Research on Coatings and Infiltration to Strengthen Ceramic Lost Cores Used in High-Pressure Die Casting Processes

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.

Experimental Evaluation of Ceramic Coatings for Die Protection in Low-Pressure Die-Casting Process

“…Furthermore, the evaporation rate leaves some air gaps within the coating and plays a critical role in the insulation capability, and hence, in the fluidity and solidification rate of the cast samples [4]. The casting surface finish depends on the particle size, so a proper selection of the coating composition is vital to achieve the desired surface quality of the cast samples [24,25]. Some examples of typical refractory materials employed in foundry coatings are silica flour, zircon flour, olivine, talc, mica, and clays.…”