Abstract:
The invention relates to a function element ( 10 ) comprising a head part ( 14 ) with an annular bearing surface ( 12 ) and tubular rivet segment ( 16 ) that is provided on the side of the bearing surface of the head part and that extends away from said head part. The invention is characterized in that a tubular guide segment ( 18 ) is concentrically disposed relative to the tubular rivet segment and radially inside said rivet segment, wherein an annular gap is provided between the guide segment and the rivet segment and the guide segment projects beyond the free end of the rivet segment.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a divisional application of U.S. patent application Ser. No. 10/472,648 filed on Mar. 30, 2004 which claims priority to PCT/EP02/03187 filed on Mar. 21, 2002 which claims priority to German Application No. 101 14 200.5 filed Mar. 23, 2001. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to a functional element having a head part with a ring-like contact surface and a tubular rivet section provided at the side of a contact surface of the head part and extending away from the head part. Furthermore, the invention relates to a component assembly comprising a sheet metal part and a functional element of this kind as well as to a method for the attachment of a functional element of this kind to a sheet metal part. 
       BACKGROUND OF THE INVENTION 
       [0003]    A functional element of the initially named kind is, for example, known from EP-A-539743 and indeed both in the form of a nut element and also in the form of a bolt element. 
         [0004]    Neither the nut element nor the bolt element of EP-A-539793 can be introduced in self-piercing manner into the sheet metal part but rather the sheet metal part must be pre-holed. Furthermore, the sheet metal preparation in EP-A-539793 includes the production of an axially projecting ring lip in the sheet metal part which bounds an opening into which the rivet section of the functional element must be inserted. In this operation the ring lip projects from the side of the sheet metal part from which the functional element is introduced. The projecting lip with the pre-manufactured opening signifies in practice, that the functional element must be aligned with high accuracy with respect to the sheet metal part in order to ensure the orderly attachment of the functional element. 
         [0005]    The object of the present invention is to provide a functional element and also a method for the attachment of the functional element to a sheet metal part which enables a favorably priced attachment of the functional element to a sheet metal part, without placing particular demands on the alignment of the functional element with the component, with the requirements for any eventually necessary preparation of the sheet metal part not being very high and with a high quality connection between the functional element and the sheet metal part nevertheless being achieved. Furthermore, a self-piercing embodiment of the element should be possible, if desired, and, in addition, a connection between the functional element and the sheet metal part should come about which enables an electrically conductive connection, even with coated metal sheets. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0006]    In order to satisfy this object there is provided, in accordance with the invention, a functional element of the initially named kind, which is characterized in that a tubular guide section is arranged concentric to the tubular rivet section and radially within the latter, with a ring gap being provided between the guide section ( 18 ) and the rivet section and with the guide section projecting beyond the free end of the rivet section. Furthermore, a component assembly is provided in accordance with the invention as well as methods for the attachment of a functional element. 
         [0007]    Because a tubular guide section is arranged concentric to the tubular rivet section and radially within the latter, with the guide section projecting beyond the second end of the rivet section, attention is paid in accordance with the invention, when using the functional element with a pre-holed metal sheet, that the guide section moves into the hole of the pre-holed metal sheet and serves, if necessary while dilating the hole, for a centering of the functional element relative to the pre-manufactured hole or relative to the dilated prepared hole. Since the guide process takes place prior to the subsequent dilation of the hole by the rivet section and the subsequent turning over of the rivet section, it is also ensured that a high quality connection always arises between the functional element and the sheet metal part. 
         [0008]    For the pre-holing of the sheet metal part this pre-holing can also be effected in such a way that no projecting ring lip is present at the side of the metal sheet from which the functional element is inserted, which likewise facilitates the alignment of the functional element with the sheet metal part. 
         [0009]    It is particularly favorable with the present invention that the guide section of the functional element can be formed as a piercing section, with the functional element being able to be introduced in self piercing manner into the sheet metal part so that a pre-holing is not necessary at all and the requirements placed on the alignment of the functional element with the sheet metal part are even lower. Through the self-piercing design of the functional element favorably priced manufacture of the component assembly is achieved, since the operation of pre-holing the sheet metal part is omitted. In this way the method of attachment of the functional element to the sheet metal part is also simplified. 
