Advanced processing technology and development of gears

As we all know, gear transmission is the most common mechanical transmission in modern machines and an important basic component of mechanical products. Compared with other mechanical transmission forms (chain drive, belt drive, hydraulic drive, etc.), it has the characteristics of 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 largest transmission form in the machine. Gear has always been prominent in industrial development and is recognized as a symbol of industrialization. From this perspective, it is extremely important to pay attention to the advanced processing technology and development trend of gears.

1. New developments in gear processing technology

In general, the gear manufacturing process includes five stages: material preparation, tooth blank machining, cutting, tooth surface heat treatment and tooth surface finishing. Finishing and heat treatment are the key to gear manufacturing and reflect the level of gear manufacturing. At present, countries around the world continue to improve the manufacturing level of gears mainly from the aspects of gear processing technology and processing equipment development.

2. Hard tooth hobbing technology

In the traditional method, the hard tooth surface of the gear needs to be machined by the tooth surface. The machining efficiency is too high due to the low machining efficiency of the grinding tooth, especially for some large diameter and large modulus gears. Large, and hard-tooth scraping as a hardened gear (40 ~ 65HRC) semi-finishing, finishing is very effective.

The hard tooth hobbing technology is also called scraping tooth processing. A special hard alloy hob is used to scrape the gear tooth surface with the tooth surface hardness of HRC58-62 after carburizing and quenching, and the scraping precision can reach 7 levels. This method can process gears with arbitrary helix angle and modulus of 1 to 40 mm. Ordinary precision (6 to 7 grade) hardened gears, generally adopting the "rolling- heat treatment -scraping" process, coarse and fine machining can be completed on the same hobbing machine; gears with higher tooth surface roughness requirements can be scraped After the arrangement of the dental caries processing; for the high-precision gears, the "rolling- heat treatment -scraping-grinding" process is used, and the semi-finishing process is replaced by scraping instead of the coarse grinding, and the heat treatment deformation of the gear is removed, leaving a small and uniform margin. Fine grinding can save 1/2 to 5/6 of the grinding time, and the economic benefits are very significant. For hardened gears with large modulus, large diameter and large width, scraping can only be used because there is no corresponding large gear grinding machine.

Temperature control is extremely important when using gear hobbing technology for gear machining. Excessive temperature can cause tool wear to accelerate and collapse, so it needs to be cooled by metalworking fluid while washing away the chips on the tool and the workpiece. Improve tool life and reduce workpiece surface roughness. Special oil-based cutting fluid is generally used as the cooling lubricating medium, such as KR-C20 hobbing gear oil, which can meet the requirements of cooling, cleaning and lubrication in the process through proper control of viscosity and excellent environmentally-friendly extreme pressure anti-wear agent. Requirements.

3. Dry cutting technology

Dry cutting, that is, non-lubricating cutting, is performed at a high cutting speed without the action of cooling or lubricating oil. High-speed dry cutting must use appropriate cutting conditions. First, use a high cutting speed to minimize the contact time between the tool and the workpiece, and then use compressed air or other similar methods to remove the chips to control the temperature of the working area. Practice has shown that when the cutting parameters are set correctly, 80% of the heat generated by cutting can be carried away by the chips. In order to further extend the tool life and improve the quality of the workpiece, 10 to 1000ml of lubricating oil per hour can be used for minor lubrication during dry gear cutting. The chips produced by this method can be considered as dry chips. The accuracy, surface quality and internal stress of the workpiece are not adversely affected by the micro-lubrication. Process monitoring can also be carried out with automatic control equipment.

4. Gearless machining of gears

Different from the traditional gear teeth forming methods such as hobbing, gear shaping, shaving and grinding, the chipless machining method of the gear is to form the tooth profile of the gear or improve the tooth surface quality by plastic deformation or powder sintering of the metal. of. The method can be divided into two types: cold forming of the workpiece at normal temperature and hot forming by heating the workpiece to about 1000 ?°C. The former includes cold rolling, cold forging, etc., the latter includes hot rolling, precision die forging, powder metallurgy, etc., which can increase the material utilization rate from 40 to 50% of the cutting process to 80 to 95%, and the productivity is multiplied. However, due to the limitation of the strength of the mold, it is generally only possible to process gears or other toothed parts with a small modulus. For gears with high precision requirements, it is still necessary to use the final finishing of the tooth shape after cutting with a chipless process.

5. Development of gear processing lubrication technology

In recent years, due to the increase of environmental and resource pressures, a variety of new green cutting processes have emerged in the field of cutting to replace traditional processing lubrication processes, such as non-lubricated dry cutting technology, micro-lubrication technology, low-temperature cold-air cutting technology, etc. It has promoted the advancement of cutting technology and put forward new requirements for machine tool structure, tool materials and lubricating media.

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