Home / News / Silicone, TPEs find their way in medical micromolding industry

Silicone, TPEs find their way in medical micromolding industry

Aug 22, 2023Aug 22, 2023

New York — In some ways, the process of micromolding is a contradiction.

As medical and health care markets demand smaller and more precisely designed components, the micromolding industry grows in importance.

When the tiny parts are removed from a press cavity, they can defy physics — jumping into the air due to static electricity, or becoming unstable if the parts are not fixed in place properly.

There are critical symmetries to this minuscule manufacturing process as well.

As part sizes drop to micron levels, the risk to the patient drops. And as innovations in the industry continue, lifesaving procedures previously considered impossible become the norm.

"We believe that from an application standpoint for the addressable market, we expect and are betting that those operations will continue to grow," Jeff Kyle, CEO of Plastic Design Co., told Rubber News, a sister publication of Plastics News. "For the reasons we talked about, there is a continued push toward miniaturization and what can be used in advanced surgery.

"We think the overall market will continue to grow here," he said.

Shot weights in micromolding typically are between 0.1 to 1 micrograms, with tolerances of 10 to 100 microns.

"And you can just about walk through the body with the applications," Kyle said.

Heart valve surgery now is performed by feeding micromolded components through the femoral artery. Opthalmology and eye surgeries have improved with miniature medical components.

And cardiovascular parts, orthopedic implants and hearing aids all feature micromolded parts.

"The demand is definitely here," said Philipp Begert, global new product development director for Trelleborg Healthcare and Medical, part of Trelleborg AB and its Trelleborg Sealing Solutions business.

"Especially if we are going to smaller and smaller implantable devices," Begert told Rubber News. "And there are other devices — smart watches, diagnostic devices — that drive the need for the technology of smaller, precise, micromolded parts."

Although many more plastics than soft durometer rubbers are used in micromolding, liquid silicone rubber still finds a place in this very large industry filled with very tiny components.

Accumold was one of the first companies to introduce the process to the world in 1985, according to Paul Runyan, vice president of sales for the Ankeny, Iowa-based company.

As the history goes, Accumold was founded by two toolmakers who developed what Runyan called "the first micromolding press" in their garage.

Accumold continues to parlay its breadth of experience into the successful medical components provider it is today.

"We got into the silicone business about six years ago," Runyan said. "Some very large customers of ours asked us to do micro-silicone overmolding as a way to help them solve a bigger issue.

"We discovered there was a nice niche in silicone overmolding and parts. Now the silicone division is doing well and growing rapidly."

Accumold micromolds with both thermoplastics elastomers and silicone, as TPEs have become increasingly popular as an alternative.

"Whatever it is, our customers drive our research and development," Runyan said.

Trelleborg Healthcare and Medical also works in the micromolded silicone realm. The challenge here, Begert said, is in marrying two different materials together, like a plastic and a silicone.

"The capability of combining an LSR onto plastic — the ability to integrate materials together, taking two parts and making it one — is the next step," Begert said.

Founded in 1991 on the cusp of the micromolding revolution, Kyle's PDC is a specialty manufacturing company focused on precision injection molding in support of medical device and life science customers.

The company has a 20,000-square-foot tooling and production facility in Scottsdale, Ariz., and typically works in PEEK, PEBA and PEI with an ISO 13485:2016 quality system.

In today's medical component manufacturing environment, it is not just micromolding that requires competency.

An understanding of micro-injection molding trends, microfluidics and microplating is required.

"Part design is our customer's responsibility, and we work with a lot of life science OEMs," Kyle said. "They bring in the part design and we take it from there, designing the tools with our own tooling shop, and take it all the way up and through injection."

Micromolded parts can be found in electronic sensors and consumer wearables as well.

Components can range in volume from thousands to millions of parts per year, Accumold's Runyan said. "Really what we look for are strategic relationships with our customers," he said. "Our large customers make us a better company because they push the limit. The key is, can you hold high tolerances during high-volume runs?"

