This application is a divisional of prior application Ser. No. 10/019,930 filed Jun. 18, 2002 now U.S. Pat. No. 6,994,486 B1. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to a method for the attachment, in particular for the liquid-tight and/or gas-tight attachment, of a functional element, in particular a fastener element, to a sheet metal part. 
     The invention further relates to a die and a functional element which can be used in the method in accordance with the invention and to a component assembly which can be manufactured by the method in accordance with the invention. 
     DESCRIPTION OF RELATED ART 
     Functional elements such as nuts or bolts are attached to sheet metal parts in the manufacture of automobiles, for example, in order to allow the most varied components to be joined to the sheet metal parts. 
     A method of the initially named kind for the attachment of a functional element to a sheet metal part is known from DE 196 47 831 A1 in which sheet metal material is brought into hooked engagement with an undercut feature of the functional element by means of a one-piece reforming die against which the functional element is pressed with the sheet metal part lying therebetween. 
     Furthermore, it is known to connect metal sheets to one another without using additional joint elements by pressing the metal sheets onto a die and drawing them by means of a plunger in the direction of a fixed anvil. Moveable lamella of the die, which are arranged to the side of the anvil, yield and move radially outwardly when the lower sheet metal part reaches the anvil. In this way a round collar is created which locks the metal sheets to one another. 
     SUMMARY OF THE INVENTION 
     The object of the invention is to provide a method of the initially named kind and apparatuses of the initially named kind, that is a die, a functional element, a component assembly consisting of a sheet metal part and a functional element attached thereto and a die arrangement, which ensure a good joint, which is as easy to manufacture as possible, between a sheet metal part and a functional element. 
     This object is satisfied in accordance with the invention methodwise in that by the functional element provided with a hollow head part being pressed against the sheet metal part supported by a die and, with a simultaneous deformation of the hollow head part and a reforming of the sheet metal part into a reforming space defined by shaped parts of the die, the sheet metal material is formed into an undercut made by deformation of the head part, with the shaped parts being immovably held during the reforming, but being partly lifted out of the die for the removal of the functional element attached to the sheet metal part. 
     The attachment of the functional element to the sheet metal part is made in accordance with the invention by a reforming joining technique in which the undercut is not present in the head part of the functional element from the start, but is only created during the attachment thereof by deformation of the head part. Although both the sheet metal part and the functional element undergo substantial deformation in this process, it is surprisingly possible to achieve a low-cost and reliable method which provides a high quality joint between the sheet metal part and the functional element and which can be performed in such a way that the sheet metal part is not pierced. 
     As a result, the sheet metal part is still absolutely liquid-tight and/or gas-tight following the attachment of the functional element and can thus also be used in environments in which such properties are indispensable. 
     It is, however, also possible to work with a pre-pierced sheet metal part if the functional element requires this or makes it meaningful, for example if the functional element is to be realized as a nut element, which is possible in principle. 
     The functional elements can be manufactured either in a known manner by cold forming or by other favourably priced methods. 
     The shaped parts of the die remain in a fixed position during the reforming, but are movably supported for the removal of the sheet metal part with the attached functional element. They can be replaced as parts subject to wear at favourable cost without having to replace the whole die. The dies can also be manufactured at a favourable price. 
     A preferred die for the performance of the method is characterized by the following features: by a hollow body having an end face which is provided to support a sheet metal part and which merges into a space receiving an abutment element via a conically tapering wall, with the abutment element being spaced from the conically tapering wall to form an annular gap of wedge-shaped cross-section and with the end face of the abutment element adjoining the end face of the hollow body being set back from the end face of the hollow body and having a dome-like projection surrounded by an annular surface, and further characterized by a plurality, preferably from two to eight, in particular of four, shaped parts, preferably shaped parts of substantially the same design, which are arranged around a longitudinal axis of the die in the wedge-shaped annular gap and are supported both on the conical wall and also on the abutment element and which project into the shaped projections of the shaped parts through a reforming space formed between the shaped parts and the set-back end of the abutment element. 
     The functional element in accordance with the invention is characterized in that the functional element comprises a shaft part and a head part designed for a riveted joint to a panel member, in particular a sheet metal part, in that at least the head part is made hollow and preferably has at least substantially the same outer diameter as the shaft part. 
     The component assembly manufactured in accordance with the invention is designed such that a hollow head part of the functional element is deformed in order to form two annular bulges which project radially outwardly, which are spaced from one another and between which there is an undercut in which the sheet metal material is received in a form-locked manner and such that the sheet metal part extends into the undercut of the functional element. 
