Abstract:
The present invention relates to a laser ablation and welding method for workpieces, in particular, metal sheets, and an automatic laser ablation and welding system, where an ablation procedure and a welding procedure are executed in an automation line.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of International Application No. PCT/EP2015/065648 filed Jul. 9, 2015, which designated the United States, and claims the benefit under 35 USC §119(a)-(d) of German Application No. 10 2014 112 888.5 filed Sep. 8, 2014, the entireties of which are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to a laser ablation and welding method for workpieces, in particular, metal sheets, and also an automatic laser ablation and welding system. 
       BACKGROUND OF THE INVENTION 
       [0003]    Systems are known in the prior art of DE 10 2010 060 958 A1, in which workpieces are positioned, aligned, and then processed in the working region of a laser. Typically, such procedures, which are highly sensitive with respect to the alignment of the workpieces, are always executed in a specialized workstation in the sequence that each processing step comprises insertion and alignment of the workpiece in a clamping device. 
         [0004]    It is disadvantageous in this case that the removal from one processing station, the insertion and positioning in a new processing station, and then the clamping for processing are accompanied by substantial handling effort, which substantially reduces the efficiency of a processing station. 
       SUMMARY OF THE INVENTION 
       [0005]    The object of the present invention is, therefore, to improve the processing of workpieces in laser processing stations in the efficiency thereof. 
         [0006]    The laser ablation and welding method according to the invention for workpieces, in particular, metal sheets, comprises the following method steps: 
         [0000]    a. inserting at least two workpieces into a clamping unit;
 
b. clamping the workpieces in the clamping unit via one first clamping mechanism each in a first position;
 
c. aligning the clamped workpieces and the first clamping mechanism, which clamps the workpieces, in a first ablation position;
 
d. ablation of at least one joining edge of at least one clamped workpiece by means of at least one laser head;
 
e. clamping a first of the at least two workpieces via a second clamping mechanism in the first position and disengaging the first clamping mechanism at the first of the at least two workpieces;
 
f. moving the first clamping mechanism in the direction of the joining edge at the first workpiece;
 
g. clamping the first workpiece via the first clamping mechanism, disengaging the second clamping mechanism, and aligning the first workpiece and the first clamping mechanism in a joining position;
 
h. clamping a second of the at least two workpieces via the second clamping mechanism in the first position and disengaging the first clamping mechanism at the second of the at least two workpieces;
 
i. moving the first clamping mechanism in the direction of the/one joining edge at the second workpiece;
 
j. clamping the second workpiece via the first clamping mechanism, disengaging the second clamping mechanism, and aligning the second workpiece and the first clamping mechanism in the joining position;
 
k. connecting, in particular laser welding the workpieces at the respective joining edge; and
 
l. disengaging the first clamping mechanism and transferring the joined workpieces to a transport unit.
 
