1 Introduction
With modern industrial technology and high-performance technology products, the requirements for machining precision, surface roughness, surface integrity, processing efficiency and batch quality stability of mechanical parts are getting higher and higher. The theory and application of grinding theory have been strengthened worldwide. New abrasive processing methods and advanced abrasive processing technologies, tools and equipment have emerged, and the ancient processing technology of abrasive processing has been rapidly advanced to new heights. And become an important part of advanced processing and manufacturing processes and equipment. High-speed / ultra-high speed, high efficiency, automation / CNC / intelligent, ultra-precision, etc. is not only the main content of the current advanced abrasive processing technology, but also an important frontier of advanced processing and manufacturing processes and equipment. The unit material removal rate of ordinary grinding is less than 10 mm3/mm·s, which is far from ordinary turning and milling. Therefore, improving the processing efficiency of abrasive grains has always been the goal that people are constantly pursuing. According to the wear removal mechanism, the material removal rate can be expressed as the product of the average wear area of ​​the wear debris, the average length of the wear debris, and the number of abrasive grains involved in the cutting per unit time. Therefore, if you want to improve the grinding efficiency:
1) High-speed and ultra-high-speed and wide-wheel grinding can be used to increase the number of abrasive grains per unit time;
2) using deep grinding to increase the length of the wear debris;
3) Use strong grinding methods such as heavy load to increase the average wear area of ​​the wear debris.
These techniques are used alone or in combination to achieve a high efficiency abrasive processing technique in which the unit material removal rate is greatly improved compared to conventional grinding. It mainly includes: high speed, ultra high speed grinding, slow feed deep grinding, high efficiency deep grinding, strong grinding and strong grinding, high speed heavy load shaving, belt grinding, hard and brittle / difficult material Cutting, high efficiency grinding and polishing. Among them, the development of high-speed and ultra-high-speed grinding, slow-feeding deep-cut grinding, high-efficiency deep-cut grinding, abrasive belt grinding and heavy-duty shaving technology is the most striking.
2 High-efficiency abrasive processing technology development
1) High speed super high speed grinding
Ultra-high-speed grinding technology is a highly integrated modern new material technology, manufacturing technology, control technology, testing technology and experimental technology. It is a perfect combination of high quality and high efficiency, and is a revolutionary revolution in grinding technology. Grinding with a wheel speed greater than 45 m/s is often referred to as high speed grinding, while grinding with a line speed greater than 150 m/s is referred to as ultra high speed grinding. Ultra-high speed grinding is developing rapidly in developed countries such as Europe, Japan and the United States. The development of high-speed ultra-high-speed grinding technology in Europe started relatively early. Initially, basic research on high-speed ultra-high-speed grinding began in the late 1960s. At that time, the grinding speed of the laboratory reached 210-230 m/s. In 1979, Professor PG Werner of the Bremen University in Germany wrote an article predicting the rationality of the existence of an efficient deep-grinding zone, thus creating the concept of efficient deep grinding. In 1983, Bremen University of Germany invested in the world's first high-efficiency deep-grinding grinding machine from Germany's Guhring Automation. The power was 60kW, the rotational speed was 10000r/min, the grinding wheel diameter was 400mm, and the circumferential speed of the grinding wheel reached 209m/s. The grinding speed of the laboratory of Aachen University of Technology has reached 500m/s, which has exceeded the working limit of current machine tools and grinding wheels. The CBN grinding wheel developed by Swiss Studer has a line speed of 60 m/s or more and develops in the direction of 120 to 130 m/s.
In the mid-1960s, the wire speed of ceramic grinding wheels began to increase. In 1967, Norton sold a grinding wheel and grinding machine with a line speed of 61 m/s. By the early 1970s, there were quite a few 60m/s grinders, and 70m/s, 80m/s or even 90m/s grinders also appeared. In 1993, the United States' Edgetek Machine Company introduced the ultra-high-speed grinding machine for the first time. It uses a single-layer CBN grinding wheel with a peripheral speed of 203m/s. It can be used to process hardened sawtooth and achieve high metal removal rate. The centerless cylindrical grinding machine of the Center for Grinding Research and Development of the University of Connecticut, USA, with a maximum grinding speed of 250m/s. In 2000, S. Malkin et al. of Massachusetts State University in the United States studied the geomorphology and grinding mechanism of the grinding wheel by grinding silicon nitride with an electroplated diamond wheel at a grinding wheel speed of 149 m/s. At present, high-efficiency grinding grinders in the United States are common, mainly using CBN grinding wheels. The grinding rate of 75mm/mm·s can be achieved at a speed of 160m/s, and the high-temperature alloy Incone1718 can be efficiently ground. After processing, Ra1～2μm, the dimensional tolerance is ±13μm. In addition, a ceramic CBN grinding wheel with a diameter of 400 mm is used to grind at a speed of 150 to 200 m/s, which can reach RaO.81 μm and a dimensional tolerance of ±2.5 to 5 μm. An important research direction for high-speed grinding in the United States is low-damage grinding of advanced ceramics.
Japan's ultra-high-speed grinding is not primarily aimed at achieving high productivity, but is more interested in the overall performance of the grinding process. In the mid-1970s, Japan was able to produce high-speed grinding machines of 45m/s and 60m/s. Around 1985, on cam and crankshaft grinding machines, the grinding speed reached 80m/s. In the 1990s, Japan introduced 120m/s and 250m/s high-speed grinding machines. Japan has widely used CBN grinding wheels to replace general grinding wheels, and its purpose is to achieve high efficiency, labor saving and unmanned processing. By the year 2000, Japan had conducted an ultra-high-speed grinding test of 500 m/s. Shinizu et al., in order to obtain ultra-high grinding speed, use a modified grinding machine to juxtapose two spindles together; one as the grinding wheel shaft and the other as the workpiece spindle, and making the tangential speed opposite at the grinding point, As a result of the relative grinding speed of Vs+Vw, the grinding line speed between the grinding wheel and the workpiece is actually close to l000 m/s. This is the highest grinding speed reported so far.
China's high-speed grinding started late, and in 1958 it began to promote high-speed grinding technology. In 1964, Zhengzhou Abrasives Grinding Research Institute and Luoyang Tractor Factory cooperated in the high-speed grinding test of 50m/s. In 1974, the Zhengzhou Abrasives Grinding Research Institute carried out a grinding test of 50-60 m/s. In October 1982, Hunan University conducted a 60 m/s high-speed powerful cam grinding process test study to develop a high-speed powerful grinding cam. Axial grinders and high-speed, powerful grinding wheels provide experimental data. In the early 1980s, Northeastern University conducted a large number of high-speed grinding experiments. The YLM-1 double-sided vertical semi-automatic grinding production line developed by Northeastern University has a grinding speed of 80m/s and a grinding pressure of 2500~5000N. In 1995, Hanjiang Machine Tool Plant used a ceramic CBN grinding wheel to perform an ultra-high speed grinding test of 200 m/s. Guangxi University carried out the grinding test research of high speed and low surface roughness of 80m/s before and after 1997. By the year 2000, Hunan University had been conducting research on high-speed grinding. At the China CNC Machine Tool Exhibition in 2000, Hunan University introduced a CNC camshaft grinding machine with a maximum line speed of 120m/s. Since 2002, Hunan University has started high-speed ultra-high-speed research on a 250m/s ultra-high-speed grinding spindle system, and designed the magnetic bearing for the first time in China. From the 1990s to the present, Northeastern University has been carrying out research on ultra-high-speed grinding technology, and first developed China's first ultra-high speed with a peripheral speed of 200m/s, a rated power of 55kW and a maximum grinding wheel speed of 250m/s. Test grinding machine, and successively carried out research on dynamic and static pressure spindle system of super high speed and high power grinding machine, design and manufacture of 200m/s electroplated CBN super high speed grinding wheel, research on ultra high speed grinding chip formation mechanism, research on super high speed grinding heat transfer mechanism, high speed steel High-speed deep-grinding research, ultra-high-speed single-particle CBN grinding test research, high-speed single-grain grinding mechanism research, ultra-high-speed grinding temperature field research, grinding friction coefficient research, ultra-high-speed grinding wheel surface airflow field research, Research on the simulation of molecular dynamics of ultra-high-speed grinding mechanism and the intelligentization of grinding, some of the research results have reached the international advanced level, and some research results are in line with the international level.
