Measuring Pull Force on Crimped Wire Terminals

A properly sized "fish scale" should do just fine for course inspection. One of those with an indicator that records the highest reading will get you in the ball park.

35 Newtons is only 7.86 pounds, not a lot of pull, you could even solder and shrinkwrap and it would hold.

If your quantities are big there are new devices for crimping which measure the quality "on line" and document all operations. I worked on such a project and the prototypes work fine.

I'd like to suggest do not use fish scales. The hooks and such flail around when the wire strands pull out and the sudden release of the energy often bends the indicator portion. (Thus dangerous and readings are unreliable.)

Try a fixed mass that represents 20N and then incremental masses to be added to come up to 40N. Fix the terminal into a clamp using the non-crimped portion and then hang the mass off the wire.

The in line crimp force analysers and pull test stands are becoming less expensive and maybe you should look at them again.

Also note BEFORE doing any crimp force testing you should measure the crimp height and width as these are excellent indicators of crimp force outcome and consistency and can provide a non-destructive indicator of process conditions.

Are you testing to destruction or just testing to ensure they meet minimum spec.

We had to meet Ontario Hydro spec for equipment going to Darlington Nuclear station so I rigged a weight equal to rated tension force and tested all connections that way by hanging the weight in line with wire. Ring terminals hung on a pin.

Furthermore I collected a sample group of 10 pieces and tested them to destruction. Interestingly enough the #26 Ga and #22 Ga wire stretched and broke before our controlled cycle crimps failed.

Typically we test to destruction.

100 pieces from initial run with the tooling to determine capability and repeatability, then we test five parts at start of each production run (and at same time calibrate crimp force analyser from those pieces) to verify the next production run.

Typically doing 10 changeovers per shift, we have 50 different applicators and 7 different wire strand configurations in three different insulation thickness options. (It's not as bad as it sounds. Good documentation and the applicators do not need to be adjusted for fitting/removal between runs, so there is really no operator adjustment, just verification.)

We have a motorised pull test stand with 500N pull force on line and have access to 500N test stand that we can plot force versus displacement to get failure curves rather than just peak values.

Thanks for your comments and suggestions. Yes, we need to test some samples to destruction and that will be preformed on batches as they leave the production line. Reading through the comments I think it will be wise to invest in a machine in the near future.

The suggestion of hanging some weights on the wire makes sense.

We have also include, in the production line, a visual testing stop where each crimp is inspected with a strong magnifying glass and any incorrect crimps are rejected.

If you consider such investments consider as well the device I mentioned which makes a total traceable quality control on line allowing a full documentation and which does not need any other destructive tests. Do not stay only with technology of yesterday and today think for tomorrow. It was designed for aeronautical and space applications where safety is a must.

A bucket and water.

Hang the bucket on the crimped connection and slowly fill it with water.

Make sure that when the crimp connection fails the bucket doesn't tip over and all water stays inside.

Then just measure the bucket and recalculate the weight to force.

A very simple way and quite accurate.

Start by making a professional looking stand that you can attach the wire on the top. Then test by clipping or wraping a 36N weight to. If no strands pull out or break crimp may be ok.

The second test is to measure the crimp height. This is done with a crimp micrometer (pointed and flat anvil) it can also be done with a calipier.

Molex has excellent visual aids for crimps.

Good Crimps and How to Recognize Them:

http://www.molex.com/molex/common/staticLoader.jsp?fileName=/tnotes/crimp.html&channel=Tech+Library&chanName=&channelId=-17162&programId=372059&progLink=Good+Crimps&chanLink=&pageTitle=Good+Crimps

If any additional help is needed,please feel to email me at david.chapman@pcprecisioneng.com

I have over 30 years working with cables and crimps

Good luck!