Abstract:
A rivet ( 1 ) includes a bearing head ( 2 ), a pulling stem ( 3 ) and an insertion body ( 4 ). The insertion body ( 4 ) includes at least two longitudinal flat surfaces ( 13 ) interrupting a notched portion ( 14 ); and at least two elastic feet ( 15 ) each having a first end elastically joined to the insertion body ( 4 ) and a second end which is free. Each of these elastic feet ( 15 ) is adapted to adopt a folded position in which it is folded along the insertion body ( 4 ), on one of the flat surfaces ( 13 ), and a tightened position in which it is arranged transversely of the general orientation of the insertion body ( 4 ). The bearing head ( 2 ) has at least one slot ( 9 ) enabling the head to deform radially.

Description:
FIELD OF THE INVENTION 
   The invention relates to the assembly of parts by tightening through an opening passing through the parts, and more particularly to a rivet comprising a bearing head and a pulling stem. 
   BACKGROUND OF THE INVENTION 
   Rivets are common components, of elongate form, making it possible to assemble for example two sheets of metal one against the other. The rivet is inserted into a hole pierced in the assembly of the two sheets of metal to make it possible to achieve “blind” assembly, that is to say solely by manipulations on the projecting part of the rivet, most often by pulling on the stem. 
   Common rivets are metallic and comprises a pulling stem of steel provided at one of its ends with a head, and also comprising a sleeve of aluminum also provided with a head, the sleeve being joined to the pulling stem such that said heads are spaced apart from each other. 
   This type of rivet is inserted, by the head of the pulling stem, into a hole passing through an assembly, that head projecting from the other side of the assembly, and then the pulling stem is pulled with respect to the head of the sleeve, which bears on the assembly, until the head of the stem deforms the body of the sleeve while tightening the members of the assembly against each other, between the head of the sleeve and the body of the deformed sleeve. 
   Other known rivets are in plastics material, which for example avoids them having to be removed from parts made of plastics material destined to be recycled. 
   These plastics rivets have the same form as corresponding rivets in steel-aluminum with the sole difference being that the sleeve generally comprises a tooth adapted to cooperate with notched portion on the pulling stem, close to the head, in order to maintain the tightened position after the stem has been pulled. 
   Although these known rivets are satisfactory in the performance of their function, they require to be manufactured from two different types of material on account of the different properties necessitated for the pulling stem (hardness, low plastic deformation, etc.) and for the sleeve (ductility, considerable plastic deformation, etc.). 
   SUMMARY OF THE INVENTION 
   The object of the invention is to improve existing plastics rivets, in particular by enabling easier and cheaper manufacture. 
   To that end, the invention relates to a rivet comprising:
         a bearing head in which an opening is provided;   a pulling stem adapted to cooperate in sliding relationship with the bearing head, through said opening;   an insertion body connected to a first end of the pulling stem and comprising, continuing on from the pulling stem, a notched portion;
 
the bearing head further comprising, on the inner faces of the opening, at least one tooth adapted to cooperate with said notched portion;
 
said rivet being characterized in that the insertion body comprises
   at least two longitudinal flat surfaces interrupting said notched portion;   at least two elastic feet each comprising a first end elastically joined to the insertion body and a second end which is free, each of these elastic feet being adapted to adopt a folded position in which it is folded along the insertion body, on one of said flat surfaces, and a tightened position in which it is arranged transversely of the general orientation of the insertion body;
 
and in that the bearing head comprises at least one slot enabling it to deform radially.
       

   Such a rivet possesses a homogeneous structure in terms of mechanical properties of the materials used. 
   Thus, firstly, the bearing head does not require to be manufactured from a highly elastically deformable material (to enable its deformation during ratcheting of the tooth on the notched portion) since the slots promote its radial deformation. Secondly, since the tightening function is no longer ensured by the deformation of a sleeve but by the movement of elastic feet, the rivet may include as one piece the pulling stem and the elastic feet since a hard material (necessary for the pulling stem) permitting slight elastic deformation (necessary for the elastic feet) can suffice for the production of that pulling stem continuing on from the insertion body. 
   None of the parts of the rivet is thus plastically deformed on tightening and materials with similar mechanical properties can thus be used to produce the pulling stem, the insertion body, and the bearing head. 
