The riser effects on solidification directionality of plate castings for alloys and pure metals were numerically examined by heat transfer and solidification simulation. The influencing factors as well as the relation to the end effects were also investigated. Numerical results showed that the riser effects have the same magnitude relation as the end effects except for the cases of pure aluminum or pure copper castings with sand molds. There were also tendencies for both greater riser effects and greater end effects to be obtained by higher mold temperatures or higher superheats. One of the main factors influencing the riser effects as well as the end effects was bcastH*/bmold (bcast and bmold : thermal diffusivity of casting and mold, respectively, H* : dimensionless latent heat). For the cases of pure aluminum or pure copper castings with sand molds, significantly smaller riser effects were however obtained due to the synergistic effects of the dimensionless solidification temperature range, ΔT* and temperature diffusivity of casting, αcast. The ΔT* and αcast change not only solidification behavior but also the solidification time of the riser part and/or the balance of the solidification time between the plate and riser part. These may affect the thermal conduction from the riser part to the plate part. In addition, most of the experimental rules or results about the riser-effective range could be explained on the basis of the riser effects. The above findings indicate that the effect due to the heat transfer caused by the riser is an important factor for the formation of the sound range.
Particle-based computational methods, such as the Smoothed Particle Hydrodynamics (SPH) method, do not require numerical mesh. Because of the mesh-less characteristics, they are suitable for the numerical simulation including the free surface or moving boundary. In the casting process, molten metal is carried in a ladle and poured into the mold. Since there is a need to treat the moving boundary in order to simulate these phenomena, particle-based methods are suitable. However, there are only a few studies on the quantitative comparison between the computational results of particle-based simulation and experimental results and that evaluate the validity of the technique used. Thus we applied the smoothed particle hydrodynamics method to the transportation and pouring processes to validate the results with experimental data. We report the technique we used and the results obtained, which show good agreement with experimental data and our numerical results.
Capillary shaping is an upward pulling solidification technique for obtaining aluminum alloy hollow products with high structural stiffness and high mechanical properties. Recently, hollow frames with inner ribs and bent geometry are increasingly desired for optimizing car body stiffness and design of lightweight car body structures. Capillary shaping is an attractive process for manufacturing these components. However, it is necessary to control thermal conditions during the pulling process for fabricating bent products with high thickness accuracy, since thermal conditions influence the thickness of products and vary at the bent section due to differences in the pulling rates at inner and outer positions. In this study, the thermally stable conditions during the capillary shaping of aluminum alloy bent tubes were investigated. It is found that bent tubes with high thickness accuracy can be fabricated without any automatic controls of cooling conditions when thermally stable conditions are maintained.
When spheroidal graphite cast iron is produced by green sand molding, sand inclusion defects are often found in the mixture of green sand and dross. In order to clarify their formation mechanism, casting experiments were carried out as follows : A comparison of inclusion defects between spheroidal graphite cast iron (which contains both Mg and Mn), flake graphite cast iron (which does not contain Mg and Mn), and flake graphite cast iron (which contains only Mn) was carried out by casting in a green sand mold. While pouring the molten metal, some loose green sand was added to the stream. A combination of Mg dross and green sand was formed in the case of spheroidal graphite cast iron, a combination of Mn-containing slag and green sand in the case of flake graphite cast iron containing Mn, and a combination of Fe-containing slag and green sand in the case of flake graphite cast iron without Mn. Thus, sand inclusion defects were formed in all cases. It was found that the dross and slag, which are oxides, were formed in the order MgO, MnO, and FeO. Na in the green sand was also seen to vaporize and adhere to voids in the sand inclusion defects.