Abstract:
An apparatus is proposed for connection of workpieces using the friction stir welding method, with a shaft ( 33, 33 ′) which can be driven such that it rotates and at whose end remote from the drive end of the shaft a pin-like projection ( 8 ) is arranged, at whose end a first stop, which is formed by a first shoulder ( 6 ), is arranged, with the first shoulder having a diameter which is larger than the diameter of the pin-like projection ( 8 ), and with a second stop ( 7, 7 ′), which is formed from a second shoulder and is arranged such that the workpieces ( 19 ) to be connected can be enclosed between the stops ( 6, 7, 7 ′), in that at least one of the stops can be moved translationally in order to enclose the workpieces ( 19 ) with a predetermined force in the direction of the other stop.

Description:
RELATED APPLICATIONS  
       [0001]     This Application claims priority of German Application Serial No. DE 10 2004 028 553.5, filed Jun. 15, 2004, which is hereby incorporated by reference herein.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The invention relates to an apparatus for connection of workpieces using the friction stir welding method with a shaft which can be driven such that it rotates and at whose end remote from the drive end of the shaft a pin-like projection is arranged, at whose end a first stop, which is formed by a first shoulder, is arranged, with the first shoulder having a diameter which is larger than the diameter of the pin-like projection, and with a second stop, which is formed from a second shoulder and is arranged such that the workpieces to be connected can be enclosed between the stops, in that at least one of the stops can be moved translationally in order to enclose the workpieces with a predetermined force in the direction of the other stop.  
         [0004]     2. Discussion of Prior Art  
         [0005]     An apparatus of this type is known (EP-B-0 615 480 and DE-C-199 57 136). Friction stir welding, a further development of friction welding and also widely known as FSW, has fundamentally been known for several years and has repeatedly been developed further.  
         [0006]     Originally, friction welding was carried out by moving two workpieces which are intended to be connected to one another by friction welding against one another in the desired connecting area, pressing them against one another with a force which can be preset in the process. The heat created by the friction in the end results in the material of the workpieces being plasticized in the connecting area. Once the material has been sufficiently plasticized, adequate thorough mixing of the materials of the two workpieces can take place at least in the area of the connection close to the surface, so that the desired welded joint is formed between the two workpieces as they cool down.  
         [0007]     In the case of friction stir welding, there is no need for any relative movement between the workpieces in order to produce the friction and the thorough mixing of the materials. Instead of this, a pin-like projection or a cylindrical projection, which is caused to carry out a sufficiently large rotation by a drive or a motor, is placed against the end area of two workpieces which are to be connected and are located such that they abut against one another or overlap one another. With suitable guidance, as can be provided, for example, by means of a specific guide apparatus or else by a robot, the pin-like projection is additionally caused, for example, to carry out a translational movement along the abutting edges of the two workpieces to be connected. The workpieces are prevented from escaping from one another by means of a robust, static opposing bearing.  
         [0008]     Once the material of the workpieces has been sufficiently plasticized after the start of the welding process by the friction heat that is produced in the adjacent material area as a consequence of the rotation of the pin-like projection with the material of the workpieces, the translational movement is carried out along the bead profile between the two workpieces while maintaining the rotational movement of the pin-like projection, thus forming, for example, a longitudinal bead.  
         [0009]     With regard to the apparatus of this generic type according to EP-B-0 615 480, the workpieces are held together by means of the known apparatus in the area around the abutting edge and the weld bead that is formed by means of two stops with a larger diameter than the pin-like projection, by the pin-like projection being enclosed between the two stops. Those faces of the two stops which face one another effectively form shoulders which each cover the surfaces of both workpieces to be connected in a rotating form on one face of the workpieces around the area of the weld bead that is to be formed. If, by way of example, pressure is exerted by means of the apparatus orthogonally with respect to the surface of the two workpieces to be connected, the contact pressure on the side of the workpieces to be connected which faces away from the pressure is reduced, corresponding to the shoulder there on the basis of the rigid separation between the two shoulders of the two stops. For this reason, special pressure means must be used with this apparatus in order to provide a suitable opposing bearing, as still possible with acceptable complexity for workpieces such as metal sheets and the like which are flat or in the form of panels, but is normally impossible for complicated welded joints produced by means of the friction stirring method owing to the complicated shapes of the workpieces.  
