CNC Machining vs
Injection Molding
When to machine, when to mold, and when to start with one and switch to the other. Cost crossover points, tolerance comparison, and a decision framework based on real production data.
Should You Machine or Mold Your Part?
This is the most expensive decision most product engineers get wrong. Choose CNC machining when you should have molded, and you overpay on every part for the life of the product. Choose injection molding too early, and you spend $20,000 on a mold for a design that changes twice before production.
The answer depends on five variables: production volume, material, geometry, tolerance, and time-to-first-part. This page gives you a framework to evaluate all five, with real cost data from our factory where we run both CNC machines and injection molding presses under the same roof.
CNC Machining vs Injection Molding Compared
The fundamental difference: CNC machining removes material from a solid block. Injection molding pushes molten material into a mold cavity. Everything else follows from that.
| Factor | CNC Machining | Injection Molding |
|---|---|---|
| Tooling cost | None | $5,000 – $100,000+ |
| Per-part cost (simple plastic) | $15 – $80 | $0.10 – $5.00 at volume |
| Best volume | 1 – 5,000 pcs | 1,000 – 1,000,000+ |
| Materials | Metals + plastics (any machinable) | Thermoplastics, some thermosets |
| Tolerance | ±0.02 mm standard | ±0.05 – 0.1 mm standard |
| Surface finish | Ra 0.4 – 3.2 µm (machined) | Mold-dependent (SPI A1 to D3) |
| Lead time (first part) | 5 – 7 days | 4 – 8 weeks (tooling first) |
| Design changes | Update CAD file, next part is different | Modify or remake mold ($$$) |
| Wall thickness | ≥ 1.0 mm (metal), ≥ 1.5 mm (plastic) | 0.5 – 3.0 mm (must be uniform) |
| Geometry limits | Tool access required (no fully enclosed voids) | Draft angles, uniform walls, no undercuts (without slides) |
| Part strength (plastic) | Full material properties (machined from stock) | May have weld lines, sink marks, internal stress |
| Waste | Chips (recyclable but material lost) | Minimal (runners recyclable) |
Cost Crossover: When Molding Becomes Cheaper
The crossover point is where the total cost of injection molding (tooling + per-part cost × quantity) drops below the total cost of CNC machining (per-part cost × quantity). This varies by part complexity and mold cost.
| Scenario | Mold Cost | Molded Part | CNC Part | Crossover |
|---|---|---|---|---|
| Simple plastic housing | $5,000 | $0.80/pc | $15/pc | ~350 pcs |
| Medium-complex enclosure | $20,000 | $1.50/pc | $45/pc | ~460 pcs |
| Multi-cavity connector | $35,000 | $0.50/pc | $25/pc | ~1,430 pcs |
| High-precision part (tight tol.) | $60,000 | $2.00/pc | $35/pc | ~1,820 pcs |
| Metal: CNC vs die cast | $15,000 | $3.00/pc | $25/pc | ~680 pcs |
Formula: Crossover = Mold cost ÷ (CNC per-part cost − Molded per-part cost). These are representative examples from Davantech production. Your actual crossover depends on geometry, material, tolerance, and surface treatment. Send your drawing and we'll calculate both options.
5 Questions to Choose the Right Process
Answer these five questions in order. Each one narrows your choice.
The Smart Approach: Start CNC, Switch to Molding
The most cost-effective product development path uses both processes in sequence, not one or the other.
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Phase 1: CNC machine the prototypes (5–50 pieces)Validate the design, test with customers, iterate freely. No tooling investment. Parts in 5–7 days per iteration. Use CNC-machined parts for engineering validation, environmental testing, and user trials.
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Phase 2: CNC machine the first production batch (100–500 pieces)Once the design is locked, produce the first commercial batch by CNC while the injection mold is being built. This lets you start selling immediately without waiting 6–8 weeks for tooling. Revenue starts flowing while the mold is made.
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Phase 3: Switch to injection molding for production (1,000+ pieces)The mold is ready, the design is proven, demand is confirmed. Switch to injection molding and reduce per-part cost by 70–90%. The CNC-machined parts served as the bridge between design and mass production.
Davantech runs both CNC machines and injection molding presses in the same factory. We manage the transition from machined prototypes to molded production as a single project, ensuring dimensional consistency across the switch. See our injection molding services and CNC machining services.
