1 Introduction
With the rapid development of automotive, aerospace and aerospace technologies, the requirements for material performance and processing technology are increasing. 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 and low coefficient of thermal expansion, which determines the tool life is very short during machining. The development of new wear-resistant and stable super-hard cutting tools is a subject of research in many universities and research institutes.
Diamond combines many excellent properties such as mechanics, optics, thermals, acoustics and optics. It has high hardness, low friction coefficient, high thermal conductivity, low thermal expansion coefficient and low chemical inertness. It is an ideal material for manufacturing tools. In recent years, some processing methods have been developed. This paper gives an overview of the current manufacturing methods of diamond tools.
2 Diamond tool application
The excellent properties of diamond determine its wide application in machining.
Processing difficult-to-machine non-ferrous metals
When processing non-ferrous metals such as copper, zinc, aluminum and their alloys, these materials adhere to the tool and should not be processed. The use of diamond diamonds with low friction coefficient and low affinity with non-ferrous metals prevents the metal from sticking to the tool. Since the modulus of elasticity of the diamond is large, the deformation of the blade portion during cutting is small, and the deformation of the non-ferrous metal to be cut is small, so that the cutting process is completed under a small deformation, and the surface quality of the cutting can be improved.
Processing difficult-to-machine non-metallic materials
When processing difficult-to-machine non-metallic materials containing a large number of high-hardness particles, such as glass fiber reinforced plastics, silicon-filled materials, and hard carbon fiber/epoxy composites, the hard spots of the material make the tool wear severe, using carbide tools. It is difficult to process, and the diamond cutter has high hardness and good wear resistance, so the processing efficiency is high.
Ultra-precision machining
With the advent of modern integration technology, machining is moving toward high precision, which puts high demands on tool performance. Due to the small friction coefficient of diamond, low thermal expansion coefficient and high thermal conductivity, it can cut very thin chips, and the chips are easy to flow out. The affinity with other substances is small, the built-up edge is not easy to occur, the heat generation is small, the thermal conductivity is high, and heat can be avoided. The influence of the blade and the workpiece, so the blade is not easy to passivate, the cutting deformation is small, and a higher quality surface can be obtained.
3 Diamond tool manufacturing method
At present, there are four main processing methods for diamond: thin film coated tools, thick film diamond welding tools, diamond sintered body tools and single crystal diamond tools.
Film coated tool
A thin film coated tool is a tool made by depositing a diamond film by chemical vapor deposition (CVD) on a collective material of high rigidity and high temperature characteristics. Since the thermal expansion of the SiN4 ceramics, the WC+Co-based cemented carbide, and the metal W is close to that of the diamond, the thermal stress generated during film formation is small, and thus it can be used as a base material of the blade body. In the WC+Co cemented carbide, the presence of the binder phase Co tends to form graphite between the diamond film and the substrate to reduce the adhesion strength, and pretreatment is required before the deposition to eliminate the influence of Co (generally by acid etching to Co). .
The chemical vapor deposition method uses a certain method to activate a gas containing a C source, and at a very low gas pressure, carbon atoms are deposited in a certain region, and the carbon atoms form a diamond phase during aggregation and deposition. At present, the CVD method for depositing diamond mainly includes: microwave, hot filament, DC arc spray method and the like.
The advantages of diamond film are that it can be applied to a variety of geometrically complex tools, such as blades with chips, end mills, reamers and drill bits; it can be used to cut many non-metallic materials with small cutting force and small deformation during cutting. The work is stable, the wear is slow, and the workpiece is not easily deformed. It is suitable for finishing with good workpiece material and small tolerance. The main disadvantage is that the adhesion of the diamond film to the substrate is poor, and the diamond film tool does not have regrind.
Diamond thick film welding tool
The manufacturing process of diamond thick film welding tools generally includes: preparation of large-area diamond film; shape and size required for cutting diamond film into tool; welding of diamond thick film and tool base material; grinding and polishing of diamond thick film cutting edge .
Preparation and cutting of diamond thick film
A commonly used method for preparing a diamond thick film is a 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 lattice is relatively tightly bonded, but the growth surface is rough. The high hardness, wear resistance and non-conductivity of the diamond film determine that its cutting method is laser cutting (cutting can be carried out in air, oxygen and argon). Laser cutting not only cuts the diamond thick film into the required shape and size, but also cuts the back angle of the tool, which has the advantages of narrow slit and high efficiency.
Welding of diamond thick film cutter
There is a high interfacial energy between diamond and ordinary metals and their alloys, so that diamonds cannot be infiltrated by ordinary low-melting alloys, and the weldability is extremely poor. At present, the weldability between diamond and metal is improved mainly by adding a strong carbide forming element to the copper-silver alloy solder or by metallizing the diamond surface.
Active solder method
The solder is typically soldered with a Ti-containing copper-silver alloy without the addition of a flux in an inert gas or vacuum. The commonly used brazing filler composition Ag = 68.8 wt%, Cu = 26.7 wt%, Ti = 4.5 wt%, and the usual preparation methods are arc melting and powder metallurgy. Ti as an active element reflects the formation of TiC during the welding process with C, which improves the wettability and bond strength of diamond and solder. The heating temperature is generally 850 ° C, kept for 10 minutes, and slowly cooled to reduce the internal stress.
