Method for forging a metallic workpiece

Abstract

During the forging of a metallic workpiece (W) with at least four forging tools (1, 2) which are mutually opposite in pairs and are mutually angularly offset about the forging axis (S), the workpiece (W) is deformed under prevention of any lateral flow during each forging stroke by the deforming forging tools (1, 2) which enclose the workpiece cross section and is subjected to a hydrostatic pressure all over. In order to achieve in addition to the favorable dense forging due to the hydrostatic pressure Iall over a kneading effect for the desired improvement of the structure, the workpiece (W), prior to the final enclosure of the workpiece cross section and the consequent deformation obstructing the lateral flows is deformed during each forging stroke by an uneven deformation effect of the mutually angularly offset pairs of forging tools (1, 2) in addition with an at least reduced obstruction to lateral flow.

Description

FIELD OF THE INVENTION

[0001] The invention relates to a method for forging a metallic workpiece with at least four forging tools which are mutually opposite in pairs and are angularly offset against one another about the forging axis, according to which the workpiece is deformed under prevention of any lateral flow during each forging stroke by the simultaneously deforming forging tools which enclose the workpiece cross section, and is subjected to a hydrostatic pressure all over.

DESCRIPTION OF THE PRIOR ART

[0002] The forging of a metallic workpiece, especially a continuously cast workpiece, is to substantially close the blowholes and pores occurring during the solidification of the molten metal and reduce the occurring segregations on the one hand, and on the other hand to break up the solidification structure with its coarse crystal structure and transfer the same to a compact grained state, with the build-up of an all-over hydrostatic pressure being responsible for the compression and thus for the elimination of cavities and a consistent deformation with its destruction of the coarse crystal structure for a re-crystallization and the dependent improvement of the structure.

[0003] The known forging methods can be principally broken down into the two-hammer and the four-hammer method, with the workpiece being forged in the two-hammer method between two forging tools which deform relative to one another and in the four-hammer method between at least four simultaneously forging tools which are disposed mutually opposite in pairs and are mutually angularly offset about the forging axis.

[0004] According to the two-hammer method, an unobstructed lateral flow of the workpiece occurs during each forging stroke through the forging tools which act only upon two mutually opposite sides of the workpiece, so that this material is strongly deformed and kneaded and only a low hydrstatic pressure is allowed to build up. This two-hammer method leads therefore to a very favorable improvement of the structure as a result of the re-crystallization initiated with the deformation. However, a respective dense forging will only occur after several forging passes due to lack of a higher hydrostatic pressure, i.e. only after large quality losses.

[0005] According to the four-hammer method, according to which the same forging tools operate synchronously in the forging plane, the forging tools enclose the workpiece during each forging stroke, thus substantially preventing any lateral flow and the material deformation substantially leading to an elongation of the workpiece, so that due to the weak kneading effect it also only possible to achieve a slight improvement in the structure. Moreover, as a result of the deformation which occurs substantially in the longitudinal direction of the workpiece, different mechanical properties of the material are obtained in the longitudinal and lateral direction. Particularly the impact value decreases in the lateral direction. However, a high hydrostatic pressure is built up by the forging tools which enclose the workpiece cross section all over, which ensures outstandingly dense forging.

SUMMARY OF THE INVENTION

[0006] The invention is therefore based on the object of providing a method of the kind mentioned above which combines in a rational manner the advantages of the two-and four-hammer method and ensures during the forging of a workpiece both a desired improvement of the structure as well as a sufficiently dense forging.

[0007] The invention achieves this object in such a way that the workpiece, prior to the final enclosure of the workpiece cross section and the consequent deformation obstructing the lateral flow, is deformed during each forging stroke by an uneven deformation effect of the mutually angularly offset pairs of forging tools in addition with an at least reduced obstruction to lateral flow.

[0008] Before the workpiece cross section is fully enclosed during forging by the forging tools, it can be kneaded and fulled in a concentrated manner within a suitable passage zone due to a respective uneven deformation effect of the mutually angularly offset pairs of forging tools, because in this passage zone the pairs of forging tools do not grasp and process the workpiece cross section in an even manner, but instead the one pair of forging tools advances in its working effect to the other pair(s) of forging tools and therefore there is only a reduced obstruction to the lateral flow or no obstruction whatsoever. During each forging stroke there is an indepth deformation as a precondition for the desired re-crystallization of the material. The complete enclosure of the workpiece cross section by the forging tools at the end of the forging stroke or in the zone of the end cross section of the forging tools also leads in each forging stroke to a high hydrostatic pressure which acts all over and ensures the respective dense forging. Although the achievable level of the hydrostatic pressure remains lower than the one achieved during the conventional four-hammer method, it is still sufficient to eliminate the cavities in the workpiece which are caused by the casting. The omission of excessive hydrostatic pressure levels allows in contrast to the known four-hammer method the structure-improving workpiece deformation with a lacking or lower obstruction to lateral flow. Relevant for the method is therefore the combination of a deformation with an obstruction to lateral flow and high hydrostatic pressure build-up and a workpiece deformation without any stronger obstruction to lateral flow with an only lower hydrostatic pressure build-up. There can be different zones of said types of deformation in the pass-through direction depending on the workpiece and material as a result of the forging tools. Merely the last zone during the exit of the material from the forging tools will preferably be a zone with deformation obstructing lateral flow in order to enable the calibration of the exiting workpiece.

