Welcome to “Small Talk”:
In the medical device design community, it’s not uncommon for the tiniest components of the device to be the enabler to the entire medical or drug delivery device. To help our readers overcome specific challenges for this growing need, Medical Design Technology is proud to announce our monthly blog called “Small Talk” exclusively written by nationally recognized micro manufacturing expert, Donna Bibber.
Each month “Small Talk” will highlight a micro fabrication component, feature, surface, or assembly topic of interest presented in a practical and solutions-based format. Materials, geometric tolerancing, tooling-based solutions, and assembly stack-up tolerance work-arounds will provide readers with a quick go-to reference with archives saved for future use.
It’s highly likely that you, as a designer, will run across a part that makes your existing molding supplier sigh, cringe or even groan. It’s times like these that you need to listen to those body sounds and seek out experienced micro manufacturers that work on tiny dust specks every day. Micro parts with challenging geometry, wall thickness, L:D or L:T ratios, or multiple materials are welcomed by those experienced and versed in the proven process of success.
This “Proven Process” will be explained in “Small Talk”, broken down into a series of proven steps that will fit for most tiny medical component and assembly designs. We will break down in deep dive fashion to this Proven Process in five key areas, easily remembered by the letters “V.I.T.A.L”.
These vital steps will guide you as the designer to check off those items along the way to mitigate risks at each step. Generally speaking, your success is directly proportional to the experience in a particular material/size/tolerance combination. For example, an implantable grade PEEK 150g material that has tiny sharp points can be replicated once it’s been previously molded. A diagnostic device channel in COC or COP that is 25 microns in width and depth can be also be replicated once it has been previously proven. “Proven” means molded in production quantities that passed a stringent validation protocol.
In this first of many technical articles, we will start with what is improperly usually last: Validation. In the world of micro molded components, understanding validation is critical to the success down the line. Starting a mold design/build and molding without understanding the critical to quality (CTQ) tolerances does not allow for error in each step of the process. For example, micro parts are getting smaller and smaller and so are the tolerances. Tolerances of +/- 10 microns require a validation protocol that starts with the mold design. Much ado is made about the injection mold design for micro molded components because it is truly the enabler to making anything tiny and precise.
The mold for a micro molded component should be built to 20 percent of tolerance, regardless of tolerance so that the rest of the process (material lot to lot variation, molding process validation, gage repeatability, humidity (for hydroscopic components)), will use some of the remaining 80 percent of error to achieve adherence to statistical capability of 1.33 Cpk. Addressing this early in the mold design phase will put a design in a position of success, whereas writing a validation protocol during or after a mold build will not include the most important aspect for achieving success. A careful selection process of micro mold builders who can achieve +/- 2 microns if the part tolerance is +/-10 microns is highly recommended as a good starting point.
In our follow-up blog post, we will dive deeper into the VITAL Proven Process of Validation.
Donna Bibber has a B.S in Plastics Engineering from the University of Massachusetts-Lowell, was voted on the 100 Most Notable People in Medical Devices, and has been keynote speaker to SME, SPE, and NSF-related technical conferences on the subject of micro molding and micro manufacturing. Donna is Vice President of Sales & Marketing for Isometric Micro Molding, Inc. www.isomicro.com