Conventional methods for removing flash from injection molded medical parts — hand trimming and, in some cases, die punching — are effective, but they come at a cost. Both are labor intensive, and, in the case of hand trimming, often produce inconsistent results. A better alternative, according to Nitrofreeze Cryogenic Solutions, is cryogenic deflashing, an automated, computer-controlled batch process that removes flash from tens to thousands of molded parts simultaneously. The patented process will not change part tolerances or surface finish, is more consistent than hand trimming, and is safe for medical plastics and medical silicones, claims Nitrofreeze.

During the cryogenic deflashing process, batches of molded parts are cooled below the polymer’s glass transition temperature (Tg), making the flash hard, brittle, and easy to remove. The parts are then blasted with a specified cryogenic-grade polycarbonate media, which comes in different diameters to meet part-specific challenges. This proven process is especially efficient at removing flash from cross-holes, blind holes, and other geometries that are hard to reach with hand tools, according to Nitrofreeze.

Using hand tools, a worker may need up to an hour to deflash just one complex part made, for example, from polyether ether ketone (PEEK). By contrast, in the same amount of time cryogenic deburring can deflash an entire batch of PEEK parts, and without the part-to-part variations that are common to hand trimming. 

In its press release, Nitrofreeze cites one medical molder who saved more than six hours of labor time per 1,000 pieces by switching to cryogenic deflashing. The molder needed to deflash silicone distal handles for a medical device in volumes of 3,000 to 4,000 parts per release. Manual buffing and trimming took upwards of 20 seconds per part. Cryogenic deflashing slashed production time, and although the flash stood as tall as 0.036 in., Nitrofreeze achieved a tight flash tolerance of only 0.005 in., according to the company.

Nitrofreeze said it has successfully removed mold flashing from products that include PEEK implants, polypropylene surgical caddies, and silicone gaskets. The Worcester, MA–based company provides a full range of services, including cryogenic burr removal, cryogenic deflashing, conventional cryogenic treatment, heat and freeze thermal cycling, shrink fitting, and dry ice (CO₂) blast cleaning. It also offers engineering services, cryogenic lab work in support of R&D, and custom equipment design for unique cryogenic applications.