Manufacturing is coming back to North America, Runyan said, so supply chains are being on-shored accordingly.

"We are seeing manufacturing coming back, so people are moving supply chains back to N.A.," he said. "Parts are shrinking down in size as people want tighter tolerances.

"We are seeing our small little pond of the past ... starting to flood [with demand]."

Accumold sees about 60 percent of its business in medical and life sciences, with microelectronics also a part of the company's market shares.

"Microelectronics fluctuates year to year," he said. "Large projects can swing the number back in favor of microelectronics [over medical]."

Automation and artificial intelligence can play a big part in micromolding, as they provide a rich data set, PDC's Kyle said.

"When we talk about becoming more accurate, we think there is opportunity to do significantly more than we already do," Kyle said. "Predictive is a good word. Milliseconds and millipascals of force matter. The magnitude of the difference that matters in many cases is commensurate with the part that we produce."

The micromolding process depends on many metrics, according to Kyle, including short dwell time; low shear-stress on the polymer melt; homogenous material preparation before molding; and precision injection and ejection.

And it can be this last step, the degating of the part, that can be troublesome.

"Those are all valid as far as specifics, but I would say any secondary operations-like an assembly or degating operation-is more complex because of the inability of an operator to handle a part that is nearly sub-visible," Kyle said. "This requires a level of sophistication that other more upstream operations do not need to account for."

Kyle offered an anecdote from a materials engineer who once told him that when a part is oriented, "don't let it go."

"Keep it well-fixtured until it's ready to release," Kyle said.

Compressibility of the material — whether a TPE or a resin — relative to shot size is one of the biggest challenges, Trelleborg's Begert said from his office in Minneapolis.

"This is a big hurdle to overcome," he said. "This is where process knowledge comes into play. The validation and inspection of micro-components is challenging, and measuring can be difficult.

"For something that is barely visible on a tweezer, how do you inspect that? It could fly away with static, especially with LSRs. You try to remove the part and static electricity can make it seem like you are cheating physics. The part actually floats in the air."

One key moving forward for micro-injection and insert molders will be to bring a "complementary set of vertical competencies to the table," the experts said.

"Such that for the customer base, it becomes a simplified supply chain," Kyle said.

Accumold runs more than 175 micromolding injection presses, with 50 percent of them built by the company itself.

And experience in the industry tends to be the calling card for most competent micromolders.

"There are a lot of people buying a micromold press and claiming to be a micromolder," Runyan said. "But you really have to have the experience and have your own tool shop.

"We have about 60 tool makers, and they are the heart of the company. You need experience to make high-tolerance tools."

The injection press matters, as does quality ancillary equipment, he said.

"We've had well over 8,000 projects in production," Runyan said. "Having the confidence and experience is very important to show the customer that, hey, we have done this before and yes, we can handle a specific application.

"Everything is important in micromolding: the micro-features, micro-tolerances, micro-size, micro-everything."

Begert agreed that the quality of machinery is vital in micromolding.

"You need a high degree of precision in small shot sizes," Begert said. "Plastics in micromolding have quite high-shear rates.

"It all comes down to the size of the injection screw or plunger. With small sizes, only a handful of machines can do that," he said.

Manufacturers should take care when switching between LSR and TPEs, as TPE is relatively warm when it enters a cooler mold. Silicone is the opposite, as it is a thermoset that is relatively cool when it enters a hot mold.

"In a different molding aspect, there are challenges going from plastic to silicone as there is a thermal difference between the material and mold," Begert said.

He added that working with a larger firm like Trelleborg can bring in critical networking solutions for customers.

"We want to work with our customers as early as possible in the process. Customers can be very innovative," Begert said. "And if we find that we cannot manufacture it, we need to have suppliers involved. We are specialists in materials and process. And we can bring these supplier relationships to the customer.

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