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Title:
METHOD OF MANUFACTURING A METAL VEHICLE WHEEL AND VEHICLE WHEEL
Document Type and Number:
WIPO Patent Application WO/2012/084177
Kind Code:
A1
Abstract:
Method of manufacturing a metal vehicle wheel (10) comprising at least a circumferential rim and a disc, comprising a hot stamping step of hot stamping a metal blank into a wheel part (12) having a circumferential rim portion (16) and an integral disc portion (14) and a quenching step of quenching the hot stamped wheel part; and providing at least one other wheel part (20); and a welding step of at least partially circumferentially welding the wheel parts (12, 20) together.

Inventors:
DEN UIJL, Nick, Johannes (Tata Steel Nederland Technology B.V, Group Intellectual Property ServicesP.O. Box 10000, CA IJmuiden, NL-1970, NL)
DE HAAN, Theobald (Tata Steel Nederland Technology B.V, Group Intellectual Property ServicesP.O. Box 10000, CA IJmuiden, NL-1970, NL)
Application Number:
EP2011/006409
Publication Date:
June 28, 2012
Filing Date:
December 19, 2011
Export Citation:
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Assignee:
TATA STEEL NEDERLAND TECHNOLOGY B.V. (P.O. Box 10000, CA IJmuiden, NL-1970, NL)
DEN UIJL, Nick, Johannes (Tata Steel Nederland Technology B.V, Group Intellectual Property ServicesP.O. Box 10000, CA IJmuiden, NL-1970, NL)
DE HAAN, Theobald (Tata Steel Nederland Technology B.V, Group Intellectual Property ServicesP.O. Box 10000, CA IJmuiden, NL-1970, NL)
International Classes:
B21D53/26; B21D53/30; B60B3/08
Domestic Patent References:
Foreign References:
US20070006461A1
US20020139161A1
DE4305091C1
Other References:
See also references of EP 2654984A1
Attorney, Agent or Firm:
KRUIT, Jan (Tata Steel Nederland Technology B.V, Group Intellectual Property ServicesP.O. Box 10000, CA IJmuiden, NL-1970, NL)
Download PDF:
Claims:
Method of manufacturing a metal vehicle wheel (10) comprising at least a circumferential rim and disc, comprising a hot stamping step of hot stamping a metal blank into a wheel part (12) having a circumferential rim portion (16) and an integral disc portion (14) and a quenching step of quenching the hot stamped wheel part; and providing at least one other wheel part (20); and a welding step of at least partially circumferentially welding the wheel parts (12, 20) together.

Method according to claim 1 , wherein all parts (12;20) are made in a hot stamping step of hot stamping a metal blank into the respective wheel part and a quenching step of quenching the hot stamped wheel parts.

Method according to any one of the preceding claims, wherein the metal blank is a low carbon steel comprising 0.08-0.30 wt.% C.

Method according to any one of the preceding claims, wherein the hot stamping step of a steel blank is carried out at a temperature above the austenizing temperature.

Method according to any one of the preceding claims, further comprising a tempering step of tempering the wheel parts prior to welding.

Method according to any one of the preceding claims, wherein the quenched hot stamped wheel part has a martensitic and/or bainitic structure.

Method according to any one of the preceding claims, wherein the welding step comprises circumferentially welding along the whole circumference.

8. Metal vehicle wheel (10) comprising at least a circumferential rim and a disc made from multiple wheel parts welded together at least partially circumferentially, at least one wheel part (12) comprising a circumferential rim portion (16) and a disc portion (14), which have been integrally hot stamped and quenched.

9. Wheel according to claim 8, wherein the metal of the hot stamped wheel part has a martensitic and/or bainitic structure.

Description:
METHOD OF MANUFACTURING A METAL VEHICLE WHEEL AND VEHICLE WHEEL

According to a first aspect the invention relates to a method of manufacturing a metal vehicle wheel, comprising at least a circumferential rim and a disc.

Another aspect of the invention relates to a metal vehicle wheel, comprising at least a circumferential rim and a disc.

A centrally circumferentially split, two-part wheel, particularly for supporting solid tyres and a production method thereof are known from GB 1 ,107,328. A wheel half is formed by stamping from sheet metal, e.g. steel sheet having a thickness of from 3 to 8 mm. Such a wheel half comprises a hub portion, an annular web portion integral with the hub portion, and a peripheral rim portion integral with the web portion. Similar wheel halves are aligned back-to-back and bolted together. It is said that a lighter wheel produced in this manner may be used to support a given load compared to a cast wheel and, as a result, the dead weight of a vehicle may be reduced.

