Method for multi-axis forming of a hollow workpiece and support core for use in such a method

Abstract

In the multi-axis forming of a hollow workpiece (W), in particular a polygonal hollow workpiece, a support core (10) is inserted into the cavity of the hollow workpiece (W) to be formed. This support core comprises two end plates (11), a free-flowing or pasty filling (13) contained between them, and a tension structure (12) connecting the end plates (11) and having a tie rod (15). Before the workpiece-support core assembly is placed in a radial press with a plurality of press jaws (7) that are synchronously radially movable on a press axis (X), and before the workpiece (W) is formed in the radial press by the action of the press jaws (7) on it, reducing at least two radial dimensions, the end plates (11) are clamped against each other by means of the tension structure (12), clamping the filling (13) in the workpiece cavity bounded by the end plates (11).

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 similar components, 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 radially inwards, synchronously, towards the pressing axis. The jaws have a concave pressing surface on the radial inside, 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] DE 10 2012 205 855 A1 discloses a method for forming a part from a workpiece containing a hollow section in a press. Also disclosed is an internal mandrel for the hollow section to be formed, which can be used in carrying out such a method. In this process, the hollow section of the workpiece is filled with mandrel material, which is transformed within the workpiece to form the mandrel. Various possible mandrel materials are mentioned, such as, in particular, gas, rubber compound, granules, clay, and sand; gelable and / or foamable materials, as well as materials that change their viscosity at a transition temperature, are also mentioned.

[0004] From JP 2002 113 524 A, a core intended for insertion into a pipe to be machined is known, which serves to prevent the occurrence of form defects during the machining of the pipe. The core consists of a cylindrical bladder which, after being inserted into the pipe, is expanded by means of a pressurized fluid to form a firm bond against the inner wall of the pipe.

[0005] US Patent 5,823,031 A discloses an expandable core designed for expanding a tube and designed to be inserted into the interior of a tube. This core comprises a cylindrical block made of a flexible material through which a tension member connected to a drive mechanism extends. By means of this tension member, two opposing pressure plates arranged at opposite ends of the block can be moved towards each other to expand the block radially. Such an expandable core is to be used, in particular, for shaping a tube in a die.

[0006] US 2013 / 125608 A1 describes a method and associated apparatus for upsetting a square or rectangular tube, wherein the apparatus has press jaws with which pressure can be applied to the outside of a tube to upset it to a smaller dimension. Inside the tube is a compressible mandrel which, during the upsetting process, applies pressure to the inside of the tube to prevent bulging of the tube wall.

[0007] The present invention is aimed at improving the prior art with regard to the multiaxial forming of hollow workpieces such as tubes or the like, in particular the multiaxial forming of such tubes, etc., with a narrowing of the enclosed cavity in the sense of reducing the cavity cross-section, with respect to the achievable result of the multiaxial forming of a hollow workpiece. In particular, a technically particularly useful solution is to be provided when a polygonal hollow workpiece, in particular a square or hexagonal tube, is to be formed multiaxially with a narrowing of the enclosed cavity.A particularly important aspect of technical usability is considered to be sufficient reproducibility of the corresponding multi-axis forming process, which in turn means in particular that the narrowing of the hollow workpiece in the area of ​​its multi-axis forming does not unintentionally lead to a change in the basic polygonal shape of the workpiece.

[0008] 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 two end plates, a free-flowing or pasty filling contained between them, and a tension structure connecting the end plates and having a tie rod; c) Clamping the end plates against each other by means of the tension structure, thereby clamping the filling into the workpiece cavity bounded by the end plates; d) Placing the workpiece-support core assembly into a radial press with a plurality of press jaws movable synchronously radially on a press axis; e) Forming the workpiece in the radial press by reducing at least two radial dimensions of the workpiece through the action of the press jaws on it; 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.

[0009] 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 means of a support core which in turn is characterized in a characteristic way by the fact that it comprises in particular two end plates clamped against each other by means of a tension structure extending through the cavity of the hollow workpiece and a free-flowing or pasty filling received between them.

[0010] The form of internal support of 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 causes 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 a temporary deformation without adverse consequences; because such a local slight bulging outwards is corrected by the press jaws that subsequently make contact there, so that 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 using the present invention to 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 at least substantially flat wall sections in the area of ​​the narrowing.

[0011] The flexibility of a free-flowing filling that completely fills the cavity of the hollow workpiece, at least in the forming zone, so that it provides defined support to the workpiece wall without hindering the forming process, can be achieved in various ways within the scope of the present invention. According to a first preferred embodiment of the invention, the free-flowing filling consists of particles of a material that is compressible in a defined manner at the pressures that arise in the filling during the forming of the workpiece. Suitable elastomers are particularly well-suited for this purpose.

