Breakthrough machining technology for through-tool cooling with a low-flow cryogenic nitrogen process has been approved by the government for standard roughing operations in production of titanium parts for the Lockheed Martin F-35 Lightning II stealth fighter, impacting the most time-consuming and cost-intensive machining processes associated with manufacturing titanium parts. MAG-IAS (Erlanger, KY) showcased the technology at imX and at EMO where it was demonstrated on five separate MAG machine applications. The attraction for the F-35 program is found in possible cost efficiencies realized through faster metal removal rates and longer tool life, which would improve machining, especially roughing titanium, which accounts for about 25% of the F-35’s content.
"The process promises to rewrite the book on machining speeds and costs for difficult-to-machine hard materials, which are critical in aerospace, and coming into common use in automotive and general industry applications as well," says Michael Judge, vice president of MAG Cryogenic Business Development. Here’s why: Cryogenic titanium machining is said to increase cutting-tool life up to a factor of 10 and double the material-removal rate, compared to conventional machining methods in certain applications. The multipatented cryogenic system delivers liquid nitrogen at -321°F (-196°C) through the spindle and through the tool directly to the point where the tool meets the cutting surface. The process literally "refrigerates" the heat away, acting as a heatsink and removing heat generated during the cutting process. This capability is especially desirable in handling difficult-to-machine materials such as titanium, Inconel, other nickel-based alloys, and CGI, as well as hardened steel. Delivering the liquid nitrogen through the five-axis head was particularly difficult, but the system is said to be suitable for motorized, belt-driven, or geared spindles.
The five machine applications showcasing the MAG cryogenic at EMO included machining an aerospace titanium blisk on a NBV 700 5X VMC, an Inconel part on a VDM 1000 vertical turning center, a hardened steel shaft on a VDF 450 TM turn-mill center, a CGI crankcase part on the hydraulic-free Specht 600E, and a robotic root end drilling system.
Cryogenic machining poses a solution for the environment, as well. There are no mist collection, filtration, wet chips, contaminated workpieces, or disposal costs to worry about. In addition, energy consumption is reduced, because there aren’t any pumps, fans, and drives needed to handle the coolant. "In addition to the increases it brings in metal-removal rates and tool life, low-flow cryogenic machining is a green manufacturing process that will produce a cascade of additional cost reductions by eliminating, or vastly minimizing, the use of liquid coolants. Liquid nitrogen is a non-greenhouse gas, so it is harmless to the environment, too," Judge points out. In that regard, the cryogenic process may come to be regarded as a significant breakthrough in coolant management. In fact, combining the process with minimum quantity lubrication (MQL) further extends the effectiveness of the process for applications like cutting with carbide.
The multipatented process was developed over a period of years by the team of Creare Inc. (Hanover, NH), H.M. Dunn Co. (Euless, TX), and MAG IAS, working with Lockheed Martin, the US Navy Small Business Innovation Research (SBIR) Program Office, and the F-35 Joint Program Office (JPO). Funding was provided by SBIR program awards. MAG IAS is commercializing the process under exclusive license, and is offering cryogenic tool-cooling technology on a range of new machines, including five-axis and turning systems, as well as providing retrofit systems. The cryogenic tool system adds between 5–30% to the cost of the machine depending on size and complexity of the application compared with a "wet" machine that uses flood coolant to wash away heat.
For more information on MAG-IAS, go to www.mag-ias.com, or telephone 859-534-4600.
Machining problems related to surface finish, feature location, and roundness are all significantly affected by spindle performance and thermal effects. For more than 10 years, the industry-standard Spindle Error Analyzer (SEA) from Lion Precision (St. Paul, MN) has been used to measure machine-tool spindle thermal growth and error motions in multiple axes. With the recent surge in micromachining spindle designs that minimize error motions, measuring those error motions will continue to present challenges to designers and end users alike. To meet the micromachining challenge, the SEA analyzer has been adapted for micromachining with a system that uses smaller versions of the noncontact probes, probe mounts, and masterball targets, along with SEA software, to perform ANSI and ISO standard tests of spindle performance.
