Since the trade friction between China and the United States, the issue of chips being "stuck" has become a topic of discussion among the country, society, and academia, and the precision problem in the manufacturing field is an important part of the "bottleneck".

The breakthrough in the first level precision of China's ultra precision gears is a typical representative of solving this precision problem, and also a typical case of China's independent mastery of key technologies. Western developed countries have imposed a technical blockade on China. In order to master the core technology independently, Wang Liding, an academician of the CAS Member, has led his team to successfully develop the Class 1 precision ultra precision standard gear in the international gear standard since 1999.

This article summarizes the "evolution" process of ultra precision gears from level 4 to level 2, and from level 2 to level 1, enriching the historical data of the development of ultra precision gear technology in China and showcasing the innovative spirit of the older generation of scientists who dared to climb new heights and take the lead.

Gears are widely used in mechanical equipment transmission.

In the precision level of gears, grades 6-8 are considered medium precision levels and can be applied to industrial equipment such as machine tools and automobiles; Levels 3-5 are high-precision levels, mainly used in applications such as ultra precision machine tools, instruments, ships, radars, and aerospace engines that require high-speed, high stability transmission; 1-2 level accuracy is the ultra precision level, mainly used as a national or international gear gauge calibration and precision transmission entity benchmark.

In the 1960s, in order to quickly establish the foundation of socialist industrialization and meet the needs of large-scale national defense engineering construction, while gears gradually became mass-produced, the requirements for gear accuracy became increasingly high.

In order to complete the manufacturing task of high-accuracy and sophisticated national defense equipment and meet the challenge of ultra precision gear technology blockade, Wang Liding, an expert in Chinese precision machinery and micro nano machinery and an academician of the CAS Member, led the team to gradually improve the gear precision from Level 7 to Level 1 after more than 40 years (the stage of gear precision from Level 4 to Level 2 ultra precision and Level 2 to Level 1 ultra precision is the most critical period of ultra precision gear technology from formation to perfection), making China catch up with the world leader from the backward position of ultra precision gear technology.

background

In 1960, a department of the Ministry of National Defense requested Changchun Institute of Optics, Precision Machinery and Physics (now Changchun Institute of Optics, Precision Mechanics and Physics, Chinese Academy of Sciences, hereinafter referred to as Changguang Institute) to develop an optoelectronic theodolite to track our and enemy aircraft and missiles.

This large-scale instrument equipment contains a large number of gear transmissions, requiring gear accuracy to reach level 6 or above. However, at that time, the accuracy of gears processed domestically was mostly level 7. Wang Liding, a research intern at Changguang Institute, participated in this project. He used the Y7131 conical grinding wheel gear grinder to grind and optimize gears, successfully completing the national defense mission. Later, he developed a level 4 standard gear on the Y7431 gear grinder.

ISO1328-1:1995 and ISO1328-2:1997 are international standards; DIN3962-1~3:1978 is a German national standard; JISB1702-1:1998 and JISB1702-2:1998 are Japanese national standards; ANSI/AGMA2015-1A01 and ANSI/AGMA2015-2 A06 are American National Standards; GB/T10095.1-2008 and GB/T10095.2-2008 are Chinese national standards

In 1965, the country planned to develop a new type of precision measurement radar, in which the shaft angle coding data transmission gearbox used in the radar azimuth angle measurement system was developed by Changguang Institute.

Changguang Institute has established a dedicated research and development team responsible for the design, process, and measurement of gearboxes. The research team is responsible for independently completing the development of gearboxes, and Wang Liding is a research intern in the team.

Difficulties and Solutions

The entire process of ultra precision gear machining can be summarized as installing the original gear blank onto a gear grinding machine, selecting and adjusting the parameters of the machine tool based on the parameters of the gear being ground, performing manual technical operations in combination with the gear grinding process, and finally measuring with a measuring instrument to achieve an accuracy of at least level 3 of international gear standards.

Gear grinding machine is the core element of ultra precision gear technology. At that time, the research team had two gear grinding machines - a worm wheel gear grinding machine imported from the UK and a domestically produced machine Y7431. Due to the latter's ability to process gears with larger diameters, Wang Liding chose this machine for modification and refinement.

