Abstract:
A method of sealing a bore, such as the threaded bore of a fastener, wherein the sealing element is preferably formed in place. The preferred sealing element is formed of a heat softenable plastically deformable material, such as a thermo-plastic resin, which is heated and deformed radially in the bore into a mechanical interlock with the bore inside the surface, such as thread. In the preferred method, a plunger or ram is driven into the sealing element which is supported on a die element in the bore. In the most preferred method, the ram simultaneously heats and deforms the sealing element, sealing the bore opening. The preferred female fastener element includes a generally tubular body portion having an axial bore which may be threaded adjacent one end. The sealing element seals the opening to the bore and the opposite end may be sealed with a disk spaced from the threads and forming a chamber. The chamber receives the sealing element upon receipt of a male threaded element, such as a bolt, in the female fastener bore. The sealed fastener may then be installed in a structural element, such as a bracket, which may then be coated or encapsulated without contamination of the bore or threads.

Description:
This is a continuation of application Ser. No. 08/157,653 filed on Nov. 24, 1993 now abandoned. 
    
    
     The present invention relates to a method of forming in place a female fastener bore opening and the fastener which, in the disclosed embodiment, is a a hat-shaped nut fastener sealed at the opposed bore openings. 
     BACKGROUND OF THE INVENTION 
     Hitherto hat-like fastener elements are known, e.g. in the form of cap or dome nuts, with an inner passage or bore which is provided with a fastening means, such as a thread or a bajonet socket and is closed at one end by means of a transverse wall. It is also entirely possible, and indeed preferred, for the fastener element to also have a rivet section at one end which can be inserted into a premanufactured aperture in a metal part and deformed by a riveting process in order to obtain a form-fitted connection between the fastener element and the sheet metal part. 
     Such hat-like fastener elements are known per se and are also of advantage when one is concerned with closing-off the thread of the fastener element or a bayonet connection at one end so that contamination can not penetrate into the thread. 
     As the fastening means, normally in the form of a thread, is normally located on the one side of the sheet metal part, while the mating screw is screwed into the nut element from the other side of the sheet metal, the riveted connection does not have to bear special forces in the assembled state of the fastener element, but rather, as a result of the threaded connection, an annular ring shoulder of the nut element on the same side of the sheet metal as the thread of the nut element is pressed by the clamping force of the screw against the sheet metal, with the riveted connection itself being largely relieved. Such cap nuts are thus also suitable for use in highly loaded screw connections. 
     A problem is however encountered when the sheet metal part with the attached hat-like fastener element has to be treated by further process steps before final assembly. Such further treatments include, for example, sand blasting, painting- in particular immersion painting and also the application of other protective layers. Through all these further treatment steps, the danger exists that the thread or the fastener means in the interior of the hat-like fastener element can be blocked or damaged so that it must either be freed from blockages or deposits in time consuming manual labor, or must indeed be scrapped. 
     It is known in the art to protect hollow cavities in critical components by plastic plugs which can be inserted and removed again. An example for this is a metal brake cylinder, the fluid supply opening of which is provided with a thread and is frequently also closed by a hat-shaped plastic plug. A problem with this solution is, however, not only that the closure plugs can be lost, but rather also that, with mass production, a large number of plastic plugs are required which must then be disposed of. 
     The present invention is based on the object of providing a fastener element or a sheet metal part with an attached fastener element which is so designed that an effective protection is achieved against blockage of or damage to the fastening means and also against deposits in the fastening means, without the parts which ensure protection being easily lost and leading to disposal problems, and with the fastener element being inexpensive to manufacture, for which purpose a special manufacturing process and a tool for the manufacturing of the fastener element should likewise be provided in accordance with the invention. 
     SUMMARY OF THE INVENTION 
     The method of sealing a fastener bore opening of this invention includes supporting a heat softenable plastically deformable sealing element in the bore opening having a diameter which is less than the bore opening, heating the sealing element to its softened plastically deformable temperature, then deforming the sealing element radially outwardly into mechanical interlocking engagement with the bore opening, which seals the bore opening when the sealing element cools. In the preferred method, the sealing element is deformed radially as described by a ram which is reciprocated through the bore opening into engagement with the sealing element. In the most preferred method of this invention, the sealing element is supported on a die member in the bore opening and the ram, which in the most preferred embodiment is heated, deforms the sealing element in the die member into mechanically interlocking relation with the female fastening element in the bore opening. As described, the female fastening element may be a threaded portion in the bore or a bayonet connection. Where the ram is heated, the ram simutaneously heats and radially deforms the sealing element in the fastener bore, as described. 
