Method for the multi-axis shaping of a hollow workpiece, and supporting core for use in the method

Abstract

In the case of multi-axis shaping of a hollow workpiece (W), in particular a polygonal hollow workpiece (W), the hollow space (H) of the latter has introduced into it a supporting core (10), which comprises a central body (11) with at least two differently oriented, inter-communicating cylinder bores (13) and also comprises pistons (17), which are accommodated in these cylinder bores and can be subjected to the action of pressure fluid through a fluid connection (21) of the central body (11). Prior to the radial shaping of the workpiece (W) in a radial press, at least two radial dimensions being decreased in the process, the supporting core (10) is expanded radially, with the pistons (17) being extended out of the cylinder bores (13) by the pistons (17) being subjected to the action of pressure fluid.

Description

[0001] The present invention relates to a method for multi-axial forming of a hollow workpiece, in particular a square tube, a hexagonal tube or another polygonal hollow workpiece.

[0002] Various technical processes require the multi-axis forming of hollow workpieces such as pipes or the like, specifically the multi-axis forming of such pipes, etc., by narrowing the enclosed cavity to reduce its cross-sectional area. For tubular and similar workpieces with a round cross-section, well-known and commonly used radial presses (see the product range of Uniflex-Hydraulik GmbH, Karben) are employed. These presses typically employ eight jaws, arranged in pairs opposite each other along a pressing axis. A drive unit (e.g., hydraulically, electrically, or manually operated) moves them synchronously radially inwards towards the pressing axis. Each jaw has a concave pressing surface on its radial inner surface, with a shape adapted to the final geometry of the round workpiece to be formed.whose target geometry after successful radial pressing, adapted geometry.

[0003] Document EP 0 017 675 A1 describes a method for the multi-axial forming of a hollow workpiece using a support core. The support core comprises a central body with differently oriented, interconnected cylinder bores and pistons housed within these bores, which can be pressurized with hydraulic fluid through a fluid connection in the central body.

[0004] The present invention aims to improve upon the existing state of the art with regard to the achievable results of multiaxial forming of a hollow workpiece. In particular, it seeks to provide a technically advantageous solution for multiaxial forming of a polygonal hollow workpiece, especially a square or hexagonal tube, involving the narrowing of the enclosed cavity. A particularly important aspect of its technical suitability is the sufficient reproducibility of the corresponding multiaxial forming process, which in turn means, in particular, that the narrowing of the hollow workpiece during its multiaxial forming process does not unintentionally alter the fundamental polygonal shape of the workpiece.

[0005] The problem stated above is solved according to the present invention by the method specified in claim 1. Accordingly, a method for the multi-axial forming of a hollow workpiece, in particular a square or hexagonal tube or other polygonal hollow workpiece, according to the present invention, comprises the following steps: a) Providing the hollow workpiece to be formed; b) Inserting a support core into the cavity of the workpiece, the support core comprising a central body with at least two differently oriented, communicating cylinder bores and pistons housed therein, which can be pressurized with hydraulic fluid through a fluid connection of the central body; c) Radially expanding the support core by extending the pistons from the cylinder bores by pressurizing the pistons with hydraulic fluid; d) Placing the workpiece to be formed into a radial press; e) Radially forming the workpiece in the radial press by reducing at least two radial dimensions; f) Opening the radial press; g) Removing the formed workpiece from the radial press; h) Removing the support core from the cavity of the workpiece.

[0006] According to the invention, the differently oriented cylinder bores (13) of the support core are offset from each other in the axial direction, wherein cylinder bores of different orientations are not arranged in a common plane.

[0007] Accordingly, a central, essential aspect of the present invention, which synergistically interacts with the other aspects of the method according to the invention, consists in supporting the - in particular polygonal - hollow workpiece during its forming from the inside, namely by a support core which in turn is characterized in a characteristic way by the fact that it comprises in particular a central body with at least two differently oriented, communicating cylinder bores and pistons received therein, which can be pressurized with hydraulic fluid through a fluid connection of the central body.Under the influence of pistons, which can be moved outwards from the central body in at least two different directions by means of a pressurized fluid, the walls of the hollow workpiece can be supported from the inside during its forming process – either directly by the pistons or by pressure plates connected to them. This support is not rigid, but rather defined and flexible, in that during radial forming of the workpiece, the pistons are forced back inwards into the central body against a hydraulic counter-pressure under the influence of the workpiece being formed by the press jaws. The direct dependence of the counter-force acting on the inside of the workpiece to be formed on the pressure applied directly, i.e.,Without any mechanical transmission elements, the hydraulic back pressure acting on the pistons allows for optimal control of the resistance, taking into account the specific individual conditions. This is because the hydraulic back pressure can be set very precisely and easily varied throughout the pressing process. Furthermore, since the pressurized cylinder bores communicate with each other, ensuring identical pressure throughout, ideal coordination of the counter-force provided by the individual pistons is possible in terms of both magnitude and timing (synchronization). At the end of the radial forming of the workpiece, the hydraulic back pressure is released by opening a hydraulic valve, allowing the pistons to retract (or be forced back) further into the central body, enabling the support core to be removed from the formed workpiece.

