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Carbon fiber reinforced polymers (CFRPs) are attractive engineering materials in the modern aerospace industry, but possess extremely poor machinability because of their inherent anisotropy and heterogeneity. Although substantial research work has been conducted to understand the drilling behavior of CFRPs, some critical aspects related to the machining temperature development and its correlations with the process parameters still need to be addressed. The present paper aims to characterize the temperature variation and evolution during the CFRP drilling using diamond-coated candlestick and step tools. Progression of the composite drilling temperatures was recorded using an infrared thermography camera, and the hole quality was assessed in terms of surface morphologies and hole diameters. The results indicate that the maximum drilling temperature tends to be reached when the drill edges are fully engaged into the composite workpiece. Then it drops sharply as the tool tends to exit the last fiber plies. Lower cutting speeds and lower feed rates are found to favor the reduction of the maximum composite drilling temperature, thus reducing the risk of the matrix glass transition. The candlestick drill promotes lower magnitudes of drilling temperatures, while the step drill yields better surface morphologies and more consistent hole diameters due to the reaming effects of its secondary step edges.

High-strength carbon fiber-reinforced polymers have been a promising alternative to conventional fibrous composites because of their extremely high properties. Mechanical drilling is a necessary operation to create boreholes for riveting and bolting different composite structures into assemblies. However, the high-strength carbon fiber-reinforced polymers pose much more serious machining issues than the conventional ones. The present work aims to investigate the drilling performance of one type of uncoated carbide brad spur tools when applied in machining of high-strength carbon fiber-reinforced polymer laminates. The wear mechanisms of uncoated carbide brad spur drills were figured out. Additionally, the tool wear influences on the thrust force, hole dimensional accuracy, and drilling-induced delamination were quantified. The acquired results indicate that the tool wear has a significant impact on the drilling process and the quality of machined hole wall surfaces. The dominant wear mode is proved to be abrasion wear. Moreover, the uncoated brad spur drills appear to exhibit high resistance to the abrasion wear in the drilling of high-strength carbon fiber-reinforced polymer laminates.

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