Experimental and analytical investigations for abrasive waterjet hole trepanning of thick Kevlar-epoxy composites used in ballistic applications

Abrasive water jet (AWJ) is widely useful for producing non-circular cutouts/holes and for drilling difficult to cut materials such as super alloys, ceramic coated materials and fiber-reinforced composites. However, in AWJ drilling or hole trepanning, due to the jet trailback, the diameter of the hole tends to increase with an increase in workpiece thickness and striation marks are also observed at the exit side. This results in an inferior quality hole due to poor dimensional tolerances, leading to hole mismatch problems during assembly. Therefore, to obtain better quality holes by AWJ trepanning, optimum selection of process parameters is very important and critical. This paper embodies a Taguchi method based experimental investigation for finding the optimum parameter settings in AWJ hole trepanning, for 6 mm thick Kevlar-epoxy composites, used for ballistic applications. Kerf taper and surface roughness have been chosen as the quality characteristics and four major operating parameters namely, water jet pressure, quality level (or traverse speed), abrasive flow rate and abrasive mesh size have been considered for experimentation. Visualization studies using SEM and optical microscope have also been conducted for investigation of delamination induced during AWJ trepanning. © BHR Group 2012 Water Jetting 21.