We have X-ray inspections for die casts, and find some inner defects such as shrinkage cavities, blow holes and shrinkage porosity existing in die casts after die casts are manufactured. We put forward the following corresponding countermeasures in order to improve defects and quality of die casts.

1. Improving the structure of the overflow box
The overflow box has the effects of eliminating the gas in the cavity, storing the mixed gas and transferring the shrinkage cavity and the shrinkage porosity. We find that we can improve defects such as shrinkage cavities and blow holes by extending and adding overflow boxes after repeated experiments. Usually, vertical overflow gates should be chosen because of much shrinkage porosity in the middle of die casts so as to avoid filling pressure being affected.

2. Optimizing the cooling system of the mold
Shrinkage cavities of die casts often occur in positions where partial temperatures of die casts are too high or walls of die casts are too thick. After the research, we find that temperatures at two sides of die casts' thick walls are high, which will easily cause shrinkage cavities. We select the smallest die cooling pipe with the diameter of 12mm at the beginning, and it can't cool the temperature of the above positions. Therefore, we adopt the high-pressure cooling equipment and the stainless steel die cooling pipe with a diameter of 4mm to improve the structure of the die cooling pipe. We cool temperatures of mold cores of die cast's two sides to 180℃, which can greatly reduce shrinkage cavities and improve quality of die casts.

3. Improving the separation of the insert
We can take the following measures to solve the separation problem between the insert and the aluminum alloy die cast. Firstly, use the diluent to clean the insert so as to improve the wettability of the insert; secondly, inspect the insert by the location hole, and inspect the appearance of the insert; use the steel wire to remove the partial spot on the insert; thirdly, preheat the insert; we find that when the temperature is over 120℃, the separation problem of the insert can be solved effectively after a research.

In conclusion, this article analyzes the difficulties of the aluminum alloy lower cylinder block's die casting technology, and puts forward the scientific design of the cylinder block die cast's running gate system. The tooth-shaped chilled exhaust block vacuum die casting technology and conducting an experiment of preheating the insert are recommended for aluminum alloy lower cylinder blocks. In addition, this article also summarizes aluminum alloy lower cylinder blocks' die casting defects such as shrinkage cavities, blow holes and shrinkage porosity and puts forward the corresponding countermeasures, which provide theories for your reference concerning aluminum alloy lower cylinder blocks' die casting processes of automobile engines.