Gas Turbine Tie Shaft Flow Forming and Thread Rolling
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Solution Overview
Problem
The manufacturing of tie shafts for gas turbine engines involves extensive and costly machining, particularly for achieving the desired shaft contour and threading, which is inefficient and costly.
Innovation Solution
A method involving vacuum induction melting and vacuum arc remelting of nickel or steel alloys to produce a tie shaft preform, followed by flow forming to achieve a near-net shape with reduced wall thickness and rolling threads with a thread roughness of less than 1260 µm, resulting in a more isotropic material with improved microstructure and reduced machining requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional machining methods are used to produce tie shafts, then the desired shaft contour and threading can be achieved, but the manufacturing cost and time increase significantly
Solution Approach 1:
The flow forming process performs preliminary shaping of the tie shaft to achieve near-net shape, reducing the amount of subsequent machining required. The preform is flow-formed to closely match the final shaft geometry before threading operations, eliminating extensive material removal steps.
Solution Approach 2:
The process changes the material state and processing parameters by using flow forming at controlled temperatures and strains to achieve the desired shaft contour. By controlling the flow forming parameters (temperature, strain rate, roller pressure), the shaft contour is formed with high precision while maintaining material integrity.
2Shape
If extensive machining is performed to achieve desired shaft contour, then the shaft geometry is improved, but the manufacturing cost increases
Solution Approach 1:
The flow forming process performs preliminary shaping of the tie shaft to achieve near-net shape, reducing the amount of subsequent machining required. The preform is flow-formed to closely match the final shaft geometry before threading operations, eliminating extensive material removal steps.
3Manufacturing precision
If traditional threading methods are used, then threads can be machined into the shaft, but the surface roughness increases and machining time extends
Solution Approach 1:
The patent replaces traditional mechanical threading with thread rolling, which uses plastic deformation to form threads. This substitution reduces machining time and produces superior surface finish while maintaining thread accuracy, as the rolling process simultaneously forms both the thread geometry and compresses the surface.
4Manufacturing precision
If wall thickness is reduced through flow forming, then near net shape is achieved, but the preform must be processed with higher strain
Solution Approach 1:
The process changes the material state and processing parameters by using flow forming at controlled temperatures and strains to achieve the desired shaft contour. By controlling the flow forming parameters (temperature, strain rate, roller pressure), the shaft contour is formed with high precision while maintaining material integrity.
Solution Approach 2:
The patent applies beforehand cushioning by controlling the flow forming parameters to prevent excessive strain concentration. The process uses controlled temperature and strain rate to cushion the material during deformation, preventing strength degradation while achieving the required wall thickness reduction and near-net shape.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This process significantly reduces machining needs, achieves a superior surface finish, and enhances the tie shaft's resistance to fretting and longevity by producing a material with a consistent microstructure and precise grain alignment, thereby minimizing critical grain growth and extending the component's life.
Implementation Method 1
melting a nickel alloy or steel alloy using vacuum induction melting
Implementation Method 2
vacuum arc remelting the alloy to produce a tie shaft preform
Implementation Method 3
flow forming the tie shaft preform to produce a near net shape tie shaft, wherein the tie shaft preform has a wall thickness, the flow forming step reducing the preform wall thickness by a minimum of 30%
Implementation Method 4
rolling threads onto the tie shaft to produce a threaded surface, wherein the threaded surface has a thread roughness of less than 1260 μm (32 microns)
Data Source
Figure 1
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AI summary
A method is disclosed for manufacturing a tie shaft for aero or land based gas turbine engine. The method includes flow forming a tie shaft preform to produce a tie shaft. 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 roll formed threaded surface having a thread roughness of less than 1260 µin (32 microns).