In order to improve the cutting performance of laser cladding TC4 alloy, the cutting performance difference of TC4 alloy under casting and laser cladding conditions was compared by designing a high-speed milling test scheme. The research results show that laser cladding titanium alloy exhibits anisotropy when milling, the milling direction is consistent with the cladding trajectory, and the main cutting force is higher than the 90° direction. When milling titanium alloy, the main cutting force continues to increase with the increase of single tooth feed, and the main cutting force increases with the increase of cutting edge. The main cutting force increases linearly under the condition of increasing milling depth, resulting in an increase in the cutting resistance of the cutting edge. When the milling speed is in the range of 100~400m/min, the main cutting force shows an upward trend when the milling speed gradually increases.
In many important industrial fields, Ti-6Al-4V titanium alloy plays an important supporting role as an alloy material. Its advantages mainly include high temperature oxidation resistance, good toughness and high specific strength. Therefore, it is widely used in the construction of precision testing instruments, transportation facilities, biomedical equipment, high-performance aviation equipment, etc., referred to as TC4[1]. In the field of aviation industry, titanium alloy, as an important strategic material, has greatly promoted the development and progress of aviation technology. Whether it is aircraft engine blades, exhaust covers, support frames, shells, or heat-resistant skins, insulation layers, exhaust covers, fairings, etc., titanium alloy materials must be used for preparation[2-3]. Titanium alloys can be divided into many types according to the forming process, including additive processing, casting, forging, etc., but at present, the most widely used alloy material is cast titanium alloy. Since titanium alloy TC4 is processed by laser additive method, it has better reliability and flexible process. The prepared protective coating has excellent high temperature resistance and can also repair defects of aviation components.
Because the mechanical properties of titanium alloy are extremely excellent, many problems arise during the processing. For example, when processing titanium alloy materials, due to the high cutting force requirements, the tool performance is easily affected by the high cutting temperature, resulting in wear or significant vibration. The processing difficulty of this alloy is extremely high[4]. Many scholars have conducted in-depth and comprehensive analysis and research on titanium alloy processing at different levels, including chip The influence of the process adjustment and material processing characteristics. Hojati[5] focused on the characteristics of titanium alloy micro-milling under casting process preparation and additive manufacturing. After comparison, it was found that the surface quality of titanium alloy micro-milling after electron beam cladding treatment was better than that of conventional titanium alloy. The similarity was that they had similar cutting forces. Huang[6] compared and studied the differences in the cutting characteristics of titanium alloy under different cooling conditions. Singh[7] tested and analyzed the changes in the processing characteristics of cast titanium alloy under different tool coatings. Wang Qingqing[8] conducted experimental analysis on the changes in the microstructure of TC4 during cutting.
According to the existing literature reports, there are still few studies on high-speed cutting of TC4 alloy by laser additive. In this paper, when comparing the cutting performance of TC4 alloy under laser cladding and casting conditions, a high-speed milling test plan was specially formulated to carry out experimental research and analysis.
1 Experimental principle and plan
1.1 Experimental materials and sample preparation
The practical sample was selected as a titanium alloy substrate. The energy control power of 3250W was adopted. Lasertel laser is used for application, and the cladding trajectory is set by R-2000iB six-axis robot. The spot size and scanning rate are set according to the standards of 12 mm×3 mm and 5 mm/s respectively. The spacing between the cladding layers is kept at 0.6 mm, and the thickness of the laid metal powder is 3 mm. The spacing between the cladding layer and the laser head needs to be controlled to 285 mm during the cladding process. Of course, in order to avoid surface oxidation of the sample during the cladding stage, argon gas needs to be continuously filled. The TC4 sample is prepared through the laser cladding step.
TC4 sample obtained by high-speed cutting after laser cladding. The titanium alloy plate is cut and processed by wire cutting according to the processing standard of 50 mm×40mm×40mm sample. A special fixture is used to fix the sample. In order to ensure that it is always parallel to the coordinate axis, the fixture position needs to be adjusted continuously, so as to ensure the precise control of the cutting force during milling.
