What is the difference between die casting and sand casting for metal parts production?

Quick Answer

Die casting injects molten metal (aluminum, zinc, magnesium) into reusable steel dies under high pressure, producing precise parts with excellent surface finish and thin walls. Sand casting pours molten metal into disposable sand molds, suitable for larger parts, ferrous metals (iron, steel), and low volumes. Die casting tolerances: ±0.002" per inch. Sand casting: ±0.030" per inch. Die casting cycle: 30-90 seconds. Sand casting: hours per part.

Process Comparison

Die Casting: Molten metal is injected at 1,500-25,000 psi into precision-machined steel dies. The high pressure ensures complete cavity fill, fine detail reproduction, and dense grain structure. Dies are water-cooled for rapid solidification. Typical cycle: 30-90 seconds. Maximum part size: typically under 600mm. Sand Casting: A pattern is pressed into sand mixed with binder to create a mold cavity. Metal is poured under gravity. The sand mold is broken to remove the casting. Typical cycle: hours to days. Maximum part size: up to several meters.

Surface Finish and Accuracy

Die cast parts have surface finishes of 1-3 microns Ra, requiring minimal post-processing. Sand castings have rough surfaces (12-25 microns Ra) requiring extensive grinding and machining. Die casting holds ±0.002" on the first inch and ±0.001" per additional inch. Sand casting holds ±0.030" on the first 6 inches, plus ±0.002" per additional inch. Die casting can produce walls as thin as 0.5mm (zinc) or 0.8mm (aluminum). Sand casting minimum wall: 3-5mm.

Cost and Volume Considerations

Die casting tooling costs $10,000-$150,000 but per-unit costs are low at high volumes. Economical above 5,000-10,000 units. Sand casting tooling (patterns) costs $500-$5,000 but per-unit costs remain higher. Economical for 1-5,000 units or very large parts. For aluminum parts over 50,000 units, die casting is 3-8x cheaper than sand casting per piece.

Why Choose SOMI Custom Parts

At SOMI Custom Parts, we offer die casting services for aluminum and zinc alloys with complete post-casting capabilities including CNC machining, heat treatment, and surface finishing. Our engineers help you determine which casting process is optimal for your specific part based on material requirements, quantity, tolerance needs, and budget. We also provide DFM feedback to optimize your part design for the selected process.

Case Study

An automotive components manufacturer needed 20,000 aluminum brackets per year. The initial design assumed sand casting at $4.50 each with extensive machining. SOMI's engineering team redesigned the bracket for die casting: thinner walls, integrated mounting bosses, and cored holes. Die casting tooling cost $35,000, but per-unit cost dropped to $1.80. The tooling cost was recovered in 13 months.

Industry Data

The global metal casting market is valued at $140 billion, with die casting accounting for 35% and sand casting 45% (North American Die Casting Association, 2025). Die casting productivity has increased 25% over the past decade through improved die cooling, vacuum assist, and automation. Sand casting remains dominant for large parts and ferrous metals.

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