     The present invention is furthermore directed to a special plunger arrangement which is, in particular, designed to perform the insertion of functional elements without the risk of deforming the shaft part and, in particular, its thread cylinder. For this purpose, the plunger arrangement in accordance with the invention is characterized by the following features: 
     by an outer plunger 
     by an inner plunger which is displaceably arranged with respect to the outer plunger within a plunger passage of the outer plunger between a receiving position for the functional element and an insertion position for the functional element, with the functional element being able to be inserted into the plunger passage preferably from the side, in the receiving position, and with the head part of the functional element projecting out of the plunger arrangement when in the insertion position; 
     and 
     by at least two segments supported by the outer plunger which preferably have shaped features at an inner side which can engage into the shaped features of the shaft part of the functional element and which are movable between an open position remote from the shaft part of the functional element and a closed position in engagement with the shaped features of the shaft part. 
     Further preferred embodiments of the method in accordance with the invention and of the die in accordance with the invention, of the functional element in accordance with the invention, of the component assembly in accordance with the invention and of the plunger arrangement in accordance with the invention, which each contribute to satisfying the underlying object of the invention, are set forth in the claims, the description and the drawing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is described below by way of embodiments with reference to the drawing. There are shown: 
         FIG. 1  an embodiment of a functional element, partly sectioned in a longitudinal direction, which can be attached to a sheet metal part by means of the method in accordance with the invention; 
         FIG. 2  the functional element of  FIG. 1  and the sheet metal part after the attachment of the member to the sheet metal part; 
         FIG. 3  an embodiment in accordance with the invention of a die for performing the method in accordance with the invention in a representation partly sectioned in a longitudinal direction in accordance with the sectional plane III-III of  FIG. 4 ; 
         FIG. 4  the die of  FIG. 3  in a plan view; 
         FIGS. 5A-5H  a sequence of drawings which represent different stages of the joining method in accordance with the invention and which each show a view sectioned in a longitudinal direction through the functional element arranged in a setting head and through the die in accordance with  FIGS. 3 and 4 ; and 
         FIGS. 6A-6C  a sequence of drawings to explain a particularly preferred embodiment of a plunger arrangement in accordance with the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The attachment of a functional element to a sheet metal part is nowadays normally performed in the working of sheet metal by means of a press or of a robot by the cooperation of a setting head and a die, with the die being mounted, for example, in a lower tool of a press, while the setting head is attached to an upper press tool or to an intermediate plate of the press. Other attachment possibilities are also possible. The die can, for example, be attached to the intermediate plate of the press and the setting head to the upper tool of the press. Reversed arrangements are also feasible where the die is attached to the upper tool and the setting head to the lower tool of the press or to the intermediate plate. It is, in addition, not absolutely necessary for the die and the setting head to be in a press; they could, for example, be moved towards and away from one another by a robot, or represent parts of a different kind of tool. 
     The respectively used setting head, or the tool associated with it, has, in a manner known per se, a frequently tubular hold down member which clamps the sheet metal part against the stationary end face of the die or against the upper side of the tool receiving the relevant die in each case. A particularly preferred embodiment of the functional element in accordance with the invention and of the die and of the method to insert this element will now be described with reference to  FIGS. 1 to 6 . 
       FIG. 1  shows first of all a functional element  210 , here in the form of a bolt element, with a shaft part  210   b  having a thread  211  and with a hollow head part  210   a  having at least substantially the same outer diameter as the shaft part  210   b . It is pointed out that the shaft part  210   b  does not necessarily have to be executed with a thread  211 , but can, as previously, have a design deviating from this which can be selected as desired to achieve the respectively intended function. The shaft part  210   b  can, for example, be made as a smooth guide spigot or as a carpet fastening pin with an annular groove allowing a snap connection to a carpet eyelet. It is particularly favourable with this element for, among other possibilities, the shaft part  210   b  and the head part  210   a  to have at least substantially the same outer diameters so that the functional element can be made at a favourable cost from bar stock or wire material or from a tubular section. 
     However, it is not absolutely necessary for the shaft part  210   b  and the head part  210   a  to have the same diameter, rather substantial differences in diameter can be present, with this, however, generally meaning a greater effort in the manufacture of the element. In other words, the outer diameter of the shaft part could be larger or smaller than that of the head part. 
     As can be seen from  FIG. 1 , the head part  210   a  has a cylinder bore  220  which forms a circularly cylindrical space  221  and can be made, for example, either by a drill or by a cold forming process. In this example, the space  221  ends in the direction towards the shaft part  210   b  shortly before the annular groove  260  representing the boundary to the shaft part  210   b , and indeed in a transverse wall  262  perpendicular to the longitudinal axis, which is made slightly concave, and via smooth radii  265  into the wall  266 . Alternatively to this, the transverse wall can have a planar or conical recess  262 . However, this is not absolutely necessary. If the member is to be made of tube material, the bore  220  would also extend through the shaft part  210   b , with, however, the diameter of the bore  220  in the region of the shaft part  210   b  then preferably being substantially smaller than the diameter of the bore  220  in the head part  210   a  so that only the head part of the functional element is deformed during the attachment to the sheet metal part  212 . 