         [0010]     Furthermore, industrial robots are used for a wide range of functions in many manufacturing areas, for example for motor vehicle construction or aircraft construction, in which it is not only difficult but even often completely impossible to provide flat or other opposing bearings for producing the welded joint and, furthermore, the robots themselves cannot also produce the required pressure forces, or can do so only in a very highly complex manner.  
         [0011]     DE-C-199 57 136 discloses an apparatus in which at least one of the stops for carrying out the welding process can be moved under the influence of the workpieces and can be enclosed with a force that can be predetermined. This makes it possible for the apparatus itself to apply the necessary pressure to both faces of the workpieces to be connected without any opposing bearing being required. Thus, even in the case of complicated workpieces, it is possible to produce weld beads, for example weld beads which run in three dimensions in space, without any substrate being required, which in the past would have had to secure the root of the weld bead, and would at the same time have had to support the workpieces. This makes it possible to avoid the handling system having to apply the force to the workpieces to be connected.  
         [0012]     In order to achieve this, a linear-movement cylinder is provided on the apparatus, connected to the rotation shaft, which linear-movement cylinder produces a translational movement when a hydraulic medium is applied appropriately, thus applying the force to the workpieces to be connected.  
         [0013]     Since the rotation shaft is directly connected to the piston and runs through it, seals are necessary at the ends of the piston. The seals, causing sliding friction during rotation, have the effect of introducing considerable heat into the apparatus. Furthermore, they influence in particular the ability of the rotation piston to perform translational movement in the cylinder. On account of cogging effects thereby produced, extremely small translational stepping increments cannot be achieved.  
       OBJECTS AND SUMMARY OF THE INVENTION  
       [0014]     The invention is based on the object of improving the abovementioned apparatus such that the translational capability of the rotational shaft is improved.  
         [0015]     The object is achieved according to the invention, in that the rotation of the shaft and the movement which produces the force are produced in the apparatus, and are introduced into the workpieces to be produced such that they are decoupled and are not influenced by one another. This considerably reduces the translational breaking-free forces, thus allowing accurately controllable starting of the translational movement process. Yield stresses which occur in particular at low rotation speeds in the translational system, and which occur suddenly when the breaking-free force is exceeded, are thus reduced, thus suppressing temperature peaks in the workpieces to be connected, so that friction stir welding can be used for connecting components for which this was not possible on account of the aforementioned problems.  
         [0016]     According to a further teaching of the invention, the second stop may be designed such that it can be fixed or likewise such that it can be rotated. In the case of rotation, the stop may rotate in the same sense or in the opposite sense. In this way, moments or temperatures can be optimally set at the surfaces of the workpieces to be connected.  
         [0017]     Rotation in the opposite sense makes it possible to set the temperature precisely so that there is no temperature gradient between the faces. The hotter face on the top of the metal sheet is opposite the cold face on the bottom of the metal sheet during rotation in opposite senses, and vice versa, so that the temperatures are immediately equalized by means of a thermal short circuit through the metal sheet. This makes it possible for thin workpieces in particular to be processed well. Furthermore, the moments which are produced by the different rotation directions also virtually cancel one another out, so that the forces and moments on a handling system for the apparatus are reduced, since the apparatus has a neutral behavior externally in this context.  
         [0018]     A further teaching of the invention provides for one component of the apparatus according to the invention to be a drive module. In this case, the drive module itself produces the rotation and the translational movement of the at least one shoulder and of the at least one stop. The provision of a drive module which produces the two types of movement separately from one another ensures that the apparatus has a simple design. A further teaching of the invention provides for the shaft, which is a component of the drive module, to be mounted on roller bearings in the apparatus in such a way that an accurate translational movement capability is ensured at high rotation speeds and when high torques have to be transmitted, thus allowing very small translational displacement movements with the full rotational load.  
