Procedure for production of vehicle wheels

Abstract: A vehicle wheel made of light metal and consisting of a hub and a rim surface is produced by a process comprising the steps of producing a substantially disc-shaped crude billet from an extruded bolt or a similar rounded solid metal body, heating of a crude billet to a hot rolling temperature and subsequently orbitally rolling the crude billet so as to obtain a rotationally symmetric preformed material, splitting off of the outer portion of the preformed material, and afterwards forming a rim surface by spinning the outer, split-off rim portion. As an alternative, the preformed material after orbital rolling and before splitting can be compressed or cold forged in order to obtain a desired specified design for the hub of the wheel.

Description: The present invention relates to a procedure for producing a one-piece light metal vehicle wheel consisting of hub and a rim portions, where in a first step a substantialy disc-shaped crude material is produced from a cast billet or a similar rounded, solid metal body, in a third step splitting off of the outer portion of a preformed material, and in a fourth step forming the rim surface by spin forging the outer, split-off rim portions. There has been an increasing interest developing from a number of factors in the use of wheels made from light metal - primarily aluminum, but also magnesium. The most important reasons are: reduced weight, particularly of the undamped mass, for better security and comfort improved dissipation of brake heat more attractive design potential improved finish and corrosion resistance suitable for recycling In recent years, the market share for aluminum wheels has therefore risen considerably. Sports cars and expensive luxury cars are areas of the strongest interest. This clearly confirms the advantageous properties of light metal wheels. The limitation on obtaining market shares among most of the less expensive cars is primarily that the higher cost relative to the traditional steel wheel is simply too high. In line with the general trend towards steadily improved performance and increasingly more reliable components, there has been rising interest in light metal wheels. At the same time, there are increasing demands for larger brakes. This will require more space and larger wheel dimensions, something which actualizes further the need for light metal wheels. Today, the market for light metal wheels is dominated by aluminium wheels manufactured by casting. This manufacture is based on well-known technology. However, the casting of the wheels is a comprehensive and time-consuming production. Another previously known method is to produce light metal wheels by plastically processing a rim of a disc whereby the rim is first forged and subsequently split and compressed during a spinning process. Such a method of production is shown in Norwegian patent No. 154908 and the Swedish patent publication Nos. 414592 and 414593. Production of light metal wheels by plastic processing using a rim as a starting point is, however, an expensive method involving large loss of material. In addition, the method gives few possibilities for designing the wheels, and therefore the method has not been widely used. Further, US-A-3822458, forming the base of the preamble of claim 1, reveals a procedure for producing a one-piece light metal wheel where in a first step a plate- or bowl-shaped blank is formed from an ingot by cutting it from such ingot; in a second step the blank is heated and warm pressed in dies of requisite cnfiguration; in a third step the plate-shaped blank is formed in a twopart die to the final configuration; and in a fourth an fifth step the finally shaped blank is split and spinforged to form the rim portions of the wheel. This known procedure is comprehensive and therefore expensive to use. Besides, since the material blank, being formed from a cast billet, is subjected to hot pressing which provides material flow only in the radial direction, there is a great danger of cracks and pores in material of the finished wheel. With the present invention is provided a procedure for producing vehicle wheels which is simpler and cheaper to use as it only comprises four steps, and which provides a wheel with high stenght and without pores or cracks in the material. According to the invention the procedure is characterized in that the second step includes heating of the crude material to a hot rolling temperature and subsequently orbitally rolling the crude billet so as to obtain the rotationally symmetric preformed material as defined in the attached claim 1. In a preferred embodiment of the present invention, the preformed material may, after orbital rolling but before splitting, be extruded or cold forged in order to obtain a specified design for the hub of the wheel. Further, the crude material may be made from an extruded bolt of an aluminium or magnesium alloy. Wheels produced by the inventive process have the following advantageous characteristics: Higher mechanical firmness giving about 15-30% lower weight, improved corrosion resistance, more alternatives for surface treatment, improved utilization of material, capacity for automated production with short process durations, high reproducibility. The invention shall now be described in further detail with the use of examples and with reference to the drawings, where: Fig. 1 shows a sketch of step 2 of the inventive procedure with a crude bolt as defined in claim 1, Fig. 2 shows an alternative procedural step, Figs. 3 and 4 show steps 3 and 4 respectively for the inventive process. As previously stated the prior art includes production of light metal wheels by plastically forming a rim of a disc whereby the rim is first forged and subsequently split and pressed during a spinning process. The requisite accuracy for the thickness and roundness of such a rim is critical to produce wheels in accordance with this known method. With the present invention, wheels may be produced without the same requisite accuracy for the basic billet. Consequently, the first step of the inventive method is stated as producing a substantially disc-shaped crude material from a cast billet or a similarly rounded solid metal body. This is a substantially more efficient solution than previously known, since cast material can be used without prior processing. Thus, not only lower material consumption is achieved , but also substantially lower material costs. In