Abstract:
A loading pin, for a joining device, having a first axial end portion connectable to an axial drive, and having a second axial end portion which is realized for the purpose of exerting an axial force onto a joining element in order to push the joining element into a holding device and/or in order to support the joining element axially during a joining process, wherein the loading pin comprises an axial hollow channel portion through which a joining element is guidable in an axial feed direction. The loading pin partially defines a lateral joining element feed opening, via which a joining element is feedable into the hollow channel portion.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority from German Patent Application No. 102016111283.6, filed on Jun. 20, 2016, the disclosure of which is incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to a loading pin for a joining device, having a first axial end portion which is connectable to an axial drive, and having a second axial end portion which is realized for the purpose of exerting an axial force onto a joining element in order to push the joining element into a holding device and/or in order to support the joining element axially during a joining process, wherein the loading pin comprises an axial hollow channel portion through which a joining element is guidable in an axial feed direction. 
         [0003]    A loading pin of this type is disclosed in document DE 80 10 343 U1. 
         [0004]    In addition, the present invention relates to a joining device having a joining element receiver which is connectable to a joining element feed device in such a manner that a fed joining element is transferred into a receiving channel, wherein the joining element receiver comprises a loading pin guide portion on which a loading pin is mounted so as to be axially displaceable between a feed position and a joining position. 
         [0005]    Finally, the present invention relates to a method for feeding a joining element into a joining device. 
         [0006]    In the area of joining technology, in particular in the area of joining elements to workpieces, such as, for example, in the case of stud welding or in the case of stud bonding, it is known to feed joining elements in an automated manner into a joining head. In this connection, individually separated joining elements such as studs are blown through a feed tube by means of compressed air toward the joining head. There they pass into the receiving channel. 
         [0007]    The receiving channel leads into a feed channel of the joining head, a loading pin being mounted so as to be axially displaceable inside said feed channel. To feed a joining element out of the receiving channel into the feed channel, the loading pin is pulled back axially until the front end of the loading pin exposes the transition between the receiving channel and the feed channel. The joining element is then braked in a holding device which comprises holding tongues. The holding tongues are certainly radially resilient but have a relatively high level of rigidity. Accordingly, it is necessary to press the joining element through the holding device by means of the loading pin until, for example, a flange portion of a stud emerges at the front out of the holding device. The high level of rigidity of the holding tongues of the holding device is preferred because during stud welding the electric weld current is transmitted between the holding tongues and the stud by means of the pressing force. 
         [0008]    These types of joining devices are known in general. In this connection, the loading pin has to complete a relatively large travel, in particular when the holding device is realized in an axially long manner in order also to be able to perform joining in places that are difficult to access. On account of the large amount of travel, a relatively large interference contour is created on the side of the joining device located axially opposite the holding device, as the loading pin has to be pushed back relatively far during a feed operation in order to expose the transition between the receiving channel and the feed channel or holding device. 
         [0009]    A further method for welding studs is disclosed in document U.S. Pat. No. 4,019,013. In this connection, a holding device is mounted so as to be axially displaceable with reference to a housing. The holding device comprises a lateral feed channel, via which a joining element can be fed in the direction toward a holding device. The holding device then moves rearward against a fixed pin such that the fed stud is pushed into a predetermined position in the holding device. The axial travel is relatively large in this connection also. 
         [0010]    Document DE 102 29 690 B4 discloses a holding device of a joining device where studs with a relatively large flange portion (in comparison to the shank portion) are also able to be fed in an automated manner, through a feed channel. The joining element is clamped in a joining position by an axially movable clamping mouth-piece being displaced against radially movable clamping elements in such a manner that a radial clamping force for holding the shank of the joining element is exerted onto the clamping elements. 
         [0011]    Finally, document DE 80 10 343 U1 discloses a joining gun which comprises a fixed feed pipe through which joining elements are feedable in an axial feed direction by means of compressed air. At the end of the fixed pipe there is provided a one-way passage, through which a joining element is able to pass, but is not able to return into the feed pipe again. The feeding of a joining element is effected, in this case, at a point in time when a previously fed joining element, which is held by a stud clamping sleeve, is joined onto a workpiece. The stud emerging out of the one-way passage, in this case, is braked and stopped by the previously fed joining element. The stud clamp sleeve is then guided in the axial direction in the direction toward the one-way passage and then clamps the last fed joining element. 
