Choosing between CNC machining vs die casting is rarely a question of which process is "better". It is a question of which process is cheaper at *your* volume, with *your* geometry, at *your* tolerance, on *your* calendar. This guide gives you the numbers that actually decide it: tooling amortisation, per-piece cost curves, a break-even formula that accounts for design changes, and the tolerance and cosmetic limits that override the arithmetic entirely. It also covers the option most programmes end up using — cast the near-net shape, then machine the features that matter.
The short answer
If you need parts next week, or your design is still moving, or your tolerances are tighter than about ±0.05 mm, or the part has to look like a consumer product — CNC machining wins, and usually by a wide margin. If you need tens of thousands of identical parts with a frozen design and moderate tolerance, die casting wins on unit cost, sometimes by a factor of five. Everything in between is arithmetic, and the arithmetic is what this article is for.
| Situation | Choose | Why |
|---|---|---|
| 1–500 parts, any year | CNC machining | No tooling to amortise |
| Design still changing | CNC machining | An ECO costs a program change, not a new tool |
| First article needed in under 3 weeks | CNC machining | Die tooling alone takes 4–10 weeks |
| ±0.01 mm features | CNC machining | As-cast capability is ±0.1–0.3 mm |
| Cosmetic anodised face | CNC machining | Cast alloys anodise grey and blotchy |
| Pressure-tight without impregnation | CNC machining | Casting porosity is inherent |
| 10,000+ parts/year, design frozen | Die casting | Cycle time collapses unit cost |
| Thin-walled, ribbed 3D shell at volume | Die casting | Near-net shape beats hogging from billet |
| Big aluminium housing, some tight faces | Both | Cast near-net, machine the critical features |
One caution before the numbers: the cost figures below are typical 2025–2026 ranges for aluminium parts quoted in Asia and North America. They are for *relative* decisions, not for budgeting a purchase order. Get real quotes at your volume before you commit.
What each process actually is
Before the arithmetic, it helps to be precise about what the CNC machining vs die casting decision is really comparing: one process adds metal to a cavity, the other removes it from a solid block. That single difference explains almost every downstream consequence — cost shape, tolerance, surface, and lead time.
High-pressure die casting
Molten aluminium alloy — most commonly ADC12 (equivalent to A383) or A380 — is injected into a hardened steel tool at 40–100 MPa and held under pressure while it solidifies. Cycle times for a palm-sized part run 30–60 seconds. The tool, usually H13 steel, is EDM'd, hardened to 46–50 HRC and fitted with slides, lifters and cooling channels. That tool is the entire economics of the process: it is expensive, it takes weeks to build, and every part it makes is cheap.
Because the metal is injected, die casting produces near-net shapes that would be wasteful to cut from solid: thin walls, ribs, bosses, internal cavities, and complex three-dimensional contours in one shot. Because the metal solidifies from a turbulent fill, it also traps gas. That is where porosity comes from, and porosity is the root of most of the problems people have with cast parts.
CNC machining
CNC machining removes material from a solid billet, plate or bar using rotating cutters on 3-, 4- or 5-axis centres. There is no dedicated tooling beyond workholding and a CAM program, so the first part costs roughly what the hundredth part costs. Setup is the dominant fixed cost, typically a few hundred dollars per operation.
What machining buys you is precision and material integrity. Wrought 6061-T6 has no porosity, a uniform grain structure and a tensile strength around 310 MPa, versus roughly 240 MPa and 1–3% porosity for ADC12 as-cast. Tolerances of ±0.01 mm are routine on a CNC machining tolerance basis; ±0.005 mm is achievable on specific features. And because the surface is wrought metal, it anodises cleanly — which is why every cosmetic audio panel we make is machined, never cast. Machining also handles geometry casting cannot: deep pockets, cross-drilled holes, sharp internal corners and true undercuts without slides. The cost side is covered in detail in our CNC machining cost guide.
