Introduction
One of the most common decisions in plastic part manufacturing is choosing between CNC machining and injection molding. Both produce high-quality parts, but their cost structures are fundamentally different — and choosing the wrong method for your volume can overpay by 5–10× per part.
CNC machining has no tooling investment but high per-unit cost. Injection molding requires a mold investment but delivers the lowest per-unit cost at volume. The break-even point depends on part geometry, material, quantity, and tolerance requirements.
As a factory that manufactures injection molds and produces plastic parts, we compare these two methods daily for OEM customers. Here is the cost framework we use.
How CNC Machining and Injection Molding Cost Structures Differ
CNC Machining: No Tooling, High Unit Cost
CNC machining cuts plastic parts from a solid block (or near-net shape) using computer-controlled cutting tools. There is no mold investment — the machine is programmed once and parts are cut directly.
The cost per part is driven by:
- Machine time: Each part requires minutes to hours of CNC time depending on complexity
- Material waste: Material removed as chips is lost (unlike injection molding, where runners can be reground)
- Setup time: Each job requires fixture preparation and tool changes
- Labor: CNC programming and machine operation require skilled staff
Typical CNC machining costs (China factory):
- Simple part, 1–10 units: $15 – $80 per part
- Medium complexity, 1–10 units: $50 – $200 per part
- Complex part, 1–10 units: $100 – $500+ per part
- Scaling to 50–100 units: discount of 20–40% per unit, but costs remain high
Injection Molding: Tooling Investment, Low Unit Cost
Injection molding requires a mold upfront, after which parts are produced rapidly — often in 15–60 second cycles for small to medium parts.
The cost per part is driven by:
- Mold cost: One-time investment of $2,000–$50,000+ depending on complexity
- Material cost: Plastic resin at $1–$6 per kg, with near-zero material waste
- Cycle time: 15–60 seconds per shot, producing multiple parts if multi-cavity
- Minimal labor: Modern injection machines run semi-automatically
Typical injection molding costs (China factory, excluding mold amortization):
- Small part, 1,000+ units: $0.15 – $0.80 per part
- Medium part, 1,000+ units: $0.30 – $1.50 per part
- Large part, 1,000+ units: $0.50 – $3.00 per part
- Mold amortization adds $0.05–$1.00 per part depending on volume
Cost Comparison by Production Volume
Here is a side-by-side comparison for a typical medium-complexity plastic enclosure part (approximately 150 mm × 100 mm × 40 mm, ABS material, moderate tolerances, cosmetic surface finish):
| Volume | CNC Machining (per part) | Injection Molding (per part + mold amortized) | Winner |
|---|---|---|---|
| 1 unit | $80 – $150 | $2,500+ (mold cost alone) | CNC Machining |
| 10 units | $60 – $120 each | $250+ each ($2,500 mold / 10) | CNC Machining |
| 50 units | $50 – $100 each | $53+ each ($2,500 mold / 50 + $3 material) | Comparable |
| 100 units | $45 – $90 each | $28 each ($2,500 mold / 100 + $3 material) | Injection Molding |
| 500 units | $40 – $80 each | $8 each ($2,500 mold / 500 + $3 material) | Injection Molding |
| 1,000 units | $35 – $70 each | $5.50 each ($2,500 mold / 1,000 + $3 material) | Injection Molding |
| 10,000 units | $30 – $60 each | $3.25 each ($2,500 mold / 10,000 + $3 material) | Injection Molding |
The break-even for this example is approximately 50–100 units. Below this volume, CNC machining costs less. Above this volume, the mold investment pays for itself through dramatically lower per-unit cost.
When to Choose CNC Machining
Prototyping and Functional Testing (1–50 units)
CNC machining is ideal for prototyping because it requires no tooling. You can iterate your design, machine new versions, and test fit and function without committing to a mold. Once the design is finalized, transition to injection molding for production quantities.
Very Low Volume Production (50–200 units annually)
If your annual volume will never exceed a few hundred units — for example, specialized industrial equipment components or replacement parts — CNC machining avoids the upfront mold investment entirely. The higher per-unit cost is offset by zero tooling expense.
Parts With Geometry Unsuitable for Molding
Some parts cannot be injection molded due to extreme undercuts, internal cavities that cannot be formed by side actions, or wall thickness ratios beyond molding capability. CNC machining handles these geometries without mold constraints.
When Lead Time Is Critical
CNC machining can deliver parts within days, while injection molding requires 4–8 weeks for mold manufacturing. If you need parts immediately, CNC is the faster option — though you pay more per part.
When to Choose Injection Molding
Production Quantities Above 100 Units
For almost any plastic part above 100 units, injection molding delivers lower total cost. The mold investment is recovered through dramatically lower per-unit material and processing costs.
