High-speed cutting tools are the key to high-speed CNC machining technology. Tool technology is one of the key technologies to achieve high-speed CNC cutting. Inappropriate tools will make complex and expensive machine tools or machining systems completely ineffective. Since high-speed cutting has a high cutting speed, and the high-speed machining line speed is mainly limited by the tool, because within the high-speed range that the current machine tool can achieve, the higher the speed, the faster the tool wears.
Therefore, high-speed cutting places higher requirements on tool materials. In addition to some basic properties of ordinary tool materials, high-speed cutting tools should also be required to have high heat resistance, thermal shock resistance, good high-temperature mechanical properties, and high reliability. Currently, commonly used high-speed cutting tool materials include polycrystalline diamond (PCD), cubic boron nitride (CBN), ceramics, coated tools, ultra-fine grain cemented carbide, and other tool materials.
High-speed Cutting Tool Materials
Diamond tool materials. Diamond milling cutters have the characteristics of high hardness, high compressive strength, good thermal conductivity, and wear resistance, and can achieve high processing accuracy and processing efficiency in high-speed cutting. Diamond tools are divided into natural diamond and artificial diamond tools. Natural diamond is expensive and difficult to process and weld. It is rarely used as a cutting tool except for a few special uses. In recent years, a variety of chemical mechanism grinding diamond tool methods and protective gas brazing diamond technology have been developed, making the manufacturing process of natural diamond tools simpler. Therefore, natural diamond plays an important role in the high-tech application field of ultra-precision mirror cutting.
Cubic boron nitride tool material. Cubic boron nitride (CBN) is a superhard material second only to diamond in hardness. Although CBN has a lower hardness than diamond, its oxidation temperature is as high as 1360℃, and it has a lower affinity with ferromagnetic materials. Therefore, it is particularly suitable for processing difficult-to-process metal materials with high hardness and high toughness. PCBN tools are the main tool materials that can meet advanced cutting requirements and are ideal tool materials for hard cutting, high-speed cutting and dry cutting. PCBN tools are mainly used for processing hardened steel, cast iron, high-temperature alloys and surface spraying materials. The foreign automobile manufacturing industry uses PCBN tools to cut cast iron materials.
Ceramic tools. Compared with cemented carbide, ceramic materials have higher hardness, red hardness and wear resistance. Therefore, when processing steel, the durability of ceramic tools is 10 to 20 times that of cemented carbide tools, and its red hardness is 2 to 6 times higher than that of cemented carbide. In addition, its chemical stability and antioxidant capacity are better than those of cemented carbide. The low strength and poor toughness of ceramic tool materials restrict its application and promotion, while the development of ultrafine powder technology and the research of nanocomposites have added new vitality to its development. Ceramic tools are the most promising high-speed cutting tools, and have attracted the attention of countries around the world. In Germany, about 70% of the processes for machining castings are completed with ceramic tools, and the annual consumption of ceramic knives in Japan has accounted for 8% to 10% of the total number of tools.
Coated tools. The development of coating materials has gone through the development stages of composite coatings and multi-component composite coatings from the initial single coating. Now, multi-component composite film materials such as TiN/NbN and TiN/CN have been developed, which greatly improves the performance of tool coatings. Among hard coating materials, TiN has the most mature technology and the most widely used.
Cemented carbide tool materials. The development of fine-grained (1~0.5um) and ultrafine-grained (<0.5um) cemented carbide materials and integral cemented carbide tools has greatly improved the bending strength of cemented carbide. It can replace high-speed steel to manufacture small-size drills, end mills, taps and other general-purpose tools with large quantities and wide ranges. Its cutting speed and tool life far exceed high-speed steel. The use of integral cemented carbide tools can significantly improve the cutting efficiency in most application fields that originally used high-speed steel tools. Another advantage of fine-grained cemented carbide is that the tool edge is sharp, especially suitable for high-speed cutting of sticky and tough materials.
Tool holder System for High-speed Cutting Rotary Tools
In high-speed cutting, the tool body structure and the blade clamping structure are subject to great centrifugal force. In order to keep the tool with sufficient clamping force, the tool structure design should fully consider the particularity of high-speed cutting processing, the tool body material should be light, the dynamic balance of the tool should be considered, and the clamping of the tool blade should be reliable. Machining centers and other N (machine tools have been using 7:24 solid taper shank tool systems for many years. This solid taper shank has the following disadvantages: Since it is only connected by the taper surface, the connection rigidity between the shank and the spindle is low, especially when the spindle speed exceeds 10,000r/min, the lack of connection rigidity is more obvious.
When using ATC (Automatic When installing the tool by the tool changing (automatic tool changing) method, the repetitive positioning accuracy is low, and it is difficult to achieve high-precision machining; when the spindle rotates at high speed, the front end of the spindle will expand under the action of centrifugal force, which can easily cause the spindle to separate from the cone surface of the tool holder, causing the radial runout to increase sharply (up to 15? um), thereby reducing the contact stiffness of the tool holder and prone to safety accidents.
Therefore, the traditional long-taper tool holder is not suitable for high-speed cutting. To solve this problem, a double-positioning tool holder has been developed that uses the cone and the spindle end face to simultaneously position. This type of tool holder is centered by the cone, and the end face of the machine tool spindle is close to the flange end face of the tool holder. This type of tool holder has a high repetitive positioning accuracy when installed (the axial repetitive positioning accuracy can reach 0.001 mm), under the centrifugal force generated by high-speed rotation, the tool holder will be firmly locked, and its radial runout does not exceed 5? um, and it can maintain high static and dynamic rigidity in the entire speed range. Therefore, this type of tool holder is particularly suitable for high-speed cutting.
High-speed Cutting Tool Monitoring Technology
Tool monitoring technology is very important for the safety of high-speed cutting. Tool monitoring technology mainly includes controlling tool wear by monitoring cutting force; indirectly obtaining tool wear information by monitoring machine tool power; monitoring tool breakage (breakage), etc. At present, the research, development and application of high-speed cutting tool monitoring technology at home and abroad are not sufficient. Since the acoustic emission signal is sensitive to the tool load, acoustic emission is used to monitor the tool condition and tool wear in high-speed cutting, and good results have been achieved. In addition, digital cameras and special fixtures are used to study the wear of high-speed cutting tools.
With the development of advanced manufacturing technology, material technology and nanotechnology, new multi-element, composite, nano-level hard coatings and CVD diamond films and other functional materials, superhard tool materials, ceramic tools, coated tools, etc. will be widely used, and high-speed cutting tool systems will become more and more perfect, becoming an important part of promoting high-speed CNC cutting.
