Abstract:
The invention concerns a clamping device for processing, in particular welding, of work pieces. It is the task of the invention to develop a device for processing work pieces, of which the clamp technique enables a high processing quality and, with respect to the work piece geometry, enables a high flexibility of the process. According to the invention, the clamp device for processing of work pieces comprises at least one first clamp element and at least one second clamp element, between which a work piece is held, wherein a tool is movable relative to the work piece, wherein the first clamp element is in the form of a clamp finger ( 1, 24 ) and engages on the side of the work piece ( 3 ) which is the side upon which the tool ( 5 ) acts, and further, that the second clamp element is in the form of a clamp roller ( 2 ) and lies against the work piece ( 4 ) on the side opposite to the tool ( 5 ).

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The invention concerns the clamping device for processing work pieces according to the pre-characterizing portion of Claim  1 .  
         [0003]     2. Related Art of the Invention  
         [0004]     When joining two or more work pieces by welding with high power intensity, such as during laser welding, electron beam welding or plasma welding, the joint gaps between the work pieces may not exceed permissible widths. In maximal permissible joint gap if a function of the welding process employed, the composition of the work pieces, and the construction specifications. For establishing and containing the joint gap within requirements, clamping devices are employed, which in the optimal case keep the joint gap in the area of the welding location as small as possible.  
         [0005]     A fixed or stationary clamping technique with non-moving fixing and clamping elements for use in the welding of work pieces is known. A multitude of clamping element sites ensures the necessary joint gap at each individual joint location as required for a laser welding process. This type of fixing and clamping elements are tailored specifically for a component, are complicated, expensive and inflexible. Due to the large number of clamping elements there are many sources of possible faults, so that it is more difficult to maintain control over such a welding process. If work pieces are simultaneously clamped in all locations, then a static redundancy results. Further, for containing the static redundancy, high clamping forces are necessary.  
         [0006]     Further, accompanying or, as the case may be, traveling clamping systems are known, which are moved over the component to be joined using robots, and of which the clamping elements locally ensure that the joint size is as necessary for the welding process. Distinctions are made herein between one-sided clamping systems with a simple pressure roller or a pressure finger and two-sided clamping systems, for example with a double roller. In the one-sided system a counter-bearing in the form of a device or a constructive counter bearing is necessary. Systems acting on both sides of the work piece are flexible in their area of employment, since the counter bearing can be moved along directly with the clamping technical apparatus. The problem with all these systems is the controlling or containment of the joint gap with increasing distance from the clamping location. For example, in the welding of sheets, the further one is from the clamping location the less control one has over the gap geometry and the greater the resulting gap clearance due to the widening of the sheets.  
         [0007]     Known clamping systems with clamping roller s have construction dictated limitations in the accessibility of welding tools at a welding location. The roller diameter herein has an interfering contour. When welding behind a roller the welding location is so far removed from the clamping location that a verifiable welding process can no longer be reliably ensured due to uncontrollable widening of the joint cap. In order to weld as close as possible to the clamping location, the welding tool in the case of the use of clamping roller s is employed beside, and not behind, a roller. The welding beside the roller requires a sufficient breadth of the joint flange at the work pieces, in order to be able to guide the roller and to form a welding seam. It is difficult for the roller to control the joint gap beside the roller with increasing distance from the roller, which makes impossible a process of reliable welding of geometric welding patterns, such as for example circular seams. Dash seams can, among other things, for this reason not be welded transversely, but rather only longitudinal to the direction of movement beside the roller.  
         [0008]     Clamping systems with clamping fingers allow welding trailing behind in the direction of movement, that is, the welding location lies behind the clamping point. In comparison to clamping roller s, clamping fingers have the advantage that small flange breadths can be realized and tighter radiuses can be maneuvered around (by the welder). Further, when welding behind a clamping finger, one can weld close to the clamping point, since there is no interfering roller diameter to interfere with accessibility.  
         [0009]     A disadvantage in the employment of clamping fingers is the difficult to control, and hardly to be guaranteed, joint gap relationships or behavior with increasing distancing from the clamping point. Clamping fingers are particularly advantageously employed in laser beam welding devices with conventional beam guidance. In these devices the laser beam is always held a constant distance from the clamping point during welding with a robot, wherein the robot movement speed is the same as the welding speed.  
