Patent Publication Number: US-2016221069-A1

Title: Rivet element

Description:
The invention relates to a rivet element for attachment to a component, in particular to a component of a fiber composite material, to a component assembly of a corresponding rivet element and a component and also to a method for the attachment of the rivet element to a component and to a method for manufacture of a rivet element. 
     For the attachment of fastener elements, such as in particular rivet elements to components of sheet metal or of fiber composite material one previously assume that it is necessary to form an opening in the component for the fastener element in preparation for the attachment process. For components of fiber composite materials in particular a procedure of this kind is however associated with considerable disadvantages, since discontinuities arise through the openings in the material which considerably weaken the material and particularly at positions where a particularly high material strength is required for the reliable anchorage of the fastener elements. 
     The object of the invention is thus to provide a possibility for attaching rivet elements to components in which the components do not have to be weakened in disadvantageous manner, with it in particular being possible to attach fastener elements to components of fiber composite materials. 
     This object is satisfied by the invention by a rivet element having the features of claim  1 , by a component assembly having the features of claim  10  and by a method having the features of claims  11  and  12 . 
     The rivet element in accordance with the invention has a flange section which contacts the component in the installed state and a rivet section. The rivet section includes a tip which converges in a direction away from the flange section with a diverging end portion being provided at the end of the tip remote from the flange section. 
     Through the formation of the rivet section as a tapering tip it is possible to first press the tip of the element into the respective material. The divergence of the end section at the end of the tip adjacent the component ensures that on pressing the rivet section into the component, the tip experiences a progressive dilation through the cooperation with the material of the component which, in the further course of the pressing in process, also includes the tip. Thus, on pressing in of the rivet section it undergoes a progressive deformation for the formation of a rivet connection. The dilated end portion thus reliably ensures that the reshaping of the rivet section takes place in a controlled manner, namely in such a way that the rivet section is beaded over outwardly. 
     For components which are manufactured from a material which enables such a pressing in of the rivet section, at least in specific states, one can dispense with the manufacturing of an opening for the rivet element. The rivet element in accordance with the invention is consequently especially suited for components of fiber composite materials which are at least temporarily in a state in which the material is efficiently soft or “pasty”. This will be discussed further in the following. Basically, the rivet elements in accordance with the invention can be used in conjunction with duroplastic or thermoplastic materials or components. 
     A further advantage of the invention lies in the fact that it is not essential to adhesively bond the fastener element to the component. An adhesive bond can however naturally also be additionally provided. 
     In accordance with an advantageous embodiment of the rivet element a restriction forming a waist is present between the end portion and the converging tip. I.e. the dilation of the end portion is executed in such a way that a minimum external circumference of the rivet section is not present at its free end but rather between the tip and the free end of the end portion, which ultimately also defines the free end of the rivet section. In particular, the end portion diverges at least regionally in the direction away from the flange portion. 
     The rivet section can include a plurality of segments which are in particular of tongue-like shape, are preferably connected to one another and which, on dilation of the rivet section during the installation of the rivet element, can be moved apart from one another in order to manufacture a rivet connection. In particular, the segments become narrower in each case along a central axis in the direction away from the flange section. At the interconnection points the segments can each have an intentional material weakness in the manner of a point of intended fracture, for example by a lower wall thickness. The dilation of the tip is in this case associated with a breaking open of the tip in order to move the segments apart from one another. Alternatively, the segments can be not connected together, at least regionally, and thus either lie in contact with one another or are slightly spaced from one another, so that in the initial state they jointly form a tip serving for the pressing of the rivet element into the component and can subsequently be moved apart from one another without breaking open of material. For example, the rivet section includes a plurality of in particular tongue-like segments which jointly form the tip and which can be moved apart during the dilation of the tip. 
