1. Introduction With the continuous progress of society and the development of science and technology, CNC systems have undergone six generations of development to adapt to market demands. Since the first three-axis CNC milling machine was introduced in the United States in 1952, CNC systems have evolved from traditional dedicated computer hardware logic control, computer direct control, microcomputer control to open CNC. Current research has surpassed the connotation of open CNC, and CNC systems are developing towards high speed, intelligence, and networking. High-speed machining (HSM) is another revolutionary technological development after 20th-century CNC technology. 2. Current Status of High-Speed ​​Machining Development In the past decade, driven by economic globalization, the transfer of manufacturing industries from developed countries to China has accelerated unprecedentedly, leading to rapid development of China's manufacturing industry. The large-scale entry of foreign capital has significantly promoted the modernization of China's domestic manufacturing industry. Driven by strong demand, China's automotive, aerospace, shipbuilding, and general machinery industries have increased the scale and speed of importing foreign technology and equipment. my country's traditional machine tool technology and equipment can no longer meet the new demands of modern manufacturing for "high quality, high efficiency, energy saving, low consumption, and environmental protection." The rapid development of my country's manufacturing industry and the relative backwardness of its cutting technology have made cutting technology a bottleneck for the rapid development of my country's machinery manufacturing industry. Therefore, it is necessary to analyze the current situation and propose corresponding countermeasures to adapt to the new circumstances. High-speed machining (HSM) is a rapidly developing new technology in today's manufacturing industry. In industrialized countries, high-speed cutting is becoming a new cutting concept. It was first proposed in 1931 by the German physicist Salomon. After the 1960s, the American scientific and industrial communities conducted extensive research on the mechanism and application of high-speed machining. After entering the practical application stage in the 1980s, high-speed machining was popularized and applied in developed Western countries such as the United States, Germany, and Japan, rapidly ushering in the era of high-speed machining. In recent years, high-speed machining has also received a response in China's manufacturing industry and has been increasingly favored and valued by domestic enterprises. High-speed machining (HSC) is a subsystem within a high-speed machining system. It refers to cutting speeds (movement speeds) of the cutting edge relative to the workpiece surface that exceed those of conventional cutting by 5 to 10 times, primarily manifested in the rapid traverse, working, and rapid retraction phases. Its advantages include: during high-speed machining, the shear slip velocity of the machined ductile metal material reaches or exceeds a certain threshold, approaching optimal removal conditions. This results in significantly better performance in terms of energy consumption, cutting force, workpiece surface temperature, tool wear, and surface finish compared to traditional cutting speeds, while also significantly increasing machining efficiency. Its basic characteristics include high cutting speeds (5 to 10 times that of conventional cutting speeds), high feed rates (40–180 m/min), and large acceleration/deceleration rates (1–2 g). High-speed machining (HSC) technology will become a crucial means to improve production efficiency, machining quality, machining accuracy, shorten production cycles, and reduce machining costs, laying a solid foundation for product market share. The fundamental premise of high-speed machining is that high-speed, low-load cutting can remove material faster than low-speed, high-load cutting. Low-load cutting means reduced cutting forces, thereby reducing vibration and deformation during the cutting process. With appropriate tools, high-hardness, difficult-to-machine materials can be cut at high speeds. Simultaneously, high-speed cutting allows most of the cutting heat to be carried away by the chips, reducing thermal deformation of the part. High-speed machining has significant advantages over conventional cutting: machining time can be reduced by approximately 60%; feed rate is increased by 5–10 times; material removal rate is increased by 3–5 times; tool life is increased by 70%; cutting forces are reduced by approximately 30%; surface roughness can reach Ra = 8–101 μm; and because 90% of the cutting heat is carried away by the chips, workpiece temperature rise is low, resulting in minimal thermal deformation and expansion. These advantages can only be achieved with a suitable machining strategy. An inappropriate strategy can, at best, shorten tool life, and at worst, lead to more serious consequences. High-speed machining is not simply about using existing toolpaths and increasing spindle speed and feed rate. Therefore, although high-speed machining has been studied for many years and has been applied in industries such as automobiles, aerospace, and shipbuilding, there are still many problems to be solved, such as the dynamic and thermal characteristics of high-speed machine tools; the problems of tool materials, geometry and durability; the interface technology between machine tools and tools (dynamic balance of tools, torque transmission); the selection of coolant and lubricant; the problem of post-processing of CAD/CAM programs; the problem of tool trajectory optimization during high-speed machining; and the problem of safety. 