Patent Publication Number: US-2022234149-A1

Title: Tool for inserting a fastener into a structure by interference and installation method for installing a fastener in a structure by interference using such a tool

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of PCT Application PCT/EP2020/079513 filed Oct. 10, 2020, which claims priority to French Application FR1911990 filed Oct. 25, 2019, the contents of all of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention belongs to the field of fasteners. 
     More particularly, the invention relates to the field of interference-fit fasteners and relates to a tool and a method for inserting fasteners in interference. 
     PRIOR ART 
     Solutions exist to insert a fastener into a bore of a structure without damaging the fastener. 
     British Patent Application GB 2 143 765 discloses a tool having a telescopic structure for insertion of a nail into a structure. The disclosed tool has a clamping means for holding the nail during attachment, a sleeve and a percussion means. The clamping means is inserted into the sleeve, close to the structure, and the nail is inserted into the clamping means. The percussion means is inserted at the other end of the sleeve; it is in contact with the head of the nail and capable of sliding in said sleeve under the effect of a strike force, generated by means of a hammer, to sink the nail. 
     One drawback of this tool is that it is not adapted to fasteners comprising a gripping element. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a tool for the interference insertion of a fastener into a bore of at least two structures, making it possible to apply a force to the fastener without damaging it. The expression “interference” indicates that the bore of the structures has a diameter less than an outer diameter of the portion of the fastener for assembling the structures. 
     The invention relates to a tool for interference installation in a bore of a structure of a fastener comprising a head housed in a sleeve flange and a gripping element. The tool includes a first body extending along a first main axis and having:
         at least one load-bearing surface, one of which also forms a load application surface;   a load transmission surface; and   a housing extending along the first main axis from a first end of said first body, said housing having a bore extending along the first main axis to a second end of said first body. According to the invention, the load transmission surface is arranged at the second end of the first body and extends perpendicularly to the first main axis, said load transmission surface being dimensioned to bear simultaneously on the head and the sleeve flange.       

     In one embodiment, the first body comprises a groove extending all along said first body along a direction of the first main axis, and from the first main axis to an outer wall of said body in a radial direction. 
     In one embodiment, the first body has a U-shaped neck at its second end. 
     In one embodiment, the second end includes at least two radially flexible fingers. 
     In one embodiment, the housing is a counterbore having a diameter greater than an average diameter of the bore, said counterbore forming a load-bearing surface and/or an impact surface. 
     A load applied to the first body is transferred directly to the fastener via the load transmission surface in contact with the head of said fastener, to allow said fastener to be inserted in interference in the structure. 
     In another embodiment, the tool comprises a second body extending along a second main axis, the second body having a shaft having a shape substantially complementary to the housing of the first body, the second body having at least one surface complementary to at least one load-bearing surface of the first body, and a bore extending along the second main axis from a first end of the second body. 
     A load applied to the second body is transferred via the at least one complementary surface to the at least one load-bearing surface, and then the loads are transferred to the fastener via the load transmission surface in contact with the head of the at least one fastener, to allow the interference fit of said fastener in the structure. 
     In one embodiment, the shaft has substantially the shape of a cylindrical sleeve having an outer diameter substantially equal to that of the counterbore and an inner diameter substantially equal to the average diameter of the bore. 
     In one embodiment, the shaft of the second body includes a groove on its outer wall in which an O-ring adapted to be received in a groove of a wall of the housing of the first body is provided. 
     In one embodiment, the second body has a load application surface. 
     The invention also relates to an assembly comprising a tool according to the invention and a fastener comprising a head housed in a sleeve flange and a gripping element. 
     In one embodiment, the shapes of the housing and the bore of the first body are at least partially complementary to a shape of the gripping element of the fastener, to enable the fastener setting in the first body along the main axis of said first body. 
     The present invention also relates to a method for installing in interference-fit a fastener in a bore of at least one structure, said fastener comprising a head housed in a sleeve flange and a gripping element, the installation being carried out by means of a tool according to the invention. The installation method according to the invention comprises the following steps:
         placing the fastener in the first body, along the main axis of said first body, so as to contact the head of the fastener and the sleeve flange with the load-transmitting surface;   positioning the tool comprising the fastener facing the bore of the structure,   applying a load to a load application surface of the tool to interference fit the fastener into the bore of the structure.       

