An exterior body panel assembly having a Class A painted surface, mold-in color or non-Class A surface, and process of infrared welding components of the assembly. Panels of the assembly are placed on a nesting structure and the inside half of the structures are brought together with the other for a fit check. Panels are separated and an infrared heating fixture then heats the various areas to be heated on the panels. The areas on the panels are heated depending on the thicknesses of the parts at each area and surface geometries to be welded. The parts are immediately clamped back together under pressure for joining and cooling of the joined surfaces in the clamped arrangement.