Development of a model to optimize the sand shape and post process parameters for parts produced by Direct Croning process

The complex sand cores and moulds for prototype sand, castings produced by Selective Laser Sintering (SLS), result fragile once they are removed from the supporting uncured sand. Therefore, they require Post Curing to become dimensionally stable and capable of successfully undergoing the rigors of the metal casting process. In this paper the effects of post curing process parameters on the performances of sand parts produce by SLS are investigated. The sand characteristics and Post Curing parameters choice must take into account the presence of two antagonistic needs: the decrease of gas production during the casting decreasing the presence of volatile components of the binder, and the improvement of the mechanical performances increasing the binder weight percentage (Subramanian K. & Al, 1995, ). Three different phenolic resin coated sands were investigated: 1) silica SiO2; 2) synthetic mullite 3Al2O32SiO2 ; 3) synthetic mullite + SiO2. The compressive strength of the sand specimen was reported VS time and temperature post process parameters. Increasing curing temperature and time, the mechanical performances improve up to a maximum value than decrease. A benchmark was defined and used to evaluate the post process parameters influence on dimensional and shape tolerance. The mechanical behaviour of a part reflects the micro joining mechanisms between the particles a model is proposed to understand how the post curing parameters can influence the performances of the SLS products.This paper examines also the reliability of stress distribution obtained by FEA, comparing the results with the experimental data obtained using the mullit+SiO2 sand. Finite Element Analysis (FEA) allows to construe the stress distribution in the grains contact as a function of the post process parameters, making it possible to define the grains shape optimising the mechanical properties of the obtained structure: the sand may be designed and its use can be optimised without long times and expensive tests