OPTIMIZATION OF OVALITY ON DRILLING GLASS FIBER REINFORCED PLASTIC COMPOSITES WITH COATED TUNGSTEN CARBIDE TOOL

Abstract: Nonlaminated composites having superior mechanical properties than laminated composites is widely used in ballistic applications. Since literature on the machinability of nonlaminated composites is scarce, an investigation was carried out to study the hole quality in drilling thick nonlaminated Glass Fiber Reinforced Plastic (GFRP) composite rods using coated tungsten carbide twist drill. The GFRP composite rods were made by pultrusion method with high fiber weight fraction. The ovality (hole diameter inaccuracy) of the drilled holes was measured using Coordinate Measuring Machine (CMM). Taguchi"s orthogonal array and analysis of variance (ANOVA) were employed to study the influence of process parameters such as feed and spindle speed on ovality of the drilled holes. The optimum level of process parameters towards minimum ovality was obtained to achieve defect controlled drilling of pultruded GFRP composite rods. Correlation for ovality with process parameters was established using a statistical software MINITAB 16. The influence of speed on ovality was insignificant. The influence of feed was significant on ovality of the drilled holes. The optimal process parameter levels within the range examined was identified as 0.15 mm/rev feed and 1000 rpm speed for pultruded GFRP composite rods using 10 mm diameter twist drill. The influence of process parameters on hole quality in nonlaminated composite rods differs with drill geometry and also differs from the influence of process parameters on hole quality in laminated composites