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First Piece Inspection (Primarily Standard Machining) Question

5

57jeeper

#1
Hello to the group:

I've been tasked with developing training for First Piece inspection, (not FAI).
We are a manufacturing company primarily involved with standard machining, (milling, Swiss turning, EDM, etc.). Lately we've experienced some rejected jobs due to bad first piece inspections.
The causes of the defects were rather simple, (missing features, angles in the wrong attitude, threads not deep enough). It's not lack of training, the people that made the mistakes are the most experienced, (20-30 year), inspectors and are more than proficient to catch the problems.
The reason that I believe that this has occurred is that the parts we produce are micro machined medical components with very close tolerances. It would appear that the inspectors are so focused on measuring the tiny features with total tolerances less than .001" that they "aren't seeing the forest for the trees" so to speak.
My question is, does anyone know of any general guidelines that I can use in my training that will give them a template or guide to follow when they start a first piece inspection, kind of like an overview when they are looking at the part and examining the features.

Thanks for any feedback.

Mike
 
#2
Re: First Piece Inspection Question

There is a method I have seen that works fairly well:

1. An excel type spread sheet that has all the required dimensions listed including pitch diameters, thread OD's, angles, etc. The person doing the First Piece (FP) inspection types in the actual measurement and if the dimension is out of tolerance the cell turns 'red' (using the conditional formatting). I have setup some excel files that if the dimension is 'good' but close to the actual tolerance it will turn the cell yellow.

Pro: This verifies that all dimensions are checked, approved, and within the tolerance that you have. Saving the file also maintains the record of FP inspection.

Con: The draw back to this method is setup time. Making these files does take time. If there is a typo you can still make bad parts. There is also the concern of training, (as bad as this sounds) I still know people who cannot use the basic 'office' programs.
 
5

57jeeper

#3
Re: First Piece Inspection Question

Thanks Michael:
We already do that type of thing for our final inspection, but the things that we missed are very nebulous. On one part there was a pocket that had different orientations based on the size of the part which was incorrect for the part produced. On another the 60 degree O.D. thread was tipped 5 degrees, so it was 25 degrees on one flank, and 35 on the other. We inspected it very accurately and recorded the dimensions, however, the thread was tipped the wrong way.
These are the type of things that if we were to start adding to reports for every conceivable problems, would not only make the reports huge, but something would still find a way to get thru the cracks.
What I'm hoping for is more of a guideline for how to approach the inspection which I can use make a checklist that gives kind of a 10,000 foot view of the inspection.
 
#4
Re: First Piece Inspection Question

Thanks Michael:
We already do that type of thing for our final inspection, but the things that we missed are very nebulous. On one part there was a pocket that had different orientations based on the size of the part which was incorrect for the part produced. On another the 60 degree O.D. thread was tipped 5 degrees, so it was 25 degrees on one flank, and 35 on the other. We inspected it very accurately and recorded the dimensions, however, the thread was tipped the wrong way.
These are the type of things that if we were to start adding to reports for every conceivable problems, would not only make the reports huge, but something would still find a way to get thru the cracks.
What I'm hoping for is more of a guideline for how to approach the inspection which I can use make a checklist that gives kind of a 10,000 foot view of the inspection.
Here is a link to an answer I gave just about a year ago to a very similar question concerning First Article (http://elsmar.com/Forums/showpost.php?p=516858&postcount=4)

The key in that case and most likely in your case is a REDUNDANT inspection (meaning a second set of eyes inspects the piece WITHOUT someone looking over his shoulder.)

It is important to make sure the folks doing this feel they are "covering their partner's butt," NOT playing "gotcha" to make the other guy look incompetent. The focus should be on ensuring the TEAM looks good to the customer AND protects the bottom line of the organization by avoiding the expense of making scrap.
 

hogheavenfarm

Quite Involved in Discussions
#5
Re: First Piece Inspection Question

We perform similar operations, and in cases like these, and since there is only one of me, I make an 'fpi-check' after each operation, checking only the features added during that specific operation. This prevents things from getting too far down the line if they are wrong. Ideally, your operators should do this with the first part, and then a spot check every nth part. I once had a setup at an earlier place where the next operator checked the previous operations part before continuing their process. A true FPI is done at the end, but I know its good since all the intricate operations were checked as we processed it.
 
#6
Re: First Piece Inspection Question

We perform similar operations, and in cases like these, and since there is only one of me, I make an 'fpi-check' after each operation, checking only the features added during that specific operation. This prevents things from getting too far down the line if they are wrong. Ideally, your operators should do this with the first part, and then a spot check every nth part. I once had a setup at an earlier place where the next operator checked the previous operations part before continuing their process. A true FPI is done at the end, but I know its good since all the intricate operations were checked as we processed it.
This is good - we usually call it "in-process inspection."

As our CNCs got ever more sophisticated, we could add sensors in the system to check both critical and control (the dimension you check to see the operation is running as planned) dimensions and shut the operation down if the checked dimension went beyond control parameters. It was a process we used in production, not just first piece.

It occurs to me the Control Plan needs to be preceded by a rigorous FMEA to ID the characteristics most likely to go out of whack.
 

hogheavenfarm

Quite Involved in Discussions
#7
Re: First Piece Inspection Question

Unfortunately here, every dimension is a critical one, so we end up checking every operation in full, rather than streamlining it with a few criticals. Breaking it up like this makes it easier for me to keep up with, and as I pointed out, when all operations are finished, there is little to check that hasnt already been done (most of the time, nothing to check), so then it is just verify the shipping requirements, totals, packaging and labeling, and this is done with sampling.
When I was in the extrusion plant, we did verify about 4 critical dimensions and a few characteristics, all plotted on a SPC chart, once per hour during the run (this depended much on the line speed though). I liked that system in that it was easy to spot an out of control condition, even before it actually occurred, by watching the trendlines.
 

Helmut Jilling

Auditor / Consultant
#8
Hello to the group:

I've been tasked with developing training for First Piece inspection, (not FAI).
We are a manufacturing company primarily involved with standard machining, (milling, Swiss turning, EDM, etc.). Lately we've experienced some rejected jobs due to bad first piece inspections.
The causes of the defects were rather simple, (missing features, angles in the wrong attitude, threads not deep enough). It's not lack of training, the people that made the mistakes are the most experienced, (20-30 year), inspectors and are more than proficient to catch the problems.
The reason that I believe that this has occurred is that the parts we produce are micro machined medical components with very close tolerances. It would appear that the inspectors are so focused on measuring the tiny features with total tolerances less than .001" that they "aren't seeing the forest for the trees" so to speak.
My question is, does anyone know of any general guidelines that I can use in my training that will give them a template or guide to follow when they start a first piece inspection, kind of like an overview when they are looking at the part and examining the features.

Thanks for any feedback.

Mike
If you use a checklist to define the First piece inspections, there should not be any "missing features." If there are, then your inspectors are pencil whipping the checksheet.
 
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