Feasibility of Calcium Sulfate Moulds Made by Inkjet 3D Printing for Rapid Casting of Aluminium Alloys

Abstract

In this research, a comparative analysis has been carried out between a traditional sand casting process and a modern mould obtained by additive manufacturing (AM), in the context of aluminium parts production. In this case of AM, an inkjet 3D printing (3DP) process allowed us to create a ceramic mould. A numerical simulation was carried out to study the filling and cooling rates of both parts. The design freedom typical of the 3DP technique allowed us to optimize the filling system. The results showed that in sand moulding, the speed in the gate suddenly increased when the liquid metal entered the part cavity, leading to severe turbulence due to the fountain effect. The input of air is related to the speed in the gate. Nevertheless, the results showed that when using the 3DP mould, the speed in the gate remained constant and the filling process was homogenous. With regard to the dimensional precision, while the staircase effect in the surface of the 3DP mould is the most critical aspect to control, in the sand casting mould the critical aspect is the dimensional precision of the pattern. Microstructures of the cross-section of the moulded parts showed folded shapes and air input in sand casting, which could be produced by the severe turbulence and the oxide film present in the melt during the filling process. On the other hand, the porosity found in parts produced with the 3DP mould corresponds to shrinkage; during the filling process, the remaining binder is vaporized, creating nucleation points. In this way, pores are formed by shrinkage and a mixture of shrinkage and gas entrapment. With these considerations, it can be concluded that AM shows feasibility and advantages as an alternative to the sand casting method for aluminium alloys.