Development and demand of the hottest high speed m

2022-07-31
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Development and demand of high speed machining

high speed machining is an important part of modern advanced manufacturing technology, which has the characteristics of high efficiency, high precision and high surface quality. This paper introduces the definition, development status, application fields and China's demand for this technology

Definition of high speed machining

high speed machining is a high-tech facing the 21st century. It is characterized by high efficiency, high precision and high surface quality. It has been more and more widely used in automotive industry, aerospace, mold manufacturing, instrumentation and other industries, and has achieved significant technical and economic benefits. It is an important part of contemporary advanced manufacturing technology

high speed cutting is the core technology to realize high-efficiency manufacturing. The intensification of processes and the generalization of equipment make it have high production efficiency. It can be said that high-speed machining is an essential technology to greatly improve machining efficiency without increasing the number of equipment. The main advantages of high-speed machining are: improving production efficiency, improving machining accuracy and reducing cutting resistance

at present, there is no unified understanding of the meaning of high-speed cutting. There are usually several views as follows: the cutting speed is very high, and it is generally considered that its speed is times higher than that of ordinary cutting; The spindle speed of the machine tool is very high. Generally, the spindle speed above r/min is defined as high-speed cutting; The feed speed is very high, usually up to m/min, up to 90m/min; For different cutting materials and cutting tool materials, the meaning of high-speed cutting is also different; In the cutting process, when the tool passing frequency is close to the dominant natural frequency of the "machine tool workpiece" system, it can be considered as high-speed cutting. It can be seen that high speed machining is a comprehensive concept

Figure 1 high speed machining range for different cutting materials

in 1992, Professor h. Schulz of Darmstadt University of technology in Germany put forward the concept of high speed machining and its coverage on CIRP, as shown in Figure 1. It is considered that for different cutting objects, the transition shown in the figure is the so-called high-speed cutting range, which is also the cutting speed expected or expected by the technicians related to metal cutting technology at that time

status quo of high speed machining technology

high speed machining has some specific requirements for machine tools, cutting tools and cutting technology. The development status and trend of high speed machining technology are described from these aspects

machine tool equipment

at this stage, in order to realize high-speed cutting, high-speed CNC machine tools and machining centers with high flexibility are generally used, and special high-speed milling and drilling machines are also used. The common feature of these equipments is that they must have both high-speed spindle system and high-speed feed system to realize the high-speed cutting process. The biggest difference between high-speed cutting and traditional cutting is that the dynamic characteristics of the "machine tool workpiece" system have a stronger influence on the cutting performance. In this system, the rigidity of machine tool spindle, the form of tool handle, the setting of tool length, the setting of spindle broaching force and tool torque are all important factors affecting the performance of high-speed cutting

in high-speed cutting, the metal removal rate (MRR), that is, the volume of material removed per unit time, is usually limited by whether "chatter" occurs in the "machine tool workpiece" process system. Therefore, in order to meet the needs of high-speed machining, we must first improve the dynamic and static stiffness of the machine tool, especially the stiffness characteristics of the spindle. At present, a key factor for the success of high-speed cutting is the ability to master and deal with the dynamic characteristics of the system

in order to better describe the stiffness characteristics of machine tool spindle, a new dimensionless parameter DN value is proposed in engineering to evaluate the adaptability of machine tool spindle structure to high-speed machining. The so-called DN value is the product of the spindle diameter and the speed per minute. Most of the newly developed machining centers' spindle DN values have exceeded 1million. In order to reduce the weight of bearings, ceramic ball bearings, which are much lighter than steel products, are also used; Most bearings are lubricated by oil-air mixture. In the field of high-speed machining, air bearings, magnetic bearings and magnetic/air hybrid spindles composed of magnetic bearings and air bearings have been developed

in terms of machine tool feed mechanism, the feed drive mechanism used for high-speed machining is usually large lead, multi head high-speed ball screw, and the ball adopts small-diameter silicon nitride (Si3N4) ceramic ball to reduce its centrifugal force and gyro torque; Hollow strong cooling technology is adopted to reduce the thermal deformation of high-speed ball screw caused by temperature rise due to friction during operation

in recent years, the high-speed feeding system driven by linear motor has come out. This feeding method cancels all the intermediate mechanical transmission links from the motor to the slide of the workbench, and realizes the zero transmission of the machine tool feeding system. Since the linear motor has no rotating components and is not subject to the centrifugal force, the feed speed can be greatly improved. Another great advantage of linear motor is that its travel is unlimited. The secondary pole of the linear motor is continuously laid on the bed of the machine tool section by section. Where the secondary pole is laid, the primary pole workbench can move to where, and it has no effect on the stiffness of the whole feeding system. Using high-speed lead screw or linear motor can greatly improve the rapid response of the machine tool feed system. The maximum acceleration of linear motor can reach g (G is gravity acceleration), and the maximum feed speed can reach m/min or higher

