Thrust force and torque profiles when drilling GLARE 2B 11/10-0

Thrust force and torque profiles when drilling GLARE 2B 11/10-0.4 at feed of 0.12 mm/rev (360 mm/min) and spindle of 3000 rev/min using tool T1 are illustrated in Figure. At the 1st stage, the chisel edge starts to penetrate into the first Al 2024 sheet which induces rapid increase in thrust force and gradual increment of torque in 2nd stage. At the 3rd stage, the drill reaches the first glass fibre/epoxy prepreg layer and then cutting force Fz and torque are decreased. The reason behind this phenomenon is the sudden change in material hardness of aluminum plate compared to S2/FM94 layer (Ashrafi et al. 2013). As the cutting edge is in full contact with the second Al 2024 sheet in 4th stage, the highest peak in thrust (175 N) and peak torque (40 N) were observed. At the 5th stage when the chisel edge is near to penetrate fully into the work piece the cutting force slightly decreases due to lower resistance by the work piece (K. Giasin, Ayvar-Soberanis, and Hodzic 2015), and finally when the drill is completely out of hole, the thrust forces and torque descends rapidly to zero (stage 6). It was noted that thrust force and torque for drilling aluminum was higher than S2/FM94 layers for all the tools and with different cutting conditions used in this study. Figure 4 showed that thrust force and torque during drilling of Al are double compared to S2/FM94 layer. This thrust is about 86 N and 167 N while torque is about 20 N.cm and 38 N.cm, respectively for GFRP and Al. This result matches with previous experimental studies carried out on drilling GLARE and aluminium/composite stacks (Shyha et al. 2010), (Zitoune, Krishnaraj, and Collombet 2010), (Coesel 1994), (Tyczyski et al. 2014), (Ashrafi et al. 2013). The change is due to the difference in their mechanical properties and behavior during drilling mechanism. Al2024 is a subject of plastic deformation and thermal softening along with chip formation, whereas in S2/FM94 layers produce fibre breakage and matrix cracking along with the plies debonding and the formation of glass fibre dust powder (K. Giasin, Ayvar-Soberanis, and Hodzic 2015).

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