Patent Application
20140023486
This disclosure relates to a tie shaft for a gas turbine engine. The disclosure also relates to a flow forming manufacturing method for producing the tie shaft.
Gas turbine engines typically include multiple spools, which are constructed from forged titanium or nickel and/or steel alloy disks connected by a shaft that is also generally made of nickel or steel alloys. Typically, an oversize long solid forging is machined to provide the desired shaft contour on the interior and exterior surfaces. This requires extensive and costly machining. In addition, any required threads must be machined into the shafts to provide securing features.
A method is disclosed for manufacturing a tie shaft for a gas turbine engine. The method includes flow forming a tie shaft preform to produce a tubular near net shape part.
In a further embodiment of any of the above, the tie shaft preform is a nickel alloy or steel alloy.
In a further embodiment of any of the above, the method includes melting the nickel alloy using vacuum induction melting and vacuum arc remelting or vacuum induction melting, electroslag remelting, and vacuum arc remelting to produce the tie shaft preform.
In a further embodiment of any of the above, the flow forming step includes engaging an outer surface of the tie shaft preform at one end with a roller and working the outer surface from the one end to an opposite end.
In a further embodiment of any of the above, the method includes the step of flow forming in either forward or reverse directions, or a combination of the two.
In a further embodiment of any of the above, the flow forming step includes imparting a minimum effective strain of 0.3 in/in (7.6 mm/mm) in the tie shaft flow-formed part.
In a further embodiment of any of the above, the flow forming step includes producing a grain size in the range of G4 to G16 per ASTM E112.
In a further embodiment of any of the above, the method includes the step of trimming opposing ends of the flow formed shape to produce a tie shaft length. The tie shaft has a length to diameter ratio of at least 6:1. The diameter is an average outer diameter.
In a further embodiment of any of the above, the tie shaft preform has a wall thickness. The flow forming step reduces the preform wall thickness by a minimum of 30%.
In a further embodiment of any of the above, the method includes the separate step of roll forming threads onto the tie shaft to produce a threaded surface.
In a further embodiment of any of the above, the threaded surface includes threads having asymmetrical flanks.
In a further embodiment of any of the above, the threads have a root radius larger than 0.010 inches (0.254 mm).
In a further embodiment of any of the above, the threaded surface has a thread roughness of less than 1260 μin (32 microns).
In one example, the tie shaft includes a nickel alloy cylindrical wall having a length to diameter ratio of at least 6:1, wherein the diameter is an average outer diameter. The wall includes a minimum effective strain of 0.3 in/in (7.6 mm/mm), and a grain size is in the range of G4 to G16 per ASTM E112. The wall includes a threaded surface having a thread roughness of less than 1260 μin (32 microns) on load flanks.
In a further embodiment of any of the above, the tie shaft includes multiple rotors that are secured to the cylindrical wall by a member that engages the threaded surface.
The disclosure can be further understood by reference to the following detailed description when considered in connection with the accompanying drawings.
One example gas turbine engine 10 is schematically illustrated in
A low pressure compressor section 16 and a low pressure turbine section 18 are mounted on the low spool 12. A gear train 20 interconnects the low spool 12 to a fan section 22, which is arranged within a fan case 30.
A high pressure compressor section 24 and a high pressure turbine section 26 are mounted on the high spool 14. A combustor section 28 is arranged between the high pressure compressor section 24 and the high pressure turbine section 26. The low pressure compressor section 16, the low pressure turbine section 18, the high pressure compressor section 24, the high pressure turbine section 26 and the combustor section 28 are arranged within a core case 34.
The engine 10 illustrated in
Instead of using a typical forged alloy material with predominantly axial grain flow for the tie shaft 36, a material is produced that is more isotropic and therefore more suitable for the tie shaft application, according to a process schematically illustrated at 100 in
For comparison,
Referring to
The tie shaft preform 110 is arranged over a mandrel 62 of a flow forming machine 60. The mandrel 62 is secured to a support 65 that is rotationally driven by a motor 64. In the example, the second end 58 is secured between the mandrel 62 and a clamp 74. The mandrel 62 may provide a generally constant inner diameter, for example.
Two or more actuators 70, 66 move rolling members 72 axially and radially. The rolling members 72 include rollers 68 that engage the outer surface 52 of the preform 110. Rollers 68 can be either axially in line or axially staggered and/or radially staggered. In the example, the rollers 68 begin at the second end 58 and work the preform 110 towards first end 56. The combined axial and radial motion of the rollers 68 cold work the tie shaft preform 48 in a direction coincident with the advance of the rollers. The cold working of the material under the rollers causes adiabatic heating which increases the material ductility and aids in material deformation. Subsequent to flow forming, the first and second ends 56, 58 are trimmed to provide test material (outside the part shape), and a desired finish length L between ends 82 (
Another flow forming machine 160 is illustrated in
The flow formed tie shaft 36 is illustrated in more detail in
In one example, the outer surface 52 includes first, second, third threaded surfaces 76, 78, 80. The threaded surfaces are provided by a thread rolling tool 84, schematically illustrated in
The tie shaft 36 manufactured according to the example manufacturing processes described above includes a nickel alloy cylindrical wall 54 having a length to diameter ratio of at least 6:1, wherein the diameter is an average outer diameter. The wall 54 includes a minimum effective strain of 0.3 in/in (7.6 mm/mm), and a grain size in the range of, for example, G4 to G16 per ASTM E112, and in another example, G8 to G12. The process produces small particle sizes and extent of stringering, which is the primary life limiting feature. The wall 54 includes multiple threaded surfaces, for example, first, second, third threaded surfaces 76, 78, 80, having a thread roughness of less than 1260 μin (32 microns) over the load flanks. The flow forming and thread rolling process produces a finished tie shaft 36 having a near-net shape requiring minimal finish machining. Superior surface finish and a compressed layer on the threads ensure increased resistance to fretting and longer life. Flow formed barrels and rolled threads result in desired alignment of grain flow.
Although an example embodiment has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of the claims. For that reason, the following claims should be studied to determine their true scope and content.
