Efficient and high-speed machining is the main theme of the current mechanical manufacturing field

Improving productivity is an eternal topic in the field of machinery manufacturing, and it is also a general concern in the field of machinery manufacturing. High-speed machining is currently an important means to obtain high productivity. The key is to create conditions and quickly popularize.
    The characteristics of the current development in the field of machinery manufacturing are: the large number of difficult-to-cut materials has significantly increased the difficulty of processing; many issues that need to be solved urgently during processing, such as hard cutting; in order to protect the environment, it is required to use less or no cutting oil. That is, dry cutting or semi-dry cutting is realized. In short, machinery manufacturing faces many difficulties. Under such circumstances, in order to increase productivity, all relevant technological advances must be comprehensively utilized. Especially in the aerospace industry system, due to the characteristics of many difficult-to-process materials, complex structure, short development cycle, and many single-piece and small-batch products, how to improve productivity and shorten the production cycle has always been an important issue for scientific and technological personnel for a long time. Problems that the system must resolve.
    On the other hand, with the rapid development of science and technology, how to transplant new technologies and processes is very urgent. It is worth noting that in today's world, the rapid development of science and technology has greatly promoted the rapid development of all aspects of machinery manufacturing, and various methods and means to increase productivity have emerged. As we all know, the grinding of single crystal natural diamond tools is very difficult. Generally, high-phosphorus cast iron grinding discs and diamond powder are used as abrasives, which is extremely inefficient.
    Recently, it was reported in Japan that stainless steel 304 (Japanese brand) with low carbon content and low thermal conductivity was used to make discs. The diamond was pressed on a 4000r/min turntable and the temperature was controlled at 800℃. The diamond removal rate was extremely high. , Up to 0.94mm3/min, do not use abrasives when working, but use physical and chemical effects, which is called thermochemical processing, which is a break from the conventional method; another example is the recent rapid prototyping (RP), which can be used without a mold The cutting speed of wire EDM can reach 70mm2/min on domestic fast-moving wire machine tools, and the machine tool of AGIE company in Switzerland can reach 500mm2/min, while that of Mitsubishi Electric The machine tool can reach 550mm2/min, reaching the general milling speed. The current high-speed grinding speed has reached 60, 120m/s, or even 200m/s, and it has reached 500m/s in the laboratory, while the general grinding speed Only 30～35m/s. High-speed grinding is a high-efficiency grinding method, with shallow depth of cut and high cutting speed; another creep grinding is just the opposite of high-speed grinding, with large cutting depth and low cutting speed, but both are efficient grinding, only cutting consumption Different, so some people liken it vividly as the "tortoise and the hare", each has its own strengths. In 1931, German Carl Salomon put forward a famous prediction: the general cutting speed and cutting heat increase simultaneously, but after a dead valley that cannot be cut, even if the cutting speed increases, the cutting heat will decrease. Today, the cutting heat will decrease. The cutting speed has reached 5000m/min, and Carl Salomon's prediction will be revealed.
    In summary, increasing the cutting speed is an important means to increase productivity. Of course, this is not all, it has yet to be developed. Because high-speed machining is mainly embodied in milling, the following will focus on machining centers.

    The development of machine tools is a prerequisite for efficient and high-speed machining

