Abstract:
The invention relates to a process for producing a hollow profiled section ( 7 ) with bulges ( 37 ) which is provided with an end-side closure cover ( 7 ), and to a jack bracket ( 32 ) produced by means of this process. To allow simple production of an expanded hollow profiled section ( 6 ) provided with a closure cover ( 7 ) and to demonstrate a jack bracket ( 32 ) produced by this process which entails only a low level of manufacturing outlay yet nevertheless ensures a high ability to withstand mechanical stresses, it is proposed that a cup-like cover ( 7 ) be pushed into the hollow profiled section ( 6 ), with the hollow profiled section ( 6 ) being placed into a hydroforming die ( 1 ). After the latter has then been closed, an axial ram ( 8 ) is introduced into the cover ( 7 ) and into the end of the hollow profiled section, in such a manner that the rim side of the cover ( 7 ) is radially pressed to the surrounding hollow profiled section ( 6 ). The hollow profiled section ( 6 ) is then widened by means of hydroforming pressure.

Description:
BACKGROUND AND SUMMARY OF THE INVENTION  
       [0001]     This invention relates to a process for producing a hollow profiled section provided with a closure cover on the end side, and to a jack bracket.  
         [0002]     The prior art, which is described by German document DE 100 49 048 C1, discloses a process for producing ends for hollow shafts. In this process, a plastic stopper is pushed into the hollow shaft. The hollow shaft together with plastic stopper is placed in a hydroforming die, after which an axial ram then acts on the end of the hollow shaft in which the plastic stopper is located. At the same time, a hydroforming pressure is generated in the hollow shaft, the effect of which, in combination with the axially acting pressure of the ram, is to press the wall of the hollow shaft onto both end sides of the plastic stopper. This captively fixes the plastic stopper in the hollow shaft, since it is held in a frictionally and positively locking manner by this compression.  
         [0003]     Furthermore, German document DE 195 28 309 C2 discloses a jack bracket which has been formed from a sheet-metal shell structure. The jack bracket has attachment regions by which it is secured to a lower sill region by means of spot-welding. The welded shell structure has an opening at its other end, into which a plastic stopper that has an indentation is fitted; a journal of a jack can be inserted into this indentation. The shell structure of the bracket is relatively complex to produce in terms of process engineering and apparatus, since it comprises a number of parts.  
         [0004]     This invention is based on the object of providing a process which makes it easy to produce an expanded hollow profiled section provided with a closure cover. Moreover, it is intended to demonstrate a jack bracket which requires only a low level of manufacturing outlay yet nevertheless ensures a high ability to withstand mechanical stresses.  
         [0005]     According to the invention, this object is achieved by the claimed process, and by the claimed jack bracket.  
         [0006]     By use of a single-piece, circumferentially continuous hollow profiled section as the base body for the jack bracket, a high flexural strength of the bracket is achieved, which is able to withstand even very high mechanical stresses without suffering damage. The hollow profiled section can be ideally matched to the periphery of the bracket by means of the hydroforming, which manifests itself in bulges which are simple to form using the hydroforming process, on account of the relatively low degrees of deformation. As a result of the absence of manufacturing tolerances from the process, it is readily possible to automate the attachment of the bracket to the lower region of the motor vehicle sill. This attachment merely requires the formation of weld flanges, which can be made by relatively simple cutting and bending operations at the corresponding end of the hollow profiled section. The opposite end of the hollow profiled section is closed off by a closure cover, to which the jack can be directly or indirectly fitted. The pressing of the closure cover within the hydroforming die, which forms the basis of the process according to the invention for joining the closure cover and the hollow profiled section, eliminates the need for additional tools, such as holding means and pressing tools, which would otherwise be required for external pressing of the cover within the hollow profiled section. Moreover, the pressing is effected by the introduction of the axial ram into the hollow profiled section, which is economical in terms of process engineering since it is in any case an operation which is imperative for the seal to be produced during the hydroforming process. On account of the hollow profiled section bearing without play between the cavity of the hydroforming die and the cover rim, which for its part bears closely against the pressure-exerting slope of the inner axial ram, the hollow profiled section maintains its contours, without undesirable creases and dents, in the pressing region. Then, the bulges are formed by introducing a hydroforming pressure into the interior of the hollow profiled section. If the cover completely closes off the hollow profiled section, the hydroforming pressure is introduced via the other end of the hollow profiled section. Overall, the apparatus requirements of the hydroforming process allow this process to be combined with the pressing process in a single die, which significantly simplifies the production of an expanded hollow profiled section with closure cover. The abovementioned need for strong sealing of the axial ram with respect to the highly pressurized fluid within the interior of the hollow profiled section produces a high frictional lock between the cover rim and the hollow profiled section, which is responsible for extremely good retaining of the cover on the hollow profiled section for any intended use.  
