CNC machining and die casting both produce aluminum and zinc parts, but they optimize for opposite ends of the volume spectrum. CNC needs no tooling and ships first articles in days; die casting needs a mold but drives per-part cost below machining once volume crosses roughly 500–2,000 pieces. The wrong choice can add weeks and thousands of dollars — here's how to pick the right route.
The short answer by volume
- 1–100 parts: CNC machining — no tooling, production material, tolerances to ±0.005 mm
- 100–500 parts: quote both — CNC may still win if geometry is simple or tolerances are tight
- 500–5,000 parts: die casting usually wins on landed cost; add CNC finishing for critical faces
- 5,000+ parts: die casting is the clear choice; amortize tooling across the program lifetime
- Thin walls (<2 mm), complex ribs, internal passages: die casting can form them; CNC must remove material
Cost: tooling vs cycle time
Die casting requires a hardened steel mold (15–25 days, typically $3,000–$15,000 depending on cavity count and complexity). Spread over 1,000 parts that adds $3–15 per piece; over 10,000 parts it drops below $0.50. CNC carries no tooling but bills cycle time for every feature: roughing, finishing, drilling, tapping. A complex housing might need 45 minutes of machine time — affordable at 10 pieces, prohibitive at 1,000.
Tolerance and surface finish
CNC machining holds ±0.02–0.05 mm standard and ±0.005 mm on precision features, with surface finishes from Ra 0.8 µm. As-cast dimensions land around ±0.1–0.3 mm depending on wall thickness and draft; critical faces are then CNC-machined to tolerance in a secondary operation. If your part needs bearing bores, sealing faces or tight hole patterns, plan on post-cast machining — SkillsProto quotes the hybrid route together.
Design constraints that decide the process
- Die casting: 1–2° draft required on all vertical walls; without it the part sticks in the mold
- Die casting: wall thickness 1.5–5 mm ideal; thick sections (>8 mm) risk porosity and sink
- CNC: no draft needed; straight walls, square corners and zero-taper bores are natural
- Die casting: ribs, bosses, stand-offs and internal passages form in one shot — impossible to machine from solid
- CNC: undercuts and internal channels need multi-axis setups or split the part
Materials: alloy families compared
Die casting uses specialized alloys: A380 and ADC12 aluminum for general housings, Zamak 3 and Zamak 5 zinc for small, detailed parts with excellent surface finish. CNC machines from wrought stock: 6061-T6 (general purpose), 7075 (aerospace strength), 2024 (fatigue resistance), plus stainless, brass and titanium. A cast A380 part is not interchangeable with a machined 6061 part — mechanical properties, corrosion resistance and weldability differ. Match the alloy to the application, not just the process.
Lead time from CAD to parts
CNC first articles ship in 3–7 working days at SkillsProto because there is no tooling — upload STEP or IGES and machining starts immediately. Die casting needs mold design, tool steel machining, heat treatment and trial shots: 15–25 days to T1 samples, then another 3–5 days to production. If you need parts this week, CNC is the only answer. If you need 2,000 pieces next quarter, die casting pays back the mold investment and delivers lower unit cost.
The hybrid route most teams overlook
Many production aluminum parts are die-cast for economy and then CNC-finished for precision: cast the housing with all its ribs and bosses, then machine the bearing seats, mounting faces and threaded holes to ±0.01 mm. SkillsProto runs both processes under one project manager, so the cast blank and the machined finish are planned together — not handed off between suppliers. Send your STEP file and we'll quote the all-cast, all-machined and hybrid options in the same 24-hour DFM response.
Frequently Asked Questions
Is die casting cheaper than CNC machining?
At low volumes (1–100 pieces) CNC is cheaper because there is no tooling cost. Above roughly 500–2,000 pieces, die casting usually wins because the mold cost amortizes into a per-part price that CNC cycle time cannot match. The exact crossover depends on part size, complexity and tolerance requirements — SkillsProto quotes both routes side by side.
What tolerance can die casting hold?
As-cast dimensions are typically ±0.1–0.3 mm. For tighter tolerances (±0.02–0.05 mm or ±0.005 mm on precision interfaces), a secondary CNC machining operation is required. SkillsProto quotes the hybrid route — cast for economy, machine for accuracy — as a single integrated project.
Can die cast parts be machined afterwards?
Yes, and it is common practice. Cast housings are machined on critical faces — bearing bores, sealing surfaces, mounting pads and threaded holes — to achieve precision that casting alone cannot deliver. This hybrid approach gives you the geometric freedom and low unit cost of casting with the accuracy of machining exactly where it matters.
What is the lead time for die casting vs CNC?
CNC first articles ship in 3–7 working days with no tooling. Die casting requires a steel mold: 15–25 days to T1 samples, plus 3–5 days to production. For urgent prototypes or small batches, CNC is faster. For production volumes above a few hundred pieces, die casting's lower unit cost justifies the longer setup.
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