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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