1. There is gas in the raw material. In the production of die castings, since the main component of the gas contained in the aluminum liquid is hydrogen, the level of hydrogen content in the aluminum alloy liquid is directly related to the number of pores produced in the casting. The holes in the casting reduce the mechanical properties, corrosion resistance & airtightness of the alloy.
2. The influence of mold gating system. The gating system determines the design quality of a die-casting mold, and it is the main factor that determines the quality of the die-casting parts in later production. The runner is open in the direction of the dense side, the molten aluminum will reach the blind spot first, and when it returns, it will produce a vortex and roll-up. The quality of the left side of the casting is reduced & the airtightness is reduced.
3. Equipment performance. Air holes, shrinkage holes, and cold zones in aluminum die castings are also the air leakage of causes in aluminum die castings, and the performance of the equipment plays an important role. For products with strict requirements on airtightness, a suitable die-casting model needs to be selected.
4. Method of operation. During the die casting process, some coatings have high volatilization points & large air volume directly affects the casting porosity. The release agent is sprayed manually, and the dosage has determined by experience. If the spray volume is too large or the spraying time is too long, a large amount of gas will evaporate. Also, low mould temperature & untimely volatilization will result in large porosity.
5. Control the machining allowance. During the moulding process of die castings, the cavity has filled at the fastest speed, molten aluminium can be rapidly solidified in the mould to form a product, and holes or shrinkage will appear inside the casting. Due to the rapid solidification, the surface layer of the casting is a fine particle layer. The mechanical properties of these fine particles are very high. The production process changes for different castings, the thickness of the dense structure layer will be different.
6. Reasonably add rebates. The pinhole degree reflects the spatial distribution density of pinholes and is a factor that affects the casting airtightness. Due to the influence of small holes and oxidized inclusions in recycled materials, there are more pinholes in the castings, resulting in a higher scrap rate of single castings in production. To save energy, waste materials and runner recycling are reused in production, resulting in a decrease in the casting airtightness.
7. Choose a reasonable pressure chamber fullness. After selecting the punch diameter and die casting machine, each casting has a different molten metal weight. If the amount of molten metal injected into the pressure chamber is insufficient (when the pressure chamber is low), the pressure chamber gas cannot remove, and turbulence will form, which is easy to participate inside. Defects such as pores and insufficient perfusion will appear at this time. Too much oxide scale in the pressure chamber will form a partition wall inside the casting, and the casting strength will reduce. Under the action of the leak test pressure, leakage is prone to occur.
According to analysis, it is difficult to solve the problem of poor air-tightness of die castings. The reason may be the comprehensive influence of various casting defects. When dealing with poor airtightness, it is necessary to analyze the alloy properties, the process, and the mold. Then find out the main reason and take targeted measures, which can effectively improve the air-tightness of aluminum alloy die castings.