Effect of freezing range on reducing casting defects through 3D sand-printed mold designs

Additive manufacturing (AM) is accepted as a transformative technology for rapid production of parts based on digital models through direct printing of a range of materials (e.g., metals, polymers, and ceramics). Recent advancements in the binder-jetting AM process (i.e., 3D sand-printing (3DSP)) enables direct production of sand molds and cores for metal casting. AM has been attractive to manufacturers due to the ability to produce complex and customized parts in low batch production. Traditional mold design for gravity castings experience higher scrap rates due to challenges in controlling turbulence and air entrapment. In this research, mathematically designed sprue geometries that can be produced via 3DSP are presented along with their effect on mechanical and metallurgical properties of castings through numerical modeling, computational simulation, and experimental validation. The casting properties are contrasted to conventional straight sprue castings for two different alloys: aluminum alloy 319 and gray cast iron class 30. Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), computed tomography scanning (CT), and 3-point bending tests are performed to characterize microstructure, casting defects, elemental composition, and mechanical properties for castings of each gating system design. For aluminum alloy 319, a statistically significant increase of 10% in flexural strength was found using the conical-helix sprue geometry as well as a reduction of 25% in casting defects. In gray cast iron class 30, no statistically significant differences are found between the flexural strength of the conical-helix and benchmark straight sprue as expected in a short freezing range alloy.