High speed machining is the main theme of the current field of machinery manufacturing
|print Collection ][ time：2013-08-16 16:23:57 Visits：11953|
Improving productivity is eternal subject field of machinery manufacturing, machinery manufacturing field is the current issues of common concern. High-speed machining is an important means to achieve high productivity, the key is to create conditions for rapid spread.
Current developments in the field of machinery manufacturing features are: large numbers of hard cutting materials significantly increased the difficulty of processing; processing also raised a number of issues need to be urgently addressed, such as the hard cutting; order to protect the environment, requiring little or no cutting oil, namely to achieve semi-dry cutting or cutting. In short, many challenges facing the machinery, in such a case, in order to increase productivity, to the utilization of all the technical progress. Especially in the aerospace industry system, due to difficult materials and more complex structure, short development cycle, single and small batch production and more features, how to improve productivity, shorten the production cycle, has been a long-term scientific and technological personnel important issues of concern, but also the aerospace The system must urgently address the issue.
On the other hand, the current rapid development of technology, how new technologies and processes transplant, very urgent. It is noteworthy that in today”s world, technology has developed rapidly, greatly promoted the mechanical aspects of the rapid development of manufacturing, there has been a variety of methods to improve productivity and means. As we all know, single crystal natural diamond grinding tool is very difficult, generally use high-phosphorus iron grinding disc to diamond powder for abrasive, low efficiency.
Japan recently reported that the use of low carbon content, low thermal conductivity of stainless steel 304 (Japanese brands) manufactured disc, the diamond back pressure on the turntable at 4000r/min, temperature controlled at 800 ℃, high removal rate of diamond reach 0.94mm3/min, do not use abrasive work, but the use of physical and chemical effects, known as the thermo-chemical process, which is to break the conventional method; Another example is the recent rapid prototyping (RP), in the absence of mold in the case molding, eliminating the mold manufacturing cycle; WEDM cutting speed in the domestic fast wire machine can reach 70mm2/min, Swiss machine AGIE company can reach 500mm2/min, while Japan”s Mitsubishi Electric machine can reach 550mm2/min, reaching speeds in general have launched a high-speed milling grinding speed has reached 60,120 m / s, and even to 200m / s, in the laboratory has reached 500m / s, and general grinding speed only 30 ~ 35m / s. Is a high-speed grinding grinding method, cutting depth, cutting speed large; another peristaltic grinding and high-speed grinding contrary, large depth of cut, the cutting speed is small, but they are efficient grinding, cutting only different, so some people liken to "Tortoise and the Hare", their own merits. In 1931, the German Carl Salomon made famous prophecy: Average cutting speed and cutting heat is increased simultaneously, but can not cut through a Death Valley, the cutting speed even increased; but there will be cutting heat down, today, the aluminum cutting speed has reached 5000m/min, CarlSalomon prophecy will be revealed.
In summary, in order to improve the cutting speed is an important means for improving the productivity, of course, this is not all, there are to be developed. Because high-speed processing is mainly reflected in the milling side, so following on machining centers mainly introduced.
Machine tool development is a prerequisite for high-speed machining
Since the current rapid development of machine tool manufacturing technology, machinery manufacturing sector is brewing tremendous changes. Developed into a multi-axis CNC machining centers, intensive variety of processes as a whole, significantly shortening the auxiliary time and improve productivity, while reducing the number of workpiece clamping improve the machining accuracy. In summary, the current machine development goals should be: to reduce the replacement process, significantly improve efficiency; tend to process intensive, easy to improve accuracy; using complex tools, ball mills and other advanced tools that can increase per unit of time cutting capacity; take the knife speed and cutting efficiency; reduce lighting after the milling process; cutting tools, automatic pallet exchange, high degree of automation, assisted significantly shortened; due to complex parts easy processing, and promote structural improvement parts and so on. From aerospace perspective, generally considered such a development machine, ideally suited for single and small batch production, so quickly, more in a single piece and small batch production systems enrich the equipment, the practice also shows that the automation equipment is in line with aerospace systems manufacturing technology development needs.
Of course, from the perspective of improving productivity, in addition to automated processing outside, there remains how to further, more rational use of various technological advances issue. From the observation of the development of machine tools, machine tool spindle high-speed significantly improved speed, higher than 10000r/min machine has been more common. Bearing technology, this may be provided. Spindle development, the most prominent is the spindle has been commercialized. Spindle lubrication technology is critical, been a matter of concern. Over the years, developed from grease to oil mist lubrication, oil lubrication, ring down (under-race) lubrication, lubrication and even cold. Along with the development of high-speed spindle, grease lubrication can not adapt, oil mist lubrication is also used as the reason to reduce pollution, is now the most widely used oil lubrication, more reasonable under the ring lubrication, so that the inner ring has been more critical good lubrication. Improved lubricity, the ball bearing can bear a high speed 70000r/min. American original in the machine spindle is used ABEC7 grade precision bearings, has now grown to ABEC9 level, indicating the bearing to improve the accuracy is a must. Since the development of materials, and the emergence of a ceramic ball, making the ball more to improve the performance, which is also the need to ensure high-speed spindle. In improving the spindle speed and accuracy, there is also gas bearing or liquid float hydrostatic bearing, and the magnetic bearing is able to reach a higher level.