     The sealing element or closure plug is so deformed that it enters into a form-fitted connection with the fastener element and thus can not be easily lost, and together with the transverse wall protects the interior of the fastener element with the fastening means, i.e. with the thread or the bayonet socket, against the penetration of undesired media such as paint, rubber, plastic or underseal. Since the plastic closure plug which has been deformed to a type of disc can be pressed inwardly, the path to the thread or to the bayonet socket is first exposed by displacement of the closure plug on insertion of the screw. The closure plug is then preferably received in a receiving chamber formed at the end of the fastener means adjacent the transverse wall and thus remains within its completed fastening. In this manner, the disposal of the closure plugs in the factory where the sheet metal part is manufactured is not necessary at all. On scrapping the article, for example a motor car, the few closure plugs which are built into the car are disposed of through the melting down of the metal. 
     The closure plugs could indeed consist of a soft metal for example a lead alloy or aluminum, however preferred are closure plugs of thermo-plastic polymeric material, such as polyethylene, since these are usually deformable with a low expenditure of force on simultaneous heating, but readopt a solid form again after deformation and are thus protected against loss. 
     In a fastener element with the form of a nut with an inner thread, the closure plug is preferably retained by a form-locked fit with the thread at the entry to the thread. In this way the thread serves a double purpose in that it functions on the one hand as a fastening means, and on the other hand, however, also forms the desired form-fitted seat for the deformed closure plug. It is accordingly not necessary to provide a special seat for the deformed closure plug, for example in the form of a special undercut, so that the constructional length of the fastener element is not unnecessarily increased and the manufacturing costs are reduced. 
     In this design the closure plug preferably projects, in at least substantially sealed manner into at least one thread turn, preferably to approximately two and a half thread turns, but should not however completely fill these out, but rather should have a spacing from the root of the thread turns and be at least substantially rounded, and preferably approximately semicircularly rounded, at its side facing the root of the thread turns. This design of the closure plug in the deformed state ensures on the one hand the sealing of the thread, and also ensures that the closure plug cannot be easily lost. On the other hand this design also facilitates the pressing of the closure plug into the thread or into a receiving chamber at the far end of the thread. 
     It is particularly favorable when the closure plug has a cup-shaped recess at the side facing the interior of the hat-like element, preferably a recess with a slightly concavely rounded base. Furthermore, the closure plug should have a slightly convexly curved surface at the outer side which extends at least substantially parallel to the slightly concavely extending base of the cup-shaped or pot-like recess. Through this design the pressure forces which are exerted during a sand blasting treatment or during an immersion treatment on the closure plug, only lead to a slight flattening of the closure plug, whereby the latter is pressed more firmly into its seat at the start of the thread. On the insertion of a screw a somewhat higher force can however be applied so that the initially convexly outwardly directed base of the closure plug is deformed into a convexly inwardly arched form, whereby the closure plug is lifted out of the thread and can then be pressed with little force to the far end of the thread. 
     It would also be conceivable to form the closure plug so that it is penetrated by the screw and thereafter forms a plastic ring which serves to secure the inserted screw against rotation. 
     As already indicated, a receiving chamber for the closure plug which has been displaced from its seat is preferably provided, with this receiving chamber lying in the interior of the hat-like fastener element close to the transverse wall and being formed as a ring chamber. The receiving chamber preferably has a diameter which corresponds, at least substantially, to the outer diameter of the counter element or to the outer diameter of the thread, but which is not smaller than the latter. 
     The transverse wall itself is preferably formed by a disc, in particular a disc generated during a stamping process. This disc preferably sits on an annular or ring-shaped shoulder of the fastener element and closes the receiving chamber for the plug at the end face of the element remote from the thread. The disc itself is preferably retained by a radially inwardly directed, annular rivet rim formed from the material of the fastening element, with the rivet rim and the ring shoulder forming a radially inwardly open ring groove in which the periphery of the disc is held in form-fitted manner. 
