Contract manufacturing
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 micro- scale 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
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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 micro- injection 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
Medical Device Developments /
www.medicaldevice-developments.com
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