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Semisolid metal processing is a well-known technology that can be used to enhance manufacturing product quality in broad industries. The technology controls the thixotropic properties of alloys within their solidus and liquidus temperature ranges. In general, most known alloys can generate semisolid slurries at high solid fractions, and the remaining can form slurries at low solid fractions. This has provided opportunities for many metals and alloys to be processed as semisolid slurries in today's casting industry. However, only a few researchers studied this technology potentially for a new metal-based additive manufacturing or 3D printing process. This article reviewed literature and findings from thixotropy rheology and semisolid metal processing methods, finally to thixotropic metal 3D printing. The survey shows that more future work is needed, including the investigation of thixotropic metal flow mechanics, the modelling and simulation of semisolid metal extrusion and further development of a fully thixotropic 3D printing system. [ABSTRACT FROM AUTHOR]

Rapid resin transfer molding is suitable for high-volume production of composite products. In this work, the epoxy systems with long pot life, i.e., with low reactivity at room temperature and low viscosity for fast injection into the mold cavity and reinforcing fabric, were developed by varying different concentrations of diluent and catalyst. Once infusion is completed, such epoxy formulations were capable of reacting fast at cure temperatures. Different formulations were developed to achieve such goals. This paper reports on the investigation of cure rate, cure temperature, cure time, glass transition temperature, and in situ cure monitoring using differential scanning calorimetry. [ABSTRACT FROM AUTHOR]

Vacuum resin infusion has been developed as a low-cost process for manufacturing fiber-reinforced composites with high fiber loading. However, it is an extremely slow process due to the long time required to prepare a vacuum-tight mold and further to cure the resin at room temperature. In this work, a new mold with a rubber cushion suitable for rapid infusion and rapid curing under complete negative pressure was designed and fabricated. Experimental results demonstrated that the new mold is suitable for rapid heating and withstand dynamic loading under complete vacuum force. Composite plaques can be produced with a short cycle time of several minutes while desired mechanical properties are still achieved. Thermal analysis and rheological measurements were performed to study epoxy curing at elevated temperatures and define an optimal process window for rapid vacuum infusion. This study leads to the development of a completely vacuum-based liquid molding process that uses simple tooling, yet is suitable for rapid production. [ABSTRACT FROM PUBLISHER]

Poly(para-phenylene), a self-reinforced rigid-chain polymer, has superb mechanical properties. Its use as a thermoplastic polymer in injection molding, however, is prohibited because of its extremely high viscosity. In this study, an injection molding process with a rapidly heated mold was used to enhance the moldability. The mold can be heated from room temperature to 250°C in 5 s and thermally cycled for 10,000 cycles without a fatigue failure. The effect of the mold heating temperature on cavity filling was investigated. The status of filling in the cavity was found to be significantly affected by the mold heating temperature. At a mold temperature of 350°C, complete fill of a 4 mm thick and 50 mm long cavity was achieved and the jetted polymer streams in the mold cavity caused by a high injection rate were thermally fused. Rheological data showed that, although it has an extremely high viscosity, poly(para-phenylene) is an extremely pseudoplastic polymer, with its viscosity strongly dependent on the shear rate. These results indicated that poly(para-phenylene) may be practically injection molded at a high injection speed with a rapidly heating mold at a mold temperature well above the polymer's glass transition temperature. [ABSTRACT FROM AUTHOR]

The characteristics of pattern replication and releasing in a roll-to-roll ultraviolet- (UV) curing embossing process were investigated. The roll embossing system was designed for large-area continuous embossing, with employment of a fast curing resin, a heat damage protector, and a surface energy reducing coating. A 60° V-groove pattern with a groove period of 30 µm was embossed. It was found that the replication quality was profoundly influenced by the pattern geometry, the pattern direction, and the mold surface energy. In particular, the pattern direction significantly affected the edge sharpness and the surface topography of replicated features. In the parallel groove mode, a significant amount of tearing and sliding occurred, whereas in the transverse groove mode, biting marks were observed on the side wall of the V-groove. A simple mechanical model was used to explain the difference in pattern releasing with different pattern layouts. The replication quality was found to be significantly improved with the application of a fluorinated coating on the roll mold. [ABSTRACT FROM AUTHOR]