     In accordance with a simple embodiment of the rivet element of the invention which is efficient to manufacture the rivet section is formed by reshaping it from the originally hollow cylindrical base body. I.e. the base body is reshaped in the course of manufacturing process of the rivet element to form a tip. In doing this the material of the base body can undergo folding, so that the tips which are produced during the reshaping process have the contour of a flower or a rosette in a cross-section perpendicular to the longitudinal axis of the rivet element. Basically, the end portion can also be shaped during the reshaping process. However, this preferably takes place in a separate step. 
     The rivet section can have a substantially cylindrical portion which is adjoined by the tip. The cylindrical portion is in particular arranged between the flange section and the tip. 
     In order to be able to dispense with an adhesive bonding of the rivet element to the component and/or to achieve a particularly reliable fixation of the element the flange section can be provided with means for providing security against rotation. These means are, for example, recesses and/or ribs which extend in the radial direction. 
     The rivet elements in accordance with the invention can be formed as a nut element or as a bolt element. 
     The invention furthermore relates to a component assembly consisting of a rivet element in accordance with at least one of the previously described embodiments and a component, in particular a component of fiber composite material. 
     In a method in accordance with the invention for the attachment of a rivet element in accordance with at least one of the above-described embodiments to a component, in particular to a component of fiber composite material, the rivet element is pressed into a non-prepared component, in particular into a component which is not provided with an opening for the element. The component thereby lies, at least in the region into which the rivet element is introduced, on a substantially planar support surface or base. In other words, in this method no die button is required. The reshaping of the rivet section for the formation of the rivet connection which fixes the rivet elements of a component takes place, as already explained, automatically as a result of the design of the end portion of the rivet section. Ultimately a planar surface functions as a “die button” which leads to considerable cost savings. 
     In a method in accordance with the invention for the manufacture of a rivet element in accordance with at least one of the above-described embodiments, the end section is shaped in that a spike is pressed into the end remote from the flange section of a pre-shaped tip provided at the rivet section. This therefore takes place before the rivet element is secured to a component. The pre-shaped tip is thus the “precursor” of the end portion formed on the finished rivet element. 
     In accordance with a preferred embodiment the method of manufacture the pre-shaped tip is formed at least regionally by reshaping a hollow cylindrical base body at least once as was already described above. The end portion is subsequently generated by pressing the spike into the free end of the pre-shaped tip. Basically it is however also possible to form the end portion during the reshaping process of the base body. 
     In order to facilitate this, provision can be made for the tip to have an insertion aid for the spike, in particular of funnel-like shape. 
     The spike is in particular made substantially in the shape of a right cone. 
     The invention can advantageously be used both in connection with fiber composite materials with relative short fibers as well as with materials with relatively long fibers. Components with short fibers can be manufactured in an injection molding process. In this connection the material mixture is readily deformable so that the tools which are used during the manufacture of these components can simultaneously be exploited for the attachment of rivet elements. With many plastic materials it is then possible, in similar manner to the deep-drawing of sheet metal parts, to press the parts by the introduction of heat and by means of a tool into a specific shape. The presses that are used for this can simultaneously be used for the introduction of the rivet element into the adequately soft composite material. 
     In both cases, both with short fiber and also with long fiber material the circumstance is exploited that the rivet element in accordance with the invention can be pressed into the material which is adequately soft at least for a time as a result of the process. 
     Preferred further developments of the invention are also set forth in the dependent claims, in the description and in the drawings. 
    
