Experimental and numerical study of section restriction effects on filling behavior in low-pressure aluminum casting

Abstract

The effect of pressurizing speed and mold geometry on mold filling in aluminum low-pressure casting was studied. The filling of cylindrical sand molds was both experimentally measured and simulated to characterize the free surface front velocity as linked to the mold geometry. Cylindrical molds with different diameters were filled with liquid AlSi 13 alloy. The mold filling velocity was experimentally measured using electrical contacts and was simulated using ANSYS Fluent® simulation software. The experimental results show that during mold filling without any section change, the filling velocity is regular and follows the Bernoulli's equations. However, adding a sudden section restriction in the mold leads to oscillating filling phenomena. Moreover, the oscillation intensity is observed to be proportional to the imposed filling pressure ramp. These oscillations lead to a temporary increased velocity of the metal front, which could induce metal oxidization and reduced mechanical properties for the cast part. The presented fluid dynamics simulation results show the importance of simulating the tube and not only the mold to catch the dynamic effects of the process on filling. Simulating the tube or the whole system, the observed filling oscillations are quantitatively predicted by the model. An analytical model is proposed to forecast the effect of the restriction function of geometry and pressure ramp. It permits to define new guidelines for low pressure casting part designs and the associated process adjustments.

Geometrical effects on filling dynamics in low pressure casting of light alloys

“…When the section restriction is stronger, the oscillatory phenomenon is clearly amplified, as already described in a previous study [14]. This parameter must definitely be considered when studying the geometry impact on filling dynamics.…”

“…Examples of vertical cross-section view of studied mold cavities are given in Figure 3 for two values of section change ratio R, for three values of transition height ℎ and for the three studied transition shapes (A), (B) and (C). By studying several system geometries, the authors showed in a previous work that the metal in the tube has an impact on the filling dynamics while the metal in the crucible and the air in the furnace can be neglected [14]. Therefore, the modelled system is made of the mold cavity and the tube.…”

“…However, in the case of a plate-shape casting of aluminum alloy, some filling oscillations were experimentally identified, while they could not be explained based only on this analytical model [8]. Similarly, several metal and water analog experiments highlighted this oscillatory phenomenon during filling by LPC [12][13] [14].…”

“…Recent work has been devoted to the understanding of the filling oscillations and their link with the process parameters in LPC. In [14], the authors identified the geometric parameters responsible for those oscillations as the horizontal sections of the furnace, the rising tube and the mold cavity. Fixing the low pressure system geometry, the impact of a sudden section change in the mold cavity has been quantified both experimentally and numerically.…”

Thin-Rib and High Aspect Ratio Non-Stochastic Scaffolds by Vacuum Assisted Investment Casting

“…Even though there have been reported casting products with extremely thin sections (~0.1 mm) and high aspect ratios [46], their application in a metallic scaffold shape is still a challenge. Vacuum assisted high pressure die [47][48][49] and low pressure casting [50,51] are able to produce thin-walled and/or high detailed structures, however, they are not suited for the manufacturing of intricate three-dimensional complex geometries. The present study shows a combination of additive manufacturing, in which fused filament fabrication (PLA) is used to produce the intermediate investment model to be cast in ceramic block by investment casting.…”