         [0019]     Furthermore, one teaching of the invention provides for the apparatus to have a basic module. The basic module has a holder for the drive module. According to a further teaching of the invention, a roller bearing is provided in the basic module, acting as a bearing for the shaft while maintaining the translational movement capability. The basic module and the drive module are in this case connected via a linear guide which, for example, is a linear bearing. The linear bearing ensures that the translational movement is guided as accurately as possible and that the lateral forces that are produced during the welding process do not act either on the rotational drive or on the translational drive, and thus cannot damage them. Furthermore, the invention provides for an element which produces the translational movement, is positioned between the drive module and the basic module and/or is connected to the drive module and the basic module to be arranged between the basic module and the drive module. This element is a linear-movement cylinder or, alternatively, a linear-movement cylinder system. The linear-movement cylinder system is controlled electrohydraulically and, if two or more cylinders are used, is coupled electronically or in some other suitable manner in order to ensure synchronous running, in which case it is advantageous to provide a stepping motor for this control process. The connection of the two modules via the movement system which produces the translation and can be moved with a controlled force allows the variable force to be maintained as exactly as possible.  
         [0020]     A connection for a handling system is provided on the basic module itself and produces a feed movement along those areas of the workpieces to be connected. One such handling system is advantageously a robot. In this case, the robot itself only has to provide the feed movement and need no longer produce any forces for the joining of the workpieces, nor need it absorb any reaction torques, since the rotation and translation are produced in the apparatus and the torques which result from the movement constraint are fully compensated for.  
         [0021]     A further teaching of the invention provides for the shaft itself to be driven rotationally via a synchronous motor. A synchronous motor allows the rotation speeds to be controlled optimally. Furthermore, the shaft and rotation drive can be connected to one another via a direction-changing gearbox. The direction-changing gearbox allows the drive to be arranged as freely as possible, thus allowing the apparatus to be handled easily.  
         [0022]     In order to allow the forces that act on the workpieces to be controlled as accurately as possible, a further teaching of the invention provides for a sensor or a sensor system to be provided for recording the force acting on the workpieces to be connected. This sensor is arranged such that it acts on the basic module, for example between the second shoulder or second stop and the drive module. The sensor is itself connected to an apparatus controller. In order to achieve good measurement accuracy, the sensor is itself prestressed. A sensor such as this is preferably a piezoelectric measurement washer, which is installed in a prestressed form for fixing purposes and for protection against being destroyed by tensile loads.  
         [0023]     From a further teaching of the invention, the second stop is arranged either on the basic module or on the drive module. If the second shoulder or the second stop is arranged on the drive module, it is possible to drive the shoulder or the stop such that it rotates. A second rotation drive is provided for this purpose. In order to likewise achieve low breaking-free forces for the movement of the second shoulder or of the second stop, the latter is likewise provided with roller bearings.  
         [0024]     A further teaching of the invention provides that the second shoulder or the second stop can be driven such that it can rotate about a hollow shaft. In this case, the rotation shaft for the first shoulder or the first stop is guided in the hollow shaft. This allows a simple design.  
         [0025]     The two rotation drives mean that a suitable controller can be used to set different rotation speeds for the shoulders or the stops, thus in turn making it possible to optimally set the temperatures to be introduced, and their distributions.  
         [0026]     Other aspects and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments and the accompanying drawing figures. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING FIGURES  
       [0027]     A preferred embodiment of the invention will now be described in detail with reference to the following schematic drawings, in which:  
         [0028]      FIG. 1  shows a perspective illustration of the apparatus according to the invention,  
         [0029]      FIG. 2  shows a perspective illustration of the basic module of the apparatus according to the invention,  
         [0030]      FIG. 3   a  shows a plan view of the apparatus according to the invention,  
         [0031]      FIG. 3   b  shows a section illustration of the apparatus according to the invention along the line A-A in  FIG. 3   a,    
         [0032]      FIG. 4   a  shows a side view of the basic module,  
         [0033]      FIG. 4   b  shows a section illustration of the basic module of the apparatus according to the invention along the line D-D in  FIG. 4   a,    
         [0034]      FIG. 5   a  shows a view from underneath of the basic module of the apparatus according to the invention,  
         [0035]      FIG. 5   b  shows a section illustration through the basic module along the line B-B in  FIG. 5   a,    
         [0036]      FIG. 5   c  shows a section view through the basic module of the apparatus according to the invention along the line C-F in  FIG. 5   a,    
         [0037]      FIG. 5   d  shows an enlargement of a detail from  FIG. 5   c,    
         [0038]      FIG. 6   a  shows a plan view of the apparatus according to the invention,  
         [0039]      FIG. 6   b  shows a section view through the drive module of the apparatus according to the invention along the line H-F in  FIG. 6   a,    
         [0040]      FIG. 6   c  shows a section view through the apparatus according to the invention along the line G-N in  FIG. 6   a,    
         [0041]      FIG. 6   d  shows a section view through the drive module of the apparatus according to the invention along the line O-R in  FIG. 6   b,    
         [0042]      FIG. 6   e  shows an enlarged illustration of an area x in  FIG. 6   b,    
         [0043]      FIG. 7  shows a schematic section view through a further embodiment of the apparatus according to the invention, and  
         [0044]      FIG. 8  shows an outline sketch of the heat distribution within the workpieces to be connected, in an alternative embodiment of the apparatus according to the invention. 
