Manufacturing Method and Application of Diamond Cutting Tool

With the rapid development of automobile, aviation and aerospace technology, the requirements for material properties and processing technology are increasing day by day. New materials such as carbon fiber reinforced plastics, particle reinforced metal matrix composites (PRMMC) and ceramic materials are widely used. These materials have high strength, good wear resistance, low coefficient of thermal expansion and other characteristics, which determines their machining tool life is very short. The development of new wear-resistant and stable superhard cutting tools is the subject of research in many universities, research institutes and enterprises.

Diamond set mechanical, optical, thermal, acoustic, optical and many other excellent properties in one, with high hardness, low coefficient of friction, high thermal conductivity, low coefficient of thermal expansion and chemical inertness, is the ideal material for manufacturing tools. This paper gives an overview of the development of diamond tool manufacturing methods in recent years.

1. Application range of diamond tools

(1) Processing of difficult-to-process non-ferrous metal materials

When processing copper, zinc, aluminum and other non-ferrous metals and their alloys, the material is easy to adhere to the tool, processing difficulties. Using the characteristics of low friction coefficient and low affinity with non-ferrous metals, diamond tools can effectively prevent metal and tool from bonding. In addition, due to the large elastic modulus of diamond, the deformation of the cutting edge is small, and the deformation of the cutting non-ferrous metal is small, so that the cutting process can be completed under small deformation, thereby improving the quality of the machined surface.

(2) Processing of difficult-to-process non-metallic materials

Processing containing a large number of high hardness particles difficult to process non-metallic materials, such as glass fiber reinforced plastics, filled silicon materials, hard carbon fiber/epoxy resin composite materials, the material of the hard point of the tool wear is serious, with hard alloy tool is difficult to process, and diamond tool hardness, good wear resistance, so the processing efficiency is high.

(3) Ultra-precision machining

With the advent of modern integrated technology, machining to the direction of high precision, the tool performance put forward a very high demand. Due to the diamond friction coefficient is small, low thermal expansion coefficient, high thermal conductivity, can cut very thin chips, chip easy to flow out, and other material affinity is small, not easy to produce debris, heat, high thermal conductivity, can avoid the influence of heat on the blade and the workpiece, so the blade is not easy to passivation, cutting deformation is small, can obtain a higher quality surface.

2. Manufacturing method of diamond tool

At present, the main processing methods of diamond are the following four: thin film coating tools, thick film diamond welding tools, diamond sintered body tools and single crystal diamond tools.

2.1 film coating tool

Thin-film coated tools are tools made of diamond films deposited on collective materials with good rigidity and high temperature characteristics by chemical vapor deposition (CVD).

Since the thermal expansion system of Si3N4 series ceramics, WC-Co series cemented carbide and metal W is close to that of diamond, the thermal stress generated during film production is small, so it can be used as the base material of the cutter body. In the WC-Co cemented carbide, the presence of the binder phase Co is easy to form graphite between the diamond film and the substrate and reduce the adhesion strength. Pretreatment is required before deposition to eliminate the influence of Co (usually by acid corrosion to Co).

The chemical vapor deposition method is to use a certain method to activate the gas containing C source, and under the extremely low gas pressure, the carbon atoms are deposited in a certain area, and the carbon atoms form diamond phase in the process of condensation and deposition. At present, the CVD methods used to deposit diamond mainly include: microwave, hot filament, DC arc jet, etc.

The advantage of diamond film is that it can be applied to tools with complex geometric shapes, such as blades with chips, end mills, reamers and drills. It can be used to cut many non-metallic materials. When cutting, the cutting force is small, the deformation is small, the work is stable, the wear is slow, the workpiece is not easy to deform, and it is suitable for finishing with good workpiece material and small tolerance. The main disadvantage is that the adhesion between the diamond film and the substrate is poor, and the diamond film tool does not have heavy grinding.

