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Quality
Waterjet Newsletter – 04/10/2007
Monitoring AWJ Cutting Using Infrared Thermography
Kovacevic et al.* found that
infrared thermography is a very promising technique
for monitoring abrasive waterjet cutting of opaque materials and nozzle wear.
Here are the highlights of their findings.
 A visualization study
of abrasive waterjet cutting was previously done by Hashish, using a
high-speed camera and transparent sample materials such as Lexan. In this study, the high-speed camera was replaced
by an infrared camera, and Lexan was replaced with
blocks of aluminum and titanium alloys. One face of the sample blocks was
coated with black enamel with a known emissivity of
0.99 and was exposed to the infrared camera. The cuts were made parallel to
this exposure face with a set distance. A smaller distance has a higher
sensitivity. An increase in cutting pressure causes an increase in workpiece temperature and thus can be detected by the infrared
camera. But change in cutting speed has a minimal effect on temperature
change and thus cannot be easily picked up by the infrared camera. Titanium,
being a poor conductor, has a “sharper” infrared image than aluminum, but
requires a smaller distance to the exposure face. The figure above is an
infrared image of the jet cutting a titanium sample (from left to right). It
shows the inclination of the jet as well as two hot spots on upper and lower
portions of the jet trajectory. The data gained from the infrared images
closely match those from measurements using thermocouples.
 The same infrared
camera was also used to monitor the wear of AWJ nozzle. The plot on the right
shows that, as the nozzle diameter increased, the peak temperature decreased
and the location of the peak temperature (indicated by the L/Ln ratio) migrated from top to bottom, indicating the downward
progress of wear pattern.
* Kovacevic, R.,
Mohan, R., & Beardsley, H.E. (1996) Monitoring of thermal energy
distribution in abrasive waterjet cutting using infrared thermography,
Journal of Manufacturing Science and Engineering, November, Vol. 118,
pp555-563.
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