Patent Publication Number: US-2022235811-A1

Title: Self-Punching Functional Element, Component Assembly and Method of Manufacturing a Component Assembly

Description:
The invention relates to a self-punching functional element for fastening to a workpiece, in particular to a high-strength sheet metal part, to a component assembly that comprises a workpiece and a functional element, and to a method of manufacturing a component assembly. 
     Such functional elements usually have a functional section that in turn serves to fasten further components. They are widely used in the automotive industry, among others. 
     Functional elements can be bolt elements, whose shaft can be provided with a thread, or nut elements that can, for example, have an internal thread. 
     Functional elements are known in different designs. On the one hand, there are, for example, rivet elements that have a rivet section that is deformed on the attachment to a sheet metal part to form a rivet bead and to form a ring-shaped receiver for the margin of a hole in the sheet metal part with the head part. With such rivet elements, the functional element is therefore deformed on the attachment to the sheet metal part. Furthermore, press-in elements are known in which the element itself is not intentionally deformed on the attachment to a sheet metal part, but the sheet metal material itself is deformed to bring it into engagement with undercuts of the respective press-in element. 
     To establish connections between a functional element and a workpiece, weld connections are often used, in particular if the workpiece is a high-strength sheet metal part. Workpieces (sheet metal parts) are designated as “high-strength” that have a strength of more than 1200 MPa, in particular approximately 1500 MPa to 1900 MPa, and that generally consist of high-strength steel. However, high-strength steel is difficult to weld. 
     Alternatively to welding, functional elements can be inserted into the workpieces during the press hardening. However, this requires a very high level of tooling technology and a homogeneous temperature control of the workpiece. 
     It is an object of the present invention to provide a functional element and a component assembly that enable a secure and stable connection with little effort and for different workpiece thicknesses. 
     This object is satisfied by the subjects of the independent claims. Advantageous embodiments are the subject of the dependent claims and are indicated in the description and the drawings. 
     A self-punching functional element in accordance with a first aspect of the invention serves for fastening to a workpiece, in particular to a high-strength sheet metal part, and comprises a functional section; and a fastening section that has a contact surface for an engagement of a setting device, an end face remote from the contact surface, and an outer peripheral surface connecting the contact surface and the end face. The end face is radially outwardly bounded by a punching edge for punching a slug out of the workpiece. At least one projection is provided at the outer peripheral surface adjacent to the contact surface, said projection rising from the outer peripheral surface in a radial direction and extending further outwardly in the radial direction than the punching edge. 
     The functional element in accordance with the invention is suitable for being pressed into a workpiece, in particular into a high-strength sheet metal part. Since the functional element is provided with a punching edge, the pre-punching of the workpiece is obsolete. On the pressing of the functional element into the workpiece, a slug is punched out of the workpiece by means of the punching edge and the functional element is pressed into the punched hole thus arising in the workpiece by means of the fastening section. The projection in so doing brings about an undercut acting in the axial direction such that the functional element is securely held in the workpiece. 
     The functional element typically consisting of steel can in particular be a bolt element or a nut element. In this respect, a shaft of the press-in bolt preferably has an external thread and forms the functional section in this manner. The nut element, in contrast, preferably has an internal thread that forms the functional section. Instead of the threads, other features can also be provided that are, for example, suitable for fastening a further component or for providing another functionality. The functional section can also be sectionally or completely formed as a smooth pin or a smooth hole. The fastening section is the section of the functional element with which the functional element is fastened to the workpiece. 
     The workpiece can in particular be a high-strength workpiece, for example a high-strength sheet metal part, composed of high-strength steel. The workpiece can have a strength of 1200 MPa or more, 1500 MPa or more, or 1800 MPa or more, in particular approximately 1500 MPa to 1900 MPa. The strength of the functional element usually amounts to a maximum of 1000 MPa or a maximum of 900 MPa. 
     The projection is expediently conical and/or, viewed relative to a longitudinal axis of the functional element, has an at least sectionally curved and/or slanted course. The projection can thereby be dimensioned such that the pressing in is not made unnecessarily difficult and such that the desired effect of the undercut produced still exists at the intended pressing-in depth into the workpiece. 
     A maximum radial extent of the projection is preferably arranged adjacent to or adjoining a transition to the contact surface. Thus, it can, for example, be achieved that the contact surface ends approximately flush with a surface of the workpiece after the pressing in. 
     In an advantageous embodiment, the projection has an axial extent that corresponds to approximately 30% to 60%, in particular approximately 35% to 45%, of an axial extent of the fastening section. It has been found that an optimum result can in this respect be achieved in which the press-in process is not made unnecessarily difficult and a secure hold is nevertheless achieved by the undercut. 
     The self-punching functional element can further have at least one feature providing security against rotation that is formed at the outer peripheral surface and that is preferably configured as a web that rises from the outer peripheral surface and that extends in an axial direction. After the pressing in, the feature providing security against rotation counteracts a torque acting on the functional element in the peripheral direction, for example, when a torque is introduced via the functional section during the assembly of a further component. 
