The Die Casting Technology of Automobile Structural Parts (Part Two)

3.3 Alloy melting and processing
For general use, Silafont-36 and Castasil-37 alloys can be used in die casting production without special treatments. However, if you need to produce die castings with good quality, you need to paid attention to the following aspects.

3.4 The way of pouring
The way of pouring refers to the way that molten metal is poured or sent to the pressure chamber. The Figure 2 shows several typical ways of pouring. Experiments show that the way of pouring has a significant effect on the elongation of die castings. The traditional top pouring method is easy to cause the impact, splashing, oxidation and entrainment between the molten metals, which will cause the defects of the casting matrix and reduce the elongation. The bottom pouring method reduces the disturbance and heat loss of the alloy liquid, and lower the possibility of oxidation of the alloy liquid, generation of scum particles and gas inhalation. Therefore, the inclusions and defects of the casting matrix are reduced, which is good for improving the elongation of the casting. However, the bottom pouring method must be partially modified for the die casting machine. Special pressure chambers and molds should be used, though the die casting machine may lose its versatility. If special measures such as optimized length of the pouring pipe, heating the pouring pipe and smooth pouring are taken, the optimization of the top pouring can also achieve the purpose of improving the elongation of the casting without modifying the die casting machine and pressure chamber, which is convenient for die casting production conversion.
 
3.5 The release agent and spraying process
Release agents or lubricants can generate gas which will enter the die casting, increasing the gas content in the die casting. Firstly, when the vacuum process is adopted, the volatilization of the release agent or lubricant is an important source of gas in the casting. When choosing a release agent or lubricant, we must verify and choose products with low gassing properties and good volatility. Secondly, select advanced spraying equipment with high dynamic characteristics and adjustable spraying parameters. Reduce the amount of spraying as much as possible to ensure rapid and precise spraying. The purpose of spraying is mainly to protect the surface of the mold and to cool the hot spots of the mold. The overall temperature control of the mold should be done by the heating or cooling pipeline inside the mold as much as possible. In the production of structural die casting, the spraying time, angle, range, distance and other factors should be optimized. There should be no residual moisture in the cavity to make the least gas enter the casting.