Patent Publication Number: US-2018036833-A1

Title: Fastening element

Description:
The invention relates to a fastening element with a shaft, of the type specified in the preamble, of claim  1 , and to a tool for setting a fastening element of this kind, of the type specified in the preamble of claim  1 . 
     DE 20 2004 014 071 U1 relates to a generic fastening element which comprises a flange with a connection region for attachment to a component. On the side of the flange which faces away from the connection region, the fastening element further comprises a shaft. For connecting the fastening element to a component, an axial force is applied on the flange surface by a drive tool having a tubular pressure piece which is slid over the shaft area. A recess is used to fix the fastening element in the direction of rotation so as to enable the fastening element to be welded to the component by rotation of the drive tool. 
     The pressure piece ensures shock-free rotation of the bolt which will thus rotate smoothly about its rotational axis which lies on the shaft axis. 
     The disadvantage of this arrangement is that it requires the inner diameter of the pressure piece to be adapted very precisely to the shaft diameter to ensure the intended function. In this arrangement, an insertion aid in the form of a conical taper facilitates the mounting of the precisely fitting workpiece. Consequently, a matching tool is required for every shaft diameter. Moreover, this arrangement is subject to wear because only slight material erosion can be tolerated in view of the requirement for high fitting accuracy. 
     It is an object of the invention to overcome the abovementioned disadvantages. 
     This object is accomplished by the characterizing features of claim  1  in combination with the features of its preamble. 
     An advantageous embodiment of the invention is specified in the dependent claims. 
     In a known manner, a fastening element for connecting to a component comprises a flange with drive structures, with a connection region being integrally formed on said flange, through the fusing of which the fastening element can be fastened to the component by friction welding. The fastening element further comprises a shaft which is arranged on the side of the flange opposite the connection region. The fastening element further comprises a guide region between the shaft and the connection region in the axial direction, which guide region comprises a guide surface that comprises at least a segment of an outer surface which segment is associated with a cone which broadens in the direction of the connection region. 
     The invention is characterized in that the guide region has an axial pressure surface on the end thereof which faces the shaft, wherein the extension of the axial pressure surface in a radial direction is greater than the diameter of the shaft. Since the axial pressure forces required for the fitting can be transmitted via the end face which is in particular planar and orthogonal to the shaft axis, the guide region merely has to perform a centering function. This considerably minimizes tool wear. Furthermore, any uneven rotary movement is thus avoided. 
     More specifically, the axial pressure surface is in the form of an annular surface which is offset from the flange or the shaft. A pressure piece having an annular surface and a conical recess for transferring the contact pressure and for providing centered guidance during operation can engage this annular surface which transitions into the lateral guide surface. As a result, most of the area within the annular surface can largely be designed freely, irrespective of any centering functions. 
     A drive tool may for example be provided for driving such a fastening element, which drive tool comprises a pressure piece having an annular surface whose recess is larger than the shaft diameter and whose outer dimensions roughly correspond to the extension of the end face. In addition, the pressure piece may be designed such that the annular surface forms the upper face of a frustum which conically widens in the fastening direction. Such, an outer surface will thus form a contact area with the guide surfaces of the guide region, with the annular surface at the same time pressing on the axial pressure surface. 
     This allows the rotating fastening element to be held securely centered during the fastening process, The presence of the lateral conical guide of the fastening element in the guide region thus allows the shaft to be designed regardless of any centering requirements. This makes it possible to use only a single drive tool for processing fastening elements of different shaft diameters which are smaller than the diameter of the recess. A uniform guide region can be provided to meet this need. 
     An arrangement of the guide region between the shaft and the flange is thus achieved in a particularly advantageous manner. This also allows the flange with its drive means to be designed irrespective of any centering requirements. In such an arrangement, the guide region extends radially within the drive means. This ensures smoother guiding. Moreover, this design is particularly well suited for production by cold forming. 
