Diamond tool manufacturing

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Difficult to process non-ferrous metals
When processing copper, zinc, aluminum and other non-ferrous metals and their alloys, these materials adhere to the tool, not suitable for processing. Diamond tools made of low friction coefficient and low affinity with non-ferrous metals can prevent the metal from sticking to the tool. Because the elastic modulus of diamond is large, the deformation of the cutting edge is small, and the extrusion deformation of the non-ferrous metal is small, so that the cutting process can be completed under small deformation, which can improve the cutting surface quality.

Non – metallic materials that are difficult to process
Machining contains a large amount of high hardness particle hard non-metallic materials, such as glass fiber reinforced plastic, silicon, hard carbon fiber/epoxy resin composite material, the hard point of material to make the tool wear serious, with carbide cutting tools are difficult to machining, high hardness, good wear resistance and the diamond tool, so the machining efficiency is high.

Ultra-precision machining
With the advent of modern integration technology, machining towards the direction of high precision, put forward a very high demand for tool performance. Because the diamond small friction coefficient, low thermal expansion coefficient, high thermal conductivity, can cut a very thin chip, chip flow, easily with other substances affinity is small, not easy to produce the devolop tumor, calorific value is small, high thermal conductivity, can avoid heat influence on the blade and artifacts, so the blade is not easy to passivation, cutting deformation is small, high quality surface can be obtained.

Method of making diamond tools

At present, there are four main processing methods of diamond: thin film coating tool, thick film diamond welding tool, diamond sintering tool and single crystal diamond tool.

Film coated tool
Thin-film coated tools are tools made by chemical vapor deposition (CVD) of diamond films on the materials with good rigidity and high temperature properties. Since the thermal expansion system of SiN4 ceramics, WC+Co cemented carbide and metal W is close to that of diamond, the thermal stress generated in the process of making the film is small, so it can be used as the matrix material of the cutting body. In WC+Co cemented carbide series, the presence of bonded phase Co easily leads to the formation of graphite between the diamond film and the matrix, thus reducing the adhesion strength. Pretreatment is required before deposition to eliminate the effect of Co (generally through acid corrosion to remove Co).

Chemical vapor deposition (CVD) is a method to activate the gas containing C source. Carbon atoms can be deposited in a certain area under extremely low gas pressure. Carbon atoms can form diamond phase in the process of condensation and deposition. At present, the CVD method for diamond deposition mainly includes microwave, hot filament, dc arc jet method and so on.

The advantage of diamond film is that it can be applied to a variety of geometrically complex cutting tools, such as blades with chips, end mills, reamers and drill bits; Can be used to cut a lot of non-metallic materials, cutting force, small deformation, smooth work, wear slow, the workpiece is not easy to deform, suitable for the workpiece material good, small tolerance finishing. The main disadvantage is the poor adhesion between the diamond film and the matrix, and the diamond film tool does not have the regrind property.

Thick film diamond welding tool
The manufacturing process of diamond thick film welding tool generally includes: preparation of diamond film with large area; Cut the diamond film into the shape and size required for the cutting tool; Welding of thick diamond film with cutting tool base material; Grinding and polishing of cutting edges of diamond thick film tools.

Dc plasma jet CVD method is commonly used to prepare thick diamond film. The diamond is deposited on WC+Co alloy (surface is processed by mirror), and the diamond film will fall off automatically during the cooling process of the matrix. This method has a fast deposition rate (up to 930 nm /h), tight lattice bonding, but rough growing surfaces. The high hardness, wear resistance and non-conductivity of the diamond film determine its cutting method is laser cutting (cutting can be done 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 the back Angle of the tool, which has the advantages of narrow slit and high efficiency.

There is high interfacial energy between diamond and common metal and its alloy, so that diamond can not be infiltrated by common low melting point alloy and its weldability is extremely poor. At present, the soldability between diamond and metal is improved mainly by adding reinforced carbides to the copper-silver alloy solder or by metallizing the diamond surface.

Solders are generally made of Ti – containing copper – silver alloy without flux in inert gas or vacuum. Common filler metal components Ag=68.8wt%, Cu=26.7wt%, Ti=4.5wt%, and the common preparation methods are arc smelting and powder metallurgy. Ti, as an active element, reacts with C in the welding process to form TiC, which can improve the wettability and bond strength of diamond and solder. The heating temperature is generally 850℃, and the temperature is kept warm for 10 minutes.

The metallization of diamond surface is to coat the diamond surface with metal by surface treatment technology, so that the surface has the properties of metal or metal-like. Generally, Ti is plated on the surface of diamond. Ti reacts with C to produce TiC, which has better wettability and bonding strength with ag-cu alloy filler. 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 covered sintering. The single coating amount of PVD method is low, and the temperature of diamond in the plating process is less than 500℃. The chemical reaction between Ti and diamond by CVD method results in strong metallurgical bonding, high reaction temperature and damage to diamond.

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

Diamond sintering tool
Use diamond thick film roll grinding damage method processed into an average particle size of 32 ~ 37 mu m diamond grain or direct use of high temperature and high pressure method, the diamond grain, the grain powder pile up on WC – Co alloy 16 wt %, and then use Ta foil isolate them, under the condition of 5.5 GPa, 1500 ℃ sintering 60 minutes, made diamond sintered body, use the sintering system into the cutter has high wear resistance.

Single crystal diamond tool
Monocrystalline diamond tools are usually diamond monocrystalline fixed on the knife head, small head with screws or platen fixed on the tool rod. The fixing methods of diamond on the knife head mainly include: mechanical reinforcement method (grinding the bottom surface of diamond and pressing surface and fixing it on the knife head with pressing plate); Powder metallurgy (where the diamond is placed in an alloy powder and sintered under pressure in a vacuum so that the diamond is fixed on a knife head); Bonding and brazing (using an inorganic binder or other binder to secure the diamond). Because the thermal expansion coefficient of diamond and matrix is very different, the diamond is easy to loose and fall off.

conclusion
At present, there are still some key problems to be solved in the industrialization of diamond, such as high speed and large area thick film deposition technology of diamond, controlling grain boundary density and defect density of diamond film, low temperature growth of diamond film, weak bonding force between diamond film and matrix, etc. The excellent performance and extensive development prospect of diamond tools have attracted numerous experts at home and abroad, some of which have made a breakthrough. It is believed that diamond tools will be widely used in modern processing in the near future.