Abstract:
A method for setting blind rivet elements in which the setting of the respective blind rivet element introduced into a pre-hole of the work piece and/or the formation of a rivet collar takes place in a setting stroke (SH) through the permanent deformation of a section of the blind rivet element by subjecting an end of the blind rivet element to a traction force by a traction element of a setting tool while simultaneously supporting another end of the blind rivet element on a support part of the setting tool counter to the traction force.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a method for setting blind rivet elements in which the setting of the respective blind rivet element introduced into a pre-hole of the work piece and/or the formation of a rivet collar takes place in a setting stroke (SH) through the permanent deformation of a section of the blind rivet element by subjecting an end of the blind rivet element to a traction force by means of a traction element of a setting tool while simultaneously supporting another end of the blind rivet element on a support part of the setting tool counter to the traction force. Prior to forming the rivet collar the state of the disposition of the respective blind rivet element on the setting tool and/or the distance corresponding to this state between the blind rivet element and the tool support part is detected. The invention also relates to a setting tool for processing or setting the blind rivet elements. 
     Blind rivet elements, according to the invention, are primarily blind rivet nuts, but can also be other normally used blind rivet elements, such as blind rivets and blind rivet bolts. 
     The setting of blind rivet elements, according to the invention, means securing the respective blind rivet element introduced into a pre-hole of a work piece by riveting, i.e. by forming a rivet collar by applying a traction force through a traction element, through a traction mandrel to an area or an end of the blind rivet element that is remote from the rivet flange of the blind rivet element on which the blind rivet element is supported on a tool support part during setting. The rivet collar is formed through permanent deformation of a rivet element section. The rivet collar secures the blind rivet element against being pressed out and/or twisting in the work piece. 
     Setting of blind rivet elements in the form of blind rivet nuts takes place with the spin-pull method. In accordance with the spin-pull method the respective blind rivet nut is screwed with its nut or inner thread formed on one end of the blind rivet nut body onto the outer thread of a traction mandrel, i.e. by spinning it on. Securing of the blind rivet nut inserted into a pre-hole of a work piece takes place by pulling the traction mandrel while simultaneously supporting the blind rivet nut on the tool support part with its blind rivet nut end or rivet flange that is remote from the inner thread, namely deforming the rivet collar from a section of the blind rivet nut body not received in the pre-hole. Pulling of the traction mandrel takes place either until a pre-defined traction force is reached or until a pulling distance (setting stroke) defined by at least one stop is reached. Upon reaching the complete setting stroke, or the traction force, the traction mandrel is screwed out of the inner thread of the set blind rivet nut. 
     A frequent cause for faulty setting of blind rivet nuts in work pieces exists in the case of manual processing, but also in the case of automatic processing due to the fact that the traction mandrel is not completely screwed into the respective blind rivet nut, i.e. spinning of the blind rivet nut onto the traction mandrel is incomplete, namely so that the blind rivet nut and the rivet flange have an axial distance from the tool support part that exceeds a pre-defined tolerance range and/or the traction mandrel is received with its threads only partially in the inner thread of the blind rivet nut. During the setting process, i.e. during pulling of the traction mandrel, this produces first a pre-stroke, which takes place without deformation of the blind rivet nut body and in which the blind rivet nut is only brought to bear against the tool support part. If the maximum stroke of the traction spindle is pre-defined by at least one stop, the actual setting stroke available for setting is reduced, namely with the result that the actual setting stroke or the actual pulling distance is not sufficient for correct formation of the rivet collar. Furthermore, the incorrect or incomplete spinning on of the respective blind rivet nut onto the traction mandrel has the disadvantage that the latter engages with only a reduced axial length in the inner thread of the blind rivet nut, resulting in stripping or damage to said inner thread, namely in particular also if the maximum stroke or pulling distance of the traction mandrel is not limited by stops, but instead the setting process is controlled by the traction force exerted on the respective blind rivet nut. 