The economics: tooling, per-piece cost and break-even
Where the money goes in each process
The two processes have almost opposite cost structures, which is exactly why the crossover in any CNC machining vs die casting comparison is so sharp: one front-loads everything into tooling, the other spreads a small fixed cost across every single part.
| Cost element | Die casting | CNC machining |
|---|---|---|
| Tooling | USD 12,000–120,000 | USD 0–2,000 (programming + fixtures) |
| Setup per run | Low once running | USD 150–500 per operation |
| Cycle time | 30–60 s per shot | 5–45 min per part |
| Material utilisation | Near net shape, little waste | 50–80% becomes chips |
| Engineering change | USD 1,500–18,000 per change | Program edit, near zero |
| First-part lead time | 4–10 weeks (tool build) | 3–10 days |
| Economic MOQ | 500–1,000 pcs | 1 pc |
Break-even, worked three ways
Static break-even is simple: tooling cost divided by the per-piece saving.
Break-even quantity = tooling cost ÷ (CNC unit price − die cast unit price)
Worked example, a 150 × 120 × 45 mm aluminium bracket:
| Annual/order quantity | CNC unit price | Die cast unit price (incl. amortised tooling) | Cheaper |
|---|---|---|---|
| 1–10 pcs | USD 180 | not economical | CNC |
| 50–200 pcs | USD 85 | USD 420 | CNC |
| 500 pcs | USD 55 | USD 48 | Marginal |
| 2,000 pcs | USD 42 | USD 16 | Die casting |
| 10,000 pcs | USD 36 | USD 7.50 | Die casting |
| 50,000 pcs | USD 34 | USD 3 | Die casting |
With USD 20,000 of tooling and a USD 43 per-piece saving, static break-even lands at about 465 pieces. That is the number most comparison articles quote, and it is the number that gets programmes into trouble — because it assumes the drawing never changes.
Real-world break-even depends heavily on part complexity. Published figures range from about 500 pieces for a simple housing with cheap tooling, through 1,200–2,500 for a structural bracket with slides, to 3,000–8,000 where tooling is complex or the per-piece gap is narrow. Treat 500 and 8,000 as the edges of a band, not as two competing facts.
The ECO tax: why your real break-even is higher
Every hardware programme issues engineering change orders between pilot build and scale-up. In die casting, the cost of a change depends on whether it is *steel-safe*:
| Change type | What it means | Cost | Lead time |
|---|---|---|---|
| Steel-safe | Add metal to the part by removing steel (bigger boss, thicker wall) | USD 1,500–4,000 | 5–10 working days |
| Non-steel-safe | Remove metal from the part by adding steel (thinner wall, moved groove) | USD 6,000–18,000 | 3–5 weeks |
| New insert / re-cut cavity | Geometry will not weld and re-machine | Full tool or sub-insert | Tool lead time again |
Fold that into the decision with a simple expected-value correction:
Effective break-even = static break-even × (1 + p(ECO) × penalty index)
| Likelihood of a geometry change before SOP | Penalty index | Effect on a 1,800-pcs static break-even |
|---|---|---|
| Design frozen, released to production | 0 | 1,800 pcs |
| Minor revisions expected (25% chance) | 0.6 | ~2,070 pcs |
| Active NPI, likely one revision (60%) | 1.2 | ~3,100 pcs |
| Early concept, two or more revisions likely (90%) | 2.5 | ~5,850 pcs |
The practical rule: do not release die casting tooling until the design freeze is real, not aspirational. For programmes still in NPI, staying on low volume CNC machining to 2,000–5,000 pieces is often cheaper in total cash than tooling early and paying for changes.
Tolerance, geometry and what the drawing can honestly ask for
Cost decides most of the CNC machining vs die casting decision, but tolerance overrules cost. If the drawing asks for something the process cannot hold, the cheap option stops being cheap the moment the parts do not assemble.
Capability comparison
| Attribute | CNC machining | High-pressure die casting |
|---|---|---|
| Linear tolerance, as produced | ±0.01–0.05 mm | ±0.1–0.3 mm |
| Achievable on critical features | ±0.005 mm | ±0.05 mm after machining |
| Flatness | 0.02 mm / 100 mm typical | 0.1–0.3 mm, poor on large spans |
| Surface finish, as produced | Ra 0.8–1.6 µm | Ra 1.6–3.2 µm |
| Minimum wall thickness | 0.5 mm (cost rises steeply) | 1.2–1.5 mm practical |
| Draft angle | None required | 1–3° |
| Minimum internal radius | Set by cutter, can be sharp-ish | 0.5 mm+ to avoid hot spots |
| Undercuts | Free with 5-axis | Needs slides/lifters, adds tooling cost |
| Threads | Cut directly, full strength | Usually machined or rolled after |
That table is the reason most "die cast" parts still visit a machining centre. A cast aluminium part rarely ships as-cast: sprue and runner trimming, flash removal, machining of mating faces and threaded holes, and finishing typically add 20–50% to the as-cast number, and sometimes more. Our CNC parts finishing article covers what those secondary operations actually cost.