     
    
       [0045]     The drawing figures do not limit the present invention to the specific embodiments disclosed and described herein. The drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the preferred embodiment.  
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0046]      FIG. 1  shows a welding apparatus according to the invention for friction stir welding  1 . The apparatus  1  comprises a basic module  2  and a drive module  3 , and is connected to a handling apparatus  17 . The handling apparatus  17  is, for example, a robot.  
         [0047]     The apparatus  1  has a double-shoulder tool  5 , which comprises a pin  8 , a first shoulder  6  which is fitted such that it is secured to the pin  8 , and a second shoulder  7 ,  7 ′ which is provided on the basic module  2  or on the drive module  3 . The double-shoulder tool  5  is inserted into a tool holder  20 .  
         [0048]     The drive module  3  has a tool drive  12  which drives a shaft  33 ,  33 ′ which is provided in a spindle bearing  14 , via a direction-changing gearbox  13 . The drive module  3  and the baseplate  2  are connected to one another via linear bearings  11 . As can be seen from  FIG. 2 , the linear bearing  11  comprises a precision shaft  21  with a stop  22  on the side facing the drive, and with a stop  30  on the side of the linear bearing  11  facing the tool.  
         [0049]     The linear bearing  11  allows a translational movement of the drive module  3  with respect to the basic module  2 . The drive is provided via a linear-movement drive  10 , which is connected to a stepping motor  9  in order to control it. The stepping motor  9  and the tool drive  12  have drive connections  15 , which supply the appropriate power to the motors  9 ,  12 . As can be seen from  FIG. 2 , the basic module  2  has a connection  4  in order to connect the welding apparatus  1  to the handling apparatus  17 . The connection  4  is provided with a centring journal  18 , via which the connection can be made. The tool holder  20  is arranged on a baseplate  25 . Measurement sensors  23  are arranged between the baseplate  25  and a base  16  of the basic module  2  and have a measurement sensor connection  24 , via which they are connected to a sensor data processing system and/or to a sensor data amplification system and an apparatus controller.  
         [0050]     The apparatus  1  is controlled via a system of drive controllers which can operate in real time and combine motion control and PLC functionality. Communication with the controllers for the handling system  17  and with higher-level control systems as well is possible by virtue of a free programming capability and access to analogue/digital inputs/outputs, as well as the capability for linking to various fieldbus systems.  
         [0051]     The tool holder  20  has a roller bearing  26 , as can be seen in  FIG. 4   b.    FIG. 4   b  shows a section view along the line D-D, which is shown in  FIG. 4   a.  A holder (shaft guide  47 ) for the shaft  33  is provided within the roller bearing  26  (see  FIG. 5   a ).  
         [0052]      FIG. 5   b  shows a section illustration along the line B-B in  FIG. 5   a , illustrating how the linear bearing  11  is screwed to the base  16  of the basic module  2 . The shaft  21  is in this case additionally secured by the stop  30  on the base  16 . At the opposite end of the shaft  21 , the stop  22  is mounted detachably on the shaft  21  by means of a cylindrical bolt  31 .  
