At present, the application of PCBN tools is quite common, and the CBN forming grinding is not widely spread due to the economics of equipment and tools. How to improve production efficiency, reduce manufacturing costs, and provide high-quality products to customers at competitive prices. Through continuous efforts, Hangzhou Tooth has realized CBN forming and grinding industrial applications that meet the accuracy requirements of product parts. In equipment investment, CBN The manufacturing cost of the grinding wheel and the service life of the tool are both economical.
CBN is the abbreviation of CubicBoron Nitride, which is a synthetic inorganic crystal material with hardness second only to diamond. It is widely used in the machining industry. Developed countries have developed CBN as an important material for high efficiency, energy conservation, ultra-precision and automated processing.
Expert research shows that when the temperature reaches about 700 °C, the hardness of diamond will have a significant downward trend, while the CBN material can still maintain a considerable hardness. This shows that the thermal stability (red hardness) of CBN is significantly better than diamond. Since iron-based metals have a strong affinity for carbon at high temperatures, diamonds composed of pure carbon elements should not be used as tool materials for processing iron-based metals. CBN is composed of boron and nitrogen. It does not easily react with iron-based metals at high temperatures. The appearance of CBN tools makes it possible to cut hardened steel.
Our company began mass production of heavy-duty automotive transmissions in 1996. Some of the typical parts involved were carburized and quenched with a surface hardness of HRC 58-63. In order to meet the design requirements of parts, it is urgent to apply CBN tools to solve the machining problems encountered in traditional process methods.
In the work practice, our company's application to CBN tools is mainly reflected in two aspects: one is to use the PCBN tool to turn hardened steel to realize the “car grinding†process; the second is to use CBN grinding wheel to realize the industrial application of CBN forming grinding. .
Applying PCBN tools to achieve "car grinding"
PCBN is an abbreviation for PolycrystallineCubicBoronNitride. PCBN tools made from PCBN tool blanks by cutting, welding and sharpening have good cutting performance, mainly in the following aspects:
High hardness and wear resistance
CBN is second only to diamond in hardness, and PCBN tools have the highest hardness for tool materials that can cut ferrous metals. The wear resistance of PCBN tools can reach 5 to 10 times that of coated tools and ceramic tools. Therefore, the use of PCBN tools can significantly reduce the number of tool changes in production and processing, improve the accuracy and interchangeability of workpieces, and shorten product production. cycle.
Good thermal conductivity and thermal stability
The hardness of PCBN cutters at 800 °C is still higher than the normal temperature hardness of cemented carbide tools and ceramic cutters. It still maintains high hardness at 1200 °C, and its thermal conductivity increases with increasing temperature. . Therefore, PCBN tools are well suited to meet the requirements of tool materials for harsh machining conditions during hard cutting, high speed cutting and dry cutting.
High chemical stability
Because CBN is particularly chemically inert, it does not chemically react with elements such as Fe, Ni, Co, etc. at 1200-1300 °C. Therefore, the chemical wear of PCBN tools during cutting is small compared to other tool materials, and can be used for processing. Workpieces of various materials.
Lower coefficient of friction
The friction coefficient between CBN and different materials is 0.1-0.3, and with the increase of cutting speed, the friction coefficient of PCBN decreases, which reduces the cutting force and reduces the sticking phenomenon of cutting during cutting, which is beneficial to improve. Machining accuracy and surface quality.
Due to the function and structure requirements of the two-axis components of our company's heavy-duty automotive transmissions, the two-axis multi-speed spline undercutting groove and the axial direction of each retaining ring groove have high dimensional accuracy, and the tolerance range is plusmn; 0.03～±0.10mm, Both have more demanding end face bounce and surface roughness requirements. The parts are made of 20CrMnTiHA3, carburized and quenched, and the surface hardness is HRC58-63. Due to material stability, heat treatment technology and other reasons, parts often have a large amount of deformation after heat. In order to meet the design requirements, the traditional process often uses grinding to achieve the finishing process after the parts are hot. The shape of the shaft is complicated, and it is difficult for ordinary grinding equipment to meet the processing requirements, and a special grinding machine must be introduced. However, such equipment is less produced at home and abroad, and the price is high, and the applicability is not satisfactory.
