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  Measurement, Test and Calibration
  Calibration items

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Author Topic:   Calibration items
IanHoughton
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posted 14 December 1999 11:51 AM           Edit/Delete Message   Reply w/Quote
I am reviewing our calibration system that consists of tape measures, hand crimp tools, continuity testers and multi-meters. My question is this:
Is it really necessary to include the hand crimp tools into the system, as they are neither inspection or test equipment. If they don't need to be calibrated what other procedures (first off tests) needs to be carried out?

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Jerry Eldred
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posted 14 December 1999 04:32 PM     Click Here to See the Profile for Jerry Eldred   Click Here to Email Jerry Eldred     Edit/Delete Message   Reply w/Quote
If you are using the crimp tools on product or on anything where you either specify the reliability of the tensile strength of the crimp, or for any other reason care about the quality of the crimp, they need to be periodically verified. I am not an expert in that area, and its been a while, but I believe there are a couple of methods to verify them. I believe one is verification of the pull strength of the crimp, and the other is a measurement of the crimped connection size. Depending on your specifics, as to which one would apply. They are not inspection equipment, but if used on product, they are production equipment, with the capability to impact product quality.

Any measurement instruments you use that can impact product quality (multitesters, etc) need to be verified/calibrated periodically.

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IanHoughton
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posted 14 December 1999 07:59 PM           Edit/Delete Message   Reply w/Quote
Thanks Jerry,
The crimp tools at present are calibrated every 6 months but this takes up a lot of my time. I was hoping to pass on the responsibility for checking crimps to the operator who will have to carry out first off pull tests before starting each batch. (These will be recorded by batch number of harness) These tests are carried out at present on a calibrated pull test machine. Will this meet ISO9000 & QS9000 requirements ?

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Jerry Eldred
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posted 15 December 1999 11:05 AM     Click Here to See the Profile for Jerry Eldred   Click Here to Email Jerry Eldred     Edit/Delete Message   Reply w/Quote
Ian,

Bear in mind in my replies that I am a Metrologist (22 years), and not necessarily a QS9000/ISO9000 guru.

I think that if you have a documented procedure for checking a harness with a properly calibrated pull tester at the start of each lot is a good direction. I might suggest that you button up the possibility for bad units to escape by checking one at the end of the lot also. That way you are validating that all connections made by the crimper in between "should" be good. The metrologist and quality engineer in me also thinks that a random sample be externally tested. Especially if you are not going to calibrate the crimpers. Perhaps as a part of your outgoing inspection.

Conversely, it is not that great of a chore to do a verification on the crimpers. Depending on what type of connector you are crimping, it may be something as simple as measuring a crimp diameter with a digital caliper.

And even a third method might be doing that caliper measurement a number of times during each lot (or the pull tester data - determine what pull force it takes to destructively pull a connection apart), and plotting that dimension on an SPC chart (X bar R). When you see a trend past a control
limit, the process is out of control and you make adjustments to bring the process back into control.

My instincts tell me, however, that only the one non-destructive check at the beginning of the lot does not guarantee that the crimp will be in spec for the whole lot. If you have a spec strength of a 10 (just an imaginary number for discussion), and you check to be sure the connector meets a 10, you may actually have a destructive strength of say 10.2. By the end of the lot, if your crimp fixturing is worn and close to the replace poit, perhaps that figure will change by the end of the lot to a 9.9. Thus, you will have had a portion of a lot which was escaped product.

Sorry if I am overly wordy. I would rather give a little too much info than too little.
Please feel free to email if I can be of further assistance.

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David Guffey
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From:St. Joseph MI, USA
Registered: Oct 1999

posted 22 December 1999 05:21 PM     Click Here to See the Profile for David Guffey   Click Here to Email David Guffey     Edit/Delete Message   Reply w/Quote
The crimper tool itself does not have to be in the calibration cycle. What you check the crimped connections with DOES have to be in the calibration cycle.

That is not to say that having the process tool (crimper) in the cal cycle is not a good idea, just that it's not necessary.

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