EP4292725A1 - Method for multi-axis forming of a hollow workpiece and support core for use in such a method - Google Patents

Abstract

During the multi-axis forming of a hollow workpiece (W), in particular a polygonal hollow workpiece, a support core (10) is introduced into the cavity of the hollow workpiece (W) to be formed, which has two end plates (11), a free-flowing or pasty filling held between them (13) and a tensile structure (12) which connects the end plates (11) to one another and has a tie rod (15). Before the workpiece-support core assembly is inserted into a radial press with a plurality of press jaws (7) which can be moved synchronously radially on a press axis (X) and the workpiece (W), through the action of the press jaws (7) on it, is reduced in the radial press is formed into at least two radial dimensions, the end plates (11) are braced against each other by means of the tensile structure (12), with the filling (13) clamped into the workpiece cavity delimited by the end plates (11).

Description

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.

Various technical processes require the multi-axial forming of hollow workpieces such as pipes or the like, namely the multi-axial forming of such pipes etc. with narrowing of the enclosed cavity in the sense of a reduction in the cavity cross-section. For tubular and comparable workpieces with a round cross-section, known and common radial presses (see the range from Uniflex-Hydraulik GmbH, Karben) are used for this purpose, in which typically eight press jaws, which face each other in pairs with respect to a press axis, are under the effect a drive unit (e.g. hydraulically, electrically or manually operated) can be moved synchronously radially inwards towards the press axis. The pressing jaws in question have a concavely curved pressing surface on the radial inside with a shape that matches the final geometry of the round workpiece to be formed, i.e. H. its target geometry after radial pressing, adjusted geometry.

The DE 10 2012 205 855 A1 discloses a method of forming a part from a hollow section containing workpiece in a press. Also disclosed is an internal mandrel that can be used in carrying out such a method for the hollow section to be formed. Here, the hollow portion of the workpiece is filled with mandrel material, which is converted to form the mandrel in the hollow portion within the workpiece. Various possible mandrel materials are mentioned, in particular gas, rubber mixture, granules, clay and sand; Also mentioned are gelable and/or foamable material and material which changes its viscosity at a transition temperature.

From the JP 2002 113 524 A a core intended for insertion into a pipe to be processed is known, which serves to prevent the occurrence of shape errors when processing the pipe. The core consists of a cylindrical bladder which, after being inserted into the tube, is expanded into firm contact with the inner wall of the tube by means of a fluid supplied under pressure.

The US 5,823,031 A discloses an expandable core intended for expanding a pipe and insertable into the interior of the pipe. This comprises a cylindrical block made of a flexible material, through which a tension member connected to a tension drive extends, by means of which two pressure plates arranged opposite one another on the front side of the block can be moved towards one another in order to expand the block radially. Such an expandable core can be used in particular to shape a tube in a die.

The present invention is aimed at addressing the state of the art that exists with regard to the multi-axial forming of hollow workpieces such as pipes or the like, namely the multi-axial forming of such pipes etc. with narrowing of the enclosed cavity in the sense of a reduction in the cavity cross-section the achievable result of the multi-axis forming of a hollow workpiece. In particular, a particularly technically useful solution is to be provided when a polygonal hollow workpiece, in particular a square or hexagonal tube, is to be formed in multiple axes while narrowing the enclosed cavity. A particularly important aspect of technical usability is considered to be sufficient reproducibility of the corresponding multi-axial forming, which in turn means in particular that the narrowing of the hollow workpiece in the area of its multi-axial forming does not unintentionally lead to a change in the basic polygonal shape of the workpiece.

1. a) Bereitstellen des umzuformenden hohlen Werkstücks;
2. b) Einbringen eines Stützkerns in den Hohlraum des Werkstücks, wobei der Stützkern zwei Endplatten, eine zwischen diesen aufgenommene rieselfähige oder pastöse Füllung und eine die Endplatten miteinander verbindende, einen Zuganker aufweisende Zugstruktur umfasst;
3. c) Verspannen der Endplatten gegeneinander mittels der Zugstruktur unter Einspannung der Füllung in den durch die Endplatten begrenzten Werkstück-Hohlraum;
4. d) Einlegen der Werkstück-Stützkern-Gesamtheit in eine Radialpresse mit einer Mehrzahl von synchron radial auf eine Pressachse bewegbaren Pressbacken;
5. e) Umformung des Werkstücks in der Radialpresse unter Verringerung mindestens zweier Radialabmessungen des Werkstückes durch Einwirkung der Pressbacken auf dieses;
6. f) Öffnen der Radialpresse;
7. g) Entnehmen des umgeformten Werkstücks aus der Radialpresse;
8. h) Entnehmen des Stützkerns aus dem Hohlraum des Werkstücks.

