MATHEMATICAL MODELING OF FRICTION FORCE AND FRICTION COEFFICIENT AT DEEP DRAWING PROCESS
This paper includes: experimental determination of process and blank holder forces at plate deep drawing, calculation of friction force and friction coefficient on the basis of achieved experimental results, determination of mathematical models Ft = f (SHP, φ, pd) and μ = f (SHP, φ, pd), as well as graphical simulations and analyses of achieved mathematical models. As substance for cooling and lubrication molybdenum disulfide and oil EP50 were used, while tribological conditions of contact surfaces were varied using phosphated and non-phosphated plate (EN 10027-1: DC04; DIN: RRSt14). Research results have shown that the best tribological conditions were achieved with molybdenum disulfide on phosphated plate, and the most influencing parameter is material deformation degree.
Experimental Friction Test by Sheet Metal Deep Drawing Process
Friction in forming processes is a very complex phenomenon depending on the workpiece material, tool work zone geometry, deformation degree and drawing speed, contact conditions quality, motion and lubricant type. The knowledge of intensity and distribution of the contact stresses and the friction coefficient in metal forming processes is the importance both from the theoretical standpoint of process analysis and the practical application. The direct contact stresses determining method has been applied. On the basis of this has been conceptually elaborated and designed a sensor for normal (pn) and tangential contact stresses (tauf) measurement by deep drawing process of sheet metal. On the basis of the measuring results it has been analyzed the dependence of the friction contact coefficient (mi) on the technological lubricant type (lambda) and degree of deformation (fi).
ROOM- AND HIGH-TEMPERATURE MAGNETIC PROPERTIES OF Sm(CobalFexCu0.088Zr0.025)7.5 (x=0.30) SINTERED MAGNETS
The effect of Fe content on room- and high-temperature magnetic properties of Sm(CobalFexCu0.088Zr0.025)7.5 (x=0-0.30) sintered magnets, prepared by the conventional powder metallurgy method, has been systematically studied. With increasing Fe content, the remanences BT and maximum energy products (BH)max at room temperature gradually increase and reach optimal values of 1.055 T with x=0.27 for BT, and 205 kJ/m3 with x=0.21 for (BH)max, respectively, and then drop sharply with further Fe increase. An excessive addition of Fe (x≥0.24) results in rapid deterioration of permanent magnetic properties due to the formation of a considerable amount of FeCo soft magnetic phase. It was found that the effect of Fe content on high temperature stability is huge. The lower the Fe content, the smaller the temperature coefficient of coercivity. When x=0.07, a temperature coefficient of coercivity of -0.14%/K (293-723 K) can be achieved, as compared with -0.23%/K for x=0.21. BT of 0.725 T, bHc of 517 kA/m, iHc of 764 kA/m, and (BH)max of 95 kJ/m3 at 723 K were obtained, and the B-H demagnetization curve remains a straight line.