OBRABOTKAMETALLOV Vol. 23 No. 3 2021 MATERIAL SCIENCE EQUIPMENT. INSTRUMENTS 6 2 4 Ta b l e 1 Chemical composition of the powder materials used Material Chemical composition, % Si Cu Mn Ni Ti P Cr S C V W Fe 0.12C-18Cr-10Ni-Ti 0.8 0.3 2.0 10.0 0.7 0.035 18.0 0.020 0.12 2.0 0.2 Bal. 304L–AW–100 0.87 – 0.2 10.63 – 0.017 18.18 0.01 0.03 – – Bal. 18Cr-4Ni-3Cu 2.0 3.0 – 4.0 – 0.03 18.0 0.05 2.0 – – Bal. Simulation model Experimental speimen a b Fig. 2. Section of the outer ring of a spherical bearing with a coordinate grid after punching: a – with a chamfer; b – without a chamfer Porosity of sintered specimens was determined by hydrostatic weighing and varied in the range of 12–25 %, the coordinate grid on the sintered blanks was applied on a CNC laser engraver JL–F20W with a laser power of 15 W with a step of 0.5 mm (Fig. 2). Molybdenumdisulfide(TU48–19–133–90),pencilgraphite(GOST23463–79)andpolytetrafluoroethylene (PTFE) (GOST 10007–80) were used to study the influence of a lubricant composition on the contact friction coefficient and deformation resistance. To simulate cold die forging of the outer ring of the spherical sliding bearing outer ring according to the scheme shown in (Fig. 3), we used the QForm program, based on a hybrid approach that combines finite element and volume methods, providing fast and accurate calculation of porosity changes and stress-strain state of the workpiece at all stages of forming [19]. The process of forming the spherical part of the inner surface of the ring 5 by cold forming (twosided pressing) and the influence of the design of the end surfaces of punches 2 and 6 on the kinetics of deformation of porous cylindrical blank were investigated using a mold, the scheme of which is shown in (Fig. 3). Results and their discussion Studies have shown that the strain resistance force Pd of powder blank 5 during cold forming of sintered blanks is influenced not only by the mechanical properties of the material, but also by the configuration of the forming surface of punches 2 and 6 (Fig. 3). By simulating in the QForm program the process of deformation of a blank with an initial relative density of 0.8 mm, a height of 14.5 mm, an outer diameter of 25 mm and a wall thickness of 2.75 mm according to the double-sided pressing scheme, it was found that at the stage of compaction of the porous molding (i.e. that is, with its relative degree of strain εz ≤ 0.08...0.1), the force Pd insignificantly depends on the angle of the internal chamfer (Fig. 4, a). In the case of using punches with a flat end face (αf = 0) and with an increase in εz above 0.15...0.16, the strain resistance force increases almost twice as compared to when αf = 40–50 deg (Fig. 4, b). In particular, if the cone angle corresponds to the angle of rotation of the spherical bearing by 45°, then the strain resistance force of the porous blank at εz = 0.25 does not exceed 50 kN, while at αf = 0 the force Pd is equal to 200 kN. Similarly, the angle αf affects the strain energy.
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