Patent Publication Number: US-2020290111-A1

Title: Method for fastening a fastener element

Description:
The invention relates to a method of fastening a fastening element to a workpiece, in particular to a sheet metal part. 
     In many areas of technology, in particular in automotive engineering, it is necessary to fasten an element to a workpiece. This element then, for example, serves to connect a further component to the workpiece. For example, the fastening element can be a nut element or a bolt element to which the component is screwed. 
     Known fastening elements of the above-mentioned kind frequently comprise a flange section provided for contact with the workpiece; and a fastening section which has a rivet section that at least sectionally bounds a hollow space in a peripheral direction and that is in particular at least sectionally produced from a metal material. The elements are frequently completely or largely composed of metal. 
     The fastening process is typically carried out as follows: First, the workpiece, for example a planar, panel-shaped component, is provided. Then, the fastening element is inserted into the workpiece and at least one section of the rivet section is reshaped (in particular by cold deformation) such that this section engages behind the workpiece at a side of the workpiece remote from the flange section. At least this section therefore passes through the workpiece. 
     The insertion and the reshaping are expediently effected by a fastening movement of the fastening element in a common fastening direction. This direction is, for example, defined by a straight line that is arranged coaxially to a longitudinal axis of the element. 
     However, considerable forces are required for this process, in particular to effect the reshaping of the rivet section. This has the result that a corresponding setting apparatus for setting the element at the workpiece has to have a very powerful and stable design. In addition, large forces that inter alia result in considerable wear likewise act on a reshaping tool that reshapes the rivet section. 
     It is therefore an object of the invention to improve the above-described method such that the components required for fastening the element are subjected to less load, but without compromises in this respect having to be made with regard to the reliability of the fastening of the element. 
     It has been recognized in accordance with the invention that this object is satisfied in a surprisingly simple manner if the fastening element is acted on by a mechanical vibration, in particular by an ultrasound vibration, at least at times during the insertion into the workpiece (e.g. a sheet metal part, a fiber-reinforced plastic component or the like) and/or during the reshaping of the rivet section. Significantly lower forces are then particularly required for the reshaping process than for conventional methods. It must be mentioned for reasons of completeness that the insertion and reshaping do not have to be strictly successive processes. It is by all means possible that the rivet section is already reshaped during the insertion of the element into the workpiece. 
     In general, it is also—additionally or alternatively—conceivable for the workpiece, and/or a reshaping tool provided for reshaping the rivet section to be acted on by a mechanical vibration, in particular by an ultrasound vibration, in order to optimize the fastening process. 
     Further embodiments of the method in accordance with the invention are set forth in the description, in the claims and in the enclosed drawings. 
     In accordance with an embodiment of the method, the fastening element, the workpiece, and/or a reshaping tool provided for reshaping the rivet section is/are acted on by a vibration that is oriented coaxially to the fastening movement. A vibration in the direction of the longitudinal axis of the element, which can also be its axis of symmetry, is designated as a longitudinal vibration. 
     It can be advantageous in various applications if an amplitude and/or a frequency of the vibration is/are varied during the insertion of the fastening element and/or during the reshaping of the rivet section. This also includes cases in which no action by vibration is provided (at times) on the insertion of the element or on the reshaping of the rivet section. The amplitude and/or the frequency of the vibration can also be kept substantially constant during the insertion of the fastening element and/or during the reshaping of the rivet section. In other words, said parameters and their variation in time (provided in this manner) can be adapted as required to the respective present situation. 
     The workpiece can be provided with an opening for receiving the rivet section (pre-punched workpiece). However, the method in accordance with the invention can be used in cases in which the provided workpiece at least does not have an opening in a region provided for the insertion of the fastening element. The element then produces an opening in the workpiece (self-piercing element) by its insertion. 
     The rivet section is preferably a continuous wall that surrounds the hollow space in the peripheral direction. For example, the wall is an annular wall that can be reshaped by a corresponding tool to produce an undercut that generates a fastening effect. It is generally preferred if the hollow space is open toward the workpiece in the direction of movement of the element. The hollow space can, for example, have a cylindrical basic shape. 
     The reshaping tool is in particular a die. 
     The present invention further relates to an apparatus for fastening a fastening element to a workpiece in accordance with a method in accordance with at least one of the preceding claims. The apparatus comprises a punch movable relative to the workpiece in a fastening direction for inserting the fastening element into the workpiece; and a die for at least sectionally reshaping a rivet section of the fastening element at least sectionally surrounding a hollow space such that a reshaped section of the rivet element engages behind the workpiece after the completion of the fastening. A first drive apparatus is provided by which a movement of the punch can be produced in the fastening direction, on which movement a mechanical vibration, in particular a vibration in the fastening direction, is superposed. In addition or as an alternative, a second drive apparatus can be provided by which the workpiece and/or a reshaping tool provided for reshaping the rivet section can be set into a vibration. The vibration produced by the second drive apparatus is preferably oriented coaxially to the fastening movement. 
     In accordance with an embodiment of the apparatus, the first drive apparatus and/or the second drive apparatus comprises/comprise an apparatus for producing an ultrasound vibration. 
     The reshaping tool can be a die which has a reshaping surface that cooperates with the rivet section, that is at least sectionally curved, and/or that is at least sectionally arranged obliquely with respect to the fastening direction and to a plane extending perpendicular thereto. 
    
