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3 Conclusion
Several major factors affecting machining accuracy during micro-axis (thread) turning are analyzed in detail. On this basis, the technical requirements for the tool in the micro-axis (thread) turning process are put forward, and the feasibility of the development and application of the traditional cutting method in the micro-machining field is discussed. The following conclusions were obtained.
Among the main factors affecting the precision of micro-axis machining, the influence of cutting force is crucial. Among them, the radial force Fr acts on the weaker radial direction of the workpiece, which has the most significant effect on the processing of the micro-axis. Under the action of radial force, the amount of bending deformation of the micro-axis is proportional to the third power of the span. Therefore, reducing the span is an effective method to increase the bending stiffness of the fine shaft. During the cutting process, the cutting heat generated by the workpiece and the tool cannot be ignored. When the tool nose tip height is not at the horizontal level of the workpiece, it will cause a radial feed error, resulting in a turning diameter error. Especially when processing the outer circle of a multi-step workpiece, the phenomenon that the steps are not directly read is encountered.
Diamond tools are the material of choice for turning fine shafts because of their high hardness, high wear resistance and strength, good thermal conductivity, low friction coefficient with non-ferrous metals and the ability to sharpen sharp edges.
According to the advantages of reducing the elastic deformation and vibration of the process system, and considering the processing of copper materials and the factors that facilitate sharpening, installation and tool setting, sharp-edged diamond tools suitable for micro-axis turning are designed and sharpened. The main parameters of the tool are: main declination Kr=93°, declination K'r=30°, rake angle g0=0°, and back angle a0=5°.
Studies have shown that in the processing of micro-axis, the amount of cutting not only affects the surface quality of the workpiece, but also whether it can be formed by turning. In the formable range, the feed rate is proportional to the surface roughness value, and has a significant effect; the back-feeding amount and the spindle speed have little effect on the surface roughness.
For the copper material, the ideal processing parameters are: feed rate f = 0.2 ~ 0.5mm / min, back knife amount ap = 0.04mm, spindle speed n = 2000 ~ 3000r / min.
Using a synthetic diamond cutter, the micro-axis limit-size turning process was studied on a precision CNC lathe, and a micro-axis with a diameter as small as 7 μm can be machined; a shaft having a diameter of 11 μm and a gold foil having a thickness of 20 μm have been used. The Ø19μm micro-hole is processed by EDM, which proves the practicality of the fine-axis for precision turning.
Based on the turning of the fine shaft, the research on the fine thread turning technology was carried out. Studies have shown that a higher rotational speed (n ≥ 2000 r / min) is required during micro-thread machining. From the results of the study of the minimum thread diameter that can be achieved with different thread lengths, it can be seen that as the length of the machined thread is shortened, the minimum thread diameter that can be achieved is also reduced. A micro screw having a length of 100 μm, a tooth height of 6 μm, and an inner diameter of 23 μm has been processed.
Research work shows that the traditional cutting method of precision turning has the advantages of high machining precision, short machining time and high machining efficiency in the processing of micro-shafts and micro-threads. It also lays a good technical foundation for precision, ultra-precision turning structures and more complex three-dimensional workpieces.
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