A method that exploits rapid prototyping has been conceived to reduce the time and cost associated with the production of small quantities of composite-material parts that have complex shapes. In this method, mandrels and dies used in forming composite layups are sized and shaped by molding them on rapid-prototype masters and are made of disintegrating mold material (DMM). The method is particularly suitable for manufacturing ventilating air ducts and water ducts for the International Space Station and manifolds and ducts for low-temperature [
In a related prior method, master parts are made of plaster; fabrication is difficult, guided by standard paper drawings, and often subject to workmanship errors. In this prior method, plaster is cast against a plaster master part, then split along appropriate lines to create a slush mold. Next, the slush mold is filled with DMM, which is a special plaster. The part thus formed in DMM is then used as a die or mandrel for layup of a composite-material part. The DMM mandrel is not reusable; it must be remade for each part to be manufactured. The temporal and monetary costs of building the master part and the slush mold and associated tooling are often greater than the other costs of the three or four detailed copies typically manufactured from each master part.
In the present method, neither a plaster master nor a slush mold is used. Instead, a master is made by rapid prototyping. DMM is then cast against the master. Once the DMM has been cured, the workpiece is placed in an oven at a temperature 225 °F (107 °C). When the DMM has been softened by heating, it is peeled away from the master. The resulting piece of DMM becomes a mandrel or mold that can be used in the custo ary manner for fabricating the desired composite-material part.
In comparison with the prior method, the present method saves considerable time and money. These savings are attributable mostly to elimination of the slush molds and associated tooling. In one application at Johnson Space Center, the method was found to cut weeks off the time needed to build the first part and to reduce the cost of the part by more than $8,000. The present method also affords greater accuracy, tolerances of ±0.005 in. (≈0.13 mm) being normal. The present method also eliminates the need for reworking masters because the rapid-prototype masters are made from computer-aided-drawing data. The total saving, relative to the prior method, is expected to amount to about 75 percent; this translates to >$240,000 per year at NASA's Palmdale, California site alone.
The present method has also been considered for use in a Marshall Space Flight center program in which a few composite-material parts are fabricated by, among other things, wrapping tapes directly on a stereolithographic master. The present method has shown potential to enhance the program by making it possible to reduce the number of steps in fabricating the master and increasing the accuracy of the master.
This work was done by Robert E. Clark, E. Wayne Shick, Ernest L. Broaden, and Fernando Schemel of Boeing North American, Inc., for Johnson Space Center. For further information, contact the Johnson Space Center Commercial Technology Office at (281)483-0474. MSC-22928