2) Fast point grinding
Quick-point Grinding is an advanced ultra-high-speed grinding technology developed and patented in 1994 by Mr. Erwin Junker of Junker, Germany. It integrates ultra-high-speed grinding, CBN super-hard abrasive and CNC flexible processing three advanced technologies, with excellent processing performance, is ultra-high-speed grinding technology in high efficiency, high flexibility and mass production of high quality stability A new development. This process is mainly used for the processing of shaft and disc parts. The axis of the CBN or synthetic diamond superabrasive grinding wheel forms a certain inclination angle with the workpiece axis in the horizontal and vertical directions, and uses a thin grinding wheel to form a small area point contact with the workpiece, and comprehensively utilizes the continuous track numerical control technology to grind at a high speed, and can be combined with the vehicle. Grinding process. It has the versatility and high flexibility of CNC turning, and has higher efficiency and precision. The grinding wheel has long service life and stable quality. It is an excellent combination of new-generation CNC turning and ultra-high speed grinding, and it becomes ultra-high speed grinding. One of the main technical forms.
Germany is currently leading the research and development of this new technology. At present, it has been applied in the foreign automobile industry and tool manufacturing industry, especially in the field of automotive parts processing, namely gear shaft or camshaft. Most of these parts include cutting, journaling, shoulder, eccentric and thread grinding processes. This process can be used for all machining in one setup, which greatly improves the machining accuracy and productivity of the parts. It also has broad application prospects in gear processing, machine tool manufacturing, textile and printing machinery manufacturing, ceramic processing, and electronics industry. Some automobile manufacturing enterprises in China have also introduced dozens of such process equipments, and have achieved significant benefits. However, the application field is still small, and it is limited to the processing of automotive engine shaft parts. As there is no systematic process theory and applied research in China, there is no mastery of its core technology and theory, and it is impossible to master the process parameter design and programming technology. It cannot support the production of grinding wheels and related accessories, and can only customize the monolithic parts of a single part. And equipment depends on imports. However, due to technological monopoly in foreign countries, there are no reports on theoretical and experimental research and related technical information on in-depth systems such as fast point grinding mechanism, regularity, grinding quality control and point grinding technology. Therefore, tracking the international advanced technology, Shenren's theoretical and applied research on rapid point grinding technology is of great significance for promoting and developing this advanced technology and improving the manufacturing technology and equipment manufacturing level in China. Domestic Northeastern University has begun research on ultra-high-speed point grinding mechanism and machine tool development.
3) Slow feed grinding
Slow-feed grinding is also called deep-cutting for strong grinding. It is characterized by a large cutting depth (1 to 30 mm, 1 to 1000 times larger than ordinary grinding) and a small workpiece feed speed (3~). 300 mm/min, which is 1/100 to 1/1000 of ordinary grinding). Slow-feed grinding increases the length of the grinding debris by increasing the depth of the grinding wheel to achieve a high removal rate (more than 5 times higher than normal grinding). This method is dominant in surface grinding and is mainly used for grinding grooves and forming surfaces. In recent years, Germany, the United Kingdom, the United States, Japan and Switzerland have developed a series of special slow-feeding forming grinding machines. In particular, the application of ball screw and linear motor technology has further promoted the practical application of the slow-feed grinding technology. The characteristics of slow-feed grinding are as follows:
· High processing efficiency. Since the grinding depth is greatly increased, the contact arc length is increased, and the number of abrasive grains participating in the cutting is increased, so that the required workpiece shape can be directly ground, the coarse and fine machining are combined, and the processing efficiency is greatly improved;
· Expanded the range of grinding processes. Since the blank can be processed at one time, it can effectively solve some difficult material processing problems, such as gas turbine blade forming surface processing, high temperature alloy, stainless steel, high speed steel surface or groove grinding, etc., and its efficiency is higher than milling. Multiple times. Using the CBN grinding wheel to slowly feed the vacuum pump rotor groove is not only more efficient than milling, but also has good processing quality and cost savings of about 40%;
·The impact damage of the grinding wheel is small, and the shape accuracy of the workpiece is stable. As the slow feed and the number of strokes are reduced, the number of collisions and collisions between the grinding wheel and the edge of the workpiece are reduced, the service life of the grinding wheel is prolonged, and the waviness of the machined surface is also reduced;
·The grinding force is large, the grinding temperature is high, the chips are long and severely deformed in the grinding zone, and the grinding wheel is easily blocked. Therefore, a large amount of cutting fluid must be sufficiently supplied during the grinding process to reduce the grinding temperature and ensure the quality of the ground surface;
The processing precision is 2 to 5 μm, and the surface roughness Ra is 0.1 to 0.4 μm.
4) Efficient deep-cut grinding (HEDG)
High Eficiency Deep Grinding (HEDG) technology is a kind of grinding wheel with high speed (100~250m/s), high feed rate (0.5~10m/min) and large depth of cut (0.1~) developed in recent years. 30mm) is an integrated high-efficiency grinding technology. The concept of efficient deep grinding was founded in 1980 by Professor Werner of the University of Bremen, Germany. At present, European companies are leading the way in the application of high-efficiency deep-grinding technology. High-efficiency deep grinding can be intuitively seen as a combination of slow-feed grinding and ultra-high-speed grinding. Different from ordinary grinding, high-efficiency deep grinding can complete the rough finishing process consisting of multiple processes such as turning, milling and grinding through a grinding stroke, and obtain a metal removal rate much higher than ordinary grinding (grinding The removal rate is 100 to 1000 times higher than that of ordinary grinding. The surface quality can also reach the level of ordinary grinding. Production efficiency is greatly improved because it uses a much faster feed rate than slow feed grinding. Later, it was further developed on the basis of CBN grinding wheel 200-300m/. Ultra-high speed deep grinding grinder. Grinding with a ceramic bond grinding wheel at a speed of 120 m/s, the specific grinding rate can reach 500-1000 mm3/mm·s, which is more than 5 times higher than turning and milling. In the United Kingdom, a low-alloy steel 51CrV4 was subjected to a 146 m/s high-efficiency deep-grinding test using a disc-shaped CBN grinding wheel. The material removal rate exceeded 400 mm3/mm·s. Germany Guhring Automation FD613 super high-speed surface grinder, 150m / s and CBN grinding width 1 ~ 10mm, depth 30mm rotor groove when the table feed speed of 3000mm / min, on the 125m / s groove grinding machine, grinding deep The 20mm drill groove can be completed in one time, and the metal grinding rate is 500400mm3/mm·s. High-efficiency forming grinding is also widely used as a kind of high-efficiency deep grinding. It can be processed with more complicated profiles by CNC system and CBN forming grinding wheel. The surface quality can be compared with ordinary grinding. This technology has been successfully used in the grinding of screws, screws, gears, rotor slots, tool grooves, etc. The process parameters of ordinary grinding, slow-feed grinding and high-efficiency deep-cut grinding are shown in Table 1.
