When designing a metal part that will be produced in moderate to high volumes, the choice between CNC turning and die casting represents a fundamental manufacturing strategy decision. Each process has a distinct cost structure, tolerance capability, and design freedom profile that makes it suitable for different production scenarios. Understanding where the crossover point falls for your specific part is the key to making the right selection.
Die casting injects molten metal under high pressure into a steel mold where it solidifies into the final part shape. The process excels at producing complex shapes with thin walls, internal cavities, and intricate surface details in a single shot. Aluminum, zinc, and magnesium alloys are the most commonly cast materials. The initial tooling investment for a die casting die ranges from $10,000 for simple single-cavity dies to over $100,000 for complex multi-cavity systems, but the per-part cost at high volumes is extremely low, often under one dollar for small parts.
CNC turning starts from a solid bar of material and removes everything that is not part of the final geometry. There is no tooling cost beyond the standard cutting tools, making it ideal for low and medium volumes. The per-part cost remains relatively constant regardless of quantity because the cycle time is determined by material removal volume rather than fixed tooling amortization. Turning achieves tolerances of ±0.010 to ±0.025 mm, which is typically 3 to 5 times tighter than die casting tolerances of ±0.050 to ±0.125 mm.
| Quantity | CNC Turning (each) | Die Casting (each) | Winner |
|---|---|---|---|
| 10-100 pcs | $20-80 | $100-500 | Turning |
| 100-1000 pcs | $8-30 | $3-20 | Depending |
| 1000-10,000 pcs | $4-12 | $0.50-3 | Casting |
| 10,000+ pcs | $2-6 | $0.10-0.80 | Casting strongly |
The crossover point where die casting becomes more economical than turning depends heavily on the part geometry. A simple cylindrical bushing might have a crossover point at 500 pieces because the turning cycle is short and the tooling cost for casting is significant relative to part cost. A complex part with multiple diameters, undercuts, and internal features might not become economical to cast until 5,000 pieces because the die cost is high and the turning cycle is long enough to make the per-part comparison more favorable.
For product development teams, a common strategy is to start with precision CNC machining for prototype and low-volume pre-production parts, then transition to die casting once the design is frozen and volumes justify the tooling investment. This approach allows design iterations to happen quickly and cheaply because turning requires no tooling modifications. The turned prototype parts also serve as benchmark standards for the eventual cast parts, providing clear dimensional targets for the die maker to achieve.
There are also parts where rapid prototyping Services using a hybrid approach makes sense: die casting the near-net shape with generous draft angles and then turning only the critical surfaces to final tolerance. This combines the low per-part material cost of casting with the tight tolerance capability of turning. The strategy is common for hydraulic valve bodies where the internal flow passages are cast to shape but the bore and sealing surfaces are turned to ±0.01 mm.
