In recent years, those within the manufacturing industry have become increasingly likely to come across micro moulding – a specialised manufacturing process that shapes and forms extremely small thermoplastics. Finished components can weigh less than one gramme and measure just a few millimetres across. Even if not directly involved in the process, at the very least manufacturers will have encountered components created in this way. For instance, micro moulding is used to make components for smartphones. In the world of medicine, it can support the creation of small and complex devices, including stent delivery systems, microcatheters and guide wires.
Yet micro moulding is not without its challenges. For one, it requires specialised equipment and quality control for tiny parts that can often be damaged or lost in transit. And the principles that typically govern the moulding of larger parts don’t always apply. With micro moulding set to surge in popularity as the industry continues to expand, how can CMOs navigate these complexities?
Cost vs benefit
Before starting any project, CMOs should ensure everyone in the team understands what they are working towards, says Davide Masato, associate professor at the University of Massachusetts Lowell’s Francis College of Engineering. Namely, it should be clear whether they’re dealing with parts that are shrunk in their overall volume and dimensions, or parts with conventional sizes that have some features or tolerances at the microscale.
“We are talking about plastic products that would be micro-injection moulded,” he says. “The distinction between the type of products is important because it leads to different design, tooling and quality control considerations.”
And once teams are clear on the requirements, their next challenge is often to explain themselves to OEMs. “Medical device manufacturers commonly struggle to justify micro moulding,” warns Masato. The small size and intricacy of the parts being made often means that production is costly.
“The need to work with a limited number of specialised contract manufacturers and the higher machine investments can create hesitation,” he says. “Additionally, micro-injection moulding machines have limited shot size and mould clamping areas, so moulds are typically smaller and have a limited number of cavities.”
However, it is common to approach microscale products with high-cavitation moulds and conventional machines, he adds. For instance, “Manufacturers commonly approach microscale products using multi-cavity moulds on conventional moulding machines to support higher productivity,” Masato explains.
Though to achieve the required product quality you need to pay attention to the mould, inserts and machine design, including the shot precision, max injection pressure, temperature controls and more, he adds. “While the approach can support higher productivity and require less upfront investment in specialised micro moulding machines, careful consideration must be given to manufacturing requirements.”
At this stage, a careful analysis of product cost versus quality is key. Micro moulding allows for unparalleled precision when creating components – you can make tiny, complex geometries – though it often comes at a price.
Small-scale considerations
Micro moulding is a different beast to conventional plastic injection moulding. So, it’s crucial that CMOs understand its unique requirements: for instance, it’s more precise, has smaller shot sizes and may call for different material choices.
“Companies serious about micro moulding need to learn how to do it effectively, repeatedly and reliably,” advises Len Czuba, president of product development organisation at Czuba Enterprises. “They must be experts in the field because it’s very different to moulding larger plastic parts.”
Micro moulding machines can inject tiny volumes with high precision, ensuring that pressure is distributed evenly within the cavity. Specialised equipment that’s precisely calibrated is used to control injection pressure and the temperature of the resin. Success also relies on the design of the part and its mould – a process that needs to be incredibly accurate at a small scale.
After making micro-parts, CMOs must test each small part for compliance to the print and that all features are made properly. The next step is handling the micro-moulded parts and getting them to where they will be used, without damaging them in transit or losing them – Czuba has seen both happen from seemingly unassuming events like a gust of wind or sneeze.
To be successful with micro-injection moulding, he stresses the need to understand metrology, flow physics and environmental control. That is: measuring and confirming design features, ensuring plastic is at the right temperature to fill the mould as required and ensuring parts are kept in environments where there’s minimal risk of loss or damage. Masato agrees: “As medical devices are miniaturised and new functionalities introduced, manufacturing challenges specific to micro moulding must be considered. This is where the design for manufacturing and design for microinjection moulding becomes critical.”
At this stage, he recommends consulting with a micro moulding expert who can guide the design process while “incorporating the peculiarities of the micro-scale”. For instance, material behaviour at the micro-scale can differ due to “high shear and pressure conditions and rapid solidification rates”.
Ben Whiteside, professor of precision engineering at the University of Bradford, has relied on his lab’s research and new process developments to overcome the challenges of micro moulding. He established his first dedicated micro moulding laboratory in 2007.