5) High-speed Meng load shortage
Heavy-duty grinding is a grinding method for the purpose of quickly cutting the machining allowance with a large normal grinding pressure. It is suitable for the grinding of steel billets, the cleaning of castings and forgings, and the rough grinding of steel sheets. It accounts for 3% to 7% of the quality of the billet. Generally, it is not necessary to dress the grinding wheel. The grinding speed is usually 50~100m/s, the normal grinding force is generally 2.5~15kN, the metal grinding rate is 1000kg/h, the grinding power is generally 100~150kW, and the individual reaches 300kW. The technology has developed rapidly in recent years, and the line speed of the grinding wheel has generally reached 80m/s, and some have reached 120m/s. Grinding normal force can reach 10,000 ~ 12000N, even up to 30,000N; material grinding rate can reach 500 ~ 600kg / h, up to 1000kg / h. The heavy-duty roughing machine has been basically automated, and the normal pressure can be automatically adjusted with the change of the feed speed and the rotation speed of the grinding wheel can be kept constant, which greatly improves the production efficiency of the waste. Northeastern University began to study the high-speed heavy-duty steel billet grinding experiment from the 0s of the year, and established a complete high-speed heavy-duty roughing theory system. In recent years, it has also developed a parallel robot for automatic grinding of steel billets. The maximum grinding pressure is 2520N. ~5000N, the maximum metal removal rate is 1780g/min. The technical characteristics of heavy load ruin include: (1) high grinding pressure, high grinding wheel speed and metal removal rate, high grinding power, and sufficient rigidity and strength of the machine tool; (2) high strength, high hardness and coarseness Heavy-duty rough grinding wheel with a particle size. Generally, resin binders and high-toughness abrasives such as brown corundum, microcrystalline corundum, sintered corundum and fused corundum are used, super hard hardness, and the grinding wheel does not need to be trimmed; (3) dry grinding method is adopted.
6) Abrasive belt grinding
Abrasive belt grinding is a new type of coating grinding process known as "universal grinding" and "cold grinding" in the precision machining of material surfaces. In the modern manufacturing industry, it has been used as a grinding wheel. Grinding is an equally important and indispensable method of machining. In industrialized countries, the application of abrasive belt grinding has become very common. The amount of abrasive belt grinding has gradually approached the grinding wheel grinding machine, and its output value ratio is almost 1:1.
Since the 1960s, new progress has been made in electrostatic sand-blasting technology, which has made great progress in the manufacturing of abrasive belts and belt grinding machines in the United States, Britain, Japan and Germany. The possession is close to the grinding wheel grinding machine, its output value is 49:51 in the United States, 45:55 in Germany, and 25:75 in Japan. The grinding belt has accounted for more than half of the total grinding volume. The coated abrasive processing has become a developed country. An important means of achieving high economic returns. The three famous belt belts in the United States have developed more than 40,000 specifications of abrasive belts, and 55 companies produce belt grinding machines. Currently, nearly 400,000 belt grinding machines and nearly 95 million square meters of abrasive belts are produced annually in countries around the world. Abrasive belt grinding is currently developing along the direction of strength, high speed, high efficiency and precision. For example, in Japan in the early 1990s, the ultra-abrasive belt was successfully developed by electrophoretic adsorption, and the processing of brittle materials such as precision ceramics, quartz and silicon wafers was carried out. Accuracy is up to a dozen nanometers and can be plastically ground. A belt grinding machine produced in the United States can complete the work of 5 milling machines. In the past, the cast iron bearing body was machined with a carbide end mill. Each processing time was 4.8 min. The powerful grinding belt grinder was used to reduce the processing time to 0.8 min. The annual processing cost will be 45,000 US dollars.
China's abrasive belt grinding research and coated abrasive manufacturing started late. In recent years, some universities and research institutes have carried out research and development of abrasive belt grinding technology. During the “Seventh Five-Year Plan†period, Zhengzhou Sanmao Institute, Huazhong University of Science and Technology and Hunan University jointly completed the research project of “Experimental Research on Abrasive Belt Grinding Processâ€. Northeastern University has experimentally studied the grinding of abrasive belts such as metal wire and blade profile; Chongqing University has successively completed projects such as “cycloid belt grinding process†and “high-precision plane belt grinding processâ€, and recently With the research of new composite grinding technology, the research on the grinding of the engine connecting rod end face and the strong gas belt of the West-East Gas Pipeline weld is carried out. The Hunan University system studied the grinding temperature of the abrasive belt. In 1992, it passed the national appraisal of the grinding process test of the 190 diesel engine cylinder head flat belt. Huazhong University of Science and Technology has carried out research on five-coordinate linkage CNC belt grinding blade profile. Recently, Huadong Textile University has proposed the application of ultra-abrasive granule electrophoresis adsorption belt to achieve plastic grinding of brittle materials, in order to break the precision limit of abrasive belt grinding and realize nano-machining. China's second grinding wheel factory and Shanghai grinding wheel factory have successively introduced complete sets of technology and equipment for belt manufacturing from Germany, Italy and Switzerland. The annual production of abrasive belts is 5×106m2 and 6×106m2 respectively.
3 Key technologies for high efficiency abrasive processing
1) High-efficiency grinding wheel
High-efficiency grinding wheel should have good wear resistance, high dynamic balance accuracy, crack resistance, good damping characteristics, high rigidity and good thermal conductivity, and its mechanical strength must withstand the cutting force during efficient grinding. Wait. High-efficiency grinding wheels can use corundum, silicon carbide, CBN, and diamond abrasives. The binder may be a ceramic, a resin or a metal bond or the like. The resin-bonded corundum, silicon carbide, and cubic boron nitride abrasive wheels can be used at speeds up to 125 m/s. The single-layer electroplated CBN grinding wheel can be used up to 250m/s and has reached 340m/s in the test. The ceramic bond grinding wheel can grind up to 200m/s. Ceramic bond grinding wheels are easier to trim than other types of grinding wheels. Compared to high-density resin and metal bond grinding wheels, ceramic bond grinding wheels can achieve a wide range of porosity through varying production processes. Norton Company of the United States has developed a method of holding abrasive grains by chemical bonding, which can make the abrasive grains protrude 50% of height without falling off, and the tensile strength of the bonding agent exceeds 1553 N/mm 2 (the plating nickel-based bonding agent is 345 ~) 449N/mm2). China's Nanjing University of Aeronautics and Astronautics has successfully developed high-temperature brazing single-layer super-hard abrasive grinding wheels to reduce grinding heat, increase grinding ratio, and achieved good results. Aheng University of Technology uses a spray technique on the aluminum base of its grinding wheel to achieve a reliable bond between the abrasive layer and the substrate. In order to ensure that the grinding wheel remains sharp throughout its service life, the structure of the grinding wheel needs to facilitate the splitting of the abrasive particles. In order to achieve the purpose of sharpening the grinding wheel, in addition to reducing the proportion of the bonding agent as much as possible, the spatial distribution of the abrasive particles should be optimized. To this end, the grinding wheel should have a complete set of finishing technology. Grinding wheel dressing is one of the key factors determining the quality of grinding. Different dressing methods have different characteristics. Therefore, it is necessary to consider the processing conditions, workpiece materials, grinding wheel materials and other factors in order to select the best dressing solution.