     The previously circularly cylindrical annual wall  266  of the head part  210   a  tapers at the end region  264  remote from the shaft part  210   b  into a rounded, bullet-like design or cigar shape  268 , with the end  270  not being closed, but open, and defining an aperture  272  which is substantially smaller than the diameter of the cylinder bore  220 . The end region  264  of the functional element  210  is, so to say, spherically rounded with a flat, open end face  270 . As can be seen from  FIG. 1 , the hollow end region  274  of the element between the end face  270  and the aperture  272  is formed in the manner of a truncated cone, and indeed such that the end region  264  of the head part  210   a  has an annular, inclined surface  274  at the inside with an included cone angle of approximately 45°. The wall thickness of the hollow region of the head part  210   a  is at least substantially the same over the total length of this region. The reference numeral  236  indicates the central longitudinal axis of the functional element  210  and it can be seen that the shaft part  210   b  and the head part  210   a  are axially arranged relative to one another with respect to this central longitudinal axis  236 . Although the head part  210   a  of the functional element is circular in cross section in this embodiment, it is feasible to select a cross-sectional shape deviating from the circular shape, for example a polygonal shape or a shape with longitudinal grooves or longitudinal ribs, in particular when an even better security against rotation is required in the installed state. 
     As stated, the functional element  210  can be made of bar stock, wire material or tubular material, and indeed by a rolling process to produce the outer design features of the functional element, optionally in combination with a drilling or boring procedure to make the cylinder bore  220 . Alternatively hereto, the element can be produced by a cold forming process or by a high-pressure reforming process, which is particularly possible when tubular material is used as the starting material for the element. 
     When a high-pressure reforming process is used, the outer design features of the functional element, such as a thread, can be formed by the shaping of the form receiving the tubular section, that is a rolling process to produce the thread would then be superfluous. 
       FIG. 2  now shows the functional element  210  in the installed state in the sheet metal part  212 . It can be seen that the head part  210   a  is substantially deformed and is joined in a form-locked manner to a pot-like recess  276  of the sheet metal part  212  formed by the attachment method, with the head part  210   a  not penetrating the sheet metal part  212 , so that a water-tight connection is present in the sense that any water underneath the sheet metal part cannot reach the upper side of the sheet metal part through the sheet metal part around the functional element  210 . 
     The component assembly in accordance with  FIG. 2  will be described in more detail below. 
     The die in accordance with  FIGS. 3 and 4  is used to attach the element to the sheet metal part. As can be seen from  FIGS. 3 and 4 , the die has four segments or shaped parts  216  which can be moved in the axial direction  222  of the die for removing the sheet metal part once the functional element has been attached. 
     In  FIGS. 3 and 4  the shaped parts  216  each have an inclined, partly conical outer surface  217   a  which contacts a shaped surface  226  in the form of a truncated cone converging in an inclined manner towards the central longitudinal axis  222 , with the shaped parts  216  having a lower side  278  extending perpendicular to the longitudinal axis  222  of the die  214  and arranged directly above an annular shoulder  280  of a centrally arranged abutment element  234 , with the abutment element  234  in this example being pressed upwardly in  FIG. 3  by a compression coil spring  228 . The compression coil spring  228  is namely located in a cylindrical bore  282  of the abutment element  234  arranged coaxially to the longitudinal axis  222  and its one end presses on the closed end of the bore  282  at the abutment element  234  and its other end onto a lower tool of the press, with the die  214  being arranged in said lower tool. Alternatively hereto, the die  214  of  FIG. 3  can be provided with a base part at its lower end against which the lower end of the compression coil spring  228  would then be braced. Such a design would have the advantage that the die would then be a unit whose individual parts cannot be lost. 
     Four pins  284  project through the cylinder wall of the die  214  in the radial direction, with the free end  286  of each pin (only one is shown) projecting into a corresponding recess  288  of the respectively associated shaped part  216 . The pins  284  in this way restrict the maximum travel outward of the shaped parts (shown in  FIG. 5H ) and hold the shaped parts  216  captive and in the desired radial arrangement in the die  214 . The width of the respective recesses  288  in the respective shaped parts  216  corresponds at least substantially to the diameter of the respective ends  286  of the pins  284  so that the pins  284  guide the segments or shaped parts  216  when they return from the opened state of the die (in accordance with  FIG. 5H ) to the closed state in accordance with  FIG. 3 . 
     As can likewise be seen from  FIGS. 3 and 4 , the abutment element  234  has a cylindrically shaped part  234   a  above the annular shoulder  280  with an end  234   b  which forms the base of a substantially cylindrical reforming space  230  which is bounded in other respects by the shaped parts  216  (see also  FIG. 5C ). One notes that in this embodiment the end  234   b  of the abutment element  234  has a centrally arranged dome-like projection  234   c  which is surrounded by an annular surface  234   d  perpendicular to the central longitudinal axis  222 . 