    Due to the rapid development of machine tool manufacturing technology, huge changes are brewing in the field of machinery manufacturing. The CNC machine tool has developed into a multi-axis machining center, which integrates various processes into one, which significantly shortens the auxiliary time and improves the productivity. At the same time, it reduces the number of workpiece clamping times and improves the processing accuracy. To sum up, the current development goals of machine tools should be: reduce the replacement of processes and significantly improve efficiency; tend to be intensive and easy to improve accuracy; use advanced tools such as composite cutters and ball end mills to increase the cost per unit of time. Cutting capacity; faster cutting speed, improved cutting efficiency; can reduce the polishing process after milling; automatic exchange of cutting tools and pallets, with high automation, and significantly shortened auxiliary time; because complex parts are easy to process, it promotes the improvement of part structure Wait. From the perspective of aerospace, it is generally believed that this development of machine tools is very suitable for single-piece and small-batch production. Therefore, these equipments have been enriched in single-piece and small-batch production systems quickly and more. Practice also shows that automation is The equipment meets the needs of the development of aerospace system manufacturing technology.
    Of course, from the perspective of improving productivity, in addition to automated processing, there is still the problem of how to make further and more reasonable use of various technological advances. Observed from the development of machine tools, the high speed of machine tool spindles has significantly increased the speed. Machine tools higher than 10000r/min have become more common. The advancement of bearing technology provides the possibility for this. The most prominent of the development of the spindle is that the electric spindle has been commercialized. The lubrication technology of the main shaft is very critical and has received attention from all quarters. Over the years, it has developed from grease lubrication to oil mist lubrication, oil-air lubrication, under-race lubrication, and even cold air lubrication. With the development of high-speed spindles, grease lubrication can no longer be adapted, and the use of oil mist lubrication is also decreasing due to pollution. Now the most widely used is oil-air lubrication, and more reasonable is under-ring lubrication, which makes the key inner ring better. Good lubrication. The improvement of lubrication performance enables the ball bearing to withstand the high speed of 70,000r/min. The United States originally used ABEC7 high-precision bearings on machine tool spindles, and now it has developed to ABEC9, indicating that the accuracy of the bearings is necessary. Due to the development of materials, ceramic balls have appeared, making the performance of the ball bearings more improved, which is also the need to ensure the high speed of the spindle. In terms of improving the speed and accuracy of the spindle, there are also air-floating hydrostatic bearings or liquid-floating hydrostatic bearings, and magnetic bearings can reach a higher level.
    A few years ago, J&L and Ingersoll in the United States introduced high-speed machine tools with linear motors, which caused huge repercussions. In terms of increasing the cutting speed, the ball screw could not reach the speed, but at that time, the cost was too high. In the application, the most frequent occurrence is to increase the pitch of the lead screw, increase the number of heads, or make a hollow large diameter lead screw, which is passed with temperature-controlled water to maintain a suitable temperature. There are also people who advocate the use of static pressure screw, but there is still a big gap in performance. The maximum acceleration can reach 1 to 1.5g, while the linear motor can reach more than 10g. Later, due to the advancement of linear motor manufacturing technology, its cost was significantly reduced and its application increased significantly. Now linear motors are also used in EDM machine tools. For example, SODICK in Japan even uses 3 linear motors. High-speed machining can only be realized by the high-speed cutting of the tool. Of course, there are still a series of technologies that need to be solved around high-speed machining, for example, the speed of pallet exchange and tool exchange must be increased.
    Companies such as Germany’s DIGMA, CHIRON, and STAMA, Japan’s Okuma, and Mikron’s Mikron are all world-renowned high-speed machine tool manufacturers. The tool exchange time of CHIRON's small machining center has reached 0.5s. At the same time, it is also required to increase the acceleration and deceleration of the spindle, so that the spindle can stop in a very short time or reach the highest speed, which can now reach about 2s.
    In order to meet the needs of high-efficiency processing, the strength, rigidity, stability, and vibration resistance of the machine tool have been challenged, so CAD methods are used in the design to lay the foundation in advance; especially in the structural materials. As a result, stone materials have emerged to replace traditional cast iron and steel, such as granite, ceramics, artificial granite, and artificial marble. In ultra-precision machine tools, there are also glass ceramics with zero expansion coefficient (called Zerodur in Germany and glass ceramic in Japan). In recent decades, in order to meet the development requirements of productivity, machine tools have undergone great changes in structural materials, and the performance of machine tools has made great progress. my country has successfully developed artificial granite earlier and has a long history of granite application. The high-speed machine tool structure material of German DIGMA company uses composite polymer concrete, which improves the rigidity of the machine tool, has superior vibration attenuation (1/6～1/8 of casting), and low thermal deformation (1/25～1/2 of casting) 1/40) features.
    In recent years, the development of machine tools is changing with each passing day. The trend of high-speed, composite, multi-functional, and high-precision is more obvious. The main theme in the field of machinery manufacturing is to increase productivity. For example, the laser milling machine center exhibited by DMG company integrates different types of work on one machine tool; in order to better solve the problem of chip removal, the German company EMAG has developed an inverted machining center; more companies currently provide 5 Axis machining centers; especially the emergence of virtual machine tools, major changes have taken place in the design of machine tools, and it is still under development.

    The improvement of cutting tool performance provides the possibility for the development of high-efficiency high-speed machining

    If you need to achieve high-efficiency and high-speed machining, cutting tools are another important factor. The current development of cutting tool materials has created relatively good conditions for processing needs. In addition to high-speed steel and cemented carbide, the development of ceramics, cermets, and superhard materials has played an important role. Especially ceramics and superhard materials provide strong support for the development of high-efficiency and high-speed machining. What's more worth mentioning is that in 1955, the American GE company succeeded in synthesizing superhard materials with high temperature and high pressure, which prompted major changes in the cutting field. On this basis, PCD and PCBN soon appeared, creating conditions for cutting, dry cutting, hard cutting, and ultra-precision cutting of difficult-to-machine materials.
    Another aspect of cutting processing is the application of surface technology to cutting tools. PVD (Physical Vapor Deposition) and CVD (Chemical Vapor Deposition) have been constantly innovating, from a single layer to a multi-layer, thousand-layer, and composite coating. It has also developed into nano-coating; the material of the coating has developed from TiN to A12O3, TiC, ZrO2, etc. According to processing requirements, in order to improve the high temperature resistance, TiCN, TiAlN, TiSiN, CrSiN, etc. have been developed. In order to reduce friction, soft coatings, such as depositing MoS2, and Molyglide used by Guehring in Germany, are used. This coating is based on MoS2, which can reduce the friction coefficient during cutting. Of course, this should be applied to the required processing separately according to the characteristics of the workpiece. Now the coating technology has developed to super hard coating (diamond-like carbon, diamond, cubic boron nitride), which has broadened the scope of cutting. It is particularly worth mentioning that the thin film coating has developed into a thick film, which is different from natural diamond and has isotropic properties. It has now been used at home and abroad, partially replacing natural diamond. Now, the synthesis technology of large-particle single crystal diamond has been solved. These changes have far-reaching impact on my country. my country is already the country with the largest output of synthetic diamond in the world, which is conducive to the development of efficient processing technology in my country.
    In order to adapt to high-efficiency and high-speed machining, auxiliary tools are also very important means. For example, in the application of the original modular fixture to the machining center, in order to improve its strength, it has developed from a slot system to a hole system. At present, the most typical application is the application of EROWA and 3R combination tools. They have developed from electrical machining to machining centers, which not only speeds up the rhythm, but more importantly, achieves high precision. These tools have developed from the original mold electrical machining to cutting Processing field. The tool holders required for shank cutting tools have also developed new structures in the process of high-efficiency and high-precision cutting, such as hydraulic and plastic. Nowadays, hot-fit tool holders are widely used. The accuracy of clamping is obviously improved, reaching 2～3μm. Now this kind of device has matured. For example, ZOLLER company in Germany has installed this kind of device directly on the tool setting instrument, indicating that this technology has advanced a step further. The advancement of tools provides strong support for efficient processing.

