Running Your First Casting Simulation
Welcome to the comprehensive, interactive guide to setting up, running, and analyzing a foundational casting simulation using PoligonSoft. In this module, we simulate a small bracket casting, taking you from raw mesh loading to defect prediction and process optimization.
1. Setup & Pre-processing
The foundation of any accurate simulation lies in meticulous setup. In PoligonSoft, this begins immediately after generating your 3D mesh (as covered in previous tutorials). Here, we assign the physical realities of our alloy and mold materials to the digital geometry.
Loading the Mesh & Geometry
Assuming the mesh from Video 6 has been exported correctly (typically in native Poligon formats or standardized formats like STL/STEP which are then meshed internally), your first step is opening the Pre-processor module. The casting (the bracket) and the mold (sand, die, or investment shell) must be defined as distinct volumetric entities.
Material Properties
PoligonSoft stores extensive alloy data within its integrated materials database. For our bracket, we might select a standard Aluminum alloy (e.g., A356) or a carbon steel.
- Heat Capacity (Cp): Determines how much energy is required to change the alloy's temperature.
- Density (ρ): Crucial for flow calculations and shrinkage volume estimation.
- Latent Heat of Fusion: The massive energy release during the liquid-to-solid phase transition.
Navigate to Database > Alloys in the main PoligonSoft menu. You can view, edit, or import custom material files containing temperature-dependent curves.
Notice the sharp drop in density as the material melts, driving shrinkage.
Initial Conditions
Before the virtual pour begins, the initial state of the system must be declared.
Pouring Temperature:
Set to 720°C for our aluminum bracket. This provides superheat above the liquidus point to prevent premature freezing during filling.
Mold Temperature:
Assuming a green sand mold, we set this to ambient 20°C. If this were a permanent die casting, the mold might be pre-heated to 250°C to reduce thermal shock and improve flow.
Solver Sequence
PoligonSoft utilizes a modular solver architecture. Rather than running a monolithic black box, you configure specific mathematical engines tailored to the phenomena you wish to simulate.
The Euler Solver: Hydrodynamics
The Euler solver computes the Navier-Stokes equations to simulate the flow of molten metal. It tracks the free surface of the fluid as it navigates the gating system and enters the mold cavity.
- Calculates fluid velocity vectors in 3D space.
- Accounts for gravity, viscosity changes as temperature drops, and backpressure from entrapped air.
- Goal: Ensure smooth, non-turbulent filling to avoid oxide inclusion and confirm the mold fills completely before freezing.
The Fourier Solver: Heat Transfer & Solidification
Once filling is complete (or concurrent with filling), the Fourier solver handles heat conduction, convection, and radiation. It tracks the temperature field over time.
- Solves the non-linear heat conduction equation.
- Calculates liquid fraction based on temperature, identifying the 'mushy zone'.
- Goal: Predict directional solidification, identify isolated hot spots, and calculate resulting shrinkage porosity or macro-cavities.
The Hooke Solver: Thermo-elastic Mechanics
Optional for basic setups, but crucial for complex geometries. As the casting cools, it contracts. If the mold restrains this contraction, stresses build up.
- Computes residual stresses, distortions (warpage), and hot tearing susceptibility.
- Goal: Ensure the final part meets dimensional tolerances and won't crack during the cooling phase or shakeout.
View Filling Results
With the Euler solver initialized, we run the filling simulation. Visually, this is represented by an advancing fluid front. The color contours typically map to variables like Velocity (m/s) or Temperature (°C) at the flow front.
Interactive Filling Simulation
Interpreting the Flow
In the interactive model, watch how the molten metal (orange) enters via the runner system, passes through the gate, and fills the bracket cavity.
Watch out for Misruns
If the leading edge of the flow drops below the liquidus temperature (turns blue/grey in thermal view) before the cavity is full, the metal will freeze prematurely. This results in a "misrun" or incomplete casting.
Turbulence & Air Entrapment
High velocity spurts entering the cavity can splash and fold over, trapping air. Ideal gating design promotes smooth, laminar bottom-up filling.
Solidification & Cooling
After filling, the Fourier solver takes over. Heat transfers from the casting into the mold. By plotting Temperature vs. Time for specific virtual nodes, we can construct Cooling Curves.
Cooling Curves: Wall vs. Center vs. Riser
Monitor thermal gradients and directional solidification behavior.
Analyzing the Curves
The chart above demonstrates directional solidification.
The Thin Wall (blue) cools rapidly, crossing the solidus line first.
The Thick Center (orange) takes longer, forming an isolated hot spot.
Crucially, the Feeder/Riser (red) must remain liquid the longest to supply molten metal to the shrinking center.
Locating Hot Spots
PoligonSoft allows you to visualize the temperature field at the moment the casting reaches a specific solid fraction (e.g., 70% solid). The areas still glowing red or yellow in the post-processor are the "hot spots". If a hot spot is isolated from a feeder by solid metal, shrinkage porosity is guaranteed to form there.
Basic Analysis & Defect Prediction
The ultimate goal of running the simulation is not just to see pretty colors, but to predict defects. We focus primarily on Shrinkage Porosity.
Macro-Shrinkage
Large internal cavities. PoligonSoft calculates this based on volume deficit. Displayed as 3D iso-surfaces where porosity > 5%. Usually caused by inadequate feeding (riser too small or neck freezing off early).
Micro-Porosity
Fine, dispersed voids. Calculated using criteria like the Niyama Criterion (ratio of local thermal gradient to cooling rate). Crucial for components requiring pressure tightness or high fatigue strength.
Charts & Export
Generate quantitative charts of total porosity volume vs. casting volume. Output detailed PDF reports summarizing defect locations and volumes for quality assurance reviews.
6. Wrap-Up & Iteration
Simulation is rarely a one-shot process. The true power of PoligonSoft lies in rapid iteration.
The Optimization Loop
If your basic analysis reveals unacceptable porosity or misruns, you do not immediately cut tooling. Instead, you modify the digital twin.
Adjust
Change gating design, increase riser size, or alter pouring temperature.
Re-run
Execute Euler and Fourier solvers on the new geometry or parameters.
Validate
Analyze the new results. Repeat until the part meets quality standards.
By mastering this basic simulation workflow in PoligonSoft, you lay the groundwork for tackling complex multi-cavity dies, investment casting clusters, and advanced stress analysis.
Learn more at Poligoncast.in