Abstract: This paper discusses in depth the application of cubic boron nitride tools in the process of cutting titanium alloy on lathe. It analyzes the characteristics of cubic boron nitride tools, describes the impact of cutting parameters on machining quality and tool life, focuses on the impact of cutting parameters on the machined surface quality, and compares the cutting effect under different conditions through experimental research, which provides a theoretical basis and practical guidance to improve the efficiency and quality of titanium alloy machining.

I. Introduction

Titanium alloy has a wide range of applications in aerospace, medical equipment and other fields due to its high specific strength, good corrosion resistance and high temperature resistance. However, the cutting and machinability of titanium alloy is poor, which is mainly manifested in low thermal conductivity, high chemical activity and large tendency of work hardening. Traditional tools often face problems such as fast tool wear and low machining accuracy when cutting titanium alloys. Cubic boron nitride (CBN) tool with its high hardness, high wear resistance, high thermal stability and other excellent properties, for the efficient cutting of titanium alloys provides a possibility.

Second, the characteristics of cubic boron nitride tools

(A) hardness and wear resistance

The hardness of cubic boron nitride is second only to diamond, and its hardness is as high as 4500 - 5000 HV. When cutting titanium alloy in lathe, it can resist the wear of titanium alloy material on the tool, and maintain the sharpness of the knife edge during the long cutting process. This high wear resistance makes CBN tools in continuous cutting operations can effectively reduce the number of tool replacement, improve machining efficiency.

(ii) Thermal stability

CBN tools have excellent stability at high temperatures. Titanium alloy cutting process will generate a lot of cutting heat, and CBN tools can maintain their hardness and chemical stability at high temperatures of more than 1000 ℃. This feature not only helps to reduce the tool due to thermal deformation caused by machining errors, but also to avoid the chemical reaction between the tool and the workpiece caused by high temperature, thereby improving machining quality.

(C) chemical inertness

Cubic boron nitride and titanium alloy in the cutting process has a low chemical affinity. Compared with traditional cemented carbide tools, CBN tools are less prone to bonding wear and diffusion wear when cutting titanium alloys. This is because its chemical structure is stable, and it is not easy to react with the elements in titanium alloys under high temperature and high pressure, which further extends the service life of the tool.

Third, the impact of cutting parameters on processing quality and tool life

(A) the impact of cutting parameters on the machining surface quality

Cutting speed

Cutting speed has a complex impact on machining surface quality. When the cutting speed is low, the friction time between the tool and the workpiece is longer, and it is easy to produce chip tumors on the surface of the workpiece. The presence of chip-accumulation can lead to an increase in the surface roughness of the workpiece and may cause deviations in the machined dimensions. As the cutting speed increases, the tendency to form chip tumors decreases and the machined surface quality improves. However, when the cutting speed is too high, the cutting heat increases sharply, which will cause thermal deformation of titanium alloy, and the high cutting temperature may lead to a decline in the performance of the tool material, resulting in increased wear of the tool, which in turn affects the machining surface quality, and surface burns, microcracks and other defects.

Feed

Feed is an important factor affecting the roughness of the machined surface. Larger feed means that the cutting edge of the tool per unit of time in the surface of the workpiece through the distance increases, will leave obvious cutting traces on the surface of the workpiece, which directly leads to an increase in the surface roughness value. In addition, too large a feed may also cause fluctuations in cutting force, affecting the flatness of the machined surface. While a smaller feed is conducive to obtaining a better surface quality, too low a feed will reduce machining efficiency and increase processing costs.

Cutting depth

The impact of the depth of cut on the machined surface quality is mainly reflected in the change of cutting force. Increasing the depth of cut will increase the cutting force, and when the cutting force exceeds a certain limit, it may lead to deformation of the workpiece and tool. The deformation of the workpiece will reduce the shape accuracy of the machined surface, and errors such as flatness and cylindricity will occur. At the same time, too large a depth of cut may also cause instability in the cutting process, generating vibration ripples on the surface of the workpiece and deteriorating the quality of the machined surface. However, the appropriate depth of cut for the removal of material and ensure machining efficiency is necessary, need to seek a balance between the two.

(ii) cutting parameters on the impact of tool life

Changes in cutting speed, feed and depth of cut can have a significant impact on tool life. As mentioned earlier, too high a cutting speed will shorten tool life due to increased cutting heat and tool wear. Excessive feed and depth of cut will increase the cutting force on the tool, which will easily lead to breakage and chipping of the tool, reducing the effective use time of the tool.

IV. Experimental Research

(I) Experimental equipment and materials

The experiments were carried out on a high-precision CNC lathe with a cubic boron nitride tool, and the workpiece material was TC4 titanium alloy. The cutting force was measured using a force gauge during the cutting process, the roughness of the machined surface was measured using a roughness meter, and the tool wear was observed by scanning electron microscope (SEM).

(ii) Experimental program

Several sets of experiments were designed with different cutting speeds, feeds and depths of cut. In each group of experiments, the cutting time of the tool, machined surface quality parameters and tool wear were recorded. By analyzing the experimental data, the influence law of cutting parameters on the machining effect was studied.

(III) Experimental results and analysis

The experimental results show that with the increase of cutting speed, the tool wear first decreases and then increases, and the tool wear is minimized at a specific cutting speed, while the machined surface roughness also shows a similar trend. The effect of feed on machined surface roughness is positively correlated, i.e., the larger the feed, the larger the surface roughness. The increase in depth of cut increases the cutting force significantly, and when the depth of cut exceeds a certain value, the tool starts to chipping phenomenon, and the machined surface quality also decreases significantly. Through SEM analysis of the tool wear surface, it was found that the main forms of wear include abrasive wear, bonded wear and oxidative wear, and the proportion of wear forms under different cutting parameters is different.

V. CONCLUSION

Cubic boron nitride tools have significant advantages in lathe cutting titanium alloy, and their high hardness, high wear resistance, thermal stability and chemical inertness provide a strong guarantee for improving the quality and efficiency of titanium alloy machining. Cutting parameters have a crucial impact on machining quality and tool life, and efficient and high-quality titanium alloy cutting can be realized by reasonably selecting cutting speed, feed and depth of cut. This study analyzes the influence law of these parameters through experiments, which provides a reference basis for the optimization of the process of cutting titanium alloy by cubic boron nitride (CBN) tools in actual production, and helps to promote the wider application of titanium alloy in the field of high-end manufacturing. Future research can further explore the optimization of the microstructure of CBN tools and the synergistic effect with new cutting fluids to further improve their cutting performance.