Materials movement sucks, and it's our job as designers, engineers or craftspersons to learn tricks to deal with it. You'll put a slight arc in a plastic surface that's supposed to be flat, so that after it comes out of the mold and cools the surface doesn't get all wavy; a furniture builder in Arizona shipping a hardwood table to the Gulf states will use joinery that compensates for the humidity and attendant wood expansion; and similar allowances have to be made when joining steel and aluminum, as they expand at different rates when the temperature changes.
On this latter front, Honda's engineers have made a breakthrough that those who work with fabrics may find interesting: They've discovered that by creating a "3D Lock Seam"—essentially a flat-felled seam for you sewists—and using a special adhesive in place of the spot-welding they'd use with steel-on-steel, they can bond steel with aluminum in a way that negates the whole thermal deformation thing.
Practically speaking, what this new process enables them to do is create door panels that are steel on the inside and aluminum on the outside. This cuts the weight of the door panels by some 17%, which ought to reduce fuel consumption. (Honda also mentions that "In addition, weight reduction at the outer side of the vehicle body enables [us] to concentrate the point of gravity toward the center of the vehicle, contributing to improved stability in vehicle maneuvering," but that sounds like spin to us.)
Unsurprisingly they're mum on how they've pulled this off or what exactly the adhesive is, but they do mention that "these technologies do not require a dedicated process; as a result, existing production lines can accommodate these new technologies." The language is kind of vague but it sounds like they're saying they don't require massive re-tooling, which is a manufacturing coup.
Honda's U.S. plants are the first to get this manufacturing upgrade, and we'll be seeing the new doors as soon as next month, on the U.S.-built Acura RLX.