Thrust and torque analyses for different strategies adapted in microdrilling of glass-fibre-reinforced plastic

Aerospace and automobile industries use components made of composites which require micromachining operations to be carried out. Microdrills are expensive and hence attempts are always made to reduce the drill breakage. In this paper, microdrilling of glassfibre-reinforced plastic (GFRP) has been attempted using a carbide drill of 0.32 mm diameter. Apart from the selection of process parameters such as speed and feed rate, drilling strategy also plays an important role in realizing good-quality holes and improved drill life. Microdrilling experiments on GFRP have been carried out using a full-factorial design with five levels for speed and feed rate and three repetitions for each run. For the purposes of comparison, microdrilling of plain sheet made out of matrix material has also been carried out. The experiments on blindhole drilling reveal that there is a reduction in maximum thrust force and torque in peck drilling. Encouraged by this, with peck cycle, through-hole drilling of 2.25 mm thick GFRP specimens has been carried out successfully. Regression models developed for the thrust force show good correlation between the measured and predicted values, while the torque values lie scattered with respect to the predicted trends. The results indicate that micro-holes of large aspect ratio could be produced by selecting proper process parameters and drilling strategy.