Walls, draft, parting line and radii
Die cast parts need uniform wall thickness to avoid hot spots and sink marks, a draft angle of 1–3° so the part releases, and generous radii at every internal corner. They also carry a parting line — a visible witness mark where the two tool halves meet — plus ejector pin marks on a non-cosmetic face. If your drawing does not say where the parting line may and may not be, the toolmaker will decide for you, and you may not like the answer.
CNC machined parts need none of that. Draft is irrelevant, walls can vary, and internal corners are bounded only by cutter diameter. This is why a 5-axis CNC machining part can be a single monolithic component replacing a cast-and-assembled subassembly — no fasteners, no sealing joint, no leak path.
Datum strategy on a cast-then-machined part
This is where hybrid parts succeed or fail. A casting is dimensionally loose; the machined features on it must be tight relative to each other. So the drawing needs two datum systems:
- Casting datums — three loosely toleranced targets used to locate the raw casting in the machining fixture.
- Machining datums — the finished features that define the functional relationship (bores, sealing faces, mounting pads).
Leave 0.5–1.5 mm of stock on every surface that will be machined, and note that machining too deep cuts through the dense casting skin into the porous core. If a sealing face ends up in porous material, no amount of impregnation will save it. Raise stock allowance on faces that must pass a leak test.
Material reality: strength, porosity and cosmetics
The third axis of the CNC machining vs die casting decision is metallurgy. Even at identical geometry and identical price, the two processes deliver different metal — and some applications simply cannot accept the cast version.
Porosity and pressure tightness
Gas porosity of 1–3% by volume is normal in HPDC. For a bracket it is irrelevant. For a housing that must hold pressure or keep water out, it is the whole problem. Mitigations, in order of effectiveness:
- Vacuum-assisted casting and controlled cooling, which reduce but do not eliminate porosity
- Machining the sealing face with adequate stock so the skin is not breached
- Vacuum impregnation with resin to seal interconnected porosity
- An explicit leak-rate specification, for example 1×10⁻³ mbar·l/s helium, with a stated test method and sampling plan
Specify the leak rate and the acceptance criterion on the drawing. "Impregnate as required" is not a specification, and impregnation on a surface that will later be anodised or plated creates its own defects.
Mechanical properties
| Property | ADC12 / A383 as-cast | 6061-T6 wrought | 7075-T6 wrought |
|---|---|---|---|
| Tensile strength | ~240 MPa | ~310 MPa | ~570 MPa |
| Yield strength | ~150 MPa | ~276 MPa | ~503 MPa |
| Elongation | 1–3% | 8–12% | 5–11% |
| Thermal conductivity | ~96 W/m·K | ~167 W/m·K | ~130 W/m·K |
| Typical use | Housings, covers, brackets | Structural, thermal, cosmetic | Aerospace, weight-critical |
Note the elongation row. A cast part is brittle: it cracks rather than bends. If your part sees impact, vibration or press-fit assembly, that 1–3% figure matters more than the tensile number.
Anodising and cosmetics — the hidden deal-breaker
This is the one that surprises people. Die casting alloys are high in silicon (ADC12 is around 10–12% Si) precisely because silicon improves fluidity and fill. Silicon does not anodise. An anodised die cast part comes out grey, mottled and darker than a machined 6061 panel, and it will not colour-match across a batch. Black anodising hides some of it; clear or coloured anodising does not.
For a hidden internal bracket, nobody cares. For a brushed and anodised audio front panel, a console face or anything a customer will look at, it is disqualifying. If cosmetics matter, the choice is not really CNC machining vs die casting — it is machined wrought aluminium, and our aluminium CNC machining and anodising pages go through the finish options in detail.
