**2. Parameter identification for CFD simulation**

In general castings such as sand casting, molten metal is poured into a hollow mold. In contrast, in full mold casting, molten metal replaces a foam model. Therefore, because the flow of metal differs greatly between full mold casting and normal casting, it is necessary to understand the phenomena that actually occur in the mold.

In full mold casting, the heat of the molten metal decomposes the foam model and generates gaseous pyrolysis products. The thermal decomposition products are successively discharged through the coating mold into the sand mold. If the gas layer of the pyrolysis products is thin, the rate of heat transfer from the molten metal to the foam model will increase, as will the rate of molten metal flow. Conversely, the thicker the gas layer of the pyrolysis products, the lower the heat transfer rate and the lower the flow rate of molten metal. Therefore, the flow metal is determined by the complex interaction of multiple factors such as the metal's temperature, its position in the mold, the material and morphology of the foam model, and the thickness and composition of the coating mold.

In the CFD software used in this study, a foam model is represented as an obstacle that disappears when heated. Therefore, the flow of molten metal is hardly affected by pressure and inertia, but depends on the heat transfer phenomenon. Specifically, the heat transferred from the metal to the foam model at their interface is calculated. Subsequently, depending on the amount of heat, the foaming model disappears and the metal migrates. Therefore, the average inflow velocity *U*front of

**73**

**Figure 1.**

*CFD simulation model for identification experiment.*

*CFD Optimization Method to Design Foam Residue Traps for Full Mold Casting*

ucts of ρ and *C*p are the density and specific heat of the foam model.

the interface between the molten metal and the foam model can be approximated

*<sup>H</sup> <sup>U</sup>* ρ

where *H*0 is the apparent heat transfer coefficient between the metal and the foam model and represents the ease of heat transfer to the foam model. The prod-

In the full mold casting, the heat of the metal decomposes the foam model and generates gaseous pyrolysis products. The pyrolysis products are discharged into the sand mold through the coating process. These products are smaller than the metal when the metal is above the foam model. Therefore, the thickness of the gas layer between the metal and the foam model due to the pyrolysis products is reduced. Therefore, the heat transfer rate is expected to be high. On the other hand, when the metal is located below the foaming model, the thickness of the gas layer between the metal and the foaming model is increased and the heat transfer rate is considered to be low. In the CFD simulator used in this study, considering this effect in the gravity direction, the flow rate of metal in the gravity direction is defined by Eqs.

front

flont

<sup>0</sup> ( )

*<sup>H</sup> <sup>U</sup>* ρ

1 *<sup>n</sup> g n*

where *g*n is the perpendicular component of the gravitational acceleration to the metal interface and *l* is the surface roughness of the metal. The product of these

<sup>⋅</sup> = ⋅+ ⋅ ⋅

*g l H H E sign g <sup>H</sup> g l*

*p*

*n*

⋅ +

0

p

*<sup>C</sup>* <sup>≈</sup> (1)

*<sup>C</sup>* <sup>≈</sup> (2)

(3)

0

ρ*C*

*p*

*DOI: http://dx.doi.org/10.5772/intechopen.95505*

(2) and (3) using the parameter *E*g [8].

by the following Equation [8].

*CFD Optimization Method to Design Foam Residue Traps for Full Mold Casting DOI: http://dx.doi.org/10.5772/intechopen.95505*

the interface between the molten metal and the foam model can be approximated by the following Equation [8].

$$U\_{\text{front}} \approx \frac{H\_0}{\rho \mathbf{C}\_{\text{p}}} \tag{1}$$

where *H*0 is the apparent heat transfer coefficient between the metal and the foam model and represents the ease of heat transfer to the foam model. The products of ρ and *C*p are the density and specific heat of the foam model.

In the full mold casting, the heat of the metal decomposes the foam model and generates gaseous pyrolysis products. The pyrolysis products are discharged into the sand mold through the coating process. These products are smaller than the metal when the metal is above the foam model. Therefore, the thickness of the gas layer between the metal and the foam model due to the pyrolysis products is reduced. Therefore, the heat transfer rate is expected to be high. On the other hand, when the metal is located below the foaming model, the thickness of the gas layer between the metal and the foaming model is increased and the heat transfer rate is considered to be low. In the CFD simulator used in this study, considering this effect in the gravity direction, the flow rate of metal in the gravity direction is defined by Eqs. (2) and (3) using the parameter *E*g [8].

$$U\_{\text{flont}} \approx \frac{H}{\rho \mathcal{C}\_p} \tag{2}$$

$$H = H\_0 \cdot \left(1 + E\_\wp \cdot \text{sign}(\mathbf{g}\_u) \cdot \frac{\sqrt{|\mathbf{g}\_u| \cdot l}}{\sqrt{|\mathbf{g}\_u| \cdot l} + \frac{H\_0}{\rho \mathbf{C}\_p}}\right) \tag{3}$$

where *g*n is the perpendicular component of the gravitational acceleration to the metal interface and *l* is the surface roughness of the metal. The product of these

**Figure 1.** *CFD simulation model for identification experiment.*

*Casting Processes and Modelling of Metallic Materials*

actively conducted using CFD simulation [6, 7].