         [0053]      FIG. 5   b  likewise shows the arrangement of the measurement sensors  23 .  FIG. 5   c  provides a section illustration through the area of the measurement sensors, running along the line C-F in  FIG. 5   a . The baseplate  25  and the base  16  of the basic module  2  are connected to one another via necked-down bolts  28 . The necked-down bolt  28  runs through the measurement sensor  23 .  FIG. 5   d  provides an enlarged illustration of the area of the baseplate  25 , of the base  16  and of the measurement sensor  23  arranged between them. The necked-down bolt  28  is in this case arranged in a centring bush  29 . The centring bush is located centrally in the measurement sensor  23 .  
         [0054]      FIGS. 6   a  to  6   e  show the design of the drive module  3 .  FIG. 6   a  shows a plan view of the drive module  3 , which has a drive module baseplate  35  that is provided with holes  34 . The precision shafts  21  are introduced into the holes  34  in order to produce the connection between the drive module  3  and the basic module  2 . A linear ball bearing  36  is provided in the holes  34 , in order to allow the precision shaft  21  to move in the hole  34  with as little friction as possible. This can be seen in  FIG. 6   c , which shows a section along the line G-N through the drive module  3 , as can be seen in  FIG. 6   a . A gearbox flange  37  is attached via centring bolts  38  to the baseplate  35 , as can be seen from  FIGS. 6   b  and  6   d .  FIG. 6   b  shows a section through the drive module  3  along the line A-F, as shown in  FIG. 6   a .  FIG. 6   d  shows a section through the drive module along the line O-R, as illustrated in  FIG. 6   b.    
         [0055]     An intermediate flange  39  is arranged between the stepping motor  9  and the linear-movement drive  10 , and has a clutch  40  in it. The stepping motor  9  acts on the linear-movement drive  10  via the clutch  40 , as can be seen from  FIG. 6   b.    
         [0056]     A claw clutch  41  is provided in the spindle bearing  14 . The claw clutch  41  comprises a clutch upper part  50  and a clutch lower part  51 . The clutch upper part  50  is connected to the shaft  33 ′ via an adjusting spring  48 . The shaft  33  is connected to the clutch lower part  51  via an adjusting spring  49 , as can be seen from  FIG. 6   d . A cap  45  which closes the apparatus at the top is provided at the upper end of the drive module  3 . The cap  45  is fitted to the direction-changing gearbox  13  via centring bolts  44 . The drive module baseplate  35  is provided with a hole in the centre through which the shaft  33  is passed. A bearing plate  46  is arranged in this hole, with a roller bearing  27  arranged in it. The roller bearing  27  is held in the bearing plate  46  via a bearing flange  42  which is connected to the bearing plate  46  via centring bolts  42 ′. The shaft  33  is guided in the roller bearing  27 . A spacing disc  55  is provided in the upper end of the roller bearing  27  and is secured by a fluted nut  53  via a locking plate  54 . The fluted nut  53  is in this case guided about the shaft  33 . The shaft  33  is provided with a flute  52 , as is illustrated enlarged in  FIG. 6   e.    
         [0057]     The gearbox flange  37  represents the outer wall of the spindle bearing  14 , and the gearbox  37  is in this case attached to the direction-changing gearbox  13  via centring bolts  43 .  
         [0058]      FIG. 3   b  illustrates the welding apparatus  1  in the assembled state. The shaft  33  is in this case inserted through the shaft guide  47  in the basic module. This also applies to the linear bearings  11 , in the case of which the precision shafts are passed through the holes  34  in the drive module baseplate  35 .  FIG. 3   b  shows a section along the line AA through the apparatus according to the invention as shown in  FIG. 3   a.    
         [0059]      FIG. 7  illustrates an alternative embodiment of the apparatus according to the invention. In this case, the second shoulder  7 ′ is formed integrally with a hollow shaft  32 . The hollow shaft  32  can be rotated via a further drive, possibly with an intermediate gearbox. The drive and gearbox are not illustrated.  