Through technical data retrieval, equipment research and economic and technical analysis, we believe that the comprehensive economic indicators of hard cutting technology are superior to the grinding process. Therefore, it was finally decided to use the PCBN tool for hard cutting (as shown in Figure 2) to achieve "car grinding".
Since the hard cutting requires the rigidity of the machine tool, the foundation is stable, and the working axis movement precision is high, we chose the CK7820 CNC lathe of Great Wall Machine Tool Plant.
Hard cutting has large cutting force and high cutting temperature. In order to ensure machining accuracy, surface quality and tool life, we have selected the appropriate PCBN tool and cooling lubricant through multiple cutting tests to determine the appropriate cutting parameters and accumulate. Practical processing experience.
The application of “car-based grinding†in the mass production of heavy-duty vehicle transmissions of our company solves the processing problems that are difficult to achieve in traditional processes, and the production efficiency is remarkable. In addition, the chips produced by the “car-grinding†process can be recycled, unlike the special waste generated by the traditional grinding process. Therefore, the application of new processes is also very beneficial to protect the environment.
CBN forming grinding industrial application
CBN grinding wheels can grind metal workpieces at high speed with high quality and high quality. They have been widely used in grinding machines in Germany and Europe. The grinding speed of the CBN grinding wheel is close to the speed of sound, which greatly increases the production efficiency. Due to the very small loss of the CBN grinding wheel, the precision of the forming grinding is extremely easy to guarantee. However, the production technology of CBN grinding wheels restricts the development of high-speed grinding technology. Therefore, how to make CBN grinding wheels with high precision has become the key to high-speed grinding technology.
The high-end CNC grinding machines such as HOFFLERHELIX400 and Gleason®245TWGThreadedWheelGrinder introduced by our company in recent years can well realize the CBN grinding wheel forming grinding process. However, due to the high comprehensive cost, the total number of similar equipment is not much, and it is difficult to form an economical scale processing capability. .
Since the company began mass production of heavy-duty vehicle transmissions in 1996, the intermediate shafts of the intermediate shafts with a tooth width of 125 mm at one end cannot be ground by ordinary grinding equipment due to structural limitations. To this end, we analyzed the accuracy requirements of the part and the availability of the existing equipment, and proposed a more economical CBN grinding wheel forming grinding process (as shown in Figures 3 and 4). First of all, we use the existing high-precision CNC lathes and CNC grinding machines inside the company to break through the processing problems of the CBN grinding wheel base. Then, the engineers in the process department mastered the CBN plating technology (The Electroplating Process) through technical literature search and technical experiments. In addition, the Replating and Refurbished technology of CBN grinding wheel ensures the high utilization rate of the grinding wheel base and reduces the manufacturing cost of the tool while maintaining the precision of repeated use of the grinding wheel. Third, we have saved the high investment in equipment by transforming the M8612A spline shaft grinder as a special grinding machine. Fourth, through the process experiment, the appropriate mineral oil was selected as the cooling lubricant, and the appropriate cutting parameters were determined.
Through the above work, we have realized the industrial application of CBN forming grinding to meet the accuracy requirements of product parts. Our existing processes are economical in terms of equipment investment, CBN grinding wheel manufacturing costs and tool life.
in conclusion
The application of PCBN tools is quite common at present. CBN forming grinding is not widely spread due to the economics of equipment and tools. Although the CBN forming grinding of our company is a simple "earth method", it has good economics. The superiority of imported CBN grinding wheels and CNC equipment abroad is of course unavoidable, so the description in this article emphasizes more "practical" industrial applications that meet the accuracy requirements of product parts.
Although we have made progress in practice, there are still many shortcomings in actual production, mainly in the following four aspects.
Proper use of PCBN tools is the key to accurately determining the durability of PCBN tools.
The relevant literature requires regular regrind when the flank wear standard of the PCBN tool reaches 0.3 to 0.5 mm (small value when finishing the car). However, re-grinding requires certain equipment and techniques, and it is best to introduce a multi-tool grinder. Due to the limited conditions, our company is still sharpening on the ordinary tool grinding machine. It is difficult to guarantee the regrind quality of the tool in terms of equipment and personnel technical quality.