         [0012]    In the case of the joining devices of the prior art described further above, the axial installation length of the respective joining device is also relatively large, on account of the respective axial feed channel or feed pipe and the relatively complicated axial relative displaceability between the feed pipe and the clamping device. 
       BRIEF SUMMARY OF THE INVENTION 
       [0013]    Against said background, it is an object of the invention to provide an improved loading pin for a joining device, an improved joining device and an improved method for feeding a joining element into a joining device. 
         [0014]    The above object is achieved in the case of the loading pin named in the introduction by the fact that the loading pin comprises a lateral joining element feed opening, via which a joining element is feedable into the hollow channel portion. 
         [0015]    In addition, the above object is achieved by a joining device of the above-named type wherein the loading pin is a loading pin according to the invention. 
         [0016]    Finally, the above object is achieved by a method for feeding a joining element into a joining device of the type according to the invention, said method having the steps of feeding a joining element into the receiving channel of the joining element receiver and from there radially via the lateral joining element feed opening into the loading pin such that the joining element passes into the hollow channel portion of the loading pin. 
         [0017]    As a result of the measure according to the invention, realizing the loading pin itself with a hollow channel and providing the loading pin, which is axially displaceable on the joining element receiver, with a lateral feed opening, it is possible to reduce the maximum necessary travel of the loading pin in a substantial manner. As the loading pin does not have to expose an outlet opening of a receiving channel of the joining element receiver completely as in the prior art such that the front end of the loading pin passes in the axial direction behind said outlet opening, the loading pin can remain arranged with its front end, which faces the holding device, still closely adjacent the holding device. On account of the lateral feed opening, the loading pin according to the invention consequently no longer has to be moved away over the entire axial distance up to the outlet opening of the receiving channel and beyond. This, in turn, makes it possible for significantly smaller interference contours to be realizable on the joining device in the region located axially opposite the holding device, such that the joining device is also suitable for applications where joining processes have to be carried out in areas that are difficult to access. 
         [0018]    In addition, it is possible to realize a holding device so that it is axially relatively long and narrow such that areas that are difficult to access are also able to be joined, for example at the bottom of beading or the like. 
         [0019]    The axial drive can be, for example, a pneumatic cylinder, but can also be an electric linear motor. The second axial end portion of the loading pin can be realized for the purpose of exerting an axial force onto a shank end of a shank portion of a joining element in order to press the joining element into the holding device or to support it axially during a joining process. As an alternative to this, it is possible, in particular in the case of so-called large flange studs, when the loading pin is designed with its second axial end portion for the purpose of exerting an axial force onto a top surface of the flange portion of such a stud in order to press said stud into a position in the holding device and/or to support it axially during a joining process. 
         [0020]    The joining element feed opening is a radial opening which preferably merges via a guide contour into the axially aligned hollow channel portion. This makes it possible for the joining element to be able to be fed from the receiving channel into the loading pin in the manner of a closed channel such that joining elements can be prevented from twisting and, for example, from being inadvertently joined in the incorrect axial alignment. 
         [0021]    The object is consequently fully achieved. 
         [0022]    According to a preferred embodiment, which represents an invention on its own in conjunction with the preamble of Claim  1 , a one-way passage for joining elements is realized on the second axial end portion, through which one-way passage at least one portion of a joining element is able to emerge in the axial feed direction, but through which one-way passage the portion of the joining element is not able to return into the hollow channel portion in the opposite axial direction. 
         [0023]    The one-way passage can be formed in different ways, for example as an active one-way passage which, by means of an actuator, enables passage in one direction, but prevents it in the other direction. 
         [0024]    It is particularly preferred when the one-way passage is realized as a mechanical one-way passage, in particular as a passive one-way passage. 
         [0025]    The achievement here is that the one-way passage can be realized in a structurally simple manner. 
         [0026]    In addition, it is preferred when the one-way passage is itself realized for the purpose of being able to transmit an axial force onto the joining element or onto a portion of the joining element. 
         [0027]    The one-way passage can be realized for the purpose of generally allowing the entire joining element through in the one direction, but not in the other one. In an alternative, it can be realized for the purpose of allowing a portion of the joining element, such as an enlarged flange portion, to pass through the one-way passage, but not in the opposite direction. 
         [0028]    According to a particularly preferred embodiment, the one-way passage is formed by a plurality of radially resilient lugs which, when at least one portion of a joining element passes through the one-way passage, are deflected radially and/or which, after the at least one portion of the joining element has passed through, are restored radially resiliently in a blocking position. 
