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Washer sitting on two different surfaces with a flush distance
4

Washer sitting on two different surfaces with a flush distance

Washer sitting on two different surfaces with a flush distance

(OP)
Hello

We have a battery enclosure and it is mounted in its place using two locator pins at the rear face. During the vibration test named SAE J2380(Vibration Testing for EV batteries), the nut got loose and hence the pin got loose in its position which resulted in test failure. We did not observe any loosening for the twin locator pin which had a glued nut (blue Loctite). Therefore we decided to replace the plain washer with a Nord-lock washer which you can see below. The Nord-lock washer pair sits on two different surfaces. These surfaces are flush, however each has +/- 0.1 mm of tolerance. So they may not be flush afterall due to tolerance. Would Nord-lock washer work in this scenario? If not, what can be done instead?

Nord-lock washer:
https://www.nord-lock.com/shop/washers/stainless-s...

RE: Washer sitting on two different surfaces with a flush distance

No.

Won't work. Not ever.

RE: Washer sitting on two different surfaces with a flush distance

Hi

Make the pin hexagonal shaped shoulder by tolerancing it so that it stays flush or sits below the enclosure surface, that way you ensure that the Nordlock washer sits on the inside face of the enclosure wall. If the hexagonal part of the pin protrudes through the enclosure wall al you achieve is the nut being locked on the pin, that would mean the whole locator pin would be free to move axially. If it were my design I would get rid of the hexagonal hole in favour of a round hole and put Nordlock washers under both the nut and the head of the stainless pin.
Round holes are much cheaper and easier to produce than hexagonal ones, also removing th hexagon shape off the pin should save some money too.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

RE: Washer sitting on two different surfaces with a flush distance

2
If Loctite did the trick, why look farther?

Is the formed aluminum piece the "enclosure"?
Any estimate of the forces on the pins during the vibration test?
Are the pins doing any locating, except during the peak of extreme events?

Are pins doing the only locating of the enclosure?
Enhanced clamping of the enclosure could turn the pins into assembly locators only.

Only the actual clamping faying surfaces of the bolted joint should touch.
As others said the (currently hex) shoulder on the pin should be below the face of the 1 mm aluminum plate the washer bears against.

All the involved faying surfaces should be smooth and flat.
Distortion, convex surfaces and burrs invite embedment and loosening.
The larger shoulder on the pin that bears against the 1 mm thick aluminum must be flat, and perpendicular the thread CL.

Torque the M8 nut appropriately to create clamping force sufficient to resist all applied loads.

For my money Nordlocks are not needed on a well designed, properly assembled structural bolted joint.

The thickness of the Aluminum wall is only about 1 mm. I'm thinking "structural joint" does not apply.

RE: Washer sitting on two different surfaces with a flush distance

Have you considered using Nyloc nuts instead? Can then just use a standard washer

RE: Washer sitting on two different surfaces with a flush distance

It's a bad setup - a hard material bearing on a much softer one; a very limited length of fastener to develop elongation to offset the likely embedment losses of initial fastener stretch which won't be much.

You might keep the nut from coming loose but it won't keep the joint tight for long.

The main contribution of that nordlock is to act as a spacer to increase the length of the amount of stretched fastener from nearly nothing to only slightly better.

I would suggest welding an aluminum round with a female mating thread to the inside where the volume of the nut is now - put a shoulder on it and groove weld from the outside and grind flush. If the round is made right one may avoid the need for filler material - just get a TIG welder (person and the tool) and they can install these faster than assembling that stack of hardware.

Then install the pin with locking compound, no hex shoulder - put a hex or torx recess in the exposed end if desired or flats to provide a gripping method. If the thread, say 4 complete threads, is only on the end with the pin necked down then this will improve the elongation of the pin and the compression of the aluminum round significantly so that minor imperfections won't later allow tension loss. Locking compound keeps the threads from fretting/corroding.

RE: Washer sitting on two different surfaces with a flush distance

(OP)
Thanks all who replied. I acknowledge that it will not work touching on two faces like that. The reason we cannot modify the locator pins is that we already have 300 in stock. So I came up with a temporary solution like below.

In order to avoid touching two different faces, I put a foam spacer (foam for anti-NVH) around the M8 thread, and put the Nord-lock washer around it to center properly. Yes it means adding one extra part, but still more economical than scrapping the pins in stock.

