilled in the art.Purely by way of example, reference is made here to the formation of the helical spring's corrosion protection layer as a zinc flake coating or a cathodic dip coating, where the term "cathodic dip coating" stands for cathodic dip coating. The production of the spring wire according to the invention and the process according to the invention for producing the helical spring according to the invention according to the present embodiment are explained in more detail below with reference to Figs. 1a to 2b.

[0030] The process for manufacturing the coil spring 2 comprises the following process steps in the specified order:

[0031] First, the spring wire core 6 is cleaned, for example, pickled. Zinc is then applied to the jacket surface of the spring wire core 6, for example using a liquid zinc bath (also not shown). A diffusion layer of zinc and iron with an intermetallic phase forms on the jacket surface of the spring wire core 6. The diffusion layer with the intermetallic phase is not shown individually in Figs. 1a to 2b. The spring wire corrosion protection layer 8, formed as a zinc-aluminum layer, is then applied to the jacket surface of the carrier layer using a liquid zinc-aluminum bath (not shown). The spring wire 4 is now produced with the overall coating 9 comprising the carrier layer and the zinc-aluminum layer 8.

[0032] In the present exemplary embodiment, the spring wire 4 is shaped at least once during production of the spring wire 4 in such a way that, before winding the spring wire 4 to produce a helical spring blank 1 of the helical spring 2, the spring wire 4 has a spring wire cross-section that deviates from a circular cross-section over substantially its entire length, namely in such a way that, before the aforementioned winding of the spring wire 4, the spring wire 4 does not have any opposing and parallel boundary surfaces on the casing side. The aforementioned shaping can, for example, be carried out in such a way that the spring wire 4 has a spring wire cross-section that, during the subsequent production of the helical spring 2 from the spring wire 4, forms a substantially circular cross-section of the spring wire 4 and thus of the helical spring 2 over the entire length of the spring wire 4.The aforementioned shaping can be carried out in any suitable manner known to those skilled in the art. Rolling and stamping are purely examples. However, such deformation of the spring wire is not mandatory. Accordingly, embodiments of the spring wire according to the invention are also conceivable in which the spring wire is used undeformed, i.e., with a circular spring wire cross-section, to produce a coil spring.

[0033] To produce the coil spring 2 from the spring wire 4 now present, the spring wire 4 produced in the above-mentioned manner is wound up in a manner known per se to the person skilled in the art. The spring wire 4 is then wound and severed using a winding machine (also not shown) to produce the coil spring blank 1. The spring wire 4 is then wound on at least one end 10 of the coil spring blank.

[0034] 1 is ground in a manner known per se to the person skilled in the art, namely in such a way that in the position of use of the coil spring 2, i.e. in the aforementioned installation position of the coil spring 2 in the motor vehicle, only this ground spring wire 4 forms a support surface of the coil spring 2 for the force-transmitting support of the coil spring 2 at this front end 10 of the coil spring

[0035] 2 against the abutment of the motor vehicle (not shown), wherein the support surface extends substantially perpendicular to the longitudinal axis 12 of the coil spring 2. Finally, only the separating surface 5 of the coil spring 2, created by the aforementioned severing of the spring wire 4, and the grinding surface 14 of the coil spring 2, created by the aforementioned grinding of the spring wire 4 of this front end 10 of the coil spring 2, are coated with the coil spring corrosion protection layer 16. See Figs. 1a to 2b for an overview. On the one hand, the coating of the separating surface 5 and the grinding surface 14 with the coil spring corrosion protection layer 16 is necessary for corrosion protection reasons, since the previously applied zinc-aluminum layer 8 of the spring wire 4 has been removed due to the aforementioned severing of the spring wire 4 and grinding in the area of ​​the grinding surface 14.On the other hand, the subsequent coating of only the separating surface 5 and the grinding surface 14 with the coil spring corrosion protection layer 16 is sufficient, since the remaining coating of the spring wire 4 has not been damaged by the cutting and grinding. After the coil spring 2 has been manufactured, it is preferably subjected to a heat treatment. For example, the coil spring 2 is stress-relieved and / or tempered, and / or the coating is baked, and / or the coil spring 2 is heat-set, i.e., heated and then driven to a block in the heated state.

