Improving the efficiency of surface-thermal hardening of machine parts in conditions of combination of processing technologies, integrated on a single machine tool base

OBRABOTKAMETALLOV Vol. 23 No. 3 2021 technology Ta b l e 4 The results of calculating the productivity and energy consumption of surface hardening by means of HEH HFC under the conditions of integrated processing Steel, mode Speed V p , m/s Specific power q s , 10 8 W/m 2 Productivity, s –1 Energy consump- tion, kW × h 45 A 0.074 3.0 0.049 0.034 B 0.081 3.4 0.054 0.035 U8A C 0.068 2.4 0.045 0.029 D 0.075 2.8 0.050 0.031 where L = 104 mm (Fig. 3), b = 10 mm (Fig. 1). The results of calculating energy consumption and productivity during thermal hardening of the part for all combinations of operating parameters and steel grades are presented in Table 4. The analysis of the obtained results shows that the use of integrated processing allows, in relation to the existing technology at the factory, to increase the productivity of surface hardening using HFC by 3.5...4.1 times, and to reduce energy consumption by 9.5...11.3 times. Figures 13-14 show the results of optical microscopy, microhardness and residual stress measurements, as well as the results of mathematical simulation for two modes: 1. Steel U8A – the mode indicated by the point C ( P p increases by 3.5 times, and E decreases by 11.3 times): q s = 2.4·108 W/m 2 , V p = 68 mm/s; 2. Steel 45 – the mode indicated by the point B ( P p increases by 4.1 times, and E decreases by 9.5 times): q s = 3.4·108 W/m 2 , V p = 81 mm/s. Analyzing the graphs of the microhardness distribution of the surface layer, three characteristic zones can be distinguished (Fig. 13 a , d and Fig. 14 a, b ): – zone I is characterized by a stable average value of the microhardness level; – zone II is a transition zone; – zone III is a zone that has not undergone structural and phase changes. The depth of the hardened layer is taken as the distance from the surface to the zone with a structure containing 50 % martensite. In turn, the transition layer is the zone between the surface layer of hardened steel with a stable average level of microhardness and the zone of the material in which no structural-phase transformations have occurred. Subsequent diamond smoothing of the surface 1 (Fig. 3) managed to achieve a roughness level of the order of Ra = 0.1 µm (Fig. 15, a ), while increasing the microhardness and the level of compressive stresses in the surface layer to values of 870 HV and s c = –650 s c = 20 MPa, respectively (Fig. 15, b ). Conclusion An original method of structural and kinematic analysis for pre-design studies of hybrid metalworking equipment is presented. Methodological recommendations for the modernization of metal-cutting machines have been developed, the implementation of which will make it possible to implement high-energy heating by high frequency currents (HEH HFC) on a standard machine system and ensure the formation of high-tech technological equipment with expanded functionality. A single integral parameter of the temperature-time effect on the structural material is proposed when assigning hardening modes with concentrated heating sources that guarantee the required set of quality indicators of the surface layer of machine parts, while ensuring energy efficiency and processing performance in general. It has been experimentally confirmed that the introduction of the proposed hybrid machine into production in conjunction with the developed recommendations for the appointment of HEH HFC modes in the conditions of integrated processing of a part of the “Plunger barrel” type in relation to the factory technology allows to increase the productivity of