Metal and Ceramic Components made via CAM-LEM Technology

CAM-LEM (Computer-Aided Manufacturing of Laminated Engineering Materials) is an SFF technology suitable for many engineering materials for which feedstock is available in sheet form; lamination and post-processing procedures are materials specific. Two methods for producing sheetstock, tapecasting and compression molding , are discussed and contrasted. Ceramic and metallic components that have been produced via CAM-LEM are described. 1. Overview of Process Computer-aided manufacture of laminated engineering materials (CAM-LEM) is a sheet-feedstock-based process for rapid prototyping capable of producing functional components directly using engineering materials (advanced ceramics, metals, or engineering polYmers). An outline of the process is given in a companion paper [1] and prior publications [2-4]. A significant unique feature to CAM-LEM is that it is a "cut-then-stack" approach in which the production of pseudo-2D contours via laser cutting and stacking are carried out as separate operations. This approach required the development of an automated process for precise manipulation of cut sheet stock [2], but offers three basic advantages. First, because each sheet is manipulated independently, it is possible to incline the feedstock during laser cutting so that the "tangent cutting" can be used to improve surface finish or increase build rate [1]. Secondly, as solid sheets are used, CAM-LEM offers a great deal of flexibility in the choice of materials that can be employed. Many materials are commercially available as sheets and essentially all powders can be pre-processed (in most cases, using a binder system) to produce sheet stock of a microstructure optimized for post-assembly thermal processing. Of particular interest for the production of ceramic and metal components, the use of a separate preprocessing step to produce sheet feedstock allows the use of very fine powders when desired without the typical flowability issues arising. Thirdly, because cut outlines are added sequentially, it is possible to build using a variety of feedstocks and to produce green assemblies that have spatially varying composition both from layer-to-Iayer and within a given layer. The issue of tangent cutting is discussed elsewhere [1]. The following will address: the characteristics of feedstock suitable for CAM-LEM processing; the processes used for fabricating sheetstock; lamination; resultant microstructures within fired components; and typical components. 2. Sheet Feedstocks The focus of this discussion is powder-based sheetstock, of which there are two classes that exhibit different characteristic behavior. The first is produced by tape casting [5]. Green tape produced by this method has roughly 55 vol. % inorganic powder, 15% organic binder, and the balance porosity. The porosity is typically finely divided, but continuous. The binder is typically linear, glassy and soluble in relatively benign solvents. Two types of alumina tapes have been used in CAM-LEM experiments; one cast from a nonaqueous suspension in a solution of polyvinyl butryal and the other cast from a suspension in a waterbased acrylic emulsion. Such tapes are characterized by a high compressibility, low stiffness, and (depending on the glass transition temperature of the binder) a susceptibility to viscous flow