Method for processing a part with an energy beam

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.

FIELD OF THE INVENTION

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

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.

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.

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.

DETAILED DESCRIPTION OF THE INVENTION

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.

InFIG. 1, a prior art laser processing path is schematically represented with respect to the additive repair or manufacture of a turbine blade tip10, 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 tip10generated 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 inFIG. 1, heat buildup is enough to cause the below noted distortion The blade tip10may 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 tip10includes a convex side12and concave side14, 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 arrows66is shown along a convex blade edge12of the blade tip10. The slashing represents the energy beam13, such as a laser beam During processing, the convex blade edge12is heated as metal deposit(s) is (are) added; however, heating of the convex edge12can cause shrinkage strains and distortion along the concave edge14of the blade tip10. Thus, as the laser processing reaches the concave edge14of the blade tip10there is a misalignment with the concave blade edge14and the laser path

The inventors have discovered that the simultaneous scanning and heating of the both convex edge12and the concave edge14results in balanced strains, reducing distortion of the edges12,14. With respect toFIG. 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 side12and concave edge14are integrally connected and then diverge downstream from point C along the energy beam paths represented by arrows16A,16B. A “run on tab” may be provided so that beam13results in a steady state and properly dimensioned deposit as it reaches the component10. In an embodiment, the laser beam13is widened as processing proceeds towards point D and along the edges12,14For 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 edges12,14continue to diverge along the beam path, the beam13is 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 edges12,14along respective beam paths16A,16B The width of the beam may be reduced to for example 4 mm wide when scanning the beams16A,16B. 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 beam13may 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 edges12,14

The beam13is controlled to stop the movement between the edges12,14and is widened into (e.g. 12 mm wide) as the beam13approaches 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 beam13may be accomplished with known multi-dimensional galvanometer-driven laser scanning optics.

This simultaneous heating and cladding of both the convex and concave edges12,14of the blade tip10provides 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 toFIGS. 3 and 4, a schematic sectional view of turbine blade tip10with convex and concave edges12,14is shown As described above, such geometries require simultaneous dual processing in close proximity For example, an energy beam13may start processing and is controlled to move between edges12,14at 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 deposit15that is not completely fused to an underlying substrate. This inter-path melt15may prevent deposition of metal immediately downstream from the points E, F where the beam13is controlled to move from one edge to the other edge. This may be the result of surface tension of the inter-path melt15resisting separation of the melt15into two paths.

A solution to this problem is illustrated inFIG. 4, which shows dual-path laser processing including staggered starting points G, H. As shown, processing of beam13along path16A is allowed to progress past the start point H of beam path16B to point G, at which time laser processing begins along beam path16B at point H As described above, the beam13may be controlled to move between edges12,14to simultaneously scan and heat powdered metal material on both edges12,14. When beam13begins scanning along beam path16B (edge14) at start point H, the metal deposit along beam path16A (edge12) 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 path16A therefore does not merge with the metal deposit of path16B.

In the embodiment shown inFIG. 4, the beam path16A follows a convex side (edge12) of the blade tip10; therefore, beam path16A is longer than beam path16B along the concave side (edge14) of the blade tip10. Accordingly, processing along the first path16A is allowed to proceed past the starting point H on the second beam path16B, so that forward processing speeds along both paths16A,16B 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 paths16A,16B As the beam13approaches an end point wherein the two edges12,14converge, the beam13is controlled to stop moving between the edges12,14, and the beam13may be widened, e.g 12 mm to cover the area at which the edges12,14converge at point I. A “run-off” tab may be provided and the beam13may be tapered (e g to 4 mm) as it moves across the area of convergence including point I onto the “run-off” tab.

In the manufacture or repair of a blade tip10, 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 edge14where no tip is required. So a second start is actually occurring at point H that is not connected with the path16A along the convex edge12

Another embodiment of a dual-path processing method is illustrated inFIG. 5, in which the dual-path laser processing is initiated from the opposite end of the blade tip10. That is, the scanning begins at the larger or wider end10A wherein the divergence of the edges is more dramatic than the divergence of the edges12,14at end10B. As described above, a “run-on” tab may be provided at end10A to initiate scanning and heating of the powdered material The beam13is widened to cover the area of convergence or divergence of the edges12,14. The beam13continues down paths16C on the concave side (edge14) and16D on the convex side (edge12) and the beam scan widths along each side is narrowed for example to about 4 mm for each path. The wider divergence angle between paths16C,16D can be of advantage in overcoming surface tension and in achieving separation of the melt.

The concave path16C is shorter than the convex path16D so for equal path travel speeds, the concave path16C finishes first. To further illustrate this staggered finish in reference toFIG. 5, when the energy beam13reaches point J along beam path16C, the energy beam13is at point K along convex beam path16D. As the convex path16D then progresses past an end10B of the concave path16C, slag (from melted and cooled flux material) covering the concave path16C deposit prevents re-melting of the underlying deposit. Rather than a delayed start in paths, this embodiment involves a delayed finish of paths As beam13completes the scan along beam path16D, the metal deposited on the edge12has 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.

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