         [0060]     A roller bearing  26 ′ is provided between the shaft  33  and the hollow shaft  32 , and guides the shafts with respect to one another. The hollow shaft  32  is in this case guided by a roller bearing  26  in the welding apparatus. Both the hollow shaft  32  and the shaft  33  can be moved translationally in order to apply the necessary force to the workpieces to be connected, for friction stir welding. The rotation of the second shoulder  7 ′ and of the first shoulder  6  in opposite senses, as is illustrated in  FIG. 8 , results in different heat distributions on the surfaces of the workpieces  19  to be connected. This results in hotter areas W and colder areas K. Heat flows between these areas in order to equalize the temperatures on the surfaces. This equalizing heat flow is positive, since this allows hotspots to be avoided, which have been found to have a negative effect, particularly when carrying out friction stir welding on thin workpieces.  
         [0061]     The apparatus  1  operates as follows:  
         [0062]     The pin  8  and the first shoulder  6  which is connected to it, are driven by the tool drive  12  via the direction-changing gearbox  13  and the shafts  33 ,  33 ′. The second shoulder  7  is either fixed or can likewise be rotated by means of a hollow shaft  32 , via a drive train that is not illustrated. In order to allow the necessary force to be applied between the shoulders  6  and  7 ,  7 ′ the linear-movement drive  10  is connected in a manner that is not illustrated to the base  16  of the basic module  2 . When the stepping motor  9  is driven, the drive module  3  is moved translationally with respect to the basic module  2  along the linear bearing  11 , so that the first shoulder  6  is pressed against the workpieces. The linear movement may in this case, for example, be 13 mm overall, and may produce forces up to 12 kN. The force that is produced by the linear-movement drive  10  is measured, and is supplied to a controller, via the sensors  23 . The controller evaluates these force measurement results and uses the stepping motor  9  to control the force that is applied via the linear-movement drive  10 . This allows the effective force to be set very accurately. Owing to the decoupling of the translational movement and rotation, the double-shoulder tool  5  or pin  8  and first shoulder  6  can be caused to rotate without any significant breaking-free moments. Furthermore, the translational movement is carried out finely without any breaking-free forces, so that the prestressing forces are distributed continuously, without any peaks. It is thus possible to start the welding process accurately, and torque peaks are avoided. Furthermore, the welding process can be matched to different material thicknesses of the workpieces to be connected by means of the controller for the linear-movement drive.  
         [0063]     The preferred forms of the invention described above are to be used as illustration only, and should not be utilized in a limiting sense in interpreting the scope of the present invention. Obvious modifications to the exemplary embodiments, as hereinabove set forth, could be readily made by those skilled in the art without departing from the spirit of the present invention.  
         [0064]     The inventors hereby state their intent to rely on the Doctrine of Equivalents to determine and assess the reasonably fair scope of the present invention as pertains to any apparatus not materially departing from but outside the literal scope of the invention as set forth in the following claims.  
       LIST OF REFERENCE SYMBOLS  
       [0000]    
       
           1  Welding apparatus  31  Cylindrical bolt  
           2  Basic module  32  Hollow shaft  
           3  Drive module  33  Shaft  
           4  Connection on the  33 ′ Shaft  
           handling apparatus  34  Hole  
           5  Double shoulder tool  35  Drive module baseplate  
           6  First shoulder  36  Linear ball bearing  
           7  Second shoulder  37  Gearbox flange  
           7 ′ Movable second shoulder  38  Centring bolt  
           8  Pin  39  Intermediate flange  
           9  Stepping motor  40  Clutch  
           10  Linear movement drive  41  Claw Clutch  
           11  Linear bearing  42  Bearing flange  
           12  Tool drive  42 ′ Centring bolt  
           13  Direction-changing  43  Centring bolt  
           gearbox  44  Centring bolt  
           14  Spindle bearing  45  Cap  
           15  Drive connection  46  Bearing plate  
           16  Base  47  Shaft guide  
           17  Handling apparatus  48  Adjusting spring  
           18  Centring journal  49  Adjusting spring  
           19  Workpiece  50  Clutch upper part  
           20  Workpiece holder  51  Clutch upper part  
           21  Precision shaft  52  Flute  
           22  Stop  53  Fluted nut  
           23  Measurement sensor  54  Locking plate  
           24  Measurement sensor  55  Stamped disc  
           connection W Hot area  
           25  Baseplate K Cold area  
           26  Roller bearing  
           26  ′ Roller bearing  
           27  Roller bearing  
           28  Necked-down bolt  
           29  Centring bush  
           30  Stop