     In the closed state of the die, the radially inwardly directed partly circular cylindrical surfaces  217   b  of the shaped parts  216  contact the cylindrical outer surface of the upper part  234   a  of the abutment element. The shaped parts  216  are furthermore each provided in the region of their upper ends with a bead-like or nose-like projection  219 , which faces the longitudinal axis  222  and with which sheet metal material of the sheet metal part  212  can be pressed in a manner to be described below into an undercut of the functional element  210  which is formed. In this embodiment, the nose-like projections  219  form the lateral boundary of the reforming space  230 . Radially extending grooves  231  are worked into the end face  232  of the shaped part  234   a  so that noses  233  lie therebetween, with the bases  235  of the grooves  231 , which are roughly semi-circular in shape in cross-section, being inclined with respect to the longitudinal axis  222  of the die, as can be seen from  FIG. 3 . The grooves  231  are generally rounded and, like the noses  233  lying therebetween, serve to provide security against rotation. A total of eight grooves  231  and eight noses  233  are present in this example—a different number would also be possible. 
     It will now be described with reference to  FIGS. 5A to 5H  how the functional element  210  can be attached to a sheet metal part  212  using the die  214 . 
       FIG. 5A  shows the starting state in which the die  214  is located in the lower tool ( 301 ) of a press, a sheet metal part  212  is arranged above the die and the shaped part  210  is held in a schematically represented setting head  300 , for example by an angular spring (not shown) made of plastic which ensures frictional contact between the shaft part  210   b  of the functional element  210  and a bore  302  of an outer plunger  303  of the setting head. One notes that the longitudinal axis  236  of the functional element  210  is aligned with the longitudinal axis  222  of the die  214  and, at the same time, the central axis of the bore  302  of an outer plunger  303  corresponds to that of the setting head  300 . One notes also that all shaped parts  216  are in their lower position in accordance with  FIG. 3 , that is the die  214  is closed in the starting position. The upper boundary of the respective recesses  288  of the shaped parts  216  lies directly—at a small distance—above the respective ends  286  of the respective pins  284 . This position arises due to the force of gravity and the guidance by the pins  284 . The compression coil spring  228  presses the abutment element  234  upwardly so that the annular shoulder  283  of the abutment element  234  contacts an annular shoulder  285  of a stepped bore  287  of the die  214  and the annular shoulder  280  of the abutment element  234  is arranged directly beneath the lower surface  278  of the respective shaped parts  216 . 5  A plunger insert  304  is located in the outer plunger  303  of the setting head  300  and its lower end  306  presses onto the upper end  292  of the shaft part  210   b  of the functional element  210 . Although the plunger insert or inner plunger  304  is movable with respect to the outer plunger  303  in the direction of the longitudinal axis  236 , it has reached its lowest position with respect to the outer plunger  303  in  FIG. 5A  and in the further  FIGS. 5B to 5G . However, it can be drawn axially upwardly with respect to the inner plunger in order to receive a new functional element  210 , as will be described below in more detail in connection with  FIG. 6 . 
     The die  214  is here located in a bore  308  of the lower tool  301  of a press, the upper side  310  of said tool  301  being arranged flush with the end face  296  of the die and of the end faces  232  of the shaped parts  216 . A plurality of stripper pins  314 , which are upwardly biased by springs  312 , are located in the lower tool  301  and support the sheet metal part  212  in its introduction into the press; however, they can be pressed downwardly due to the force exerted by a hold down member  316  of the setting head  300  when the press is closed so that the sheet metal part  212  comes into contact with the end face  296  of the die  214  and with the upper side  310  of the lower tool  301  in the region of the die and is immovably clamped therebetween the hold down member  316  and the die  214  or the lower tool  301 . 
     Three such spring-biased stripper pins  314  can, for example, be provided which are arranged, for example, at equal annular intervals around the central longitudinal axis  222 , with only the one stripper pin  314  being visible due to the sectional drawing. 
     The hold down member  316  is also biased in the direction towards the sheet metal part  212 , and indeed by springs  318  which—like the spring  312 —are here indicated schematically as compression coil springs, even though other spring types can also be used which are very well-known in tool making. 
     In this example, three springs  318  are likewise arranged at equal annular intervals around the central longitudinal axis  222  so that the hold down member  316  is pressed evenly downwards under the force of these springs. 
       FIG. 5B  shows the first step of the joining method in which the setting head  300  has moved downwardly towards the die  214  in comparison with the representation of  FIG. 5A  due to the closing movement of the press, so that the hold down member  316  has immovably clamped the sheet metal part  212  between it and the upper side  310  of the lower tool  301  and the upper side  296  and  232  of the die and the shaped parts  216 . The stripper pins  314  have been pressed downwardly against the force of the spring  321  until their upper ends are flush with the upper side  310  of the lower tool. The end  270  of the functional element  210  has pressed the sheet metal part  212  onto the dome-like projection  234   c.    