         [0010]    At this point reference should briefly be made to DE-C-3446978 and DE-C-3447006. DE-C-3446978 describes, amongst other things, a nut element which is introduced in self-piercing manner into a sheet metal part whereas DE-C-3447006 discloses a similarly conceived bolt element. Neither the nut element nor the bolt element in accordance with the above-named German patents has a guide section in addition to the rivet section, so that the rivet section must execute both the piercing function and also the riveting function, which is ultimately more complicated and places stricter requirements on the rivet section and on the die than is used that is the case for the present invention. 
         [0011]    It is particularly preferred when the free end of the wall of the ring-like rivet section, when viewed in an axial section plane, is rounded both at the radially outer side and also at the radially inner side and has for example a semi-circular shape or a shape resembling an arrow tip. 
         [0012]    As already indicated the guide section of the functional element leads, on attachment of the functional element to a sheet metal part, to a conical recess in the sheet metal part and indeed, with a preholed sheet metal part, during the dilation of the hole by the guide section and, with a self-piercing embodiment of the functional element, prior to the cutting out of a punching slug by the guide section forming a piercing section, with the conical recess then being dilated by the rivet section. The rounded design of the outer wall of the rivet section in the region of its free end is a favorable shape for the further dilation of the hole and the corresponding deformation of the conical wall of the recess. The rounded shape at the inner side of the free end of the rivet section helps in contrast by adjoining the turning over of the rivet section which takes place in a corresponding, concavely arched, ring surface of the die. This shape also enables the ring gap to be kept as small as possible without impairing the process of the turning over of the rivet section. Since the ring gap can be kept as small as possible, and can indeed amount to 0 mm (which signifies that the inner wall of the rivet section contacts the outer circumference of the guide section), the diameter of the functional element as a whole can be kept as small as possible, whereby material can be saved and costs can be reduced. 
         [0013]    The ring gap preferably has a radial dimension in the range between 0 mm and approximately 3 mm. 
         [0014]    The ring gap preferably ends at an axial spacing from the ring-like contact surface at the rivet section side of the ring-like contact surface. This design leads to a stable attachment of the rivet section to the head part of the element and favors a firm attachment of the functional element to the sheet metal part. 
         [0015]    When the guide section is formed as a piercing section it preferably has a ring-like cutting edge at its end face remote from the contact surface and this cutting edge cooperates with a correspondingly shaped cutting edge of a central bore of a die in order to punch out a clean piercing slug from the sheet metal part during the attachment of the functional element to the sheet metal part. 
         [0016]    It is particularly preferred when features providing security against rotation are provided in the region of the ring-like contact surface and/or at the rivet section and/or at the jacket surface of the head part adjacent to the contact surface. When the features providing security against rotation are provided in the region of the jacket surface of the head part then these can be produced by a polygonal or grooved shape of the jacket surface. The features providing security against rotation in the region of the ring-like contact surface and/or at the rivet section and optionally at the jacket surface can be formed by noses or by groove-like recesses. 
         [0017]    When noses provided security against rotation are provided these can be present in raised form at the contact surface and at the rivet section in the region of the transition from the contact surface into the rivet section. 
         [0018]    The functional element can be present as a hollow element, for example with a cylindrical recess for a rotatively journalled shaft or for a thread cutting or thread forming screw, or as a latch recess for the pin of a clip or other article. 
         [0019]    Moreover, the functional element can be formed as a nut element, i.e. the functional element has a thread cylinder which can be provided either in the head part or in the guide section, or at least partly in the head part and in the guide section. The functional element can, moreover, have a cylindrical bearing surface at the outer side of the guide section and it can also be realized as a bolt element. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    The invention will now be explained in the following in more detail with reference to embodiments and to the drawings which show: 
           [0021]      FIG. 1  a side view of a functional element in accordance with the invention in the form of a hollow body element, 
           [0022]      FIG. 2  a plan view on the upper end face of the functional element of  FIG. 1 , 
           [0023]      FIG. 3  a perspective representation of the functional element of the  FIGS. 1 and 2 , 
           [0024]      FIG. 4  a representation of the functional element of  FIG. 1 to 3  which is partly sectioned in the longitudinal direction and in the initial stage of the attachment of the functional element to a sheet metal part using a die, 
           [0025]      FIG. 5  a representation similar to  FIG. 4  but at a later face of the attachment of the functional element to the sheet metal part, 
           [0026]      FIG. 6  a representation similar to  FIG. 5  but at a later stage of the attachment of the functional element to a sheet metal part, 
           [0027]      FIG. 7  a representation similar to  FIG. 6  after completion of the attachment of a functional element to the sheet metal part and 
           [0028]      FIG. 8  the component assembly of  FIG. 7  after the removal from the tool for the manufacture of the component assembly. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0029]    With reference to the  FIGS. 1 to 4  the functional element  10  shown there is provided with a head part  14  having a ring-like contact surface  12  and a tubular rivet section  16  provided at the side of the contact surface  12  of the head part  14  and extending away from the head part  14 . The functional element has a central longitudinal axis  11 . 
