LOS ANGELES -- It's called a "draw," which in layman's terms is a concave surface of a car's sheet metal. A draw that is too "deep," or too concave, tests the limits of metal-stamping technology on the manufacturing line.
That was the challenge in manufacturing the Acura ZDX's rear-quarter side panel and fender. Designers envisioned a look akin to the area surrounding a woman's collarbone. The vertical fender would have a mild outward bulge, ending at a sharp character line, then sloping sharply inward as it made its way toward the rear-side window.
Acura designers had asked for the section to be a single piece of stamped steel. But manufacturing engineers were resigned to making it in two parts because that seemed physically impossible, said Gary Evert, chief engineer of the ZDX.
"The problem with two pieces is that you end up with a seam, plus the panel gaps are hard to maintain, and it drives up cost," Evert said. "We knew doing it in one piece was going to be hard."
For a time, Acura had parallel development of one-piece and two-piece panels, but the look of the two-piece was all wrong. Meanwhile, the single-piece team found that reducing the depth of the 320 mm of draw ruined the character of the vehicle's design. It was all or nothing.
Using computer-aided design and manufacturing software helped with the trial and error, but real-world stampings failed because of the steel tearing or wrinkling under the stresses it was asked to endure, Evert said. Hydroforming was tried, and it also failed.
As to how Acura finally accomplished the feat, Evert slipped into jargon, such as "N- and R-value," "flow patterns" and "skin thicknesses."
Finally, a low-friction phosphate coating between the die and steel panel improved its formability, and Acura was able to make the section in a single piece.