Abstract:
A device for connecting two components by welding with a laser beam, in which the components are overlapping in a partial region of their mutually facing surfaces. The device includes an optical beam divider that has an inlet for the laser beam and a device for alternately distributing the laser beam to a plurality of outlets. Each of the outlets is optically coupled via a beam-guiding device to a laser welding head which contains a focusing and deflection lens system for guiding the focused laser beam over a surface of a component facing the laser welding head.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This is a continuation of copending International Application PCT/EP97/04298, filed Aug. 7, 1997, which designated the United States. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to an apparatus for welding together by a laser beam two components that overlap in a subregion of their mutually facing surfaces. 
     When welding components together, it is known to use not only so-called butt welds but also lap welds. Such lap welds, in which the components to be joined together overlap in a subregion of their mutually facing surfaces, are suitable in particular for the use of laser welding methods, since great welding depths with at the same time low heat input and an associated high welding quality can be achieved with a laser beam with high welding speeds. For production and commercial reasons, in the case of lap welds the components to be joined together are generally joined by a plurality of spaced-apart spot welds. 
     An apparatus for spot welding with a laser beam is known, for example, from European Patent 0 440 002 B1. In the case of the known apparatus, a laser welding head is disposed at the free end of a multi-jointed robot arm. With such a robot arm, the welding head can be guided freely over the surface of the component to be joined and stopped at the positions predetermined for spot welding. For this purpose, the welding head is positioned with the aid of the robot arm by a fixing element, by which the two components are pressed firmly against each other in an overlapping region. The fixing element includes two clasp-like clamping elements, one of which is provided with a central opening. The laser welding head is positioned and fixed over the central opening. This permits spot welding at a location of the overlapping region at which the components are pressed firmly against each other and as far as possible without any gaps therebetween. With the aid of the robot arm, the laser welding head can be brought successively up to a plurality of spaced-apart clamping elements, in order to ensure the strength of the joint by a multiplicity of such spot welds. 
     It is known from U.S. Pat. No. 4,654,505 to provide, instead of a single laser welding head which can be guided by a robot arm, a plurality of laser welding heads which are disposed on a clamping apparatus and into which the laser beam produced by a laser and spreading out freely is fed at successive times by adjustable mirrors. 
     However, the spot weld produced by the laser beam has a relatively small diameter, with the result that the required strength of the joint is ensured only by a correspondingly high number of spot welds. This entails increased expenditure with respect to process engineering, which calls into question the cost-effectiveness of spot-welding methods carried out with a laser beam. 
     German Patent 43 31 827 C1 discloses an apparatus for securing a screwed joint by a multiplicity of microwelded points produced by a laser beam and provided around the circumference of the screw head or the nut. In the case of this known apparatus, two or more part-beams are formed by a beam splitter disposed in the laser welding head, with the result that a plurality of microwelded points are produced simultaneously. An additional turning of the entire optical configuration within the laser welding head permits multiple setting of the microwelded points around the circumference of the screwed joint, by a single stationary laser welding head. 
     Japanese Laid-Open Application No. JP 58-68492 discloses an apparatus for spot welding by a laser beam, in which a rotatably mounted deflecting and focussing optical system is disposed in the laser welding head and is turned during the welding operation, with the result that the welded points form a circular line and the strength of the weld is increased. 
     SUMMARY OF THE INVENTION 
     It is accordingly an object of the invention to provide an apparatus for welding together two components that overcomes the above-mentioned disadvantages of the prior art devices of this general type, in which high cost-effectiveness and speed are accompanied by a welded joint having high strength. 
     With the foregoing and other objects in view there is provided, in accordance with the invention, an apparatus for welding together with a laser beam two components which overlap in a subregion of their mutually facing surfaces, including: a laser welding head; a beam-guiding device; an optical beam distributor having an input for receiving a laser beam, a plurality of outputs each coupled optically to the laser welding head via the beam-guiding device, and a distributor for alternately distributing the laser beam between the plurality of outputs; and a focussing and deflecting optical system disposed in the laser welding head receiving, guiding, and focussing the laser beam over a surface of a component facing the laser welding head. 