     In the abovementioned embodiment, the guide region can be offset from the flange. This allows the pressure region and the guide region and drive region to be separated from one another. 
     In yet another embodiment, the flange may comprise the guide region. This means that in the direction of the connection region, the guide region transitions smoothly and without any offset into the flange with the drive structures. 
     In a preferred embodiment, the guide surface takes the form of a completely circumferential outer surface of the associated cone, This is a particularly rotationally symmetrical design which thus avoids imbalances around the shaft axis. 
     Preferably, the cone of the guide region can form an angle of between 35° and 65° with the axis of the fastening element. This angle range allows a particularly good centering effect to be achieved during rotation. 
     The extension of the pressure surface, which is in particular of annular shape, is chosen such that the contact pressures required for setting the fastening element can be transferred from the pressure piece of the drive tool to the fastening element via this pressure surface. 
     The extension of the pressure surface is essentially dependent on the material of the component and on the material of the fastening element. 
     Dimensions sufficient for transmitting the contact, pressure may be present if the extension of the end face facing the shaft is larger by at least 10% than the diameter of the shaft. This allows a sufficient pressure surface to be provided for the fastening element. For a common shaft diameter of 6 mm, an end face diameter of at least 7 mm is reasonable, for example. 
     Another preferred embodiment is obtained if the outer diameter of the end face is 7 mm and the outer diameter of the shaft is 6 mm or 5 mm or 4 mm. The specific design of the guide region and the flange thus makes it possible to use a single drive tool design for reliably attaching a multitude of different standard shaft diameters, without having to change the drive tool. 
     More specifically, the shaft is of the threaded type, with the shaft diameter corresponding to the outer diameter of the thread. 
     The end face is preferably normal to the shaft axis and thus has a particularly rotationally symmetrical design which very much improves centering during the setting process. 
     The fastening element may preferably comprise a connection region having an end which is designed such that it fixes a contact area. 
     In a particularly advantageous embodiment, the fastening element may be designed such that the contact area determined by the connection region is plane-parallel to the end face, preferably both are orthogonal to the shaft axis. The plane-parallel orientation of the contact area and the end face makes it possible to ensure particularly smooth running of the fastening element during rotation. 
     The invention furthermore relates to a fastening system comprising a fastening element for connection to a component, wherein the fastening, element comprises a flange with drive structures, with a connection region being integrally formed on the flange through the fusing of which the fastening element can be fastened to the component by friction welding, wherein the fastening element has a shaft which is arranged on the side of the flange opposite the connection region. The fastening element further comprises a guide region between the shaft and the connection region in, the axial direction, which guide region comprises a guide surface which comprises at least one segment of an outer surface that is associated with a cone which broadens in the direction of the connection region. 
     The fastening system further comprises a tool for attaching a fastening element of the abovementioned type, said tool having a drive recess for transmitting a rotary movement, and comprises a pressure piece which is partially hollow and which has a frustum-shaped recess on its end which faces the fastening element, said recess constituting a tool-side guide surface. 
     According to the invention, the pressure piece and the axial pressure surface are adapted to one another so as to reliably transmit the pressure force required for the setting process, and the guide surface on the tool side and the guide region on the fastening element side are adapted to one another so as to enable the pressure piece and the flat pressure surface to abut on one another and the guide region and the guide surface to be brought into contact with each other by an eccentric position of the inserted fastening element. 
     More specifically, the guide surfaces of the tool and the guide surfaces of the fastening element have the same angle. When the axial pressure surfaces of the tool and of the centrally inserted fastening element contact each other, the guide surfaces will be parallel and slightly spaced from one another. Said minor spacing can preferably be between 10 μm and 1 mm. 
     The fastening element may preferably be of the above mentioned design. 
    
