Effect of varying part geometry and mold constraints on dimensional deviations of sand cast parts

The application of various allowances and thermo-mechanical behaviour of metal cooling inside the mold cavity makes metal cast parts heavier than the original designs. This has to be either accepted by the original equipment manufacturers or machined off, leading to increased cost, which needs to be borne by the manufacturer due to the typical contract agreements between customer and supplier. In this work, dimensional variations arising due to varying part geometry in aluminum alloy castings produced in no-bake molds have been investigated. Four benchmark shapes (rectangular plate, plate with hole, C-shape and L-shape) were designed, and their tooling was fabricated in aluminum. Three-part chemically-bonded no-bake binder system was used to prepare the molds (4 shapes x 3 repetitive experiments). AlSi12 alloy (melting range 575–585 °C) was melted and poured into the molds. The cast parts were inspected using a 3D scanner with 5-micron accuracy and studied for dimensional changes between sand mold and cast part. The unconstrained regions of the parts showed more dimensional deviation compared to constrained regions. The deviation near the cavity is reported less compared to the section away from the cavity. Similarly, the outer surface of the benchmark part (plate with hole, C-shape and L-shape) observed more dimensional changes than the inner surface. The part dimensional deviations are governed by the varying heat transfer rate in different geometrical features and the constraints imposed by the mold cavity. This study is expected to help in better design of the part and tooling to achieve high-quality near-net cast parts.