[0036] Due to the inventive design of the spring wire 4, the coil spring 2, and the method for producing the coil spring 2, a coil spring 2 can be produced cost-effectively. This applies in particular to the aforementioned use of the coil spring 2 in the automotive sector, and here in particular to the use of the coil spring 2 as a compression spring for the drive for opening and closing the tailgate of the motor vehicle, wherein the corrosion protection of the coil spring 2, namely of the spring wire 4 used for this purpose, is essential for the correct functioning of the coil spring 2 in the long term. In contrast to conventional methods, the coating of the spring wire core 6 according to the invention before the production of the coil spring 2 from the spring wire 4 formed therefrom is significantly easier in terms of production technology.

[0037] Of course, other spring wire corrosion protection coatings and coil spring corrosion protection coatings suitable for the specific application are also conceivable. The method according to the invention for producing the coil spring according to the invention can be adapted accordingly to other requirements.

[0038] The invention is not limited to the present exemplary embodiment. For example, the invention can also be advantageously used for other applications, not only in the automotive sector. The spring wire can, as already explained in the introduction to the description, be designed, for example, as a spring steel wire. The aforementioned terms "winding" and "winding machine" are to be interpreted generally here and include all types of winding and winding as well as all types of winding machines or winding machines used for this purpose. Furthermore, the method according to the invention can comprise further method steps in addition to the method steps explicitly mentioned above. This applies both to the production of the spring wire core and to the production of the spring wire according to the invention and the helical spring according to the invention.Furthermore, it should be added that the coil spring corrosion protection layer 16 can be applied in any suitable manner familiar to a person skilled in the art. Purely by way of example, immersion, electrochemical coating methods such as cathodic dip coating, spraying, printing, rolling, and brushing are mentioned here. To increase the durability of the coating, namely the coil spring corrosion protection layer 16, subsequent heat treatment of this coating, such as baking, curing, or drying, can be carried out. This naturally also applies to the other coatings mentioned. As an alternative to the coatings already mentioned, such as cathodic dip coatings and zinc flake coatings, the use of other coating types, for example, the application of a single-component or multi-component paint, is also possible.

[0039] However, not only springs, in particular not only coil springs, can be produced from the spring wire according to the invention. The production of other bent wire parts is also advantageously possible from the spring wire according to the invention.

Claims

Patent claims 1. Spring wire (4) for producing helical springs (2), comprising a spring wire core (6) with a martensitic structure and with a jacket surface that delimits the spring wire core (6) to the outside, a carrier layer formed on the entire jacket surface of the spring wire core (6) with a jacket surface that delimits the carrier layer to the outside, characterized in that a spring wire corrosion protection layer (8) is applied to the entire jacket surface of the carrier layer.

2. Spring wire (4) according to claim 1, characterized in that the spring wire core (6) is designed as an alloyed and tempered spring wire core (6), preferably as a SiCr-alloyed and tempered spring wire core (6), particularly preferably as a SiCrV-alloyed and tempered spring wire core (6).

3. Spring wire (4) according to claim 1 or 2, characterized in that the spring wire corrosion protection layer (8) is formed as a zinc-aluminum layer, preferably that the zinc-aluminum layer has an aluminum content of up to 15%, preferably from 3% to 7%.

4. Spring wire (4) according to one of claims 1 to 3, characterized in that the spring wire (4) has a circular spring wire cross-section over substantially its entire length, preferably that the spring wire (4) of a helical spring (2) made from this spring wire (4) does not have two mutually opposite and mutually parallel boundary surfaces on the casing side.

5. Spring wire according to one of claims 1 to 3, characterized in that the spring wire has a spring wire cross-section deviating from a circular cross-section over substantially its entire length, preferably that the spring wire has no opposing and mutually parallel boundary surfaces on the casing side.