     Equivalent or similar problems also occur during setting of other blind rivet elements, which during blind riveting likewise are secured in the work piece with their rivet flange bearing against a tool support part by the traction force exerted by a traction element of the blind rivet tool to a traction mandrel or rivet mandrel of the blind rivet element, thus forming a rivet collar. Here again in case of incorrect disposition of the respective rivet element on the blind riveting tool, i.e. in case of a distance between the rivet flange and the tool support part exceeding a pre-defined tolerance range, this will result at least in incomplete formation of the rivet collar. 
     Up to now, incorrectly set blind rivet elements must be removed and/or repaired in a time-consuming process. 
     It is an object of the invention is to present a method that avoids the aforementioned disadvantages and in which the setting process is discontinued or paused or a correction of the setting stroke takes place in advance, i.e. before actual setting, if the respective blind rivet element is not correctly disposed on the blind riveting tool, i.e. its distance from the tool support part exceeds a pre-defined tolerance range. 
     SUMMARY OF THE INVENTION 
     A special characteristic of the blind riveting tool is that the respective setting stroke is variable, preferably continuously variable and/or variable by means of a motor-actuated end stop. This embodiment offers the fundamental advantage that the same riveting or setting tool can be used to process different blind rivet elements, especially also in case of different work piece or sheet metal thicknesses. Preferably, the setting stroke is variable in a program-controlled manner. 
     Further embodiments, advantages and possible applications of the invention are disclosed by the following description of exemplary embodiments and the drawings. All characteristics described and/or pictorially represented, alone or in any combination, are subject matter of the invention, regardless of their being summarized or referenced in the claims. The content of the claims is also included as part of the description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is described in the following based on exemplary embodiments for setting blind rivets. The invention is illustrated in the drawings, where: 
         FIG. 1  shows a schematic representation of a work piece manufactured from a flat material, for example from a flat metal material or metal sheet, together with a blind rivet nut in the initial state and in the riveted or set state; 
         FIG. 2  shows an enlarged schematic partial representation of the blind rivet nut set in the work piece, together with the traction mandrel and the tool support part of a blind rivet or setting tool for the spin-pull method; and 
         FIG. 3  shows a schematic functional representation of the setting tool, together with a monitoring and electronic control circuit. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the drawings, a work piece  1  is manufactured from a flat metal material, e.g. from sheet steel or sheet aluminum, with a pre-hole  2 . Into the pre-hole  2 , a blind rivet nut  3  is inserted, which is shown in  FIG. 1  at the left in its not yet deformed state that it has, immediately after insertion or introduction into the pre-hole  2 , and which is shown in  FIG. 1  at the right in its deformed or riveted or set state. The blind rivet nut  3  is manufactured from a metal material, for example, from steel or aluminum, and consists in the manner known to persons skilled in the art essentially of a sleeve-like blind rivet nut body  4  having a continuous opening  5  disposed on the same axis with the axis BA of the blind rivet nut  3  and having a rivet flange  6  radially protruding over the outer surface of the blind rivet nut body  4  on the upper end of the blind rivet nut  3  as shown in  FIG. 1 . body  4 , which is cylindrical in shape on the outer and inner surface, comprises essentially two sections, namely the section  4 . 1  that is remote from the flange  6  and on which the opening  5  is provided with a nut or inner thread  7 , and the section  4 . 2 , which merges into the rivet flange  6  and in which the opening  5  is threadless and is embodied with an enlarged cross section. In riveted or set state, the blind rivet nut  3  lies with its rivet flange  6  against the one work piece side  1 . 1  of the work piece  1 , which as depicted in  FIG. 1  is the top side. The section  4 . 2  not received in the pre-hole  2  is, in the manner depicted in  FIG. 1  at the right, permanently deformed into a bead-shaped rivet collar  8  enclosing the axis BA in a ring-like manner, the rivet collar is pressed against the other work piece side  1 . 2  of the work piece, so that the blind rivet nut  3  is secured in the work piece  1  all the way around in the area of the pre-hole against being pressed out or turned or twisted in the work piece  1 . Since the wall thickness of the blind rivet nut body  4  in the section  4 . 2  is reduced, the defined deformation of the blind rivet nut body  4  to form the rivet collar  8  takes place in this area not received in the pre-hole  2 . 
