Abstract:
A laser processing machine includes a beam splitter for splitting an incoming laser beam into a first laser beam having a first intensity and a second laser beam having a second intensity, a first focusing mirror for focusing the first laser beam onto a first laser processing site on a workpiece at an angle from a direction directly above the workpiece, a second focusing mirror for focusing the second laser beam onto second laser processing site on the workpiece at an angle from a direction directly above the workpiece, and a supplementary laser processing element for supplementing laser processing of the workpiece, wherein the supplementary laser processing element is disposed directly above the first or second laser processing site.

Description:
CLAIM OF PRIORITY  
       [0001]     This application claims priority under 35 USC § 119(a) to European Patent application number 04004604.7, filed on Feb. 28, 2004, the entire contents of which are hereby incorporated by reference. 
     
    
     TECHNICAL FIELD  
       [0002]     This disclosure relates to a laser processing machine.  
       BACKGROUND  
       [0003]     Sensors have been used in prior art laser processing machines to continuously follow the welding seam during laser welding. The sensor can monitor the exact position of the joint, and, in conjunction with a regulation and control unit, maintain tolerances during the welding process. It is thereby ensured that the laser welding head is always located directly above the joint. Welding seam tracing sensors and/or process control sensors are important mainly when used in connection with industrial robots, for example, for controlling the seam geometry of the weld. Process control is also important in addition to welding seam tracing. Thus, during laser processing, the degree of coupling of the laser beam, the production of splashes, and the welding depth can be monitored.  
         [0004]     An additional way to supplement a laser welding process is by supplying a solid or gaseous additional material, for example, a process gas or a wire, during the welding.  
         [0005]     The sensor and/or the means for supplying the additional material are generally disposed at a corresponding separation distance from the laser welding beam. The sensor is directed either at an angle toward the processing point (i.e., the sensor “faces” the processing location at an angle) or is located in a perpendicular orientation to a location in front of or behind the processing location (i.e., the sensor does not “face” processing itself, but a location that is leading or trailing relative to the processing location). However, because the laser beam typically is directed toward the workpiece from directly above the workpiece, the sensor or other supplementary laser processing element cannot also be located directly above the workpiece, because it would interfere with the laser beam or the laser beam optics. Thus, because of the orientation of the sensor (or other supplemental elements) with respect to the laser beam, in conventional arrangements, an exact rapid response by the sensor or by the additional material in three-dimensional laser processing is difficult or requires demanding technical solutions. For example, additional axes to move the sensor or the additional material can be required. The supplied data is either distorted or is not derived from the process itself. A further disadvantage is the increased size of the head, and the so-called interference contour.  
       SUMMARY  
       [0006]     The invention is based, at least in part, on arranging a supplementary laser processing element directly above the surface of the processed workpiece while directing two laser beams to the processed workpiece at slight angles to the overhead direction, which permits a rapid response from the supplemental element without orientation problems in three-dimensional laser processing and also minimizes the interference contour during laser processing.  
         [0007]     In one general aspect, a laser processing machine includes a beam splitter for splitting an incoming laser beam into a first laser beam having a first intensity and a second laser beam having a second intensity, a first focusing mirror for focusing the first laser beam onto a first laser processing site on a workpiece at an angle from a direction directly above the workpiece, a second focusing mirror for focusing the second laser beam onto a second laser processing site on the workpiece at an angle from a direction directly above the workpiece, and a supplementary laser processing element for supplementing laser processing of the workpiece, wherein the supplementary laser processing element is disposed directly above the first or second laser processing site.  
         [0008]     Implementations can include one or more of the following features. For example, the first and second laser processing sites can be different or identical laser processing sites (i.e., they are the same site). The supplementary laser processing element can be an optical sensor adapted and arranged for monitoring laser processing of the workpiece. The supplementary laser processing element can also be an optical element adapted and arranged for directing light to a remote optical sensor that is adapted for monitoring laser processing of the workpiece. The optical element can be a mirror. The optical element can be an end of an optical fiber. In certain embodiments, the supplementary laser processing element can be a mounting element for supporting and supplying additional material to the first or second laser processing site, or to both. The supplementary laser processing element can also be a gas supply nozzle for supplying a process gas to the first or second laser processing site, or to both.  
         [0009]     In various embodiments, the first intensity can be the same or different from the second intensity. For example, the first intensity can be more than about twice as great as the second intensity. In some embodiments, the beam splitter can be a knife-edge mirror.  
         [0010]     The laser processing machine can further include an actuating drive adapted to pivot the supplementary laser processing element in different directions above the workpiece. The laser processing machine can further include an actuating drive adapted to displace the supplementary laser processing element above the workpiece.  
