Investigation of Drilling Holes in CFRP for Aircraft Using cBN Electroplated Ball End Mill Using Helical Interpolation Motion

Abstract

Carbon fiber reinforced plastic (CFRP) is a lightweight material with exceptional mechanical properties such as high specific strength, high specific modulus, and retained fatigue strength. It exhibits outstanding characteristics derived from its carbon content such as electrical conductivity, low thermal expansion, chemical stability, and high thermal conductivity. These unique features make CFRP a highly versatile material. It can be extensively used across various industries, offering advantages over steel, aluminum, and glass fiber reinforced plastic. Moreover, its anisotropic nature allows for innovative design possibilities, providing different mechanical properties for different fiber orientations. The increasing demand for CFRPs, particularly in the aerospace and automotive industries, is attributed to their high reliability and design flexibility. Consequently, the requirement for efficient and high-quality CFRP processing techniques has led to numerous studies focusing on trimming and hole drilling of CFRP parts. Previous research has also highlighted the significant impact of processing temperature on the quality of CFRP and other fiber reinforced plastics, such as aramid fiber reinforced plastic. However, many existing reports are limited to specific processes such as trimming or hole drilling, without addressing broader concerns such as tool wear, burrs, fiber damage owing to heat, or the lack of multi-purpose cutting tools suitable for CFRP when considering tool costs. In addition, the aerospace industry demands precise hole drilling for thousands of holes, facilitating assembly with rivets or screws; this requires high-precision hole drilling processes. To address CFRP hole drilling challenges, this study proposes and develops a cBN electroplated ball end mill to enable an efficient and high-quality hole drilling in CFRPs. As machining demands evolve with diverse workpiece materials, technological innovations are continuously being sought in hole drilling processes, exploring alternatives beyond conventional drilling such as employing end mills and enhancing tool functionality. In this study, we employed a ball end mill and helical interpolation motion to tackle CFRP hole drilling. The delamination occurring at the exit side of the drilled holes was investigated using strain gauges. Additionally, finite element analysis was employed to compare and analyze experimental results, leading to guidelines for an efficient and high-quality hole-drilling approach that balances productivity and workpiece integrity. We achieved high-efficiency hole drilling while maintaining the quality by adjusting the cutting parameters under conditions that prevent delamination. The proposed cBN electroplated ball end mill offers promising potential for advancing CFRP processing methods, addressing the growing demand for this exceptional material in various applications.