[0008] This form of internal support for the hollow workpiece, made possible by the present invention, substantially reduces the risk of the hollow workpiece unintentionally changing its basic shape during forming; because, as explained, the support core provides internal support for the workpiece, counteracting the collapse of the walls. This is particularly true when forming a polygonal hollow workpiece; for here, the advantageous effect of the invention—namely, counteracting the inward collapse of the initially flat wall sections of a polygonal hollow workpiece, each bounded by two adjacent edges—is especially pronounced.Insofar as the internal support core acting within the workpiece allows or does not prevent a (slight) bulging of the initially flat wall sections bounded by two adjacent edges at the beginning of the radial pressing process – when forming a polygonal workpiece, this typically starts at the edges of the polygonal workpiece after the press jaws first make contact there – this remains only a temporary deformation without adverse consequences; because such a local slight bulging outwards is corrected again by the press jaws that subsequently make contact there, so that at least at the end of the radial pressing process the basic polygonal shape of the radially pressed workpiece optimally corresponds to that of the workpiece before the radial pressing.By reliably preventing the walls from collapsing in the application of the present invention, it is possible, for example, to produce locally narrowed square or hexagonal tubes which have a square or hexagonal cross-section with four or six flat wall sections in the area of ​​the narrowing.

[0009] To avoid any misunderstandings, it is emphasized that the sequence of the process steps can be varied within the scope of the present invention. This applies in particular to the sequence of steps b), c), and d). In one feasible variant of the method according to the invention, for example, the workpiece can be inserted into the radial press before the support core is placed into the cavity of the workpiece. Alternatively, the workpiece can be inserted into the radial press with the support core already inserted, i.e., as a workpiece-support core assembly; however, the support core is only expanded after the workpiece has been inserted into the radial press. A similar flexibility applies to the sequence of steps f), g), and h).

[0010] Furthermore, it should be emphasized that while the advantages achievable with the invention are particularly pronounced in the radial forming of polygonal hollow workpieces, they are not limited to this application. The present invention can also be used to advantage with tubes or other hollow workpieces with other cross-sectional geometries – e.g., round or oval. It should also be emphasized that the present invention is particularly suitable for applications where the tube or other hollow workpiece is to be multiaxially formed at one of its two ends to create a cross-sectional constriction at the end. The invention is therefore by no means limited to applications where the workpiece is to be provided with a constriction between two undeformed areas.

[0011] According to the preceding explanations of the method according to the invention, and according to another aspect of the present invention, a support core suitable for use in the method according to the invention is characterized in that it comprises a central body with at least two differently oriented, communicating cylinder bores and pistons received therein, which can be pressurized with hydraulic fluid through a fluid connection of the central body. The differently oriented cylinder bores are axially offset from one another. In this way, they do not interfere with each other, so that, as a result, larger movements of the pistons can be achieved—given a specific cross-section of the central body—compared to an arrangement of the pistons and bores in a common plane. It should be noted, as a precaution to avoid any misconceptions, that the central body is by no means necessarily straight, i.e.,It does not necessarily have to be prismatic or cylindrical. Rather, it can also have a curved geometry, i.e., extend, for example, along an arc-shaped centerline. A support core with such a non-straight central body is particularly suitable for use with curved hollow workpieces, especially pipe bends.

[0012] Particularly preferably, the cylinder bores are designed as through bores, each accommodating two counter-rotating pistons driven by pressure in a space located between them. This design allows for central, axially symmetrical support of the workpiece, unlike a support core intended for the radial forming of a square tube, where only two of the workpiece walls are supported by pistons (or pressure plates connected to them), while the other two walls are supported directly by the central body against them. In a particularly preferred embodiment, at least two pairs of cylinder bores, oriented parallel to each other, are provided axially offset from one another.The resulting distribution of the support forces across a larger number of pistons allows for smaller piston dimensions, which facilitates the use of the invention with comparatively small workpieces. Several pistons acting in the same direction are particularly preferably connected and coupled to each other via the pressure plates already mentioned above.

