Research On Machinability Of Titanium Matrix Composites In High-speed Grinding

Titanium matrix composites, as the newly developed metal matrix composites, have broad application prospect in the aerospace industry due to their excellent comprehensive mechanical properties, such as high specific strength, good anti-fatigue ability, high temperature durability and good corrosion resistance. Titanium matrix composites belong to the typical difficult-to-cut material. The disadvantageous effects, i.e., rapid tool wear, low material removal rate and poor machined quality, have been an important barrier in improving the machining efficiency and raising the surface quality in cutting titanium matrix composites. Therefore, the development of high-speed grinding technology is expected to realize high efficiency and precision machining of titanium matrix composites. In the current investigation, experimental research on the machinability of titanium matrix composites in high-speed grinding with the vitrified CBN grinding wheel and the electroplated CBN wheel is conducted. The grinding force and force ratio,grinding temperature and heat distribution, surface topography and damage are analyzed to reveal the grinding difficulty of titanium matrix composites. The removal mechanism is also studied. The results obtained have an important theoretical and engineering value in achieving the high efficiency and precision machining of titanium matrix composites.The main work and results are summarized as follows:(1) The grinding force and force ratio in high-speed grinding titanium matrix composites are investigated. The results indicate that, compared to Ti-6Al-4V titanium alloy, large grinding force is not the most significant difficulty in grinding titanium matrix composites. On the whole, the grinding force increases with an increasing workpiece speed and depth of cut. However, the grinding forces decrease with an increasing wheel speeds. The grinding force ratios vary at the range of 3.47-4.49.(2) The grinding temperature and heat transfer behavior during high-speed grinding titanium matrix composites are investigated. It is found that, compared to Ti-6Al-4V titanium alloy, higher grinding temperature is the major reason of the difficulty in grinding titanium matrix composites.The grinding temperature increases with an increase in wheel speed, workpiece speed, and depth of cut. The grinding temperature with the vitrified CBN grinding wheel is always higher than that with the electroplated CBN grinding wheel. The grinding parameters are optimized in order to control the grinding temperature. At the same time, the grinding temperature is simulated. When the material removal rate is lower than 1.75 mm3/(mm·s), the simulation grinding temperature based on the triangular distribution model is more close to the measured temperature. On the contrary, the simulation grinding temperature based on the uniform distribution model is more close to the measured value.(3) The ground surface morphology and the sub-surface damage of titanium matrix composites during high-speed grinding are discussed. The results display that the Ti-6Al-4V metallic matrix is removed in the mode of plastic cutting, while the removal of reinforcements is mainly by means of pull-out, fracture or crushed, micro-cracks, voids, and smearing. The sub-surface damage layer depth and the chip appearance are observed and analyzed under different grinding conditions. The collaboration removal of titanium metallic matrix and reinforcements is achieved with the optimal grinding parameters. The sub-surface damage is accordingly controlled.