Method and device for producing a steering rack
A toothed rack is formed by shaping a rod-shaped blank in a noncutting fashion. For this purpose, two shaping tools are provided, specifically an upper die and a lower die. Negative teeth are provided in the upper die, and in contrast a negative back (that is to say a bed for the back—having a round section—of the toothed rack) is provided in the lower die. Viewed in cross-section through the upper die, the negative teeth extend on both sides as far as into the regions of the lateral burrs which are formed during the shaping process. As a result, the ends of the teeth which are not completely shaped may be removed, together with the lateral burrs, after the shaping process (for example, by milling).
The present invention relates to a method and a device for manufacturing a toothed rack, for use, e.g., in steering gear mechanisms for motor vehicles.
The present invention relates to a method that includes a noncutting shaping process in which the desired toothing of the toothed rack is formed on a blank using shaping tools. For example, the following may be provided in this process: the teeth of the toothed rack are formed by corresponding negative teeth which are provided in one of the two shaping tools (for example in the upper die). The back of the toothed rack is formed by a negative back which is provided in the other shaping tool (for example in the lower die). During the shaping process, two lateral burrs are formed from excess material between the two shaping tools.
BACKGROUND INFORMATIONAccording to German Published Patent Application No. 32 02 254, the negative back which is formed in the lower die is shaped such that the cross-section of the finished toothed rack has an approximately y-shaped section. However, a toothed rack which has a round section is also conventional. An example embodiment of the present invention may be applied in both cross-sectional shapes and also with other possible cross-sectional shapes.
According to German Published Patent Application No. 32 02 254, the length of the negative teeth in the upper die is equal to the desired tooth width in the finished toothed rack. In practice, attempts have been made, by applying orbital pressing, to influence the flow of the material such that the negative teeth are filled as completely as possible with material. In this manner, the desire was to obtain a clean sectional shape over the entire tooth width, as far as possible without subsequent working. However, it has become apparent that such an ideal profile of the shaping process is generally not achievable. In particular, it has not been possible to bring about a situation in which the material in the individual negative tooth penetrates completely into the two end faces of the negative tooth. As a result, only a reduced effective tooth width could therefore be achieved. In other words, the toothing could not be shaped completely in the lateral direction. This has resulted (for example when a conventional toothed rack is applied in a vehicle steering gear mechanism) in a situation in which the compressive load per unit area on the tooth edges increased unacceptably, and there was thus the risk of premature wear.
SUMMARYAn example embodiment of the present invention may provide a method for manufacturing a toothed rack in which the noncutting shaping process may be used to shape the teeth of the toothed rack completely, i.e., the usable tooth width of the toothing is to extend as far as possible over the entire available cross-section of the finished toothed rack. In this context, as in the past, a rod-shaped blank is to be shaped in a noncutting fashion in a single procedure.
An example embodiment of the present invention may provide a device which is suitable for carrying out the method.
According to an example embodiment of the present invention, the noncutting shaping process is configured such that a larger flow of material than in the past occurs on both sides into the lateral burrs. A feature here is that a sufficient quantity of material is pressed into elongations of the negative teeth. In comparison with the past, an enlarged tooth width which extends into the regions of the lateral burrs is thus formed. If the elongated negative teeth are not filled with material completely as far as their end faces, the usable tooth width is nevertheless sufficiently large. Generally, it will extend at least over the entire cross-section of the toothed rack, or even beyond it. If the two burrs with the protruding toothing regions which are not completely formed are disruptive during the later use of the toothed rack, they may be removed, for example, by a cutting processing procedure.
An aspect of an example embodiment of the present invention is that during operation the compressive load per unit area on the tooth edges of the toothed rack assumes at maximum the normal, acceptable value, and the previously existing risk of premature wear may therefore be eliminated.
The device which is suitable for carrying out the previously described method according to an example embodiment of the present invention may have the feature that, viewed in cross-section through the upper die, the length of the negative teeth extends on both sides as far as into the regions of the lateral burrs which are formed.
The free flow of material which may be achieved according to an example embodiment of the present invention (on both sides into the burrs) may be improved even further by pressing some of the material into a widened portion of the negative back. For this purpose there may be provided in the lower die for the negative back to have, on each side in the region of the pressing plane, a recess which extends into the region of the lateral burr which is formed. As a result, thicker lateral burrs than before may be formed, but primarily the material may penetrate into the negative teeth better than before. A the device according to an example embodiment of the present invention, according to which the central axis of the toothed rack is lower in the lower die than the pressing plane, also serves this purpose.
BRIEF DESCRIPTION OF THE DRAWINGS
The rod-shaped blank 11 (with length L1) which is illustrated in
In the upper die 16, negative teeth are provided for shaping the teeth 13 of the toothed rack 12. In a similar manner, a negative back is provided in the lower die 17 for shaping the back 14 of the toothed rack 12. If the blank 11 already has a shape which corresponds to the desired shape of the back 14, the lower die 17 serves, during the shaping of the teeth 13, essentially only to support the blank, and possibly to increase the surface quality of the toothed rack back 14.
The lateral burrs which form between the dies 16 and 17 during the noncutting shaping process are designated by 15 in
The noncutting shaping process may take place using the orbital pressing process described in German Published Patent Application No. 32 02 254. The orbital angle is designated by w in
In the toothed rack 12a and 22a according to
The manufacturing method for the toothed rack 12b or 22b illustrated in
- 11 Blank
- 12, 12a, 12b Toothed rack
- 13, 13a, 13b Teeth
- 14, 14a, 14b Back
- 15, 15a, 15b Burr
- 16, 16a Upper die
- 17, 17a Lower die
- 18 End shaping tool
- 19 Centering element
- 20 Negative teeth
- 22, 22a, 22b Finished toothed rack
Claims
1-8. (canceled)
9. A method for manufacturing a toothed rack, comprising:
- shaping a rod-shaped blank in an orbital pressing process in a non-cutting manner by two shaping tools that are pressed against one another, the shaping including: forming teeth of the toothed rack by corresponding negative teeth arranged in a first one of the two shaping tools; forming a back of the toothed rack by a negative back arranged in a second one of the two shaping tools; forming two lateral burrs from excess material between the two shaping tools; pressing material into elongations of the negative teeth to form an enlarged tooth width that extends into regions of the lateral burrs; and lengthening the blank.
10. The method according to claim 9, wherein the two shaping tools include an upper die, the negative teeth arranged in the upper die.
11. The method according to claim 9, wherein the two shaping tools include a lower die, the negative back arranged in the lower die.
12. The method according to claim 9, wherein the lateral burrs are formed in the lateral burr forming step by pressing material into recesses arranged in a region of a pressing plane of a lower die of the two shaping tools, the lateral burrs formed in the recesses.
13. The method according to claim 9, wherein the lengthening step includes forming a centering device in a region of at least one of two end faces of the blank.
14. The method according to claim 13, wherein the centering device is an internal centering device.
15. The method according to claim 13, wherein the centering device is an external centering device.
Type: Application
Filed: Nov 28, 2002
Publication Date: Jun 2, 2005
Inventor: Alfred Brenner (Heubach)
Application Number: 10/502,580