    
     
       The invention will now be explained in the following purely by way of example with reference to an advantageous embodiment and to the drawings. In which are shown: 
         FIG. 1  a perspective view of an embodiment of the rivet element of the invention, 
         FIG. 2  a partly sectioned side view of the rivet element in accordance with  FIG. 1 , 
         FIG. 3  an end view of the rivet element in accordance with  FIG. 1 , 
         FIG. 4  a sectional view of the rivet element in accordance with  FIG. 1  in a plane perpendicular to the longitudinal axis which intersects the rivet section, 
         FIG. 5  a side view of the rivet element of  FIG. 1  before the dilated end portion is formed, 
         FIG. 6  a side view of the rivet element in accordance with  FIG. 1  after the dilated end portion has been formed with the aid of a spike, 
         FIG. 7  a rivet element in accordance with  FIG. 1  shortly before the penetration into the component, 
         FIG. 8  a rivet element in accordance with  FIG. 1  shortly after the penetration into the component, and 
         FIG. 9  the rivet element in accordance with  FIG. 1  in a state fixed to the component. 
     
    
    
       FIG. 1  shows an embodiment  10  of a rivet element in accordance with the invention. The rivet element  10  includes a flange section  21  which extends radially with respect to a central axis  15  of the element. A fastener portion  27  which can, for example, be provided with an external thread, extends in the axial direction from a side of the flange section  21  remote from the component in the installed state. 
     In this embodiment the rivet element  10  is consequently formed as a bolt element. This is however not essential. In an alternative embodiment the rivet element in accordance with the invention can, for example, also be formed as a nut element which has a bore or an opening provided with an internal thread as the fastening portion. 
     The lower side of the flange section  21  remote from the fastener portion  27  serves as a contact surface  23  for a component  51  (see in particular  FIG. 9 ) to which the rivet element  10  is to be attached. The contact surface  23  is provided with a plurality of recesses  25   b  and projecting ribs  25   a  which extend in the radial direction and which serve as a security against rotation. 
     A rivet section  11  extends in the axial direction from the side of the flange portion  21  remote from the fastener portion  27 . Starting from the flange section  21  the rivet section  11  first has a short substantially cylindrical portion  19  which merges into a tip  12   a . The tip  12   a  tapers or converges in a direction away from the flange section  21 . At the end of the tip  12   a  remote from the flange section  21  an end portion  12   b  is provided which, in contrast to the tip  12   a , has a divergent shape. A restriction  12   c  of the rivet section  11  is present between the tip  12   a  and the end portion  12   b . Here the outer diameter of the rivet section  11  is minimal so that a waist is formed. The waisting of the rivet section  11  is, in the present embodiment, comparatively pronounced. The rivet section  11  can in certain cases admittedly be even more pronouncedly waisted. As a rule however a less pronounced restriction is sufficient in order to achieve the desired effect. It is indeed also possible for the end portion  12   b  to have an only slightly diverging almost coaxial design, since a slight dilation of the end portion  12   b  ultimately also leads to an outward bending of the rivet section  11  on being pressed into the component  51 . 
     The rivet section  11  is formed by a plurality of tongue-like segments  13  which extend from the flange section  21  and form the converging tip  12   a  of the rivet section in the manner of a closed bud, with the end portion  12   b —pictorially described—indicating an opening of the bud. The four segments  13  in this embodiment—more than four or less than four segments could also be provided—are consequently formed in such a way that they become narrower along the middle axis  15  starting from the flange section  12 . 
     The walls of radially inwardly projecting bends  16  of the connections between the segments  13  have contact surfaces  14 —as will be explained in more detail in the following—which arise during the dilation of the end portion  12   b.    
     The rivet section  11  of the rivet element  10  makes it possible to press the rivet element  10  into a sufficiently soft component to which the rivet element  10  is to be attached without it being necessary to form an opening for the rivet element  10  in the component in a preparatory step. 
       FIG. 2  shows a partly sectioned view of the rivet element  10  in accordance with  FIG. 1  in order to make clear the shaping of the tip  12   a  converging in the axial direction and the dilation of the end portion  12   b.    
       FIG. 3  shows a side view of the rivet element  10 . It can be seen that the rivet section  12  is produced by folding so that the rosette-like contour of the end portion  12   b  and of the tip  12   a  results. The comparatively straight contour sections  13   a  in the regions of the segment  13  are connected to one another by radially inwardly projecting bends. The bends  16  define, in a three-dimensional consideration, valleys the beds of which approach the central axis  15  in the region of the tip  12   a  with an increasing distance from the flange section  21 . 
