METHOD FOR PRODUCING A SHEET METAL VEHICLE WHEEL

Description

[0001] The invention relates to a method for producing a vehicle wheel with a rim for receiving a tire and a wheel disc connected to the rim in a material, force and / or form-fitting manner with a connection area for detachable connection to a wheel carrier, comprising the following steps: a) cold forming or cold preforming of a rim, b) cold forming or cold preforming of a wheel disc, and c) joining the wheel disc to the rim to form a vehicle wheel, wherein a hardenable steel material having a carbon content of at least 0.15 wt.%, in particular of at least 0.22 wt.%, preferably of at least 0.27 wt.% is provided for the rim or rim and wheel disc. Technical background

[0002] Conventionally manufactured vehicle wheels, such as motor vehicle wheels, particularly those made of sheet steel, consist of a rim for accommodating a tire and a wheel disc that is bonded to the rim by a material, force, and / or form-fitting connection, with a connection area for detachable connection to a wheel carrier. The wheel disc and the rim are conventionally cold-formed from a micro-alloyed fine-grain structural steel or dual-phase steel, such as DP600.

[0003] A weight reduction compared to conventionally manufactured vehicle wheels can be achieved by using materials with higher strength or fatigue strength to reliably absorb operating loads, and by implementing geometric adjustments to compensate for the loss of stiffness due to thinner material thicknesses. However, as the strength of the materials increases, their formability also generally decreases. Thus, lightweight construction with cold-formable steels reaches its technical limits. In these cases, so-called "hot forming" can provide a solution, meeting the requirement for high degrees of forming while simultaneously achieving high strength in the final formed components.

[0004] Hot-formed steels, such as manganese-boron steels, offer potential for lightweight construction today, as they can absorb mechanical loads such as dynamic alternating stresses. The state of the art, particularly for the production of wheel discs from hot-formed steel, which can be press-hardened at least in some areas, is referred to in the publications DE 10 2007 019 485 A1, DE 10 2013 114 245 B3, and DE 10 2014 108 901 B3. In the publication DE 10 2007 019 485 A1, the joining of the hardened individual components (rim / wheel disc) is proposed, among other things, by welding or brazing. MAG welding, established in vehicle wheel construction, results in melting of the base material and, in hot-formed steels, causes additional tempering effects in the heat-affected zone, forming a softening zone ("hardening pocket").This softening zone in the area surrounding the weld zone is characterized by low strength and ductility and forms a "metallurgical notch", which can have a detrimental effect on the fatigue strength of the joint or the entire component and lead to premature failure, so that the material strength cannot be transferred globally to the entire vehicle wheel.

[0005] Furthermore, as further prior art for the production of vehicle wheels, reference is made to the documents US 2004 / 0041458 A1, JP 05-038901, DE 103 23 833 A1 and JP 2001-246901.

[0006] US 2007 / 006461 A1 describes the production of automotive structural parts from an air-hardening martensitic stainless steel.

[0007] With regard to the state of the art, there is further potential for improvement of vehicle wheels, particularly with regard to the use of conventional production lines while simultaneously ensuring high operational strength and safety of the manufactured vehicle wheels, particularly with the lowest possible weight and low production costs. Summary of the invention

[0008] The invention is therefore based on the object of providing a method for producing vehicle wheels which can be implemented as easily as possible in existing production lines and can ensure high operational stability and safety of the (lightweight) vehicle wheels produced, as well as to specify a corresponding use of the (lightweight) vehicle wheels produced.

[0009] This problem is solved by a method having the features of patent claim 1.

[0010] The inventors have discovered that by providing hardenable steel materials, conventional production lines can continue to be used and, consequently, individual components for vehicle wheel manufacturing can be manufactured cost-effectively. These hardenable steel materials, in their as-delivered or cold-processed state, exhibit moderate strengths comparable to those of previously conventionally used steel materials. They therefore possess suitable forming properties, particularly suitable for cold (pre-)forming the wheel disc and / or rim. The potential of hardenable steel materials has not yet been fully exploited after (cold) forming. The steel material provided is a heat-treatable steel, in particular of grade C22, C35, C45, C55, C60, 42CrMo4, a manganese-containing steel, in particular of grade 16MnB5, 16MnCr5, 20MnB5, 22MnB5, 30MnB5, 37MnB4, 37MnB5, 40MnB4, or a case-hardening steel.

