The ceramic-composite advanced tow-placement (CCATP) process is a means of laying down continuous-fiber-reinforced, ceramic-matrix composite (CMC) materials in patterned layers to form objects that could have complex three-dimensional shapes. The CCATP process is a member of the growing family of solid-freeform processes in art of rapid prototyping.
In preparation for CCATP, tows of fibers (of which the main ingredients are typically graphite or silicon carbide) are first coated with an interfacial material (e.g., pyrolytic graphite or boron nitride) to prevent damage in subsequent processing.
The fibers are then coated with a mixture of a ceramic matrix material in powder form plus a thermoplastic or other low-temperature binder. The resulting tows of coated fibers are wound on spools.
The CCATP process is effected by use of advanced tow-placement (ATP) equipment that includes, among other things, a robotic head that is moved to deposit the tows in the specified patterned layers. As the robotic head moves, the tows are paid out from the spools, heated, and pressed onto the surface of the object to be formed. The process parameters and the motion of the robotic head can be controlled by use of output data from a computer-aided design (CAD) system.
The head includes two rollers and two hot-nitrogen-gas torches that heat the rollers and the deposited material. The first torch and roller preheat both the incoming material and the previously deposited material or substrate. The first roller serves further to press and thereby tack the incoming material onto the previously deposited material or substrate. The second torch provides through-the-thickness heating to facilitate both consolidation of the just-deposited tow material and further bonding (beyond mere tacking) of the just-deposited tow material to the previously deposited material. The second roller completes the consolidation and bonding by pressing the just-deposited and previously deposited material together with enough force to prevent the formation of voids in the material.
A workpiece can be formed to nearly the desired net size and shape in the CCATP process. The size and shape can include allowances for small changes that occur in the next processing step, in which the workpiece is heated to burn out the binder and sinter the ceramic matrix to complete the synthesis of the composite material.
This work was done by Michael R. Effinger of Marshall Space Flight Center; Ranji K. Vaidyanathan, Mark Fox, Mark J. Rigali, and Anthony C. Mulligan of Advanced Ceramics Research, Inc.; and John W. Gillespie, Jr. and Shridhar Yarlagadda of The Center for Composite Materials, University of Delaware. For further information, contact the company at (520) 573-6300 or access the Technical Support Package (TSP) free on-line at www.nasatech.com/tsp under the Manufacturing category. In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to:
In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to:
Advanced Ceramics Research, Inc.
3292 E. Hemisphere Loop
Tucson, AZ 85706