         [0007]     In a refinement of the process according to the invention, the cover is fitted loosely into the hollow profiled section outside the forming die. This has the advantage that closure cover and hollow profiled section can be preassembled in advance and then placed in the hydroforming die as a single unit for further processing.  
         [0008]     In a further advantageous refinement of the invention, which should be regarded as an alternative to the refinement just described, the closure cover is fed to the hollow profiled section, which has been placed in the forming die, by means of the axial ram, and pressing is effected as this feeding operation takes place. In this case, economically in terms of process engineering, the feeding of the closure cover is carried out in a single operation together with the pressing. Furthermore, the closure cover is centered on the axial ram even before it is introduced into the hollow profiled section, and is therefore arranged in the desired way.  
         [0009]     In a further expedient refinement of the invention, before inserting the closure cover into the hollow profiled section, the cover is designed with an external diameter which is larger than the internal diameter of the hollow profiled section. On account of the specific design of the two diameters, introduction of the cover into the hollow profiled section results in a particularly high level of press fit if the axial ram additionally also has a pressure-exerting contour. In the other case, the press fit is less strong, but it is possible to make do without a special configuration of the pressure-exerting contour of the axial ram. However, for the diameters indicated, an insertion slope on the cover rim is useful, to make it easier for the closure cover to be introduced into the hollow profiled section.  
         [0010]     In a further advantageous configuration of the invention, the cover rim is clamped in place by the hollow profiled section by means of hydroforming pressure combined, at the same time, with axial advancing of the axial ram. Hollow profiled section material is displaced into a space delimited by a closure edge of the cover rim and an opposite shoulder of the axial ram by means of the advancing operation in combination with the hydroforming pressure. The hydroforming pressure in combination with the pressure-exerting force of the axial ram on the one hand produces an inwardly protruding thickened section on the hollow profiled section, which bears against the cover rim; on the other side, the hollow profiled section material which flows into the space on account of the hydroforming pressure and the advancing operation engages behind the cover rim. This produces a positive lock between hollow profiled section and closure cover, which boosts the retaining force between the two components still further.  
         [0011]     In a further expedient configuration of the invention, an opening in the cover base and a widening of the hollow profiled section are formed by a pressurized fluid which is introduced into the interior of the hollow profiled section via a passage in the axial ram and the opening in the cover base. Forming the opening in the cover base and providing a fluid passage in the axial ram provides the latter with an extremely useful multiple function, namely that of sealing off the supply of pressurized fluid and pressing the rim of the cover onto the hollow profiled section. The opening at the cover base can subsequently, after the forming of the hollow profiled section, serve as a receiving element for a further component.  
         [0012]     In another refinement, an extension in the shape of a bottleneck is formed around the opening in the cover base at the cover, into which extension a molded projection in the form of a hollow journal on the end side of the axial ram is introduced. If the cover formed in this manner has already been fitted into the hollow profiled section, the bottleneck-shaped extension serves as a centering means for the axial ram, which can then be docked to the closure cover without jamming, and with its journal-like molded projection on the end side projecting through the opening in the cover base. This additionally retains the axial ram on the cover and—via the latter—on the hollow profiled section. If the closure cover is not yet retained loosely on the hollow profiled section, but rather is only to be supplied together with the axial ram, the cover can easily be fitted together with the axial ram, so that the closure cover is held captively on the axial ram as it is fed to and introduced into the hollow profiled section.  
         [0013]     In a further expedient refinement of the invention, after the widening of the hollow profiled section has taken place, the closure edges of the hollow profiled section and of the cover rim are acted on by means of a slide, which is integrated guidably within the forming die and engages in an axial running groove of the axial ram, which is open toward the end side of the axial ram. The slide in this case prevents the closure cover from being released from its press-fit to the hollow profiled section and also being pulled outward after the axial ram has been pulled out. The movement of pulling out the axial ram remains unaffected by the slide, on account of the open groove.  
         [0014]     In a further advantageous configuration of the invention, the closure edges of the cover rim are shaped so as to protrude radially outward. The annular collar which is then formed creates an axial stop for the closure cover, which axial stop is supported against the closure edge of the hollow profiled section, so that in the event of axially higher mechanical loads on the pressed assembly of hollow profiled section and closure cover, which are exerted from the cover side of the hollow profiled section, the cover cannot be pressed into the interior of the hollow profiled section.  