[0011] The wheel disc and the rim are formed or preformed in steps a) and b) by means of compression forming, tensile forming, tensile compression forming, bending forming, shear forming, flow forming, deep drawing or by means of a combination of the aforementioned manufacturing processes.

[0012] In step c), the wheel disc is connected to the rim by a material, force-fit, and / or form-fit connection. Preferably, the wheel disc is at least partially connected to the rim via a joining seam, which can be implemented as a MIG, MAG, laser, weld, or solder seam. Alternatively, the wheel disc can also be connected to the rim by adhesive bonding and / or resistance welding. Alternatively or cumulatively, a force-fit connection via an (additional) press fit between the wheel disc and rim is also conceivable, particularly to relieve the load on additional fasteners. The use of form-fit mechanical joining methods, such as clinching, riveting, or with functional elements, is also possible. The connection between the wheel disc and rim does not necessarily have to be conventional in a so-called "drop center." Wheel designs, such as semi- or full-face disc wheels, or with a multi-part design, are also conceivable.

[0013] According to the invention, prior to step c), the cold-formed or cold-preformed rim, or the cold-formed or cold-preformed rim and the cold-formed or cold-preformed wheel disc, are first fully heated in a step j) to a temperature above the A c1 temperature, preferably above the A c3 temperature. After heating or soaking, the warm rim, or the warm rim and warm wheel disc, are subsequently partially hardened in a step k) or fully hardened in a step i). The hardened area has an essentially martensitic microstructure. Additional forming during hardening is also possible.

[0014] Depending on the composition of the steel material, the A c1 temperature corresponds to the temperature at which the microstructure transforms into austenite, and the A c3 temperature corresponds to the temperature at which the transformation to austenite is completely complete. Partial or complete hardening requires a cooling rate sufficiently high to transform the microstructure, which is initially essentially in the austenitic state, into a substantially martensitic microstructure, allowing partially or fully hardened areas to form. Depending on the composition of the hardenable steel material, the corresponding parameters can be obtained from so-called TTT diagrams.

[0015] Through extensive fatigue strength tests, the inventors have determined that the strength range of 800 - 1200 MPa and / or the hardness range of 250 - 370 HV10 are particularly suitable for vehicle wheels, since in this range a good compromise between cyclic bending fatigue strength and notch sensitivity can be achieved, which has an extremely positive effect on component performance.

[0016] According to a first embodiment of the invention, the fully hardened rim or the fully hardened rim and the fully hardened wheel disc are partially tempered in a step m) after step I) or fully tempered in a step n). Depending on the design of the vehicle wheel to be produced, the microstructure of the fully hardened rim or the fully hardened rim and wheel disc can be partially or fully heat-treated, preferably aiming for a tensile strength in the tempered range between 800 and 1200 MPa and / or a hardness between 250 and 370 HV10, preferably between 850 and 1100 MPa and / or a hardness between 265 and 340 HV10, particularly preferably between 900 and 1050 MPa and / or a hardness between 280 and 330 HV10.

[0017] According to a second embodiment of the invention, the partially hardened rim or the partially hardened rim and the partially hardened wheel disc are tempered after step k) in a step o), wherein the heat treatment aims to achieve a microstructure in the partially hardened area with preferably a tensile strength between 800 and 1200 MPa and / or a hardness between 250 and 370 HV10, preferably between 850 and 1100 MPa and / or a hardness between 265 and 340 HV10, particularly preferably between 900 and 1050 MPa and / or a hardness between 280 and 330 HV10.

[0018] After starting according to step m), n) or o), the wheel disc is connected to the rim to form a vehicle wheel, step c) is carried out.