[0012] In a preferred alternative embodiment, the material from which the particles forming the free-flowing filling are made is not compressible at the pressures that arise; however, the filling particles are deformable (plastically and / or elastically) in such a way that, under the pressure that builds up in the cavity of the workpiece during its deformation, the packing density of the filling particles (and thus the density of the filling as a whole) increases, reducing the pore volume remaining between the filling particles.A comparable effect can be achieved with a filling material in which the filling particles break down into several fragments during the forming of the hollow workpiece – under the influence of the increasing pressure during the forming process; this also leads to a reduction in the pore volume remaining between the (partially fragmented) filling particles and thus a defined increase in the density of the filling as a whole, if a correspondingly high pressure builds up in the cavity of the hollow workpiece during forming. In this respect, a mineral and / or ceramic material is particularly suitable for the filling particles. A suitable filling material for typical applications of the invention is sand, which may be...may contain chemical additives that modify pressure resistance and / or flowability; for example, the filling material can be adjusted to a pasty consistency, similar to soft putty.

[0013] With regard to the multiple reusability of the free-flowing filling, the variant with elastically deformable particles is particularly preferable among the variants presented above.

[0014] Yet another preferred embodiment of the inventive method, in which the (possibly pasty) filling does not change its density (or at least not significantly) during the forming of the hollow workpiece, is characterized by the fact that the distance between the end plates increases precisely during the forming of the workpiece in the radial press. The reducing cross-section of the workpiece in the forming zone is thus (at least partially) compensated for by a defined expansion of the filling along the axis of the workpiece. This can be achieved in particular by a defined expansion of the tensile structure that clamps the two end plates between which the filling is held.Technical embodiments for this can include, in particular, an extension of the tension anchor extending between the two end plates or a compression of compression springs (arranged outside the cavity filled with the free-flowing material), by means of which the end plates are supported on the tension anchor passing through them.

[0015] It is evident, and this should be pointed out as a precaution to avoid misconceptions, that several of the mechanisms described above can also be implemented in a combinatorial manner within the scope of the present invention.

[0016] The filling material located between the two end plates, which fills the cavity of the workpiece to be formed, is—according to a preferred embodiment of the invention—enclosed in a flexible, e.g., membrane-like, shell whose characteristic properties, such as strength and elasticity, can be particularly similar to those of a commercially available balloon. In this way, the free-flowing or pasty filling material does not come into direct contact with the inner wall of the hollow workpiece. This reduces the risk of filling particles adhering to the inner surface of the workpiece during forming and thus contaminating the inside. Furthermore, such "encapsulation" of the filling material offers advantages when removing the support core from the workpiece and subsequently reusing it.

[0017] The easy removal of the support core from the workpiece after forming is facilitated if the end plates do not fit precisely into the workpiece, but rather a slight annular gap remains between the end plate and the workpiece. To prevent the ingress of filling material into this annular gap, a seal is preferably arranged on the side of each end plate facing the filling material. This seal bridges the annular gap and fits tightly against both the end plate and the inner surface of the workpiece.

[0018] 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 advantageously used for tubes or other hollow workpieces with other cross-sectional geometries – e.g., round or oval.

[0019] Another preferred embodiment of the present invention is characterized in that the tension structure, acting as a tension anchor, comprises at least one rod, at least partially provided with an external thread, and a clamping nut cooperating with it. Optionally, particularly when an increase in the distance between the end plates is desired during the forming of the workpiece (so), but the rod has very low compliance, the tension structure can additionally include a compression spring (e.g., in the form of a disc spring or a disc spring assembly, or a helical spring) arranged between the clamping nut and the adjacent end plate of the support core, providing a defined level of compliance.

[0020] Regardless of the individual design of the free-flowing filling and the tensile structure of the support core, a further preferred embodiment of the inventive method provides that, when removing the support core from the cavity of the workpiece (after its forming), the two end plates are removed from the cavity of the workpiece from different sides. In other words, in this embodiment, after the polygonal workpiece has been formed, the support core is disassembled within the formed workpiece in such a way that at least one of the two end plates is separated from the tensile structure, so that it can be removed from the workpiece from a different side than the tensile anchor of the tensile structure.Such a disassemblable support core allows for a very precise adaptation of the geometry of the support core's end plates to the cross-section of the cavity of the polygonal workpiece outside the deformation zone. This proves advantageous for the forming result, particularly in terms of a high degree of reproducibility. In this way, the end plates can help to define and limit the area of ​​forming of the workpiece through its radial compression in the axial direction.

[0021] According to the foregoing 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 by comprising two polygonal end plates, a tension structure connecting them, and a free-flowing filling that can be received between the end plates. With regard to further preferred design features of the support core, reference is made—to avoid repetition—to the foregoing explanations and to the following description of a preferred embodiment of the present invention, which is illustrated in the drawing.

[0022] This shows Fig. 1 shows a 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 and Fig. 3 a longitudinal section through the workpiece support core assembly removed from the radial press after completion of the radial pressing and opening of the radial press.

[0023] 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.

[0024] 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.