A major challenge he encountered with micro moulding came early on, when it was considered “a curio”. However, Whiteside recalls “quickly building national and international networks of interested partners in the academic research, mould tooling and manufacturing spaces to explore the potential of these new processes and accelerate the route to market for high-precision components and assemblies”.
Since then, as micro moulding requests have become more frequent, there have been different kinds of challenges. For instance, materials that perform well in conventional processes can exhibit unexpected flow behaviour under the high pressures and stresses in micro moulding, causing quality issues or material degradation. A lot of these have been overcome by fusing Whiteside’s department’s research findings with developments from their new processes, such as bespoke machine vision and complementary assembly systems. Additionally, with the need to focus on process sustainability and life cycle assessments, they have developed a “broad device portfolio” that includes implants, dental devices, surgical tools, drug delivery systems and devices with functional surfaces. Here, Whiteside feels there will be further challenges owing to “significant pressure” on medical device designers and manufacturers to “pivot towards multi-use devices with sustainability credentials without posing extra risks to patients”.
Sharing knowledge
Distributing insight and collaboration is crucial in not only driving production forward but preparing for challenges on the horizon, says Masato. This may include adapting to still-emerging concepts, such as automation and AI. And this will be “critical to ensure global competitiveness”, he adds. Here, clear and active communication is key. Whiteside agrees: “Ultimately, excellent teams of designers, researchers, equipment/ tooling providers and a CMO with streamlined communication lines and complementary skills provide a solid foundation for navigating challenges of bringing a disruptive device to market.
“Partnerships are important and we have collaborators worldwide to support our work,” he continues. For instance, his department doesn’t focus on tooling – rather, Whiteside says their expertise is “understanding links between material formulations, process environments and functional properties of resulting components”.
For instance, many of the polymers they use are highly sensitive to heating rates, flow rates and stresses typical of microinjection moulding processes. This may sound challenging, but it provides an opportunity to create manufacturing processes for optimised products, he adds. “This can be particularly important for drug/polymer systems where poor choice of process parameters can result in reduced efficacy of active ingredients, due to degradation… a good knowledge of materials and process can actually allow us to control the pharmacokinetic behaviour of the systems.”
Yet the team has dedicated years to building relationships with field leaders who provide micromachining, laser machining and lithography-based approaches, to access tools with the necessary precision and durability. Whiteside also encourages knowledgesharing conversations to begin early. Crucially, this can help manufacturers also avoid potential hurdles down the line: from ensuring that new processes align with downstream implementation expectations and realising potential cost efficiencies during the scaling-up periods.
That includes swapping notes with the next generation of specialists, adds Masato. “Looking ahead, a key aspect will continue being workforce development… micro moulding knowledge must be transferred to younger engineers and technicians to ensure broader diffusion of the technology plus more efficient design and manufacturing processes.”
Regulatory hurdles
And then there’s the need to ensure new processes are aligned with regulations. One way that manufacturers can avoid slipping up is to regularly update their knowledge base in this area.
“A significant shift from standard manufacturing processes can introduce hurdles as you advance through the technology readiness levels and engage CMOs to address scale-up and regulatory requirements,” warns Whiteside. Technology readiness levels (TRL) are a scale from one to nine that measure the maturity of a particular technology. Here, TRL 9 means that the technology has been qualified.
“CMOs can provide innovative manufacturing approaches, but methods that stray significantly from standard manufacturing processes can result in increased risk. So, it’s important to have effective communication between the research and CMO teams to work together to view challenges from both perspectives and develop effective solutions,” he suggests. Whiteside’s department has expertise in ancillary systems, like in-line machine vision for process quality assurance, robotic assembly systems and packaging solutions for fragile components. As a result, he says they can collaborate effectively with CMOs to define optimal strategies, while they, in turn, advise on meeting regulatory requirements, such as ISO 13485 compliance, and identifying the most suitable sterilisation methods. Ultimately, through forwardplanning, communication and strong regulatory knowledge, CMOs should be able to overcome the inevitable hurdles they will come across during their micro moulding projects. These aren’t necessarily the easiest of tasks, but with research, persistence and flexibility, they can be overcome – and prove fruitful.