     The apparatus for welding together with a laser beam two components which overlap in a subregion of their mutually facing surfaces includes according to the invention an optical beam distributor. The optical beam distributor has an input for receiving the laser beam and a device for alternately distributing the laser beam between a plurality of outputs which are respectively coupled optically to a laser welding head via a beam-guiding device. In addition, there is a focussing and deflecting optical system disposed in the laser welding head for guiding and focussing the laser beam over the surface of the component facing the laser welding head. 
     By these measures, a linear weld can be produced without moving the laser welding head. That is to say even with the laser welding head disposed stationarily on the apparatus for receiving the parts to be joined, by guiding, i.e. moving, the laser beam over the surface of the component. In other words, instead of a number of spatially separated linear welds corresponding to the number of laser welding heads, the linear form is predetermined by the movement of the focussing and deflecting optical system in the laser welding head. As a result, the strength of the joint between the components is increased, without requiring an increase in the number of welds. 
     In an advantageous development of the invention, a focussing deflecting mirror is provided in the welding head for focussing the laser beam. As a result, the number of optical elements required in the welding head is reduced. 
     In particular, the focussing deflecting mirror is mounted in a linearly displaceable manner. As a result, a weld can be produced along a straight line. 
     In a further advantageous development of the invention, a lens is provided for focussing the laser beam. A plane-parallel plate which can be pivoted about an axis oriented perpendicularly with respect to the center axis of the laser beam is disposed in front of the lens in the direction of propagation of the laser beam. As a result, a weld can likewise be produced along a straight line. 
     In an advantageous development, a prism mounted rotatably about the center axis of the laser beam is disposed in front of the lens. In this way, a circular weld can be produced. This circular line, the diameter of whose circle can be chosen to be significantly greater than the line width, has the effect of simulating virtually a spot weld of large diameter, and similar strength values are achieved with improved welding quality. 
     A light-conducting fiber is preferably provided between the beam distributor and the laser welding head as a beam-guiding device. This permits a greater flexibility in the selection of the location of the laser welding heads, since the beam guidance is simplified in comparison with an apparatus in which the laser beam spreads out freely. 
     In the beam distributor in particular, pivotable or displaceable path-folding mirrors are disposed in the path of rays of the laser beam. 
     In a particularly preferred development, a path-folding mirror, which is rotatable about the axis of the laser beam falling onto it and to which a plurality of outputs are disposed in a stellar formation about this axis are assigned, is disposed in the path of rays of the laser beam in the beam distributor. As a result, the number of movable path-folding mirrors required for beam distribution is reduced. 
     Other features which are considered as characteristic for the invention are set forth in the appended claims. 
     Although the invention is illustrated and described herein as embodied in an apparatus for welding together two components, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. 
     The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagrammatic illustration of a basic representation of an apparatus according to the invention; 
     FIG. 2 is a longitudinal section view of a laser welding head of the apparatus; 
     FIGS. 3 and 4 are illustrative representations of embodiments of a focussing and deflecting optical system disposed in the laser welding head; and 
     FIGS. 5 and 6 are illustrative representations of embodiments of a beam distributor, by which the laser beam of a laser can be distributed between a plurality of laser welding heads. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In all the figures of the drawing, sub-features and integral parts that correspond to one another bear the same reference symbol in each case. Referring now to the figures of the drawing in detail and first, particularly, to FIG. 1 thereof, there is shown two components  2  and  4  to be joined together and disposed in a clamping device  6 . The components  2  and  4  overlap in a subregion of their mutually facing surfaces and are braced against each other in the overlapping region by a multiplicity of clamping elements  8 , of which only one is represented in the figure. In the exemplary embodiment, the clamping element  8  respectively includes a mounting  10 , which can move, for example in a linear guide, and on which a laser welding head  12  is fixed. Instead of a linearly movable mounting, a pneumatically or hydraulically pivotable lever may also be provided. 
     The laser welding head  12  is pressed by its end face  13  in the overlapping region of the two components  2  and  4  against the surface of the component  4  facing it and makes the mutually facing surfaces of the components  2  and  4  bear against each other as far as possible without any gaps in a region in which a laser weld is to be carried out. The clamping element  8  consequently serves at the same time as a positioning device for positioning and fixing the laser welding head  12  over the surface of the component  4 . 