     The feature providing security against rotation can preferably merge into the projection. In this respect, a radial extent of the feature providing security against rotation can advantageously substantially correspond to a maximum radial extent of the projection. It is further possible that the feature providing security against rotation is provided at the projection. 
     To increase the resistance to a torque in the peripheral direction of the functional element, a plurality of features providing security against rotation can expediently be provided that are arranged distributed, in particular uniformly distributed, in a peripheral direction at the outer peripheral surface. The securities against rotation can preferably be aligned in parallel with one another and/or can be oriented perpendicular to the peripheral direction. 
     The contact surface and/or the end face can preferably be ring-shaped. The width of the end face ring is preferably greater than 70%, greater than 80%, or greater than 90% of the axial extent of the fastening section or of the axial extent of the outer peripheral surface. The width of the end face ring can in particular also be equal to or greater than the axial extent, for example more than 100%, more than 150%, or more than 200% of the axial extent. An outer diameter of the punching edge (the maximum outer diameter in the case of a non-circular design) preferably amounts to more than 300%, more than 400%, more than 500%, or more than 600% of the axial extent of the fastening section or of the axial extent of the outer peripheral surface. 
     The end face preferably has a recess that is in particular centrally arranged. This benefits a displacement of material at the end face that can in particular be effected by means of a die plunger to produce a second undercut described in more detail later. 
     In an advantageous embodiment, the fastening section and/or the punching edge has/have a geometry that deviates from a circular shape. A polygonal, oval, or square geometry can in particular be considered. Such a shape effects a security against rotation of the fastening section in the workpiece in the peripheral direction in addition to the features providing security against rotation described above or as a sole security against rotation. 
     The projection can in particular be continuous in the peripheral direction in order to achieve an undercut that is as effective as possible and thereby to achieve a secure connection between the workpiece and the functional element. 
     Alternatively thereto, at least two projections arranged separately from one another in the peripheral direction can be provided, whereby an automatic security against rotation in the peripheral direction is effected after the pressing in. For example, a plurality of uniformly distributed projections can be arranged in the peripheral direction and can be formed in the same manner or differently in cross-section. 
     The functional section is preferably provided with a thread or a latch device. As already indicated, a bolt element is in this respect generally an external thread; however, it is also conceivable that the bolt element has a hollow shaft having an internal thread. In the case of a nut element, the thread is an internal thread. 
     In accordance with a further aspect, the invention relates to a component assembly that has a workpiece, in particular a high-strength sheet metal part, having a first surface, a second surface disposed opposite the first surface, and a punched hole that forms an inner peripheral surface. A self-punching functional element in accordance with at least one of the above-described embodiments is pressed into the punched hole while separating a punching slug such that the outer peripheral surface of the functional element contacts the inner peripheral surface of the punched hole and the projection engages into the first surface of the workpiece or cooperates therewith such that a first undercut acting in the axial direction is provided. Displaced material of the fastening section forms a second undercut that engages around the workpiece at the second surface to secure the functional element to the workpiece. 
     Due to the two undercuts acting in the axial direction, a secure hold of the functional element in the sheet metal part is achieved, wherein a pre-punching of the workpiece can be omitted. The formation of the second undercut is in this respect only possible after the pressing in, in particular by means of a die plunger, whereby a large range of possible workpiece thicknesses can be covered. 
     In an advantageous embodiment, the contact surface is aligned approximately flush with the first surface. 
     The fastening section can have a depression at the end face, from which depression the second undercut extends outwardly in the radial direction. The depression is in particular produced by the engagement of a tool, for example the die plunger, at the end face such that the material of the fastening section is radially outwardly displaced from there to form the second undercut. 
     To be able to form the second undercut, the fastening section advantageously has an axial extent that is greater than the thickness of the workpiece. 
     In accordance with a further aspect, the invention relates to a method of manufacturing the component assembly, said method comprising the steps:
         providing a self-punching functional element in accordance with the invention;   providing a workpiece, in particular a high-strength sheet metal part, that is not pre-punched at least in a region that is provided for fastening the functional element;   pressing the end face of the functional element against the workpiece such that a punched slug is separated from the workpiece by the punching edge while forming a punched hole, wherein the functional element is pressed into the workpiece at least until the projection enters into engagement with the first surface of the workpiece and/or with the inner peripheral surface of the punched hole to form the first undercut; and   reshaping the fastening section at least in a region adjacent to the punching edge to form the second undercut, in particular while engaging into the end face.       

