Evaluation and analysis of delamination on drilled holes of industrial waste based novel agave sisalana/glass fiber reinforced hybrid composites

Natural fiber-reinforced polymer composites are gaining attention due to their low cost, renewable nature, corrosion resistance, and favorable mechanical properties. However, most studies on drilling of natural fiber composites report delamination at only one side of the hole, limiting their applicability in assembly and industrial use. The objective of this study is to fabricate a novel hybrid composite using 30 wt% of sisal fiber, 5 wt% of woven glass fiber, 60 wt% of polyester matrix, and 5 wt% of red mud filler, and to investigate the delamination at both entry and exit sides of drilled holes to optimize machining performance. The composite was fabricated via hand lay-up and compression molding. Drilling experiments were conducted on a numerically controlled vertical drilling machine using HSS drill bits, varying spindle speed (1000, 1250, 1500 rpm), feed rate (50, 100, 150 mm/min), and drill diameter (6, 9, 12 mm) according to an L9 orthogonal array. Delamination was measured using stereo microscopy and ImageJ software, and optimized using Taguchi S/N ratio analysis and ANOVA. Delamination at entry ranged from 1.0403 to 1.1248, and at exit from 1.0400 to 1.1237, showing close agreement. Minimum delamination was achieved at 1250 rpm spindle speed, 150 mm/min feed rate, and 12 mm drill diameter. ANOVA confirmed that drill diameter was the most significant factor, contributing 39.43% at entry and 34.84% at exit, followed by spindle speed and feed rate. Morphological analysis revealed that maximum delamination occurred at 1500 rpm of spindle speed, 100 mm/min of feed rate, and 6 mm of drill diameter, due to fiber pull-out and matrix damage. These results demonstrate that industrial waste-based hybrid sisal/glass fiber composites can achieve good mechanical performance and controlled machinability, providing quantitative guidance for selecting optimal drilling parameters and supporting their use in structural and industrial applications.