PCBN tool welding technology still needs to be improved. At present, 10% to 30% of tool damage is caused by poor welding quality;
The service life of CBN grinding wheel still needs to be improved, and the practical improvement of CBN plating technology is the key;
The manufacturing precision of the CBN grinding wheel base is still not very satisfactory.
CBN is the abbreviation of CubicBoron Nitride, which is a synthetic inorganic crystal material with hardness second only to diamond. It is widely used in the machining industry. Developed countries have developed CBN as an important material for high efficiency, energy conservation, ultra-precision and automated processing.
Expert research shows that when the temperature reaches about 700 °C, the hardness of diamond will have a significant downward trend, while the CBN material can still maintain a considerable hardness. This shows that the thermal stability (red hardness) of CBN is significantly better than diamond. Since iron-based metals have a strong affinity for carbon at high temperatures, diamonds composed of pure carbon elements should not be used as tool materials for processing iron-based metals. CBN is composed of boron and nitrogen. It does not easily react with iron-based metals at high temperatures. The appearance of CBN tools makes it possible to cut hardened steel.
Our company began mass production of heavy-duty automotive transmissions in 1996. Some of the typical parts involved were carburized and quenched with a surface hardness of HRC 58-63. In order to meet the design requirements of parts, it is urgent to apply CBN tools to solve the machining problems encountered in traditional process methods.
In the work practice, our company's application to CBN tools is mainly reflected in two aspects: one is to use the PCBN tool to turn hardened steel to realize the “car grinding†process; the second is to use CBN grinding wheel to realize the industrial application of CBN forming grinding. .
Applying PCBN tools to achieve "car grinding"
PCBN is an abbreviation for PolycrystallineCubicBoronNitride. PCBN tools made from PCBN tool blanks by cutting, welding and sharpening have good cutting performance, mainly in the following aspects:
High hardness and wear resistance
CBN is second only to diamond in hardness, and PCBN tools have the highest hardness for tool materials that can cut ferrous metals. The wear resistance of PCBN tools can reach 5 to 10 times that of coated tools and ceramic tools. Therefore, the use of PCBN tools can significantly reduce the number of tool changes in production and processing, improve the accuracy and interchangeability of workpieces, and shorten product production. cycle.
Good thermal conductivity and thermal stability
The hardness of PCBN cutters at 800 °C is still higher than the normal temperature hardness of cemented carbide tools and ceramic cutters. It still maintains high hardness at 1200 °C, and its thermal conductivity increases with increasing temperature. . Therefore, PCBN tools are well suited to meet the requirements of tool materials for harsh machining conditions during hard cutting, high speed cutting and dry cutting.
High chemical stability
Because CBN is particularly chemically inert, it does not chemically react with elements such as Fe, Ni, Co, etc. at 1200-1300 °C. Therefore, the chemical wear of PCBN tools during cutting is small compared to other tool materials, and can be used for processing. Workpieces of various materials.
Lower coefficient of friction
The friction coefficient between CBN and different materials is 0.1-0.3, and with the increase of cutting speed, the friction coefficient of PCBN decreases, which reduces the cutting force and reduces the sticking phenomenon of cutting during cutting, which is beneficial to improve. Machining accuracy and surface quality.
Due to the function and structure requirements of the two-axis components of our company's heavy-duty automotive transmissions, the two-axis multi-speed spline undercutting groove and the axial direction of each retaining ring groove have high dimensional accuracy, and the tolerance range is plusmn; 0.03～±0.10mm, Both have more demanding end face bounce and surface roughness requirements. The parts are made of 20CrMnTiHA3, carburized and quenched, and the surface hardness is HRC58-63. Due to material stability, heat treatment technology and other reasons, parts often have a large amount of deformation after heat. In order to meet the design requirements, the traditional process often uses grinding to achieve the finishing process after the parts are hot. The shape of the shaft is complicated, and it is difficult for ordinary grinding equipment to meet the processing requirements, and a special grinding machine must be introduced. However, such equipment is less produced at home and abroad, and the price is high, and the applicability is not satisfactory.
Through technical data retrieval, equipment research and economic and technical analysis, we believe that the comprehensive economic indicators of hard cutting technology are superior to the grinding process. Therefore, it was finally decided to use the PCBN tool for hard cutting (as shown in Figure 2) to achieve "car grinding".
