OBRABOTKAMETALLOV MATERIAL SCIENCE Том 23 № 3 2021 EQUIPMEN . INSTRUM TS Vol. 6 No. 2 2024 Fig. 10. Scheme of radial deformation for determining contact stresses: 1 – punch; 2 – annular specimen; 3 – matrix; 4 – stand To determine the contact stresses τc and the friction coefficient, we used the method of transverse deformation of the sintered blank using a punch with different diameters (Fig. 10). The initial height of the sintered ring blanks was 14.5 mm, outer diameter was 25 mm, wall thickness (hr) was 2.75 mm. Before testing, lubricants in the form of suspensions consisting of graphite, molybdenum disulfide and polytetrafluoroethylene (PTFE) particles were applied to the inner surface of the sintered blanks. As an example, Fig. 11 shows the effect of lubricant composition on the work (Ad) and transverse deformation resistance (Pd) of a 304L–AW–100 powder blank with an initial porosity of 17 % at a relative radial strain εr = 0.24. The minimum resistance to transverse deformation of the porous blank at εr = 0.24 was obtained in the case of coating the inner surface of the billet with PTFE (Fig. 11, b, curve 3). The maximum strain resistance in all cases was obtained at 12–14 mm displacement of the punch. With increasing degree of radial deformation Pd smoothly increases from 0.5 to 45–50 kN, and at εr ≥ 0.24–0.25 the force of deformation resistance increases more intensively (Fig. 12). It should be noted that regardless of the composition of lubricants, the strength of resistance to transverse deformation of the workpiece at εr ≤ 0.24–0.25, determined experimentally and by simulating using the QForm program, practically does not differ (Fig. 12). Let us assume that the work of friction forces on the contact surface of the blank with the matrix is much less than on the punch-blank surface (Fig. 10, a). Then on the inner surface of the blank the elementary work dA of tangential forces in the deformation center with height dh [21] a b Fig. 11. Dependence of energy (a) and resistance to transverse strain (b) of the sintered blank at Δr = 0.65 mm on the lubricant composition: 1 and 4 – pencil graphite; 2 – MoS2; 3 – PTFE
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