Patent Publication Number: US-2016234958-A1

Title: Fastening element for fixating two components at each other

Description:
RELATED APPLICATIONS 
     This application is a continuation of International Application PCT/DE2014/200230 filed on May 21, 2014 claiming priority from German patent applications 
     DE 20 2013 006 326.2 filed on Jul. 15, 2013,
 
DE 20 2013 006 325.4 filed on Jul. 15, 2013,
 
DE 20 2013 007 589.9 filed on Aug. 24, 2013, and
 
DE 20 2014 001 330.6 filed on Feb. 17, 2014,
 
all of which are incorporated in their entirely by this reference.
 
    
    
     FIELD OF THE INVENTION 
     The invention relates to a fastening element for fixating a first component such as a circuit board fitted with a LED at a second component such as a lamp element. 
     BACKGROUND OF THE INVENTION 
     Fastening elements of this type are not known in the lamp industry. Similar fastening elements, however, exist in the automotive field. Reference is made herein for example to WO 2005/071273 A1. These fastening elements are typically used for attaching inner fairing elements at a vehicle body. Thus, the inner fairing element has a pass through opening for example a bore hole which penetrates the inner fairing element in its entirety. On a side of the body typically a sheet metal component is also provided which includes a bore hole. The pass through opening of the inner fairing element and the bore hole of the vehicle body are matched. Then the fastening element typically also designated as an expanding rivet is inserted into the bore hole through the pass through opening. Anchoring the expanding rivet in the bore hole at the vehicle body can be performed through friction locking, for example by plastic lamellas which are configured at the shaft of the fastening element. Interlocking connections are also feasible in that interlocking hooks of the fastening element engage interlocking recesses. 
     Mass produced lamps are typically produced with LEDs as illuminants today. Particular LED types become more and more common. Thus, it is typical to apply LEDs to printed circuit boards and to provide these as components to the lighting industry for further use. Though materials and shapes of the printed circuit boards vary as well as the LEDs applied thereto with respect to number and distribution, however, an attachment of the printed circuit board at the lamp element is required in any case. An even contact pressure of the printed circuit board at the surface of the lamp element thus provides optimum heat dissipation from the LEDs. 
     In the art connecting elements for circuit boards of this type are known from DE 10 2008 005 823 B4 or DE 10 2012 003 520 B4. These connection elements combine circuit board attachment with the option of supplying voltage to the LEDs arranged on the circuit board. 
     Though these connecting element combining fastening and voltage supply are advantageous in many cases, fastening devices are required for lamps which are useable for widely automated production due to various circuit board designs and various manufacturing methods. It is furthermore necessary that the attachment devices support the circuit board of the LED under a defined contact pressure on the lamp element in order to provide good heat transfer. 
     BRIEF SUMMARY OF THE INVENTION 
     This object is achieved by a fastening element for fastening a first component at a second component, the fastening element comprising a shaft which includes at least one spring elastic support element which anchors the fastening element at the second component; a shaft head which has a larger diameter than the shaft and which is arranged at a first end of the shaft; and a clamping element which clamps the first component against the second component with a defined contact pressure, wherein the first component is a circuit board which is fitted with LEDs and includes a first pass through opening and the second component is a lamp element which includes a recess which is configured as a dead hole or a second pass through opening, wherein the clamping element is formed by a spring elastic clamping arm which is displaceable in a spring elastic manner and which forms a portion of the shaft head and which contacts a surface of the first component, wherein the shaft is formed by three arms that are integrally made from one piece of material, wherein the shaft head is formed by three lobes, wherein each of the three lobes respectively forms a portion of one respective arm of the three arms, wherein the three arms are formed by two crimps in a stamped blank along two deformation lines and the three lobes are provided by two incisions along the two deformation lines, wherein a length of the two incisions exceeds a length of the three lobes, wherein the three lobes are formed respectively by crimps along a respective deformation line that is oriented transversal to a longitudinal axis of the shaft, and wherein the two incisions separate arm sections of the three arms in a portion of the shaft from each other, wherein the arm sections are displaceable in a spring elastic manner relative to the longitudinal axis of the shaft. 
     It is an advantage of the invention that the described fastening element provides the option to safely attach a circuit board at a lamp element by simply inserting the shaft through the pass through opening of the printed circuit board and into the recess of the lamp element. Thus, the fastening element is advantageously made from metal and thus formed by crimping a stamped component. This way a high level of material stability is provided for lamp elements that are very small compared to the non related art known in the automotive industry. The attachment elements proposed herein typically have a shaft head with a diameter of 6 mm or less and a shaft length of not more than 7 mm with a diameter of 3 mm at the most. 
