Current situation and development trend of high-sp

2022-08-17
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Current situation and development trend of high-speed machining technology in China

1 introduction

for mechanical parts, high-speed machining is to process at a faster production pace. One production cycle: seven basic production links: part feeding - positioning and clamping - tool fast forward - tool feeding (detection) - tool fast retreat - tool loosening and unloading - quality detection. High speed cutting refers to that the cutting motion (or movement) speed of the cutting edge of the tool relative to the surface of the part is 5 ~ 10 times faster than that of ordinary cutting, which is mainly reflected in the three links of tool fast forward, tool forward and fast backward. It is a subsystem of high speed machining system technology; For the whole automatic production line, the characterization of high-speed processing technology is to produce and process with a simpler process flow and a shorter and faster production pace. This requires breaking through the traditional concept of machining and reforming the original processing technology (mode) on the premise of ensuring product quality: either adopt one station with multiple processes, one knife with multiple blades, or replace grinding with turning, reaming, milling, or replace rolling, inserting, milling and other processes (modes) with broaching, rubbing, extruding, rolling processing (modes), so as to shorten the process flow of the whole production line as much as possible; For a product, high-speed processing technology also means that enterprises should complete all kinds of information collection and processing, design and development, processing and manufacturing, marketing and feedback information of R & D products with a shorter production cycle. This has something in common with the agile manufacturing engineering concept

high speed machining technology came into being in the dynamic and changeable global market economic environment in modern times. In the fierce market competition, enterprises are required to have high product quality, low cost, fast listing, good service, clean environment and timely product innovation, which leads to the continuous development of high-speed processing technology. Since the 1980s, high-speed machining technology has gradually developed into a comprehensive system engineering technology based on traditional metal (non-metal) cutting technology, automatic control technology, information technology and modern management technology. It has been widely used in production process manufacturing enterprises (such as modern car (car) production enterprises); With the increasing social demand for personalized products, their production conditions are multi variety, single piece and small batch manufacturing (in machinery manufacturing, this production mode will account for 70% of the total output value). High speed machining technology will be further applied and developed in discrete or mixed production process enterprises (such as mold, energy equipment, shipbuilding, aerospace... And other manufacturing enterprises)

At the end of the 20th century, China reformed the planned economic system, carried out reform and opening up, and built a socialist market economic system with Chinese characteristics. Practical high-speed machining technology has been widely used in the machinery manufacturing industry with the introduction of advanced CNC automatic production lines, cutting tools (tools) and CNC machine tools (equipment), and the corresponding management mode, technology and concept have been integrated into the enterprise. Entrepreneurs are increasingly aware of the important position and role of modern information technology and enterprise systems and mechanisms in future sustainable development and market competition. The socialist market economic environment not only promotes the transformation of enterprises, adjustment of industry, product structure and technological transformation, but also shows a good and broad prospect for enterprises to apply and develop high-speed processing technology

2 China has introduced high-speed machining technology in the automatic production line of CNC cars. Since the 1980s, China has successively introduced many more advanced automatic production lines of CNC cars from Germany, the United States, France, Japan... And other countries, which has led to the unprecedented development of China's car manufacturing industry. The typical ones are the automatic production lines of FAW Volkswagen Jetta car from Germany and Shanghai Volkswagen Santana car, which are at the international level in the mid-1990s. Among them, many practical high-speed machining technologies are applied. From this part, we can understand the current situation and development trend of high-speed machining technology in the world. This paper focuses on the FAW Volkswagen Jetta car transmission and development production line

2.1 overview of the imported Jetta CNC car automatic production line

FAW Volkswagen Jetta car automatic production line is composed of high-speed production lines such as stamping, welding, coating, final assembly, engine and driver. Meanwhile, the parallel engineering management mode and management technology of Volkswagen AG are introduced, and various automatic lines are operated. The annual production capacity of cars is 150000, and the manufacturing pace is 1.50 points/vehicle. Among them, the engine and driver production line has a total of 627 various machining equipment, 253 imported and 374 domestic, which are basically CNC rigid automatic production lines. There are 9 kinds of self-produced engine parts, 27 kinds of transmission parts, and the rest are social supporting. The annual output is 270000 engines and 180000 transmissions. It produces 4-cylinder and 6-cylinder Jetta Audi car five valve EFI Engines and supporting drivers at the international level in the 1990s. The production pace is 30 ~ 40 seconds/set. The production line adopts air-cooled dry cutting technology. Its machining process reflects the most advanced technical level in contemporary car manufacturing industry. Car marketing is mainly in the domestic market. Due to the lack of independent intellectual property rights of cars, the research and development of new models is based on the existing FAW Volkswagen Jetta auto production line, and continues to import relevant information and technology from Volkswagen AG (the situation of Shanghai Volkswagen Santana Auto production line is similar)

2.2 overview of the blank technology of FAW Volkswagen car engine and driver (engine and transmission)

the blank of key parts of FAW Volkswagen Jetta Audi car engine and driver are high-strength cast iron, cast aluminum and precision die forged structural steel parts formed by precision casting, and some parts adopt precision powder metallurgy sintering forming process. Its high-speed machining technology requires that in the process of batch production, the machinability of materials is good and stable, and the cutting allowance of parts blank is controlled within 1.2 ~ 4mm ± 0.3mm. At the beginning of the production line, the parts are imported. Since 1997, relevant domestic enterprises have successively overcome the technical problems of precision forming technology, chemical element selection and matching of part materials and heat treatment technology of batch production parts blanks after several key problems, aiming to achieve the technical indicators of high-speed machining automatic production line (Technology) that have high requirements for the machinability and dimensional accuracy consistency of part blank materials, and the localization of driver parts blanks has reached more than 95%

