Abstract:
A method of processing a component ( 10 ) with an energy beam ( 13 ) comprises simultaneously scanning and heating a first portion ( 12 ) and second adjacent portion ( 14 ) of the component with an energy beam ( 13 ) At a point or area of divergence of the portions of the component, the energy beam is controlled to repeatedly move back and forth between the portions of the component. This simultaneous heating of adjacent portions ( 12, 14 ) of the component is configured to keep a thermally-induced distortion of the component within a predefined tolerance. This dual-path processing may be performed on a bed of fluidized powdered material including a powdered metal material and a powdered flux material.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention is generally related to manufacturing techniques for forming or repairing a component, such as airfoils for blades or vanes for a combustion turbine engine; and, more particularly, to a method for processing a component involving use of an energy beam, such as a laser beam. 
       BACKGROUND OF THE INVENTION 
       [0002]    Combustion turbine engines, such as gas turbine engines, typically include a turbine section having alternating arrangements of components, such as rotatable blades and stationary vanes A flow of hot gases from a combustor section expands against respective airfoils of the blades and vanes to rotationally drive the blades in the turbine section, where mechanical energy is extracted to turn a shaft, which may power a compressor section of the turbine engine. 
         [0003]    During engine operation, the hot gases produce an environment that corrosively attacks the surfaces of the blades and vanes and often results in oxidation and corrosive pitting. The hot gases, soot from combustion, particles within the flow of hot gases, and other foreign objects also wear against the turbine blades and vanes and erode the surfaces of the blades, vanes, and other turbine engine components, which may undesirably reduce the useful life of the blades or vanes Additionally, the tip region (e g., a squealer tip) of the turbine blades is often subjected to a substantial amount of wear. For example, the blade tip may be abraded when it rubs up against a shroud of a casing in which the turbine blade rotates. High temperatures and stresses further degrade such components by thermo-mechanical fatigue (TMF) and result in cracking of components that are subjected to such loadings. 
         [0004]    It is known to use laser-based processes for forming or repairing such components of turbine engines. United States Patent Application Publication No. US 2013/0136868 A1, authored by the present inventors, discloses improved methods for depositing superalloy materials that are otherwise difficult to weld. Those methods include the laser melting of powdered superalloy material together with powdered flux material to form a melt pool under a layer of protective slag. The slag performs a cleaning function in addition to protecting the molten alloy material from the atmosphere. Upon solidification, the slag is removed from the newly deposited superalloy material to reveal a crack-free surface and deposit. Such methods have been shown to be effective even for superalloy materials which are beyond the traditional region of weldability. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]    The invention is explained in the following description in view of the drawings that show: 
           [0006]      FIG. 1  is a schematic illustration of conventional single path energy beam processing of a component. 
           [0007]      FIG. 2  is a schematic illustration of dual-path energy beam processing of a component. 
           [0008]      FIG. 3  is a schematic of another embodiment of dual-path energy beam processing of a component 
           [0009]      FIG. 4  is a schematic of a dual-path energy beam processing of a component illustrating an inter-path melt pool 
           [0010]      FIG. 5  is another embodiment of dual path energy beam processing of a component. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0011]    The present inventors have innovatively recognized certain limitations in connection with known techniques that utilize a beam of energy, e g, lasing energy or other modalities of energy, for processing a component that may involve a relatively complex geometry For example, airfoils of blades, vanes, etc., that may be used in a combustion turbine engine involve such complex geometries. Non-limiting applications may include various additive manufacturing processes, including without limitation laser cladding, selective laser melting (SLM) or selective laser sintering (SLS) as may be used to fuse and deposit a layer of superalloy powder onto a superalloy substrate, etc. 
