#1 Cause for Rejects? MASKING!
We did a study once to meet a Statistical Analysis Quality Requirement and it was very surprising in some ways and not so surprising on others. What did this study tell us? The #1 cause for rejects?
Masking failures.
What wasn’t surprising were the defects we could anticipate happening but couldn’t prevent.
Tape or dots that peeled off in the process as there’s no way to measure the adhesion of the masking.
Plugs that came out due to the tenuous nature of plugging some holes while the parts are being jostled and agitated in solutions.
Leakage under liquid masking around edges or thin surfaces. Hard to assure that the lacquers will hold up through the hot / cold, acid / alkaline, hotter / colder / really hot, cold / cold / hot of the processes.
These causes for rejection are very hard to anticipate, measure or predict.
What was surprising? How many mistakes that could have been avoided.
And for many of those mistakes we had a partner in crime that helped us make them. Those partners? The engineer that designed the part. Whoever drew the blue print in such a way that the masking requirement seemed clear but wasn’t. Or perhaps…. Even our customer who didn’t give us enough or the right information and lead us down the road to hell. Paved with good intentions of course!
Blueprints and an engineer's description of masking requirements can leave a lot to be desired. “Mask this surface” with an arrow that points to the bottom of a pocket machined into a part. Do we mask the walls of the pocket too? Do you even care if the walls are masked? And if we have to use paint to mask the bottom of the pocket, the paint has a thickness so we’ll be climbing up that wall some amount. Is that okay?
"Mask all holes". Okay, does that include the 4” bore in the middle? Technically a hole and what a disaster if we do / don’t do it. "Mask all mounting surfaces”. Are they indicated? How do we know? "Mask all holes, threads and critical surfaces. No rack marks allowed”. You have now taken all of the typical places we can rack from away form us. Now what?!?
I could go on but you get it. So what's the solution?
Never quote another job that requires masking? That's not happening for either of us.
Develop ways to machine off areas that require masking so we can plate or anodize all over and there is no masking? Yes please!!! Count us in on that…. When it’s possible. If it’s possible.
Employ the old “you touched them last” strategy and blame the plater? That works. That also leads to another strategy, the “get another plater” strategy.
Or… We can communicate.
We can look at alternatives like post machining or making jigs, fixtures or tooling that makes the masking easier and builds quality in. Heck you can even come and visit us and inspect the 1st article so we know the masking is in the right places. There are lots of ways we can communicate and eliminate, or at least reduce, the agony of a masking reject.
And whatever you do please! When a part is worth $10,000 let us know! If we’re going to be masking a part that is virtually irreplaceable, please give us fair warning. Then we can look even harder at the application so we don’t cause heartbreak for either or both of us. I never want to go through THAT again... Again.
When you’ve been around as long as I have you’ve made pretty much every mistake possible. I tried to learn form each and every one as the hard way is the only way we learn. Let my past pain be our future gain!
And call me! I’m around!