When CNC Machining Always Wins
- Aluminium, steel, brass, titanium
- Cannot be injection molded
- Die casting is the alternative at high volume
- CNC wins below 3,000 pcs
- ±0.02 mm or tighter required
- Bearing seats, press fits, sealing surfaces
- Injection molding cannot achieve this reliably
- CNC wins regardless of volume
- Below 500 pieces lifetime
- Tooling cost never amortises
- CNC has zero fixed cost
- Even at $50/part, total cost is lower
- Still prototyping or testing
- Changes expected after first batch
- CNC: change the file, run again
- Molding: pay for mold modification
- Parts needed in 1–2 weeks
- No time for mold fabrication
- CNC: 5–7 days from CAD file
- Molding: 4–8 weeks for tooling
- CNC parts are machined from stock material
- No weld lines, sink marks, or flow issues
- Critical for structural or load-bearing parts
- Molded parts can have internal weaknesses
When Injection Molding Always Wins
- Above 5,000 pieces per year
- Tooling cost amortises quickly
- Per-part cost drops to $0.10–$5.00
- CNC cannot compete on unit cost
- Walls below 1.0 mm
- Difficult and expensive to CNC machine
- Injection molding handles 0.5–1.0 mm easily
- Consumer electronics, thin enclosures
- Snap fits, living hinges, internal ribs
- Cannot be CNC machined efficiently
- Designed for molding from the start
- Integral fastening reduces assembly
Case Study: Electronic Enclosure
A customer needed a plastic electronic enclosure in ABS for an IoT gateway device. The design was finalised and annual volume was expected at 3,000 pieces. Here's the cost comparison we provided:
| Cost Element | CNC Machined | Injection Molded |
|---|---|---|
| Tooling | $0 | $12,000 |
| Per-part cost | $38 | $1.80 |
| Total for 3,000 pcs | $114,000 | $17,400 |
| Lead time (first part) | 6 days | 5 weeks |
| Crossover point | ~331 pieces | |
Decision: at 3,000 pieces, injection molding saved $96,600 compared to CNC machining. The customer CNC-machined 50 prototypes first to validate the design, then invested in the mold once testing was complete. The CNC prototypes cost $1,900. The mold cost $12,000. Total development cost: $13,900, with per-part production cost of $1.80 going forward.
CNC Machining vs Die Casting
The same CNC-vs-molding logic applies to metal parts, but the alternative to CNC is die casting, not injection molding. The crossover is higher because die casting molds are more expensive and per-part savings are smaller.
| Factor | CNC Machined | Die Cast + CNC Finished |
|---|---|---|
| Tooling | None | $10,000 – $50,000 |
| Per-part cost (aluminium) | $25 – $80 | $3 – $10 at volume |
| Best volume | 1 – 3,000 pcs | 3,000 – 100,000+ |
| Tolerance (as-produced) | ±0.05 mm | ±0.1 – 0.3 mm (CNC-finished: ±0.05 mm) |
| Lead time (first part) | 5 – 7 days | 6 – 10 weeks (mold) |
For a detailed comparison of all metal fabrication methods, see our 5 ways to fabricate aluminum parts and aluminum enclosures manufacturing pages.
CNC vs Molding Questions
At what quantity should I switch from CNC to injection molding?
The crossover point is typically between 500 and 5,000 pieces for plastic parts, depending on mold cost and part complexity. A simple housing with a $5,000 mold crosses over at around 350 pieces. A complex multi-cavity part with a $60,000 mold crosses over at around 1,800 pieces. Calculate it as: mold cost ÷ (CNC per-part cost minus molded per-part cost).
Can I CNC machine a plastic part that will later be injection molded?
Yes, and this is the recommended approach. CNC machine prototypes and first batches from the same material grade (e.g., ABS rod stock for CNC, ABS pellets for molding). The material properties are similar but not identical because molded parts have flow orientation and weld lines that machined parts don't. For functional testing this difference is usually acceptable.
Is CNC machining more precise than injection molding?
Yes. CNC machining holds ±0.02 mm standard and ±0.005 mm on critical features. Injection molding holds ±0.05 to ±0.1 mm at best, and achieving the tighter end requires expensive tooling and careful process control. For parts with bearing fits, press fits, or O-ring grooves, CNC is more reliable regardless of volume.
What about 3D printing as an alternative?
3D printing is faster than both for 1–5 concept models (1–3 days, no CAM programming), but the parts are weaker, less precise (±0.1–0.2 mm), and more expensive per unit than CNC above 10–20 pieces. For functional prototypes in the final material, CNC machining is better. For visual models and form-checks, 3D printing is fine. Neither replaces injection molding at production volumes.
Do I need separate suppliers for CNC and injection molding?
Not necessarily. Davantech operates both CNC machining centers and injection molding presses in the same factory in Dongguan. This means prototyping, design validation, mold fabrication, and production happen under one roof with one quality system. The dimensional consistency between CNC prototypes and molded production parts is verified in-house.
How much does an injection mold cost?
A simple single-cavity aluminum prototype mold costs $2,000–$5,000 and lasts 5,000–10,000 shots. A production steel mold (P20) costs $5,000–$30,000 and lasts 100,000+ shots. A high-volume hardened steel mold (H13) costs $20,000–$100,000+ and lasts 500,000+ shots. Mold cost depends on part size, complexity, number of cavities, and steel grade.
Can Davantech quote both processes for the same part?
Yes. Send your 3D model and specify your expected volume. We'll return a dual quote showing CNC machining cost per part and injection molding cost (tooling + per-part), with a crossover analysis so you can see at what quantity the switch makes sense. Upload your drawing here.