3 Sharpening characteristics of natural single crystal diamond tools
In ultra-precision machining, the two basic accuracies of a single crystal diamond tool are the accuracy of the blade profile and the blunt radius of the cutting edge. It is required that the circular tool cutting edge for machining an aspherical lens has a roundness of 0.05 μm or less, and the blade straightness for processing a polyhedral mirror is 0.02 μm; the blunt radius of the cutting edge (Ï value) indicates the cutting edge of the tool. Sharpness, in order to adapt to various processing requirements, the blade edge radius ranges from 20nm to 1μm.
3.1 Crystal face selection of single crystal diamond cutters Diamond crystals belong to the cubic crystal system. Due to the difference in atomic arrangement and atomic density on each crystal plane and the difference in crystal plane distance, the anisotropy of natural diamond crystals is caused. Not only the physical and mechanical properties of each crystal face are different, the manufacturing difficulty and the service life are different, and the microscopic damage strength of each crystal face is also significantly different. The microscopic strength of diamond crystals can be determined by the Hertz test method. Since diamond is a typical brittle material, its strength value generally deviates greatly, mainly depending on the shape and distribution range of the stress distribution, so it is suitable for analysis by probability theory. When the applied stress is the same, the (110) crystal plane has the highest damage probability, the (111) crystal plane is the second, and the (100) crystal plane has the smallest probability of damage. That is, under the action of external force, the (110) crystal plane is most likely to be broken, the (111) crystal plane is second, and (100) is the most difficult to break. Although the grinding rate of the (110) crystal plane is higher than that of the (100) crystal plane, the experimental results show that the (100) crystal plane has higher resistance to stress, corrosion and thermal degradation than other crystal planes. Combined with the micro-strength comprehensive consideration, using the (100) surface as the front and back knives of the tool makes it easy to sharpen the high-quality cutting edge and is less prone to micro-cracking.
The crystal face selection of single crystal diamond tools should normally be selected according to the requirements of the tool. In general, if the diamond tool is required to obtain the highest strength, the (100) crystal face should be selected as the front and back face of the tool; if the diamond tool is required to resist mechanical wear, the (110) crystal face is selected as the front and back of the tool. If the diamond tool is required to resist chemical wear, the (110) crystal face should be used as the rake face of the tool, the (100) crystal face should be used as the flank face, or the front and back facets should be (100) crystal faces. These requirements need to be achieved by means of crystal orientation technology.
3.2 Directional methods for diamond tools Currently, there are three main methods for crystal orientation: manual visual orientation, laser crystal orientation, and X-ray crystal orientation.
(1) Manual visual observation of crystal orientation This method is based on the external crystal geometry, surface growth, corrosion characteristics of the natural crystal and the geometrical relationship between the crystal faces, and the rough crystals observed and tested by the operator's long-term work experience. Orientation. The method is simple, easy, and does not require the use of equipment, but the accuracy of the orientation result is poor, the operator's experience is high, and the tool for processing and losing the characteristics of the natural single crystal crystal can no longer be manually determined.
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