Abstract:
An oscillating welding method is provided. The oscillating movement during welding in the vertical and/or horizontal direction results in smaller grains being obtained, the smaller grains preventing the development of cracks during welding.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to PCT Application No. PCT/EP2014/071904, having a filing date of Oct. 13, 2014, based off of German application No. 102013225490.3 having a filing date of Dec. 10, 2013, the entire contents of which are hereby incorporated by reference. 
     
    
     FIELD OF TECHNOLOGY 
       [0002]    The following relates to a welding method in which the welding beam is moved in oscillation. 
       BACKGROUND 
       [0003]    During laser deposition welding of nickel-based superalloys having a high fraction of metallic phase γ′, hot cracks can form during solidification of the melt. Reducing the beam diameter of the laser with circular intensity distribution raises the cooling rate and makes it possible to avoid solidification cracks. However, this reduces the rate of deposition of the material. 
       SUMMARY 
       [0004]    An aspect relates to specifying a welding method by means of which it is simultaneously possible to achieve high cooling rates and high deposition rates. 
         [0005]    The method generates, simply and more rapidly, crack-free microstructures during welding. 
     
    
     
       BRIEF DESCRIPTION 
         [0006]    Some of the embodiments will be described in detail, with reference to the following FIGURES, wherein like designations denote like members, wherein: 
           [0007]      FIG. 1  shows, schematically, the arrangement of an embodiment of a deposition welding setup with a laser and a powder feed. 
       
    
    
       [0008]    The FIGURE and the description represent only exemplary embodiments of the invention. 
       DETAILED DESCRIPTION 
       [0009]    An oscillating motion in the horizontal and/or vertical direction, and in the variation of the laser radiation, causes the solidification front to change constantly so as to produce an oscillating solidification form. A constantly changing solidification function interrupts grain growth during solidification of the melt and the lattice solidifies as a single grain. The fine-grained quality of the lattice causes the resulting remaining welding residual stresses to be distributed over the grain boundaries so as to avoid cracks in the welding seam or in the welding bead or therebetween. 
         [0010]    The welding method can be remelt welding or deposition welding. Both methods produce a melt and a solidification front. 
         [0011]      FIG. 1  shows a device  1  for a welding method, in particular a laser welding method. 
         [0012]    The method is not restricted to laser welding methods, but is also applicable to electron beam welding methods and other welding methods such as plasma welding methods or also other additive production methods. 
         [0013]    Material is deposited onto a substrate  4  which, in the case of turbine blades, is a nickel- or cobalt-based superalloy having a high γ′ fraction and is therefore an alloy having generally poor weldability. A welding bead  6 , as part of the deposition weld, has already been generated. 
         [0014]    At those points where a laser with its laser radiation as exemplary energy source  13  is oriented onto the substrate  4 , there is a melt pool  7 . Via a powder nozzle as exemplary material feed  10 , the powder  8  is molten. 
         [0015]    This laser radiation is in particular pulsed and the material  8  is supplied in the form of powder, but can also be supplied as a wire. 
         [0016]    The laser radiation or the energy supply  13  can be moved back and forth along the direction  16  that is vertical with respect to the surface  5  of the substrate  4 , so as to vary the laser beam diameter at the surface of the welding track  7 . The deflection is preferably between 1 mm and 2 mm. 
         [0017]    It is alternatively or additionally possible to carry out an oscillating motion perpendicular to the direction  16 , preferably in the form of a horizontal motion  19  that is transverse to the forward motion of the energy supply  13  of the laser radiation and the powder feed  10  relative to the melt pool  7 . The deflection of the oscillating motion is preferably between 1 mm and 2 mm. 
         [0018]    The area to be welded has, in at least one direction, a length greater than or equal to 4 mm, i.e. preferably multiple welding beads are generated or deposited next to one another and may also overlap. 
         [0019]    The vertical  16  and/or horizontal  19  motion can be used individually or combined with one another, both in remelting and deposition welding, and is superimposed over the forward motion of the energy supply  13  with respect to the substrate  4 . 
         [0020]    There results, in the case of an oscillating motion in the direction  19 , a zigzag motion, a meandering motion or a sinusoidal motion as seen in the direction  16  in plan view onto the substrate  4 . The same holds for a view perpendicular to the direction  16  in the case of an oscillating motion in the direction  16 . 
         [0021]    On the basis of embodiments of the invention, this procedure achieves improved material properties. 
         [0022]    Although the present invention has been disclosed in the form of preferred embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention. 
         [0023]    For the sake of clarity, it is to be understood that the use of “a” or “an” throughout this application does not exclude a plurality, and “comprising” does not exclude other steps or elements.