Experimental confirmation of physical metal penetration generation and press casting production considering molten metal's pressure control

摘要

This paper presents a control technique of molten metal's pressure using a new type of iron casting method called sand mold press casting to realize high-productivity and high-quality product. In this method, only a lower sand-mold is set on the production line firstly. Next, molten metal is directly poured into the lower mold with a ladle, and then pressed to fill the cavity by the upper sand-mold being lowered down by the pressing machine. Our past test results using this method showed a casting yield of 90-95%, while conventional methods show a casting yield of 60-70%. This is because the press casting method doesn't need sprue cup and runner channel part. However, the theoretical analysis and design of pressing process haven't been sufficiently studied up to the present, and therefore this paper presents theoretical process design algorithm and its experimental confirmation. A simple mathematical model of molten metal's pressure during pressing is built by comparing the complicated model analysis of CFD (Computational Fluid Dynamics). The exact and simple pressure model is derived by considering Bernoulli's theorem and wall shearing stress depending on viscous increasing related to temperature decrease. Substituting information of the mold shape from 3D-CAD, the poured liquid volume and the initial liquid temperature into a control input generator based on the proposed mathematical model, an optimal pressing velocity for defect-free and high-speed production is instantaneously calculated. To keep the quality of the cast surface, the pressure limitation for defect-free production is set as a design parameter in proposed pressing control algorithm. Experimental confirmations for the proposed pressure control method in press process are achieved for brake-drum production. Pressing velocity input realizes pressure suppression under condition of the pressure constraint is designed by multi-switching pattern, because the filling flow path area is discontinuously changed. For pressure fluctuation increasing discontinuously, pressing motion changes from higher speed to lower speed. Finally the press casting productions with reasonable casting quality for each initial temperature condition has been demonstrated through CFD simulations and molten metal experiments.