         [0010]     In laser welding processes with specific engagement in the beam positioning by beam deflection or steering systems, the laser beam, during welding of geometric patterns, is not maintained at a constant distance from the clamping point, and accordingly the robot speed of advance is not equal to the welding speed. The produced geometric seam pattern, for example in the form of circles, ovals or brackets, have a planer design, so that they extend into zones further removed from the clamping point, and for this the permissible joint gap must be maintained. A further disadvantage of purely finger clamping systems is the application of force upon a work piece to be joined respectively due to the friction between the clamping finger and the work piece. This disadvantage occurs above all in work pieces which require greater clamping forces and in which the clamping forces are built up locally upon a joint location, wherein during a robot movement the clamping fingers are removed from the respective work piece. Further, clamping fingers cause grooves and scratch marks, which compromise or preclude a visual presentability of a joint location.  
         [0011]     From DE19501869C1 a device for welding of work pieces with laser beams is known, in which for the gap free guidance of the work piece two roller pairs are provided in equal separation respectively ahead of and behind of the welding location. The roller s have a closed and structured surface. The area of the welding location is additionally acted upon by a pressure plate and a slide block. For allowing the passage through of laser beams, the pressure plate has a conical aperture opening. This device is voluminous, elaborate and expensive and limited in its employability.  
       SUMMARY OF THE INVENTION  
       [0012]     It is the task of the invention to develop a device for processing work pieces, of which the clamping technique allows a high working quality and, with respect to the work piece geometry, makes possible a high flexibility in processing.  
         [0013]     The task is solved with a device having the characteristics of Claim  1 . Advantageous embodiments are set forth in the dependent claims.  
         [0014]     According to the invention, a clamping technique is employed during processing, which includes a combination of at least one clamping finger and at least one clamping roller. The term “processing” in the sense of the invention includes all processes which require the clamping of one or more work pieces during joining by welding, soldering or adhering, during separating or trimming, during coating, during shaping or during changing of the material characteristics.  
         [0015]     By the appropriate design and arrangement of the clamping fingers and the clamping roller, joint gaps can be produced and maintained between the work pieces over a large surface area. The geometry of the joint gap can be well controlled. The invention unites the advantages of clamp finger and clamp roller, so that there is free access for a tool at a processing location, in particular in the area exposed to view no scratch and/or marking of the clamp finger occurs upon the work piece and only small force applications need be applied to the work piece to be processed. Therewith there results, during use of this accompanying or traveling clamping system, an improved controllability of joint gaps over relatively large surfaces.  
         [0016]     Particularly in laser welding with precise employment of the beam positioning by beam deflection systems, there results in accordance with the invention, as a result of the large surface area controllable joint gap, new possibilities in the realization of geometric seam patterns in combination with flexible clamping systems. The flexible clamping possibilities are also present in laser welding with conventional processing optics or lenses, that is, even without beam deflection.  
         [0017]     The invention makes it possible to control a joint gap locally at a joint location better than with conventional accompanying solutions. The invention further makes possible the realization of light weight or simplified construction techniques, such as for example reduced flange breadth on body parts. The inventive clamping process is not limited to flanges but is applicable to the entire work piece. Thereby there results a high flexibility with regard to the possible variability of the target component. Particularly in the provision of planar or flat processing patterns there results in the employment of the invention a good accessibility of the welding tool to a clamping point from different directions. Welding patterns spreading out geometrically in a plane, such as circles, ovals or brackets, require in comparison to conventional, for example conventional processing lens produced dash seams, a more flat controlling of the joint gap. In particular in welding processes, with specific or targeted intervention in the beam positioning of the laser beam, the results, due to the flexible clamping, new possibilities to carry out the welding process. Further, with the invention it is possible to minimize imprints from the clamping elements on one of the two work piece surfaces, in particular component surfaces intended to be visible. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]     The invention will be described in greater detail in the following on the basis of the illustrative embodiment, wherein there is shown:  
