Development and Experimental Validation of Novel Evaluation Criteria for Turbulent Two-Phase VOF Simulations in High-Pressure Die Casting

TL;DR

This work demonstrates that compressible, two-phase VOF simulations in OpenFOAM can capture critical HPDC filling phenomena, including cavity pressurization and air entrapment, when turbulence is modeled with a $k$-$\varepsilon$ closure. The authors introduce three concrete evaluation metrics—Time-Integrated Free Surface Area ($\text{TIFSA}$), Temporal Mean Volume Fraction ($\text{TMVF}$), and Time-Integrated Volumetric Flow ($\text{TIVF}$)—to quantify oxidation risk, filling continuity, and surface exposure, enabling objective comparison across operating conditions and time windows. Experimental validation using photogrammetry and X-ray CT porosity confirms that the simulations reproduce key defect mechanisms and align with observed porosity distributions, surface loading, and flow patterns. Collectively, the approach provides a validated framework for linking filling dynamics, air entrapment, and porosity formation, with direct implications for gating design, shot speed, and process optimization in HPDC. The methodology, grounded in physically meaningful metrics and validated against industrial data, offers a path toward more reliable predictions and reduced defect rates in automotive HPDC production.

Abstract

Air entrapment during mold filling critically affects porosity and overall casting quality in High Pressure Die Casting. This study assesses the feasibility of applying the vof method within OpenFOAM to simulate compressible, turbulent mold filling in a thin-walled geometry. Three-dimensional simulations with the "compressibleInterFoam" solver were carried out under ambient initial cavity conditions, using both laminar flow and the k-e turbulence model. The free surface dynamics were examined across a range of inlet velocities to evaluate their influence on interface morphology, cavity pressurization, and gas entrapment. To quantify these effects, three evaluation criteria were introduced: the TIFSA as a measure of oxidation risk, the TMVF as an indicator of filling continuity and air entrapment, and the TIVF as a proxy for surface loading. Results show that turbulence modeling accelerates pressurization and limits the persistence of entrapped gas, with velocity governing the balance between smooth filling, turbulent breakup, and exposure duration. Comparison with experimental casting trials, including CT based porosity analysis and photogrammetric surface evaluation, validated that the model captures key defect mechanisms and provides quantitative guidance for process optimization.

Figures (14)

• Figure 1: Casted plate of 3mm thickness: (a) model with for fluid flow $EV_{FF}$, for inlet velocity $EP_{iv}$ and inlet pressure $EP_p$ as well as (b) photograph with for the TIVF criterion $ES_{TIVF}$. Both views also highlight the , , and used in simulation and experiment.
• Figure 2: Mesh (a-d) and multiphase fluid flow for four test cases (#1-4), in side view (i-l) and top view (e-h) illustrating mesh dependency with increasing mesh resolution
• Figure 3: Numerical stability metrics for the test plate (see Fig. \ref{['fig:CADmodel']}): (a) mean and maximum number; (b) residual histories of the governing equations.
• Figure 4: Evolution of cavity pressure $p$ for different inlet velocities with turbulence modeling.
• Figure 5: Velocities as a function of time: (a) ingate velocities evaluated at the centroids of the along the left side of the gating system, and (b) mean velocities $\bar{v}$ evaluated over the in the and ; compare Fig. \ref{['fig:CADmodel']}.