Surface metallization and soldering
Metallization of the diamond surface is performed by surface treatment techniques to plate the surface of the diamond with metal or metalloid properties. Generally, Ti is plated on the surface of diamond, and Ti reacts with C to form TiC. TiC and Ag-Cu alloy brazing filler metal have good wettability and bonding strength. 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 deposition and powder coating sintering. The PVD method has a low single plating amount, and the temperature of the diamond during the plating process is lower than 500 ° C. The plating layer is physically attached to the diamond and is not chemically metallurgy. The CVD method Ti chemically reacts with diamond to form a strong metallurgical bond with high reaction temperature and damage to diamond.
Sharpening of thick film diamond cutter
Diamond thick film cutters are processed by mechanical grinding, hot metal disc grinding, ion beam, laser beam and plasma etching.
Diamond sintered body cutter
The diamond thick film is processed into a diamond grain having an average particle size of 32 to 37 μm by rolling and grinding, or a diamond grain is directly obtained by a high temperature and high pressure method, and the grain powder is stacked on the WC-16 wt% Co alloy, and then used. The Ta foil was isolated and sintered at 5.5 GPa and 1500 ° C for 60 minutes to prepare a diamond sintered body, and the turning tool made of the sintered body had high wear resistance.
Single crystal diamond cutter
The single crystal diamond tool usually fixes the diamond single crystal on the small cutter head, and the small cutter head is fixed on the cutter bar by screws or pressure plates. The fixing method of diamond on the small cutter head mainly includes: mechanical reinforcement method (flattening the bottom surface of the diamond and the pressing surface, and fixing it on the small cutter head with a pressure plate); powder metallurgy method (putting the diamond in the alloy powder, adding Pressing in a vacuum to fix the diamond on the small head); bonding and brazing (using an inorganic binder or other binder to fix the diamond). Due to the great difference in thermal expansion coefficient between diamond and matrix, diamond is easy to loosen and fall off.
4 Conclusion
At present, there are still some key problems to be solved in the industrialization of diamond, such as high-speed large-area diamond thick film deposition process, control of grain boundary density and defect density of diamond film, low-temperature growth of diamond film, and bonding of diamond film to substrate. Weak and so on. The excellent performance and extensive development prospects of diamond tools have attracted countless experts from home and abroad to conduct research. Some have made breakthroughs. It is believed that diamond tools will be widely used in modern processing in the near future.
With the rapid development of automotive, aerospace and aerospace technologies, the requirements for material performance and processing technology are increasing. 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 and low coefficient of thermal expansion, which determines the tool life is very short during machining. The development of new wear-resistant and stable super-hard cutting tools is a subject of research in many universities and research institutes.
Diamond combines many excellent properties such as mechanics, optics, thermals, acoustics and optics. It has high hardness, low friction coefficient, high thermal conductivity, low thermal expansion coefficient and low chemical inertness. It is an ideal material for manufacturing tools. In recent years, some processing methods have been developed. This paper gives an overview of the current manufacturing methods of diamond tools.
2 Diamond tool application
The excellent properties of diamond determine its wide application in machining.
Processing difficult-to-machine non-ferrous metals
When processing non-ferrous metals such as copper, zinc, aluminum and their alloys, these materials adhere to the tool and should not be processed. The use of diamond diamonds with low friction coefficient and low affinity with non-ferrous metals prevents the metal from sticking to the tool. Since the modulus of elasticity of the diamond is large, the deformation of the blade portion during cutting is small, and the deformation of the non-ferrous metal to be cut is small, so that the cutting process is completed under a small deformation, and the surface quality of the cutting can be improved.
Processing difficult-to-machine non-metallic materials
When processing difficult-to-machine non-metallic materials containing a large number of high-hardness particles, such as glass fiber reinforced plastics, silicon-filled materials, and hard carbon fiber/epoxy composites, the hard spots of the material make the tool wear severe, using carbide tools. It is difficult to process, and the diamond cutter has high hardness and good wear resistance, so the processing efficiency is high.
Ultra-precision machining
With the advent of modern integration technology, machining is moving toward high precision, which puts high demands on tool performance. Due to the small friction coefficient of diamond, low thermal expansion coefficient and high thermal conductivity, it can cut very thin chips, and the chips are easy to flow out. The affinity with other substances is small, the built-up edge is not easy to occur, the heat generation is small, the thermal conductivity is high, and heat can be avoided. The influence of the blade and the workpiece, so the blade is not easy to passivate, the cutting deformation is small, and a higher quality surface can be obtained.
3 Diamond tool manufacturing method
At present, there are four main processing methods for diamond: thin film coated tools, thick film diamond welding tools, diamond sintered body tools and single crystal diamond tools.
