Cooling and Feeding System Design
Shrinkage porosity is one of the most common defects in metal castings. As metal solidifies and contracts, regions that freeze last can develop voids if there is no pathway for liquid metal to feed in and compensate for the volume loss. Designing an effective feeding system means knowing where those last-to-freeze regions will be, and ensuring that risers are sized and positioned to feed them before they are isolated by surrounding solid metal.
The Cooling and Feeding System Design tools in FLOW-3D CAST give casting engineers two powerful diagnostics to guide riser and chill placement: the Last Places to Freeze map and the Thermal Modulus calculation. Both are generated automatically from a solidification simulation, turning the simulation results directly into actionable design guidance.
Last Places to Freeze
The Last Places to Freeze tool identifies and visualizes the locations in the casting that solidify after all their neighboring regions. These hot spots mark exactly where shrinkage porosity is most likely to form. Rather than requiring engineers to interpret solidification time contours manually, FLOW-3D CAST places particles automatically at each hot spot location as it forms during the simulation.
Each hot spot particle carries attributes that quantify the risk at that location: the cell solidification time, a sequential hot spot ID showing the order in which regions froze, and the local thermal modulus. Together these give engineers a clear, ranked view of where feeding is most critical and which locations are at greatest risk of defect formation.
Thermal Modulus
Thermal modulus is a well-established method for riser design in foundry practice. The principle is straightforward: a riser must solidify later than the section it is feeding, so the riser needs to be designed with a larger modulus than the casting section it serves. Modulus is essentially the ratio of a section’s volume to its cooling surface area. A thick, enclosed section cools slowly and has a high modulus; a thin fin cools fast and has a low modulus. Because modulus is a geometric quantity, comparing moduli is simpler and more direct than comparing solidification times.
What makes FLOW-3D CAST’s Thermal Modulus tool particularly powerful is that it goes beyond simple geometry. Rather than computing modulus from shape alone, it derives an equivalent thermal modulus from the actual solidification simulation, which already accounts for the effects of chills, insulating risers, exothermic sleeves, and variable heat transfer across the mold. This means the thermal modulus map reflects real process conditions, not just the casting geometry in isolation.
The result is a spatial map of modulus values across the casting that engineers can directly compare against riser modulus to validate feeding system designs. Regions where the casting modulus is high relative to neighboring areas indicate potential feeding challenges that need riser coverage.
Case Study: Steam Turbine Cylinder
A case study demonstrating the Cooling and Feeding System Design tools was carried out for the gravity casting of half a steam turbine cylinder, courtesy of Flow Science China. The outer dimensions of the part are approximately 2.83 x 2.34 x 1.10 m, making it a large and complex casting where manual riser design would be extremely difficult.
Applications
The Cooling and Feeding System Design tools are used in FLOW-3D CAST for:
- Identifying hot spot locations to guide riser placement in gravity, permanent mold, and sand casting
- Sizing risers using thermal modulus to ensure proper feeding without oversized, wasteful risers
- Evaluating the effect of chills and insulating risers on the solidification sequence
- Comparing alternative feeding system designs to select the most efficient option
- Diagnosing shrinkage porosity defects in existing castings by mapping the solidification sequence
- Supporting casting design for large, complex parts where manual feeding analysis is impractical
