Just about every cleaning process is performed in the interest of providing a clean part. This makes the “deliverable” a clean part! Part cleanliness, however, is often not the variable that is tracked in the interest of quality control. Let’s talk about that.
It would be nice if there was a simple way to test every part for cleanliness before it is shipped. Short of the limited number of cases where a dirty part can be reliably and quickly detected by visual or other non-invasive means, this is pretty much impossible.Testing procedures used to verify cleanliness of many parts are frequently very complex and time consuming. Also, they often destroy or render the actual part tested unfit to ship. For this and other reasons, most cleaning processes are monitored using “Process Validation.”
Process Validation statistically monitors variables that affect the cleaning process in real time. Time, temperature, chemical concentration, flow rates, liquid levels, ultrasonic intensity and a host of other variables can be presented as numbers that can be compared to target values to indicate the “health” of the cleaning process. It is assumed that if the numbers are met, the parts will be clean. If the numbers go awry, corrections can be made immediately (and often automatically) to assure that the process remains in control. Shortcomings are found immediately, not hours or days later after a sample part has been evaluate and hundreds or thousands of “suspect” parts have been produced and, perhaps, shipped. Data can not only be utilized in real time but can also be collected and stored for review in case “issues” arise at a later date.
All of this sounds GREAT! Process control is a snap! BUT, DOES IT ASSURE A CLEAN PART EVERY TIME? Unfortunately, it does not. Process Validation assumes a consistent incoming part. But we all know that the goal of part consistency is not always met. Any process change prior to the cleaning step such as a change in raw material, a coolant, an abrasive, an adhesive, or whatever, may present the cleaning system with a part it is not able to effectively clean. Process Validation has no way of knowing that the part isn’t getting clean although all its target values are being met.
A word to the wise – Don’t be over-confident replacing Cleanliness Validation with Process Validation unless suitable process controls are in place and verified effective in every process step leading up to the cleaning machine. Periodic cleanliness validation is the only way to assure that the parts being produced and shipped meet cleaning specifications. Cleanliness Verification is not as fast as Process Validation and Process Validation is a good idea in every cleaning process, but periodic Cleanliness Verification is great insurance in the long run.