Should I choose die casting or CNC machining for high-volume aluminum parts?

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For production volumes above 10,000 units, die casting is 3-10x more cost-effective than CNC machining per unit. The breakeven point is typically between 3,000-8,000 units depending on part complexity. Die casting is ideal for thin-walled, complex geometries with moderate tolerances (±0.003"). CNC machining is better for small volumes, tight tolerances (±0.0005"), solid monolithic parts, and parts requiring features impossible to cast.

Cost Comparison at Scale

For a typical aluminum bracket (100g): CNC machining at 1,000 units: $8-15 each. At 10,000 units: $6-10 each. Die casting at 1,000 units (including tooling amortization): $15-30 each. At 10,000 units: $2-5 each. At 50,000 units: $1-3 each. The breakeven point where die casting becomes cheaper is typically 3,000-8,000 units depending on tooling cost. Higher tooling costs push the breakeven point higher.

Performance and Quality Comparison

CNC machined parts have superior mechanical properties (no porosity, uniform grain structure) and tighter tolerances (±0.0005" vs ±0.003"). Die cast parts can have minor porosity (1-3% by volume) that may affect pressure tightness. CNC parts require no draft angles; die cast parts need 1-3 degrees. CNC can produce undercuts; die casting requires slides and lifters. CNC surface finish: 0.8-3.2 Ra. Die casting: 1-3 Ra (as-cast).

Design Freedom Comparison

Die casting excels at producing complex shapes with thin walls, internal cavities, and intricate details in a single operation. CNC machining excels at precision features like threaded holes, precision bores, flat surfaces with tight flatness, and three-dimensional contours. The best approach is often a hybrid: die cast a near-net shape, then CNC machine critical features.

Why Choose SOMI Custom Parts

At SOMI Custom Parts, we offer both die casting and CNC machining services, allowing us to recommend the optimal process -- or combination of processes -- for your project. We frequently recommend die casting for the main body with selective CNC machining of critical features. This hybrid approach delivers the cost efficiency of casting with the precision of machining.

Case Study

A lighting manufacturer needed 80,000 aluminum LED heatsink housings per year. The complex fin geometry required thin walls (1.2mm) and precise fin spacing for thermal performance. Die casting was the only economical option, but the critical mounting surface needed ±0.0005" flatness. SOMI produced the housings as near-net die castings, then CNC-machined the mounting surface in a secondary operation. Cost: $2.50 each versus $12 for all-CNC.

Industry Data

The average die casting tooling cost for an aluminum part is $25,000-$60,000, compared to minimal tooling for CNC machining. However, at volumes above 10,000 units, die casting per-unit costs are 60-85% lower than CNC machining (NADCA, 2025). The hybrid cast + machine approach is growing 12% annually as manufacturers seek to balance cost and precision.