Method for manufacturing a wheel disc of a wheel

Abstract

The present invention relates to a method for manufacturing a wheel disc (3) for a wheel.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a wheel disk for a wheel. Background Art

[0002] The production of wheel disks for wheels, especially from hardenable steel, is state of the art, see for example DE 102018 209 879 A1 and DE 10 2018 209 878 A1.

[0003] Furthermore, it is also known that by means of a spinning method, the wall thickness is designed according to the load, so that the wheel disk made of a steel plate has a particularly light design. The spinning method described in the prior art is only used to form a wheel disk from a circular blank in the cold state. Summary of the Invention

[0004] Therefore, the object of the present invention is to provide a method for manufacturing a wheel disk, by means of which a load-compliant wheel disk for a wheel can be manufactured at a more favorable manufacturing cost, and a corresponding wheel is provided.

[0005] This object is achieved by a method for manufacturing a wheel disk having the features of claim 1. Further embodiments are specified in the dependent claims.

[0006] According to a first teaching, the present invention relates to a method for producing a wheel disk for a wheel, wherein the method comprises the following steps: - providing a circular blank made of hardenable carbon steel; - heating the circular blank at least sectionally to a temperature of at least Ac1; - forming the at least sectionally hot circular blank into an at least sectionally hot wheel disk-shaped part by means of spinning; - actively cooling the at least sectionally hot wheel disk-shaped part at least sectionally, so that after the active cooling, in the wheel disk, an organizational structure composed of martensite and / or bainite is established at least sectionally in the actively cooled section, and thereby the wheel disk has at least sectionally a tensile strength R of at least 1000 MPa m .

[0007] The provided circular blank is made of hardenable carbon steel in order to be able to provide corresponding strength on the manufactured wheel disk during the heat treatment process and to be able to meet the corresponding requirements, especially in order to be able to reduce the thickness of the material due to a corresponding increase in strength, and thereby the wheel disk can be implemented with a lighter texture due to the low thickness. The circular blank is stamped from a steel strip or a steel plate.

[0008] Before forming, the round blank is heated to a temperature of at least Ac1, either only in one section or in multiple sections, or completely. This temperature can especially also be at least Ac3 or higher. At least sectional heating of the round blank can be carried out by induction, by conduction or by radiation using appropriate devices. The at least sectionally hot round blank is formed into an at least sectionally hot disk-shaped part by spin forming. By spin forming, a load-bearing and lightweight disk can be produced in a particularly efficient manner, because by this technique, the thickness of the disk in the radial direction can be adjusted individually, so that different thicknesses can be set in the radial direction, which in turn favors further weight reduction.

[0009] Furthermore, the at least sectionally hot disk-shaped part is at least sectionally actively cooled after forming, so that after active cooling, in the disk, an organizational structure composed of martensite and / or bainite is at least sectionally established in the actively cooled section, and thereby the disk at least sectionally has a tensile strength R of at least 1000 MPa m .

[0010] The round blank is preferably completely heated, so that the disk-shaped part is preferably also completely hot and the disk-shaped part can preferably be completely actively cooled in order to preferably be able to establish a uniform organizational structure throughout the disk.

[0011] Depending on the composition of the carbon steel, or by a suitable selection of the carbon steel, the tensile strength R can be set individually m , so that it at least sectionally has a tensile strength R of especially at least 1100 MPa, preferably at least 1200 MPa, more preferably at least 1300 MPa, particularly preferably at least 1400 MPa, further preferably at least 1500 MPa m is also possible, and in order to obtain an organizational structure composed of martensite and / or bainite. Therefore, in order to establish the required properties in the disk, a hard organizational structure is required, which contains at least 70% martensite and / or bainite, especially at least 80% martensite and / or bainite, preferably at least 90% martensite and / or bainite, where the remaining organizational structure components may exist in the form of ferrite, pearlite, cementite, austenite and / or retained austenite. Preferably, a hard organizational structure with at least 70% martensite, especially at least 80% martensite, preferably at least 90% martensite is established, where the remaining organizational structure components may exist in the form of ferrite, pearlite, bainite, cementite, austenite and retained austenite.

