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Advanced Machining of Aerospace Materials

Description:

TECHNOLOGY AREA(S): Materials 

OBJECTIVE: Develop and demonstrate an internally-cooled cutting tool solution to address the cost and lead time of a cryogenic material removal process for difficult-to-machine aerospace materials. 

DESCRIPTION: Demand for low-cost systems using advanced aerospace materials such as Ti-alloys and Ni-alloys is growing within the Air Force (AF), thus requiring improved manufacturing processes. These alloys present machining challenges like higher machining-induced temperatures and lower material removal rates (MRR). High machining-induced temperatures can be detrimental to the cutting tools used to remove material from the components, requiring special cutting tools to achieve the desired surface finishes and integrity. Cutting tool longevity can still be unfavorably low. Consequently, machining is often a large percentage of the manufacturing cost associated with producing various structural and engine components of various sizes (e.g. Remotely Piloted Aircraft, small engines).One way to combat high-machining induced temperatures and effects on tool wear and MRR is to use liquid nitrogen (LN2) as a coolant medium to internally cool the cutting tool. Previous Small Business Innovation Research efforts managed by the AF have demonstrated success of a cryogenic machining system using LN2 as the cooling medium, instead of the conventional flood cooling, for rough milling operations in Ti-6-4 with benefits including cycle time reductions, tool life increases, and surface finish improvements. As a result of this effort and others, cryogenic machining hardware and software has matured to a point where it is commercially available.However, while cryogenic machining systems have matured, internally-cooled cryogenic-specific cutting tools (ICCT) are the least well-developed area of this technology. Previous studies have shown that cryogenic machining can improve the life of a tool up to 10x in some cases and increase MRR by 2x, but this has not been widely demonstrated in production environments due to commercially available cutting tools being inadequate. As such, adequate ICCTs must be brought to market. Milling operations are heavily utilized in Ti- and Ni-alloy machining and therefore will be the focus of this effort, but the effort may extend into drill bit development depending on progress. ICCT development for milling can include solid cutters or indexable cutters with inserts for Ti-alloys, and may be pursued for Ni-alloys depending on customer needs. One aspect of this effort will be demonstrating a clear understanding of ICCT material properties as they perform in a cryogenic environment and affect the machining process. It is encouraged that the contractor utilize existing modeling and on-machine testing capabilities to analyze variables such as tool geometry and thermodynamic effects between the tool, coolant medium (LN2), and workpiece to understand their influence on tool performance (wear, MRR, etc.). ICCTs, as compared to conventional (flood cooled) cutting tools, should demonstrate a tool life increase by 2x with an objective to improve by 10x. The ICCT should also demonstrate an MRR increase by 2x while maintaining the tool life of comparable, conventional tools with an objective to improve by 2x while meeting the threshold tool life (2x increase). It is also desired that ICCT tool wear characteristics are stable and predictable. On-machine testing at varying speeds, feeds, depths-of-cut, etc. should be performed to develop and document tool-life curves that can be used by engineers and machine operators. It is encouraged that the proposed solution leverages commercially available hardware and software for the design of ICCTs. It is also highly encouraged to work with aerospace OEMs and larger tool manufacturers to further understand machining and tool design/manufacturing requirements for successful transition. 

PHASE I: Test and evaluate currently available cutting tool materials and/or coatings to initiate development of tool-life curves and ICCT design. Phase I final report will provide results to support how the process can meet the requirements and address the broader scope capability for a Phase II. Identify user requirements and risks for adopting the process. Begin developing cost models. 

PHASE II: Further develop ICCT design and testing from Phase I on representative aerospace components, develop tool-life curves, validate cost models to ensure potential ICCT cost markup does not outweigh performance benefits, and develop an implementation strategy for the technology/process developed in Phase I. Develop and document process to MRL 5-6 maturity as defined at www.dodmrl.com. 

PHASE III: Continue process refinement and MRL maturity to level 8, as defined at www.dodmrl.com, of the developed system to meet end user requirements. The end goal of a Phase III activity is the transition of a system to the end user for incorporation into production environment. 

REFERENCES: 

1: E.O. Ezugwu, J. Bonney, Y. Yamane "An overview of the machinability of aeroengine alloys", Journal of materials Processing Technology, 134, pp. 233-253, 2003

2:  Ajay Kale, N. Khanna "A Review of Cryogenic Machining of Super Alloys Used in Aerospace Industry", International Conference on Sustainable Materials Processing and Manufacturing, Procedia Manufacturing, 7, pp. 191-197, 2016

3:  R. Ghosh, Z. Zurecki, J. H. Frey "Cryogenic Machining with Brittle Tools and Effects on Tool Life", Proceedings of International Mechanical Engineering congress & Exposition (IMECE ’03), Washington, D.C.

4:  "AFRL Small Business Office partners with industry to save on aircraft costs" http://www.wpafb.af.mil/News/Article-Display/Article/818470/afrl-small-business-office-partners-with-industry-to-save-on-aircraft-costs/

KEYWORDS: Machining, Manufacturing, Ultrasonic, Cryogenic, Electrochemical, Laser, Engines, Propulsion, Small Engines, Aircraft Structures, Aircraft Parts 

CONTACT(S): 

Mr. Jason Wolf (AFLCMC/LPE) 

(937) 904-4387 

jason.wolf.7@us.af.mil 

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