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 1 Chemical compositions of initial material Steel grade Weight of elements, [%] C Si Mn S P Cr Ni Cu 45 0.44 0.23 0.61 0.013 0.019 0.11 0.15 0.17 U8A 0.80 0.21 0.21 0.017 0.022 0.11 0.15 0.18 The final stage of the factory technological process of manufacturing the part consisted of the following operations: turning (turning and screw-cutting lathe model 16K20); hardening of HFC (industrial tube gen - erator brand VCHG 6-60/0.44 with an operating current frequency of 440 kHz); grinding (circular grinding machine model 3M151V ). The finishing mechanical operation is carried out according to the mortise grind - ing scheme. At the same time, the processing cycle is divided into three stages: preliminary grinding, final grinding and sparkout. Due to the fact that the processing is carried out on a hardened surface and in order to avoid changing the properties of the surface layer, grinding is carried out on “soft” modes. Pre-grinding is carried out in the following modes: the value of the excess material t = 0.2 mm, the workpiece speed V p = 30 m/min, the radial feed S r = 0.004 mm/rev. Final grinding – t = 0.1 mm, V p = 30 m/min, S r = 0.001 mm/rev. The time of sparkout is t s = 10 s. The final stage of the technological process of manufacturing a part using hybrid metalworking equipment was carried out on a modernized screw-cutting lathe of the UT16PM model and consisted of three transitions: turning, surface hardening using the HEH HFC, diamond smoothing. The machine system was equipped with an additional energy source, which was used as an ultra-high-frequency generator of the microwave-10 thyristor type with an operating current frequency of 440×kHz. A digital oscilloscope of the Hantek DSO 1000S Series model was used to measure and control the operating frequency of the induction heater. Rough turning was carried out with a pass-through cutter equipped with replaceable polyhedral plates (RPP) (cutting plate material is a hard alloy of the following composition: WC 79 %, TiC 15 %, Co 6 %), in the following modes: V p = 90 m·min -1 ; S O = 0.35 mm/rev.; t = 1 mm. During surface quenching, a loop-type inductor equipped with ferrite of the N87 grade was used. The heating process was carried out according to a deep scheme (the thickness of the hardened layer did not exceed the depth of current penetration into the hot metal – 0.6...0.8 mm) in a continuous-sequential way [14, 15, 24, 26]. The studies were carried out using intensive water shower cooling of the surface in the following range of processing modes: the spe- cific power of the source q s = (1.5-4.0) × 108 W m -2 , the speed of movement of the part under the inductor V p = (0.05...0.1) m s -1 . The width of the active inductor wire was R s = 2 mm, and its length b = 10 mm. The processing was carried out with a gap of δ = 0.1...0.2 mm. Finishing turning was performed in the fol- lowing modes: V p = 130 m/min ( n p = 882 min -1 ); S O = 0.025 mm/rev.; t = 0.01...0.015 mm. For rough and finish turning, the sulfurized mineral oil “Sulfofresol” was used as a coolant-cutting fluid (CCF). Diamond smoothing was carried out according to a two-pass scheme using a designed and manufactured holder with an elastic head, in which diamond tips (TU2-037-631-88) of radius R = 1 mm were installed. The radial component of the smoothing force of the P y , taking into account the rigidity of the technological equipment, the hardness of the surface layer of the workpiece after surface hardening of the HFC (700...800 HV) and the radius of the diamond sphere, respectively, was equal to 150 N. At the same time, the circumferential speed of the workpiece was V smooth = 24 m/min; and the feed values were S O smooth = 0.018 mm/rev. Industrial oil of the I-20A brand was used as a coolant-cutting fluid for diamond smoothing [59]. To determine the linear operational dimensions, the theory of dimensional chains and the method presented in [60, 61] were chosen according to the conditions of ensuring the required depth of the heat- strengthened layer. In the study, the Uone JD520 and Form Talysurf Series 2 profilograph profilometers were used to simultaneously measure shape deviations, waviness and surface roughness. The surface topography was evaluated using a Zygo New View 7300 laser profilograph profilometer.