Wet vs dry CFRP drilling: Influence of cutting fluid on tool performance

Carbon fibre reinforced polymer (CFRP) cutting operations have core features which include; i) chip types consisting of sub 50 micron particles and ii) aggressive abrasion-dominated tool wear. The workpieces used in this investigation were manufactured in a single batch from aerospace-grade, out-of-autoclave, quasi-isotropic, thermoset prepreg materials. Initially, a number of conventional tests were performed to assess the performance of isolated cutting fluid chemicals. The fluid-to-fluid variance was shown to be less significant in these tests when compared against dry conditions. A 6 percent basic micro-emulsion concentrate produced the best results with dry setup produced lower torque results than any cutting fluid tested. Production-style drilling trials were undertaken to investigate the tool life under varying fluid conditions from basic to commercially available. These trials indicated that dry, tip-extracted conditions enabled an extended tool life prior to coating failure against the best cutting fluid with identical parameters, machine tool, cutting tool and workpiece material manufacture conditions. The hypothesis for this reduction in tool performance under general wet conditions is that heat introduced by the drilling process changes the CFRP polymer’s visco-elastic properties thus reducing the abrasive interaction between tool and workpiece during material removal processes. The best cutting fluid, a 5 percent semi-synthetic, commercially available chemistry, produced approximately 60 holes more than the poorest performing chemistry.