Analysis of High Speed ​​Cutting (HSC) Technology

First, the original definition of high-speed cutting

In 1931, the German cutting physicist Dr. Carl S. J. Salomon made the hypothesis that he applied the Solomon principle of the German with high cutting speeds in the same year: the material being processed has a critical cutting speed. V0, before the cutting speed reaches the critical speed, the cutting temperature and tool wear increase as the cutting speed increases. When the cutting speed reaches 5 to 6 times the normal cutting speed, the cutting edge temperature starts to increase with the cutting speed. However, the tool wear decreases as the cutting speed increases. When cutting plastic materials, the traditional processing method is “heavy cutting”, and the amount of chips to be cut by each knife is large, that is, the knife is large, but the feed speed is low and the cutting force is large. Practice has shown that as the cutting speed increases, the chip morphology evolves from strips, flakes, and crumbs. The required unit cutting force increases at an early stage and then drops sharply. This shows that high-speed cutting is faster than conventional cutting. The mechanism is also different.

Second, the concept of modern high-speed cutting technology


The starting point of the Solomon principle is the use of conventional tools for high-speed cutting, which increases productivity. So far, the principle is still not confirmed by modern scientific research. But the success of this principle should not be limited to this. High-speed cutting technology is one of the important development directions of cutting technology. From the perspective of modern science and technology to define high-speed cutting exactly, there is currently no agreement because it is a relative concept, different processing methods, and different cutting materials have different High speed cutting speed and processing parameters. This includes high-speed soft cutting, high-speed hard cutting, high-speed wet cutting, and high-speed dry cutting.

In fact, high-speed cutting technology is a very large and complex system engineering. It covers the research and selection of machine tool materials, machine structure design and manufacturing technology, high-performance CNC control systems, communication systems, high-speed, high-efficiency cooling, and high precision. High-power spindle system, high-precision rapid feed system, high-performance tool clamping system, high-performance tool materials, tool structure design and manufacturing technology, high-efficiency and high-precision test measurement technology, high-speed cutting mechanism, high-speed cutting technology, suitable for high-speed machining The programming software, programming strategies, and many other related hardware and software technologies. Only on the basis of the full development of these technologies, the established high-speed cutting technology has real significance. Therefore, to realize the superior performance of high-speed cutting, it must be a perfect combination of CAD/CAM systems, CNC control systems, data communications, machine tools, tools, and processes.

Third, the development status and advantages of high-speed cutting technology


Since the patent application of Solomon's principle, the development of high-speed cutting technology has undergone theoretical exploration, application exploration, preliminary application and mature application. In particular, after the 1970s, various industrialized countries have invested large amounts of manpower, material resources, and financial resources to research and develop high-speed cutting technologies and related technologies. The rapid development has taken place, and manufacturing powers such as Germany, the United States, Sweden, Switzerland, the United Kingdom, and Japan have stepped in. The world leader. In recent years, with the rapid advancement of science and technology and the strong promotion of economic development, the rapid progress of high-speed cutting machine tools, cutting tool technology and related technologies has enabled HSC (High Speed ​​Cutting) technology to be applied to spacecraft with high efficiency and high quality. In the industries such as aviation, automotive, tooling and machine tool industries, various cutting methods and materials are almost omnipotent, especially high-speed milling and high-speed turning. This technology is a "light cutting" method. Each blade has a small amount of cuttings and a small depth of cut, ie, ap and ae are small, but the cutting speed is large, which is 3 to 5 times that of the conventional one, and the feed rate is large, which is traditional. 5 to 10 times. Its advantages are:


Short processing time and high efficiency. High-speed cutting material removal rate is usually 3 to 5 times.

The cutting condition of the tool is good, the cutting force is small, and the bearing of the spindle, the tool, and the workpiece are all subject to forces. Because the cutting speed is high, the amount of knife is small, the shear deformation area is narrow, the deformation coefficient ξ is reduced, and the cutting force is reduced by about 30% to 90%. At the same time, due to the small cutting force, the knife is also small, improving the processing quality.

