Method for multi-axis forming of hollow workpieces and support core for use in method

Abstract

In a multi-axis forming process of a hollow workpiece (W), in particular a polygonal hollow workpiece (W), a support core (10) is inserted into a cavity (H) of the workpiece, the support core comprising a central body (11) with at least two differently oriented cylinder bores (13) communicating with one another, the support core further comprising pistons (17) accommodated in said cylinder bores, the pistons can be acted upon by means of a pressure liquid via a fluid connection (21) of the central body (11). According to the invention, the piston (17) is moved out of the cylinder bore (13) by acting on the piston (17) by a pressure liquid before the workpiece (W) is radially shaped by reducing at least two radial dimensions in a radial press, whereby the support core (10) is radially expanded.

Description

[0001] The invention relates to a method for multi-axis forming a hollow workpiece, wherein the hollow workpiece is in particular a square tube, a hexagonal tube or other polygonal hollow workpieces.

[0002] Various technical processes require multi-axial forming of hollow workpieces such as tubes, i.e., multi-axial forming of such tubes etc. in such a way that the enclosed cavity is narrowed in the sense of reducing the cavity cross section. For this purpose, radial presses known per se and commonly used (see the product range of Uniflex-Hydraulik GmbH, Karben) can be used for tubular workpieces with a circular cross section, in which usually eight pressing jaws, which are arranged in pairs opposite to each other with respect to the press axis, are moved synchronously radially inwards towards the press axis under the action of a drive unit (e.g., hydraulically, electrically or manually operated). The relevant pressing jaws are each provided with a concavely arched pressing surface radially on the inside, the geometry of which is adapted to the final geometry of the circular workpiece to be formed, i.e., the target geometry after the radial pressing has been completed.

[0003] The technical problem to be solved by the present invention is to improve the prior art in this respect with respect to the achievable effects of multi-axial forming of hollow workpieces. In particular, a technically particularly usable solution is provided when polygonal hollow workpieces, in particular square or hexagonal tubes, are multi-axially formed by narrowing the enclosed cavity. A particularly important aspect of the technical usability is sufficient reproducibility of the corresponding multi-axial forming, which in turn means in particular that the narrowing of the hollow workpiece within its multi-axial forming range does not inadvertently lead to a change in the shape of the basic polygon of the workpiece.

[0004] According to the present invention, the above technical problem is solved by the method given in claim 1. Accordingly, according to the present invention, a method for multi-axis forming of a hollow workpiece, the hollow workpiece is especially a square tube, a hexagonal tube or other polygonal hollow workpiece, the method comprises the following steps:

[0005] a) providing a hollow workpiece to be formed;

[0006] b) inserting a support core into a cavity of the workpiece, wherein the support core comprises a central body having at least two differently oriented, interconnected cylinder bores, and further comprising pistons received in the cylinder bores, which can be acted upon by means of a pressurized liquid via a fluid connection of the central body;

[0007] c) moving the piston out of the cylinder bore by applying pressure fluid to the piston, thereby radially expanding the support core;

[0008] d) placing the workpiece to be formed into a radial press;

[0009] e) radially forming the workpiece in the radial press by reducing at least two radial dimensions;

[0010] f) opening the radial press;

[0011] g) removing the formed workpiece from the radial press;

[0012] h) Removing the support core from the cavity of the workpiece.

[0013] According to this, the main, important aspect of the invention, which works in conjunction with the other aspects of the method according to the invention, is that a hollow workpiece, in particular a polygonal hollow workpiece, is supported from the inside during its forming process, i.e., by a support core, which is characterized in that the support core comprises in particular a central body with at least two differently oriented, interconnected cylinder bores, and pistons accommodated in the cylinder bores, which can be acted upon by means of a pressure fluid via the fluid connection of the central body. Under the action of the pistons, which can be moved outwards from the central body in at least two different directions by means of the pressure fluid, the wall of the hollow workpiece can be supported from the inside during its forming process directly by the pistons or by a pressure plate connected to the pistons. In this case, the support is not rigid, but rather flexible by definition, because during the radial forming of the workpiece, the pistons are pushed inwards back into the central body against the hydraulic back pressure under the action of the workpiece formed by the pressure jaws. The corresponding holding force acting on the inner side of the workpiece to be formed depends directly on the hydraulic back pressure acting directly on the piston, i.e. without any mechanical transmission elements, which allows an optimal influencing of the resistance taking into account the respective individual conditions, since the hydraulic back pressure can be adjusted very accurately and can also be easily changed during the pressing process. In addition, since the cylinder bores to which pressure is applied are connected to one another and the same pressure is therefore present everywhere, the corresponding holding forces provided by the individual pistons can be optimally coordinated in terms of magnitude and time course (synchronization). At the end of the radial forming of the workpiece, the hydraulic back pressure is released by opening the hydraulic valve, so that the piston is retracted (or pushed back) further into the central body, so that the support core can be removed from the formed workpiece.

