In die casting, the gas inside the injection sleeve and the mold affect the product quality. For this reason, it is necessary to discharge the gas out of the mold as much as possible, and exhaust gates are usually provided for this purpose. However, as product shapes become more complex and the variety of products becomes smaller, the difficulties involved in designing the exhaust gates of such products and the time required for the design process are increasingly becoming challenging issues. On the other hand, recent design methods based on iterative calculations are difficult to apply to the design of exhaust gates because the entire mold needs to be calculated. In this study, we developed a system to automatically design the position and width of exhaust gates that can properly discharge the gas out of the mold without the need for iterative calculations by ranking the best areas of the mold for installing the exhaust gates based on the filling time of molten metal. Finally, experiments were conducted using actual die castings and the results showed that the proposed exhaust gate shape can reduce the blowhole inside the product well.

  In die casting, since the air inside the shot sleeve and the mold affects product quality, discharging the gas out of the mold is an important process. When designing exhaust systems such as exhaust runners or overflows, it is necessary to discharge the molten metal with gas entrained outside the mold as much as possible. Overflows can be installed over a wider range than exhaust runners, allowing discharge of molten metal with entrained gas that cannot be discharged with exhaust runners. Therefore, it is important to take into account the overflow position and volume. In recent years, researches have been conducted on the optimal overflow position by combining optimization theory and CFD, but optimization of the overflow position only causes gas entrapment in the product and excessive discharge of molten metal due to excess/insufficient overflow volume. In addition, if the entire mold area is analyzed, the calculation will take considerable time, making it difficult to apply this method to the design of an exhaust system that meets our research target. This research proposes an optimal design system that automatically designs the optimal overflow position and volume for completely discharging molten metal with gas entrained in products by estimating the molten metal flow direction during filling. Finally, the effectiveness of the proposed method was verified through CFD including the proposed overflow.

  Japanese Industrial Standards (JIS G 5502 : 2001) for ductile cast iron defines tensile properties using two types of cast samples (Y Block type and Knock off type). However, their tensile strength and elongation are expected to be different since their casting weight and sand mold material are not specified. We performed experiments using two types of cast samples with different mold materials, and investigated measurements of tensile strength and elongation, micro structure, cooling curve of cast sample and heating curve of sand mold. The Y Block type showed lower tensile strength and higher elongation than the Knock off type. Although the changes in tensile strength and elongation due to mold material could not be confirmed, the cooling curve and microstructure of green sand mold differed from the CO₂ type and self-curing type.

  In this study, SEM-EDS analysis was applied to the measurement of the contamination percentage of artificial sand in recycled sand as follows. (1) For the count number-based contamination percentage measurement, the number of mixed-sand particles n_nec necessary for achieving accuracy Δp_nec was formulized by an equation : Δp_nec was assumed to be a confidence interval width in statistics, and a true value of contamination percentage p_true was used as a parameter. Next, by using mixed sands to resemble recycled sands, contamination percentages were experimentally measured by varying of p_true and n_nec values. The measured contamination percentages agreed very well within the confidence interval width Δp_nec derived from the equation, which shows the effectiveness of the equation. (2) The contamination percentages by count number were transformed into those by mass% as follows. First, using EDS mapping images, the cross-sectional areas of particles on a polished surface were converted into diameters of equivalent-area circles. Secondly, approximating the sand particles as sphere, the diameters on polished surfaces were furthermore converted into orthogonal projective diameters of spheres. Thirdly, using the orthogonal projective diameters, the volumes of sand particles were calculated, and were multiplied by true densities. Finally, the volumes of sand particles were accumulated for all the exposed artificial and silica sand particles to estimate the contamination percentage of artificial sand by mass%. The estimated contamination percentages by mass% more or less agreed with the several compounding values. As a result, it was confirmed that the SEM-EDS analysis-based measurement method is effective when there is no significant difference in the grain size distributions, which was evaluated using AFS Grain Fineness Number (AFS GFN) in this work, between silica sand and artificial sand. The method should be further studied focusing on the large differences between the AFS GFNs.