The tool and workpiece are less affected by heat. Most of the heat generated by cutting is taken away by high-speed chips, so the thermal deformation of workpieces and tools is small, and the machining accuracy is effectively improved.

The workpiece surface quality is good. First of all, ap and ae are small, the workpiece roughness is good, followed by a high cutting speed, the machine tool excitation frequency is much higher than the natural frequency of the process system, so the process system vibration is very small, very easy to obtain a good surface quality.

High-speed cutting tools have good thermal properties, and most of the cutting heat is carried away by the high-speed flow of chips, enabling high-speed dry cutting, eliminating the use of coolant, reducing environmental pollution, and enabling green processing.

It can complete the processing of high hardness materials and hardened steels with hardness up to HRC40-62. If cemented carbide tools with special coating (TiAlN) are used, high hardness materials and hardened steels can be processed under conditions of high speed, large feed, and small amount of cutting, which is not only efficient (EDM) 3 to 6 times, and get a very high surface quality (Ra0.4), basically without bench polishing.


Fourth, high-speed cutting system


High-speed cutting system consists of high-speed cutting CNC machine tools, high-performance tool clamping systems, high-speed cutting tools, high-speed cutting CAM system software and other components.


High-speed cutting CNC machine

(1) High-stability machine tool support parts Supporting parts such as the bed of high-speed cutting machine tools should have good dynamic and static stiffness, thermal stiffness, and optimal damping characteristics. Most machine tools use high-quality, high-rigidity and high-strength gray cast iron as the supporting component material. Some machine tool companies also add high damping polymer concrete to the base to increase their vibration resistance and thermal stability. Not only ensure the stability of the machine tool accuracy, but also prevent the chattering of the tool during cutting; The closed bed design, the overall casting bed, the symmetrical bed structure and the dense ribs, such as the bridge structure or gantry of Germany Deckel Maho Company The DMC series of high-speed vertical machining centers of the structure, the VMC series of vertical machining centers of Bridgeport Corporation of the United States, and the VS series of high-speed machining centers of Hitachi Seiki of Japan make the machine tools more stable in terms of static and dynamic stability. In the design process of some machine tool companies, modal analysis and finite element structure calculations are also used to optimize the structure and make the machine tool support components more stable and reliable.

(2) High-speed spindle system High-speed spindle is the most important key technology of high-speed cutting technology, and it is also the most important part of high-speed cutting machine tools. It requires high balance of dynamics, good rigidity, high rotary precision, good thermal stability, sufficient torque and power transmission, high centrifugal force resistance, accurate temperature measurement device and efficient cooling device. High-speed cutting generally requires spindle speed capability of not less than 40000 r/min and spindle power of more than 15 kW. Spindle motor integrated electric spindle components are usually used to achieve direct transmission without intermediate links. Induction motor integrated spindle motors are mostly used for motors. With the advancement of technology, a permanent magnet motor using a rare material crucible has recently been developed. The motor can be more efficient, transmit power with high power, and transmit torque. It is easy to control the temperature rise generated during use, and the cooling is simple. It does not need to install an expensive cooler. In addition, the motor has a small size and a compact structure, so it greatly replaces the induction type integrated spindle motor. The maximum spindle speed is limited by the performance of the spindle bearing. Increasing the dn value of the spindle is the key to increasing the spindle speed. At present, more commonly used are hot-pressed silicon nitride (Si3N4) ceramic bearings and hydrodynamic and hydrostatic bearings and air bearings. Lubrication mostly uses oil-air lubrication, jet lubrication and other technologies. In recent years there have also been the use of magnetic bearings with excellent performance. Spindle cooling generally uses the internal water cooling or air cooling of the spindle.

