Crimp inspection and process verification

JonnyB

Starting to get Involved
Hi all,

I have been battling this one for a while now and am looking for some advice.
I work in a company producing cable harness assemblies, predominantly for aerospace but also a selection of other industries. We generally work at low volume and high mix parts.

I have been in my position for just over a year and have always been slightly skeptical of our verification of crimping activities (full-cycle hand tools only).
Our tools are calibrated every 30 days (checked with Go/No-Go gauge, when specified by the manufacturer, and subjected to a pull force test).
However our in-process crimp checks are limited to visual inspection only (100% of crimps). I am currently working on an MSA study to confirm the effectiveness of this.

My ideal scenario is a pull force test at the start of production, and every time the tool setting is changed. Unfortunately in most instances (especially with Aero) the contacts are supplied with the connector and do not contain any spare parts - as such there is no scope for destructive testing on the scale I'd like.

I must assume there are others with a similar issue, in which case, how do you qualify your crimping process per job without destructive testing? I am familiar with the other common crimp inspections (crimp height & width etc...) however, I am struggling to apply those characteristics to machined contacts. Any insight would be greatly appreciated!
 

ChrisM

Quite Involved in Discussions
One option you have is to buy one additional connector with crimp terminals for each "run" and you perform destructive tests on those additional terminals. Not ideal, but it is a solution. It's a good few years since I was involved in routine crimp joint testing and inspection; we used to perform two additional crimp joints prior to starting each job, we had a motorised pull tester and one joint was tested to its prescribed force, the second was left intact as a reference sample. Both were identified and bagged up, retained with the job records (paperwork) in case of any possible query or concern in the future. In-process and end-of job testing was non-destructive, pull to required force (as per the initial sample at job start) with only additional visual inspection that there was no evidence of impending failure.

You should not have to qualify your production crimping process every time you perform crimping (unless it is sporadic and someone has requested it); your qualification activity should be a one time event to prove that the process works. Each time you run the process, you should only need to conduct verification that it is working and this need not involve destructive testing (someone please correct me if I am wrong).

I also worked elsewhere and we had to validate the crimp joint process on several combinations of wire sizes and terminal sizes by examining the fill-to-voids ratio.... happy (!) memories of examining prints of cross-sectioned crimp joins and drawing rectangles and triangles on them to do the calculations. Initially someone said they had some software that would do this automatically from the print via optical scanning and clever processing, but they were in error.....
 

JonnyB

Starting to get Involved
Thanks for your response!
Fill-to-voids ratio sends a shiver down my spine. I used to work in automotive and micro-sectioning crimps was the standard. Of course we were producing at huge volumes, especially compared to what I am experiencing now, so the time it took for the analysis was worth it. I am sure we did have some software that could calculate it automatically though, which sounds a lot less tiresome than a manual effort.

The idea of purchasing an additional connector would indeed solve the problem, however, the cost of some of these parts are astronomical and because of our high mix, we would quickly notice the additional costs. This even holds true for attempting to purchase just the contacts in a lot of cases - Think MOQs of 100 and the contacts costing £6 each!

Each time you run the process, you should only need to conduct verification that it is working and this need not involve destructive testing (someone please correct me if I am wrong).
I agree with this statement, although my knowledge of crimp verification (as limited as it may be) is that short of doing destructive testing, it is difficult to know the actual condition of each crimp.
My current plan is get an MSA study done to hopefully provide some insight into whether we are effectively verifying the process. I wonder if anyone else has performed a similar exercise for crimp inspections, ensuring there are a few non-conforming samples? I am not sure if this would constitute MSA sacrilege or if manipulating the samples into non-conformance is acceptable.
 

optomist1

A Sea of Statistics
Super Moderator
X-RAY/CT, crimped connector/wire to prove crimp location and integrity, etc of same , not inexpensive but sure fire and non-destructive, I've had great success with Zeiss Metrology (there are other vendors), below a link, if you can rationalize such an expenditure across many harness lines/products, the business case becomes less challenging... hope this helps Optomist1

X-Ray Systems
 

optomist1

A Sea of Statistics
Super Moderator
a bit more, whether Aero or Auto (especially with move to EVs), what typically is the least expensive component in relative terms is in fact the one of the most important; harness assemblies, stranded/solid conductors and terminations or crimps...

Cheers
Optomist1
 

QMS Junkie

Registered
Hey Jonny, I'm in a similar industry and we use manufacturing instructions for all crimpers. Frequency established is 1 year. If destructive testing is required, it is charged to whatever job the tooling will be used for.
 
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