EP0286587B1 - Profiling method for ring-shaped objects, and apparatus for carrying out this method - Google Patents

Description

The present invention relates to a method for profile-forming workpieces designed as ring bodies, in particular for the production of vehicle rims, according to the preamble of patent claims 1. Such a method is known from document GB-A-2 007 134.

For profile shaping of workpieces designed as annular bodies, in particular for the production of vehicle rims, devices are known which have two rotary body-shaped tools which act on a workpiece from opposite sides by changing the mutual distance between them. For molding a vehicle rim, for example, it is clamped with its edge between the upper and lower tools, the molding pressure being produced by reducing the mutual distance between the two tools, between which the rim rim is clamped. The workpiece designed as a rim rotates between the two pressed-on rollers, one roller engaging on the outer side and the other roller on the inner side of the rim. The disadvantage of this method is that the surface pressure on the outer side is approximately three times greater than the corresponding surface pressure on the inner side of the rim. This is apparent from the consideration of Fig. 1, which is the basic arrangement represents such a device purely schematically. With 1 the roller-shaped, upper tool, with 2 also the roller-shaped lower tool and with 3 the workpiece. The tools 1 and 2 are pressed against the workpiece 3 with a force P. The specific pressure on the outside of the workpiece 3 is denoted by P _a and the specific pressure on the inside of the workpiece 3 by P _i . The corresponding radii of the rollers and the workpiece are labeled ra, ri and rw.

verwendet. Dabei bedeutet rm den mittleren Radius der beiden Rollkörper mit den Radien r1 und r2; L die Rollkörperlänge und E den Elastizitätsmodul. Dabei wäre noch zu berücksichtigen, dass: $$\frac{\text{1}}{\text{rm}}\text{=}\frac{\text{1}}{\text{r1}}\text{+}\frac{\text{1}}{\text{r2}}\text{.}$$

To calculate the specific pressure on the outside and inside, the Herz formula is:

used. Here rm means the mean radius of the two rolling elements with the radii r1 and r2; L the roll body length and E the elastic modulus. It should also be taken into account that: $$\frac{\text{1}}{\text{rm}}\text{=}\frac{\text{1}}{\text{r1}}\text{+}\frac{\text{1}}{\text{r2}}\text{.}$$

Dies bedeutet, dass der spezifische Druck auf der Aussenseite des Werkstückes 2,77-mal grösser ist als der spezifische Druck auf der Innenseite des Werkstückes.Using these relationships, the person skilled in the art can easily calculate that the following relationship applies: $$\text{pa = pi 2.77.}$$

This means that the specific pressure on the outside of the workpiece is 2.77 times greater than the specific pressure on the inside of the workpiece.

This disadvantage is accepted in the manufacture of steel rims, so that they can be formed in three rolling operations. The situation is different in the production of light metal ring bodies, e.g. made of aluminium. This disadvantage cannot be accepted here because the soft aluminum reacts too strongly to the uneven surface pressures.

For this reason, the production of vehicle rims from aluminum is particularly difficult and expensive. The production takes place in such a way that appropriately dimensioned aluminum plates are bent into pipes and the free edges are connected to one another by welding, whereupon the machining is carried out in numerous work steps using rotary body-shaped tools.

This manufacturing process has major disadvantages. First of all, the structure of the aluminum ring body at the welding point is changed by giving it a cast-like structure, which significantly reduces the strength at the welding point. The tests carried out showed that in particular the fatigue strength is reduced to a fraction of the original strength, so that a rim formed in this way is prone to breakage at the seams, which can have fatal consequences.

In addition, the uneven surface pressure causes further major disadvantages. The aluminum, which is soft compared to steel, reacts strongly to uneven surface pressures, so that external influences such as impacts easily lead to deformation of the rim.

The purpose of the invention is now to remedy the disadvantages mentioned above and to propose a method for producing profiled workpieces designed as annular bodies, in particular vehicle rims made of aluminum, so that the disadvantages described at the outset are avoided. This purpose is achieved using the proposed method. The method according to the invention consists in the fact that the ring-shaped body to be machined is set in rotation so as to be freely suspended on the circumference and is profiled at the support point with the same specific pressure both on the inside and on the outside.

