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] Method for multi-axial forming of a hollow workpiece and support core for use in the method

[0002] The present invention relates to a method for the multi-axial forming of a hollow workpiece, in particular a square tube, a hexagonal tube or another polygonal hollow workpiece.

[0003] Various technical processes require the multi-axis forming of hollow workpieces such as pipes or the like, namely the multi-axis forming of such pipes etc. with a narrowing of the enclosed hollow space in the sense of a reduction in the hollow space cross-section. In the case of tubular and similar workpieces with a round cross-section, known and conventional radial presses are used for this purpose (cf. the product range of Uni f lex-Hydraulik GmbH, Karben). In these presses, typically eight press jaws, which are arranged opposite one another in pairs with regard to a press axis, are moved synchronously radially inwards in the direction of the press axis under the action of a drive unit (e.g. hydraulically, electrically or manually operated). The press jaws in question each have a concavely curved press surface on the radial inside with a shape adapted to the final geometry of the round workpiece to be formed, i.e.whose target geometry after radial pressing, adjusted geometry.

[0004] The present invention is aimed at improving the existing state of the art with regard to the achievable result of the multi-axial forming of a hollow workpiece. In particular, a technically particularly usable solution is to be provided when a polygonal hollow workpiece, in particular a square or hexagonal tube, is to be multi-axially formed with a narrowing of the enclosed hollow space. A particularly important aspect of technical usability is sufficient reproducibility of the corresponding multi-axial forming, which in turn means in particular that the narrowing of the hollow workpiece in the region of its multi-axial forming does not unintentionally lead to a change in the basic polygonal shape of the workpiece.

[0005] The above-mentioned object is achieved according to the present invention by the method specified in claim 1. Accordingly, according to the present invention, a method for the multi-axial forming of a hollow workpiece, in particular a square or hexagonal tube or other 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 at least two differently oriented, communicating cylinder bores and pistons received in these and pressurized with hydraulic fluid through a fluid connection of the central body; c) Radially spreading the support core while extending the pistons from the cylinder bores by pressurizing the pistons with hydraulic 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;

[0006] A central, essential aspect of the present invention, which interacts synergistically with the other aspects of the method according to the invention, accordingly consists in the support of the - in particular polygonal - hollow workpiece during its forming from the inside, namely by means of a support core, which in turn is characterized in that it comprises in particular a central body with at least two differently oriented, mutually communicating cylinder bores and pistons accommodated in these and which can be pressurized with hydraulic fluid through a fluid connection of the central body.Under the action of the pistons, which can be moved outwards out of the central body in at least two different directions using pressurised 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. The support is not rigid but rather flexible in a defined way. During radial forming of the workpiece, the pistons are pushed back inwards into the central body against a hydraulic counterpressure under the action of the workpiece formed by the press jaws. The direct dependence of the counter-holding force acting on the inside of the workpiece to be formed on the - directly, i.e.The hydraulic counterpressure acting on the pistons - without any mechanical transmission elements - allows optimal influence on the resistance, taking into account the respective individual circumstances, as the hydraulic counterpressure can be adjusted very precisely and, moreover, can be easily changed over the course of the pressing. In addition, as the pressurised cylinder bores communicate with one another and the pressure is therefore identical everywhere, ideal coordination of the counterforce provided by the individual pistons in terms of amount and timing (synchronisation) is possible. At the end of the radial forming of the workpiece, the hydraulic counterpressure is reduced by opening a hydraulic valve, so that the pistons can retract (or be pushed back) even further into the central body, so that the support core can be removed from the formed workpiece.

[0007] This form of support of the hollow workpiece from the inside, which is possible in implementation of the present invention, substantially reduces the risk of the hollow workpiece unintentionally changing its basic shape during its forming; because the support core provides, as explained, an effect that supports the workpiece from the inside and counteracts the collapse of the walls. This applies particularly when forming a polygonal hollow workpiece; because here the advantageous effect of the invention, namely that the inward collapse of the initially flat wall sections of a polygonal hollow workpiece, each delimited by two adjacent edges, is counteracted, is particularly pronounced.To the extent that the support core acting inside the workpiece at the start of the 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 a (slight) outward bulging of the initially flat wall sections delimited by two adjacent edges, this remains only a temporary deformation with no disadvantageous consequences; because such a local slight outward bulging is corrected again by the pressing jaws which later touch down there, so that at the end of the radial pressing the basic polygonal shape of the radially pressed workpiece optimally corresponds to that of the workpiece before the radial pressing.By applying the present invention, it is possible to reliably prevent the walls from collapsing, making it 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 region of the narrowing.

