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1 Introduction
As we all know, gear transmission is the most common kind of mechanical transmission in modern machines and is an important basic component of mechanical products. Compared with other mechanical transmission forms (chain transmission, belt transmission, hydraulic transmission, etc.), it has features such as large power range, high transmission efficiency, accurate transmission, and long service life. Therefore, it has become an indispensable transmission component for many mechanical products, and it is also the most important form of transmission in the machine.
The design and manufacturing level of gears will directly affect the performance and quality of mechanical products. For example, in the modern and prosperous automotive industry, there are usually 18 to 30 teeth in each car. The quality of the gears directly affects the noise and stability of the car. Sex and service life. The processing technology and equipment of gears usually greatly affect the highest level of manufacturing that can be achieved in the industrial field. Advanced countries with advanced modern industries such as the United States, Germany, and Japan are also manufacturing powers for gear processing technology and equipment. Therefore, the status of gears in the industrial development has been prominent, and it is recognized as a symbol of industrialization. From this perspective, it is of great importance to pay attention to the advanced processing technology and development trend of gears.
2 The new development of gear processing technology
In general, the gear manufacturing process includes five stages of material preparation, gear blank machining, gear cutting, tooth surface heat treatment, and tooth surface finishing. Tooth machining and finishing after heat treatment are the key to the manufacture of gears and also reflect the level of gear manufacturing. The development of gear manufacturing technology is largely reflected in the improvement of accuracy level and production efficiency. At present, all countries in the world continuously improve the manufacturing level of gears from two aspects: gear processing technology and processing equipment development.
2.1 Hardened tooth hobbing technology
In the traditional method, the hard tooth surface of the gear needs to be ground through the tooth surface. Because the grinding tooth machining efficiency is too low, the processing cost is too high, especially for some large diameter and large modulus gears. Because of this, since the 1980s, domestic and foreign companies have gradually adopted hard tooth scraping as a semi-finishing and finishing method for hardened gears (40 to 65 HRC).
Hard-tooth hobbing technology, also known as scraping tooth processing, uses a special carbide hob to shave gear tooth surfaces with a hardness of HRC58-62 after carburizing and quenching. The scraping accuracy can be Reached level 7. This method can process gears with any helix angle and module of 1-40mm. Ordinary precision (6~7 grade) hardened surface gear, generally adopts "roll-heat treatment-scraping" process, coarse and fine machining can be completed on the same hobbing machine; gears with higher tooth surface roughness can be scraped After the arranging tooth processing; for high-precision gears, the use of "roll - heat treatment - scraping - grinding" process, using scraping as a semi-finishing process instead of coarse grinding, removal of the gear heat treatment deformation, leaving a small and uniform margin Grinding can save 1/2 to 5/6 grinding hours and the economic benefits are significant. For large modulus, large diameter, and large width hardened gears, generally no scrapers can be used because there is no corresponding large gear grinding machine.
The most important feature of hardened surface scraping is that the production efficiency is 5-6 times higher than that of grinding teeth. In addition to this, the excessively large amount of deformation of the heat treatment carburized quenched gear can be scraped before grinding, which not only eliminates the deformation of gears. The quantity guarantees the smoothness of the gears in the grinding process and also improves the grinding efficiency and protects the accuracy of the grinding gears.
Temperature control is extremely important when using hard-tooth hobbing technology for gear machining, because excessive temperatures will make the tool wear faster and easier to chip; therefore, it needs to be cooled by the metalworking fluid and at the same time the cutting on the tool and the workpiece is washed away. , Improve tool life and workpiece surface roughness. General use of special oil-based cutting fluid as a cooling lubricant medium, such as KR-C20, through the appropriate control of the viscosity and the use of environmentally friendly extreme pressure anti-wear agent to meet the process cooling, cleaning and lubrication requirements.
2.2 Dry cutting technology
Dry cutting, ie, no lubrication cutting, is one of the development trends in metal cutting. The technology began to be researched in the 1980s, but it has been slow to develop due to the constraints of machine tools and tool materials. With the machine tool design technology, carbide tool and surface coating technology, new ceramic tooling, and process theory in the past ten years or so. With the development of research, dry cutting has greatly increased production efficiency and significantly improved surface quality, while also reducing production costs.