In 1963, Wang Liding first replaced the sliding friction machining spindle of Y7431 with a high-precision and low friction torque dense bead rolling shaft system, which laid an important technical foundation for the later development of coded gears in precision radar and was also a major innovative measure for machine tool refinement.

After the first National Mechanical Transmission Annual Conference, Wang Liding followed his colleagues to Shanghai Machine Tool Factory to investigate the indexing technology in battery equipment. They found that the rotary shaft system of the magnetic recording machine they developed was composed of multiple high-precision steel balls, which directly ensured the accuracy of the magnetic recording disk.

This technology inspired Wang Liding to solve the problem of machine tool spindle structure design. He added 400 steel balls to the machine tool spindle, greatly improving the spindle stiffness, ensuring that the bearings are not easily bent, and also promoting the homogenization effect of errors. The spindle accuracy was reduced from the original 2 μ m error to 0.5 μ m, which is higher than the domestic production level.

Gear grinding machine tools can be divided into three technical modules based on their functionality: grinding wheel system, expansion system, and indexing system.

Wang Liding believes that the indexing accuracy of machine tools is the key to improving gear accuracy, and the indexing plate is the core element of the indexing system, whose accuracy determines the indexing accuracy of gears.

Wang Liding installed high-precision polyhedral prisms at the position of the gear of the gear grinding machine, with the indexing plate device behind the dial. By using a precise axis system to transmit the accuracy of the polyhedral prisms to the indexing plate, the accuracy of the indexing plate was improved to 10-20 arcseconds, but further improvement is needed.

Wang Liding drew a mathematical model diagram of the error of the dividing plate, which was shown as a sine curve. He assumed that this sine curve was caused by the installation eccentricity, and drew an inverse sine curve in the opposite direction to offset the actual sine and reduce the error in the vertical axis. Adjusting the dividing plate according to the inverse and sine curves greatly improved the accuracy of the dividing plate. This is the "sine reduction method" created by Wang Liding.

Then, Wang Liding used a small file to grind the teeth of the indexing plate in sequence. After 2 weeks of continuous grinding day and night, the accuracy of the indexing plate reached the processing requirements.

However, ultra precision gear machining requires a constant temperature, dust-proof, and shockproof experimental environment. The equipment in domestic ultra precision gear laboratories is rudimentary and cannot meet the requirements of ultra precision gear machining.

Wang Liding asked his assistant to perform semi precision machining during the day, while he himself performed ultra precision machining in a relatively quiet environment at night. He worked until around 5am every day and then opened the laboratory door to quickly cool down the gears, making it easier for laboratory personnel to conduct measurements after work during the day.

One year later, Wang Liding and others completed the development task of coding gears as scheduled. Afterwards, Wang Liding participated in the development of five batches of radar coding gears, all of which were loaded onto China's most precise radar and have not encountered any problems so far.

But Wang Liding was not satisfied with his existing scientific research achievements. In order to change the passive situation of China's ultra precision gear application field, he resolutely decided to continue to study and overcome the technical difficulties of ultra precision gears, until he developed a first level ultra precision gear, making China's ultra precision gear technology not only keep up with the pace of developed countries, but also lead the international level.

In order to fully meet the requirements of developing second level precision gears for the machine tool indexing system, Wang Liding thoroughly modified the indexing mechanism and added an automatic end tooth indexing mechanism. The end tooth automatic indexing mechanism was equipped on machine tools, especially precision machine tools, for grinding teeth, which was the first of its kind in China.

In 1977, Wang Liding modified the end tooth indexing mechanism to the Y7413 machine tool. The modified machine tool was able to stably grind "small module standard gears" with a second level precision according to the West German gear standard DIN3962-1977.

The "small module standard gear" with German DIN level 3 and level 2 accuracy developed by him won the major scientific and technological achievement award of the Chinese Academy of Sciences and the National Science Conference award in 1978.

In addition, Wang Liding developed the "end gear automatic indexing mechanism" from 1976 to 1978 to replace the indexing disc on traditional gear grinders.