         [0019]      FIG. 1 a  schematic of a clamping device with a clamping finger and a clamping roller,  
         [0020]      FIG. 2-7  embodiments of clamping roller s,  
         [0021]      FIG. 7-10  embodiments of clamp fingers,  
         [0022]      FIG. 11 a  schematic of a clamping device without offset of the clamp locations,  
         [0023]      FIG. 12 a  schematic of a clamping device with offset of the clamping locations,  
         [0024]      FIG. 13-16  examples of use for clamping device to produce through-going weld seam,  
         [0025]      FIG. 17-20  examples of use for clamping device with production of welded in seam in the area of a clamping roller  
         [0026]      FIG. 21-27  a schematic for carrying out a sheet joining welding  
         [0027]      FIG. 28-29  an example of use for the compelling of off-gas pockets, and  
         [0028]      FIG. 30-31  a schematic of a clamping device with a supplemental clamping element. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0029]      FIG. 1  shows a principle schematic of a clamping device with a clamping finger  1  and a clamping roller  2  for clamping of two sheets  3 ,  4  during welding with a laser beam  5 . The laser beam  5  impinges perpendicularly upon the surface of the sheet  3 . The clamping device is activated or operated, that means, clamp fingers  1  and clamping roller  2  are positioned against the sheets  3 ,  4  and they exercise upon the sheets  3 ,  4  a clamping force, which presses together the sheets  3 ,  4  at the welding location  6 . On the welding location  6  the sheets  3 ,  4  lie tight against each other. In the absence of the effect of the clamping force gaps  7 ,  8  exists between the sheets  3 ,  4  outside of the welding location  6 . The clamping device, inclusive of actuating process, can be provided on an arm of a robot, or in the clamping finger  1  and the clamping roller  2  can be applied and retracted for moving of the clamping location  9  to clamping location  9  on the sheets  3 ,  4 . The movement of clamping position  9  to clamping position  9  can also occur with maintenance of the clamping force, wherein the clamping roller  6  rolls about its axis  10  upon the surface of the sheet  4  and the clamping finger  1  slides along the surface of the sheet  3 . The tip  11  of the clamping finger  1  is hemispherically or convexly shaped in the vicinity of the welding location  6 . The clamping finger  1  is seated diagonally at the clamping location  9  in the welding direction  12  upon the surface of the sheet  3 . This makes it possible to place welding seams close to the clamping location  9 . For producing special seam patterns the laser beam  5  can be brought to act in the environment of the clamping location  9  by a deflection device.  
         [0030]     To the extent that already mentioned reference numbers are employed in the following description, these would concern elements with equivalent function.  
         [0031]     Clamping roller  2  and clamping finger  1  are adapted to the welding process and the respective work piece. Therein various combinations of clamping finger  1  and clamping roller  2  are possible.  
         [0032]      FIGS. 2-7  show multiple possible embodiments of clamping rollers  2 . The clamping rollers  2  according to  FIGS. 2 and 3  have, in their profile or tread, a planar or, as the case may be, convex running surface  13  and  14 . The running surface  15  of the clamping roller  2  according to  FIG. 4  has a profile with a radius. In  FIG. 5 a  clamping roller  2  is shown with a furrow or narrow channel running symmetrically in the circumferential direction.  
         [0033]     In the clamping roller  2  according to  FIG. 6 a  U-shaped circumferential groove  17  is symmetrically introduced. During welding through of work pieces the groove  17  bridges over the weld seam, so that the clamping roller  2  does not interfere with the formation of the welding seam either by thermal extraction or by mechanical loading.  
         [0034]     From its profile or cross section the clamping roller  2  according to  FIG. 7  has the shape of the clamp roller  2  according to  FIG. 6 . In addition, the clamp roller  2  according to  FIG. 7  has a core  18  of elastic material with a receptacle bore hole  19  for a mounting bolt. By the elastic mounting of the clamping roller  2  there results a slight possibility of yield, in order to counteract a one-sided load. The clamp roller  2  lies, in any case, against the work piece  4  at two points. Depending upon tilt or orientation of the clamping surface the orientation of the clamping roller  2  adapts thereto within the limits of the elasticity of the core  18 , which is indicated symbolically by the angle α between the axis  10 . 1  and  10 . 2 .  
         [0035]      FIGS. 8-10  respectively show in profile and in employment multiple embodiments of clamping fingers  1 , which can be varied in form, material, coating, number and positioning.  
         [0036]     The clamping finger  1  applied diagonally against a work piece according to  FIG. 8  is rotation symmetric with a conically narrowing tip  11 . Close to a clamping location  9  on the work piece a closed circular shaped welding seam  20  is produced with a laser beam  5 .  
