- Dongguan Zhuohang Ltd (Registration No. 91441900MA4UWT6X39), operating as Zhuohang Precision Machining Factory, established 2005; 100+ CNC machines; certified to ISO 9001:2015, IATF 16949:2016 (excluding clause 8.3 product design) and ISO 14001:2015; holding ±0.003 mm CNC milling / ±0.002 mm CNC turning tolerance.
- CNC Machining removes material from a solid billet; casting pours molten metal into a mould.
- CNC Machining wins on tolerance, material properties and low-volume flexibility; casting wins on per-part cost at high volume and on hollow/complex shapes.
- The cost curves cross somewhere in the low thousands of parts — batch size, not the part itself, usually decides.
How the two processes make the part
CNC Machining is subtractive: a billet of wrought metal is held in a vice or fixture and cut to shape with rotating or moving tools. Every feature is defined directly by the toolpath, so the first article can ship in days with no part-specific tooling and design changes cost nothing but a CAD edit. Casting is formative: molten alloy is poured or forced into a mould that reproduces the part shape, including internal cavities that CNC Machining cannot reach. The mould is the cost and the lead-time driver, and changing the design later means changing the tool.
Side-by-side comparison
| Factor | CNC machining | Casting |
|---|---|---|
| Tooling | CAD/CAM + standard cutters; near-zero part-specific tooling, first article in 1–3 days | Pattern + mould or steel die; die casting tooling often $5k–$100k+, lead time weeks |
| Lead time (first article) | 1–3 days from released CAD | 2–8 weeks including tool making |
| Economic batch | 1-off to low-volume; no amortisation hurdle | 1,000–50,000+ parts where tooling cost is spread across the run |
| Tolerance | ±0.003–0.05 mm achievable | Sand ±0.5 mm; die cast ±0.1–0.2 mm |
| Surface finish | Machined Ra 0.4–1.6 µm directly | As-cast 3.2–12.6 µm; usually requires machining to seal surfaces |
| Materials | Any wrought stock: 6061/7075, steels, stainless, titanium, Inconel | Castable alloys only: A380/ZL aluminium, cast iron, zinc, magnesium |
| Wall thickness | No absolute minimum (thin features become fragile) | Die cast ~3 mm min; sand cast thicker |
| Design freedom | Limited to cutter-accessible geometry; deep cavities need 5-axis/EDM | Hollow sections, internal cores and complex shapes come naturally |
| Material structure | Wrought, dense, isotropic; superior fatigue strength | As-cast grain with possible shrinkage porosity and lower fatigue life |
| Design change cost | Edit CAD and re-run — near zero | New or modified tooling — expensive |
| Post-processing | Deburr, anodise, plate, heat treat | Trim, blast, frequently CNC machining of mating faces |
| Typical applications | Brackets, housings, fixtures, precision components | Engine blocks, pump bodies, large enclosures |
Where CNC Machining wins, where casting wins
CNC Machining is the stronger choice when you need tight tolerances (±0.003–0.05 mm), superior mechanical properties from wrought stock, a handful of prototypes through to a few hundred production parts, or a material that is not readily castable (titanium, Inconel, hardened steel). It is also the natural finishing step for castings — most die-cast housings are machined on mating faces anyway, because the as-cast surface cannot hold a seal or a bearing bore to the needed accuracy.
Casting is the stronger choice for runs of thousands where the tooling can be amortised, for parts with hollow sections or internal cores, and for very large components where a solid billet would be uneconomic to buy and to cut. Expect to machine the surfaces that must seal or locate, and to budget for non-destructive testing on safety-critical castings.
Material structure and properties
Because CNC Machining starts from wrought stock, the grain is dense and effectively isotropic, giving reliable fatigue and impact performance that you can predict from the mill certificate. Cast parts solidify from the melt: the grain is coarser and shrinkage porosity or cold shuts can appear, so cast alloys are typically specified with a property margin and verified by X-ray or magnetic-particle inspection on load-bearing items. For a part where failure is not an option, the predictability of wrought stock is a real argument for CNC Machining.
