Meso-scale machining capabilities and issues Page: 2 of 14
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an illustration of the relative size of critical dimensions for miniature, meso,
and micro machining. In general, meso-machining processes should be
capable of machining feature sizes of 25 microns or less. Unlike LIGA which
is an additive technology, the meso-machining technologies that are being
developed are subtractive in that material is removed to fabricate a part.
These subtractive technologies are, focused ion beam machining, micro-
milling, micro-turning, laser machining, and micro electro-discharge
machining. Sandia is driven to develop micro- and meso-scale fabrication
technologies to meet the needs of the nuclear weapons stockpile.
The focused ion beam (FIB) machines metals by bombarding the work
piece with a nanometer scale diameter beam of gallium ions. The material
removal rate for focused ion beam machining is very low, on the order of 0.5
cubic microns per second. Given the low material removal rate, the effort is
placed upon fabricating tools that can be used repetitively to remove material
at much faster rates. Examples of these tools are 25 micron diameter end
mills, masks for photolithography and masks for laser machining. Sandia has
successfully milled square channels having a cross section of 25 microns by
25 microns in PMMA, aluminum, brass, and 4340 steel using a high precision
milling machine. The work related to using the FIB to fabricate hard tooling,
has been a joint effort between Sandia National Laboratories and Louisiana
Tech University.
The two laser machining processes that are being developed are
nanosecond excimer and femtosecond Ti-sapphire. The excimer laser, which
has a nanosecond pulse width, can readily machine meso-scale holes and
channels in polymers and ceramics. A mask projection technique can be
introduced in the expanded portion of the excimer laser beam to project a
complex de-magnified replica of the mask onto the workpiece. The
femtosecond Ti-sapphire laser can readily machine micro-scale holes and
channels in metals. The femtoscond laser machining process can fabricate a
one micron diameter, high aspect ratio hole in metal with minimal debris.
Laser machining can be used to create three dimensional features because
depth of cut is very well correlated to exposure time.
Sandia's Agie Compact 1 micro-sinker electro-discharge machine (EDM)
is being used to machine features as small as 25 microns in difficult materials
such as stainless steels and kovar. This class of EDM technology employs a
micro-generator that is capable of controlling over-burn gaps to as little as
three microns. LIGA technology is being employed to fabricate small
intricate copper electrodes. These are mounted to the micro-sinker EDM to
machine the complementary shape into these difficult materials.
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BENAVIDES,GILBERT L.; ADAMS,DAVID P. & YANG,PIN. Meso-scale machining capabilities and issues, article, May 15, 2000; Albuquerque, New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc702211/m1/2/: accessed April 23, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.