An approach to designing lightweight metal-polymer composite structures in a manner that decomposes the structure into at least two parts. In one specific embodiment, the approach is a manufacturing process for a vehicle that includes attaching an impact beam to a vehicle structure. The process includes providing a vehicle structure including a back plate of the impact beam being made of a suitable material, such as a metal, that can withstand high temperature processes. A front part of the impact beam including a front plate and a polymer core is attached to the back plate. The back plate is designed to provide structural integrity that allows the vehicle structure to go through the high temperature processes and/or the vehicle structure provides structural integrity that allows the back plate to go through the one or more processes. The back plate is also designed to provide desired functional characteristics of the beam.