     The plunger  304  has further pressed the end  270  of the functional element  210  and the sheet metal material into the reforming space  230  and thus moved the abutment element  234  slightly downwardly against the force of the spring  228  so that the reforming space  230  has become deeper. In doing so a recess  212   a  is formed there in the sheet metal part  212 . The annular shoulder  280  moves away from the lower side  278  of the shaped parts  216  and the annular shoulder  283  likewise moves away from the annular shoulder  285 . The force which is exerted on the sheet metal part  212  via the setting head and the functional element does not result in a movement of the shaped parts  216  as these always remain in the same position up to the completion of the attachment of the functional element to the sheet metal part  212 . As the press continues to close, the inner plunger  304  and the outer plunger  303  move lower with respect to the hold down member  316  and in so doing press the abutment element  234  into its lowest position in accordance with  FIG. 5C , with the recess  212   a  in the sheet metal part becoming deeper. 
     As the closing movement of the press continues, the recess  212   a  of the sheet metal part  212  becomes wider at its lower end without any axial escape movement of the shaped parts  216  taking place, until finally the sheet metal part  212  is clamped between the dome like projection  234   c  of the abutment element  234  and the end  270  of the head part  210   a  of the functional element  210 , with the dome like projection  234   c  generating a dent  212   b  directed slightly upwardly in the sheet metal part so that this is slightly pressed into the aperture  270  at the end of the functional element. 
     In a further stage of the closing movement of the press, the force exerted on the head part  210   a  of the functional element  210  results in a deformation of its lower end so that the form is produced which is shown in  FIG. 5D . It can be seen that the sheet metal part  212  has laid itself around the rounded edges of the nose-like projections  219 , that the end  270  of the head part  210   a  of the functional element has partly laid the sheet metal part around the dome like projection  234   c  at  212   b  and that during these deformations the end of the head part  210   a  is itself deformed so that the functional element is expanded slightly radially outwardly in the region of its lower end, while the region around the previous end face  270  has been deformed axially inwardly and the aperture  272  is now located in a con-cave region  210   c  of the head part  210   a.    
     The representation of  FIG. 5E  is similar to the representation of  FIG. 5D , but here a more advanced deformation of the sheet metal part  212  can be seen. 
     The lower end of the outer plunger  303  of the setting head  300  of the die  214  has further approached the sheet metal part  212 . It can be seen in  FIG. 5E  that the cylindrical wall region of the head part  210  has now been compressed such that a bulge  320  projecting radially outwardly has formed due to a folding of the cylindrical wall region. It can also be seen that a further pronounced annular fold or annular bulge is present at the point  322  where the axially directed wall of the head part  210   a  merges into the radially inwardly directed region  212   b  which is formed from the former end region  264  of the head part  210   a.    
     On reaching the state in accordance with  FIG. 5F , the compression of the head part  210   a  of the functional element  210  is now so large that the annular fold at the point  322  has now moved beneath the radially inwardly directed projections  219  of the shaped parts within the deformation space  230  and the sheet metal part  212  has bent correspondingly around these projections. Furthermore, the lower end of the head part  210   a  has pressed the sheet metal part against the annular shoulder  234   d  of the abutment element so that the deformation space  230  is almost completely filled. The annular fold  320  is even more pronounced in comparison with  FIG. 5E  and the annular fold  326  of the sheet metal part  212  around the projections  219  is already trapped in the radially inwardly directed annular bulge  324  being formed between the annular fold  320  and the annular fold  322 . 
     The further annular fold  328  of the sheet metal part in the region of the transition from the wall of the cup-like recess in its base region follows the annular fold  322  of the head part  210   a  of the functional element so that a form-locked joint is also present here between the sheet metal part and the functional element. The lower end  330  of the outer plunger has further approached the die  214  in the state of  FIG. 5F . 
     The closing movement of the press continues until, as shown in  FIG. 5G , the closed state of the press is reached, the sheet metal part  212  is completely captured between the end of the outer plunger  303  of the setting head  300  and the end  296  of the die  214  adjoining it or the ends  232  of the shaped parts  216 . The result of this further compression movement is that the annular undercut  324 , in which the annular ring fold  325  of the sheet metal part is fixedly clamped, has formed completely between the annular folds  320  and  322  in the region of the bulge-like projections  220 . Furthermore, the annular fold  322  of the head part  210   a  is fixedly clamped within the annular fold  328  of the sheet metal part. The plunger projection  342  at the end  330  of the outer plunger  303  has compressed the annular fold  320  such that the two material layers of the annular fold  320  and/or the annular bulge formed thereby fixedly contact one another, with the upper side  321  (see  FIG. 2 ) of the annular fold  320  being located beneath the plane of the flat sheet metal part  212 . 