[0014] This form of supporting the hollow workpiece from the inside, which is achieved in the embodiment of the invention, significantly reduces the risk that the hollow workpiece will inadvertently change its basic shape during its forming process; because the support core, as explained, provides the effect of supporting the workpiece from the inside and counteracting the collapse of the wall. This applies quite particularly to the forming of polygonal hollow workpieces, because the advantageous effect of the invention is particularly prominent here, namely that the inward collapse of the initially flat wall sections of the polygonal hollow workpiece, which are respectively bounded by two adjacent edges, is counteracted. Insofar as the support core acting inside the workpiece allows or does not prevent the initially flat wall sections, which are respectively bounded by two adjacent edges, from bulging outwards (slightly) at the beginning of radial pressing (during the forming process of polygonal workpieces, the support core usually first contacts the edges of the polygonal workpiece before the pressure jaws are placed there), this is still only a temporary deformation without any adverse consequences; because this local slight outward bulging is corrected again by the pressure jaws that are subsequently placed there, so that at least at the end of the radial pressing, the basic polygonal shape of the radially pressed workpiece corresponds optimally to the shape of the workpiece before the radial pressing. Due to the reliable prevention of wall collapse in the use of the invention, it is possible to produce, for example, locally narrowed square tubes or hexagonal tubes which have a square or hexagonal cross section with four or six flat wall sections in the narrowed region.

[0015] In order to avoid misunderstandings, it is emphasized as a precaution that within the scope of the invention, the order of the method steps can be completely changed. This applies in particular to the order of steps b), c) and d). In a feasible variant of the method according to the invention, for example, the workpiece can be placed in a radial press before the support core is inserted into the workpiece cavity. Alternatively, although the workpiece is placed in the radial press together with the support core already inserted therein, i.e. as a workpiece support core as a whole, the support core is not expanded until after the workpiece has been placed in the radial press. A corresponding flexibility also applies to the order of steps f), g) and h).

[0016] It should also be emphasized that, although the advantages achievable by the invention are particularly prominent in the case of radial forming of polygonal hollow workpieces, they are not limited to this application. The invention can also be advantageously used for tubes or other hollow workpieces with other, for example circular or oval, cross-sectional geometries. It should also be emphasized that the invention is also suitable and particularly suitable for use in applications in which tubes or other hollow workpieces are to be multiaxially formed at one of their two ends in order to produce a cross-sectional narrowing at the end. The invention is therefore by no means limited to applications in which the workpiece is provided with a constriction between two undeformed regions.

[0017] According to the above explanation of the method according to the invention, according to a further aspect of the invention, a support core suitable for use in the method according to the invention is characterized in that the support core comprises a central body having at least two differently oriented, interconnected cylinder bores, and the support core also comprises pistons accommodated in the cylinder bores, which can be acted upon by means of a pressure liquid via the fluid connection of the central body. Here, the differently oriented cylinder bores are mutually offset in the axial direction. In this way, the cylinder bores do not interfere with each other, so that, with a predetermined cross-section of the central body, the piston can achieve a greater movement than if the piston and the bore are arranged in a common plane. In order to avoid misunderstandings, it should be pointed out as a precaution that the central body does not have to be straight, i.e., in particular, it does not have to be designed as a prismatic or cylindrical shape. On the contrary, the central body can also have a curved geometry, i.e., for example, it extends along a center line of an arcuate curve. A support core with such a non-straight central body is particularly suitable for curved hollow workpieces, in particular curved pipes.

[0018] Particularly preferably, the cylinder bore is designed as a through hole, in which two pistons are respectively accommodated, which move in opposite directions by acting on the pressure chamber located between them. In this design, an axisymmetric support of the center of the workpiece can be achieved, which is different from the following support core provided for radial forming of square tubes, in which only two wall portions of the workpiece are supported by the piston (or the pressure plate connected thereto), while the other two wall portions are supported directly by the center body resting thereon. Similarly, in a particularly preferred design, at least two cylinder bores oriented parallel to each other in pairs are respectively provided axially offset from each other. In this way, it is possible to distribute the supporting force to more pistons, which can achieve smaller piston sizes, which is conducive to the use of the present invention for relatively small workpieces. It is particularly preferred here that a plurality of pistons acting in the same direction are connected and coupled to each other via the pressure plate already mentioned above.

