CNC Machining vs Injection Molding
The question isn't "which is better" — it's "which is cheaper at my quantity, with my material and tolerance." Here's where the curves cross and a table to decide.
Cite this page
Used this in a report, quote justification or internal standard? A link back helps other engineers find the same reference. Suggested anchor text — reword freely:
<a href="https://www.ataimeisen.com/cnc-machining-vs-injection-molding.html">CNC Machining vs Injection Molding — FSCPRECISION</a>
No permission needed. Please do not rehost the page — link to it instead so the numbers stay current.
The one number that decides it: quantity
Injection molding needs a steel tool that can cost thousands to tens of thousands of dollars. That cost is fixed, so it spreads across the run — and the per-part price collapses as volume rises. CNC machining has no tool: every part carries its own setup and machining time, so its per-part cost stays roughly flat. The two lines cross somewhere around 5,000–10,000 identical parts, earlier for small simple parts, later for large or tight-tolerance ones.
| Factor | CNC Machining | Injection Molding |
|---|---|---|
| Tooling cost | None | High (steel mold, $k–$$k) |
| Best quantity | 1 – ~10,000 pcs | 10,000+ pcs |
| Lead time to first part | Days (program the model) | Weeks–months (design + cut + prove the mold) |
| Design changes | Cheap — edit the model, re-run | Expensive — modify the mold |
| Materials | Metal and plastic both | Thermoplastics only (plus some liquid silicone) |
| Geometry | Almost anything millable/turnable | Needs draft, no undercuts without side-actions |
| Per-part cost at volume | Flat, relatively high | Very low once tool is paid |
| Tolerance consistency | Holds per part; slight run-to-run variation | Near-identical across millions once proven |
How to choose for your part
Choose CNC machining if…
- You need under ~10,000 pieces, or you're not sure of the volume yet.
- The part is metal (molding can't do aluminium or steel).
- The design will change — CNC absorbs edits for almost nothing.
- You need the first parts in days, not months.
- The geometry has no draft or has internal features molding hates.
Choose injection molding if…
- You're committed to 10,000+ identical plastic parts.
- The part is a simple thermoplastic shape that molds cleanly.
- Per-part cost dominates and you can wait for the tool.
- Annual volume justifies the tooling investment.
The in-between case
Prototypes and bridge production almost always start in CNC even when the end game is molding — it proves the design fast and cheaply, then you commit to the tool once the part is settled. We do a lot of that bridge work; see prototyping and low-volume production. And if the part is metal or low-volume, molding isn't even an option — CNC vs 3D printing is the more relevant comparison.
A caveat on the numbers
The crossover isn't a fixed rule. A large, complex moulded part may never beat CNC at your volume; a tiny simple part may cross at 3,000. The only way to know is to price both for your actual drawing — our cost calculator gives a CNC range in seconds, and we'll quote molding-vs-machining honestly if you ask.
Not sure which process fits your part?
Send the drawing and tell us the target volume. We'll quote CNC and tell you straight whether molding would beat it at that quantity.
Related: CNC vs 3D Printing · Reduce CNC Cost · Cost Calculator