         [0029]    The lugs of such a one-way passage are preferably arranged distributed over the periphery concentrically to a longitudinal axis of the loading pin. Proceeding from a base portion of the loading pin, the lugs can extend in the axial direction such that they taper conically towards one another, forming an axial end of the loading pin, via which the axial force is then to be transmitted. For this purpose, thickenings or radial projections, which provide an enlarged support area on the joining element, either on the shank end thereof or on the flange portion thereof, can be realized on the axial free ends of the lugs. 
         [0030]    In addition, the lugs can be formed curved in cross section such that they obtain a certain rigidity in the axial direction in order to be able to transmit the axial force via the lugs. 
         [0031]    Accordingly, it is preferred when the lugs are realized such that in the blocking position they are able to transmit an axial force. 
         [0032]    In addition, it is preferred overall when the axial hollow channel portion is defined/limited by a guide contour in a region of the lateral feed opening. 
         [0033]    The guide contour, which can be formed by a base portion of the loading pin, is realized in particular for the purpose of guiding a fed joining element from a generally radial feed direction via the lateral feed opening into an axial direction, i.e., in the direction of the axial feed direction. The guide contour is preferably realized on an end of the hollow channel portion that faces the first axial end portion. When the loading pin is situated in a feed position in a joining device, the guide contour is aligned preferably with a guide contour of a receiving channel of a joining element receiver or is arranged flush with said joining element receiver, on which such a loading pin is mountable so as to be axially displaceable. 
         [0034]    The guide contour ensures that a fed joining element maintains its relative position with reference to the feed direction, that is to say does not twist or tilt in any other way at the transition from a joining element receiver into the hollow channel portion of the loading pin. Faults can be prevented from occurring during the feed in this manner. In addition, a joining element can be prevented from being joined to a workpiece in an incorrect manner. A further advantage is that shorter studs are able to be processed and/or that air consumption during the feed process is reduced. 
         [0035]    In the case of the joining device according to the invention, it is preferred when a maximum travel of the loading pin is smaller than 1.5 times the maximum length of an axial joining element. 
         [0036]    The axial joining element maximum length is the longest axial length of a set of joining elements which can be joined by means of the joining device. For example, joining elements of various axial lengths can be joined by means of such a joining device. The joining element maximum length is the length of the longest joining element of such a set of joining elements. A maximum travel of the loading pin travel is preferably smaller than the axial length of the holding device. 
         [0037]    Since, as mentioned in the introduction, the second end portion of the loading pin can be arranged closely adjacent to a joining element holding device in the axial direction on account of the lateral feed opening, the maximum travel can consequently be very small. 
         [0038]    The maximum travel also determines the interference contour of the joining device on the end of the joining device which faces the first axial end portion, and which can consequently be realized very small. 
         [0039]    In addition, it is advantageous overall when a joining element holding device, which comprises a plurality of radially resilient holding tongues, is mounted on the joining element receiver. 
         [0040]    The holding tongues of the holding device can be realized in general so as to taper substantially conically in such a manner that a portion of a joining element that is guided through the one-way passage of the loading pin is, as a rule, stopped by means of the holding device. 
         [0041]    The radial resilience of the holding tongues is preferably clearly less than the radial resilience of the lugs of a one-way passage. The levels of resilience, in this case, are preferably matched such that a joining element that is fed at a certain kinetic energy passes with at least one portion thereof through the one-way passage, the lugs of the one-way passage being widened in a radially resilient manner and then springing back again into a blocking position. In addition, the levels of resilience are matched to one another such that at the predetermined kinetic energy of the joining element, said portion of the joining element is precisely not able to pass through the holding device, but is preferably stopped by said holding device. 
         [0042]    When stud welding, an electric weld current is preferably transmitted by means of the radially resilient holding tongues. 
         [0043]    In addition, the plurality of radially resilient holding tongues can include in each case three axial portions. A first axial portion, in this case, is preferably adjacent to the joining element receiver and comprises a greater inside diameter than the maximum outside diameter of the joining element. A second axial portion is arranged on the free end of the holding tongues and is aligned in a substantially axial manner such that in said second axial region, the holding tongues are able to abut, over a large distance and a large surface, against a shank or against an assembly located therebetween in order to reduce electric contact resistance in this manner. A third axial portion can be located between the first and the second axial portion and is realized in a substantially conical manner, preferably having a cone gradient which makes it possible, for example, for a flange portion of a stud to widen the holding tongues radially in the case of a relative axial movement with respect to said holding tongues such that the flange portion is able to pass through until the second axial portion abuts against the shank of the stud. 