     The invention also includes a sheet metal part with at least one hat-like fastener element of the previously described kind which is secured therein by a riveting process. The sheet metal part can also be a semi-finished product which is sand blasted or particle blasted on at least one face and is covered with a plastic, rubber or paint layer. Three specific examples for such sheet metal parts are, for example, a suspension strut mount of a vehicle, an engine bearer consisting of sheet metal and rubber for a vehicle, or a mounting device for an anti-roll bar consisting of a sheet metal bracket with inserted rubber. 
     A particular method for the manufacture of a hat-like fastener element, in particular a fastener element as previously described, wherein the hat-like mounting element has an inner passage which is provided with a fastening means, such as a thread or a bayonet socket, and is closed at or close to one end by means of a transverse wall, with the fastener element preferably having a riveting section at one end, is characterized in that a closure plug consisting of a deformable material is introduced into the fastener element which is at least partly received in a matrix and is squashed and plastically deformed between the matrix and a ram moved into the passage in such a way that it is held in a form-fitted manner in a seat provided within the fastener element and hereby closes the one end of the passage; and in that the respective other end of the passage is subsequently closed by a disc forming the transverse wall which is placed on a ring shoulder of the fastener element and is preferably retained in contact with this ring shoulder by a rivet rim formed by a forming process from the material of the fastener element. 
     Whereas, with a customary sealing technique requiring the insertion of a removable plug, this plug is inserted into the otherwise finished fastener element, in the method of the invention the closure plug is first inserted and then the disc forming the transverse wall. This method makes it possible to apply to the closure plug the forces which are necessary to deform it. When the closure plug consists of thermo-plastic polymeric material, then the ram is preferably heated, to reduce the force required for deformation of the plug. Here the temperature of the ram should be selected so that the plug does not melt, but rather simply becomes softened or somewhat pasty and can easily be brought into the final form. Through the deformation of the closure plug, the latter then also comes into contact with an extended surface of the hat nut element and also the matrix, whereby heat is withdrawn from the closure plug, and at least an initial solidification is achieved which ensures that the ram can be removed without simultaneous removal of the closure plug. A spray mist of a parting agent can be sprayed into the passage of the nut, or onto the end face of the ram, so that the ram does not stick to the closure plug. In similar manner a small quantity of a parting agent can previously be sprayed into the toolholder in order to avoid a sticking of the closure plug here. 
     The disc is preferably formed by a slug stamped out of a piece of sheet metal which represents a favorably priced possibility for the manufacture of the disc, and thus of the fastener element. 
     The toolholder preferably contains a movable ejection pin which serves for the ejection of the fastening element after the insertion of the closure plug and presses against a metallic surface of the fastener element. In this way it is prevented that the ejection pin solely presses on the plastic plug and possibly prematurely displaces the plug from its seat. 
     When the method is carried out with a movable ejection pin then the end face of the ejection pin is preferably also exploited for the squashing process in the sense that it serves as the counter pressure element to the ram. 
     The method is preferably carried out as follows with a multi-station tool: 
     a) in a first station the fastener elements are individually received in the matrices, 
     b) in a second station, which can optionally be integrated into the first or third station, and then omitted as a separate station, the balls forming the closure plugs are individually inserted into the respective fastener elements, 
     c) in a third station the ram is moved into the passage of the fastener element to squash and deform the ball forming the closure plug and, on laying out of the tool for closure plugs consisting of thermo-plastic material, the ram is heated, 
     d) in a fourth station a piece of sheet metal in strip form is guided transverse to the direction of movement of the fastener elements through the stations over the still open end face of the respective fastener element and, while using the open end face of the respective fastener element as a stamping matrix, a disc-like stamping slug is stamped out of the sheet metal and placed in firm contact against a ring shoulder of the respective fastener element by means of a stamping tool, 
     e) in a fifth station the edge of the respective fastener element which projects upwardly above the stamped slug is formed by means of a forming tool into a radially inwardly directed rivet rim, and hereby the stamped slug is fixed in form-fitted manner in the respective fastener element, and 
     f) in a sixth station the finished hat-like fastener elements are ejected by means of an ejection pin movably arranged in the matrix, wherein a plurality of matrices are provided and are movable around a transport circuit from station to station in order to hereby bring about the transport of the respective fastener elements into the various stations. 