2.2 diamond thick film welding tool

The production process of diamond thick film welding tools generally includes: the preparation of large-area diamond film; the diamond film is cut into the required shape and size of the tool; the welding of diamond thick film and tool substrate material; the grinding and polishing of the cutting edge of the diamond thick film tool. (1) Preparation and cutting of diamond thick film The commonly used process method for preparing diamond thick film is DC plasma jet CVD method. The diamond is deposited on the WC-Co alloy (the surface is mirror-finished), and the diamond film automatically falls off during the cooling of the substrate. This method has a fast deposition rate (up to 930 μm/h), and the crystal lattice is closely combined, but the growth surface is relatively rough. Diamond film hardness, wear resistance, non-conductive determines its cutting method is laser cutting (cutting can be carried out in the environment of air, oxygen and argon). Laser cutting can not only cut the diamond thick film into the required shape and size, but also cut out the back angle of the tool, which has the advantages of narrow slit and high efficiency.

(1) Welding of diamond thick film tools

The interface energy between diamond and general metal and its alloys is very high, so that the diamond can not be infiltrated by the general low melting point alloy, and the weldability is very poor. At present, the weldability between diamond and metal is mainly improved by adding strong carbide forming elements to copper silver alloy solder or by metallizing the diamond surface.

① Active solder method solder is generally used with Ti-containing copper-silver alloy, without flux welding in inert gas or vacuum. The commonly used solder components Ag = 68.8wt%,Cu = 26.7wt%,Ti = 4.5wt%, and the commonly used preparation methods are arc melting and powder metallurgy. Ti as an active element in the welding process and C reflect the formation of TiC, can improve the wettability of diamond and solder and bond strength. The heating temperature is generally 850 ℃, heat preservation for 10 minutes, slow cooling to reduce internal stress.

② Welding after surface metallization

Metallization of diamond surface is to plate metal on the surface of diamond by surface treatment technology, so that the surface has the properties of metal or metal. Generally, Ti is plated on the surface of diamond, and Ti reacts with C to generate TiC. TiC has better wettability and bonding strength with Ag-Cu alloy solder. At present, the commonly used titanium plating methods are: vacuum physical vapor deposition (PVD, mainly including vacuum evaporation plating, vacuum sputtering plating, vacuum ion plating, etc.), chemical vapor plating and powder covering sintering. PVD method single plating amount is low, the temperature of diamond in the plating process is lower than 500 ℃, between the coating and diamond is physical adhesion, no chemical metallurgy. CVD method Ti and diamond chemical reaction to form a strong metallurgical bond, the reaction temperature is high, damage to diamond.

(2) Thick film diamond tool grinding

The processing methods of diamond thick film tools are: mechanical grinding, hot metal disc grinding, ion beam, laser beam and plasma etching.

2.3 diamond sintered body tool

The diamond thick film is processed into diamond grains with an average particle size of 32~37 μm by rolling grinding destruction or directly by high temperature and high pressure method, the grain powder is stacked on WC-16wt Co alloy, then isolated with Ta foil, sintered at 5.5GPa, 1500 ℃ for 60 minutes, made of diamond sintered body, with this sintered body made of turning tools with high wear resistance.

2.4 single crystal diamond tool

Single crystal diamond tools are usually fixed on a small tool head, and the small tool head is fixed on the tool bar with screws or pressure plates. The main methods of fixing diamond on a small cutter head are: mechanical reinforcement (grinding the diamond bottom and pressurizing surface flat, and fixing it on the cutter head under pressure with a pressing plate); powder metallurgy (placing diamond in alloy powder and sintering under pressure in vacuum to fix the diamond on the cutter head); bonding and brazing (using inorganic binder or other binder to fix the diamond). Due to the difference between the thermal expansion coefficient of diamond and the matrix, the diamond is easy to loosen and fall off.

3. Conclusion

At present, there are still some key problems to be solved in the industrialization of diamond, such as high-speed and large-area diamond thick film deposition process, control of the grain boundary density and defect density of diamond film, low-temperature growth of diamond film, and weak binding force between diamond film and substrate. The excellent performance and broad development prospects of diamond tools have attracted numerous experts at home and abroad to conduct research, and some have made breakthroughs. It is believed that diamond tools will be widely used in modern processing in the near future.

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