Observe Figure 1 and find that at high During the high-speed milling process, the Kis-tler 9265B piezoelectric detector was set in the dynamometer. During the cutting process, the main cutting force (Ft) has a greater impact, and it acts on the tangent along the milling cutter circle, with the largest power consumption. The following will deeply analyze and explore the factors affecting the main cutting force.
1.2 Experimental plan
Table 1 shows the specific milling test parameters. The reverse milling method is mainly used during the experimental test. According to the single factor plan, the performance differences of the cutting force under different cutting depths, cutting rates and single tooth feed rates are carefully compared.
2 Experimental results analysis
2.1 Effect of milling direction on the main cutting force
Figure 2 shows the changes in the main cutting force in different milling directions during the milling process of titanium alloy TC4 after it was prepared by casting process and laser cladding. The experimental test shows that the laser cladding titanium alloy exhibits anisotropy when it is processed by milling, and the milling direction and The cladding trajectory is consistent, and the main cutting force is higher than the 90° direction. The main reason for this situation is that during the additive processing, heat is generated under the action of the laser. The superimposed cladding layers are formed under the action of the laser energy. In the crystallization stage, the material temperature begins to fluctuate when the spot position moves forward. The metallographic structure of the material under different temperature gradient conditions is also very different, which further affects the micromechanical properties of the material and the macroscopic cutting force is abnormal.
2.2 Effect of feed per tooth on main cutting force
Figure 3 shows the change of the main cutting force of titanium alloy under different single tooth feed setting conditions. The parameters ae and v are set according to the standard of 0.8 mm and 400 mm/min. When milling titanium alloy, the main cutting force continues to increase with the continuous increase of single tooth feed. The main reason for this situation is that the maximum cutting thickness of a single cutting edge is larger after the single tooth feed increases, and the volume of the uncut layer formed is larger, which in turn affects the increase of cutting resistance. Of course, in the process of milling, due to the spiral structure of the surface of the cemented carbide milling cutter, the main cutting force of the titanium alloy is increased. The cutting edge has an angular shape, so cutting in and out of the cutting edge will bring many unfavorable results. During the milling stage, the main cutting force increases as the cutting edge continues to increase. The test requirement that the main milling force is minimum in the 90° direction can be achieved in both titanium alloy milling test links.
2.3 Effect of milling depth on main cutting force
The main cutting force results shown in Figure 4 correspond to different milling depths, fz is 0.06 mm, v is 200 mm/min. By comparison, it is found that the main cutting force increases linearly under the condition of increasing milling depth. The main reason for this situation is that the energy that needs to be overcome by material removal increases as the milling depth increases, which in turn leads to an increase in the cutting resistance of the cutting edge.
2.4 Effect of milling speed on main cutting force
Figure 5 shows the main cutting force results of TC4 milling corresponding to different milling speeds, ae is 0.4mm, fz is 0.04mm. By comparison, it is found that when the milling speed is in the range of 100~400m/min, the main cutting force shows an upward trend as the milling speed gradually increases. However, after rising to a certain extent, the main cutting force is relatively stable after the milling speed continues to increase. The analysis and test results show that the processing performance of titanium alloy can be effectively improved by appropriately increasing the cutting rate.
3 Conclusion
(1) Laser cladding titanium alloy exhibits anisotropy when processed by milling. The milling direction is consistent with the cladding trajectory, and the main cutting force is higher than the 90° direction.
(2) When milling titanium alloy, the main cutting force continues to increase with the increase of single tooth feed, and the main cutting force increases with the increase of cutting edge.
(3) The main cutting force increases linearly under the condition of increasing milling depth, resulting in an increase in the cutting resistance of the cutting edge.
(4) When the milling speed is in the range of 100~400m/min, the main cutting force shows an upward trend when the milling speed gradually increases.