In another method currently practised a rectangular metal strip is bent into a cylindrical shape and the adjacent ends are welded together. The thus produced annular half product is subjected to cold deformation in order to achieve the appropriate size and shape. Typically then a wheel disc is welded to an outer peripheral rim edge. The rejection rate of wheels produced in this manner is relatively high due to failure of the tangential weld in the wheel rim and/or the dimensions being out of tolerance. Also sometimes there are problems related to pores and enclosed oxides in the tangential weld. Furthermore the weld itself is a weak spot in the rim.

US 3,771 ,843 A has disclosed a track idler wheel especially made for heavy- duty tractor applications having two formed metallic discs disposed in abutting concentric relationship and joined by circumscribing weld joints in such a manner as to minimize stresses inherent in the composite disc idler wheel structure. The discs are made by forging.

From WO 2010/031863 A1 a rim for a motor vehicle is known, comprising a wheel disc and a rim strip. Both wheel parts are made by cold forming.

US 3,611 ,535 A discloses a method of manufacturing a vehicle wheel comprising a cast aluminium wheel disc and a rolled or stamped sheet steel rim rigidly interconnected by a steel ring insert cast into the aluminum body and a continuous welded joint between the steel insert and the rim.

DE 30 16 285 A1 relates to a vehicle wheel, in particular a lightweight wheel, made from two parts, wherein each part comprises a rim portion and a disc portion. The visible part is shaped by forging or casting, while the other part is shaped by deep drawing. The parts thus shaped are welded together.

An object of the present invention is to provide a metal wheel manufacturing process having low rejection rates. Another object is to manufacture a cheap wheel, in particular to reduce material costs, the wheel having similar or improved strength properties compared to the earlier described prior art wheels.

According to a first aspect, the invention provides a method of manufacturing a metal vehicle wheel comprising at least a circumferential rim and a disc, comprising a hot stamping step of hot stamping a metal blank into a wheel part having a circumferential rim portion and an integral disc portion and a quenching step of quenching the hot stamped wheel part; and providing at least one other wheel part; and a welding step of at least partially circumferentially welding the wheel parts together.

In the present specification the expression "hot forming" is meant to comprise any shaping process such as hot stamping at elevated temperature, including heating the article to be shaped and cooling the shaped article. In the method according to the invention at least one wheel part, advantageously all parts, is/are manufactured starting from metal sheet material. This flat material optionally obtained from a coil and cut to an appropriate size, is subjected to a hot stamping operation, wherein the two- dimensional shape of the blank is changed into a three-dimensionally shape of the wheel part. At least one wheel part made through hot stamping has a circumferential rim portion and a substantially circular inner portion integral with the rim portion. Hot stamping allows high degrees of deformation and therefore detailed designs, in particular relevant for the rim shape, may be obtained. The hot stamping step may be performed in two or more substeps. The final hot stamped wheel part is subjected to quenching, typically in the stamping device directly after the final hot stamping stage. At least one other part having at least a circular rim portion is also provided. Preferably this wheel part is also made by hot stamping, as explained above. Thereafter two wheel parts, which may have an identical shape, are joined together by applying a circumferential weld over at least part of the circumference. The weld may be applied discontinuously, e.g. at only 4 or 5 positions along the circumference. Preferably the multiple wheel parts are welded together along the whole circumference. The wheel thus produced has a (partially) circumferential seam, but not a tangential seam, the latter being a rejection source of prior art wheels. Compared to a state of the art wheel having a tangential seam the circumferential weld seam is positioned at a more favourable spot in view of load during use. During manufacturing and use there is little or no risk of tearing at the weld position in the rim. Furthermore, the method according to the invention offers the possibility to reduce the amount of welding stations, because of the absence of a tangential weld. Moreover, with respect to other manufacturing methods cited above, hot stamping allows downgauging, thereby saving material, while strength levels are maintained at a sufficient level. Downgauging also allows to produce relatively light wheels.

A further advantage of the present invention is that there is only one welding seam present, compared to some of the above designs according to the prior art. As each weld is potentially a cause of failure(s), reduction of the number of welds is advantageous. The rejection rate of the method according to the invention is small. Additionally, contrary to a cold rolled rim, a wheel part made by hot stamping does not exhibit spring back, but retains its shape close to the dimensions of the dies used in the press.

