Tool Wear Study in Turning Ti-6Al-4V and Edge Trimming of Carbon Fiber Reinforced Plastics (CFRP)

Lightweight materials such as titanium alloys and carbon fiber reinforced plastics (CFRP) are highly desirable due to their low density and high strength properties for many aerospace, chemical, petroleum, automotive, and sports applications. However, both materials are considered difficult to machine due to various factors.In machining titanium alloys, the low thermal conductivity and highly reactive nature of titanium with cutting tools cause the temperature to rise quickly, producing a segmented or “saw-tooth” chip. Chip segmentation caused a periodic loading on the tool and affected the cutting process. Ti-6Al-4V depending on the heat treatment, produces four distinct types, elongated (ELO), mill-annealed (MIL), solution treated and aged (STA), and lamellar (LAM). In this dissertation, four different microstructures of Ti64, ELO, MIL, STA, and LAM, are machined at 61, 91, and 122 m/min. The machining chips were collected and characterized to study the impact of the microstructure. In addition, the crater wear for different types of Ti64 was measured and compared. A finite element numerical simulation was developed using the chip morphology measured, which enables estimating the cutting temperature for Ti64-STA. Electron backscatter images of the cutting chips (EBSD) and crater wear surfaces were also analyzed to verify the wear mechanism. The findings suggested a high interface temperature during cutting enables faster tool diffusion. Another machinability study of turning Ti64-STA using a variety of coated tools was conducted. The coated tool materials include TiAlN, AlTiN, AlMgB14(BAM), ZrN, and (AlCrSi/Ti)N. The performance of these cutting tools was assessed using cutting force data, flank wear, and crater wear measurements. In conjunction with the coating experiments, another machining study was conducted in minimum quantity lubrication (MQL) using oil mixed with solid additives such as hBN, WS2, MoS2, and xGnP. For CFRP, the abrasion from the fibers was the leading cause of tool wear. Three distinctly different types of CFRPs with T300 PAN-based carbon fibers as standard modulus (SM), IM-7 PAN-based carbon fibers as intermediate modulus (IM), and K13312 pitch-based carbon fibers as high modulus (HM) are used. Tool wear during the edge-trimming process of three types of CFRP laminates is analyzed for four different ply angles, namely 0°, 45°, 90°, 135°, to investigate the interactions between the fiber type and the fiber orientation.