Turbine Engine Shaft Bore Fabrication via Pre-Forging Insert
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Solution Overview
Problem
The fabrication of turbine engine shafts with increasing length and decreasing inside diameter, made from stronger materials, becomes increasingly difficult due to geometrical constraints and machining challenges, particularly in the boring or drilling step, where alignment issues and material hardness complicate the process.
Innovation Solution
A method where a metal billet is pre-drilled with a complementary insert before hot forging, allowing the insert to deform and maintain the bore's shape, facilitating easier machining by reducing the drilling distance and using materials with similar yield stresses and thermal expansion coefficients, enabling the insert's withdrawal post-forging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the shaft length is increased and inside diameter is decreased to meet new generation turbine engine requirements, then the shaft performance is improved, but the machining difficulty particularly in boring or drilling step increases significantly
Solution Approach 1:
The bore is drilled in the billet before forging instead of after, performing the difficult machining operation when the workpiece is shorter and more manageable. The insert is placed in the bore before forging to maintain cylindrical shape during deformation, enabling subsequent easy removal to achieve the final precise bore in the forged shaft
2Manufacturing precision
If conventional drilling methods are used on the forged blank, then the alignment of the drilling tool with the longitudinal axis can be maintained, but the drilling distance is too long causing considerable risks of misalignment and bore deviation
Solution Approach 1:
The bore is drilled in the billet before forging when the drilling distance is shorter, eliminating alignment risks associated with long-distance drilling of the finished shaft. The insert is then placed in the pre-drilled bore to maintain cylindrical shape during forging
3Strength
If stronger materials are used to make the shafts, then the shaft strength is improved, but the machining difficulty increases due to material hardness
Solution Approach 1:
The bore is drilled in the billet before forging when the material is in a more machinable state, avoiding the extreme hardness of the final strong material. The insert maintains the bore shape during forging of the strong material, and the final bore is achieved after insert removal
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 method simplifies the drilling process by reducing the distance and complexity, using conventional tools, and ensures accurate bore dimensions, overcoming the challenges of machining longer, smaller-diameter shafts from stronger materials.
Implementation Method 1
the materials of the insert and of the billet have substantially the same behavior during forging
Implementation Method 2
its material has a coefficient of thermal expansion that is different from that of the blank such that the insert can be withdrawn from the blank by heating or cooling the blank and the insert
Data Source
AI summary
A method of fabricating a turbine engine shaft from a metal billet of generally cylindrical shape, the method including drilling the billet to form a through axial cylindrical bore therein, engaging a cylindrical insert in the bore, the insert being made of a material having yield stress close to that of the material of the billet so that the materials of the insert and of the billet have substantially the same behavior during forging, hot forging the billet to form a forged blank of length greater than that of the billet, withdrawing the insert, and machining the blank.