Research on high-speed precision machining of diamond tools (2)

Cutting speed

Traditional precision and ultra-precision machining are mostly performed at lower cutting speeds. For high-precision machining of LY12 aluminum alloy during production (R _a ≤0.06μm), the cutting speed is usually about v=80m/min, and the operation is The processing experience of personnel has high requirements. In this cutting test, the effect of the cutting speed v on the surface roughness of the machined surface is shown in Fig. 1.

(f=0.02mm/r, a p =0.03mm) Figure 1 Effect of cutting speed on the surface roughness of the machined surface

(v=800m/min, a p =0.03mm) Figure 2 Effect of feed rate on the surface roughness of the machined surface

(v=800m/min, f=0.01mm/min) Figure 3 Effect of the amount of back-feeding knife on the surface roughness of the machined surface

Starting from v=400m/min, as the cutting speed increases, the surface roughness of the machined surface increases continuously, but the variation rules of the two diamond tools are slightly different. When v=400m/min, the surface roughness value of the machined surface is the smallest, and the surface of R _a =0.04μm can be processed by natural diamond cutter; when the v=800m/min, the surface roughness of the processed diamond diamond tool is slightly increased. However, the increase in surface roughness of natural diamond tools is relatively large. When the cutting speed is increased to v=1200m/min, the roughness value of the surface of the natural diamond tool is reduced compared with v=800m/min. In general, the lower surface roughness can be obtained in the high-speed cutting area, and the surface roughness value does not change much with the increase of the cutting speed, especially the natural diamond tool is not sensitive to the change of the cutting speed.

Cutting tests were performed over a wider range of cutting speeds while measuring cutting forces and vibrations. The test results show that when the cutting speed is v=100m/min, the vibration of the machine tool and the workpiece is large, and the machining surface is rough (this is also verified in the cutting test of 45 steel); but when the cutting speed is increased to v When =400m/min (speed n=910r/min), the vibration of machine tools and workpieces is significantly reduced, and the machined surface becomes smoother. In the range of cutting speeds of 400-1200m/min, the vibration of machine tools and workpieces is better. Small, a smooth machined surface is available. Obviously, under the premise of meeting the precision machining requirements (R _a ≤ 0.1μm), the CNC machining with 800-1200m/min cutting speed can greatly improve the production efficiency and automation level of precision cutting.

Effect of feed rate

In the cutting test, the influence of feed rate on the surface roughness of the machined surface is shown in Fig. 2. When the artificial polycrystalline diamond tool is cut with a feed rate of f=0.015mm/r, the surface roughness value has a jump; while at f=0.005mm/r and f=0.02mm/r, the surface roughness of the machining is not much different. When f>0.02mm/r, the surface roughness value of the machined surface will increase rapidly, indicating that the feed rate is not suitable for ultra-precision machining. When the natural diamond tool is cut at a feed rate of f < 0.02 mm/r, the surface roughness value of the machined surface changes little. In order to obtain a highly polished surface, a very small feed is generally used for precision machining. Tests have shown that when cutting with a small feed of f=0.005mm/r, the machined surface is very smooth and the built-up edge on the tool is small; when the f value is increased, the surface roughness of the polycrystalline diamond tool is improved. The height of the built-up edge changes, and the surface roughness of the natural diamond tool hardly changes. This is because the natural diamond tool has a sharp cutting edge, a smooth surface, and a small coefficient of friction with the workpiece material. The sarcoma is small. However, it has also been found in the cutting test that when the cutting is performed with a smaller feed amount, the surface of the workpiece is more markedly pressed and adhered, the surface roughness value is increased, and the processing efficiency is further lowered. It can be seen from the test results in Fig. 2 that a reasonable feed rate should be selected as f = 0.02 mm / r, at which time the same processing surface quality (R _a = 0.06 μm) can be obtained with f = 0.005 mm / r, and the processing efficiency Can be increased by 4 times.

The impact of backing the amount of knife

The size of the backing knife a _{p has} a great influence on the quality of the machined surface. Ordinary precision cutting generally uses a small amount of backing knife. Under high-speed cutting conditions, the influence of the amount of back-feeding on the surface roughness of the machine is shown in Figure 3. It can be seen from the figure that there are differences in the variation of the surface roughness of the two diamond tools. As the amount of backing knife increases, the surface roughness value of the polycrystalline diamond tool will increase slowly. In the range of a _p =0.025~0.10mm, the surface roughness value R _a ≤0.1μm can meet the precision. Processing requirements. Observations show that when the amount of backing knife a _p ≤0.025mm, the height of the built-up edge does not change much, that is, it has little effect on the surface roughness of the processing; when the amount of backing knife a _p >0.025mm, the built-up edge will follow As the value of a _p increases, it increases because of the change in the cutting temperature and the bonded area at the bottom of the built-up edge. Due to the sharp edge of the natural diamond tool, it is possible to cut with a smaller backing knife. It can be seen from the figure that when a _p is increased from 0.01 mm to 0.02 mm, the surface roughness of the machined surface changes little; when a _p = 0.03 mm, the obtained surface roughness value is the lowest; and when a _p < 0.005 mm, Although the chip is extremely thin, the machined surface is not smooth. After analysis, this is because the radius r of the tool edge used in the test is large. When the depth of the cutting layer is extremely small, the cutting is difficult, and the surface roughness is likely to occur. Increase. In order to make the processing surface smooth, the cutting process is stable, and the processing efficiency is improved. In other cutting tests, the amount of backing knife of a _p = 0.03 mm is used.

5 Conclusion

Natural diamond tools and polycrystalline diamond tools can obtain _a smooth surface with R _a <0.1μm in the high-speed cutting range of v=400～1200m/min; natural diamond tools can obtain R _a =0.05μm at v=1200m/min. The high-gloss surface, while the polycrystalline diamond tool has the advantage of lower price; under the premise of meeting the precision machining quality, the tool material, cutting amount and cutting conditions have a large selection space. Through the cutting test and analysis, the following conclusions can be drawn:

The use of a special emulsified cutting fluid in high-speed precision cutting can greatly improve the surface roughness of the machined surface and achieve the same processing results as conventional precision cutting using lubricating oil.

The surface quality of natural diamond tools is better than that of polycrystalline diamond tools, which can significantly reduce the maximum height value R _{y of} surface profile curve fluctuations. However, polycrystalline diamond tools have cost advantages and can meet the requirements of high-speed precision cutting with good economic benefits. .

The choice of cutting speed is mainly affected by the vibration characteristics of the machine tool and the process system. The cutting speed should be reasonably selected within the range of vibration with small vibration.

Within a certain range of values ​​(f ≤ 0.02 mm / r), the change in feed rate has little effect on the surface roughness of natural diamond tool processing, and the larger feed rate can be selected as much as possible according to the processing benefit requirements.

Natural diamond tools can use a relatively small amount of backing knife, but the smallest backing knife can not obtain the highest smooth surface, and the best back knife value can be determined by cutting test. For polycrystalline diamond tools, the surface roughness value will increase slowly as the amount of backing knife increases, so try to use a smaller amount of backing knife.

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