         [0030]    A tubular guide section  18  is arranged concentric to the tubular rivet section  16  and radially within the latter, with a ring gap  20 , which is only evident from  FIG. 4 , being provided between the guide section  18  and the rivet section  16 . 
         [0031]    As likewise evident from  FIG. 4  the free end  22  of the wall of the ring-like rivet section  16  is rounded when seen in the axial section plane of  FIG. 4 , both at the radially outer side  24  and also at the radially inner side  26  and has here a rounded shape resembling an arrow tip. The tip of the shape resembling an arrow tip could however likewise be rounded, whereby a semicircular shape would result, which is however not shown. 
         [0032]    In the representation of  FIG. 4  the ring gap has a radial dimension of 0 mm, i.e. the rivet section contacts the guide section  18 , is however first connected to the guide section  18  where the ring gap  20  finishes at a short axial distance “a” in front of the ring-like contact surface  12 . 
         [0033]    The functional element of  FIGS. 1 to 4  is normally manufactured by a cold heading process, the basic principles of which are well known. For the manufacture of the rivet section, which closely contacts the guide section, it can be necessary to first manufacture the rivet section with a certain radial spacing from the guide section by cold heading and to subsequently press the rivet section against the guide section in a further face of the cold heading process, or to dilate the guide section until it contacts the rivet section, or to achieve the reduction of radial spacing by a combination of both measures. It is favorable when the ring gap  20  has the smallest possible radial width since this leads to a compact design of the functional element and saves material. 
         [0034]    The guide section  18  is formed here as a piercing section and has a ring-like cutting edge  28  at its end face remote from the contact surface  12 , i.e. at its free end. 
         [0035]    The  FIGS. 1 to 4  furthermore show features  30  providing security against rotation in the region of the ring-like contact surface  12  and at the rivet section  16 , with the features providing security against rotation being formed here by noses which are present in raised form at the contact surface  12  and at the rivet section  16  in the region of the transition from the contact surface into the rivet section  16 . The noses providing security against rotation shown here are provided with side flanks  30  and  32  which lie in planes extending in the longitudinal direction of the element. The noses providing security against rotation, which have sharp edges in  FIGS. 1 and 4  at  34  and  36 , can instead be provided with rounded edges. The noses providing security against rotation can also be realized by recesses in the contact surface or in the rivet section. The possibility also exists of providing the jacket surface  36  of the head part  14  with a polygonal or grooved shape. The functional element is realized here as a nut element and has a thread cylinder  38  which is arranged coaxial to the longitudinal axis  11  of the functional element and in this example is present partly in the guide section  18 . A further special feature of the nut element of  FIGS. 1 to 4  is to be seen in the two lugs  40  which project out from the upper end face of the element  10  and which are produce in that material is displaced upwardly from the regions  42  during the cold heading process so that corresponding recesses arise at the points  42 , with the designation “upwardly” to be understood only in regard to the representation of  FIG. 1  and, as other descriptions of position in this application, is only used in relation to the Figures, and does not represent any spatial restriction of the subject of the invention. The lugs  40  ensure that a cable shoe can be secured on the functional element by means of a screw inserted from above without the cable shoe being rotated with the screw during the attachment of the screw, since a co-rotation of the cable shoe is prevented by the lugs  40 . As is in particular evident from  FIG. 4  the functional element  10  has cylindrical recesses  44  and  46  above and below the thread cylinder  38 , with these free spaces having a diameter which is normally made fractionally larger than the outer diameter of a screw which is screwed into the thread cylinder  38 . 
         [0036]    Although the thread cylinder  38  is present here partly in the head  10  part  14  and partly in the guide section  18  of the functional element it could also be arranged fully in the head part or fully in the guide section. 
