CNC machining (typical)
- Strong for metals and very low quantities
- No mold investment, pay per machined hour
- Complex internal geometry can be expensive or impossible without assembly
Process comparison
Injection Molding vs CNC Machining: Volume, Geometry, and Unit Cost
CNC removes material from stock for low quantities and metals. Injection molding forms plastic parts in seconds once a steel tool exists.
Process choice
Subtractive metal versus formed plastic
CNC excels when you need metal, one offs, or frequent design changes without tooling lead time. Molding wins when plastic geometry is stable and quantity makes a tool pay back.
NetProto does not offer CNC machining as a service. This guide routes plastic programs that outgrow machined prototypes.
If the part must stay metal, CNC or casting remains the path. If the design can move to plastic, compare unit economics on the molding quote.
Side by side
Typical decision drivers
Neither process replaces the other. Volume and material usually decide.
Injection molding (NetProto)
- Plastic parts in high volume with repeatable cycle time
- Steel tool investment with falling unit cost as quantity rises
- Geometric complexity often cheaper than equivalent machined plastic
Routing table
When to move from CNC prototypes to molding
Qualitative signals only. Upload CAD for molding economics.
| Signal | Stay on CNC longer | Move to molding |
|---|---|---|
| Quantity | Tens of parts per revision | Hundreds plus per revision |
| Material | Must be aluminum or steel | Performance met by engineered plastic |
| Revision rate | Weekly geometry changes | Design frozen for tooling |
| Timeline | Need parts tomorrow | Can absorb tool build on qualified programs |
Molding readiness
Plastic conversion checklist
Confirm these before you quote a steel tool.
Wall thickness and draft suitable for ejection
Material chosen from the materials library
Critical dimensions identified for first article inspection
Acceptance that DFM may request rib or gate changes
Continue exploring
Related guides
Process first, then resin.
Compare hub
All comparison guides.
Compare hubMaterials library
Resin selection after process is decided.
Materials libraryInjection molding vs urethane casting
When rubbery prototypes differ from production plastic.
Injection molding vs urethane castingFAQ
Common questions
Can CNC plastic prototypes predict molded shrink?
Machined stock does not experience the same fill, pack, and cooling as molded resin. Use molded T1 for production approval.
Does NetProto use short life tooling before steel?
No. NetProto quotes hardened steel tools for production molding. Other shops may iterate in faster wearing tooling first; that path is outside NetProto's offer.
Next step
Quote plastic production when CNC unit cost flattens
Upload CAD for steel tool and piece price. NetProto manufacturing is ISO 9001 certified.