CNC Machining vs Injection Molding
Engineers and buyers often face a fundamental decision: CNC machining or injection molding? Both produce plastic parts — but the economics, timelines, and design constraints are very different. Here is a practical comparison to help you choose the right process.
How They Work:
CNC machining removes material from a solid plastic block using computer-controlled cutting tools. Injection molding injects molten plastic into a steel mold under high pressure. The fundamental difference? Subtractive vs. formative manufacturing.
When to Choose CNC Machining:
- Low to medium volumes (1-1000 parts)
- You need parts fast (1-2 weeks typical lead time at PlasticPartsCustom)
- Tight tolerances are critical (±0.01mm achievable)
- The design may change — no mold investment to protect
- You are in prototyping or R&D phase
- Material flexibility: switch between PEEK, PTFE, POM without tooling changes
When to Choose Injection Molding:
- High volumes (5000+ parts)
- Per-part cost must be minimized over the production run
- The design is finalized and will not change
- You can absorb the upfront mold cost ($3,000-$50,000+) and 4-8 week mold fabrication time
- Part weight and material usage are critical
Cost Comparison:
| Factor | CNC Machining | Injection Molding |
|---|---|---|
| Setup cost | Low (no tooling) | High (mold fabrication) |
| Per-part cost (100 pcs) | $20-200 | $0.50-5.00 |
| Per-part cost (10,000 pcs) | $20-200 | $0.10-1.00 |
| Lead time (first parts) | 3-10 days | 4-8 weeks |
| Design change cost | Minimal | Potentially new mold |
Material Considerations:
Both processes work with most engineering plastics. However, some high-performance materials like PEEK with carbon fiber fill are easier to machine than to mold. Conversely, flexible materials like TPE are better suited to injection molding.
The Hybrid Approach:
Many successful projects use both processes in sequence. CNC machine prototypes to validate the design. Once confirmed, invest in an injection mold for production scaling. PlasticPartsCustom offers both CNC machining and injection molding services — you can transition seamlessly without changing suppliers.
Still Not Sure?
Send us your part design. Our engineers will assess your volume, geometry, and material requirements and recommend the most cost-effective manufacturing route. No obligation, just expert advice.