A micromolded part sitting on top of a finger shows the relative size of such parts.

The design and placement of internal components for tiny medical devices is critical. And questions pertaining to micromolding are many. These include: How will the design proceed? Exactly how are parts manufactured and validated? And how do working parts interface with each other? Here are our Top 10 Tips to help guide you through the micromolding process.

Tip 1 — Distinguish between micro and miniature. Unfortunately, the micromolding industry does not clearly define the difference between micro and miniature parts. In general, though, it is safe to assume that a micromolded component yields 10,000 parts/lb; is less than 0.003 cubic inches in size; and weighs 0.04 grams or less. Parts a bit larger than this are usually considered “miniature.” Miniature parts need special consideration, too, but they typically use processes similar to larger parts, just scaled to their miniature size. A miniature part might have micro features that can be done with a standard process. Micro parts benefit from specialized technology designed specifically for their small size and detailed features. Micromolding also minimizes the runner system, which can be important should the application requires expensive resin.

Tip 2 — Oversize to understand. Sometimes it makes sense to “oversize” a microcomponent to better understand it. That’s because different part-size iterations can help you understand critical dimensions difficult to visualize otherwise. For instance, a change of only 0.0001 in. in a micro part can sometimes make a previously non-producible part into one that can be manufactured. Also, testing somewhat larger parts can help check things such as assembly fit and function and even materials. Budgeting for such testing can help ensure a manufacturable part and cut costs in the long run.

With part sizes starting at 0.003 cubic inches and smaller, most micromolded components need a microscope to see fine details.

Tip 3 — Study those shots. Material choice can make or break your micro program. Material use and runner requirements obviously affect part cost. It’s important to understand what a particular supplier can provide because special medical materials can cost thousands of dollars per pound and they may require minimum buys. Also, find out what percentage of the full shot is the part and what percentage is scrap. A part that is only 1% to 5% of the shot size may not be feasible because the part is too small compared to the over-all shot size. The use of multiple cavities can help offset material usage, but this may not always be an option due to tolerance variations between cavities. Experienced micromolders typically use one cavity, while controlling material usage. In this scenario, parts are about 60% to 80% of the shot size, which allows better control of the process.

Tip 4 — Banish tooling preconceptions. The micro process is not the same as traditional molding and thus the tooling differs. Tools for micromolding must be more reliable and accurate than those for conventional molding. Because standard moldmaking equipment may not be suitable, specialized equipment is often needed. Examples: cutters for 0.001-in. diameter wire or shapers for hard steel with a 0.002-in. diameter. Polishing and lapping, too, are specialized. It is possible to create tools now that years ago were almost unimaginable. Be sure to discuss tooling options with the supplier.

Tip 5 — Try to keep it simple. Micro parts have many of the same features as traditional molded parts such as gates, ventings, knit lines, and parting lines. But ejector pins may not be an option. Instead, pulling the mold apart in many directions with special slides or stripper plates may be the only way to eject the part. Success lies in how such features are handled. Keeping the part as simple as possible helps in the building of workable tooling.

Tooling for micro molding is not the same as traditional molding so specialized machines and tools often must be used to create reliable and accurate molds.

Tip 6 — Design for manufacturability. Drawing a great-looking part in CAD doesn’t necessarily mean it can be molded. We often work with OEMs with a component design critical to the success of a device, but the company does not know if the part can be manufactured. Don’t jump to conclusions without talking to a good supplier. Keep an open dialog about your requirements, what the part will do, and how it will function. This communication and keeping an open mind regarding minor changes in the design can often create successful parts regardless of the size.

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