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 are limited, we can expect an increase in the diameter by 8...10 µm for each millimeter of the thickness of the hardened layer. In our case, the quenching depth according to the factory technology is 1.05...1.15 mm, therefore the value of A P = 0.0084...0.0115 mm, δ P = 0.0031 mm. Based on this, you can determine the value of the tolerance 1 − ′d i . 1 1 i i p − − ′d = d + d = 0.1 + 0.0031 = 0.1031 mm In this case 1 0.025 0.1031 2 0.3 0.23595 2 2 i i e t − D ′ d + d + d = d − = − = mm. 3. Determine the possible value of the spatial deviations ∑ d ei , taking into account the operational toler- ances d ei for misalignment, the sequence of operations, the methods of basing and positioning. At finishing operations 20 and 25, the factory technology provides for processing on a rigid mandrel. In this case, the error of basing the part on a rigid mandrel can be determined as follows e B 1 = d 0 + d 1 + d 2 = 0.02+ 0.13 + 0.021 = 0.171 mm, where d 0 is the minimum gap, d 1 , d 2 are the tolerances of the hole and mandrel, mm. The error of basing the mandrel in the centers of e b 2 = 0.02 mm. The error of fixing the part and the mandrel e F = 0.03 mm. The total error of the part positioning is determined as: e P = e B 1 + e B 2 + e F = 0.171 + 0.02 + 0.03 = 0.221 mm. In addition to the positioning error, the value of the total spatial deviation is influenced by the amount of deformation δ c and (curvature, warping) of the hollow cylinder after surface hardening, which occurs due to the uneven depth of the hardened layer and depends on the wall thickness, the ratio of the wall thickness and the cylinder diameter, and the relative depth of the hardened layer. Hardening of the outer surface leads to the appearance of a “barrel”. For this case, the value of δ c = 0.010 mm. Then 2 Sd еi = e p + d c = 0.221 + 0.010 = 0.231 mm In this case, the condition ∑ d ei ≤ d e D is being executed. 4. We determine the desired size – the technological depth of the heat-strengthened layer A T . Limit val- ues of the closing size А Kmax = А Tmax – t min and А Kmin = А Tmin – t max (2) High-quality final surface processing after thermal hardening is possible under the condition t i min ≥ ( R z + T ) i– 1 , where Rz , T is the surface roughness and the depth of the defective layer on the previous processing. Such a minimum value of the allowance should also be provided for an unfavorable combina- tion of parameter values that affect its value: when D i- 1 max and D i- 1 min . At operation 15, a semi-rough turn- ing is carried out: R z = 0.05 mm, T i– 1 = 0.05 mm. Hence, t min = 0.05 + 0.05 = 0.10 mm, and t max = t min + d t = = 0.10 + 0.30 = 0.40 mm. Solving equations (2) with respect to the desired size, we obtain А T max = А К max + t min = 1.0 + 0.10 = 1.10 мм; А T min = А К min + t max = 0.6 + 0.4 = 1.0 мм. 5. Determine the allowance for final processing by the equation z i min = 2( R z + T ) i- 1 + 2 Sd еi = 2 × 0.10 + 0.231 = 0.431 мм. 6. In this case, the size of the preprocess 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 R min , then D 1 = 46 + 0.431 + 0.10 – 0.008 = 46.523 mm. According to the factory technology, D 1 is assumed to be equal to 46.5 mm.