     It is an essential advantage of the invention that the shaft head itself forms the clamping element in that it includes a clamping arm. The clamping function which provides a defined contact of the  2  components, namely the LED circuit board and the lamp element at one another is thus taken over by the clamping head. Additional components which could make production and assembly difficult are omitted. 
     In particular it is possible this way that the fastening element which is provided by crimping a stamped sheet metal blank which assures efficient fabrication. 
     It is provided that the clamping arm configured as a portion of the shaft head is sloped downward starting from a shaft longitudinal axis to the surface of the first component, wherein a movement building up a spring reset force is forced upon the clamping arm by contacting a surface of the first component when inserting the fastening element into the recess. 
     In view of the fact that the shaft head is formed by lobes which are arranged at one end of the shaft and configured so that they contact the surface of the first component it becomes clear that the arms which form the shaft head can be configured as clamping arms so that they perform a double function. On the one hand side the arms retain the fastening element on the first component, on the other hand side the attachment arms apply a clamping force for clamping the two components relative to each other. 
     In particular it is provided that the shaft is formed by at least two arms which are obtained by crimping a piece of sheet metal along a first deformation line that is parallel to a longitudinal axis of the shaft. It is furthermore provided in a particular embodiment that the arms are obtained by an incision along a deformation line that is parallel to the longitudinal axis of the shaft and crimping the head ends of the arms thus obtained into a position that is suitable for contacting the first component, in particular into a position that is inclined relative to the first component. 
     An embodiment is particularly advantageous which is characterized in that the incisions separate arm sections in the shaft portion from each other and that at least one of the arm sections can be displaced in a spring elastic manner towards the longitudinal axis of the shaft 
     The essential advantage of the spring elastic arm sections of the shaft is that the spring elastic arm sections of the shaft additionally support the clamping function of the shaft head. Thus, when the fastening element moves through the cut out of the first component into the recess of the second component, initially the clamping arms of the shaft head contact the surface of the first component. 
     When the clamping arms are inclined according to the embodiment described supra from the shaft longitudinal axis towards the surface of the first component they are displaced against the insertion direction X building up a spring reset force and thus already apply a particular clamping force. Additionally a displacement of the spring elastic arm sections of the shaft in a direction of the shaft longitudinal axis building up an additional spring reset force leads to a reinforced clamping force which impacts components that are to be attached at each other. 
     A third arm is provided which is obtained by crimping the sheet metal along a second deformation line that is parallel to the longitudinal axis of the shaft and wherein the third arm receives the first arm between itself and the second arm, wherein the third arm is advantageously shaped like the second arm, in particular when the arms differ with respect to their length and a free end of the first longer arm which is oriented away from the shaft head forms the support element configured as a spring arm. 
     It is furthermore provided that the free end of the first longer arm is oriented at least transversal to, advantageously however against an insertion direction x of the shaft through forming. 
     It is furthermore provided that the free end of the second shorter arm that is oriented away from the shaft head forms a contact surface for the spring arm of the first arm. 
     It is furthermore provided that an insulation element, for example an elastomeric disc is arranged in a shaft direction below the shaft head. This elastomeric disc advantageously includes a central pass through opening through which the shaft of the fastening element is run. This insulation element initially has the function to insulate the metal head of the fastening element relative to electrically conductive components like e.g. conductor paths. When this is a spring elastic insulating element it can be deformed in a spring elastic manner when inserting the fastening element and it can impart a force that is directed against the insertion direction. 
     When the shaft is formed by at least two arms as recited supra which are obtained by crimping a piece of sheet metal along a first deformation line that is parallel to the longitudinal axis of the shaft this has a substantial advantage in that the shaft is stabilized this way against bending and kinking forces. 
     When the arms differ in length and the free end of the first longer arm forms the support element configured as a spring arm and it is furthermore provided that the free end of the first longer arm is formed by crimping at least transversal to, advantageously however against an insertion direction of the shaft, it is assured that the support element configured as a spring arm can be fabricated in a simple and cost effective manner. By connecting the spring arm at the first arm the spring arm can have a length that is greater than the dead hole diameter which influences the spring properties in a positive manner and which prevents a plastic deformation. 
