Minimization of heat accumulation and shrinkage defects via locally induced forced convection in 316L stainless steel investment casting of vortex flow meters

Abstract

Investment casting is widely used for precision manufacturing of complex parts, such as vortex flow meters (VFM), where shrinkage defects are unavoidable but controllable. X-ray examinations revealed defects in the gating area, with the longest defect measuring 16.7 mm, exceeding the standard upper control limit (UCL) of 10 mm. This study investigated the causes of these defects and proposed solutions to mitigate them. Thermal imaging and finite element method (FEM) simulations identified heat accumulation as the primary cause of shrinkage defects. To address this, we introduced forced convection, which reduced the temperature in the heat accumulation area by up to 550 °C and increased the heat transfer coefficient (HTC) to a maximum of 1930 W/m² K. Temperature-dependent HTC data were incorporated into the simulation software, and the results confirmed that forced convection effectively eliminated hot spots, which was subsequently validated experimentally. This solution also reduced the secondary dendrite arm spacing (SDAS) length from 57.77 ± 1.2 to 38.64 ± 0.82 μm, marking a 33% reduction, thereby enhancing the product’s mechanical properties. In actual production, forced convection reduced defects in the gating area to 0%, with the maximum defect length decreasing from 16.7 to 9.7 mm, demonstrating a significant improvement. While effective, this solution requires manual operation and additional equipment, highlighting the need for future research to develop automated and more sustainable solutions for mass production.

Graphical abstract