A few years ago, the United States J & L and Ingersoll has introduced a high-speed machine with linear motor caused great repercussions in increasing the cutting speed has played a ball to reach the speed, but at that time because the cost is too high, in the specific applications, the more there is the greater pitch of the screw, increasing the number of heads, or made into a hollow large diameter screw, through a temperature of the water, maintain the appropriate temperature. Also advocate the use of hydrostatic lead screw, but from the performance is still relatively large gap, which can reach a maximum acceleration of 1 ~ 1.5g, while the linear motor can reach more than 10g. Later, due to the linear motor manufacturing technology, its costs are significantly reduced, the application significantly increased. EDM is now also used linear motors, such as Japan SODICK even use the three linear motors. Only take the knife of high-speed, high-speed processing can really be achieved. Of course, there are still around a series of high-speed machining techniques need to be addressed, such as pallet exchange, tool exchange rate also increases.
Germany DIGMA, CHIRON, STAMA, Japan, Okuma, Ruitu MIKRON other companies are world famous manufacturer of high-speed machines. CHIRON machining centers for small tool exchange time has been reached 0.5s. Also requires improved acceleration and deceleration of the spindle, the spindle in a very short period of time or reached the speed stop, has up to now about 2s.
In order to meet the needs of high-efficiency machining, machine strength, stiffness, stability, vibration resistance and so accepted the challenge, so from the design using CAD methods, pre-lay the foundation; especially in structural materials have a relatively clear changes, there the stone materials to replace the traditional cast iron and steel, methods such as granite, ceramic, artificial granite, artificial marble and so on. In the ultra-precision machine tools are used by the zero expansion coefficient glass (Germany called Zerodur, Japan called glass ceramic)”s. In recent decades, the productivity of the machine in order to meet the development requirements of the structural materials has undergone great changes, the performance of the machine has made substantial progress. China earlier successfully developed artificial granite, granite application already has a long history. Germany”s high-speed machine tools DIGMA structural material on the use of composite polymer concrete to improve the machine”s rigidity, excellent vibration attenuating (as castings 1/6 to 1/8), low thermal deformation (for the casting of 1/25 ~ 1/40) characteristics.
In recent years, the rapid development of machine tools, high-speed, complex, multi-functional, high-precision trend more obvious, machinery manufacturing is the theme of improving productivity. For example demonstrated laser milling from DMG machining centers, different types of intensive in one machine; chip in order to better solve the problems, the German company developed a inverted EMAG machining centers; currently more and more companies are providing a five- axis machining centers; especially the emergence of the virtual machine, from the design of the machine has undergone major changes, and now it is still in developing.
Improved performance cutting tools for the efficient development offers the possibility of high-speed machining
If you need to achieve efficient high-speed machining, cutting tools is another important factor. Current development of cutting tool materials for processing needed to create a relatively good conditions, in addition to high-speed steel, carbide outside, ceramics, metal ceramics, superhard materials has played an important role. Especially ceramics, superhard materials, the development of efficient high-speed machining to provide a strong support. It is worth mentioning that in 1955 the U.S. company GE high-temperature, high-pressure synthesis of superhard material success, prompting significant changes occurred in the field cutting. On this basis, soon appeared PCD, PCBN, difficult machining materials, cutting, dry machining, hard machining, ultra precision cutting and other processing to create the conditions.
In another aspect of the machining, the cutting tool is on surface technology applications, PVD (physical vapor deposition), CVD (chemical vapor deposition) constantly, by the development of a multi-layer, Melaleuca, composite coatings, are has developed into a nano-coating; coating materials from TiN development A12O3, TiC, ZrO2, etc., according to processing requirements, to improve the high temperature performance, and the development of a TiCN, TiAlN, TiSiN, CrSiN so on. To reduce friction, the soft coating, such as deposition of MoS2, and if the German company uses Guehring Molyglide, this coating is to MoS2-based, it can reduce the friction coefficient of the cutting. Of course, this should be processed according to the characteristics, respectively the desired processing of the application. Coating technology has now developed to a superhard coatings (diamond, diamond, cubic boron nitride), more so to broaden the scope of cutting. Of particular mention is the development of a thick film coating, which is different from natural diamond, isotropic, has now been applied at home and abroad, a partial replacement of natural diamond. Now been resolved large single crystal diamond particle synthesis technology, these changes are very far-reaching impact on China, China has the world”s largest country in production of synthetic diamond, which is conducive to China”s development of efficient processing technologies.