[0012] The transformation of the microstructure into austenite starts at Ac1. When reaching Ac3 and above, there is a microstructure that is basically entirely austenite. After heating, the hot (partially) austenitized round blank is processed into a disk-shaped part by spin forming. Due to the at least partially austenitized microstructure, the forming force can be reduced because of the reduced resistance or flow resistance of the material. After forming, the disk-shaped part is actively cooled using a suitable device so that, after active cooling, a microstructure composed of martensite and / or bainite is established at least sectionally in the actively cooled sections in the disk. By active cooling implemented at a cooling rate of at least 20 °C / s, austenite transforms into martensite when reaching the Ms temperature and / or into bainite when reaching the Bs temperature. Thus, a microstructure preferably consisting essentially only of martensite or composed of martensite and bainite can be established. The higher the cooling rate, for example at least 30 °C / s, 40 °C / s, 50 °C / s and higher, a microstructure consisting essentially of martensite is established. The heating and cooling curves for establishing the desired microstructure depend on the chemical composition of the hardenable and selectively temperable carbon steel used, and these curves can be taken from or derived from the so-called TTA (ZTA) or TTT (ZTU) diagrams. Variables such as Ac1, Ac3, Ms and Bs can also be obtained or derived from these diagrams. Thus, a basically martensitic microstructure can achieve the ultra-high (tensile) strength of the carbon steel used.

[0013] Spin forming is a non-cutting forming method for hollow bodies with rotational symmetry. During this process, the round blank is tensioned and / or fixed on an extrusion chuck and rotated. At least one pressure plate / roller or other suitable device is moved against the rotating round blank so that forming is partially carried out by the pressure stress introduced into the round blank material through a radially guided spin forming operation. The material flows, and the profile of the inner extrusion chuck is obtained during the axial machining process from one end to the other end of the round blank. The extrusion chuck is basically circular, so the "spin formed" disk-shaped part obtains a cylindrical internal geometry. During spin forming, at least one pressure plate / roller causes plastic deformation of the material by direct pressure action, and the defined axial movement of at least one pressure plate / roller can cause the initial wall thickness of the round blank to be reduced to an adjustable (final wall thickness) or minimum thickness. Spin forming conforms to the prior art.

[0014] Optionally, the disk can subsequently be tempered within the annealing range. The tempering can be carried out at a temperature of 200 to 500 °C for a duration of 5 seconds to 30 minutes, accompanied by a reduction in tensile strength but an increase in ductility. The tempered disk contains at least one-third, especially at least half, of annealed martensite in the martensitic microstructure.

[0015] Depending on the use, i.e., whether the wheel is designed for private or commercial vehicles, and also depending on the size or diameter of the wheel in inches, the thickness of the circular blank can be, for example, between 4.0 and 20 mm. The thickness is in particular at least 5 mm, preferably at least 6 mm, and is in particular limited to a maximum of 18 mm, preferably a maximum of 16 mm. The diameter of the circular blank can vary depending on the size of the wheel to be manufactured, in particular between 250 and 650 mm.

[0016] Depending on the complexity of the disc to be produced, heating once to at least Ac1 and a higher temperature may be sufficient to carry out spin forming in the corresponding thermal state and to ensure that a reproducible microstructure can be established in the disc without prematurely cooling the temperature (in the hot section) unrestrictedly below Ms before the disc-shaped part is made during the spin forming process, and thus causing an undesired microstructure transformation at this point in time. If the process heat generated during the spin forming process is sufficient and thus the spin forming can be carried out with a temperature above Ms in at least one hot section until the disc-shaped part is made, no further reheating measures are required. If this cannot be ensured, at least sectional reheating is carried out according to an embodiment of the method according to the invention before active cooling to prevent cooling below the temperature Ms. This is intended to mean that the circular blank is reheated at least sectionally before spin forming and / or the disc-shaped part is reheated at least sectionally during spin forming into the disc-shaped part and / or the disc-shaped part is reheated at least sectionally after spin forming. Thus, at least sectional reheating is intended to prevent cooling below the temperature Ms before active cooling or during forming / spin forming. The at least sectional reheating can be carried out, for example, to a temperature of at least Ac1 to ensure that no unrestricted or uncontrolled microstructure transformation occurs. The at least sectional reheating can also be carried out by induction, by conduction or by radiation using a suitable device. A burner with an open flame can also be used.

