When designing a medical device, every decision matters. But when it comes to manufacturing, few decisions are as pivotal as choosing between CNC machining and injection molding.
Both methods take essential roles in medical device production, yet they serve different needs, timelines, and budgets. Understanding which process fits your device can mean the difference between a smooth launch and a costly redesign.
Let’s break down the differences, advantages, and trade-offs, and explore where each shines in the journey from prototype to production.
Understanding the Basics
CNC Machining: Precision Through Subtraction
CNC (Computer Numerical Control) machining is a subtractive process, meaning it starts with a solid block of material (metal or plastic) and removes layers with high-speed tools until the desired shape emerges.
In medical device development, CNC machining is prized for its accuracy and flexibility. These machines can rapidly produce prototypes or low-volume components that match exact design tolerances, often within a tolerance of ±0.001 inches.
Common applications include:
The key advantage? Speed and precision, especially in the early stages of product development.
(For a detailed guide on CNC machining standards, see The American Society of Mechanical Engineers - ASME.)
Injection Molding: Efficiency Through Repetition
Injection molding is the opposite. It’s an additive, high-volume process where melted plastic is injected into a custom mold cavity and cooled to form the final part.
Once the mold is made, each part takes just seconds to produce, labeling this process as the gold standard for mass production.
Injection molding is used across countless medical products:
The key advantage? Scalability and consistency. When your device moves from prototype to market, injection molding ensures every unit looks, feels, and performs identically.
Speed vs. Scale: When Time Matters More Than Volume
In early development, speed is everything. Before you even think about production tooling, you need to validate the design, confirm ergonomics, and ensure your prototype performs under realistic conditions.
That’s where CNC machining wins.
You can think of CNC machining as the test bench of medical device design; it allows you to experiment and refine before committing to costly mass production.
Injection molding, by contrast, is best once the design is frozen. Creating steel molds can take 4–8 weeks and cost tens of thousands of dollars, depending on part complexity. But once that’s done, production becomes extremely cost-effective on a per-part basis.
In other words:
Cost is often the deciding factor, but it’s not always as simple as “CNC is expensive, molding is cheap.”
CNC Machining Costs
Injection Molding Costs
(For a cost analysis calculator, check out Protolabs’ cost comparison tool.)
Material Considerations
Material choice can also sway the decision.
CNC-Compatible Materials
CNC machining supports a wide range of biocompatible materials, like 316L stainless steel, titanium, PEEK, and Delrin (POM). These are commonly used in:
Injection Molding Materials
Injection molding is ideal for thermoplastics such as polycarbonate (PC), polypropylene (PP), PEEK, and TPE (thermoplastic elastomers) materials all found in wearables, disposables, and housings.
Medical-grade plastics can even be pre-certified for FDA or ISO 10993 biocompatibility, speeding up regulatory approval.
(For reference, see ISO 10993 biological evaluation standards.)
Surface Finish and Tolerances
For surgical tools or implant components, the surface finish can determine not just aesthetics but also hygiene and usability.
CNC machining leaves smooth surface finishes straight from the mill, and components can be polished or anodized afterward. It’s perfect for instruments that require both form and feel.
Injection molding, however, offers design versatility; texture, matte finishes, and micro-patterns can be built directly into the mold. That makes it ideal for consumer-facing devices, where grip and appearance matter as much as function.
Risk and Regulatory Implications
In medical device design, manufacturing isn’t just an engineering decision; it’s a regulatory one.
Regulatory bodies, like the FDA, require manufacturers to document and validate every step of production. Changes to your manufacturing method after design freeze can trigger revalidation, delays, and even new regulatory submissions.
That’s why early-stage teams often use CNC machining to gather verification data (dimensions, strength, usability) before moving to injection molding for final design validation.
Once the device is in production, consistency becomes king, and injection molding’s repeatability helps meet FDA and ISO requirements with minimal process drift.
Real-World Examples
Case 1: Diagnostic Housing Development
A startup developing a portable diagnostic device used CNC machining to produce its first 50 enclosures. The early feedback from clinicians led to ergonomic adjustments, including contour changes and better cable routing.
Once the design was finalized, they switched to injection molding. The upfront tooling cost ($35,000) was offset after the first 5,000 units, reducing per-part cost by over 90%.
The team’s ability to fail fast with CNC and scale fast with molding shortened their time to market by nearly six months.
Case 2: Surgical Instrument Prototyping
A manufacturer of minimally invasive surgical tools used CNC machining to build test handles and tip assemblies in stainless steel. The prototypes were tested under repeated sterilization cycles, validating material selection and performance.
When transitioning to injection molding for production, they opted for glass-filled nylon to reduce weight and cost, keeping the validated geometry and user-tested ergonomics.
This hybrid approach ensured that performance data from the CNC prototypes carried seamlessly into the final molded product.
When to Use Both
Many successful medical device companies don’t pick one method; they use both strategically.
Some even use bridge tooling, temporary aluminum molds for low-volume molding, as a transition step between prototyping and full-scale production.
This hybrid workflow minimizes downtime, spreads out costs, and ensures every stage of the design process builds on proven data.
(For more on bridge tooling, see Xometry’s guide to low-volume molding.)
Looking Ahead: Hybrid Manufacturing and Innovation
New technologies, like hybrid CNC–additive manufacturing and digital mold simulation, are blurring the lines between prototyping and production. Engineers can now 3D print inserts for molds, simulate fill patterns, or CNC-machine complex geometries that were once impossible.
These innovations are helping startups and OEMs reduce iteration time, improve manufacturability, and maintain compliance, all while controlling cost.
As the medical device industry continues to evolve, the smartest companies won’t simply choose one process over the other; they’ll engineer a balance that supports both innovation and scalability.
Final Thoughts
Choosing between CNC machining and injection molding isn’t about which is “better.” It’s about matching the method to the stage of your device’s life cycle.
Both have their place in the journey from sketch to sterile packaging. The key is knowing when to switch, and ensuring every step of the process aligns with the ultimate goal: safe, reliable, and accessible medical technology.
If you have questions about the development process, feel free to reach out for help. We do hundreds of free consults every year to help guide innovators along their path of device development.