         [0012]    In  FIG. 1 , a prior art laser processing path is schematically represented with respect to the additive repair or manufacture of a turbine blade tip  10 , or it may also represent an airfoil for a turbine blade. Prior energy beam processing techniques used low power (e.g. 300 w) energy beam processing. The heat input to the blade tip  10  generated at such low power is low enough that the blade does not distort regardless of path progression. The inventors have discovered that using high power (e.g 2000 w) energy beam processing and one pass wrapping the blade in the continuous clockwise (or counterclockwise) path, as shown in  FIG. 1 , heat buildup is enough to cause the below noted distortion The blade tip  10  may be repaired or manufactured according to the above-described laser processing using a feeding of material coaxial with the laser beam or pre-placement of material such as in a bed of powdered metal material. The blade tip  10  includes a convex side  12  and concave side  14 , both of which are substrates that exist in the initial casting and which may be further extended or repaired by laser clad deposition. From point A to point B a single rastered programmed laser path represented by arrows  66  is shown along a convex blade edge  12  of the blade tip  10 . The slashing represents the energy beam  13 , such as a laser beam During processing, the convex blade edge  12  is heated as metal deposit(s) is (are) added; however, heating of the convex edge  12  can cause shrinkage strains and distortion along the concave edge  14  of the blade tip  10 . Thus, as the laser processing reaches the concave edge  14  of the blade tip  10  there is a misalignment with the concave blade edge  14  and the laser path 
         [0013]    The inventors have discovered that the simultaneous scanning and heating of the both convex edge  12  and the concave edge  14  results in balanced strains, reducing distortion of the edges  12 ,  14 . With respect to  FIG. 2 , a rastered programmed dual-path energy beam processing is shown from a start point C to an end point D. As shown, at or adjacent to point C the convex side  12  and concave edge  14  are integrally connected and then diverge downstream from point C along the energy beam paths represented by arrows  16 A,  16 B. A “run on tab” may be provided so that beam  13  results in a steady state and properly dimensioned deposit as it reaches the component  10 . In an embodiment, the laser beam  13  is widened as processing proceeds towards point D and along the edges  12 ,  14  For example, the beam may be widened from about 4 mm to about 12 mm. Three dimensional scanning optics are available to handle up to 10 kW of processing power. For this widened beam about 1 kW to 2 kW may be required for processing power. As the edges  12 ,  14  continue to diverge along the beam path, the beam  13  is controlled to move from one edge, e.g.  12 , to the other edge, e.g.  14 , to simultaneously and selectively heat powdered metal onto the edges  12 ,  14  along respective beam paths  16 A,  16 B The width of the beam may be reduced to for example 4 mm wide when scanning the beams  16 A,  16 B. The power may be increased to about 3 kW, or the travel speed could be slowed to ensure good fusion between the metal deposits and underlying substrate. The beam  13  may move from one edge to the other edge at a jump speed of 3 m/s at which speed it is not likely to generate enough heat to melt any powdered metal between the edges  12 ,  14   
         [0014]    The beam  13  is controlled to stop the movement between the edges  12 ,  14  and is widened into (e.g. 12 mm wide) as the beam  13  approaches end point D and then is tapered into a smaller width beam (e.g 4 mm) onto for example a “run-off” tab The movement and rastering of the beam  13  may be accomplished with known multi-dimensional galvanometer-driven laser scanning optics. 
         [0015]    This simultaneous heating and cladding of both the convex and concave edges  12 ,  14  of the blade tip  10  provides balanced shrinkage resulting in balanced strains, and reduced distortion thereby preventing the above-described misalignment. Another advantage of this multi-path simultaneous scanning and heating is that it involves a single pass/single layer and melted metal deposits do not overlap a previously solidified metal deposit. With respect to  FIGS. 3 and 4 , a schematic sectional view of turbine blade tip  10  with convex and concave edges  12 ,  14  is shown As described above, such geometries require simultaneous dual processing in close proximity For example, an energy beam  13  may start processing and is controlled to move between edges  12 ,  14  at points E and F. Simultaneous dual path processing at such a location may lead to melt pools, which tend to melt together into a single, wide melt forming an inter-path deposit  15  that is not completely fused to an underlying substrate. This inter-path melt  15  may prevent deposition of metal immediately downstream from the points E, F where the beam  13  is controlled to move from one edge to the other edge. This may be the result of surface tension of the inter-path melt  15  resisting separation of the melt  15  into two paths. 