     In one embodiment, when placing the fastener into the first body, the gripping member of the fastener is received in the bore of the first body. 
     In one embodiment, a second body is placed on the first body of the tool, so as to contact at least one load-bearing surface of the first body with at least one complementary surface of the second body, the load being applied to a load application surface of the second body. 
     In one embodiment, when placing the second body on the first body, the load is applied by means of a tool to a load application surface of the first body or the second body. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic representation of a fastener comprising a smooth portion, a head, and a gripping member. 
         FIG. 2  is a perspective view of a fastener, in the form of a blind rivet. 
         FIG. 3  is a perspective view of an assembly comprising a fastener and a tool according to the invention, assembled together for installation of the fastener. 
         FIG. 4  is a perspective view of an assembly comprising a fastener and a tool according to the invention, prior to placing the second body on the first body. 
         FIG. 5  is a vertical sectional view of an assembly comprising a fastener and a tool according to the invention, assembled together for installation of the fastener, 
         FIG. 6  is a schematic vertical sectional view of a tool according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  schematically shows a fastener  10  to be put in place by interference in a structure by means of a tool  20  according to the invention. The fastener  10  extends along a longitudinal axis  11  and comprises a substantially cylindrical portion  12 , a head  13  and a gripping member  14  intended to be separated from the rest of the fastener after installation of said fastener in one or more structures. The head  13  has an outer diameter D 13  greater than a maximum outer diameter D 14  of the gripping member. 
     With reference to  FIG. 2 , the fastener  10  may for example be a blind rivet comprising a screw inserted into a tapped sleeve  12 , said sleeve being able to form an outer bulb under the effect of a traction or a torsion exerted on the gripping element  14 . In this case, the head  13  of the fastener is a screw head housed in a flange of complementary shape of the sleeve  12 . The cylindrical portion is the body of the screw and of the body of the sleeve  12 . In addition to the above-mentioned elements, the rivet  10  may comprise a breaking groove  15  making it possible to facilitate the breaking of the gripping element  14 . 
     With reference to  FIGS. 3 to 5 , a preferred embodiment of a tool  20  according to the invention comprises a first body  30  and a second body  40 . 
     The first body  30  extends along a first main axis  31  and has a base  301  of substantially frustoconical shape extended at its large base by a skirt  302  of substantially cylindrical shape of revolution. The first body  30  thus forms an integral part, substantially of revolution about its first main axis  31 . 
     The first body  30  has a housing extending from a free end of the skirt  302 , corresponding to  FIGS. 3 to 5  at an upper end of said first body, towards the base  301  along the first main axis. In the example illustrated, the housing corresponds to a counterbore  306 . The counterbore  306  extends along the first main axis by a bore  307  opening at a free end of the base  301 , corresponding to  FIGS. 3 to 5  at a lower end of the first body  30 . 
     The first body  30  also has a groove  308  extending vertically from the free end of the base  301  to the free end of the skirt  302 , from the first main axis  31 , over the entire thickness of the first body  30 , that is to an outer peripheral wall of the first body. The groove  308  thus has a substantially U-shaped cross-section over the entire height of the bore. In  FIG. 5  representing a cross-sectional view of the tool  20  according to the invention, the unhatched area of the first body  30  corresponds to the groove  308 . 
     The first body  30  has two load-bearing surfaces and a load-transmitting surface all three in the form of crowns truncated by the groove: a first load-bearing surface  303   a  at the free end of the skirt  302 , a second load-bearing surface  303   b  at the interface between counterbore  306  and bore  307  and a transmission surface  303   c  at the free end of the base  301 . 
     The first body  30  also includes a U-shaped neck  304  at the free end of the base  301 . 