     The functional element can expediently be pressed against the workpiece by a setting device that acts on the contact surface of the functional element. 
     Furthermore, a downholder can preferably be provided by which the second surface of the workpiece is pressed against a contact surface of a die to securely hold the workpiece during the pressing process. 
     A die plunger is preferably provided that is pressed against the end face of the fastening section to reshape the fastening section. 
     A further downholder can be provided that fixedly holds the functional element in the axial direction during the pressing against of the die plunger. For example, the downholder engages at the contact surface. The setting device can also act as a downholder, for example, if the reshaping takes place immediately after the pressing in. 
     The die plunger preferably has a reshaping surface that diverges, viewed from the end face, to urge material of the fastening section radially outwardly in order to form the second undercut in this manner. 
    
    
     
       The invention will be explained purely by way of example in the following with reference to advantageous embodiments. In the drawings, which schematically illustrate the embodiments, 
         FIG. 1 a    shows a perspective view of a functional element configured as a bolt element in accordance with an embodiment example; 
         FIG. 1 b    shows a further perspective view of the functional element from  FIG. 1 ; 
         FIG. 2  shows a perspective view of a functional element configured as a nut element in accordance with an embodiment example; 
         FIG. 3  shows a cross-sectional view of a functional element and of a workpiece during a method step for manufacturing a component assembly in which the functional element is pressed against the workpiece by a setting device; 
         FIG. 4  shows a cross-sectional view of a functional element and of a workpiece during a further method step in which a punched hole is formed by pressing the functional element against the workpiece and a punched slug is separated from the workpiece; 
         FIG. 5  shows a cross-sectional view of a functional element and of a workpiece during a further method step in which a die plunger engages at the end face of the fastening section; and 
         FIG. 6  shows a cross-sectional view of a functional element and of a workpiece during a further method step in which an undercut is formed at the fastening section by means of the die plunger. 
     
    
    