         [0037]     The clamping finger  1  according to  FIG. 9  has on its tip  11  a profile with two flat parts  21 ,  22 . During clamping, the clamp finger  1  is seated diagonally upon the work piece surface, as a result of which the flat parts  21 ,  22  lie in the direction of a laser beam  5 . As a result the clamping finger  1  shows its narrow side in the direction of the laser beam  5 , so that it is possible to form a bow-shaped welding seam  23  very close to a clamping location  9 .  
         [0038]     The clamping finger  1  can remain at the clamping location  9  during welding or may be moved. In the moving operation the bow-shaped welding seam  23  can be closed to form a circular seam.  
         [0039]      FIG. 10  shows a pliers-shaped double finger  24  respectively with flattened fingertips  25 ,  26 . During the welding process the fingertips  25 ,  26  are simultaneously seated upon the work piece surface diagonally and arranged parallel. The double finger  24  is equipped with a movement balancing perpendicular to the work piece surface. In case the double finger  24  is seated diagonally upon the work piece surface, the work piece lies diagonally or is non-planar, it is insured by the movement balancing or compensation that always both fingertips  25 ,  26  contribute to clamping. In cooperation with a clamping roller  2  three pressure points are established on the work pieces  3 ,  4 , whereby an optimal clamping force introduction results.  
         [0040]     A clamping finger  1  can be provided to be adjustable with regard to its angle of tilt relative to the work piece surface. The possibility of tilting a clamping finger  1  in various angles to a work piece exists in particular in the processing direction or as the case may be robot direction of movement and transverse thereto.  
         [0041]     Depending upon combination of clamping finger  1 , clamping roller  2 , desired welding seam shape, welding seam type and work piece geometry, there results the possibility to displace the pressure points of clamping finger  1  and clamping roller  2  relative to each other, as shown in great detail in  FIGS. 11 and 12 .  
         [0042]     According to  FIG. 11 , the pressure points  9 . 1  and  9 . 2  of clamping finger  1  and clamping roller  2  exhibit no offset in the robot movement direction x and in direction y transverse to the robot movement direction. The pressure points  9 . 1  and  9 . 2  lie on a joining or fusing line  27 , which is perpendicular to the directions x, y and parallel to direction z. The work pieces  3 ,  4  lie in a plane parallel to the x-y-plane. The laser beam  5  impinges perpendicular upon the surface of the work piece  3 , wherein for production of a circular shaped weld seam  20  the laser beam  5  exhibits a small space or a separation from the connecting line  27 .  
         [0043]     In distinction to  FIG. 11  the welding device according to  FIG. 12  exhibits at the pressure points  9 . 1  and  9 . 2  a displacement delta x in the robot movement direction x. The pressure points  9 . 2  of the clamp roller  2  lie in the z-direction below the welding location  6 . The clamping roller  2  has a design according to  FIG. 6  or  7 .  
         [0044]     The displacability of clamping fingers  1  and/or clamping roller  2  can be in all coordinate directions x, y, z. Thereby multi-faceted employment possibilities are provided for production of highly controllable gap relationships. It is possible to detect the gap condition or proportion by measurement techniques and to control or regulate the position of the clamp finger  1  and clamp roller  2  during welding relative to each other. Depending upon the combination of clamp finger  1  and clamp roller  2  and their arrangement relative to each other, it is possible to produce a planar seam pattern, such as circles, ovals or brackets, with a system deflecting a laser beam  5 , as well as also simple seams with conventional processing optics.  
         [0045]      FIGS. 13-16  show two illustrative embodiments for clamping devices with producing welded-through seams  20  respectively in two views.  
         [0046]     In the variants according to  FIGS. 13 and 14 , clamp finger  1 , clamp roller  2  and laser beam  5  are simultaneously moved in the welding direction  12 , whereby a dash or line seam  20  is formed. The laser beam  5  brings about a welding-through of the two sheets  3 ,  4 . The clamp roller  2 , as best described in the text in association with  FIG. 6 , is provided with a circumferential groove  17 . The groove  17  lies in the z-direction symmetric to the dash or line seam  20 , so that the clamp roller  2  does not interfere with the formation of the dash or line seam  20  on the lower side of the sheet  4 . The axis  10  of the clamp roller  2  lies parallel to the y-direction.  
