The first thing to talk about is the physical phenomenon of titanium alloy processing. Although the cutting force of titanium alloy is only slightly higher than that of steel of the same hardness, the physical phenomenon of titanium alloy processing is much more complex than that of steel processing, which makes the difficulty of titanium alloy processing rise linearly.
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 ° C or more, 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 deformable 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. It can be said that "heat" is the "root of the disease" that leads to the difficulty of titanium alloy processing.