the second step, the crude material 1 is processed by a spin-forge roller as shown in Fig. 1a into a rotationally symmetrical material 2 with a particularly specified cross-sectional geometry as shown in Fig. 1b. The rotation occurs between an operatively rotating (not shown) lower implement 3 and a free running upper implement 4, a so-called "sinker". The rotational axes of the two implements form a fixed angle, most often between 1 and 10 degrees. The implements are shaped to give the product its characteristic form. If desired, the lower implement is equipped with plungers 5 in order to facilitate handling of the billet. During orbital rolling, the billet is heated to a rolling temperature dependent upon the type of its constituent material (for example, 450-520 degrees C). The heated material 1 is put on the lower implement (Fig. 1a) which is then rotated. The upper implement moves downwardly and begins to rotate when it meets the workpiece (material). When the material has finished rolling, the upper implement is returned and the finished material can be taken out. For wheels with a rotationally symmetric design of the wheel disc (hub), the orbital rolling constitutes the entire plastic processing of the hub (wheel disc) of the finished wheel product. Aluminium alloys are, however, very well-suited for supplementary plastic cold processing since the alloys are very easily shaped in a soft state. Then, through various processing operations, especially cold forging, one has access to processes giving greater flexibility and many possibilities of variation with substantial freedom of design while the structural and mechanical properties are improved. The process may be conducted in one or several steps, and gives possibilities for great designing complexity, great geometric accuracy and a smooth and fine surface finish. With cold forging, designing possibilities are opened which extend well over the purely rotational symmetric. In practice, the above-mentioned methods provide great possibilities and only very slight limitations in designing freedom. In Figs. 2 a), b) and c), examples of cold forging are shown. The material 2, after the step of orbitally rolling, is pressed between an upper 6 and a lower 7 die in order to give the material a desired design. As indicated above, this procedural step is an optional alternative, not a requisite step of the invention. After the material 2 is orbitally rolled, or alternatively pressed/cold forged, the outer portion which will form the rim surface for the wheel is split off. This is the third step of the inventive process, and is further illustrated in Figs. 3a and 3b. The material, as shown in the drawings, is fixed in a rotating holder 8 and is split along its periphery by a splitting roller 9 into two rings 10 and 11. From the split off material 13, the rim surface is subsequently spin forged into shape in a press as shown in Figs. 4a and 4b. The material is held in a rotating implement comprising upper and lower pressure dies 16 and 17. A roller 12 rolls and stretches the rings 10 and 11 (Fig. 3b) (cf. Fig. 4a) outwardly to rim frame 14,15 which have different lengths (Fig. 4b). This final and fourth step of the inventive process facilitates an optimal material distribution which again results in low material consumption with beneficial economy of weight. Because of improved steadiness in feeding, the spin forged surface also has an advantageous structure and quality compared with cast and machined surfaces. Example 1 A crude material in the form of a disc is produced (cut) from a cast or extruded billet of an AlMgSi-alloy (step 1). The crude disc is heated to an appropriate hot rolling temperature of 520 degrees C and is subsequently orbitally rolled in a roller (step 2) in order to obtain a particular form and size prior to further processing (the sinker of the roller determines the form of the billet). The rolled material can now be further processed in accordance with steps 3 and 4 of the inventive process. But since it is desirable to give the wheel a particular design deviating from the rotationally symmetric, the rolled material is cold forged. Following cold forging, the material is fixed to a splitting operation and is split along the material's periphery (step 3). Subsequently, the rim surface is spin forged (step 4) and after this the wheel has obtained its final form. The wheel undergoes subsequent heat treatment, machining and surface treatment, but these steps are not part of the inventive process. Example 2 A crude material disc is made from a cast or extruded magnesium bolt of the alloy AZ31 (step 1). The crude material is heated to 480 degrees C and is orbitally rolled (step 2). In connection with this heat processing of the billet, recrystallization occurs. So that the preformed billet material will have an adequate toughness during cold forging, the material must be held at a temperature of at least 220 degrees C. After cold forging, the material (step 3) is split and is stress annealed at 450 degrees C. Spinning of the rim surface (step 4) takes place finally at a temperature exceeding 220 degrees C.

Claims: A procedure for producing a one-piece light metal vehicle wheel (18) consisting of hub (19) and a rim portions (14,15), where in a first step a substantially disc-shaped crude material is produced form a cast billet or a similar rounded, solid (1) metal body, in a third step splitting off of the outer portion of a preformed material (2), and in a fourth step forming the rim surface (14,15) by spin forging the outer, split-off rim (14,15) portions (10,11), characterized in that the second step includes heating of the crude material (1) to a hot rolling temperature and subsequently orbitally rolling the crude billet so as to obtain the rotationally symmetric preformed material (2). Procedure according to claim 1, characterized in that the preformed material (1) after orbital rolling and before splitting is pressed or cold forged in order to obtain a desired specified design for the hub of the wheel. Procedure according to claims 1 and 2, characterized in that the crude material (1) is cut from an extruded bolt of an aluminium alloy. Procedure according to claim 1 and 2, characterized in that the crude material (1) is produced from an extruded bolt of a magnesium alloy.

Inventors: BERG OTTO, BERG, OTTO
Applicants: NORSK HYDRO AS, NORSK HYDRO A.S.
Application year: 1992
Main classification: B21K1
IPC codes: B21K1, B21J9, B21H1