Abstract: A method of producing a casting utilizing an expendable polymeric foam pattern along with unbonded sand having specific thermal properties. The pattern, formed of a material such as polystyrene, has a configuration corresponding to that of the article to be cast. The pattern is placed with an outer flask and unbonded sand surrounds the pattern as well as filling the cavities in the pattern. The sand has a heat diffusivity greater than 1500 J/m.sup.2 /.degree.K./s1/2. The molten hypereutectic aluminum silicon alloy is fed into the flask in contact with the pattern causing the pattern to vaporize with the vapor being entrapped within the interstices of the sand while the molten metal fills the space initially occupied by the foam pattern to produce a cast article. The thermal properties of the sand reduces the particle size of the precipitated primary silicon particles in the casting, thereby increasing the machinability of the casting.

Abstract: A method of producing dimensionally predictable metal castings utilizing an expendable polymeric foam pattern along with unbonded sand having specific thermal properties. The pattern, formed of a material such as polystyrene, has a configuration corresponding to that of the article to be cast. The pattern is placed with an outer flask and unbonded sand surrounds the pattern as well as filling the cavities in the pattern. The sand has a linear expansion of less than 1% from 0.degree. C. to 1600.degree. C., a heat diffusivity greater than 1500 J/m.sup.2 /.degree.K/S1/2, an AFS grain fineness number of 25 to 33, and an AFS base permeability number of 450 to 500. A molten metal, such as an aluminum alloy or a ferrous alloy, is fed into the mold in contact with the pattern causing the pattern to vaporize with the vapor being entrapped within the interstices of the sand while the molten metal fills the space initially occupied by the foam pattern to produce a cast article.