- Two different cost shapes. Machining carries a small fixed cost and a steady per-part cost; injection moulding carries a large fixed cost (the mould) and a tiny per-part cost.
- The crossover is volume, not "which is cheaper". Below roughly 5,000–10,000 identical parts, machining usually wins; above it, moulding does.
- Material freedom vs material lock-in. Machining cuts any certifiable metal or plastic; moulding is tied to mouldable polymers (and a few niche feeds).
- Tolerance. Machining holds ±0.003 mm as routine; moulding holds ±0.1–0.2 mm and fights shrinkage and parting-line variation.
- The usual answer: machine the prototype and the low-volume run, move to moulding only when the design is frozen and volume justifies the tool.
What each process actually is
3-axis CNC machining is subtractive: a rotating cutter removes material from a solid block or bar under numerical control, following a toolpath generated from a 3D model. The part off the machine is the model minus everything the cutter reached. There is no tool to build — just a program, a fixture, and the stock.
Injection moulding is formative: a steel mould is machined to the part's negative, molten polymer is injected under pressure, the part cools and is ejected. The mould is the product; the parts are its by-product. Everything about the economics flows from that one fact — the mould is expensive and slow to make, and the parts are cheap and fast once it exists.
That single structural difference, not any question of "which technology is more advanced," is what settles almost every comparison between the two.
The quantified comparison
| Factor | 3-axis CNC machining | Injection moulding |
|---|---|---|
| Fixed cost to start | Low — programming, fixture, first-article; typically hundreds to a few thousand USD | High — mould design and steel mould; typically USD 2k–50k+, rising with size and cavities |
| Variable cost per part | Moderate and falling with volume (machine time + scrap) | Very low — grams of polymer and seconds of cycle |
| Tooling lead time | Days (program + fixture) | 4–12 weeks (design, steel, sampling, validation) |
| Repeat part lead time | Minutes to hours of cutting, queue-dependent | Seconds to minutes of cycle, plus moulded cooling |
| Typical tolerance | ±0.003 mm (mill) / ±0.002 mm (turn); ±0.002 mm ground | ±0.1–0.2 mm; ±0.05 mm on critical features only |
| Material range | Any machinable metal or plastic, certifiable to stock spec | Mouldable thermoplastic / thermoset / LSR; no metal |
| Material properties | Isotropic from wrought stock; certifiable | Flow-direction dependent; weld lines and sink possible |
| Geometry freedom | Limited by tool access; sharp internal corners possible | Thin walls, ribs, bosses; undercuts need sliders/lifters |
| Design change cost | Cheap — edit program/fixture | Expensive — cut or re-work steel |
| Best quantity band | Prototype through mid-volume production | High volume (thousands+ identical parts) |
The practical test: if the part must be metal, must carry a certified material, must hold a tight tolerance, or will be made in low-to-mid volume, machining is the answer. If it is a plastic part needed in the tens of thousands with a frozen design, moulding is.
Why the two processes separate the way they do
The dividing line is the mould. An injection mould is itself a precision machined component — often more complex than the parts it makes — and it must be designed, steel-cut, sampled, and validated before a single production part exists. That front-end cost and weeks of lead are amortised over the run. Spread across ten parts, the mould makes each one wildly expensive; spread across a hundred thousand, it disappears.
Machining has no such front-end. The fixed cost is a program and a fixture, both cheap to change, so the first part and the thousandth cost roughly the same per unit. The trade is that every part pays for machine time, so machining never gets as cheap per part as moulding at very high volume.
Properties follow the same logic. A machined part is cut from wrought stock — rolled or forged material whose grain runs through the part — so its strength is effectively the same in every direction and can be certified. A moulded part's properties depend on how the melt flowed and cooled: weld lines where flow fronts meet, sink on thick sections, and a directional dependence between flow and transverse directions. None of that is a defect of moulding; it is a direct consequence of how the part is formed, and it is why moulded structural parts are qualified against moulding parameters, not a raw-material certificate.
Where the two genuinely overlap
The overlap band is low-to-mid volume plastic parts. Here the question is rarely "which is possible" but "which is cheaper once tooling is counted". A machined plastic prototype that will be moulded later is common, because it verifies the design without committing to steel. The mistake is committing to a mould before the design is settled — a mould change costs real money and weeks, whereas a program change costs an afternoon.
