Investigation of cutting parameters affecting burr formation in drilling of Al-5005 material

In this study, Al-5005 material was subjected to drilling experiments using CNC milling machine under dry cutting conditions. The experiments, using HSS drills (5 and 10 mm diameter), spindle speeds (400, 800 and 1200 rev/min), feed rates (0.1, 0.2 and 0.3 mm/rev) and drill point angles (90°, 118°, 130° and 140°), were achieved. After the experiments, hole?s microhardness, roughness, the types of burr formed at the hole exit, height and thickness were analyzed.According to the experimental results, generally, the burr sizes were increased with the increase in drill diameter, feed rate and spindle speed, and decreased with the increase in drill point angle. Also, it was observed that the microhardness values measured in the neighborhood of the drilled surface were high while those measured in distant regions were low. Furthermore, it was found that the more increase in the microhardness values the more increased in burr sizes. In accordance with the increase in drill feed rate and diameter an increase, and with the increase in spindle speed and drill point angle a decrease in surface roughness was measured. It was found that, the roughness values measured with respect to the spindle speed were not effective, but the other parameters were effective on burr sizes. In general, for point angles 130° and 140° uniform burr types, but for 90° and 118° beside uniform, crown and transient burr types were observed. The other drilling parameters were not effective for point angles 130° and 140°, while being effective for point angles 90° and 118°. Considering these results, in order to mathematically model the burr sizes at the exit of the hole, an artificial neural network (ANN) model was constructed. This ANN was trained and tested in accordance with the experimental data. The model successfully demonstrated the simulation of the experiment with a sensitivity of 94% and 96% for burr height and thickness respectively.In addition, in this study, to reduce the size of burrs in the exit region of the hole, a new method called as ?unstable drilling? was introduced. With this new method, benefiting from the features of CNC milling machine, unstable drilling parameters along the hole were formed and, according to this, new experiments were designed. In the experiments, 140° point angle drills, by which the smallest burr sizes were obtained through the stable drilling experiments mentioned above, were used. The unstable drilling conditions were achieved by automatically reducing the feed rate, which is the most effective parameter other than point angle according to the stable experiment?s results, as the drill comes nearby the hole exit, and according to this the changes in burr sizes were analyzed. Based on the results obtained from unstable method a reduction of 25% in burr heights and 35% in burr thickness was found.