Medical Musings: Give thermoforming a closer look

Recent prize-winning parts show the significant potential of the thermoforming process for medical component design. New applications feature innovative cost-saving packaging as well as functional parts. The growing success of thermoforming is due in part to adoption of new technology, ranging from tooling concepts to new materials.

This one-piece package won a 2011 Worldstar Award for Prent.

For example, Prent Thermoforming (Janesville, WI) won its 13^th Worldstar Award from the World Packaging Organization for a one-piece medical package that is cutting tooling and assembly costs for Cook Urological. A universal thermoformed clamshell design accommodates 35 different products, including two different handle configurations. In one neat design feature, pouch abrasion is eliminated due to the design and location of a small, strategically placed fold-over hinge.

Captive tooling

Prent operates one of the largest in-house tool centers in the industry. At the recent MD&M show in Minneapolis, Prent even showed parts with a material it has developed specifically for medical device packaging. It's significantly less dense than PVC, polycarbonate or polyester, cutting costs.  

In other examples of interesting thermoformed medical products, a medical scanner enclosure assembly developed by Productive Plastics (Mt. Laurel, NJ) uses a tool featuring numerous under-cut details, secondary tooling, and precise finishing. A tray from Perfecseal has undercut snap fits. TEQ is using state-of-the-art plug assist material to solve quality problems with sterile packaging.

One area of technology development in thermoforming has been introduction of new syntactic foams as plug-assist materials to assist sheet stretching prior to total contact with the mold. CMT's new plug-assist

New syntactic foams optimize material distribution.

materials are said to optimize material distribution and offer easier machining and better optical properties.

Why medical fits

Medical is a good fit for thermoforming for a variety of reasons. For one, lower volumes favor thermoforming because tool costs (usually aluminum) are much lower.  And because less pressure is used to form parts there is significantly less residual stress. Millions of cycles are possible.  Sophisticated material combinations can be achieved through use of multiplayer layers of sheet.

Of course, some designs may fit better with the injection molding process. Parts are formed over the surface of a single mold in thermoforming. So if a feature such as a rib is required on the reverse side, that would require additional expense. And the injection molding process can produce very strong and intricate parts. Injection molding can also produce parts at a faster rate if large volumes are required quickly.

New materials choices

There are considerable choices in materials, but designs for thermoformed products are limited to the types of materials available in sheet. That's changing, however. DuPont, for example, now offers polyacetal in sheet--with the specific goal of penetrating medical applications because of the material's chemical resistance. Ensinger/PennFibre has also introduced nylons and polyphenylene sulfide  in sheet stock in thermoforming grades.

Very generally speaking, thermoforming is a good fit for large flat parts. Injection molding is a good fit for small, complex parts.

Thermoforming probably has been overlooked to some extent for medical applications. Another look probably is in order.