[0017] According to an embodiment of the method according to the invention, at least a sectionally hot round blank is positioned on an extrusion chuck, the extrusion chuck with the round blank is rotated, and the rotating round blank is formed into a disk-shaped part by means of at least one adjustable pressure roller. In this process, the disk-shaped part assumes the contour of the extrusion chuck on the side facing away from the pressure roller. "Adjustable" is to be understood as meaning that at least one of the pressure rollers is spatially movable and can thus follow the contour of the extrusion chuck axially and radially, or spin the round blank onto the contour of the extrusion chuck. The contour of the extrusion chuck is designed without undercuts and in particular includes a demoulding slope which prevents locking and thus enables the disk-shaped part or the finished disk to be easily removed / pushed off the extrusion chuck. The extrusion chuck preferably includes at least one radially adjustable sliding element; there can be one or more sliding elements, for example in the form of pins or studs, distributed circumferentially in the extrusion chuck and arranged in the region of the flange to be produced on the disk-shaped part, and the at least one sliding element is adjusted to the extended position before the round blank is formed into the disk-shaped part, whereby during forming, the material in the flange region surrounds the sliding element and thus an undercut is produced in the flange. Alternatively, the round blank can also be positioned on the extrusion chuck in the cold state and only then is the round blank heated at least sectionally.

[0018] According to an embodiment of the method according to the invention, after forming / spin forming, the disk-shaped part remains on the extrusion chuck and is actively cooled. This has the advantage that the process time can be shortened and no additional equipment, such as hardening tools, is required, whereby the method according to the invention can be operated economically. In addition, undesired distortion is advantageously prevented, since the active cooling causes the disk on the extrusion chuck to contract and thus ensures reproducible dimensional accuracy. Therefore, the process steps of forming and active cooling are advantageously carried out in a spinning device.

[0019] On the one hand, the active cooling of the disk-shaped part can be carried out by applying a directly contacting cooling fluid, that is to say, the cooling fluid is applied to the disk-shaped part located on the extrusion chuck, so that the required properties are established in the disk by forced cooling. Water can be sprayed as the cooling fluid, or alternatively a cooling emulsion, preferably oil, which can bring about improved cooling performance and in particular can prevent the ingress of diffusible hydrogen. A housing can preferably be used which has a corresponding device in the form of a sprayer for spraying the cooling fluid onto the at least sectionally hot disk-shaped part. This active cooling by contacting the cooling fluid is a very economical form.

[0020] On the other hand, especially in order to provide a "cleaner" alternative compared to the cooling fluid in contact, the active cooling of the disk-shaped part can be carried out by bringing an adjustable die with a contact surface into contact with the disk-shaped part on the side remote from the extrusion chuck. The die is arranged around a mandrel (Vorsetzer) and can be moved in the axial direction. The contact surface substantially corresponds to the contour of the disk-shaped part facing it, such that the disk-shaped part is substantially form-fittingly contacted by the die in a bell shape, in order to achieve a controlled removal of heat from the disk-shaped part and thus targeted active cooling. Due to the substantially form-fitting contact, it is also possible to manufacture especially improved, dimensionally accurate and reproducible disks.

[0021] In order to prevent thermal loading, the extrusion chuck, the mandrel and / or the die can in particular be actively cooled. The mandrel and / or the die are preferably provided with internal cooling, for example with drill holes through which a cooling medium flows, in order to be able to ensure sufficient heat dissipation to establish the required properties.

[0022] According to a design of the method according to the invention, after active cooling, at least one sliding element is adjusted to the retracted position and the disk is thus released for removal. By fixing the sliding element in an undercut manner to the disk-shaped part or the disk to be manufactured, it is possible to manufacture dimensionally accurate disks. After active cooling, the at least one sliding element is retracted again into the extrusion chuck, thus simplifying the pushing off of the manufactured disk.

[0023] According to a design of the method according to the invention, the hardenable carbon steel contains, in addition to Fe and inevitable impurities due to production limitations, the following chemical elements in % by weight:

[0024] C: 0.01 to 0.5%,

[0025] Si: 0.01 to 3.0%,

[0026] Mn: 0.01 to 3.0%,

[0027] N: at most 0.1%,

[0028] P: at most 0.1%,

[0029] S: at most 0.1%,

[0030] Optionally at least one or more elements selected from the group (Al, Cr, Cu, Mo, Ni, Nb, Ti, V, B, Sn, Ca, rare earth elements REM):

[0031] Al: at most 1.0%,

[0032] Cr: at most 1.0%,

[0033] Cu: at most 1.0%,

[0034] Mo: up to 1.0%,

[0035] Ni: up to 1.0%,

[0036] Nb: up to 0.2%,

[0037] Ti: up to 0.2%,

[0038] V: up to 0.2%,

[0039] B: up to 0.01%,

[0040] Sn: up to 0.1%,

[0041] Ca: up to 0.1%,

[0042] REM: up to 0.2%.

