METHOD FOR THE MULTI-AXIS SHAPING OF A HOLLOW WORKPIECE AND SUPPORTING CORE FOR USE IN THE METHOD

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation under 35 U.S.C. § 120 of International Application PCT/EP2023/065602, filed Jun. 12, 2023, which claims priority to German Application No. 10 2022 114 973.0, filed Jun. 14, 2022, the contents of each of which are incorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates to a method for multiaxial forming of a hollow workpiece, in particular a square tube, a hexagonal tube or another polygonal hollow workpiece.

BACKGROUND

Various technical processes require the multiaxial forming of hollow workpieces such as tubes or similar, namely the multiaxial forming of such tubes etc. with narrowing of the enclosed cavity in the sense of a reduction of the cavity cross-section. For tubular and similar workpieces with a round cross-section, well-known and commonly used radial presses are used for this purpose (see the product range of Uniflex-Hydraulik GmbH, Karben), in which typically eight pressing jaws, which are positioned opposite each other in pairs with respect to a pressing axis, are moved synchronously radially inwards in the direction of the pressing axis driven by a (e.g. hydraulically, electrically or manually operated) drive unit. The relevant pressing jaws each have a concave pressing surface radially inwards with a geometry adapted to the final geometry of the round workpiece to be formed, i.e. its nominal geometry after radial pressing has taken place.

SUMMARY

The present disclosure is directed to improving the existing state of the art in this respect with regard to the achievable result of multiaxial forming of a hollow workpiece. In particular, a technically particularly useful solution is to be provided if a polygonal hollow workpiece, in particular a square or hexagonal tube, is to be formed in multiple axes while narrowing the enclosed cavity. Sufficient reproducibility of the corresponding multiaxial forming is regarded as a particularly important aspect of technical usability, which in turn means in particular that the narrowing of the hollow workpiece in the area of its multiaxial forming does not unintentionally lead to a change in the basic polygonal shape of the workpiece.

The above-mentioned problem may be solved in accordance with method disclosed herein. Accordingly, according to the present disclosure, a method for multiaxial forming of a hollow workpiece, in particular a square or hexagonal tube or another polygonal hollow workpiece, comprises the following steps:

• • a) Providing the hollow workpiece to be formed;
  • b) Inserting a support core into the cavity of the workpiece, wherein the support core comprises a central body with differently oriented cylinder bores communicating with one another and with pistons which are accommodated therein and can be pressurized by a pressurized fluid through a fluid connection of the central body, the differently oriented cylinder bores being offset from one another in the axial direction and cylinder bores of different orientation not being arranged in a common plane;
  • c) Radial expanding of the support core while extending the pistons out of the cylinder bores by pressurizing the pistons (17) with pressurized fluid;
  • d) Inserting the workpiece to be formed into a radial press;
  • e) Radial forming of the workpiece in the radial press with reduction of 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.

Accordingly, a central aspect of methods in accordance with the present disclosure, which interacts synergistically with the other aspects of the method, consists in the support of the—in particular polygonal—hollow workpiece during its forming from the inside, namely by a support core, which in turn is characterized by the fact that it comprises in particular a central body with at least two differently oriented cylinder bores communicating with one another and pistons accommodated therein which can be pressurized by pressurized fluid through a fluid connection of the central body. Under the influence of the pistons, which can be extended (moved) together outwards out of the central body in at least two different directions by the pressurized fluid, the walls of the hollow workpiece can be supported from the inside by the pistons directly or by pressure plates connected to them during the forming process. The support is not rigid, but rather flexible in a defined manner, in that during radial forming of the workpiece the pistons are displaced back inwards into the central body against a hydraulic counter-pressure under the effect of the workpiece formed by the pressing jaws. The direct dependence of the counter-holding force acting on the inside of the workpiece to be formed on the hydraulic counter-pressure acting directly on the pistons, i.e. without any mechanical transmission elements, allows optimum influence on the resistance, taking into account the respective individual conditions, since the hydraulic counter-pressure can be set very precisely and can also be changed easily over the course of the pressing operation. In addition, as the pressurized cylinder bores communicate with each other and therefore the same pressure prevails everywhere, it is possible to ideally coordinate the counter-pressure force provided via the individual pistons in terms of dimension and temporal progression (synchronization). At the end of the radial forming of the workpiece, the hydraulic counter-pressure is released—by opening a hydraulic valve—so that the pistons can be retracted (or pushed back) even further into the central body so that the support core can be removed from the formed workpiece.

