Sand Casting

Sand casting forms metal parts by pouring molten alloy into a sand mold, handling large sizes and complex shapes with moderate tolerances and low tooling cost.

Overview

Sand casting (often green sand casting) pours molten metal into a mold made from compacted sand around a pattern, then breaks the mold to remove the part. It supports very large castings, complex external geometry, and many alloys with relatively low upfront tooling compared to hard tooling processes.

Choose sand casting for prototypes through low-to-medium volumes, especially when part size is large, weight is high, or geometry isn’t practical to machine from solid. Expect draft, parting lines, and gates/risers that require cleanup, plus secondary machining for datum surfaces, bores, and sealing faces.

Tradeoffs: dimensional accuracy and surface finish are modest, repeatability depends on foundry controls, and thin walls are harder to achieve than precision casting methods. Design and simulation of gating/feeding matter; poor feeding drives porosity and scrap. Plan for machining stock and realistic tolerances on as-cast features.

Common Materials

  • Gray iron
  • Ductile iron
  • Carbon steel
  • Stainless steel 316
  • Aluminum A356
  • Bronze C95400

Tolerances

±0.03–0.06 in (±0.8–1.5 mm) as-cast; tighter with machining

Applications

  • Pump housings and volutes
  • Valve bodies
  • Machine tool bases
  • Gearbox housings
  • Manhole covers
  • Engine exhaust manifolds

When to Choose Sand Casting

Sand casting fits parts that are too large or too geometry-heavy to machine economically, where moderate as-cast tolerances are acceptable. It’s a strong choice for prototypes and low-to-medium volumes, and for designs that will be finish-machined on critical interfaces. It works well when you need flexibility in alloy selection and want to avoid expensive permanent tooling.

vs Die Casting

Choose sand casting when the part is large, the alloy is iron/steel, or volumes don’t justify high-cost die tooling. Sand casting also tolerates thicker sections and design iteration with lower tool-change cost. Expect lower accuracy and rougher surfaces than die casting.

vs Investment Casting

Choose sand casting when part size is larger, section thickness is heavier, or you want lower pattern/tooling cost and faster changes. Sand casting is better for big housings and bases where surface finish and tight as-cast tolerances aren’t the driver. Investment casting wins on fine detail, thin walls, and near-net features.

vs Permanent Mold Casting

Choose sand casting when you need iron/steel alloys, larger dimensions, or geometry that would make a permanent mold complex and expensive. Sand molds handle cores and design revisions more easily. Permanent mold typically delivers better finish and consistency but with higher tooling investment.

vs Shell Mold Casting

Choose sand casting when part size is larger, the design needs substantial coring, or you want the lowest pattern cost and fastest iteration. Shell molding improves finish and tolerance but is less forgiving on very large or heavy-section castings. Sand casting remains the workhorse for big, robust parts.

vs Centrifugal Casting

Choose sand casting for non-axisymmetric parts (housings, complex external shapes) and designs needing internal passages via cores. Centrifugal casting excels for round, hollow parts like sleeves and pipes with dense walls and low porosity. Sand casting is more flexible on shape but less uniform on wall density.

Design Considerations

  • Add draft on all vertical faces (typically 1–3°) and call out the intended parting line early
  • Avoid abrupt section changes; use generous fillets and transitions to reduce hot spots, shrinkage, and cracking
  • Set realistic minimum wall thickness (often ~0.20–0.30 in / 5–8 mm depending on alloy and size) and avoid long thin fins
  • Identify critical machined datums and specify machining stock on those faces rather than tightening as-cast tolerances
  • Design cores with robust prints and avoid deep, unsupported cores that can shift and blow tolerance
  • Call out porosity requirements by location (e.g., pressure boundary) and plan for gating/feeding and inspection accordingly