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 Ra = 0.4 microns is assumed through the use of the diamond smoothing process. Based on this, the value of Rz = 0, therefore, t min = 0, t max = t min + δ t = 0 + 0.0201 = 0.0201 ≈ 0.02 mm. Solving equations (2) with respect to the required size, we obtain А T max = А K max + t min = 1.0 + 0 = 1.0 mm; А T min = А K min + t max = 0.6 + 0.02 = 0.62 mm. 5. Determine the allowance for finishing according to the equation z i min = 2( R z + T ) i- 1 + 2 Sd еi = 0. 6. In this case, the preprocessing size of the surface 1 , taking into account the swelling, will be equal to D i- 1 = D i + z i min + δ i- 1 – A Рmin = 46 + 0 + 0.01 – 0.00496 = 46.00504 mm. Thus, the required parameters are: technological quenching depth A Т = 0.62 +0.38 mm; preprocessing size D 1 = 0.025 0.050 46 − − mm; allowance for final processing z min = 0. According to the proposed processing scheme, the first transition is the preliminary turning of the part in size D = 0.025 0.050 46 − − mm. Due to the fact that the preprocessing is carried out of raw (non-hardened) mate- rial, turning is carried out in more “rigid” modes, in relation to the factory technology. In addition, the considered integrated technology allows improving the technology of forming during machining due to additional heating of the workpiece with a concentrated energy source. Heating of the part with high-fre- quency currents, carried out before the cutting tool, allows to reduce the cutting resistance, making the workpiece more pliable for shaping, thereby achieving an additional effect that allows to intensify the op- erating parameters during rough turning. At the same time, the subsequent transition of “HFC quenching” due to heating of structural steel for quenching will make it possible to reduce the effect of the dangerous level of the stress-strain state of the surface layer of the workpiece on the final state of the material. In order to assign rational modes of surface quenching under hybrid processing conditions, the relation- ship of the numerical values of the integral temperature-time characteristic with the processing modes of the HEH HFC and with the hardening depth was established. Figure 11 shows the established minimum values of the S ∈ (4.3 > S > 2.5) ° С · s, which must be imple - mented in the surface layers during quenching of pre-eutectoid, eutectoid and trans-eutectoid steels using high-energy heating by high-frequency currents, which ensure the production of carbon-homogeneous aus- tenite at different states of the initial structure of the material [28]. It should be noted that these dependen- cies (Fig. 11) are obtained as a result of cosimulation of temperature fields and structural-phase transforma - tions in the material, and line 2 is the minimum value of the characteristic S for obtaining 50 % of martensite after cooling. However, as the numerical and full-scale experiment has shown, in most cases the maximum values of the characteristic exceed these values. This is due to the uneven distribution of the characteristic S over the depth of the material. Moreover, the smaller the depth of the hardened layer, the closer the values of the characteristic S are to the recommended values, which once again confirms the greater efficiency of the deep heating scheme in relation to the surface [28, 43–45]. The regularity of the change in the value of the characteristic S corresponds to the nature of the change in the values of the maximum temperatures in the depth of the material. The maximum values of this characteristic for HEH HFC are reached at a depth of about 0.2 mm. Based on this, the dependences of the values of the characteristic S , realized at a depth of 0.2 mm, on the value of the resulting hardened layer were established: S 45 ( h ) = 0.55 + 3.69 · h – 5.95 · h 2 + 38.62 · h 3 (3) S U 8 ( h ) = 0.90 + 3.19 · h – 5.14 · h 2 + 0.18 · h 3 (4)