EP1144139B1 - Method and device for hydroforming a tubular element - Google Patents

Abstract

The invention concerns a method and a device for hydroforming a tubular element. The matrix (1) is produced in the form of a series of assemblies (5, 6) constituting elementary matrices, juxtaposed successively along the tubular element (3), and maintained in their juxtaposed position by being longitudinally locked on either side of the tubular element (3), the locking of each assembly (5, 6) being ensured by the reaction forces generated in said assembly in response to stresses exerted by the tubular element subjected to hydroforming. The invention is useful for producing rectilinear tubular parts provided with deformed portions suitable for forming assembly nodes.

Description

Field of the invention

The subject of the present invention is a method and a hydroforming device for a tubular element, plus particularly of a tubular element essentially straight, according to the preambles of claims 1 and 5.

State of the art

Hydroforming techniques are well known and are growing in popularity due to the fact that they allow, in a single step, to achieve complex shapes from a blank in the form of a tubular element. The adequately sealed blank is held in a matrix made up of two half-shells appropriately shaped and hydroformed by injecting high pressure fluid into the blank while the die is kept closed with a hurry.

The efforts involved mean that in practice, when the dimensions of the blank increase, more and more tools heavier must be used to maintain of the matrix in the closed state.

A device of this type, requiring the use of a press to keep the die closed, is described in patent GB-A-392,635 on which the preambles of claims 1 and 5 are based. This document further reveals the use of a bar, constituting at its central part an oblong core intended to be inserted in the element tubular to be formed, core whose length substantially corresponds to the length of said element tubular. This bar does not play any role in a any maintenance of the matrix in the assembled state. At on the contrary, in the embodiment (fig. 1) where a sealing of the tubular element is ensured by pinching of the wall of the latter between conical surfaces, the axial pinching stresses, ensuring sealing, have in the matrix a radial component which conjugates with efforts communicated to the said matrix by the element tubular subjected to hydroforming, to act in the direction of an opening of the matrix. The presence of this bar therefore increases the effort required of the press to maintain the closed matrix.

Finally, note that such a device, provided for operate with superheated steam or gas explosion giving, in a very short time, a volume large forming fluid, would not be suitable for hydroforming techniques which, given the very small flow rates used at high pressure, require absolute sealing of the element to be hydroformed.

Yet another device is known, making it possible to carry out localized deformations in hydroforming a tubular element, by patent GB 523 962 A. In this case however, the matrix does not contain all of the tubular element but is limited to the location of the deformation. In addition the action of pressure is limited, by sealing means which are difficult to implement, to the area of the tubular element contained in the matrix.

Subject of the invention

The object of the present invention is to make it possible to make use of hydroforming techniques for the production, from tubular elements, hydroformed elements essentially straight, without requiring the setting important material for the maintenance of closed matrix. It also aims to allow the realization by hydroforming, in one step, of long pieces.

These aims are achieved by the method of the invention which consists in a hydroforming process in which a hydroforming fluid is injected under pressure into a rectilinear tubular element made otherwise watertight received entirely in a matrix made up of two half-shells of suitable shape, held together to resist hydroforming forces transmitted by the tubular element, to realize the matrix in the form of a series of matrices elementary, succeeding each other in a juxtaposed way along the tubular element, in the longitudinal direction thereof, to assemble each elementary matrix individually to using retainers, retaining dies elementary in position juxtaposed in the direction longitudinal by a longitudinal blocking carried out on both sides on the other side of the matrix, and to keep assembled each elementary matrix by the reaction forces generated during hydroforming in the assembly considered.

According to a preferred embodiment of the method of the invention, the retention in juxtaposed position of the dies elementary is ensured by tightening all said elementary matrices between clamping means provided at both ends of a core bar, axially passing through said tubular element.

According to a preferred embodiment of the method of the invention, the hydroforming fluid is injected into the tubular element through the bar constituting core, and the sealing of the ends of the element tubular on the core is made, at each end of the core, by clamping the corresponding end of the tubular element between said end of the core and the corresponding axial clamping means.