The characteristics of fluid flows confined within microscale space are of theoretical and practical interest. Research has shown that the rheological properties, such as viscosity, of a microscale fluid film are different from its bulk behavior. Microrheometers have been designed to investigate the microscale fluid properties. However, currently available microrheometers are mostly drag-flow based and limited in load capacity. In this research, a new pressure-driven radial flow-based microrheometer is developed to study the high-shear pressure-driven flow. The new device is capable of self-aligning to maintain the fluid film uniformity, which is verified using finite difference methods. In addition, a prototype is built and instrumented to verify the design concept. The error involved in the fluid film thickness measurement is analyzed and compensated by the average fluctuation of the disk surface. The compensated testing results of viscosity are close to that tested by the traditional capillary rheometer for both Newtonian and non-Newtonian fluids. [ABSTRACT FROM AUTHOR]

In the accompanying paper, Part I, the advantages of the rapid thermal response (RTR) molding process were investigated for thin-wall-mold filling by employing coupled analysis of flow and heat transfer. Besides the complete filling of the cavity, frozen-in molecular orientation is another major quality issue in thin wall molding. The frozen-in orientation causes residual stress and birefringence, and potential part distortion. The present work focuses on the prediction and visualization of birefringence in RTR-molded parts. To calculate birefringence, flow-induced residual stress is computed first and the stress-optical law is then applied. The simulation results show that the amount of molecular orientation, residual stress, and birefringence level considerably decrease in the RTR-molding process. The effect of the mold temperature on the level of birefringence was also studied and predicted birefringence patterns were compared with experimental results for a thin-walled rectangular strip. Both predicted and experimental patterns of birefringence are in agreement on the observation that the birefringence level diminishes significantly when the mold temperature is raised to above the glass transition temperature. [ABSTRACT FROM AUTHOR]

The rapid thermal response (RTR) injection molding is a novel process developed to raise the mold surface temperature rapidly to the polymer melt temperature prior to the injection stage and then cool rapidly. The resulting filling process is achieved inside a hot mold cavity by prohibiting formation of frozen layer so as to enable thin wall injection molding without filling difficulty. The present work covers flow simulation of thin wall injection molding using the RTR molding process. Both 2.5-D shell analysis and 3-D solid analysis were performed, and the simulation results were compared with the prior experimental results. Coupled analysis with transient heat transfer simulation was also studied to realize more reliable thin-wall-flow estimation for the RTR molding process. The proposed coupled simulation approach based on solid elements provides reliable flow estimation by accounting for the effects of the unique thermal boundary conditions of the RTR mold. [ABSTRACT FROM AUTHOR]

Injection molded parts are driven down in size and weight especially for portable electronic applications. While gains are achieved via cost reduction and increased portability, thinner parts encounter more difficulty in molding due to the frozen layer problem. To increase moldability in thin wall molding, a rapid thermal response (RTR) mold was investigated. The RTR mold is capable of rapidly raising the surface temperature to the polymer melt temperature prior to the injection stage and then rapidly cooling to the ejection temperature. The resulting filling process is done inside a hot mold cavity and formation of frozen layer is prohibited. Concepts of scalable filling and low-speed filling are discussed in the article to address the benefit of this molding method. Simulation results showed that significant reduction in injection pressure and speed can be achieved in RTR molding. In contrast to the filling behavior in conventional molding, the injection pressure in RTR molding decreases as the injection speed decreases, and therefore, extremely thin parts can be molded at lower injection speeds. Filling lengths of both RTR and conventionally molded polycarbonate samples, with two levels of thickness, under two levels of injection speed were experimentally studied. The experimental results demonstrated the advantage of the new molding method. [ABSTRACT FROM AUTHOR]