3 Key technologies that need to be solved to realize high-speed CNC machining The core content of the research required to realize high-speed CNC cutting machining includes high-speed cutting machining theory, high-speed spindle unit, high-speed feed system, high-speed CNC system, high-performance tool system, machine tool support technology drive system and auxiliary unit technology. 3.1 High-speed cutting mechanism The high-speed cutting mechanism is the theoretical basis for the application and development of high-speed cutting technology. It plays a guiding role in the application of high-speed cutting technology and occupies a very important position. At present, there are three theories of high-speed cutting machining mechanism: (1) Dr. Salomon theory. In 1929, German cutting physicist Dr. Carl Salomon began conducting ultra-high-speed simulation experiments and published his famous ultra-high-speed cutting theory in 1931, proposing the high-speed cutting hypothesis and applying for a patent in Germany. This hypothesis states that within the conventional cutting speed range, the cutting temperature increases with increasing cutting speed. For different workpiece materials, there exists a speed range; when the cutting speed exceeds this range, the cutting force decreases significantly with increasing cutting speed, and the cutting temperature also decreases. According to this hypothesis, cutting in a high-speed range with a certain speed will result in lower cutting temperatures and lower cutting forces. This not only makes it possible to perform ultra-high-speed cutting with existing tools, significantly shortening cutting time and multiplying machine tool productivity, but also brings a series of excellent characteristics to the cutting process. The hypothesis is that after entering the "dead valley" zone, the cutting temperature is too high and no tool can withstand it, so cutting cannot be carried out. The hypothesis is shown in Figure 1. In the conventional cutting speed range A, the cutting temperature increases with the increase of the cutting speed. When the cutting speed exceeds B and enters the high-speed C zone, the cutting temperature decreases with the increase of the cutting speed, which can significantly shorten the cutting time and improve the machine tool productivity. Figure 1 Relationship between tool temperature and speed during cutting (2) Later scholars questioned Salomon's theory based on the results of high-speed cutting experiments. They believed that when cutting cast iron, steel and difficult-to-machine materials at high speed, there is no dead valley like B even in a very high cutting speed range, and the tool durability always decreases with the increase of the cutting speed. (3) In the mid-1970s, Robert I. King and McDonald J., scientists from Lockheed Missiles and Space Corporation in the United States, began to verify and develop Vauglan's research conclusions. They proposed a relatively complete and reliable high-speed cutting mechanism, which theoretically proved the feasibility and superiority of high-speed cutting. Their research focuses primarily on chip formation theory, metal fracture, abrupt slip, adiabatic shear, and chip formation in various materials. A series of cutting experiments show that compared to conventional cutting, high-speed machining can reduce cutting forces by about 30% and improve tool durability by about 70%, but there is currently no mature high-speed cutting theory to explain these experimental results. Research on the basic methods and theories of high-speed cutting in my country started relatively late and is at a lower level. Currently, Nanjing University of Aeronautics and Astronautics has derived the cutting equation under concentrated shear slip conditions in high-speed cutting, establishing a theoretical foundation for further development of high-speed cutting technology; Shandong University mainly explored the selection of cutting parameters and surface quality control in high-speed cutting; Harbin Institute of Technology and Harbin University of Science and Technology, among others, studied tool wear in high-speed cutting. Research on cutting forces, cutting heat, chip formation mechanisms, tool wear, and surface quality in high-speed cutting can provide theoretical guidance for the development of high-speed machine tools and high-speed machining tools, as well as for the reform of processes and testing technologies. Domestic scholars mainly conduct research on localized theories, without truly applying them to actual production. Most high-speed CNC machine tools in China are imported, with almost no market for domestically produced machine tools. To break through the bottleneck of rapid industrial development and lagging cutting technology, the domestic manufacturing industry must do the following: (1) further improve the high-speed cutting mechanism; (2) conduct high-speed cutting experiments and establish a complete high-speed cutting database and process parameter expert system; (3) develop corresponding virtual simulation software for high-speed cutting processes based on the database and computer technology in (2). 