[0025] 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 below) is inserted into the square tube 8. Fig. 3) is inserted. This comprises two end plates 11 with a geometry adapted to the inner cross-section of the (undeformed) square tube, a tension structure 12 connecting the two end plates 11, and a free-flowing filling 13 contained in the interior of the square tube 8 between the two end plates 11. The tension structure 12 itself comprises a tension anchor 15 in the form of a tie rod with threads 14 at its ends, which passes through bores 16 provided essentially centrally in the end plates 11 on both sides, as well as a clamping nut 17, a pressure plate 18 with bores through it, and a compression spring 19 at each of the two end regions of the tension anchor 15. The latter is supported on the outside by the associated end plate 11 and thus exerts a preload force on it against the free-flowing filling 13. This filling consists of quartz sand.

[0026] During the radial pressing of the square tube 8, the cross-section of the cavity is reduced in the forming area U. If this reduction in cross-section cannot be compensated for by a corresponding compression of the free-flowing filling 13 enclosed between the two end plates 11, it is displaced axially, with a corresponding outward displacement of the end plates 11 against the preload force of the compression springs 19. Depending on the individual design (length, diameter, material) of the tie rod 15 and its matching to the spring stiffness of the compression springs 19, the tie rod can lengthen to a greater or lesser extent during the radial pressing of the square tube 8, synchronously with the compression of the compression springs 19.

[0027] After completion of the radial pressing and opening of the radial press, the formed square tube 8, together with the support core 10 (i.e., the entire workpiece-support core assembly), is removed from the radial press. The tension structure 12 is released by unscrewing the clamping nut 17 from the drawbar on one side and removing the clamping nut 17, pressure plate 18, and compression spring 19 from the cavity of the square tube 8. The drawbar is then driven out of the square tube 8 in the opposite direction (along with the clamping nut 17, pressure plate 18, and compression spring 19 located on that side). Finally, the two end plates 11 are removed from the square tube 8 on opposite sides, and the filling 13 is shaken out.

[0028] It is recognizable in Fig. 3- exemplified by the end plate 1 shown on the left - the design of the end plate 11 also has a contour reduced in such a way as to leave a narrow annular gap 20 between the end plate 11 and the square tube 8. This annular gap 20 is bridged by a seal 21 resting on the inside of the end plate 11, with its circumferential edge in close contact with the inner wall of the square tube 8.

Claims

1. Method for multi-axial forming of a hollow workpiece (W), in particular a rectangular tube (8), a hexagonal tube or another polygonal hollow workpiece, comprising the following steps: a) providing the hollow workpiece (W) to be formed; b) introducing a support core (10) into the cavity of the workpiece (W), wherein the support core (10) comprises two end plates (11), a pourable or pasty filling (13) received between them and a tensile structure (12) with a tie rod (15) connecting the end plates (11) to each other; c) tensioning the end plates (11) against each other by means of the tensile structure (12) while clamping the filling (13) into the cavity of the workpiece (W); d) inserting the workpiece-support core assembly into a radial press having a plurality of press jaws (7) which can be moved synchronously radially to a press axis (X); e) forming the workpiece (W) in the radial press while reducing at least two radial dimensions of the workpiece by the action of the press jaws (7) thereon; f) opening the radial press; g) removing the formed workpiece (W) from the radial press; h) removing the support core (12) from the cavity of the workpiece (W).

2. The method according to claim 1, characterized in that the particles of the pourable filling (13) consist of a compressible material.

3. The method according to claim 1, characterized in that the particles of the pourable filling (13) consist of an incompressible material.

4. The method according to claim 2 or claim 3, characterized in that during the forming of the hollow polygonal workpiece (W) the packing density of the particles of the pourable filling (13) is increased against a resistance.

5. The method according to claim 1, characterized in that a pasty filling consisting of sand and at least one chemical additive modifying the compressive strength and / or the flowability is used.

6. The method according to one of claims 1 to 5, characterized in that in step e) the distance between the end plates (11) increases.

7. The method according to claim 6, characterized in that in step e) the tensile structure (12) is stretched.

8. The method according to claim 7, characterized in that in step e) the tie rod (15) is stretched.

9. The method according to claim 6 or claim 7, characterized in that in step e) at least one compression spring (19) belonging to the tensile structure (12) is compressed.

10. The method according to one of claims 1 to 9, characterized in that in step h) the two end plates (11) are removed from the cavity of the workpiece (W) on different sides.

11. Support core for use in the method according to claim 1, comprising two end plates (11), a pourable or pasty filling (13) receivable between the end plates and a tensile structure (12) with a tie rod (15) connecting the end plates (11) to each other.

12. The support core according to claim 11, characterized in that the pourable filling (13) consists of mineral material.

13. The support core according to claim 12, characterized in that the pourable filling (13) consists of ceramic particles.

14. The support core according to one of claims 11 to 13, characterized in that the tie rod (15) of the tensile structure (12) is provided at least on one end section with an external thread with which a clamping nut (17) interacts.

15. The support core according to claim 11, characterized in that the pasty filling consists of sand and at least one chemical additive modifying the compressive strength and / or the flowability.

16. The support core according to one of claims 11 to 15, characterized in that the filling (13) is received in a flexible, e.g. membrane-like, cover.

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