[0019] These pressing plates can be designed differently depending on the geometry of the workpiece to be formed. If the support core is used for multi-axis forming of rectangular tubes, straight hexagonal tubes or other straight polygonal hollow workpieces, the pressing plates usually have flat workpiece support surfaces, which can be oriented in particular parallel to the axis of the central body. In the case where the central body is curved in an arc, the pressing plates are usually also designed to be similarly curved. The pressing plates can also be bent or folded in other ways, one-dimensionally or two-dimensionally, in particular in the longitudinal direction of the support core and / or transversely to the longitudinal direction of the support core, for example, in such a way that these pressing plates each have a middle section extending parallel to the axis of the central body and one or two end sections connected to the middle section and oriented at an angle relative to the central axis. The pressing plates can also each have a workpiece support surface oriented obliquely relative to the central axis, so that the pressing plate as a whole presents a pyramidal or conical geometry.

[0020] To avoid repetition, reference is made to the above description and the following explanation of a preferred embodiment of the present invention, which is shown in the drawings, for other preferred design features of the support core.

[0021] In the attached picture:

[0022] Figure 1 A partially schematic vertical section through a radial press designed as a yoke press extending perpendicularly to the press axis in this critical region is shown with an inserted workpiece support core assembly and in a completely open state before the start of radial pressing;

[0023] Figure 2 Show according to Figure 1 A radial press having a workpiece support core assembly inserted therein, the radial press being in a fully closed state after radial extrusion is completed;

[0024] Figure 3 In more detail, see Figure 1 and Figure 2 A perspective view of the support core used in the embodiment of FIG. 1 when the piston and the pressure plate are fully moved in; and

[0025] Figure 4 Show according to Figure 3 A combined illustration of a support core, the illustration comprising a partial longitudinal section (above) and a partial side view (below).

[0026] The radial press, which is partially schematically illustrated in the figure, follows the well-known prior art in terms of its design, construction and function as well as its structural features (see, for example, document DE 10 2011 015 706 A1 and the product concept of Uniflex-Hydraulik GmbH DE-61184 Karben). The radial press comprises a base (not shown), a lower yoke 1 fixed relative to the base and an upper yoke 2, which can be moved vertically up and down relative to the lower yoke 1 (see double-headed arrow B) by a drive unit, which is only shown in the region of a tie rod 3. In a known manner, the radial press has eight pressure jaw seats 4 arranged uniformly and concentrically around the press axis X, which can be moved synchronously due to the relative movement of the upper yoke 2 and the lower yoke 1 relative to each other, i.e., when the upper yoke 2 is lowered, these pressure jaw seats can be moved synchronously radially towards the press axis X, and when the upper yoke 2 is raised, these pressure jaw seats can be moved synchronously radially away from the press axis X. A return spring 5 acts between the pressure jaw seats 4 adjacent to each other. The pressure jaw seats 4 each have a cylindrically curved contact surface 6 radially inwardly for a pressure jaw 7 which is replaceably mounted on the pressure jaw seat.

[0027] Since the radial press is used for radially pressing a polygonal workpiece W, for example, a square tube 8 with a square cross section, the pressing surface 9 arranged radially inside the pressing jaws 7 is specially designed; four of the pressing jaws 7 have a flat pressing surface 9.1, while the pressing surfaces 9.2 of the other four pressing jaws 7 are provided with angular grooves. Here, the designs of the pressing surfaces 9.1 and 9.2 are matched to each other, so that when the radial press is fully closed (see Figure 2 ), these extrusion faces define a square cross-section.

[0028] The square tube 8 is subjected to radial compression in a correspondingly prepared radial press (see Figure 1 and Figure 2 ) before the support core 10 (see also Figure 3 and Figure 4 ) is inserted into the square tube 8, i.e. into the cavity H of the square tube. The support core comprises a substantially prismatic central body 11 having a central hole 12 extending along the axis A and a total of sixteen cylinder bores 13. The cylinder bores are distributed in two planes perpendicular to each other and intersecting the axis A. Each two cylinder bores 13 are diametrically opposed and aligned with each other, since the two cylinder bores are each part of a through hole 14 extending transversely through the central body 11. Thus, a total of eight through holes 14 are oriented alternately offset from each other in the axial direction, i.e. in the direction of the axis A. The central hole 12 forms a channel 15, through which the eight through holes 14 (and therefore the sixteen cylinder bores 13) are in fluid communication with each other.

[0029] In each cylinder bore 13 sealed by an embedded seal 16 , a piston 17 is accommodated and guided displaceably along a respective cylinder axis Y perpendicular to the axis A. In this case, four pistons 17 acting in the same direction are mechanically coupled to one another in parallel, more precisely via a (common) pressure plate 18 , which is connected to the four correspondingly assigned pistons 17 via screws 19 .

