Only by combining advanced processing equipment with high-performance CNC tools can they fully exert their due performance and achieve good economic benefits. With the rapid development of tool materials, the physical, mechanical properties and cutting performance of various new tool materials have been greatly improved, and their application scope has also continued to expand.
Basic properties that CNC tool materials should have
The selection of CNC tool materials has a great impact on tool life, processing efficiency, processing quality and processing cost. Tools must withstand high pressure, high temperature, friction, impact and vibration when cutting.
(1) Hardness and wear resistance. The hardness of the tool material must be higher than the hardness of the workpiece material, which is generally required to be above 60HRC. The higher the hardness of the tool material, the better the wear resistance.
(2) Strength and toughness. Tool materials should have high strength and toughness to withstand cutting forces, impact and vibration, and prevent brittle fracture and chipping of the tool.
(3) Heat resistance. The tool material has good heat resistance, can withstand high cutting temperatures, and has good oxidation resistance.
(4) Process performance and economy. Tool materials should have good forging performance, heat treatment performance, welding performance; grinding performance, etc., and should pursue high performance-price ratio.
Regarding the types, properties and applications of CNC tool materials
Diamond is an allotrope of carbon and is the hardest material found in nature. Diamond cutting tools have high hardness, high wear resistance and high thermal conductivity, and are widely used in the processing of non-ferrous metals and non-metallic materials. Especially in high-speed cutting of aluminum and silicon-aluminum alloys, diamond tools are the main type of cutting tools that are difficult to replace. Diamond tools that can achieve high efficiency, high stability, and long service life are indispensable and important tools in modern CNC machining.
Natural diamond tools: Natural diamonds have been used as cutting tools for hundreds of years. Natural single crystal diamond tools have been finely ground to make the cutting edge extremely sharp. The cutting edge radius can reach 0.002μm, which can achieve ultra-thin cutting and can be processed. Producing extremely high workpiece precision and extremely low surface roughness, it is a recognized, ideal and irreplaceable ultra-precision machining tool.
PCD diamond cutting tools: Natural diamonds are expensive. The most widely used diamond in cutting processing is polycrystalline diamond (PCD). Since the early 1970s, polycrystalline diamond (Polycrystauine diamond, referred to as PCD blades) prepared using high-temperature and high-pressure synthesis technology has been successfully developed. Since then, natural diamond tools have been replaced by artificial polycrystalline diamond on many occasions. PCD raw materials are abundant in sources, and their price is only a few tenths to a dozen times that of natural diamonds. PCD tools cannot grind extremely sharp edges. The surface quality of the processed workpiece is not as good as that of natural diamond. It is not yet convenient to manufacture PCD blades with chip breakers in the industry. Therefore, PCD can only be used for precision cutting of non-ferrous metals and non-metals, and it is difficult to achieve ultra-precision Mirror cutting.
CVD diamond cutting tools: Since the late 1970s to the early 1980s, CVD diamond technology appeared in Japan. CVD diamond refers to the use of chemical vapor deposition (CVD) to synthesize a diamond film on a heterogeneous matrix (such as cemented carbide, ceramics, etc.). CVD diamond has exactly the same structure and characteristics as natural diamond.
Performance characteristics of diamond tools:
① Extremely high hardness and wear resistance: Natural diamond is the hardest substance found in nature. Diamond has extremely high wear resistance. When processing high-hardness materials, the life of diamond tools is 10 to 100 times that of carbide tools, or even hundreds of times.
② Has a very low friction coefficient: The friction coefficient between diamond and some non-ferrous metals is lower than that of other cutting tools. The friction coefficient is low, and the deformation during processing is small, which can reduce the cutting force.
③ The cutting edge is very sharp: The cutting edge of the diamond tool can be ground very sharp. The natural single crystal diamond tool can be as high as 0.002~0.008μm, which can carry out ultra-thin cutting and ultra-precision processing.
④ It has high thermal conductivity: diamond has high thermal conductivity and thermal diffusivity, so cutting heat is easily dissipated, and the temperature of the cutting part of the tool is low.
⑤ Has a lower thermal expansion coefficient: The thermal expansion coefficient of diamond is several times smaller than that of cemented carbide, and the change in tool size caused by cutting heat is very small, which is particularly important for precision and ultra-precision machining that requires high dimensional accuracy.
Applications of diamond tools:
Diamond cutting tools are mostly used for fine cutting and boring of non-ferrous metals and non-metallic materials at high speeds. Suitable for processing various wear-resistant non-metals, such as fiberglass powder metallurgy blanks, ceramic materials, etc.; various wear-resistant non-ferrous metals, such as various silicon-aluminum alloys; and finishing processing of various non-ferrous metals.
Ceramic cutting tools have the characteristics of high hardness, good wear resistance, excellent heat resistance and chemical stability, and are not easy to bond with metal. Ceramic tools play a very important role in CNC machining. Ceramic tools have become one of the main tools for high-speed cutting and processing of difficult-to-machine materials. Ceramic cutting tools are widely used in high-speed cutting, dry cutting, hard cutting and cutting of difficult-to-machine materials. Ceramic tools can efficiently process high-hard materials that traditional tools cannot process at all, realizing “turning instead of grinding”; the optimal cutting speed of ceramic tools can be 2 to 10 times higher than that of carbide tools, thus greatly improving cutting production efficiency. ; The main raw materials used in ceramic tool materials are the most abundant elements in the earth’s crust. Therefore, the promotion and application of ceramic tools are of great significance for improving productivity, reducing processing costs, and saving strategic precious metals. It will also greatly promote the development of cutting technology. progress.