Film coated tool
A thin film coated tool is a tool made by depositing a diamond film by chemical vapor deposition (CVD) on a collective material of high rigidity and high temperature characteristics. Since the thermal expansion of the SiN4 ceramics, the WC+Co-based cemented carbide, and the metal W is close to that of the diamond, the thermal stress generated during film formation is small, and thus it can be used as a base material of the blade body. In the WC+Co cemented carbide, the presence of the binder phase Co tends to form graphite between the diamond film and the substrate to reduce the adhesion strength, and pretreatment is required before the deposition to eliminate the influence of Co (generally by acid etching to Co). .
The chemical vapor deposition method uses a certain method to activate a gas containing a C source, and at a very low gas pressure, carbon atoms are deposited in a certain region, and the carbon atoms form a diamond phase during aggregation and deposition. At present, the CVD method for depositing diamond mainly includes: microwave, hot filament, DC arc spray method and the like.
The advantages of diamond film are that it can be applied to a variety of geometrically complex tools, such as blades with chips, end mills, reamers and drill bits; it can be used to cut many non-metallic materials with small cutting force and small deformation during cutting. The work is stable, the wear is slow, and the workpiece is not easily deformed. It is suitable for finishing with good workpiece material and small tolerance. The main disadvantage is that the adhesion of the diamond film to the substrate is poor, and the diamond film tool does not have regrind.
Diamond thick film welding tool
The manufacturing process of diamond thick film welding tools generally includes: preparation of large-area diamond film; shape and size required for cutting diamond film into tool; welding of diamond thick film and tool base material; grinding and polishing of diamond thick film cutting edge .
Preparation and cutting of diamond thick film
A commonly used method for preparing a diamond thick film is a 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 lattice is relatively tightly bonded, but the growth surface is rough. The high hardness, wear resistance and non-conductivity of the diamond film determine that its cutting method is laser cutting (cutting can be carried out in air, oxygen and argon). Laser cutting not only cuts the diamond thick film into the required shape and size, but also cuts the back angle of the tool, which has the advantages of narrow slit and high efficiency.
Welding of diamond thick film cutter
There is a high interfacial energy between diamond and ordinary metals and their alloys, so that diamonds cannot be infiltrated by ordinary low-melting alloys, and the weldability is extremely poor. At present, the weldability between diamond and metal is improved mainly by adding a strong carbide forming element to the copper-silver alloy solder or by metallizing the diamond surface.
Active solder method
The solder is typically soldered with a Ti-containing copper-silver alloy without the addition of a flux in an inert gas or vacuum. The commonly used brazing filler composition Ag = 68.8 wt%, Cu = 26.7 wt%, Ti = 4.5 wt%, and the usual preparation methods are arc melting and powder metallurgy. Ti as an active element reflects the formation of TiC during the welding process with C, which improves the wettability and bond strength of diamond and solder. The heating temperature is generally 850 ° C, kept for 10 minutes, and slowly cooled to reduce the internal stress.
Surface metallization and soldering
Metallization of the diamond surface is performed by surface treatment techniques to plate the surface of the diamond with metal or metalloid properties. Generally, Ti is plated on the surface of diamond, and Ti reacts with C to form TiC. TiC and Ag-Cu alloy brazing filler metal have good wettability and bonding strength. 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 deposition and powder coating sintering. The PVD method has a low single plating amount, and the temperature of the diamond during the plating process is lower than 500 ° C. The plating layer is physically attached to the diamond and is not chemically metallurgy. The CVD method Ti chemically reacts with diamond to form a strong metallurgical bond with high reaction temperature and damage to diamond.
Sharpening of thick film diamond cutter
Diamond thick film cutters are processed by mechanical grinding, hot metal disc grinding, ion beam, laser beam and plasma etching.
Diamond sintered body cutter
The diamond thick film is processed into a diamond grain having an average particle size of 32 to 37 μm by rolling and grinding, or a diamond grain is directly obtained by a high temperature and high pressure method, and the grain powder is stacked on the WC-16 wt% Co alloy, and then used. The Ta foil was isolated and sintered at 5.5 GPa and 1500 ° C for 60 minutes to prepare a diamond sintered body, and the turning tool made of the sintered body had high wear resistance.
Single crystal diamond cutter
The single crystal diamond tool usually fixes the diamond single crystal on the small cutter head, and the small cutter head is fixed on the cutter bar by screws or pressure plates. The fixing method of diamond on the small cutter head mainly includes: mechanical reinforcement method (flattening the bottom surface of the diamond and the pressing surface, and fixing it on the small cutter head with a pressure plate); powder metallurgy method (putting the diamond in the alloy powder, adding Pressing in a vacuum to fix the diamond on the small head); bonding and brazing (using an inorganic binder or other binder to fix the diamond). Due to the great difference in thermal expansion coefficient between diamond and matrix, diamond is easy to loosen and fall off.
4 Conclusion
At present, there are still some key problems to be solved in the industrialization of diamond, such as high-speed large-area diamond thick film deposition process, control of grain boundary density and defect density of diamond film, low-temperature growth of diamond film, and bonding of diamond film to substrate. Weak and so on. The excellent performance and extensive development prospects of diamond tools have attracted countless experts from home and abroad to conduct research. 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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