     The free end of the second shorter arm that is oriented away from the shaft head can form a contact surface for the spring arm of the first arm. The contact surface is thus arranged so that it protects the spring elastic spring arm before it reaches a displacement which exceeds the spring reset force and which causes a plastic deformation. Thus, it is assured that the spring reset force of the spring arm is sufficient to safely support the fastening element in the recess at the lamp element to attach the circuit board at the lamp element. 
     The shaft head is advantageously formed by arms which are arranged at an end of the shaft that is oriented away from the spring arm, in particular when the arms are obtained by an incision along the deformation line parallel to the shaft longitudinal axis and crimping the head ends of the arms thus obtained into a position that is approximately transversal to the shaft longitudinal axis. When the lobes are inclined with their ends relative to their component they can take over the function of an elastic insulating element when no such insulating element is used and can impart axial clamping forces onto the components. This way it is assured that the attachment element, in particular its head can be produced in a simple and effective manner while crimping the stamped blank. 
     In order to further improve stability of the shaft of the fastener element it is provided that a third arm is provided which is obtained by deforming the sheet metal along a second deformation line that is parallel to the longitudinal axis of the shaft and which receives the first arm between itself and the second arm. Thus, it is provided that the third arm corresponds to the second arm with respect to its configuration. Furthermore an embodiment is preferred which is characterized in that the shaft formed from the three arms has an approximately triangular cross section. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further advantages and a better comprehension of the invention are apparent from the subsequent description of an embodiment with reference to the drawing figures, wherein: 
         FIG. 1  illustrates a stamped blank for producing a fastener element according to the invention; 
         FIG. 2  illustrates the fastener element according to the invention after deforming the stamped blank; 
         FIG. 3  illustrates the fastening element according to  FIG. 2  in a first side view; 
         FIG. 4  illustrates the fastening element according to  FIG. 2  in a second side view; 
         FIG. 5  illustrates a top view of the fastening element according to  FIG. 2 : 
         FIG. 6  illustrates a side view of the fastening element in an installed condition; 
         FIG. 7  illustrates a sectional view according to the section line A-A in  FIG. 6 ; 
         FIG. 8  illustrates a top view of the illustration according to  FIG. 6 ; 
         FIG. 9  illustrates a sectional view along the section line B-B in  FIG. 8 ; 
         FIG. 10  illustrates an exploded view of lamp element, circuit board and fastening element and an assembly tool; 
         FIG. 11  illustrates a vertical sectional view for illustrating the effect of the assembly tool; 
         FIG. 12  illustrates the representation according to  FIG. 10 , however with a disassembly tool; 
         FIG. 13  illustrates the disassembly process; 
         FIG. 14  illustrates an alternative embodiment of the fastening element according to the invention in a first side view; 
         FIG. 15  illustrates the fastening element according to  FIG. 14  in a second side view; 
         FIG. 16  illustrates the fastening element in a sectional view according to the section line A-A in  FIG. 14 ; 
         FIG. 17  illustrates a top view of the fastening element according to  FIG. 14  in a mounted configuration; and 
         FIG. 18  illustrates a sectional view according to the section line B-B in  FIG. 17 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A fastening element according to the invention is designated overall with the reference numeral  10  and illustrated in a first embodiment in  FIGS. 1-12 . 
     The fastening element  10  includes a shaft  11 , a shaft head  12  which is arranged at an end of the shaft  11  and a spring arm  13  which is supported by a free end of the shaft  11  which is arranged opposite to the shaft head  12 . 
     The shaft  11  is formed by three arms that are integrally connected in one piece, wherein the first arm has the reference numeral  14 , the second arm has the reference numeral  15  and the third arm has the reference numeral  16 . The shaft head  12  is formed by three lobes, wherein the first lobe has the reference numeral  17 , the second lobe has the reference numeral  18  and the third lobe has the reference numeral  19 . The first lobe  17  is part of the first arm  14 , the second lobe  18  is part of the second arm  15 , and the third lobe  19  is part of the third arm  16 . The lobes  17 ,  18 ,  19  are thus oriented approximately transversal to a shaft longitudinal axis L and are arranged offset relative to each other in the embodiment illustrated herein under an approximately identical circumferential angle. In particular the lobes  17 ,  18 ,  19  are sloped from the shaft longitudinal axis L in a direction of the surface of the first component  24  and configured spring elastic. The lobes  17 ,  18 ,  19  are provided to contact the first component  24 . 