3.2 High-speed spindle unit Traditional machine tools transmit power from the motor to the spindle through intermediate links such as gears and belts, thereby controlling the movement of the machine tool spindle. Since the accuracy of traditional spindle movement is affected by many factors, especially at high speed, it cannot achieve the required accuracy and can no longer meet the requirements of high-speed machining. The spindle components of high-speed machining tools require bearings that are resistant to high temperature, high speed, and can withstand large loads. At the same time, the spindle has good dynamic balance performance, good thermal stability, can transmit sufficient torque and power and can withstand high centrifugal force. The spindle should have good rigidity, constant torque and be equipped with overheat detection and cooling devices. Therefore, CNC machine tool electric spindles with corresponding high speed and high precision, high speed precision and high efficiency characteristics have emerged. The high-speed electric spindle is designed by directly integrating the stator and rotor of the spindle motor into the spindle assembly. This means placing the high-speed motor inside the precision spindle; the motor rotor is the spindle itself, and the spindle housing serves as the motor base. This achieves integrated operation of the variable frequency speed control motor and spindle, with the motor directly driving the spindle. The electric spindle eliminates intermediate transmission links, resulting in a zero transmission chain and achieving true "zero transmission" in the machine tool spindle system, avoiding the impact of intermediate links on accuracy. An electric spindle is a complete assembly, including the spindle itself and its corresponding components: the electric spindle, high-frequency inverter, oil mist lubricator, cooling system, built-in encoder, tool changer, etc. Achieving high speed in an electric spindle primarily addresses bearing heat and vibration from a mechanical perspective; stator and rotor power density and winding heat from a motor design perspective; and speed regulation performance from a drive and control perspective. To address the above three issues, the following measures can be taken: (1) High-speed and high-rigidity bearings are widely used on high-speed precision spindles, such as ceramic bearings and liquid hydrostatic bearings in general, and air-lubricated bearings and magnetic levitation bearings in special cases; the bearings are lubricated by timed and quantitative oil-air lubrication instead of grease lubrication. (2) The spindle motor mainly adopts vector-controlled AC asynchronous motors. (3) The built-in high-speed motor of the electric spindle is driven by a high-frequency inverter to achieve speeds of tens of thousands or even hundreds of thousands of revolutions per minute, and the output frequency of the inverter even reaches several thousand Hz. 3.3 High-speed drive system The drive system to date consists of a rotary motor, gearbox or coupling, lead screw and drive nut, lead screw support bearing, etc., which all affect or even limit the performance of the machine tool. For example, electric motors have a maximum speed limit; as speed increases, the output torque decreases. Under high acceleration, the motor shaft can twist, deform, or even develop positional errors. Gearboxes increase system inertia and create backlash. If the motor is directly connected to the lead screw, it will cause twisting deformation, backlash, and hysteresis. The lead screw itself is affected by critical speed, backlash, twisting, pitch error, friction, etc., and its vibration decay time is very long. Linear motors, on the other hand, straighten and unfold the primary winding of a traditional cylindrical motor, transforming the closed magnetic field of the primary into an open magnetic field. The stator of a rotating motor becomes the primary of a linear motor, and the rotor becomes the secondary. When three-phase symmetrical sinusoidal currents are passed through the three-phase windings, an air gap magnetic field is generated between the primary and secondary windings. The distribution of this air gap magnetic field is similar to that of a rotating motor, exhibiting a sinusoidal distribution along the unfolded straight line. As the three-phase currents change over time, the air gap magnetic field moves linearly according to a directional phase sequence; this air gap magnetic field becomes a traveling wave magnetic field. When the secondary is fixed, it can move linearly along the direction of the traveling wave magnetic field, thus realizing the feed mode of linear motor drive for high-speed machine tools. The primary and secondary of the linear motor are installed on the worktable and bed of the high-speed machine tool, respectively. Since the transmission chain of this feed transmission mode is shortened to 0, it is called the "zero transmission" of the machine tool feed system. Compared with the "rotary servo motor + ball screw" transmission mode, the direct drive of the linear motor has the following advantages: (1) High speed, the current maximum feed speed can reach 100~200m/min; (2) High acceleration, up to 2~10g (g=9.8m/s); (3) High positioning accuracy. Since only closed-loop control can be used, its theoretical positioning accuracy can be 0. However, due to the installation and measurement errors of the detection element, the actual positioning accuracy cannot be 0. The highest positioning accuracy can reach 0.1~0.01m; (4) Unrestricted stroke. Since the secondary (stator) of the linear motor can be laid on the machine tool bed in sections, no matter how far, it will not affect the rigidity of the system. A linear motor feed system is a drive device that directly converts electrical energy into linear motion mechanical energy without any intermediate transmission links. Its application transforms traditional rotary motion into linear motion, thus completely improving the speed, acceleration, stiffness, and dynamic performance of machine tools. By employing digital control technology, linear motors can utilize high gain to improve control effectiveness, reducing servo lag in high-speed movement and achieving high positioning accuracy. This effectively overcomes the shortcomings of traditional rotary motor drives, such as long transmission chains, large size, low efficiency, high energy consumption, and poor precision. 