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Titanium alloys have been widely used in aerospace, military, chemical and other fields because of their good mechanical properties, low density, high strength and corrosion resistance. However, due to its large chemical activity, low thermal conductivity and small deformation coefficient, problems such as large cutting force, high cutting temperature, serious tool wear and significant work hardening occur in the cutting process. The cutting force of titanium alloy processing is only slightly higher than that of steel of the same hardness, but the physical phenomenon of processing titanium alloy is much more complex than that of processing steel, which makes the processing of titanium alloy face great difficulties.
The thermal conductivity of most titanium alloys is very low, only 1/7 of steel and 1/16 of aluminum. Therefore, the heat generated in the process of cutting titanium alloy will not be quickly transferred to the workpiece or taken away by the chips, and gathered in the cutting area, the temperature generated can be as high as 1 000℃, so that the cutting edge of the tool rapidly wear, crack and generate chip tumors, rapid wear of the blade, but also make the cutting area produce more heat, further shorten the life of the tool.
The high temperature generated during the cutting process also destroys the surface integrity of the titanium alloy parts, leading to the reduction of the geometric accuracy of the parts and the work hardening phenomenon that seriously reduces their fatigue strength.
The elasticity of titanium alloy may be beneficial to the performance of parts, but in the cutting process, the elastic deformation of the workpiece is an important cause of vibration. The cutting pressure causes the “elastic” workpiece to leave the tool and rebound, so that the friction between the tool and the workpiece is greater than the cutting action. The friction process also generates heat, which aggravates the problem of poor thermal conductivity of titanium alloys.
This problem is even more serious when processing thin-walled or torus and other easily deformed parts, and it is not an easy task to process thin-walled titanium alloy parts to the expected dimensional accuracy. Because when the workpiece material is pushed away by the tool, the local deformation of the thin wall has exceeded the elastic range and produced plastic deformation, and the strength and hardness of the material at the cutting point have increased significantly. At this time, machining at the previously determined cutting speed becomes too high, further leading to sharp tool wear.