         [0015]     According to a further advantageous configuration of the invention, the cover rim is perforated, and after the cover has been pressed to the hollow profiled section, hollow profiled section material is pressed into the hole which has in each case been formed in the cover rim by means of a ram that is integrated guidably in the forming die. This produces a local positively locking connection between the hollow profiled section and the cover, which on the one hand prevents the closure cover from being entrained in the same direction when the axial ram is being pulled off and on the other hand also prevents the closure cover from being pressed into the interior of the hollow profiled section on account of higher mechanical axial loads from both axial directions.  
         [0016]     In a further expedient development of the process according to the invention, the hollow profiled section and the cover, when the axial ram is being introduced, are pressed onto a section of the cavity of the forming die which widens conically toward the axial ram, so as to form surfaces of matching contour on the cover rim and on the hollow profiled section. In this refinement, the pressed assembly of hollow profiled section and closure cover is strengthened still further. Furthermore, the closure cover is also prevented from being pressed into the interior of the hollow profiled section.  
         [0017]     Finally, in an expedient further configuration of the jack bracket according to the invention, the bracket, on the cover base, has an opening which forms a receiving element for a stopper to which a jack can be attached. On account of the accurate positioning of the closure cover within the hollow profiled section, which for its part has been produced without manufacturing tolerances on account of the use of the hydroforming process, the opening for receiving the stopper is very accurately defined. This enables a lifting platform designed as a jack, which is completely automatically controlled, always to be fitted to the correct position on the jack bracket when the motor vehicle is in the workshop.  
         [0018]     In the text which follows, the invention is explained in more detail on the basis of a number of exemplary embodiments illustrated in the drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]      FIG. 1  shows, for a process according to the invention, an arrangement of a hydroforming die, a hollow profiled section, a closure cover and an axial ram in the form of a longitudinal section through a partial exploded view,  
         [0020]      FIG. 2  shows a longitudinal section, for the process according to the invention, through a closure cover with bottleneck-shaped extension and an axial ram with a journal-like molded projection, in an exploded view,  
         [0021]      FIG. 3  shows the arrangement of  FIG. 1  in the position in which closure cover and hollow profiled section are being pressed together with the axial ram introduced,  
         [0022]      FIG. 4  shows a longitudinal section, for the process according to the invention, through a hollow profiled section and a closure cover with closure edges shaped so as to protrude radially outward, in the form of an exploded illustration,  
         [0023]      FIG. 5   a  shows, for a process according to the invention, a longitudinal section through part of an arrangement of a hydroforming die, a hollow profiled section, a closure cover and an axial ram in the pressing position of the axial ram, with the hollow profiled section engaging behind the closure cover at the rim side,  
         [0024]      FIG. 5   b  shows an enlarged excerpt from the location of the closure cover which is being engaged behind in  FIG. 5   a,    
         [0025]      FIG. 6  shows, for a process according to the invention, an arrangement of hollow profiled section, closure cover and a hydroforming die as well as an axial ram in the pressing position of the axial ram with a slide acting on the closure edges of hollow profiled section and closure cover,  
         [0026]      FIG. 7   a  shows, for a process according to the invention, an arrangement of hydroforming die, hollow profiled section, axial ram and closure cover with a ram which displaces hollow profiled section material into a hole in the closure cover,  
         [0027]      FIG. 7   b  shows an enlarged excerpt from the pressed assembly of hollow profiled section and closure covers shown in  FIG. 7   a  at the location at which hollow profiled section material is being displaced into the hole in the closure cover,  
         [0028]      FIG. 8  shows, for a process according to the invention, a longitudinal section through an arrangement of a hydroforming die, an axial ram, a hollow profiled section and a closure cover in the pressing position with a section of the cavity of the forming die which widens conically toward the axial ram,  
         [0029]      FIG. 9  shows a jack bracket according to the invention in the form of a side view of an exploded illustration, and  
