Auxiliary Grain Duct for Monocrystalline Turbine Blade Casting
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Solution Overview
Problem
In the manufacturing of monocrystalline turbomachine blades using the lost wax foundry process, issues such as delayed solidification of mold cavity parts leading to porosities, parasitic recrystallized grains, and dimensional variations or deformations are prevalent, particularly affecting the platform and heel regions.
Innovation Solution
A ceramic mold with an auxiliary grain duct is introduced, featuring specific angled and shaped portions to ensure uniform solidification, reduce residual stresses, and facilitate easier demolding, thereby minimizing defects like porosities and recrystallized grains. The auxiliary grain duct includes a first portion extending from the foot to the platform and a second portion connecting to the heel, with strategically positioned masses and a narrowing section to enhance metal flow and reduce ceramic thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If the mold cavity is designed to form the blade platform and heel fins, then the blade structure is complete, but these parts solidify with delay causing porosity defects
Solution Approach 1:
The auxiliary grain conduit is segmented into a first portion opening into the foot cavity and a second portion opening into the heel/beak cavities. This segmentation allows independent control of metal flow and solidification timing for different blade regions, ensuring uniform solidification across the entire blade structure including platform and heel fins.
Solution Approach 2:
The auxiliary grain conduit acts as an intermediary channel that mediates metal flow between the pouring system and the blade cavities. It controls the sequence and rate of metal filling, ensuring that platform and heel regions receive metal at appropriate times to prevent delayed solidification and porosity formation.
2Shape
If the blade platform and heel fins are formed in the mold cavity, then the blade structure is complete, but porosity appears due to delayed solidification
Solution Approach 1:
The auxiliary grain conduit is divided into distinct portions that open into different cavities (foot, platform, heel). This segmentation enables tailored metal flow control for each region, ensuring that platform and heel fins solidify at appropriate times without forming porosity, while maintaining complete blade structure.
Solution Approach 2:
The auxiliary grain conduit serves as an intermediary that regulates metal distribution to the platform and heel regions. It prevents direct rapid filling that would cause porosity, instead providing controlled metal flow that ensures complete structure formation without defects.
3Stress or pressure
If heat treatment is applied after directional solidification, then residual stresses are relieved, but unwanted recrystallized grains appear in certain areas
Solution Approach 1:
The auxiliary grain conduit performs preliminary action by establishing controlled metal flow patterns during casting that create a more uniform stress distribution from the beginning. This preliminary stress distribution control reduces the severity of residual stresses, allowing heat treatment to relieve stresses without triggering recrystallization and maintaining single-crystal structure integrity.
Solution Approach 2:
The invention changes the parameters of the casting process through the auxiliary grain conduit, specifically the metal flow rate and filling sequence. These parameter changes result in a more uniform solidification process that creates a more favorable initial stress state, preventing recrystallization during subsequent heat treatment while still allowing stress relief.
4Ease of manufacture
If the blade is manufactured without auxiliary support, then the manufacturing process is simple, but dimensional variations and twisting occur
Solution Approach 1:
The auxiliary grain conduit acts as an intermediary support structure during the casting process. It provides mechanical support to the molten metal and emerging solid blade, preventing dimensional variations and twisting. After casting, the conduit can be easily removed, maintaining manufacturing simplicity while achieving high dimensional accuracy.
Solution Approach 2:
The auxiliary grain conduit serves as a temporary support structure that is discarded after fulfilling its function. It provides necessary support during casting to ensure dimensional accuracy, then is removed (recovered) easily, maintaining the simplicity of the manufacturing process while achieving precise dimensions.
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
The use of the auxiliary grain duct in the mold ensures reduced porosities and recrystallized grains, maintains desired dimensions, and minimizes twisting, resulting in a more stable and mechanically sound monocrystalline blade with reduced residual stresses, achieved through controlled solidification and heat treatment.
Implementation Method 1
During the controlled solidification of the molten metal in the blade-shaped mold, the parts of the mold cavity forming the platform and heel fins solidify with a certain delay compared to other parts of the cavity
Implementation Method 2
following heat treatment after directional solidification, the blade may exhibit unwanted recrystallized grains in certain areas
Data Source
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AI summary
The invention relates to a mould (3) made of a ceramic material intended to be used to mould a turbomachine blade from a molten metal, the blade comprising a base, a platform, a vane, and a root; the mould comprising: a cavity (4) having the shape of the blade, and an auxiliary grain duct (5) comprising a first portion (51) and a second portion (52) extending the first portion, said first portion leading, at one end (511), into a first part (40) of the cavity forming the base of the blade and, at another end (512), into a second part (412) of the cavity forming a spoiler of the blade platform, said second portion (52) leading, at one end (521), into said second part (412) of the cavity and, at another end, (522) into a third part (432) of the cavity forming a spoiler of the blade root. The invention also aims for an installation and a method of manufacture implementing such a mould.