Quality
Waterjet Newsletter – 09/26/2006
Enhanced
AWJ Cutting Through Modulation The research community of the
waterjet industry is constantly striving for improvement of productivity and
quality of cut. One of these efforts was from Henning and Westkamper*,
on enhancing AWJ cutting through modulation. Here are the highlights. Two main characteristics that
affect AWJ quality of cut are jet lag and striation marks. Striation marks
mainly affect the appearance of the part while jet lag will cause inaccuracy
around corners and small arcs. Currently reduction of jet lag and striation
are done by reducing the cutting speed. In this experimental study, three
kinds of modulation were tested, targeting reduction of jet lag and striation
without reducing the cutting speed. Two of these were done by superimposing a
constant linear cutting speed with a sine-oscillation, parallel or
perpendicular to the cutting direction.
The average cutting speed was kept unchanged. The oscillation
frequency varied from 0.5 to 3 Hz and amplitude from 0.3 to 1.2 mm. The third
modulation was done by periodically interrupting the abrasive flow while
maintaining the same average flow rate. The interruption frequency was 1 Hz. The
proportion of Off time-vs-On time varied from 1:2
to 1:10. Among the three modulations, the
parallel oscillation has the most favorable impact on jet lag and striation.
Significant jet lag reductions were shown for all the tested oscillation
frequencies and amplitudes while low frequencies were slightly better (see
below*).
Perpendicular oscillation and
abrasive modulation also showed slight reduction of jet lag. Striation
magnitude was also reduced with parallel oscillation, but not as significant
as the jet lag reduction. Small oscillation amplitudes (0.3 and 0.6 mm) and
high frequency (2.5 Hz) produced the best result for striation reduction.
Striation got worse with perpendicular oscillation and toggling abrasive had
a mixed result, with the best result achieved at 1:6 OFF/ON ratio. For
overall performance parallel oscillation at high frequency and low amplitude
was recommended. * Henning,
A. & Westkamper, E. (2003) Modulation of
cutting operation with abrasive waterjets, Proceedings
of the 2003 WJTA American Waterjet Conference, Houston, Texas, USA, August
17-19, Paper 5-G. |
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