         [0047]     In the variant according to  FIGS. 15 and 16  the clamp finger  1  and clamp roller  2  have no offset in the x-direction. The clamp finger  1  has a narrow shape, as described in the text in association with  FIG. 9 . The clamp roller  2  is a narrow embodiment with a radius according to  FIG. 4 . As can be seen from  FIG. 15 , the laser beam  5  lies in the x-direction on the height or level of the pressure point  9 . 1  and  9 . 2  of clamp finger  1  and clamp roller  2  on the two sheets  3 ,  4 . As can be seen from  FIG. 16 , the laser beam  5  impinges in the y-direction close beside the clamp finger  1  or, as the case may be, beside the connecting line  27  of the two pressure points  9 . 1 ,  9 . 2 .  
         [0048]      FIGS. 17-20  show two applications of clamp devices during production of welded-in seams  20  respectively in two views.  
         [0049]     In the variation according to  FIGS. 17 and 18  the clamp finger  1  and clamp roller  2  have the geometry described in association with  FIG. 12 . In distinction to the variation according to  FIGS. 13, 14 , here a welded-in seam  20  is produced, in which the material of the sheet  4  is molten to about one half of the sheet thickness. As clamp roller  2  a spherical embodiment according to  FIG. 3  is employed. Of course, another design of clamp roller  2  can be employed.  
         [0050]     In the embodiment according to  FIG. 19, 20  a circular shaped seam  20  is produced as a welded-in seam  20 . In distinction to the embodiment according to  FIGS. 15, 16 , here a clamp roller  2  is employed, which provides or offers a pressure line  9 . 2  below the sheet  4 . The projection of the pressure point  9 . 1  halves or divides the pressure line  9 . 2 . During the formation of the circular shape seam  20  the laser beam  5  is guided with a deflection system close about the pressure point  9 . 1 .  
         [0051]     The invention can advantageously be employed in clamping welding processes, as described in greater detail on the basis of  FIGS. 21-27 . The clamp welding operation is preferably carried out with welding devices, in which a laser beam  5  is positioned by beam deflection units and a scanner system. In the case of production of geometric seam patterns such as circles, ovals or brackets, it is necessary for the welding process to ensure an optimal joint gap over a large surface area. In the operating condition of the clamping device, first tack seams are made very close to a clamp point, whereby small joint gaps result, which can be controlled or checked over a large surface area. The joining seam or tack seam fixes the work pieces to be joined to each other and locally freezes the joint gap. Thereafter the actual weld seam is produced. When carrying out the final weld seam a clamping of the work piece in the area of the weld seam is no longer necessary. Clamp finger  1  and clamp roller  2  can already be moved to the next joint location during the carrying out of the actual welding process in order to affect there a clamping process for a further clamp welding process. The clamp seams can differ in their embodiment shape, in particular with respect to position on the work piece, shape, type and number, depending upon combination of clamp finger  1  and clamp roller  2  and their orientation or positioning relative to each other.  
         [0052]      FIG. 21  shows a clamping situation with a clamp finger  1  and a clamp roller  2  in an arrangement according to  FIG. 15, 16  or  19 ,  20 . First, with a laser beam  5 , a clamping or holding seam or two short clamping seams or tack seams  28 ,  29  are produced for the joining close beside a flat clamp finger  1 . Thereafter clamp finger  1  and clamp roller  2  are moved together in the direction of the arrow  30  to the next clamp location and repositioned. The sheets  3 ,  4  remain fixed in their spacing to each other at the location of the tack seams  28 ,  29 . As shown in  FIG. 22 , then the final weld seam  20  can be produced. In the illustrated case a circular shaped weld seam  20  is produced around the tack seams  28 ,  29 .  
         [0053]     The embodiment according to  FIG. 23, 24  shows the production of a dash or line seam  31  with a preceding tack seam  32 . The clamping device has the design according to  FIG. 13, 14  or  17 ,  18 . After the sheets  3 ,  4  are pressed against each other with the clamp finger  1  and a clamp roller  2  at the clamp location  9 . 1  and  9 . 2 , first a short dash-shape tack seam  32  is formed in the direction x. Thereafter the clamp finger  1  and clamp roller  2  are moved in the x-direction about the path s, as indicated with the arrows  30 , respectively to the next clamp location  9 . 3  and  9 . 4  and there are actuated for clamping. This situation is shown in  FIG. 24 . Subsequently the laser beam  5  executes, beginning from the immediate vicinity of clamp location  9 . 3 , in the direction of clamp location  9 . 1 , a line seam  20 , which passes over tack seam  31 . Thereafter, clamp finger  1  and clamp roller  2  are again displaced about path s in the x-direction to the next clamp location and a new line seam with advance or preceding tack seam is put in place. These processes are repeated until the seam line  31  is produced step-wise over the intended joint length.  
