[Technology] Application scope and manufacturing method of diamond cutters
With the rapid development of automotive, aerospace and aerospace technology, the requirements of material properties and processing technology are increasing. New materials such as carbon fiber reinforced plastics, particulate 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 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 has many excellent properties, such as mechanics, optics, thermology, acoustics, optics, etc. It has high hardness, low friction coefficient, high thermal conductivity, low thermal expansion coefficient and chemical inertia. It is an ideal material for cutting tools. In this paper, the development of diamond cutting tools in recent years is reviewed.
1. Application scope of diamond tools
(1) Machining of difficult to process nonferrous metals
When processing non-ferrous metals such as copper, zinc and aluminum, their materials are easy to adhere to tools and difficult to process. Because of the low friction coefficient and low affinity with non-ferrous metals, diamond cutting tools can effectively prevent metal from bonding with cutting tools. In addition, because the elastic modulus of diamond is large, the deformation of cutting edge is small, and the extrusion deformation of non-ferrous metal is small, the cutting process can be completed under small deformation, thus improving the surface quality.
(2) Machining of difficult to process nonmetallic materials
When machining hard 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 particles of the materials make the tool wear seriously, and it is difficult to process with carbide tools, while the 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 toward high precision, which puts forward quite high requirements for tool performance. Because diamond has small friction coefficient, low thermal expansion coefficient, high thermal conductivity, can cut very thin chip, chip is easy to flow out, and has little affinity with other substances, is not easy to produce chip tumors, low heat generation, high thermal conductivity, can avoid the influence of heat on the blade and workpiece, so the edge is not easy to passivation, cutting deformation is small. High quality surfaces 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 tools and single crystal diamond tools.
2.1 thin film coated tools
Thin film coated tools are tools made of diamond films deposited by chemical vapor deposition (CVD) on collective materials with good rigidity and high temperature characteristics.
As the thermal expansion system of Si3N4 ceramics, WC-Co cemented carbides and W metals is close to that of diamond, the thermal stress produced in the film-making process is small, so it can be used as the base material of the cutter body. In WC-Co cemented carbides, the presence of the bonding phase Co can easily lead to the formation of graphite between diamond film and substrate and reduce the adhesion strength. Pretreatment is necessary to eliminate the influence of Co (usually by acid corrosion) before deposition.
Chemical vapor deposition (CVD) uses a certain method to activate the gas containing C source. Under very 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, the CVD method for depositing diamond mainly includes microwave, hot filament and DC arc injection.
The advantages of diamond film are that it can be applied to various cutting tools with complex geometry, such as chipped blades, end milling cutters, reamers and drills; it can be used to cut many non-metallic materials, cutting force is small, deformation is small, work smoothly, wear slowly, workpiece is not easy to deformation, suitable for workpiece with good material quality, small tolerance precision. Processing. The main disadvantage is that the adhesion between diamond film and substrate is poor, and the diamond film cutting tool does not have regrindability.
2.2 diamond thick film welding tools
The manufacturing process of diamond thick film welding tool generally includes: preparation of large area diamond film; cutting diamond film into the shape and size needed by the tool; welding of diamond thick film and tool matrix material; grinding and polishing of cutting edge of diamond thick film cutting tool. (1) preparation and cutting of thick diamond films
The commonly used method for preparing thick diamond films is the direct current plasma jet CVD method. Diamond films are deposited on WC-Co alloys (mirror machined on the surface). During the cooling process, the diamond films fall off automatically. This method has a fast deposition rate (up to 930 micron/h), and the lattice bonds closely, but the growth surface is rough. The high hardness, wear resistance and non-conductivity of diamond film determine that the cutting method of diamond film is laser cutting (cutting can be carried out in air, oxygen and argon). Laser cutting can not only cut the thick diamond film into the desired shape and size, but also cut the back angle of the tool. It has the advantages of narrow slit and high efficiency.
This paper is transferred from metalworking network.