Introduction, selection and orientation of single crystal diamond cutter

Single crystal diamond tools play an important role in the field of machining, and are widely used in the processing of ultra-precision mirror parts such as mirrors, missiles and rocket navigation gyroscopes, computer hard disk substrates, and accelerator electron guns. Single crystal diamond tools can also be used to manufacture medical tools such as ophthalmology, brain surgery scalpels, and ultra-thin bio-dissection knives. In addition, the application of single crystal diamond tools in the processing of civilian products has become increasingly widespread, from the processing of watch parts, aluminum pistons, jewelry, etc. For the processing of pens, high-grip signs and non-ferrous metal mirror decorative parts, the application has entered the mechanical processing A variety of fields.

Introduction of single crystal diamond

Diamond is a crystal of a single carbon atom, and its crystal structure is the equiaxed face-centered cubic system with the highest atomic density. The bond between carbon atoms in the diamond crystal is sp3 hybrid covalent bond, which has strong binding force, stability and directionality. Diamond's unique crystal structure gives it the highest hardness, rigidity, refractive index and thermal conductivity in nature, as well as extremely high abrasion, corrosion and chemical stability.

The excellent properties of single crystal diamond can meet most of the requirements of precision and ultra-precision cutting tool materials, and it is an ideal material for precision cutting tools. The uniform crystal structure of diamond without internal grain boundary makes the cutting edge of the tool theoretically reach the atomic level flatness and sharpness. The cutting ability is strong, the precision is high, the cutting force is small; its high hardness and good wear resistance Strain, corrosion resistance and chemical stability ensure long tool life for long-term continuous cutting and reduce the impact of tool wear on part accuracy; its high thermal conductivity reduces cutting temperatures and parts Thermal deformation.

How to choose single crystal diamond material

Due to the anisotropy of single crystal diamond, the performance varies greatly in different crystal planes and in different directions. The correct material selection and orientation can not only simplify the processing process, reduce the manufacturing cost, but also improve the cutting edge quality and service life. Take advantage of the excellent performance of diamond tools.

According to the impurities contained in the diamond crystal, it can be classified into four types: Ia type, Ib type, IIa type and IIb type. Generally, the particle size (weight), shape, integrity, transparency, crack, number of inclusions, color and uniformity of the diamond crystal are used as the basis for assessing the quality of the diamond. The quality requirements of diamond for cutting tools are: crystal integrity, shape of dodecahedron, curved octahedron or transitional crystal, crystal diameter is generally not less than 4mm, color is colorless, light green, yellow brown, etc., no crack is allowed The crystal surface may allow inclusions and etch pits of not more than 0.5 mm and weigh 0.7 to 3 carats. For ultra-precision machining tools such as ophthalmology, brain surgery scalpels, laser mirrors, etc., which require extremely high precision, it is necessary to select materials from the drawing die class I or even gem-quality rough stones. Finally, the internal stress is selected by a polarizing microscope or a more precise instrument. The diamond is used as a tool blank.

Synthetic single crystal diamond is of type Ib. Since the nitrogen atom in the lattice uniformly replaces carbon atoms, the possibility of nitrogen atoms accumulating at the edge of the chip is reduced, and the hardness is slightly higher than that due to the uniform distortion of the crystal lattice. Single crystal diamond. In addition, due to the increased optimization process to remove internal stress, the cutting performance is more stable, reliable, and the dispersion is smaller. The direction of the crystal axis is precisely determined at the time of shipment, so it is more suitable for the production of cutting tools. The disadvantage is that the Ib-type artificial single crystal is more brittle, and it is more difficult to process than a natural single crystal, and a fine sharpening method is required to obtain a high-quality cutting edge.

Single crystal diamond orientation

The purpose of orienting the natural single crystal diamond is not only to maximize the life of the tool, but also to minimize the friction between the flank and the machined surface and the stress on the cleavage surface near the edge. The orientation of the single crystal diamond tool should include two aspects: the crystal plane on which the front and back flank are placed and the crystal axis direction in which the crystal grows. Studies have shown that the orientation of the tool is related to its wear mechanism during the cutting process. The wear of diamond cutters is a very complicated physical and chemical reaction process. The wear patterns and proportions of different processing conditions and different workpiece materials are different. The wear rate depends on the dissolution rate of diamond in different materials. Wear forms include mechanical wear, thermal chemical wear, and micro-cracking. Generally, the front and back flank surfaces are fixed on (110, 100) or (100, 100) crystal faces, and the (111) crystal faces are not easy to be ground in any direction and should be avoided.

The method of crystal orientation can be divided into an orientation of an instrument (for example, an X-ray diffraction analyzer) and a manual orientation. The instrument has high orientation accuracy but is expensive. The manual direction is determined by determining the position and direction of the crystal axis of the crystal according to the number and relative position of the atomic crystal planes. For example, an octahedral crystal, the three mutually perpendicular lines connected by three pairs of symmetric vertices are the X, Y, and Z axes of the crystal. The crystal plane of the octahedron is the (111) plane, and the apex is perpendicular to the axis to obtain the eight squares, which is the (100) plane; and the two sides that are intersected with the edges are grounded at equal angles. Get (110) face.