Types of ceramic tool materials:
The types of ceramic tool materials can generally be divided into three categories: alumina-based ceramics, silicon nitride-based ceramics, and composite silicon nitride-alumina-based ceramics. Among them, alumina-based and silicon nitride-based ceramic tool materials are the most widely used. The performance of silicon nitride-based ceramics is superior to that of alumina-based ceramics.
Performance characteristics of ceramic cutting tools:
① High hardness and good wear resistance: Although the hardness of ceramic cutting tools is not as high as PCD and PCBN, it is much higher than that of carbide and high-speed steel cutting tools, reaching 93-95HRA. Ceramic cutting tools can process high-hard materials that are difficult to process with traditional cutting tools and are suitable for high-speed cutting and hard cutting.
② High temperature resistance and good heat resistance: Ceramic cutting tools can still cut at temperatures above 1200°C. Ceramic cutting tools have good high-temperature mechanical properties. A12O3 ceramic cutting tools have particularly good oxidation resistance. Even if the cutting edge is in a red-hot state, it can be used continuously. Therefore, ceramic tools can achieve dry cutting, thus eliminating the need for cutting fluid.
③ Good chemical stability: Ceramic cutting tools are not easy to bond with metal, and are corrosion-resistant and have good chemical stability, which can reduce the bonding wear of cutting tools.
④ Low friction coefficient: The affinity between ceramic tools and metal is small, and the friction coefficient is low, which can reduce cutting force and cutting temperature.
Applications of ceramic cutting tools:
Ceramics are one of the tool materials mainly used for high-speed finishing and semi-finishing. Ceramic cutting tools are suitable for cutting various cast irons (grey cast iron, ductile iron, malleable cast iron, chilled cast iron, high alloy wear-resistant cast iron) and steel materials (carbon structural steel, alloy structural steel, high strength steel, high manganese steel, quenched steel etc.), can also be used to cut copper alloys, graphite, engineering plastics and composite materials.
The material properties of ceramic cutting tools have the problems of low bending strength and poor impact toughness, making them unsuitable for cutting at low speeds and under impact loads.
Performance and characteristics of coated tool materials and application of tools
Coating the cutting tools is one of the important ways to improve the performance of the cutting tools. The emergence of coated tools has brought about a major breakthrough in the cutting performance of cutting tools. Coated tools are coated with one or more layers of refractory compounds with good wear resistance on the tool body with good toughness. It combines the tool matrix with the hard coating, thereby greatly improving the tool performance. Coated tools can improve processing efficiency, improve processing accuracy, extend tool service life, and reduce processing costs.
Types of coated tools:
According to different coating methods, coated tools can be divided into chemical vapor deposition (CVD) coated tools and physical vapor deposition (PVD) coated tools. Coated carbide cutting tools generally use chemical vapor deposition method, and the deposition temperature is around 1000°C. Coated high-speed steel cutting tools generally use physical vapor deposition method, and the deposition temperature is around 500°C;
According to the different substrate materials of coated tools, coated tools can be divided into carbide coated tools, high-speed steel coated tools, and coated tools on ceramics and superhard materials (diamond and cubic boron nitride).
According to the properties of the coating material, coated tools can be divided into two categories, namely “hard” coated tools and ‘soft’ coated tools. The main goals pursued by “hard” coated tools are high hardness and wear resistance Its main advantages are high hardness and good wear resistance, typically TiC and TiN coatings. The goal pursued by “soft” coating tools is a low friction coefficient, also known as self-lubricating tools, which friction with the workpiece material The coefficient is very low, only about 0.1, which can reduce adhesion, reduce friction, and reduce cutting force and cutting temperature.
Features of coated tools:
① Good mechanical and cutting performance: Coated tools combine the excellent properties of the base material and the coating material. They not only maintain the good toughness and high strength of the base material, but also have the high hardness, high wear resistance and low Friction coefficient. Therefore, the cutting speed of coated tools can be increased by more than 2 times than that of uncoated tools, and higher feed rates are allowed. The life of coated tools is also improved.
② Strong versatility: Coated tools have wide versatility and significantly expand the processing range. One coated tool can replace several non-coated tools.
③ Coating thickness: As the coating thickness increases, the tool life will also increase, but when the coating thickness reaches saturation, the tool life will no longer increase significantly. When the coating is too thick, it will easily cause peeling; when the coating is too thin, the wear resistance will be poor.
④ Regrindability: Coated blades have poor regrindability, complex coating equipment, high process requirements, and long coating time.
⑤ Coating material: Tools with different coating materials have different cutting performance. For example: when cutting at low speed, TiC coating has advantages; when cutting at high speed, TiN is more suitable.
Applications of coated cutting tools:
Coated tools have great potential in the field of CNC machining and will be the most important tool variety in the field of CNC machining in the future. Coating technology has been applied to end mills, reamers, drill bits, composite hole processing tools, gear hobs, gear shaper cutters, gear shaving cutters, forming broaches and various machine-clamped indexable inserts to meet various requirements of high-speed cutting processing. The needs of materials such as steel and cast iron, heat-resistant alloys and non-ferrous metals.