[0019] According to a second alternative embodiment, after hardening according to step k) (partially hardened rim or partially hardened rim and partially hardened wheel disc) or after step l) (fully hardened rim or fully hardened rim and the fully hardened wheel disc), the wheel disc is joined to the rim to form a vehicle wheel, step c) is carried out. The vehicle wheel is partially tempered in a step p) or completely tempered in a step q), wherein, depending on the design of the vehicle wheel, a tensile strength in the tempered range between 800 and 1200 MPa and / or a hardness between 250 and 370 HV10, preferably between 850 and 1100 MPa and / or a hardness between 265 and 340 HV10, particularly preferably between 900 and 1050 MPa and / or a hardness between 280 and 330 HV10 is aimed for in order to be able to ensure optimal operational strength and safety of the entire vehicle wheel.In addition, weak points such as the heat-affected zone in material-to-material joints with heat input (welding, soldering) or critical load areas with high notch effect, such as the connection area to a wheel carrier, in particular the area of the wheel bolt connection and the area in which ventilation openings / holes are provided, can be reduced.

[0020] According to one embodiment, tempering is carried out at a temperature of at least 200°C, in particular at least 300°C, preferably at least 400°C and below the A c1 temperature, preferably below 650°C. The duration of tempering depends on the composition and material thickness of the corresponding steel material as well as on the strength to be achieved in the hardened area. Tempering can achieve high toughness with sufficient strength and ductility in the predominantly martensitic microstructure, which can be brittle, resulting in a microstructure that is optimal for the cyclic loading of vehicle wheels. Furthermore, tempering and the associated relaxation of the microstructure can reduce the risk of hydrogen-induced cracking. The heat-treated microstructure essentially corresponds to tempered martensite.

[0021] To ensure high dimensional accuracy combined with high operational strength and safety, a further refinement involves calibration between the start of the tempering process and the return to room temperature. Calibration can also be performed after the tempering process. During this manufacturing step, the component geometry of the vehicle wheel and / or rim and / or wheel disc is calibrated using suitable means to maintain the required dimensional accuracy. Calibration may include minor shaping to make any necessary adjustments to achieve the desired geometry.

[0022] According to a further embodiment, hardening is carried out only in the surface layer of the hardenable steel material. Through-hardening, particularly across the entire material thickness, is very energy-intensive, for example, for sheet thicknesses > 10 mm, which are used for the manufacture of commercial vehicle wheels, preferably for the wheel discs of truck wheels. Since high hardness is particularly evident in the area near the surface of components subjected primarily to flexural fatigue, surface hardening is more economical from a manufacturing perspective. Preferably, for larger sheet thicknesses, for example > 6 mm, in particular > 8 mm, and particularly preferably > 10 mm, essentially only surface hardening is carried out.

[0023] Surface hardening leaves the core material unchanged (tough) and causes additional compressive stresses to be introduced at the surface, which can have a positive effect on the fatigue strength of the vehicle wheel.

[0024] Vehicle wheels manufactured according to the invention are used in commercial vehicles, trucks, special vehicles, buses, coaches, whether with combustion engines and / or electric drive, and trailers. Depending on the vehicle type, the vehicle wheel, with its wheel disc and rim, is designed with appropriate material thicknesses, which can also vary along the respective cross-section, for load- and / or weight-optimized performance. The wheel disc is not limited to a single-piece design; rather, it can be designed as a tailored product and / or assembled from a multi-piece design. Short description of the drawings

[0025] The invention is explained in more detail below with reference to the drawings. In detail: Fig. 1 shows a sequence of a method according to an embodiment not according to the invention, Fig. 2 shows a sequence of a method according to an embodiment of the invention and Fig. 3 shows the essential components of a vehicle wheel in a perspective view. Description of the preferred embodiments

[0026] In Fig. 1a sequence of method steps according to an embodiment not according to the invention is shown. For the rim (1) to be produced and / or the wheel disc (2) to be produced, hardenable steel materials with a carbon content of at least 0.15 wt.%, in particular of at least 0.22 wt.%, preferably of at least 0.27 wt.% are provided. In steps a) and b), the rim (1) and the wheel disc (2) are cold-formed or pre-formed by means of compression forming, tensile forming, tensile compression forming, bending forming, shear forming, flow forming, deep drawing or by means of a combination of the aforementioned production methods, in particular also in several stages on, for example, transfer or progressive presses. In step c), the wheel disc (2) is bonded to the rim (1) in a material-locking, force-locking and / or form-locking manner to form a vehicle wheel (3).Preferably, the wheel disc (2) is at least partially connected to the rim via a joining seam, which can be a MIG, MAG, laser, weld, or soldered seam. After assembly, the vehicle wheel (3) is first completely heated in a step d) to a temperature above the A c1 temperature, preferably above the A c3 temperature.

