Preassembly Cryogenic Drilling in Carbon Fiber Sandwich Sheets with Inner Foam Core

A study of cryogenic drilling in sandwich composites was carried out. The materials used were carbon-fiber-reinforced polymer sandwich sheets with an inner foamed polyvinyl chloride core, composites with applications including protection structures of polar engineering equipment. The purpose of this study was to determine the feasibility of drilling at low temperatures using this composite by analyzing the thrust forces and the inlet and outlet diameters of the hole due to their influence on hole quality and their importance in a preassembly operation. Experimental tests were performed in laminates with thicknesses of 12 mm and 6 mm, drilling with liquid nitrogen (LN2) as a refrigerant to reach temperatures below -120 degrees C under cutting conditions of 2000-6000 rpm for drill bit rotation speeds and 200-600 mm/min for feed rates. Variables such as thrust forces and circularity error were measured, and a design of experiments, analysis of variance, and regression models allowed us to identify the influence of cutting conditions and foam thickness. Optimal cutting conditions were identified and contrasted: 2100-3100 rpm for drill bit rotation speeds and 200-320 mm/min for feed rates. The diameters achieved low deviations, H7 and H8 tolerances for inlet and outlet diameters, respectively, which allows for avoiding additional preassembly operations, which can be important during plate assembly using LN2 and in maintenance operations. Although good results have been obtained with other materials such as glass-fiber- and carbon-fiber-reinforced polymers, this sandwich material is lighter.