How to Use Ultra-Precision Micro Tools, Molding and Automation to Unlock High-Volume Medical Device Miniaturization

Medical device companies play a crucial role in enhancing health care by developing innovative technologies that not only save lives but also improve patient comfort. These advancements lead to shorter hospital stays and faster recovery times, ultimately benefiting both patients and health care providers. In this pursuit, R&D engineers are designing thermoplastic, bioresorbable and liquid silicone rubber (LSR) parts that present significant molding challenges due to their miniature dimensions, ultra-thin walls, tight tolerances, sharp features and complex geometries.

The resins selected for many of these parts are high-temperature engineering grades with fillers or thermally sensitive bioresorbable resins, further complicating the processing methods. The volume requirements for such parts start low during the R&D phase but can quickly ramp up to millions (if not hundreds of millions) per year. Medical device companies require help from innovative mold builders and molders to not only help them manufacture seemingly impossible parts but also to manufacture them at high volumes, maintaining high yield rates.

To help medical OEMs achieve their goals of sustaining, improving and saving lives, the tooling, molding and automated assembly experts at Nissha Medical Technologies – Isometric Micro Molding Center of Excellence in New Richmond, WI, have developed ultra-precision tooling solutions falling within five key areas:

Affordable Sub-Micron Precision Tooling

Designers tasked with inventing life-saving medical devices are engineering plastic components with extreme precision. As boundaries continue to be pushed, they are demanding part tolerances of less than +/-9 microns (0.00035"). While their corresponding assemblies require even stricter positional tolerances, clocking in at less than +/- 5 microns (0.0002"), which requires the manufacturer to be capable of producing tooling with a precision of +/-1 micron (0.000039"). Pioneering part designs feature intricate elements like sharps and channels measuring below 3 microns (0.000118").

These precise numbers present a major challenge to traditional moldmakers and molders. Achieving such precision is a formidable task, especially when working with plastics, which pose even greater challenges compared to steel. The majority of moldmakers globally adhere to steel tolerances within the realm of +/- 0.05mm (0.002"), with only the most exceptional shops achieving tolerances as tight as +/- 0.002mm (0.000079"). However, these standards, while impressive, fall short when faced with the complexities of molding intricate and demanding components for low volumes, and even more important for high volumes.

It's the fusion of meticulous engineering and advanced tooling that empowers the seamless integration of diverse components, propelling the frontier of medical innovation.

To circumvent the limitations of traditional tooling, Nissha Medical Technology’s micromolding experts have pioneered a proprietary methodology for constructing tooling that is below +/- 0.001mm (0.000039") in precision, involving micro, micron-toleranced processes, using state-of-the-art five-axis micro machining, micro wire EDM and micro sinker EDM technologies. Crucially, this innovative approach doesn't substantially escalate the cost of tooling, presenting a solution for achieving unparalleled precision at an affordable price.

Achieving sub-micron tooling precision at an affordable price requires:

• Expertise in Precision Tooling: Individuals with a wealth of experience in constructing sub-micron precision tooling play a pivotal role in achieving affordability without compromising on quality.

• Cultural Emphasis on Precision: Fostering a culture where a fraction of a micron matters ensures a commitment to surpassing a mere +/- 2 micron accuracy standard, emphasizing the importance of meticulous precision.

• Comprehensive Metallurgical Knowledge: A deep understanding of metallurgy, encompassing metal selection, metal machining, costing and heat treatment, is indispensable for optimizing the tooling process and managing costs effectively.

• Cutting-Edge Machining Technology: Utilizing state-of-the-art ultra-high-speed 5-axis machining, micro EDM and micro wire EDM machines, all well-maintained, is essential for achieving the required sub-micron precision.

• Effective Monitoring and Control Systems: Implementing advanced tool machining monitoring and control systems ensures continuous oversight, contributing to the reliability and precision of the machining processes.

• Optimal Environmental Conditions: Operating in a temperature-controlled environment is crucial for maintaining consistent conditions that are conducive to achieving and sustaining sub-micron tooling precision.

• Rigorous Inspection and Quality Control: Establishing extremely diligent tool inspection and quality control systems helps identify and rectify any deviations, ensuring the final product meets the stringent sub-micron standards.

Micro Size and Features

Designers of life-saving medical devices are pushing the boundaries of miniaturization. They require plastic parts that are less than 0.0005g in weight with micro features. Manufacturing tooling for such parts requires moldmakers with more patience and skill than the most precise Swiss watchmakers.

Nissha Medical Technologies' highly skilled toolmakers in New Richmond successfully built tooling for a part that weighs 0.00004g with 75 microns (0.003") wall thickness. Accomplishing this task necessitated the utilization of micro sink EDM and micro wire EDM, employing wire with a diameter less than 30 microns (0.0012"). In addition, the team utilized its knowledge as subject matter experts, years of experience and Nissha Medical Technology’s defined micro process of five-axis milling, sinker and wire EDM equipment. Also, the implementation of innovative solutions such as micro EOAT, gate trimming and vision inspection systems was imperative for successful execution.