For metal parts there is no overlap at all: moulding cannot make them, so the comparison is moot and the only question is which machining process (3, 4, or 5-axis) fits the geometry.
Decision checklist — machining or moulding?
- Choose injection moulding if the part is plastic, the design is frozen, and you need thousands of identical units — the mould cost and lead are justified by the volume, and unit cost falls to pennies.
- Choose 3-axis machining if the part is metal, needs a certified material, must hold a tight tolerance or a machined datum relationship, is needed in low-to-mid volume, or the design may still change.
- Choose machining as a bridge when you need parts now and volume is unproven: prototype and early production in machined parts, then re-evaluate moulding once the design and quantities are certain.
- Still unsure — send the model and the expected annual quantity; the right answer is almost always visible from the geometry and the volume alone.
What design decisions move the machining cost
Three decisions drive most of the cost on a machined part: internal corner radii matched to a real cutter diameter, cavity depth kept within about four times the tool diameter, and a general tolerance on every feature that does not mate. Each one changes the tool that can be used, and the tool determines how much material can be removed per minute — which is why these matter more than any process selection. Raising them at quote stage, not after the first article, is where most savings are found.
What the certification position is
ISO 9001:2015, IATF 16949:2016 (excluding clause 8.3 product design), and ISO 14001:2015 — each with a certificate number verifiable with the registrar.
What capacity sits behind the machining option
over a hundred machines with depth in every relevant family — 50+ three-axis, 20+ four-axis, 20+ five-axis, 25+ turning centres, plus Swiss-type, grinding, and wire EDM. The spare capacity in that family is what lets a part move to another lane rather than sit in a queue when a machine is pulled for service, which is what protects a delivery date.
Which entity is responsible for the work?
Dongguan Zhuohang Ltd, Registration No. 91441900MA4UWT6X39, in operation since 2005.
What this shop actually runs
Capability evidence should come as specifics, not slogans. Behind this guide is a 6,800 m2 plant in Dongguan, China running 100+ CNC machines with 100+ staff. The machine list by category:
- 5-axis machining centres (10+) - Mazak VARIAXIS I-600 (510/910/510 mm travel, 12,000 rpm, 22 kW, 71.6 N·m, 30-tool BT40) and Mazak INTEGREX I-250H S (B-axis 0.0001°, 24 kW, 124 N·m, 38-tool HSK-A63). Cut on compound-angle parts, single-setup multi-face prismatic work, and aerospace fittings where datum transfer loss is unacceptable.
- 3-axis / 4-axis machining centres (50+) - Brother SPEEDIO S500Z2N / S700Z2N (10,000 rpm, 14/21-tool ATC, 0.7 s tool-to-tool, Z-axis 2.2 G) and Mazak VCE-430A L / VCE-570C L (10,000 rpm, 118 N·m, 24-tool ATC). Cut on prismatic parts, plates, brackets, housings.
- Swiss-type turning centres (10+) - Citizen Cincom A20-3F7 (Φ20 mm, 10,000 rpm), TSUGAMI B0206-III / B0205-III (Φ20 mm, 0.1 µm), STAR SR-32JII / SR-32J Type N (Φ32 mm, 8,000 rpm). Cut on long, slender rotational parts at ±0.002 mm.
- CNC turning centres (20+) - HEADMAN T70M/1250 (720 mm swing, 117 mm bore, 3,000 rpm, BMT75 12-station turret). Cut on shafts, bushings, flanges up to ±0.002 mm.
- Wire EDM (5+) - Sodick AQ535L (550/350/300 mm travel, ±20° taper, 800 kg workpiece). Cut on hardened tool steel, internal splines, sharp internal corners that milling cannot reach.
- Inspection: Hexagon CMM + 20+ gauges - Hexagon CMM for coordinate measurement, plus vision system, profilometer, hardness tester, coating thickness gauge, XRF for material verification. The 10:1 rule (gauge 10x more accurate than the band) is applied to every feature.