3.4 High-Performance Tool Systems In high-speed cutting, failure modes vary significantly depending on the machining conditions and workpiece material. These include tool tip breakage, simultaneous wear of the rake and flank faces, and tool shank breakage, among others. Furthermore, different tool combinations with different workpiece materials produce different effects. Selecting appropriate high-speed cutting tools to extend tool life and maximize tool performance is a crucial technology for high-speed cutting applications. To adapt to high-speed cutting, tool materials must have good wear resistance and stable cutting performance under dry cutting high-temperature conditions. Currently, the main materials for high-speed cutting tools include coated cemented carbide, metal-based ceramics, alumina-based ceramics, silicon nitride-based ceramics, polycrystalline diamond, and polycrystalline cubic boron nitride. In the machine tool spindle-chuck-tool system, the asymmetrical shape of the tool and the fixture, the connection gap of the system components and the inaccuracy of clamping, the circular runout and wear of the spindle, the offset of the tie rod-disc spring in the spindle tool clamping mechanism, and the influence of the cooling lubricant can all cause imbalance in the tool system. During high-speed machining, even a small imbalance of the tool can generate a large centrifugal force, which seriously affects the normal operation of the spindle. In response to this situation, the following measures should be taken: (1) Establish dynamic balancing standards. Currently, the international standard ISO 1940 specifies the technical indicators for dynamic balancing. Each manufacturer can specify the corresponding dynamic balancing standards for its products according to the international standard and the actual situation of the factory. (2) Perform dynamic balancing on the tool system, and perform dynamic balancing on the tool, the chuck and the spindle. (3) Perform a dynamic balancing on the chuck and the tool as a whole. (4) When the tool system is clamped onto the spindle, clamping errors will occur. For high-speed machining, an automatic balancing system should be used to achieve online dynamic balancing. The TABS (Dynamic Dynamic Balancing Automatic Adjustment System) developed by Kennametal in the United States can be installed on the machine tool. When the tool is rotating dynamically at high speed, it can achieve fully automatic dynamic balancing adjustment of the tool within 2 seconds, effectively solving the problem of rapid dynamic balancing adjustment of the tool system in high-speed machining. 3.5 High-speed CNC system A numerical control system (digital control system) refers to a system in which software and hardware modules are organically integrated to realize the functions related to numerical control technology. It is the carrier of numerical control technology. The information in the digital control system is digital quantity, which is relative to analog control. With the development of computer technology, the numerical control system has evolved from the initial hard-wired numerical control system composed of digital logic circuits to the computer numerical control (CNC) system with the computer as the core. Compared with the hard-wired numerical control system, the control function of the CNC system is mainly implemented by software and can handle complex information that is difficult for logic circuits to handle, thus having higher flexibility and higher performance. The most basic requirements for CNC in high-speed machining are: processing NC data at a sufficiently high speed and generating impact-free theoretical values ​​for acceleration and deceleration of each feed axis. High-speed machining CNC functional modules, compared to ordinary CNC, extend this with post-processors, offline preprocessing functions, and spline decoding capabilities. The core technologies of high-speed machining CNC are real-time spline interpolation and impact-free accelerators. Splines should not be linearized; direct interpolation should be used to avoid reducing accuracy. The machine tool feed drive system must have high dynamic performance, generating impact-free theoretical values—ramp functions—for acceleration and deceleration of the machine tool feed axes. That is, the acceleration-time curve of the machine tool feed axis must not have abrupt jumps; only in this way can the high accuracy and sufficiently high feed rate of high-speed machining be guaranteed. CNC machining instructions encompass all technological processes. An excellent high-speed machining CAM programming system should have high calculation speed, strong interpolation capabilities, automatic tool holder and fixture interference checks, feed rate optimization functions, machining trajectory monitoring functions, tool path optimization functions, and machining residue analysis functions, etc. High-speed cutting programming must first ensure the safety and effectiveness of the machining method; secondly, it must strive to ensure a smooth and stable tool path, as this directly affects machining quality and the lifespan of machine tool components such as the spindle; finally, it must aim for uniform tool load, as this directly impacts tool life. Ordinary NC programs have low information content and require preprocessing offline before execution. Preprocessing includes converting ASCII to binary format, syntax checking and operator interaction, decomposing fixed loops and subroutines, and performing parameter and formula calculations. Programming is primarily based on the ISO 6983 standard, but ISO 6983 does not support high-speed cutting in five-axis milling and curve machining. Current CNC software uses ISO 6983 (G, M codes) as the standard. For high-speed machining (HSM), programming can only be done on the basis of the original CNC, focusing on the tool center path, resulting in large program sizes. For different high-speed machining centers, dedicated post-processors are also required. STEP-NC (ISO 14649) is an extension of the STEP standard developed by the International Organization for Standardization (ISO) to define data for numerical control (NC) equipment. It adopts the EXPRESS language and feature-oriented programming principles, extending the STEP standard for product model data exchange to the CNC field, redefining the interface between CAD/CAM and CNC, and forming a new international standard for NC programming data interface (ISO 14649). STEP-NC can significantly reduce the machining time of traditional CAD/CAM systems, eliminate the need for post-processors in the manufacturing process, and support faster, safer, and more intelligent machining equipment in the future. 