       FIGS. 1 a  and 1 b    each show a functional element  10  configured as a bolt element and  FIG. 2  shows a functional element  10  configured as a nut element. 
     The functional elements  10  each comprise a functional section  11  and a fastening section  13 . In the case of the functional element  10  configured as a bolt element in accordance with  FIGS. 1 a  and 1 b   , the functional section  11  has a shaft  30  that is provided with an external thread  31 . The functional element  10  configured as a nut element in accordance with  FIG. 2 , in contrast, has a central opening  32  that is provided with an internal thread  31  that is not shown in more detail. 
     The fastening section  13  is provided with a contact surface  15  and an end face  17  that is remote from the contact surface  15  and that has a centrally arranged recess  29 . The contact surface  15  is connected to an outer peripheral surface  19 , which connects the contact surface  15  and the end face  17  to one another, by means of a transition  25 . In a transition region from the outer peripheral surface  19  to the end face  17 , the fastening section  13  is provided with a peripheral punching edge  21  that is circular in the present example. 
     The functional element  10  further has, adjacent to the contact surface  15 , a projection  23  that is a peripheral projection in the present example, that projects radially away from the outer peripheral surface  19 , and that extends further outwardly in the radial direction than the punching edge  21 . In the present embodiments, the projection  23  is conical, with the point of the maximum radial extent of the projection  23  being located at the transition  25 . 
     The fastening section  13  is also provided with a plurality of features providing security against rotation  27  that project from the outer peripheral surface  19  and that merge into the projection  23  at their end facing the contact surface  15 . This means that the radial extent of the features providing security against rotation  27  corresponds to the maximum radial extent of the projection  23 . The features providing security against rotation  27  are formed as webs or ribs that extend in parallel with the longitudinal axis  33  of the functional element  10  and that are arranged at equal spacings from one another along the outer peripheral surface  19 . 
     A method of manufacturing a component assembly  100  will be described in the following, in particular in view of  FIGS. 3 to 6  and with exemplary use of the functional element  10  from  FIGS. 1 a    and  1   b.    
     First, the self-punching functional element  10  and a workpiece  50 , in the present example a high-strength sheet metal part, are provided. As  FIG. 3  clearly shows, the workpiece  50  has a first surface  53  and a second surface  55  disposed opposite the first surface  53  and is not pre-punched, at least in the region into which the functional element  10  is to be inserted. An axial extent of the fastening section  13  is in this respect greater than the thickness T 50  of the workpiece  50 . 
     To accurately position and to securely hold the workpiece  50  during the method steps, the second surface  55  of the workpiece  50  is first placed on a die  110  such that the second surface  55  is disposed on a contact surface  111  of the die  110 . The die  110  can in particular have a central recess  113  that is at least so large that a slug  51  separated on the punching, see  FIG. 4 , can fall through the recess  113 . For this purpose, the workpiece  50  is aligned with the recess  113  with the region in which the functional element  10  is to be attached. 
     The workpiece  50  is pressed onto the contact surface  111  of the die  110  by means of a downholder  130  in that the downholder  130  engages at the first surface  53 . The workpiece  50  is thereby securely held on the die  110  to prevent slippage during the pressing. 
     The functional element  10  is then pressed onto the workpiece  50  by a setting device  140  acting with a contact surface  141  on the contact surface  15  such that the end face  17  of the functional element  10  is pressed against the first surface  53  of the workpiece  50  and the punching edge  21  thereby forms a punched hole  57  in the workpiece  50  in conjunction with the acting pressing force, wherein, as  FIG. 4  shows, a punched slug  51  is separated. 
     In the present example, as  FIGS. 4 to 6  show, the pressing process takes place at least until the projection  23  enters into engagement with the first surface  53  of the workpiece  50  and an inner peripheral surface  59  of the punched hole  57 . The projection  23  in this respect forms a first undercut  61  acting in the axial direction. 
     The setting device  140  is provided with a central recess  143  that is in particular so large that the shaft  30  of the functional element  10  can just fit therein and can be received in the recess  143 . For example, the recess  143  can be designed as a bore such that the setting device  140  can receive a shaft  30  that, as in the present example, may be provided with a thread  31 , but is cylindrical in its basic shape. In this case, both the contact surface  141  and the contact surface  15  are of ring-shaped design, wherein an application of force acting uniformly on the functional element  10  can be achieved. 
     As is clearly shown in  FIGS. 5 and 6 , in a next step, the fastening section  13  is formed at least in a region adjacent to the punching edge  21  to form a second undercut  63 . In the present embodiment example, this takes place by means of a die plunger  120  that has a reshaping surface  121 , which diverges viewed from the end face  17 , and that is pressed against the end face  17  of the fastening section  13 . In this respect, material of the fastening section  13  is urged radially outwardly such that the second undercut  63  that likewise acts in the axial direction is produced. 
     The pressing in of the functional element  10  and the formation of the second undercut  63  preferably take place directly subsequent to one another. However, it is also possible to implement these two processes in different tools, wherein the functional element  10  with the workpiece  50  are removed from the first tool after the pressing in of the functional element  10  and are transported to the second tool. The second undercut  63  is then formed in the second tool. A downholder can likewise be used here. For example, the downholder is designed such that it simultaneously fixes the workpiece  50  and the element  10  in the axial direction. 
     In the component assembly  100  manufactured in this manner, the outer peripheral surface  19  of the functional element  10  contacts the inner peripheral surface  59  of the punched hole  57 . The contact surface  15  is aligned approximately flush with the first surface  53  of the workpiece  50  and the projection  23  engages into the material of the workpiece  50  and into the first surface  53  and cooperates with the latter, wherein the first undercut  61  acting in the axial direction is formed. The material of the fastening section  13  displaced by means of the die plunger  120  forms the second undercut  63  that extends radially outwardly from a depression  35 , which is formed at the end face  17  and is produced by the engagement of the reshaping surface  121  of the die plunger  120 , and that engages behind the workpiece  50 . 
     A secure and stable connection between the functional element  10  and the workpiece  50 , in particular a high-strength sheet metal part, can thus be established by the functional element  10  shown here and the component assembly  100 . Since the workpiece  50  does not have to be pre-punched and a complex welding process is obsolete, this is possible with comparatively little effort. Moreover, the component assembly  100  can be produced with a wide application range of thicknesses of the workpiece  50 . 
     REFERENCE NUMERAL LIST 
     
         
           10  functional element 
           11  functional section 
           13  fastening section 
           15  contact surface 
           17  end face 
           19  outer peripheral surface 
           21  punching edge 
           23  projection 
           25  transition 
           27  feature providing security against rotation 
           29  recess 
           30  shaft 
           31  thread 
           32  opening 
           33  longitudinal axis 
           35  depression 
           50  workpiece 
           51  slug 
           53  first surface 
           55  second surface 
           57  punched hole 
           59  inner peripheral surface 
           61  first undercut 
           63  second undercut 
           100  component assembly 
           110  die 
           111  contact surface of the die 
           113  recess 
           120  die plunger 
           121  reshaping surface 
           130  downholder 
           140  setting device 
           141  contact surface 
           143  recess 
         T 50  thickness of the workpiece