Optimization and effects of machining parameters on delamination in drilling of pure and Al₂O₃/SiO₂-added GFRP composites

The present study concentrates on optimization and the effect of machining parameters on delamination that occurs during drilling operation of pure glass fiber-reinforced polymer (GFRP) composites and added GFRP composites which were developed for resistance to erosion wear. Contribution of drilling parameters to delamination was investigated by using Taguchi method and analysis of variance (ANOVA). Relationship between machining parameters and delamination was modelled by using response surface methodology. Correlations were established between the machining parameters by quadratic regression using response surface methodology (RSM). Delamination factors in the hole entrance and exit were obtained in drilling of pure glass fiber epoxy, and SiO₂- and Al₂O₃-added GFRP materials using the experimental plan. Delamination factors at the hole exits were found bigger than delamination factors at the hole entrances. The smallest delamination values were obtained in GFRP/epoxy composite compared to Al₂O₃/SiO₂-added GFRP composites at the hole exit. In the investigation of machinability of composites, considering the material as a variable, it has been determined that the material has a greater effect on delamination than the cutting parameters. A new machinability index defined and the material having the best machinability of the three materials was Al₂O₃-added GFRP composite at the entrance. Good machinability was obtained in drilling of pure GFRP/epoxy composite at the hole exit. It has been found that the effect of feed rate on delamination is greater than the cutting speed and the cutting speed has a low effect. Optimization of the multi-objective function created for maximizing the material removal rate, minimizing the delamination, was performed, and the optimum drilling parameters were obtained. As a result of the experimental study, it was found that the amount of delamination increased although the low mechanical property-added GFRP composites with the high resistance to erosion wear in accordance with pure epoxy GFRP composites due to the lack of a strong bond between the epoxy and the fibers in Al₂O₃ and SiO₂. It was observed that the delamination amounts of pure epoxy GFRP, Al₂O₃-added GFRP, and SiO₂-added GFRP composites increased respectively, while the compressive and tensile strengths of these three materials decreased.