3.6 High-Speed ​​Machine Tool Support System The dynamic characteristics of the machine tool are crucial during high-speed machining. The basis for achieving high dynamic performance is that each component of the machine tool should have optimal damping characteristics, and the entire system should have high stability. These characteristics can be achieved through structural optimization design and selection of suitable machine tool materials, such as using a highly stable gantry structure and an optimized high-rigidity bed. Most manufacturers of high-dynamic-performance machine tools use concrete as the material for various non-moving structural components, such as the machine bed and crossbeam. The impact forces generated by the movement of high-dynamic machine tool components are completely absorbed by the concrete bed. In contrast, cast iron has an advantage in compressive and tensile strength when manufacturing moving components such as the spindle box. Cast iron can be used to manufacture lighter components with excellent strength and stability. High-speed machining also requires the machine tool to have good acceleration and deceleration capabilities, i.e., it is necessary to maintain reasonable acceleration and jerk control. The feed rate may change constantly during high-speed machining, resulting in varying acceleration and deceleration, i.e., jerk, and mechanical shock and vibration. Therefore, it is necessary to control excessive acceleration and deceleration changes. If the acceleration is too large (abrupt), acceleration can be achieved in a short time, but at the same time, it will cause machine tool vibration, resulting in striations on the machined surface and reducing surface quality. If the acceleration is too small, high surface quality can be achieved, but it is difficult to achieve rapid acceleration. Therefore, reasonable machine tool acceleration and deceleration are very important to ensure high-quality surface machining at high speeds. 3.7 Auxiliary Unit Technology High-speed cutting processes generate a large amount of high-temperature hot chips, which must be removed from the worktable promptly to prevent thermal deformation of the machine tool, cutting tools, and workpiece. High-pressure, high-flow-rate cutting fluid not only cools the machining area of ​​the machine tool but is also an effective method for chip removal. Currently, many machine tools are equipped with high-pressure coolant pumps necessary for high-speed machining. Research on high-speed cutting mechanisms shows that the high temperature in the basic shear zone helps accelerate plastic deformation and chip formation. While the extensive use of coolant under high-speed cutting conditions can significantly improve tool durability, it greatly reduces the plastic flow rate of the workpiece, thus lowering overall production efficiency. Appropriate selection of cooling and lubrication methods is a prerequisite for ensuring machining quality. For the most demanding spindle bearings, lubrication methods include grease lubrication, oil bath lubrication, spray lubrication, and oil-air lubrication. A new type of gas bearing also employs forced air supply lubrication. Adopting a forced-air cutting method fundamentally improves the cutting environment, saving direct investment in cutting fluid and costs associated with waste fluid treatment and environmental protection. In high-speed machining, dry cutting technology is essential for protecting the environment and personal safety, reducing production costs, improving productivity, and ensuring machining quality. Therefore, it is necessary to develop more energy-efficient machine tools and more practical dry cutting technologies. For example, using low-temperature gas cooling can reduce the temperature rise of the workpiece, tool, and machine tool, while equipping the machine with a suction system for dust prevention and chip removal ensures a clean machining area. In some machining processes, pure dry cutting is difficult to achieve; therefore, minimal lubrication techniques, also known as quasi-dry cutting, can be used. Dry cutting techniques that utilize localized heating of the machined surface (such as laser heating or conductive heating) can also be employed to improve material machinability, reduce cutting forces, and facilitate dry cutting. 4. Conclusion Since the 1980s, the development of electronic technology, information technology, network technology, and fuzzy control technology has greatly improved the level of next-generation CNC systems, promoting the vigorous development of the CNC machine tool industry. Meanwhile, high-speed machining technology has gradually evolved from being based on traditional metal (non-metal) cutting techniques, automatic control technology, information technology, and modern management technology into a comprehensive systems engineering technology. CNC machine tools have made significant progress in terms of high speed, high precision, high reliability, and multi-functionality, networking, intelligence, flexibility, and greenness. Modern manufacturing has ushered in a new technological revolution, and CNC high-speed machining technology will lead the rapid development of the manufacturing industry.