    
     
       Additional advantages, features and possible applications of the present invention may be gathered from the description which follows, in connection with the embodiments illustrated in the drawings. 
       Throughout the description, claims and drawings, those terms and associated reference signs are, used as are listed in the List of Reference Signs below. In the drawings, 
         FIG. 1  is a view of a friction element which can be connected to a component via a rotary movement and the application of an axial force; 
         FIG. 2  is a view of another embodiment of a friction element according to the invention; 
         FIG. 3 a    is a cross-sectional view of a fastening element of  FIG. 1 ; 
         FIG. 3 b    is a view of the fastening element completely received in the drive tool; 
         FIG. 4  is a view of an embodiment in which a drive tool is provided which comprises a pressure piece that is provided radially outside the drive means; 
         FIG. 5 a    is a cross-sectional view of a fastening system before a fastening element is completely received in a tool, and 
         FIG. 5 b    is a cross-sectional view of a fastening system after a fastening element has been completely received in a tool. 
     
    
    
       FIG. 1  is a view of a fastening element  10  according to the invention which can be connected to a component  12  by means of a rotary movement and the application of an axial force F. The fastening element  10  comprises a flange  14  with drive means thereon for transmitting a rotary movement from a tool to the fastening element  10 , The drive means are provided in the form of an external hexagon drive. In the direction of the shaft  16 , a guide region  18  follows after the flange  14 . The guide region  18  is frustum-shaped and offset from the flange  14 . On its end facing the shaft, the frustum has a flat surface  20  which constitutes an annular surface. The contact pressure required for the friction welding connection is, transmitted from the flat surface  20  to the fastening element  10 . A frictional connection can thus be achieved between the fastening element  10  and the component  12  through the fusing of a connection region  22 . The conical guide surface  24  acts to center the fastening element  10  on associated guide surfaces of a drive tool (not shown) during the fastening process. This ensures uniform rotation of the fastening element  10  about its axis and ensures shock-free running of the fastening element  10  during the friction welding process. 
     The way the fastening element  10  cooperates with the tool will now be described with reference to the next Figures. 
       FIG. 2  is a view of another embodiment of a fastening element  30  according to the invention. In this embodiment, the connection region  32  fleshly transitions into the flange  24 . On the one side of the flange  34 . the fastening element has a connection region  36  and, on the side opposite the connection region, a shaft  38 . The drive means are provided in the form of toothing  35 . A cross-sectional view of this embodiment of the fastening element  30  will now be described in more detail with reference to  FIGS. 3 a  and 3 b   . The required contact pressure forces are transmitted via the flat annular axial pressure surface  37 . 
       FIG. 3 a    is a cross-sectional view of a fastening element  30  of  FIG. 1 . The fastening element  30  has drive means  35  which are formed in the flange  34  as recesses. Respective associated drive means  52  for transmitting the rotary movement are integrally formed on the drive tool  50 . The drive tool  50  also has a pressure piece  54 . 
     The pressure piece  54  is used to transmit the contact pressure to the fastening element  30 . For this purpose, the fastening element  30  has an annular axial pressure surface  56  which transitions into a conical guide surface  58 . In the feeding operation, the fastening element  30  is first clasped by the drive means  35  and then its guide region  32  is inserted into a matching recess in the pressure piece  54 . The annular axial pressure surface  56  thus presses down on the axial pressure surface  37 , which is formed as an annular surface around the shaft, in the fastening direction. During rotation, the fastening element  30  is centered via the guide surfaces  34  and the corresponding conical guide surface  58  of the drive tool  50 . This ensures smooth running of the fastening element  30  without any wear due to the high contact pressures since no contact pressure is exerted on the conical guide surface  58  of the drive tool  50 . 
     The fastening element  30  is thus first guided by the drive portion of the drive tool  50  and its axial pressure surface  37  is then made to contact the annular axial pressure surface  56  of the pressure piece  54 . 
       FIG. 3 b    is a view of the fastening element completely accommodated within the drive tool  50 . Once the axial pressure surfaces  37  of the fastening element abut on the axial pressure surface  56  of the pressure piece  54 , the drive means  52  will be spaced from the drive means  35  of the fastening element. This will prevent jamming of the fastening element  30  with the drive means  52  as the fastening element  30  is balanced and/or centered by the pressure piece  54 . The corresponding guide surfaces  34 ,  58  have so much play that there will be no axial forces acting on the guide surface  34  of the fastening element  30  if it is in an ideal centric and straight position. 
     The corresponding axial pressure surfaces  37  of the fastening element  30  and the axial pressure surface  56  of the drive tool  50  reliably transmit the axial force F required for the frictional welding process, with the guide surface  58  of the drive tool  50  together with the corresponding guide surface  34  ensuring a stable position during insertion. 
       FIG. 4  is a view of an embodiment in which the axial pressure surface  90  is provided radially outwardly of the drive means  84 . The fastening element  80  has a guide region  82  which is arranged between the flange  86  with the drive means  84  and the connection region  88 . 
     This design allows the entire area which is radially inwardly of the annular axial pressure surface  90  of the centering element  82  to be designed freely without having to ensure the stabilization of the element. Consequently, in particular with such a design, premounted elements, e.g. a fastening element  80  in the present case, can be mounted on a component with a nut  92 , which still allows a stable attachment ensuring smooth running. 
       FIG. 5 a    is a view of a fastening system  100  comprising a fastening element  102  as well as a tool  104  for attaching a fastening element  102 . As already described before, the fastening element comprises a flange  106  having drive structures  108 . A connection area  110  is integrally formed on the flange  106  through the fusing of which the fastening element  102  can be connected to its surface. Between its shaft  112  and its connection area  110 , the fastening element  102  has a guide region with a guide surface  114 . The fastening element  102  further comprises an axial pressure surface  116 . This axial pressure surface  116  cooperates with an axial pressure surface  118  of the tool  104  so as to transmit the contact pressure from the tool to the fastening element  102 . The guide surface  114  of the fastening element  102  is arranged so as to be parallel to the guide surface  120  of the tool. The guide surface  120  of the tool is designed as a conical recess and thus adapted to correspond to the conical guide surface  114  of the fastening element  102 . 
     As may be seen in  FIG. 5   b,  which is a cross-sectional view of the fastening element  102  fully inserted, the pressure force is transmitted via the axial pressure surfaces  116 ,  118  which come to lie on one another, with a small distance remaining between the guide surfaces  120 ,  114  which distance will not affect the transmission of the axial pressure but will act to keep any tipping of the fastening element  102  from its rotational axis within narrow limits. Particularly secure and high-quality fastening is thus achieved.