         [0030]      FIG. 10  shows the jacket bracket from  FIG. 9  in the form of a perspective view after the pressing of hollow profiled section and closure cover. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0031]      FIG. 1  illustrates an open hydroforming die  1  comprising a top die part  2  and a bottom die part  3 , which with an inner cavity  4  define a hydroforming space  5 . A hollow profiled section  6 , which may be formed from a light metal or steel and may be in the form of a blank made from a drawn tube or a plate which has been rolled up and then welded with a longitudinal seam, has already been placed into the lower die part  3 . The arrangement shown, comprising the forming die  1  and the hollow profiled section  6 , also comprises a closure cover  7  and an axial ram  8 , which are in this case separate from one another outside the forming die  1 , in order to explain the production process according to the invention, but are in each case arranged aligned with the hollow profiled section  6  in order to stipulate the direction in which they are pushed together. The closure cover  7  is of cup-shaped design; its base  9  rests on the side facing the hollow profiled section  6 . The cover  7  may be a deep-drawn sheet-metal part or a casting, in particular a hot-chamber die casting. The axial ram  8  narrows toward its end side  10  facing the closure cover  7  by way of a shoulder  11 , from where it merges, via spherically rounded pressure-exerting flanks  12 , into the planar end side  10 . The rounding of the flanks  12  is intended to prevent the closure cover  7  from being damaged by sharp edges which would otherwise be present during introduction of the axial ram  8  into the closure cover  7  or during pressing to the hollow profiled section. The height of the shoulder  11  is such that it is of the same size as the wall thicknesses of the hollow profiled section  6  and of the closure cover  7  together. If the closure cover  7  has already been inserted loosely into the hollow profiled section  6  in advance, with the result that the hollow profiled section  6  together with the closure cover  7  is placed into the forming die  1  as an assembly to be pressed, the diameter of the axial ram  8  in the region of its pressure-exerting flanks  12  is greater than the internal diameter of the closure cover  7 . The profile of the rim  13  of the closure cover  7  substantially matches the spherical contour of the axial ram  8  in the region of its pressure-exerting flanks  12 . This produces uniform pressing of hollow profiled section  6  and closure cover  7 , thereby optimizing the retaining of the closure cover  7  on the hollow profiled section  6 . However, if the closure cover  7  is pushed onto the axial ram  8  in order for them to be jointly introduced into the forming die  1 , the internal diameter of the closure cover rim  13  is of course larger than the diameter of the axial ram  8  in the region of its pressure-exerting flanks  12 . To achieve appropriate pressing to the hollow profiled section  6 , the closure cover rim  13 , at its external diameter in this region, is overdimensioned all the way around with respect to the internal diameter of the hollow profiled section  6 . The axial ram  8  has a centrally running passage  14  which opens out at the end side  10 . The closure cover  7  has a central opening  15  in its base  9 .  
         [0032]     To carry out the process, the hollow profiled section  6  is placed into the forming die  1 , which is then closed. As has been mentioned, the closure cover  7  may previously have been fitted loosely into the hollow profiled section  6  or the closure cover  7  may have been pushed onto the axial ram  8 . In the later case, the opening in the closure cover  7  is aligned with the point where the passage  14  of the axial ram  8  opens out. Then, the axial ram  8  together with the closure cover  7  is introduced into the end of the hollow profiled section, with the result that the closure cover  7  is pressed to the hollow profiled section end, on account of its dimensions and the pressure-exerting flanks  12  of the axial ram  8 . The pressed assembly produced in this way as illustrated in  FIG. 3  is then placed under hydroforming pressure by a pressurized fluid being introduced into the hollow profiled section interior  16  via the passage  14  in the axial ram and the central opening  15  in the closure cover  7  and pressurized by means of a pressure-generating system which is connected to the rear side of the passage  14 . As a result of the hydroforming pressure generated, the hollow profiled section  6  is widened until it comes to bear against the cavity  4  of the forming die  1 , so as to form bulges  37  (cf.  FIGS. 5-10 ). The molding space  5  within the die  1  is now completely filled. It is in principle conceivable for a closure cover  7  to be introduced, successively or simultaneously, into both ends of the hollow profiled section  6 .  
         [0033]      FIG. 2  shows a variant of the axial ram  8  and the closure cover  7 . In this case, the end side  10  of the axial ram  8  has a journal-like molded projection  17 , through which the passage  14  passes. Accordingly, with matching contours, the closure cover  7  has a bottleneck-shaped extension  18 , in which the molded projection  17  of the axial ram  8  can be fitted. This provides particularly good retaining of the closure cover  7  on the axial ram  8 . As can be seen from  FIG. 4 , in a further structural variant of the closure cover  7 , the closure edges  19  of the cover rim  13  can be shaped so as to protrude radially inward, producing a lip-like annular collar.  
