Abstract:
A through-hole self-piercing rivet  30  is assembled with two metal plates  50  and  52  to retain the plates together as a workpiece  54.  When the rivet  30  is to be removed, a pin, such as a contact pin  56,  is attached to the rivet by fusion, or a pin, such as a threaded mandrel  78,  is attached threadedly to the rivet. The contact pin  56  or the threaded mandrel  78  is withdrawn from the workpiece  54  to thereby withdraw the attached rivet  30  from the workpiece. Devices  62  and  84  provide facility for effecting the attachment of the contact pin  56  and the threaded mandrel  78,  respectively, with the rivet  30,  and for the extraction of the rivet from the workpiece  54.

Description:
This application is a continuation-in-part of U.S. Ser. No. 09/099,142, filed Jun. 18, 1998, now U.S. Pat. No. 6,108,890 the disclosure of which is incorporated herein by reference thereto. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to methods of removing self-piercing rivets set into a workpiece, and to devices for implementing the methods. In particular, this invention relates to methods of removing through-hole rivets set in a workpiece, and to devices for implementing the methods. 
     A through-hole self-piercing rivet has a first opening and a second opening formed in spaced portions of an outer surface thereof and a passage extending between and in communication with the first and second opening. An example of a through-hole self-piercing rivet is a tube-shaped self-piercing rivet shown in German Patent Application No. DE 197 01 780. The tube-shaped self-piercing rivet is formed with an axially symmetric design with a cutting edge at each of a leading axial end and a trailing axial end thereof. During the riveting process, the cutting edge of the leading axial end pierces a workpiece, while the cutting edge of the trailing axial end is deformed outwardly so that a riveted joint is produced thereby. 
     Producing riveted joints with such tube-shaped self-piercing rivets results in essentially permanent connection of, for example, two metal sheets, which are to be riveted together, and in the context of this description, form the workpiece into which the tube-shaped self-piercing rivet is set. In order to detach the riveted metal sheets from one another, such as, for example, in the case of essential repair work, the riveted joint has to be undone. This is usually accomplished by a chisel-like tool, or the like, which is driven between the metal sheets so that the rivet connecting the metal sheets is torn forcibly out of its seat. The result is not only destruction of the rivet but also deformation of the workpiece, i.e., the two metal sheets, at the point where the rivet is torn out, which is undesirable and makes it necessary to machine the relevant sheets when re-use of at least one sheet is required. Further, this method is undoing the riveted joint is a costly and uncontrollable operation which is also rendered more difficult by the fact that riveted joints are often situated in accessible places. 
     Therefore, there is a need for methods which will facilitate the removal of the tube-shaped self-piercing rivets set into a workpiece, and for devices which implement such methods. 
     SUMMARY OF THE INVENTION 
     It is, therefore, an object of this invention to provide methods of removing tube-shaped self-piercing rivets from a workpiece. 
     Another object of this invention is to provide devices for implementing methods of removing tube-shaped self-piercing rivets from a workpiece. 
     With these and other objects in mind, this invention contemplates a method of removing a self-piercing rivet from a set position in a workpiece. The self-piercing rivet has a first opening and a second opening formed in spaced portions of an outer surface thereof and a passage extending between and in communication with the first and second opening. The self-piercing rivet is further formed with an attachable portion. The method of removing the self-piercing rivet includes the steps of placing a pin adjacent the attachable portion of the self-piercing rivet, attaching the pin to the attachable portion of the self-piercing rivet, applying a force to the workpiece by an abutment supported on the workpiece, and retracting the pin and the attached self-piercing rivet from the workpiece counter to the applying of the force to the workpiece, whereby the self-piercing rivet is withdrawn from the workpiece. 
     This invention further contemplates a method of removing a self-piercing rivet from a set position in a workpiece. The self-piercing rivet has a first opening and a second opening formed in spaced portions of an outer surface thereof and a passage extending within the self-piercing rivet between and in communication with the first and second openings. The self-piercing rivet is further formed with an attachable portion. The method includes the steps of placing a pin in engagement with the attachable portion of the self-piercing rivet to provide a contact area between the pin and the self-piercing rivet, heating the contact area between the pin and the self-piercing rivet to a fusion temperature, cooling the contact area, applying a force to the workpiece by an abutment supported on the workpiece, and retracting the pin and the attached self-piercing rivet from the workpiece counter to the applying of the force to the workpiece, whereby the self-piercing rivet is withdrawn from the workpiece. 
