Ceramic tools are made of special ceramic materials and belong to non-metallic materials. Because the purity and granularity of raw materials are controlled, various carbides, nitrides, borides and oxides are added to improve their properties, and their fracture toughness is improved through the synergistic effect of particles, whiskers, phase transformation, microcracks and several toughening mechanisms. Not only the bending strength has been improved to 0.9~ 1.0GPa (as high as 1.3 ~ 1.5 GPA), but also the fracture toughness and impact resistance have been greatly improved, and the application scope has been expanded day by day, from the original aerospace and other high-tech fields to industrial ceramic tools, which have been widely used in civil ceramic tools in recent two years, not only exceeding steel, but also being acid and alkali resistant. It is a typical green product, which can cut meat and other foods under frozen conditions, and has the characteristics of no discoloration of cut fruits and no glare of cut onions. In industry, it can be used for general finishing and semi-finishing as well as rough machining under impact load. It is internationally recognized as the most potential tool to improve production efficiency.
Ceramic cutter is based on alumina (Al2O3), zirconia (ZrO2 _ 2) and silicon nitride (Si3N4), which has the characteristics of high working efficiency, long service life and good machining quality. In the past, because of its low bending strength and high brittleness, it has been mainly used as a finishing tool for a long time, accounting for a small proportion in all kinds of tool materials. However, in recent years, ceramic tools can process steel, cast iron and its alloys at a high speed of 200~ 1000m/min, and the tool life is several times or even dozens of times that of cemented carbide. For example, the RT200 series monolithic ceramic drill and ceramic end mill introduced by Guhring Company in Germany have a finishing cutting speed of 1000m/min. At the same time, its appearance changed the traditional concept of technology. Turning and milling can directly replace grinding (or polishing) hardened parts with ceramic tools, and single process can replace multiple processes, which greatly shortens the process flow. In production, it can be used not only for general turning, boring and milling, but also for precision hole machining more successfully. It can be used not only for ordinary machine tools, but also for efficient equipment such as numerical control machine tools. Compared with superhard tools such as diamond and CBN (cubic boron nitride), the price of ceramics is relatively low, so some people think: "With the continuous improvement of the material properties of modern ceramic tools, it will become the three main tools for high-speed machining together with coated cemented carbide tools, diamond and CBN."
Two commonly used tool materials
The commonly used tool materials are tool steel, high speed steel, cemented carbide, ceramics and superhard tool materials, and the most commonly used tools are high speed steel and cemented carbide. Table 6-2 shows the brands, properties and uses of common tool materials.
1) high speed steel
High-speed steel is a kind of high-alloy tool steel containing more alloying elements such as tungsten, chromium and vanadium, which has good comprehensive properties. Its strength and toughness are the highest among existing tool materials. The manufacturing process of high-speed steel is simple, and it is easy to grind a sharp cutting edge. The deformation of forging and heat treatment is very small, and it still occupies the main position in manufacturing complex tools, such as twist drills, taps, broaches, gear tools and forming tools.
High speed steel can be divided into ordinary high speed steel and high performance high speed steel.
Ordinary high-speed steel, such as W 1J8c24v, is widely used to manufacture all kinds of complex tools. The cutting speed is generally not too high, and it is 40-60m/min when cutting ordinary steel.
High-performance high-speed steel, such as W 12Cr4V4Mo, is made by adding certain carbon content, vanadium content and cobalt to ordinary high-speed steel.
Aluminum and other elements are melted. Its durability is 1.5-3 times that of ordinary high-speed steel.
Powder metallurgy high-speed steel is a kind of high-speed steel put into the market in 1970s. Its strength and toughness are improved by 30%-40% and 80%-90% respectively, and its durability can be improved by 2-3 times. At present, our country is still in the experimental research stage, and the production and use are still very few.
2) cemented carbide
According to GB 2075-87 (refer to 190 standard), it can be divided into three categories: P, M and K. P-type cemented carbide is mainly used to process ferrous metals with long chips, with blue as the symbol. Class M is mainly used for processing ferrous and nonferrous metals, marked with yellow, also known as general cemented carbide, and Class K is mainly used for processing ferrous, nonferrous and nonmetallic materials with short chips, marked with red.
P, m, k (Arabic numerals at the back indicate its performance and processing load or processing conditions. The smaller the number, the higher the hardness and the worse the toughness.
Class P is equivalent to the original tungsten-titanium drill in China, and its main component is WC-TiC-Co, code name YT.
Class K is equivalent to the original tungsten drill in China, and its main component is WC-Co, code name YG.
Class M is equivalent to the original general alloy of tungsten, titanium, tantalum and cobalt in China, and its main component is WC+TiC+TaC(NbC) Co, code YW.
Brief introduction of three-layer cutter.
