Sand vs Investment Casting

Rough big cheap.
Fine small precise.
Process defines part.

Q: When does casting beat machining?

Casting beats machining when: (1) Complex geometry — internal passages, hollow shapes, intricate features. (2) Production volume — tooling amortization over many parts. (3) Cost per part critical — casting often cheaper than machining from billet. (4) Specific materials — some alloys more practical in cast form. Typical break-even vs CNC: 100-500 parts for investment casting, 50-200 parts for sand casting. For one-off or precision parts: CNC usually better.

Q: Casting then machining — common?

Yes, very common. Near-net-shape casting reduces CNC work 80-90% vs starting from billet. Standard workflow: cast to approximate shape → CNC machine critical features (bearing bores, mating surfaces, flanges, threaded holes) → finish processing. Combines casting's geometry advantage with CNC's precision. Cost effective for production volumes 500+ parts.

Q: Surface finish expectations?

Sand cast raw surface: Ra 6-25 µm, coarse texture visible. Often painted or coated to improve appearance. Machined surfaces applied where needed. Investment cast raw: Ra 1.6-3.2 µm, much smoother — often usable without machining for non-mating surfaces. For cosmetic requirements better than investment cast raw, machining or grinding needed.

Q: Tolerance realistic expectations?

Sand casting: ±0.8% to ±2% typical. For 100 mm dimension: ±0.8-2 mm. Cannot hold ±0.1 mm directly — need machining for precision features. Investment casting: ±0.3-0.5%. For 100 mm: ±0.3-0.5 mm. Tighter features possible but cost increases. For precision features, designate them for post-cast machining. Cast and machined hybrid is the practical approach.

Q: Which materials cast well?

Sand casting: virtually any metal — gray iron (standard), ductile iron, steel, bronze, aluminum, zinc, magnesium. Any ferrous alloy, many non-ferrous. Investment casting: most common are carbon steel, stainless (17-4 PH, 316L, Duplex), superalloys (Inconel, Hastelloy), aluminum, bronze. Some specialty alloys difficult to investment cast due to shrinkage characteristics. Cast iron less common in investment casting.

Q: Prototype casting options?

For sand cast prototypes: 3D printed sand molds enable rapid prototyping without physical pattern (1-2 weeks lead time for first parts). For investment cast prototypes: 3D printed wax patterns (SLA resin patterns burn out acceptably) enable rapid prototyping (2-3 weeks). Both methods used to validate casting designs before committing to permanent tooling. We coordinate casting prototypes through partner foundries for both processes.

Sand casting is the oldest and cheapest casting process — handles huge parts with rough surfaces. Investment casting (lost wax) produces fine detail with smooth surfaces at moderate cost. This guide maps process selection to part requirements.

Get a Quote DFM guide

01 · At a glance

Side-by-side summary.

Option A

Sand Casting

Molten metal poured into sand mold. Mold destroyed after casting. Huge size range — grams to tonnes. Rough surface (Ra 6-25 µm). Loose tolerance. Low tooling cost. Any metal castable.

Option B

Investment Casting

Lost-wax process. Wax pattern coated with ceramic slurry, wax melted out, metal poured in. Excellent surface (Ra 1.6-3.2 µm), tight tolerance, intricate geometry. Moderate tooling cost.

02 · Detailed comparison

Feature-by-feature breakdown.

Attribute	Sand casting	Investment casting
Surface finish (Ra)	6-25 µm	1.6-3.2 µm
Dimensional tolerance	±0.8% to ±2%	±0.3% to ±0.5%
Minimum wall thickness	3-5 mm	1-3 mm
Size range	Grams to 200+ tonnes	Grams to 100 kg
Complexity	Moderate	Very complex achievable
Material options	Virtually all castable metals	Ferrous, nickel, aluminum
Tooling cost (prototype)	Low ($500-5,000)	Moderate ($3,000-20,000)
Tooling cost (production)	Moderate	Higher
Production volume	1 to millions	10 to 100,000
Lead time for tooling	1-2 weeks	3-6 weeks
Typical applications	Engine blocks, architectural, heavy	Turbine blades, gun parts, jewelry
Scrap/rework rate	Higher (typical 5-15%)	Lower (typical 1-3%)

03 · Decision guide

When to choose each.

Choose Sand Casting when:

Large parts (>50 kg)
Prototype castings (cheap tooling)
Low volume production (<100 parts)
Simple or moderate complexity geometry
Cost-sensitive applications
Materials hard to investment cast (certain steels)

Choose Investment Casting when:

Complex geometry with fine features
Near-net-shape parts (minimal machining)
Parts requiring smooth surface
Small to medium parts (0.01-50 kg)
Moderate to high volume (1,000+ parts)
Turbine blades, gun parts, impellers