First, high-speed cutting technology.
(i) Suggestions for high-speed cutting 193 1, German cutting physicist Dr. Karl. J.Salomon put forward a hypothesis, namely Salomon principle, and applied for a German patent in the same year: all materials to be processed have a critical cutting speed. Before the cutting speed reaches the critical speed, the cutting temperature and tool wear increase with the increase of cutting speed. When the cutting speed reaches 5 ~ 6 times of the ordinary cutting speed, the traditional processing method is "heavy cutting" when cutting plastic materials, and the chip removal of each tool is large, that is, the tool is large, but the feed speed is low and the cutting force is large. Practice has proved that with the increase of cutting speed, the chip shape develops from strip and flake to chip shape, and the required unit cutting force rises in the initial stage, and then drops sharply, indicating that high-speed cutting is lighter than conventional cutting, and their mechanisms are different.
(2) The concept of modern high-speed cutting technology The starting point of Solomon's principle is to use traditional tools for high-speed cutting, thus improving productivity. So far, its principle has not been confirmed by the Institute of Modern Science. 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. At present, there is no consensus on the exact definition of high-speed cutting from the perspective of modern science and technology, because it is a relative concept, and different processing methods and different cutting materials have different high-speed cutting speeds 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 huge and complicated system engineering, which covers the research and selection technology of machine tool materials, machine tool structure design and manufacturing technology, high-performance numerical control system, communication system, high-speed, high-efficiency cooling, high-precision and high-power spindle system, high-precision fast feed system, high-performance tool clamping system, high-performance tool materials, tool structure design and manufacturing technology, high-efficiency and high-precision test and measurement technology, high-speed cutting mechanism and high-speed cutting technology. Only on the basis of fully developing these technologies can the established high-speed cutting technology have real significance. Therefore, to give full play to the superior performance of high-speed cutting, it must be a perfect combination of CAD/CAM system, CNC control system, data communication, machine tools, tools and technology.
(III) Development Status and Advantages of High-speed Cutting Technology This new technology began in the early 1980s, with the United States, Germany, France and other countries in the leading position, followed by Britain, Japan, Switzerland and other countries. By the late 1980s, these countries had formed new industries with an annual output value of several billion dollars, and it was still increasing year by year. Recently, China Taiwan Province Province has also started, but the mainland is still blank. The Institute of Modern Manufacturing Technology of Tongji University has established a project cooperation relationship with darmstadt University, and achieved initial results.
At present, aviation, automobile, power machinery, molds, bearings, machine tools and other industries in industrialized countries have benefited from this new technology at first, which has significantly improved the product quality of these industries, greatly reduced their costs and gained market competitive advantages. Ultra-high speed cutting technology is the direction of cutting in the future and the product of the development of the times.
Second, high-speed cutting technology and equipment
(1) High-speed cutting machine tool High-speed machine tool is the premise and basic condition to realize high-speed machining. In modern machine tool manufacturing, the high speed of machine tools is an inevitable development trend. While the machine tool is required to be high-speed, it is also required to have high precision and high static and dynamic stiffness.
In order to adapt to rough machining, light and heavy cutting and fast movement, and ensure high precision (positioning accuracy of 0.005mm), a machine tool with good performance is the key factor to realize high-speed cutting. The key technologies are as follows:
1. High-speed spindle. High-speed spindle is the core component of high-speed cutting machine tool, which largely determines the cutting speed, machining accuracy and application range that the machine tool can achieve. The performance of high-speed spindle unit depends on design method, material, structure, bearing, lubrication and cooling, dynamic balance, noise and many other related technologies. With the increasing demand for spindle speed, the traditional gear belt variable speed transmission system can no longer meet the requirements due to its own vibration and noise, and it is replaced by a novel functional component-electric spindle, which combines the spindle motor with the machine tool spindle to realize the spindle motor. The motorized spindle adopts electronic sensor to control the temperature, and has its own water-cooling or oil-cooling circulation system to keep the spindle at a constant temperature when rotating at high speed. Generally, the set temperature can be controlled within the range of 20 ~ 25, and the accuracy is 0.7. At the same time, new technologies such as oil mist lubrication and mixed ceramic bearings are adopted to make the spindle maintenance-free, long life and high precision.
2. High-speed precision bearings. High-speed bearing is the core of high-speed cutting machine tool and the most critical component that determines the life and bearing capacity of high-speed spindle.
(1) magnetic bearing. The magnetic bearing suspends the spindle without mechanical contact through electromagnetic force. Its rotating speed can reach 45,000 rpm and its power is 20kW. This method has high accuracy and is easy to realize real-time diagnosis and online monitoring. It is an ideal supporting element, but its price is higher.
(2) hydrostatic and hydrostatic bearings. The combination of hydrodynamic force and static force makes the spindle rotate in the oil film support, which has the advantages of small radial and axial runout, good rigidity, good damping characteristics, suitability for rough machining and finishing and long service life. But it is not universal and difficult to maintain.
(3) Hybrid ceramic bearings. The ball made of silicon nitride is combined with steel track, which is the most widely used supporting element on the spindle of high-speed cutting machine tool at present. When rotating at high speed, the centrifugal force is small, the rigidity is good, the temperature is low, the service life is long, the power can reach 80kW, and the rotating speed can reach 150000r/min. It has high standardization, easy maintenance and low price.
