The top and bottom sections look like this after the seam is welded.
Marcel then grinds the welds to create a peak that runs the length of the bumper.
Once the center section and corners are made, they get clamped together over the old bumper. All sections are intentionally made a little too long or too wide, so Marc uses a scribe to show where cuts need to be made to fit the pieces together.
Marc trims the excess metal off each piece using hand shears.
Source : http://www.customrodder.com