Sand Casting

Sand casting forms metal parts by pouring molten metal into expendable sand molds, ideal for large, complex, low-to-medium volume castings with low tooling cost.

Overview

Sand casting (green sand casting) uses packed sand molds to form complex metal shapes, from a few ounces to several tons. A pattern creates the cavity, cores form internal passages, and molten metal is poured, solidified, then shaken out and cleaned. Tooling is relatively cheap and quick to modify, which makes sand casting flexible for prototypes, design changes, and lower production volumes.

You should consider sand casting for large parts, thick sections, and complex internal cavities where surface finish and tight as-cast tolerances are not critical. Expect a relatively coarse surface, draft on vertical walls, and machining on functional surfaces and tight-fit features. Tradeoffs: slower cycle time, more dimensional variation, and higher post‑processing compared to more precise casting methods, but with much lower tooling investment and far better suitability for big, heavy, or geometrically intricate components.

Common Materials

  • Gray iron
  • Ductile iron
  • Carbon steel
  • Stainless steel 304
  • Aluminum 356
  • Bronze C932

Tolerances

±0.015" to ±0.060" as-cast depending on size

Applications

  • Engine blocks and cylinder heads
  • Pump and compressor housings
  • Gearbox and transmission housings
  • Machine bases and bed plates
  • Valve bodies and manifolds
  • Counterweights and pulley sheaves

When to Choose Sand Casting

Use sand casting when you need large or heavy metal parts, moderate accuracy, and low to medium production volumes with minimal tooling cost. It suits complex shapes, thick sections, and internal cavities where you plan to machine critical surfaces afterward. Choose it when flexibility and scalability matter more than fine surface finish or tight as-cast tolerances.

vs Die Casting

Choose sand casting over die casting when part size is large, geometry is heavy-sectioned, or required volumes don’t justify expensive hardened steel dies. Sand casting also makes sense for ferrous alloys and higher-melting-point metals that are not practical in standard die casting.

vs Investment Casting

Choose sand casting instead of investment casting when you can accept coarser surface finish and looser as-cast tolerances in exchange for much lower part cost on larger parts. Sand is better for big, robust components where machining critical surfaces is already planned.

vs Permanent Mold Casting

Use sand casting over permanent mold casting when you need larger, heavier parts, frequent design changes, or lower tooling investment. Sand suits thicker sections and more complex cores, while permanent molds are better reserved for stable designs and higher, repeatable volumes.

vs Centrifugal Casting

Select sand casting instead of centrifugal casting when your part is not primarily a rotationally symmetric ring, tube, or sleeve. Sand works better for irregular shapes, housings, and complex cored geometries that can’t be formed by spinning metal in a rotating mold.

vs Shell Mold Casting

Choose sand casting over shell mold casting when minimizing tooling cost and handling very large or heavy castings is more important than tighter tolerances or better surface finish. Traditional green sand setups are more flexible and easier to adjust for big or evolving designs.

Design Considerations

  • Aim for uniform wall thickness and gradual transitions between sections to reduce hot spots and shrinkage defects
  • Add 1–3° draft on vertical faces relative to the parting line to allow pattern withdrawal and reduce mold damage
  • Avoid very thin walls; keep most sections ≥4–6 mm (0.16–0.25") and clearly call out any thinner features for the foundry
  • Provide machining stock on critical surfaces (typically 1.5–3 mm / 0.06–0.12") and clearly identify all machined faces on the drawing
  • Use generous fillets and radii at internal corners to improve metal flow and reduce stress concentrations in the casting
  • Design cores to be robust and well-supported; avoid long, slender cores and call out core prints and parting lines clearly in the model and drawing