(3) High-precision rapid feed system High-speed cutting is a combination of high cutting speed, high feed rate, and small cutting amount, and the feed rate is 5 to 10 times that of the conventional one. This requires a high feed rate and good acceleration and deceleration characteristics of the machine's feed system. General requirements of rapid feed rate is not less than 60m/min, program editable feed rate is less than 40m/min, axial positive and negative acceleration is greater than 10m/s2 (1g). Most machine tool builders use small-lead, large-size, high-quality ball screws or large-lead multi-head screws with full-closed position servo control. With the development of motor technology, advanced linear motors have been introduced and successfully applied to CNC machine tools. The advanced linear motor drive eliminates the problems of mass inertia, advancement, hysteresis, and vibration in CNC machines, accelerating the servo response speed, and improving servo control accuracy and machining accuracy. Not only can the machine tool be processed at a feed rate higher than f = 60m/min at high speeds, but also with a fast moving speed of f=120m/min and an acceleration of 2g, which improves the machining accuracy of the parts. However, in the use of linear motors, there are problems such as low bearing capacity and heat, which need to be improved.

(4) Efficient cooling system High-speed cutting machine spindle, ball screw, guide rails, etc. generate a lot of heat, if not effective cooling, will seriously affect the accuracy of the machine. Most of them use powerful high-pressure and high-efficiency cooling systems, and use temperature-controlled circulating water or other media to cool the spindle motor, spindle bearings, ball screws, linear motors, and hydraulic oil tanks. Yamazen Co., Ltd. passes coolant with a pressure of 6.8 MPa through the center hole of the spindle to cool the machine tool spindle, tool, and workpiece. Japan Hitachi Seiki Co., Ltd. has developed a ball screw cooler for the purpose of stably processing the cooling screw by transferring the coolant in the hollow ball screw. In order to avoid the influence of the temperature rise of the guide rails, Hitachi and the bearing manufacturer jointly developed Eeo-Eeo's guide rail grease. The grease has good lubrication and cooling effects, no harmful substances, and can be automatically lubricated without special equipment. Hitachi Seiki Machine Tool Company VS series CNC high-speed milling uses this grease, which has good use and economic effect.

(5) High-performance CNC control system High-speed machining requires that the CNC control system has the ability to quickly process data to ensure high-speed interpolation accuracy. It is generally required that the program segment transfer rate is 1.6 to 20 ms, the RS232 serial data interface is 19.2 Kbit/s (20 ms), and the Ethernet data transmission is 200 Kbit/s (1.6 ms). The new generation of high-performance CNC control system uses 32-bit or 64-bit CPU, and the block processing time is as short as 1.6ms. In recent years, network technology has become the main communication method and control tool in CNC machine tool processing. It is believed that in the near future, an advanced network manufacturing system will be formed, and communication will be faster and more convenient. A large amount of processing information can be transmitted and exchanged in real time through the network, including design data, graphic files, process data, and processing status, which greatly increase productivity. However, the most used one is still to use the Internet to improve services, provide technical support to users, and so on. Cincinati Machine developed a network manufacturing system that allows users to purchase the required software, modems, network cameras, and headsets, so that they can surf the Internet without having to install a network server. Through the exchange of a variety of information online, productivity has improved. The open CNC system of the universal user interface developed by Hitachi Seiki Machine Tool Co., Ltd. can connect the machine tool CNC operating system software to the Internet and exchange information.

(6) High-security machine tool safety door covers High-speed cutting machine tools generally adopt full-closed safety door covers, observation windows made of high-strength transparent materials, and other comprehensive security measures to ensure the safety of machine operators and on-site personnel around machine tools. Avoid damage to related facilities such as machine tools, tools and workpieces. Some machine tool companies have also developed machine tool intelligent identification functions in the CNC system to identify and avoid conditions that may cause major accidents and ensure product yield and quality.

(7) High-precision, high-speed sensing technology This includes technologies such as position detection, tool status detection, workpiece status detection, and machine condition monitoring.

