Cold Forming Countersunk Holes

• Oct 25, 2019

• #2

3DDave

Aerospace

May 23, 2013

11,491

US

How big is the countersink? Bolt don't normally need them and, if required for clearance with the bolt fillet, is usually achieved with a washer ID that clears the fillet.

Where is the upset material supposed to go?

 

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• Oct 26, 2019

• #3

dhengr

Structural

Sep 22, 2009

4,669

US

Bduff:
Like 3DDave, I don’t understand why you need a countersink detail for a ¾” bolt on a hole in a ¾” pl. either. You could probably do what you are trying to do, if you heated the plate sufficiently and provided some forming pressure on the edge of the pl. in the immediate area of the hole. That certainly seems like the hard way to do this when a countersink and a drill motor would do the trick.

 

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• Oct 26, 2019

• #4

BridgeSmith

Structural

May 22, 2009

5,109

US

3DDave said:

Where is the upset material supposed to go?

Click to expand...

That was going to be my question. I doesn't seem like what you're proposing can work. The plate would have to deform, so if you did manage to get it so it doesn't split the plate (which would likely require heating it substantially), you'd end up with a bump on the back side of the plate. You can't change the volume of the steel; what is displaced from the countersink has to go somewhere.

Rod Smith, P.E., The artist formerly known as HotRod10

 

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• Oct 26, 2019

• #5

berkshire

New member

Jun 8, 2005

4,429

US

Normally when cold forming countersunk holes into sheet metal or plate, the initial hole is made oversized by formula, to allow the metal to cold flow to the center of the hole at the correct diameter, this cold flow operation then yields a double conical hole with the smallest diameter at the center of the plate with some minor cracking around the hole. Sometimes if this cracking is undesirable, a secondary drilling operation is used to remove this stress cracking. Normal edge distance for this is 2.5 D, you are close but 2.5D is 1.875. I would investigate the plate for manufacturing flaws.
B.E.

You are judged not by what you know, but by what you can do.

 

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• Oct 26, 2019

• #6

Agent666

Structural

Jul 2, 2008

3,080

NZ

Not sure if relevant to your end use, but this wouldn't be allowed if it's end use was as a structural element subject to seismic. The hardworking as you've found out results in fracture, just because holes with larger edge distances didn't fracture under fabrication doesn't rule out that they may when subject to loading.

 

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• Oct 30, 2019

• #7

Guest

You're asking a lot of any steel to survive that kind of operation.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

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• Oct 30, 2019

• Thread starter
• #8

bduff

Mechanical

Nov 1, 2012

17

US

Thanks for all your replies and I agree with all of them. I knew this was a long shot but just wanted to put it out there just in case someone had done this previously. Currently we do this process by machining and were just looking for ways to cut time without creating a hot work plate (for safety reasons). I agree this is a lot of material to cold form without wedging the plate apart. We are going to continue to investigate and I will update if anything comes of it.

Thanks to All!!!

 

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