On high efficiency and high speed machining

2022-07-26
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High efficiency and high speed machining

improving productivity is an eternal topic in the field of machinery manufacturing, and it is also a common concern in the field of machinery manufacturing. High speed machining is an important means to obtain high productivity at present. The key is to create conditions for rapid popularization

the characteristics of the current development in the field of mechanical manufacturing are: the emergence of a large number of difficult cutting materials has significantly increased the difficulty of machining; There are also many urgent problems to be solved in machining, such as hard cutting; In order to protect the environment, it is required to use less or no cutting oil, that is, to realize dry cutting or semi dry cutting. In short, machinery manufacturing faces many difficulties. Under such circumstances, in order to improve productivity, we must make comprehensive use of all relevant technological advances. In particular, the aerospace industry system, due to the characteristics of many difficult to process materials, complex structure, short development cycle and many small batch products per piece, how to improve productivity and shorten production cycle has always been an important issue of long-term concern for scientific and technological personnel, and it is also a problem that aerospace systems must pay close attention to

on the other hand, with the rapid development of science and technology, it is urgent to transplant new technologies and processes. 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 mechanical manufacturing, and there have been a variety of methods and means to improve productivity. As we all know, it is very difficult to grind single crystal natural diamond tools. Generally, high phosphorus cast iron grinding disc is used, and diamond powder is used as abrasive, so the efficiency is very low

recently, it was reported in Japan that stainless steel 304 (Japanese brand) with low carbon content and low thermal conductivity was used to make a disc. The diamond was pressed on a 4000r/min rotating disc, and the temperature was controlled at 800 ℃. The removal rate of diamond was very high, reaching 0.94mm3/min. Instead of using abrasive, the physical and chemical effects were used during operation, which was called thermochemical processing, which was an unconventional method; Another example is the recent rapid prototyping (RP), which can be formed without a mold, eliminating the mold manufacturing cycle; The cutting speed of WEDM can reach 70mm2/min on domestic fast wire walking machine tools, 500mm2/min on Swiss Agie machine tools, and 550mm2/min on Japanese Mitsubishi electric machine tools, reaching the general milling speed. Now the high-speed grinding speed has reached 60, 120m/s, even 200m/s. In the laboratory, it has reached 500m/s, while the general grinding speed is only 30 ~ 35m/s. High speed grinding is an efficient grinding method with shallow cutting depth and high cutting speed; The other kind of creep grinding is just the opposite to high-speed grinding, with large cutting depth and low cutting speed, but they are all high-efficiency grinding, but the cutting parameters are different. Therefore, some people figuratively compare it to "tortoise and rabbit race", and each has its own advantages. In 1931, carlsalomon of Germany put forward a famous prediction: generally, the cutting speed and cutting heat increase synchronously, but after a dead valley that cannot be cut, even if the cutting speed increases; Instead, the cutting heat will decrease. Today, the cutting speed of aluminum has reached 5000m/min, and carlsalomon's prediction will be revealed

to sum up, increasing the cutting speed is an important means to improve productivity. Of course, this is not all, and it needs to be developed. Since high-speed machining is mainly reflected in milling, the following will focus on the introduction of machining centers

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

at present, due to the rapid development of machine tool manufacturing technology, great changes are brewing in the field of mechanical manufacturing. The development of CNC machine tools into multi axis machining centers integrates various processes, significantly shortens the auxiliary time, improves the productivity, reduces the clamping times of workpieces, and improves the machining accuracy. To sum up, the current development goals of machine tools should be: reduce the replacement of processes and significantly improve efficiency; It tends to be intensive and easy to improve accuracy; The cutting amount per unit time can be increased by using advanced tools such as compound cutters and ball end mills; The cutting speed is accelerated and the cutting efficiency is improved; It can reduce the polishing process after milling; The automatic exchange of cutting tools and pallets has a high degree of automation, and the auxiliary time is significantly shortened; Because complex parts are easy to process, the improvement of part structure is promoted. 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 equipment are rapidly and more enriched in the single piece and small batch production system. The practice also shows that the automatic equipment is in line with the needs of the development of aerospace system manufacturing technology

of course, from the perspective of improving productivity, in addition to automatic processing, there are still problems of how to make further and more rational use of various technological advances. From the development of machine tools, the high-speed of machine tool spindle has significantly increased the speed, and machine tools higher than 10000r/min have been more common. The progress of bearing technology makes it possible. The development of spindle, the most prominent is that motorized spindle has been commercialized. The lubrication technology of the spindle is very important and has been concerned by all aspects. 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 spindle, grease lubrication has been unable to adapt, and the use of oil mist lubrication is also decreasing due to pollution. Now the most widely used is oil-gas lubrication, and the more reasonable is under ring lubrication, which makes the key inner ring better lubricated. With the improvement of lubrication performance, the ball bearing can also withstand the high speed of 70000r/min. In the United States, ABEC7 high-precision bearings were originally used on machine tool spindles, but now ABEC9 bearings have been developed, which shows that it is necessary to improve the accuracy of bearings. Due to the development of materials, ceramic balls have emerged, which makes the performance of ball bearings more improved, which is also the need to ensure the high-speed spindle. In terms of improving the speed and accuracy of the main shaft, air floating hydrostatic bearings or liquid floating hydrostatic bearings are also used, while magnetic bearings can reach a higher level