[0013] These pressure plates can be designed differently depending on the geometry of the workpiece to be formed. If the support core is used in the multi-axis forming of a straight square tube, a straight hexagonal tube, or another straight polygonal hollow workpiece, the pressure plates typically have flat workpiece support surfaces, which can be oriented parallel to the axis of the central body. However, with an arc-shaped central body, the pressure plates are typically also curved. The pressure plates can also be one- or two-dimensional in other ways, i.e.,The pressure plates may be curved or angled, particularly in the longitudinal direction of the support core and / or transversely to the longitudinal direction of the support core, for example, by each having a central section extending parallel to the axis of the central body and one or two end section(s) adjoining this, oriented at an angle to the central axis. The pressure plates may also each have such a workpiece support surface oriented obliquely to the central axis, so that their entirety describes a pyramidal or conical geometry.

[0014] Regarding further preferred design features of the support core, reference is made – to avoid repetition – to the preceding statements and to the following explanation of a preferred embodiment of the present invention, which is illustrated in the drawing.

[0015] This shows Fig. 1 shows a partially schematic vertical section, perpendicular to the press axis, through the relevant area of ​​a radial press designed as a yoke press with the workpiece-support core assembly inserted, in a fully open configuration before the start of radial pressing. Fig. 2 shows the radial press with the workpiece-support core assembly inserted. Fig. 1 In a fully closed configuration after completion of the radial pressing, Fig. 3 shows a perspective view in greater detail of the embodiment according to the Figures 1 and 2 The inserted support core with the pistons and pressure plates fully retracted and Fig. 4 in a combined representation comprising a partial longitudinal section (top) and a partial side view (bottom) show the support core after Fig. 3 .

[0016] The radial press, partially illustrated schematically in the drawing, is based on the well-known state of the art with regard to its conception, construction, function, and structural features (see, for example, DE 10 2011 015 706 A1,2 and the product range of Uniflex-Hydraulik GmbH, DE-61184 Karben). It comprises a base (not shown), a lower yoke 1 stationary relative to it, and an upper yoke 2, which can be moved vertically up and down relative to the lower yoke 1 by means of a drive unit – indicated only by the circumference of the tie rods 3 – (see double arrow B).The radial press has eight base jaws 4 arranged uniformly and concentrically around a press axis X, which, as a result of the relative movement of the upper yoke 2 and lower yoke 1 with respect to each other, are movable synchronously – radially towards the press axis X when the upper yoke 2 is lowered and radially away from the press axis X when the upper yoke 2 is raised. Return springs 5 ​​act between adjacent base jaws 4. Each base jaw 4 has a cylindrically curved contact surface 6 on its radial inner surface for press jaws 7 that can be interchangeably attached to it.

[0017] Since the radial press is designed for radially pressing a polygonal workpiece W, exemplified as a square tube 8 with a square cross-section, the pressing surfaces 9 provided radially inside the press jaws 7 are specifically designed; four of the press jaws 7 have flat pressing surfaces 9.1, while the pressing surfaces 9.2 of the other four press jaws 7 are angled and grooved. The design of the pressing surfaces 9.1 and 9.2 is coordinated in such a way that they form a single contact when the radial press is completely closed (see Figure 1). Fig. 2 ) define a square cross-section.

[0018] Before the square tube 8 is placed in the appropriately prepared radial press for radial pressing (see Figures 1 and 2 ) is subjected to, a support core 10 (see also) is inserted into the square tube 8, i.e. into its cavity H. Figures 3 and 4) introduced. This comprises an essentially prismatic central body 11 with a central bore 12 extending along axis A and a total of sixteen cylindrical bores 13. These are distributed across two mutually perpendicular planes that intersect at axis A. Two cylindrical bores 13 are diametrically opposed to each other and aligned with one another by each forming part of a through bore 14 extending transversely through the central body 11. The eight through bores 14 are thus oriented alternately offset from one another in the axial direction, i.e., in the direction of axis A. The central bore 12 forms a channel 15 through which the eight through bores 14 (and thus the sixteen cylindrical bores 13) communicate fluidically with each other.

[0019] In each cylinder bore 13, a piston 17 is mounted and sealed by means of an inserted seal 16. The piston is guided slidably along the respective cylinder axis Y, which is perpendicular to axis A. Four pistons 17, each acting in the same direction, are mechanically coupled to one another in parallel via a (common) pressure plate 18, which is connected to the respective four pistons 17 by means of screws 19.

[0020] While the central bore 12 at one end of the central body 11 of the support core 10 is tightly sealed by a plug 20 screwed into it, a fluid connection 21 is provided at the opposite end of the central body 11. The channel 15 can be pressurized with hydraulic fluid via this connection, and the sixteen cylinder bores 13 can, in turn, be pressurized simultaneously and at identical pressure via this channel 15. Such pressurization with hydraulic fluid causes the pistons 17 to extend from the central body 11 (arrow C), thereby moving the pressure plates 18 away from the axis A. During this extension of the pistons 17, the two O-rings 24, which serve as retaining rings 22 and are each positioned around pins 23 arranged on the end faces of the pressure plates 18 and extending parallel to the axis A, are stretched accordingly.In the case of replacing the O-rings 24 with veritable, correspondingly strong ring springs, the extension of the pistons 17 takes place against an effective restoring force; in this case, the ring springs would each be part of a restoring device provided at the end of the support core 10.

