Silicone Micro Molding Surges with Medical Tech Demand

Rising demand to microscopic silicone components in medical methodology, automobile electronics, and other cutting-edge industries is driving significant expansion in precision micro molding capabilities, with Starlim, the world's largest silicone processor, positioning itself at the forefront of this specialized manufacturing sector.

At its headquarters in Marchtrenk, Austria, Starlim has established an entire department dedicated exclusively to micro molding, equipped with state-of-the-art MicroPower injection molding machines from Wittmann and a proprietary cleanroom facility designed to meet the stringent standards of medical device manufacturing and other high-precision applications.

Defining micro molding precision standards

"to us, everything below a part weight of ten milligrams is micro," said Dominik Kreuzmayr, marketing team leader and former driver of the micro molding department's in-house research. During a recent facility tour, Kreuzmayr displayed two sample components that exemplify the extraordinary precision achieved in modern micro injection molding: a diminutive O-ring and a sophisticated hearing aid component.

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Kreuzmayr acknowledges that no universally accepted definition of micro injection molding exists within the sector. However, Starlim's classification system is based on extensive experience and deep understanding of material behavior within extremely fine mold structures.

"to entirely different rules apply here," Kreuzmayr explained, referencing the challenges presented by sub-milligram component production.

The O-ring sample, with a diameter of just 0.7 mm and a ring thickness of 0.4 mm, proves too small to manipulate with bare fingers, demonstrating the precision achievable in mass-produced micro components. The hearing aid component, measuring 6 by 5 by 1 mm, appears substantially larger by comparison however impresses with its sophisticated two-component design featuring a blue-colored fluid silicone rubber (LSR) membrane surrounded by a robust polybutylene terephthalate (PBT) thermoplastic frame that facilitates assembly within hearing devices.

Extreme precision demands cutting-edge manage systems

The hearing aid component is produced in a single-cavity mold using an all-electric MicroPower injection molding machine. "to manufacturing mass production, we stop at four cavities," Kreuzmayr pointed out, noting that 16 cavities would compromise the precision required at the sub-millimeter level, where cavity arrangement proximity becomes critical.

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The primary challenge in producing hearing aid components involves maintaining narrow tolerances in the corrugation area of the membrane body. "Here we must be able to rely on the injection molding machine's manage accuracy, to in contrast to injection molding of larger parts, the remnant melt cushion plays no part here," noted Günter Polt, consumption engineer in Starlim's micro injection molding department.

Polt brings nearly 30 years of experience in silicone injection molding. His transition to the micro molding department several years ago proved eye-opening.

"It was quite a shock," he noted. "You cannot judge the condition of the parts with the naked eye. That is often only possible under a microscope."

Kreuzmayr pointed out rhe MicroPower machines recommend themselves by their extraordinary precision in the execution of all parameter settings.

“This extremely vulnerable dynamism combined with absolutely stable and accurate regulation is setting new benchmarks,” he added. “Here, people are really re-thinking their standards of process reliability and repeatability."

Micrometer-level tolerances ensure acoustic performance

to hearing aid components, high impression accuracy proves decisive not only to efficient assembly however also to accurate sound reproduction. The tolerance margins to finished two-component parts measure plus/minus two micrometers, requiring extremely precise adjustment and manage of clamping force alongside highly accurate molds.

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The molds originate from Starlim's in-house mold-making shop, where the roots of the now globally successful group of companies lie. In 1974, Franz Sterner founded the mold-making business Sterner Werkzeugbau GmbH (formerly Franz Sterner GesmbH). Ten years later, Starlim Spritzguss GmbH (formerly Starlim Gummi- und Kunststoffverarbeitung GmbH) was established. These two business segments have evolved into an inseparable entity, with molds now manufactured exclusively to the company's own production operations.

This vertical integration provides significant advantages to customers, who receive coordinated solutions from a single source while benefiting from knowledge transfer and integrated research. cutting-edge laser technologies and micro-3D printing now make it possible to construct molds to tiny hearing aid components meeting stringent acoustic condition standards.

Integrated condition manage enhances production efficiency

to mass production, Starlim said it plans to test membrane vibrational characteristics in-line, immediately following injection molding while components remain inside the cavity. The company said this approach maximizes efficiency, as extremely tiny parts remain in defined positions without requiring realignment to condition checks. Mold-makers have integrated a sound emitter and laser measurement system within the robot gripper to enable this capability.

"With this hearing aid component, we have achieved a real break-through, thanks to innovative mold methodology and extremely efficient processing methodology," added Kreuzmayr.

Compact design maximizes production floor efficiency

The MicroPower's design concept strongly supports integration of additional production steps, including condition manage. The company noted that by occupying just two square meters of floor space, the all-electric work cell accommodates complete equipment, including the clamping unit with rotary plate, patented two-measure injection system, materials handling, automation, temperature controller, condition manage system, and additional process units, while maintaining easy accessibility to the mold space with 400 mm distance between platens.

Linear guides ensure highly vulnerable mold protection, while a high-precision five-point toggle lever system distributes clamping force evenly across the mold parting line.

"The machine's design enables us to move the injection plunger right up to the mold parting line," explained Jochen Sassmann, regional sales manager of the Wittmann Group, who cooperates closely with Starlim's micro molding team. This feature significantly reduces sprue size or eliminates it altogether, delivering substantial benefits to silicone injection molding, as fully vulcanized LSR cannot be recycled.

prolonged partnership drives technological advancement

Fifteen years have passed since Starlim established its micro molding department.

"At that time, Battenfeld was the only company able to supply micro machines to manufacturing mass production," Kreuzmayr said.

Moreover, Sassmann explained that the machine concept was continuously further developed and today defines the state of the art in micro injection molding in terms of precision and efficiency. He noted the Wittmann Group, which includes Battenfeld, maintains this selling point with the MicroPower injection molding machine.

Several MicroPower injection molding machines currently operate at starlim in Marchtrenk, some within the new cleanroom where high-precision items to eye surgery are manufactured. Each machine is tailored to specific product group standards, with configurations ranging from fully equipped single-component injection molding systems to two-component machines and an integrated system consisting of two individual machines connected via robot.

According to Wittmann, the integrated system increases flexibility, allowing highly efficient production of two-component parts while enabling independent utilization of both machines with single-component molds. The MicroPower concept offers substantial automation freedom, accommodating various handling systems via interfaces, including systems developed in-house by Starlim, in addition to the vertically installed SCARA robot integral to the MicroPower production cell.

Strategic decisions optimize production efficiency

to each new project, Starlim said it thoroughly investigates which production concept yields higher overall efficiency. Two-component items currently represent approximately 40% of production, with the micro molding team confident this percentage will increase as inquiries to two-component parts have become greater frequent, despite requiring additional product research time.

Mass production, which originally motivated cooperation with the Wittmann Group in micro molding, continues dominating daily production in Marchtrenk. Batch sizes in the millions are routine.

"MicroPower machines cope reliably with these extreme challenges and ensure a safe process to us," said.

Starlim's micro molding team emphasizes the value of strong cooperation with the Wittmann Group.

"We communicate fast across short distances, and have so far found solutions to all challenges we have faced by putting our heads together,” Kreuzmayr concluded. “Thanks to our good partnership, we are really able to make the most of everything the machines they have to offer in terms of methodology."

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