For many product teams, the early stage always comes with the same headache: when you only need a few dozen plastic parts, should you go with CNC machining or invest in injection molding?
The choice isn’t just about cost—it directly affects lead time, iteration speed, and how quickly you can respond to market feedback.
Let’s walk through a real case from a medical startup.
Case Study: 50 Housings, One Decision
A young medical company was developing a portable diagnostic device. For their first round of clinical trials, they only needed 50 plastic housings. The team debated two paths:
- Injection molding: Low per-part cost, but the upfront tooling would run several thousand dollars and take at least four weeks.
- CNC machining: Much higher per-part cost, but they could get parts in just a few days and move straight to testing.
During the discussion, the R&D lead said something that hit the nail on the head: “What we need isn’t cheap parts—it’s parts fast. The market won’t wait for us.”
They went with CNC. A week later, the parts were in hand, clinical testing was underway, and the project didn’t lose momentum.
CNC Machining: Flexible, but Expensive
The biggest advantage of CNC is flexibility. No molds, no tooling—just machine the parts straight out of plastic stock. If you need to tweak the design, you can do it immediately. For runs of 10–100 parts, CNC is usually the fastest way forward.
But flexibility comes at a price. Take something the size of a smartphone shell: CNC machining might cost $60–$100 per piece. At 20 or 50 parts, that’s manageable. But once you start talking hundreds, the math gets painful.
In other words, CNC is more of a “speed-first” option—you pay more per piece, but you save time and stay nimble.
Injection Molding: Invest Once, Save Long-Term
Injection molding flips the equation. You pay upfront for a mold, inject molten plastic, and out come consistent parts at high speed.
Here’s what that same smartphone shell might look like:
- Mold cost: $3,000–$5,000 (for a rapid tool)
- Per-part cost: $2–$5
- Lead time: 2–4 weeks
For a small team, the mold price can feel like a wall. But once you scale beyond 500 units, molding usually pays for itself.
That same medical startup saw it play out this way. After clinical trials, they secured a few hundred pilot orders. CNC no longer made sense. They invested in a rapid tool, cut their per-part cost by nearly 90%, and gained the added benefit of consistent appearance and assembly quality.
Side-by-Side: Cost and Lead Time
| Method | Best for | Upfront Cost | Per-Part Cost (smartphone-sized part) | Lead Time | Typical Use Case |
|---|---|---|---|---|---|
| CNC Machining | 10–100 pcs | None | $60–$100/pc | 3–7 days | Prototypes, functional testing, urgent needs |
| Rapid Tooling + Injection Molding | 200–2000 pcs | $3,000–$5,000 | $2–$5/pc | 2–4 weeks | Small-batch pilot runs, market trials |
| Production Tooling + Injection Molding | 5000+ pcs | $10,000+ | <$2/pc | 4–6 weeks | Full-scale production |
How to Choose
- Exploration stage (dozens of parts): Go CNC. Speed matters more than cost.
- Pilot runs (hundreds of parts): Rapid tooling is the sweet spot—lower cost per part, plus reliable consistency.
- Market-ready (thousands of parts): Production molds are the clear winner. The upfront hit pays off quickly.
That medical startup followed a very typical path:
CNC prototyping (50 pcs) → Rapid tooling (300 pcs) → Production tooling (5000+ pcs).
Each step aligned with market needs, without wasted time or money.
Final Thoughts
CNC and injection molding aren’t rivals—they’re tools for different stages of the same journey. If speed is your priority, go CNC. If cost per unit is the goal, molding wins. If you need a balance, consider rapid tooling.
At RJC Mold, we support both CNC machining and injection molding (rapid and production tooling). We know how tight resources can be in the early stages, so our job is to match the right process to your current phase. If you’re weighing your options, let’s talk—we’ll help you find the most efficient path forward.
Continue Reading:
5 Design Pitfalls to Avoid When Switching Metal Parts to Plastic