2.3 FAW Volkswagen car production line high speed cutting tools, high-speed machine tools and processing technology

FAW Volkswagen Jetta Audi car engine and driver parts production line, almost all cutting tools and auxiliary tools (tools) are imported products (from 49 foreign companies), and the equipment (machine tools) of key processes are also special rigid CNC products imported with the economic recovery. Its typical technical features are briefly described as follows:

selection of tool materials: mainly superhard tool materials. CBN, sin ceramics, Ti based ceramics and TiCN coated tool materials are used to process high-strength iron castings, and the milling speed is up to 2200m/min; Using PCD and ultra-fine cemented carbide tools to process high Si Al castings, the milling speed is also up to 2200m/min, and the drilling and reaming speed is up to 80 ~ 240m/min; Using sin ceramics, Ti based ceramics and TiCN coated tools to process precision forged structural steel parts, the turning speed is up to 200m/min; The high-speed steel integral broach, hob, shaving cutter with high Co powder metallurgy surface coated with TiCN and the special broach for cemented carbide machine clamp combination are used to process all kinds of precision forged steel parts and cast iron parts. The broaching speed is 10 ~ 25m/min, the hobbing speed is 110m/min, and the shaving cutting speed is 170m/min

typical structure and processing technology of the tool: the part hole processing tool adopts a multi edge composite structure (knife edge machine clamp, inlay welding combination), which uses reaming and extrusion instead of grinding to finish the hole in the process of one-time cutting, and the rotating speed is up to 3000r p. M, the cutting speed is 1.5 ~ 3m/min, the accuracy is 5 ~ 7 levels, and the roughness is ra0.7 m (the speed of gun drill is 8000r/min, ra2 m); The high-speed dense tooth surface milling cutter with dense teeth, over positioning and repeated clamping structure and adjustable radial and axial direction is mostly used for plane milling of parts. diameter φ 250 ~ 400mm, axial runout <± 0.0025mm. The machining of part assembly plane is to replace grinding with milling, with roughness ra0.7 m and unevenness <0.02mm; The crankshaft main journal and connecting rod journal are processed with two station turning and broaching special tools. Cutter head diameter φ 700mm, equipped with 40 carbide coated blades on the circumference, every 10 blades are a group, the cutting speed is 150m/min, the fast forward speed is 4.6m/min, the cutting allowance is 1.5 ~ 3mm/radial, and the shift production is 350 pieces; The crankshaft main shaft bearing cover is processed with side mounted and arrayed machine clamp compound forming broaching special tools. Three kinds of 713 indexable cemented carbide coated (TiCN) blades are installed, the feed speed is 25m/min, the shift production is 1750 pieces, and the broaching cutting allowance is 1.5 ~ 3mm; The machining of the assembly arc surface and side of the cylinder block crankshaft and cylinder head camshaft spindle adopts the combined, axial series, special disc milling cutter with three side cutting edges of the machine clamp, which is assembled by 6 ~ 8 cutter discs in groups, and a total of about 146 pieces of indexable coating blades of the machine clamp are installed. In one radial cutting, the milling of 10 sides is completed with a machining allowance of 1.5 ~ 2mm; The outer ring involute teeth and three equal straight grooves of the synchronous gear ring seat of the driver are processed with a barrel type special external broach with a length of 1800mm. The broaching speed is 10m/min, and 1440 pieces are produced in a three station shift; The spline tooth profile (m=0.8mm) on the five transmission shafts of the engine is processed by using the special tools for rubbing and extruding chip free processing, which are configured in pairs with two stations. With one reciprocating motion, the spline tooth profile is rubbed and extruded into shape, and a total of 800 pieces are produced per shift; The gear processing of the driver adopts multi head small-diameter coated high-speed hobs and radial gear shaving cutters to roll and shave, and shaving is used instead of grinding, with a shift production of 800 pieces; The boring of the spherical surface in the differential housing adopts the implementation of the new EU regulations with the built-in spindle of the machine tool, and the axial reciprocating motion of the push-pull rod, which drives the boring head to move in a two-dimensional semicircular trajectory, superimposes the rotation motion of the housing, and completes the spherical surface forming boring processing with one-time tool walking; The cylinder bore of the cylinder block is bored with a double station, built-in spindle of the machine tool, axial reciprocating push-pull rod mechanism, with a cutting speed of 800m/min. the tool is moved forward - rough boring, and the tool is moved again - fine boring; For the machining of the outer cylindrical surface of the shaft end of some parts, the special tools for forming combined excircle milling and reaming are used, and the rough machining of the excircle and end face is completed by one-time cutting, multi edge milling and reaming, replacing the single edge turning process The above special high-speed and efficient tool structures are numerous, and the production pace of each processing station combined with the corresponding special CNC machine tool is 20 ~ 40 seconds. 60% - 80% of the accuracy and quality of parts depend on the accuracy and quality of these special tools and CNC machine tools, and 20% - 40% depend on the accuracy and quality of part blanks. In the production process, the quality monitoring process is post machine sampling inspection

a total of more than 250 CNC machine tools in the two production lines of engine and driver adopt HSK high-speed hollow tool handle, with a total of 6 specifications: 32, 40, 50, 63, 80, 100, of which 40, 50, 63 are the most used. HSK hollow tool handle, together with the above-mentioned multi edge special milling cutters and composite hole machining tools, forms a high-speed tool system, which completes the cutting of more than 250 processes and stations, and its high-speed dynamic balance accuracy is ≤ 2.5G

high speed special CNC machine tools: most of the processing technologies of key parts of FAW Volkswagen car engine and driver have broken through the traditional machining concept, and its high-speed special CNC machine tools have also broken through the traditional structural design form. Generally speaking, the structural design of its machine tool is based on various high-speed multi blade special forming tools and machining

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