Having a reliable external injection molded components supplier on speed dial seems like a more common requirement for today’s medical device design engineer. However, prior to making that choice, there are a number of aspects to evaluate as it relates to molding and prototyping. This article reviews several considerations.



This part was designed by Vascular Solutions Inc. and is a catheter adaptor for a vascular medical application.

This part was designed by Vascular Solutions Inc. and is a catheter adaptor for a vascular medical application.

Injection molded plastic is omnipresent in today’s medical devices. It makes them light, ergonomic, and strong. It resists corrosion and protects sensitive circuitry. It is long-lasting, affordable, and, with hundreds of resins available, able to meet virtually any requirement.



Today, few medical device manufacturers are able to manufacture plastic parts in-house. Fortunately, the options for outsourcing, either domestically or overseas, have grown as well. The challenge is choosing a vendor that can meet the developer’s needs reliably, affordably, and in a timely manner.


Many factors influence product development and choice of outsourced parts vendor. Price is an important consideration, but factors like product design, quality, and consistency can be even more critical–especially in medical applications. In today’s fast-moving markets, eliminating delays in development and production can be equally important, particularly in regulated industries with strict testing and approval requirements.

In theory, the process of outsourcing plastic parts or prototypes is simple: present a design, define a timeframe, and choose the best price. In reality, it is far more complicated. Say, for example, that after several prospective vendors have presented bids, another suggests that, with a small change in a design, they could offer a significantly lower price. Is the change rejected, the lower bid accepted, or the process started over? Or a vendor offers a lower price if production can be delayed. Or, as sometimes happens, a flaw in your design is discovered after molds have been made. 

This part is a retaining ring; it holds a fluidic assembly together. The medical company that designed the part had it injection molded for prototyping.
This part is a retaining ring; it holds a fluidic assembly together. The medical company that designed the part had it injection molded for prototyping.

Potential problems can be even thornier if outsourced to an overseas vendor. A review in the March 2010 issue of Modern Casting magazine of the book Poorly Made in China by Paul Midler describes some of the potential issues. For example, prices can increase or quality may erode after a buyer is so deeply committed that changing vendors is impossible. This is not to say that outsourcing overseas cannot work, but it highlights more complexities of outsourcing. And even in the best of cases, supply lines are longer, communications can be slower, and changes can be difficult.

The fundamental problem is that, in choosing to outsource, direct control is sacrificed to leverage the specialized capabilities of the chosen vendor. The likelihood of unexpected problems can be minimized by taking advantage of the factors that can be controlled, and that means careful and thorough prototyping.



Prototyping is a multimodal process entailing methods ranging from quick, easy, and essentially free to more costly and involved. “Quick and free” provides less detailed information but is ideal for the earlier stages of part development. The more costly options, on the other hand, provide a wealth of accurate, real-world information. This level of detail is critical in the late stages of development when a company is preparing to commit time, money, and its reputation to full-scale production.

In the early stages of development prototyping, software can create virtual parts based on 3D CAD models and characteristics of the chosen resin. These virtual models can be challenged using techniques, like finite element analysis, to mimic various stresses. The output is, of course, approximate and limited by the stresses defined. The advantage is that virtual models can be easily tweaked and re-tested.


 Through a rapid injection molding, Tensys was able to build the prototypes it needed to support a new product development program.
 Tensys Medical Inc. often relies on prototyping to identify potential improvements in the design of its medical devices. But tight turnaround times and limited budgets have historically restricted Tensys’ ability to build functional prototypes. Fortunately, through a rapid injection molding, Tensys was able to build the prototypes it needed to support a new product development program.

In the middle stages of development, plastic models can be ordered (or produced in-house) using any of a variety of additive manufacturing methods, like stereolithography, selective laser sintering, or fused deposition modeling. These offer limited resin choices, and the resulting parts don’t have the structure of injection molded parts, so they may not be suitable for functional testing. Additionally, since they use additive processes, they obviously can’t identify potential moldability problems. But they are useful for testing fit and definitely have a place in the development process.

Functional testing usually requires prototypes that are structurally and materially similar to production parts. Fully automated CNC machining from 3D CAD models provides these by cutting solid parts from solid stock. These are cost-competitive with the layered additive prototypes and can be turned around in as little as one day. For larger quantities of parts, the best solution is rapid injection molding.


Rapid Injection Molding

Rapid injection molding produces injection molded parts in any of hundreds of resins. Like automated machining, it is affordable, can produce parts in as little as one day, and uses production resins and the same standard process as traditional injection molding. Further, since the resulting parts are molded, the process will help identify any potential moldability problems. These “production-like” molded parts let engineers test in harsh, real-world conditions and fine-tune designs that can then be outsourced (domestically or overseas) with relative certainty that the follow-on production parts will meet expectations.

In some cases, engineers may be tempted to prototype with steel tooling that can then be used for production. Whether done domestically or overseas, this can be risky. Domestically, it is both time-consuming and costly, and only beneficial if the prototypes test successfully and can go directly to production. Overseas, molded prototypes may be cheaper, but they are subject to all the risks mentioned in Midler’s book, and tend to lock the company into a vendor relationship earlier in the process than is desired.

The most insidious aspect of this approach is the temptation to protect the investment in hard tooling and accept flaws that might otherwise be corrected. In today’s medical market, the consequences of such an omission could be crushing. Rapid injection molding, on the other hand, is fast, inexpensive, domestic, and doesn’t discourage the fine tuning of a design. In addition, once a design is finalized, rapid injection molding for prototyping need not delay production. Rapid injection molding can be used as bridge tooling to produce 1,000 to 10,000 parts while the “high-volume” production molds are being made by the outsourcing supplier. In short, the same process that ensures that the prototype parts are “done right” can also help ensure that the production parts are “done now,” and in today’s environment, that is a powerful competitive tool.


Brad Cleveland is president and CEO of Proto Labs. The company is a provider of rapid custom CNC machined and injection molded parts. Cleveland can be reached at