Spindle and its bearing technology
The performance of the high-efficiency grinding machine spindle unit largely determines the limit of high-efficiency grinding. Therefore, in order to achieve high-efficiency grinding, the grinding wheel drive and bearing speed are often required. The high speed of the spindle requires sufficient rigidity of the spindle, high rotation precision, good thermal stability, reliability, low power consumption and long life. To meet these requirements, the manufacture and dynamic balance of the spindle, the support of the spindle (bearing), the lubrication and cooling of the spindle system, and the rigidity of the system are important. The spindle bearing can be a ceramic rolling bearing, a magnetic bearing, an aerostatic bearing or a hydrodynamic bearing. Ceramic ball bearings have the advantages of light weight, small thermal expansion coefficient, high hardness, high temperature resistance, dimensional stability at high temperature, corrosion resistance, high life and high modulus of elasticity. The disadvantage is that it is difficult to manufacture, high in cost, and sensitive to tensile stress and notched stress. The highest surface speed of the magnetic bearing can reach 200m / s, which may become an option for future ultra-high speed spindle bearings. At present, the main problem of the magnetic floating bearing is that the rigidity and the load capacity are low, and the magnet used is too large and expensive compared with the size of the rotating body. The aerostatic bearing has the characteristics of high rotation precision, no vibration, low frictional resistance, durability, and high-speed rotation. For high speed, light load and ultra precision applications. Hydrodynamic and hydrostatic bearings have too much power loss when no load is used, mainly for low speed and heavy duty spindles.
High efficiency grinding machine
High-speed and efficient machining not only requires a high spindle speed and power, but also requires a high feed rate and acceleration of the machine table. It is also necessary to combine as many grinding functions as possible to achieve all the grinding processes on one grinding machine. In addition, the machine is required to have high dynamic accuracy, high damping, high vibration resistance and thermal stability, and a highly automated and reliable grinding process.
The grinding machine support member is a supporting base member of the grinding wheel frame, the head frame, the tail frame, the work table and the like. It is required to have good static stiffness, dynamic stiffness and thermal stiffness. For high-speed super-high-speed grinding machines, polymer concrete (artificial granite) is used to manufacture beds and columns at home and abroad, and some columns and bases are cast in cast iron, and steel plates are welded and damping materials are used. Filling its inner cavity to improve its shock resistance, these have received good results. The feed system is one of the important indexes for evaluating the performance of high-speed ultra-high-speed grinding machines. With the development of high-speed ultra-high-speed machining, linear servo motor direct drive technology and high dynamic performance linear motor combined with digital control technology are widely used at home and abroad. For example, the linear feed motor of Siemens Germany can reach a maximum feed speed of 200m/min, its maximum thrust can reach 6600N, and the maximum displacement distance is 504mm.
Grinding fluid supply technology
At high speeds, the airflow barrier prevents the grinding fluid from effectively entering the grinding zone and may also have the effect of film boiling. Therefore, it is extremely important to increase the effective part of the grinding fluid into the grinding zone by using the proper injection method to improve the cooling and lubrication effects, and to improve the quality of the workpiece and reduce the wear of the grinding wheel. Commonly used grinding fluid injection methods are: manual liquid supply method and pouring method, high pressure injection method, air baffle assisted cut off air flow method, grinding wheel internal cooling method, using slotted grinding wheel method, and the like. In the case of ultra-high speed conditions, in order to achieve cooling of the grinding zone and to wash away the chips, the injection of the grinding fluid must have sufficient momentum to break the high-speed airflow around the grinding wheel and allow the grinding fluid to reach the grinding zone. In order to ensure the surface quality of ultra-high-speed grinding, improve the utilization rate of grinding fluid, and reduce the adverse effects of residual impurities in the grinding fluid on the processing quality and machine tool system, a high-efficiency and high-precision grinding fluid filtration system must be adopted. The grinding fluid sprayed from the nozzle on the grinding wheel will form a severe oil mist under strong centrifugal force. Therefore, the super high-speed grinding machine should also close the grinding zone and extract the oil mist in time. The oil and gas separation is then carried out by means of centrifugation and electrostatics.
Grinding wheel, workpiece installation positioning and safety protection technology
High-speed and ultra-high-speed grinding wheels have great kinetic energy. High-strength semi-closed or closed grinding wheel guards must be installed. It is best to lay buffer materials in the cover to absorb or reduce the secondary ejection of the grinding wheel fragments.
Grinding state detection and numerical control technology
In the high-efficiency grinding process, due to the extremely high speed of the grinding wheel, the grinding phenomenon caused by the ultra-high speed of the grinding wheel often occurs. The monitoring of the grinding wheel crushing and wear state is related to the smooth progress of the grinding work and the guarantee of the processing quality and the complete surface of the part. The key to the nature; in ultra-high-speed machining, the accuracy of the grinding wheel and the workpiece, the accuracy of the grinding wheel and the dressing wheel will directly affect the dimensional accuracy of the workpiece and the dressing quality of the grinding wheel. Therefore, in the ultra-high speed grinding process, The online intelligent monitoring system is an important factor in ensuring the quality of grinding and improving the processing productivity. At present, acoustic emission technology has been successfully used for non-destructive testing of ultra-high-speed grinding, using various acoustic emission sources generated during the grinding process, such as elastic contact between the grinding wheel and the workpiece, cracking of the grinding wheel adhesive, grinding of the grinding wheel and friction of the workpiece, Elastic waves can be emitted from surface cracks and burns, contact between the grinding wheel and the dressing wheel. These factors are closely related to the material of the workpiece, the grinding conditions, and the state of the surface of the grinding wheel. Changes in these factors will inevitably cause changes in the amplitude, spectrum, etc. of the acoustic emission signal, which allows us to discriminate the grinding state by detecting changes in the acoustic emission signal. Therefore, the acoustic emission technology can be used to monitor the grinding crack and the grinding burn, the grinding wheel crushing wheel wear, the grinding wheel is in contact with the workpiece, the grinding wheel is in contact with the dressing wheel, and satisfactory results are obtained. In addition, online monitoring technology for workpiece dimensional accuracy, shape accuracy, positional accuracy and surface quality, high-precision, high-reliability, practical testing techniques and instruments are essential for high-efficiency grinding.
4 Conclusion
Efficient grinding technology is an advanced manufacturing technology that completely solves the high-precision and low-efficiency processing limitations of traditional grinding. It achieves high efficiency and high precision while achieving high surface integrity for various materials and shapes. Processing and reducing costs. Under the existing conditions in China, it is of great significance to strengthen the research, promotion and application of high-efficiency grinding processing technology to improve the processing level of China's machinery manufacturing industry and accelerate the development of new products. Today's applications of superhard materials are becoming more widespread, and high-speed and high-efficiency grinding is the preferred process for processing superhard materials and difficult-to-cut materials. Due to the application of superabrasives, the development of high-speed, high-power precision machine tools and CNC technology, the development of new grinding fluids and wheel dressing, high-speed ultra-high-speed grinding and high-efficiency grinding technology, grinding automation and The development of technologies such as intelligence makes high-efficiency abrasive grain processing have a more important position in the field of mechanical manufacturing and has a good development prospect.