6. Spring wire according to claim 5, characterized in that the spring wire has a spring wire cross-section over substantially its entire length such that the spring wire of a helical spring made from this spring wire has two opposing and mutually parallel boundary surfaces on the casing side, wherein preferably the two opposing and mutually parallel boundary surfaces of the spring wire are oriented perpendicular to a longitudinal axis of the helical spring made from this spring wire.

7. Coil spring (2) made of a spring wire (4), characterized in that the spring wire (4) is designed according to one of claims 1 to 6.

8. Coil spring (2) according to claim 7, characterized in that the spring wire (4) of the coil spring (2) is ground on at least one front end (10) of the coil spring (2) in such a way that in a position of use of the coil spring (2) only this ground spring wire (4) forms a support surface of the coil spring (2) for the force-transmitting support of the coil spring (2) at this front end of the coil spring (2) against an abutment, wherein the support surface extends substantially perpendicular to a longitudinal axis (12) of the coil spring (2).

9. Coil spring (2) according to claim 8, characterized in that only a separating surface (5) of the coil spring (2) produced by severing the spring wire (4) and a grinding surface (14) of the coil spring (2) produced by the aforementioned grinding of the spring wire (4) of this front end (10) of the coil spring (2) are coated with a coil spring corrosion protection layer (16).

10. Coil spring (2) according to claim 9, characterized in that the coil spring corrosion protection layer (16) is designed as a zinc flake coating or a cathodic dip coating.

11. Coil spring (2) according to one of claims 7 to 10, characterized in that the spring wire (4) of a coil spring (2) made from the spring wire (4) does not have two opposing and mutually parallel boundary surfaces on the casing side.

12. Coil spring according to one of claims 7 to 10, characterized in that the spring wire in the produced coil spring has two mutually opposite and mutually parallel casing-side boundary surfaces, wherein the mutually parallel casing-side boundary surfaces are preferably oriented perpendicular to a longitudinal axis of the coil spring.

13. A method for producing a coil spring (2) according to any one of claims 7 to 12, wherein the method comprises the following method steps in the specified order: - Cleaning the spring wire core (6); - producing the carrier layer on the entire jacket surface of the spring wire core (6); - applying the spring wire corrosion protection layer (8) to the entire surface of the carrier layer; - winding up the spring wire (4) produced in the above-mentioned manner; - winding the spring wire (4) by means of an automatic winding machine and cutting the spring wire (4) to produce a coil spring blank (1); - grinding the spring wire (4) on at least one front end (10) of the coil spring blank (1) in such a way that, in a position of use of the coil spring (2), only this ground spring wire (4) forms a support surface of the coil spring (2) for force-transmitting support of the coil spring (2) at this front end (10) of the coil spring (2) against an abutment, wherein the support surface extends substantially perpendicular to a longitudinal axis (12) of the coil spring (2); - coating only a separating surface (5) of the helical spring (2) produced by the aforementioned cutting of the spring wire (4) and a separating surface (5) of the helical spring (2) produced by the aforementioned grinding of the spring wire (4) of this grinding surface (14) of the coil spring (2) produced at the front end (10) of the coil spring (2) with a coil spring corrosion protection layer (16).

14. Method according to claim 13, characterized in that the spring wire (4) is shaped at least once during the production of the spring wire (4) according to one of claims 1 to 6 in such a way that the spring wire (4) has a spring wire cross-section deviating from a circular cross-section over substantially its entire length before the spring wire (4) is wound to produce the helical spring blank (1), preferably that the spring wire (4) has no opposing and mutually parallel boundary surfaces on the casing side before the aforementioned winding of the spring wire (4).

15. Method according to claim 13 or 14, characterized in that the coil spring blank (1) and / or the coil spring (2) are subjected to a heat treatment and are preferably stress-relieved and / or tempered and / or hot-set and / or that the coating is baked.

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