     The second body  40  extends along a second main axis  41  and comprises a shaft  401  having substantially a cylindrical sleeve shape adapted to be received in the housing formed by the counterbore  306  of the first body  30 . Opposite the free end of the shaft  401 , said free end corresponding to  FIGS. 3 to 5  at a lower end, the second body  40  has a shoulder defining a first complementary surface  403   a . The free surface, corresponding to  FIGS. 3 to 5  to a bottom surface, defines a second complementary surface  403   b.    
     In the example illustrated in  FIGS. 3 to 5 , the second body  40  also includes a counterbore  406  and a bore  407 , the counterbore  406  extending from an upper free end of the second body  40 , with reference to the figures, and being extended by the bore  407  that extends to a lower free end of said second body, with reference to the figures. With reference to  FIG. 3 , the second body  40  comprises opposite the shaft  401  an enlarged flange  404 . 
     An average diameter of the bore  307  of the first body  30  is substantially equal to an average bore diameter  407  of the second body  40 . 
     The implementation of the tool  20  for placing the fastener  10  in interference in a structure is detailed below. 
     The fastener  10  is slid into the first body  30  by the groove  308 , such that the gripping member  14  of said fastener is placed inside said first body and that the head  13  and the sleeve are placed outside said first body and both in contact with the transmission surface  303   c . The fastener  10  is thus brought into abutment in the first body  30  such that the longitudinal axis  11  of the fastener is substantially coincident with the first main axis  31  of said first body. For this purpose, the inner surface of the bore  307  of the first body  30  has been machined so as to form an at least partially complementary imprint of the gripping element  14 . By way of example, a groove  305  as illustrated in  FIG. 5  makes it possible to receive a part of the gripping element  10  of the fastener, of complementary shape to said groove. In the same manner, the neck  304  conforms to the shape of the breaking groove  15  of the fastener  10 , and retains said fastener in a vertical direction carried, in the figures, by the first main axis  31  of the first body  30 . 
     The second body  40  is then placed over the first body  30  to cover the gripping element  14  of the fastener  10 . The bore  407  extending along the second main axis  41  makes it possible to receive said gripping element, such that when the second body  40  is placed on the first body, the first main axis  31 , the second main axis  41  and the longitudinal axis  11  of the fastener are substantially coincident. 
     The diameters of the bores  307  and  407  are adapted to be able to receive the gripping element  14  of the fastener  10 . For example, these two diameters are at least greater than the maximum diameter D 14  of the gripping element, but may also be each adapted to the maximum diameter of the portion of the gripping element  14  which they receive. The bore  407  has, in particular, a function of centering the gripping element  14  and, therefore, the fastener in the tool  20 . 
     When the second body  40  is placed on the first body  30 , the first bearing surface  303   a  is in contact with the first complementary surface  403   a  and the second bearing surface  303   b  is in contact with the second complementary surface  403   b.    
     The second body  40  is held assembled to the first body  30 , for example by means of an O-ring  408  arranged in a groove of the shaft  401 , said O-ring being compressed when the shaft  401  is sleeved in the counterbore  306 , for example in a groove intended to receive said O-ring on the cylindrical surface of the counterbore wall  306 . 
     The fastener  10  is positioned in front of a previously made bore in the structures to be joined, having a diameter smaller than an outer diameter of the cylindrical portion  12  of the fastener, and a percussive or continuous load is then applied to a load application surface  409  of the second body  40 , by means of a suitable tool, for example a multi-strike tool, in order for the fastener to penetrate into the bore the fastener into the bore. The load application surface  409  corresponds to the bottom of the counterbore  406  of the second body. 
     In a preferred embodiment, said tool is inserted at least partially into the counterbore  406 , so as to be brought into contact with the load application surface  409 , whereby the impact load or continuous load is thus applied on said surface for applying a force  409  by means of the tool, said counterbore having the function of maintaining said tool in the center of the tool  20 , and the widened flange  404  protecting the hand of an operator holding the tool  20  by the second body  403   b . The contacts between the first bearing surface  303   a  and the first complementary surface  403   a , between the second bearing surface  303   b  and the second complementary surface  403   b  and between the head  13  of the fastener  10  and the transmission surface  303   c  make it possible to transfer the impact or continuous load to the fastener  10  in order to insert said fastener into interference in one or a plurality of structures (not shown), without damaging the fastener. 