     The invention will now be explained in more detail with reference to embodiments and to the drawing in which are shown: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 a longitudinal cross-section through a finished hat-like fastener element in the form of a hat nut 
     FIG. 2 a side view of a part of the hat nut of FIG. 1 in the direction of the arrow II in FIG. 1, 
     FIGS. 3A to  3 C three manufacturing steps during the manufacture of a sheet metal element in the form of a wheel strut mount with an attached fastener element. 
     FIGS. 4A to  4 H various steps during the manufacture of the fastener element, and 
     FIGS. 5A to  5 C representations of the fastener element in relation to the various stations of its manufacture, with FIG. 5A showing the starting element, FIG. 5B the semi-finished element with the inserted plug, and FIG. 5C finally reproducing the finished fastening element once again, the FIGS. 5A,  5 B and  5 C being aligned with the respective manufacturing steps in accordance with FIGS. 4A to  4 H. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1, a hat-like fastener element in accordance with the invention in the form of a dome nut  10  is shown in longitudinal cross-section, with the central longitudinal axis of the dome nut being given by the reference numeral  12 . A passage  11  extends in the longitudinal direction of the fastener element through the latter. 
     The dome nut  10  includes at its upper end a disc  14  which sits on an inner ring shoulder  16  of the dome nut and is held in form-fitted manner by means of a radially inwardly deformed end  18  of the dome nut. In other words, the rivet rim  18  and the annular ring shoulder  16  together form a ring-like recess  20  in which the edge region of the circular disc  14  is fixed. Directly beneath the disc  14 , there is located a cylindrical receiving chamber  22 , the diameter “D 1 ” which corresponds to the outer diameter of the threaded part  24 . At its lower end in FIG. 1, the dome nut has a flange portion  26  which has a relatively large contact surface  28  area-wise at its lower side which, in the in-built state of the dome nut, lies in areal contact with one side of the sheet metal part. This ring surface  28  merges via a small step  30  into a further annular ring surface  32  which finally also forms a part of the contact surface of the dome nut. This ring surface  32  then leads into a short conical portion  34  of the dome nut with a relatively steep cone angle of approximately 30°. This cone-shaped portion  34  finally merges into a ring-like rivet section  36  with a rounded shoulder  38  at the outer side, and on the inner side a ring-like chamfer  40  which represents part of a conical surface with an included angle of approximately 90°. This short, partly conical, surface  40  then merges into a cylindrical recess  42  of the dome nut, i.e. a recess at the entry side of the thread. The inner diameter D 2  in the cylindrical ring space  42  is somewhat larger than the outer diameter D 1  of the thread. 
     The upper portion of the dome nut has a cylindrical outer wall  44  which, in this example, is of right cylindrical shape, but which could, however, also have a different shape if one desired this for a specific reason. For example, a polygonal shape of the here cylindrical part  44  would be conceivable. 
     Uniformly distributed around the ring surface  32  are rounded nose-like projections  46 , eight in this example, which extend radially to the surface  32  and have limbs which run in the axial direction along the conical section  34 . The purpose of these noses is to form a security against rotation on inserting the dome nut element into a sheet metal part so that on inserting the bolt or screw, the dome nut does not turn in the panel. 
     FIG. 1 also shows the deformed sealing element in the form of a plastic plug  50  which closes the thread  24  at the opening or entrance. One notices that the length of this closure plug, i.e. in the direction of the central longitudinal axis  12  of the dome nut, amounts to from about two and a half to three thread turns and that the plug partly projects into the thread. The plastic material of the plug  50  does not, however, reach to the root of the thread, but rather a space  52 , which is approximately triangular in cross-section, i.e. spacing between the material of the closure plug and of material of the dome nut remains. If one considers the shape of the closure plug as a type of thread, then the thread has thread turns which are approximately semi-circular in cross-section. At the core diameter of the inner thread  24  the closure plug lies in intimate contact at  56  and forms a sealed connection here. 