The problem stated above is solved according to the present invention by the method specified in claim 1. Accordingly, according to the present invention, a method for multi-axial forming of a hollow workpiece, in particular a square or hexagonal tube or other polygonal hollow workpiece, comprises the following steps:

1. a) providing the hollow workpiece to be formed;
2. b) Introducing a support core into the cavity of the workpiece, the support core having two end plates, a free-flowing one between them pasty filling and a tensile structure connecting the end plates to one another and having a tie rod;
3. c) Bracing the end plates against each other by means of the tensile structure while clamping the filling into the workpiece cavity delimited by the end plates;
4. d) inserting the workpiece support core assembly into a radial press with a plurality of press jaws that can be synchronously moved radially onto a press axis;
5. e) forming the workpiece in the radial press, reducing at least two radial dimensions of the workpiece through the action of the press jaws on it;
6. f) opening the radial press;
7. g) removing the formed workpiece from the radial press;
8. h) Removing the support core from the cavity of the workpiece.

A central, essential aspect of the present invention, which interacts synergistically with the other aspects of the method according to the invention, is therefore the support of the - in particular polygonal - hollow workpiece during its reshaping from the inside, namely by a support core, which in turn is characterized in a characteristic way is characterized in that it comprises, in particular, two end plates braced against one another by means of a tensile structure extending through the cavity of the hollow workpiece and a free-flowing or pasty filling received between them.

The possible form of supporting the hollow workpiece from the inside in implementation of the present invention substantially reduces the risk that the hollow workpiece will unintentionally change its basic shape during its reshaping; because, as explained, the support core provides an effect that supports the workpiece from the inside and counteracts the collapse of the walls. This is particularly true when forming a polygonal hollow workpiece; because here the advantageous effect of the invention, namely the inward collapse of the initially flat wall sections of a polygonal hollow workpiece, each delimited by two adjacent edges, is particularly pronounced. As far as the support core acting on the inside of the workpiece at the beginning of the radial pressing - when forming a polygonal workpiece, this typically first starts at the edges of the polygonal workpiece, after the pressing jaws first touch down there - a (slight) bulging of the edges caused by two adjacent edges limited, initially flat wall sections to the outside, this remains a temporary deformation without adverse consequences; Because such a local, slight bulging outwards is corrected again by the pressing jaws that are placed there later, so that at least 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 using the present invention to prevent the walls from collapsing, locally narrowed square or hexagonal tubes can be produced, for example, which have a square or hexagonal cross-section with four in the area of the narrowing or have six at least essentially flat wall sections.

The flexibility of a free-flowing filling that fills the cavity of the hollow workpiece at least in the forming zone, so that it has an effect that supports the wall of the workpiece in a defined manner but does not prevent the forming, 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 which is compressible in a defined manner at the pressures that arise in the filling when the workpiece is formed. Suitable elastomers in particular come into consideration here.

In a preferred alternative embodiment, the material from which the particles forming the free-flowing filling are made is, however, not compressible at the pressures that arise; However, the filling particles are deformable (plastically and/or elastically) in such a way that the packing density of the filling particles (and thus the density of the Filling as a whole) increased. A comparable effect can be achieved with a filling material in which filling particles break down into several fragments when the hollow workpiece is formed - under the effect of the pressure that increases during the forming process; because this also leads to a reduction in the between the (partially comminuted) filling particles remaining pore volume and thus a defined increase in the density of the filling as a whole if a correspondingly high pressure builds up in its cavity during the forming of the hollow workpiece. In this respect, a mineral and/or ceramic material is particularly suitable for the filling particles. A filling material that is suitable for common applications of the invention is sand, which can optionally be mixed with chemical additives that modify the pressure resistance and/or flowability; For example, the filling material can be adjusted to a pasty consistency comparable to soft dough.

With regard to the multiple use of the free-flowing filling, of the variants presented above, those with elastically deformable particles are particularly preferred.

Another preferred development of the method according to the invention, in which the (possibly pasty) filling does not change its density (or at least not significantly) when forming the hollow workpiece, is characterized by the fact that the distance is precisely when forming the workpiece in the radial press between the end plates increases. 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 braces the two end plates between which the filling is clamped against one another. Technical designs This can in particular be an expansion of the tie rod extending between the two end plates or a compression of compression springs (arranged outside the cavity filled with the free-flowing filling) via which the end plates are supported on the tie rod passing through them.

As can be seen, which should be pointed out as a precautionary measure in order to avoid misconceptions, several of the mechanisms explained above can also be implemented in a combinatorial manner within the scope of the present invention.

