In general a minimum bend relief is equal to the material thickness plus the inside bend radius.
Sheet metal corner relief size.
Generally capabilities of of 0 9mm 20mm in thickness are able to be manufactured from sheet 3mm or plate 3mm but this tolerance depends mainly on the part.
If you use the close 2 bend corner tool you can take the two corner types shown above and they will look like the closed corner shown below with the flat pattern to the right.
To eliminate this a bend relief is added so the edge of the sheet metal is perpendicular to the bend.
This option is straight forward.
The way this one works is that you select the tool first found on the home tab sheet metal group.
For a 3 width ratio when the part is 1 mm in thickness the width of the slot will be 3 mm.