Effects of As Cast Holes on Cooling Patterns in Directional Solidification of Plate Castings

Abstract

The directional solidi cation characteristics and generation patterns of isolated pools of liquid metal in plate castings with as cast holes were numerically examined, and fundamental concepts for the casting design, including the holes, were also investigated. For the as cast hole effects H/T (H: as cast hole effective range, T: plate thickness), there were differences depending on the hole size as well as the casting and mold materials, which re ect the directional solidi cation characteristics associated with the cooling effects due to the hole. For the nite-width plate castings with as cast holes, isolated liquid pools occurred at locations between a hole and an end face or between the holes under speci c conditions. The generation status of isolated liquid pools indicated that the conditions with larger values of the difference between the end and as cast hole effects (E−H)/T (E: end-effective range) in the range of 1.8-5.3 are preferable for preventing the generation of isolated liquid pools. Therefore, the consideration of (E−H)/T is useful for the casting design. In addition, the generation of isolated liquid pools could be prevented by the appropriate use of chills. Moreover, the generation was sometimes prevented by a temperature decrease of the melt during mold lling. The success of these techniques in preventing shrinkage defects was experimentally con rmed.

Solidification Simulation of Pure Metal Castings by Considering the Effects of Shrinkage Cavity Formation Process on Heat Transfer Behavior

“…The casting and mold elements were surrounded by air elements. Table 2 shows the physical properties 2,7,10,18,20,21) and initial temperatures of the materials used in the simulation. The air elements were isothermalized by setting the value of thermal conductivity and specific heat sufficiently high.…”

“…Other Table 2 Physical properties and initial temperatures of materials. 2,7,10,18,20,21) Table 3 Interfacial heat resistance between materials (unit: m 2 ·K/W). conditions were same as those shown in Section 2.2.…”

“…In addition, these products are manufactured via a casting process to achieve near-net-shape production of their complex shapes containing fins or as-cast holes. 1,2) However, the generation of casting defects can cause some serious problems in the process, such as porosity and shrinkage cavities. An effective approach to manufacture sound castings is to predict the generation of the defects using a casting simulation.…”

“…Conventional prediction techniques for the shrinkage defects, thus, cannot be used always to create pure metal castings. 2,11,13,14) In particular, small temperature gradient and/or low solidification directionality would not always cause shrinkage defects due to the greater feeding ability of pure metal castings than that of common alloys. 2,1315) Meanwhile, macroscale shrinkage cavities are often formed in pure metal castings instead of microporosity.…”

“…2,11,13,14) In particular, small temperature gradient and/or low solidification directionality would not always cause shrinkage defects due to the greater feeding ability of pure metal castings than that of common alloys. 2,1315) Meanwhile, macroscale shrinkage cavities are often formed in pure metal castings instead of microporosity. 14,16,17) Although simulation techniques have also been developed for predicting the shapes of shrinkage cavities, they are still not optimal because of the applicability to pure metal castings and/or the practicality such as reasonable calculation time.…”