William Thomas Carter

A parallel finite element method and its prototype implementation on a hypercube

Abstract This paper describes a parallel implementation of the finite element method on a multiprocessor computer. The proposed strategy does not require the formation of global system equations. An element or substructure is mapped onto each processor of the multiple-instruction, multiple-data multiprocessing system. Throughout the program, each processor stores only the information relevant to its element (substructure) and generates the local stiffness matrix. A parallel element (substructure) oriented conjugate gradient procedure is employed to compute the displacements. Each processor then determines the strains and stresses for its associated element (substructure). A prototype implementation of this parallel finite element program strategy on a hypercube computer is discussed. Examples for both linear and nonlinear analyses are presented.

Direct Laser Sintering of Metals

The use of a directed laser bealn source to selectively sinter multiple layers of binderless metal powder for the purposes of rapid prototyping is described. The work in this paper is restricted to -325 mesh iron powder, which was sintered using a C\V 50 W Nd:YAG laser to approximately 3.5% density. A subsequent post-treatlnent was perfornled to achieve a fully dense saulple. It is envisioned that such a system can be used to manufacture functional metallic prototypes directly from CAD without part-specific tooling.

Superalloys made by conventional vacuum melting and a novel spray forming process

Abstract Wrought Ni-base superalloys used in modern gas turbine engines are typically produced by vacuum induction melting (VIM) plus consumable remelting (ESR and/or VAR). For the more advanced alloys, these processes have certain limitations; namely, the ability to produce sound ingots of a reasonable size, free of harmful segregation related defects, which can readily be converted into wrought product. Powder metallurgy processes have been developed to overcome these problems but substitute another problem: high cost. To address these concerns, a clean, ceramicless spray forming process has been developed which uniquely combines electroslag remelting (ESR), bottom pouring through a cold induction guide (CIG) and spray forming (Osprey Metals Ltd). This paper discusses some of the issues encountered in current superalloy manufacturing processes and describes the clean metal spray forming (CMSF) plant which has been constructed to address them.

Spray Forming of Nickel Superalloys

Superalloy parts are conventionally manufactured using either cast, cast & wrought, or powder metallurgy processing. When cast, superalloys are usually precision-cast to final shape using the lost wax investment casting process. In the cast & wrought process, an ingot is cast and remelted, then converted into a forging billet via thermomechanical processing. In the powder metallurgy process, a billet is prepared by gas atomizing liquid metal to form powder that is consolidated into a fully dense solid. Spray forming offers a high-production-rate alternative that bypasses many of the steps associated with both cast & wrought and powder metallurgy processes.