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 method of diamond cutter

Currently, there are three main methods for crystal orientation: artificial visual orientation, laser crystal orientation, and X-ray crystal orientation.

(1) Manual visual inspection of crystal orientation

The method is based on the external crystal geometry, surface growth, corrosion characteristics of the natural crystal and the geometric relationship between the crystal faces, and the rough crystal orientation made by observation and experiment by the operator's long-term work experience. 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.

(2) Laser crystal orientation

The laser crystal orientation is irradiated onto the surface of the diamond crystal by a laser with better coherence. The regular crystal lattice and microscopic pits formed in the growth process are reflected on the screen. Diffracted light image. However, in fact, due to external interference factors, the regular crystal lattice and microscopic pits formed naturally are not obvious or can not be observed at all. Therefore, the crystal is subjected to appropriate artificial etching before orientation to form a characteristic topography.

(3) X-ray crystal orientation

Since the wavelength of the X-ray is close to the lattice constant of the crystal, diffraction occurs when the X-ray passes through or is reflected back from the crystal surface. A dedicated X-ray crystal orientation instrument has been developed using this principle. This crystal orientation method has high precision, but because X-rays have certain harm to the human body, it is necessary to pay attention to the protection of operators when using.

3.3 Diamond tool crystal orientation selection

The diamond is anisotropic, so not only the hardness and wear resistance of each crystal face are different, but also the wear resistance of the same crystal face in different directions. If the crystal orientation is not properly selected, the sharpening efficiency will be greatly reduced even if the crystal face is selected correctly. At the same time, since the compressive strength of the diamond crystal is 5-7 times larger than the tensile strength, the easy-grinding direction of the crystal face should be selected during the sharpening process, and the cutting edge should face the positive direction of the sharpening wheel speed (ie, take Back grinding) to ensure sharpening efficiency and reduce the degree of microscopic cleavage of the cutting edge.

3.4 Grinding and damage of diamond cutters

The wear mechanism of diamond cutters is complex and can be divided into macroscopic wear and microscopic wear. The former is mainly mechanical wear, while the latter is mainly based on thermal chemical wear. Common diamond tool wear and tear forms are flank wear, flank wear and edge cracking. In the single crystal diamond tool sharpening process, it needs to be worn to sharpen the tool that meets the requirements, but if the unnecessary wear is generated, the sharpened front and back flank surfaces may be damaged. The edge cracking (ie, chipping) occurs when the stress on the cutting edge exceeds the local bearing capacity of the diamond tool, and is generally caused by microscopic cleavage damage of the diamond crystal along the (111) crystal plane. In ultra-precision machining, the cutting edge of the diamond cutter has a relatively small radius, which is itself a hard and brittle material. At the same time, due to its anisotropy and the (111) surface is prone to cleavage, along with the vibration and the grinding wheel to the cutting edge The impact of the mouth is often accompanied by a chipping phenomenon.

4 sharpening test

The test was carried out on an EWAG RS-12 sharpener. In the test, due to the lack of effective crystal orientation means, only through the structural analysis of the scrapped tool, the direction of the crystal plane of the tool is roughly determined, and then the contact force and contact sound of the tool and the surface of the grinding wheel during the sharpening process are taken into consideration, and the speed of the grinding wheel is taken into consideration. The parameters such as the reciprocating speed of the spindle and the swing amplitude are carefully searched for the appropriate sharpening angle of the tool. When the sound of the sharpening is more boring and the machine tool has a large vibration, the tool should be immediately withdrawn to avoid damage to the grinding wheel and re-adjust the angle. After the adjustment is appropriate, the sound of the sharpening is lighter and softer, the vibration of the hand-feeling machine is small, and the continuous knife is 0.05mm, and the machine does not have vibration fluctuations.

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