## 3 Results and Discussions
### Feeding Capacity under Different Process Conditions  
In order to evaluate the shrinkage porosity, seven locations were detected: five dorsal traps and two thick parts (lower left corner and upper right corner). If more than half of them had obvious shrinkage porosity, the risk level was set as 2. If less than half of them had slight shrinkage porosity, the risk level was set as 1. If no shrinkage porosity was found, the risk level was set as 0. In order to evaluate the gas porosity, three locations were detected: two parts near the ingate and one part far from the ingate. If more than half of them had obvious gas porosity, the risk level was set as 2. If less than half of them had slight gas porosity, the risk level was set as 1. If no gas porosity was found, the risk level was set as 0. The typical scanning results of industrial CT are shown in Figure 11. It could be found that the degree of shrinkage porosity was different under different process conditions. Specifically, under the process conditions of test No. 1, 6, 11 and 16, there existed obvious shrinkage porosity in the thick position of the casting body and in the dorsal trap. Under the process conditions of test No. 2, 5 and 12, there existed slight shrinkage porosity. Under the process conditions of test No. 3, 4, 7, 8, 9, 10, 13, 14 and 15, there was no shrinkage detected. The shrinkage porosity results are summarized in Table 4, and the orange analysis results are shown in Table 6. The results show that the piston velocity of fast stage had obvious impact. If the piston velocity of fast stage was increased, the shrinkage porosity could be reduced to a large extent. Comparatively, the melt injection temperature and the piston velocity of the slow stage did not show an obvious influence on reducing the shrinkage porosity. \begin{table}
\begin{tabular}{c c c c c} \hline \multirow{2}{*}{**Factors**} & **Melt Injection** & **Piston Velocity** & **Piston Velocity** & **Pressure** \\  & **Temperature** & **of Slow Stage** & **of Fast Stage** & **Maintaining Time** \\  & **A (°C)** & **B (m/s)** & **C (m/s)** & **D (s)** \\ \hline K1 & 12.00 & 14.00 & 11.00 & 14.00 \\ K2 & 15.00 & 14.00 & 15.00 & 14.00 \\ K3 & 15.00 & 14.50 & 15.50 & 14.50 \\  
According to Figure 11, it could be found that the degree of gas porosity was different under different process conditions. Specifically, under the process conditions of test No. 1 and 2, the gas porosity was widely distributed in the large plane of casting. Under the \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Factors**} & **Melt Injection** & **Piston Velocity** & **Piston Velocity** & **Pressure** \\  & **Temperature** & **of Slow Stage** & **of Fast Stage** & **Maintaining Time** \\  & **A (\({}^{\circ}\)C)** & **B (m/s)** & **C (m/s)** & **D (s)** \\ \hline K1 & 3.00 & 3.00 & 8.00 & 3.00 \\ K2 & 3.00 & 3.00 & 3.00 & 3.00 \\ K3 & 3.00 & 2.00 & 0.00 & 3.00 \\ K4 & 2.00 & 3.00 & 0.00 & 2.00 \\ k1 & 0.75 & 0.75 & 2.00 & 0.75 \\ k2 & 0.75 & 0.75 & 0.75 & 0.75 \\ k3 & 0.75 & 0.50 & 0.00 & 0.75 \\ k4 & 0.50 & 0.75 & 0.00 & 0.50 \\ Range & 0.25 & 0.25 & 2.00 & 0.25 \\ Sequence & & & C \(>\) A \(>\) D \(>\) B & \\ Optimization Level & A4 & B3 & C4 & D4 \\ Optimum E. R. & & & A4 B4 C4 D4 & \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Table of shrinkage porosity by means of range analysis. Figure 11: The typical scanning results of industrial CT (The red circle indicates the area of shrinkage porosity and the red rectangle indicates the area of gas porosity): (**a**) under the process conditions of test No. 1, (**b**) under the process conditions of test No. 2, (**c**) under the process conditions of test No. 3 and (**d**) under the process conditions of test No. 10.  
process conditions of test No. 3, 4, 5, 6, 8, 11, 12, 15 and 16, a small amount of gas porosity was found around the ingate. Under the process conditions of test No. 7, 9, 10, 13 and 14, there was no gas porosity detected.