         [0011]     The first laser processing site can be a focus of the first laser beam, the second laser processing site can be a focus of the second laser beam, and the first and second laser processing sites can be located at the same position. The supplementary laser processing element can be disposed directly above the first and second laser processing sites. In certain embodiments, the first laser beam and the second laser beam can define a cone directly above the workpiece in which the supplementary laser processing element is located.  
         [0012]     In another general aspect, the invention features a method of processing a workpiece by providing a supplementary laser processing element directly above the workpiece and providing an input laser beam. The input laser beam is split into a first laser beam having a first intensity and a second laser beam having a second intensity. The first laser beam is focused onto a first laser processing site on a workpiece at an angle from a direction directly above the workpiece, and the second laser beam is focused onto second laser processing site on the workpiece at an angle from a direction directly above the workpiece.  
         [0013]     Implementations can include one or more of the following features. For example, the method can further include sensing light reflected from the first and/or second laser processing site with the supplementary laser processing element and adjusting an optical property of the first or second laser beam in response to the sensed light. The first intensity can be the same or different from the second intensity. The method can further include providing a material to the first or second laser processing site from the supplementary laser processing element.  
         [0014]     Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described below. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting.  
         [0015]     The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features and advantages will be apparent from the description and drawings, and from the claims. 
     
    
     DESCRIPTION OF DRAWINGS  
       [0016]      FIG. 1  is a schematic perspective view of a laser processing machine having a double focusing unit.  
         [0017]      FIG. 2  is a sectional view of the laser processing machine along the line II-II of  FIG. 1 .  
         [0018]      FIG. 3  is a sectional view of the laser processing machine along the line III-III of  FIG. 1 .  
         [0019]      FIG. 4  is a schematic perspective view of a laser processing machine having a double focusing unit.  
         [0020]      FIG. 5  is a schematic perspective view of a laser processing machine having a double focusing unit. 
     
    
       [0021]     Like reference symbols in the various drawings indicate like elements.  
       DETAILED DESCRIPTION  
       [0022]     A simple arrangement of a laser processing element that permits rapid follow-up without orientation problems and also minimizes the interference contour during three-dimensional laser processing can be achieved by splitting the laser beam into two beam portions that are focused onto the workpiece and arranging the laser processing element between the two beam portions.  
         [0023]     As shown in  FIG. 1 , a double focusing unit  1  of a laser processing machine includes an angle apparatus  2 , a beam splitter  3  and two focusing mirrors  4  and  5 . A laser beam  6  that enters the double focusing unit  1  is initially deflected and split by the beam splitter  3  into two laser beam portions  7  and  8 . The beam splitter  3  can be, for example, a knife-edge mirror that can be passed into a portion of the beam to split the beam. The two laser beam portions  7  and  8  are subsequently reflected by focusing mirrors  4  and  5  and directed to a common focus  9  on a workpiece surface  10  of a workpiece  11  or  11 ′. A light-gathering optical sensor  12  is provided to track a welding seam  13  as the double focusing unit  1  of the laser processing head moves across the workpiece surface  10 .  
         [0024]     The two focusing mirrors  4  and  5  can be adjusted and/or pivoted in three dimensions independently of each other using piezo actuating drives. Instead of one single focus  9 , two foci that are disposed closely next to or behind each other can be generated by the focusing mirrors  4  and  5 . The foci may be adjusted relative to each other.  
         [0025]     The beam splitter  3  can be fixed in the center of the impinging laser beam  6 . The beam splitter  3  (e.g., a knife-edge mirror) may also be disposed to be movable and be moved out of the center of the laser beam  6 , thereby permitting correction of the position of the foci or obtaining an asymmetric distribution of the power in the laser beam portions  7  and  8 , such that the two laser beam portions  7  and  8  can have different intensities. For example, one laser beam portion  7  can have a minority of the overall power (e.g., about 25, 30, 35, 40, or 45%) of the laser beam  6  and serve for pre-heating the workpieces  11  and  11 ′. The other laser beam portion  8  can have a majority of the overall power (e.g., about 55, 60, 65, 70, or 75%) of the laser beam  6  and be used for welding the workpieces  11  and  11 ′.  
         [0026]     The beam splitter  3  can be a prism disposed in the usual position of a single focusing mirror of a conventional focusing unit that does not include a beam splitter. This arrangement generates a space directly above focus  9  of the laser beam portions  7  and  8  on the workpieces  11  and  11 ′ with good accessibility through which the laser processing of the workpieces  11  and  11 ′ can be centrally monitored by a sensor  12  and/or through which an additional material may be centrally supplied to the laser processing site. This arrangement facilitates precise follow-up in three-dimensional processing with the sensor or other supplementary elements. For precise follow-up, the light-gathering optical sensor  12  may be immovably connected to the movable laser processing head, or the sensor  12  can be connected to the laser processing head, such that the sensor can be pivoted and displaced in the space below the beam splitting region, for example, directly above the welding joint.  