Gas-assisted injection molding has been widely used to provide promising solutions to problems in conventional molding. With additional process parameters introduced, optimization in gas-assisted injection molding is much more complex than in conventional injection molding. This paper proposes an automated design methodology for gas-assisted injection molding with robustness in consideration. By introducing a definition of gas penetration cost, the optimization problems dealing with multiple quality issues can be modeled as constrained optimization problems, with the gas penetration cost as main objective function and other quality quantities as constraints. A direct search-based optimization procedure, the Complex method, is used to optimize a bounded single-criterion problem. To illustrate the proposed methodology, a case study is carried out on simulation results. [ABSTRACT FROM AUTHOR]

Eliminating flow-induced birefringence and stresses and reducing thermally induced stresses in the injection molded parts have been studied using rapid thermal response (RTR) molding technique. In the RTR molding, mold surface temperature can be rapidly raised above Tg in the filling stage, while the normal injection molding cycle time is still maintained. Therefore, the melt can fill the cavity at temperatures above Tg, which enables the flow-induced stresses to relax completely in a short time after filling and before vitrification. Residual stresses and birefringence in a RTR molded strip specimen are compared with the conventional molded parts by applying layer removal method and retardation measurement. For the material (Monsanto® Lustrex Polystyrene) and process conditions chosen, the birefringence level decreased as the RTR temperature approached and exceeded the glass transition temperature until it almost disappeared at a RTR temperature of 180°C. Reduction of magnitude and shift of peak location were observed in the gapwise stress profile for RTR molded specimen. *Any opinions, findings, and conclusions or recommendations expressed in this publication are those of the authors and do not necessarily reflect the views of the National Science Foundation. [ABSTRACT FROM AUTHOR]

Injection-molding part designers are frequently faced with multiple quality and cost issues. These issues are usually in conflict with each other; thus, a trade-off needs to be made to reach a final compromised solution. Because evaluation of part quality and cost via injection-molding simulation is very time-consuming, implementation of a conventional multicriteria optimization procedure for injection-molding problems is economically unfavorable. However, many injection-molding problems dealing with multiple quality and cost issues can be modeled as constrained problems, with the total cost as the objective function and quality quantities as the constraints. By introducing a concept of penalized total cost, such constrained problems are further simplified into bounded single-criterion problems. The bounded single-criterion problems are then optimized using a direct search-based optimization procedure. Strategies of modeling, transformation, and optimization for these problems are discussed in this article. A case study is provided. [ABSTRACT FROM PUBLISHER]

The multicomponent injection-molding process is a sequential molding process in which one plastic material (overmold) is molded onto a previously filled and solidified plastic part (substrate). This innovative manufacturing process is gaining popularity among plastic manufacturers because of its flexibility and potential to produce multifunctional plastic parts. In contrast with increasing popularity, an integrated computer simulation software for this process is currently unavailable, partially because of the difficulty in mapping the boundary between the substrate and the overmold. As a matter of fact, multicomponent molders are still using the trial-and-error approach while the computer-aided engineering prevails in the conventional injection-molding practice. When the flow pattern of the overmold is of interest, it may be justifiable to use the conventional mold-filling simulation to predict the pattern. It is postulated that the influence of the interface boundary on the flow pattern of the overmold is insignificant due to the high filling rates normally encountered in the multicomponent injection-molding process. In this article, the flow patterns of the overmold of the handle of Gillette's shaving razor for ladies are predicted based on an approach where an integrated filling-packing-cooling simulation is first run for the substrate; upon completion of the substrate cooling, the substrate surface temperature is used as the initial boundary condition for the overmold in the second-stage analysis. Boundary interface techniques are applied to map the boundary condition from the substrate to the over-mold. The predicted flow pattern is found to be in reasonably good agreement with that obtained using the conventional injection-molding simulation as well as with the experimental results. [ABSTRACT FROM PUBLISHER]