Both dies are mounted into the Piccolo, and you can see what shape they will create. Note the tab at the back of the die-this is a stop guide for the edge of the metal that will be fed through the dies.
You can get the curve of a bumper (how it fits around the back half of a body) two ways. The hard way is to cut a straight piece of metal, then stretch it so it gets the right curve. The easy way is to cut the section with the curve already in it, then just form the edge. Using the second method, Marc and Marcel then fed the curved section through the dies.
What you get is a slightly curved center section (which follows the car body) with a lip formed over one edge. Two of these center section pieces are made-one for the top, one for the bottom.
Again using the old bumper as a form, the two sections are clamped in place before Marc begins to tack them together. Marcel keeps an eye on the sections so they fit together perfectly.
Source : http://www.customrodder.com