Helical Milling and Drilling for Hole-Making in CARALL: Experimental Evaluation

Abstract

Carbon fiber-reinforced aluminum laminates, known as CARALL, have wide applications in aircraft structures. However, numerous holes must be processed to assemble these structures, which is conventionally practiced through drilling. However, the drilling process exhibits certain limitations when utilized for hole-making in heterogeneous materials. In the recent past, helical milling has positioned itself as an alternative to the drilling process. However, helical milling performance examination during hole-making in CARALL is scant and needs further evaluation. The present study compares the milling process to the drilling process considering important performance indices, including cutting forces, surface roughness, chip morphology, machining temperature, and burr size. Additionally, microscopic characterization of the boreholes is performed to verify the presence of surface damage and delamination defects. Helical milling successfully lowered the thrust and radial forces and restrained the machining temperature below the levels attained via drilling. The diametrical deviation is higher at entry and lower at exit for both processes; however, helical milling produced holes with much higher accuracy. Helical milling developed smaller sized holes in comparison to drilling. Moreover, rougher surfaces due to the abrasion of continuous chips were observed in drilling, while a smoother finish was noted in helically milled holes. Based on the comprehensive comparative analysis, helical milling positions itself as an acceptable alternative to conventional drilling for machining fiber metal laminates.