High-speed dry cutting is performed at high cutting speeds without cooling or lubricating oil. High speed dry cutting must use proper cutting conditions. First, use high cutting speeds to minimize the contact time between the tool and the workpiece. Use compressed air or other similar methods to remove the chips to control the temperature in the work area. Practice has proved that when the cutting parameters are set correctly, 80% of the heat generated by the cutting can be taken away by the chips.
The high-speed dry cutting method not only makes the machine tool compact, but also greatly improves the processing environment and reduces the processing cost. In the gear processing, in order to further extend the tool life and improve the quality of the workpiece, it is possible to use 10 to 1000 ml of lubricating oil per hour to perform micro-lubrication in the gear dry cutting process. Chips produced by this method can be considered as dry chips. The precision, surface quality and internal stress of the workpiece are not affected negatively by trace amounts of lubricating oil. Process monitoring can also be performed using automatic control equipment.
According to data [], the total cost of dry cutting in developed countries such as the United States, Japan, and Germany is about 70% of the traditional cutting process. According to statistics from US companies, cutting fluid accounts for 14% to 16% of the total cost in the centralized cooling processing system, while tooling costs only account for 2% to 4%. According to estimates, if 20% of the cutting process is dry, the total manufacturing cost can be reduced by 1.6%. The advantages of dry cutting technology are also reflected in the improvement of the surface quality of parts and the improvement of geometric accuracy. According to foreign data, the workpiece surface roughness value of the dry cutting process can be reduced by about 40%. In addition, the importance of dry cutting for resources and the environment is self-evident. Germany is in the leading position in the field of high-speed dry cutting. Currently, about 8% of companies use dry cutting, which indicates that high-speed dry hobbing technology will be a direction for future gear processing.
It can be foreseen that the domestic use of dry cutting technology in hobbing, slotting, forming grinding and other processing areas will have great potential. With the advancement of gear machine tools, gear materials, gear cutters, and processing technology, it is only a matter of time to replace traditional processes.
2.3 No chip processing
Different from traditional gear teeth forming methods such as hobbing, slotting, shaving and grinding, the chipless machining method uses metal plastic deformation or powder sintering to finalize the tooth shape of the gear or improve the tooth surface quality. of. This method can be divided into two types: cold forming in which the workpiece is processed at normal temperature and hot forming in which the workpiece is heated to about 1000C. The former includes cold rolling, cold forging, etc.; the latter includes hot rolling, precision die forging, powder metallurgy, and the like.
No chip processing gear can improve the material utilization rate from 40 to 50% of the cutting process to 80 to 95% or more, and the productivity can also be doubled. However, due to the limitation of the strength of the mold, currently only the gears or other toothed parts with a smaller module are generally processed. At the same time, the gears with a higher precision need to use the final finishing tooth after the forming without chipping. shape. No chip processing gear needs to use special equipment, and the initial investment is relatively large. Only when the production volume is large (generally over 10,000 pieces) can the production cost be significantly reduced.
3 Development of Gear Processing Lubrication Technology
The development of modern cutting and processing lubrication technology is always linked with the progress of processing equipment and processing technology. In order to adapt to new equipment and process requirements, the lubricating medium has also been continuously improving.
In traditional gear machining, cutting fluids have dominated in recent decades. The traditional cutting lubrication process uses oil-based cutting fluid and water-based cutting fluid for the lubrication and cooling of tools and workpieces, and functions as chip removal and rust prevention.
In recent years, due to the increase in pressure on the environment and resources, many new types of green cutting processes have emerged in the field of cutting to replace the traditional lubrication processes, such as non-lubrication dry cutting technology, micro-lubrication technology, low-temperature cold air cutting technology, etc. It promotes the advancement of cutting technology, and also puts forward new requirements for machine tool structure, tool materials, and lubricating media.
3.1 Trace Lubrication Technology
In efficient dry cutting, controlling the spread and diffusion of heat is a big problem. For this reason, cold wind (up to -100°C or less), micro-lubrication, high-speed cutting and other technical means are used in dry cutting to improve processing quality. Reduce losses.