Lead time, tooling risk and the design-freeze gate
| Milestone | CNC machining | Die casting |
|---|---|---|
| Quote turnaround | 24–48 h typical | 3–10 days (tooling must be scoped) |
| First article | 3–10 days | 4–10 weeks (tool design + build) |
| T1 samples then correction | 1 week | 2–5 weeks per iteration |
| Production ramp | Immediate | After tool tryout and approval |
| Design change after tooling | Program edit | USD 1,500–18,000 + 1–5 weeks |
Time is the fourth input, and it is the one most often left out of the CNC machining vs die casting comparison. A workable sourcing sequence that avoids the traps:
- Concept and prototype — CNC prototyping, 3–7 day samples, design still free to move
- Pilot / bridge production — CNC at 50–500 pieces, validate the market and the fit
- Design freeze gate — a written milestone. No geometry changes after this date.
- Tooling release — only after the gate, with volume commitment that justifies it
- Mass production — cast near-net, machine critical features, finish, inspect
Programmes that skip step 3 are the ones that end up with an 8,000-piece effective break-even on a part they thought would break even at 1,800.
The hybrid route: cast near-net, machine the critical features
Framed as CNC machining vs die casting, the question sounds binary. In practice most mature programmes are not either/or. They cast the body and machine the features that carry function — and this is also where a CNC shop like ours fits in, whether the blank comes from your foundry or from a billet.
What to machine after casting
| Feature | As-cast | Post-machined | Comment |
|---|---|---|---|
| Mating / sealing face | ±0.2 mm, wavy | Flatness 0.05 mm | Almost always machined |
| Bore for bearing or shaft | Draft tapered, ±0.2 mm | H7, ±0.01 mm | Boring or reaming |
| Threaded holes | Not cast to size | Cut or roll-formed | Cast-in holes are usually cored then tapped |
| Mounting pads | Coplanarity poor | Machined coplanar | Critical for EMI gaskets |
| Thermal interface face | 0.2–0.4 mm wavy | 0.05 mm flatness | Directly sets thermal resistance |
| Cosmetic face | Porous skin, parting line | Machined + brushed + anodised | The only route to a retail finish |
Stock allowance rules
- 0.5–1.0 mm on small faces up to 50 mm across
- 1.0–1.5 mm on faces over 100 mm, where casting warp is larger
- 1.5–3.0 mm on any face that must pass a pressure or leak test
- Never machine below the casting skin on a sealing surface — call out minimum remaining wall thickness on the drawing
A hybrid route is also the natural answer when a design is thermally demanding: cast or extrude the fin array, then machine the base flatness and the mounting features. Our heat sink CNC machining guide covers that specific case.
Requesting comparable quotes: a 12-line RFQ
The most common mistake in this comparison is comparing an as-cast price with a machined price. They are not the same thing. Ask every supplier, for both processes, to quote these twelve lines:
- Tooling cost and who owns the tool
- Tooling amortisation method and the quantity it is spread over
- As-produced unit price at your actual order quantity
- Secondary operations itemised: trim, deburr, post-machining, finishing
- Scrap and reject allowance, by operation
- Impregnation, if required, and whether it is included
- Finishing specification and cost, including masking
- Packaging and freight to your dock
- First article lead time and FAI documentation level
- MOQ and economic order quantity
- Cost and lead time of one engineering change
- Payment terms and any tooling milestone payments
If a supplier will not fill in lines 4, 5 and 11, you do not have a comparable quote. This checklist is the practical version of what we describe in choosing a CNC supplier.
Industry playbooks
Audio and professional audio equipment
Cosmetics and tactile quality dominate. Machined 6061 or 6063 with brushed grain plus black anodising is the standard for front panels, knobs and console chassis; die castings cannot match the colour consistency. Volumes are usually 100–5,000 per SKU, well inside the CNC band. See audio mixer console machining.
Automotive and EV
This is die casting's home territory: engine brackets, transmission housings, sensor bodies, structural nodes at 50,000+ per year. But prototypes, pre-production builds and low-volume derivatives stay machined, and IATF 16949 documentation is required either way. Our automotive CNC machining and EV motor housing articles cover the automotive case, and IATF 16949 explained covers the documentation.
