Top 5 Injection Molding Defects in Medical Applications

Complex injection molders entrusted with producing plastic components for medical and other critical-use applications assume a high degree of responsibility to ensure the device performs properly, without fail in sometimes life-endangering situations.

A molder’s experience will dictate how well they understand what can go wrong in the molding process and how to troubleshoot injection molding defects for critical-use medical applications. Kaysun has confronted and resolved a number of molding challenges on behalf of our customers, and we’ve compiled a list of common injection molding defects and their impact on part aesthetics and performance:

Residual Stress results from internal forces that accumulate while a part is cooling in the mold and can’t shrink into a shape the resin naturally wants to, but instead it must conform to the mold. Residual stress often fluctuates due to a tooling or injection molding machine change. The fluctuations are imperceptible visually and, despite dimensions and all other factors being the same, residual stress could cause a part to perform poorly in the field.

Warping is an unplanned and unwanted bend, curve or geometry in a molded part. Warping typically appears either during prototyping or full-scale production, introducing potentially significant increases in project time and cost.

Sink marks are visual, measurable marks — usually in the form of depressions or craters — that appear on a plastic part. Sink marks are not only aesthetically displeasing, they can be detrimental to component functionality and how it assembles to other parts.

Short Shots are voids in a molded part where plastic is physically missing. Short shots form incomplete molded parts that can be misshapen, the wrong size or will not hold correct dimensions — making them unusable.

Flash is liquid resin that escapes from a mold parting line and solidifies on the outside of a part. Flash can be extremely sharp, making general handling dangerous. It can also easily damage packaging or cut through O-rings and seals.

Understanding what can go wrong in the molding process and how those defects influence medical application performance is a top priority for injection molders, but solving them is the true end game. Check out Part 2 of this blog series, where we discuss how to proactively prevent and fix defects in injection molded medical parts and products.