Creare’s Indirect Cooling System (ICS) for the High-Performance Machining of Advanced Materials.

Creare engineers weren’t the first to consider using liquid nitrogen to cool cutting tools to machine the extremely hard materials used in aerospace manufacturing, but Creare is the first to successfully move from concept to a viable hardware solution. Both Bell Helicopter-Textron and Lockheed Martin Aeronautics, prime contractors for the V-22 tiltrotor and Joint Strike Fighter military aircraft, respectively, are considering implementing our technology for their machining processes of titanium aerospace components.

Titanium’s high strength and low density make it an exceptional material for aerospace purposes, but these qualities also make it extremely difficult to machine. Effective cooling of the cutting tools becomes imperative as machining speeds are increased to improve productivity and lower costs. Typical machining coolants, however, are environmentally unfriendly, thermally inefficient, and potentially hazardous to the health of operators.

Our first efforts focused on designing our Indirect Cooling System (ICS) for lathe tooling. Since the cutting tool is stationary, the design was simplified. We next developed designs and analytical models based on our high-efficiency heat exchangers and two-phase flow expertise. We built the first proof-of-concept models of our cooling system in Creare’s machine shop, achieving significant performance improvements. Originally our goal was to equal the performance of traditional coolants, but we found our technology enabled tools to last significantly longer while increasing the speed of machining operations. In addition, liquid nitrogen is inert and inexpensive, and we used just 1% of the coolant volume used by conventional machining coolants or previous systems based on liquid nitrogen.

We next designed our ICS for milling systems, the process used in most aerospace manufacturing. It’s a more complex design issue for a number of reasons. Unlike lathe tooling, the tool itself moves, spinning at speeds as fast as 10,000 rpm. In addition, the challenges of moving liquid nitrogen from a stationary container to the top of a rotating tool involved a very detailed two-phase system design. As a result, we developed and manufactured a custom Cryogenic Rotary Coolant Holder (C-RCH), then worked with machine tool operators and builders to address their needs with Creare’s initial version of the ICS. Our modifications minimized the pressure drop of the two-phase cryogenic flow, and the overall performance of our system is significantly better than our competitors’ due to superior thermal design. Currently, we are working on approaches that more tightly integrate with the machine tool. Creare’s key differentiation from other R&D firms in this technology area has been our desire to integrate our technology into real-world manufacturing environments.

Our work not only applies to titanium machining, but other advanced materials such as nickel super alloys or ceramic matrix composites (CMCs); the latter is used in the fabrication of jet engine components. CMCs in particular are so hard that they wear out machining tools in a matter of minutes, even though the tools themselves are constructed with polycrystalline diamond cutting edges. By enabling faster manufacturing and extended tool life, our innovation decreases cycle time and creates multi-million dollar savings in manufacturing costs for large military or commercial aerospace manufacturers.

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