Study on the Frictional Heat at Tool-Work Interface when Drilling CFRP Composites

Abstract

Carbon fiber reinforced polymer (CFRP) composites are rather difficult to drill because of their inhomogeneity in structures and anisotropy in properties. To improve the quality of drilled holes in a fibrous composite, optimizations of tool geometries and process parameters based on the heat transfer and force distribution mechanisms of tool-work interface are necessary. However, the friction behavior and the heat generation localized at the flank tool-work interface during drilling CFRP still remain poorly understood. This work aims to shed light on some implicit physical phenomena associated with the heat generation through the use of a designed tribometer to simulate the conditions of the flank tool-work interface analogous to the realistic environment of drilling CFRP laminates. The study presents a series of quantitative results of the interfacial friction coefficients with respect to different sliding velocities. The phenomenon of the elastic recovery effect of machining fibrous composites was rigorously considered throughout the experimental tribo-drilling analysis. The temperature changes of the tool-work interface were recorded in-situ using the thermocouples embedded in the drill bits and friction pins. The results show that the interfacial friction coefficient of the flank tool-work surface decreases as the cutting speed increases while the friction-induced temperature tends to account for a larger proportion of the overall drilling temperature with the elevated cutting speed.