   Moreover, it is possible to produce the rivet using a single material. 
   The operations of manufacture and assembly are thus considerably simplified, it being possible to mold the two parts of the rivet in a single operation, in the same mold, by introducing material only once. 
   According to one embodiment, each of the elastic feet is additionally adapted to adopt a free position, between the folded position and the tightened position, the elastic foot spontaneously adopting this free position without being urged, in which its free end projects from the insertion body, the elastic foot being orientated substantially at 45° with respect to the general orientation of the insertion body, its free end being closer to the pulling stem than its joined end. 
   This position adopted by the elastic feet at rest enables them to have a non-return function. Thus the insertion body may be introduced into a through aperture, the elastic feet moving into folded position on contact with the inner walls of the aperture, but cannot be extracted since the elastic feet, freed on exiting from the other side of the aperture, move into tightened position in case the stem is pulled. 
   To increase this effect, the insertion body may further comprise a return foot, projecting from the insertion body towards one of the elastic feet, said return foot being adapted to exert a force tending to push back the corresponding elastic foot to its free position, when the latter is in its folded position. 
   According to another embodiment, the pulling stem comprises at least two longitudinal flat surfaces joined together by other surfaces, each of these flat surfaces being positioned to continue on from one of said flat surfaces of the insertion body, and in that said opening provided in the bearing head comprises longitudinal flat surfaces, of the same profile as the flat surfaces of the pulling stem, adapted to cooperate with said flat surfaces of the pulling stem to prevent the bearing head from rotating with respect to the pulling stem. 
   These flat surfaces avoid having to angularly position the bearing head with respect to the insertion body, during tightening of the rivet, such that the tooth of the insertion head is located in register with the notched portion. 
   The alignment of the flat surfaces of the insertion body with the flat surfaces of the pulling stem enables the bearing head to be positioned angularly from the time of its being mounted on the pulling stem, and to maintain that angular position along the length of its travel on the pulling stem and the insertion body. 
   Moreover, the flat surfaces of the opening provided in the bearing head, and said slot in the bearing head may be angularly offset. 
   This makes it possible to position the slots in the bearing head on the notched portion of the insertion body, on tightening of the rivet. 
   Furthermore, the bearing head may comprise a collar having a bearing surface substantially perpendicular to the pulling stem, as well as an annulus projecting substantially perpendicular to said bearing surface, said opening passing completely though the collar and being coaxial with the annulus. 
   Said slot and said tooth of the bearing head may furthermore be provided on said annulus. 
   This is a preferred construction for the bearing head to fulfill its functions optimally: the collar bears on the surface surrounding the aperture in which the insertion body is introduced, whereas the projecting annulus penetrates into the hole with the pulling stem, the bearing head thus providing a transversal bearing and a longitudinal surface for the work of the slot. 
   To ensure the stability of the tightened position of the elastic feet, the insertion body may comprise at least one stop surface arranged transversally to the general orientation of the insertion body and adapted to form an abutment for the elastic feet when they are in the tightened position. 
   Similarly, the insertion body may further comprise at least one blocking surface provided transversally to the general orientation of the insertion body, facing said stop surface and spaced from it by a distance substantially equal to the thickness of said elastic feet, said blocking surface being adapted to form a counter abutment for the elastic feet when they are in the tightened position. 
   According to one embodiment, the connection of the pulling stem and the insertion body is made by a weakened zone which is narrower than the pulling stem. 
   At the end of the tightening of the rivet, this weakened zone is adapted to rupture in order to separate the pulling stem from the insertion body, the assembly formed by the insertion body onto which the bearing head is ratcheted remaining fixed onto the parts to be assembled. 
   The insertion body may further comprise, at its end opposite the pulling stem, an insertion head flaring out from a small end to a large end, the small end being furthest from the pulling stem and the large end being adapted such that the elastic feet, when they are in the folded position, are totally retracted with respect to the outline of the large end. 
   Such a rivet has at its end a chamfer facilitating its introduction into an aperture. 