[0043] According to a second teaching of the invention, the wheel comprises at least one disc manufactured according to the invention, which disc is arranged within an opening of the rim ring and is connected thereto in a force-fitting and / or form-fitting manner.

[0044] According to a third teaching of the invention, the wheel is for a road vehicle, in particular for a private vehicle, a commercial vehicle, a bus or a trailer. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] The invention is explained in more detail below with reference to the drawings. Identical parts are provided with identical reference signs. Specifically:

[0046] Figure 1 Two schematic perspective views showing the steps for at least sectionally heating a round blank (upper figure) and for completely heating a round blank (lower figure) are shown,

[0047] Figure 2 A schematic perspective view showing the step after forming the round blank into a disc-shaped part by spin forming is shown;

[0048] Figure 3 A schematic perspective view showing the step after actively cooling the disc-shaped part to a disc according to a first embodiment is shown,

[0049] Figure 4 A schematic perspective view showing the step after actively cooling the disc-shaped part to a disc according to a second embodiment is shown,

[0050] Figure 5 A schematic partial perspective view showing the profile of the clamping chuck is shown, and

[0051] Figure 6 A schematic partial perspective view showing an adjustable sliding element within the clamping chuck is shown. Detailed Embodiment

[0052] A circular blank 1 made of hardenable carbon steel is blanked out from a steel strip or steel plate (not shown) and supplied to a method for manufacturing a vehicle wheel disc. When required, the circular blank 1 can also be provided with a drilled hole / openings, such as a central drilled hole 1.1, during or after the blanking process. The thickness of the circular blank 1 can be, for example, between 4.0 and 20 mm. Depending on the wheel size to be produced (not shown), the diameter of the circular blank can vary between 250 and 650 mm.

[0053] Figure 1 Two schematic perspective views showing the steps for using an inductor 11 to inductively heat the circular blank at least sectionally or completely (upper figure) and for completely heating the circular blank by radiation in a furnace 10 (lower figure) are shown. Before forming, the circular blank 1 is heated to a temperature of at least Ac1 only in one section or in multiple sections, or preferably completely. In particular, the temperature can also be at least Ac3 or higher.

[0054] The at least sectionally hot, preferably completely hot, circular blank is formed into a at least sectionally, preferably completely hot, disc-shaped part by spin forming. The spin forming can be carried out in a conventional spin forming device. The circular blank 1 is positioned on an extrusion chuck 21 in an at least sectionally, preferably completely hot state. Alternatively, the circular blank 1 can also be positioned on the extrusion chuck 21 in a cold state and subsequently heated to a temperature of at least Ac1 at least sectionally, preferably completely. For this purpose, corresponding devices can be integrated into the spin forming device. Here, an adjustable inductor 23 is taken as an example, which can be spatially moved axially and radially, as indicated by the double arrows. The extrusion chuck 21 with the circular blank 1 is rotated, and the rotating circular blank 1 is formed into a disc-shaped part 2 by at least one adjustable extrusion roller 20, where the extrusion roller can be spatially moved axially and radially, as indicated by the double arrows. See Figure 2 , where the disc-shaped part 2 presents the contour 22 of the extrusion chuck on the side facing away from the extrusion roller 20. See Figure 5 . The extrusion chuck 21 includes at least one radially adjustable sliding element 24. See Figure 6 , which is arranged in the region of a flange 2.1 to be manufactured on the disc-shaped part 2. At least one sliding element 24 is adjusted to an extended position before the circular blank 1 is formed, as indicated by the double arrows, such that the material in the region of the flange 2.1 surrounds the sliding element 24 during forming and in this way an undercut 4 is produced in the flange 2.1. See Figure 6 .

[0055] If it is not possible to rule out the case that cooling to below the temperature Ms cannot be prevented before active cooling, at least sectional reheating should be carried out, in particular to at least the temperature Ac1. For this purpose, for example, a device integrated in the equipment can be used, here taking the inductor 23 as an example, for targeted reheating before, during or after forming and before active cooling.

[0056] The basic steps for producing the disk 3, such as selective heating, forming and active cooling, are advantageously carried out in a spinning device. Therefore, preferably, after forming / spin forming, the disk blank 2 is held on the extrusion chuck 21 and actively cooled; at least sectional, preferably completely thermal disk blank 2 is subjected to at least sectional, preferably complete active cooling, so that after active cooling, in the disk 3, at least sectional, preferably completely in the active cooling section (preferably completely), an organizational structure composed of martensite and / or bainite is established, and thus the disk 3 at least sectional, preferably completely has a tensile strength Rm of at least 1000 MPa.