The filling existing between the two end plates and filling the cavity of the workpiece to be formed is - according to a preferred development of the invention - in a flexible, e.g. B. membrane-like shell, the characteristic properties such as strength and stretchability can be particularly similar to those of a commercially available balloon. In this way, the free-flowing or pasty filling does not come into direct contact with the inner wall of the hollow workpiece. This reduces the risk of filling particles sticking to the inner surface of the workpiece when forming it and thus contaminating the inside of the workpiece. Furthermore, such “encapsulation” of the filling has advantages when removing the support core from the workpiece and its subsequent reuse.

The easy removal of the support core from the workpiece after its forming is helped if the end plates do not fit exactly into the workpiece, but rather a clear annular gap remains between the end plate and the workpiece. In order to prevent filling from penetrating into this annular gap, a seal is particularly preferably arranged on the side of the respective end plate facing the filling, which - bridging the annular gap - fits tightly both on the end plate and on the inner surface of the workpiece.

It should be emphasized that the advantages that can be achieved with the invention are particularly noticeable in the radial forming of polygonal hollow workpieces, but are not limited to this application. Even with pipes or other hollow workpieces with other - e.g. B. round or oval cross-sectional geometries, the present invention can be used to advantage.

Another preferred development of the present invention is characterized in that the tension structure comprises, as a tie rod, at least one rod which is provided with an external thread at least in sections and a clamping nut which interacts with it. If necessary, namely in particular when an increase in the distance between the end plates during the forming of the workpiece (see above) is desired, but the rod only has very little flexibility, the tensile structure can also have one between the clamping nut and the adjacent end plate of the support core arranged compression spring providing a defined flexibility (e.g. in the form of a disc spring or a disc spring package or a helical spring).

Regardless of the individual design of the free-flowing filling and the tensile structure of the support core, according to another preferred development of the method according to the invention, it is provided that when the support core is removed from the cavity of the workpiece (after its reshaping), the two end plates are removed from the cavity of the workpiece on different sides Workpiece can be removed. In this development, in other words, after the polygonal workpiece has been formed, the support core in the formed workpiece is dismantled in the sense that at least one of the two end plates is separated from the tensile structure so that it emerges from the workpiece to another side can be removed as the tie rod of the tensile structure. Such dismantling of the support core allows a very precise adaptation of the geometry of the end plates of the support core to the cross section of the cavity of the polygonal workpiece outside the deformation zone, which proves to be advantageous for the result of the forming, especially in the sense of a high degree of reproducibility . In this way, the end plates can help to define the area of deformation of the workpiece through its radial compression in the axial direction.

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 has two polygonal end plates, one connecting them to one another Tensile structure 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 above statements and to the following explanation of a preferred exemplary embodiment of the present invention, which is illustrated in the drawing.

Fig. 1

einen senkrecht zur Pressachse geführten Vertikalschnitt durch den hier maßgeblichen Bereich einer als Jochpresse ausgeführten Radialpresse mit eingelegter Werkstück-Stützkern-Gesamtheit, und zwar in vollständig geöffneter Konfiguration vor Beginn der Radialverpressung,

Fig. 2

die Radialpresse mit eingelegter Werkstück-Stützkern-Gesamtheit gemäß Fig. 1 in vollständig geschlossener Konfiguration nach Abschluss der Radialverpressung und

Fig. 3

einen Längsschnitt durch die der Radialpresse nach Beendigung der Radialverpressung und Öffnen der Radialpresse entnommene Werkstück-Stützkern-Gesamtheit.

This shows

Fig. 1

a vertical section taken perpendicular to the press axis through the relevant area of a radial press designed as a yoke press with the workpiece and support core inserted as a whole, in a completely open configuration before the start of the radial pressing,

Fig. 2

the radial press with the workpiece and support core assembly inserted in accordance with Fig. 1 in a fully closed configuration after completion of radial compression and

Fig. 3

a longitudinal section through the workpiece and support core assembly removed from the radial press after completion of the radial pressing and opening of the radial press.

The radial press, partially illustrated schematically in the drawing, is based on the well-known state of the art in terms of its conception, its construction and functionality as well as its structural features (cf. for example DE 10 2011 015 706 A1 ,2 as well as the product range of Uniflex-Hydraulik GmbH, DE-61184 Karben). It comprises a base (not shown), a lower yoke 1 that is 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 - only indicated in the circumference of the tie rods 3 (see double arrow B). . In a known manner, the radial press has eight base jaws 4 arranged uniformly and concentrically around a press axis Raising the upper yoke 2 - can be moved 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 radially on the inside for press jaws 7 that can be interchangeably attached to them.

Since the radial press is prepared for radial pressing of a polygonal workpiece W, which is designed, for example, as 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 grooved at an angle. The design of the pressing surfaces 9.1 and 9.2 is coordinated with one another in such a way that they can be used when the radial press is completely closed (cf. Fig. 2 ) define a square cross section.