In medical device manufacturing, OEMs often require larger components that incorporate intricate micro features, such as microchannels used in microfluidic applications. To illustrate, consider the overall size of a component roughly the same as a U.S. quarter, featuring a microchannel that transitions from a depth and width of 250 microns (0.010”) down to 3 microns (0.000118”). To put this into perspective, the diameter of a human hair is approximately 100 microns (0.004”). Now, envision a piece of steel that is merely 3% the thickness of a human hair. Maintaining that piece of steel is a remarkable challenge, as it could be effortlessly wiped away with a simple swipe of a finger. 

Nissha Medical Technologies has pioneered a proprietary methodology for constructing tooling that is below +/- 0.001mm (0.000039") in precision, involving micro, micron-toleranced processes, using state-of-the-art five-axis micro machining, micro wire EDM and micro sinker EDM technologies.

Such micro features have become a necessity for many life-saving diagnostic applications and to enable the manufacturing of such devices, Nissha Medical Technology’s team has learned how to manufacture intricate high-cavitation tooling, inject plastic so as not to deform the micron-thin steel, inspect the parts and maintain the tools. The successful execution of this task requires proficiency in the fabrication of sub-micron precision tooling, utilization of high-precision molding machines characterized by single-digit millisecond response times, a profound comprehension of polymer rheology — particularly the impact of viscosity curve slope on flow distribution, adept implementation of advanced velocity profiling techniques, deployment of sophisticated laser vision inspection systems with 28000x zoom capabilities and the establishment of a robust tool preventive maintenance program.

Complex Side Actions

Many life-saving medical plastic parts require features that have undercuts. These undercuts require slides, lifters and collapsible cores to be able to eject the parts from the tools successfully. Complex side actions are exponentially more difficult as the part size gets smaller. In one example, the part is the size of a U.S. quarter and has multiple features that go against the mold opening direction. This part would have been deemed impossible to mold by conventional methods.

Nissha Medical Technologies developed a mold with 14 CAMs and 25 moving pieces of steel in a 1 cubic inch footprint — to mold and eject this part and enable a life-saving procedure. The accomplishment of this task necessitated the capability to manufacture sub-micron precision tooling, the ingenuity of a creative and innovative tool designer, proficiency in manufacturing and assembling micro tooling inserts and the integration of micro actuators.

Ultra-Thin Wall Sections

Thermoplastics are non-Newtonian materials. As they flow through channels in an injection mold, the material near the walls solidifies, which effectively reduces the size of the channel. To mold thin walls, high pressure and high speed are necessary. There was a time when designers were told not to design plastic parts with wall thicknesses less than 1mm (0.040"). Now, medical device OEMs are designing plastic parts such as cannulas that have wall thicknesses 0.1mm (0.004"), 10x smaller.

To mold such geometries, injection pressures over 60,000 psi can be required. These parts have core pins that must withstand these high pressures. Nissha Medical Technologies’ Isometric Micro Molding team has developed a proprietary solution to injection mold cannulas with wall sections less than 0.025mm (0.001") and aspect ratios greater than 250:1. Not only do these features have to be created in steel, but they also cannot be molded with short shots or flash.

Some solutions require thin wall sections with highly viscous materials such as PEEK. Material suppliers recommend that the wall section for PEEK should not be less than 0.020". One part was molded out of PEEK and has a wall section that is 0.007". PEEK is a highly rigid material, at a thickness of 0.007" PEEK is flexible.

By developing a solution to build tight-tolerance tooling for PEEK and developing a proprietary process to mold PEEK at 0.007" and aspect ratios greater than 150:1, Nissha Medical Technology has enabled medical OEMs to invent solutions that were once deemed impossible. Molding extremely thin-wall parts requires advanced knowledge of polymer rheology and processing, a deep understanding of the effect of temperature and shear rate on shear viscosity, the effect of pressure on the transition temperature of thermoplastics, innovative tooling techniques to support thin steel features and cores, extremely high pressure and high response molding machines, and sub-micron precision tooling.

Automated High Precision Assembly

Emerging medical advancements demand intricate assemblies comprising both sizable and minute components. These complex processes entail handling fragments smaller than 0.001g and precisely integrating them with an accuracy of +/- 0.001mm (0.000039"). The integration of such diverse elements necessitates a paradigm of sub-micro precision tooling and fixtures, enabling the realization of stringent tolerances in automated assembly.

This specialized tooling not only facilitates the manipulation of minuscule parts but also ensures their seamless incorporation into larger structures, elevating the precision and reliability of intricate medical technologies. It's the fusion of meticulous engineering and advanced tooling that empowers the seamless integration of diverse components, propelling the frontier of medical innovation.

It is the responsibility of tooling and polymer experts to innovate to enable medical device OEMs to push the boundaries of miniaturization.