Abstract
Lost cores used to manufacture complex aluminium components through high-pressure die casting (HPDC) processes need to withstand very high injection velocities and pressures. The conventional sand cores used in other casting processes, such as sand casting or low-pressure die casting, do not support the aggressive process parameters of the HPDC, so advanced ceramic cores must be used. These cores must be strong enough not to get broken during the casting process, but, at the same time, they must have a minimum porosity to be easily removed from the casting to obtain the finished part. Due to this porosity, the aluminium penetrates the core surface during the casting process. So, the criterion here is to find the necessary compromise between strength and porosity and to protect the core surface from the aluminium penetration. In this work, two research lines have been followed to address these challenges. On the one hand, different refractory coatings have been applied to the ceramic core surface with the aim of sealing it. Amongst the coatings analysed, boron nitride-based one has been found to be the most suitable and cost-effective solution to avoid aluminium penetration. On the other hand, silica has been proved to be a suitable infiltration agent to increase the strength of the core.
Highlights
high-pressure die casting (HPDC) is the most widely used casting process to manufacture aluminium components,[1] thanks to its versatility, high production rate and the possibility of producing thinwalled and, lighter components.[2]
Visual inspection performed on the samples coated with different refractory paints after pouring molten aluminium over them did not reveal any sign of penetration of the aluminium in the ceramic, which was attributed to the absence of applied pressure
In order to confirm the good behaviour of these two refractory coatings, some of the castings with cores coated with RC4 and RC5 were used in the de-coring trials to confirm that the ultra-high-pressure water jetting machine developed by FerroCrtalicwas able to completely remove the cores from inside the aluminium part
Summary
HPDC is the most widely used casting process to manufacture aluminium components,[1] thanks to its versatility, high production rate and the possibility of producing thinwalled and, lighter components.[2]. The aluminium penetrates the core surface during the casting process. The microstructural analysis of the castings revealed that in the uncoated ceramic core a cermet layer of around 200 lm thickness was formed as a result of the penetration of aluminium during the casting (Figure 3a).
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