         [0044]    As an alternative to this, the plurality of radially resilient holding tongues can also be realized in a similar manner to clamping tongues as are described in document DE 102 29 609 B4, the disclosure content of which is to be included by reference in the present case. 
         [0045]    It is particularly advantageous when a one-way passage of the loading pin and the joining element holding device are arranged in such a manner with reference to one another that a joining element is conveyable completely through the hollow channel portion and through the one-way passage and is stoppable in an intermediate position by the holding tongues. 
         [0046]    In the case of said development, the lugs of the one-way passage preferably snap back into a blocking position in which they are then able to exert an axial force onto an end of a shank of the joining element. 
         [0047]    It is additionally advantageous, in this connection, when the joining element holding device is realized for the purpose of holding a joining element in a joining position as a result of the holding tongues directly abutting radially against the joining element. 
         [0048]    Said embodiment has already been described above. The direct radial abutment is realized then in a preferred manner by the above-described second axial portion of the holding tongues. 
         [0049]    In an alternative development, a one-way passage of the loading pin and the joining element holding device are arranged in such a manner with reference to one another that a flange portion of the joining element is conveyable through the hollow channel portion and through the one-way passage and is stoppable by the holding tongues. 
         [0050]    In the case of said development, in said intermediate position a shank of the joining element is preferably still located in the radial direction between the lugs of the one-way passage. 
         [0051]    The blocking position is set up in this connection as a result of the lugs of the one-way passage snapping back again into a blocking position in which they are then able to exert an axial force onto the top surface of said flange portion. 
         [0052]    In the case of said development, it is additionally advantageous when the joining element holding device is realized for the purpose of holding a joining element in the joining position by the holding tongues pressing from radially outside onto lugs of a one-way passage of the loading pin. 
         [0053]    In the case of said development, advancing the loading pin from the feed position into the joining position of the loading pin can preferably result in the lugs of the one-way passage pressing axially onto the flange portion of a joining element and pressing the flange portion through the holding tongues of a holding device. In addition, the holding tongues of the holding device then abut radially outwardly against the lugs of the one-way passage. 
         [0054]    For example, an electric weld current can be transmitted in this connection onto the joining element via the holding tongues and the lugs. 
         [0055]    An articulated sleeve, which provides that where there is relative movement, a sufficient radial clamping force is able to be exerted onto the lugs of the one-way passage, can additionally be arranged in a radial region between the lugs and holding tongues. 
         [0056]    In addition, it is overall advantageous when the loading pin comprises a one-way passage with a plurality of radially resilient lugs, as has already been mentioned above. 
         [0057]    It is also overall advantageous when the loading pin guide portion has a guide cross section at least in portions, wherein the loading pin has a loading pin cross section at least in portions which is adapted to the guide cross section. 
         [0058]    The guide cross section and the load pin cross section can be circular in form. In many cases, however, it is preferred when said cross sections deviate from a circular form, for example in the form of a polygonal cross section. In said case, an alignment of the lateral feed opening can be realized in a simple manner in the peripheral direction with an outlet opening of a receiving channel. 
         [0059]    In addition, it is possible in this case to transmit torque from the joining element receiver onto the loading pin and vice versa. 
         [0060]    The maximum travel of the loading pin is preferably independent of the size of the joining element receiver and preferably independent of the length of the joining element holding device, in particular of the length of the radially resilient holding tongues. 
         [0061]    The maximum travel of the loading pin is preferably a function of a length of the above-described second portion and of the length of the above-described third portion of holding tongues of a joining element holding device. Preferably, the maximum travel of the loading pin is also independent of the length of the joining element, but is preferably smaller than a maximum length of the axial joining element. 
         [0062]    In the case of joining elements which have a relatively small ratio of flange diameter to shank diameter, the embodiment preferred is where the joining element overall passes through the one-way passage and then passes between an axial end of the one-way passage and the holding tongues to an intermediate position. In the case of so-called large flange studs which have a relatively large ratio of flange diameter to shank diameter, the variant preferred is preferably where the lugs of the one-way passage are closed into a blocking position in which they are subsequently able to transmit an axial force onto a top surface of the flange portion. 
