OBRABOTKAMETALLOV Vol. 23 No. 3 2021 MATERIAL SCIENCE EQUIPMENT. INSTRUMENTS 6 2 4 Fig. 12. Strain resistance under radial deformation of a ring specimen with porosity 17 %: dotted line – simulation data; solid line – natural data 1 – soap solution; 2 – graphite + oil; 3 – phosphate + soap; 4 – PTFE + oil; 5 – МoS2 + oil; 6 – graphite + oil 2 1 2 c a s c s c r dA rd rda h = τ = σ µ = σ µ ε , (12) where σs is the yield strength of the workpiece material; μc is the contact friction coefficient; r is the inner radius of the powder workpiece after radial deforming; α is the punch cone angle. From expression (12) we find: 2 2 d c s r r dA rh µ = σ ε . (13) Since in the process of radial deformation the work and the strain resistance force depend on the relative degree of radial deformation and the displacement of the punch (Fig. 11, b), for each value of hr the coefficient of contact friction for the given values of the yield strength of the material was determined by formula (13). In particular, Fig. 13 shows the influence of the degree of radial deformation εr of vacuum sintered ring specimens with porosity of 17 % from 304L–AW–100 powder, depending on the composition of lubricant and punch displacement on the coefficient of contact friction. Similarly, we determined the work of friction forces on the inner contact surface as a result of moving the punch along the entire height of the blank by the following equation: 2 2 ( ) sin 2 c s c r a À r h = σ µ ∆ . (14) Formulas (13) and (14) do not take into account the effect of blank porosity on the contact friction coefficient at all stages of transverse deformation. As can be seen from (Fig. 13, d), μc will be influenced not only by the initial porosity of the blank, but also by the nature of its height distribution, as well as by the concentration of solid lubricant particles located in open pores. The strain energy calculated by formula (10), using the results of experimental studies μc (Fig. 13, b curve 1), is noticeably greater than determined experimentally (Fig. 11, a). Therefore, depending on the design, operating conditions, technological properties of antifriction and lubricating materials we recommend to use the variant of sintered blanks design developed by the authors and methods of calculation of energy-force parameters, creation of new technology for obtaining non-displacement spherical sliding bearings. The results of research can be used in the development of technology for cold and hot die forging of powdered parts from other materials, as well as in the calibration of sintered blanks.
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