Turbine Blade Wax Model Core Shell Assembly
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Solution Overview
Problem
The manufacturing of turbomachine blades by lost-wax casting faces challenges due to the high breakage rate of wax models, particularly in forming the fir tree region, caused by the thinness of the core and material shrinkage, leading to cracks and rupture during wax injection.
Innovation Solution
A method involving the use of a core surrounded by a lower and upper surface shell, which are bonded around the core and integrated into the wax model, reducing the wax volume needed for the fir tree region and providing protection against injection forces, thereby minimizing the risk of core rupture and material shrinkage-induced cracks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If the core thickness is reduced to enable thinner supply cavities in cooling circuits, then the cooling circuit design is improved, but the core breakage rate increases significantly during wax injection
Solution Approach 1:
The core is segmented into multiple parts: a central core body and separate shell components (first shell and second shell) that can be assembled around the core. This segmentation allows the core to maintain structural integrity while enabling thin supply cavities, as the shells provide additional support without requiring the entire core to be thick.
Solution Approach 2:
The invention uses a composite structure combining the core material (ceramic or metal) with shell material (wax or polymer) to create a hybrid core-shell system. This composite approach allows the thin-walled supply cavities to be supported by the shell structure, preventing core breakage while maintaining the desired cooling circuit geometry.
2Shape
If the core thickness is reduced to achieve thinner supply cavities, then the cooling performance is improved, but material shrinkage causes cracks during wax injection
Solution Approach 1:
The shell components are positioned around the core beforehand to provide protective cushioning during wax injection. This pre-positioned support structure absorbs and distributes the injection forces, preventing stress concentration that would otherwise cause cracks in the thin-walled supply cavities due to material shrinkage.
Solution Approach 2:
The shell is made of flexible material (wax or polymer) that can deform elastically during wax injection to accommodate material shrinkage and pressure changes. This flexibility allows the thin supply cavity walls to maintain their integrity without cracking, while still providing the necessary structural support.
3Reliability
If shells are added around the core to prevent breakage, then core protection is improved, but the device complexity increases
Solution Approach 1:
The shell components are merged with the core to form an integrated core-shell assembly that functions as a single unit during wax injection. The shells are designed to fit tightly around the core with minimal clearance, creating a unified structure that provides protection without requiring complex fastening or assembly mechanisms.
Solution Approach 2:
The shell serves multiple functions simultaneously: it protects the core from breakage, provides support for thin supply cavities, accommodates material shrinkage, and forms part of the final wax model geometry. This multi-functionality reduces the need for additional protective measures or complex assembly procedures.
Data Source
AI summary
A method for forming a wax model for the manufacture of turbine blades by lost-wax casting, in which a core is provided, a lower surface shell and an upper surface shell are positioned and bonded on either side of ducts of the core adjacent to the root, the core equipped with the lower surface shell and with the upper surface shell is positioned in an injection mold, wax is injected around the core equipped with the lower surface shell and with the upper surface shell, so as to form a wax model including a blade airfoil and a blade root including a fir tree, the lower surface shell and the upper surface shell being positioned around the core so as to form a portion of the fir tree of the wax model.