[0030] The central bore 12 is sealed at one end of the central body 11 of the support core 10 by a plug 20 screwed into the central body, while a fluid connection 21 is provided at the opposite end of the central body 11. Through this fluid connection, the channel 15 can be acted upon by a pressurized fluid, and through this channel 15, the sixteen cylinder bores 13 can in turn be acted upon simultaneously and with equal pressure. This application of pressurized fluid causes the piston 17 to be moved out of the central body 11 (arrow C), so that the pressure plate 18 moves away from the axis A. During the movement of the piston 17, two O-rings 24 serving as a loss prevention device 22 are stretched accordingly, and the two O-rings are respectively arranged around a pin 23 arranged at the end of the pressure plate 18 and extending parallel to the axis A. If the O-rings 24 are replaced by actual, correspondingly stronger annular springs, the piston 17 is moved out against the effective restoring force; in this case, these annular springs are each part of a restoring device arranged at the end of the support core 10.

[0031] Before the radial pressing of the workpiece W placed in the radial press begins, the four pressure plates 18 are internally pressed against the hollow polygonal workpiece W to be formed due to the displacement of the piston 17 by applying pressure thereto; the workpiece support surface S then comes into contact with the corresponding inner surface of the square tube 8. Subsequently, the pressure liquid is supplied to the support core 10 via the fluid connection 21 to the pressure liquid that is clamped by the back pressure valve. Therefore, during the subsequent radial pressing of the workpiece W, the pressure plate 18 is pushed toward the axis A, and the piston 17 is moved into the cylinder bore 13 in such a controlled manner that the pressure liquid is discharged in a controlled manner through the fluid connection 21 of the central body 11 while maintaining the back pressure, i.e. flows back to the tank. The back pressure is adjustable here, so that the back pressure can be adapted to the corresponding workpiece W.

[0032] After the radial pressing is complete, the back pressure valve is opened (or a bypass is opened for this purpose) in order to release the pressure in the pressure fluid and the piston 17 can be retracted into its maximum retracted position under the action of the two restoring devices 22. By correspondingly retracting the pressure plate 18, the support core 10 assumes its configuration with the smallest cross section, as long as the pressure plate has not been pushed into its relevant end position during the radial pressing of the workpiece W, and the support core can be removed from the formed workpiece W before or after the radial press is opened and, if necessary, before or after the formed workpiece W is removed from the radial press.

[0033] According to the above description of the support core 10 designed for the internal support of a square tube, those skilled in the art can easily design a support core for the internal support of, for example, a hexagonal tube or other hollow polygonal workpiece by appropriate transfer.

Claims

1. A method for multi-axis forming of a hollow workpiece (W), wherein the hollow workpiece is in particular a square tube (8), a hexagonal tube or other polygonal hollow workpiece (W), the method comprising the following steps: a) providing a hollow workpiece (W) to be formed; b) inserting a support core (10) into a cavity (H) of a workpiece (W), wherein the support core (10) comprises a central body (11) having at least two differently oriented, interconnected cylinder bores (13), and pistons (17) received in the cylinder bores, which can be acted upon by means of a pressurized liquid via a fluid connection end (21) of the central body (11); c) moving the piston (17) out of the cylinder bore (13) by applying pressure fluid to the piston (17), thereby radially expanding the support core (10); 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).

2. The method according to claim 1, characterized in that In step e), the piston (17) is moved into the cylinder bore (13) in a controlled manner.

3. The method according to claim 2, characterized in that In step e), the pressure fluid is discharged in a controlled manner through the fluid connection (21) of the central body (11) while maintaining the back pressure.

4. A support core for use in the method according to claim 1, the support core comprising a central body (11), the central body having at least two cylinder holes (13) which are mutually offset, differently oriented, and interconnected along the axial direction of the support core (10), the support core also comprising pistons (17) accommodated in the cylinder holes, which can be acted upon by means of pressurized liquid through the fluid connection end (21) of the central body (11).

5. The support core according to claim 4, characterized in that: The cylinder bores (13) are designed as through holes (14), in which two pistons (17) are respectively accommodated and move in opposite directions.

6. The support core according to claim 4 or 5, characterized in that: These cylinder holes (13) are connected to each other through an axial passage (15).

7. The support core according to any one of claims 4 to 6, characterized in that At least two cylinder holes (13) oriented in pairs and parallel to each other are arranged offset from each other in the axial direction, that is, in the axial direction of the support core (10).

8. The support core according to claim 7, characterized in that The pistons (17) acting in the same direction are coupled to each other via a pressure plate (18).

9. The support core according to claim 8, characterized in that The pressing plates (18) each have a flat workpiece supporting surface (S).

10. The support core according to claim 8, characterized in that The pressure plates (18) each have a non-planar workpiece support surface (S), in particular a one-dimensionally or two-dimensionally arched or curved workpiece support surface.

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