         [0063]    All in all, at least one of the following advantages are produced, where applicable, in the case of the above embodiments. The size of a drive unit, in particular of an axial drive, is independent of the size of a joining element receiver. The size of such a drive unit is preferably independent of the length of a joining element holding device. In particular, extra-long joining element holding devices are realizable, e.g., for weld positions in beading, indentations, undercuts, etc. 
         [0064]    In the case of overhead joining, for example after a malfunction in a power for feeding the joining elements, for example in the case of a blast air malfunction, it is no longer possible for a joining element to pass back into a shooting channel or a feed channel or into a receiving channel. 
         [0065]    It is obvious that the features named above and the features yet to be explained below are usable not only in the combination provided in each case, but also in other combinations or standing on their own without departing from the framework of the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0066]    Exemplary embodiments of the invention are explained in more detail in the following description and are shown in the drawings. 
           [0067]      FIG. 1  shows a schematic longitudinal sectional view through a first embodiment of a joining device with a loading pin according to the invention in a joining position. 
           [0068]      FIG. 2  shows the joining device of  FIG. 1  in a feed position in which a joining element is situated in an intermediate position. 
           [0069]      FIG. 3  shows a schematic representation, comparable to  FIG. 2 , of a further embodiment of a joining device in a feed position, a joining element being situated in an intermediate position. 
           [0070]      FIG. 4  shows the joining device of  FIG. 3  in a joining position in which a joining element is situated in a joining position. 
           [0071]      FIG. 5  shows a side view of a loading pin of the joining device of  FIGS. 3 and 4 . 
           [0072]      FIG. 6  shows a side view of the loading pin of  FIG. 5  rotated by 90°. 
           [0073]      FIG. 6 a    shows a schematic sectional view along the line VIa-VIa of  FIG. 6 . 
           [0074]      FIG. 6 b    shows a schematic sectional view along the line VIb-VIb of  FIG. 6 . 
           [0075]      FIG. 7  shows a side view of an articulated sleeve of the joining device of  FIGS. 3 and 4 . 
           [0076]      FIG. 8  shows a further side view of the articulated sleeve of  FIG. 7 . 
           [0077]      FIG. 9  shows a perspective view of the articulated sleeve of  FIGS. 7 and 8 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0078]      FIG. 1  shows a schematic representation of a joining system which is designated in general with the reference  10 . As an example, the joining system  10  includes a robot  12  which, on a three-dimensionally freely movable arm  14 , carries a joining head  16  which forms a joining device. 
         [0079]    The joining system  10  additionally includes a feed device  18  which is realized for the purpose of feeding individually separated joining elements  20 , which can be realized in the present case as studs with a shank portion  48  and a flange portion  50 , to the joining head  16  by means of a feed tube  22 , in an automated manner. The feeding can be effected, for example, by means of a blast of pressurized air. 
         [0080]    The joining head  16  comprises a joining element receiver  28 . A receiving opening  30 , to which the feed tube  22  can be connected and via which joining elements can be fed, preferably with the flange portion in the front, is realized on the joining element receiver  28 , which is preferably realized fixed to the housing with reference to the joining head  16 . 
         [0081]    The receiving opening  30  merges into a curved receiving channel  32  of the joining element receiver. The receiving channel  32  ends in an outlet opening  33  which opens out into a loading pin guide portion  34 . A loading pin  36  is mounted in the loading pin guide portion  34  so as to be axially displaceable with reference to the joining element receiver  28 . 
         [0082]    The loading pin includes an axial hollow channel portion  38  in which joining elements are fed in an axial feed direction  39 . 
         [0083]    The joining head  16  further includes a joining element holding device  40  which is secured to the joining element receiver  28  by means of a fastening device  42 , for example in the form of a fastening nut  44 . 
         [0084]    In the present case, the holding device  40  includes a plurality of holding tongues  46  which are arranged distributed over the periphery and comprise a first axial portion, which faces the joining element receiver  28  and comprises an inside diameter D ID1  which is greater than a maximum outside diameter D ODM  of a joining element  20  to be fed. 
         [0085]    On one free end  47 , the holding tongues  46  comprise in each case a second axial portion where the holding tongues are aligned in a substantially straight manner and which, in a relaxed position, that is to say not deflected radially, define an inside diameter D ID2  which is smaller than an outside diameter D ODS  of a shank portion of a joining element  20 . A third axial portion of the holding tongues, which is realized in a substantially conical manner, and which is realized as a stop portion, as will be explained again below, is located in between. 
