Method for processing a part with an energy beam

A method for processing a part (10) with an energy beam A mask (70, 80) is arranged between a source of the energy beam and the part. The mask is configured with a beam-transmissive portion (71) in correspondence with mutually opposed portions (12, 14) of the part. Simultaneously heating the mutually opposed portions of the part is performed with energy beamlets passing through the beam-transmissive portions of the mask This simultaneous heating is configured to keep a thermally-induced distortion of the part within a predefined tolerance. Scanning of the mask with the energy beam may be performed without precisely tracking the mutually opposed portions of the part, thereby avoiding a need for complicated numerical programming for tracking a relatively complex geometry defined by the mutually opposed portions of the part.

FIELD OF THE INVENTION

The present invention is generally related to manufacturing techniques for forming or repairing a part, such as airfoils for blades or vanes for a combustion turbine engine; and, more particularly, to a method for processing a part 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 parts, 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 parts that are subjected to such loadings

It is known to use laser-based processes for forming or repairing such parts 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 part 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 deposit a layer of superalloy powder particles onto a superalloy substrate, etc

Using a known process as schematically illustrated inFIG. 5, when repairing or forming an airfoil5, a laser beam may be used to track a path including a convex-shaped edge6of the airfoil5followed by a concave-shaped edge8of the airfoil5. The present inventors have found, however, that the beam may miss the desired target area to be processed because of lateral distortion that may be induced in the airfoil5due to a thermal differential that arises between edges6,8of the airfoil during the laser tracking process. In this example, since convex edge6is processed by the laser beam before concave edge8, then convex edge6would be at a relatively higher temperature relative to concave edge8. Similarly, lateral distortion would also arise in the part if concave edge8was processed before convex edge6.

In view of such recognition, the present inventors propose an innovative technique for processing a part with an energy beam, where such lateral distortion in the part can be avoided or may be kept within a predefined tolerance As conceptually illustrated inFIG. 1, mutually opposed portions of the part, such as convex and concave edges12,14of a part10may be simultaneously heated. In this case, thermal expansion and contraction of a metal alloy constituent of the part is balanced between the mutually opposed portions of the part, and this is effective to keep the thermally-induced distortion of the part within a predefined tolerance. In one example embodiment, this simultaneous heating of the mutually opposed portions of the part may be accomplished without use of complicated numerical programming for precisely tracking the mutually opposed portions of the part or laser power coordination; or use of costly part-maneuvering equipment

In the following detailed description, various specific details are set forth in order to provide a thorough understanding of such embodiments. However, those skilled in the art will understand that embodiments of the present invention may be practiced without these specific details, that the present invention is not limited to the depicted embodiments, and that the present invention may be practiced in a variety of alternative embodiments In other instances, methods, procedures, and components, which would be well-understood by one skilled in the art have not been described in detail to avoid unnecessary and burdensome explanation

Furthermore, various operations may be described as multiple discrete steps performed in a manner that is helpful for understanding embodiments of the present invention. However, the order of description should not be construed as to imply that these operations need be performed in the order they are presented, nor that they are even order dependent unless otherwise so described Moreover, repeated usage of the phrase “in one embodiment” does not necessarily refer to the same embodiment, although it may. Lastly, the terms “comprising”, “including”, “having”, and the like, as used in the present application, are intended to be synonymous unless otherwise indicated

In the embodiments illustrated inFIGS. 2 and 3, a mask70may be arranged between a source of the energy beam (e.g., a laser beam) and the part As may be appreciated inFIGS. 2 and 3, mask70(e.g., a static mask) may include a beam-transmissive portion71having a geometric shape in correspondence with the mutually opposed portions of the part being processed, such as the tip edge region of an airfoil for a turbine blade

Simultaneous heating of the mutually opposed portions of the part being processed is thus accomplished with energy beamlets passing through beam-transmissive portion71. In one example embodiment, the mask70may be scanned with the energy beam so that energy beamlets passing through the beam-transmissive portion of the mask can simultaneously heat the mutually opposed portions of the part. It should be appreciated that a beamlet, as disclosed herein, may be a subset, e.g., small portion, of the energy beam passing through the beam transmissive portion71. For example, as a wide dimension energy beam is projected over the mask70, the wide dimension energy beam would be subdivided into energy beamlets wherever the beam is allowed to pass through the beam-transmissive portion71. This scanning may be performed without precisely tracking the mutually opposed portions of the part. This would avoid a need for complicated numerical programming for tracking the relatively complex geometry defined by the mutually opposed portions of the part

In one example, embodiment, mask70may be made of a laser energy tolerant material that is opaque relative to a laser beam20. Such materials may include graphite which is opaque to a wide range of laser beam wavelengths. Copper may also be used, but may be reflective to a laser beam so the angle at which the laser beam impinges the masking beam should be adjusted to avoid back reflection to laser optics Although the description below refers to a single laser beam20, it will be appreciated by those skilled in the art that the laser beam which is directed toward the mask70may comprise a combination of multiple laser beams either from multiple sources, or from a single laser source where the beam is split into multiple beams.

As illustrated by way of example inFIG. 2, an area energy beam20from an energy source30, such as may be produced by a diode laser, may be scanned from left to right as indicated by arrow C. Alternate to moving beam and stationary part, the same processing may be accomplished with stationary laser beam and part moved from right to left. As further shown, a width dimension of beam20may be maintained generally constant to encompass at least a maximum width of the profile defined by beam-transmissive portion71. Alternatively, as illustrated inFIG. 3, a point energy beam22may be rastered along a width dimension of the mask70and may have a predefined variable-width as rastered beam22scans the mask70in the direction of arrow C. This predefined variable width may be chosen to overshoot by a predefined margin a varying width of the profile defined by the beam-transmissive portion71.

Mask70may be a single masking element that is held stationary, or it may be moveable between passes of the energy beam as the part10is repeatedly heated in layers, such as during an additive manufacturing process By way of example, airfoils for a turbine vane or blade may define a gradual twist from the platform to the tip of the blade or vane Accordingly, masking element70may be rotated around a central axis “B” as the airfoil is developed.

With respect toFIG. 4, an example embodiment is depicted where the mask comprises a plurality of masking elements80that may be arranged side-by-side on a common plane The masking elements80may take the form of graphite rods with beveled ends to achieve the desired shape or configuration for the beam-transmissive portion71. In this example, the rods or masking elements80may be operatively connected to a control mechanism to move the masking elements80laterally (as conceptually represented by arrows “E” and “F”) in accordance with the configuration of the mutually opposed portions of a part being formed or repaired. In this example embodiment, a core81masking element may be provided to account for a hollow interior of the airfoil, and may be stationary or moveable in accordance with a predetermined shape of the airfoil. In other embodiments, portions of the mask may be located in different planes perpendicular to the beam direction, with variable overlapping of the portions being used to define a variable shape in the transmissive portion71

While various embodiments of the present invention have been shown and described herein, it will be apparent 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.