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In-process and final inspections of which dimensions

In-process and final inspections of which dimensions

(OP)
Hello,

I am an engineer but not in Manufacturing or Quality. The company that I'm working for does first article inspection (FAI), in-process inspection (IPI), and final inspection (FI) on any part manufactured in house. My understanding is that the company's FAI looks at all dimensions on the engineering drawing and that the FI looks at just critical dimensions.

The IPI's sampling frequency for a part is based on the tolerances, the expected tool wear over 30-60 minutes of cumulative run time, and the hindrance to machine operator efficiency. The FI's sample size is based on a C = 0 sampling plan where AQL = 1.0%.

I've recently been told that no dimensions should have FI that don't have IPI. If FI is based on criticality, not manufacturing considerations, does that make sense? Can a dimension have FAI and FI but not IPI?

RE: In-process and final inspections of which dimensions

Quote (Who?)

I've recently been told that no dimensions should have FI that don't have IPI.

By who? Someone random on the street? Someone random on the internet? The director of quality at your company? An auditor? A customer?

Turn it around: "All dimensions that get FI must have IPI."

Makes sense to me.

RE: In-process and final inspections of which dimensions

(OP)
Can't a dimension be critical but, for example, the tool to machine its feature not be subject to excessive wear, thus requiring FI but not IPI?

RE: In-process and final inspections of which dimensions

We still check the dimension at IPI to watch out for shift changes, tooling set ups, et cetera (First Part Inspects can help with that too.) The parts we run are not huge so it is just as quick for the CMM to run all dimensions rather than just some.

RE: In-process and final inspections of which dimensions

Assuming the drawing/MBD is toleranced properly* then with a few exceptions the idea of 'critical' is a bit nonsensical.

To me the process capability factors you mention for IPI are more critical in deciding what tolerances to check with what frequency.

I.E. check the tolerances that are hardest to meet/most likely to be missed etc.

(*I.E. the loosest tolerance that will still ensure part functionality is assigned.)

Posting guidelines FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm? (probably not aimed specifically at you)
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?

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