Patent Application
20090056400
The invention relates to a method and a device for transversely rolling stepped hollow shafts or cylindrical hollow parts from a pipe. In particular, pipe blanks for manufacturing divided and undivided pipe stabilisers for motor vehicles can be produced in an advantageous manner. They are characterised by virtue of the fact that they have variable diameters and wall thicknesses in regions over their longitudinal axis, which on the one hand leads to a reduction in component weight and on the other hand permits optimal usage of the installation space available. Furthermore, the load-adapted cross-sections permit a uniform tension distribution and thus optimal usage of the material used. When utilising the invention for the pipe-stabiliser application, further advantages can be achieved by eliminating wall thickness fluctuations in the pipe used and by improving the material quality of the pipe surfaces by stretching any decarburization regions present and so-called “phosphate edges”.
Various solutions for transversely rolling stepped hollow shafts or hollow bodies or cup-shaped hollow parts over a mandrel are already known.
In accordance with DD 99 521 A or even DE 199 05 038 A1, the blank is axially compressed between wedge-shaped tools with inner forming tools at the same time during the rolling process and is rolled out starting from the centre to form a double-sided cup-shaped hollow body. The outer contour of the inner forming tools (mandrels) corresponds to the inner contour of the hollow body.
In the broadest sense, the solutions for rolling bearing seats and outer toothings (EP 0 248 983 A1 or DE 199 58 343 A1) or inner toothings (e.g. U.S. Pat. No. 5,765,419) are classified in this group of transverse rolling with profiled mandrels or transverse rolling tools.
Longer hollow shafts are reduced substantially only in wall thickness on a continuously cylindrical mandrel, either continuously (WO 02/55226 A1 or DE 20 04 444 C3) or in sections (DE 101 15 815 A1). The last solution is a type of transverse rolling of a stepped hollow shaft. However, only the outer diameter of the hollow shaft is stepped in sections. The inner diameter is unchanged over its entire length and corresponds to the outer diameter of the mandrel.
In order to produce a pipe-shaped stabiliser for motor vehicles by forming, rotary swaging can be utilised. However, it is not particularly productive in spite of high technical outlay.
It is the object of the invention to provide a solution with which stepped hollow shafts or cylindrical hollow parts with the most varied dimensions and also longer lengths can be rolled in a flexible manner from a pipe using a small number of simple tools.
The object is achieved in accordance with the invention by virtue of the fact that by means of rolling tools which can be radially advanced and are disposed in a planet-like manner around the workpiece the contour of the transition from a central diameter in one portion of the workpiece to the central diameter in an adjacent portion is rolled by means of co-ordinated control of radial advance of the rolling tools and axial feed of the workpiece and a mandrel head having an outer diameter which is adapted to the smallest inner diameter of the two portions is disposed underneath the rolling tools.
It has been found that these transitions can also be rolled without the assistance of a mandrel whose outer profile corresponds to the inner profile of the transition. At the beginning of a transition from a large central diameter to a smaller one, the outer periphery of the mandrel head does not lie against the inner periphery of the workpiece at the instantaneous forming site. Only towards the end of this transition and during rolling of continuous portions having a constant inner diameter does the mandrel perform its typical function. For this purpose, it is disposed underneath the rolling tools.
Tests have demonstrated that it is possible to produce a pipe-shaped stabiliser for motor vehicles with two regions, which are stepped on the end side, and one long central part, which is reduced in diameter and wall thickness, from a pipe having a length of 1.6 m, ca. 22 mm outer diameter and a wall thickness of ca. 4 mm. The process is very productive. It is fundamentally possible to produce the stabiliser in a clamping system.
The friction between the workpiece and the mandrel head is restricted to a minimum. This is achieved on the one hand by a relatively short mandrel head and on the other hand by means of a clearance fit, which is typical for displacement, between the outer and inner diameters of the mandrel head and the workpiece. Moreover, in addition to this clearance a further clearance of at least 0.1 mm is preferably provided which promotes forming and is to be defined as flexing clearance.