Since the hard cutting requires the rigidity of the machine tool, the foundation is stable, and the working axis movement precision is high, we chose the CK7820 CNC lathe of Great Wall Machine Tool Plant.
Hard cutting has large cutting force and high cutting temperature. In order to ensure machining accuracy, surface quality and tool life, we have selected the appropriate PCBN tool and cooling lubricant through multiple cutting tests to determine the appropriate cutting parameters and accumulate. Practical processing experience.
The application of “car-based grinding†in the mass production of heavy-duty vehicle transmissions of our company solves the processing problems that are difficult to achieve in traditional processes, and the production efficiency is remarkable. In addition, the chips produced by the “car-grinding†process can be recycled, unlike the special waste generated by the traditional grinding process. Therefore, the application of new processes is also very beneficial to protect the environment.
CBN forming grinding industrial application
CBN grinding wheels can grind metal workpieces at high speed with high quality and high quality. They have been widely used in grinding machines in Germany and Europe. The grinding speed of the CBN grinding wheel is close to the speed of sound, which greatly increases the production efficiency. Due to the very small loss of the CBN grinding wheel, the precision of the forming grinding is extremely easy to guarantee. However, the production technology of CBN grinding wheels restricts the development of high-speed grinding technology. Therefore, how to make CBN grinding wheels with high precision has become the key to high-speed grinding technology.
The high-end CNC grinding machines such as HOFFLERHELIX400 and Gleason®245TWGThreadedWheelGrinder introduced by our company in recent years can well realize the CBN grinding wheel forming grinding process. However, due to the high comprehensive cost, the total number of similar equipment is not much, and it is difficult to form an economical scale processing capability. .
Since the company began mass production of heavy-duty vehicle transmissions in 1996, the intermediate shafts of the intermediate shafts with a tooth width of 125 mm at one end cannot be ground by ordinary grinding equipment due to structural limitations. To this end, we analyzed the accuracy requirements of the part and the availability of the existing equipment, and proposed a more economical CBN grinding wheel forming grinding process (as shown in Figures 3 and 4). First of all, we use the existing high-precision CNC lathes and CNC grinding machines inside the company to break through the processing problems of the CBN grinding wheel base. Then, the engineers in the process department mastered the CBN plating technology (The Electroplating Process) through technical literature search and technical experiments. In addition, the Replating and Refurbished technology of CBN grinding wheel ensures the high utilization rate of the grinding wheel base and reduces the manufacturing cost of the tool while maintaining the precision of repeated use of the grinding wheel. Third, we have saved the high investment in equipment by transforming the M8612A spline shaft grinder as a special grinding machine. Fourth, through the process experiment, the appropriate mineral oil was selected as the cooling lubricant, and the appropriate cutting parameters were determined.
Through the above work, we have realized the industrial application of CBN forming grinding to meet the accuracy requirements of product parts. Our existing processes are economical in terms of equipment investment, CBN grinding wheel manufacturing costs and tool life.
in conclusion
The application of PCBN tools is quite common at present. CBN forming grinding is not widely spread due to the economics of equipment and tools. Although the CBN forming grinding of our company is a simple "earth method", it has good economics. The superiority of imported CBN grinding wheels and CNC equipment abroad is of course unavoidable, so the description in this article emphasizes more "practical" industrial applications that meet the accuracy requirements of product parts.
Although we have made progress in practice, there are still many shortcomings in actual production, mainly in the following four aspects.
Proper use of PCBN tools is the key to accurately determining the durability of PCBN tools.
The relevant literature requires regular regrind when the flank wear standard of the PCBN tool reaches 0.3 to 0.5 mm (small value when finishing the car). However, re-grinding requires certain equipment and techniques, and it is best to introduce a multi-tool grinder. Due to the limited conditions, our company is still sharpening on the ordinary tool grinding machine. It is difficult to guarantee the regrind quality of the tool in terms of equipment and personnel technical quality.
PCBN tool welding technology still needs to be improved. At present, 10% to 30% of tool damage is caused by poor welding quality;
The service life of CBN grinding wheel still needs to be improved, and the practical improvement of CBN plating technology is the key;
The manufacturing precision of the CBN grinding wheel base is still not very satisfactory.
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