     Additionally, this invention contemplates a method of removing a self-piercing rivet from a set position in a workpiece. The self-piercing rivet has a first opening and a second opening formed in spaced portions of an outer surface thereof and a passage extending between and in communication with the first and second openings. The self-piercing rivet is further formed with an attachable portion located on a wall of the passage. The method includes the steps of removing at least portions of the workpiece, previously located within the passage of the self-piercing rivet when the self-piercing rivet was assembled with the workpiece, to expose the attachable portion located on the wall of the passage of the self-piercing rivet, attaching a pin to the attachable portion of the self-piercing rivet, applying a force to the workpiece by an abutment supported on the workpiece, and retracting the pin and the attached self-piercing rivet from the workpiece counter to the applying of the force to the workpiece, whereby the self-piercing rivet is withdrawn from the workpiece. 
     Still further, this invention contemplates a device for implementing the removal of a through-hole self-piercing rivet from a workpiece, where the rivet has a first opening and a second opening formed in spaced portions of an outer surface thereof and a passage extending therebetween, which includes a pin, means for attaching the pin to an attachable portion of the through-hole self-piercing rivet, and means for retracting the pin, with the self-piercing rivet attached thereto, from the workpiece. 
     Also, this invention contemplates a device for implementing the removal of a through-hole self-piercing rivet from a workpiece, where the rivet has a first opening and a second opening formed in spaced portions of an outer surface thereof and a passage extending therebetween, which includes a pin, means for placing the pin in contact with an attachable portion of the through-hole self-piercing rivet at a contact area, means for heating the contact area to a fusion temperature to fuse and attach together the pin and the attachable portion of the rivet, means for cooling the heated contact area, and means for retracting the pin, with the self-piercing rivet attached thereto, from the workpiece. 
     This invention contemplates yet another device for implementing the removal of a through-hole self-piercing rivet from a workpiece, where the rivet has a first opening and a second opening formed in spaced portions of an outer surface thereof and a passage extending therebetween, which includes a pin, means for forming an attachable portion on the through-hole self-piercing rivet, means for attaching the pin to the attachable portion of the self-piercing rivet, and means for retracting the pin and the attached self-piercing rivet from the workpiece whereby the self-piercing rivet is withdrawn from the workpiece. 
     Other objects, features and advantages of the present invention will become more fully apparent from the following detailed description of the preferred embodiment, the appended claims and the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings: 
     FIG. 1 is a sectional view showing a through-hole self-piercing rivet which is axially symmetrically formed; 
     FIG. 2 is a perspective view showing the through-hole self-piercing rivet of FIG. 1; 
     FIG. 3 is a sectional view showing an assembly of two metal sheets, forming a workpiece, held together by the through-hole self-piercing rivet of FIG. 1; 
     FIG. 4 is a sectional view showing the assembly of FIG. 3 with a contact pin located adjacent the through-hole self-piercing rivet; 
     FIG. 5 is a sectional view showing the pin of FIG. 4 in contact with the assembled through-hole self-piercing rivet in accordance with certain principles of the invention; 
     FIG. 6 is a sectional view showing an abutment in engagement with the workpiece and the contact pin of FIG. 4 in contact with the through-hole self-piercing rivet, in accordance with certain principles of the invention; 
     FIG. 7 is a sectional view showing the pin and the self-piercing rivet attached thereto being withdrawn from assembly with the two metal sheets, in accordance with certain principles of the invention; 
     FIG. 8 is a partial sectional view of a device, which includes the pin of FIG. 4, used for implementing a method of removing the through-hole self-piercing rivet from the workpiece in accordance with certain principles of the invention; 
     FIG. 9 is a sectional view showing a punch, or tappet, aligned with the assembly of FIG. 3 in accordance with certain principles of the invention; 
     FIG. 10 is a sectional view showing the punch of FIG. 9 having punched a plug from the center or core of the through-hole self-piercing rivet in accordance with certain principles of the invention; 
     FIG. 11 is a sectional view showing a threaded mandrel being worked through, and threadedly attaching to, the core of the through-hole self-piercing rivet of FIG. 10 in accordance with certain principles of the invention; 
     FIG. 12 is a sectional view showing the threaded mandrel and the threadedly attached self-piercing rivet being withdrawn from the two metal sheets in accordance with certain principles of the invention; 