With modern industrial technology and high-performance technology products, the requirements for machining precision, surface roughness, surface integrity, processing efficiency and batch quality stability of mechanical parts are getting higher and higher. The theory and application of grinding theory have been strengthened worldwide. New abrasive processing methods and advanced abrasive processing technologies, tools and equipment have emerged, and the ancient processing technology of abrasive processing has been rapidly advanced to new heights. And become an important part of advanced processing and manufacturing processes and equipment. High-speed / ultra-high speed, high efficiency, automation / CNC / intelligent, ultra-precision, etc. is not only the main content of the current advanced abrasive processing technology, but also an important frontier of advanced processing and manufacturing processes and equipment. The unit material removal rate of ordinary grinding is less than 10 mm3/mm·s, which is far from ordinary turning and milling. Therefore, improving the processing efficiency of abrasive grains has always been the goal that people are constantly pursuing. According to the wear removal mechanism, the material removal rate can be expressed as the product of the average wear area of ​​the wear debris, the average length of the wear debris, and the number of abrasive grains involved in the cutting per unit time. Therefore, if you want to improve the grinding efficiency:
1) High-speed and ultra-high-speed and wide-wheel grinding can be used to increase the number of abrasive grains per unit time;
2) using deep grinding to increase the length of the wear debris;
3) Use strong grinding methods such as heavy load to increase the average wear area of ​​the wear debris.
These techniques are used alone or in combination to achieve a high efficiency abrasive processing technique in which the unit material removal rate is greatly improved compared to conventional grinding. It mainly includes: high speed, ultra high speed grinding, slow feed deep grinding, high efficiency deep grinding, strong grinding and strong grinding, high speed heavy load shaving, belt grinding, hard and brittle / difficult material Cutting, high efficiency grinding and polishing. Among them, the development of high-speed and ultra-high-speed grinding, slow-feeding deep-cut grinding, high-efficiency deep-cut grinding, abrasive belt grinding and heavy-duty shaving technology is the most striking.
2 High-efficiency abrasive processing technology development
1) High speed super high speed grinding
Ultra-high-speed grinding technology is a highly integrated modern new material technology, manufacturing technology, control technology, testing technology and experimental technology. It is a perfect combination of high quality and high efficiency, and is a revolutionary revolution in grinding technology. Grinding with a wheel speed greater than 45 m/s is often referred to as high speed grinding, while grinding with a line speed greater than 150 m/s is referred to as ultra high speed grinding. Ultra-high speed grinding is developing rapidly in developed countries such as Europe, Japan and the United States. The development of high-speed ultra-high-speed grinding technology in Europe started relatively early. Initially, basic research on high-speed ultra-high-speed grinding began in the late 1960s. At that time, the grinding speed of the laboratory reached 210-230 m/s. In 1979, Professor PG Werner of the Bremen University in Germany wrote an article predicting the rationality of the existence of an efficient deep-grinding zone, thus creating the concept of efficient deep grinding. In 1983, Bremen University of Germany invested in the world's first high-efficiency deep-grinding grinding machine from Germany's Guhring Automation. The power was 60kW, the rotational speed was 10000r/min, the grinding wheel diameter was 400mm, and the circumferential speed of the grinding wheel reached 209m/s. The grinding speed of the laboratory of Aachen University of Technology has reached 500m/s, which has exceeded the working limit of current machine tools and grinding wheels. The CBN grinding wheel developed by Swiss Studer has a line speed of 60 m/s or more and develops in the direction of 120 to 130 m/s.
In the mid-1960s, the wire speed of ceramic grinding wheels began to increase. In 1967, Norton sold a grinding wheel and grinding machine with a line speed of 61 m/s. By the early 1970s, there were quite a few 60m/s grinders, and 70m/s, 80m/s or even 90m/s grinders also appeared. In 1993, the United States' Edgetek Machine Company introduced the ultra-high-speed grinding machine for the first time. It uses a single-layer CBN grinding wheel with a peripheral speed of 203m/s. It can be used to process hardened sawtooth and achieve high metal removal rate. The centerless cylindrical grinding machine of the Center for Grinding Research and Development of the University of Connecticut, USA, with a maximum grinding speed of 250m/s. In 2000, S. Malkin et al. of Massachusetts State University in the United States studied the geomorphology and grinding mechanism of the grinding wheel by grinding silicon nitride with an electroplated diamond wheel at a grinding wheel speed of 149 m/s. At present, high-efficiency grinding grinders in the United States are common, mainly using CBN grinding wheels. The grinding rate of 75mm/mm·s can be achieved at a speed of 160m/s, and the high-temperature alloy Incone1718 can be efficiently ground. After processing, Ra1～2μm, the dimensional tolerance is ±13μm. In addition, a ceramic CBN grinding wheel with a diameter of 400 mm is used to grind at a speed of 150 to 200 m/s, which can reach RaO.81 μm and a dimensional tolerance of ±2.5 to 5 μm. An important research direction for high-speed grinding in the United States is low-damage grinding of advanced ceramics.
Japan's ultra-high-speed grinding is not primarily aimed at achieving high productivity, but is more interested in the overall performance of the grinding process. In the mid-1970s, Japan was able to produce high-speed grinding machines of 45m/s and 60m/s. Around 1985, on cam and crankshaft grinding machines, the grinding speed reached 80m/s. In the 1990s, Japan introduced 120m/s and 250m/s high-speed grinding machines. Japan has widely used CBN grinding wheels to replace general grinding wheels, and its purpose is to achieve high efficiency, labor saving and unmanned processing. By the year 2000, Japan had conducted an ultra-high-speed grinding test of 500 m/s. Shinizu et al., in order to obtain ultra-high grinding speed, use a modified grinding machine to juxtapose two spindles together; one as the grinding wheel shaft and the other as the workpiece spindle, and making the tangential speed opposite at the grinding point, As a result of the relative grinding speed of Vs+Vw, the grinding line speed between the grinding wheel and the workpiece is actually close to l000 m/s. This is the highest grinding speed reported so far.
China's high-speed grinding started late, and in 1958 it began to promote high-speed grinding technology. In 1964, Zhengzhou Abrasives Grinding Research Institute and Luoyang Tractor Factory cooperated in the high-speed grinding test of 50m/s. In 1974, the Zhengzhou Abrasives Grinding Research Institute carried out a grinding test of 50-60 m/s. In October 1982, Hunan University conducted a 60 m/s high-speed powerful cam grinding process test study to develop a high-speed powerful grinding cam. Axial grinders and high-speed, powerful grinding wheels provide experimental data. In the early 1980s, Northeastern University conducted a large number of high-speed grinding experiments. The YLM-1 double-sided vertical semi-automatic grinding production line developed by Northeastern University has a grinding speed of 80m/s and a grinding pressure of 2500~5000N. In 1995, Hanjiang Machine Tool Plant used a ceramic CBN grinding wheel to perform an ultra-high speed grinding test of 200 m/s. Guangxi University carried out the grinding test research of high speed and low surface roughness of 80m/s before and after 1997. By the year 2000, Hunan University had been conducting research on high-speed grinding. At the China CNC Machine Tool Exhibition in 2000, Hunan University introduced a CNC camshaft grinding machine with a maximum line speed of 120m/s. Since 2002, Hunan University has started high-speed ultra-high-speed research on a 250m/s ultra-high-speed grinding spindle system, and designed the magnetic bearing for the first time in China. From the 1990s to the present, Northeastern University has been carrying out research on ultra-high-speed grinding technology, and first developed China's first ultra-high speed with a peripheral speed of 200m/s, a rated power of 55kW and a maximum grinding wheel speed of 250m/s. Test grinding machine, and successively carried out research on dynamic and static pressure spindle system of super high speed and high power grinding machine, design and manufacture of 200m/s electroplated CBN super high speed grinding wheel, research on ultra high speed grinding chip formation mechanism, research on super high speed grinding heat transfer mechanism, high speed steel High-speed deep-grinding research, ultra-high-speed single-particle CBN grinding test research, high-speed single-grain grinding mechanism research, ultra-high-speed grinding temperature field research, grinding friction coefficient research, ultra-high-speed grinding wheel surface airflow field research, Research on the simulation of molecular dynamics of ultra-high-speed grinding mechanism and the intelligentization of grinding, some of the research results have reached the international advanced level, and some research results are in line with the international level.