    Create conditions for the realization of high-efficiency and high-speed machining

    As we all know, the aerospace industry is multi-variety and small-batch production from the perspective of output. Therefore, it is considered that it has little relationship with automated processing and often does not use automated equipment. Since the emergence of NC machine tools, especially after the birth of various machining centers, people's concepts have begun to undergo subtle changes. Since the introduction of a large number of machining centers, after ten or twenty years of practice, the processing automation of small batch parts has not only played an important role, but also has significantly improved the cycle and quality, and the number of tooling has also been significantly reduced. , Especially in the processing of box parts with many processes, long cycles and complex structures, it shows the superiority of the center.
    A question worth considering is how to use high-speed machining to serve efficient machining. Recently, the equipment displayed at major exhibitions around the world emphasizes more on high efficiency. On this basis, it also emphasizes the use of high-speed processing, that is, comprehensive utilization of technological progress. Most of the spindle speeds of the machining center shown are about 20000r/min. This may be the current theme-efficient and high-speed machining.
    In order to achieve high-efficiency high-speed machining, various aspects must be considered, such as the reasonable selection of machine tools and tools; the appropriate use of cutting parameters; the maintenance of high-speed spindles; safety protection and timely cleaning of chips. In these aspects, further discussion is needed. Take the machine tool as an example, a high-speed, high-power spindle should be used; the machine tool has sufficient rigidity and strength; the tool holder must be in contact with the cone and end surface of the machine tool spindle to prevent loosening during high-speed rotation; in terms of protection, chipping must be prevented The cutting fluid must be able to be injected into the cutting point, especially during high-speed grinding, in order to prevent burns on the workpiece, the nozzle design is particularly important. Yokogawa Kazuhiko of Meiji University in Japan has issued many opinions, which are worthy of reference; due to the high-speed cutting The amount of chips is large, so the chips must be removed in time. Taking cutting tools as an example, the current coating development is very fast, and it is necessary to select the object to be processed; in order to improve the quality of the processed surface, it is appropriate to use a ball-end milling cutter. Since the cutting speed at the center is zero, when using The end mill can be tilted at an angle. In order to improve the milling chatter caused by the end mill, the milling cutter with round corners is used. This is a recent development trend; in order to improve the cooling effect, tools with oil holes are used; Vibration, the grooves are made into unequal or different spiral grooves; in high-speed cutting, the cutter head of the milling cutter is made of aluminum alloy, and the cutter handle of the cutting knife is often weak in strength. Therefore, Sumitomo Corporation of Japan proposed the use of cemented carbide to solve the problem of chipping When processing deep holes, use a new type of slot drill, such as the RT series of Geuhring drills. The core thickness is increased, the rigidity is improved, the chip groove is widened, and the chips are easy to discharge, so It is conducive to deep hole processing; in the machining center, CNC tools must be used. This understanding is consistent, but the price has increased. Now the large number of composite tools can not only improve efficiency, but also reduce the number of tools. ISCAR's turning tools are the most typical. The combination of cutting tools significantly reduces the number and time of tool changes

In the meantime, the tool magazine of the machine tool becomes smaller, which inevitably improves efficiency.
     Judging from the current situation, some units have introduced thousands of new automated machine tools, but few have the spindle speed greater than 10000r/min. The reason is that there is a doubt about high-speed machining. According to the introduction of the German DMG company, the life of the high-speed spindle provided by the company is 2 years, and the key is how to apply it reasonably. When discussing the introduction of equipment, almost all hope to introduce high-speed equipment, which also reflects the mentality of technicians.
     Mikron believes that there is no strict definition of high-performance cutting. However, in actual applications, although both high-speed cutting and high-performance cutting milling methods belong to the scope of high-performance cutting technology, high-speed cutting is in most cases , Is significantly different from high-performance cutting. High-speed cutting is only one aspect of high-performance cutting, and another factor that high-performance cutting pays attention to is metal removal rate. This is a problem that we need to consider when we introduce equipment.