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 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.
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