2) Fast point grinding
Quick-point Grinding is an advanced ultra-high-speed grinding technology developed and patented in 1994 by Mr. Erwin Junker of Junker, Germany. It integrates ultra-high-speed grinding, CBN super-hard abrasive and CNC flexible processing three advanced technologies, with excellent processing performance, is ultra-high-speed grinding technology in high efficiency, high flexibility and mass production of high quality stability A new development. This process is mainly used for the processing of shaft and disc parts. The axis of the CBN or synthetic diamond superabrasive grinding wheel forms a certain inclination angle with the workpiece axis in the horizontal and vertical directions, and uses a thin grinding wheel to form a small area point contact with the workpiece, and comprehensively utilizes the continuous track numerical control technology to grind at a high speed, and can be combined with the vehicle. Grinding process. It has the versatility and high flexibility of CNC turning, and has higher efficiency and precision. The grinding wheel has long service life and stable quality. It is an excellent combination of new-generation CNC turning and ultra-high speed grinding, and it becomes ultra-high speed grinding. One of the main technical forms.
Germany is currently leading the research and development of this new technology. At present, it has been applied in the foreign automobile industry and tool manufacturing industry, especially in the field of automotive parts processing, namely gear shaft or camshaft. Most of these parts include cutting, journaling, shoulder, eccentric and thread grinding processes. This process can be used for all machining in one setup, which greatly improves the machining accuracy and productivity of the parts. It also has broad application prospects in gear processing, machine tool manufacturing, textile and printing machinery manufacturing, ceramic processing, and electronics industry. Some automobile manufacturing enterprises in China have also introduced dozens of such process equipments, and have achieved significant benefits. However, the application field is still small, and it is limited to the processing of automotive engine shaft parts. As there is no systematic process theory and applied research in China, there is no mastery of its core technology and theory, and it is impossible to master the process parameter design and programming technology. It cannot support the production of grinding wheels and related accessories, and can only customize the monolithic parts of a single part. And equipment depends on imports. However, due to technological monopoly in foreign countries, there are no reports on theoretical and experimental research and related technical information on in-depth systems such as fast point grinding mechanism, regularity, grinding quality control and point grinding technology. Therefore, tracking the international advanced technology, Shenren's theoretical and applied research on rapid point grinding technology is of great significance for promoting and developing this advanced technology and improving the manufacturing technology and equipment manufacturing level in China. Domestic Northeastern University has begun research on ultra-high-speed point grinding mechanism and machine tool development.
3) Slow feed grinding
Slow-feed grinding is also called deep-cutting for strong grinding. It is characterized by a large cutting depth (1 to 30 mm, 1 to 1000 times larger than ordinary grinding) and a small workpiece feed speed (3~). 300 mm/min, which is 1/100 to 1/1000 of ordinary grinding). Slow-feed grinding increases the length of the grinding debris by increasing the depth of the grinding wheel to achieve a high removal rate (more than 5 times higher than normal grinding). This method is dominant in surface grinding and is mainly used for grinding grooves and forming surfaces. In recent years, Germany, the United Kingdom, the United States, Japan and Switzerland have developed a series of special slow-feeding forming grinding machines. In particular, the application of ball screw and linear motor technology has further promoted the practical application of the slow-feed grinding technology. The characteristics of slow-feed grinding are as follows:
· High processing efficiency. Since the grinding depth is greatly increased, the contact arc length is increased, and the number of abrasive grains participating in the cutting is increased, so that the required workpiece shape can be directly ground, the coarse and fine machining are combined, and the processing efficiency is greatly improved;
· Expanded the range of grinding processes. Since the blank can be processed at one time, it can effectively solve some difficult material processing problems, such as gas turbine blade forming surface processing, high temperature alloy, stainless steel, high speed steel surface or groove grinding, etc., and its efficiency is higher than milling. Multiple times. Using the CBN grinding wheel to slowly feed the vacuum pump rotor groove is not only more efficient than milling, but also has good processing quality and cost savings of about 40%;
·The impact damage of the grinding wheel is small, and the shape accuracy of the workpiece is stable. As the slow feed and the number of strokes are reduced, the number of collisions and collisions between the grinding wheel and the edge of the workpiece are reduced, the service life of the grinding wheel is prolonged, and the waviness of the machined surface is also reduced;
·The grinding force is large, the grinding temperature is high, the chips are long and severely deformed in the grinding zone, and the grinding wheel is easily blocked. Therefore, a large amount of cutting fluid must be sufficiently supplied during the grinding process to reduce the grinding temperature and ensure the quality of the ground surface;
The processing precision is 2 to 5 μm, and the surface roughness Ra is 0.1 to 0.4 μm.
4) Efficient deep-cut grinding (HEDG)
High Eficiency Deep Grinding (HEDG) technology is a kind of grinding wheel with high speed (100~250m/s), high feed rate (0.5~10m/min) and large depth of cut (0.1~) developed in recent years. 30mm) is an integrated high-efficiency grinding technology. The concept of efficient deep grinding was founded in 1980 by Professor Werner of the University of Bremen, Germany. At present, European companies are leading the way in the application of high-efficiency deep-grinding technology. High-efficiency deep grinding can be intuitively seen as a combination of slow-feed grinding and ultra-high-speed grinding. Different from ordinary grinding, high-efficiency deep grinding can complete the rough finishing process consisting of multiple processes such as turning, milling and grinding through a grinding stroke, and obtain a metal removal rate much higher than ordinary grinding (grinding The removal rate is 100 to 1000 times higher than that of ordinary grinding. The surface quality can also reach the level of ordinary grinding. Production efficiency is greatly improved because it uses a much faster feed rate than slow feed grinding. Later, it was further developed on the basis of CBN grinding wheel 200-300m/. Ultra-high speed deep grinding grinder. Grinding with a ceramic bond grinding wheel at a speed of 120 m/s, the specific grinding rate can reach 500-1000 mm3/mm·s, which is more than 5 times higher than turning and milling. In the United Kingdom, a low-alloy steel 51CrV4 was subjected to a 146 m/s high-efficiency deep-grinding test using a disc-shaped CBN grinding wheel. The material removal rate exceeded 400 mm3/mm·s. Germany Guhring Automation FD613 super high-speed surface grinder, 150m / s and CBN grinding width 1 ~ 10mm, depth 30mm rotor groove when the table feed speed of 3000mm / min, on the 125m / s groove grinding machine, grinding deep The 20mm drill groove can be completed in one time, and the metal grinding rate is 500400mm3/mm·s. High-efficiency forming grinding is also widely used as a kind of high-efficiency deep grinding. It can be processed with more complicated profiles by CNC system and CBN forming grinding wheel. The surface quality can be compared with ordinary grinding. This technology has been successfully used in the grinding of screws, screws, gears, rotor slots, tool grooves, etc. The process parameters of ordinary grinding, slow-feed grinding and high-efficiency deep-cut grinding are shown in Table 1.