- Machine highlights - VARIAXIS I-600: one-setup multi-face 5-axis + MAZA-CHECK auto-calibration; INTEGREX I-250H S: DONE-IN-ONE mill-turn, B-axis 0.0001° + Ai thermal shield; SPEEDIO S500Z2N / S700Z2N: Z-axis 2.2 G + 0.7 s ATC; Swiss-type: guide-bush switchable + 0.1 µm resolution.
Tolerance: ±0.003 mm CNC milling / ±0.002 mm CNC turning / ±0.002 mm grinding and wire EDM. Capability: Ppk >= 1.67 initial on key characteristics, Cpk >= 1.33 ongoing.
Certificates: ISO 9001:2015 (116024/A/0001/UK/En), IATF 16949:2016 (131941/A/0001/SM/En, with design clause 8.3 excluded, stated openly) and ISO 14001:2015 (116024/B/0001/UK/En), issued to Dongguan Zhuohang Ltd, registration 91441900MA4UWT6X39, founded 2005.
Where we ship: Austria, Belgium, the Czech Republic, Denmark, France, Germany, Greece, Hungary, Ireland, Italy, the Netherlands, Spain, Sweden and the United Kingdom in Europe; Brazil, Canada, Mexico and the United States in the Americas; China, Israel, Japan, Singapore and Sri Lanka in Asia; Australia and New Zealand in Oceania; and South Africa in Africa — plus other countries and regions worldwide, shipped from our base in Dongguan, China.
Contact: Felipe Iglesias, [email protected], +86 13126536955.
Not sure which process fits your volume?
Send the model and the expected annual quantity, and get a straight answer on machining versus moulding — including where a design change would cut cost. Reach Felipe Iglesias at [email protected] or +86 13126536955.
Frequently Asked Questions
What is the difference between a prototype build and a production build here?
Usually only quantity and scheduling. Both run on the same machines and the same process, which is what makes a later ramp a scheduling change rather than a re-qualification.
Can a printed part be machined afterwards?
Yes, and it frequently is. Sealing faces, bearing seats, and threaded features are machined on printed parts as a matter of course when they have to hold a tolerance or a fit.
Is 3D printing cheaper than CNC machining?
At quantity one, sometimes. Above the crossover quantity — which depends on size, material, and tolerance — machining is cheaper, and the gap widens with volume. A printed part that needs its interfaces machined carries both costs.
Can I audit the factory before placing an order?
Yes — on-site and video audits are both welcome at No. 8, Shuibian Songyuan Road, Hengli Town, Dongguan, Guangdong, China 523470.
Do you sign NDAs before reviewing drawings?
Yes — an NDA can be signed before any files change hands, and drawings stay inside the quoting system rather than circulating by email.
Is inspection documentation included in the quote?
It should be stated explicitly. A first-article report is a document someone has to produce, and whether it is a full dimensional report or a sample plan changes both the cost and what you receive.
How are parts packed for export?
Packing is set per part — finished surfaces bagged and boxed individually, with corrosion protection for steel. It belongs in the quote because it changes both the cost and the condition the parts arrive in.
Can a machined part be the prototype for a later moulded part?
Yes, and it is the standard route. A machined plastic or metal prototype validates fit, function, and design before any steel is committed; the design is then frozen and, if volume justifies it, moved to moulding.
Is injection moulding cheaper than CNC machining?
At volume, yes — once the mould is amortised, per-part cost falls far below machining. Below the crossover quantity (commonly a few thousand identical parts) machining is cheaper because it has no mould to pay back.
What tolerances can you hold on machined parts?
In short, ±0.003 mm on CNC milling and ±0.002 mm on CNC turning, and ±0.002 mm where precision grinding or wire EDM is used. The achievable tolerance depends on geometry, material, and datum structure, so it is fixed for each feature at the quote rather than guessed from a single quoted figure.
What materials do you machine?
Aluminum, stainless steel, titanium, brass, copper, and Inconel for metals; PEEK and Delrin (POM) for plastics. Material certificates are verified on incoming stock.
Continue reading: 4 Axis CNC Machining · 5 Axis CNC Machining
Standards referenced on this page
- ASTM A582/A582M-12 — Standard Specification for Free-Machining Stainless Steel Bars
- ASTM B348/B348M-21 — Standard Specification for Titanium and Titanium Alloy Bars and Billets
- ISO 9001 — Quality management systems — Requirements