What do you think? Is there any other way to center the Nord-lock washer without using a spacer?

Nut tightening torque is 15 Nm

RE: Washer sitting on two different surfaces with a flush distance

Glue it to the nut? / spot weld?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Washer sitting on two different surfaces with a flush distance

How much will failure cost?

You build 300 of these. How many warranty repairs equals the cost of 300 scrapped locator pins?

RE: Washer sitting on two different surfaces with a flush distance

(OP)
They will not be glued to the nut but they can have an adhesive surface which can help to fix on position. I do not expect the adhesive to be necessary.

Can there be another fastener solution to enable using a large inner Ø Nord-lock washer correctly in position as shown in the image?

RE: Washer sitting on two different surfaces with a flush distance

Hi Managuensis

The Nordlock washer has an inside diameter of 8.7mm so that leaves a 0.35mm gap alround for you to get a spacer to sit on the M8 thread and centralise the Nordlock washer? I am having trouble understanding that. The hexagonal spigot on the pin used to locate the pins position, what are the dimensions of it? On the subject of cost if you scrap 300 pins compare the cost of that to the cost of the additional components you have to buy but more importantly your time spent on trying to resolve the issue.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

RE: Washer sitting on two different surfaces with a flush distance

dersrtfox,

What Mana didn't point out is that he or she is now using an M12 washer on an M8 stud, hence why the space is now bigger than it was in the original case.

Mana - You asked is there any way to centralise the washer and I suggested gluing or otherwise fixing the washer to the nut before you screw it on. your reply is a little strange, but you could use double sided sticky tape if you want, but a couple of dabs of glue onto the washer and carefully centralising it should work and is cheap and simple. Just get some reasonably strong glue.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Washer sitting on two different surfaces with a flush distance

Hi Littleinch

I missed that so thanks for pointing it out 👍.

I don’t think using an oversized washer is a good idea either, because of the reduced surface area of the clamped parts in contact with the washer, particularly in this case where they are much softer than the washer material. The reduced surface area in contact with washer could easily reach the yield stress value during tightening which means you won’t have the clamping force you desire. Another problem is that he spacer would absorb the excess material of the hexagonal spigot if the tolerancing was such that the spigot protrudes past the hole surface and so as the nut is tightened the spacer gets pinched and I have no idea how stiff the spacer is but I imagine it might act a bit like a compression spring and produce an opposite axial force which act to reduce the clamping force intended.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

RE: Washer sitting on two different surfaces with a flush distance

Honestly, this is a good case for an adhesive mount pin. You don't have good grip length. Any movement at all will cause fretting and rapidly lead to loosening of the fastener. You have stress concentrations at the edges of the washers. Make a simple flanged pin and glue it in with an acrylic structural adhesive. Many adhesives allow loading within 30 minutes.

RE: Washer sitting on two different surfaces with a flush distance

We must be discussing fasteners again, bc this board is once again recommending all manner of expensive convoluted solutions.

Forget the foam spacer, that does exactly nothing for NVH. Forget the Nord-loc and Loctite, both are expensive and unnecessary. Use a properly sized plain washer (larger than the tiny ones shown) and the proper torque. You need torque to achieve thread stretch which prevents loosening, and you also need sufficient bearing area to prevent damaging the housing. Not sure where you have two surfaces subject to differing 0.1mm tols, but that should not affect this joint.

RE: Washer sitting on two different surfaces with a flush distance

(OP)
Hi LittleInch,

Thanks for the reply. Your glueing suggestion sounds tempting. But I could not understand where exactly the Nordlock washer and the M8 nut would be glued/taped, so that the mating surface between these two would not be contaminated by the chemical. AFAIK, we need some rotational movement between these two elements during tightening, where the serrations on the Nordlock washer will penetrate into the nut flange face.

RE: Washer sitting on two different surfaces with a flush distance

No washer or nut. Use the glue to retain the pin. You won't be able to use your current pin, you'll have to make one similar to this bushing minus the threads.

https://www.clickbond.com/product-detail/bushings/...

RE: Washer sitting on two different surfaces with a flush distance

what's the problem with Loctite on the threads?

RE: Washer sitting on two different surfaces with a flush distance

Because it doesn't solve the problem that the slightest amount of fretting wear will render the system loose.

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