High-performance tool

Clamping system The high-speed Milling Machine's tool clamping system requires a very high balance of dynamics. The spindle is required to have a balancing ability above 30000 r/min and absolute centering. Spindles, tool holders, and cutters should have extremely high concentricity when they are rotated, so that high-speed, high-precision machining can be guaranteed. Otherwise, the higher the speed, the greater the centrifugal force. When it reaches the critical state of the system, the tool system will be excited. As a result, the machining quality will be reduced, the tool life will be shortened, and the spindle bearing will be accelerated. In severe cases, the tool and the spindle will be damaged. The shank system and the spindle taper hole should be combined tightly. Now the tool shank generally adopts the double positioning taper shank with which the taper part and the spindle end face contact simultaneously. Such as Japan's BBT holder, Germany's HSK hollow holder. The tool holding device generally uses a spring chuck that has been balanced by a dynamic balance. However, there is now a hydraulic vacuum blade with a better effect, and a strong milling head is used.

High-speed cutting tool

Tool technology and machine tool manufacturing have been mutually reinforcing from the very beginning. It is no exaggeration to say that high-speed cutting technology has only been promoted by the continuous development of tool technology and machine tool technology. High-speed cutting tools should have good mechanical properties and thermal stability, that is, have good impact resistance, wear resistance and thermal fatigue resistance. The tool material used is mainly cemented carbide and tool coating technology is commonly used. The coating materials are titanium nitride (TiN), titanium aluminum nitride (TiALN), and the like. The coating technology has evolved from a single coating to a multilayer, multiple coating material coating. This technology has become one of the key technologies for improving high-speed cutting capabilities. The world's major cemented carbide cutting tool manufacturers generally invest 3-11% of their sales revenue in research and development, a considerable part of which is used for basic research of cemented carbide and coating materials. For high-speed cutting of steel materials, P-type hard alloys, coated cemented carbides, cubic boron nitride (CBN), and CBN composite tool materials (WBN) with high thermal and fatigue strengths should be used as tool materials. For cutting cast iron, fine-grained K-type hard alloys should be used for roughing, and composite silicon nitride ceramics or polycrystalline cubic boron nitride (PCNB) composite tools should be used for finishing. For precision machining of non-ferrous or non-metallic materials, polycrystalline diamond PCD or CVD diamond-coated tools should be used. When selecting the cutting parameters, the concept of effective diameter should be taken into consideration for round inserts and ball end mills. High-speed milling tools should be designed and manufactured according to dynamic balance. The rake angle of the tool is smaller than that of the conventional tool, and the back angle is slightly larger. The major and minor cutting edge connections should be rounded or chamfered to increase the tool nose angle to prevent thermal wear at the tool tip. The cutting edge length and tool material volume near the tool tip should be increased to increase the tool rigidity. The tool material and the material to be cut should have a small chemical affinity. Most high-speed milling uses carbide tools. Under the condition of ensuring safety and meeting the processing requirements, the tool overhang is as short as possible and the center of the cutter body is better in toughness. The shank is thicker than the tool diameter and the connecting shank has an inverted taper to increase its rigidity. As far as possible, coolant holes are left in the center of the tool and tool system. The ball end mill must consider the effective cutting length. The cutting edge should be as short as possible. The two spiral groove ball end mills are usually used for rough milling of complex surfaces, and the four spiral groove ball end mills are usually used for fine milling of complex surfaces.

High-speed cutting mechanism

The research on the mechanism of high-speed cutting is, in general, still in the process of exploration and application. The mechanism of high-speed cutting mainly includes cutting force in high-speed cutting, the law of cutting heat change, the law of tool wear, the forming mechanism of chips, and the influence of these laws and mechanisms on machining. At present, the research and application of the high-speed cutting mechanism of aluminum alloy are relatively successful, but the research and application of the high-speed cutting mechanism of black metal and difficult-to-machine materials are still under continuous exploration. The application is also under the guidance of immature theory. In addition, the research and application of high-speed cutting mechanisms have entered the cutting methods such as drilling hinges and tapping, but they are still in the exploration stage. With the development of science and technology, more in-depth analysis and research will be made on the cutting force, cutting heat, chip formation, tool wear, tool life, machining accuracy, and surface quality of high-speed cutting.

