This isnt fold forming, its basic sheet metal work.
there are 2 ways to do this.
- you need to get 2 pieces of square steel 150mm long by 5 mm sq.
one stays as it is, the other has 2 45deg bevels cut so it looks like
a triangle with the top cut off. this is also reduced in width to 3.5
these 2 bits of steel are located together with drilled holes say 20
mm in from each end through which you put some well fitting bolts
and wing nuts to tighten up.
you put your silver in between the 2 steels, clamp up on the scribed
lines and dress over to 45 Deg with a soft mallet.
Slacken off the bolts, remove one, slide the silver out, and finish
of by dressing down flat.
- The other way is to take your 10mm strip and turn into a tube.
solder up the long seam, true up in a draw plate then again dress
down flat with the seam in the middle of one side.
Ill leave you to find out how to make tube from strip.