The machinability of titanium alloy is 20-40% of 45# steel, and the hardness < HB300 will cause strong sticking knife phenomenon. The hardness of HB > 370 makes it difficult to process. The best titanium alloy with hardness HB300-370 is processed. The main reasons affecting the machinability of titanium alloys are summarized as follows: 1) Gas impurities (oxygen, nitrogen and hydrogen, etc.) have a great influence on the machinability of titanium alloys, because the chemical activity of titanium is high and it is easy to combine with gas impurities. When the temperature exceeds 600 degrees, titanium is oxidized to form a brittle layer, the so-called "tissue alpha layer"; hydrogen brittleness is produced with hydrogen; and hard and brittle TiN is formed with nitrogen at high temperature. 2) Titanium alloy has little plasticity, which obviously affects its plastic deformation in cutting. The deformation coefficient of titanium alloy is only 1 or even less than 1, while that of common carbon steel is about 3. When cutting, the chip and the rake face have very small contact surface, which makes the contact area pressure and local temperature high and tool wear fast. 3) Severe work hardening will occur during the processing of titanium alloys. 4) When C > 0.2%, Titanium alloy will form hard carbide, which will cause abrasive wear of cutting tools and reduce the machinability.