One can bend some pretty thick sheet metal in a vise. You may want to add some auxillary surfaces to the vise to prevent marring the sheet, if your vise has really heavy "teeth" on the gripping surfaces. You can initially push the metal over with a piece of wood, then hit it with a wooden mallet. Do not cut the metal- you risk breaking it. If the metal is very thick, say 1/16 inch or thicker, you should indeed use an extra jaw piece, and radius the top of it, so that there is not a super-sharp bend. Do a google search on "bend radius." The bend radius should be at least about equal to the sheet thickness.
You can also consider making a bending brake. It is easy enough to make and can be done in wood- my first brake was a wooden one from plans in a magazine. Then I bought a real one, not super expensive and I have had it for about forty years- they do not wear out in ordinary use.
There is also a new style break that is quite cheap, but I have not used one. It is a piece of metal with a v-shaped groove in it and you push or hit a square cross-section piece of something down into metal placed over the block which is covered with the piece of metal you want to bend. Micro Mark sells them.