         [0007]    It is essential that the workpieces never have to be removed from the clamping mechanism, even if a plurality of processing steps is performed, so that effort for handling the workpieces is nearly entirely omitted. 
         [0008]    After the first insertion of at least two workpieces into a clamping unit, the workpieces remain in the clamping unit until the removal after the processing. Solely controlled and defined repositioning and alignment of the clamped workpieces are performed in the processing cycle, without a removal being required. 
         [0009]    The processing steps of ablation and welding by means of laser are sufficiently known to a person skilled in the art. For the sake of completeness, it is to be noted that laser ablation, also called laser vaporization, refers to the removal of material from a surface by bombardment using preferably pulsed laser radiation. The laser radiation having high power density which is used in this case results in rapid heating at the surface, whereby material is removed. Welding by means of laser is a welding method in which the required energy for connecting the workpieces is provided by means of a laser. 
         [0010]    In one advantageous refinement of the method, it is provided that before the insertion, an automated pre-positioning step is executed by a transfer from a first robot via a positioning device to a second robot. 
         [0011]    The pre-positioning or pre-picking enables insertion of identical or different blanks with increased precision into the clamping unit, in particular, by an insertion robot having a single handling device (for example, suction head) for the at least two workpieces. First alignment step b) is thus facilitated and can be executed more rapidly. 
         [0012]    Furthermore, it is preferable for at least one alignment in method step c), g), or j) to be performed by a movement in a floating manner of the workpieces toward a stop or the like with subsequent clamping fixation of a respective suspension of the respective first clamping mechanism. 
         [0013]    The floating movement for positioning of the clamped workpieces takes place via movement of the workpieces in the horizontal plane, without a defined linear movement axis being predefined. The workpieces are moved in a floating manner, i.e., so they are pivotable or rotatable about an axis perpendicular to the plane, to a stop, until a contact at at least two points and, therefore, a defined alignment of a workpiece edge in the plane has occurred. The clamping device is then fixed by its suspension in this position, so that exact positioning in the plane occurs and is secured. 
         [0014]    In addition, it is preferably provided that the ablation in method step d) is executed via at least two laser heads, wherein preferably one laser head is arranged on a workpiece upper side and one laser head is arranged on a workpiece lower side. 
         [0015]    The typically planar workpieces made of metal sheet sections, so-called “blanks”, are to be connected to one another by welding while carrying out the method according to the invention. For this purpose, joining edges, i.e., edges for forming the connection, are pretreated by ablation in the method. The workpiece upper side and the workpiece lower side are to be understood as the faces of the workpieces in this case. Typically, the lower side will be at least partially in contact with the first clamping mechanism, while the upper side is preferably free. 
         [0016]    The processing using one laser head each on the workpiece upper side and on the workpiece lower side enables increased processing speed and avoids complex repositioning of the laser head from above to below with precise alignment on the joining edge to be processed. 
         [0017]    During this processing, it is furthermore advantageous if the laser heads travel down the joining edges of the workpieces successively on a circumferential path, wherein, in particular, the laser heads are not directly diametrically opposite on workpiece upper side and workpiece lower side at any point in time. 
         [0018]    The successive movement of the laser heads on a circumferential path, which lies in the processing plane of the workpieces, avoids the laser heads mutually influencing one another, in particular, the laser beams of one laser head striking the other laser head and being able to damage it in this case. Influencing the workpieces themselves by overload with laser radiation is also avoided. 
         [0019]    It is furthermore preferably provided that automatic cleaning of the joining edge, in particular, brushing or polishing, is performed between method step d) and e). 
         [0020]    The cleaning of the edges processed by ablation offers advantages for the further processing. In particular residues of removed material or contaminants can be lastingly removed in the joining edge region in this case, if the quality of the joining edges is improved by means of brushing or polishing. 
         [0021]    According to the present invention, an automatic laser ablation and welding system is also disclosed for joining at least two workpieces, in particular, two metal sheets, wherein the ablation and welding system comprises at least one clamping unit, a first positioning station, an ablation station, a second positioning station, and a welding station: the laser ablation and welding system is characterized in that the at least two workpieces can be ablated, joined, and welded in a single clamping unit. 
         [0022]    The present invention offers the advantage that handling and re-clamping of a processing step is avoided, whereby the processing time is shortened and therefore the efficiency is increased. 
         [0023]    In one preferred embodiment of the ablation and welding system, it is provided that it comprises a turntable having a plurality of clamping units, wherein the clamping units are movable via the turntable from position to position. 
         [0024]    The arrangement of the clamping units on a turntable enables each cycle of the method to be carried out successively in a revolving manner, and the clamping units having clamped workpieces to pass through various processing stations in succession in the form of a processing train or processing line. 
         [0025]    It is particularly advantageous in this case if the clamping unit comprises at least one clamping magnet per workpiece. 