         [0034]     In a variant of the invention, as shown in  FIGS. 5   a  and  b , in the pressed-assembly position, the axial ram  8  is advanced even further, so that sufficient hollow profiled section material can be supplied to the region of the bulge  37  to be produced, thereby ensuring that the hollow profiled section  6  is widened in a reliable process. During the advancing of the axial ram  8 , with hydroforming pressure P i  accordingly acting on all sides as indicated by the arrows, on the one hand a thickened formation  20  is formed on the hollow profiled section  6  immediately adjoining the pressed region, and on the other hand hollow profiled section material, at the continuing end of the profiled section, is displaced into a space  21  delimited by the closure edge  19  of the closure cover rim  13  and the opposite shoulder  11  of the axial ram  8 . The thickened portion  20  pressing the cover rim  13  inward and the hook-like closure  22  of the hollow profiled section end causes the closure rim  13  to be clamped in a positively locking manner toward its end, resulting in particularly good retaining of the closure cover  7  on the hollow profiled section  6  as a result of the axial fixing achieved. After the desired expanding  37  of the hollow profiled section  6  and of the pressed assembly of hollow profiled section  6  and closure cover  7  has ended, the hydroforming pressure is relieved and the axial ram  8  is withdrawn from the hydroforming die  1 , after which the forming die  1  is opened and the finished assembly comprising hollow profiled section  6  and closure cover  7  is removed.  
         [0035]     In a further variant of the invention,  FIG. 6  reveals a slide  23 , which is integrated guidably in the forming die  1  within a guide bore  24  which runs radially with respect to the cavity  4 . To prevent the closure cover  7  from being released from the pressed assembly with the hollow profiled section  6  during retraction of the axial ram  6  after the widening of the hollow profiled section  6  on account of particularly high friction by being pulled along with it, the slide  23  engages in an axially running groove  25  in the axial ram  8 , which is open toward the end of the hollow profiled section. In this position, the closure edges  19  and  26  of the cover rim  13 , on the one hand, and of the hollow profiled section  6 , on the other hand, are supported against the side wall  27  of the slide  23  which faces them. The use of a plurality of radially movable slides  23  arranged offset with respect to one another in the circumferential direction improves the support and ensures that the pressed assembly is retained even more firmly.  
         [0036]     A further variant of the invention is illustrated in  FIGS. 7   a  and  7   b . After the bulge  37  has been formed, in the region of the pressing, hollow profiled section material is pressed into corresponding holes  30  in the cover rim  13  by means of a plurality of rams  29  which are integrated guidably in the forming die  1  in corresponding guide bores  28  running radially with respect to the cavity  4  of the forming die  1 , these holes being produced on the closure cover  7  during or shortly after its production.  
         [0037]     In a further variant of the invention as shown in  FIG. 8 , the cavity  4 , adjoining the molding space  5 , is widened conically with a shallow opening angle toward the axial ram  8 . The hollow profiled section  6  and the closure cover  7  are pressed onto this conically widened section of the cavity  4  during insertion of the axial ram  8 , with surfaces with contours corresponding to the part  31  of the cavity  4  being formed at the cover rim  13  and at the hollow profiled section  6 .  
         [0038]      FIG. 9  illustrates a jack bracket  32  which has been produced using the process according to the invention. For the sake of clarity, in the illustration the closure cover  7  with its bottleneck-shaped extension  18  is illustrated separately from the hollow profiled section  6 . The hollow profiled section  6  also has a plurality of flanges  34  at its end  33  remote from cover  7 , which flanges  34  are partially turned over and serve on the one hand as a stop and on the other hand as joining surfaces for a lower region of a sill of the motor vehicle. To attach the bracket  32  to the sill and any other peripheral body regions of the motor vehicle, for example by means of spot-welding, passages  36  are formed in a side wall  35  of the bracket  32 , via which passages lateral access into the hollow profiled section  6  to the adjoining inner walls is possible in a simple way. It is conceivable, in a manner which is economical in terms of process engineering, for these passages  36  to be produced by perforating during the hydroforming operation which expands the hollow profiled section  6 .  
         [0039]      FIG. 10 , as a modification to  FIG. 9 , shows the pressed assembly of the hollow profiled section  6  and the closure cover  7 , with the closure edge  26  of the hollow profiled section  6  projecting beyond the closure edge  19  of the rim  13  of the closure cover  7 . It should also be pointed out once again at this point that the opening  15  at the cover base  9  serves as a receiving element for a stopper to which a jack can be fitted. Furthermore, the process according to the invention is not restricted only to the production of jack brackets. In addition to the brackets, the process can be used for all components which are to be hydroformed with closure covers that are intended to at least partially close off one or more holes at the component, such as structural elements of a motor vehicle, in particular including closure nodes in a frame structure.