High-speed cutting CAM system software

High-speed cutting has special technological requirements than traditional cutting. In addition to high-speed cutting machines and high-speed cutting tools, it is also crucial to have suitable CAM programming software. An excellent high-speed machining CAM programming system should have a high calculation speed, a strong interpolation function, automatic over-cut inspection and processing capabilities, automatic tool holder and fixture interference check, bypass function, feedrate optimization processing functions , To be processed track monitoring function, tool path editing optimization function, processing residual analysis function and so on. CNC programming can be divided into geometric design (CAD) and process planning (CAM). When using the CAM system for high-speed CNC programming, in addition to the tool and processing parameters selected according to the specific circumstances, the choice of processing methods and programming strategies used become The key. An excellent programming engineer using CAD/CAM workstations should also be a qualified designer and technologist. He should have a correct understanding of the geometry of the part and have the knowledge and concepts of ideal process planning and reasonable tool path design. . First of all, we must pay attention to the safety and effectiveness of processing methods; Second, we must do everything possible to ensure a smooth and stable tool path, which will directly affect the machining quality and the life of the machine tool spindle and other parts; Finally, we should try to make the tool load uniform, which will directly affect the tool Life expectancy.

In addition, not all of the numerous CAD/CAM softwares at home and abroad are suitable for high-speed cutting CNC programming. Among them, mature programs suitable for high-speed machining include: DelCAM's PowerMill software module from UK, Japan's Makino's FFCUT software (its FF processing module is integrated into UGS' CAM software), Israel's Cimatron software, and US PTC. The company's Pro/ENGINEER software, CAXA-ME software, etc.


Fifth, the application of high-speed cutting technology


At present, high-speed cutting technology is mainly used in the automotive industry and mold industry, especially in the field of machining complex surfaces, and the workpiece itself or the processing field where the tool system requires a high rigidity shows a powerful function. Its high efficiency and high quality are respected by people. The research and application of domestic high-speed machining technology began in the 1990s and was applied to the mold, aerospace, aerospace and automotive industries. However, high-speed cutting CNC machines, high-speed cutting tools and CAD/CAM software are mainly imported. With the vigorous development of China's socialist market economy, the mold industry, which is an important foundation for manufacturing, has developed rapidly. This provides a broad space for the application and development of high-speed milling technology. The high-speed milling technology has a short processing time and high product accuracy, and can obtain a very smooth machining surface, can efficiently process high hardness materials and hardened steel, and avoid electrode manufacturing and time-consuming electrical processing (EDM) time, greatly reducing The fitter's grinding and polishing amount. At the same time, the white hard layer on the die surface disappeared due to electrical processing (EDM), and the distortion disappeared, which increased the life of the die and reduced the rework. Because the manufacturing work of the electrode is not required, the mold modification only needs to pass CAD/CAM to speed up the modification. Some thin-walled mold parts that are increasingly needed in the market, high-speed milling can be completed quickly and well. And at the high-speed milling CNC Machining center, the multi-step machining can be completed by one clamping of the mold. These advantages are very suitable for today's fast-turning funds, urgent delivery times, and fierce product competition. Therefore, high-speed milling has been rapidly and widely promoted. In turn, this has promoted the development of high-speed milling technology.

Sixth, concluding remarks


High-speed cutting technology is one of the major development directions of cutting processing technology. It will move to a higher level with the development of basic technologies such as CNC technology, microelectronic technology, new materials, and new structures. However, we should also be clear-headed that high-speed cutting technology has its own problems that need to be solved, such as the cutting mechanism of high-hardness materials, the damage of cutting tools during load changes, the establishment of a high-speed cutting database, and the development of high-speed cutting. Processing status monitoring technology and green manufacturing technology and so on. At the same time high-speed cutting used CNC machine tools, vehicles, milling, drilling and other tools, CAD / CAM software and other high-tech, expensive, high-speed cutting investment, which to a certain extent, restricting the popularization and application of high-speed cutting technology.

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