         [0026]    Workpieces in the form of metal sheets or the like may be fixed, positioned, and disengaged precisely via clamping magnets, without mechanical chucking devices having to be adapted to the workpiece contour. 
         [0027]    An expanded embodiment provides that at least one clamping magnet per workpiece is arranged so it is movable in a floating manner in the clamping unit and is fixable, in particular via chucking devices, in a position approached in a floating manner. 
         [0028]    In this manner, the clamping and the above-described movement in a floating manner toward the positioning means may be implemented more easily, because only the floating movement of the magnet head has to be executed in one plane, in particular, by incremental movement of two feed axes, which are parallel but not synchronous and are spaced apart from one another, for the clamping magnets. 
         [0029]    In addition, it is to be noted that both the first and also the second clamping mechanism can be embodied as clamping magnets. In practice, it has been shown that designing the first clamping mechanism as a clamping magnet and the second clamping mechanism as a friction-locked clamping-chucking device represents the preferred cost-effective and most efficient solution. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0030]    The present invention will be explained hereafter on the basis of schematic exemplary embodiments. However, the invention is not restricted to the illustrated embodiment. 
           [0031]      FIG. 1 a    shows an ablation and welding system in a top view; 
           [0032]      FIG. 1 b    shows a flow chart of an ablation and welding method; 
           [0033]      FIG. 2 a    shows a schematic illustration of a clamping unit; 
           [0034]      FIG. 2 b    shows a schematic illustration of a clamping unit with workpiece; 
           [0035]      FIG. 3 a    shows a schematic illustration of the movement of the laser heads in the ablation step; 
           [0036]      FIG. 3 b    shows a schematic illustration in the longitudinal direction of the laser heads in the ablation step; and 
           [0037]      FIG. 4  shows the sequence of the alignment from an ablation position into a joining position. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0038]    In detail,  FIG. 1 a    shows a laser ablation and welding system  1  according to the present invention in a perspective top view. The laser ablation and welding system  1  comprises a turntable  2  having a total of six clamping units  3  arranged at six different processing positions I to VI. The processing positions I to VI are arranged circumferentially around the axis of rotation  4  and can be transferred one into another via a rotation by 60° in the processing cycle. 
         [0039]    Linear traverses  10 ,  11 , and  12  are arranged at the processing stations II, III, and V. A laser ablation device  13  is arranged on the linear traverse  10 , which can be moved by displacement on the linear traverse  10  into a region above and below the clamping unit  3  in the position II, to carry out the processing step of laser ablation. 
         [0040]    The linear traverse  11  carries a processing head for the optional procedure of cleaning by brushing or polishing, wherein this procedure is also performed by retracting the processing head  14  into the region of the clamping unit  3  in the processing station III. 
         [0041]    A chucking holder  15  is arranged in the station IV, which fixes the workpieces in the processing station on the clamping unit  3  at position IV for repositioning the first clamping mechanism, to provide the alignment of the joining edges for the subsequent welding procedure in position V. 
         [0042]    The linear traverse  12  is provided at position V, which in a corresponding manner embodies the laser welding head  16  as linearly movable into and out of the processing region of the clamping unit  3  at the position V. 
         [0043]      FIG. 1 b    schematically shows the sequence of the processing method according to the present invention in accordance with an arrangement on a turntable  2  according to  FIG. 1 a   . Method steps a and b and c take place in the position I. The clamping unit  3  is then moved further into the position II for processing in the ablation station  13  by rotating the turntable  2 . Method step d is executed therein. The optional method step of cleaning is performed in position III, wherein, as described above, a brush head  14  cleans, in particular polishes, the joining edges after completed ablation. The application of the brush head or the polishing unit can be performed either from above, from below, or on both sides. 
         [0044]    In position IV, re-clamping and alignment (joining) of the treated joining edges of the workpieces to be welded to one another is performed, wherein method steps e to j are executed. 
         [0045]    By further rotation by 60° of the turntable  2 , the clamping unit  3  is transferred from the position IV into the position V, where the welding of the workpieces aligned in the joining position is then performed by means of the laser welding head  16 . 
         [0046]    After completion of the processing method and further rotation of the turntable  2  with the clamping unit  3  out of the welding station V into the removal position VI, the finished processed plate, consisting of two workpieces welded to one another, is provided for unloading. 
         [0047]      FIG. 2 a    shows a schematic illustration of a clamping unit  20 , which has clamping mechanisms  21 ,  22  in the form of clamping magnets. The clamping mechanisms  21 ,  22  are arranged so they are displaceable on a frame  23 ,  24  and can be moved toward or away from one another in a floating manner via in each case two parallel threaded spindles ( 25 ,  26  and  27 ,  28 ) spaced apart from one another. The threaded spindles ( 25  to  28 ) are driven in this case by drive units  29 ,  30  such that workpieces (not shown) held on the clamping mechanisms  21 ,  22  can be moved toward one another. For exact positioning in a first ablation position, a stop  31  having positioning pins  32  is introduced in the direction  33  between the clamping mechanisms  21  and  22  having workpieces arranged thereon, so that the joining edges of the workpieces are moved in a floating manner toward the positioning pins  32  by moving the clamping mechanisms  21 ,  22  via the threaded spindles  25  to  28  and can be stopped. As soon as the first ablation position is reached, the positions of the clamping mechanisms  21 ,  22  are locked via blocking devices  40  to  43 , so that during further processing of the workpieces on the clamping unit  20  in another processing station (I to VI) the positioning is maintained, because the clamping unit remains connected to the workpieces until the completion of the processing. Alternatively or additionally to the blocking devices, the possibility also exists of fixing the clamping mechanism via the drive units  29 ,  30 . 
