NIST Industrial ImpactPowerful Prototype Spindles Boost Machine Tool PerformanceWith 200 million holes cut in vehicle components in the United States every year, almost anything that makes the process more efficient is an economic windfall. So it is with a novel manufacturing spindle that has the potential to halve the number of machining stations needed to make a particular transmission component, saving the U.S. auto industry more than 100,000 machining hours annually. At $60 per hour for machine time, that's more than $6 million in savings per year, not including the related savings on tools, fixtures, maintenance, and other intangibles. And that's just for one part. In fact, within one year, the benefits from one spindle application producing one automotive part are expected to exceed the cost of the project. The additional economic benefits that could be derived from this award-winning spindle system, as well as the two other prototype spindles designed and built with support from NIST's Advanced Technology Program (ATP), could extend to dozens more applications in many industries. That's because spindles--the rotating shafts that hold cutting instruments in machine tools--are everywhere. They support burrs in dental drills and cutters to configure composite materials. Spindles also make parts for pumps and compressors used in the oil industry, the rolls that produce sheet metal for the automotive sector, the molds used to make tires for the aircraft sector, and parts for the appliance industry. Spindles, critical in manufacturing because they are used to make both parts and the tools that make parts, strongly influence production rates and parts quality. Innovation in spindle technology has been needed for years, because current models cannot provide the dynamic performance and torque-speed characteristics needed to make a machine tool sufficiently small and agile to machine advanced materials or implement flexible, high-velocity machining. "The ATP has allowed the first substantial spindle research program that I know of, and I have been in this business a long time," says Jack McCabe, program manager for the National Center for Manufacturing Sciences, Inc. (NCMS), the project sponsor. Among the achievements:
The ATP success has not come easily. Machine tools are complex systems typically consisting of motors, mechanical means of transferring motion to the cutting tool, balance controls, and bearings to minimize vibration. To engineer systems that break new ground in performance, the ATP project is "pushing the envelope in lots of directions," McCabe says. Ideas that drew skepticism initially have been turned into practical solutions. "This NIST project allows us to fail and recover," McCabe says. "That's critical for making non-trivial improvements. We would never have had the gee-whiz stuff we have now if we were working for a single-company end user." Among the gee-whiz innovations is a hydrostatic spindle system, which uses pressurized water as a bearing lubricant instead of more conventional rolling-element bearings. Hydrostatic bearings tolerate high speeds because the liquid reduces friction; however, this technology tends to be expensive. The system designed by the ATP team, a bundle of four spindles for making "cluster holes" in automobile transmissions and engines, reduces life-cycle costs by eliminating the need for ball-bearing replacement and offers improved performance characteristics. The innovative design also could improve industrial productivity. Cluster holes need to be spaced and shaped very precisely. For the vehicle part and process chosen for the ATP demonstration, vehicle makers currently drill the holes at one station and finish them at a second station; the ATP design has the potential to produce high-quality results in a single pass at a single station, McCabe says. The U.S. auto industry currently has 30 dual-station installations operating an estimated 16 hours per day on 220 days per year, so eliminating one station could save more than 100,000 machining hours annually. Preliminary cutting tests indicate the new technology may be capable of outperforming the system currently used in General Motors Corp. powertrain plants. A product based on the ATP-funded research, the HydroSpindle™, is being commercialized. This is a single-spindle system that automatically maintains optimal properties for existing conditions. It offers high cutting accuracy at very high speeds (up to an estimated 60,000 revolutions per minute [rpm], 50 percent faster than conventional spindles) without overheating or excessive power loss. Spindle manufacturing costs are reduced because the machined features are on the outside of the shaft, rather than the inside of the housing. "The analogy would be: everyone used to wear Swiss watches to have the most accurate time, and we invented the digital watch. Now everyone can tell time cheaply," says Alexander Slocum, a professor of mechanical engineering at the Massachusetts Institute of Technology, who patented the design before it was prototyped in the ATP project. His company, Aesop, Inc., recently signed a license agreement with Setco Sales Co., which will build and sell the new spindles. The HydroSpindle won an R&D 100 award from R&D Magazine in 1996. The two other spindles designed in the ATP project use rolling-element bearings. Designed for flexible production, they are unusually lightweight, compact, and powerful. One durable spindle, with a 75-horsepower (hp) motor, bored the cylinders and milled the flat surface of a Ford Motor Co. cast-iron V-8 engine block at twice the metal removal rate of current processes, an economic advantage that could extend to dozens of other applications. Tests on a 35-hp spindle show that it can deliver accurate results at speeds ranging from 2,500 rpm to 20,000 rpm, making it useful for shops that machine different types of metals. Spin-offs derived from the ATP research--some already being sold--include new motor, motor drive, and roller-bearing technology as well as analytical tools for testing advanced spindle designs. In one spin-off project, the NCMS, Aesop, the National Science Foundation, and Boston Digital Corp. won an R&D 100 award in 1997 for designing the TurboTool™. The tool weighs and costs less, produces more, and lasts longer than competing spindles, R&D Magazine noted. Because it offers high power (100 kilowatts) at ultrahigh speed (100,000 rpm), the TurboTool concept has drawn interest from the aerospace industry as a possible means of manufacturing improved air frames at reduced costs. National Center for Manufacturing Sciences, Inc.
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