     The closure plug has, moreover, a cup-shaped or pot-like recess  58 , the base boundary  60  of which is slightly concavely rounded. The lower side of the closure plug in FIG. 1 is correspondingly convexly rounded and extends approximately parallel to the base surface  60  of the pot-like recess  58 . 
     The lower side  62  of the closure plug has an outer diameter “D 3 ” which is as large as or larger than D 1 , but smaller than D 2 . In this way, a ring-shaped annular lip  64  is formed which lies flush on the entrance to the thread and serves for a 100% seal of the thread at this position. The ring-shaped sealing lip  64  is relatively thin. 
     An example for the use of this dome nut is shown by the FIGS. 3A to  3 C. In FIG. 3A one can see a partial cross-section through a strut mount of a motor car, i.e. through the so-called turret, which has three dome nuts  10  in accordance with FIG. 1 arranged in equal angular intervals around the turret, with only one dome nut being visible as a result of the illustration. The sheet metal part  70  is pre-apertured at the position of the dome nut, and the dome nut  10  has already been connected to the sheet metal part  70  by a riveting process. Through the riveting process, the noses  46  and also the ring surface  32  have been pressed into the material of the sheet metal  70  and the rivet section  30  has been so deformed that a form-fitted connection arises between the dome nut and the sheet metal part  70 . One notes that the plastic closure plug  50  has withstood this riveting process undamaged. On carrying out the riveting process, a correspondingly shaped tool can, for example, be inserted into the cylindrical part  42  of the riveting section of the dome nut with the diameter “D 2 ”, while pressure is exerted on the flange part  26  via a ram, with a concavely rounded ring shoulder formed on the matrix driving the material of the riveting section  36  outwardly in order to form the form-fitted connection. The noses  46  prevent the dome nut turning on the insertion of a screw (as shown further below in FIG.  3 C). 
     After the insertion of the dome nut  10 , the sheet metal part  70  is first sand or bead-blasted with the blast impinging on the part both from above and from below. Penetration of the stream of beads into the interior of the dome nut is prevented on the one hand by the disc  14 , and on the other hand by the closure plug  50 . 
     After carrying out the blasting process, a massive protective coating layer  72 , such as synthetic rubber, is cast onto the sheet metal part  70  and around the dome nut. This rubber layer principally forms a noise damping layer which prevents noises transmitted from the street via the wheel suspension radiating into the interior of the vehicle and there contributing to the general noise level. The rubber coating  72  also forms rust protection against premature rusting of this safety critical part. The rubber layer  72  can be seen in FIG.  3 B. 
     FIG. 3C finally shows the assembly in the installed state, i.e. the in-built position in the motor car vehicle where the spring mount is placed on a further correspondingly shaped piece of sheet metal  74  and secured to the latter by a bolt  76 , with a washer  78  being inserted between the head of the bolt  76  and the sheet metal part  74 . 
     On the insertion of the bolt  76 , the closure plug  50  is displaced, as can be easily be seen from FIG. 3C, into the ring-like chamber  22  of the dome nut. It can, however, also be seen from FIG. 3C that the riveted connection is not particularly loaded by the bolt. Instead, both the ring surface  32  and also the ring surface  38  of the dome nut are pressed against the sheet metal part  70 , with this surface being so selected that the surface pressure which arises lies beneath the limiting value for the material of the sheet metal  70  or of the material of the dome nut  10 . 
     The manufacture of the dome nut  10  of FIGS. 1 and 2 will now be explained in more detail in the following with reference to FIGS. 4A to H and also to the FIGS. 5A-C. 
     FIG. 5A first shows the blank fastener element  10  as it is received from an earlier manufacturing step, such as a cold heading machine. The entire chip forming machining of the fastening element has been completed so that it already has essentially the final shape, with the thread  34  being finally cut. 
     The arrow  100  shows that the fastener element  10  is moved downwardly via a non-illustrated separating device, which is however well known per se, and is placed into a toolholder  102 . In this, the rivet section of the nut element  10  lies downwardly. 
     The toolholder has a receiving chamber  101  which is so formed that the ring surface  32  of the fastener element  10  lies on a ring step of the receiving chamber. 
     The toolholder  102  includes a movable ejection pin  104  which is so shaped at its upper end that precisely this end fits into the cylindrical ring space of the fastener element  10 . The end face of the ejection pin  104  corresponds in its shape to the lower side of the finished inserted plastic closure plug of FIG. 1; that is, the end surface of the pin is slightly concavely shaped at the center. 
     As can be seen from FIG. 4A, the ejection pin  104  has a ring-like collar  106  which is accommodated in a cylindrical chamber  108  of the toolholder. The toolholder is closed at its lower side in FIG. 4A by a plate  110  which has a centrally arranged opening  112 . A cylindrical projection  114  of the ejection pin  104  extends through this opening. One notes from FIG. 4A that the collar  106  lies flush against the plate  110 , i.e. the ejection pin  104  is located in its lowermost position. Beneath the cylindrical projection  114 , there is located a pneumatic ejection cylinder  116 , the piston  118  of which is likewise located in the lowermost region. The matrix with the ejection cylinder  118  is located on a conveyor belt, for example formed by two chains extending parallel to one another, and serves not only for the support of the fastener element  10 , but rather also for the transport of the respective fastener element  10  through the various stations of the multi-station tool. This signifies that a plurality of toolholders  102  arranged at the respective spacing of the stations are provided on the conveyor belt formed by the chains. In this way, all stations of the multi-station tool can operate in synchronism so that a very economic and cost effective manner of operation can be achieved. Although the toolholder is moved from station to station by the two non-ilustrated chains, it is braced at the lower side of the plate  110  on a fixed foundation in order to pick up the pressure forces which arise in the subsequent process steps. 
     After the fastener element  10  in the toolholder  102  has been received in the first station of the multi-station tool of FIG. 4A, and after one has checked that a fastener element  10  is actually present in the toolholder, for example by means of a light barrier or an air nozzle or a proximity switch or the like (not shown), the chains are moved on one step further to the right so that the toolholder  102  is now located in the second station of FIG.  4 B. Here, for the sake of illustration, only a part of the toolholder and also of the ejection pin is shown. One notes, however, that the level of the toolholder has not changed. 
     In this second station of FIG. 4B the closure plugs are individually inserted into the respective mounting elements. The separating device is characterized here by  120 , and one notes that this separating device has a central passage  122  in which a row of plastic balls of thermoplastic plastic material lie closely behind one another. Such plastic balls are continually topped-up so that the passage  122  is always full. Two plates  124  and  126  are located in the separating device  120  and have a mutual vertical spacing which corresponds to the diameter of the plastic balls  128 . A hole  130  is located in the upper plate which is aligned in the illustration of FIG. 4B with the passage  122 . The lower plate  126  also has a hole  132  which in the illustration of FIG. 4B is arranged displaced relative to the first hole  130 , and indeed so that the hole  132  lies on the right hand side of the passage  122 . One also notes from FIG. 4B that the upper plate  124  has an inclined ramp  134  on the right hand side of the passage. Both plates  124  and  126  are secured to a slider  138  which is movable to and fro in the direction of the double arrow  136 . 
     In the illustration of FIG. 4B, a ball  128  already lies in the lower region of the fastener element  10  and lies in the concave recess of the end face of the ejection pin  104  centered relative to the central longitudinal axis  12  of the fastener element. As the slide  138  is still located in its extreme right hand position, the plate  126  completely closes the passage  122  so that the balls  128 ′ which are located above the plate  126  cannot fall into the fastener element  10 . The ball  128  also prevents further balls from sliding down into the fastener element. 
     After the insertion of the ball  128  into the fastener element  10  in accordance with FIG. 4B, the toolholder is transported by a further movement step of the conveyor means into the position of FIG.  4 C. At the same time, a further toolholder (not shown) with an “empty” fastener element  10  moves into the position of FIG.  4 B. The slider  138  is then moved to the left in accordance with the double arrow  136 , and indeed through a distance which corresponds approximately to the diameter of the ball  128  so that the ball  128 ′ of FIG. 4B now falls through the hole  132  into the new fastener element  10 . As a result of this movement of the slide member  138  to the left, the plate  124  is also moved to the left, and the ramp  134  lifts the further balls  128  upwardly so that no further balls can drop down into the fastener element  10 . After the one ball has fallen into the “new” fastener element, the slide  138  is then moved again to the right, whereby a further ball falls through the hole  134  onto the plate  126  so that the position of  4 B has been established again for the new fastener element. 