To form the tubular blank, molten aluminum is either poured into a corresponding permanent metal mold or fed to the mold under high pressure.

In order to achieve the desired uniform specific pressure on the inside and the outside of the ring body, the profile is formed with the convex outside of one tool and with the concave inside of the other tool, which tools are used together and in each case at the same location on the ring-shaped part will.

The device for performing the method has an outer tool with an inner profiling surface and an inner tool arranged inside the outer tool with an outer profiling surface.

It is shown below that if the features defined above are observed, the requirement is met by the specific pressure on the inside and on the outside of the workpiece remaining approximately the same. However, this means that both steel and light alloy rims can be easily manufactured with the same device if required. This significantly simplifies and improves rim production.

• Fig. 1 die rein schematische Anordnung einer bekannten Anlage;
• Fig. 2 die rein schematische Anordnung einer Anlage wie vorgeschlagen;
• Fig. 3 einen Vertikalschnitt durch eine Einrichtung, geeignet für die Ausführung DES VERFAHRENS GEMASS DER ERFINDUNG.
• Fig. 4 einen Horizontalschnitt durch die Einrichtung; und
• Fig. 5 eine schaubildliche Darstellung derselben.

An exemplary embodiment of the subject matter of the invention is shown on the accompanying drawing, namely:

• Figure 1 shows the purely schematic arrangement of a known system.
• Figure 2 shows the purely schematic arrangement of a system as proposed.
• Fig. 3 is a vertical section through a device suitable for carrying out the PROCESS GEM A SS OF THE INVENTION.
• 4 shows a horizontal section through the device; and
• Fig. 5 is a diagrammatic representation of the same.

To produce a tubular blank, which must not have a seam, an aluminum tube is produced with the help of an extrusion press, by means of which a large change in shape is achieved in a single forming step under all-round pressure. A tube is made of initially cast, round strands, which are heated to the press temperature and inserted into the block receiver of an extrusion press and pressed through a die by means of a punch. The result is a tubular structure which has no seam and which is then broken down into individual ring-shaped parts. The ring-shaped parts have a width which corresponds approximately to the width of the ring body which is to be shaped into rims. With this The process is profiled on the outside with the same specific pressure as on the inside.

Further processing takes place in the system according to FIG. 2. The workpiece 4 is designed as an annular body and is profile-shaped with the aid of two interacting, rotary body-shaped tools. For this purpose, an inner roller 5 is provided, by means of which the inner side of the workpiece 4 is machined along the common line of contact at A. The outer surface of the workpiece 4 is formed with the help of an outer roller 6, which touches the workpiece along the same line A, but outside. The inner roller 5 touches the workpiece 4 with its convex outer surface, while the outer roller 6 touches the workpiece 4 with its inner, concave inner surface. The surface pressure on the outside is called P _a and the surface pressure on the inside is called P _i . The inner roller 5 has a radius ri, the workpiece has a radius rw and the outer roller, which is expediently designed as a ring, has a radius ra.

The calculation of the specific internal pressure and external pressure P _i and P _a is again carried out using the Herz formula and results as a result that: pi = pa.

The ratio of the radius rw of the workpiece 4 to the radius ri of the inner roller 5 can be, for example, 1.5.

3, 4 and 5, the practical structure of an example of a device is now suitable for practicing the method, n a explained here:

Such a device has e.g. a housing 7 in which, with the help of ball bearings 8, an outer ring 9 is mounted, which serves to receive the outer tool 10. This outer tool 10 is ring-shaped and has an inner profiling surface 11. An inner tool 12 cooperates with the outer tool 10, which is also designed as a rotating body and has an outer profiling surface 13 which corresponds to the impression of the profiling surface 11. The diameter of the inner tool 12 is substantially smaller than the diameter of the outer tool 10, the arrangement being such that the outer surface of the inner tool 12 touches the inner surface of the outer tool 10. At the point of contact, the workpiece 14 is profiled in such a way that the inner tool 12 is pressed against the outer tool 10. The housing 7 is delimited at the front by an annular bearing cover 15.

