Patent Application
20160074922
The invention relates to a method and a device for forming a hollow and essentially rotation-symmetric workpiece.
Methods of the type in question are known from the prior art and are there referred to as pressure rolling method. It is regularly the objective of this method to form an essentially rotation-symmetric hollow piece, for example, a tube shaped hollow piece, wherein its diameter and its wall thickness decrease due to the plastic deformation. Due to the decrease in diameter and wall thickness, the length of the hollow piece regularly increases along a rotation-symmetric axis, i.e., in axial direction. This enables the forming of hollow-shaped workpiece in methods and devices of the type in question in that a forming tool acts on the outer contour of the workpiece, while the workpiece rotates around an axis of rotation, which corresponds to the rotation-symmetric axis of the workpiece within the scope of the manufacturing tolerances of the workpiece. Due to plastic deformation, the material of the workpiece is first displaced through the outer forming tools onto the inner forming tool, until the movement of the material is restrained by the inner forming tool.
As a result, a plastic material flow occurs with three movement components, namely an axial, i.e., oriented parallel to the axis of rotation, a radial, i.e., directed toward the axis of rotation movement component of the flowing material, and one directed perpendicular to these two direction components in the circumferential direction. The workpiece elongates during plastic forming due to the axial movement component.
The disadvantage of such forming methods is that there are high demands on the uniformity of the wall thickness of the used workpiece in the circumferential direction. A so-called whip arm effect as shown in
The occurrence of this so-called whip arm effect when processing workpieces that have great wall thickness irregularities in the direction of the circumference is thus far an unsolved problem for the methods in question.
Even with modified devices that have additional forming tools, for example, as shown in
The problem addressed by the invention is therefore to demonstrate a method and device of the type in question that allows for processing of workpieces with greater irregularities in the wall thickness than is the case according to the prior art.
The method according to the invention provides for a machining process of an area of the workpiece still to be formed during the forming procedure. The device according to the invention is designed accordingly such that a machining tool of the device can act upon the outer contour of the workpiece at the same time as the forming tool.
It has been shown that the undesired, so-called whip arm effect is based on the fact that an irregular wall thickness of the workpiece to be formed in the direction of the circumference leads to an increased material flow in the axial direction in the area of the greatest wall thickness and thus to an increased elongation in the respective area of the workpiece during forming. Although a material flow in the circumferential area is also generated in the direction of the circumference, when the irregularities in the wall thickness become too great, this may no longer be sufficient to bring about an equal distribution of the material around the circumference during forming. The respective surplus material in the gap-like forming zone between outer and inner forming tools can then only evade the forming pressure in the axial direction, which leads to the already described buckling of the formed workpiece.
The outer forming tool, which is preferably a forming roll, is arranged in the axial direction, preferably in the end zone of the inner forming tool. Advantageously, this inner forming tool can be designed as an inner mandrel around which the workpiece to be formed is arranged at the beginning of forming. The preferably free end of the mandrel preferably forms the counter support for the forming process, i.e., it provides the surface against which the inner contour of the workpiece to be formed is pressed during forming.
Preferably, when carrying out the method according to the invention, a first partial area of the workpiece in the axial direction is initially formed by using a machine tool to make the workpiece circumference uniform in size, preferably in the end section such that the formed partial section comes to rest against the inner forming tool. This defines the position of this end zone of the workpiece to be formed relative to the inner forming tool and the area of the workpiece that is formed in this manner will be able to better absorb the reaction forces that arise during the following beginning machining action and introduce them into the forming tools.
These and other features and advantages of the present invention will be better understood by reading the following detailed description, taken together with the drawings herein:
FIG. 1—shows a schematic presentation of a forming method according to the prior art;
FIG. 2—shows a schematic sectional presentation of a forming device according to the prior art; and
FIG. 3—shows a schematic sectional presentation of an exemplary device according to the invention.
The device 1 according to the invention, like the presented device 1,
When carrying out the forming method, the workpiece 4 to be formed is made to rotate around the axis of rotation X relative to the outer forming tool 2. Through the movement of the workpiece 4 to be formed in the feeding direction 5, the workpiece 4 to be formed is pressed through between the outer forming tool 2 and the inner forming tool 3. The superimposition of the feeding movement 5 and the rotation around the axis X results in a helical track that the forming tool 2 follows relative to the workpiece 4 to be formed.
Forming causes the length of the formed workpiece 6 to be elongated compared to the workpiece 4 to be formed.
In the shown example, a first wall thickness 7 of the workpiece 4 to be formed is greater than the second wall thickness 8 of the workpiece 4 to be formed, wherein the areas with the first wall thickness 7 and the second wall thickness 8 are offset to each other in the direction of the circumference.
The differences between the wall thicknesses 7 and 8 lead to an eccentricity of the workpiece 4 to be formed, which leads to the centerline 9 of the outer contour 10 of the workpiece 4 to be formed not to coincide with the axis of rotation X. With the known method, the whip arm effect shown in
The device according to the invention has a machining tool 15,
When carrying out the method according to the invention, it may be useful to pre-form or pre-size a certain area of the workpiece 4 to be formed in advance, without the machining tool 15 machining the workpiece 4 to be formed as the forming is taking place but rather doing this step prior to forming the workpiece. In the shown example, this is the axial area 19 that has an expansion in the axial direction, preferably of at least 1 and/or at most 10 mm.
Another feature of the present invention is the optional provision of a cooling liquid or agent 21 provided by a cooling apparatus 23 comprising a hose and nozzle connected to a source of cooling liquid, as is well known in the art.
Accordingly, the present invention provides a machining tool that is designed and placed such that the machining tool can act upon the outer contour of the workpiece at the same time as that of the forming tool in order to insure that the diameter of the workpiece is uniform before the workpiece is acted upon by the forming tool, to prevent whip or curvature in the workpiece.
Modifications and substitutions by one of ordinary skill in the art are considered to be within the scope of the present invention, which is not to be limited except by the allowed claims and their legal equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 14 003 140.2-1702 | Sep 2014 | EP | regional |