**2. Parameter identification for CFD simulation**

model, and the thickness and composition of the coating mold.

actual full mold casting.

Traditionally, these casting conditions and schemes have been determined based on the experience and intuition of skilled workers. In recent years, however, the use of computational fluid dynamics (CFD)-based simulations has made it possible to study appropriate conditions and solutions in advance based on the analytical results of the melt flow and solidification processes, thereby reducing the cost and time required for trial manufacture and experimentation. Particularly, solidification simulations are used to study casting conditions and solutions for shrinkage cavity defects, which can be estimated with high accuracy by comparison and verification with experiments [1]. The authors have also been optimizing the shapes of the runners in die castings by using CFD simulation and the shape optimization method for molten metal flow [2]. In recent years, the full mold casting method and the vanishing model casting method have been actively researched. Maruyama et al. have collected, analyzed, and investigated the pyrolysis products generated during the filling of molten metal in the vanishing model casting process [3]. Koroyasu et al. reported on the adiabatic properties of a coating in the vanishing model casting method and conducted a simple simulation of molten aluminum alloy flow in that method to investigate the influence of the air permeability of the coating, the presence or absence of depressurization, and casting methods on molten metal flows [4]. Karimian et al. investigated the influences of the coating thickness on product quality. When the coating film is thin, the amount of pyrolysis gas emitted from the foamed model is higher, and the amount of residue due to pyrolysis is reduced [5]. In addition, studies on the analysis of molten metal flow behavior in vanishing model casting have been

This study proposes a new casting design for the production of large castings by full mold casting. In this method, a residue trap is installed at the product part to prevent the occurrence of residue defects, and the optimal design of the residue trap is realized by using CFD simulation and the shape optimization method. The effectiveness of this method is demonstrated through casting experiments using an

In general castings such as sand casting, molten metal is poured into a hollow mold.

In contrast, in full mold casting, molten metal replaces a foam model. Therefore, because the flow of metal differs greatly between full mold casting and normal casting, it is necessary to understand the phenomena that actually occur in the mold. In full mold casting, the heat of the molten metal decomposes the foam model and generates gaseous pyrolysis products. The thermal decomposition products are successively discharged through the coating mold into the sand mold. If the gas layer of the pyrolysis products is thin, the rate of heat transfer from the molten metal to the foam model will increase, as will the rate of molten metal flow. Conversely, the thicker the gas layer of the pyrolysis products, the lower the heat transfer rate and the lower the flow rate of molten metal. Therefore, the flow metal is determined by the complex interaction of multiple factors such as the metal's temperature, its position in the mold, the material and morphology of the foam

In the CFD software used in this study, a foam model is represented as an obstacle that disappears when heated. Therefore, the flow of molten metal is hardly affected by pressure and inertia, but depends on the heat transfer phenomenon. Specifically, the heat transferred from the metal to the foam model at their interface is calculated. Subsequently, depending on the amount of heat, the foaming model disappears and the metal migrates. Therefore, the average inflow velocity *U*front of

**72**

values expresses the difficulty of heat dissipation of the foam model. Although the model expressed by this equation does not exactly represent the generation of pyrolysis products and the thickness of the gas layer, it is thought that the flow of metal, which is close to the real phenomenon can be expressed by setting appropriate values for each parameter. In this study, casting experiments and molten metal flow analysis were conducted for the model shown in **Figure 1** to obtain the appropriate values of the unknown parameters *H*0 and *E*g in Eq. (3).

The metal was FC300 gray cast iron, and the pouring temperature was set at 1683 K. Foamed polystyrene with a foaming factor of 60 times was used for the model. A water-based mold coating agent for full-molded cast iron was used for the coating, and the coating film was about 2 mm thick. Silica sand with an AFS grain size index of 36.7 was used as the casting sand. A stopper system was used for pouring the metal. The arrival time of the metal was measured by inserting a touch sensor into the end of the model; this sensor emitted. The experimental results show that the start to the finish of pouring was 7.2 s. The casting weight was 35 kg.

Next, CFD simulations were performed. The parameters in Eq. (3) were set to ρ = 16.7 kg/m3 and Cp = 2100 J/(kg-K). In order to make the arrival time of the metal consistent with that of the experiment and the simulation, the parameter H0 was adjusted based on the definition of Eq. (3), and good results were obtained at H0 = 5500 W/(m2-K) and Eg = 0.5. We therefore use these values in the simulations in this study.
