1. Model of Surface Roughness and its Verification in Abrasive Waterjet Cutting of 1 inch Thick
Graphite/Epoxy Composite
Prabhakar Bala1
and Grzegorz Galecki2
1
MS Graduate, Manufacturing Program – Mechanical and Aerospace Engineering department, Missouri
University of Science and Technology
2
Senior Research Investigator - Rock Mechanics and Explosives Research Center, Director Waterjet
Laboratory, Missouri University of Science and Technology
Abrasive waterjet (AWJ) cutting of 1-inch-thick graphite/epoxy composite has been studied in this
research. Since composites are jointed with other structures, surface roughness parameter becomes of interest.
At the moment, the surface quality can only be characterized by selection of the cut quality from the software
provided by major abrasive waterjet cutting equipment manufacturers. This is possible through the research by
Zeng and Kim who introduced the machining numbers into waterjet cutting control system. To fulfill the
requirement for qualitative surface roughness characterization, Box-Behnken design methodology was applied
in design of experiments leading to building a model. In these experiments, pressure, traverse speed and
abrasive flow rate (AFR) were chosen as variables. Pressure was investigated in the range of 60-90 ksi; AFR in
the range of 1-2 lb/min with increment of 0.5 lb/min and traverse speed was selected at 20, 40 and 60 in/min.
For these experiments, surface roughness of 1” thick graphite/epoxy composite was identified and based on the
experimental data, mathematical models for surface roughness at different cutting depth were established using
Minitab 17. The models were verified for parameters randomly selected from the 3D response surface plots. To
create the surface plots, statistical software JMP was used. For model verification, correlation coefficient R2
was used. The best fit of the model was found up to depth of cut of ¼”. To better understand the generation of
surface in AWJ cutting, disintegration effect of abrasives during its acceleration in the cutting head was
analyzed. Based on experimental data, pressure increase resulted in higher percentage of disintegration. To
carry out the experiments, a 5 axis PaR system coupled with 90,000 psi/125 HP KMT PRO waterjet and Auto
line II cutting head with a combination of 0.014”/0.043” ratio of orifice to focusing tube diameter was used. In
all experiments, standoff distance of 0.125” and 80 HPX Barton garnet was used. Since in many applications a
stack of thin components is considered for cutting, in this research, analysis of 1” thick composite in
comparison to a 4 layer of ¼” composite is provided. These experiments revealed the importance of vibration
on the surface roughness.
The authors are acknowledging great support of the Center for Aerospace Manufacturing Technologies
(CAMT) and Rock Mechanics and Explosive Research Center/Waterjet Laboratory at the Missouri University
of Science & Technology-Rolla.
References:
Bala, Prabhakar., “Prediction od surface roughness in abrasive waterjet cutting of composites using response
surface methodology,” Master’s Thesis, Manufacturing Program – Mechanical and Aerospace Engineering
department, Missouri University of Science and Technology, 2016, Thesis number 10813.
Zeng, J. and Kim, T.J., “Development of an abrasive waterjet cutting kerf cutting model for brittle materials,”
Jet Cutting Technology, 1992, Kluwer Acad. Press, Dordrecht, pp 483-501.
Galecki, G., Mazurkiewicz, M. and Jordan, R., "Abrasive disintegration effect during jet ejection," International
Water Jet Symposium, September 1987, Beijing, China, pp. 4.71-4.77
Galecki, G. and Mazurkiewicz, M., “Hydro abrasive Cutting Head - Energy Transfer Efficiency,”
Paper presented at the 4th
U.S. Waterjet Conference, the University of California, Berkeley, August 26-28,
1987, pp. 107-119.