Sunday, April 25, 2010

Annual review of received parts' dimensions

Many companies perform an annual review of every dimension or 100% inspection on all received parts. While this may serve as a halfway decent preventive action, I'm not convinced it is worth it. If you have automated inspection methods, maybe then it is not too much effort, but we're still using hand tools or manual adjustments for the majority of our parts.

You could argue that you have a critical device, we have to check for dimension drift. Well why aren't you checking for that anyway? And if it is so critical shouldn't you have insured that the supplier's process was capable before you even signed up with them? If it is truly critical and you're not checking it but once a year, good luck with that.

Additionally, if you do find something out of specification, nine times out of ten it is going to be on a non-critical dimension, or else you would have caught it in receiving inspection or manufacturing anyway. Once you find the out of spec item, you have to go back to your inventory, check it, then justify why it is either okay and change the specification, or send it back, and jump through hoops to justify why it was okay to use on the ones sold, but not okay to use going forward, or whatever other contortions QA wants.

In my experience these generally boil down to unclear or unnecessary specifications or measurement issues, where to start measuring a curve, a hole over specified, etc. Another argument for doing it right the first time and checking your supplier's process.

However, this if often a difficult battle, as new parts are generally part of R&D efforts and the team from R&D is behind schedule and they always try to make up schedule time by trying to get either quality or manufacturing to compromise on one issue or another (I *may* have pointed this out at a meeting once). If this happens and you don't have time to ensure supplier process capability, it is not the worse thing in the world, you can always blame the vendor and shop around for a new one that has no familiarity with the part and uses the same process that can't meet the specification. Sometimes the best you can do is make the risks clear.



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