Research On PCD Tools Cutting Titanium Alloys

Due to their excellent combination of high strength-to-weight ratio and exceptional resistance to corrosion, titanium alloys have been used extensively in aerospace and chemistry industry etc. But the machinability of titanium alloys is poor. Nowadays, both in home and abroad, titanium alloys are machined using uncoated carbide cutting tools,and the cutting speed is under 45m/min. So it is crucial to enhance the machining efficiency level. Compared with uncoated carbide cutting tools, the polycrystalline diamond (PCD) cutting tools can have higher cutting speed and have longer tool life. The cutting force and the thermoplastic shear instability can directly influence on machining precision, tool life and surface roughness. In this paper the static and dynamic cutting force, surface roughness and thermoplastic shear instability during cutting of Ti-6A1-4V alloy is investigated in order to provide a theoretical basis for the production of titanium alloys in a smooth and efficient processing. The main content is listed as following:1) According to the cutting experiments, the static and dynamic cutting force in different cutting parameters was investigated, and the results was explained.2) According to the orthogonal experiment, surface roughness of the workpiece with the cutting parameters was analyzed, and the results was explained. Index R_a, R_z were also analyzed respectively with the method of variance analysis and the results showed that feed and depth of cut had a prominent impaction on both R_a and R_z.3) Adiabatic shear bands were observed using optical microscope and scanning electron microscopy(SEM).The deformation inside the chip, the change of chip shear bands and the influence of cutting speed on adiabatic shear band width and spacing when the thermoplastic shear instability happened were analyzed. The result showed that slip and shear deformation was happened in a narrow area inside the chip.The adiabatic shear band was white after erosion and the microstructure was fined. But the microstructure around the shear band was small deformation. The deformation bands change into the transformation bands as the cutting speed increases. The adiabatic shear band width and spacing were in inverse proportion to cutting speed.4) Morphological parameters of the segmented chip were measured and analyzed by Digimizer software. The influence of cutting conditions on adiabatic shear band adjacent tooth distance, degree of segmentation, chip segmentation frequency and chip segment angles was investigated.5) Microstructure transformation was studied under different cutting conditions. It proved that phase transformation was happened through calculating shear strain within the segment, measuring microhardness and analyzing X-ray diffraction.