   Furthermore, the maximum transverse diameter of the large end determines the minimum diameter for piercing the aperture adapted to receive the rivet. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other features and advantages of the invention will appear in the light of the following description of a preferred embodiment, given by way of non-limiting example, and made with reference to the accompanying drawings in which: 
       FIG. 1  is a perspective view of a rivet according to the invention, the bearing head being engaged on the notched portion; 
       FIG. 2  is a longitudinal cross-section of the rivet of  FIG. 1 , the rivet clamping two sheets of metal against each other, this cross-section being arranged angularly such that a side view of the elastic feet as well as the notched portion both appear on the same drawing; 
     Feature  3  is a similar view to that of  FIG. 2 , the pulling stem having been removed; 
       FIG. 4  is a perspective view of the rivet of  FIG. 1 , the bearing head being disposed at one end of the pulling stem; 
       FIG. 5  is a plan view of the rivet of  FIG. 4 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  represents a rivet  1  in perspective comprising a bearing head  2  as well as an assembly formed by a pulling stem  3  connected to a insertion body  4 , the pulling stem  3  and the insertion body  4  each being a continuation of the other. 
   The bearing head  2 , also visible from the side in  FIG. 4 , comprises a circular collar  5  having a transverse bearing surface  6  as well as a frusto-conical annulus  7  projecting perpendicularly from the bearing surface  6  and being coaxial with it, the portion of largest diameter of the frusto-conical annulus  7  being adjacent to the bearing surface  6 . 
   An opening  8  passes completely through the bearing head  2 , perpendicularly and coaxially to the collar  5  and to the annulus  7 . 
   This opening has a cross-section formed by two mutually parallel rectilinear segments, joined by two arcs of a circle, this opening being the complementary form of a cylinder which would have two diametrically opposed flat surfaces. 
   The bearing head  2  furthermore comprise two slots  9  made through the full thickness of the annulus  7  and opening at its end opposite to the collar  5 . 
   These slots  9  are diametrically opposite along a diameter of the annulus  7  perpendicular to the diameter having the flat surfaces of the opening  8 , each slot  9  thus being angularly offset by 90° with respect to each flat surface of the opening  8 . 
   Finally, the bearing head  2  comprises two teeth  10  of substantially triangular section projecting from the inner faces of the annulus  7  which extend along the curved surfaces of the opening  8  and are interrupted by the slots  9  and the flat surfaces of the opening  8 . 
   Apart from this bearing head  2 , the rivet is formed from an elongate part made up of the pulling stem  3  connected to an insertion body  4 . 
   The pulling stem  3  is generally cylindrical although it comprises two longitudinal flat surfaces  11  which are diametrically opposed. 
   This pulling stem  3  is connected by one of its ends to the insertion body  4 , via a weakened zone  12  of smaller diameter than the pulling stem  3 . 
   The insertion body  4  extends from that weakened zone  12 , as a continuation from the pulling stem  3 . It comprises two diametrically opposite flat longitudinal surfaces  13 , similar to the flat surfaces  11  of the pulling stem and disposed adjacent to them. 
   The two flat surfaces  13  of the insertion body  4  are connected by two curved surfaces  14  bearing transversal notches, these notches being of triangular section adapted to cooperate with the teeth  10  borne by the bearing head  2  for the purposes of longitudinal blocking. 
   Continuing on from that notched portion  14 , there are arranged two elastic feet  15  and then an insertion head  16 . 
   The elastic feet  15  are each formed from a bearing wall  17  of curved form as well as from an elastically deformable tab  18  linking the bearing wall  17  to the insertion body  4  such that the bearing wall  17  is mobile due to the elastic deformation of the tab  18 . 
   The insertion head  16  is adjacent to the elastic feet  15  and forms the end of the insertion body  4 . 
   This insertion head  16  is frusto-conical, its base  19  of larger diameter being on the side of the insertion body  4  and its base  20  of smaller diameter constituting the end of the insertion body  4 , so as to form a chamfer facilitating the introduction of the rivet  1  by its insertion head  16  into an adapted aperture (that is to say of diameter greater than the greatest diameter  19  of the insertion head  16 ). 
   The insertion head  16  further comprises, for the purpose of its cooperation with the elastic feet  15 , two diametrically opposite stop surfaces  21  each facing one of said elastic feet  15 . 
   Similarly, two transverse blocking surfaces  22  are provided on the insertion head  16 , which are diametrically opposite and each facing one of the elastic feet  15  while being opposite the stop surfaces  21 . 
   The separation between a stop surface  21  and the corresponding blocking surface  22  corresponds substantially to the thickness of the walls  17  of the elastic feet  15 . 
