EP4540005A1 - Method for the multi-axis shaping of a hollow workpiece, and supporting core for use in the method - Google Patents

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

METHOD FOR MULTI-AXIS FORMING A HOLLOW WORKPIECE AND SUPPORT CORE FOR USE IN THE METHOD

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 are used for this purpose (cf. the range from Uniflex-Hydraulik GmbH, Karben), in which typically eight press jaws, each facing each other in pairs with respect to a press axis, can be moved synchronously radially inwards towards the press axis under the action of a drive unit (e.g. hydraulically, electrically or manually operated). The pressing jaws in question each have a concave, 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 present invention is aimed at improving the existing state of the art with regard to the achievable result of multi-axial forming to improve 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.

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: a) providing the hollow workpiece to be formed; b) introducing a support core into the cavity of the workpiece, the support core comprising a central body with at least two differently oriented, mutually communicating cylinder bores and pistons accommodated therein which can be acted upon with hydraulic fluid through a fluid connection of the central body; c) Radial expansion of the support core while extending the pistons from the cylinder bores by applying pressure fluid to the pistons; d) placing the workpiece to be formed into a radial press; e) Radial forming of the workpiece in the radial press, reducing 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.

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, a central body with at least two differently oriented cylinder bores that communicate with one another, as well as pistons accommodated in these and which can be acted upon with hydraulic fluid through a fluid connection of the central body. Under the influence of the pistons, which can be moved together outwards from the central body in at least two different directions with the help of a pressurized fluid, the walls of the hollow workpiece can be pressed - by the pistons directly or by pressure plates connected to them - during its forming support from the inside. The support is not rigid, but rather flexible in a defined manner, in that the pistons are under the influence during radial forming of the workpiece of the workpiece formed by means of the press jaws is pushed back inwards into the central body against a hydraulic counter pressure. The direct dependence of the counter-holding force acting on the inside of the workpiece to be formed on the - in a direct way, i.e. H . without any mechanical transmission elements - hydraulic counter-pressure acting on the pistons is permitted, since the hydraulic counter-pressure can be set very precisely and can also be easily changed over the course of the pressing, an optimal influence on the resistance that takes into account the respective individual circumstances. In addition, since the pressurized cylinder bores communicate with each other and therefore the identical pressure prevails everywhere, an ideal coordination of the counter-holding force provided by the individual pistons is possible in terms of dimensions and timing (synchronization). 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 retreat further into the central body (or be pushed back) so that the support core can be removed from the formed workpiece can .

This form of supporting the hollow workpiece from the inside, which is possible in implementation of the present invention, substantially reduces the risk that the hollow workpiece unintentionally changes 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 in the case of... 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 two adjacent ones Edges limited, initially flat wall sections allow to the outside or. If not prevented, this will only be a temporary deformation without any adverse consequences; Because such a local, slight outward bulging is corrected again by the pressing jaws that are placed there later, 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 reliably preventing the walls from collapsing using the present invention, it is possible, for example, to produce locally narrowed square or hexagonal tubes that have a square or hexagonal shape in the area of the narrowing. Hexagonal cross section with four or have six flat wall sections.

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

Furthermore, 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. The present invention can be used with advantage in round or oval cross-sectional geometries. Furthermore, it should be emphasized that the present invention is also and especially suitable for use in applications in which the pipe or other hollow workpiece is to be formed in a multi-axial manner at one of its two ends in order to form a cross-sectional constriction at the end. The invention is in no way limited to applications in which the workpiece is to be provided with a constriction between two undeformed areas.

According to the above explanations of the method according to the invention, according to another aspect of the present invention, there is a suitable one for use in the method according to the invention Support core characterized in that it comprises a central body with at least two differently oriented, mutually communicating cylinder bores and pistons accommodated in these, which can be acted upon 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 each other, so that as a result - with a given cross section of the central body - larger movements of the pistons can be achieved, compared to the arrangement of the pistons and bores in a common plane. As a precaution, in order to avoid misconceptions, it should be pointed out that the central body is by no means necessarily straight, i.e. H . in particular must be prismatic or cylindrical. Rather, it can also have a curved geometry, i.e. H . For example, extend along an arcuate center line. A support core with such a non-straight central body is particularly suitable for use in connection with curved hollow workpieces, in particular pipe bends.

The cylinder bores are particularly preferably designed as through bores, in each of which two counter-rotating pistons are accommodated - by acting on a pressure chamber located between them. With this configuration, a central, axisymmetric support of the workpiece can be realized, unlike in the case of a support core intended for the radial forming of a square tube, in which only two of the walls of the workpiece are supported by (or with) pistons connected pressure plates), while the other two walls are supported directly via the central body adjacent to them. Likewise, in a particularly preferred embodiment, at least two cylinder bores oriented parallel to one another in pairs are provided, axially offset from one another. The achievable distribution of the supporting forces over a larger number of pistons allows 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 already mentioned above.

Those pressure plates can be designed differently depending on the geometry of the workpiece to be formed. If the support core is used in 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 are oriented in particular parallel to the axis of the central body can . In the case of an arcuately curved central body, the printing plates are typically also curved in the same way. The printing plates can also be one- or two-dimensional in other ways, i.e. H . in particular 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 central sections, oriented at an angle to the central axis (n ) Have end section (s). They can too Pressure plates each have such a workpiece support surface that is oriented obliquely to the central axis, so that their entirety forms a pyramidal or describes conical geometry,

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.

