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The dimensional variation of an injection-molded, semicrystalline polymer part is larger than the variation of an amorphous polymer part because the shrinkage of a crystalline polymer is generally greater than the shrinkage of an amorphous one. We investigated the warpage of film-insert-molded (FIM) specimens to determine the effect of the crystallization behavior on the deformation of FIM parts. More perfect crystalline structures and higher crystallinity developed in the core region of the FIM specimens versus other regions. Relatively imperfect crystalline structures and low crystallinity developed in the adjacent regions of the inserted films, whereas a thin, amorphous skin layer developed in the adjacent regions of the metallic mold wall. The crystallizable substrate in the FIM specimens caused very large warpage because nonuniform shrinkage occurred in the thickness direction of the specimens. Therefore, the warpage of an experimentally prepared FIM poly(butylene terephthalate) specimen was greater than that predicted numerically because of its complex crystallization behavior.

Complex automotive parts were produced by film insert molding and the ejected parts were annealed to investigate the viscoelastic deformation. Warpage of the part was predicted by numerical simulation of mold filling, packing, and cooling stages with non-isothermal three-dimensional flow analysis. The flow analysis results were transported to a finite element stress analysis program and the stress analysis was performed by using time-temperature superposition principle to investigate viscoelastic deformation. Predicted residual stresses, viscoelastic deformation, and warpage showed good agreement with experimental results. Thermal shrinkage of the inserted film and relaxation of the residual stress affected the viscoelastic deformation of the part significantly during annealing. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Impregnation of the multi-layered fiber preform with injected resin was analyzed by using the control volume finite element method for three-dimensional mold filling simulation of the resin transfer molding (RTM). Numerically predicted flow fronts were compared with experimental data to validate accuracy of the numerical results and applicability of the numerical code developed in this study. Since isothermal Newtonian flow was assumed, Darcy's law and continuity equation were used as governing equations and permeability tensors employed for each layer. Flow simulation was conducted for the two types of mold geometries, i.e., rectangular plate and hollow cylinder. It was proven by comparing numerical results with experimental data that the simulation code is accurate enough to predict the flow patterns, especially when multi-layered preforms were placed in the cylindrical mold. It was also found that the filling time was reduced by using outer gates compared with the case of inner gates. Three-dimensional numerical simulation provided useful information for mold filling and can be used to design an optimum mold and make the RTM process efficient. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Thermotropic liquid crystal polymer (TLCP)/ poly(ethylene 2,6-naphthalate) (PEN) were prepared by a melt blending, and were melt spun by a spin-draw process. In this study, we suggest novel drawing technology using the CO2 laser that can directly and uniformly heat up fiber inside to prevent the formation of ununiform structures in conventional heat drawing process. The properties of the heat/laser drawn TLCP/PEN blend fibers were superior to those of any other handled fibers, and were rather more excellent than those of TLCP/PEN blend fibers annealed at 1358C for 10 min. It was confirmed that the CO2 laser draw- ing made it possible to achieve the optimal drawing effect by draw ratio. The combined heating and CO2 laser-drawing method has a great potential for industrial applications as a novel fiber-drawing process, and it can also be applied con- tinuously to conventional spin-draw system. 2007 Wiley

Rectangular plates of the size of 1800 × 600 × 12 mm3 and 1200 × 600 × 12 mm3 were selected for injection molding and injection compression molding, respectively, in order to investigate warpage characteristics of the large-sized polymer plates with orthogonal stiffener. To determine the mold system and to reduce warpage of the specimen, numerical analyses for injection molding and injection compression molding were performed by using a commercial simulation code. Experiments were performed to verify the suggested mold system and warpage of the specimen. Relatively large warpage of the injection molded product was observed and small warpage of the injection compression molded product was generated. Compression force of the injection compression molding was only 6% of the clamp force of the injection molding. Warpage of the product was reduced significantly by using the injection compression molding. The injection compression molding will be used to substitute expensive and disused wood forms with inexpensive and recyclable polymer plates for concrete casting. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

In this study, experimental and numerical studies were performed to investigate the relationship among the functionalization method, weight fraction of MWCNTs, thermal imidization cycle, and mechanical properties of various PAI/MWCNT composite films. Poly(amide-co-imide)/multiwalled carbon nanotube composite films were prepared by solution mixing and film casting. The effects of chemical functionalization and weight fraction of multiwalled carbon nanotubes on thermal imidization and mechanical properties were investigated through experimental and numerical studies. The time needed to achieve sufficient thermal imidization was reduced with increasing multiwalled carbon nanotube content when compared with that of a pure poly(amide-co-imide) film because multiwalled carbon nanotubes have a higher thermal conductivity than pure poly(amide-co-imide) resin. Mechanical properties of pure poly(amide-co-imide) and poly(amide-co-imide)/multiwalled carbon nanotube composite films were increased with increasing imidization time and were improved significantly in the case of the composite film filled with hydrogen peroxide treated multiwalled carbon nanotubes. Both the tensile strength and strain to failure of the multiwalled carbon nanotube filled poly(amide-co-imide) film were increased substantially because multiwalled carbon nanotube dispersion was improved and covalent bonding was formed between multiwalled carbon nanotubes and poly(amide-co-imide) molecules. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Virgin injection-molded tensile specimens without any inserted film and four kinds of film insert molded (FIM) tensile specimens were prepared. They were annealed at 80°C to investigate the effect of residual stresses and thermal shrinkage of the inserted film on thermal deformation of tensile specimens. The FIM specimens with the unannealed film were bent after ejection in such a way that the film side was protruded and the warpage was reversed gradually during annealing and the film side was intruded. Warpage of the FIM specimen with the film annealed at 80°C for 20 days was not reversed during annealing. Processing of the FIM specimens have been modeled numerically to predict thermoviscoelastic deformation of the part and to understand the warpage reversal phenomenon (WRP). Nonisothermal three-dimensional flow analysis was carried out for filling, packing, and cooling stages. The flow analysis results were transported to a finite element stress analysis program for prediction of deformation of the FIM part. The WRP was caused by the combined effect of thermal shrinkage of the inserted film and relaxation of residual stresses in the FIM specimen during annealing. It is expected that this study will contribute towards the improvement of the FIM product quality and prevention of large viscoelastic deformation of the molded part. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009