     The compression caused by the plunger projection  342  has also resulted in the sheet metal of the sheet metal part being formed into the recesses  231  of the shaped parts  216 , while the noses  233  therebetween have penetrated into the sheet metal part. This deformation of the sheet metal part  212  leads to a corresponding deformation of the material of the ring fold  320  so that an intermeshed engagement is present in this region between the sheet metal material and the material of the head part  210   a  of the functional element which serves as security against rotation. Where the shaped parts  216  have recesses  231 , the completed component assembly has noses  334  which can be seen best in  FIG. 2 , but also in  FIG. 5H . Recesses  231  are located therebetween which are formed by the noses  233  of the shaped parts. An intimate connection has therefore taken place in the region of the head part  210   a  so that the form-locked joint to the sheet metal part is a really secure joint, that is both secure against rotation and secure against forces acting in an axial direction. 
     When the state in accordance with  FIG. 5G  has been reached, the press opens and moves to the state in accordance with  FIG. 5H . The component assembly ( 210 + 212 ) can now be removed. When the press opens, the shaped parts  216  move up and pivot outwardly under the effect of the spring  312  and of the stripper pins  314  and/or of an engagement between the setting head  300  and the shaft part  210   b  so that the open starting position of the die is reached. After the component assembly has been removed, the shaped parts fall back into the starting position of  FIG. 5A , the cycle just described is repeated with a new functional element  210  and a new sheet metal part  212 . The press is opened so far that the component assembly formed in this way, which is shown alone in  FIG. 2  to a large scale, can be removed from the press or transported to the next station in the progressive tooling, if such is used. When the press is opened, the abutment element  234  returns to the position of  FIG. 5A  due to the force of the spring  228 . Although the springs  228 ,  312  and  318  are shown here as compression coil springs, they can be replaced by different springs, for example by fluid pressure springs, which are well known per se. 
     If, as mentioned above, the functional elements  210  are provided with a non-circular cross-section in the region of the head part  210   a , for example with a polygonal cross-section or with ribs and/or grooves, the method is carried out exactly as described above. The sheet metal material is joined intimately and in a form-locked manner to the outer form of the head part, whereby increased security against twist-out is to be expected. With such a design, care must be taken that the features of shape on the outer side of the head part  210   a  are not so pronounced that they impermissibly damage the sheet metal material. Here, too, an adhesive could be used, for example a pressure-sensitive adhesive which is applied to the head part  210   a  of the functional element and activated under pressure and which leads to a bonded joint between the sheet metal part and the functional element. 
     It is moreover possible to pre-pierce the sheet metal part at the point of application of the functional element, whereby the edge of the piercing will come to rest between the folds  320  and  322 . The piercing could also be performed such that when the functional element is made as a nut element, which is generally possible, an electrically conductive connection, i.e. a connection to earth in accordance with German patent application 198 48 617.0, can be achieved. To realize a nut element, it would only be necessary to make the shaft part  210   b  hollow and to provide it with an internal thread, which can be done before or after the attaching to the sheet metal part, for example subsequently by means of a thread-forming or thread-cutting screw. In the embodiment as a nut element, the corresponding screw can be screwed into the element either from the shaft part side of the metal sheet part or from the opposite side of the sheet metal part. 
       FIG. 6A  now shows a possible plunger arrangement  400  in detail which can be used advantageously in place of the plunger arrangement  303 ,  304  in accordance with  FIG. 5 . 
     The outer plunger  403  is provided with a plunger passage  402  which is arranged coaxially to the longitudinal axis  405  and displaceably receives the inner plunger  404 . A supply passage  406  is shown on the right-hand side of the sectional drawing in accordance with  FIG. 6A  through which functional elements  210  are led from a feed device (not shown) into the plunger passage formed by the bore  402 . One notes that the longitudinal axes  236  of the individual functional elements are parallel to the longitudinal axis  405  of the plunger passage  402  and that the individual functional elements are arranged in rows contacting one another. However, due to the dimensions of the plunger passage  402 , only one functional element  210  at a time can be located in the plunger passage  402 . 
     When the press is opened, the outer plunger  403  is displaced downwards 5 with respect to the inner plunger  404 , usually under the pressure of a corresponding spring (not shown), until the end face  408  of the inner plunger  404  approximately reaches the level of the upper boundary of the supply passage  406  so that a functional element  210  can be inserted into the plunger passage  402  by pressure in the direction of the arrow  410 . 
     The outer plunger  403  is made in a plurality of parts in this embodiment and comprises a lower annular part  412  which is fastened to an upper part  414  by screws (not shown). The lower annular part  412  has a central aperture  416  with an annular wall  418  of circularly cylindrical shape which merges into a conical region  420 . Both the annular wall  418  and the conical region  420  are arranged concentrically to the longitudinal axis  405 . The upper part  414  of the outer plunger  403  is provided with a conical recess  422  which merges into the plunger passage  402  via an annular shoulder  424 . The conical region  422  and the annular shoulder  424  are also arranged concentrically to the longitudinal axis  405  of the plunger arrangement. 
