The process of die casting involves several steps, the most important being the injection of the molten metal. During this process, several defects can occur that can affect the physical properties of the finished component. One such issue is gases, which may become trapped during the injection of the molten metal.
The absorption of gases into the melted metal can occur due to a variety of reasons. One common cause for this is the turbulent flow of the casting material through the cavities. This can cause the gases to get trapped and enter the molten metal.
Turbulence refers to the variations that occur in both the direction and the speed of flow of the liquid metal when casting. Besides, there are numerous other reasons for gas to be trapped in the molten metal as well. For instance, gases can get into the material or the air present in the crucible during the preparation phase.
The reactions that occur between the molten metal and the mold material can also result in the trapping of gases. However, the higher solubility of liquid metal than solid metal ensures that these gases are expelled normally. Any failure in the gases to escape can lead to the formation of vacant spaces inside the material leading to porosity and other defects in the metal casting.
Note that these vacant spaces in the casted material can be cased due to some other factors as well and not because of gas trappings always. However, there is a way to identify whether the vacant spaces had been formed from gas buildup. Spherical and smooth vacant spaces in the casted components are usually caused due to gas trapped beneath, but if the vacant spaces resemble angular and rough, it is caused due to shrinkage.
In metal casting, various methods are adopted to prevent gas from being trapped inside and thus cause defects. These techniques are adopted by most of the die cast industries in order to ensure that their finished components bear no internal weaknesses in the form of porosity and other defects. The inclusion of a proper venting system in the mold can prevent any gas defects to occur in the mold.
This is usually done in the manufacturing design stage of the die casting process. The other includes reducing the amount of turbulence in the flow of the molten metal, which will considerably minimize the absorption of gas into the metal. Slag removal is another method that will remove any gases and other impurities in the casting material. Other techniques like vacuum casting are also utilized to eliminate gases from the metal casting.