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Rivet compression

Not strickly a SW question but it is likely that the expertise is found in this list...

How would one calculate the diameter and thickness of the shop head of a rivet?

I want to put together a model of MS20470 type rivets where I can indicate the thickness of material to be fastened and have the model generate the shop head automatically. This is important any time you want to check if the shop head clears any other structures in the design.

Can I just treat it as an incompressible fluid and simply figure out that for a given shop head height the diameter would simply be that which would give me the same solid volume that existed before the rivet was clinched?

I've already created this by using a design table driven part that encapsulates the incompressible fluid volume approach within the underlying math in Excel. A simple form allows input of the desired clamping thickness and rivet diameter. The design table then selects the closest rivet length that allows for a head thickness of at least that in published standards. With this in place, it is a simple matter to calculate the volume of the portion of the rivet's shaft that protrudes past the material to be clamped and "squeeze" it based on the volume formula.

Because there are infinite combinations of shop head diameter and thickness that result in the same volume I chose to lock the shop head diameter to match the diameter of the rivet's factory head. With that locked down the thickness of the shop head is easy math.

Any thoughts?

Thanks,

-Martin

Reply to
m
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Sounds like you have it licked. I used a similar approach for designing reliefs under coined countersinks in stamped parts.

Re: choosing a diameter--gotta start somewhere. Too many variable otherwise.

Reply to
That70sTick

I thought I had posted a reply but it didn't show up so if this is a repeat post I apologise.

We obviously rivet a lot in the aerospace industry, such as the one you mention.

Rule of thumb.

Cut rivets to a length in excess of the grip by 1.5 x rivet diameter The resultant bucked head is 1.5 x rivet diameter in diameter and 0.5 x rivet diameter in thickness.

We use these guidlines for auto rivetter clearances.

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Reply to
Anonymous

One more thing to remember.

The rivet shank expands into the hole during bucking.

This compresses the surfaces of the holes and work hardens them giving a much better joint. Some of the unbucked rivet volume will be used up in this process that is why the volume of the bucked head will not match exactly the volume of excess of the rivet outside the joint before rivetting.

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Reply to
Anonymous

diameter in thickness.

Is this practical for commercial (non military/aerospace) production though? I haven't studied rivetting equipment. Are these tools setup to make trimming the rivet to length a relatively simple process?

On a slightly different topic. The MS docs spec a #30 hole for a 1/8 in rivet. My fabricator likes to use a #29. The difference isn't huge, but I am wondering if I should insist that they go with #30. This is for electronic enclosure for commercial markets. I don't think it matters for my application.

-Martin

Reply to
m

As long as its a minimum clearance hole it should't matter as the rivet fills the hole anyway.

As to trimming the rivet length you can get commercial hand tools to cut the rivet to length after installing in the hole, ie install the rivet and then using the hand tool cut the tail. The hand tool has an anvil that will use the last stacked up sheet metal face as the gauge stop. These tools are adjustable and good for multiple diameter sized rivets.

Reply to
Anonymous

send me an email and I will send some data on minimum sheet sizes to be used with what diameter rivets, hole sizes, grip length versus rivet diameter etc.

Reply to
Anonymous

sed with what diameter rivets, hole sizes, grip length versus rivet diamete= r etc.

Thanks for the help. email on the way.

-Martin

Reply to
m

If you want to pull up some additional info ...

AC 43.13-1B Chapter 4

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MIL-HDBK-5
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MIL-STD-40007
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(tho' you can probably get it from DOSSAP, too)

I wonder if the parts were being assembled by hand in China if they'd use the #30 holes that have been standard for the last seventy years? ;^) ________________________________________________________________________

with what diameter rivets, hole sizes, grip length versus rivet diameter etc.

Thanks for the help. email on the way.

-Martin

Reply to
Tutha

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