         [0048]    To also be able to accommodate and handle large workpieces in a simple and precise manner, the clamping unit  20  has support means  45 , which are only shown by way of example in the present case. 
         [0049]      FIG. 2 b    shows an embodiment of the clamping unit  49  with arranged workpieces  50 ,  51 . The clamping magnets  52 ,  53  hold the workpieces and are moved in a floating manner via the drives  54 ,  55  in accordance with the above-described embodiment toward the stop pins  56  and positioned. The workpieces  50 ,  51  are shown in shortened form in the present case, so that the supports  58  are visible. The entire clamping unit  49  is mounted on a turntable  60 . A pre-positioning step (not shown) enables the insertion of the workpieces  50 ,  51  by means of a single robot handling device, for example, a suction gripper on a multiaxis robot, so that comparatively precise alignment of the joining edges  61 ,  62  of the workpieces  50 ,  51  is already performed in the pre-positioning. 
         [0050]    For the sake of completeness, it is to be noted that instead of the threaded spindles  25  to  28 , other devices, for example, linear adjusters, pneumatic or hydraulic adjusters, or other actuators come into consideration, which enable a floating approach in the meaning of the invention by corresponding arrangement and fixing. In particular the use of pneumatic cylinders can offer the additional advantage that a defined force can be exerted during the floating approach via the pneumatic control pressure, to set the position as exactly as possible, before it is locked by means of blocking devices. 
         [0051]      FIG. 3 a    shows a schematic illustration of the movement of the laser heads in the ablation step. The two workpieces  80 ,  81  aligned in the ablation position are processed at the joining edges  82 ,  83  thereof by means of a first laser head  84  from the upper side thereof and a second laser head  85  from the lower side thereof. The laser heads run in this case along the path described by arrows  86 ,  87 ,  88 , and  89  successively following the contour of the joining edges  82 ,  83 , so that the ablation step occurs without the laser heads being diametrically opposed at any processing point in time. 
         [0052]      FIG. 3 b    shows a schematic illustration in the longitudinal direction of the laser heads  84  and  85 , wherein the laser head  84  is ready at the end of the path  86  to change along the path  87  and the laser head  85  performs the change along the path  89 . The workpieces  80 ,  81  are held by clamping magnets  90 ,  91 , wherein for improved precision of the processing at the joining edges  82 ,  83  using the laser heads  84 ,  85 , tracked roller pairs  92 ,  93  and  94 ,  95  are moved to hold the joining edges  82 ,  83  exactly in the processing position thereof in vertical alignment. 
         [0053]      FIG. 4  shows the sequence in seven steps of the displacement of the first clamping mechanism according to features e) to j) of the method according to the present invention. 
         [0054]    The workpieces  100  and  101  are introduced into the station IV and are held at this point in time using the first clamping mechanisms  102  and  103  in the form of clamping magnets. The second clamping mechanisms  104  and  105  are open at this point in time and do not exert clamping force on the workpieces  100 ,  101 . After introduction into the station IV, a stop  106  is introduced. In a second step of the sequence in the station IV, the second clamping mechanisms  104 ,  105  are closed by closing an upper clamping jaw  107  against a lower clamping block  108  in the region of the first workpiece  100  and closing an upper clamping jaw  109  against a lower clamping block  110  in the region of the workpiece  101 . The first clamping mechanisms  102  and  103  are then disengaged and moved toward the stop  106  along a movement direction  111  and  112 . This can be performed via the above-described drives for the floating approach of a position. The second clamping mechanisms  104  and  105  hold the workpieces  100  and  101  in position in this case. 
         [0055]    After completion of the movement of the first clamping mechanisms  102  and  103  in step  4 , the second clamping mechanisms  104 ,  105  are disengaged, after the first clamping mechanisms  102 ,  103  have again securely clamped the workpieces  100 ,  101 , in that the magnetic field of the clamping magnets was activated. In step  5 , a first movement of the workpiece  101  via movement of the clamping mechanism  103  having clamped workpiece  101  toward the stop  106  is then performed for alignment in a joining position for a subsequent welding step. In step  6 , the stop  106  is then removed, after which, in step  7 , via movement of the first clamping mechanism  102  having workpiece  100  fixed thereon, this workpiece  100  is moved with its joining edge  113  on the stop toward the joining edge  114  of the second workpiece  101 . The positions of the first clamping mechanisms  102  and  103  are then locked in a known manner and the clamping unit is introduced into the laser processing station V, so that the workpieces  100 ,  101  can be welded to one another. 
         [0056]    After completed welding, the resulting, processed workpiece is transferred into the position VI for unloading, for example, by an unloading robot, after which the clamping unit can be rotated further into the position I for renewed loading and first alignment. 
         [0057]    The first and the second clamping mechanisms can also be designed differently than described in the exemplary embodiments. In particular, the second clamping mechanism can consist of a stationary arrangement of clamping jaws in the station IV and a tracked clamping block, for example, in the form of the support  45 ,  58 . 
       LIST OF REFERENCE NUMERALS 
       [0000]    
       