Still according to a preferred embodiment of the method of the invention, the ends of the element tubular are constricted on the ends cores, before tightening the corresponding axial clamping means.

The invention also relates to a device hydroforming of a straight tubular element of the type comprising a matrix made up of two half-shells of suitable shape, held together to resist hydroforming forces, a bar, constituting at its part central an oblong core intended to be inserted in the element tubular to be subjected to hydroforming, core whose length roughly corresponds to the length of said tubular element, and at each end of the bar, means for sealing the ends of the element tubular, device which comprises, for the realization of the method of the invention, elementary matrices juxtaposed along the tubular element, forming the matrix, individual assembly means of each elementary matrix, self-locking under the effect of forces hydroforming, and at each end of the bar, fixing means for axial clamping means, the cooperating axial clamping means, on either side of end walls of the matrix consisting of the matrices elementary juxtaposed, with the said fixing means, and the sealing means cooperating with the ends of the nucleus.

According to a preferred embodiment of an elementary matrix of the device according to the invention, an assembly constituting a matrix elementary consists of two half-matrices whose ends are formed to constitute by their meeting, when closing the elementary matrix, tenons intended to cooperate with corresponding mortises formed in locking pieces.

According to a preferred embodiment of the matrix elementary, the corresponding tenons and mortises have a slight taper, sufficient to facilitate the introduction of the post in the mortise, but sufficiently reduced to allow blockage such as the forces of friction oppose expulsion, during hydroforming of the locking part in which is formed the mortise.

According to another preferred embodiment of a matrix elementary of the device of the invention, an assembly constituting elementary matrix consists of two assemblies of half-dies, juxtaposed so that the plane of closure of one of the assemblies is arranged at right angles relative to the closing plane of the other assembly, and assembled by studs parallel to the axis of the die elementary thus formed, arranged on both sides of each of the assembly closure plans and fitting into corresponding housing assemblies.

According to a preferred embodiment of the device the invention, the bar comprises a cylindrical core, of diameter slightly smaller than the internal diameter of the tubular element and corresponding length substantially the length of the tubular member to hydroformer, nucleus that connects to each of its ends, by a conical shoulder, at one end threaded, while the clamping means are constituted, at each end, a nut screwing on the end threaded from the bar and a thrust plate pierced with a conical orifice to cooperate with the conical shoulder of the bar, and that at least one end of the bar is formed, through the threaded end, a conduit supply of hydroforming fluid which leads to the nucleus surface.

According to a preferred embodiment of the device of the invention, at the transition between the core and the threaded end of the bar, a straight shoulder of low height is formed between the core and the conical shoulder.

The invention will be better understood by referring to the description together with the accompanying drawing which represents, by way of example only, a mode of production adapted to the production of tubular elements comprising deformations suitable for making of forms of assembly of the bars of a grid. Indeed, although it applies to any achievement by hydroforming of tubular parts obtained at the start of straight tubular elements, the invention finds a particular application in the realization by hydroforming of tubular parts provided with deformations suitable for making assembly nodes, and more particularly such tubular parts reproducing the assembly forms obtained by hot expansion of solid bars used in forged grids.

Brief description of the drawings

• la fig. 1 est une vue en perspective d'un mode de réalisation d'un assemblage constituant matrice élémentaire, adaptée au maintien d'un élément tubulaire dans sa forme initiale,
• la fig. 2 est une vue en perspective d'un autre mode de réalisation d'un assemblage constituant matrice élémentaire, adaptée à la constitution dans l'élément tubulaire d'une forme d'assemblage,
• la fig. 3 est une vue de détail, partiellement en coupe, d'une extrémité d'une barre constituant noyau et du dispositif de serrage associé
• la fig. 4 est une vue d'ensemble, en coupe, d'un dispositif d'hydroformage suivant l'invention d'un élément tubulaire comme mentionné ci-avant, l'alimentation en fluide d'hydroformage n'étant pas représentée, et
• la fig.5 est une vue partielle d'une grille réalisée à partir d'un élément tubulaire hydroformé suivant l'invention.

