Quality
Waterjet Newsletter – 03/20/2007
AWJ Cutting of Engineering Plastics Abrasive Waterjet (AWJ) can
effectively cut hard materials such as tool steels. So we know that it has no
problem in cutting plastics. However, we don’t really know the characteristics
of plastic parts cut with AWJs. Last year Seo
and Ramulu* presented a paper on this subject. This
review will share their main findings. Their paper described an
experimental study of cutting a thermoplastic material MC901 nylon with AWJs. The experimental conditions include water pressure
of 250-320 MPa, 80 mesh garnet
at 7.8 g/sec flow rate, stand-off distance of 2-5 mm, and cutting speed
between 33 and 1350 mm/min. The maximum cutting speed is 1350 mm/min for a 15
mm thick MC nylon. Surface roughness Ra is in the range of 3 to 36.7 mm, greater than that of metals. By examining the cut surfaces
under scanning electronic microscope (SEM), it was found that the material
removal mechanism of MC nylon is shearing due to scooping, scratching, and
plowing actions of the abrasive particles. Compared to metals, the scratched
marks of MC nylon appeared to be more protruded and rounded, probably due to
the visco-elastic and plastic nature of the plastic
materials with long polymer chains. The polymer chains tend to align with the
direction of shearing and remain attached to the cut surfaces as micro burrs
(see pictures below). As a result, the surface texture deteriorated. By
analyzing the roughness profile, it was found that the AWJ cut surface of MC
nylon is negatively-skewed, with peaks and valleys caused by scratch marks
and micro burrs. The ratio of the two roughness parameters Rq/Ra is about 1.24, closely
resembling that of grinding (1.2).
* Seo, Y.W. & Ramulu, M.
(2006) Characteristics of abrasive waterjet machined engineering plastics
(nylon), in Wang et al. (ed.), Proceedings of the 8th Pacific Rim
International Conference on Water Jet Technology & The 12th
China Water Jet Technology Symposium, Qingdao, China, October 10-12, Paper 26. Beyond High
Pressure
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