Press Tools, Plunged Holes

[finman]

I need help with the following problem;

I need to produce a plunged hole in a piece of Stainless Steel (304, Bright Annealed) 1.2mm thick, the bore of the plunged hole has to be 73mm Diameter.

Does anybody know how to calculate the maximum length of the plunging before the metal splits or tears?

From the application I know a "Rule of Thumb" will suffice as I aim to stay on the safe side.

 

[unclesyd]

Come back with a little more information on exactly what your definition of plunging is?

We used the word when we were making flared openings in metals by various means. We pushed/formed a bubble and trimmed the material to get the opening we desired.

When I made HP rupture disks I could easily get a 3 x dia width before rupture using hydraulics. This had a lot or variables, rate of forming, the quality of stainless, and the configuration of the die.

 

[finman]

Thanks for the interest unclesyd.

Imagine blanking a round hole somewhat smaller than 73mm diameter in a piece of 1.2mm Bright Annealed Stainless Steel, then forcing a punch of 73mm diameter through the material concentrically with the first hole. The result is a hole with a collar around it or as I would call it a "Plunged hole".

We currently do this but with far thinner material and smaller holes(0.120MM thick with a 12mm diameter hole). our customers usually do not ask for or need long collars but in this instance our customer is asking for us to quote the longest collar that we can produce.

The other point that may be a limiting factor, is that I can only use 2 blows of the press, 1 for the blanking op and a 2nd for the plunging op.

Hope this clarifies the problem.

 

[unclesyd]

I'm still looking for my info on S/S. Have plenty of information on Al but can't dig up information on anything else. Understand the dilemma as to tooling.
I don't think you will get much with out the possibility of tearing.
This type hole is often used for reinforcing or lightening of sheet metal. This is also called fairing a hole.

I hate to keep asking questions but are these holes within a sheet or are they on individual blanks?
What is the radius allowed?
Can the plunge part have a taper or does it have to be straight?
We need a tin bender to jump in.

 

[finman]

Hi unclesyd.
The holes are within an individual blank, although when we move into full production it will be in a continuous strip ie a 6" wide strip running thru' the press.

On the components we usually make we allow a 1 x material thickness as the radius.

Ideally the collar should be parallel but in practice this rarely happens due to both spring back of the material and the effects of the ejection mechanism in the press tool.

If nothing else, "Thanks for listening".