Kazanskiy (Privolzhskiy) Federal University, Naberezhnye Chelny Institute (Affiliate) (Naberezhnye Chelny, Russia):

V. G. Shibakov, Dr. Eng., Prof., Head of the Dept. of Machine-building
D. L. Pankratov, Dr. Eng., Director of the Higher Engineering School
R. V. Shibakov, Cand. Eng., Associate Prof., Dept. of Machine-building
R. S. Nizamov, Post-graduate Student, E-mail: nizamovrs@yandex.ru

Strength, durability and ultimate loads of gear teeth are determined by both the properties of steel on the working surfaces and the condition (continuity, macro- and microstructure) of the subsurface layers of the metal. Therefore, to increase the durability of gears, it is necessary to create production conditions that exclude the occurrence of defects in these areas and provide high mechanical properties (strength, hardness). One of the most unpredictable and dangerous defects in terms of consequences during the operation of gears is rolled or stamped scale-a surface defect that is interspersed with high-temperature oxides of steel, depressed during hot rolling or stamping. In this regard, the main factors that determine the quality of the surface of the gear ring during precision hot forging are described: the quality of the surface of the initial metal roll, the calcification during the heating of the workpiece, during the stamping process, and when the forging cools. Methods for improving the quality of the toothed crown surface are proposed: use of rolled metal products, lowering the temperature of the forming, use of low-oxygen heating, choice of material with increased scale resistance, selection of a rational precipitation scheme for scaling the surface of the workpiece, removing scale from the surface of the stamp engraving. Experimental technological modes of precision stamping operations and corresponding results of laboratory studies are presented. The influence
of the studied factors on the quality of the forgings obtained as a result of experimental stamping was evaluated through: presence of defects (stamped scale and cavities from the scale that fell from the calibrated surface of the tooth), micro-and macrostructure of the tooth body, mechanical properties (hardness of forgings and microhardness at different depths from the tooth surface), roughness of the tooth profile surface depending on the calibration.

1. Peterson R. E. Discussion of acenturi ago concerning the nature of fatigue, and reviews of some of subsequent researches concerning mechanism of fatigue. Bulletin of the American Society for Testing and Materials. 1990. Vol. 164. pp. 50–56.
2. Clarc W. G. In Fracture Mechanics in Fatigue. Experimental Mechanics. 1971. Vol. 11, Iss. 9. pp. 421–428.
3. Shibakov V. G., Ponkratov D. L., Khairullin R. A., Ponkratov D. D., Nizamov R. S. Substantiation of requirements for forging`s accuracy for precision stamping of gears. Zagotovitelnye proizvodstva v mashinostroenii. 2019. Vol. 17. No. 7. pp. 310–312.
4. Gubinskiy V. I., Minaev А. N., Goncharov Yu. V. Decrease in scale formation during rolling production. Kiev: Tekhnika, 1981. 135 p.
5. Hibbe P., Hirt G. Analysis of the bond strength of voids closed by open-die forging. International Journal of Material Forming. 2020. Vol. 13, Iss. 1. pp. 117–126.
6. Shibakov V. G., Pankratov D. L., Nizamov R. S., Nizamova L. M., Khairullin R. A. Justifi cation of requirements to quality and accuracy of blank for precision stamping. IOP Conf. Series: Materials Science and Engineering. 2019. Vol. 570, Iss. 1. Art. No. 012093.
7. GOST 4543–2016. Structural alloy steel products. Introduced: 01.10.2017.
8. Petrov P. А., Krutina Е. V., Kalpin Yu. G. Heating and heating systems in forgings: tutorial for universities Moscow: MGTU “MAMI”, 2010. 110 p.
9. Belur B. K., Grandhi R. V. Geometric deviations in forging and cooling operations due to process uncertainties. Journal of Materials Processing Technology. 2004. Vol. 152, Iss. 2. pp. 204–214.
10. Pachurin G. V., Shevchenko S. M., Mukhina M. V., Kutepova L. I., Smirnova J. V. The factor of structure and mechanical properties in the production of critical fixing hardware 38XA. Tribology in Industry. 2016. Vol. 38, Iss. 3. pp. 385–391.
11. Shibakov V. G., Pankratov D. L., Nizamov R. S., Nizamova L. M. Assessment of the impact of technological parameters of hot stamping on the cost of the product. IOP Conference Series: Materials Science and Engineering. 2019. Vol. 570, Iss. 1. Art. No. 012092.
12. Manyurov Sh. B. Development of the technology to reduce surface oxidation and decarburization of steel billets during heating using short-term technological protective coatings: Dissertation … of Candidate of Engineering Sciences. Moscow, 2014.
13. Technical Specifi cation 14-1-5561–2008. Long rolled products from 18KhGR grade steel designed for manufacture of gears and motor shafts.
14. GOST 8479–70. Structural carbon and alloyed steel forgings. General specifications. Introduced: 01.01.1971.