     The setting tool  9  comprises a traction mandrel  11  provided on one end with a thread  10  and a tool head  13  enclosing the traction mandrel  11 , the tool head  13  forms a ring-shaped support part enclosing the traction mandrel  11 . 
     In detail, the setting of the respective blind rivet nut  3  takes place according to the spin-pull method. As such, the blind rivet nut  3  provided at a pick-up position (not depicted) is screwed or spun with the inner thread  7  onto the thread  10  of the traction mandrel  11  by turning the traction mandrel  11  disposed on the same axis as the axis BA and inserted by the rivet flange  6  into the opening  5 , namely so that the blind rivet nut  3  in the end ideally bears with the side of the blind rivet nut body  4  that is remote from the thread  7  and/or with the rivet flange  6  against the support part  13  of the tool body  12 . Held in this manner on the setting tool  9 , the blind rivet nut  3  is inserted into the pre-hole  2  so that the rivet flange  6  bears against the work piece side  1 . 1 . Turning of the traction mandrel  11  during spinning on takes place by means of a rotary drive  14 , which is depicted schematically in  FIG. 3 . After insertion of the blind rivet nut  3  into the work piece  1 , the setting takes place through relative movement between the traction mandrel  11  and the tool head  13 , namely in the manner that with the tool head  12  bearing against the rivet flange  6 , a traction force is exerted via the traction mandrel  11  on the end of the blind rivet nut body  4  provided with the thread  7 , therefore deforming the section  4 . 2  to form the rivet collar  8 . 
     Due to tolerances and also due to the deformability of the blind rivet nut  3  and/or of the work piece  1 , in many cases, a relative movement between the traction mandrel  11  and the tool body  12  and/or the tool head  13  takes place in the form of a small pre-stroke VH prior to the actual setting and/or deformation of the section  4 . 2  to form the rivet collar  8 . The relative movement between the traction mandrel  11  and the tool body  12  and/or the tool head  13  needed for setting the blind rivet nut  3  is achieved by means of a drive  15  acting between these tool parts, e.g. in the form of at least one piston-cylinder arrangement or a hydraulic cylinder, indicated schematically in  FIG. 3 . 
     To ensure correct formation of the rivet collar  8  and in particular also to prevent stripping of the inner thread  7  due to excessively high traction forces exerted by the traction mandrel  11  during setting it is common to limit the distance of the setting stroke SH and/or the traction force exerted by the traction mandrel  11  to a pre-defined value. 
     Especially if the drive  15  consists of a piston-cylinder arrangement, for example a hydraulic cylinder, the maximum setting stroke SH is pre-defined by corresponding stops. 
     In the case of manual processing of the blind rivet nuts  3 , the respective setting tool  9  is designed as a manually operated tool, and also in automated processing of the blind rivet nuts  3 , the setting tool  9  is part of a production system or a work station of such a system, it cannot be ruled out that blind rivet nuts  3  are to some extent spun insufficiently onto the traction mandrel  11 , so that their rivet flange  6  is still at a distance from the tool head  13 . 
     If, after being spun on the distance between the rivet flange  6  and the tool head  13  is greater than a pre-defined tolerance range, this results in a larger pre-stroke VH and therefore a reduction of the setting stroke SH available for setting. 
