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Innovative approaches to produce narrow, long and curved core passages in large metallic investment castings


OBJECTIVE: Produce narrow, long and curved core passages in large metallic investment castings. DESCRIPTION: The newly developed controlled solidification investment casting (CSIC) process provides many advantages over traditional sand casting process such as: 1) thinner walls, 2) better process control, 3) improved mechanical properties, and 4) less defects/more uniform casting quality. With increasing adaptation of the CSIC process within the foundry industry, the process has seen broader acceptance by original equipment manufacturers (OEMs) and aerospace community. However, one critical drawback of the process is its difficulty in handling complex lubrication core passages in comparison with the sand casting process which limits its use for castings with complex lubrication passageways, particularly with large housings for large aircraft. Normally direct passageway construction process requires large passage diameters [1]. For narrow, long, and curved passageways the current approach relies on a combination of several techniques, such as steel tubes, access ports, and drilling [2, 3]. All these techniques have their own limitations and often bring about more complications to the casting and manufacturing process and none is suitable for castings like helicopter gearboxes with long, narrow and curved core passages. For instance, the steel tube method causes differential thermal expansion leading to cracking, the access port method necessitates welding of the casting degrading quality and the drilling method works only for straight passages. There is strong need of developing innovative techniques to address the complex lubrication core passage issues encountered particularly with military aerospace hardware. Any new techniques for the construction of core passage of investment casting process should take into account the following requirements: 1) Easy removal after casting, 2) Use of existing mold material, or new material that is compatible with the existing mold material, 3) Eliminating the need for welding, 4) Capable of handling complex lubrication passage structures, 5) Avoiding use of metal other than the casting material, and 6) Attaining uniform casting quality. It is expected that development of such innovative techniques would make it possible to produce large and complex core passage castings in investment casting process with improved manufacturing control and mechanical properties, resulting in significantly enhanced hardware/component reliability and overall cost effectiveness. PHASE I: Develop an innovative approach that enables the construction of complex cored passageways in aluminum investment casting for military aircraft applications and demonstrate feasibility of the developed concept. PHASE II: Fully develop the concept demonstrated during Phase I through a process specification and demonstration of industrial reproducibility. Perform testing and property comparisons with the casting hardware end users and develop the data-base. PHASE III: Perform verification and validation of the developed process and transition the technology to appropriate platforms. PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: The proposed cored passageway technology will benefit military and civilian applications equally. Given the factor that transition from magnesium to aluminum gearbox housing hardware is accelerating in both military and commercial helicopter applications, more aluminum housings with complex passageways can benefit from this technology development for a wide range of military aircraft, such as CH-53K, Naval and Black Hawks, and future search and rescue helicopters as well as S-92, 76 aircraft used for off-shore and VIP applications. REFERENCES: 1. Casting Design and Performance, ASM International, 2009. 2. Aluminum Casting Technology, 2nd edition, AFS, 1986. 3. ASM Handbook, Vol. 15. Casting, 1988.
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