Direction of vibration Eo Tool Figure 8: Mechanism of ultrasonic vibration cutting PCD ve= cutting speed f vibration frequency: IT cutting distance during one period of tool vibration [24] This cutting speed is called"critical cutting speed" in the vibration cutting and is calculated by ve 2raf, where a is the amplitude of the tool vibration and f is its frequency ( ir 100 this study Vc=110 m/min) Cutting speed'Vc(m/min) The mechanism of ultrasonic vibration cutting is shown in Figure 8. The performance of ultrasonic vibration cutting Figure 6: Tool life for carbide and pcd tools vs. cutting strongly depends on the cutting distance during one speed in turning of epoxy matrix CFRP(Vt= 40 %)[15] period of the tool vibration IT Vo/f. It was experimentally confirmed that lr must be smaller than the fibre diameter (7 um in this study) to take advantage of ultrasonic 100 vibration cutting. By making l smaller than the fibre diameter the matrix and the fibre, which have different O DCC mechanical properties, can be sheared separately Hereby, the fibres do not prevent the shearing of the plastic matrix and, consequently, the surface quality is 50 improved even if the angle between fibre orientation and cutting direction is 90 A comparison of surface roughness between conventiona and ultrasonic vibration cutting is shown in Figure 9. Wher Ir is larger than the fibre diameter, the surface roughness 8 in ultrasonic vibration cutting is similar to that of conventional cutting(Figure 9a). On the contrary, when IT is smaller than the fibre diameter, the roughness in ultrasonic vibration cutting becomes smaller than that of conventional cutting(Fi 103mmin3.103 Conventional cutting vibration cutting Cutting Speed Vc 8 Figure 7: Tool life of diamond-coated and uncoated 6 54 carbide tools vs. cutting speed in turning of polyamide matrix CFRP (V+=40%)[15] As regards cutting parameters, speed and feed primarily nfluence the life of the cutting edge(Figure 7 4590 0 45 The tool life of both uncoated and diamond-coated carbide Fibre orientation(deg) Fibre orientation(deg)D tools reveals that wear is reduced by the diamond layer (a)Ir =18 um>7 um An increase in thermal stress of the cutting edge is (b)hr=36μm<7pm connected with the increase in cutting speed. Due to the high thermal conductivity of the diamond layer, an Figure 9: Surface roughness for conventional and ultrasonic vibration cutting [24] increase in thermal load capacity is available and ccordingly, higher cutting speeds are allowed for because of the difficulty in machining CFRP composites 目 Conventional cutting■ Vibration cutting h high efficiency, in [24] it was proposed to apply ultrasonic vibrations in turning of CFRP pipes using a iamond-coated tool The performance of the ultrasonic vibration cutting was 810 evaluated in terms of cutting force, burr formation and 12 surface roughness Ultrasonic vibration cutting allows to obtain good surface quality when machining difficult-to-cut materials. This is due to the fact that the ultrasonic vibration avoids the 04590 continuous contact between the tool rake face and the Fibre orientation(deg) Fibre orientation(deg) hip. As reported in [25], when the cutting speed beco faster than the speed of the tool vibration, the tool rake Figure 10: Cutting forces for conventional and vibration face is not separated from the chip and consequently cutting for a cutting speed 4 m/m ultrasonic vibration cutting loses its effectiveness corresponding to IT =3.6 um [24Figure 8: Mechanism of ultrasonic vibration cutting. vc = cutting speed; f = vibration frequency; IT = cutting distance during one period of tool vibration [24]. This cutting speed is called "critical cutting speed" in the vibration cutting and is calculated by vc = 2naf, where a is the amplitude of the tool vibration and f is its frequency (in this study vc = 110 m/min). The mechanism of ultrasonic vibration cutting is shown in Figure 8. The performance of ultrasonic vibration cutting strongly depends on the cutting distance during one period of the tool vibration IT = vJf. It was experimentally confirmed that IT must be smaller than the fibre diameter (7 pm in this study) to take advantage of ultrasonic vibration cutting. By making IT smaller than the fibre diameter, the matrix and the fibre, which have different mechanical properties, can be sheared separately. Hereby, the fibres do not prevent the shearing of the plastic matrix and, consequently, the surface quality is improved even if the angle between fibre orientation and cutting direction is 90". A comparison of surface roughness between conventional and ultrasonic vibration cutting is shown in Figure 9. When IT is larger than the fibre diameter, the surface roughness in ultrasonic vibration cutting is similar to that of conventional cutting (Figure 9a). On the contrary, when IT is smaller than the fibre diameter, the roughness in ultrasonic vibration cutting becomes smaller than that of conventional cutting (Figure 9b). Figure 6: Tool life for carbide and PCD tools vs. cutting speed in turning of epoxy matrix CFRP (Vf= 40 %) [I51 Figure 7: Tool life of diamond-coated and uncoated carbide tools vs. cutting speed in turning of polyamide matrix CFRP (Vf = 40%) [I 51. As regards cutting parameters, speed and feed primarily influence the life of the cutting edge (Figure 7). The tool life of both uncoated and diamond-coated carbide tools reveals that wear is reduced by the diamond layer. An increase in thermal stress of the cutting edge is connected with the increase in cutting speed. Due to the high thermal conductivity of the diamond layer, an increase in thermal load capacity is available and, accordingly, higher cutting speeds are allowed for. Because of the difficulty in machining CFRP composites with high efficiency, in [24] it was proposed to apply ultrasonic vibrations in turning of CFRP pipes using a diamond-coated tool. The performance of the ultrasonic vibration cutting was evaluated in terms of cutting force, burr formation and surface roughness. Ultrasonic vibration cutting allows to obtain good surface quality when machining difficult-to-cut materials. This is due to the fact that the ultrasonic vibration avoids the continuous contact between the tool rake face and the chip. As reported in [25], when the cutting speed becomes faster than the speed of the tool vibration, the tool rake face is not separated from the chip and consequently ultrasonic vibration cutting loses its effectiveness. Figure 9: Surface roughness for conventional and ultrasonic vibration cutting [24]. Fibre orientation (deg) Fibre orientation (deg) Figure 10: Cutting forces for conventional and vibration cutting for a cutting speed = 4 m/min corresponding to IT = 3.6 pm [24]