[0009] In order to achieve the adjacency of deformations with stronger or lower obstruction to lateral flow, the forging tools can be provided with respectively adjusted impact surface shapes and the movement sequences of the forging tools can be influenced in a suitable manner. It is understood that the two measures can also be combined with one another.

[0010] The uneven deformation effect of the mutually angularly offset pairs of forging tools is achieved by using forging tools with differently shaped impact surfaces which converge into the same end cross section, however, as a result of which the one pair of tools with impact surfaces which are bulged in comparison with the impact surfaces of the other pair of tools touches down at first on the workpiece during synchronous forging tool movements and can deform the material in the zone of said bulging with free lateral flow in the time until the later touchdown of the other pair of tools. The end cross section of the impact surfaces which is the same in all tools then finally not only leads to the build-up of a high hydrostatic pressure all over, but also to the calibration of the workpiece leaving the tools.

[0011] A further possibility of an uneven deformation effect is obtained when the mutually angularly offset pairs of forging tools are stroke-moved with a different stroke height from the same lower dead center position, as a result of which there is an uneven immersion in the workpiece despite the simultaneous deformation of the forging tools. The joint lower dead center position again produces the required high hydrostatic pressure and the desired workpiece calibration.

[0012] If the mutually angularly offset pairs of forging tools, which can also be provided with an identical arrangement, are subjected to a different stroke movement which can each be triggered per se, the unevenness of the deformation effect of said pairs of tools can be varied within wide ranges and be adjusted to the respective forging conditions.

BRIEF DESCRIPTION OF THE DRAWING

[0013] The subject matter of the invention is shown schematically in the drawings, wherein:

[0014] FIG. 1.1 to FIG. 1.4 show the performance of the forging method according to the invention on the basis of four tool positions during the forging stroke in a crosssectional view along line I-I in FIG. 3 and 4;

[0015] FIG. 2.1 to FIG. 2.3 show a modified mode of operation according to this forging method on the basis of three tool positions in a forging stroke also in a crosssectional view along line I-I in FIG. 3 and 4;

[0016] FIGS. 3 and 4 show axial sectional views along lines III-III and IV-IV of FIG. 1.4 and 2.3, respectively, and

[0017] FIG. 5 shows a cross-sectional view along line V-V of FIG. 3 and FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] For the purpose of forging a metallic workpiece W with at least four forging tools 1, 2 which are mutually disposed opposite of one another in pairs and are mutually angularly offset about the forging axis S, the workpiece W is deformed by the forging tools 1, 2 enclosing the workpiece cross section during each forging stroke by obstructing lateral flow and subjected to a hydrostatic pressure all over, so that favorable dense forging occurs. In order to also ensure a desired improvement in the structure, the workpiece W, prior to the final enclosure of the workpiece cross section and the thus linked deformation that prevents lateral flow, is additionally deformed during each forging stroke by an uneven deformation effect of the mutually angularly offset pairs of forging tools 1, 2 with at least a reduced obstruction to lateral flow.

[0019] For this purpose, as is indicated in FIGS. 1.1 to 1.4 for example, pairs of forging tools 1, 2 with differently shaped impact surfaces 3, 4 which converge into the same end cross section, however, as a result of which the one pair of tools 1 with its impact surfaces 3 which are bulged as compared with the other pair of tools 2 touches down first on the workpiece W during synchronous forging tool movements and can deform the material of the workpiece W in the zone 5 of said bulging with free lateral flow (FIG. 1.2, FIG. 1.3) in the time until the later touchdown of the other pair of tools 2.

[0020] Another possibility of such an uneven deformation effect is obtained (as is indicated in FIGS. 2.1 to 2.3) when the mutually angularly offset pairs of forging tools 1, 2 are stroke-moved with a different stroke height (FIG. 2.1, FIG. 2.2) from the same lower dead center position (FIG. 2.3), as a result of which there is again an uneven immersion of the forging tools in the workpiece W. This method with different stroke height can be performed with forging tools 1, 2 both of similarly and also differently arranged impact surfaces 3, 4.

[0021] The end of the forging stroke (FIG. 1.4, 2.3) then also leads during each forging stroke to a high hydrostatic pressure all over due to the tools enclosing the workpiece cross section, which hydrostatic pressure ensures the respective dense forging. In the zone of the end cross section of the pairs of forging tools (FIG. 5)9 a zone 6 which obstructs lateral flow and with calibrating deformation will be provided at the exit of the workpiece from the forging tools.

Claims

1. A method for forging a metallic workpiece with at least four forging tools which are mutually opposite in pairs and are mutually angularly offset about the forging axis, according to which the workpiece is deformed under prevention of any lateral flow during each forging stroke by the simultaneously deforming forging tools which enclose the workpiece cross section and is subjected to a hydrostatic pressure all over, wherein the workpiece, prior to the final enclosure of the workpiece cross section and the consequent deformation obstructing the lateral flow, is deformed during each forging stroke by an uneven deformation effect of the mutually angularly offset pairs of forging tools in addition with an at least reduced obstruction to lateral flow.

2. A method as claimed in claim 1, wherein the uneven deformation effect of the mutually angularly offset pairs of forging tools is achieved by using forging tools with differently shaped impact surfaces which converge into the same end cross section,

3. A method as claimed in claim 1 or 2, wherein the mutually angularly offset pairs of forging tools are stroke-moved with a different stroke height from the same lower dead center position.

4. A method as claimed in claim 1 or 2, wherein the mutually angularly offset pairs of forging tools are subjected to a different stroke movement which can each be triggered per se.