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The diamond tool is commonly used in micro-machining as it can
withstand the micro hardening of the workpiece surface during
micro-machining. This micro-hardening creates enough resistance
to break the tool bit easily in micro milling, but not a diamond
tool. Micro-machining using diamond tool could be performed at
high speeds and generally fine speeds to produce good surface
finish such as mirror surfaces and high dimensional accuracy in
non-ferrous alloys and abrasive non-metallic materials.
However, if a diamond tool were to be used to cut steel, one of
the most common engineering materials used in industries, the
diamond tool will face severe tool wear. While diamond only
softens at 1350 degree Celsius and melts at 3027 degree Celsius,
and is also the hardest material in the world, it has a
weakness. Diamond succumbs to graphitization, which means that
it will change its crystal structure to graphite crystal
structure at 200 degree Celsius in the presence of a catalyst
metal such as carbon steel and alloys with titanium, nickel and
cobalt.
There have been various attempts to improve the tool life of the
diamond tool while cutting steel so as to improve the efficiency
and profitability of this operation. Such processes include
micro-cutting the steel workpiece in a carbon-rich gas chamber
as well as a cryongenically cooled chamber. However, these
methods require costly equipment modification and restrict
direct supervision of the micro-cutting process.
The latest breakthrough came when the diamond tool was subject
to ultrasonic vibration during micro-cutting. It has been shown
that a diamond tool subject to ultrasonic vibration can cut the
steel well enough to produce a mirror surface finish with
acceptable tool life. The ultrasonic vibration at the diamond
tool tip allows the tool face to cool down considerably during
the cutting process and delays the chemical reaction between the
diamond tool and the steel workpiece. As a result, the diamond
tool life is increased by a few hundred times.
For example, a single crystal diamond tool with feedrate 5
micron/revolution, cutting speed zero to 5m/min and depth of cut
10 micron was attached to a ultrasonic vibration generator so
that the diamond tool tip vibrated about 4 microns while it was
used to cut stainless steel. The mirror surface finish of the
cut steel surface was measured at 8 nm Ra!
With more and more machining companies moving into the niche
micro machining field, such ultrasonic vibration assisted
cutting can only help the progressive company to achieve process
leadership and innovative differentiation.
Author Ken Yap is a director of Suwa Precision Engineering Pte
Ltd in Singapore and represents metal">http://www.suwaprecision.com">metal stamping, precision
machining, miniature precision balls and PCB manufacturers from
Suwa, also called "The Oriental Switzerland" in Japan due to
its Swiss resemblance for rich watch-making industry, its
mountainous terrain and its precision component making industry.
About the author:
Ken Yap is a director of Suwa Precision Engineering in
Singapore, and represents precision component manufacturers from
Suwa, Japan. He is also a partner in Attisse Pte Ltd providing
business consultancy and research services to Japanese
investors.
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