Coated tool is a new tool material that has appeared in recent 20 years. It is an important breakthrough in tool development and an effective measure to solve the contradiction between hardness, wear resistance and strength and toughness in tool materials. Coated tools are obtained by coating a layer of refractory metal compounds with high wear resistance on the matrix of some cemented carbide or high speed steel tools with good toughness. Commonly used coating materials are TiC, TiN and Al2O3. In the early 1970s, the cutting speed of ordinary cemented carbide was increased from 80m/min to 180m after a layer of titanium carbide (TiC) was plated on cemented carbide substrate for the first time. N. 1976 titanium carbide-alumina double-coated cemented carbide appeared again, and the cutting speed was increased to 250 m/min. 198 1 year, titanium carbide-alumina-cobalt nitride three-layer cemented carbide appeared again, and the cutting speed increased to 300 m/iijn.
Tool coating on high-speed steel substrate is mostly tin, which is usually coated by physical vapor deposition (PVD). It is usually used on complex tools, such as drills, taps, milling cutters and hobs. The thickness of the coating is several microns, and the hardness of the coating can reach 80HRC, which is equivalent to that of ordinary cemented carbide. The durability can be improved by 2-5 times, and the cutting speed can be improved by 20%-40%.
Cemented carbide coating is a layer of high wear-resistant refractory metal compound with a thickness of several microns to more than ten microns on a cemented carbide substrate with good toughness. Generally, chemical vapor deposition (CVD) is used. The coated cemented carbide produced by Zhuzhou Cemented Carbide Factory in China has a coating thickness of 9um and a surface hardness of 2500—4200HV.
At present, the research and popularization of coated tools in developed countries are developing very rapidly. Sweden, which is in the leading position, uses 70%-80% coated cemented carbide blades in turning and more than 50% in milling. However, coated tools are not suitable for machining high-temperature alloys, titanium alloys and non-metallic materials, nor for rough machining forged castings with sand inclusion and hard skin.
Four-diamond cutter
Diamond tools are divided into natural diamond and artificial diamond tools. Natural diamond has the highest hardness and thermal conductivity C among natural substances, but because of its high price, it is very difficult to process and weld, and it is rarely used as a cutting tool in industry except for a few special purposes (such as watch precision parts, lighting, jewelry carving). With the development of high technology and ultra-precision machining. For example, micro parts of micromechanics, mirrors in high-tech fields such as nuclear reactors, navigation gyroscopes in missiles or rockets, computer hard disk chips, accelerator electron guns and other ultra-precision parts can be processed, and single crystal diamond can meet the above requirements. In recent years, the chemical mechanism of various grinding diamond tools and the development of protective atmosphere brazing technology make the manufacturing process of natural diamond tools easier. Therefore, natural diamond plays an important role in ultra-precision mirror cutting, a high-tech application field.
After synthesizing diamond powder artificially by high temperature and high pressure technology in 1950s, polycrystalline diamond (PCD), a diamond-based tool, was manufactured in 1970s. PCD grains are arranged in an impermissible order and have no directionality, so the hardness is uniform. It has high hardness and thermal conductivity and low thermal expansion coefficient. High elastic modulus and low friction coefficient, the blade is very sharp. It can be used to add various non-ferrous metals and high-performance non-metallic materials, such as aluminum, copper, magnesium and their alloys, cemented carbide, fiber plasticizing materials, metal-based composite materials, wood composite materials and so on.
The performance characteristics of three main diamond tool materials-PCD, CVD thick film and artificial single crystal diamond are as follows: PCD has the highest weldability, mechanical grindability and fracture toughness, the middle wear resistance and cutting edge quality, and the worst corrosion resistance. CVD thick film has the best corrosion resistance, medium mechanical grindability, medium cutting edge quality, fracture toughness and wear resistance, and poor weldability. The cutting edge of artificial single crystal diamond has the best quality, wear resistance and corrosion resistance, and the worst weldability, mechanical grindability and fracture toughness.
Diamond tool is an ideal tool material for cutting aluminum alloy at high speed (2500~5000m/min), but it is not suitable for cutting iron and its alloy workpiece because of the affinity between carbon and iron, especially at high temperature.
Pentcubic boron nitride
Cubic boron nitride (CBN) is a pure synthetic material. It is the second superhard material-CBN micropowder, which was synthesized in the late 1950s by a method similar to diamond manufacturing. Because of the poor sintering performance of CBN, it was not until the 1970s that cubic boron nitride aggregates (polycrystalline cubic boron nitride PCBN) were made, which were sintered by fine CBN powder and a small amount of binder phases (Co, Ni or TiN, TiC or Al2O3) at high temperature and high pressure. CBN is a dense phase of boron nitride, which has high hardness (second only to diamond) and heat resistance (1300, 1500 degrees), excellent chemical stabilizer (far superior to diamond) and thermal conductivity, and low friction coefficient. PCBN has low affinity with Fe group elements and is an ideal tool material for cutting ferrous metals at high speed.