Process-selection checklist
- Need <100 parts or a 1-off prototype? → CNC Machining.
- Need ±0.01 mm or better, or titanium/Inconel? → CNC Machining.
- Need 5,000+ identical parts with internal cavities? → evaluate casting.
- Cast part must carry load or seal a face? → plan for secondary CNC Machining finishing.
- Wall sections under 3 mm at high volume? → die casting leads.
Post-processing
CNC Machining parts need deburring and then the specified surface treatment (anodise, passivate, plate, paint). Cast parts need gate/flash removal, shot blasting and frequently CNC machining of the datum and sealing faces; impregnation may be required to stop porous leak paths, and cosmetic surfaces may need bespoke finishing.
Frequently Asked Questions
When should I choose CNC Machining instead of casting?
In short, Choose CNC Machining for low to medium volume, tight tolerance, difficult-to-cast materials, or any part where wrought mechanical properties matter. Choose casting when the tooling can be spread across a very large run or the geometry is hollow and complex.
What tolerance can CNC Machining hold versus casting?
CNC Machining routinely holds ±0.003–0.05 mm. Sand casting is around ±0.5 mm and die casting ±0.1–0.2 mm; both usually need machining on functional surfaces.
Is casting cheaper than CNC Machining?
Per part, yes — but only above the volume where the mould cost is amortised (often a few thousand parts). Below that, CNC Machining is cheaper because there is no tooling to recover.
Can cast parts be machined afterwards?
Yes. It is common to cast a near-net shape and finish the critical faces, bores and threads by CNC Machining to reach the required tolerance and surface.
Cost crossover in practice
When you are choosing, the question is rarely which process is "better" and almost always about batch size. As a working rule for a part of moderate complexity: CNC Machining costs a few tens of dollars in machine time per piece with no upfront tooling, so 100 parts might total a few thousand dollars. Casting needs tooling in the low five figures, so the same 100 parts would be far more expensive once the tool is paid for — but at 10,000 parts the per-piece tooling share falls to cents and the formative process wins decisively. The practical crossover for most components lands between 1,000 and 5,000 pieces; above it, amortised tooling dominates, below it, CNC Machining is cheaper and far more flexible. Always quote both before you commit, because material yield, secondary operations and scrap rate shift the exact break-even for your part.
Design-for-manufacturing tips
- Keep functional tolerances at ±0.02–0.05 mm where cnc precision machining is used; reserve ±0.003 mm (milling) / ±0.002 mm (turning) for critical datums only — every tighter band adds cost.
- Design for standard stock sizes and minimise deep, narrow cavities that need long-reach or 5-axis tooling.
- If volume will rise, design the part so it can later move to casting without changing the interface — locate on the same datums.
- Specify surface finish only where it matters; machined finish is cheap, plating and anodising are the cost drivers.
Porosity, dimensional drift, and where post-machining wins
The choice between CNC milling from solid and casting-then-machining turns on three failure modes that casting introduces and milling does not: porosity, dimensional drift, and surface inclusions. A cast part is solidified from liquid metal, and the solidification process traps gas, shrinks at phase transitions, and pulls inclusions from the mold material. A milled part is cut from solid bar or plate that has been hot-rolled or forged and inspected at the mill — defects are removed before the part is cut, not after. The difference is reliability, not strength: a cast part can fail at any feature where a pore happens to sit; a milled part fails only where the load exceeds the material's bulk strength.
