How to level SS 304 sheet metal after perforation?

[Tarun Tanwat]

I had a stainless steel of Diameter 1000mm with a sheet thickness of 1mm. I have perforated that whole sheet through punching machine and there is 25mm margins (border) along the circumference. Now, that sheet is not flat now due to the expansion , I guess. I made a single cut equal to the radius of that round sheet and found that cut now overlaps about 5mm and the sheet becomes flat after cut. So could you help me making the perforated sheet levelled without cutting. Thanks

 

[berkeman]

Welcome to PF.

I have perforated that whole sheet through punching machine and there is 25mm margins (border) along the circumference.

So you have a round sheet of SS that is 1m in diameter and 1mm thick, and have punched a single hole that is a little under 1m in diameter in it? Or have you punched a series of smaller holes in the sheet? If a series of smaller holes, what is the spacing between them and how are they distributed?

How "flat" do you need the final product? What specifications are you trying to meet?

Can you post a picture of the sheet? Use the "Attach files" link to upload a PDF or JPEG file with the image in it. Thanks.

 

[Baluncore]

Now, that sheet is not flat now due to the expansion , I guess. I made a single cut equal to the radius of that round sheet and found that cut now overlaps about 5mm and the sheet becomes flat after cut.

If the sheet is not flat after punching, it will form a cone, or a saddle. It seems you have an overlap near the circumference, so you have a saddle, caused by shrinking of the area that has been punched. Maybe metal has been dragged at the edge of each hole.

There are two remedies to an existing saddle. You can expand the area that has been punched by beating it (to flatten and thin it there), or you can shrink the circumference by heating and quenching, which is more involved.

If you will repeat the punching process many times, you should change the profile of the punch to neither expand nor contract the circumference of each hole as it is punched. Do you lubricate the punch?

"Saw hammering" is an art that involves beating a circular saw blade so that it will be flat when spinning at the working RPM. There are automatic rolling machines available that will flatten circular saw blades by rolling the steel. One of those machines could resolve your problem.

We need to see pictures of the plate you have punched, the overlap after your cut, and the profile of the edge of a punched hole.

Edit: Here is a link to a supplier of rolling machines that show the configuration used.
https://www.williamsandwhiteequipment.com/tensioning-and-leveling

 

[jrmichler]

In addition to the previous posts, look at the sharpness of the punch and die, and the clearance between the punch and die. The figure below, from Manufacturing Processes for Engineering Materials, by Serope Kalpakjian, shows the effect of changing the punch/die clearance on the size of the deformation zone.

The deformation zone has high residual stress. The larger the zone of high residual stress, the greater the tendency to warp the finished product. The sharpness of the punch and die also affect the size and amount of the residual stress zone. The book has additional discussion on the subject. I recommend that you get that book, or a similar one, for your personal library.