     The fastening element  10  according to the invention is formed from the stamped blank  22  of a piece of sheet metal. The stamped blank is illustrated in  FIG. 1 . By crimping along the deformation lines U 1  and U 2  which extend along the longitudinal axis of the shaft the three arms  14 ,  15 ,  16  are formed. The second arm  15  and the third arm  16  receive the first arm  14  between each other. Thus, the second arm  15  and the third arm  16  are configured shortened relative to first arm  14  at an end oriented towards the spring arm  13 . The deformation for obtaining the second arm  15  and the third arm  16  thus occurs in the same direction, wherein both arms are oriented towards each other with their free outer edges oriented parallel to the shaft longitudinal axis. 
     The shaft head  12  or its three lobes  17 ,  18 ,  19  are obtained by providing the stamped blank with two incisions S 1  and S 2 . The incisions are introduced at an end of the press blank  22  oriented away from the spring arm  13  along the deformation lines U 1  and U 2 . The depth of the incisions S 1  and S 2  thus exceeds a length of the lobes. Subsequently the lobes  17 ,  18 ,  19  have to be shaped along the deformation line U 4  until they are oriented approximately transversal to the shaft longitudinal axis L and are oriented away from the shaft longitudinal axis L. The deformation line U 4  is oriented approximately transversal to the shaft longitudinal axis L. 
     The spring arm  13  is obtained in that the section of the first arm  14  which is extended relative to the arms  15  and  16  is bent over along the deformation line U 3  until this section is oriented against an insertion direction X of the fastening element  10 . Thus the spring arm  13  is oriented along the free longitudinal edges of the second and third arm  15 ,  16 . The lower narrow sides  23  of the shorter arms  15 ,  16  form a contact surface for the spring arm  13  wherein the contact surface forms an end point of a spring elastic deflection movement of the spring arm  13  when inserting the fastening element  10  into the recess of a lamp element  25  so that the spring arm  13  is protected against a plastic deformation. 
     With reference to  FIGS. 6-9  a function of the fastening element  10  according to the invention is described in more detail.  FIGS. 6 and 8  illustrates the mounting situation of the fastening element  10  in a side view and in a top view. The fastening element  10  supports a printed circuit board  24  on a lamp element  25  in the cited illustrations. As apparent in particular from  FIGS. 8 and 9  the printed circuit board  24  includes a pass through opening  26  which is arranged in alignment with a lamp element recess  27  herein configured as a dead hole. The circuit board  24  contacts a top side of the lamp element  25 . The fastening element  10  was initially run through the pass through opening  26  in insertion direction x with the spring arm  13  forward and inserted into the dead hole recess  27 . Thus, the spring arm  13  impacts the wall  28  of the recess  27  and is displaced by the wall  28  in a spring elastic manner in a direction towards the first shaft arm  14 . Thus, a spring force is generated that is oriented against the displacement, wherein the spring force presses the spring arm  13  against the wall  28  and thus establishes a friction locking connection between the fastening element  10  and the recess  27 . This friction locking supports the fastening element  10  against movements against the insertion direction x. An interlocking connection is conceivable when the recess  27  is provided with an inner circumferential groove or a thread that is cut in. 
     The shaft head  12  which has a larger diameter than the pass through opening  26  and the recess  27  contacts the circuit board top side. The shaft head retains the circuit board  24  on the light element  25  in this manner. 
     The shaft head  12  thus represents the clamping element  1 . In detail its lobes  17 ,  18 ,  19  respectively form a clamping arm. The lobes are pressed into the recess  27  against the circuit board  24  when inserting the fastening element  10 . Thus, the lobes  17 ,  18 ,  19  are deflected in a spring elastic manner from the idle positions inclined relative to the circuit board  24  against the insertion direction x. The lobes impart a force onto the conductor plate  24 , wherein the force is directed against the insertion direction x and they clamp the circuit board  24 , the spring arm  13  is used as a reaction bearing, in a defined manner against the lamp element  25 . This is advantageous in that a defined heat transfer can be obtained through the defined contact pressure force between the circuit board  24  and the lamp element  25 , wherein the heat transfer provides heat dissipation from the circuit board  24  and thus from the LEDs not illustrated herein to the lamp element  25  which is used as a cooling element. 
     It is evident from  FIG. 7  which represents a sectional view according to the sectional line A-A in  FIG. 6  that the shaft arms  14 ,  15 ,  16  provide an approximately triangular cross sectional contour to the shaft based on their arrangement relative to each other when the lobe depth is extended far enough so that the free edges that are parallel to the longitudinal shaft axis of the second and third shaft lobe  15 ,  16  contact each other. Alternatively also here an approximately trapezoid cross sectional contour is provided when the free edges of the second and third shaft lobe  15 ,  16  which edges are parallel to a longitudinal axis of the shaft are connected with one another by a straight line as illustrated in  FIG. 7 . 