In the drawing:

• fig. 1 is a perspective view of an embodiment of an assembly constituting an elementary matrix, suitable for maintaining a tubular element in its initial form,
• fig. 2 is a perspective view of another embodiment of an assembly constituting an elementary matrix, adapted to the constitution in the tubular element of an assembly form,
• fig. 3 is a detail view, partially in section, of one end of a core bar and of the associated tightening device
• fig. 4 is an overall view, in section, of a hydroforming device according to the invention of a tubular element as mentioned above, the supply of hydroforming fluid not being shown, and
• Fig.5 is a partial view of a grid made from a hydroformed tubular element according to the invention.

Description of a preferred embodiment of the invention

Referring first to the overview of the Figure 4, a hydroforming device according to the invention of a straight tubular element consists of a matrix 1, of a bar 2 constituting a through core axially a blank or tubular element 3 to hydroforming, and clamping means 4, 4 '. The matrix 1 consists according to the invention of a series of assemblies 5, 6 forming elementary matrices. These various constituents will be described in more detail below, with reference to Figures 1, 2 and 3.

Fig. 1 illustrates an assembly 5 constituting a matrix elementary, suitable for maintaining the part concerned with a tubular element in its original form. Such an assembly 5 consists of two partial assemblies 7, 7 ' juxtaposed with half dies 8, 8 'respectively 8 ", 8" each having a housing 9 respectively 9 'intended to receive the tubular element, and a closure plane 10, respectively 10 '. The partial assemblies 7, 7 'are juxtaposed so that the closure plan 10 of the partial assembly 7 is arranged at right angles by relative to the closing plane 10 'of the partial assembly 7 '. The partial assemblies 7, 7 'are brought together in the form of an assembly 5 by studs 11 inserted in the housings 12 to be arranged parallel to the axis 13 of the elementary matrix thus constituted. The studs are housed in a half-matrix 8 of a partial assembly 7, on the same side of the closure plane 10, are also housed in the half dies 8 ", 8" 'of the partial assembly juxtaposed 7 ', on either side of the closing plane 10'.

Fig. 2 illustrates an assembly 6 constituting a matrix elementary, comprising a recess 14 suitable for production of an assembly form 15 of bars wire rack. This assembly consists of two half-dies 16, 16 ', extending into projections of semi-circular section 17, 17 'respectively 17 ", 17"', oriented perpendicular to the axis 13 'of the elementary matrix thus constituted. These semi-circular section projections are designed to form by their meeting 17, 17 " respectively 17 ', 17 "', a tenon of circular section intended to cooperate each time with a mortise 18 corresponding in a locking piece 19. Only one locking piece 19 with mortise 18, intended for cooperate with the tenon formed from the ends 17 ', 17 "', is shown in the drawing.

According to the illustrated embodiment, the tenons formed by the combination of projections 17, 17 "and 17 ', 17"', and the corresponding mortises 18, have a slight taper. For example, a taper of 1% is considered sufficient taper to facilitate the introduction of the tenon in the mortise, while allowing, under the effect of friction forces, a blocking of the post in the mortise during hydroforming.

Fig. 3 shows a detail view, partially in section, from the end of a bar 2 and means for tightening 4 associated, cooperating with the blank or element tubular 3. The bar 2 proper consists of a cylindrical body 19, constituting a core, of diameter slightly smaller than the internal diameter of the element tubular 3 in order to leave between the core 19 and the tubular element 3, in section, an annular space of reduced size. On the one hand, this limits the amount of fluid required for hydroforming, and other apart from limiting the pressure application surface generating in the tubular element 3 the axial component some efforts. The cylindrical body 19 is connected, by a frustoconical shoulder 20, at a threaded end 21 intended to cooperate with the clamping means 4. These clamping means 4 consist of a part 22 nut component, acting on a clamping plate 23. The clamping plate 23 is pierced with an orifice 24 for engage on the threaded end 21 of the bar 2, orifice 24 ending in a tapered portion 25 of taper corresponding to that of the shoulder 20. Preferably the shoulder 20 has a straight portion 26 of weak dimension making transition between the cylindrical core 19 and the frustoconical part of the shoulder 20. A channel supply 27 for the hydroforming fluid crosses the threaded end 21 to reach the surface of the core 19.

