The development of gear machinery manufacturing industry in the world can be divided into three stages according to the characteristics and requirements of gear manufacturing technology. The first stage can be called “forming” manufacturing of gears. It is a manufacturing technology that takes cost, time and space as technical criteria and meets the requirements of shape, position, surface roughness and other design drawings. The main body of the machine is cutting, and the landmark index is surface roughness Ra, with the goal of precision and efficiency. In the past 60 years, under the guidance of the concept of “have or not” for gear equipment, China has developed the gear machinery manufacturing industry by introducing and imitating foreign technologies, established a good gear “forming” manufacturing platform, and become a major gear manufacturing country. However, China is still stagnant in the traditional gear “forming” manufacturing level. Because the “forming” manufacturing of gear is not directly related to the service performance of gear, and cutting is the main source of surface stress concentration, it is easy to induce the stress concentration sensitivity of fatigue strength, so it becomes the main reason of “three major problems” of heavy structure, short life and poor reliability of gear. The second stage can be called “surface integrity” manufacturing of gears. From 1948 to 1970, the American Gear manufacturing industry complied with the development demand of machinery manufacturing industry and researched and developed the “surface integrity” manufacturing of gears. The purpose of this manufacturing is to control the surface integrity of gears. It is a manufacturing technology that takes fatigue performance as the main criterion and improves fatigue strength. Different from “forming” manufacturing, it not only meets the requirements of shape, position, surface roughness and other design drawings, but also achieves the design performance of key components. Its characteristic index is the “standard data group” with surface roughness Ra, residual stress and fatigue performance as the main index, and its goal is precision, high efficiency and fatigue performance, and the main body is still machining. The main achievements are as follows:
① In 1970, the landmark achievement “guide to surface integrity of machined components” was released;
② In 1971, the U.S. Air Force issued the “military aircraft safety life design code”;
③ The lifetime of the third generation fighters has increased from 3000 flight hours to 5000 flight hours.
Since 1970, the American Gear manufacturing industry has innovated and developed the new surface modified and integrated manufacturing technology of various gears, and put forward the concept of economic affordability in the early 1990s, so that the service life of gear equipment can be continuously improved and maintenance can be reduced.
The third stage of the development of gear manufacturing technology can be called “anti fatigue” manufacturing of gears. Zhao Zhenye, academician of Beijing Institute of aeronautical materials, based on decades of research on the anti fatigue manufacturing of key components with long life, made the landing gear reach and exceed the maximum specified life abroad, put forward the concept of “stress free concentration” anti fatigue, innovated theoretical research, put forward and vigorously advocated the “anti fatigue” manufacturing of key components in close combination with engineering application. The so-called “anti fatigue” manufacturing is to control the surface integrity and surface modification layer, taking the fatigue performance as the main criterion and the manufacturing technology to improve the fatigue strength; the surface integrity is to control the non damaged or strengthened surface state formed by the processing technology; the surface modification layer is to control the non damaged or strengthened sub surface state formed by the processing technology. Different from the “surface integrity” manufacturing, the anti fatigue manufacturing should not only meet the requirements of shape, position, surface roughness and other design drawings and achieve the design performance of key components, but also ensure the long service life of key components. In addition to “standard data group” such as surface roughness Ra, there is also “surface modification layer data group” among its landmark indicators. The goal and mission of anti fatigue manufacturing are transformed into precision, long life and economic affordability, and the main body is transformed into Anti fatigue machining and high-energy or high-energy composite surface modification. The results show that the fatigue life of key components is dozens to hundreds of times higher than that of “forming” manufacturing, and the reliability is one to several orders of magnitude higher. Anti fatigue manufacturing will bring China’s key components and machinery manufacturing into a new era of long life, high reliability, structural weight reduction and economic affordability, a new era of green, environmental protection, humanization and sustainable development, and a new era of occupying the international advanced level and competitive position.
The core of anti fatigue manufacturing is surface modification, especially high energy or high energy composite surface modification. However, in the key component manufacturing plant, more than 80% of the process is cutting, and cutting is the main cause of “three major problems” and the inducer of stress concentration effect of fatigue strength of key components. In the key component manufacturing plant, there are few or no surface modification processes, let alone workshops. Surface modification, especially high-energy or high-energy composite surface modification, is the key technology to restrain the effect of stress concentration of fatigue strength of key components and solve the “three major problems”. It is a revolution to realize anti fatigue manufacturing. Its connotation not only involves manufacturing concept, management concept, manufacturing technology and practitioners, but also includes manufacturing workshop, process and process setting. Surface modification, especially high-energy or high-energy composite surface modification, is the core and leading factor.
The key point and difficulty of the research on gear anti fatigue manufacturing is to establish the relationship between the anti fatigue processing parameters (processing parameter input), the surface and sub surface performance, and the service performance of gear parts.
Research and development of new gear anti fatigue manufacturing technology, research and development of deep carburizing and nitriding of gear, new technology of high-energy composite surface modification, innovation of high-performance equipment and new technology, further improvement of the hardness and residual compressive stress level of gear surface and its certain toughness will be the main direction of gear anti fatigue manufacturing technology and equipment research in the future.
It will be the key point of gear anti fatigue inspection research to establish the quality inspection system and health monitoring platform of gear anti fatigue manufacturing, develop new nondestructive and online inspection technology, health monitoring and related equipment. The fatigue resistance of the manufactured gear can be ensured to meet the requirements through inspection, and the damage degree of the surface and sub surface performance of the gear can be controlled through health monitoring, so as to realize the purpose of long life, high reliability and safe use of the gear.
The future development trend of gear anti fatigue manufacturing technology can be summarized as high, fine, fine and deep. High is the high requirement of the surface performance of the gear; the surface of the fine is the final finishing of the gear; the fine is the finer requirement of the gear processing technology; the deep is the deep surface modification layer of the gear, which can bear high load and has a long service life.