[0008] To avoid any misunderstandings, it is emphasized as a precaution that within the scope of the present invention the sequence of the method steps can be varied. This applies in particular to the sequence of steps b), c) and d). In a 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 introduced into the cavity of the workpiece. Or the workpiece is inserted into the radial press with the support core already inserted, 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. Corresponding flexibility applies with regard to the sequence of steps f), g) and h).

[0009] It should also be emphasized that the advantages achievable with the invention, although particularly evident in the radial forming of polygonal hollow workpieces, are not limited to this application. The present invention can also be used to advantage with pipes or other hollow workpieces with other cross-sectional geometries, e.g. round or oval. It should also be emphasized that the present invention is also and particularly suitable for use in applications in which the pipe or other hollow workpiece is to be multi-axially formed at one of its two ends in order to form a cross-sectional constriction at the end. The invention is therefore in no way limited to applications in which the workpiece is to be provided with a constriction between two undeformed areas.

[0010] 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 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 in these and pressurized with hydraulic fluid through a fluid connection of the central body. The differently oriented cylinder bores are offset from one another in the axial direction. In this way, they do not interfere with one another, so that as a result - for 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 precaution, to avoid misconceptions, it should be pointed out that the central body does not necessarily have to be straight, i.e.In particular, it must be prismatic or cylindrical. Rather, it can also have a curved geometry, i.e., extend, for example, along an arcuate centerline. A support core with such a non-straight central body is particularly suitable for use in connection with curved hollow workpieces, especially pipe bends.

[0011] The cylinder bores are particularly preferably designed as through bores, in each of which two counter-rotating pistons are accommodated by the pressure applied to a pressure chamber located between them. With this design, a central, axis-symmetrical support of the workpiece can be achieved, in contrast to 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 by pistons (or pressure plates connected to them), while the other two walls are supported directly by the central body resting against them. Likewise, in a particularly preferred design, at least two pairs of cylinder bores oriented parallel to one another are provided, axially offset from one another.The distribution of the supporting forces among a larger number of pistons achieved in this way allows for smaller piston dimensions, which favors the use of the invention with comparatively small workpieces. Several pistons acting in the same direction are particularly preferably connected and coupled to one another via the pressure plates mentioned above.

[0012] These pressure plates can be designed in different ways, depending on the geometry of the workpiece to be formed. If the support core is used for 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 in particular be oriented parallel to the axis of the central body. In the case of an arc-shaped curved central body, the pressure plates are typically also curved in a similar way. The pressure plates can also be one- or two-dimensional in another way, i.e.In particular, they can be curved or edged 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 adjoining end sections oriented at an angle to the central axis. The pressure plates can also each have such a workpiece support surface oriented obliquely to the central axis, so that their entirety describes a pyramidal or conical geometry.

[0013] With regard to further preferred design features of the support core, reference is made - in order to avoid repetition - to the above statements and to the following explanation of a preferred embodiment of the present invention, which is illustrated in the drawing.

[0014] This shows

[0015] Fig. 1 is 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,

[0016] Fig. 2 shows the radial press with the workpiece support core assembly inserted according to Fig. 1 in a fully closed configuration after completion of the radial pressing,

[0017] Fig. 3 shows a perspective view in greater detail of the support core used in the embodiment according to Figures 1 and 2 with the pistons and pressure plates fully retracted and

[0018] Fig. 4 shows a combined representation of the support core according to Fig. 3, comprising a partial longitudinal section (top) and a partial side view (bottom). The radial press, which is partially schematically illustrated in the drawing, is based on the well-known prior art in terms of its conception, design and function, as well as its structural features (cf., for example, DE 10 2011 015 706 A1, 2 and the product range of Uni f lex-Hydraulik GmbH, DE-61184 Karben). It comprises a base (not shown), a lower yoke 1 stationary thereto, 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 (cf. double arrow B), which is only indicated in the circumference of the tie rods 3.The radial press has, in a known manner, eight base jaws 4 which are arranged evenly and concentrically around a press axis X and which, as a result of the relative movement of the upper yoke 2 and the lower yoke 1, can be moved synchronously with one another - when the upper yoke 2 is lowered - radially in the direction of the press axis X and - when the upper yoke 2 is raised - radially away from the press 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 radial inside for exchangeable press jaws 7 which can be attached to them.

[0019] Since the radial press is designed for the radial pressing of a polygonal workpiece W, for example in the form of a square tube 8 with a square cross-section, the pressing surfaces 9 provided radially on the inside of the pressing jaws 7 are specifically designed; 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 angled. The design of the pressing surfaces 9.1 and 9.2 is coordinated with one another in such a way that they define a square cross-section when the radial press is completely closed (cf. Fig. 2).

