Micrometer-Scale Machining of Metals and Polymers Enabled by Focused Ion Beam Sputtering Page: 4 of 7
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mills and demonstrate their usefulness by machining metal alloys. All micro-tools made in this
study successfully mill for hours without breaking.
The focused ion beam system  consists of a liquid metal ion source, beam deflectors,
sample stage, and channelplate detector for imaging. The ion gun produces an energetic beam of
Ga+ ions. The beam intensity is roughly Gaussian with a full-width at half-maximum diameter
of 0.4 gm. Currents are typically 2 nanoamperes giving a current density of about 0.5 Amp/cm2.
The beam is deflected by a digitally driven vector scan system with sub-micron resolution. A
computer controls stage motion with 1pm accuracy, and samples can be rotated by 0.15 0 per
step with an external controller. The Ga+ source chamber is ion pumped and maintains a
pressure of 10-9 Torr. The target chamber is oil diffusion pumped with working pressures of 10-8
Torr during sputtering. A small aperture separates the two chambers for efficient differential
Tool blanks are purchased from a commercial vendor and are made of M42 cobalt high
speed steel. Blanks are 5.3 cm long and have a 2.28 mm diameter. One end of each tool is
tapered by diamond grinding. This end is approximately 25 m in diameter and cylindrical over
a length of - 90 m. Once mounted inside the FIB system, the tapered end is first shortened to
85 pm by sputtering. Facets are then fabricated into the cylindrical length by ion beam
sputtering. The sharp edges of facets are designated as cutting edges for ultra-precision milling.
All sputtering involves energies of 20 keV.
Ultra-precision machining with FIB fabricated micro-tools requires a high precision milling
apparatus. In this study, a Boston Digital milling system uses laser interferometry to control x, y
and z position to 0.5 pm resolution. Spindle speeds for this study are 10,000 or 18,000 rpm, and
feed rates are 2 mm/minute unless otherwise specified. For milling, the radial runout of a tool is
less than 2 pm, and the axial depth of cut is 0.5 or 1.0 micron per pass. Samples machined by
micro-tools are cleaned afterwards by rinsing with methanol. Different lubricants are used during
ultra-precision machining depending on the workpiece material.
Several micro-tools are made using FIB sputtering as shown in Figure 1. These micro-end
mills have 2, 4 or 6 facets with 2, 4 or 5 cutting edges, respectively. With the tool stationary,
Figure 1. SEM micrographs of micro-end mills made with focused ion beam sputtering.
Tools have 2, 4 and 5 cutting edges.
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Adams, D.P.; Benavides, G.L. & Vasile, M.J. Micrometer-Scale Machining of Metals and Polymers Enabled by Focused Ion Beam Sputtering, article, December 22, 1998; Albuquerque, New Mexico. (digital.library.unt.edu/ark:/67531/metadc673350/m1/4/: accessed October 17, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.