PROCESS FOR PRODUCING A ROTATIONALLY SYMMETRIC HOLLOW PART AND HOLLOW PART PRODUCED THEREBY
A process for producing a rotationally symmetric hollow part, especially a shaft, including: providing a bar-shaped solid material involving the steps of heating the solid material substantially to forging temperature; cross wedge rolling of the solid material so as to cause weakening in the core zone of the solid material; and inserting at least one rotating mandrel, driven at a predetermined velocity, substantially along the central axis of the cross-wedge-rolled solid material, thus creating a through-hole and to a rotationally symmetric hollow part, especially a shaft.
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1. Field of the Invention
The invention relates to a process for producing a rotationally symmetric hollow part, especially a shaft, as well as to a cross-wedge-rolled rotationally symmetric hollow part.
2. Description of Related Art
It has become increasingly common to produce rotationally symmetric hollow parts that may also serve as a preform for further forming, e.g., stepped shafts, and especially gear shafts, by means of cross wedge rolling. This is performed on flat or round jaw machines. As a result of the rolling process, the outer zones of the cross-wedge-rolled shafts are hardened. The use of solid material results in high weight, which is especially undesirable when such shafts are used in automotive industry. This is why gear shafts are produced or welded with high costs from hollow shafts by using rotary swaging machines, or the shafts are mechanically wrought (gun drilled).
From German Patent Application DE 10 2006 031 564 A1 and corresponding U.S. Patent Application Publication 2009/0312110 A1, the following steps are taken for the production of a hollow rotationally symmetric part:
-
- providing bar-shaped solid material;
- heating the solid material substantially to forging temperature;
- cross wedge rolling of the solid material, thus causing weakening in the core zone of the solid material; and
- inserting at least one mandrel substantially along the central axis of the cross-wedge-rolled solid material, thus creating a through-hole.
However, the resulting hollow parts, especially shafts, still have the drawback that the inner bore has rungs or helicoidal threads, which are created when using pressure mandrels. Finishing work on the inner contour of the hollow shaft is costly and also leads to weakening of the fiber orientation within the shaft. The fact that the shaft is weakened also means that more material is necessary to achieve the same strength, i.e., the weight of the shaft is increased. This is undesirable in view of lightweight construction requirements. Besides, a non-round inner contour leads to considerable problems with centering the shaft, requires extensive refinishing work and inhibits unproblematic, smooth running.
It is therefore a primary object of the present invention to create a process for producing a rotationally symmetric hollow part, so that hollow parts with a smoother inner contour can be produced.
According to the invention, this object is achieved by using rotating mandrels, which can be driven in an appropriate manner to allow controlling of a relative motion between the mandrel and the solid material to be indented so that the inner contour is substantially smooth and the thickness of the walls is substantially constant in every cross section. Thus, it becomes possible to produce a smoother-running hollow part which requires only minor or no balancing work.
Further, the invention relates to a cross-wedge-rolled rotationally symmetric hollow part, especially a shaft, which can be a gear shaft, cam shaft, drive shaft, output shaft, starter clutch shaft, hollow shaft or a preform for other forming parts, which is produced according to the process.
Thus, by inserting the driven rotating mandrels into the inner zone which is weakened during the rolling process as the crystal lattice of the forgeable material is weakened by the rolling movement, a smoothed-out through-hole can be achieved, so that a rotationally symmetric hollow part, such as a hollow shaft, can be easily produced with high precision. This weakening of the bar core during cross wedge rolling is also known as the Mannesmann effect. Due to the high external pressure on the bar during cross wedge rolling, the outer layer of the bar-shaped material is hardened, so that widening the walls becomes easier. By inserting the at least one driven rotating mandrel, a high workpiece precision can be attained as the material remains formed by the exterior forming tools, while the hardening resulting form rolling leads to a shaft with corresponding load capacity.
The at least one mandrel can have any shape, such as a tooth shape, a hexagon, a spin profile, etc. It is also advantageous to have a rounded mandrel front part, so that a smoother inner contour of the hollow part can be obtained. A rotational drive for the mandrel, which is preferably controlled, is well known to a person skilled in the art.
Thus, the process can easily be performed for high piece numbers, where, thanks to the deployed forming technique, a shape is attained that practically corresponds to the final shape, so that there is substantially no need for further finishing of the resulting workpiece, as it requires only minor or no balancing work.
Substantial savings can be realized not only for the workpiece itself, i.e., by saving material, but also by reducing production costs through the simplification of the complex balancing process, which so far has made costly finishing steps necessary.