   This is because, by the possible movement of the elastic tabs  18 , the elastic feet  15  may adopt two extreme positions: a folded position and a tightened position, with, between these two positions, a free position. 
   The free position corresponds to the undeformed position of the tabs  18 , that is to say that this position is adopted spontaneously by the elastic foot  15 , in the absence of exterior forces. This is the position of the elastic feet  15  as represented in  FIGS. 1 ,  4  and  5 : the free end of the foot  15  projects and the wall  17  is oriented at 45° to the general orientation of the insertion body. 
   In the folded position, the elastic tabs  18  are deformed such that the walls  17  are folded against the flat surfaces  13  of the insertion body  4 , the elastic feet  15  then being entirely retracted with respect to the largest diameter  19  of the insertion head  16 . The insertion body comprises two return feet  23  projecting towards the elastic feet  15  and facing them, these return feet  23  being adapted to exert a force tending to push back each elastic foot  15  towards its free position, when it is in the folded position. 
   In the tightened position, the elastic tabs  18  are deformable such that the walls  17  are brought into abutment against the stop surfaces  21  and into opposite abutment against the blocking surfaces  22 , as shown in  FIGS. 2 and 3 . 
   The rivet which has just been described may be manufactured and used in the following manner. 
   For manufacture, a conventional mold is used which is adapted to form the unit comprising pulling stem  3  plus insertion body  4 . 
   The mold comprises in addition a cavity adapted to form the bearing head  2  disposed at the end of the cavity adapted to form the pulling stem  3 , to obtain a rivet in a single piece, as in  FIGS. 4 and 5 . The mold is provided such that the linking webs of the bearing head  2  and the pulling stem  3  are of small thickness, in comparison with the other thicknesses of the rivet, and, moreover, an insert is arranged in the mold to form the internal opening of the bearing head. 
   Molding is then carried out by a single injection of polymer and, on extraction from the mold, said insert is removed by virtue of the elasticity of the bearing head  2  permitting sufficient deformation to extract the teeth  10  formed by that insert. 
   The item of  FIGS. 4 and 5  is thus obtained in the mold which is a rivet  1  of which the bearing head  2  is attached to the pulling stem  3  by a fine frangible zone. 
   The mold is furthermore provided with an ejection device adapted to slip the bearing head  2  onto the pulling stem  3 , causing the rupture of said frangible zone to produce the rivet of  FIG. 1 . For this, the head  2  is slipped along the pulling stem  3 , the profile of the opening  8  and the flat surfaces  11  cooperating to ensure the longitudinal sliding and to prevent the rotation of the bearing head  2  with respect to the pulling stem  3 . 
   This sliding results in the engagement of the bearing head  2  on the notched portion  14  of the insertion body  4  and, consequently, in the ratcheting of the teeth  10  of the head  2  on the notches. 
   The rivet is finally ejected from the mold and ready to use. 
   The user having to assemble parts, such as two sheets of metal  24 ,  25  as shown in  FIGS. 2 and 3 , with such a rivet, first of all provides a hole  26  passing completely through the two sheets of metal  24 ,  25 . 
   This hole  26  must have a diameter greater than the greatest diameter  19  of the insertion head  16  and less than the span E ( FIG. 2 ) of the elastic feet  15  in the tightened position. 
   The rivet  1  is introduced into this hole  26  by the insertion head  16 . On entry of the insertion body  4 , the elastic feet  15  being in their free position, the walls  17  come into contact with the edges of the hole  26  and the movement of introduction of the rivet causes folding of the elastic feet  15  into the folded position, while the hole  26  is passed through. 
   Once the insertion body  4  emerges from the other side of the hole  26 , the elastic feet  15  immediately return to their free position, while the bearing surface  6  of the bearing head comes into contact with one of the sheets of metal. 
   The ratcheting of the teeth  10  on the notches continues as far as is enabled by the thickness of the parts  24 ,  25  to be assembled ( FIG. 2 ) and is carried out with the use of conventional riveting pliers capable of pulling on the pulling stem  3  relative to the bearing head  2 . 
   When the two parts  24 ,  25  have been tightened as much as possible, continued pulling on the stem  3  gives rise to its rupture, at the weakened zone  12 , so giving the final disposition of the items in  FIG. 3 .