         [0037]      FIG. 4  shows the functional element  10  in a first stage of the attachment to the sheet metal part, with the sheet metal part  50  being supported in the representation of the  FIG. 4  on a die  52  and being pressed against the die  52  by means of a ring-like hold-down member  54 , with the hold-down member  54  preferably being provided but not being essential. 
         [0038]    The representation of  FIG. 4  assumes that the attachment of the functional element to the sheet metal part  50  takes place in a press, with the die being arranged in the lower tool of the press (not shown) and the functional element  10  being pressed by means of a likewise not illustrated setting head onto the sheet metal part  50 , with it being possible for the setting head to be attached to an intermediate plate of the press or to an upper tool of the press. Such setting heads and hold-down members  54  are extremely well known in the prior art and are thus not especially described here. It should however also be brought to expression that other arrangements within a press are possible. For example, the die  52  can be arranged in an intermediate plate of the press, with the setting head with or without a hold-down member then being attached to the upper tool of the press. It is also possible to provide the die  52  at the upper tool of the press and to then attach the setting head with or without a hold-down member on an intermediate plate of the press or on the lower tool of the press, i.e. to attach the functional element  10  in the inverse direction beneath the sheet metal part  50 . 
         [0039]    It is also entirely possible to attach the functional element  10  to the sheet metal part  50  by a robot, with the robot or an auxiliary robot then holding the die  52  beneath the sheet metal part and serving for the application of the pressing force onto the functional element  10  which is required for the attachment. 
         [0040]    In  FIG. 4  a two-part design of the die  52  is shown. This consists of an outer ring-like die part  54  and an inner likewise ring-like die part  56  with a central longitudinal bore  58 . In this example the inner die part  56  has a slightly conically extending outer wall which cooperates with a correspondingly shaped conically extending inner wall  53  of the outer die part  54  so that the upper end face  60  of the inner die part  56  comes to lie below the upper end face  62  of the outer die part  54  and hereby forms a recess  64 . The upper end  60  of the inner die part  56  thus forms the base surface of the recess  64  and has in other respects a ring-like, concavely arched surface  66 . The central bore  58  of the central die part  56  has a diameter which is fractionally larger than the outer diameter of the guide section  18 . The recess  64  has a diameter which is somewhat larger than the outer diameter of the head part  14  of the functional element  10  plus twice the thickness of the sheet metal part  50 . 
         [0041]    Both the inner die part  56  and also its bore  58  and also the outer die part  54  and the recess  64  defined between the two die parts are arranged coaxial to the central longitudinal axis  11  of the functional element  10 . The die  52  could also be formed in one piece. 
         [0042]    Starting from the stage of  FIG. 4  the functional element  10  is now pressed against the sheet metal part  50  in accordance with  FIG. 5  by the application of a force in the direction of the arrow  70  onto the upper end face of the functional element  10  by means of the setting head, for example in the press, or by using a robot and with simultaneous support of the die, with the optionally provided hold-down member  54  having been omitted in  FIG. 5  for the sake of the illustration. 
         [0043]    One sees that the guide section presses the sheet metal part against the upper end face  60  of the inner die part  56  and has drawn the metal sheet into a conically extending recess  72 . At this stage the ring-like cutting edge  28  of the guide section which is formed as a piercing section  18  has not yet started to cut through the sheet metal part  50  and the free lower end  22  of the rivet section  16  has not yet contacted the sheet metal part  50 . 
         [0044]    In the further stage of  FIG. 6  the guide section  18  has cut out a piercing slug  74  from the base of the conical recess of the sheet metal part and has partly pressed the latter through the central bore  58  of the die, with it being possible for this central bore  58  to be formed so that it also diverges slightly downwardly, so that the piercing slug can be disposed off via this central longitudinal bore by gravity, optionally with pneumatic assistance. 
         [0045]    After the separating out of the piercing slug the rounded outer wall  64  at the free end of the rivet section  16  has also pressed the wall of the conical recess of the sheet metal part  50  away from the central longitudinal axis  11 , i.e. brought the wall into a somewhat steeper position and dilated the hole  76 , which has arisen by the cutting out of the piercing slug  74 , to such an extent that the free end of the rivet section  16  can now be pressed through the hole  76 , so that the inner curved wall  26  of the free end of the rivet section can be brought into contact with the ring-like recess  66 , whereby, during a further downwardly directed movement of the functional element as a result of the pressure in the direction of the arrow  70 , the tubular rivet section  16  is turned over to form a rivet bead  78  in accordance with  FIG. 7 . Through this turning over (or riveting) process the sheet metal part  50  is so deformed in the region of the previous conical recess that it is clamped in form-fitted manner between the ring-like contact surface  12  and the turned over rivet section. At the same time the noses  30  providing security against rotation are pressed into the sheet material so that a corresponding security against rotation also arises. When the features providing security against rotation are formed by corresponding recesses then the sheet material is pressed into such recesses whereby a security against rotation likewise arises. 
