The Competitive Edge Research Priorities for U.S. Manufacturing (1991) / Chapter Skim
Currently Skimming:
Manufacturing of and with Advanced Engineered Materials
Manufacturing of and with Advanced Engineered Materials
Pages 78-97
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 78... ...
It presents examples of classes of engineered materials and considers the state of the art of processing science and simulation as well as the goals of design for manufacturability and economic modeling and projections. Future needs and directions are presented from the focus of advanced materials, since their use can introduce barriers to optimization outside the normal scope of manufacturing science and engineering.
|
From page 79... ...
In multilayer materials for electro-optic applications, whose properties stem directly from the ability to control and exploit processing parameters, controlling growth of pseudomorphic layers is not only integral to the manufacturing process, but is, in effect, the driver. STATE OF THE ART Issues of simulation and the scientific, engineering, and economic bottlenecks associated with AEMs, are examined in light of the following considerations: · stability of microstructure and interfaces throughout processing, manufacturing, and use; · lack of property and predictability data bases, and of appropriate institutional settings for disseminating such information; · existence of niche markets and boutique materials; · special processing requirements and manufacturing equipmeet, and transient and nonequilibrium processes; - need for flexible and accurate process control;
|
From page 80... ...
As another example, liquid crystalline polymers are highly ordered within domains, but the macroscopic orientation of the domains depends strongly on the material's processing history. The properties of all of these composite and compositelike materials are functions of the microstructure- that is, of the sizes, shapes, and arrangements of the component phases or materialsand are determined by the nature of, and forces at, the interfaces.
|
From page 81... ...
In addition, neither property requirements nor processing methods are fully understood in relation to the detailed macroscopic and microscopic configuration of the multicomponent array and with the interfaces between the components in the array. These considerations translate into several major concerns that must be resolved if MMCs are to become a major option for a broad range of manufactured products.
|
From page 82... ...
The main concerns are structural {fiber-matrix} variables, property requirements, and processing options, including variables such as fiber composition, structure, relative dimensions and orientation in the matrix, nature and stability of bonding at the interfaces, and matrix mechanical and physical properties. These structure, property, and processing options form a three-dimensional matrix through which well-defined paths need to be identified to optimize properties and performance while controlling processing and structural complexity.
|
From page 83... ...
In short, materials processing has lost ground in materials engineering education in terms of emphasis and technical timeliness. The timing of this lag is unfortunate because structure, properties, and processing are inseparably melded in AEMs, and the required processing is rarely a simple extension or adaptation of traditional processing methods.
|
From page 84... ...
The use of plasma-enhanced processes, flash lamps for annealing, high-pressure oxidation, ion implantation, and other advanced processing methods permits fabrication of semiconductor devices at much lower temperatures than is possible by more traditional means, leading to devices with smaller geometries and fewer defects. New crystal growth techniques, such as molecular beam epitaxy and organometallic chemical vapor deposition, which not only allow growth of multilayer heterostructures of compound semiconductors, but also the combination of silicon with III-V compounds (e.g., gallium arsenide and indium phosphide)
|
From page 85... ...
Process simulation can facilitate rapid prediction of materials characteristics (e.g., shape, microstructure, and residual stresses) as a function of processing parameters, which leads naturally to appropriate control strategies.
|
From page 86... ...
Prediction of the influence of thermal and fluid flow and deformation processing on residual stresses and microstructure is especially difficult because of the relative lack of sophistication of microstructural modeling and the difficulty of symbolically describing microstructural features. Ideally, the process simulator should be usable in several modes to enhance material quality and speed the move from materials development to production implementation.
|
From page 87... ...
More powerful expert systems are clearly needed to represent more expressively materials and process engineering knowledge and to facilitate operation of intelligent control systems. A major challenge is to build intelligent controllers that are capable of translating materials and process understanding and reasoning approaches into planning and control formulations that can be executed by computer programs.
|
From page 88... ...
Development of such intelligent control relies on advances in understanding of materials processing, AI-based planning, and control technology. Determination of materials' microstructures, residual stress states, and processing pathways and identification of related reasoning strategies are all within the province of materials scientists and process engineers.
|
From page 89... ...
Another, an engineering-based approach called technical cost modeling, uses computer simulation to determine the cost of producing components by alternative processing methods. Here is one common formulation of the materials selection problem: Given a set of materials X, each possessing properties x, select the material Xi that, when used in product Y
|
From page 90... ...
Only in extremely specialized circumstances can the best selection be made without an explicit treatment of the preferences of the decision maker. This point can best be demonstrated by a specific example of technical cost modeling (Figure 4-11.
|
From page 91... ...
Technical cost modeling is an extension of engineering process modeling, with particular emphasis on capturing the cost implications of process variables and economic parameters. With cost estimates grounded in engineering knowledge, critical assumptions, such as processing rates and energy and materials consumption, interact in a consistent, logical, and accurate framework for analysis.
|
From page 92... ...
Research in polymers, for example, should be directed at Problems of fairly general or wide applicability, -- or ~ - - ~ ~ problems that, by their nature, will require the application of a variety of scientific and engineering disciplines. Examples include pultrusion with high viscosity thermoplastic matrices, effects of flow fields on discontinuous fiber orientation, and dispersion and adhesion of immiscible polymer melts.
|
From page 93... ...
Possible alternatives include liquid infiltration into long-fiber windings, tape methods analogous to those used for polymeric matrix materials, and vapor methods, including infiltration of fiber in vapor form into a porous matrix and infiltration of matrix vapor into a fiber preform. These and more radical processing approaches should first be modeled, then explored in the laboratory.
|
From page 94... ...
Research is required to develop process modeling tools that relate processing conditions to materials characteristics and materials characteristics to materials properties and product quality. This research must yield a common modeling basis that can be exploited by simulations of disparate physical phenomena in order to arrive at better models of complex (fluid/heat)
|
From page 95... ...
, potentially useful in printed circuit boards or structural applications; new, dieless forming processes driven by computer-aided design (CAD) data typified by commercially available systems for plastic parts; compound semiconductor {e.g., gallium arsenide)
|
From page 96... ...
The installed MBE machines at university, industrial, and government laboratories, advanced IC processing lines such as those at SEMATECH, and the flexible turning/machining cells at university productivity centers are examples of existing teaching facilities, many of them very new as a result of university instrumentation programs and state efforts to create centers of manufacturing excellence. The payoff from expanding such facilities and applying the teaching factory concept will be designers temperamentally geared to exploit AEMs early.
|
From page 97... ...
ALADIN uses symbolic reasoning to develop an abstract plan for the alloy design. This abstract plan contains decisions about the general microstructural features of the alloy to be designed as well as the alloying elements present and the processing methods uses.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.