         [0086]    As explained, the joining element  20  comprises a shank portion  48  and a flange portion  50  with a larger diameter. 
         [0087]    In the joining position shown in  FIG. 1 , such a joining element  20  is shown in a joining element joining position  20 F in which the shank portion  48  is surrounded by the second axial portion of the holding tongues  46  which press radially against the shank portion  48 . The flange portion  50  and part of the shank portion can protrude in relation to the radial end of the holding device  40 . 
         [0088]    An electric weld current  52  can be transmitted by the holding device  40  and is then transmittable via the holding tongues  46  onto the shank portion  48 . As a result, in a manner known per se, such a joining element  20  can be joined during so-called stud welding onto a top surface of a workpiece  54  (for example a metal sheet), which preferably forms an opposite pole, for example an earth for the electric weld current, such that an electric arc can be drawn for stud welding between the joining element  20  and the workpiece  54 . 
         [0089]    It can be seen additionally in  FIG. 1  that an axial force  56 , which is directed in the same direction as the axial feed direction  39 , can be exerted onto the loading pin  36 . 
         [0090]    For this purpose, for example a first axial end portion  60  of the loading pin  36  can be connected to an axial drive  62 , by means of which the loading pin  36  is movable axially relative to the joining element receiver  28  between the joining position FP shown in  FIG. 1  and the feed position SP shown in  FIG. 2 . 
         [0091]    A second axial end portion  64 , on which a mechanical one-way passage  66  is provided, is realized on an axial end of the loading pin  36  which is located opposite the first axial end portion  60 . The one-way passage  66  is formed by a plurality of lugs  68 , which are arranged distributed over the periphery, connect to the hollow channel portion  38  and, proceeding from there, taper conically in the feed direction. On their free ends  69 , the lugs  68  can comprise respective radial projections  70  or thickenings such that the lugs  68  are able to abut against a shank end of the shank portion  48  and the axial force applied onto the loading pin  36  can be transmitted onto the joining element  20 , as is shown in  FIG. 1 . 
         [0092]    The loading pin  36  comprises a lateral joining element feed opening  76 . The lateral joining element feed opening  76  is realized in the axial direction between the first and the second axial end portions  60 ,  64  and in the feed position SP shown in  FIG. 2  is aligned with the outlet opening  33  of the receiving channel  32 . 
         [0093]    In said region, the loading pin  36  comprises a guide contour  78  which is in alignment with a guide contour of the receiving channel  32  when the loading pin  36  is situated in the feed position SP. 
         [0094]    The guide contour  78  consequently forms a continuation of the receiving channel  32  and leads to a type of closed channel between the receiving channel  32  and the hollow channel portion  38  in such a manner that joining elements  20  are not able to rotate or tip in the region of the transition between the receiver  28  and the loading pin  36 . 
         [0095]    The receiving channel  32  and the guide contour  78  together form a curved contour in order to align joining elements  20 , which are fed substantially in the radial direction into the loading pin  36  by means of the lateral joining element feed opening  76 , ultimately in an axial manner such that in the hollow channel portion  38  they are guided in axially the feed direction  39 . 
         [0096]    During the feeding process, the joining elements  20  are fed at a certain kinetic energy, for example by means of blast air. During the feeding process, on account of their kinetic energy, the joining elements  20  press the lugs  68  radially outward, which is shown in  FIG. 2  by the reference  80 , such that the joining element  20  passes completely through the one-way passage  66  and is braked by means of the holding tongues  46  of the holding device  40 , in an intermediate position  20 Z in which the joining element  20 Z is situated in the axial direction between the one-way passage  66  and the free end  47  of the holding tongues  46 . 
         [0097]    Said intermediate position region is shown in  FIG. 2  by way of the reference  82 . 
         [0098]    The loading pin  36  is then guided out of the feed position SP into the joining position FP in which the loading pin exerts an axial force  56  onto the joining element  20  by use of the one-way passage  66  via lugs  68  with radial projections  70  in order to press said joining element  20  through the holding tongues  46  until the position shown in  FIG. 1  is reached. In this connection, the holding tongues  46  of the holding device  40  also perform a radial movement which is shown in  FIG. 2  by way of the reference  84 . 
         [0099]      FIGS. 1 and 2  also show the maximum travel  86  of the loading pin  36 . It can be seen that said travel  86  can be smaller than 1.5 times a maximum length  88  of a joining element  20 . 
