Analysis of the numerical simulation results of the casting process of the double hydraulic valve body

1.Simulation results and analysis of filling process

The filling process of multi way valve casting is as shown in the figure. It can be seen from the figure that when the liquid metal just enters the cavity, i.e. before 5.5s, the filling is not stable, resulting in splashing and the phenomenon of multiple streams of liquid converging. However, in the later filling process, the pouring is gradually stable, which can effectively prevent the formation of air entrainment and slag inclusion defects. The main reason for the unsteadiness at the beginning of pouring is that the liquid metal is introduced into the cavity from the middle of the casting. When the liquid metal just enters the cavity, it impacts the lower surface of the cavity, resulting in unstable filling and splashing. In addition, the liquid metal is introduced from one end of the casting. Because the cavity of the casting is complex and variable, and the flow resistance is large, multiple streams of liquid metal appear when the liquid metal just enters the cavity The pouring is not stable.

2.Simulation results and analysis of solidification process

The figure shows the cloud chart of solidification time in the casting process of valve body. It can be seen from the figure that the casting solidifies from all sides to the inside, and the final solidification position is the middle part of the casting, which is near the middle position of multi way valve boom joint. The reason is that the outer surface of the casting is in direct contact with the mold, with large heat dissipation area and temperature gradient, the casting is easy to cool and then solidify; the inner part of the casting is subject to the outer layer It is difficult to cool and has a long solidification time.

The figure shows the distribution of shrinkage cavity when the porosity is greater than 1% (macro shrinkage when the porosity is greater than 1%). It can be seen from the figure that there are many places of shrinkage cavity in the valve body, with the maximum porosity of 72.7%; among them, there are shrinkage cavity near the last solidified part of the valve body, i.e. the middle oil inlet of the multi way valve boom joint; in addition, there are shrinkage cavity near the important oil passage of the valve body, which seriously affects the performance of the multi way valve; in addition, there are also shrinkage cavity around the four screw holes Shrinkage cavity.

The main reason is that the casting always solidifies from the outside to the inside. During the solidification process, an isolated liquid-phase area will inevitably form. With the continuous cooling, the solidified part needs to complete the solid-phase shrinkage, while the isolated liquid-phase area needs to complete the liquid-phase shrinkage, volume expansion and solid-phase shrinkage. The expansion volume is not enough to make up the shrinkage of the liquid metal, and there is no liquid to supplement the shrinkage. Therefore, in the casting In addition, due to the complex structure of multi-channel valve body, there are many narrow and long special-shaped holes and grooves in the complex inner cavity valve body with high integration degree, forming hot spot, which makes the casting shrinkage resistance larger during solidification, and finally forming shrinkage cavity.

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