         [0054]     In  FIGS. 25-27  a further example for the carrying out of the welding process with joining welding is shown. The clamp device has the configuration described in  FIG. 13, 14  or  17 ,  18 . In a first step, with actuated clamping device, a short line shaped tack seam  33  is produced with a laser beam  5 , as shown in  FIG. 25 . The tack seam  33  lies directly ahead of the clamp point  9 . 1  of clamp finger  1  and extends transverse to the direction of advance  30  of the clamp finger  1  or, as the case may be, clamp roller  2 , in the y-direction. In a next step clamp finger  1  and clamp roller  2  are displaced about the path s in the y-direction and actuated for clamping of the clamp points  9 . 3 ,  9 . 4 . In a further step again a tack seam  34  is produced directly ahead of the clamp point  9 . 3 . The tacks seams  33 ,  34  likewise have the spacing s as shown in  FIG. 26 . In a next step clamp finger  1  and clamp roller  2  are together guided along path s to the next clamp location. As shown in  FIG. 27 , in a next step a final square seam  35  is produced between the previously produced tack seams  33 ,  34 . The welded-out seam  35  could be circular shaped, oval or likewise be in the form of a bracket. Subsequently a tack seam is renewed produced at the next clamp location. These steps are repeated over the length of the joint of the sheets  3 ,  4 .  
         [0055]     During welding of sheets with low melting coatings, such as for example zinced sheets, it can be necessary to provide off-gassing possibilities. If the distance between the sheets is almost zero and the coating or, as the case may be, zinc is caused to evaporate explosively, than this leads to a throwing out of melt pool material and therewith to faulty weld seams. The invention makes it possible to exercise influence upon the off-gassing behavior, by the targeted production of off-gassing pockets. For this, the clamp devices can be provided or equipped with a path control for clamp finger  1  and/or clamp roller  2 . Therein an off-gas gap can be predetermined and the desired total sheet thickness can be added up. A further possibility is comprised therein, to intentionally produce corrugations in the sheet metal using clamping forces, as illustrated in greater detail in  FIGS. 28, 29 .  
         [0056]      FIG. 28  shows a clamp device with a clamp finger  1  and clamp roller  2 . The clamp finger  1  corresponds to the embodiment according to  FIG. 9  and the clamp roller to the embodiment according to  FIG. 6 . Shown is the clamp device with view upon the direction of movement of the clamp roller  2 . The projection of the contact point  9 . 1  of the clamp finger  1  upon the sheet  3  lies exactly between the contact or application points  9 . 2 ,  9 . 3  of the clamp roller  2  upon the sheet  4 . The clamp finger  1  and the clamp roller  2  act respectively with a force against the sheets  3 ,  4 , so that the sheets  3 ,  4  are deformed. The sheets  3 ,  4  are pressed into the groove  4  of clamp roller  2 , whereby the sheets  3 ,  4  in the elastic region are variously strongly bent or bowed. Thereby, off-gas gaps  36 ,  37  result between the sheets  3 ,  4 , so that zinc vapor  38  can escape.  
         [0057]     In  FIG. 29 a  clamp device with a clamp finger  1  and clamp roller  2  is illustrated in side view. If clamp force F acts in the x-direction upon two superimposed lying sheets  3 ,  4  with offset lines of action to each other in the direction z, then the sheets  3 ,  4  are subject to shear, and deform in the elastic area, so that off-gas gaps  36 ,  37  result, from which zinc vapor  38  can escape.  
         [0058]     In a further embodiment of the invention active or passive clamp elements can be provided supplementally to the clamp finger  1  and clamp roller  2 . This supplemental clamp element preferably act by following the weld position and can be provided one-sided or two sided on the work pieces  3 ,  4 . As supplemental clamping elements there can, depending upon application, be employed roller or fingers. The pressure force of the supplemental clamp elements can be applied with springs, which are activated during closing of a main clamp device containing the clamp finger  1  and clamp roller  2 , via a mechanism. The supplemental clamping elements serve to improve the joint gap control during difficult clamping situations, in starting points on the work pieces  3 ,  4 , or in the case of greatly spaced apart joining points.  