     The laser welding head  12  is optically coupled via a beam-guiding device  14 , in the exemplary embodiment a light-conducting fiber, to an output  16  of an optical beam distributor  18 , each output  16  being assigned a laser welding head  12 . The optical beam distributor  18  includes a number of pivotable path-folding mirrors  20  corresponding to the number of outputs  16 . The path-folding mirrors  20  are disposed in series and by which a laser beam  22 , which is produced by a laser  15  and in the exemplary embodiment is freely guided, can be successively distributed between the different outputs  16 , according to the pivoting position of the path-folding mirrors  20 . In the optical beam distributor  18 , each output  16  is preceded by a focussing optical system  24 , by which the laser beam  22  is fed into the beam-guiding device  14 . 
     The laser welding head  12  serves in the exemplary embodiment at the same time as part of the clamping element  8 , by which the clamping force is transferred to the overlapping components  2  and  4 . 
     According to FIG. 2, the laser welding head  12  includes a collimating unit  26  with a collimating optical system  27 , which is depicted by dashed lines and in which the laser beam  22  emanating from the light-conducting fiber of the beam-guiding device  14  is collimated. Disposed at an output of the collimating unit  26  is a fixed deflecting mirror  28 , by which the collimated laser beam is deflected by 90°. In addition to the collimating unit  26 , there is disposed a focussing unit  29 , which includes a focussing deflecting mirror  30 , by which the laser beam  22  is focussed and deflected toward the end face  13 . The focussing deflecting mirror  30  is disposed displaceably in the focussing unit  29 , parallel to the direction of propagation of the collimated laser beam  22  falling onto it, with the result that it can be used to produce a linear weld. The length of the linear weld is limited by the maximum possible linear displacement of the focussing deflecting mirror  30 . Drive elements  32  required for the linear displacement of the focussing deflecting mirror  30  are likewise disposed in the focussing unit  29 . With the clamping device  6 , which includes a plurality of such laser welding heads  12 , the components  2  and  4  (FIG. 1) are joined together by a stitch weld. 
     The focussing unit  29  also includes a welding nozzle  34 , such as is known, for example, from International Patent Application WO 95/03911. The welding nozzle  34  is disposed in a pressure-stable housing part  36  which is open at the bottom, can be placed onto the surface of the component  4  and transfers to the component  4  the clamping force exerted by the mounting  10  (FIG. 1) on the housing of the focussing unit  29  fixed in it. 
     In the exemplary embodiment according to FIG. 3, a laser welding head  40  is provided, in which a lens  42  is provided instead of the focussing deflecting mirror  30  provided in FIG. 2 for focussing the laser beam  22  collimated by the collimating optical system  27 . Disposed in front of the lens  42  in the path of rays of the collimated laser beam  22 , i.e. in the direction of propagation of the laser beam  22 , is an optically transparent plane-parallel plate  44 , which is mounted pivotably about an axis  46  oriented perpendicularly with respect to the center axis of the collimated laser beam  22 . By pivoting the plane-parallel plate  42 , the laser beam can be moved back and forth on the surface of the component  4  along a straight line  48 . 
     In the embodiment according to FIG. 4, a prism  52 , which is transparent for the laser beam  22 , is disposed in front of the lens  42  in the collimated laser beam  22 , i.e. between the lens  42  and the collimating optical system  27 . The prism  52  is mounted pivotably, preferably rotatably, about a center axis  54  of the laser beam  22 . A rotation of the prism  52  through 360° has the effect that the focus of the laser beam  22  on the component  4  describes a closed curve  56 , in the example a circle. 
     According to FIG. 5, a beam distributor  60  is provided, which, as a departure from the exemplary embodiment represented in FIG. 1, includes a multiplicity of linearly displaceable mirrors  62  disposed one behind the other. 
     According to FIG. 6, in an advantageous development, a beam distributor  70  is provided, which includes a path-folding mirror  72  which is rotatable about the axis of the laser beam  22  falling onto it, is inclined at  450  with respect to this axis and with which the laser beam  22  can be distributed in a radial or stellar manner between outputs  16  disposed on the circumference of the beam distributor  70 .