The hollow shaft has a reduced weight compared to conventional shafts made of solid material, while at the same time maintaining their strength. By inserting a driven and controlled rotating mandrel, the material in the core is displaced outward in a controlled manner. With the material thus pressed against exterior forming tools, a high workpiece precision can be attained.
It can be advantageous to insert two controlled driven rotating mandrels along the ends of the bar-shaped solid material. In this way, the path of the mandrel is shortened and a higher cycle time can be attained. Here, the mandrels are only inserted to the point where they are almost touching each other. In the course of the process, one mandrel is pulled back while the second mandrel is inserted further along an overlap zone.
The mandrels can be advantageously inserted so that they are rotated simultaneously by means of a rotational drive. However, it is also possible to insert the mandrels so that they rotate asynchronously.
A typical shaft according to the invention which is applied as a main gear shaft or layshaft has a diameter of approximately 30 to 200 mm, preferably of 60-150 mm. Of course, higher or lower diameters can also be realized. The shaft advantageously consists of a ductile wrought alloy, such as a 16MnCrS4, 20MnCr5, 20MoCrS4 steel, an aluminum or magnesium alloy, precipitation-hardened steels or any conventional steel known to a person skilled in the art.
In the following, the invention is described in more detail by using an exemplary embodiment of a hollow shaft, to which, however, it is by no means limited, as well as the accompanying drawings.
Thereby, a cross-wedge-rolled hollow shaft is created, for which also bigger diameters are conceivable depending on the size of the machine. Typical dimensions of the shaft are diameters from 30 to 200 mm, and preferably 60-150 mm. Appropriate materials are ductile materials, such as malleable wrought alloys. However, the alloys are by no means restricted to iron alloys—appropriate non-iron alloys or alloys having lower iron content, such as ductile aluminum, titanium or magnesium alloys, may also be used.
For a better understanding of the process,
Through the reciprocating movement of the tool 14, the outer zone 4 of the shaft is hardened, while the negative relief of the tool 12, 14 is transferred as a positive form to the shaft 2 and the shaft core is weakened.
While the invention has been described by way of preferred embodiments, various alternative designs and embodiments for practicing the invention, as defined in the accompanying claims, will be evident to persons skilled in the art.
Claims
1. Process for producing a rotationally symmetric hollow part, comprising the steps of:
- providing a bar-shaped solid material;
- heating the solid material substantially to forging temperature;
- cross wedge rolling of the solid material in a manner causing weakening in a core zone of the solid material; and
- inserting at least one rotating mandrel driven at a predetermined velocity substantially along a central axis of the cross-wedge-rolled solid material in a manner creating a through-hole.
2. Process according to claim 1, wherein said at least one rotating mandrel comprises two rotating mandrels, each of which inserted into a respective one of opposite ends of the bar-shaped solid material.
3. Process according to claim 2, wherein the mandrels are inserted simultaneously.
4. Process according to claim 2, wherein the mandrels are inserted asynchronously.
5. Cross-wedge-rolled rotationally symmetric hollow part in the form of one of a gear shaft, cam shaft, drive shaft, output shaft, starter clutch shaft, hollow shaft and a preform for other forming parts produced by the process of claim 1.
6. Cross-wedge-rolled rotationally symmetric hollow part according to claim 5, wherein the part has a diameter of approximately 30 to 200 mm.
7. Cross-wedge-rolled rotationally symmetric hollow part according to claim 5, wherein the part has a diameter of approximately 60-150 mm.
8. Cross-wedge-rolled rotationally symmetric hollow part, to claim 5, wherein the part is made of a ductile wrought alloy.
9. Cross-wedge-rolled rotationally symmetric hollow part, according to claim 5, wherein the part is made of a material from the group comprising 16MnCrS4, 20MnCr5, and 20MoCrS4 steel.
10. Cross-wedge-rolled rotationally symmetric hollow part, according to claim 5, wherein the part is made of a material from the group comprising a non-iron alloy, aluminum alloy, titanium alloy and magnesium alloy.
Type: Application
Filed: Nov 12, 2012
Publication Date: May 30, 2013
Applicant: GESENKSCHMIEDE SCHNEIDER GMBH (Aalen)
Inventor: Gesenkschmiede Schneider GmbH (Aalen)
Application Number: 13/674,524
International Classification: B21K 1/06 (20060101); B21H 1/18 (20060101);