Strengthening of selective laser sintering coated sand by the heat treatment and infiltrating silica sol as well as sodium silicate was investigated comparatively. The characteristics and adaptability of three strengthening process were analyzed comparatively. The results show that the SLS coated sand presents the highest tensile strength of 2.78 MPa after heat treatment at 200 ℃ for 2 h

which is closed to that of one made by metal die molding

and can meet the casting requirements for conventaional castings. Infiltration of high-temperature resistant adhesive silica sol can increase slightly the room temperature strength of the coated sand

while it cann’t provide high temperature strength. Vacuum infiltration of sodium silicate can increase significantly the room temperature strength and high temperature strength of the coated sand. The room temperature strength reaches 6.87 MPa

and the residual strength is 0.86 MPa after treatment of holding for 2 h at 700 ℃. The infiltration of sodium silicate can be applied for hot mold casting of complex thin-wall castings. The infiltration depth can be controlled by adjusting vacuum degree and infiltration time to meet the requirement of different castings.