3. High-speed servo system In order to realize high-speed cutting, the machine tool should not only have a high-speed spindle, but also have a high-speed servo system, which is not only to improve production efficiency, but also a necessary condition for maintaining the normal work of the tool during high-speed cutting.
(1) linear motor servo system. Linear motor is a kind of thrust device that directly converts electric energy into linear mechanical motion, which shortens the length of machine tool feed transmission chain to zero. Agile dynamic response, high transmission stiffness, high precision, large acceleration and deceleration, unlimited travel, low noise and high cost. It is the choice of servo system when the acceleration is greater than1g.
(2) Ball screw drive. Ball screw is still the main driving device of high-speed servo system. It is directly driven by AC servo motor and adopts hydraulic bearing. The feed speed can reach 40 ~ 60m/min, the acceleration can exceed 0.6g, and the cost is low, only 1/2.5. 4 of linear motor. High performance numerical control system.
(2) High-speed cutter is one of the important technical equipment for machining. Because the centrifugal inertia force increases rapidly with the increase of rotating speed, the combination of the end of high-speed spindle and the head of tool rest has many special features in structure and size. At present, HSK form and series are basically adopted, so it is necessary to determine the tool rest parameters according to the spindle parameters of machine tools to make them consistent. Because of the high cutting and feed speed, the tool life in high-speed cutting is generally reduced. It is necessary to take measures from the aspects of tool material, geometric parameters, overhang length, cutting parameters, cutting geometric relationship, tool path, lubrication and cooling to minimize the life loss.
The rake angle of HSC tool is about10 smaller than that of ordinary tool, and the rake angle is about 5 ~ 8. At the same time, the cutting part of HSC tool should be as short as possible to improve the rigidity of the tool and reduce the damage rate of the blade.
High-speed cutting tools should be made of materials that can adapt to high-speed cutting. In order to obtain higher machining quality and service life, besides cemented carbide, cermet, coated cutting materials and cutting ceramics, single crystal and polycrystalline cutting materials are also used. In addition to technical requirements, these cutting materials should also meet the requirements of economy and environmental protection. In high-speed cutting, PKD (Polycrystalline Diamond) and cubic boron nitride (CBN) can significantly improve the machining efficiency.
In addition to selecting suitable tool materials, in the process of tool design, the reliability of fixed tool parts under centrifugal force should be considered first, and the "balanced" structure should be paid attention to. It is necessary to test the speed of the tool. In addition, good manufacturability is also very important when manufacturing tools. From the pretreatment of cutter to the manufacture of blade, valuable and reliable manufacturing methods are of decisive significance, especially for PKD or CBN blade cutters.
In the application of HSC tools, in order to achieve machining quality and economic performance, we should not only consider the tool itself, but also consider the interface between the tool and the clamping system, that is, the connection surface between the spindle and the tool and the stability of workpiece installation. For the interface part and extension rod, radial swing accuracy, cantilever length, vibration performance and interchangeability are particularly important. In order to meet the requirement of radial swing precision of cylindrical tool holder in finishing, the connection mode of hydraulic chuck, shrinkage chuck and force chuck is selected at first. When these chucks are matched with HSC interface, the radial swing accuracy can reach 0.003 mm.
(3) Supporting equipment for high-speed machining machine tools
1. In order to shorten the auxiliary working hours, most HSC machine tools are equipped with tool depots with tool positions above 15 ~ 30 and automatic tool changing devices, which become HSC machining centers;
2. The cooling and lubrication system is an indispensable supporting equipment, which includes the automatic cooling and lubrication function and chip removal function of all parts of the machine tool;
3. The electronic handwheel and the interface between the CAD/CAM system and the high-speed numerical control system are necessary supporting equipment that affect the operation and control performance of the machine tool;
4. Laser or infrared system that can automatically measure the diameter and length of tools and detect damage;
5. The probe can be installed on the spindle to detect the contour of the workpiece. 6. In order to reduce the time of downtime for repair after failure, a high-speed spindle is reserved under the condition of more machine tools and high utilization rate.
The safety protection device of HSC machine tool, including hardware and software, should ensure that the operator's personal safety can be reliably protected even in the extreme case of high-speed breaking and ejection of the tool, and can prevent accidental interference and collision between machine tool parts, tools and workpieces.
Third, the main application fields of high-speed cutting at present
(1) A large number of production fields, such as the automobile industry, such as the HVM800 horizontal machining center developed by Ford Motor Company and ingersoll Company in the United States and the single-axis boring cylinder machine tool used for boring cylinders, are actually used in Ford's production line.
(2) In the processing field where the rigidity of the workpiece itself is insufficient, such as aerospace industrial products or some other products, for example, the thinnest wall thickness of the workpiece milled by ingersoll Company using high-speed cutting technology is only1mm. ..
(3) Machining complex curved surfaces, such as mold and tool manufacturing.
(4) In the field of difficult-to-machine materials, such as ingersoll's "high-speed module", the cutting speed of processing aviation aluminum alloy is 2438m/min, automobile aluminum alloy is 1829m/min, and cast iron is 12 19m/min, which is several to dozens times higher than the conventional cutting speed.