The starting material is heated to its deformation temperature. A preferred starting material for use in the method according to the invention is a steel blank.. If the metal blank comprises a steel blank, then advantageously the steel blank is heated above its austenizing temperature. Steel heated above the austenizing temperature transforms to an fee structure, which has better (hot) formability than a bec structure being the original ferrite matrix and than a bet structure, which is the resulting martensite upon quenching carbon rich fee. The way of heating is not limited and can be done e.g. using a furnace or induction heating. To avoid oxidation a protective or inert atmosphere is preferably applied. The blanks may be maintained at elevated temperature prior to hot stamping. Typically the steel blank is held in the range of 900- 950°C for a period of time sufficient to attain a homogeneous austenite structure, such as 3-10 minutes. If held much longer above the austenizing temperature, growth of the austenite grains will occur thereby lowering the temperature at which formation of martensite occurs during rapid cooling. However, the resulting microstructure obtained after hot formation is not affected significantly, if care is taken to avoid lowering the martensite final temperature below room temperature. Otherwise too many austenite would remain.. Following stamping the material is quenched due to heat loss from the blanks to the stamps or dies (press hardened), which may have a forced cooling system. A separate quenching step immediately following hot stamping is also possible. Quenching transforms the material into a hard martensitic structure of very high strength, e.g. up to 1500 MPa, compared to about 800 MPa for traditionally manufactured wheels. Depending on the strength desired, a (partial) bainite structure is also possible Preferably the metal blanks are made from hot stamping steel types like boron- alloyed steels e.g. 22MnB5, and HpF™ . Such steel types are relatively cheap compared to high strength steels such as high strength low alloyed steels (HSLA) and advanced high strength steels. Advantageously the steel composition comprises at least 0.08 wt. % C (carbon) allowing the formation of martensite during and/or after hot stamping. Advantageously, the steel composition comprises equal to or less than 0.30 wt. % C thereby avoiding the formation of too brittle martensite. Contrary to the known production method, wherein the rim attains its strength by means of the mechanical work using cold forming, in the present invention the wheel has a high strength due to quenching at or after hot stamping. The hot stamped wheel part shows a reduction of its spring back behaviour compared to the state of the art wheels, allowing a high accuracy of its dimensions, retention of its shape and reproducibility and repeatability.

After hot stamping and quenching, typically the wheel parts are transferred from the stamping apparatus to the welding equipment. An intermediate storage step may be inserted. Optionally a tempering step may be applied prior to welding at a temperature below austenizing temperature in order to increase the toughness of the material, in particular when the stamping step has resulted in very hard (too brittle) martensite. The tempering heat treatment, bake hardening or other annealing step may be applied to a whole wheel part or locally, the latter allowing variation of strength and hardness over a wheel part.

Welding the wheel parts, which may be different or similar, completes the manufacturing of a complete wheel. Examples of suitable welding techniques comprise fusion welding including inter alia laser welding and arc welding, and force welding such as resistance upset welding and friction welding. Fusion welding can be done with and without a filler material. Welding is not necessary at critical positions subjected to heavy loads during use, thus improving the fatigue properties. The peripheral weld is a supported weld. Optionally, excess material resulting from stamping and welding is removed. The wheels may be subjected to further processing steps, such as painting or otherwise coating. The method according to the invention using hot stamping of wheel parts offers the possibility of manufacturing (very) high strength wheels from relatively cheap steel types, allowing downsizing in gauge thereby saving weight and material, as well enlarging the production in terms of number of wheels produced per ton steel.

According to a further aspect the invention provides a metal vehicle wheel comprising at least a circumferential rim and a disc made from multiple wheel parts welded together at least partially circumferentially, at least one wheel part comprising a circumferential rim portion and a disc portion, which have been integrally hot stamped and quenched. In particular the wheel is made from steel and its structure is essentially comprised of a martensite or bainite or combinations thereof. Here "essentially" means that at least the hot stamped parts of the wheel according to the invention have a martensite structure or bainite structure or a combination thereof. E.g. in low carbon steel (e.g. 0.08 wt % C) it is feasible that a bainite structure is obtained, at least partially.

The invention is further illustrated by means of the attached drawing and description thereof. Figure 1 is a diagrammatically depicted wheel according to the invention, generally indicated by reference numeral 10. The wheel consists of two parts. A first part 12 comprises an annular web portion or disc 14 and integral rim portion 16, which are made in one piece due to the hot stamping and press hardening process used to manufacture this part 12. The rim portion 16 has a small projection 18 at its free edge in order to prohibit a tyre from running of the rim during use. A second part 20 comprises a comparable circular rim portion 22 without annular web portion. The parts 12 and 20 are welded together, such that a continuous welding seam 24 results. Depending on the design of the wheel the welding seam may be positioned at a less critical position, where the seam is not subjected to (cyclic) mechanical load. When both wheel parts are provided with a disc portion, then the disc portions are joined with their backs turned to one another. The resulting wheel may be symmetrical, such as for heavy vehicles.