Patent Publication Number: US-9416809-B2

Title: Rivet stud

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation of and claims priority from pending U.S. patent application Ser. No. 13/682,854, filed Nov. 21, 2012, which claims priority from German Patent Application No. DE 102011055724.5, filed on Nov. 25, 2011, the disclosure of which is incorporated herein by reference 
    
    
     BACKGROUND OF THE INVENTION 
     The invention concerns a rivet stud, having a rivet body that has an elongated shank with a head end, a foot end, and an axial bore, wherein the shank is intended to be inserted foot end first into an opening in a workpiece and a radially extending flange that serves to make contact with one side of the workpiece is located at the head end, and said rivet stud having, located in the bore of the rivet body, a tension mandrel, which has a mandrel shank with a drawing end projecting out of the head end of the rivet body that is separable from the mandrel shank at a predetermined breaking point, and which mandrel has a mandrel head that is supported by the foot end of the rivet body in order to transmit a force to the rivet body during setting of the rivet stud. 
     A rivet stud of the specified type is known from DE 3,610,976 A1. In this prior art rivet stud, the drawing end is separated from the mandrel shank by a predetermined breaking point that is located at such a distance from the flange of the rivet body that there remains, between the flange and the predetermined breaking point, a region designed as a profile stud, wherein the tension mandrel remaining in the rivet body after the setting process supports the profile stud so as to project away from the flange. In this design, the predetermined breaking point that is broken after the setting process forms a sharp-edged end of the profile stud that can lead to damage of parts to be installed on the profile stud and can result in injuries during handling and installation. 
     A blind rivet is known from WO 2009/09843 A1 that is intended to permanently join workpieces that are in contact with one another. The workpieces typically have holes passing through them that are brought into alignment with one another and into which the blind rivet is placed and then fastened by deformation. A fastened blind rivet usually results in a clearance-free seating of the rivet body in the holes of the workpieces and clamps the workpieces together. 
     BRIEF SUMMARY 
     The object of the invention is to create a rivet stud of the specified type that avoids the risk of damage to the component and the risk of injury during installation and handling. 
     The object is attained according to the invention by a rivet stud with the features specified in claim  1 . 
     According to the invention, the rivet stud comprises a rivet body that has an elongated shank with a head end, a foot end, and an axial bore, wherein the shank is intended to be inserted foot end first into an opening in a workpiece and a radially extending flange that serves to make contact with one side of the workpiece is located at the head end, and comprises a tension mandrel located in the bore of the rivet body, which mandrel has a mandrel shank with a drawing end projecting out of the head end of the rivet body that is separable at a predetermined breaking point from the mandrel shank, and which has a mandrel head that is supported by the foot end of the rivet body in order to transmit a force to the rivet body during setting of the rivet stud, wherein the mandrel shank is provided with locking means that secure the mandrel shank in the rivet body after setting of the rivet stud, wherein a mounting stud that projects from the mandrel head on the side opposite the mandrel shank is located on the mandrel head, and wherein the predetermined breaking point is located such that the breaking point lies inside the bore of the shank after setting of the rivet stud. 
     In the rivet stud according to the invention, the mandrel head is elongated on the side opposite the mandrel shank to form a mounting stud that, in cooperation with suitable fastening elements such as a nut, a clip, or the like, can serve to fasten components. To this end, the mounting stud can have a cylindrical shape with fastening means including a surface that is smooth, ribbed, or provided with an external thread, or can also be provided with a differently designed fastening end, for example in the manner of a T-stud with a flange. Preferably the tension mandrel and mounting stud are produced as a single piece. However, it is also possible to join the tension mandrel by welding to a separately manufactured mounting stud. If the mounting stud is provided with an external thread, then it is advantageous according to the invention for there to be means for transmitting a torque between the tension mandrel and the rivet body, for example projections or longitudinal ribs. Preferably, the locking means that secure the part of the tension mandrel that is separated from the drawing end in the rivet body after setting can additionally be designed to transmit a torque. 
     The rivet stud, and in particular the rivet body, is designed according to the invention in such a manner that, during the setting process, the rivet body forms a disk on the blind side of the penetrated workpiece that rests uniformly against the workpiece. The formation of the disk supports an orientation of the rivet stud perpendicular to the surface of the workpiece, since the axial clamping force acting between the mandrel head and the flange during setting generates a moment of force that tends to move the rivet stud into a perpendicular position. The disk formed by the rivet body also increases resistance to loads on the set rivet mandrel that are oriented perpendicular to the longitudinal axis of the rivet body. During the setting process, the disk formed by the bulging of the rivet body moves axially against the workpiece, wherein the radial expansion of the rivet body is reduced within the opening of the workpiece. As a result, the rivet stud is also suitable for placement in thin and soft workpieces. The disk-shaped bulging of the rivet body also reduces the tendency of the rivet body to pull into the opening of the workpiece during setting. 