           1  system 
           2  turntable 
           3  clamping unit 
           10  linear traverse 
           11  linear traverse 
           12  linear traverse 
           13  laser ablation device 
           14  processing head 
           15  chucking holder 
           16  laser welding head 
           20  clamping unit 
           21  clamping mechanism 
           22  clamping mechanism 
           23  frame 
           24  frame 
           25 - 28  threaded spindle 
           29  drive unit 
           30  drive unit 
           32  positioning pin 
           33  direction 
           40 - 43  blocking device 
           45  support means 
           49  clamping unit 
           50  workpiece 
           51  workpiece 
           52  clamping magnet 
           53  clamping magnet 
           54  drive 
           55  drive 
           60  turntable 
           61  joining edge 
           62  joining edge 
           80  workpiece 
           81  workpiece 
           82  joining edge 
           83  joining edge 
           84  laser head 
           85  laser head 
           86 - 89  path 
           90  clamping magnet 
           91  clamping magnet 
           92 - 95  roller pair 
           100  workpiece 
           101  workpiece 
           102  clamping mechanism 
           103  clamping mechanism 
           104  clamping mechanism 
           105  clamping mechanism 
           106  stop 
           107  upper clamping jaw 
           108  lower clamping block 
           109  upper clamping jaw 
           110  lower clamping block 
           111  movement direction 
           112  movement direction 
           113  joining edge 
           114  joining edge