This form of supporting the hollow workpiece from the inside, which is possible in the implementation of the present disclosure, substantially reduces the risk of the hollow workpiece unintentionally changing its basic shape during its forming; because the support core, as explained, provides an effect which supports the workpiece from the inside and counteracts the collapse of the walls. This applies in particular to the forming of a polygonal hollow workpiece, because here the advantageous effect of the method is particularly pronounced, namely that the inward collapse of the initially flat wall sections of a polygonal hollow workpiece, which are each bounded by two adjacent edges, is counteracted. Insofar as the support core acting inside the workpiece at the start of radial pressing-when forming a polygonal workpiece, this typically starts at the edges of the polygonal workpiece after the pressing jaws first touch down there-allows or does not prevent (slight) outward bulging of the initially flat wall sections, which are each bounded by two adjacent edges, this remains only a temporary effect without detrimental consequences, because such a local slight outward bulging is corrected again by the pressing jaws that touch down there later, so that in any case at the end of radial pressing the basic polygonal shape of the radially pressed workpiece corresponds optimally to that of the workpiece before radial pressing. By using the present method to reliably prevent the walls from collapsing, 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.

To avoid misconceptions, it is emphasized by way of precaution that the sequence of the process steps can certainly be varied within the scope of the present invention. This applies in particular to the sequence of steps b), c) and d). In a feasible variant of the method, for example, the workpiece can be inserted into the radial press before the support core is inserted into the cavity of the workpiece. Or the workpiece is inserted into the radial press with the support core already inserted into it, i.e. as a workpiece-support core assembly, but the support core is only expanded after the workpiece has been inserted into the radial press. A corresponding flexibility applies with regard to the sequence of steps f), g) and h).

It should also be emphasized that although the advantages achievable with the method disclosured are particularly pronounced in the radial forming of polygonal hollow workpieces, they are not limited to this application. The present method can also be used with advantage for tubes or other hollow workpieces with other—e.g. round or oval-cross-sectional geometries. Furthermore, it should be emphasized that the present method is also and especially suitable for use in applications in which the tube or other hollow workpiece is to be formed multi-axially at one of its two ends in order to form a cross-sectional constriction at the end. The invention is therefore by no means limited to applications in which the workpiece is to be provided with a constriction between two undeformed areas.

According to the above explanations of the method according to the invention, according to another aspect of the present invention, a support core suitable for use in the method is characterized in that it comprises a central body with at least two differently oriented cylinder bores communicating with one another and pistons accommodated therein which can be pressurized by pressurized fluid through a fluid connection of the central body. The differently oriented cylinder bores are offset from each other in the axial direction. In this way, they do not interfere with each other, so that as a result—with a given cross-section of the central body—larger movements of the pistons can be realized compared to the arrangement of the pistons and bores in a common plane. As a precautionary measure to avoid misconceptions, it should be pointed out that the central body does not necessarily have to be straight, i.e. in particular prismatic or cylindrical. Rather, it can also have a curved geometry, i.e. extend along an arcuately curved center line, for example. A support core with such a non-straight central body is particularly suitable for use in connection with curved hollow workpieces, especially pipe bends.

The cylinder bores are preferably realized as through bores, in each of which two pistons travelling in opposite directions are accommodated by applying pressure to a pressure chamber located between them. With this design, a central axially symmetrical support of the workpiece can be realized, unlike in the case of a support core provided for the radial forming of a square tube, in which only two of the walls of the workpiece are supported via pistons (or pressure plates connected to them), while the other two walls are supported directly via the central body resting against them. In a particularly preferred embodiment, at least two pairs of cylinder bores oriented parallel to each other and axially offset to each other are provided. The distribution of the supporting forces to a larger number of pistons that can be achieved in this way allows smaller piston dimensions, which favors the use of the method with comparatively small-dimensioned workpieces. Several pistons traveling in the same direction are preferably connected and coupled to each other via the pressure plates mentioned above.

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 multiaxial 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 in particular be oriented parallel to the axis of the central body. In the case of an arcuately curved central body, however, the pressure plates are typically also curved in the same way. The pressure plates can also be curved or canted in other ways in one or two dimensions, i.e. in particular in the longitudinal direction of the support core and/or transversely to the longitudinal direction of the support core, for example in that they each have a central section extending parallel to the axis of the central body and one or two end section(s) adjoining the central section and oriented at an angle to the central axis. The pressure plates can also each have such a workpiece support surface oriented at an angle to the central axis, so that their entirety describes a pyramidal or conical geometry.

BRIEF DESCRIPTION OF THE DRAWING

With regard to further preferred design features of the support core, reference is made—in order to avoid repetition—to the above explanations and to the following explanation of a preferred embodiment of the present invention, which is illustrated in the drawing.

