The present invention relates to a process for forming a long gas turbine engine blade having a main wall with a thin portion near a tip.
Due to high operating temperatures, gas turbine engine blades are typically formed from a high density, nickel-based superalloy. Due to typical large flowpath diameters of gas turbine engines, the linear velocity of tips of corresponding turbine blades is extremely high. Hence, material at each blade tip exerts large centrifugal forces on the remainder of the blade. Any extra material at the blade tip cascades down the blade increasing radial blade pull. In order to cast longer blades, it is desirable to reduce the wall thickness at the blade tip to reduce radial blade pull. It is difficult, though, to cast long turbine blades having thin-walled portions near the tips. This is because a ceramic core, used during the casting process, shifts within process tolerances during casting, resulting in an uncertain position of the core relative to the tip of the blade. Hence, during the design process, wall thickness reduction at or near the tip is limited because of core shifting during casting. If wall thickness is reduced too much, the core may break through the wall near the tip during casting.
In accordance with a first aspect of the present invention, a process is provided for forming an airfoil for a gas turbine engine comprising: forming a casting of a gas turbine engine airfoil having a main wall and an interior cavity, the main wall having a wall thickness extending from an external surface of the main wall to the interior cavity, an outer radial section of the main wall having a wall thickness greater than a final thickness; collecting, using a thickness measuring device, non-destructive first wall thickness data of the casting at the main wall outer section; comparing, using a computer system, the collected first wall thickness data with stored model thickness data to determine an initial amount of wall thickness material to be removed from the casting along the main wall outer section; and effecting movement of a material removal apparatus and the casting relative to one another such that a first layer of material is removed from the casting at a plurality of radial portions along the main wall outer section. Thereafter, the process may further comprise collecting, using the thickness measuring device, non-destructive second wall thickness data of the casting at the main wall outer section; comparing, using the computer system, the collected second wall thickness data with the stored model thickness data to determine an additional amount of wall thickness material to be removed along the main wall outer section; and effecting movement of the material removal apparatus and the casting relative to one another such that a second layer of material is removed from a subset of the plurality of radial portions along the main wall outer section.
The thickness measuring device may comprise one of an ultrasonic device, an X-ray inspection apparatus, an eddy current measurement apparatus and a thermal imaging device.
The airfoil casting may define a gas turbine engine blade and the main wall outer section may extend from a location between a base and a tip of the airfoil casting to the tip.
The subset of the plurality of radial portions along the main wall outer section may extend to the tip of the airfoil casting.
The material removal apparatus may comprise a grit blasting apparatus emitting a working fluid comprising an abrasive grit in a fluid medium against the casting. The grit blasting apparatus may spray the working fluid at the casting at a non-orthogonal angle to the external surface of the main wall of the casting.
The casting may define a gas turbine engine blade have an airfoil length of from about 26 inches to about 35 inches.
In accordance with a second aspect of the present invention, a process is provided for forming an airfoil for a gas turbine engine comprising: forming a casting of a gas turbine engine airfoil having a main wall and an interior cavity, the main wall having a wall thickness extending from an external surface of the main wall to the interior cavity, an outer radial section of the main wall extending from a location between a base and a tip of the airfoil casting to the tip and having a wall thickness greater than a final thickness; collecting, using a thickness measuring device, non-destructive wall thickness data of the casting; comparing, using a computer system, the collected wall thickness data with stored model thickness data to determine a desired amount of wall thickness material to be removed from one or more radial portions along the outer section of the main wall of the casting; effecting movement of a material removal apparatus and the casting relative to one another such that a layer of material is removed from the casting at one or more radial portions along the main wall of the casting; and repeating the collecting, comparing and effecting steps one or more times until the outer section of the main wall of the casting has a desired thickness.
Wherein the repeating of the collecting, comparing and effecting steps one or more times preferably result in the thickness of the outer section of the main wall of the casting varying along the length of the outer section and, preferably, varying in a generally smooth continuous manner from the location between the base and the tip to the tip.
The thickness of the outer section of the main wall near the tip may be less than the thickness of the outer section at the location between the base and the tip of the airfoil casting.
Preferably, material is only removed from the casting at the outer section of the main wall.
While the specification concludes with claims particularly pointing out and distinctly claiming the present invention, it is believed that the present invention will be better understood from the following description in conjunction with the accompanying Drawing Figures, in which like reference numerals identify like elements, and wherein:
In the following detailed description of the preferred embodiment, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration, and not by way of limitation, a specific preferred embodiment in which the invention may be practiced. It is to be understood that other embodiments may be utilized and that changes may be made without departing from the spirit and scope of the present invention.
Referring now to
The blades are coupled to a shaft and disc assembly (not shown). Hot working gases from a combustor section (not shown) in the gas turbine engine travel to the rows of blades. As the working gases expand through the turbine section, the working gases cause the blades, and therefore the shaft and disc assembly, to rotate.
The turbine blade 10 comprises an airfoil 20, a root 30 and a platform 40, which, in the illustrated embodiment, may be formed as a single integral unit from an alloy material such as a metal alloy 247. The root 30 functions to couple the blade 10 to the shaft and disc assembly in the turbine section. The airfoil 20 comprises a main wall 120 extending radially from the root 30. The main wall 120 defines a first generally concave pressure sidewall 122 and a second generally convex suction sidewall 124, see
In the illustrated embodiment, the main wall 120 comprises a mid-point MP located between a base 20A of the airfoil 20 and a tip 20B of the airfoil, see
The outer section OS has a final wall thickness that generally varies along its length such that the final thickness is greatest near the mid-point MP, see thickness TA in
As noted above, casting an airfoil having a long length L with a thickness of the main wall being very thin near the airfoil tip is difficult. In accordance with the present invention, an airfoil is cast such that the main wall thickness at the outer section OS is greater than a final thickness, i.e., the main wall thickness is cast so as to be overly thick. For example, the outer radial section OS may be cast such that it has a substantially constant thickness when moving radially from near the mid-point MP to the tip 20B such that the additional main wall material gradually increases in a generally continuous manner when moving radially from near the mid-point MP to the tip 20B. Preferably, the main wall thickness of an inner radial section IS of the airfoil 20 extending from the base 20A to or near the mid-point MP is cast to the final thickness for the inner section IS such that no material removal from the inner section IS is required. Subsequently, the outer section OC of the airfoil casting is machined to a final desired thickness taking into account the locations of the interior cavities 130 formed via ceramic cores during the casting operation.
In
In accordance with the illustrated embodiment, the material removal device comprises a grit blasting apparatus 70, see
Preferably, the grit blasting apparatus 70 is used to remove material from the outer section OS of the main wall 120 on a layer by layer basis. The grip blasting apparatus 70 may be moved relative to the casting C, which may be held stationary via a fixture (not shown) or the casting C may be moved relative to the grit blasting apparatus 70. Movement of the grit blasting apparatus 70 and/or the casting C may be effected using a conventional moving device, which may be controlled via the computer system 60. It is contemplated that each layer of material removed from the casting C may have a thickness of from about 0.05 mm to about 0.25 mm.
As noted above, three radial portions RP1-RP3 are illustrated in
As illustrated in
While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.
This invention was made with U.S. Government support under Contract Number DE-FC26-05NT42644 awarded by the U.S. Department of Energy. The U.S. Government has certain rights to this invention.