         [0046]    The sheet material is however simultaneously partly pressed into the recesses  42  which have arisen through the formation of the lugs  40  so that a security against rotation also arises in this region. Should the head part  14  with the functional element  10  have a polygonal or grooved or ribbed shape, then a corresponding form-fitted connection between the sheet metal part and the functional element is also produced in this region. 
         [0047]    One can see from  FIG. 7  that the guide section  18  enters ever deeper into a central bore  58  of the inner die  56  during the attachment of the functional element  10 , whereby a reliable guidance of the functional element is achieved. 
         [0048]    The finished component assembly consisting of the functional element  10  and the sheet metal part  50  is then shown in  FIG. 8  after the removal out of the attachment tooling, i.e. out of the press or out of the robot or out of attachment tools which are conceived differently. 
         [0049]    One can see that the guide section projects significantly beyond the turned over rivet section  16  and it is thus possible to subsequently use this guide section as a cylindrical bearing surface. This likewise applies to the jacket surface of the head part  14  which projects out of the sheet metal part  50  at the other side of the sheet metal part. It is in other respects also possible to dimension the arrangement such that the body part  14  is accommodated still further within the recess in the sheet metal part or indeed fully within this recess. In the finished state in accordance with  FIG. 8  a further component, i.e. another sheet metal part or a cable shoe can be secured either to the upper end face of the functional element or to the lower end face of  FIG. 8 , i.e. the corresponding screw can be introduced into the thread cylinder coming from above or from below. It would be possible to attach components both at the bottom and also at the top. Furthermore, both the guide section  18  and also the head part  14  can act as a spacer element, so that the element can be introduced into a hollow component consisting of two sheet metal parts. However it would here probably be necessary to pre-hole the component  50 , which is basically also possible and indeed also when the sheet metal part is on its own, i.e. is not assembled to a further sheet metal part to form a hollow component. The lugs  40  are only optionally provided and indeed in particular when the element is to be used as an electrical connection element, for example as a earth connection element in a vehicle body. 
         [0050]    The functional element  10  in accordance with the present invention has the special advantage that it can also be used with sheet metal parts  50  provided with protective layers or paint layers and nevertheless generates an excellent electrical connection, and indeed in the region of the pierced hole, with the noses providing security against rotation which locally cut through the protective coating, especially with a sharp edged design of the noses providing security against rotation and serving for a metallic connection to the sheet metal part  50 . Moreover, the protective layer is damaged at points which lie within the form-fit between the sheet metal part  50  and the functional element so that a seal takes place there and corrosion is prevented. The form-fitted connection between the sheet metal part and the functional element is so intensive that the connection represents a sealed connection which, when a special seal is required, can also be assisted by the application of an adhesive to the element of the sheet metal part. Through the recess of the sheet metal part  50  in the region of the functional element an excellent connection to the sheet metal part is ensured, so that a high resistance against pullout forces in both directions is generated and, moreover, a high resistance against shear forces and torsional forces is present. In addition the element can be used with alternating dynamic loadings and fatigue effects with dynamic loadings are not to be feared. 
         [0051]    The functional elements described here can for example be manufactured from all materials which reach the strength class 5.6 or higher. Such metal materials are normally carbon steels with 0.15 to 0.55% carbon content. 
         [0052]    In all embodiments all materials can be named as an example for the material of the functional elements which achieve the strength values of class 8 in accordance with the ISO standard in the context of cold deformation, for example a 35B2 alloy in accordance with DIN 1654. The so formed fastening elements are suitable, amongst other things, for all commercially available steel materials for drawing quality sheet metal parts as well as for aluminium or its alloys. Aluminium alloys, in particular those of higher strength, can be used for the functional elements, for example AlMg5. Moreover, functional elements of higher strength magnesium alloys such as, for example, AM5O can also be considered.