Consumer electronics and 3C
Short product cycles — often 9–18 months — mean the design freeze gate comes late and lifetime volume is uncertain. Machining wins through the pilot phase; casting only pays if the SKU clearly runs past the break-even band. More in consumer electronics machining.
LED, thermal and power electronics
Thermal performance is a flatness and conductivity problem, and ADC12's 96 W/m·K is roughly half of 6061's 167 W/m·K. Where the housing is also the heat path — LED fixtures, inverters, power modules — machining usually wins on performance even when casting wins on price.
Medical and robotics
Volumes are low, traceability requirements are high, and surfaces must be cleanable and non-porous. Machining is the default. See ISO 13485 machining and robotics CNC parts.
FAQ
At what volume does die casting become cheaper than CNC machining?
There is no single number, which is why die casting vs CNC machining comparisons that quote one are misleading. For a simple aluminium part with modest tooling, the published crossover sits around 500–1,000 pieces. For a structural bracket requiring slides and lifters, expect 1,200–2,500; for complex tooling or a narrow per-piece gap, 3,000–8,000. If design changes are likely, multiply that figure by the ECO correction in this article — an 1,800-piece break-even easily becomes 5,000 in an active NPI programme.
Can a die cast part hold ±0.01 mm?
Not as-cast. Typical HPDC capability is ±0.1–0.3 mm. ±0.01 mm is reached by machining the feature after casting, which is the standard practice for bores, sealing faces and mounting pads. Budget the secondary operation and the stock allowance in the casting design.
Is die cast aluminium as strong as machined 6061-T6?
No. ADC12 is around 240 MPa tensile with 1–3% elongation; 6061-T6 is around 310 MPa with 8–12% elongation. The elongation gap matters more than the strength gap: cast parts are brittle and crack under impact or press fits where a machined part would deform.
Why do die cast parts fail leak tests?
Gas porosity of 1–3% by volume is inherent to high-pressure fill. Interconnected porosity near a sealing face creates a leak path, and machining that face too deep removes the dense skin and opens more of it. Control it with vacuum-assisted casting, adequate machining stock, a specified leak rate and — where acceptable — vacuum impregnation with a written acceptance criterion.
Can you anodise die cast aluminium to match a machined panel?
Not reliably. Casting alloys carry 10–12% silicon, which does not anodise, so the result is grey, mottled and darker than anodised 6061, with batch-to-batch colour variation. Hidden parts are fine; any visible or retail-facing surface should be machined from wrought aluminium.
How long does die casting tooling take compared with a CNC first article?
Die tooling is typically 4–10 weeks for design, steel cutting, EDM, heat treatment and tryout, plus 2–5 weeks per correction iteration. A CNC first article is 3–10 days, and low-volume production can start immediately after approval.
Is a hybrid cast-plus-machined part worth the extra step?
Usually yes, above the break-even band. Casting handles the bulk shape cheaply, machining delivers the ±0.01 mm bores, flat sealing faces and cosmetic surfaces. The extra cost is one additional operation; the alternative is either an unaffordable all-machined part or a casting that does not assemble.
Do I need different drawings for CNC and die casting?
Yes. The die casting drawing adds draft angles, uniform wall thickness, fillet radii, parting line location, ejector pin zones, machining stock allowance and a separate casting datum system. The CNC drawing drops all of that and simply calls out tolerances per feature. Never send the same file to both unless it is a fully dimensioned model with process-neutral tolerancing.
Getting a decision on your part
If you send us a 3D model, a dimensioned drawing and your annual quantity, we will run the CNC machining vs die casting arithmetic with you and tell you honestly whether machining is the right answer — and if it is not, we will say so. Where the volume clearly justifies tooling, we machine the cast blanks and hold the critical features, so you get one supplier across the transition instead of two.
Send the files for a 24-hour quote, or read our DFM analysis service first if you want the drawing reviewed before it goes out. Everything is produced under IATF 16949, ISO 9001:2015 and ISO 13485, with 200+ CNC machines, 23+ years of machining experience and ±0.01 mm capability — see the about page for the equipment list and certifications.