The working environment of engine cylinder head in the engine is poor, which needs to bear high thermal load and mechanical load. It is required to have high strength and high precision. Its casting precision directly affects the installation and commissioning of other parts.
The structure of engine cylinder head is complex, the minimum wall thickness is thin and the overall wall thickness is very uneven, so the production process is difficult and special manufacturing technology is needed. At present, the production methods often used by enterprises are: metal mold gravity casting, sand mold casting, lost foam casting, etc. Among them, sand casting produces aluminum alloy cylinder head with low cost and strong operability. It is suitable for single piece and small batch trial production. In the casting process, high-temperature liquid metal fills the mold cavity through the gating system under the action of gravity, which requires the gating system to make the liquid metal enter the whole mold cavity smoothly, avoid defects such as insufficient pouring and cold shut, and obtain castings with complete overall shape and clear outline. At the same time, the riser and gating system should ensure that the liquid metal can achieve good feeding during solidification, avoid casting defects such as shrinkage cavity and porosity, and obtain castings with dense internal structure.
Therefore, we will investigate whether the sand mold gravity casting process scheme is reasonable and optimize the gating system from the following aspects:
① Is the metal liquid filling stable? Whether there are “rolling up”, “sand washing” and other phenomena?
② Can liquid metal fill the mold cavity smoothly?
③ After the liquid metal fills the cavity, does the solidification meet the sequential solidification conditions?
④ Can the riser completely feed the casting during solidification of liquid metal?
According to the comprehensive calculation and design, the pouring position is selected in two ways: top and bottom. The component proportion of the gating system is closed open gating system. Finally, three schemes are determined, as shown in the table:
| Option 1 | Option 2 | Option 3 | |
| Gating system location | Single side top injection | Symmetrical top injection | Single side bottom injection |
| advantage | Top injection type can ensure the smooth filling of molten metal; An inner gate is set at the top of the casting, which is conducive to sequential solidification and meets the feeding conditions. At the same time, the top casting type has convenient modeling and simple structure. | The water inlet is more evenly dispersed, and the rising rate of liquid level will be relatively stable compared with scheme 1. | The direct impact of liquid metal on molding sand is avoided, and the rise of liquid level is relatively gentle. |
| disadvantage | Large impact force, unstable filling, splashing, oxidation and air entrainment of liquid metal in the cavity; Defects such as sand holes, pores and inclusions are easy to appear in castings. | The impact force is large, and there will be liquid metal intersection in the middle, which is prone to casting defects such as inclusion, entrainment and turbulence. | Vulnerable to insufficient horizontal static pressure and insufficient pouring in mold filling. |