Statistical terms used in tray sealing: CPK and standard deviation

Process capability (CPK) is a statistical measurement that describes the accuracy and repeatability of a tray sealing process. Using an archery target as a metaphor, an ideal tray sealing process is like getting a tight grouping of arrows in the bullseye. A tight clustering of arrows on the target, but not on the bullseye, shows repeatability, but not accuracy.

An occasional arrow on the bullseye shows some accuracy, but little repeatability. The best tray sealing processes are both accurate and repeatable. Historically, the medical device industry has assigned that goal a CPK value of 1.3. The medical device industry is now moving away from a minimum required CPK to a CPK of what is the maximum achievable given a package’s design.

Standard deviation is another statistical measurement that describes the amount of variation or dispersement in a set of values. It provides another way of looking at process capability (CPK). Manufacturer continually eye process improvements to be able to defend the highest possible CPK, not just what is an acceptable CPK.





Processes used for validating tray sealers: IQ, OQ, and PQ

The processes that are used for validating a tray sealer are installation qualification (IQ), operation qualification (OQ), and process qualification (PQ). The IQ process enables a user to verify that their tray sealer is installed correctly according to the vendor’s instructions. Then during the OQ process, the user can verify that the tray sealer is operating in a reliable, repeatable manner and producing the expected output.

Finally, during the PQ process,  operator actions for interfacing with the equipment are assessed. Many heat sealer vendors can offer IQ and OQ documents, or at least some level of support documentation. It is difficult for them to offer PQs because key components of the PQ are the package itself and operator functions, both of which are independent of the vendor.

Tray sealer validation is an ongoing process

In the medical device industry, tray sealers must be validated for repeatability and accuracy. The industry standard is that this validation process happens annually when the sealers are calibrated. At that time, any margin of error that has creeped into the system is corrected, so that from year to year, the output is stable. Most medical device manufacturers validate their tray sealers annually. Others calibrate their tray sealers every six months or so.