Mastering Porosity & Shrinkage
An interactive guide to interpreting Fourier solver outputs, identifying critical hot spots, and optimizing feeding systems using PoligonSoft simulation software.
1. Interpreting Output Data: Void Fractions
This section details how to read the porosity and void fraction results generated by the PoligonSoft Fourier solver. The solver calculates the progression of the solidification front and identifies areas where liquid metal cannot reach due to prior solidification pathways closing off. The resulting lack of material is expressed as a "Void Fraction".
Interactive Color Scale (Porosity %)
Hover your mouse over the scale below to understand the physical implication of the color output seen in the 3D visualizer.
Indicates perfectly sound metal to very dispersed micro-porosity. This is typically acceptable in non-critical structural components. The Fourier solver predicts excellent directional solidification here.
Indicates massive macro-shrinkage cavities. These are critical failures. This color implies that an isolated pool of liquid metal existed here, and as it solidified and contracted, no feed metal was available to compensate for the volumetric reduction.
2. Identifying Hot Spots (Last Solidified Regions)
A "hot spot" is a thermal center within the casting that solidifies later than its surrounding geometry. Identifying these is crucial because they are the natural locations for shrinkage cavities to form. We identify these by plotting Time vs. Temperature for various nodes in the mesh.
Cooling Curves Analysis
The chart shows temperature dropping over time. The red line represents a node deep inside a thick section (Hot Spot). Notice how it crosses the solidus line much later than the surface node.
Key Takeaways
- ⏱️ Thermal Gradient: The solver calculates the temperature at every node. Nodes remaining liquid the longest are isolated hot spots.
- 📉 Solidus Crossing: The critical moment is when the curve crosses the solidus temperature (dashed line).
- 🎯 Actionable Insight: To prevent porosity, a riser must be placed such that the thermal center shifts from the casting into the riser itself.
3. Quantitative Analysis & Feeding Optimization
PoligonSoft doesn't just show colors; it calculates exact volumes of shrinkage cavities and total porosity percentages. As cited in industry literature, "placing risers directly over identified hot spots is critical to ensure directional solidification and provide the necessary liquid feed metal to compensate for volumetric shrinkage" [5†L109-L112].
Use the simulator below to adjust the Riser Volume and observe the quantitative reduction in casting porosity.
Feeding Simulator
Adjust the simulated riser size to see the impact on calculated void fraction.
Increasing riser volume pushes the thermal center out of the casting.
Total Porosity Volume (cm³)
⚠️ Critical Caution: Mesh & Inputs
While PoligonSoft's Fourier solver is immensely powerful, it is governed by the principle of "Garbage In, Garbage Out". The accuracy of porosity prediction depends heavily on two critical factors:
1. Finite Element Mesh Quality
The discretization of the 3D model must be sufficiently fine, especially in areas with thin walls or drastic geometry changes. A coarse mesh will average out thermal gradients, completely missing localized hot spots and failing to predict micro-porosity. Ensure a high-density tetrahedral mesh is applied to critical zones.
2. Thermophysical Inputs
The solver requires highly accurate data for heat transfer coefficients (HTC) at the metal-mold interface, specific heat capacity, latent heat of fusion, and thermal conductivity curves across the temperature spectrum. Incorrect alloy definitions will drastically skew the cooling curves and invalidate the porosity results.
For precise calibration and software licensing details, always refer to the official documentation at poligoncast.in.
Comprehensive Metallurgical Theory & Algorithms
This section contains an exhaustive academic breakdown of the thermodynamic principles, mass transfer equations, and computational methodologies utilized by the PoligonSoft solver. Warning: Highly technical content.