According to Lion Precision’s President, Don Martin, "The performance demands for micromachining are at such a high level that every error source must be measured and addressed for it to realize its full potential. What would have been considered an insignificant error a few years ago, must now be measured and remedied." He cites the conclusions of a Sandia National Labs report (Gill & Jokiel, 2004, "Next Generation Spindles for Micromilling") that stated that "faster spindles with reduced tool runout are the path to achieve efficient mesoscale milling."
The SEA system measures spindles at operational speeds up to 300,000 rpm with resolutions less than 1 nm. The SEA system includes high-resolution noncontact capacitive displacement sensors, precision probe mounts, precise masterball targets with less than 100 nm of roundness error, temperature sensors, and software to acquire and analyze the measurements. Results are presented in polar or linear plots, and values are listed for synchronous and asynchronous errors, TIR, and more. Spindle displacement can be plotted against temperature and rpm to show critical relationship between these variables.
For more information on Lion Precision go to www.lionprecision.com, or telephone 651-484-6544.
Deep Horizontal Cavity Burn
In this special customer application developed by GF AgieCharmilles (Lincolnshire, IL), an extremely small rib-shaped closed/blind horizontal cavity is burned to a depth of 16" (406 mm) on a FO 550 SP diesinker. Typically, such burns are limited to depths of 4–6" (101.6, 152.4 mm) at best. For the application, a special right-angle attachment is used that is made of long thin tool steel with a small portion of graphite electrode mounted at its end. The tool was produced using a wire EDM, which cut a jig-saw type interlocking pattern for securing the electrode portion to the rest of the tool. The tool also features tiny though holes running the entire length for flushing during burning. The system generates consistent surface finish and size through the entire length of the cavity.
The FO550 SP is designed with a double thermostabilization system and DPControl (Dynamic Process Control) which allows it to produce shine surface finishes equal to or less than 0.4 µm. DPControl is designed to suggest ideal electrode undersize and rationalize the number of electrodes necessary for effective machining. The machine’s double thermostabilization system includes pulsed air, circulating in the cabinet for cooling in real time according to the temperature of the dielectric recorded by a double differential temperature probe. The whole of the main frame and the X, Y, Z axes are thermostabilized in the same way as the whole of the machine. Circulation of the dielectric is integrated into the worktable, which prevents the risk of thermal shocks when filling the tank. The machine is equipped with Accura-C, a high-precision C axis that provides positioning accuracy down to 3.6 arc sec to counteract the effects of pulsation movements in the dielectric fluid and increase stability. The C axis can withstand maximum inertia of up to 1708 lb in2, boosting productivity and allowing precision machining with electrodes weighing up to 110 lb (50 kg). The Accura-C features a liquid-cooling system to eliminate inaccuracy from thermal instability.
For more information on GF AgieCharmilles, go to
www.gfac.com/us, or telephone 800-282-1336.
Fixturing Augers for Welding
The 50' (15-m) long augers that move grain into and out of silos and through the material handling/transportation cycle require precise alignment and rigid stability. Typically, weld fixtures have to adapt quickly, yet accurately, to the changing requirements for high-mix and low-volume welding applications. The fixture is constructed from elements of the modular fixturing system from Bluco Corp. (Aurora, IL) and consists of a five-sided welding table with a regular pattern of precision 28-mm bores on accurate 100-mm centers.
To ensure long life, the surfaces are all hardened to RC 55, which prevents spatter from sticking while providing resistance to abrasion and rust. In this application, the locating stops and angles are also hardened and are machined with matching bores and precision slots for maximum flexibility in building fixtures. Joining these components together is accomplished with a positioning and clamping bolt that allows for fast and accurate assembly while providing 26.5 kN clamping force.
For more information on Bluco Corp., go to www.bluco.com, or telephone 800-535-0135.
This article was first published in the November 2011 edition of Manufacturing Engineering magazine. Click here for PDF.