This Small Business Innovation Research (SBIR) Phase I project aims to develop an ultrahigh speed, precision, micro-milling spindle. The trends in industrial and military products that demand miniaturization, design flexibility, reduced energy consumption and high accuracy continue to accelerate -- especially in the medical, biotechnology, telecommunications and energy fields. These industry segments require high-precision, three-dimensional components with sizes and geometric features ranging from tens of micrometers to a few millimeters. Because the cutting tools used for generation of such products are small, high cutting speeds are needed to increase the machining efficiencies. This project is aimed at developing a new, ultrahigh speed micro-milling spindle for machining at speeds in excess of 500,000 revolutions per minute. The spindle design relies on unique oil-free foil bearings. The principal advantages of the proposed micro-milling spindle include higher production rates and precision obtained through the implementation of the ultrahigh speed machining that will decrease the cutting forces and tool vibrations.
The broader impact/commercial potential of this project includes enabling cost-effective manufacture of micro-components needed across a broad range of industrial sectors relying on micro-fabrication technology. Since the underlying scientific principles of micro-machining at the proposed cutting speeds are not known, the availability of the proposed spindle will allow for basic studies to uncover the response of materials under ultrahigh cutting speeds. Such basic information could lead to new scientific discoveries and further extend the micromachining processes. The data and information generated will undoubtedly be used in the future for training of graduate students. The broad impact of this project includes expansion of micro-manufacturing research, and research opportunities for next-generation scientific researchers and technology developers to pursue micro-machining and micro-manufacturing related efforts in the broader fields of micro-positioning devices, micro-die-and-mold manufacturing, micro-sensing and monitoring systems, and micro-factory integrations and optimization. Commercialization of the micro-milling spindle will be instrumental in the development of new businesses and industries, and high value added jobs.
The objective of this SBIR project is to develop an ultrahigh speed micro-spindle for micromachining. The proposed spindle is unique in achieving ultrahigh speeds near 500,000 rpm. Following systematic design analysis that included attention to the design of foil bearings, rotordynamic analysis, motor selection, and air-turbine design, the spindle was fabricated and performance tested. The spindle performed as expected up to 475,000 rpm. Micro-milling tests were performed with the air-turbine driven spindle at speeds up to 350,000 rpm to allow a safe speed margin below the maximum operating point. Channels were cut in an aluminum ally using micro-end mills (with diameters ranging from 80 to 480 µm) using a range of machining parameters to establish optimum machining conditions. While no performance issues were discovered with the spindle, the smaller cutting tools proved to be inadequate for machining at such high speeds and caused a limitation in the milling parameters that could be used. Inspection of cut surfaces confirmed that ultrahigh speed allows machining at optimum linear cutting speeds recommended for each material and cutting tool type, and greatly reduces the potential for burr formation. As a final test, a high strength nitride was successfully machined with a diamond micro-grinding tool at 300,000 rpm that resulted in a linear cutting speed equivalent to speeds obtained in surface grinding.
