Characterization of drillability of sandwich structure of carbon fiber reinforced epoxy composite over titanium alloy
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[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] Composite-over-Titanium structures are the major candidates for substitution of conventional materials in aerospace industries. This paper investigates the main effects of cutting parameters (cutting speed, feed and tool condition) on hole quality, force and torque during drilling of a sheet of IM7/977-3 composite material over 6Al-4V Titanium alloy sheet. The work piece is mounted on a developed fixture on top of a CNC vertical milling machine and a force and torque sensor was embedded in the tool holder that wirelessly transmitted force and torque signals that were sampled and stored in a personal computer. The dimensional accuracy of the holes was then measured using DP-4 touch probe by CENTROID and the surface roughness of the composite was measured using Mitutoyo Surftest 402 profilometer. Response surface methodology, RSM, was used to design a set of experiments to determine the behavior of the process parameters when changing the cutting speed and feed. The process outputs: holes' accuracy, surface roughness of the composite, force and torque were then fitted to 3-D surfaces with the output on the Z-axis and the speed and feed on the X and Y axis. Process contour maps were then derived for each output parameter giving an outline of the effect of feeds and speeds on each output and the optimum process conditions were found for each parameter. The optimum process conditions found using RSM were then used in a Taguchi robustness analysis to find the set of independent parameters (speed, feed and tool condition) that would yield a robust process regardless of noise factors. Noise-to-signal ratio analysis was conducted and the means were plotted to define the optimal robust levels of independent factors for each of the output parameters.
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