Manufacturing method of the hottest diamond tool

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

diamond integrates many excellent properties such as mechanics, optics, thermology, acoustics, optics, etc. it has extremely high hardness, low friction coefficient, high thermal conductivity, low thermal expansion coefficient and chemical inertia. It is an ideal material for manufacturing tools. This paper summarizes the development of diamond tool manufacturing methods in recent years

1. application scope of diamond tools

(1) processing of difficult to machine non-ferrous metal materials

when processing non-ferrous metals and their alloys such as copper, zinc, aluminum, etc., the materials are easy to adhere to the tools and the processing is difficult. Taking advantage of the low friction coefficient of diamond and its low affinity with non-ferrous metals, diamond tools can effectively prevent metal from bonding with tools. In addition, due to the large elastic modulus of diamond, the deformation of the cutting edge during cutting is small, and the extrusion deformation of the non-ferrous metal being cut is small, the cutting process can be completed under small deformation, which can improve the quality of the machined surface

(2) processing of difficult to machine non-metallic materials

processing is mainly used to test the tensile and compressive strength of various elastic components such as spiral springs. When difficult to machine non-metallic materials containing a large number of high hardness particles, such as glass fiber reinforced plastics, silicon filled materials, hard carbon fiber/epoxy resin composites, the hard points of the materials make the tools seriously worn, which is difficult to machine with cemented carbide tools, while diamond tools have high hardness Good wear resistance, so the processing efficiency is high

(3) ultra precision machining

with the advent of modern integrated technology, machining is developing towards high precision, which puts forward quite high requirements for tool performance. Due to the low friction coefficient, low thermal expansion coefficient and high thermal conductivity of diamond, it can cut extremely thin chips, which are easy to flow out, have low affinity with other substances, are not easy to produce chip nodules, have low calorific value and high thermal conductivity, and can avoid the influence of heat on the cutting edge and workpiece. Therefore, the cutting edge is not easy to passivate, and the cutting deformation is small, so a high-quality surface can be obtained

2. Manufacturing methods of diamond tools

at present, there are four main diamond processing methods: thin film coated tools, thick film diamond welding tools, diamond sintered body tools and single crystal diamond tools

2.1 thin film coated tools

thin film coated tools are tools made by depositing diamond films by chemical vapor deposition (CVD) on collective materials with good rigidity and high temperature characteristics

because the thermal expansion system of Si3N4 ceramics, WC Co cemented carbide and metal W is close to that of diamond, the thermal stress generated during film making is small, so it can be used as the matrix material of tool body. In WC Co cemented carbides, the existence of bonding phase CO is easy to form graphite between diamond film and matrix and reduce the adhesion strength. Pretreatment is required before deposition to eliminate the influence of CO (generally CO is removed by acid corrosion)

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

the advantage of diamond film is that it can be applied to various tools with complex geometric shapes, such as blades with chips, end mills, reamers and drill bits; 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, and the workpiece is not easy to deform. It is suitable for finishing machining with good workpiece material and small tolerance. The main disadvantage is that the adhesion between diamond film and matrix is poor, and diamond film tools do not have regrinding property

2.2 diamond thick film welding tool

the manufacturing process of diamond thick film welding tool generally includes: the preparation of a large area of diamond film; Cut the diamond film into the shape and size required by the cutter; Welding of diamond thick film and tool base material; Grinding and polishing of diamond thick film cutting edge. (1) Preparation and cutting of diamond thick film

the common process for preparing diamond thick film is DC plasma jet CVD. When diamond is deposited on WC Co alloy (the surface is mirror machined), the diamond film will fall off automatically during the cooling process of the substrate. This method has fast deposition speed (up to 930 μ M/h), the lattice is closely bound, but the growth surface is rough. The high hardness, wear resistance and non conductivity of diamond film determine that 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 corner of the tool. It has the advantages of narrow slit and high efficiency

(1) welding of diamond thick film tools

there is a high interface energy between diamond and general metals and their alloys, so that diamond cannot be soaked by general low melting point alloys, and the weldability is extremely poor. At present, the solderability 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

the solder is generally copper silver alloy containing Ti, which is welded in inert gas or vacuum without flux. The commonly used solder composition is ag=68.8wt%, cu=26.7wt%, ti=4.5wt%. The commonly used preparation methods are arc smelting method and powder metallurgy method. As an active element, Ti reacts with C in the welding process to generate tic, which can improve the wettability and bonding strength between diamond and solder in vain. The heating temperature is generally 850 ℃, holding for 10 minutes, and cooling slowly to reduce internal stress

② welding after surface metallization

metallization of diamond surface is to coat metal on the diamond surface through surface treatment technology, so that its surface has the properties of metal or metalloid. Generally, Ti is plated on the surface of diamond, and Ti reacts with C to form tic. Tic and Ag Cu alloy solder have good wettability and bonding strength. At present, the commonly used titanium plating methods are: vacuum physical vapor deposition (PVD, mainly including vacuum evaporation, vacuum sputtering, vacuum ion plating, etc.), chemical vapor deposition and powder covering sintering. PVD method has a low single plating amount, and the temperature of diamond in the plating process is lower than 500 ℃. The products of the plating project have been used in many cement enterprises. There is physical attachment between the coating and diamond without chemical metallurgy. The chemical reaction between Ti and diamond by CVD method forms a strong metallurgical combination, and the reaction temperature is high, which damages the diamond

(2) grinding of thick film diamond tools

the processing methods of diamond thick film tools include: mechanical grinding, hot metal disk grinding, ion beam, laser beam and plasma etching

2.3 diamond sintered tool

the thick diamond film is processed into an average particle size of 32 ~ 37 by rolling and grinding μ M of diamond grains or directly use the high temperature and high pressure method to obtain diamond grains. Stack the grain powder on wc-16wt%co alloy, and then isolate it with TA foil. Its thermoplastic K series products have recently been used by the famous Spanish brand circulator SA and sintered at 1500 ℃ for 60 minutes to make diamond sintered body. The turning tool made of this sintered body has high wear resistance

2.4 single crystal diamond tools

single crystal diamond tools usually fix the diamond single crystal on the small cutter head, which is fixed on the turning tool rod with screws or pressing plates. The fixing methods of diamond on the small cutter head mainly include: mechanical reinforcement method (grinding the bottom surface of diamond and pressure surface, and fixing it on the small cutter head with pressure plate); Powder metallurgy method (put the diamond in the alloy powder and sinter it in vacuum under pressure to fix the diamond on the small cutter head); Bonding and brazing method (fixing diamond with inorganic binder or other binders). Due to the great difference between the thermal expansion coefficient of diamond and matrix, 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, controlling the grain boundary density and defect density of diamond film, low-temperature growth of diamond film, weak adhesion between diamond film and matrix, etc. The excellent performance and wide development prospect of diamond tools have attracted countless experts at home and abroad to study, and some have made breakthroughs. It is believed that diamond tools will be widely used in modern processing in the near future. (end)