         [0059]     In  FIG. 30-31  the employment of a supplemental assist clamp roller  39  is shown in a main clamp device comprising a clamp finger  1  and clamp roller  2  in the opened and closed positions.  
         [0060]     In the open position according to  FIG. 30  the clamp finger  1  and clamp roller  2  are withdrawn from the sheets  3 ,  4 . Between the sheets  3 ,  4  there is still a gap  40 . The clamp roller  2  is rotatably mounted on a mount  42  via a bolt  41 . In an extension of the mount  42  a bar  44  is pivotably held via a pin  43 . On the other end of the bar  43  an assist clamp roller  39  is rotatably mounted via a bolt  45 . In the vicinity of the bolt  45  there is on the bar  44  a bolt  46 , on the one end of which a spring  47  is secured. The other end of the spring  47  is secured to a bolt  48  on the mount  42 . By the force of the spring  47  in the non-operating condition of the main clamp device the assist roller  39  is held on a z-level higher than the clamp roller  2 . The spring  47  can be provided with an adjustable pretensioning.  
         [0061]     Upon closing of the main clamp device the clamp finger  1  and the clamp roller  2  inclusive of the assist clamp roller  39  are moved toward each other in the z-direction. Due to the higher level of the assist clamp roller  34  this contacts the lower side of the sheet  4  first, whereupon the spring  47  is compressed. The sheets  3 ,  4  come closer together, so that the gap  40  disappears. Finally the clamp roller  2  also contacts the lower side of the sheet  4 . In the condition shown in  FIG. 31  there are applied, on the one hand, the main clamp forces F between the clamp finger  1  and clamp roller  2  and, on the other hand, the assist clamp force due to compression of the spring  47 . During application of the clamp roller  2  against the lower side of the sheet  4  the assist clamp roller  39  is pivoted against the bias of the spring force about bolt  43 . Therewith the spring  47  urges the assist clamp roller  39  against the lower side of the sheet  4  with a z-component F F . The direction of action of the clamp forces F and F F  of the main clamp roller  2  and the assist clamp roller  39  in the z-direction lie offset by a distance or separation “a” in the x-direction. The line of action or effect of the clamp force F of the clamp finger  1  in the z-direction lies between the effect lines of clamp forces of clamp roller  2  and assist clamp roller  39  close to the clamp roller  2 . In the operating condition of the clamp device a planar seam  20  can be created in the vicinity of clamp location  9  of clamp finger  1  by a laser beam  5 .  
         [0062]     The clamp force of a clamp device can be produced with electromechanical elements, in particular a screw link actuator, as well as pneumatic or hydraulic elements. In order to avoid a piling up of folds of the sheet and to avoid unnecessary finger or, as the case may be, roller prints upon the work piece, the clamp force necessary for the clamping process need be built up only at the actual joint location. Traveling up to the next joint location, the clamp force is reduced or removed from the work piece.  
         [0063]     When a laser weld robot is employed, then the clamp device can be moved along on an arm together with the processing optics. In a further variation the clamp device can be mounted on an arm of a separate clamp robot. Further, the clamp device can be provided stationary together with a laser optic, wherein the work pieces are is moved through the clamp device, for example with the aid of an industrial robot.  
       LIST OF REFERENCE NUMBERS  
       [0000]    
       
         
           
               1  Clamp Finger  
               2  Clamp Roll  
               3 ,  4  Sheet  
               5  Laser Beam  
               6  Weld Location  
               7 ,  8  Gap  
               9  Tensioning or clamping location  
               10  Axis  
               11  Tip  
               12  Welding direction  
               13 - 14  Running surface  
               16  Groove  
               17  Channel or groove  
               18  Core  
               19  Receptacle bore hole  
               20  Weld seam  
               21 ,  22  Flat part  
               23  Weld seam  
               24  Double finger  
               25 ,  26  Fingertip  
               27  Connecting line  
               28 ,  29  Tack seam  
               30  Arrow  
               31  Line seam  
               32 - 34  Tack seam  
               35  Seam  
               36 ,  37  Off-gas gap  
               38  Zinc vapor  
               39  Assist clamp roller  
               40  Gap  
               41  Bolt  
               42  Mount  
               43  Pin  
               44  Bar  
               45 ,  46  Bolt  
               47  Spring  
               48  Bolt