Casting Process Simulation: A Complete Workflow from Modeling to Defect Prediction

Casting process simulation is an engineering method that utilizes computer numerical simulation technology to virtually reproduce the entire process of molten metal filling, solidification, cooling, and stress-deformation. It enables the prediction of defect locations and causes—such as shrinkage porosity, shrinkage cavities, gas porosity, and hot tearing—before actual pouring, thereby significantly reducing trial production costs and shortening development cycles. Below, the core steps of casting process simulation are systematically introduced from two dimensions: simulation workflow and analysis essentials.

I. Basic Workflow of Casting Process Simulation

Casting process simulation typically follows three major stages: “Pre-processing → Solver Computation → Post-processing Analysis,” which can be further subdivided into the following key steps:

1. Geometry Import and Cleanup

The starting point of simulation is the 3D CAD model of the casting (common formats include STL, STEP, IGES, etc.). After import, geometric cleanup is required to ensure topological integrity of the model. For complete models that include gating systems, risers, chills, sand cores, and other process attachments, each component must be imported separately and assembled.

2.Mesh Generation

The continuous geometric model is discretized into a finite number of computational elements (mesh), which forms the foundation of numerical solution. Mesh quality directly affects computational accuracy and convergence. Commonly used mesh types include tetrahedral and hexahedral meshes, with attention to quality metrics such as element size, aspect ratio, and skewness. For critical regions such as thin-walled sections and hot spots of the casting, local mesh refinement is typically required.

3. Material Parameter Setup

Materials are assigned to different regions including the casting, mold (sand mold / metal mold), and sand cores. General simulation software already includes commonly used material properties: density, specific heat capacity, thermal conductivity, viscosity, liquidus / solidus temperatures, latent heat, and other thermophysical parameters. Some software supports custom material properties, which can be added manually or imported from professional software such as J-MATPRO.

4.  Boundary and Initial Condition Definition

This is the most critical and error-prone step in simulation setup, mainly including:

Initial Conditions: Pouring temperature of the molten metal, initial temperature of the mold, etc.

Boundary Conditions: Heat transfer coefficient between the mold outer surface and the environment, cooling channel temperature and flow rate, contact thermal resistance at the parting surface, etc.

Pouring Parameters: Pouring speed, filling time, ladle type (top pouring / bottom pouring), etc.

Proper boundary condition setup is the prerequisite for obtaining reliable simulation results.

5. Solver Computation

After setup is complete, the model is submitted to the solver for numerical computation. Casting simulation typically involves coupled solution of the following physical fields:

Flow Field Analysis: Based on Computational Fluid Dynamics (CFD), the filling process of molten metal is simulated to predict flow front, air entrapment, turbulence, etc.

Temperature Field Analysis: Computes the temperature distribution and evolution of the casting and mold during filling and solidification.

Solidification Analysis: Based on temperature field results, predicts solidification sequence, solid fraction distribution, isolated liquid zones, etc.

Stress Field Analysis: Based on thermal history, computes residual stress, deformation, and hot tearing tendency.

6. Post-processing and Result Visualization

After solving, the post-processing module is used for visualization and quantitative analysis of computational results. Common result display formats include temperature contour plots, solidification front animations, velocity vector diagrams, defect prediction distribution maps, stress / deformation contour plots, etc. Engineers use these results to judge the rationality of the process plan and guide subsequent optimization.

II. Core Content of Simulation Analysis

1. Filling Process Analysis

Filling analysis focuses on the flow behavior of molten metal after entering the mold cavity, mainly evaluating the following aspects:

Filling Sequence: Whether the molten metal fills smoothly along the expected path, avoiding turbulence and air entrapment.

Flow Front Convergence: Whether cold shuts or slag inclusions are likely to form at the convergence of multiple metal streams.

Filling Time: Excessive duration may cause cold shuts or misruns; too short may induce turbulence.

2. Solidification Process and Defect Prediction

Solidification analysis is the top priority in casting simulation. The core objective is to achieve “directional solidification”—that is, the casting solidifies sequentially from the region farthest from the riser toward the riser, ensuring unobstructed feeding channels. Analysis essentials include:

Hot Spot Identification: Identifying the last-to-solidify regions (hot spots) in the casting, which are most prone to shrinkage porosity and shrinkage cavities.

Isolated Liquid Zones: When a region is surrounded by already-solidified solid phase and loses its feeding source, shrinkage porosity or shrinkage cavities will form.

“Temperature Gradient and Solidification Rate”: Together, these determine the solidification mode and defect tendency of the casting.

3.  Stress and Deformation Analysis

During cooling, castings develop thermal stress due to inconsistent cooling rates among different regions. After superimposing phase transformation stress, residual stress is formed. Stress analysis helps predict:

Hot Tearing Risk Regions: Areas with stress concentration and within the brittle temperature range.

Dimensional Deformation: Warpage and dimensional deviation of the casting after mold removal.

Effect of Residual Stress on Fatigue Life: Studies have shown that casting residual stress can reduce component fatigue life by 30%–70% or more.

4. Process Parameter Optimization

A major value of simulation lies in supporting “virtual trial-and-error.” By adjusting pouring temperature, pouring speed, riser size and location, chill placement, cooling channel parameters, etc., and comparing simulation results of different schemes, the optimal process combination can be found. Some software also supports DOE (Design of Experiments) and response surface methodology for multi-parameter joint optimization.

III. Commonly Used Casting Simulation Software

Currently, mainstream casting simulation software in the industry includes:

IV.   Summary

Casting process simulation transforms traditional “empirical trial-and-error” into “scientific prediction.” Its core values include:

Reducing Trial Production Costs: Completing process verification on the computer, reducing the number of physical trial pours.

Improving Casting Quality: Identifying and eliminating defect risks in advance.

Shortening Development Cycles: Accelerating the process from new product design to mass production.

Accumulating Process Knowledge: Forming reusable simulation databases and standard workflows.

For casting engineers, mastering simulation technology is not only a tool-level improvement but also a mindset shift from “relying on experience” to “relying on data.” It is recommended that beginners start with simple sand mold gravity casting cases, gradually familiarizing themselves with the complete workflow of “Modeling → Meshing → Parameters → Solving → Analysis,” and then delve into multi-physics coupled analysis in combination with practical problems.