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Crimpers for automotive

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Siwastaja:

--- Quote from: nctnico on March 09, 2024, 05:50:17 pm ---But let's apply some back on the envelope math:

In this PDF https://mtmmachines.ca/wp-content/uploads/2020/11/MTM-TP-Cold-Welding-R0.pdf it says that for cold welding to happen, you need to apply pressures over 12000kg/cm^2 (= 120kg/mm^2).

If you take a Molex KK-256 contact for example, the crimping area is about 6mm^2. For the cold welding process to happen you'll need 6*120 = 720kg of force on the jaws. Say you get a 1 to 7 lever effect from the Engineer PAD-11 (which is advertised for use with Molex KK-256), you'll need to produce a force of 720 / 7 =  103kg with your hands. An average man can produce 49kg of force by hand in his prime years. All this while assuming the Engineer pliers do not bend when they need to cope with these kind of forces. I hope this makes it clear that the engineer pliers are not suitable for reliable crimps as they simply can't produce the pressure required for the cold welding process. I hope it also shows why the likes of Molex, JST, etc don't supply simple crimping pliers for use with their crimp contacts; these won't create reliable crimp connections.

--- End quote ---

The problem with "back of the envelope" calculations are while they are excellent to rule out ideas that are wrong by many orders of magnitude, being too close the actual numbers and their suitability for the case starts to matter. So you say producing 103kg of force with your hands is a problem. It sure is, but is 10kg, which would be off by just 10x?

So let's question your numbers, 120kg/mm^2 is a worst-case number "as high as" for a process which has absolutely nothing to do with cable crimping, but is a complete different process namely making mechanically robust joints between two sheet materials. I can imagine the force required is higher as the materials need to flow into each other deeper than when the idea is to just make a gas-tight electrically low-resistance joint as in crimping (where the deformation of the lug provides the mechanical support.)

And sure enough, if you take a look at for example https://uk.milwaukeetool.eu/en-gb/m18-force-logic-hydraulic-53-kn-cable-crimper/m18-hcct/ They claim they can crimp lugs for 300mm^2 wire. 300mm^2 wire lug has diameter of around 26mm or so, for a 10mm long crimp the surface area to apply pressure to is then 26mm*3.14*10mm = 800mm^2. Per your number, 120kg/mm^2 * 800mm^2 = 96000kg = 960 kN of force is needed to do that. Yet the Milwaukee only produces 53kN, less than a tenth of what you claim is needed. Does the Milwaukee live to its promises? I have no reason to doubt it. Now, can an adult apply 10kg of force with their hands? Sure they do, but doing that all day long would suck. Then again the Engineer product is not meant for all day long production work. I'm sure it survives the force of 100N for a long time, though.

So clearly the document which does not talk about wire crimping at all was not a very good resource, as expected. I understand why you chose it, though: it seems impossible to find any numerical data of electrical cable crimping pressure online. A lot of sources talk about how you should not apply "too little" or "too much", but no numbers.

Now I won't question the 1:7 lever ratio, from the photos it seems close.

Conclusion: calling something impossible by re-interpreting some numbers from completely out-of-context source is, while interesting, a risky business. I mean, all you need to do is to buy the tool and test it in real world use. Therefore I value the actual experience people are sharing, and the fact well known distributors keep selling this product, way higher than your theoretical back-of-the-envelope calculations trying to prove it would not work.

nctnico:
How do you get to using the circumfence for a process that applies pressure from 1 side? It doesn't make sense. Like in a vise, force from one side gets opposed from the other side. And judging by the image, the length of the Milwaukee crimp is far shorter than 10mm. Besides that it likely takes a bit more math & modelling to calculate the amount of force needed / applied to a die to deform / compress a big round object compared to a small object that can be simplified to being flat and square.

Also, generic tool specifications doesn't mean they are actually suitable for the job. Sales people dream up all kinds of specs. You'd have to check the manufacturer's specification for the lugs you are using. And thinking that because well known distributors sell something, it is a high quality or even a suitable product is a mistake. Farnell -for example- sells lots of crap like leaky squeeze bottles (FFS!) and rebranded Owon/Hantek gear. I have been calling their Multicomp brand 'Multicrap' for good reasons for years. I also don't trust people who just look at crimps and say 'that looks nice'. I want to see data from pull-tests, analysis of the cold-weld process, etc before I (recommend) use (of) general purpose crimpers for connections which need to be reliable.

To get back to your 300mm^2 lug example, for this 300mm^2 lug:
https://www.etscablecomponents.com/product/two-bolt-copper-cable-lug-300mmsup2sup-w-m12-stud-holes-ct-300-c/

The manufacturer recommends this 130kN hydraulic crimper:
https://products.cembre.com/en/usa-canada-mexico/product/ht131-c

So likely the Milwaukee you found is not going to cut it unless it crimps a shorter area compared to the Cembre crimper. Electrical code is likely to say few words about the lenght of the crimps.

Anyway, the OP is looking to crimp low power contacts so discussing 300mm^2 crimps is quite far off the point.

Siwastaja:
OK, so nctnico's list of...

Well Known and Respected Tool Manufacturers Who Still Manufacture Unusable Tools as Based on nctnico's Napkin Calculations:


* Engineer (the Japanese tool company)
* Milwaukee (professional series)
More?


--- Quote ---Anyway, the OP is looking to crimp low power contacts so discussing 300mm^2 crimps is quite far off the point.
--- End quote ---
Yeah, still closer than non-crimping application of cold welding. You are free to post sources that state crimping forces for smaller connectors. I did not find any so I scaled down from a 300mm^2 crimp application for which numbers were available. Still closer than your non-crimping application.

bookaboo:
I'm no expert on mechanical calculations, so this is a genuine question...
Doesn't the mechanical force need to take into account the area onto which it is applied? I.e the smaller the surface being crimped the larger the force acting on the crimp will be for the same input force and lever ratio?

But back to the real world, there are a hell of a lot of different crimps out there, probably thousands. Even if you take the 80/20 principle there are dozens of different crimps that a hobbyist or small workshop will come across. Hell even a large firm wont want to purchase expensive tooling for small volume or prototypes, so "good enough" tools often are well.... good enough.

I've made some very complicated looms for CAT and Deutz engines, if you are unlucky enough to have to build your own Exhaust After Treatment loom (don't do it kids), then this alone can be dozens of different styles of crimps. The PAD range is the best I've seen for getting close enough, and with some careful checking we have never had an issue (and these do on crushing and screening equipment so get a hell of a shaking).

Would I want these used on high volume production or safety critical equipment, probably not. But for most applications these are more than good enough.

shabaz:
Hi,

A pull test will confirm the huge difference between a non-ratchet crimp result, and one done with a ratcheting crimper.
You can do that test using a tool that looks like a luggage weighing hanging device, but one that stores the value. After seeing the difference, you won't ever want to go back to non-ratchet (apart from non-critical use like prototypes for lab use).
For automotive, I'd be really unhappy to know if the engineer used a non-ratchet crimper.

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