     In this example, three segments  426 , which are arranged at equal annular intervals around the central longitudinal axis  405 , are located in the region between the upper part  414  and the lower part  412  of the plunger arrangement  403 . The three segments  426 , of which only two can be seen in  FIG. 6 , together form a receiver  430  arranged coaxially to the longitudinal axis  405  for a respective functional element  210 . The lower surfaces  432  of the segments  426  pointing radially inwards are made as a segment of a thread cylinder which is designed to be complementary to the thread cylinder  211  of the shaft part  210   b  of the functional elements  210 . The upper surfaces  434  of the segments  426  pointing radially inwards together form a passage  436  having a diameter which is somewhat smaller than the outer diameter of the head part  210   a  of the respective functional elements  210 . The radially outer surfaces  438  of the segments  426  are designed as partly conical surfaces which are complementary to the conical surface  422  of the corresponding recess of the upper part  414  of the outer plunger  403 . The axially upper surfaces  440  of the segments  426  are designed complementary to the annular shoulder  424  so that in the position of  FIG. 6A , the partly conical surfaces  438  of the segments  426  and the partly circular surfaces  440 ′ fully contact the respective opposing surfaces of the outer plunger  403 , that is the conical surface  422  and the annular shoulder  424 . In this position, the through passage  436  formed by the segments  426  and concentric to the longitudinal axis is made such that it is smaller in diameter than the outer diameter of the head part  210   a  of the functional element  210 . The respective functional element  210  can thus initially not fall between the segments  426 , but is rather supported at the upper end of the segments  426  as is shown in  FIG. 6A . 
     The upper region of the respective segments  426  merges into a partly cylindrical wall part  444  via a partly conical surface  442 . The partly conical surfaces  442  of the segments  426  are opposite the conical surface  42  of the lower part  412  of the plunger arrangement  400  in the position in accordance with  FIG. 6A  and are spaced from this surface  420 . The partly cylindrical surfaces  444  of the segments  426  are opposite the partly cylindrical surface  418  of the lower part  412  of the plunger arrangement  400  and are radially spaced therefrom in each case. 
     To ensure that the segments  426  always return to the centered starting 5 position of  FIG. 6A , tappets  448  biased by springs  446  are provided whose axes  450  are inclined with respect to the longitudinal axis  405  of the plunger arrangement  400  and perpendicular to the conical surface  420  of the lower part  412  of the plunger arrangement  400 . The spring bias causes the tappets  448  to be pressed against the partly conical surfaces  442  of the segments  426  contacting them directly such that when the press is open, these always assume the position shown in  FIG. 6A . The spring bias is not very strong. 
     If the press is now closed, the inner plunger  404  is pressed downwards with respect to the outer plunger  403  and in this process presses the respective functional element  210  located in the plunger passage  404  against the upper end face  440  of the segments  426 . As a result of the sloped entrance to the passage  436  and the correspondingly inclined outer surface in the region of the lower end face  270  of the respective functional element  210 , the force exerted on the inner plunger  404  is sufficient to press the segments downwards in the axial direction  405  and radially outwards so that they press the tappets  448  downwards until the partly conical surfaces  442  come into contact with the conical surface  420  of the lower part  412  of the outer plunger  403 . The radially outwardly directed movement of the segments  426  causes the inner diameter of the passage  436  bounded by these segments to increase so that the respective functional element located in the plunger passage  402  is pressed into the passage between the segments  426  under the force of the inner plunger  404 . An intermediate stage of this movement is shown in  FIG. 6B , and this movement subsequently continues until the upper shaft part  210   b  of the respective functional element  210  provided with an external thread is located in the lower region of the segments  426 . These then move radially inwardly and upwardly under the force of the spring  446  biasing the tappets  448  until the part turns in the radially inwardly directed lower surfaces  432  of the segments  426  engage in a form-locked manner into the thread cylinder  211  of the functional element  210 . This situation is shown in  FIG. 6C  and it can be seen that the front section  452  of the inner plunger  404 , which has a smaller outer diameter than the upper part of the inner plunger  404 , is arranged in a form-locked manner inside the passage  436  formed by the segments  426 . The functional element  210  in  FIG. 6C  has now reached a position which is comparable to that of  FIG. 5A , and the punching process to insert the element can now begin and runs in accordance with  FIG. 5 . 