    
     
       The present invention will be explained in the following purely by way of example with reference to an advantageous embodiment and to the enclosed drawings. There are shown: 
         FIGS. 1 to 3  different stages of an embodiment of the method in accordance with the invention. 
     
    
    
       FIGS. 1 to 3  show three different states during a fastening of an internal thread  11  of a rotationally symmetrical rivet element  10  to a sheet metal part  12 . It is understood that rivet elements of a different design can also be used instead of the rivet element  10  and that they do not necessarily have to be rotationally symmetrical. Rivet elements comprising a bolt section—with or without a thread—are also conceivable. 
       FIG. 1  shows a starting situation before the fastening process, wherein the rivet element  10  is arranged above the sheet metal part  12  in  FIG. 1 . A die  14  is present at the oppositely disposed side of the sheet metal part  12 . The sheet metal part  12  is supported on spacers  16  that are fixedly connected to the die  14 . This means that the spacers  16  do not move in the course of the fastening process. Dynamic spacers are likewise conceivable that e.g. have to escape downwardly when a threshold value of a force acting on them is exceeded. 
       FIGS. 1 to 3  are divided into two parts into a cross-sectional view at the left side and into a side view at the right side. The boundary between the two views extends through an axis of symmetry A that relates to the rotationally symmetrical rivet element  10 , the sheet metal part  12 —at least in a region around the fastening point—, and the die  14 , as will be explained in more detail further below. 
     The spacers  16  extend in parallel with the axis A, wherein the spacers are screwed into corresponding bores  17  of the die  14  and are therefore releasably connected thereto. The spacers  16  are each made in the manner of pins and have an end section  20  that projects out of a contact surface  18  of the die  14 . The length of the end sections  20  is set uniformly such that the sheet metal part  12  is horizontally supported on the spacers  16 , i.e. perpendicular to the axis A. A spacing D is thereby set between a lower side  21  of the sheet metal part  12 —i.e. the side of the sheet metal part  12  facing the contact surface  18 —and the contact surface  18 . Each end section  20  comprises a substantially convex support surface  22  facing the sheet metal part  12 . 
     The spacing D can be adapted by an adjustment of the spacers  16  if necessary, e.g. if a different rivet element  10  should be used. 
     The die  14  has a conical die plunger  24  (here static, a die plunger escaping downwardly in a dynamic manner is also conceivable) that partly projects into a circular hole  26  provided at the sheet metal part  12 . The axis A extends through the corresponding centers of the die plunger  24  and of the hole  26 . In this respect, the axis A is thus an axis of symmetry for the sheet metal part  12 —at least in the region around the hole  26 —and for the die  14 . The hole  26  was produced before the fastening process described here. 
     The sheet metal part  12  is planar in the region around the hole  26  and does not have a flare in this region. Optionally, however, the sheet metal part  12  can also be completely planar—as in the embodiment described here. However, this does not necessarily have to be the case. 
     A gap  30  is formed between a wall  28  of the hole  26  of the sheet metal part  12  and the lower side  21  of the sheet metal part  12 , on the one hand, and the die plunger  24 , on the other hand. 
     The rivet element  10  arranged above the sheet metal part  12  has a rivet section  32  that surrounds a cylindrical hollow space  33  in the peripheral direction and that is open toward the workpiece  12 . The section  32  is an annular wall in the present example that extends away from a flange section  36  of the rivet element  10  in the axial direction. It has an end edge  34  that is rounded at the outside and conical at the inside. A functional section that supports the thread  11  at least in part is provided at the other side of the flange sections  36 . The rivet element  10  is a nut element. 
     A peripheral groove  38  is provided in a transition region between the flange section  36  and the rivet section  32 . 
     The outer diameter of the rivet section  32  is slightly smaller than the diameter of the hole  26  so that the rivet section  32  can be introduced into the hole  26 . 
     Starting from the state shown in  FIG. 1 , the rivet element  10  is now moved in the axial direction in the direction toward the die  14  (direction of movement B), wherein the rivet section  32  is aligned with the hole  26  of the sheet metal part  12  (coaxial alignment). 
       FIG. 2  shows the arrangement of  FIG. 1  in a second state in which the rivet section  32  is introduced into the hole  26 . On a further movement of the rivet element  10  in the direction B toward the die  14 , the inwardly disposed part of the end edge  34  of the rivet section  32  cooperates with a concave reshaping surface  40  of the die plunger  24  and the rivet section  32  is reshaped radially outwardly so that the rivet section  32  engages into the gap  30  and engages behind the sheet metal part  12 . At least one part of the rivet section  32  has thus completely passed through the workpiece  12 . 
     The rivet element  10  is displaced further in the direction toward the die  14  (direction of movement B) during the reshaping of the rivet section  32 , wherein the flange section  36  comes into contact with a contact surface  37  at the sheet metal part  12 . The length of the rivet section  32  or the spacing D is adapted such that the flange section  36  only comes into contact with the sheet metal part  12  when the rivet section  32  at least partly engages behind the sheet metal part  12  in the course of the reshaping, in particular when the reshaping that produces the engagement behind is completed. 