Compared to the non-lubricated cutting technology, the micro-lubrication technology introduces cooling lubricant media, which greatly improves the cutting conditions and the application field is even wider. The Minimal Lubrication Technology (MQL) incorporates a small amount of lubricating oil into the compressed gas to replace the large amount of cutting fluid to provide cooling lubrication to the cutting point. MQL is an effective green manufacturing technology. The cutting fluid is supplied in the form of high-speed droplets, which increases the permeability of the lubricant medium, improves the cooling lubrication effect, and improves the surface processing quality of the workpiece. The micro-lubrication technology combines the advantages of dry and traditional wet lubrication technologies to reduce the amount of cutting fluid to an extremely small extent. The amount of cutting fluid used is only one ten-thousandth of the amount of conventional cutting fluid, which greatly reduces the cooling fluid. The cost, but also the lowest level reduces the cutting fluid environment and the human body burden, avoids the problem of handling waste liquid. Moreover, the technology system is simple, the area is small, and it is easy to install on various types of machine tools, thereby greatly enhancing the practical performance. . Therefore, many companies are committed to the development and production of micro-lubrication systems, such as the German Lubfix company, the German company VOGEL (VOGEL), the Italian company Technosystems (Technosystems), Japan Fuji BC Technology Co., Ltd. and so on. Ford Motor Company has applied micro-lubrication technology to the processing of automotive powertrain components; Grob Corporation, as an equipment manufacturer, used a one- or two-channel minimum-lubrication system in the machining of cylinders and gearboxes; Guehring noted that MQL is not only economically superior to conventional wet processing but also contributes to chip treatment. The company has achieved significant results with the use of MQL on solid carbide drills.
3.2 Low-temperature micro-lubrication technology
The cooling effect of micro-lubrication is generally unsatisfactory, and the high temperatures generated in the processing area cause various negative effects, such as high-temperature chips affecting the safety of the operator, the workpiece and the tool, etc., which are affected by the temperature and reduce the machining accuracy. Due to the demand for improved cooling capacity, the development of low-temperature micro-lubrication technology has been promoted.
Low-temperature and micro-lubrication technology [] is the mixing of low-temperature compressed gas (air, nitrogen, carbon dioxide, etc.) with a very small amount of lubricating oil (10 ml/h~200 ml/h) to form droplets of micron-sized lubricant media. To the processing area, lubricate the machining area between the tool and the workpiece. This technology integrates low-temperature gas cooling, medium lubrication, and high-pressure injection, and has excellent cooling and lubricating capabilities. It has a lot of room for development in high-speed machining of difficult-to-machine materials such as titanium alloys, high-temperature alloys, and high-hardness materials. .
4 gear processing lubricant selection
At present, the gear processing lubricant medium is mainly based on oil-based cutting fluids, and some of the rough machining areas also use water-based cutting fluids.
The common gear processing methods are broaching, hobbing, inserting, shaving, grinding, boring and the like, and are suitable for different types of gear cutting. In gear machining, cutting force and cutting temperature are the main factors that cause tool wear. Therefore, effective lubrication and cooling technology is used to reduce cutting temperature and improve cutting friction, thereby reducing cutting force and suppressing tool wear. It is a further improvement of machining efficiency. The main technical approach.
In the selection of gears for processing lubrication media, for oil-based cutting fluids, it is important to select suitable viscosity and lubrication performance. In general, gear hobbing, inserting and other processing use high viscosity oils, shaving, grinding and other processing Use the oil with lower viscosity to obtain the best use effect. In addition, we must consider the color, smell, oil mist, and whether there are heavy metal elements such as germanium in the selection of products, and choose products that are safe to the environment and human body.
For water-based cutting fluids, it is necessary to focus on the stability, lubricity, rust resistance, biological stability, and other indicators, and select the appropriate type of water-based cutting fluid according to the specific processing conditions. In addition, we must also consider the environmental protection and safety of products. Products must not contain nitrites, organic phenols, heavy metals, dioxins and other substances harmful to the human body, so as to ensure the health of on-site operation workers.
Whether it is oil-based or water-based metal processing media, in addition to the need to meet the lubrication and cooling requirements of the processing process, but also to meet the requirements of environmental protection, safety and other aspects, so the continuous improvement of technology is particularly important. Nanjing Kerun Industrial Media Co., Ltd. has always insisted on continuous innovation and progress in technology, has always paid attention to the high quality of products and the importance of adapting to the human body and the environment, and strive to become a leader in gear processing green lubrication technology.
5 Conclusion
Gear processing technology combines the advanced achievements of material science and technology, machinery manufacturing, numerical control technology, simulation, lubrication technology, detection technology and many other fields. With the continuous introduction and development of new equipment, new processes and new technologies, the domestic gear processing industry Will make great progress.
As an inevitable path in the era of industrialization, the development of gear processing technology to improve the level of gear processing is of great significance to improving the competitiveness of China's gear manufacturing industry in the international market.
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