By Sean Fenske, Editor-in-Chief

The world of healthcare continues to get smaller as patients and their physicians have a significant interest in minimally invasive solutions that contribute to better outcomes. As such, medical device manufacturers must respond to the demand with technologies that meet this need. In turn, they rely on their supply chain partners for capabilities and innovations that help them achieve the reduction in size of their products.

One critical aspect of this trend involves molding components at such a small size, certain details can’t even be seen with the naked eye. Micromolding provides miniaturized plastic parts that are used in the aforementioned minimally invasive devices. However, while the molded components appear similar to their larger, injection molded counterparts, a very different technique is used for their fabrication that requires a unique skill set and testing/inspection methods.

To help explain the differences between traditional molding and micromolding is Patrick Haney, R&D Engineer at MTD Micro Molding. In the following Q&A, Haney provides insights on a variety of topics involving this manufacturing process. He offers clarification on when micromolding should be used, material considerations, and how small components can be made.

Sean Fenske: What are the primary differences between traditional injection molding and micromolding?

Patrick Haney: Micromolding is not simply a smaller version of traditional injection molding—it’s a fundamentally different discipline that requires a different mindset, deeper technical knowledge, and a much greater sensitivity to process nuances. One of the key distinctions lies in material behavior. On the micro scale, rheology and viscosity behave differently. Non-Newtonian fluid characteristics shift significantly, and this alters how you develop a stable injection molding process (Figure 1). These changes affect the microstructure of the molded material, which can lead to variations in properties that wouldn’t occur at the macro scale. As a result, micromolding isn’t just about miniaturization—it’s about engineering for a completely new scale of physics and materials science.

Another major difference is visual inspection is no longer a reliable quality check. A good part and a defective one might look identical to the naked eye. Take thermocouple placement, for example—it may appear correct, yet the sensor could be gathering data from a point several steel plates removed from the actual heat zone. That readout isn’t what it seems—and you’d never know without hypothesizing, testing, and validating through rigorous experimentation. This is the reality of working at the micro scale: many problems are invisible and must be detected through data analysis, expert intuition, and a deep understanding of how materials and machinery behave under precise conditions.

When challenges arise in conventional injection molding, it’s typically sufficient to troubleshoot within a single primary system: process, mold, robotics, die heaters, camera systems, and so on. Because of the nuanced sensitivity of micromolding, however, we’ve found it’s critical to use a systems thinking approach, analyzing the interactions and influences. How does the process impact the mold? How does the mold interact with the robotics? We’ve solved the most complex challenges because our team approaches the manufacturing process as a combined, interconnected system. For example, we once solved a part deformation issue by analyzing the interplay between the mold, die heater, and process settings (Figure 2). These kinds of challenges are where micromolding lives, and they demand a level of systemic thinking that’s simply not required in most macro-scale work.

What makes all of this possible is the culture and cross-disciplinary expertise we’ve built. At MTD, our team members don’t operate in silos. Molding engineers understand tooling intricacies. Metrology experts are fluent in material science. Toolmakers think like designers. This integrated knowledge base allows us to manage the “chaos” that naturally exists at the micro scale, where even factors like steel density, humidity, or ambient vibration can affect final part quality. We expect these variables and build systems to manage them. If we can’t control them directly, like in fitting a tool, we compensate through polishing, grinding, and precision adjustments by hand.

Micromolding also requires a different level of precision in mold making. The tolerance stack-up is so sensitive that two inserts cut from the same CAD file, on the same machine, on different days, might behave differently due to the slightest variation in steel. These differences can’t be seen, but they are appreciated when the inserts are assembled. That’s why our post-machining processes are just as critical as our CNC programming.

It’s important for OEMs to recognize when a part has moved beyond traditional injection molding boundaries. Knowing general guidelines for plastic part design, mold functionality, and material selection is an excellent start. But when your application begins to push those limits—when feature sizes shrink, tolerances tighten, or performance depends on microscopic detail—it’s time to work with a micromolder.

Finally, micromolding also introduces a new definition of scale. In many cases, a part design might be smaller than the tolerance window for a typical macro part. Handling, inspecting, and even orienting these parts for inspection becomes a specialized skill. An inexperienced inspector might take hours to assess something that a trained micromolding expert can inspect in minutes. That’s the level of expertise required. Every aspect—from concept to production—must be adapted to this scale, because at the micro level, everything behaves a little differently.

Fenske: For what applications is micromolding being used for medical device manufacturing?

Haney: Micromolding is increasingly being used across a wide range of medical device applications, particularly where there is a need for small, highly functional, and complex components. At MTD Micro Molding, we often say any application in the medical device or healthtech space can be a candidate for micromolding, as long as the design or functional requirements push the limits of what’s traditionally considered feasible in plastics manufacturing. This includes parts with ultra-fine features, tight tolerance needs, or material performance demands that challenge the norms of conventional injection molding.

In many cases, when a medical device is made up of multiple components, the most critical part—the one responsible for precision, performance, or safety—is often the smallest. That’s the component most likely to benefit from micromolding. These parts tend to be not only physically small but also highly complex, requiring intricate geometries or exacting dimensional control that can’t be achieved through standard molding practices.

Micromolding becomes essential when an application starts “breaking the rules” of conventional injection molding—whether due to feature size, material behavior, tolerances, or performance in use. And while the core focus is on medical devices, we find this applies just as much to medtech-adjacent applications as it does to regulated Class I–III components. Whether it’s a minimally invasive surgical tip, a diagnostic insert, or a wearable drug delivery part, the common thread is the need for reliable, reproducible results at an incredibly small scale.