Table 1 Comparison of process parameters of ordinary grinding, slow-feed grinding and high-efficiency deep-cut grinding
| parameter | Ordinary grinding | Slow feed grinding | Efficient deep grinding |
| Ap(mm) | 0.001 to 0.05 | 0.1 to 30 | 0.1 to 30 |
| V w (m/min) | 1 to 30 | 0.05~0.5 | 0.5 to 10 |
| V s (m/s) | 20~60 | 20~60 | 80~200 |
| Z w (mm 3 /mm·s) | 0.1 to 10 | 1.0 to 10 | 50～2000 |
| Grinding wheel | WA60HV | WA60HV | WA60HV |
| Grinding fluid | Water-based grinding fluid | Oil-soluble grinding fluid | Water-based grinding fluid |
Heavy-duty grinding is a grinding method for the purpose of quickly cutting the machining allowance with a large normal grinding pressure. It is suitable for the grinding of steel billets, the cleaning of castings and forgings, and the rough grinding of steel sheets. It accounts for 3% to 7% of the quality of the billet. Generally, it is not necessary to dress the grinding wheel. The grinding speed is usually 50~100m/s, the normal grinding force is generally 2.5~15kN, the metal grinding rate is 1000kg/h, the grinding power is generally 100~150kW, and the individual reaches 300kW. The technology has developed rapidly in recent years, and the line speed of the grinding wheel has generally reached 80m/s, and some have reached 120m/s. Grinding normal force can reach 10,000 ~ 12000N, even up to 30,000N; material grinding rate can reach 500 ~ 600kg / h, up to 1000kg / h. The heavy-duty roughing machine has been basically automated, and the normal pressure can be automatically adjusted with the change of the feed speed and the rotation speed of the grinding wheel can be kept constant, which greatly improves the production efficiency of the waste. Northeastern University began to study the high-speed heavy-duty steel billet grinding experiment from the 0s of the year, and established a complete high-speed heavy-duty roughing theory system. In recent years, it has also developed a parallel robot for automatic grinding of steel billets. The maximum grinding pressure is 2520N. ~5000N, the maximum metal removal rate is 1780g/min. The technical characteristics of heavy load ruin include: (1) high grinding pressure, high grinding wheel speed and metal removal rate, high grinding power, and sufficient rigidity and strength of the machine tool; (2) high strength, high hardness and coarseness Heavy-duty rough grinding wheel with a particle size. Generally, resin binders and high-toughness abrasives such as brown corundum, microcrystalline corundum, sintered corundum and fused corundum are used, super hard hardness, and the grinding wheel does not need to be trimmed; (3) dry grinding method is adopted.
6) Abrasive belt grinding
Abrasive belt grinding is a new type of coating grinding process known as "universal grinding" and "cold grinding" in the precision machining of material surfaces. In the modern manufacturing industry, it has been used as a grinding wheel. Grinding is an equally important and indispensable method of machining. In industrialized countries, the application of abrasive belt grinding has become very common. The amount of abrasive belt grinding has gradually approached the grinding wheel grinding machine, and its output value ratio is almost 1:1.
Since the 1960s, new progress has been made in electrostatic sand-blasting technology, which has made great progress in the manufacturing of abrasive belts and belt grinding machines in the United States, Britain, Japan and Germany. The possession is close to the grinding wheel grinding machine, its output value is 49:51 in the United States, 45:55 in Germany, and 25:75 in Japan. The grinding belt has accounted for more than half of the total grinding volume. The coated abrasive processing has become a developed country. An important means of achieving high economic returns. The three famous belt belts in the United States have developed more than 40,000 specifications of abrasive belts, and 55 companies produce belt grinding machines. Currently, nearly 400,000 belt grinding machines and nearly 95 million square meters of abrasive belts are produced annually in countries around the world. Abrasive belt grinding is currently developing along the direction of strength, high speed, high efficiency and precision. For example, in Japan in the early 1990s, the ultra-abrasive belt was successfully developed by electrophoretic adsorption, and the processing of brittle materials such as precision ceramics, quartz and silicon wafers was carried out. Accuracy is up to a dozen nanometers and can be plastically ground. A belt grinding machine produced in the United States can complete the work of 5 milling machines. In the past, the cast iron bearing body was machined with a carbide end mill. Each processing time was 4.8 min. The powerful grinding belt grinder was used to reduce the processing time to 0.8 min. The annual processing cost will be 45,000 US dollars.
China's abrasive belt grinding research and coated abrasive manufacturing started late. In recent years, some universities and research institutes have carried out research and development of abrasive belt grinding technology. During the “Seventh Five-Year Plan†period, Zhengzhou Sanmao Institute, Huazhong University of Science and Technology and Hunan University jointly completed the research project of “Experimental Research on Abrasive Belt Grinding Processâ€. Northeastern University has experimentally studied the grinding of abrasive belts such as metal wire and blade profile; Chongqing University has successively completed projects such as “cycloid belt grinding process†and “high-precision plane belt grinding processâ€, and recently With the research of new composite grinding technology, the research on the grinding of the engine connecting rod end face and the strong gas belt of the West-East Gas Pipeline weld is carried out. The Hunan University system studied the grinding temperature of the abrasive belt. In 1992, it passed the national appraisal of the grinding process test of the 190 diesel engine cylinder head flat belt. Huazhong University of Science and Technology has carried out research on five-coordinate linkage CNC belt grinding blade profile. Recently, Huadong Textile University has proposed the application of ultra-abrasive granule electrophoresis adsorption belt to achieve plastic grinding of brittle materials, in order to break the precision limit of abrasive belt grinding and realize nano-machining. China's second grinding wheel factory and Shanghai grinding wheel factory have successively introduced complete sets of technology and equipment for belt manufacturing from Germany, Italy and Switzerland. The annual production of abrasive belts is 5×106m2 and 6×106m2 respectively.
3 Key technologies for high efficiency abrasive processing
1) High-efficiency grinding wheel
High-efficiency grinding wheel should have good wear resistance, high dynamic balance accuracy, crack resistance, good damping characteristics, high rigidity and good thermal conductivity, and its mechanical strength must withstand the cutting force during efficient grinding. Wait. High-efficiency grinding wheels can use corundum, silicon carbide, CBN, and diamond abrasives. The binder may be a ceramic, a resin or a metal bond or the like. The resin-bonded corundum, silicon carbide, and cubic boron nitride abrasive wheels can be used at speeds up to 125 m/s. The single-layer electroplated CBN grinding wheel can be used up to 250m/s and has reached 340m/s in the test. The ceramic bond grinding wheel can grind up to 200m/s. Ceramic bond grinding wheels are easier to trim than other types of grinding wheels. Compared to high-density resin and metal bond grinding wheels, ceramic bond grinding wheels can achieve a wide range of porosity through varying production processes. Norton Company of the United States has developed a method of holding abrasive grains by chemical bonding, which can make the abrasive grains protrude 50% of height without falling off, and the tensile strength of the bonding agent exceeds 1553 N/mm 2 (the plating nickel-based bonding agent is 345 ~) 449N/mm2). China's Nanjing University of Aeronautics and Astronautics has successfully developed high-temperature brazing single-layer super-hard abrasive grinding wheels to reduce grinding heat, increase grinding ratio, and achieved good results. Aheng University of Technology uses a spray technique on the aluminum base of its grinding wheel to achieve a reliable bond between the abrasive layer and the substrate. In order to ensure that the grinding wheel remains sharp throughout its service life, the structure of the grinding wheel needs to facilitate the splitting of the abrasive particles. In order to achieve the purpose of sharpening the grinding wheel, in addition to reducing the proportion of the bonding agent as much as possible, the spatial distribution of the abrasive particles should be optimized. To this end, the grinding wheel should have a complete set of finishing technology. Grinding wheel dressing is one of the key factors determining the quality of grinding. Different dressing methods have different characteristics. Therefore, it is necessary to consider the processing conditions, workpiece materials, grinding wheel materials and other factors in order to select the best dressing solution.
