molded medical parts | medical injection molding | medical silicone parts

Medical Injection Molding and Flash Removal


Medical injection molding can produce complex and highly-precise components with part-to-part integrity across high production volumes. Whether the material is plastic, silicone, or another polymer or elastomer, medical injection molders need to avoid warping, sink marks, short shots, and residual stresses that can cause defects. Molders also want to minimize flash or flashing, excess material that escapes from the mold’s parting line and solidifies on the surface of the injection molded component.

Manual Deflashing and Die Punching

Although proper tool design can minimize mold flash, some amount of flashing still occurs – even with flash-less tooling. Worn tooling can cause parting line mismatches, and residues or contaminants can prevent a mold’s core and cavity from mating tightly  and closing properly. Flashing can also be caused by improper venting, inadequate clamping pressure, poor sprue bushing support, and excessively low viscosity of the mold material.

Traditionally, injection molders removed flash by hand. Yet, manual deflashing is time-consuming and labor-intensive. Processes such as manual trimming can also result in parts with different levels of surface quality. Workers risk removing too much material and changing critical part tolerances. They also risk repetitive motion injuries or hand injuries from trimmers, knives, or scissors. Plus, employees can only deflash one part a time.

Medical injection molders can use die punching instead, but there are disadvantages to this process. With die punching, workers place the injection molded part into a die, or tool, that is shaped like the finished component. The parts are then punched out onto a flash mat for more consistent quality than manual trimming can achieve. Die punching is still labor-intensive, however, and injection molders who are struggling to find workers want ways to improve efficiency.

Cryogenic Deflashing for Medical Injection Molding

Nitrofreeze cryogenic deflashing for injection molded parts offers important advantages over manual trimming and die punching. Because it’s a computer-controlled batch process, cryogenic deflashing  eliminates the variability associated with manual operations and processes multiple parts to a consistent and repeatable level of quality. Nitrofreeze performs initial sampling both before and deflashing, and we  can save your cryogenic deflashing recipe for future batches of the same part.

Although cryogenic deflashing uses very low temperatures to embrittle mold flash for ease-of-removal, Nitrofreeze’s process won’t change the physical or mechanical properties of your parts. The blast media, a cryogenic-grade polycarbonate, enables flash removal without impacting critical tolerances or surface finishes. This media comes in a range of lengths and diameters for solving tough challenges such as removing flash from blind holes, through holes, and other hard-to-reach areas.

Nitrofreeze® cryogenic deflashing is a well-established process for removing flash from injection molded silicone and injection molded plastic. At our facility in Worcester, Massachusetts (USA), Nitrofreeze® has defalshed silicone blocks, bumper stops, distal handles, housings, O-rings, overmolded springs, and gaskets. We’ve also worked with PEEK, an engineering thermoplastic that’s used in medical applications, and many other plastic materials.

Better Flash Removal for Medical Injection Molding

For better results than hand trimming or die punching can provide, try Nitrofreeze® cryogenic deflashing for your next medical molding project. If your part is a viable candidate for our fast, consistent, and cost-effective technology, we can perform sampling for proof-of-concept. The consultation is free of charge. To get started, contact Nitrofreeze at the phone number and email listed below.

(508) 459-7447 x 105