Sand Casting​

Sand casting uses sand (typically silica sand mixed with binders) as the mold medium, offering low mold costs and high flexibility in shaping. This makes it ideal for large or complex-shaped castings, such as engine blocks (often weighing 50–200kg), large pump housings, and heavy machinery casings. The process involves creating a cavity in sand using a pattern (usually made of wood or metal), pouring molten metal (like gray iron, ductile iron, or carbon steel) into the cavity, and breaking the sand mold after cooling to retrieve the part. However, its drawbacks are obvious: the sand surface is rough, leading to castings with poor surface finish (Ra 12.5–50μm) and relatively low dimensional accuracy (tolerance ±1–3mm). As a result, most sand-cast parts require additional machining (e.g., milling or drilling) to meet final size and surface requirements, increasing post-processing time and cost. It is particularly suitable for low-to-medium batch production (10–1000 units) where part size or complexity makes other processes impractical.​

Die Casting​

Die casting relies on metal molds (usually made of heat-resistant steel) and injects molten metal into the mold cavity under high pressure (typically 10–150MPa). It excels with low-melting-point metals like aluminum alloys (6061, ADC12), zinc alloys (ZAMAK 3, ZAMAK 5), and magnesium alloys—materials widely used in lightweight, high-volume parts. The high-pressure injection ensures castings have excellent surface quality (Ra 3.2–12.5μm) and stable dimensional accuracy (tolerance ±0.1–0.5mm), minimizing the need for post-processing. This makes it perfect for mass-produced items: consumer electronics casings (e.g., smartphone frames), precision automotive parts (like transmission housings), and decorative exterior components. The main limitation is the high initial investment in metal molds (costing tens of thousands to hundreds of thousands of dollars), which means it is only economical for large production runs (10,000+ units). Additionally, the high pressure can trap air, so die-cast parts may have internal pores, making them less suitable for high-load structural applications.​

Precision Casting

Precision casting—most commonly investment casting (or "lost wax casting")—uses a wax pattern and ceramic shell to form the mold. The process starts with creating a detailed wax model (matching the final part), coating it with multiple layers of ceramic slurry to form a hard shell, melting and removing the wax (hence "lost wax"), and pouring molten metal (such as stainless steel, superalloys, or bronze) into the ceramic cavity. This method achieves extremely complex geometries (e.g., internal channels or thin walls as thin as 1–2mm) with high dimensional accuracy (tolerance ±0.05–0.2mm) and smooth surface finish (Ra 3.2–6.3μm), often eliminating the need for machining. It is the top choice for parts demanding precision and detail: turbine blades (used in aircraft engines, where airfoil accuracy directly affects efficiency), precision pump impellers, gear housings for high-speed machinery, and even art pieces or jewelry (where intricate designs are critical). While it offers superior quality, precision casting has higher per-unit costs and longer production cycles compared to sand or die casting, making it suitable for small-to-medium batches (10–5000 units) of high-value parts.​

Conclusion

Overall, the choice depends on part size, complexity, required surface/dimensional accuracy, and production volume.