Paul Runyan, VP of sales, Accumold highlights all you need to know about micro injection moulding of thin wall cannulas.
Accumold
High-volume production of small and thin-walled cannulas using traditional methods like extrusion, tipping, and gluing to a metal hub presents several limitations that hinder efficiency and quality.
Extrusion becomes challenging for extremely small dimensions due to the risk of material inconsistency, wall thickness irregularities, and potential defects. Tipping, the process of adding a plastic or metal tip to the cannula, introduces variability in terms of bonding strength and tip alignment, impacting the precision required for medical procedures.
Moreover, the gluing process poses reliability concerns as adhesives might degrade over time, leading to potential detachment of the cannula from the hub and compromising patient safety.
Furthermore, these traditional methods are labour-intensive and time-consuming, making it difficult to meet the demands of high-volume production efficiently.
Micro injection moulding to the rescue
Modern manufacturing technologies like micro injection moulding offer a more streamlined approach. Micro injection moulding enables the creation of intricate and consistent cannula designs with precise wall thickness control. It eliminates the need for separate extrusion, tipping, and gluing steps by producing the entire cannula in a single mould, enhancing product reliability and reducing the risk of defects.
This approach not only improves the quality and reliability of the cannulas but also offers a more scalable and cost-effective solution for meeting the demands of high-volume production in the medical industry.
What to consider
Material choice is paramount when optimising outcomes in micro moulding cannulas due to its profound influence on product performance, reliability, and manufacturability. The unique challenges posed by micro-scale manufacturing, such as precise cavity filling and intricate geometry replication, demand materials with specific properties like low viscosity, excellent flowability, and minimal shrinkage. Material selection also impacts the durability and biocompatibility of medical devices, ensuring they can withstand the rigours of use while being safe for patient interaction.
Several critical design for manufacturability (DFM) considerations must also be addressed. Ensuring uniform wall thickness is paramount, as variations can lead to warping, cooling inconsistencies, and inadequate filling. Proper gate placement is essential, influencing material flow and minimising stress points, while suitable venting channels are crucial to prevent air traps that can result in surface defects. Incorporating appropriate draft angles facilitates seamless ejection from the mould and prevents potential damage.
Furthermore, maintaining accurate parting line alignment prevents flash and surface mismatches. Strategic placement of features like ribs and supports enhances structural integrity without compromising the overall design, while carefully considering the positioning of ejector pins prevents interference with critical features during demoulding.
Additionally, addressing assembly considerations in some instances can be vital, particularly if the cannula is part of a larger device. Ensuring mating surfaces, alignment features, and interlocking mechanisms are well-designed enables smooth integration.
Avoiding potential challenges
Maintaining a balanced aspect ratio is essential to avoid challenges associated with flow dynamics, cooling, and structural integrity. An excessively high aspect ratio can lead to difficulties in material flow and cavity filling, potentially resulting in uneven thickness and defects. Conversely, an aspect ratio that is too low might hinder proper cooling and cause warping, making it vital to strike the right balance that promotes both accurate moulding and structural stability.
One other variable that has been critical is the use of proprietary micromoulding presses, developed over generations at Accumold. Cannulas were moulded on conventional presses and on Accumold’s presses, and it was discovered that conventional micromoulding presses had problems with non-fill and flash. Through the use of our fully automated in-house developed micromoulding presses and 16 cavity micromould tooling, we achieved reliable, repeatable, and high-volume production of 40 million parts a year from a single production cell.