Patches give way to polyurethane in B-I-W development – bodies-in-white
According to Giuliano Zuccato, a man who spent more than 30 years with Ford at its Design Center and who is now at Concepts International (Northville, MI), the traditional method for building prototype bodies-in-white – using a combination of sheet metal, machinable board, and carbon fiber – leaves much to be desired: “With bodies-in-white built from conventional materials, when a design changes, a small area of the property is cut out and replaced with a patch incorporating the updated surface. Over time, the body-in-white is literally covered with patches. While these new sections indicate the overall effect of design changes, they do not provide the needed accuracy.”
So Zuccato developed a new system, for which a patent is pending, which utilizes modular sections of CNC-machined polyurethane board. According to Chrysler’s Bruce Mattarella, manager, Vehicle Packaging, Truck Platform Engineering, “With the modular body-in-white, we can quickly and economically update design data during the development of wiring harnesses, trim panels, and other vehicle components. When a new section is reinstalled in the property, it represents a first-generation, precise surface that helps increase accuracy and eliminate potential design errors.”
The process employs Polyboard 140 modeling material, an easy-to-cut polyurethane, supplied by Ciba Specialty Chemicals Corp. (East Lansing, MI). The stock is grain-free: it resists warping, as can occur with wood. The surface is nonporous: it requires minimal – if any – secondary finishing. The board provides good edge definition when it is cut; it exhibits dimensional accuracy and stability. It is strong and durable: provides a Shore 62D hardness, a tensile strength of 1,800 psi, and a compressive strength of 1,750 psi (0.2% offset).
In application, a big time-savings benefit is the speed with which changes can be made to the model, either by machining an existing piece of board or cutting a new one. Observes Lee Philips, manager, SLA Tooling Applications, Jeep and Truck Engineering, Chrysler, “In the past, by the time a metal part of the body-in-white was re-formed, more changes had occurred. The net effect was that the design was obsolete before the reworked section ever got back to the car.
“Now because we can quickly alter the Polyboard material and reinstall board modules, the body-in-white is truly our ‘control center.’ If someone wants to see where the program is, they can go to the property and be assured it will always be the most up-to-date version of the design.”
Should it be necessary to ship out a portion of the body-in-white to a supplier, it is easily accommodated. This enhances security (i.e., it isn’t necessary to ship the whole vehicle). And after a vehicle is launched, the model can be retained so that it will be available to check out minor design modifications.
The build process for a modular body-in-white that Concepts International employs starts with bonding together a series of Polyboard 140 boards with a Ciba epoxy adhesive, Ren Weld 103. The clamped boards cure overnight. For a body-in-white floor pan for a mid-sized vehicle, some 30 blocks are assembled. Then it is a matter of cutting the material to the required shape. Board sections are typically milled with two-flute carbide or hardened steel cutters. Roughing is performed at 30 to 40 ipm, 2,000 rpm. Finishing is performed at 100 ipm, 2,500 rpm. “Polyboard,” says Zuccato, “is easy to cut with little cutter wear and offers excellent dimensional stability, even in thin sections.”
In order to minimize the development time for a body-in-white, different suppliers can be contracted to machine various components. By using this approach, an entire body-in-white can be produced in six weeks.
Once the pieces are machined, they are painted with an automotive lacquer. The modules are assembled, installed on a metal base, and shipped to Chrysler.
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