Before the square tube 8 is radially pressed in the appropriately prepared radial press (cf. Figures 1 and 2 ) is subjected, a support core 10 is inserted into the square tube 8 (cf. Fig. 3 ) brought in. This comprises two end plates 11 with a geometry adapted to the inner cross section of the (undeformed) square tube, a tensile structure 12 connecting the two end plates 11 to one another and a free-flowing filling 13 accommodated in the interior of the square tube 8 between the two end plates 11. The tensile structure 12 in turn comprises a tie rod 15 in the form of a tie rod provided with threads 14 at the end, which passes through holes 16 provided essentially centrally in the end plates 11 on both sides, as well as a clamping nut 17 at each of the two end regions of the tie rod 15, a pressure plate 18 which in turn is drilled through a compression spring 19. The latter is supported on the outside of the associated end plate 11 and thus exerts a biasing force against the free-flowing filling 13. This consists of quartz sand.

During the radial compression of the square tube 8, the cross section of the cavity in the forming area U is reduced. To the extent that this cross-sectional reduction cannot be compensated for by a corresponding compression of the free-flowing filling 13 enclosed between the two end plates 11, its displacement takes place in the axial direction with a corresponding displacement of the end plates 11 outwards against the preload force of the compression springs 19. Depending on the individual design (length , diameter, material) of the tie rod 15 and the coordination with the spring hardness of the compression springs 19 can be synchronized in the course of the radial compression of the square tube 8 Compression of the compression springs 19 lengthens the pull rod to a more or less pronounced extent.

After the radial pressing has been completed and the radial press has been opened, the formed square tube 8 together with the support core 10, i.e. H. the workpiece and support core entirety is removed from the radial press. The tension structure 12 is released by unscrewing the tension nut 17 from the tension rod on one of the two sides and removing the tension nut 17 as well as the pressure plate 18 and the compression spring 19 from the cavity of the square tube 8. The pull rod is then driven out of the square tube 8 in the opposite direction (including the clamping nut 17, pressure plate 18 and compression spring 19 on that side). Finally, the two end plates 11 are removed from the square tube 8 on different sides and the filling 13 is shaken out of it.

Can be seen in Fig. 3 - exemplified by the end plate 1 shown on the left - also the design of the end plate 11 with a contour that is reduced compared to the inner dimensions of the square tube 8 in such a way that a narrow annular gap 20 remains 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 and with its peripheral edge close to the inner wall of the square tube 8.

Claims (16)

Method for the multi-axis forming of a hollow workpiece (W), in particular a square 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), the support core (10) having two end plates (11), a free-flowing or pasty filling (13) held between them and one connecting the end plates (11) to one another, comprises a tension structure (12) having a tie rod (15); c) bracing the end plates (11) against each other by means of the tensile structure (12) while clamping the filling (13) into the workpiece cavity delimited by the end plates (11); d) inserting the workpiece support core assembly into a radial press with a plurality of pressing jaws (7) which can be synchronously moved radially onto a press axis (X); e) forming the workpiece (W) in the radial press, reducing at least two radial dimensions of the workpiece through the action of the press jaws (7) on it; 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). Method according to claim 1, characterized in that the particles of the free-flowing filling (13) consist of a compressible material. Method according to claim 1, characterized in that the particles of the free-flowing filling (13) consist of an incompressible material. Method according to claim 2 or claim 3, characterized in that when forming the hollow polygonal workpiece (W), the packing density of the particles of the free-flowing filling (13) is increased against resistance. Method according to claim 1, characterized in that a pasty filling consisting of sand and at least one chemical additive that modifies the compressive strength and / or flowability is used. Method according to one of claims 1 to 5, characterized in that in step e) the distance between the end plates (11) increases. Method according to claim 6, characterized in that in step e) the tensile structure (12) is stretched. Method according to claim 7, characterized in that in step e) the tie rod (15) is stretched Method according to claim 6 or claim 7, characterized in that in step e) at least one compression spring (19) associated with the tensile structure (12) is compressed. 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. Support core for use in the method according to claim 1, comprising two end plates (11), a tensile structure (12) connecting them to one another and a free-flowing or pasty filling (13) which can be received between the end plates. Support core according to claim 11, characterized in that the free-flowing filling (13) consists of mineral material. Support core according to claim 12, characterized in that the free-flowing filling (13) consists of ceramic particles. Support core according to one of claims 11 to 13,
characterized in that the tie rod (15) of the tension structure (12) is provided with an external thread at least on one end section, with which a clamping nut (17) interacts. Support core according to claim 11, characterized in that the pasty filling consists of sand and at least a chemical additive that modifies the compressive strength and/or flowability. Support core according to one of claims 11 to 15, characterized in that the filling (13) is in a flexible, e.g. B. membrane-like shell is included.

Images