Patent ID: 7677297

Claim:
A method of making a sand particle-containing mold body for casting articles of light metal alloys where article-shaping surfaces of the mold body are heated by the cast metal and at least a portion of the surface of the cast article shrinks against an article-shaping surface of the mold body as the cast metal solidifies and cools, the method comprising: identifying a region of the mold body wherein a surface of the cast article may shrink against a portion of the article-shaping surface of the mold body during solidification of cast light metal alloy and sustain residual compressive or tensile stresses in that surface of the cast article; selecting a wax composition and amount for mixing with sand particles used in making at least the identified region of the mold body, the wax composition and amount being selected to soften the identified region after an initial solidified shell of the cast article has formed during solidification of the casting and to reduce compressive or tensile stresses in the surface region of the cast article shrinking against the article-shaping surface of the mold, the amount of wax in the identified region being up to the weight of the sand particles; and mixing the selected wax composition and amount with sand particles in forming at least the identified region of the mold.