[0027] According to a first alternative not according to the invention, the warm vehicle wheel (3) can be partially hardened after heating or soaking in a step e), following the arrow l. The partially hardened vehicle wheel (3) is tempered after step e) in a step i), wherein the heat treatment aims to achieve a microstructure in the partially hardened region with preferably a tensile strength between 800 and 1200 MPa and / or a hardness between 250 and 370 HV10, preferably between 850 and 1100 MPa and / or a hardness between 265 and 340 HV10, particularly preferably between 900 and 1050 MPa and / or a hardness between 280 and 330 HV10, whereby optimal operational strength and safety of the entire vehicle wheel (3) can be ensured.

[0028] According to a second alternative not according to the invention, the warm vehicle wheel (3) can be fully hardened after heating or soaking in a step f) following arrow II. The fully hardened vehicle wheel (3) can be partially tempered after step f) in a step g) following arrow III or fully tempered in a step h) following arrow IV. Depending on the design of the vehicle wheel (3), the microstructure of the fully hardened vehicle wheel can be partially or fully heat-treated, preferably aiming for a tensile strength in the tempered range between 800 and 1200 MPa and / or a hardness between 250 and 370 HV10, preferably between 850 and 1100 MPa and / or a hardness between 265 and 340 HV10, particularly preferably between 900 and 1050 MPa and / or a hardness between 280 and 340 HV10.

[0029] In Fig. 2a sequence of method steps according to one embodiment of the invention is shown. For the rim (1) and / or the wheel disc (2) to be produced, hardenable steel materials with a carbon content of at least 0.15 wt.%, in particular of at least 0.22 wt.%, preferably of at least 0.27 wt.% are provided. The rim (1) and the wheel disc (2) are cold formed or preformed in steps a) and b) by means of compression forming, tensile forming, tensile compression forming, bending forming, shear forming, flow forming, deep drawing or by means of a combination of the aforementioned production methods, in particular also in several stages on, for example, transfer or progressive presses. In contrast to the embodiment in Fig. 1the cold-formed or cold-preformed rim (1) and / or the cold-formed or cold-preformed wheel disc (2) is / are first fully heated to a temperature above the A c1 temperature, preferably above the A c3 temperature, in a step j). Step j) can be carried out, as required, either on the cold-formed or cold-preformed rim (1) alone or on both components (1, 2), and is therefore shown in dashed lines. After heating or soaking, the warm rim (1) or the warm rim (1) and the warm wheel disc (2) are then partially hardened in a step k) or fully hardened in a step l).

[0030] Following the arrow V, the partially hardened rim (1) or the partially hardened rim (1) and the partially hardened wheel disc (2) are tempered after step k) in a step o), wherein the heat treatment aims to achieve a microstructure in the partially hardened region with preferably a tensile strength between 800 and 1200 MPa and / or a hardness between 250 and 370 HV10, preferably between 850 and 1100 MPa and / or a hardness between 265 and 340 HV10, particularly preferably between 900 and 1050 MPa and / or a hardness between 280 and 330 HV10. The rim (1) and the wheel disc (2) are then joined together to form a vehicle wheel (3); step c) is carried out.

[0031] Following arrow VI, the fully hardened rim (1) or the fully hardened rim (1) and the fully hardened wheel disc (2) are partially tempered in a step m) after step l) or fully tempered in a step n). Depending on the design of the vehicle wheel (3) to be produced, the microstructure of the fully hardened rim (1) or the fully hardened rim (1) and wheel disc (2) can be partially or fully heat-treated, preferably aiming for a tensile strength in the tempered range between 800 and 1200 MPa and / or a hardness between 250 and 370 HV10, preferably between 850 and 1100 MPa and / or a hardness between 265 and 340 HV10, particularly preferably between 900 and 1050 MPa and / or a hardness between 280 and 330 HV10. The rim (1) and the wheel disc (2) are then joined together to form a vehicle wheel (3), step c).

