What is a single crystal tool? Differences and connections between ND/MCD/CVD/PCD tools

What is a single crystal tool? Differences and connections between ND/MCD/CVD/PCD tools

Single crystal cutting tools are currently the main cutting tools in the field of ultra-precision machining. The cutting tools generally have a mass greater than 0.1g and a minimum diameter length of not less than 2mm. They can achieve mirror processing and can process extremely high workpiece precision and extremely low surface roughness. , the cutting effect is very bright, and it is recognized as an ideal ultra-precision machining tool.There are two types of single crystal cutting tools: natural and artificial. Natural single crystal diamond is small in quantity and expensive. It is mainly used in high-precision optical fields.

Performance advantages of single crystal cutting tools:

(1) Single crystal diamond cutting tools have extremely high hardness (10000HV), thus achieving good wear resistance;

(2) The cutting edge of single crystal diamond tools can be ground very sharp. It is not suitable to stick to the tool and produce built-up edge during cutting, and it can carry out ultra-thin cutting and ultra-precision machining;

(3) The friction coefficient is low, and the deformation during processing is small, which can reduce the cutting force;

(4) The cutting edge has no defects when observed under an 800x Nomarski (Nikon) microscope. When processing non-ferrous metals, the surface roughness can reach Rz0.1~0.05μm, and the shape accuracy of the workpiece to be processed is controlled below 50nm;

(5) Using selected single crystal diamond tool particles, the consistency is good, and the service life is 100 times, or even hundreds of times, that of carbide tools.

Single crystal tool category

Depending on the equipment (CNC machine tools, CNC machining centers, etc.) and cutting processes used in different working conditions, single crystal cutting tools can be welded on different cutter bodies as needed to make different cutting tools. Commonly used types of single crystal cutting tools There are: natural diamond blades (single crystal cutter grains), single crystal diamond turning tools, single crystal milling cutters, single crystal chamfering cutters, natural diamond high-gloss cutters, single crystal ball milling cutters, etc.

The difference between ND/MCD/CVD/PCD tools

(1) Different materials:

1. ND is natural diamond. About 98% of natural diamonds belong to type Ia nitrogen [N] (~2500ppm). Most of the formation of natural diamonds is produced in rocks that are at least 2.5 billion years old, and about 140 years ago. Formed ~200 kilometers underground, the strong pressure (1.5 million pounds per square foot) and extremely high temperature (about 2800°C) at this depth cause rare carbon atoms to gather together tightly to form a crystal structure.

2. MCD is an artificial single crystal made by high temperature and high pressure method. Artificial single crystal diamond is one of the type Ib single crystal synthetic diamonds. Nitrogen [N] is mostly dispersed or in solid solution state inside the crystal. Artificial single crystal diamond, as the name implies, is made of artificial Synthetic, synthesized in an oxygen-free, high-temperature (above 1000°C) and high-pressure (500 MPa) environment, it has high hardness, high wear resistance and high thermal conductivity comparable to diamond. Single crystal cutting tools synthesized by high temperature and high pressure method are generally yellow in color.

3. CVD is a single crystal made by chemical vapor deposition method. It is one of the type IIa diamond single crystal synthetic diamonds. Nitrogen [N] <1 ppm, [B] < 0.05 ppm. The process environment of CVD synthetic single crystal diamond is in It is synthesized using chemical vapor deposition (CVD) in a cavity of hydrogen-carbon mixture. CVD single crystals are generally colorless and transparent crystals. This is a high-quality single crystal diamond synthesized by ultra-high technology. It can be completely colorless and transparent, with almost no impurities. It has higher wear resistance and better thermal conductivity, and can make the workpiece possess Higher quality processing surface, and if doping gas is selectively introduced during the growth process, a variety of colored diamonds can be produced.

4. PCD is polycrystalline diamond, which uses natural or synthetic diamond powder and binding agents (containing cobalt, nickel and other metals) in a certain proportion to produce high-temperature (1000-2000°C) and high-pressure (50,000 to 100,000 atmospheres) PCD composite sheets with fixed diameter and thickness are then sintered and then processed into PCD cutting tools through cutting, welding, sharpening and other processes. Normally, the layer thickness of PCD composite sheets is about 0.3~1.0mm. It can be made into PCD inserts, PCD turning tools, PCD milling cutters, PCD reamers, PCD drill bits and other structural forms.

5. CVD diamond thick film cutting tools use the plasma time-flow CVD method to deposit a diamond film on the Mo substrate to obtain an independent diamond thick film (0.3-1.3mm). The CVD diamond thick film is then welded to cemented carbide or cemented carbide through a welding process. On the substrate of other materials to form a CVD diamond thick film tool or blade

(2) Different appearance:

Natural single crystal cutting tools are generally transparent, artificial single crystal cutting tools are generally yellow or colored (CVD method), and PCD cutting tools are generally black.

(3) Performance difference: "PCD tools are most suitable for processing aluminum and other non-ferrous alloys with good toughness (such as copper, brass and bronze), as well as highly abrasive composite materials (such as graphite, carbon-carbon materials, carbon-added materials, etc.) phenolic, fiberglass and porous sealing materials).

Single crystal diamond is used almost exclusively for high-precision finishing, and its ability to cut extremely thin ensures extremely high dimensional accuracy. PCD and CVD diamond can be used in many of the same machining areas, but PCD is more suitable for rough machining and machining situations that require higher tool fracture toughness. CVD diamond is better at finishing, semi-finishing and continuous turning because of its excellent wear resistance and high hardness, which allows it to process more precise workpieces.