According to the process of the invention, applied to the mode of realization illustrated in the drawing, for the realization of a grid bar 28 (see fig. 5), insert into the tubular element 3 constituting a blank, cut to length suitable, bar 2, of length provided for correspond to a determined assembly of matrices elementary 5, 6. The ends 29 of the tubular element 3 are constricted on the frustoconical shoulder 20 at each end of the bar 2. The elementary matrices 5, 6 are put in place and assembled, and the clamping means 4 are in place. The thrust of nut 22 on the plate clamp 23 ensures both holding in position juxtaposed of elementary matrices and sealing of the annular space remaining between the tubular element 3 and the cylindrical body 19 of the core 2. This sealing is ensured by the cooperation of the shoulder 20 and the frustoconical orifice 25 to crush the constricted part 29 of the tubular element 3. The part right 26 of the shoulder 20 promotes this sealing by constituting a corner to penetrate the constricted portion 29.

The hydroforming fluid is then brought through the conduit 27 in the annular space remaining between the core 19 and the tubular element 3. Under the effect of the pressure, the tubular element 3 is deformed in line with the recesses 14, the generated form being determined to use the matter available to the right of the deformation without contribution neighboring areas. To present the required qualities of malleability and weather resistance, we will preferably use, for the realization of these elements of grid, stainless steel blanks.

Under the effect of the constraints generated by hydroforming, the elementary matrices 6 are locked in the closed position by the tendency to expansion of posts 17, 17 "and 17 ', 17"' in the corresponding mortises 18. Similarly, the elementary matrices 5 are locked in position closing by constraints perpendicular to the axis of studs 11, exerted in two perpendicular directions between them at the passage of the stud considered in the partial assembly 7 respectively in the assembly partial 7 '.

After hydroforming, the clamping means 4 are loose, the elementary matrix assemblies released and the ends of the hydroformed bar 28 cut out for allow removal of the bar 2.

This hydroformed bar can then be machined so suitable for making in assembly forms 15 the cuts required to allow the introduction and welding of cylindrical bars 30 for the creation of a grid.

Of course, the invention also applies to the production of hydroformed tubular elements other than grating bars, the realization of these having been described only as an example of a mode of preferred embodiment of the invention.

For example, by planning along the draft 3 of the various orientations of the assemblies 6 constituting elementary matrix, we obtain an element comprising deformations suitable for making three-dimensional structural assembly forms, usable in furniture, or in load-bearing structures.

Finally, it should be emphasized that the achievement of a matrix from elementary matrices, due precisely the modular nature of the matrix produced, allows great flexibility of use in adaptation of the device to different embodiments.

Claims (10)

1. Method for hydroforming a tubular member, wherein a hydroforming fluid is injected under pressure in a straight tubular member (3), which is sealed and is completely received within a mould (1) formed by two suitably shaped half shells, maintained assembled to resist the hydroforming forces transmitted by the tubular member, characterized in that it consists of

   making the mould (1) in the form of a series of elementary moulds (5, 6), succeeding each other juxtaposed along the tubular member (3), in the longitudinal direction thereof,

   assembling each elementary mould (5, 6) individually through holding components (11, 12, 17, 17', 17'', 17''', 18),

   holding the elementary moulds (5, 6) in juxtaposed position in the longitudinal direction, by a longitudinal locking on each side of mould (1),