[0032] Following the arrow VII, after hardening according to step k) (the partially hardened rim (1) or the partially hardened rim (1) and the partially hardened wheel disc (2)) or after step l) (the fully hardened rim (1) or the fully hardened rim (1) and the fully hardened wheel disc (2)), the rim (1) and the wheel disc (2) are joined together to form a vehicle wheel (3), step c).The vehicle wheel (3) is partially tempered in a step p) following the arrow VIII or completely tempered in a step q) following the arrow IX, wherein, depending on the design of the vehicle wheel, a tensile strength in the tempered range between 800 and 1200 MPa and / or a hardness between 250 and 370 HV10, preferably between 850 and 1100 MPa and / or a hardness between 265 and 340 HV10, particularly preferably between 900 and 1050 MPa and / or a hardness between 280 and 330 HV10 is aimed for in order to be able to ensure optimal operational strength and safety of the entire vehicle wheel.

[0033] In Fig. 3 a perspective view of a rim (1), a wheel disc (2) and a vehicle wheel (3) which is composed or formed from a rim (1) and a wheel disc (2) connected to the rim (1) in a material, force and / or form-fitting manner is shown.

Claims

1. Method for producing a vehicle wheel (3) in sheet metal construction, having a rim (1) for receiving a tire and a wheel disc (2) which is connected to the rim in a material-, force- and / or form-locking manner and has a connection region for releasable connection to a wheel carrier, comprising the following steps: a) Cold forming or cold preforming of a rim (1), b) Cold forming or cold preforming of a wheel disc (2), and c) Connecting the wheel disc (2) to the rim (1) to form a vehicle wheel (3), wherein a hardenable steel material with a carbon content of at least 0.15% by weight, in particular of at least 0.22% by weight, preferably of at least 0.27% by weight, is provided for the rim (1) or the rim (1) and wheel disc (2), characterized in that before step c), the cold-formed or cold-preformed rim (1) or the cold-formed or cold-preformed rim (1) and the cold-formed or cold-preformed wheel disc (2) are first completely heated to a temperature above the Ac1 temperature in a step j), preferably above the Ac3 temperature, and then the warm rim (1) or the warm rim (1) and the warm wheel disc (2) is partially hardened in a step k) or is completely hardened in a step l) and the vehicle wheel (3) is used in commercial vehicles, trucks, special-purpose vehicles, buses, coaches, whether with internal combustion engine and / or electric drive, trailers or semi-trailers, wherein the steel material provided is a case-hardening steel, a manganese-containing steel or a heat-treatable steel.

2. Method according to claim 1, characterized in that after step l), the fully hardened rim (1) or the fully hardened rim (1) and the fully hardened wheel disc (2) are partially tempered in step m) or fully tempered in step n).

3. Method according to claim 1, characterized in that after step k), the partially hardened rim (1) or the partially hardened rim (1) and the partially hardened wheel disc (2) are tempered in step o).

4. Method according to claim 2 or 3, characterized in that is carried out after step m), n) or o) step c).

5. Method according to claim 1, characterized in that is carried out after step k) or l) step c).

6. Method according to claim 5, characterized in that the vehicle wheel (3) is partially tempered in step p) or fully tempered in step q).

7. The method according to any one of claims 2, 3, 4, 5 or 6, characterized in that the tempering is carried out at a temperature of at least 200°C, in particular at least 300°C, preferably at least 400°C and below the Ac1 temperature, preferably below 650°C.

8. Method according to claim 7, characterized in that calibration can be carried out between the start of the tempering process and the return to room temperature or after the tempering process, in particular to ensure dimensional accuracy.

9. Method according to claim 1, characterized in that hardening is only carried out in the surface layer of the hardenable steel material.

10. A method according to any one of the preceding claims, characterized in that the heat-treatable steel corresponds to grade C22, C35, C45, C55, C60, 42CrMo4 or the manganese-containing steel corresponds to grade 16MnB5, 16MnCr5, 20MnB5, 22MnB5, 30MnB5, 37MnB4, 37MnB5, 40MnB4.