     The insufficient spinning on of the blind rivet nut  3  onto the traction mandrel  11  and/or the thread  10  there and the resulting increased pre-stroke VH cause the rivet collar  8  to be formed incorrectly, which means that the anchoring of the blind rivet nut  3  in the work piece  1  is faulty. Furthermore, the insufficient spinning of the blind rivet nut  3  onto the traction mandrel  11  causes the thread  10  to engage in the inner thread  7  only over a shortened axial length so that it becomes stripped during pulling and/or deformation of the section  4 . 2 . In current practice, such an incorrectly set blind rivet nut  3  must be removed from the work piece  1  in a time-consuming repair procedure and replaced by a correctly set blind rivet nut  3 . This disadvantage is avoided by the electronic monitoring and control circuit  16  with a processor  17  as depicted in  FIG. 3  and allocated to the setting tool  9  and comprising at least the following: 
     a sensor  18  that measures the path of the relative movement between the traction mandrel  11  and the tool body  12  and sends a measuring signal based on this path to the processor  17 ; 
     a pressure sensor  19  that serves to measure the hydraulic pressure present at the drive  15  and/or in a cylinder chamber there and sends a corresponding measuring signal to the processor  17 ; 
     a control valve arrangement  20  that is controlled by the processor  17 , namely for control of the drive  15  and/or for controlling the pneumatic or hydraulic pressure medium, e.g. hydraulic oil, supplied to said drive via a hose  21 ; 
     an interface arrangement  22  by means of which data transfer takes place between the processor  17  and the sensors  18  and  19  and the control valve arrangement  20  and which also serves as an external connection for data traffic with other peripheral devices and/or for controlling other functional units of the setting tool  9  or a system comprising said setting tool. 
     The monitoring and control apparatus  16 , by detecting the spinning-on state of the respective blind rivet nut  3 , allows different methods for preventing incorrect setting of the respective blind rivet nut  3 , namely either by interrupting or stopping the setting process or by correcting the size of the setting stroke SH and/or the traction force exerted on the traction mandrel  11  during setting based on the detected pre-stroke VH. The latter can then be detected or measured directly by the sensor  18  or indirectly by the drive  15  and/or the at least one piston-cylinder arrangement forming said drive being subjected to the highly pressurized pressure medium or hydraulic oil one time or several times consecutively by temporary opening of the control valve arrangement  20  and then measuring, with the pressure sensor  19 , the respective pressure at the drive  15  and, based on this pressure, calculating the size of the pre-stroke VH in the processor  17 . 
     In detail, the following operating methods are possible: 
     1. After inserting the respective blind rivet nut  3  into the pre-hole  2 , upon triggering of the setting process and/or in a detection phase, a traction force is first exerted via the drive  15  on the traction mandrel  11 , which (force) is reduced so far that it does not yet cause deformation of the blind rivet nut  3 . If the blind rivet nut  3  is only insufficiently spun onto the traction mandrel  11 , this results in an enlarged pre-stroke VH in the form a relative movement between the traction mandrel  11  and the tool head  13 , relative movement is detected by the sensor  18 . If the relative movement or the pre-stroke VH exceeds a pre-defined tolerance range, the setting process is stopped before deformation of the blind rivet nut  3  and/or formation of an insufficient rivet collar  8  occurs. The blind rivet nut  3  is then either spun onto the traction mandrel  11  correctly in a follow-up process or it is replaced by another blind rivet nut  3  that is correctly spun onto the traction mandrel  11 . Implementation of this method requires only the position sensor  18  or a corresponding position measuring system. 
     2. Further, it is possible to design the sensor  18  as a switch or microswitch, which is then actuated if, after triggering of the setting process initially with low force, due to the distance between the rivet flange  6  of an insufficiently spun on blind rivet nut  3  and the tool support part  13  the relative movement between the traction mandrel  11  and the tool body  12 , i.e. the pre-stroke VH, exceeds a value that is outside of the permissible tolerance range. After triggering of the switch the setting process is likewise stopped. The design of the sensor  18  as a switch has the special advantage that said switch can be used to stop the setting process directly, therefore allowing a purely mechanical, pneumatic or hydraulic control without electronics, i.e. without the processor  17 . 
