Novel sprue designs in metal casting via 3D sand-printing

Abstract

The opportunity to improve the quality of metal castings by enabling fabrication of complex gating systems via 3D Sand-Printing (3DSP) has been recently established. Among the different components of a gating system (often called rigging), sprue design offers a major opportunity to exploit the unlimited geometric freedom offered by 3DSP process. In this study, conventional principles of casting hydrodynamics is advanced by validated novel numerical models for novel sprue designs to improve melt flow control. Computational flow simulations demonstrate that conical-helix sprue satisfy the critical velocity condition by reducing the ingate velocity below 0.5 m/s. Multiple approaches to integrate 3DSP into conventional manufacturing to fabricate complex gating systems through “Hybrid Molding” are presented. 3DSP molds featuring two optimized sprue profiles and a benchmark straight sprue are fabricated to pour 17-4 stainless steel. Computed tomography scans (CT) shows that parabolic sprue casting (PSC) and conical-helix sprue casting (CHSC) reduced overall casting defects by 56% and 99.5% respectively when compared to straight sprue casting (SSC). Scanning electron microscopy (SEM) analysis confirms the presence of globular oxide inclusions and that PSC and CHSC exhibits 21% and 35% reduced inclusion when compared to the SSC. Three point flexural testing reveals that CHSC and PSC exhibits an increase of 8.4% and 4.1% respectively in average ultimate flexural strength than SSC. The findings from this study demonstrate that numerically optimized gating systems that can only be fabricated via 3DSP have the potential to significantly improve both mechanical and metallurgical performance of sand castings.