     A variety of materials may be used to manufacture the rivet stud according to the invention. All parts may be made of steel or stainless steel, of aluminum, or of plastic. Moreover, combinations of materials in which the tension mandrel is made of steel, stainless steel, or plastic and the rivet body is made of aluminum or plastic are advantageous. Thus, the rivet stud can be implemented in a corrosion-resistant material such as stainless steel or plastic. 
     The rivet stud according to the invention presents advantages and application possibilities. The anchoring of the rivet stud in one or more workpieces ensures high resistance to pull-out, since the rivet stud is supported on the workpiece by its flange, which can be made to have large dimensions, particularly when the mounting stud is under tensile loading. Due to the interlocking connection of the tension mandrel and rivet body, and the contact pressure of the disk-shaped setting head, the anchoring of the rivet stud in the workpiece can withstand high dynamic loads. The connection between the rivet stud and workpiece is impervious to splash water. 
     Setting of the rivet stud according to the invention can be carried out easily and quickly, and only requires one side of the workpiece to be accessible. Setting of the rivet stud can be performed fully automatically using existing blind rivet installation tools, but can also be done with simple hand-operated tools, and its use requires little training. The rivet stud can be set in soft materials in which it is not possible to use other methods, such as stud welding, adhesive stud bonding, self-piercing riveting, press fit studs, etc. The rivet stud can be set in a single workpiece or can join multiple workpieces together by setting. As a result, it is suitable for joining multilayered components without limitation with regard to the arrangement of the individual layers, their materials, or their thicknesses. The rivet stud can be set in even the thinnest-walled materials, such as films of 0.1 mm. On the other hand, it can have a wide clamping range, for example in material thicknesses from 1.5 to 5 mm for a rivet body diameter of 4.8 mm. Consequently, multiple components can be joined, and the requirement for different versions of rivet studs is low as a result. The rivet stud does not place any special requirements on the surface finish of the workpiece, and does not damage existing anti-corrosion coatings on the workpiece. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       The invention is explained in detail below with reference to an exemplary embodiment that is shown in the drawings. They show: 
         FIG. 1  a cross-section of a rivet stud according to the invention, and 
         FIG. 2  a partial section of a fastening arrangement according to the invention. 
         FIG. 3A  is a first alternative embodiment of a rivet stud according to the invention. 
         FIG. 3B  is a second alternative embodiment of a rivet stud according to the invention, and 
         FIG. 4  is another alternative embodiment of a rivet stud according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows a rivet stud  10 , which is composed a rivet body  11  made of aluminum or steel, and a tension mandrel  12  made of steel. The rivet body  11  is mounted on the tension mandrel  12  and has an elongated shank  13  with a through-bore  14 , in which the tension mandrel  12  is located. Formed at a head end of the shank  13  is a flange  15 , which takes the form of an annular disk and is intended to contact a workpiece. The side of the flange  15  facing away from the shank  13  is provided with a flat support surface  16  for supporting the forward end of a riveting tool. 
     At its end opposite the flange  15 , the shank  13  forms a foot end  17 , which is set off from the shank  13  by a first constriction  18 . A second constriction  19  divides the shank  13  into an essentially cylindrical first section  20  and a barrel-shaped second section  21  that curves slightly outward. On its outside, the first section  20  is provided with multiple flat indentations  22  spaced at regular intervals from one another that extend in the axial direction over nearly the entire length of the first section  20 . As a result of the indentations  22  produced by way of cold forming, the strength of the shank  13  in the region of the first section  20  is increased with the result that the first section  20  is no longer expanded or is only slightly expanded during setting of the rivet stud  10 . In the region of the first section  20  and in the region of the foot end  17 , the rivet body  11  is in contact with the tension mandrel  12 ; in the central region that curves outward, an annular clearance is present between the rivet body  11  and the tension mandrel  12 . 
     The tension mandrel  12  has a mandrel shank  23  that bears a mandrel head  24  at one end, and an elongated drawing end  25  at the other end. The mandrel head  24  has a greater diameter than the mandrel shank  23 , and has, on the underside facing the mandrel shank  23 , flat contact surfaces  26  for the foot end  17  of the shank  13 . The contact surfaces  26  are inclined at an acute angle of approximately 70° to 80° with respect to the longitudinal axis of the tension mandrel  12 . In place of the flat contact surfaces  26 , a concave conical surface with corresponding inclination may also be provided. The end of the mandrel head  24  opposite the contact surfaces  26  has a conical shoulder  27 , which is adjoined by a mounting stud  28  coaxial to the mandrel shank  23 . The mounting stud  28  has an external thread  29 , but can also be smooth  41  or provided with a T-head  40  as depicted respectively in  FIGS. 3B and 3A . If the mounting stud ( 28 ) is provided with an external thread ( 29 ) or other fastening means subject to a torque force when a nut or other device is secured to the stud ( 28 ), then it is advantageous according to the invention for there to be means for transmitting a torque between the tension mandrel and the rivet body, for example projections or longitudinal ribs  42  as depicted in  FIG. 4 . 
