Blanks of sheet metal with a thickness of 3 – 5mm will be more accurate and easier to bend at home if they are pre-trimmed along the fold lines using the grinder (and if the workpiece is not very long, and with a hand saw) about a third of the thickness of the sheet. And the bend radius will be much smaller.
Bend “cold”:
1 – sheet metal with a slit for bending; 2 – finished part after the bend; 3 – bench vise; 4 – padded corners; 5 – detail in the manufacture; 6 – hammer (mallet)