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4 Phase-Change Processes
Pages 51-66

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From page 51...
... These products range in size from steel castings of several hundred tons that are used in power generation plants to small, precision castings, such as delicate jewelry produced in investment molds. These processes are typically characterized by their molding process or by the casting process itself.
From page 52...
... Consequently, primary metals producers benefit from advances in energy conservation and pollution control. Continuous or direct casting processes produce a cast sheet or thin slab close to the final hot-rolled dimensions, thereby eliminating hot rolling as a processing step with a corresponding reduction in investment and operating costs.
From page 53...
... The productivity gain has been achieved through improved scheduling and extended sequence casting. Product quality has been improved through process optimization; process control; and a substantial upgrade of overall product flow, monitoring, and integrated supervision of downstream functions including slab cutting, marking, and direct charging to the reheat furnace at the hot strip mill.
From page 54...
... A suitable process control strategy must be developed that will allow production of high-quality strip on a reproducible basis and within narrow product specifications. Such a control strategy requires improved understanding of process dynamics, so that available computing capabilities can be used to interpret sensory inputs and to apply the resulting information to control the casting process in real time.
From page 55...
... The current R&D emphasis has centered around these factors and has included the following areas: . melt rheology during processing; modeling and simulation of process dynamics; polymerization and kinetics in reactive processing; structural changes under processing conditions; material properties characterization; unit processes for composites; and · process control and sensor technologies.
From page 56...
... Many users of mold analysis software tools are reporting better product quality and shorter lead time and, in some cases, are eliminating the need for prototyping. Recent developments in processes for resin transfer molding and
From page 57...
... Phase-Change Processes Table 4-3 Polymer Phase-Change Processes 57 Materials Processes Thermoplastics Thenno sets Injection Molding X X Compression Molding X X Polymer Casting X X Rotational Molding X X Co-Injection Molding X Gas-Assisted Injection Molding X Foam Molding X Calendering X Cold Forming X Extrusion X Blow Molding X Ihemoforming X Transfer Molding X Reaction Injection Molding X Liquid Injection Molding X Rubber Injection Molding X Reinforced Injection Molding X structural reaction injection molding have shown great potential for mass producing low-cost structural parts made from composite materials. Effective use of gas-assisted injection molding could significantly increase the flexibility of plastic part design.
From page 58...
... Casting technology for discontinuously reinforced MMCs experienced a development spurt roughly fifteen years ago. Cast composite technology then suffered from the stigma of castings having highly segregated microconstituents that resulted in nonunifo~ and variable product properties.
From page 59...
... To date, highly controlled processing techniques such as powder metallurgy, thermal spraying, and diffusion bonding have not been found to be cost-effective. Although extensive effort has been devoted to manufacturing processes that emphasize techniques to optimize structure and properties of the MMC, the lag in the development of such techniques that are also cost-effective represents one major barrier to the widespread use of MMCs.
From page 60...
... A number of new processes have shown considerable promise and are in various stages of commercialization. These processes include near-net shape casting, pressure die casting, rheocasting, rapid solidification, metal-matrix composites, powder process technologies, and vapor/solid processes for films and coatings (Flemings and Brown, 1988~.
From page 61...
... Improvements in numerical techniques for three-dimensional simulations of anisotropic material behavior are required for process design of polymer composite parts. Expanded simulation of solidification events in polymer processing, detailed predictions of component thermal shrinkage, and thermomecharlical modeling of part distortion are also key future needs for improved part quality and process productivity.
From page 62...
... This process development must include consideration of the influence of process conditions on the property levels and durability of the MMC components. Realistic modeling and simulation approaches to identify optimal processing conditions are
From page 63...
... Development offiber coatings andfiber preforms for in-mold liquid metal infiltration techniques of continuous-fiber MMC. Research on improving the manufacture of continuous fiber MMCs requires an integration of process technologies, sensors, controls, and materials characterization.
From page 64...
... 1988. Continuous Casting Design and Operations, Volume 4, Pp.
From page 65...
... 1987. Technologies that have made direct concatenation of continuous casting and hot rolling possible.


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