Two of the most common questions a buyer faces when moving from prototype to production are "should we machine these, or cast them?", and the honest answer is almost always "it depends on your quantity." This guide compares CNC machining and die casting on the dimensions that actually decide the outcome: tooling investment, per-part cost, tolerance capability, and the break-even volume where the economics flip.
At a Glance: CNC Machining vs Die Casting
| Dimension | CNC Machining | Die Casting |
|---|---|---|
| Tooling investment | None (fixtures + program) | $15K–$40K production tool (aluminum, multi-cavity) |
| Prototype tooling | , | $5K–$12K single-cavity |
| Per-part cost trend | Flat (linear in quantity) | Falling with volume (tool amortization) |
| Minimum practical quantity | 1 piece | 500–1,000 pieces (tool amortization) |
| Typical break-even volume | Cheaper below | Cheaper above (1K–10K, size-dependent) |
| Standard tolerance | ISO 286 IT6–IT7 | CT5–CT7 (ISO 8062 / GB/T 6414) |
| Minimum wall thickness | ~1.5–2 mm (aluminum) | 1.0–1.5 mm (aluminum) |
| Material range | Any machinable metal (steel, Ti, Al, brass…) | Al, Zn, Mg alloys only |
| Geometric freedom | Limited by tool access (5-axis mitigates) | High, ribs, thin walls, complex cores |
| Lead time to first parts | Days–2 weeks | 4–10 weeks (tool build + T1 samples) |
The Cost Model: Why Break-Even Volume Decides Everything
CNC machining is a subtractive process: every part repeats the same cutting time, so the per-part cost is essentially flat and the total cost is a straight line against quantity. Die casting inverts the shape, a large fixed tool cost is front-loaded, and each shot costs only material plus machine time. The two total-cost lines cross at the break-even volume.
| Cost element | CNC route | Die casting route |
|---|---|---|
| Setup / programming | Low (hours of CAM + fixture) | High (tool design, steel, machining, T1 trials) |
| Fixed cost driver | Fixture complexity | Tool cavities, slides, cooling layout |
| Variable cost driver | Cutting time, material removed | Cycle time (20–90 s), alloy price, trim/finish |
| Material efficiency | Billet minus chips (often 40–70% waste) | Near-net shape (5–15% scrap + runner) |
| Cost slope | Flat | Declining with cumulative volume |
Two consequences follow. First, quantity is the single most important input to the decision, more than geometry or material. Second, parts with high material removal (large envelopes machined from solid) cross the break-even line earlier, because CNC wastes both time and material, while casting only pays for what the part weighs plus the runner.
When CNC Machining Wins
Low volume
Under roughly 1,000 pieces, tooling amortization dominates everything else. Machining needs no tool, so prototypes and pilot runs start within days at a predictable cost.
Exotic materials
Steel, stainless, titanium, brass, and engineering plastics are all routine on CNC centers. Die casting cannot touch ferrous or titanium alloys at all, their melting points destroy die steels.
Precision features
Bores, threads, sealing faces, and fits at IT6–IT7 are native to machining. Cast parts reaching those grades need secondary machining anyway, so the question becomes "casting plus machining" versus "machining only."
When Die Casting Wins
Volume above break-even
Once quantities clear the break-even line (commonly 2,000–10,000 pieces for small aluminum parts), per-part cost drops below any subtractive route and keeps falling as the tool amortizes.
Thin, complex geometry
Ribs, thin uniform walls, bosses, and complex internal cores are formed directly under 30–80 MPa intensification pressure. Machining the same geometry from solid is slow, wasteful, or impossible.
Consistency at scale
A stable process delivers part-to-part variation defined by the tool, not by operator setup. Over tens of thousands of parts, that consistency is worth more than any single-part tolerance advantage.
The Hybrid Route: Cast Blank + CNC Finishing
The most under-used answer is "both." A die cast near-net-shape blank can be finished on CNC machines for the features that genuinely need tolerance, bores, mounting faces, sealing surfaces, threaded holes. The casting does the bulk material removal efficiently; the machining step only touches a fraction of the geometry.
This route is the default choice when three conditions hold: volumes above roughly 5,000 pieces, geometry with a casting-friendly body plus a few CNC-critical faces, and a drawing demanding tighter tolerance than CT5–CT7 on selected features only. It is also the standard rescue when a production tool already exists and a drawing revision tightens specific faces. At FHY, die casting blanks and CNC finishing sit under one roof, so the process split is an engineering decision rather than a shipping schedule between two suppliers.
Decision Framework by Annual Volume
| Annual volume | Recommended route | Rationale |
|---|---|---|
| 1–500 pcs | CNC machining | No tool cost; days to first parts |
| 500–2,000 pcs | CNC (default) / soft tool casting (if casting validation needed) | Tool amortization rarely recovers; consider prototype tooling only if production casting is certain |
| 2,000–10,000 pcs | Quote both, decide by geometry | Break-even zone, geometry and material removal swing the answer |
| 10,000+ pcs | Die casting (+ CNC finishing where needed) | Per-part economics dominate; tool amortizes quickly |
| Any volume, few tight-tolerance faces | Cast blank + CNC finishing | Combines near-net-shape efficiency with machined precision |
How FHY Helps You Choose
Because FHY runs CNC machining and aluminum/zinc die casting under one roof, process selection is an engineering question rather than a sales pitch. Send the 3D model, target annual volume, and critical tolerances, and the review covers break-even math on your actual geometry, tooling options at each volume tier, and a recommendation for the cast-plus-machine split where it applies. The review is free, and the answer is the same whether or not you place the order: quantity first, geometry second, material third.