     FIG. 4C shows a third station of the multi-station tool in which the toolholder  102  with the ejection pin  104  cooperates with a two-part press head  140 . This press head  140  consists of a lower part  142  which has a cylindrical accommodation bore  144  for the outer circumference of the fastener element  10 , and also a downwardly directed cylindrical projection  146  which is pressed against the ring surface  148  of the flange  26  of the fastener element  10  and holds the latter firmly in the receiving chamber of the matrix  102 . Between the lower part  142  of the two-part press head  140  and the upper part  150  there are located spring elements which are schematically illustrated and provided with the reference numeral  152 . Within the two parts  142 ,  150  of the press head  140 , there is located a movable ram  154  which is heated via an inductive beating device  156  to a temperature at which the thermoplastic ball does not melt, but is however softened or pasty and easily formable. 
     In the station of FIG. 4C the illustration has been selected so that the two-part press head  140  has already travelled downwardly onto the fastener element, i.e. onto the toolholder, the heated ram has however not yet started to deform the ball  128 . One notes from the illustration of FIG. 4C, that the end face  158  of the ram  154  which contacts the ball  128  has a convexly rounded shape which serves for the formation of the cup-shaped recess of the finished closure plug. 
     FIG. 4D then shows a further position in the third station in which the press head  140  has moved further downwardly so that the ram  154  has already pressed the plastic ball  128  into its final shape in accordance with the illustration of FIG.  1 . FIG. 5B which is located directly above FIG. 4D then shows the shape of the fastener element  10  after this step, with the arrow  160  which extends from the illustration of FIG. 5A to FIG. 5B schematically illustrating the movements of the fastener element through the press between the first and third stations. 
     After the manufacturing step of FIG. 4D, the press head  140  is lifted so that the part  142  of the press head, and also the ram  154 , can be removed from the fastener element, whereby a further step movement of the matrix with the respective fastener element  10  into the fourth station of FIG. 4E is possible. 
     With respect to the illustration of FIGS. 4C and 4D, it should also be noted that this apparatus succeeds in achieving about 30 strokes of the press head per minute so that the entire tool operates with a corresponding rhythm. The plastic balls are pressed at a temperature of the ram  154  of approximately 180° C. with a force of 1000 newtons. This is a continuous movement of the press head without a dwell time at bottom dead center, with the press head being lowered with a speed of approximately 25 to 30 mm/s, but being raised again in fast gear. It should also be mentioned that the presence of the plastic ball  128  in the fastener element  10  is checked in the stations of FIGS. 4B and 4C. 
     It i also noted that, although the illustration of FIGS. 4A-4D shows the preferred embodiment, it would eventually be conceivable to integrate the separating device  120  of FIG. 4B either in the first station of FIG. 4A or in the third station of FIG.  4 C. The separating device  120  and the press head  140  could, for example, be movably arranged transverse to the conveyor direction so that first the separating device  120  and then the press head  140  come into use in the same station. 
     In the fourth station of FIG. 4E the fastener element  10  has the same shape as shown by the manufacturing step of FIG. 4D so that the illustration in FIG. 5B also applies for the illustration of the fourth station in FIG.  4 E. In this station, the disc which forms the transverse wall of the fastener element  10  is produced from a steel strip  160  using the stamping tool  162 . 
     The steel strip  160  is delivered from a supply roll behind the stamping tool  162  in the illustration of FIG.  4 E and the apertured steel strip which remains after stamping out of a circular slug is either rolled up at the right side of the knife and tool or is simply stamped through and broken up into small sections which then fall into a tub and can subsequently be disposed of. In other words, the band  160  moves transversely to the conveyor direction of the matrix  102  through the multi-stage tool. 
