With the rapid development of automobile, aviation and aerospace technology, 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 have been widely used. These materials have the characteristics of high strength, good wear resistance, and small coefficient of thermal expansion, which determine that the tool life is very short when they are machined. The development of new wear-resistant and stable superhard cutting tools is a research topic for many universities, scientific research institutes and enterprises. Diamond integrates many excellent properties such as mechanics, optics, heat, 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 article gives an overview of the development of diamond tool manufacturing methods in recent years.
Diamond saw blade application range
(1) Processing of non-ferrous metal materials that are difficult to process
When processing copper, zinc, aluminum and other non-ferrous metals and their alloys, the materials are easy to adhere to the tool and difficult to process. Taking advantage of the characteristics of low friction coefficient of diamond and low affinity with non-ferrous metals, diamond tools can effectively prevent metal and tools from bonding. In addition, due to the large elastic modulus of diamond, the edge deformation is small during cutting, and the extrusion deformation of the cut non-ferrous metal is small, so that the cutting process can be completed under small deformation, thereby improving the quality of the processed surface.
(2) Processing of non-metallic materials that are difficult to process
When processing difficult-to-process non-metallic materials containing a large number of high-hardness points, such as glass fiber reinforced plastics, silicon-filled materials, hard carbon fiber/epoxy composite materials, the hard points of the material cause severe tool wear, and it is difficult to use cemented carbide tools Processing, and diamond tools have high hardness and good wear resistance, so the processing efficiency is high.
(3) Ultra-precision machining
With the advent of modern integrated technology, machining is developing in the direction of high precision, which puts high demands on tool performance. Due to the small friction coefficient, low thermal expansion coefficient, and high thermal conductivity of diamond, it can cut extremely thin chips, the chips are easy to flow out, and the affinity with other materials is small, and it is not easy to generate built-up edge, the heat is small, and the thermal conductivity is high, which can avoid heat The impact on the blade and the workpiece, so the blade is not easy to be dull, the cutting deformation is small, and a higher quality surface can be obtained.
6 Manufacturing methods of diamond tools
There are currently four main processing methods for diamond: thin-film coating tools, thick-film diamond welding tools, diamond sintered body tools and single crystal diamond tools.
1 Thin film coating tool
Thin film coating tools are tools made by depositing diamond film on a collective material with good rigidity and high temperature characteristics by chemical vapor deposition (CVD).
Since the thermal expansion system of Si3N4 ceramics, WC-Co hard alloys, and metal W is close to that of diamond, the thermal stress generated during film formation is small, so it can be used as the base material of the cutter body. In WC-Co series cemented carbide, the presence of the binder phase Co can easily cause graphite to form between the diamond film and the substrate and reduce the adhesion strength. Pretreatment is required before deposition to eliminate the influence of Co (usually to remove Co by acid corrosion) .
The chemical vapor deposition method uses a certain method to activate the gas containing the C source. Under extremely low gas pressure, carbon atoms are deposited in a certain area, and the carbon atoms form a diamond phase in the process of condensation and deposition. The CVD methods currently used to deposit diamond mainly include: microwave, hot filament, and DC arc spraying.
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, with small cutting force and small deformation during cutting. It works smoothly, wears slowly, and the workpiece is not easily deformed. It is suitable for finishing with good material and small tolerances. The main disadvantage is that the adhesion between the diamond film and the substrate is poor, and the diamond film cutter does not have the ability to regrind.
2Diamond thick film welding tool
The manufacturing process of diamond thick film welding tools generally includes: preparation of large area diamond film; cutting the diamond film into the shape and size required by the tool; welding the diamond thick film and the tool base material; grinding and polishing the cutting edge of the diamond thick film tool .
(1) Preparation and cutting of diamond thick film
The commonly used process for preparing thick diamond films is the DC plasma jet CVD method. The diamond is deposited on the WC-Co alloy (mirror processing on the surface), and the diamond film will automatically fall off during the cooling process of the substrate. This method has fast deposition speed (*up to 930μm/h), and the bonding between the crystal lattices is relatively tight, but the growth surface is relatively rough. The high hardness, wear resistance, and non-conductivity of the diamond film determine its cutting method is laser cutting (cutting can be carried out in an 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 the clearance angle of the tool, which has the advantages of narrow cutting gap and high efficiency.
(2) Welding of diamond thick film tools
Diamond has a high interface energy with general metals and their alloys, so that diamond cannot be infiltrated by general low melting point alloys, and the weldability is extremely 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 metalizing the diamond surface.
① Active solder method
The solder generally uses a copper-silver alloy containing Ti, and is soldered in an inert gas or vacuum without flux. Commonly used solder composition Ag=68.8wt%, Cu=26.7wt%, Ti=4.5wt%, and the commonly used preparation methods are arc melting and powder metallurgy. As an active element, Ti reacts with C to generate TiC during the welding process, which can improve the wettability and bonding strength of diamond and solder. The heating temperature is generally 850°C, keep for 10 minutes, and slowly cool down to reduce internal stress.
②Welding after surface metallization
The metallization of the diamond surface is to plate metal on the diamond surface by surface treatment technology to make the surface have metal or metal-like properties. Generally, Ti is plated on the surface of diamond. Ti reacts with C to form TiC. TiC and Ag-Cu alloy brazing filler metal have good wettability and bonding strength. Currently commonly used titanium plating methods are: vacuum physical vapor deposition (PVD, mainly including vacuum evaporation plating, vacuum sputtering, vacuum ion plating, etc.), chemical vapor plating and powder coating sintering. The PVD method has a low single coating amount, the temperature of the diamond during the coating process is lower than 500 ℃, and the coating is physically attached to the diamond without chemical metallurgy. CVD method Ti and diamond chemically react to form a strong metallurgical bond, the reaction temperature is high, and the diamond is damaged.
(3) Sharpening of thick film diamond tools
The processing methods of diamond thick film tools include: mechanical grinding, hot metal disc grinding, ion beam, laser beam and plasma etching.
3Diamond sintered body tool
The thick diamond film is processed into diamond grains with an average particle size of 32～37μm by rolling and grinding, or the diamond grains are prepared directly by high temperature and high pressure method, and the grain powder is stacked on the WC-16wt%Co alloy, and then used Ta foil isolates it and sinters it at 5.5GPa and 1500°C for 60 minutes to form a diamond sintered body. The turning tool made from this sintered body has high wear resistance.
4Single crystal diamond tool
The single crystal diamond tool usually fixes the diamond single crystal on a small cutter head, and the small cutter head is fixed on the tool shaft of the turning tool with a screw or a pressing plate. The main methods of fixing diamond on the small cutter head are: mechanical reinforcement method (grind the bottom surface and pressure surface of the diamond flat, and fix it on the small cutter head with a pressure plate); powder metallurgy method (put the diamond in the alloy powder and add Press in a vacuum to sinter to fix the diamond on the small cutter head); bonding and brazing (using inorganic adhesives or other adhesives to fix the diamond). Due to the large difference in thermal expansion coefficient between diamond and substrate, diamond is easy to loosen and fall off.
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 the grain boundary density and defect density of the diamond film, low-temperature growth of the diamond film, and the bonding force between the diamond film and the substrate. Weak and so on. The excellent performance and broad development prospects of diamond tools have attracted countless experts at 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.