In order to meet the high-speed processing, the auxiliary tool is also very important means, such as a combination of the original clip in the machining center applications in order to improve its strength, has been developed into a system from the holes of grooves. Typically a current EROWA and 3R combination tool applications, has from the electrical processing, the development of machining centers, not only to speed up the rhythm is more important to achieve high precision, these tools mold processing power from the original development of the cutting processing areas. Shank cutting tools in the desired handle, also with high-efficiency, high-precision machining during the development of a new structure, such as hydraulic, plastic, and now widely used in thermal loading of the shank, which significantly improved the accuracy of the clamp, to 2 ~ 3μm. Such a device is now ripe for companies such as Germany”s ZOLLER has such a device mounted directly on the knife, the description of the technology and a step forward. Tools for the efficient processing advances to provide a strong support.
For the efficient creation of conditions for the realization of high-speed machining
As we all know, the aerospace industry from the perspective of production belong to many varieties of small batch production, so that the relationship with the automated processing is relatively small, often do not use automated equipment. Since the emergence of NC machine tools, especially after the birth of a variety of machining centers, people”s attitudes are beginning to subtle changes. Since the introduction of a large number of machining centers later, after twelve years of practice, small quantities of parts automation not only played an important role, but also in the cycle, the quality has significantly improved, tooling also significantly reduced the number of , particularly in the multi-step, long cycle, the complex structure of the box parts processing, but also shows the superiority of the center.
An issue worth considering is how to use high-speed processing for the efficient processing services. Recently, the world”s major exhibition display equipment more emphasis on high-efficiency, on this basis, but also emphasizes the use of high-speed processing, that is, to the comprehensive utilization technology. Show machining center spindle speed 20000r/min most about. Perhaps this is the current theme - high speed machining.
In order to achieve efficient high-speed processing, must take into account various aspects, such as machine tools, tools of rational choice; cutting proper use; speed spindle maintenance; chip security and timely clean-up. In these areas, need to be further discussed. In machine tools, for example, should be high-speed, high-power spindle; machine has sufficient rigidity and strength; handle must be selected spindle cone and face contact when turning at high speed in order to prevent loosening; protection aspects in the need to prevent swarf splash; cutting oil must be injected into the cutting point, particularly in the high-speed grinding, in order to prevent the workpiece burns, nozzle design is particularly important, Meiji University, Yokokawa Kazuhiko many opinions, it is also useful; Because high-speed cutting chip capacity, so the chip must be excluded from such a timely manner. The cutting tool as an example, the current coating is developing very fast, for object selection processing is necessary; in order to improve the surface quality, the use of ball mill is suitable, due to its central cutting speed is zero, so use cutter can be tilted at an angle in order to improve the milling cutter chatter caused by using the cutter with rounded corners, which is a recent trend; To improve the cooling effect of the use of a tool with a hole; mills in order to prevent vibration, the groove made unequal or different helical groove; in high speed cutting, milling cutter aluminum, cutter blade knife is often poor strength, so the Japanese Sumitomo made with carbide, in order to solve the chips treatment, using the appropriate breaker blade; deep hole in the processing time, using new flute drill bits, such as Geuhring company RT series drill, its core thickness increase, increased stiffness, flute widened, chip easy to discharge, so conducive to deep processing; mechanical machining centers, CNC tool must be used, this understanding is the same, but the price increased. Now composite tools have emerged, not only can improve efficiency, but also reduce the number of tools, ISCAR”s turning is the most typical. Composite cutting tool significantly reduces the frequency and duration of tool, machine tool magazine smaller, are bound to improve efficiency.
From the current situation, and some units have been introduced thousands of new automation tools, but the spindle speed is greater than 10000r/min very little, the reason is that there is a concern for high-speed machining. According to the German DMG”s introduction, the company provides high-speed spindle life is two years, the key issue is how to reasonably apply. Explore the introduction of equipment, when almost all hope to introduce high-speed equipment, which also reflects the technical staff of mind.
Mikron company believes high performance cutting now no strict definition, however, in practice, although the high-speed cutting and high performance cutting both high-performance milling methods belong within the scope of the cutting process, but in most cases, high-speed cutting , and high-performance cutting is significantly different. Cutting speed cutting is just one aspect of performance, but rather the high-performance cutting Another element of concern is the metal removal rate, which is the introduction of equipment we need to consider.
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