Cold Forming Countersunk Holes

[bduff]

I am investigating a manufacturing process in our shop where we are cold forming (pressing) the countersink detail into the plate rather than machining it. The countersink is for a 3/4" bolt and a 3/4" plate. Problem is the plate is splitting to the end of the plate which is 1.625" from the end of the plate to the center of the hole. The material is a 50ksi yield plate.

Do any of you have any tips or tricks to correct this issue? It may be that we are just asking for too much and to get there is just overstressing the plate.

Thanks in Advance!
bduff

 

[3DDave]

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?

 

[dhengr]

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.

 

[BridgeSmith]

Where is the upset material supposed to go?

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

 

[berkshire]

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.

 

[Agent666]

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.

 

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."

 

[bduff]

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!!!