Experimental investigation on the effect of dry and multi-jet cryogenic cooling on the machinability and hole accuracy of CFRP composites

Abstract

In this work, the drilling performance of carbon fibre reinforced plastic (CFRP) composites is analysed in terms of thrust force (Fn), torque (Mz), specific cutting energy (SCE), delamination factor (Fd), and hole quality under dry and cryogenic cooling conditions. An in-house developed multi-jet liquid nitrogen (LN2) delivery setup is used for experimental trials. This LN2 delivery system is retrofitted to an existing machine tool to enable the movement of jets along the axis of the spindle for better reachability of LN2 to the cutting zone during the drilling operation. Experiments are conducted using the full factorial technique considering four levels of spindle rotational speed (N), four levels of feed rate (fr), and two cutting conditions i.e., dry and cryogenic cooling. Results show increased Fn up to 35% and decreased Mz up to 24.46% using cryogenic drilling as compared to dry drilling. Moreover, SCE is reduced up to 35% using cryogenic drilling than in dry drilling. Entry Fd is decreased up to 21.55% under cryogenic drilling as compared to dry drilling. At higher N input and lower fr, the exit Fd can be reduced by up to 9% using cryogenic drilling as compared with dry drilling. In terms of hole quality, cylindricity (CYL) decreased by up to 42.69%, lower deviation in average hole size, and decreased average surface roughness (Ra) up to 20% when using cryogenic drilling. The results show that using the multi-jet cryogenic cooling system provides enhanced composite machinability and sustainability for industrial use.