       FIG. 4  shows, by way of clarification of this shape, a section through the rivet section  11  above the restriction  12   c.    
       FIG. 5  shows an intermediate state of the rivet element  16  during its manufacture. In a basic state the rivet element  10  has a hollow cylindrical base body  12   a ″ which projects away from the flange section  21  as is indicated in broken lines in the left part of the drawing. The pre-shaped tip  12   a ′ is formed by reshaping of the base body  12   a ″. Through the shaping process a funnel-like introduction aid  17  for a spike  31  (see  FIG. 6 ) formed in the pre-shape tip  12   a ′ serves for the dilation of the pre-shaped tip  12   a′.    
       FIG. 6  shows the finished rivet element  10  after the end portion  12   b  has been formed by pressing of the spike  31  into the pre-shaped tip  12   a ′. In this connection the contact surfaces  14  have arisen at the inner sides of the folds  16 . The gradient of the flanks of the spike and its depth of penetration into the pre-shaped tip  12   a ′ determine the degree of dilation of the end portion  12   b.    
     A possible sequence for the attachment of the rivet element  10  in accordance with the invention to component  51  is shown in  FIGS. 7 to 9 . 
       FIG. 7  shows the planar support  53  which serves as a support surface for the component  51  during the pressing in of the rivet element. In contrast to customary processes no die button is required to bring about the beading over of the rivet section  11 . 
     As can be seen in  FIG. 8  the end portion  12   b  first penetrates into the component  51 . As a result of the dilated shape of the end portion  12   b  this if further spread apart by the material of the component  51  which penetrates into the interior of the rivet section  11 . The material is thereby plastically deformed or indeed partly “formed into crumbs”. 
     In the further course of the pressing in process, the free end of the rivet section  11 , which is in the process of being spread apart, enters into contact with the planar support  53 . In this way, the section  11  is now fully beaded over until the end state shown in  FIG. 9  results. It can be seen that the rivet element  10  has been pressed so far into the component  51  that the flange section  21  does not project out of the component in the axial direction, but rather terminates flush with its surface. 
     The degree of dilation of the end portion  12   b  suitable for the specific application—i.e. its depth in the axial direction and its width defined by the gradient of the flanks of the spike—depends, amongst other things, on the material and the thickness of the component, on the mechanical characteristics of the rivet section  11  and on the pressing in forces/pressing in speeds. Surprisingly, the dilation of the end portion  12   b  does not lead to an uncontrolled reshaping of the rivet section  11  but rather initiates—with a suitable matching of the above named parameters—to the dilation of the rivet section  11  which is subsequently bent over, by the cooperation with the planar support surface  53  in order to complete the rivet connection. 
     The degree of the dilation is to be selected such that on the one hand it is not to large. Then the rivet section  11  would possibly spread too quickly and can eventually not penetrate fully into the component  51 . On the other hand the dilation may not be too small because otherwise it cannot be reliably ensured that the spreading of the rivet section  11  takes place sufficiently quickly. It has however been shown that often a comparatively small dilation of the end portion  12   b  leads to the desired reshaping of the rivet section  11  when it is pressed into the component  51 . 
     The above described manufacturing process is assisted when the material is at least temporarily heated and thus becomes softer, so that the rivet element  10  can be more easily pressed into the material. 
     The invention thus makes it possible to attach rivet elements into components of fiber composite materials which are also termed “organic sheet metals” without having to form openings for the rivet elements in the material. Disadvantageous weakening of the material is hereby avoided in advantageous manner. 
     REFERENCE NUMERAL LIST 
     
         
           10  rivet element 
           11  rivet section 
           12   a  tip 
           12   a ′ pre-shaped tip 
           12   a ″ base body 
           12   b  end portion 
           12   c  restriction 
           13  segment 
           13   a  contour section 
           14  contact surface 
           15  central axis 
           16  bend 
           17  introduction aid 
           19  cylindrical portion 
           21  flange section 
           23  contact surface 
           25   a ,  25   b  means for providing security against rotation (rib and recess) 
           27  fastener portion 
           31  spike 
           51  component 
           53  support surface/base