in 2002, the maglev track steel beam processing in Shanghai Pudong maglev train project attracted worldwide attention was realized by using the super long feeding system high-speed large-scale processing center produced by Zoje friendship company of Shenyang machine tool holding Co., Ltd. The feed system of the machine tool is linear guide rail and gear rack transmission. The maximum feed speed of the workbench is 60m/min, the fast travel is 100m/min, the acceleration is 2G, the maximum speed of the spindle is 20000r/min, and the power of the main motor is 80kW. Its X-axis travel is up to 30m, and the error of cutting 25m long maglev track steel beam is less than 0.15mm, which provides a strong technical guarantee for the successful completion of the maglev train project

in addition, the motion performance of the machine tool will also directly affect the machining efficiency and accuracy. In the high-speed machining of dies and free-form surfaces, the machining method of small cutting depth and large feed is mainly used. It is required that the machine tool should have high-precision positioning function and high-precision interpolation function under the condition of large feed speed, especially arc high-precision interpolation. Circular arc machining is an essential machining method when machining parts or moulds with end mills or thread cutters

cutting tools

development of tool materials: the history of the development of high-speed cutting technology, that is, the history of the continuous progress of tool materials. The representative tool material for high-speed cutting is cubic boron nitride (CBN). When CBN cutter is used for end milling, its cutting speed can be as high as 5000m/min, which is mainly used for cutting gray cast iron. Polycrystalline diamond (PCD) tools are called the tools of the 21st century. It is especially suitable for cutting aluminum alloy materials containing SiO2. This metal material has light weight and high strength. It is widely used in the shell and base of automobiles, motorcycle engines and electronic devices. At present, the cutting speed of 5000m/min has reached the practical level when using polycrystalline diamond tools to mill aluminum alloys. In addition, ceramic tools are also suitable for high-speed machining of gray cast iron

coated tools: Although CBN and diamond tools have good high-speed cutting performance, the cost is relatively high. The application of coating technology can not only make the cutting tools cheap, but also have excellent performance, which can effectively reduce the processing cost. At present, the end milling cutters for high-speed machining are mostly treated by the composite multi-layer coating technology of TiAIN system. For example, when dry cutting aluminum alloy or non-ferrous metal materials, DLC (diamond like carbon) coated cutters have received great attention, and it is expected that their market prospects are very promising

tool clamping system: the tool clamping system is an important technology to support high-speed cutting. At present, the two-sided clamping tool system is the most widely used. The two-sided clamping tool systems that have been officially put on the market as commodities mainly include: HSK, km, bigplus, NC5, aho and other systems

in the case of high-speed cutting, the rotary balance performance of the tool and fixture will not only affect the machining accuracy and tool life, but also affect the service life of the machine tool. Therefore, when selecting tool system, products with good balance performance should be selected as far as possible

process parameters

the cutting speed of high-speed machining is about 10 times of the conventional cutting speed. In order to keep the feed rate per tooth of the tool basically unchanged, so as to ensure the machining accuracy, surface quality and tool durability of the parts, the feed rate must also be increased by about 10 times, reaching more than 60m/min, and some even as high as 120m/min. Therefore, high-speed machining usually adopts the cutting process parameters of high speed, large feed and small cutting depth. Because the cutting allowance of high-speed cutting is often very small, the chip formed is very thin and light, which quickly takes away the heat generated during cutting; If new tool materials and coatings with better heat resistance are used, the dry cutting process is also an ideal process scheme for high-speed machining

applicable fields of high-speed machining

high efficiency flexible production line

a high-efficiency flexible production line (FTL or FML) is composed of high-speed machining centers, which is characterized by miniaturization, outstanding flexibility and easy to change the processing content. Figure 2 shows an example of an engine company of SAIC Group using this production line to process engine block, cylinder head, filter base and other workpieces

Figure 2 small ftl

mold processing composed of high-speed machining centers

in order to meet the needs of new models as soon as possible, the manufacturing cycle and production cost of automobile body covering molds and resin impact stop forming molds must be shortened. Therefore, the minimum model of this kind of experimental machine that must be vigorously promoted to high-speed mold production is 50kN. SAIC's affiliated companies believe that: compared with the past finishing, it will further achieve high precision; At the same time, the accuracy requirements of surface roughness and curvature must be met. Therefore, appropriate manual finishing machining should be carried out. Due to the great improvement of cutting speed, the machining cycle should be greatly shortened compared with the previous finishing processes. Figure 3 shows the shortening of mold making time after adopting high-speed and high-precision processing technology

Figure 3 shorten the mold manufacturing cycle by high-speed and high-precision machining

development and application of multi-functional and special tools suitable for high-speed cutting

in order to give full play to the advantages of high-speed cutting technology and automatic tool change function represented by turning centers and boring and milling machining centers, and improve machining efficiency, the principle of centralized process should be adopted for the machining of complex parts as far as possible, That is, it is required to realize the centralized processing of multiple processes in one clamping, desalinate the boundaries of different cutting processes such as traditional turning, milling, boring and thread processing, and give full play to the high-speed cutting function of equipment and tools. It is an effective way to improve the efficiency of CNC machine tools and speed up product development. Therefore, a new multi-functional requirement is put forward for the tool, which requires that a tool can complete the processing of different processes of parts, reduce the number of tool changes, save the tool change time, and reduce the number and inventory of tools

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