Drilling performance analysis of glass fiber reinforced polymer composites by symbolic regression method

In this thesis, the effects of drilling method and drilling parameters on cutting force and deformation factor in drilling of glass fiber reinforced polymer (CFTP) composites having ±45° orientation angle were experimentally investigated and analyzed by symbolic regression method. Drilling of CFTP composites was performed with both drill and punch. Drilling by drill was performed at six different cutting speeds (6.25; 12.50; 25; 50; 100 and 200 m/min) and four different feed rates (0.025; 0.05; 0.1 and 0.2 mm/rev); drilling by punch was performed at three different feed rates (250, 500 and 1000 mm/min) by punches having four different tip angles (straight, 15° \ angled, 15° ˅ angled and 15° ˄ angled). As a result of the experiments, it was observed that feed rate and cutting speed had a significant effect on the cutting force occurred in drilling with a drill. Increasing feed rate increased the cutting force. Increasing cutting speed decreased the cutting force at the beginning and started to increase the cutting force after a certain level. The highest cutting force in drilling with drill was observed at high feed rate and cutting speed. The values of cutting forces occurred in drilling by punch were much higher than those in drilling by drill. The cutting forces varied depending on the punch type and feed rate. The highest values in drilling by punch were obtained from the experiments performed with a punch with a flat tip angle. In symbolic regression analyses for the cutting force; it was seen that the most important factor on the cutting force in drilling with a drill is the feed rate, and the most important factor on the cutting force in drilling with a punch is the punch type. In drilling with a drill, the deformation factor at the hole entrance was lower than the deformation factor at the hole exit. The deformation factor increased as the cutting speed and feed rate increased. On the other hand, in drilling by punch, the deformation factor occurring at the hole entrance was generally higher than the deformation factor occurring at the hole exit. The deformation factor, depending on the punch type and the feed rate, varied. In the symbolic regression analyses for the deformation factor, it was analyzed that the deformation occurring at the hole entrance is affected the most by the cutting speed, and at the hole exit the most is affected by the feed rate. In the drilling experiments with punch, it was seen that the most important parameter affecting the deformation at the hole entrance and exit is the punch type. Mathematical expressions from all symbolic regression analyses were tested to be quite good at predicting experimental data.