a few years ago, JL and Ingersoll introduced high-speed machine tools using linear motors, which caused huge repercussions. In terms of increasing the cutting speed, they played a role that the ball screw could not reach. However, at that time, due to the high cost, in specific applications, it was more common to increase the pitch of the lead screw, increase the number of heads, or make it into a hollow large-diameter lead screw, and use temperature controlled water to maintain the appropriate temperature. Some people also advocate the use of static pressure lead screw, but there is still a big gap in performance. It can reach the maximum acceleration of 1 ~ 1.5g, while the linear motor can reach more than 10g. Later, due to the progress of linear motor manufacturing technology, its cost was significantly reduced and its application was significantly increased. Now linear motors are also used in EDM machine tools. For example, Sodick in Japan even uses three linear motors. Only with the high-speed cutting, high-speed machining can be truly realized. Of course, there are still a series of technologies to be solved around high-speed machining. For example, the speed of pallet exchange and tool exchange should also be increased

digma, Chiron, STAMA in Germany, Okuma in Japan, Mikron in Switzerland and other companies are world famous 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 or reach the highest speed in a very short time. Now it can reach about 2S

in order to meet the needs of high-efficiency machining, the strength, stiffness, stability and vibration resistance of the machine tool have been challenged, so CAD method is adopted in the design to lay a good foundation in advance; In particular, there have been obvious changes in structural materials. There have been stone materials to replace the traditional cast iron and steel, such as granite, ceramics, artificial granite, artificial marble, etc. On ultra precision machine tools, glass ceramics with zero expansion coefficient (called zerodur in Germany and glass ceramics in Japan) are also used. In recent decades, in order to meet the development requirements of productivity, great changes have taken place in the structural materials of machine tools, and the performance of machine tools has made great progress. Artificial granite has been successfully developed in China earlier, and has a long history in the application of granite. Composite polymer concrete is used as the structural material of the high-speed machine tool of German digma company, which improves the rigidity of the machine tool and has the characteristics of superior vibration attenuation (1/6 ~ 1/8 of the casting) and low thermal deformation (1/25 ~ 1/40 of the casting)

in recent years, the development of machine tools has changed with each passing day. The trend of high-speed, compound, multi-function and high-precision is obvious. The main theme in the field of machinery manufacturing is to improve the commitment rate of 14 backbone electrolytic aluminum enterprises. For example, the laser milling machine center displayed by DMG company concentrates different types of work on one machine tool; In order to better solve the problem of chip removal, German Emag company has developed an inverted machining center; At present, many companies provide 5-axis machining centers; Especially with the appearance of virtual machine tools, great changes have taken place in the design of machine tools. Now it is still developing

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

if high-efficiency high-speed machining is required, cutting tool is another important factor. At present, the development of cutting tool materials has created relatively good conditions for the needs of machining. 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 is worth mentioning is that in 1955, Ge successfully synthesized superhard materials with high temperature and high pressure, which led to significant changes in the cutting field. On this basis, PCD and PCBN soon appeared, creating conditions for the machining of difficult to machine materials, such as cutting, dry cutting, hard cutting, ultra precision cutting, etc

another aspect of machining is the application of surface technology in cutting tools. PVD (physical vapor deposition) and CVD (chemical vapor deposition) continue to innovate, from single layer to multi-layer, thousand layer, composite coating, and now to nano coating; The coating materials have been developed from tin to A12O3, tic, ZrO2, etc. according to the 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 are used, such as MoS2 deposition, or molyglide adopted by German Guehring company. This kind of coating is mainly MoS2, which can reduce the friction coefficient in cutting. Of course, this should be applied to the required processing respectively according to the characteristics of the machined parts. Now the coating technology has developed to superhard coating (diamond-like carbon, diamond, cubic boron nitride), which widens the range of cutting processing. It is particularly worth mentioning that the thin film coating has developed into a thick film, which is different from natural diamond and has isotropy. Now it has been applied at home and abroad, partially replacing natural diamond. At present, the synthesis technology of large particle single crystal diamond has been solved. These changes have a far-reaching impact on China. China has the largest output of synthetic diamond in the world, which is conducive to the development of efficient processing technology in China

in order to adapt to high-efficiency and high-speed machining, auxiliary tools are also very important means, such as the original combination

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