Titanium alloy material with high strength, high hardness and low density material characteristics, such as titanium alloy Ti-6Al-4V (referred to as Ti-6-4) tensile strength of 900MPa, hardness of 250 ~ 375HB, density of 4.42 g/cm3, so that titanium alloys as a whole structural components in addition to the modern military aircraft have been widely used in modern large passenger aircraft are also gaining more and more applications. The weight of titanium alloy used in the aircraft structure has shown a rapid increase in the total weight ratio, and has begun to exceed the steel structural components. Therefore, the realization of titanium alloy structural parts of high-efficiency machining has become the key to large aircraft manufacturing production. However, compared with aluminum alloy, titanium alloy is a very difficult metal to process, mainly in the following aspects:
Titanium alloy processing cutting force is only slightly higher than the same hardness of steel, but the physical phenomenon of processing titanium alloy is much more complex than processing steel, thus making titanium alloy machining faces 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 alloys will not be rapidly transferred to the workpiece or taken away by the chips, but gathered in the cutting area, the resulting temperature can be as high as 1,000 ℃ or more, so that the cutting edge of the tool is rapidly worn out, chipping and generating chip tumors, and the rapid emergence of a worn out blade, and the cutting area to generate more The rapid wear of the cutting edge, and the cutting area produces more heat, further shortening the life of the tool.
The high temperatures generated during the cutting process also destroy the surface integrity of the titanium alloy part, leading to a reduction in the geometric accuracy of the part and the emergence of work-hardening phenomena that severely reduce its fatigue strength.
The elasticity of titanium alloys may be beneficial to part performance, but the elastic deformation of the workpiece during the cutting process is a significant cause of vibration. Cutting pressure causes the "elastic" workpiece to move away from the tool and bounce back, resulting in more friction between the tool and workpiece than cutting. The friction process also generates heat, exacerbating the problem of poor thermal conductivity of titanium alloys.
This problem is exacerbated when machining deformable parts such as thin-walled or toroidal shapes. Machining titanium alloy thin-walled parts to the desired dimensional accuracy is not an easy task. Because as the workpiece material is pushed away by the tool, the local deformation of the thin wall has exceeded the elastic range and produce plastic deformation, the cutting point of the material strength and hardness increased significantly. At this point, machining at the originally determined cutting speed becomes too high, further leading to sharp tool wear.