   maintaining each elementary mould (5, 6) assembled by the reaction forces generated in the assembly during hydroforming.
2. Method according to claim 1, characterized in that the holding in juxtaposed position of the elementary moulds (5, 6) is made by clamping the whole assembly (1) of said elementary moulds between clamping means (4) provided at both ends of a core forming rod (2), axially passing through said tubular member (3).
3. Method according to claims 1 and 2, characterized in that the hydroforming fluid is injected in the tubular member (3) through the rod (2) forming a core (19), and in that the sealing of the ends (29) of the tubular member (3) on the core (19) is obtained, at each end of the core (19), by clamping the corresponding end (29) of the tubular member (3) between said end (20) of the core (19) and the corresponding axial clamping means (4).
4. Method according to claim 3, characterized in that the ends (29) of the tubular member (3) are swaged on the corresponding ends (20) of the core (19), before tightening of the corresponding axial clamping means (4).
5. Apparatus for hydroforming a straight tubular member, comprising

   a mould (1) formed by two suitably shaped half shells, maintained assembled to resist the hydroforming forces,

   a rod (2), the central portion of which constitutes an oblong core (19) to be inserted in the tubular member (3) to be hydroformed, the length of the core (19) corresponding substantially to the length of said tubular member,

   at each end of the rod (2), sealing means (23) for the ends of the tubular member,

   characterized in that it comprises, for performing the method according to claims 1 to 4

   elementary moulds (5, 6) juxtaposed over the whole length of the tubular member (3) and forming said mould (1),

   separate assembly means (11, 12, 17, 17', 17'', 17''', 18) self locking under the action of the hydroforming forces, for each elementary mould (5, 6),

   at each end of the rod, fastening means (21) for axial clamping means (4),

   said axial clamping means cooperating with said fastening means (21), on each side of the end walls of the mould (1) formed by the juxtaposed elementary moulds (5, 6), and

   sealing means (23) cooperating with the ends of the core (19).
6. Apparatus according to claim 5, characterized in that an elementary mould forming assembly (6) comprises two half moulds (16, 16') provided with projections (17, 17', 17'', 17''') shaped to form, by their assembly on closing of the elementary mould (6), mounting pins intended to cooperate with corresponding mortises (18) formed in locking members (19).
7. Apparatus according to claim 6, characterized in that said mounting pins (17, 17''; 17', 17''') and said corresponding mortises (18) are slightly tapered, sufficiently to assist the entry of the mounting pin into the mortise (18), but sufficiently limited for allowing a locking such that the friction forces resist to the expulsion of the locking member (19) in which the mortise (18) is formed, during hydroforming.
8. Apparatus according to claim 5, characterized in that an elementary mould forming assembly (5) is made by two assemblies (7, 7') of half moulds, juxtaposed in such a way that the closing plane (10) of one of the assemblies (7) is at right angle in relation to the closing plane (10') of the other assembly (7'), and assembled by studs (11) parallel to the axis (13) of the so formed elementary mould, disposed on each side of each closing planes (10, 10') of the assemblies (7, 7') and inserted in corresponding housings (12) of the assemblies (7, 7').
9. Apparatus according to claim 5, characterized in that the rod (2) comprises a cylindrical core (19), of a diameter slightly lower than the internal diameter of the tubular member (3), of a length corresponding substantially to the length of the tubular member (3) to be hydroformed, which core (19) connects at each of its ends, by a tapered shoulder (20), to a threaded end (21), in that the clamping means (4) are formed, at each end, by a nut (22) screwing on the threaded end (21) of the rod, and by a pressure plate (23) provided with a hole (24) comprising a tapered section (25) for cooperating with the tapered shoulder (20) of the rod (2), and in that at least at one end of the rod bar (2), a conduit for feeding hydroforming fluid (27) is formed through the threaded end (21), and opens at the surface of the core (19).
10. Apparatus according to claim 9, characterized in that, at the junction between the core (19) and the threaded end (21) of the rod (2), a short straight shoulder (26) is formed between the core (19) and the tapered shoulder (20).

Images