The inner tool 12, which is not shown in FIG. 5, is mounted on a shaft 16 which extends through the housing 7 and is mounted outside the housing with the aid of two bearings 17 and 18 which are vertically movable in height . At the other end of shaft 16 facing away from inner tool 12, a hydraulic motor 20 is flanged by means of a flexible coupling 19.

For the vertical height shift of the shaft 16, the bearings 17 and 18 are arranged in sliding paths 21 and 22, which in turn are accommodated in bearing guides 23 and 24. The sliding members 21 and 22 are under the influence of hydraulic presses 25 and 26, the piston rods 27, 28 of which are connected to the sliding members 21 and 22. The hydraulic press 25 is dimensioned much larger than the hydraulic press 26, because, due to the lever arm conditions, a much greater pressure must be exerted with the press 25 than with the press 26, the movement of the two presses being coupled and with the aid of Glass scales 29 is monitored.

30 is another hydraulic motor, which serves to drive the external tool 10. For the sake of completeness, it should also be mentioned that a further shaft 31 serves to receive a side guide 32, by means of which the workpiece 14 is centered in a manner not described in any more detail. The workpiece is transported in and out with the aid of a loading / unloading basket, not shown, which is received on an axially displaceable shaft 33. Finally, it should also be mentioned that a pneumatic cylinder 34 with translation is provided for pivoting the side guide 32 and is fastened to the side plate 35.

The rims to be machined are fed automatically, the rim transport device required for this being attachable to the flanges 36 of the housing 7. The workpiece to be machined 14 reaches the inner tool 12, which is much smaller in diameter than the smallest rim to be machined. The centering takes place by means of the side guide 32. In all these operations, the shaft 16 assumes a lower position in which the piston rods 27 and 28 are retracted. To carry out the profiling, pressure is exerted by means of the hydraulic presses 25 and 26, so that the piston rods 27 and 28 extend and move the shaft 16 upwards, which always maintains a horizontal position. This can be checked by means of the glass scales 29. The actual profiling takes place in cooperation with the external tool 10 in such a way that the corresponding parts are set in rotation, pressure being exerted at the same time. After completion of the workpiece, ie after it has assumed the desired profile shape, the piston rods 27 and 28 are retracted so that the finished workpiece rests on the inner tool 12 and is no longer held by the outer tool 10. With the help of the loading-unloading baskets, the finished workpiece is lifted from the inner tool 12 and transferred to a transporter for further conveyance.

With the device described, workpieces designed as ring bodies, in particular vehicle rims, can be machined both from steel and from light metal, such as aluminum. As mentioned at the beginning, the surface pressures occurring during the profiling process on the inside and on the outside of the workpiece are the same, so that during machining no problems arise from aluminum rims. In this way, the production of vehicle rims can be simplified, cheaper and accelerated.

Claims (2)

1. Method for the profiling of work-pieces constructed as an annular member, in particular for the production of vehicle rims of aluminium, from a seamless, shaped, tubular blank, which is divided into individual annular parts, whereof the width corresponds to the width of the annular member, in which method the annular part to be machined is supported so that it is suspended freely on the periphery, is set in rotation and is profiled at the support point, in which the profiling takes place by means of the convex outer side of a first inner tool in the shape of a body of revolution and with the concave inner side of a second outer tool in the shape of a body of revolution, characterised in that the profiling takes place with the same specific pressure on the inner and outer side, the ratio of the radii of the outer and inner tool used simultaneously at the support point as well as of the work-piece being determined according to the Hertzian formula;

with the condition of identical surface pressure on the inner side and outer side of the work-piece, in which formula r_m represents the average radius of the two tools, L the length of the tool body, E the modulus of elasticity and P the force by which the outer tool and the inner tool is pressed against the work-piece.

2. Method according to Claim 1, characterised in that the profiling takes place with a radius r_i of the inner tool and a radius r_a of the outer tool, which correspond to the relationship $$\frac{{\text{r}}_{\text{a}}}{{\text{r}}_{\text{i}}}\text{=}\frac{{\text{r}}_{\text{w}}{\text{/ r}}_{\text{i}}}{{\text{2 - r}}_{\text{w}}{\text{/ r}}_{\text{i}}}$$

wherein r_w is the radius the work-piece.

Images