     3. Further, it is possible to subject the traction mandrel  11  and/or the drive  15  for a short defined time to the full force or with the full pressure of the pressure medium in the hose  21 , namely until reaching a pre-defined pressure monitored by the pressure sensor  19  that is not sufficient to deform the blind rivet nut  3  inserted into the pre-hole  2  and/or to form a rivet collar  8 . The path of the relative movement occurring during this time between the traction mandrel  11  and the tool head  12  is likewise detected and constitutes a measure for the incomplete spinning on of the blind rivet nut  3  and for the axial distance between the rivet flange  6  and the tool support part  13 . For pressure monitoring, the pressure sensor  19  or a load cell or a strain gauge can be used. The path is again detected by the sensor  18 ; other analog or digital position measuring systems or one or more electric switches, for example microswitches, can be used to detect the relative movement between the traction mandrel  11  and the tool body  12  and/or for detecting the pre-stroke VH. If said pre-stroke VH exceeds a pre-defined tolerance range, the setting process will again be stopped. 
     4. It was assumed above that based on the pre-stroke VH detected directly or indirectly in a detection phase the setting process is executed within a pre-defined tolerance range or discontinued outside a pre-defined tolerance range. Generally, it is also possible to correct the setting stroke SH based on the detected pre-stroke VH, i.e. to increase it, in the manner that the actually executed, corrected setting stroke SH is the sum of the detected pre-stroke VH and a pre-defined setting stroke, which is defined by the type of blind rivet nuts  3  used and in particular also by the thickness of the respective work piece  1 . If the size or the maximum path of the relative movement generated with the drive  15  between the traction mandrel  11  and the tool body  12  is defined by stops, then the correction of the setting stroke takes place for example by motorized adjustment of these stops. Further, the correction of the setting stroke SH can also be achieved by constant monitoring of the relative movement between the mandrel  11  and the tool body  12  with the sensor  18  or another position measuring system and/or constant monitoring of the pressure of the pressure medium and therefore of the traction mandrel  11  with the sensor  19  and after reaching pre-defined values corresponding to the corrected setting stroke, the drive  15  is immediately switched off by the processor  19 , by closing the control valve arrangement  20 . Prerequisite, yet at least expedient for this method, is that the correction of the setting stroke takes place only if the pre-stroke VH first detected after initiation of the setting process in the detection phase is within a tolerance range that ensures that the traction mandrel  11  engages with its thread  10  at least over such an axial length in the inner thread  7  of the blind rivet nut  3 , the axial length reliably prevents stripping of the inner thread  7  at the traction force exerted by the traction mandrel  11  necessary for correct forming of the rivet collar  8 . 
     The invention was described above based on exemplary embodiments. Of course, numerous modifications and adaptations are possible, without abandoning the underlying idea upon which the invention is based. All embodiments or methods have in common that at the start of the respective setting process, the state of the spinning of the respective blind rivet nut onto the traction mandrel  11  is detected in a detection phase and then, based on this state, the setting process is executed or interrupted or the setting stroke is corrected. 
     Different methods for setting blind rivet nuts  3  are described above. It goes without saying that the invention is not limited to blind rivet nuts, but refers in general to blind rivet elements, for example also to blind rivet bolts. 
     REFERENCE LIST 
     
         
         
           
               1  work piece 
               1 . 1 ,  1 . 2  work piece side 
               2  pre-hole 
               3  blind rivet nut 
               4  blind rivet nut body 
               4 . 1 ,  4 . 2  section of blind rivet nut body 
               5  opening of blind rivet nut 
               6  flange of blind rivet nut 
               7  inner thread of blind rivet nut 
               8  rivet collar 
               9  tool 
               10  threads 
               11  traction mandrel 
               12  tool body 
             tool head 
               14  drive for spinning on the blind rivet nuts 
               15  drive for producing an axial relative movement between traction mandrel  11  and tool body  12   
               16  monitoring and control apparatus 
               17  processor 
               18  sensor for position measurement 
               19  pressure sensor 
               20  control valve arrangement 
               21  hose for hydraulic medium or hydraulic oil under operating pressure 
               22  interface arrangement 
             BA blind rivet nut axis 
             VH pre-stroke 
             SH setting stroke