     The rivet element  10  is now moved further in the direction toward the die  14 , wherein the sheet metal part  12  is moved along in the direction toward the contact surface  18  of the die  14 . In this respect, the sheet metal part  12  is reshaped locally in the region of the spacers  16  so that the end sections  20  of the spacers  16  engage into the sheet metal part  12  and the sheet metal part  12  comes into contact with the contact surface  18 . In this connection, the end sections  20  of the spacers  16  that reshape the sheet metal part  12  cause a respective elevated portion  41  of the sheet metal part  12  at the side remote from the die  14 , as will be explained in more detail further below. 
     In  FIG. 3 , the sheet metal part  12  is shown with the rivet element  10  after the completion of the fastening process. It can be seen that the sheet metal part  12  is reshaped in the region of the rivet section  32  which engages behind the sheet metal part  12  during its movement B from the position shown in  FIG. 2  in the direction toward the die  14 . In this respect, the region of the sheet metal part  12  originally adjacent to the hole  26  deflects due to a cooperation with the rivet section  32  that engages behind the sheet metal part  12  and that is pressed into the groove  38  of the rivet element  10 . At the same time, the engaging-behind rivet section  32  is completely displaced into the plane of the sheet metal part  12  that extends perpendicular to the axis A by a cooperation with the reshaping surface  40  of the die plunger  24  so that the lower side  21  of the sheet metal part  12  facing the die  14  is substantially planar. This means that the reshaped rivet section  32  does not project out of the plane of the lower side  21 . In addition, the rivet section  32  is deformed in part such that the rivet section  32  nestles against the sheet metal part  12 . A particularly good shape matching and force transmission between the rivet element  10  and the sheet metal part  12  are hereby achieved. 
     As mentioned above, the end sections  20  of the spacers  16  engage into the sheet metal part  12  in the course of the movement of the sheet metal part  12  toward the contact surface  18  of the die  14 . As a result, the already mentioned elevated portions  41  are thereby produced at the upper side of the sheet metal part  12  ( FIG. 3 ). 
     The above statements serve as a purely exemplary explanation of a fastening process of a fastening element. It is understood that such an element—when using a suitable die—can also be fastened to a workpiece that is not prepared or that is not pre-punched. The element is then self-piercing. 
     The design of the die  14  provided for reshaping the rivet section  32  can also differ from that shown. It is therefore conceivable that no spacers  16  are present, but that the sheet metal part  12  rather lies directly on the contact surface  18 . The die then preferably has a (possibly annular) recess which receives the end of the rivet section  32  that penetrated the part  12  and/or contributes to its reshaping. 
     In accordance with the invention, the rivet element  10  is acted on by a vibration on the insertion into the sheet metal part  12  in order to minimize the force required for the insertion. The vibration is superposed on the movement B and oriented coaxially thereto, as indicated by the double arrow S in  FIG. 1 . The vibration S is consequently a longitudinal vibration. In general, it is also—additionally or alternatively—possible to provide a transverse vibration component, i.e. a vibration in a plane that is arranged perpendicular to the direction of movement B. 
     Superpositions with vibrations in the ultrasound range have proven to be particularly efficient. 
     The vibration S is preferably also maintained at least at times during the reshaping of the rivet section  32  since this process is associated with a substantial exertion of force that can exceed (frequently even by a multiple) the exertion of force required for the insertion of the element  10  into the sheet metal part  12 . In many cases, this even applies to self-piercing elements. 
     The exertion of force required for the fastening of the element  10  is reduced by the vibration-superposed movement B, S of the element  10 , which enables a simpler design of a corresponding setting apparatus. In addition, the wear of the die  14  is reduced. 
     However, it is not absolutely necessary to provide a movement B, S acted on by vibration during the insertion of the element  10  into the sheet metal part  12 . It very generally applies that the vibration S can be superposed on the movement B as required. It can vary over time, be it with respect to its amplitude and/or its frequency. This also applies to transverse vibration components—if provided. 
     Reference Numeral List 
       10  rivet element 
       11  internal thread 
       12  sheet metal part 
       14  die 
       16  spacer 
       17  bore 
       18  contact surface 
       20  end section 
       21  lower side of the sheet metal part 
       22  support surface 
       24  die plunger 
       26  hole 
       28  wall 
       30  gap 
       32  rivet section 
       33  hollow space 
       34  end edge 
       36  flange section 
       37  contact surface 
       38  groove 
       40  reshaping surface 
       41   41  elevated portion 
     A axis of symmetry 
     B direction of movement 
     S vibration