     When the underside of the head of the fastener  10  comes into contact with the structure in which said fastener is inserted, said tool is removed by sliding it to disengage, by the groove  308 , the gripping member  14  of the first body  30 , then another tool can be used to finalize the placement of the fastener into the structure. 
     It should be noted that it is not necessary that the first bearing surface  303   a  and the second bearing surface  303   b  are in contact respectively with the first complementary surface  403   a  and the second complementary surface  403   b ; only one of these two contacts is sufficient to implement the fastener by means of the tool according to the invention. 
     However, it is essential that the transmission surface  303   c  is designed so as to be in contact with all of the elements forming the head of the fastener, ie both with the head of the screw and with the flange of the sleeve when the fastener  10  is a blind rivet comprising a screw and a sleeve receiving the screw. In fact, the support of the first body  30  only on the sleeve flange would irreversibly damage the sleeve flange upon application of a load. Also, the support of the first body  30  only on the head of the screw would result in a necking of the body of the sleeve: the body of the sleeve would elongate and decrease in thickness, compromising the interference between the fastener and the structure. This configuration is not desirable in particular when interference is sought to discharge electric current potentials in the structures in the event of lightning strike on the head of the fastener or to increase the mechanical strength of the assembly, particularly in fatigue. 
     Thus, a shape of the load transmission surface  303   c  of the first body is complementary to a shape of the surface of the head  13  of the fastener oriented towards the gripping element to maximize a contact surface between these two elements. 
     The tool according to the invention thus makes it possible to install a fastener in interference in a structure without damaging the fastener, the loads being taken up in the majority by the tool, and transmitted to the fastener via the load-bearing surfaces and their complementary surfaces, as well as by the transmission surface. 
     The tool  20  is preferably made of metallic material to resist the forces of the tool. 
     In one embodiment not shown, the tool  20  includes an offset handle positioned transversely to the second body  40  to improve the ergonomics of the tool and to avoid the risk of injury if the tool accidentally impacts the enlarged flange  404  instead of the load application surface  409 . In this case, the tool  20  may have an enlarged collar of less diameter than in the absence of a handle. 
     In another embodiment not shown, the first bearing surface  303   a  and the first complementary surface  403   a  and/or the second bearing surface  303   b  and the second complementary surface  403   b  are frustoconical. 
     A tool suitable for implementing the insertion method according to the invention does not necessarily comprise two bodies. 
     In one embodiment, the tool may comprise only the first body in which the second load bearing surface  303   b  at the interface between the counterbore  306  and the bore  307  constitutes the load application surface that directly receives the load of the tool. In this case, the height of the housing and the load application surface must be dimensioned so that the tool does not come into contact with the gripping element  14 , so as not to damage it, and can effectively bear directly on the load application surface formed by the second bearing surface  303   b.    
     In another embodiment shown in  FIG. 6 , the tool includes the first body and optionally the second body. In this embodiment, the first body has no longitudinal groove  308 , and the bore  307  of the first body is provided with at least two fingers  400  extending in an axial direction, radially flexible, for inserting the gripping member into the housing in an axial direction. The fingers are for example created by making axial slots  309  along a periphery of the bore  307 , two slots  309  being illustrated to produce four fingers,  400   a  and  400   b  being illustrated in  FIG. 6 . 
     It is understood by “radially flexible” that the fingers are flexible to allow radial deformation. 
     To facilitate insertion of the gripping member into the bore, three, four or more flexible fingers may be provided. To hold the fingers radially inward upon application of the force to the tool, and thus maintain the transmission surface  303   c , formed by the free ends of the fingers, in contact with the head  13  of the fastener and the sleeve flange  12 , the first body  30  is provided with a clamping means such as a sliding ring  402  on the outer surface of the body, between a position in which the flexible fingers are free to move radially (bold lines), and a position where the movement of the fingers is blocked in all directions (dashed lines). It is understood that the holding of the fingers radially inward can be achieved by any other clamping means, such as an elastic means or a self-tightening means.