       FIGS. 10-13  illustrate the assembly method for the fastening element  10  using a mounting tool  29  as well as a dismounting method using a dismounting tool  30 . 
       FIGS. 10 and 12  illustrate an exploded view of the mounting situation and the dismounting situation of the fastening element  10 .  FIGS. 11 and 13  essentially correspond to the exploded view according to  FIG. 9 , however they additionally show a mounting tool  29  or a dismounting tool  30 . 
     The mounting tool  29  according to  FIGS. 10 and 11  is configured as a plunger whose operating surface  31  oriented towards the circuit board includes a recess for receiving the shaft head  12 . A centering mandrel  32  that is parallel to the longitudinal shaft axis extends from the operating surface  31 , wherein the centering mandrel  32  engages a centering opening  33  at the shaft head (c.f.  FIG. 5, 8, 11 ). The operating surface  31  can be magnetized in order to support the shaft head in the mounting tool  29 . Thus, it is also conceivable that the centering mandrel  32  is supported friction locking in the centering opening  33  so that the centering mandrel support the fastening element  10  at the mounting tool  29 . 
     In order to mount the fastening element  10  the fastening element  10  is applied to the operating surface  31  of the mounting tool  29  and introduced with the shaft  11  forward through the pass through opening  26  of the circuit board  24  into the recess  27  of the lamp element  25 . The lobes  17 ,  18 ,  19  of the shaft head  11  that are inclined relative to the surface of the circuit board  24  impact the top side of the circuit board and are displaced building up a spring reset force. After completing the insertion movement the spring arm supports the fastening element  10  in the recess  27  against the spring reset force of the lobes  17 ,  18 ,  19 . The spring reset force thus clamps the components  24  and  25  relative to each other 
     One embodiment provides that only the shaft lobes  17 ,  18 ,  19  build up the spring reset force in that they are displaced against the insertion direction x until they are approximately in a horizontal position that is parallel to the top side of the circuit board  24 . However when incisions S 1  and S 2  like in the illustrated embodiment are deeper than a length of the lobes  17 ,  18 ,  19  they separate the sections of the arms  14 ,  15 ,  16  from each other that are proximal to the shaft head. The arm sections are also displaceable from each other in a spring elastic manner and thus in a direction towards the shaft longitudinal axis L. When inserting the fastening element  10  into the recess  27  the arm sections are moved by the respective lobes  17 ,  18 ,  19  and by the insertion force impacting the lobes in a direction of the longitudinal shaft axis L. The spring reset force of the arm sections thus applied clamps the components  24  and  25  through the lobes  17 ,  18 ,  19 . A respective lobe  17 ,  18 ,  19  forms a respective clamping arm with the associated arm section. 
     Thus, it is even possible to configure the arm sections spring elastic and to omit a spring force of the lobes  17 ,  18 ,  19 . 
     After removing the mounting tool  29  the mounting process is completed 
     Also for dismounting the fastening element  10  a tool is provided. The tool has the reference numerals  30  and includes a disengagement mandrel  35  which is pressed through a centering opening  33  of the fastening element  10  into a receiving cavity  27  in order to disengage the fastening element  10 . Thus, the disengagement mandrel  35  impacts the spring arm  13  and presses the spring arm  13  from its anchoring position in an insertion direction causing a plastic deformation of the spring arm  13 . Thus, the friction locking between the spring arm  13  and the wall  28  is disengaged from the recess  27  and the fastening element  10  can be removed from the recess  27 . This is advantageously also performed by the dismounting tool  30  in that inserting the disengagement mandrel  35  through the centering opening  33  into a shaft interior causes a friction locking connection between the shaft arms  14 ,  15  and  16  and the outer surface of the disengagement mandrel  35 . This way the fastening element  10  follows the disengagement mandrel  35  when it is removed from the recess  27 . 
     The guide embossing  36  of the first arm  14  will now be appreciated ( FIG. 13 ). This guide embossing forces the disengagement mandrel  35  towards the free end of the spring arm  13  so that the disengagement mandrel  35  deforms the spring arm  13  in the insertion direction. Thus, the guide embossing  36  prevents that the disengagement mandrel  35  slips on the spring arm  13  in a direction towards its deformation range which would generate a risk that the shaft  11  is pressed deeper into the recess  27  instead of providing a disengaging deformation of the spring arm  13 . 