         [0027]     A light-gathering optical element, for example, a mirror or the end of a light guide or optical fiber, can be disposed at this position instead of the sensor  12 , and the optical element can guide light to a remotely located sensor. This arrangement is favorable if a sensor is used that is too large to be located in the position above the focus  9  of the laser beam portions  7  and  8 .  
         [0028]     As shown in  FIGS. 2 and 3 , the laser beam  6  is deflected by a deflecting mirror  14  housed in the angle apparatus  2  toward the beam splitter  3 . The beam splitter  3  splits the laser beam  6  into laser beam portions  7  and  8  that are directed towards focusing mirrors  4  and  5 , respectively. The laser beam portion  8  is focused onto the workpieces  11  and  11 ′ (e.g., sheet metal) using the focusing mirror  5 .  
         [0029]     The sensor  12  can monitor, for example, the degree of coupling between the laser beam portions  7  and  8 , the formation of splashes from the workpieces  11  and  11 ′, and/or the welding depth. Changes in the region of the workpiece surface  10  can be detected by the sensor  12  during laser welding. The sensor  12  is mechanically connected to the angle apparatus  2  in a manner that allows positioning of the double focusing unit  1  and additional adjustment of the sensor  12  with respect to the double focusing unit  1 . The sensor  12  is electrically connected to a regulation and control unit  15 , although, for clarity, the cables and connections between the sensor and the control unit  15 , which are integrated in the laser processing machine, are not shown. The sensor  12  in combination with the control unit  15  can be used to control optical properties of the laser beam portions  7  and  8  (e.g., the total and relative intensities of the laser beam portions  7  and  8 ). For example, the control unit  15  can control the position of a knife-edge mirror beam splitter  3  in response to feedback from the sensor to vary the relative intensity of the laser beam portions  7  and  8 .  
         [0030]     Actuating drives for the two focusing mirrors  4  and  5  and for the beam splitter  3  can be provided in the focusing unit  1  and can be connected to the regulation and control unit  15 , such that their positions and/or orientations can be controlled as a function of data detected by the sensor  12 .  
         [0031]     The beam splitter  3  and beam portions  7  and  8  define a space  30 —a “triangle” as shown in  FIG. 3 —below the beam splitter  3  and starting from or above the welding joint on the workpiece  11 . The sensor  12  is arranged within this “triangle.” Beam portions  7  and  8  impinge onto the welding joint at an angle &lt;90° from the side rather than directly from above the workpiece  11 , and enclose together an angle α that opens from the joint. Thus, a space  30  is provided directly above the welding joint, and the sensor  12  is located in the space  30 . The sensor  12  is disposed to be pivotable and displaceable (as shown by the double arrows  32  and  34  in  FIGS. 2 and 3 ), such that the sensor  12  can be disposed between the two beam portions  7  and  8  within the angle α directly above the welding joint.  
         [0032]     In other implementations, the space  30  between the two laser beam portions  7  and  8  can be used to position other materials or parts directly above the workpiece, either in place of, or in conjunction with, sensor  12 . For example, as shown in  FIG. 4 , a mounting element  102  is provided in the region of the focusing unit  101  (which substantially corresponds to the focusing unit  1  of  FIG. 1 ) and can be provided to support and supply an additional material (e.g., a wire or rod  103 , for example, a welding rod or wire) to the welding seam  13  of the two workpieces  11  and  11 ′ from directly above the workpieces  11  and  11 ′ and between the two laser beam portions  7  and  8 . The mounting element  102  can be, for example, a pliers, a collet, a tube, or a plurality of tubes or rings for supporting the additional material  103 , and the additional material  103  can be fed through the mounting element to the welding seam  13 .  
         [0033]     As shown in  FIG. 5 , a process gas supply  202  (e.g., a nozzle) can be disposed between the laser beam portions  7  and  8  directly above the welding seam  13  in the region of a focusing unit  201  (which substantially corresponds to the focusing unit  1  of  FIG. 1 ). The process gas  203  can be supplied to the laser processing region from directly above the laser processing region. The process gases  203  (e.g., protective gases and/or working gases) can be supplied to the welding location in or on the laser processing head.  
       Other Embodiments  
       [0034]     It is to be understood that while particular implementations have been described, the foregoing description is intended to illustrate and not limit the scope of the invention that can be claimed. For example, it is clear that an implementation may include the sensor  12 , the supply of additional material  103  and the supply of process gases  203 .