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 inserted workpiece-support core assembly, in a fully open configuration before the start of radial pressing,

FIG. 2 shows the radial press with inserted workpiece-support core assembly as shown in FIG. 1 in fully closed configuration after completion of radial pressing,

FIG. 3 shows a perspective view in greater detail of the support core used in the embodiment shown in FIGS. 1 and 2 with the piston and pressure plates fully retracted, and

FIG. 4 shows a combined representation comprising a partial longitudinal section (top) and a partial side view (bottom) of the support core according to FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The radial press illustrated partially schematically in the drawing is based on the sufficiently known state of the art in terms of its design, its construction and mode of operation as well as its 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 stationary lower yoke 1 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-only indicated as the tie rods 3 (see double arrow B). In a known manner, the radial press has eight base jaws 4 arranged evenly and concentrically around a pressing axis X, which, as a result of the relative movement of the upper yoke 2 and the lower yoke 1 with respect to each other, can be moved synchronously—when the upper yoke 2 is lowered—radially in the direction of the pressing axis X and—when the upper yoke 2 is raised—radially away from the pressing axis X. Return springs 5 act between adjacent base jaws 4. The base jaws 4 each have a cylindrically curved contact surface 6 on the inside for replaceable pressing jaws 7.

Since the radial press is configured for radial pressing of a polygonal workpiece W, for example a square tube 8 with a square cross-section, the pressing surfaces 9 provided radially on the inside of the pressing jaws 7 are configured specifically; four of the pressing jaws 7 have flat pressing surfaces 9.1, while the pressing surfaces 9.2 of the other four pressing jaws 7 are grooved at an angle. The design of the pressing surfaces 9.1 and 9.2 is coordinated in such a way that they define a square cross-section when the radial press is completely closed (see FIG. 2).

Before the square tube 8 is subjected to radial pressing in the appropriately prepared radial press (see FIGS. 1 and 2), a support core 10 (see also FIGS. 3 and 4) is inserted into the square tube 8, i.e. into its cavity (hollow space) H. The support core comprises an essentially prismatic central body 11 with a central bore 12 extending along the axis A and a total of sixteen cylinder bores 13. These are distributed over two mutually perpendicular planes, which intersect in the axis A. In each case, two cylinder bores 13 are diametrically opposite each other and are aligned with each other in that they are each part of a through bore 14 extending transversely through the central body 11. The total of eight through bores 14 are thus oriented alternately offset to one another in the axial direction, i.e. in the direction of axis A. The central bore 12 forms a channel 15 via which the eight through bores 14 (and thus the sixteen cylinder bores 13) communicate with each other fluidically.

In each cylinder bore 13, sealed by means of an inserted seal 16, a piston 17—guided for displacement along the respective cylinder axis Y, which is perpendicular to the axis A—is accommodated. In each case, four pistons 17, which functionally act in the same direction, are mechanically coupled to each other in parallel via a (common) pressure plate 18, which is connected to the four associated pistons 17 by means of screws 19.

While the central bore 12 at one end of the central body 11 of the support core 10 is sealed tightly by means of 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 pressurized fluid via this connection, and the sixteen cylinder bores 13 can in turn be pressurized simultaneously and with identical pressure via this channel 15. This pressurized fluid application causes the pistons 17 to extend out of the central body 11 (arrow C), causing the pressure plates 18 to move away from the axis A. During this extension of the pistons 17, the two O-rings 24, which serve as anti-loss devices 22 and are placed around pins 23 arranged on the end faces of the pressure plates 18 and extending parallel to axis A, are stretched accordingly. If the O-rings 24 are replaced by veritable, correspondingly strong annular springs, the pistons 17 are extended against an effective restoring force; in this case, the annular springs would each be part of a restoring device provided at the end of the support core 10.

Before radial pressing of the workpiece W inserted into 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 extending the pistons 17 and applying pressure to them as described; the workpiece support surfaces S are then in contact with the associated inner surfaces of the square tube 8. The supply of pressurized fluid into the support core 10 via its fluid connection 21 is then switched to holding the pressurized fluid via a counterpressure valve. As a result, during the radial pressing of the workpiece W, during which the pressure plates 18 are displaced in the direction of the axis A, the pistons 17 move into the cylinder bores 13 in a controlled manner so that the pressurized fluid is drained in a controlled manner through the fluid connection 21 of the central body 11, i.e. flows back into the tank, while maintaining a counterpressure. The back pressure is adjustable so that it can be adapted to the respective workpiece W.

After radial pressing is complete, the counterpressure valve (or a bypass for this purpose) is opened so that the pressure in the pressurized fluid is released and the pistons 17—under the action of the two restoring devices 22—can retract to their maximum retracted position. By retracting the pressure plates 18 accordingly, provided they have not already been displaced into their respective end position during radial pressing of the workpiece W, the support core 10 assumes its configuration with minimum cross-section and can be removed from the formed workpiece W before or after the radial press is opened and, if necessary, the formed workpiece W is removed from it.

In view of the above description of a support core 10 configured for the internal support of a square tube, a person skilled in the art can easily design a support core for the internal support of a hexagonal tube or another hollow polygonal workpiece, for example, by means of a corresponding transfer.