         [0100]    Only a very small interference contour is created in the region of the first axial end portion  60  on account of the small travel  86  such that it is also possible to use the joining head  16  in difficult joining situations. 
         [0101]    In addition, the holding device  40  can be realized so as to be long in the axial direction, as is also shown in  FIG. 2 , such that the joining head  16  can also be used for joining at inaccessible places, for example at the bottom of beading or the like. 
         [0102]      FIG. 2  shows a schematic representation of an insulation sleeve  90  which is able to insulate the loading pin  36  electrically in relation to the holding device  40  in order to avoid an electric weld current  52  also being transmitted onto the joining element via the one-way passage  66 . 
         [0103]      FIGS. 3 and 4  show a further embodiment of a joining system  10 ′ having a joining head  16 ′ which comprises a loading pin  36 ′. The embodiment in  FIGS. 3 and 4  corresponds in general with regard to design and method of operation to the embodiment in  FIGS. 1 and 2 . Identical elements are consequently provided by identical references. Substantially the differences are explained below. 
         [0104]    The difference in the present case is substantially in the region of the holding device  40 ′. The holding device  40 ′ is realized for the purpose of being able to widen the holding tongues  46 ′ relatively far in order, in this way, also to be able to join joining elements  20 ′ where the ratio of flange portion  50 ′ to shank portion  48 ′ is very large, in particular in the form of so-called large flange studs. 
         [0105]    In this connection, the one-way passage  66 ′ is initially realized such that a fed joining element is not fed completely through the one-way passage  66 ′, but only the flange portion  50 ′ thereof which is then subsequently stopped by the holding tongues  46 ′, in the intermediate position  20 Z′ shown in  FIG. 3 . 
         [0106]    The lugs  68 ′ of the one-way passage  66 ′, where applicable, rest against a top surface of the flange portion  50 ′. When the axial movement (axial force  56 ) is executed, said lugs  68 ′ consequently press onto the flange portion and press it through the holding tongues  46 ′ until the flange portion  50 ′ protrudes out of the holding device  40 ′. 
         [0107]    The holding tongues  46 ′, in this case, abut radially outwardly against the lugs  68 ′. 
         [0108]    An articulated sleeve  96 , which, during the relative movement between the loading pin  36 ′ and the holding device  40 ′, provides that clamping force  98  is exerted in the radial direction such that it can be ensured that an electric weld current experiences a small amount of contact resistance, is arranged in the region of the holding device  40 ′ in order to obtain a sufficient radial clamping force 
         [0109]      FIGS. 5 and 6  show the loading pin  36 ′ from the joining device  16 ′ of  FIGS. 3 and 4 . The lateral joining element feed opening  76 ′ and the lugs, which are provided in  FIGS. 5 and 6  with the references  68   a ′ and  68   b ′, can be seen. 
         [0110]    The lugs  68 ′ of the loading pin  36 ′, in this connection, are not realized in a constantly conical manner as in the case of the embodiment in  FIGS. 1 and 2 , but comprise a first axial portion I 1 , in which they are realized in a conical manner, and a second axial portion I 2 , in which they are realized in a straight manner, in order to enable a large-surface abutment against the shank portion  48 ′. 
         [0111]      FIG. 6 a    shows a cross section of the loading pin  36 ′ in the form of a loading pin cross section  100  which, in the present case, is realized in a polygonal manner. Accordingly, it can be ensured that a correspondingly polygonal cross section of the loading pin guide portion  34  is able to provide an anti-rotation device between the joining element receiver  28  and the loading pin  36  such that it is also possible to absorb torque therebetween. 
         [0112]      FIG. 6 b    shows additionally that the lugs  68   a ′,  68   b ′,  68   c ′ can be realized in each case curved in cross section in order to be able to transmit axial forces well and in order to enable a large-surface abutment against the shank portion  48 ′. 
         [0113]      FIGS. 7 to 9  show the articulated sleeve  96  of the holding device  40 ′ in  FIGS. 3 and 4 . It can be seen that the articulated sleeve comprises a plurality of radially movable, substantially elongated members which are arranged distributed over the periphery and are held together by means of resilient means, for example by an O-ring seal. 
         [0114]    The members are realized in each case such that, where there is a relative movement between the loading pin  36 ′ and the holding tongues  46 ′, they exert a radial clamping force  98  onto the lugs  68  so that they are able to abut tightly and at sufficient force against the shank portion  48 ′. 
         [0115]    Although exemplary embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes may be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.