Cutting characteristics When the hardness of titanium alloy is greater than HB350, cutting is particularly difficult, and when the hardness is less than HB300, it is prone to sticking and cutting is also difficult. However, the hardness of titanium alloy is only one aspect that is difficult to cut. The key lies in the combination of the chemical, physical and mechanical properties of the titanium alloy itself. Its cutting characteristics are particularly difficult when the hardness of titanium alloy is greater than HB350, and it is easier when the hardness is less than HB300. The sticking phenomenon occurs, and it is also difficult to cut. But the hardness of titanium alloy is only one aspect that is difficult to cut. The key lies in the influence of the combination of chemical, physical and mechanical properties of titanium alloy on its machinability. Titanium alloy has the following cutting characteristics: (1) Small deformation coefficient: This is a significant feature of titanium alloy cutting processing, and the deformation coefficient is less than or close to 1. The sliding friction distance of chips on the rake face is greatly increased, which accelerates tool wear. (2) High cutting temperature: Because the thermal conductivity of titanium alloy is very small (only equivalent to 1/5 to 1/7 of 45 steel), the contact length between the chip and the rake face is extremely short, and the heat generated during cutting is not easy to transfer It is concentrated in a small area near the cutting area and the cutting edge, and the cutting temperature is very high. Under the same cutting conditions, the cutting temperature can be more than twice as high as when cutting No. 45 steel. (3) The cutting force per unit area is large: the main cutting force is about 20% smaller than when cutting steel. Because the contact length between the chip and the rake face is extremely short, the cutting force per unit contact area is greatly increased, which is easy to cause chipping. At the same time, due to the small modulus of elasticity of titanium alloy, it is prone to bending deformation under the action of radial force during processing, causing vibration, increasing tool wear and affecting the accuracy of parts. Therefore, the process system is required to have good rigidity. (4) Chilling phenomenon is serious: due to the high chemical activity of titanium, it is easy to absorb oxygen and nitrogen in the air to form a hard and brittle skin at high cutting temperatures; at the same time, plastic deformation during cutting will also cause surface hardening . Chilling phenomenon not only reduces the fatigue strength of parts, but also aggravates tool wear, which is a very important feature when cutting titanium alloys. (5) The tool is easy to wear: After the blank is processed by stamping, forging, hot rolling and other methods, it will form a hard and brittle uneven skin, which can easily cause chipping, making the removal of the hard skin the most difficult process in titanium alloy processing. In addition, due to the strong chemical affinity of titanium alloy to the tool material, the tool is prone to bond wear under the conditions of high cutting temperature and high cutting force per unit area. When turning titanium alloy, sometimes the wear of the rake face is even more serious than that of the flank; when the feed rate f<0.1 mm/r, the wear mainly occurs on the flank; when f>0.2 mm/r, the front The blade face will be worn; when using carbide tools for fine turning and semi-finishing turning, the wear of the flank face is more suitable for VBmax<0.4 mm. Tool material The cutting process of titanium alloy should start from the two aspects of lowering the cutting temperature and reducing the adhesion. Choose tool materials with good red hardness, high bending strength, good thermal conductivity, and poor affinity with titanium alloys. YG cemented carbide is more suitable. Due to the poor heat resistance of high-speed steel, tools made of cemented carbide should be used as much as possible. Commonly used cemented carbide tool materials include YG8, YG3, YG6X, YG6A, 813, 643, YS2T and YD15. Coated inserts and YT-type cemented carbide will have a violent affinity with titanium alloys, which will aggravate the bonding and wear of tools, and are not suitable for cutting titanium alloys. For complex and multi-edge tools, high-vanadium high-speed steel (such as W12Cr4V4Mo ), high-cobalt high-speed steel (such as W2Mo9Cr4VCo8) or aluminum high-speed steel (such as W6Mo5Cr4V2Al, M10Mo4Cr4V3Al) and other tool materials, suitable for making drills, reamers, end mills, broaches, taps and other tools for cutting titanium alloys. Using diamond and cubic boron nitride as tools for cutting titanium alloys can achieve significant results. For example, the cutting speed can reach 200 m/min under the condition of emulsion cooling with natural diamond tools; if the cutting fluid is not used, the allowable cutting speed is only 100 m/min at the same amount of wear. Previous: Heat treatment of titanium alloy Next: Matters needing attention in cutting titanium alloy