If your design pushes boundaries, challenges conventional limits, or demands more from the material or molding process than usual, that’s where micromolding truly excels.

Fenske: Are there material restrictions with micromolding? Are there materials you can’t use?

Haney: At MTD Micro Molding, we approach material selection with precision and respect for the complexities it introduces at the micro scale. While most thermoplastics can be used in micromolding, certain materials require closer scrutiny, especially those that release corrosive outgassing or degradation byproducts under stress. Since micromolding involves extremely high shear rates and ultra-small flow channels, materials are pushed to their limits more quickly than in conventional molding. If those limits are crossed, the byproducts can damage steel tooling and compromise part quality.

That said, there are no absolute material exclusions in micromolding. Every material has its unique characteristics, and success depends on how it pairs with the part geometry and mold design. In micro, the relationship between material, part design, and tooling must be tightly coordinated. In fact, thoughtful material selection can often expand what’s possible in part design, allowing us to solve complex challenges through a combination of processing expertise and smart tradeoffs.

The boundaries of what’s possible in micromolding shift depending on how well these three elements—material, mold, and application—are aligned.

Fenske: What’s the smallest you can get with micromolding? What are the current challenges in going smaller?

Haney: At MTD Micro Molding, we’re often asked, “What’s the smallest you can mold?” And while our tooling and molding capabilities continue to push the boundaries of miniaturization, the real challenge—and true measure of success—lies in our ability to accurately validate those features through precise measurement.

In micromolding, achieving tight tolerances is critical. For example, when working with materials like polycarbonate, a feature tolerance of ±0.0005 inches (±12.7 µm) requires the tooling to be machined to a tolerance of ±0.0002 inches (±5 µm). That level of tooling precision sets the stage, but confirming those results is just as important as achieving them.

To verify such tight tolerances, measurement systems must be significantly more precise than the features they measure. At MTD, we follow the 10:1 rule, meaning a measurement system should have a resolution ten times finer than the tolerance it is verifying. For example, to accurately measure a ±45 µm tolerance, the system must have a resolution of at least ±4.5 µm. This approach ensures we’re not just hitting the numbers—we’re confidently verifying them.

This level of precision is essential not only for ensuring dimensional accuracy but also for passing gauge repeatability and reproducibility (GR&R) studies. GR&R evaluates whether a measurement system is both repeatable (consistent results from the same operator and equipment) and reproducible (consistent across different operators and conditions).

For critical micro-scale components, a validated measurement system is not just a best practice, it’s a necessity. It ensures dimensional data is reliable, supporting informed decisions throughout development and production. Without this step, measurements may seem accurate but can vary depending on equipment or conditions—a bit like using a “rubber ruler” that subtly changes every time it’s used.

While molding ultra-small features is an impressive technical feat, the true value lies in being able to measure and confirm those features with the same level of rigor.

Fenske: Earlier, you mentioned testing is different with micromolding. What about verification? And how do the techniques and technologies differ?

Haney: In micromolding, testing and verification are not simply scaled-down versions of conventional methods—they require fundamentally different strategies. The parts we mold can be incredibly small, often with functional features no larger than a dust particle, which presents unique challenges in both processing and measurement. Traditional scientific injection molding approaches, such as determining gate freeze time by weighing parts, often fall short at this scale. In many cases, the parts are so light that their weight can’t even be reliably measured using conventional equipment.

To overcome these challenges, our engineers must adapt techniques to suit the scale. For instance, relationships between viscosity, shear rate, and flow behavior behave very differently at the micro level. This means our process development often relies on indirect methods, advanced sensing, and custom tools to gather the data we need. High-resolution metrology systems like CT scanning become essential to verify tight tolerances and feature dimensions that can’t be accessed with traditional measurement tools.

Fenske: What are some of the most misunderstood aspects of micromolding, and how do you help to clarify these?

Haney: One of the most common misunderstandings about micromolding is the level of precision engineering required. Because parts are so small, it’s easy to assume the work is simple or quick. But in reality, every micron matters. A customer may request a dimensional change as small as two ten-thousandths of an inch—something invisible to the naked eye—but implementing that change involves a highly complex chain of events. It requires reworking tooling components, ultra-precise fitting of the tool, new sampling iterations, and tailored process adjustments. What seems like a minor tweak on paper can translate into a significant engineering effort.

This is why part drawings, tolerances, and up-front collaboration matter so much. Drawing tolerances not only influence the technical feasibility of a part but also directly impact program cost and lead time. At the micro scale, tolerance stack-up across the tool assembly becomes even more critical, and misalignment at this level can derail a program. The most successful programs are those that begin with open, collaborative dialogue around realistic tolerances, material behavior, and functional goals. It’s okay not to know every detail at the outset, but working with a micromolder early helps align expectations and de-risk the path forward.

In many cases, we’re brought in to rescue projects that struggle because this alignment didn’t happen from the start. Programs with moving design targets or shifting specs create serious challenges in micromolding. That’s why we emphasize extensive due diligence and design for manufacturability before quoting takes place. Micromolding pushes the boundaries of what’s possible, and that inherently comes with more unknowns—and more risk. But with the right expertise, the right culture, and the right mindset, those challenges can be transformed into opportunities for breakthrough success.

Click here to learn more about MTD Micro Molding >>>>>