     On part of its length, the mandrel shank  23  has locking means in the form of annular ribs  30 , which are spaced apart from one another and have a sawtooth-like cross-section that is composed of conical surfaces and radial surfaces. The conical surfaces of the ribs  30  face the mandrel head  24 . Located between the mandrel head  24  and the rib  30  adjacent thereto is an annular rib  31 , which is embedded in a groove  32  in the foot end  17  and holds the tension mandrel  12  in place in the rivet body  11  against the recoil that attempts to drive the tension mandrel  12  out of the rivet body  11  when the drawing end  25  pulls off during setting of the rivet stud  10 . The rib  31  also ensures an effective seal between the rivet body  11  and the tension mandrel  12  after the rivet stud  10  has been set. The bore  14  is adapted to the outside contour of the ribs  30 ,  31  by radial deformation of the rivet body  11 , forming an interlocking connection between the mandrel shank  23  and the shank  13 . As a result of the interlocking connection, the tension mandrel  12  is held fast in the bore  14  of the shank  13  by the ribs  30 ,  31 , so that the rivet body  11  and the tension mandrel  12  compose an easy-to-manipulate structural unit. During setting of the rivet stud  10 , the ribs  30 ,  31  contribute to the transmission of tensile forces to the rivet body  11 , and after setting, they secure the tension mandrel  12  in the rivet body  11  that is joined to the workpiece. Preferably, the locking means that secure the part of the tension mandrel that is separated from the drawing end in the rivet body after setting can additionally be designed to transmit a torque from the mounting stud ( 28 ) into the rivet body ( 11 ). 
     The drawing end  25  is connected to the mandrel shank  23  by means of a constricted parting section that forms a predetermined breaking point  33 . The pre-determined breaking point  33  is located in the bore  14  of the rivet body  11  and has a spacing from the flange  15  such that the breaking point on the mandrel shank  23  is located in the bore  14  even after setting of the rivet stud  10 . 
       FIG. 2  shows a fastening arrangement with two workpiece components  35 ,  36  joined by a rivet stud  10 . The components  35 ,  36  have bores  37 ,  38 . For the purpose of joining the components  35 ,  36 , the rivet stud  10  is inserted in the aligned bores  37 ,  38  of the components  35 ,  36 . With the aid of a setting tool that bears on the support surface  16  of the rivet stud  10 , a tensile force is then exerted on the drawing end  25  of the tension mandrel  12 , and the rivet body  11  is deformed, causing the foot end  17  to approach the flange  15 . During this process, the barrel-like second section  21  on the blind side of the components  35 ,  36  folds to form a disk-shaped flange  39  that lies flat against the component  35  and presses the components  35 ,  36  against one another and against the flange  15 . Consequently, components made of plastic do not require any reinforcement by additional components or intermediate layers made of metal, since the flange  39  rests virtually flat against the component  35 . The component  35  experiences only a reduced radial load, because the flange  39  forms as a disk shape rather than as a cone shape. The cylindrical first section  20  is located in the bores  37 ,  38  and is loaded in compression by the tensile force that is exerted. The increased strength of the section  20  that has been produced by the indentations  22  prevents or reduces a radial expansion in the section  20 , however, so that no radial pressure, or at most a slight radial pressure, takes place between the section  20  and the walls of the bores  37 ,  38 . As a result, the stress on the components  35 ,  36  in the radial direction is low, and the risk of overloading or damaging the components during setting of the rivet stud is avoided. Only in the blind-side end region of the bore  37  in the component  35  may a limited radial pressure resulting from radial expansion of the shank  13  be desirable in order to achieve a better seal between the rivet body  11  and component  35 . 
     The region of the foot end  17  of the rivet body  11  is compression set during the setting process, and thereby pressed more firmly against the teeth formed by the ribs  30 ,  31 . In this way, the interlocking anchoring of the mandrel shank  23  in the rivet body  11  is reinforced and a tension-resistant connection is created between the two parts, so that the mounting stud  28  can transfer high pull-off forces to the components  35 ,  36  and does not come loose even under dynamic loading. In the case of a rivet stud  10  with a rivet body diameter of 4.8 mm, the mounting stud  28  withstood pull-off forces of more than 800 N in the axial direction. 
     Although exemplary embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes may be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.