Consistent Material Properties
Injection molding produces parts with uniform density and predictable mechanical properties because the entire part is formed from the same melt under controlled conditions. CNC-machined parts may have residual stress from the machining process or property variations if cut from different areas of a plastic block.
Cosmetic Surface Finishes
Injection molding produces consistent surface finishes directly from the mold cavity — from mirror polish (SPI A-1) to textured (VDI, EDM finishes). CNC machining leaves tool marks that require post-processing (sanding, vapor polishing) to achieve comparable cosmetic quality, adding cost.
Scalability
If you anticipate volume growth, starting with injection molding — even with a simple single-cavity mold — establishes the production process. Scaling up means adding cavities or building a high-volume mold using validated parameters. Switching from CNC to injection molding mid-lifecycle requires re-validating part quality.
The Outcome: Right Method, Right Cost
For most OEM projects producing 100+ identical parts, injection molding delivers the lowest total cost — even after accounting for the upfront mold investment. The key is matching the manufacturing method to your volume, part geometry, and quality requirements before committing. A side-by-side cost analysis for your specific part removes the guesswork and prevents the 5–10× per-part overpay that comes from choosing the wrong method at your volume.
Free Design Review — Determine the Best Manufacturing Method for Your Part
Not sure whether CNC machining or injection molding is right for your project? The answer depends on your part geometry, material, quantity, and quality requirements.
Send your 3D drawings to Hua Zi Industrial. Our engineers will analyze your part, deliver a side-by-side cost comparison between CNC and injection molding, and recommend the most cost-effective path — without bias toward either method.
Upload your drawing for a free manufacturing method analysis →
- ✅ Cost comparison: CNC machining vs. injection molding for your specific part
- ✅ Volume break-even analysis
- ✅ Material and surface finish recommendations
- ✅ No obligation — make an informed manufacturing decision
Frequently Asked Questions
What is the break-even volume between CNC and injection molding?
The break-even typically falls between 50 and 200 units, depending on part complexity. Simple parts with low mold cost ($2,000–$3,000) break even around 50–100 units. Complex parts requiring expensive molds ($10,000+) may take 200–500 units to break even. The best approach is to request a cost comparison for your specific part geometry, material, and quantity.
Can I CNC machine a few parts and then switch to injection molding?
Yes, this is a common development path. CNC machine 5–20 functional prototypes for design validation, then build an injection mold for production. However, keep in mind that CNC-machined and injection-molded parts may have slightly different mechanical properties (molded parts have flow orientation; machined parts retain stock material properties). Plan a small injection-molded validation batch before full production.
Is CNC machining cheaper than injection molding in China?
For volumes under 50–100 units, yes. Chinese CNC machining rates are $15–$40 per hour, making low-volume machining cost-effective. However, Chinese injection molding also benefits from lower mold costs ($2,000–$10,000 for a typical mold vs. $5,000–$25,000 in the West) and lower machine rates ($3–$20 per hour), shifting the break-even point lower. This makes Chinese injection molding viable at volumes that would not justify it from a Western manufacturer.
What if my part has features that make injection molding difficult?
Some features make injection molding expensive or impossible: deep undercuts without access for side actions, internal threads that cannot be unscrewed, extreme wall thickness variations, or very large parts exceeding available clamp tonnage. In these cases, CNC machining may be the only viable option regardless of volume. Discuss your part geometry with a plastic injection molding manufacturer who can evaluate moldability during DFM review.
Does Hua Zi manufacture both CNC machining and injection molding?
Hua Zi manufactures injection molds and produces plastic injection-molded parts. Our 20 CNC machining centers are dedicated to mold making — producing high-precision mold components in-house. We do not perform standalone CNC part machining. If injection molding is recommended for your project, we handle the full manufacturing process from mold design to production.
Read the full system guide: Prototype to Production Transition Hub — Complete transition system: prototype evaluation, mold manufacturing, and production ramp-up.
Related Services
Hua Zi Industrial manufactures injection molds and produces injection-molded parts in one factory:
- Custom Plastic Injection Molding Services — 45 injection molding machines (90T–800T), in-house DFM, material selection, and ISO 9001:2015 certified quality. From small batch to high volume.
- Injection Mold Manufacturing Services — In-house mold design, 20 CNC machining centers, CMM inspection, and complex mold structures. Single-cavity to multi-cavity production molds.
Get a Free Quote Within 24 Hours
Decided that injection molding is right for your project? Or need a cost comparison to confirm?
Send your 3D drawings and quantity requirements to Hua Zi Industrial. Our engineers will deliver a detailed quotation for your injection molding project — including mold cost, per-unit part cost, and lead time — within 24 hours.
Upload your drawing and get a free manufacturing quote →
- ✅ Engineering review and cost estimate within 24 hours
- ✅ Upload STEP, IGES, DWG, or PDF files
- ✅ DFM feedback included with quotation
- ✅ ISO 9001:2015 certified factory in Guangdong, China