     The stamping tool  162  is of two-part construction and has a lower part  164  which, as shown in FIG. 4F, is first pressed downwardly during the movement of the stamping tool  162  onto the upper side of the steel strip  160  and holds the latter in firm abutment on the fastener element  10 . The upper part  166  of the two-part stamping tool is separated from the lower part by spring elements  168  and carries a stamping or cutting plunger  170  with a centrally arranged pin  172 . The centrally arranged pin  172  is movably arranged by a small distance “H” relative to the upper part  166  of the stamping tool  162 . 
     During downwardly directed movement of the stamping tool out of the position of FIG. 4E, the pin  172  first comes into contact with the steel strip  162  and is pushed upwardly by the downwardly directed movement of the stamping tool so that the distance “H” is reduced. As soon as the distance “H” has become substantially smaller, a signal is transmitted by the sensor  174  which shows that a steel strip  160  is actually present. 
     During the further downwardly directed movement of the stamping tool  162  the stamping plunger  170  moves downwardly sufficiently far that the disc which forms the transverse wall of the fastener element is stamped out from the steel sheet  160  and pressed down into contact with the ring shoulder of the fastener element. The process of stamping out takes place via a stamping or cutting plunger  170  which is a component of a stamping tool or of a part of a stamping too. This is then the position of the stamping tool  162  of FIG.  4 F. During the stamping process the upper end of the fastener element serves as a stamping die. The stamping tool  162  is then lifted again and returns into the position of FIG. 4E with a compression coil spring  178  pressing the movable pin  172  downwardly again and hereby resetting the signal transducer  174 . The signal transducer  174  can, for example, be a pneumatic device or a proximity sensor. 
     After the working step of FIG.  4 F and the lifting of the stamping tool  162  the toolholder  102  moves on one step further to the right into the fifth station of the multi-station tool of FIG.  4 G. Here, the rivet rim  18  is formed by means of a forming tool  180  and the rivet rim holds the disc firmly on the ring shoulder  16  of the fastener element  10 . One notes that the forming tool  180  likewise has a centrally arranged hold-down pin  182  which is displaceably arranged relative to the forming tool  180 , with this hold-down pin  182  having a cylindrical collar  184  which is displaceably mounted in a chamber  186  and is pressed downwardly by the compression coil spring  188 . The hold-down pin  182  is guided in the axial direction through the guide wall  190 . 
     After the pressing process in which the forming tool  180  is pressed downwardly in order to form the rivet rim, the fastener element  10  itself is finished, i.e. the matrix  102  can be moved on by one step further to the right through the lifting of the forming tool  180  into the ejection station of FIG.  4 H. Here the pneumatic cylinder  116  is energized so that the piston  118  moves upwardly and the piston rod  194  drives the ejection pin  104  upwardly until the collar  106  contacts the upper boundary of the ring-like receiving chamber  108 . One can see that the fastener element  10  is then lifted and is largely located outside of the toolholder  102 . The fastener element is, however, still arranged on the upper end of the ejection pin  104 . Through the further movement of the matrix  102 , the fastener element strikes against a fixed abutment  196 , as indicated by the arrow  198 , so that the fastener element  10  executes a tilting movement and drops down from the ejection pin  104  into a suitably inclined channel from which it can pass into a non-illustrated connecting box. 
     FIG. 5C indicates that the fastener element  10  is now finished, i.e. has the precise form of FIG.  1 . The further movement of the fastener element  10  through the press from the station of FIG. 4E up to the ejection in accordance with FIG. 4H is schematically illustrated with the arrow  200 . 
     It should at this stage also be pointed out that several matrices  102  can be arranged in parallel alongside one another so that in each station two or more fastener elements  10  can be simultaneously processed. In this way, the output of the multi-station tool can be doubled or multiplied without a substantial additional effort, depending on how many fastener elements are located alongside one another in each station. 
     Finally, the empty toolholder in the station of FIG. 4H return on the lower side of the conveyor device back to the first station of FIG. 4A where they are ready to accept further blank fastener elements. 
     It should be emphasized that the stations of the multi-station tools need not necessarily be arranged in a row, they could for example be arranged in a circle at the circumference of a conveyor means formed as a carrousel.