Choosing between investment casting and sand casting is one of the first decisions an OEM buyer faces when sourcing cast metal parts. The two processes overlap in materials but differ sharply in tolerance, surface finish, tooling cost and economy of scale. Picking the wrong one usually means paying for precision you do not need, or grinding away excess material on parts that could have been cast closer to net shape.
As a supplier of both processes in Shandong, China, we put together this practical comparison to help buyers match the process to the part - not the other way around.
How the Two Processes Work
Investment Casting (Lost Wax Casting)
A wax pattern of the part is injection molded, assembled into a tree, coated with ceramic slurry layers, then dewaxed and filled with molten metal. Because the ceramic shell is broken away after casting, no draft angle is required and extremely fine detail can be reproduced. Typical materials: stainless steel 304/316, carbon steel, alloy steel.
Learn more about our precision casting capabilities.
Sand Casting
A pattern (wood, resin or metal) is pressed into resin-coated or green sand to form the mold cavity. Cores create internal cavities. After pouring and shakeout, the sand is reclaimed and reused, keeping tooling cost low. Typical materials: grey iron, ductile iron, cast steel, aluminum. See our sand casting line.
Side-by-Side Comparison
| Factor | Investment Casting | Sand Casting |
|---|---|---|
| Dimensional tolerance | CT4-CT6 (ISO 8062) | CT10-CT12 |
| Surface roughness | Ra 3.2-6.3 µm | Ra 12.5-25 µm |
| Minimum wall thickness | about 2 mm | about 5-6 mm |
| Typical part weight | grams to ~50 kg | 0.5 kg to several tons |
| Tooling cost | higher (aluminum die for wax) | low (pattern equipment) |
| Unit cost at volume | drops sharply above ~500 pcs | competitive across small and large batches |
| Best suited materials | stainless steel, alloy steel | grey iron, ductile iron, cast steel |
| Typical lead time (first article) | 4-7 weeks | 2-4 weeks |
Choose Investment Casting When...
- The part is small to medium (under ~50 kg) and complex in shape - impellers, valve internals, pump components, marine hardware.
- Tolerances and surface finish matter: you want to machine only critical surfaces instead of everything.
- The material is stainless steel or another difficult-to-machine, expensive alloy - near-net-shape casting saves material.
- Volume is moderate to high, so the wax tooling cost is amortized.
Choose Sand Casting When...
- The part is large or heavy - machine bases, valve bodies above 50 kg, pump housings, counterweights.
- Material is grey or ductile iron, where machining allowance of 2-4 mm is affordable.
- You need a small batch or prototypes without expensive tooling.
- Wall sections are thick and internal cavities are simple enough for cores.
When in Doubt: Cast + CNC Machining
Most real-world OEM parts combine both philosophies: cast near-net-shape, then CNC machine the sealing faces, bores and threads. What matters is that your supplier controls the full chain. A casting supplier without in-house machining will quote a low casting price and let the machining margin explode downstream.
Our typical workflow: casting blank with controlled machining allowance, stress-relief annealing where needed, then CNC machining of critical surfaces - all under one quality plan.
How to Get an Accurate Quotation
Whichever process you lean toward, a fast accurate quote needs: a 2D drawing with tolerances marked (or 3D model STEP/IGES), material grade, estimated annual quantity, and any surface treatment or pressure testing requirements. Send these to sales01@ythongshengindustry.com and we will recommend the more economical process for your part - even if it is not the one you asked about.