       FIGS. 14-18  illustrate a second embodiment of the invention. The fastening element  10  is quite similar to the fastening element  10  according to the first embodiment. Therefore identical reference numerals are used for analogous components and reference is made to the preceding description. Subsequently mostly differences between both embodiments are discussed. 
     The fastening element  10  according to the second embodiment is also formed from a stamped blank, however it includes a shaft with a shaft head  12 , wherein the shaft  11  and the shaft head  12  are formed according to the first embodiment. In particular the shaft  11  includes three shaft arms  14 ,  15  and  16  and the shaft head  12  is formed by three lobes  17 ,  18  and  19 . Also in this embodiment the shaft head  12  with its lobes  17 ,  18  and  19 , optionally using shaft arm sections that are divided from each other by incisions S 1  and S 2 , is used as a clamping element. As can be derived from  FIG. 16  the shaft  11  is essentially formed as a triangle or trapezoid which significantly improves stability. 
     The essential difference between both embodiments can be found in the support elements of the second embodiment. The first embodiment is provided in particular for fixation in a dead hole of a lamp element  25  and therefore includes only one spring arm  13  which mostly provides a friction locking engagement in the dead hole. 
     The fastening element  10  according to  FIGS. 14-18 , however, is provided for interlocking fixation. For this purpose at least one of the shaft arms  14 ,  15  and  16  includes an interlocking element  37 ,  38 . In the present embodiment the shaft arms  15  and  16  respectively include an interlocking arm  37 , the shaft arm  14  includes a interlocking spring  38 . The interlocking elements  37 ,  38  are displaced relative to the shaft arms  14 ,  15  and  16  so that a circumference is expanded and they are displaced from their idle position in a spring elastic manner when they penetrate the pass through opening  26  in a direction of the longitudinal shaft axis L. The same occurs when the interlocking elements  37 ,  38  penetrate the portion of the recess  27  of the lamp element  25 . 
     Also the recess  27  of the lamp element  25  is configured as a pass through opening in the second embodiment so that the end section of the shaft  11  that is oriented away from the shaft head  12  can not only penetrate the pass through opening  26  of the circuit board but also the recess of the lamp element  25 . During this insertion process in the insertion direction x the lobes  17 ,  18  and  19  forming the shaft head and/or the shaft arm sections that are divided from each other by the incisions S 1  and S 2  go through a spring elastic displacement and thus build up tension forces which generate a defined contact pressure between the circuit board  24  and the lamp element  25 . The insertion process in the insertion direction is performed until the interlocking arms  37  and the interlocking spring  38  have moved through the recess  27  and move back into their resting positions. In this resting position the interlocking arms  37  and the interlocking spring  38  reach behind or below the bottom side of the lamp element  25  and thus fixate the components  24  and  25  at each other. This can be derived in particular from  FIG. 18 . 
     It is appreciated that the second embodiment only provides an alternative fixation of the fastening element  10  in the recess  27 , however the function and configuration of the clamping element by the lobes  17 ,  18  and  19  of the shaft head  12  and/or the shaft arm sections that are separated from each other are configured identical to the first embodiment. 
     The bevel  39  at the interlocking arms  37  can be used to compensate certain tolerances in the total thickness of the components  24  and  25  without significantly influencing the clamping function that is provided by the lobes  17 ,  18  and  19 . Especially during the typical use of plural fastening elements  10  the evenness of the individual clamping forces is an essential feature for a contact pressure over an entire surface. 
     REFERENCE NUMERALS AND DESIGNATIONS 
     
         
         
           
               10  fastening element 
               11  shaft 
               12  shaft head 
               13  spring arm 
               14  first arm 
               15  second arm 
               16  third arm 
               17  first lobe 
               18  second lobe 
               19  third lobe 
               20  insulating element 
               21  perforation 
               22  stamped blank 
               23  narrow sides 
               24  circuit board 
               25  lamp element 
               26  pass through opening 
               27  recess 
               28  wall 
               29  mounting tool 
               30  dismounting tool 
               31  operating surface 
               32  centering mandrel 
               33  centering opening. 
               35  disengagement mandrel 
               36  guide embossing 
               37  interlocking arm 
               38  interlocking spring 
               39  bevel of  37   
             L longitudinal shaft axis 
             U 1  deformation line  1   
             U 2  deformation line  2   
             U 3  deformation line  3   
             U 4  deformation line  4   
             S 1  incision  1   
             S 2  incision  2   
             x insertion direction