     FIG. 13 is an enlarged sectional view showing the threaded attachment of the threaded mandrel of FIG. 11 in threaded attachment with the core of the through-hole self-piercing rivet in accordance with certain principles of the invention; 
     FIG. 14 is an enlarged sectional view showing the arrangement of FIG. 13 with a punch, or tappet, formed integrally with and extending from a forward portion of the threaded mandrel of FIG. 11 in accordance with certain principles of the invention; 
     FIG. 15 is an enlarged sectional view showing the arrangement of FIG. 13 with a drill pin, or bit, formed integrally with and extending from a forward portion of the threaded mandrel of FIG. 11 in accordance with certain principles of the invention; 
     FIG. 16 is a partial sectional view showing a device, which includes the threaded mandrel of FIG. 11, used for implementing a method of removing the through-hole self-piercing rivet from the workpiece in accordance with certain principles of the invention; and 
     FIG. 17 is a partial sectional view showing the device of FIG. 16, which includes the threaded mandrel of FIG. 11, and the punch of FIG. 14 used for implementing a method of removing the through-hole self-piercing rivet from the workpiece in accordance with certain principles of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1, a self-piercing rivet  30  is formed with a first opening  32  and a second opening  34  formed in spaced portions of an outer surface  36 , with a passage  38  extending between and in communication with the first and second openings. The rivet  30  is formed axially symmetric about an axis  40 , and is formed with a stamping side  42  contiguous with the first opening  32  and a bottom side  44  contiguous with the second opening  34 . Also, the rivet is formed with a circumferential cutting edge  46  at the stamping side  42  and a circumferential cutting edge  48  at the bottom side  44 . The self-piercing rivet  30  is illustrated in perspective in FIG.  2 . 
     As shown in FIG. 3, a riveted joint of two metal sheets  50  and  52 , which form a workpiece  54 , is effected by use of the self-piercing rivet  30 . Referring to FIG. 4, a pin  56 , referred to as a contact pin, is being moved toward the stamping side  42  of the self-piercing rivet  30  which is in assembly with the workpiece  54 . As shown in FIG. 5, the contact pin  56  is moved into engagement with the stamping side  42  of the rivet  30 . The area of contact between the contact pin  56  and the stamping side  42  of the rivet  30  is then heated, which can be accomplished, for example, by a welding process, to fuse, bond or connect together the engaging portions of the contact pin  56  and the stamping side  42  of the rivet  30 . 
     Thus, the stamping side  42  of the self-piercing rivet  30  is an attachable portion of the rivet provided for attachment with the pin  56 . 
     The connecting together of the contact pin  56  and the rivet  30  can be effected by arc welding, in the area of a bold line  58  (FIG.  5 ). The weld is effected in a manner customary when welding studs using arc welding. By retracting the contact pin  56  for several milliseconds, the necessary burning time was obtained to fuse together the adjacent portions of the pin and the rivet. The pin  56  is then lowered into the molten mass and a cooling is effected to provide a strong, loadable connection between the pin and the rivet  30 . 
     Following the fusing operation, an abutment  60  is placed on the metal sheet  50  as shown in FIG. 6, and the contact pin  56  is withdrawn from the workpiece  54 , in the direction shown in FIG.  7 . 
     During the withdrawal of the contact pin  56 , at least in the immediate area of the abutment  60 , the metal sheet  50  and the metal sheet  52  encounter only specific residual damage thereof at the seat point of the rivet  30 . The remaining region of the two metal sheets  50  and  52  are unaffected by the withdrawal process. 
     As shown in FIG. 7, as the pin  56  is withdrawn, the two metal sheets  50  and  52  are separated, and the rivet  30  remains attached to the pin. Thus, the two disassembled metal sheets  50  and  52  may be removed for further treatment, such as, for example, for recycling, with the only damage thereto being at the relevant point of the removal of the self-piercing rivet  30 . 
     Referring to FIG. 8, to produce the connection between the contact pin  56  and the self-piercing rivet  30  by arc welding, a device, such as a stud welding gun  62 , is advantageously used. Such a stud welding gun is described, for example, in Great Britain Patent Specification No. GB 636 343. The stud welding gun  62  has a chuck  64 , which grips the pin  56  and permits execution of the axial movements which are required during the arc welding. The movements are effected by a motion mechanism  66 , which may be of various known types such as that shown in U.S. Pat. No. 5,502,291, the disclosure of which is incorporated herein by reference thereto. The motion mechanism  66  is housed in the interior of the stud welding gun  62 . 
     A tool of the type shown in FIG. 8 may alternatively be used to produce a resistance weld, the tool merely having to be equipped with a suitable power supply and a suitable motion control program. Such tools are known. 