         [0016]    A solution to this problem is illustrated in  FIG. 4 , which shows dual-path laser processing including staggered starting points G, H. As shown, processing of beam  13  along path  16 A is allowed to progress past the start point H of beam path  16 B to point G, at which time laser processing begins along beam path  16 B at point H As described above, the beam  13  may be controlled to move between edges  12 ,  14  to simultaneously scan and heat powdered metal material on both edges  12 ,  14 . When beam  13  begins scanning along beam path  16 B (edge  14 ) at start point H, the metal deposit along beam path  16 A (edge  12 ) is solidified and somewhat cooled. In addition, the use of the above described powdered flux material forms a layer of slag over the recently deposited metal, and this layer of slag insulates the metal deposit and provides resistance to re-melting of the deposition. The metal deposited along beam path  16 A therefore does not merge with the metal deposit of path  16 B. 
         [0017]    In the embodiment shown in  FIG. 4 , the beam path  16 A follows a convex side (edge  12 ) of the blade tip  10 ; therefore, beam path  16 A is longer than beam path  16 B along the concave side (edge  14 ) of the blade tip  10 . Accordingly, processing along the first path  16 A is allowed to proceed past the starting point H on the second beam path  16 B, so that forward processing speeds along both paths  16 A,  16 B are similar or substantially the same. The magnitude of staggering between point G and starting point H may be on the order of 5 to 10 millimeters to avoid inter-path melting In another embodiment, a “run-on” tab may be added to the substrate of the second beam path to allow for additional separation of the beam paths  16 A,  16 B As the beam  13  approaches an end point wherein the two edges  12 ,  14  converge, the beam  13  is controlled to stop moving between the edges  12 ,  14 , and the beam  13  may be widened, e.g 12 mm to cover the area at which the edges  12 ,  14  converge at point I. A “run-off” tab may be provided and the beam  13  may be tapered (e g to 4 mm) as it moves across the area of convergence including point I onto the “run-off” tab. 
         [0018]    In the manufacture or repair of a blade tip  10 , also referred to as a squealer, the above described staggered delayed start, re-melting does occur at point H. This is due, at least in part, because the blade tip often has a short (e.g. 10 or 20 mm) gap along the concave edge  14  where no tip is required. So a second start is actually occurring at point H that is not connected with the path  16 A along the convex edge  12   
         [0019]    Another embodiment of a dual-path processing method is illustrated in  FIG. 5 , in which the dual-path laser processing is initiated from the opposite end of the blade tip  10 . That is, the scanning begins at the larger or wider end  10 A wherein the divergence of the edges is more dramatic than the divergence of the edges  12 ,  14  at end  10 B. As described above, a “run-on” tab may be provided at end  10 A to initiate scanning and heating of the powdered material The beam  13  is widened to cover the area of convergence or divergence of the edges  12 ,  14 . The beam  13  continues down paths  16 C on the concave side (edge  14 ) and  16 D on the convex side (edge  12 ) and the beam scan widths along each side is narrowed for example to about 4 mm for each path. The wider divergence angle between paths  16 C,  16 D can be of advantage in overcoming surface tension and in achieving separation of the melt. 
         [0020]    The concave path  16 C is shorter than the convex path  16 D so for equal path travel speeds, the concave path  16 C finishes first. To further illustrate this staggered finish in reference to  FIG. 5 , when the energy beam  13  reaches point J along beam path  16 C, the energy beam  13  is at point K along convex beam path  16 D. As the convex path  16 D then progresses past an end  10 B of the concave path  16 C, slag (from melted and cooled flux material) covering the concave path  16 C deposit prevents re-melting of the underlying deposit. Rather than a delayed start in paths, this embodiment involves a delayed finish of paths As beam  13  completes the scan along beam path  16 D, the metal deposited on the edge  12  has sufficiently cooled to avoid the above-referenced inter-path melt at adjacent substrates that are in such close proximity Moreover, to the extent that a flux material is used a layer of slag insulates an underlying recently deposited metal providing resistance to melting. 
         [0021]    The above-described embodiments of dual-path energy beam processing may be performed in a preplaced bed or fluidized bed of powdered metal material and powdered flux material or by specialized feeding of such powders. In case multiple pass deposits are required, and because a layer of slag will form over the metal deposit, a slag removal tool may be provided to remove slag from the deposited metal layers 
         [0022]    While various embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by way of example only. Numerous variations, changes and substitutions may be made without departing from the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.