[0057] The active cooling of the disk blank 2 can be implemented by applying a directly contacting cooling fluid 41, for example, in a corresponding axially adjustable housing 40 with a sprinkler (not shown), see Figure 4 , or by bringing an adjustable die 31 with a contact surface 32 into contact with the disk blank 2 on the side away from the extrusion chuck 21, and the contact surface corresponds to the contour of the side of the disk blank 2 facing the contact surface 32, see Figure 3 . The mandrel 30 and the die 31 can be adjusted in the axial direction. The mandrel 30 and the die 31 can also be actively cooled.

[0058] After active cooling, at least one sliding element 24 is adjusted to the retracted position and thus the disk 3 is released for removal.

[0059] Selective final tempering can improve the ductility of the disk 3.

Claims

1. A method for manufacturing a wheel disk (3), wherein the method comprises the following steps: - Provide a circular blank (1) made of carbon steel capable of hardening; - Heat the circular blank (1) at least sectionally to a temperature of at least Ac1; - By spin forming, form the at least sectionally hot circular blank (1) into an at least sectionally hot disk-shaped part (2), wherein the at least sectionally hot circular blank (1) is positioned on an extrusion chuck (21), the extrusion chuck (21) comprising at least one radially adjustable sliding element (24) arranged in the region of a flange (2.1) to be manufactured on the disk-shaped part (2), and at least one of the sliding elements (24) is adjusted to an extended position before forming the circular blank (1) into the disk-shaped part (2), whereby during forming, the material in the region of the flange (2.1) surrounds the sliding element (24), and thereby an undercut is produced in the flange (2.1); - Actively cool the at least sectionally hot disk-shaped part (2) at least sectionally such that, after active cooling, in the disk (3), an organizational structure composed of martensite and / or bainite is at least sectionally established in the actively cooled section, and thereby the disk (3) at least sectionally has a tensile strength R of at least 1000 MPa m .

2. The method according to claim 1, wherein before active cooling, at least sectional reheating is carried out to prevent cooling below the temperature Ms.

3. The method according to claim 1, wherein an extrusion chuck (21) with a circular blank (1) rotates, and the rotating circular blank (1) is formed into a wheel disk-shaped part (2) by at least one adjustable pressure roller (20), wherein, The disk-shaped part (2) presents the contour (22, 23) of the extrusion chuck on the side facing away from the pressure roller (20).

4. The method according to claim 3, wherein after forming, the wheel disk-shaped part (2) remains on the extrusion chuck (21) and is actively cooled.

5. The method according to claim 4, wherein the active cooling of the wheel disk-shaped part (2) is carried out by applying a directly contacting cooling fluid (41).

6. The method according to claim 4, wherein the active cooling of the wheel disk-shaped part (2) is carried out by bringing an adjustable mold (31) having a contact surface (32) into contact with the wheel disk-shaped part (2) on the side away from the extrusion chuck (21), and the contact surface corresponds to the contour of the side of the wheel disk-shaped part (2) facing the contact surface (32).

7. The method according to claim 1, wherein after active cooling, at least one of the sliding elements (24) is adjusted to the retracted position, and thereby the wheel disk (3) is released for removal.

8. The method according to any one of the preceding claims, wherein the hardenable carbon steel contains, in addition to Fe and inevitable impurities due to production limitations, the following chemical elements in weight %: C: 0.01 to 0.5%, Si: 0.01 to 3.0%, Mn: 0.01 to 3.0%, N: at most 0.1%, P: at most 0.1%, S: at most 0.1%, Optionally at least one or more elements selected from the group (Al, Cr, Cu, Mo, Ni, Nb, Ti, V, B, Sn, Ca, REM): Al: at most 1.0%, Cr: at most 1.0%, Cu: up to 1.0%, Mo: up to 1.0%, Ni: up to 1.0%, Nb: up to 0.2%, Ti: up to 0.2%, V: up to 0.2%, B: up to 0.01%, Sn: up to 0.1%, Ca: up to 0.1%, REM: up to 0.2%.

9. A wheel comprising at least one disk (3) manufactured by the method according to any one of the preceding claims, said disk being arranged within an opening of a rim ring and being connected thereto in a force-fitting and / or form-fitting manner.

10. Use of the wheel according to claim 9 for a road vehicle.

11. Use of the wheel according to claim 9 for a private vehicle, a commercial vehicle, a bus or a trailer.

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