by David Kachoui
Last week I spoke at the “Microfluidics Regenerated” conference hosted by BioDot. I presented some of the challenges to expect now that the industry is increasingly transitioning into the injection molding phase, especially for high production. This transition regularly requires some design changes, so it is important for development stakeholders to understand why.
Flatness is often a critical requirement to achieve the right sealing of the channels. This is a challenge because deflection, shrinkage, and fill are inherent risks in injection molding. These can be managed to work, which often involves some sort of modification or moving around of features. A lot has to be squeezed into a very tight area of real estate, so the impact of a single change can have a domino effect on other features. This is not necessarily unfeasible; it might just require time for a meticulous review.
Microfluidics generally entails micro molding. The rules of plastic start to change when moving into the realm of micro molding. Micro molding does not just entail micro parts. Micro features and micro tolerances are also squarely within the realm of micro molding. These geometries are often unique from one application to the next, so the need for individual analysis is great, and some experimentation of feature design might be necessary to find what works.
The part design that works in the hundreds or low thousands is not always feasible in the higher quantities. For example, micro distances between features can create thin areas of the tool that are vulnerable to injury. This can be acceptable when the quantities are low, but as the quantities increase, the certainty goes up that wear and tear in those areas accelerates. This means that mold maintenance increases over time and reduces the operational time of the mold. By the time this design issue is a reality, the design has been locked in place, and design revision and revalidation are necessary to address the root cause.
Taking care of these issues during the design phase offers huge benefits. A solid review of design for manufacture and design for assembly on the part will help address issues in advance. A good modeling of the part in relation to the mold design such as mold flow analysis will help make more informed decisions for a more optimized fill.