How does sand casting handle complex internal and external geometries?

Mold Cavity and Cores: The Key to Complexity

Sand casting handles complex geometries through its fundamental principle of using a disposable mold. The external shape of a part is formed by the cavity within the assembled sand mold, created using a pattern. For complex internal geometries—such as hollow sections, undercuts, and internal passages—the process employs separate sand cores. These cores are pre-formed shapes made of bonded sand that are inserted into the mold cavity before pouring. The molten metal flows around these cores, creating the internal features once the core is subsequently broken out and removed after the casting solidifies. This use of cores is what allows for the production of intricate parts like engine blocks with water jackets and complex manifolds.

Versatility in Core Creation and Placement

The ability to create highly complex cores is a significant advantage. Traditional methods use core boxes to form the cores. However, in modern and Rapid Prototyping applications, cores can be directly 3D printed from sand. This additive manufacturing technique eliminates the need for core boxes and allows for the creation of internal geometries that would be impossible or prohibitively expensive to produce with traditional tooling. Multiple cores can be assembled within a single mold to create exceptionally complex internal networks, giving designers significant freedom.

Design Considerations and Limitations

While sand casting is remarkably versatile, certain design rules must be followed to ensure a successful cast. Features must include draft (a slight taper) to allow the pattern and cores to be removed from the mold without breaking the sand. Wall thickness should be as uniform as possible to prevent defects like shrinkage porosity. While sand casting can produce very complex parts, extremely fine details, sharp corners, or very thin walls might be challenging and require alternative processes or subsequent Post Machining. Early collaboration with our die castings Engineering team is crucial to optimize the design for the process.