     Although not shown in  FIG. 6A , the arrangement is made such that the inner plunger  404  cannot move any further downwards than as shown in  FIG. 6C . This can, for example, be prevented by the upper part of the inner plunger  404  being provided with a head (not shown) which has come into contact with the outer part  403  of the plunger in its “lowest” position in accordance with  FIG. 6C . The force of the press is now transferred via the inner plunger  404  to the end face  292  of the functional element  210  and via the outer plunger  403  and the segments  426  to the thread  211  of the functional element. It is ensured in this way that the thread cannot be damaged as it is received in a form-locked manner inside the complementary thread parts of segments  426  so that the thread cylinder cannot be compressed. If the shaft part  210   b  of the functional element is intended to be made hollow, the cylindrical projection  452  of the inner plunger  404  can be designed accordingly arid can extend via an annular shoulder (not shown) pressing onto the end of the functional element  210  into the inner bore of the shaft part so that the pressing forces can be transmitted to the functional element  210  without any damage to this element by the pressing together of the walls of the hollow shaft part needing to be feared, as this element is supported by the extended projection of the inner plunger. 
     It should be pointed out at this point that the number of segments  426  is 10 not limited to three. The minimum number required to realize this embodiment is two; however, three, four or more such elements can also be used, with preferably one respective tappet  448  with bias spring  446  being provided for each member. 
     The lower ends of the segments  426  can, if required, be provided with noses  454  which jointly form the plunger projection  342  of  FIG. 5 . 
     After the attachment of the functional element  210  in accordance with the drawing sequence of  FIG. 5 , the press opens again, whereupon either the sprung hold down member  316  and/or the shaped parts  216  exert a force on the sheet metal part  212  with the attached functional element  210 , with said force being sufficient to draw the segments  426  downwards into the position of  FIG. 6B  in order to release the shaft part  210   b . As the spring tension of the spring  446  is small, the release of the functional element when the press is opened is carried out without damaging the respective functional element  210  just attached. 
     After the release of the functional element  210  just attached, the opening of the press further results in the outer plunger  403 , which is biased downwards by the spring force, being pressed downwards, while the inner plunger  404  is drawn upwards until it reaches the starting position where the lower end face  408  of the inner plunger  404  has reached the level of the upper boundary of the passage  406 , whereby a new element is introduced into the plunger passage  402  by the pressure in the direction of the arrow  410 . The working cycle then begins afresh with a new sheet metal part and with a new functional element  210 , namely the functional element that is now located in the plunger passage  402 . 
     Although the abutment element  234  is shown and was described as movable in  FIGS. 3 to 5 , this is not absolutely necessary. The abutment element  234  could instead have a fixed position within the die  214  which would correspond to the lowest position in accordance with  FIGS. 5D ,  5 E,  5 F and  5 G. 
     The tool arrangement can be a station in progressive tooling where a strip of sheet metal is led through a plurality of stations to carry out a plurality of operations. The tool arrangement can, however, also be used in a punching press which manufactures a single part for every stroke. The attachment of the tool arrangement to a robot or another kind of tool is also possible. 
     Although the segments  426  are preferably provided with features of shape which engage into corresponding form features on the shaft part of the functional element, this is not required for some applications. The segments could, for example, have a purely partly cylindrical surface which would be sufficient with a solid shaft part to hold the corresponding functional element by frictional contact. The plunger arrangement can furthermore be used in setting heads which are used for the attachment of other functional elements. 
     The functional elements described here can, for example, be made of all materials which reach the strength class 5.6. Such metal materials are usually carbon steels with a carbon content of 0.15 to 0.55%. 
     In all embodiments, all materials can also be named as examples for the material of the functional elements which reach strength values of Class 8 of the ISO standard in the context of cold forming, for example a 3532 alloy in accordance with DIN 1654. The fastening elements formed in this way are suitable, among other things, for all commercial steel materials for sheet metal parts capable of being drawn as well as for aluminium or their alloys. Aluminium alloys, in particular such with a high strength, can also be used for the functional elements, e.g. AlMg 5 . 
     The trials carried out up to now have shown that when the material  3532  is used, the ratio of the radial wall thickness of the head part to the outer diameter of the head part is in the region of between 0.15 and 0.2. Higher values are desired as they increase the yield forces and the pull-out forces. However, it must be ensured that the pressing-in forces do not lead to an impermissible deformation. With a diameter of 8 mm, a radial thickness of 1.2 mm has proved to be favourable.
A method for placing a functional element, especially a fastening element, in an especially liquid-tight and/or gastight manner, on a metal part. In this method a functional element provided with a hollow head segment is pressed against the metal part ( 212) witch is supported by a die ( 214). The metal material is deformed into an undercut ( 324) by deforming the head segment when simultaneous deformation of the hollow head segment occurs and the metal part is shaped in a forming area defined by parts ( 216) of the die ( 214). The parts ( 216) are kept in a stationary position during the forming process but are partially removed from the die to enable the functional element which is placed on the metal part ( 212) to be extracted. The invention also relates to a die, a functional element, an assembly element and a die arrangement.