     Also, a tool of the type shown in FIG. 8 may be used for friction welding, wherein the motion mechanism  66  is a known type of rotary drive which sets the pin  56  held by the chuck  64  in rotation and presses the pin against the rivet  30  in the relevant contact area to produce a weld. 
     Referring to FIG. 9, the workpiece  54 , with the assembled self-piercing rivet  30  in place, is aligned with a pin, such as a punch or tappet  68 , in a manner similar to the alignment of contact pin  56  with the workpiece and assembled rivet. The punch  68  is being advanced toward a portion  70  of the workpiece  54  which is confined within the passage  38  of the rivet  30 . Ideally, the punch  68  is formed with a truncated cone  72  at an advancing end thereof closest to the workpiece to facilitate eventual penetration of the portion  70 . It is noted that the advancing end of the punch  68  could be flat or concave, rather than as the truncated cone  72 , without departing from the spirit and scope of the invention. 
     As shown in FIG. 10, the punch  68  is moved through the passage  38  of the assembled rivet  30  and, in the process, pushes or punches a punched plug  74  of the workpiece  54 , which was formerly the portion  70  of the workpiece located within the passage of the rivet. With continued movement of the punch  68 , the plug  74  is moved away from the workpiece  54  and the assembled rivet  30 . The portion  70  of the workpiece  54  can also be removed by drilling through the passage  38  of the rivet  30  without departing from the spirit and scope of the invention. 
     The punch  68  is then removed and, as shown in FIG. 11, a rotating and axially-advancing feed screw  76 , having a pin, formed as a threaded mandrel  78 , at an advancing end thereof, is positioned to move the threaded mandrel into the passage  38  of the assembled rivet  30 . Upon continued axial advancement and rotation, a wall of the passage of the rivet  30  is thereby threaded or furrowed, to create a threaded or form fitting connection with the mandrel  78 . 
     Thus, the wall of the passage  38  forms the attachable portion of the self-piercing rivet  30 . 
     The abutment  60  is then positioned on the metal sheet  50  and, as shown in FIG. 12, the screw  76  and the mandrel  78  are withdrawn in the direction of the arrow  80 . During this action, the rivet  30  is drawn against the retaining force of the abutment  60 , whereby the rivet is extracted from the riveted joint, and the two metal sheets  50  and  52  are separated. 
     In this process, there is little chance that the metal sheet  50 , adjacent the abutment  60 , and the metal sheet  52  will be deformed, with only a limited degree of damage to the two metal sheets occurring at the seat of the rivet  30 . The remaining area of the two metal sheets  50  and  52  remain unaffected by the removal process. 
     The solid connection created by the threading or furrowing between the threaded mandrel  78  and the self-piercing rivet  30  prevents the mandrel from being torn out of the rivet, with the result that the rivet is finally extracted from the riveted joint completely. 
     An enlarged illustration of the threaded mandrel  78  in its form-fitting connection with the self-piercing rivet  30  is illustrated in FIG.  13 . 
     Referring to FIG. 14, in another embodiment of the present invention, a punch  80  or tappet is formed forward of the threaded mandrel  78 , and serves to punch or push the slug  74  (FIG. 10) from the assembled workpiece and rivet  30 , immediately preceding the threaded or furrowed attachment of the mandrel with the rivet. 
     As shown in FIG. 15, in still another embodiment of the present invention, a drill bit  82  is formed forward of the threaded mandrel  78 , and serves to drill through the portion  70  (FIG. 9) of the workpiece  54  and through the passage  38  of the rivet  30 , immediately preceding the threaded or furrowed attachment of the mandrel with the rivet. 
     Referring to FIG. 16, a device  84 , according to the invention, is provided for extracting the rivet  30 . To determine the path covered by the threaded mandrel  78 , with the punch  80  or the drill bit  82  forward thereof, the device  84  includes a measuring a measuring device  86 . The measuring device  86  is positioned in such a way that measurement of the rotating and pulling movements of the clamping jaws  64  or the feed screw  76  can be attained, so as to provide information on the specific movement executed by the threaded mandrel  78 . A control circuit is connected between the measuring device  86  and a drive (not shown) of the device  84 , and can provide process data on the device  84  by way of other sensors and can thereby assure a reliable and precise process for the extraction of the self-piercing rivet  30 . 
     Referring to FIG. 17, the mandrel  78 , with the punch  80 , is shown with the device  84 . 
     In general, the above-identified embodiments are not to be construed as limiting the breadth of the present invention. Modifications, and other alternative constructions, will be apparent which are within the spirit and scope of the invention as defined in the appended claims.