This shows

Fig. 1 a partially schematic vertical section, taken perpendicular to the press axis, through the area relevant here of a radial press designed as a yoke press with the workpiece and support core entirety inserted, 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 according to FIG. 1 in fully closed configuration after completion of radial pressing,

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

Fig. 4 in a combined representation, comprising a partial longitudinal section (top) and a partial side view (bottom), the support core according to FIG. 3. 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 (see, for example, DE 10 2011 015 706 Al, 2 and the Uniflex product range). 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 - indicated only in the circumference of the tie rods 3 (cf. Double arrow B). In a known manner, the radial press has eight base jaws 4 arranged uniformly and concentrically around a press axis Press axis X and - when raising the upper yoke 2 - can be moved radially away from the press axis X. Restoring springs 5 act between adjacent base jaws 4. The base jaws 4 each have, radially on the inside, a cylindrically curved contact surface 6 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, the pressing surfaces 9. In contrast, 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 define a square cross section when the radial press is completely closed (see FIG. 2).

Before the square tube 8 is subjected to radial compression in the appropriately prepared radial press (see Figures 1 and 2), the square tube 8, i.e. H . in its cavity H, a support core

10 (see also Figures 3 and 4). This includes an essentially prismatic central body

11 with a central bore 12 extending along axis A and a total of sixteen cylinder bores 13. These are distributed over two mutually perpendicular planes, which intersect at 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 holes 14 are in the axial direction, i.e. H . oriented alternately offset from one another in the direction of axis A. The central bore 12 forms a channel 15 through which the eight through bores 14 (and thus the sixteen cylinder bores 13) communicate fluidly with one another.

In each cylinder bore 13, sealed by means of an inserted seal 16, a piston 17 is accommodated - guided in a displaceable manner along the respective cylinder axis Y, which is perpendicular to the axis A. Four pistons 17 that function in the same direction are mechanically connected in parallel to each other coupled to each other, namely via a (common) pressure plate 18, which is connected to the four assigned pistons 17 by means of screws 19.

While the central bore 12 is tightly closed at one end of the central body 11 of the support core 10 by means of a plug 20 screwed into it, a fluid connection 21 is provided at the opposite end of the central body 11. Via this, the channel 15 can be acted upon with hydraulic fluid, and via this channel 15 the sixteen cylinder bores 13 can in turn be acted upon simultaneously and with identical pressure. Such pressurized fluid allows the pistons 17 to move out of the central body 11 (arrow C), as a result of which the pressure plates 18 move away from the axis A. During this extension of the piston 17, the two O-rings 24 serving as captive devices 22, which are each placed around pins 23 arranged on the front side of the pressure plates 18 and extending parallel to the axis A, are stretched accordingly. If the O-rings 24 are replaced by veritable, correspondingly strong ring springs, the pistons 17 are extended against an effective restoring force; In this case, the ring springs would each be part of a restoring device provided at the end of the support core 10.

Before the start of the radial pressing of the workpiece W inserted into the radial press, the four pressure plates 18 are brought into contact on the inside of the hollow polygonal workpiece W to be formed - by extending the pistons 17 as described above by applying pressure to them; The workpiece support surfaces S are then in contact with the assigned inner surfaces of the square tube 8. The supply of hydraulic fluid into the support core 10 via its fluid connection 21 is then switched to holding the clamped hydraulic fluid via a counter-pressure valve. As a result, during the radial compression of the workpiece W, during which the pressure plates 18 are displaced in the direction of the axis A, the pistons 17 are retracted into the cylinder bores 13 in a controlled manner in the sense that hydraulic fluid is controlled through the fluid connection 21 of the while maintaining a counter pressure Central body 11 is drained through, i.e. H . flows back into the tank. The counter pressure is adjustable so that it can be tailored to the respective workpiece W.

After the radial compression has been completed, the counter-pressure valve (or a bypass for this) is opened so that the pressure in the hydraulic fluid is reduced and the pistons 17 can retreat into their maximum retracted position - under the influence of the two reset devices 22. By retracting the pressure plates 18 accordingly, unless they have 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 - before or after opening the radial press and if necessary. the removal of the formed workpiece W from this - removed from the formed workpiece W. 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 as the internal support, for example of a hexagonal tube or another hollow polygonal workpiece .

Claims

Claims Method for multi-axis 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) introducing a support core (10) into the cavity (H) of the workpiece (W), the support core (10) having a central body (11) with at least two differently oriented cylinder bores that communicate with one another (13) and pistons (17) accommodated therein which can be acted upon with hydraulic fluid through a fluid connection (21) of the central body (11); c) radial expansion of the support core (10) while extending the pistons (17) from the cylinder bores (13) by applying pressure fluid to the pistons (17); d) placing the workpiece (W) to be formed into a radial press; e) Radial forming of the workpiece (W) in the radial press, 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) move into the cylinder bores (13) in a controlled manner. Method according to claim 2, characterized in that in step e) the pressure fluid is drained in a controlled manner through the fluid connection (21) of the central body (11) while maintaining a counterpressure. Support core for use in the method according to claim 1, comprising a central body (11) with at least two differently oriented, communicating cylinder bores (13) which are offset from one another in the axial direction of the support core (10) and received therein by a fluid connection (21). Pistons (17) which can be acted upon with hydraulic fluid through the central body (11). Support core according to claim 4, characterized in that the cylinder bores (13) are designed as through bores (14), in each of which two opposing pistons (17) are received. Support core according to one of claims 4 or 5, characterized in that the cylinder bores (13) communicate with one another via an axial channel (15). Support core according to one of claims 4 to 6, characterized in that each is offset axially from one another, ie in the axial direction of the support core (10). at least two cylinder bores (13) oriented parallel to one another in pairs are provided. Support core according to claim 7, characterized in that the pistons (17) acting in the same direction are coupled to one another 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 one- or two-dimensionally arched or curved workpiece support surface (S).