The forming procedure is further assisted by virtue of the fact that the workpiece is mounted in support rollers.
Preferably, three support rollers are disposed in each case in one plane in a planet-like manner around the workpiece and are mounted in a stand. They can be radially advanced onto the workpiece. The stands are displaceable in parallel with the workpiece axis. At least one stand is disposed in a stationary manner in proximity to the rolling tools. Particularly in the case of longer workpieces, at least one further stand is provided which preferably moves simultaneously with the workpiece end, to which it is allocated. Overall, the support rollers serve to absorb the “transverse forces” which result from the forming procedure and which are not neutralised by the rolling tools and the active part of the rolling mandrel. Such remaining transverse forces also occur primarily during rolling of the transitions. Moreover, they support the weight of the workpiece parts which protrude over the active (engaged) part of the rolling mandrel.
Preferably, the forming procedure is performed using rolling tools which have a smoothing shoulder and a forming shoulder, wherein preferably the free edge of the smoothing shoulder is rounded off with a radius of 0.5 to 3 mm. Primarily, the short transitions are rolled with this edge. In order to roll transitions which on one portion are short on both sides, the workpiece is preferably turned.
Portions having greater wall thicknesses and consisting of materials which are difficult to form (e.g. high-tensile steels) are heated prior to rolling.
Further features in accordance with the invention are described in the claims and in the exemplified embodiment.
The invention will be demonstrated hereinunder in several exemplified embodiments. In the drawings,
a to 4h show the stepwise formation of a pipe into a hollow shaft.
The device for transversely rolling stepped hollow shafts from a pipe as shown in
Rolling tools 3 are provided at the forming site. They are mounted in radial rolling carriages 2. These rolling carriages can be displaced transversely with the respect to the workpiece 1. The rolling tools 3 are radially advanced therewith. For this purpose, they have a dedicated, preferably hydraulic, drive. The rolling tools 3 are driven about axes in parallel with the workpiece axis by means of the rolling spindle drive 4. During forming, the workpiece 1 is pulled with the axial rolling carriage 5 to the left and at the same time is rotated with the rolling tools 3. The clamping device 6 for clamping the workpiece 1 is located on the axial rolling carriage 5. The forces for pulling the workpiece 1 are applied against the rolling tools 3 by two hydraulic pistons which are disposed in a pivotable manner in the axial rolling carriage 5.
As shown more clearly in
Any remaining transverse forces applied to the workpiece 1 immediately adjacent to the forming site and in each case at the furthest spaced interval from the forming site are absorbed by the support rollers 9.
As shown in
a to 4h illustrate the sequence of forming a hollow shaft which has multiple steps in its central part.
In each case, the workpiece 1 is clamped in the clamping device 6 and is pulled the distance of a feeding path sax. The rolling tools 3 are advanced radially by the distance sr. The respective path length is indicated by the length of the arrow. The direction is given by + and −. During axial feeding, + in the drawing denotes the movement to the left (in the direction of tension of the clamping device 6). The radial advance of the rolling tools in the direction of the workpiece axis is denoted by +, and the opposite direction is denoted by −. Rolling mandrels 8a to 8c which have an outer diameter corresponding to the respective smallest inner diameter of the workpiece are used. The mandrel head has not been illustrated.
In
In
In the next step (
In the steps 4d and 4e (cf.
f and 4g illustrate on the one hand a repetition of the above-described forming steps with the smallest diameter rolling mandrel 8c. A feature of
In the final stage,
In practical tests, a hollow shaft was rolled from an approximately 1.5 m long pipe consisting of 34MnB5 having an outer diameter of about 25 mm and an wall thickness of about 4 mm. In a central portion (ca. 400 mm long) and at the two ends (ca. 200 mm long), the pipe was stepped by about 2 mm at the outer diameter. The wall thickness of the stepped parts was reduced by about 1 mm. The forming portions were heated. The average rolling temperature was 600° C.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2007 041 149.0 | Aug 2007 | DE | national |
