Apologies for the overly “English major” headline of this issue’s Roundtable (a nod to Robert Frost’s famous poem), but given the responses to one of the questions provided to the participants, it seemed appropriate.

For the topic of extrusion, I had asked if there was an aspect of this process that was commonly overlooked or not considered by medical device design engineers when working on a new project. I was surprised to receive five answers from the participants that were different enough from each other to make them each uniquely valuable. Following are those responses.

Gordon Knott, medical market leader with Alexandria Industries, said, “People often forget that aluminum extrusions can provide improved mechanical properties over castings when comparing the same alloy, including decreased porosity, greater impact resistance, and ductility, as well as other strength characteristics. Extrusion tooling brings a more cost-effective solution compared to casting, forging, and injection molding. Due to the ability to make near-net shape components, aluminum extrusion can reduce the number of overall components and the need for additional manufacturing processes. It also eases assembly by designing in features, such as snap-fit assemblies, screw chases, or circuit board grooves for mating with other components. Aluminum extrusion also generally offers shorter turnaround times than other manufacturing processes, which can benefit today’s busy OEMs by beating their competition to market.”

“Unrealistic tolerances — the tight tolerances achieved in injection molding simply cannot be achieved in extrusion,” responded Dominic Feeley, technical account manager at Kelpac Medical Ireland. “Extrusion, relative to injection molding, is a low pressure process and has variations in viscosity and molecular weight within the polymer melt, which the processor has no control have a much greater effect on dimensional stability.

Timothy Roy, manufacturing engineer at New England Catheter, shared some insights that are familiar when a component fabrication company is asked about how to get the most out of a supply partner. “Significant economic advantages can be realized when designers and manufacturers collaborate early in the development of new devices or components. Many times, the tube can provide the needed performance characteristics using continuous processing, or at least more continuous processing to reduce discreet piece processing and associated cost.” He went on to add, “Choosing optimal raw materials can also ease manufacture and reduce cost. Examples include variable pick rate braiding to vary shaft stiffness rather than multi-durometer designs, and replacing PTFE liners with thermal melt fluoropolymers or HDPE. Even conformal coatings can have a significant positive impact on cost.”

In the September 2014 issue of MDT, we featured a process that was a potential alternative process to extrusion (i.e., polymer solution casting). That contributor, Avalon Laboratories still weighed in on this topic involving extrusion itself.

Cecile Redington, a product engineer with the company, shared her thoughts. “Polymer solution casting is a very versatile technology and lends itself well to many catheter designs, since it offers the flexibility of easily varying the material stiffness along the length of the catheter, as well as creating as a single-piece and seamless design.  By using conventional extrusions to create a complex catheter design, the manufacturing process will require several different extrusions to be bonded together to achieve transitions in stiffness, while the same can be much more easily achieved by modifying the layering order and location of different types of polymers.  Avalon has also perfected creating smooth and feathered catheter tips, which has presented itself to be much less traumatizing to the patient than the extruded counterparts. Polymer solution casting also allows for designs with varying wall thicknesses along the length with seamless and naturally occurring tapered transitions that cannot be easily achieved with conventional extrusions.”

Redington’s comment not only serves to introduce some to the capabilities and benefits of a new technology process for component fabrication of tubing, but also to illustrate the importance of maintaining communication with assorted suppliers should one of them offer something new that better suits your needs for a particular component or technology. (Check out more on polymer solution casting in the article previously mentioned at the MDT website)

Sonia E. Schwantes, product specialist, medical components at Saint-Gobain Performance Plastics, brings up the topic that always seems to be a part of every component fabrication discussion. And the same interest level is true of industry members who constantly request more information about it. The topic — materials. “Material is an important consideration not just for the way it processes, but also how it will work in the application. A datasheet gives a limited amount of information from tests conducted with very specific settings and not always applicable to the real situation. It is very important to understand all the conditions the tubing or profile will see in order to avoid problems especially as your customer gets closer to launch.”

Full Responses
To see the full responses of the participants, view these links: