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History
• The roots of ultrasonic technology can be traced
back to research on the piezoelectric effect
conducted by Pierre Curie around 1880.
• He found that asymmetrical crystals such as quartz
and Rochelle salt (potassium sodium titrate)
generate an electric charge when mechanical
pressure is applied.
• Conversely, mechanical vibrations are obtained by
applying electrical oscillations to the same crystals.
One of the first applications for Ultrasonic was sonar (an
acronym for sound navigation ranging). It was employed
on a large scale by the U.S. Navy during World War II to
detect enemy submarines.
• Frequency values of up to 1Ghz (1 billion cycles per
second) have been used in the ultrasonic industry.
• Today's Ultrasonic applications include medical imaging
(scanning the unborn fetus) and testing for cracks in
airplane construction.
Ultrasonic waves
• The Ultrasonic waves are sound waves of
frequency higher than 20,000 Hz.
• Ultrasonic waves can be generated using
mechanical, electromagnetic and thermal
energy sources.
• They can be produced in gasses (including air),
liquids and solids.
Piezoelectric transducers employ the inverse
piezoelectric effect using natural or synthetic
single crystals (such as quartz) or ceramics
(such as barium titanate) which have strong
piezoelectric behavior.
• Ceramics have the advantage over crystals in
that they are easier to shape by casting,
pressing and extruding.
Principle of Ultrasonic Machining
In the process of Ultrasonic Machining,
material is removed by micro-chipping
or erosion with abrasive particles.
• In USM process, the tool, made of
softer material than that of the
workpiece, is oscillated by the Booster
and Sonotrode at a frequency of about
20 kHz with an amplitude of about
25.4 um (0.001 in).
• The tool forces the abrasive grits, in
the gap between the tool and the
workpiece, to impact normally and
successively on the work surface,
thereby machining the work surface.
Principle of Ultrasonic Machining
During one strike, the tool moves down from its most upper
remote position with a starting speed at zero, then it speeds
up to finally reach the maximum speed at the mean position.
• Then the tool slows down its speed and eventually reaches
zero again at the lowest position.
• When the grit size is close to the mean position, the tool hits
the grit with its full speed.
• The smaller the grit size, the lesser the momentum it receives
from the tool.
• Therefore, there is an effective speed zone for the tool and,
correspondingly there is an effective size range for the grits