Spindle and its bearing technology
The performance of the high-efficiency grinding machine spindle unit largely determines the limit of high-efficiency grinding. Therefore, in order to achieve high-efficiency grinding, the grinding wheel drive and bearing speed are often required. The high speed of the spindle requires sufficient rigidity of the spindle, high rotation precision, good thermal stability, reliability, low power consumption and long life. To meet these requirements, the manufacture and dynamic balance of the spindle, the support of the spindle (bearing), the lubrication and cooling of the spindle system, and the rigidity of the system are important. The spindle bearing can be a ceramic rolling bearing, a magnetic bearing, an aerostatic bearing or a hydrodynamic bearing. Ceramic ball bearings have the advantages of light weight, small thermal expansion coefficient, high hardness, high temperature resistance, dimensional stability at high temperature, corrosion resistance, high life and high modulus of elasticity. The disadvantage is that it is difficult to manufacture, high in cost, and sensitive to tensile stress and notched stress. The highest surface speed of the magnetic bearing can reach 200m / s, which may become an option for future ultra-high speed spindle bearings. At present, the main problem of the magnetic floating bearing is that the rigidity and the load capacity are low, and the magnet used is too large and expensive compared with the size of the rotating body. The aerostatic bearing has the characteristics of high rotation precision, no vibration, low frictional resistance, durability, and high-speed rotation. For high speed, light load and ultra precision applications. Hydrodynamic and hydrostatic bearings have too much power loss when no load is used, mainly for low speed and heavy duty spindles.
High efficiency grinding machine
High-speed and efficient machining not only requires a high spindle speed and power, but also requires a high feed rate and acceleration of the machine table. It is also necessary to combine as many grinding functions as possible to achieve all the grinding processes on one grinding machine. In addition, the machine is required to have high dynamic accuracy, high damping, high vibration resistance and thermal stability, and a highly automated and reliable grinding process.
The grinding machine support member is a supporting base member of the grinding wheel frame, the head frame, the tail frame, the work table and the like. It is required to have good static stiffness, dynamic stiffness and thermal stiffness. For high-speed super-high-speed grinding machines, polymer concrete (artificial granite) is used to manufacture beds and columns at home and abroad, and some columns and bases are cast in cast iron, and steel plates are welded and damping materials are used. Filling its inner cavity to improve its shock resistance, these have received good results. The feed system is one of the important indexes for evaluating the performance of high-speed ultra-high-speed grinding machines. With the development of high-speed ultra-high-speed machining, linear servo motor direct drive technology and high dynamic performance linear motor combined with digital control technology are widely used at home and abroad. For example, the linear feed motor of Siemens Germany can reach a maximum feed speed of 200m/min, its maximum thrust can reach 6600N, and the maximum displacement distance is 504mm.
Grinding fluid supply technology
At high speeds, the airflow barrier prevents the grinding fluid from effectively entering the grinding zone and may also have the effect of film boiling. Therefore, it is extremely important to increase the effective part of the grinding fluid into the grinding zone by using the proper injection method to improve the cooling and lubrication effects, and to improve the quality of the workpiece and reduce the wear of the grinding wheel. Commonly used grinding fluid injection methods are: manual liquid supply method and pouring method, high pressure injection method, air baffle assisted cut off air flow method, grinding wheel internal cooling method, using slotted grinding wheel method, and the like. In the case of ultra-high speed conditions, in order to achieve cooling of the grinding zone and to wash away the chips, the injection of the grinding fluid must have sufficient momentum to break the high-speed airflow around the grinding wheel and allow the grinding fluid to reach the grinding zone. In order to ensure the surface quality of ultra-high-speed grinding, improve the utilization rate of grinding fluid, and reduce the adverse effects of residual impurities in the grinding fluid on the processing quality and machine tool system, a high-efficiency and high-precision grinding fluid filtration system must be adopted. The grinding fluid sprayed from the nozzle on the grinding wheel will form a severe oil mist under strong centrifugal force. Therefore, the super high-speed grinding machine should also close the grinding zone and extract the oil mist in time. The oil and gas separation is then carried out by means of centrifugation and electrostatics.
Grinding wheel, workpiece installation positioning and safety protection technology
High-speed and ultra-high-speed grinding wheels have great kinetic energy. High-strength semi-closed or closed grinding wheel guards must be installed. It is best to lay buffer materials in the cover to absorb or reduce the secondary ejection of the grinding wheel fragments.
Grinding state detection and numerical control technology
In the high-efficiency grinding process, due to the extremely high speed of the grinding wheel, the grinding phenomenon caused by the ultra-high speed of the grinding wheel often occurs. The monitoring of the grinding wheel crushing and wear state is related to the smooth progress of the grinding work and the guarantee of the processing quality and the complete surface of the part. The key to the nature; in ultra-high-speed machining, the accuracy of the grinding wheel and the workpiece, the accuracy of the grinding wheel and the dressing wheel will directly affect the dimensional accuracy of the workpiece and the dressing quality of the grinding wheel. Therefore, in the ultra-high speed grinding process, The online intelligent monitoring system is an important factor in ensuring the quality of grinding and improving the processing productivity. At present, acoustic emission technology has been successfully used for non-destructive testing of ultra-high-speed grinding, using various acoustic emission sources generated during the grinding process, such as elastic contact between the grinding wheel and the workpiece, cracking of the grinding wheel adhesive, grinding of the grinding wheel and friction of the workpiece, Elastic waves can be emitted from surface cracks and burns, contact between the grinding wheel and the dressing wheel. These factors are closely related to the material of the workpiece, the grinding conditions, and the state of the surface of the grinding wheel. Changes in these factors will inevitably cause changes in the amplitude, spectrum, etc. of the acoustic emission signal, which allows us to discriminate the grinding state by detecting changes in the acoustic emission signal. Therefore, the acoustic emission technology can be used to monitor the grinding crack and the grinding burn, the grinding wheel crushing wheel wear, the grinding wheel is in contact with the workpiece, the grinding wheel is in contact with the dressing wheel, and satisfactory results are obtained. In addition, online monitoring technology for workpiece dimensional accuracy, shape accuracy, positional accuracy and surface quality, high-precision, high-reliability, practical testing techniques and instruments are essential for high-efficiency grinding.
4 Conclusion
Efficient grinding technology is an advanced manufacturing technology that completely solves the high-precision and low-efficiency processing limitations of traditional grinding. It achieves high efficiency and high precision while achieving high surface integrity for various materials and shapes. Processing and reducing costs. Under the existing conditions in China, it is of great significance to strengthen the research, promotion and application of high-efficiency grinding processing technology to improve the processing level of China's machinery manufacturing industry and accelerate the development of new products. Today's applications of superhard materials are becoming more widespread, and high-speed and high-efficiency grinding is the preferred process for processing superhard materials and difficult-to-cut materials. Due to the application of superabrasives, the development of high-speed, high-power precision machine tools and CNC technology, the development of new grinding fluids and wheel dressing, high-speed ultra-high-speed grinding and high-efficiency grinding technology, grinding automation and The development of technologies such as intelligence makes high-efficiency abrasive grain processing have a more important position in the field of mechanical manufacturing and has a good development prospect.
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