[0021] Before the radial pressing of the workpiece W placed in the radial press begins, the four pressure plates 18 are brought into contact with the inside of the hollow polygonal workpiece W to be formed by the extension of the pistons 17 via their pressurization, as described above; the workpiece support surfaces S are then in contact with the corresponding inner surfaces of the square tube 8. The supply of pressurized fluid to the support core 10 via its fluid connection 21 is then switched to holding the pressurized fluid via a counter-pressure valve. During the subsequent radial pressing of the workpiece W, in which the pressure plates 18 are displaced towards the axis A, the pistons 17 are controlled and retract into the cylinder bores 13 in such a way that pressurized fluid is released in a controlled manner through the fluid connection 21 of the central body 11, i.e., flows back into the tank, while maintaining a counter-pressure.The counter-pressure is adjustable, so that it can be tailored to the respective workpiece W.

[0022] After completion of the radial pressing, the counter-pressure valve (or a bypass thereof) is opened, thus relieving the pressure in the hydraulic fluid and allowing the pistons 17 to retract to their fully retracted position under the influence of the two return mechanisms 22. By retracting the pressure plates 18 accordingly, unless they were already displaced to their respective end positions during the radial pressing of the workpiece W, the support core 10 assumes its configuration with a minimal cross-section and can be removed from the formed workpiece W – either before or after opening the radial press and, if necessary, removing the formed workpiece W from it.

[0023] In view of the above description of a support core 10 designed for the internal support of a square tube, it is possible for a person skilled in the art, by appropriate transfer, to design a support core serving for the internal support of, for example, a hexagonal tube or another hollow polygonal workpiece.

Claims

1. Method for multiaxial forming of a hollow workpiece (W), in particular a square tube (8), a hexagonal tube or another polygonal hollow workpiece (W), comprising the following steps: formed; a) Providing the hollow workpiece (W) to be formed; b) Inserting a support core (10) into the cavity (H) of the workpiece (W), wherein the support core (10) comprises a central body (11) with differently oriented cylinder bores (13) communicating with one another and with pistons (17) which are accommodated therein and can be pressurized by a pressurized fluid through a fluid connection (21) of the central body (11); c) Radial expanding of the support core (10) while extending the pistons (17) out of the cylinder bores (13) by pressurizing the pistons (17) with pressurized fluid; d) Inserting the workpiece (W) to be formed into a radial press; e) Radial forming of the workpiece (W) in the radial press with reduction of at least two radial dimensions; f) Opening the radial press; g) Removing the formed workpiece (W) from the radial press; h) Removing the support core (10) from the cavity (H) of the workpiece (W), characterized by, the differently oriented cylinder bores (13) being offset from one another in the axial direction and cylinder bores of different orientation not being arranged in a common plane.

2. Method according to claim 1, characterized in that in step e) the pistons (17) move into the cylinder bores (13) in a controlled manner.

3. Method according to claim 2, characterized in that in step e) the pressurized liquid is discharged in a controlled manner through the fluid connection (21) of the central body (11) while maintaining a counterpressure.

4. Support core for use in the method according to claim 1, comprising a central body (11) with differently oriented, mutually communicating cylinder bores (13) and pistons (17) which are accommodated therein and can be pressurized by pressurized fluid through a fluid connection (21) of the central body (11), characterized by the differently oriented cylinder bores (13) being offset from one another in the axial direction and cylinder bores of different orientation not being arranged in a common plane.

5. Support core according to claim 4, characterized in that the cylinder bores (13) are realized as through bores (14), in each of which two pistons (17) travelling in opposite directions are accommodated.

6. Support core according to one of claims 4 or 5, characterized in that the cylinder bores (13) communicate with each other via an axial channel (15).

7. Support core according to one of claims 4 to 6, characterized in that at least two pairs of cylinder bores (13) oriented parallel to one another are provided, offset axially relative to one another, i.e. in the axial direction of the support core (10).

8. Support core according to claim 7, characterized in that the pistons (17) traveling in the same direction are coupled to one another via pressure plates (18).

9. Support core according to claim 8, characterized in that the pressure plates (18) each have a flat workpiece support surface (S).

10. Support core according to claim 8, characterized in that the pressure plates (18) each have an uneven, in particular a one- or two-dimensionally domed or curved workpiece support surface (S).

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