He also carried out research on a variety of modular gears, among which the "standard gear with medium modulus" won the first prize of the Chinese Academy of Sciences for scientific and technological progress, and the Chinese Academy of Metrology used it as the national gear accuracy entity benchmark.

background

In 1985, China officially launched a comprehensive reform of its scientific and technological system. In the first stage, the breakthrough was to explore the technology market, guide scientific and technological work towards economic construction, and promote the close integration of science and technology with the economy.

The National Natural Science Foundation of China was established in 1986 to promote the development of basic research in natural sciences.

In this context, Wang Liding applied for a National Natural Science Foundation project with the research topic of "Research on the Formation Law and Optimal Forming Scheme of Involute Error", aiming to develop a first-class precision standard gear. "In scientific research, we need to compare with the world and contribute to China's scientific cause".

innovate

The tooth profiles of commonly used gears include cycloid, arc, involute and other curves. Involute gears have the advantages of smooth transmission, low vibration, constant output speed without fluctuations, and are the most widely used gears in modern mechanical devices.

Ultra precision gears are designed with involute profiles, and the key to reducing gear profile errors is to improve the accuracy of the involute cam of the machine tool.

In 1993, Wang Liding not only developed a double roller involute grinding device, but also further designed and manufactured an involute measuring device, providing calibration instruments for the Chinese Academy of Metrology.

The high-precision involute template developed by Wang Liding can not only be used for machine tool grinding to produce first level precision tooth profiles, but also serve as a benchmark for involute accuracy transmission at the Chinese Academy of Metrology. This achievement won the third prize of National Science and Technology Progress Award in 1999.

Through the application of innovative technologies such as dense bead rolling axis system, "sine reduction method", end tooth indexing mechanism, and involute template grinding and measuring device, the accuracy of the gear grinding machine has met the requirements for grinding level 1 precision ultra precision gears. However, the grinding of ultra precision gears still needs to be innovated in the machining process.

Wang Liding imitated the error law of the indexing plate, rotated the gear 180 ° and ground half of the gear, stopped grinding the remaining part of the gear, and increased the gear accuracy from the original 60 "to 45". He named this gear grinding process the "displacement method".

Wang Liding believes that the key to the invention of the "transposition method" lies in paying special attention to experimental phenomena. He placed an office desk next to the machine tool, which was convenient for analyzing and recording while machining gears. He also paid attention to listening to the sound of grinding teeth to judge the degree of gear machining.

In practical work, only by paying special attention to various phenomena and seizing each problem one by one can we carry out technological innovation and continuous progress.

In addition, with the help of new technology, Wang Liding led his team to successfully develop five ISO standard level 1 precision standard gears, and conducted a scientific and technological achievement appraisal in 2016, concluding that "the precision indicators have reached the international leading level".

significance

China is the first country to master the core technology of Level 1 precision benchmark standard gears, so its successful research and development have important scientific research value and application prospects.

In terms of research value

The grinding machine Y7125 and its grinding process developed by Wang Liding have filled the gap in the manufacturing process of first level precision gears at home and abroad, established China's leading position in the field of ultra precision gears internationally, broke through the quality difficulties of ultra precision gear manufacturing, improved the technical level of China's gear manufacturing industry, and laid a solid foundation for China to become a strong gear manufacturing country;

Level 1 ultra precision gears are used as gear accuracy transmission benchmarks by the Chinese Academy of Metrology and enterprises to identify gears or gear measuring instruments with ordinary accuracy, improving gear detection efficiency and making them suitable for large-scale production;

Ultra precision gear technology plays a crucial role in multiple important fields such as industrial production, aerospace, and military equipment, and holds an important strategic position.

In terms of application prospects

The high-precision involute template developed by Wang Liding in the 1990s is mainly used for refining involute camshafts to grind gears, while the reference grade gear involute template and gear helix template specifically refer to gear involute and helix templates with a precision of level 1 or above, used as national level gear involute and helix value transmission benchmarks.

In addition, as a representative of high-end intelligent manufacturing, industrial robots have seen a significant increase in production demand. However, China's slow start and reliance on imports have greatly limited the development of industrial robots in China.

Due to the inclusion of a large number of gear transmissions in reducers, precision reducers have extremely high requirements for gear accuracy. Therefore, accelerating the localization of precision reducers has become the main topic of China's future industrial robot development strategy and a major research direction in the field of ultra precision gear technology.

Source: Technology News