The economics of casting-then-machining versus full CNC from solid are dominated by the casting pattern cost and the post-casting machining volume. A sand casting pattern for a 300 mm housing runs $2,000-8,000; an investment casting pattern for the same part runs $8,000-25,000; a die casting die for the same part runs $25,000-120,000. The pattern amortises across the parts run through it: at $15,000 pattern cost and $4 per part post-machining, the break-even against $30 for full CNC is at 580 pieces ($15,000 / ($30 - $4) = 577). Below 580 pieces CNC from solid wins; above 580 casting-then-machining wins — for that part geometry and tolerance. The rule of thumb that casting wins above 1,000 pieces is true for a simple housing and wrong for parts where porosity risk or post-machining volume pushes the break-even to 2,000+.
Three failure modes shift the casting decision. Porosity: die casting produces 1-3 percent porosity by volume, sand casting produces 2-5 percent, investment casting produces 0.5-1 percent. A pore in a sealed surface is a leak path; a pore in a fatigue-critical feature is a crack initiator. For hydraulic manifolds, fuel system components, and pressure-rated housings, porosity disqualifies casting entirely and full CNC from solid is the only path. Dimensional drift: cast parts hold ±0.5-2 mm in the as-cast condition on most features; features at ±0.1 mm or tighter need post-machining. The post-machining adds $3-12 per part and pushes the break-even to 1,500-2,500 pieces for high-tolerance parts. Surface inclusions: sand casting traps mold material inclusions in 5-15 percent of parts; investment casting traps ceramic inclusions in 1-3 percent. Both require visual inspection, x-ray, or both, which adds $0.50-3 per part and is a hidden cost that casting shops rarely quote.
The hybrid strategy is investment casting for the rough geometry and CNC milling for the precision features. A 300 mm housing at 800 pieces with ±0.003 mm on the bore and ±0.5 mm on the external walls is investment-castable to ±0.5 mm on the walls and post-machinable to ±0.003 mm on the bore. The investment pattern is $15,000, the post-machining is $6 per part, the unit is $10 against $35 for full CNC. The hybrid wins at 600 pieces. A shop that can cast and machine under one roof — or that subcontracts the casting with in-house post-machining — is the one that can quote the hybrid; one that runs only CNC pushes full-machining on parts that should be cast-then-machined.
The honest answer for you choosing "CNC milling vs casting" is: for low-stress parts above 1,000 pieces where porosity is acceptable, casting-then-machining wins on cost. For pressure-rated or fatigue-critical parts, or parts below 1,000 pieces, full CNC from solid wins on reliability. A shop that runs both processes is the one that picks the right path per part; one that runs only one process is the one that pushes the wrong path.
What this shop actually runs
If you ask for capability evidence, you deserve a specific answer. This facility operates 100+ CNC machines across 6,800 m2 in Dongguan, China, staffed by 100+ people. The machines, listed 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). Intended for 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). Intended for 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). Intended for 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). Intended for shafts, bushings, flanges up to ±0.002 mm.
- Wire EDM (5+) - Sodick AQ535L (550/350/300 mm travel, ±20° taper, 800 kg workpiece). Intended for 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 bands: ±0.003 mm milled, ±0.002 mm turned, ±0.002 mm ground or wire-cut. Capability indices: Ppk >= 1.67 at the initial study; Cpk >= 1.33 ongoing in production.
Certifications: ISO 9001:2015 (116024/A/0001/UK/En) · IATF 16949:2016 (131941/A/0001/SM/En, design clause 8.3 excluded) · ISO 14001:2015 (116024/B/0001/UK/En), held by Dongguan Zhuohang Ltd (USCC 91441900MA4UWT6X39, since 2005).
Service area: we supply 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, with worldwide delivery from China.
Contact: Felipe Iglesias, [email protected], +86 13126536955.
Continue reading: 3 Axis CNC Precision Machining · 4 Axis CNC Precision Machining · 5 Axis CNC Precision Machining
Standards referenced on this page
- ASTM B211/B211M-19 — Standard Specification for Aluminum-Alloy Rolled or Cold Finished Bar, Rod, and Wire
- ASTM A484/A484M-24 — Standard Specification for General Requirements for Stainless Steel Bars, Billets, and Forgings
- ISO 9001 — Quality management systems — Requirements