[0020] Before the square tube 8 is subjected to radial pressing in the correspondingly prepared radial press (see Figures 1 and 2), a support core is inserted into the square tube 8, i.e. in its cavity H.

[0021] 10 (see also Figures 3 and 4). This comprises an essentially prismatic central body

[0022] 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 . Two cylinder bores 13 are diametrically opposed to one another and are aligned with one another 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 so as to be alternately offset from one another in the axial direction, i.e. in the direction of the 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 fluidically with one another.

[0023] In each cylinder bore 13, a piston 17 is received, sealed by means of an inserted seal 16, and guided so as to be displaceable along the respective cylinder axis Y, which is perpendicular to the axis A. Four pistons 17, each acting in the same functional direction, are connected in parallel to one another and mechanically coupled to one another via a (common) pressure plate 18, which is connected to the four associated pistons 17 by means of screws 19.

[0024] While the central bore 12 at one end of the central body 11 of the support core 10 is tightly closed by means of a plug 20 screwed into the latter, a fluid connection 21 is provided at the opposite end of the central body 11. Via this connection, the channel 15 can be pressurised with hydraulic fluid, and via this channel 15, the sixteen cylinder bores 13 can in turn be pressurised simultaneously and with identical pressure. Such pressurisation with hydraulic fluid causes the pistons 17 to extend out of the central body 11 (arrow C), whereby the pressure plates 18 move away from the axis A. As the pistons 17 extend, the two O-rings 24 which serve as loss prevention devices 22 and which are each placed around pins 23 which are arranged on the end faces of the pressure plates 18 and extend parallel to the axis A, are stretched accordingly.If the O-rings 24 are replaced by genuine, 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.

[0025] 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 described extension of the pistons 17 via their pressurization; the workpiece support surfaces S are then in contact with the associated inner surfaces of the square tube 8. The system then switches from the supply of pressure fluid to the support core 10 via its fluid connection 21 to holding the clamped pressure fluid via a counter-pressure valve. As a result, during the subsequent radial pressing of the workpiece W, during which the pressure plates 18 are displaced in the direction of the axis A, the pistons 17 are moved into the cylinder bores 13 in a controlled manner such that the pressure fluid is drained through the fluid connection 21 of the central body 11 in a controlled manner while maintaining a counter-pressure, i.e. flows back into the tank.The counter pressure is adjustable so that it can be adapted to the respective workpiece W.

[0026] After the radial pressing has been completed, the back pressure valve (or a bypass for this purpose) is opened so that the pressure in the hydraulic fluid is reduced and the pistons 17 can retract into their maximum retracted position under the action of the two return devices 22. By the corresponding retraction of the pressure plates 18, provided they have not already been displaced into their respective end position 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 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 designed for the internal support of a square tube, a person skilled in the art can, by appropriate transfer, easily design a support core serving for the internal support of, for example, a hexagonal tube or another hollow polygonal workpiece.

Claims

Claims: Method for the multi-axial 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: 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 at least two differently oriented, mutually communicating cylindrical bores (13) and pistons (17) included therein, which can be pressurized with hydraulic fluid through a fluid connection (21) of the central body (11); c) radially expanding the support core (10) by extending the pistons (17) from the cylinder bores (13) by pressurizing the pistons (17) with hydraulic fluid; d) placing the workpiece (W) to be formed into a radial press; e) radially forming the workpiece (W) in the radial press by reducing 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). Method according to claim 1, characterized in that in step e) the pistons (17) are controlled as they move into the cylinder bores (13). Method according to claim 2, characterized in that in step e) the pressurized fluid is released in a controlled manner through the fluid connection (21) of the central body (11) while maintaining a back pressure. Support core for use in the method according to claim 1, comprising a central body (11) with at least two differently oriented, mutually communicating cylinder bores (13) offset from each other in the axial direction of the support core (10), and pistons (17) accommodated therein, which can be pressurized with pressurized fluid through a fluid connection (21) of the central body (11). Support core according to claim 4, characterized in that the cylinder bores (13) are designed as through bores (14) in which two counter-rotating pistons (17) are accommodated.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). Support core according to one of claims 4 to 6, characterized in that they are offset axially from each other, i.e., in the axial direction of the support core (10). at least two pairs of parallel cylindrical bores (13) are provided. Support core according to claim 7, characterized in that the pistons (17) acting in the same direction are coupled to each other via pressure plates (18). Support core according to claim 8, characterized in that the pressure plates (18) each have a flat workpiece support surface (S). Support core according to claim 8, characterized in that the pressure plates (18) each have an uneven, in particular a one- or two-dimensionally curved or bent workpiece support surface (S).

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