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Injection Molding (IM) is the most important process for mass-producing plastic products. The difficulty of optimizing an IM process is that the performance measures (PMs), usually show conflicting behavior. The aim of this work is to demonstrate a method utilizing CAE, statistical testing, artificial neural networks (ANNs), and data envelopment analysis (DEA) to find the best compromises between multiple PMs and their variability. Two case studies are presented. A case study based on a virtual part is presented in detail in order to illustrate this method. The second case study is experimentally based, using the American Society of Testing Materials (ASTM) mold, to illustrate how this approach applies when only experimental results are available.
In-mold coating (IMC) is carried out by injecting a liquid low viscosity thermoset material onto the surface of the thermoplastic substrate while it is still in the mold. A computer code based on the Control Volume based Finite Element Method (CV/FEM) has been developed to predict the fill pattern and pressure distribution during the coating flow using the Sisko viscosity model and taking apparent slip into account during. Both these factors lead to a better prediction of pressure distribution. The rheological parameters and the apparent slip parameter are ascertained by using a slit rheometer. Simulation and rheology results are presented in this paper.
This study attempted to improve the mechanical properties – and impact resistance, in particular – of rice hull/polypropylene composites with the aid of styrene-ethylene/ butylene-styrene (SEBS) and maleated styrene-ethylene/ butylene-styrene (SEBS-MA). The results suggested that both types of additives increased the impact strength of the composites significantly as their content was increased, but only SEBS-MA improved the tensile and flexural strength of the composites. The results also indicated that the SEBS-MA composites consistently showed better mechanical properties – strength and modulus in both tensile and flexural tests and impact strength – than the SEBS counterparts at a given content of additives.
The object of enterprises management is to obtain the competition advantage by better efficiency, quality, innovation, and customer responds. As such, most enterprises implement the product life management (PLM) system to assist design and development, however, the interaction between PLM and CAD is mainly for viewing purpose. Therefore, this research is to develop a web-based conceptual design navigating system which can provide standard and automatic component to shorten the process of conceptual design by seamlessly integrating with CAD system. Furthermore, this system can greatly help the inexperienced designer and provide the collaborative environment of designing process.
Injection molding of thin-wall parts with micro-scale grooves of polypropylene (PP) and cycloolefin copolymer (COC) were performed to clarify the processability and surface structure of the molded products. Effects of cavity thickness and process conditions on processability and structure of the molded products were evaluated. The replication property and optical anisotropy of molded products were analyzed by polariscope, polarizing microscope, SEM, and confocal laser scanning microscope. The optical anisotropy in the vicinity of the gate was higher than that of any other position, and the optical anisotropy increased with a decrease in cavity thickness. The replication property in the vicinity of the gate also was higher than that of the flow end, and the replication ratio was slightly increased with increasing mold temperature. It was found that the replication properties were correlated closely with skin-shear thickness inside products.
Precision micromolding of polypropylene (PP), polyoxymethylene (POM) and polycarbonate (PC) were performed to develop a micro-scale miniature disk and to clarify the mechanism of structure development in micromolded products. Especially effects of process condition and cavity thickness on processability and structure formation in micromolding were evaluated. The processability and high-structures of molded products were also analyzed by polariscope, birefringence, and AFM measurements. In case of PC micro-disk, the molecular orientation in the vicinity of the gate was higher than that of any other position. Birefringence increased with decreasing cavity thickness. Furthermore it was found that the resin flow became unstable in the cavity thickness of 0.1 mm. The molecular orientation of PP products also showed the similar tendency as the case of PC, where birefringences in the vicinity of the gate were higher than any other position.
Modeling of deformation processes in vacuum thermoforming for a preliminary stretched thermoplastic sheet (plug-assist vacuum thermoforming) is investigated in this paper. The model can be used for production of polymeric articles with minor wall-thickness variation. A nonlinear rheological model is implemented for developing the process model. It describes deformation process of a pre-stretched sheet at any phase of vacuum thermoforming process. This process is described by a set of deformation processes that each on them is specified by an appropriate boundary conditions. For model validation, a comparative analysis of the theoretical and experimental data is presented. The wall-thickness distributions obtained from modeling results corresponded well with experiments. The satisfactory result establishes a method for prediction and enhancement of the final products quality in criterion of wall-thickness distribution.
Thermoplastic olefins (TPO) are widely used in the automotive industry as painted exterior plastic parts such as fascias and bumpers. The overall production process includes injection molding of parts, surface treatment, painting and finally baking at 120°C for 30 min. During the injection process, residual stresses are generated by chain orientation and thermal gradients. After the paint process, more stresses and deformations are added. This work focuses mainly on baking conditions and the micro-structural changes as a source of final surface defects. As a first step, we used DSC to simulate the baking process and study the effect of injection molding and baking conditions on unpainted samples. By controlling the scanning rates and the residence time within the DSC furnace, this alternative technique can reveal some interesting results. Samples were also annealed in an oven in the same conditions then analyzed by DSC. The results of both approaches are compared and discussed.
A numerical analysis using a renormalization group (RNG), k-? model and Fluent software was performed to predict the static pressure distribution around the bubble as well as the flow field of cooling air in the film blowing process. Bubble instabilities were experimentally studied using an in-line scanning camera system developed in our laboratory. The combination of experimental measurements and numerical analysis indicated that different bubble shapes led by various cooling rate produced significant differences in dynamics of bubble instability. When the gradient of static pressure along the axis of the bubble is minimized, the stability of the bubble increases.
Following first work reported last year, this paper presents additional information regarding novel polyamide-6/nanoclay nanocomposites having platelets volumetrically oriented and localized within alternating platelet rich and virgin polyamide layers of nano-scale thicknesses. These novel nanocomposites were produced with a continuous chaotic blender (CCB). A variety of structural arrangements among platelets in extruded films are presented. Methods are applicable to other polymer types and additives having platelet shapes. A theoretical permeation model was implemented to assess influences on permeability of structure parameters such as platelet orientation and layer number. By localizing and orienting platelets within multilayers and neglectling crystallinity changes, model results indicate that such nanocomposites may have very low permeabilities. Permeability measurements and evaluations of crystallinity changes are subjects of future work.
The fractographic study of a polycarbonate component used in a prototyped medical device is reported of fracture mode, origin and mechanism, based on the examinations of the fracture surface and the interpretation of various fracture markings as observed using scanning electron microscopy (SEM). An explanative kinetics of fracture is given for describing the fracture process and various associated fracture events. The time and temperature effects on the fracture properties and fracture kinetics of polycarbonate are qualitatively considered to explain the causes of material brittleness. It has been noted that under complex long-term loading and varying time-temperature conditions, the fracture origins might be preexisting or newly created in a fracture event. Therefore, caution should be used in assigning the likely causes of material failure for design and manufacturing processes.
A constitutive model for tensile behavior of PMMA/clay nanocomposite foams was developed in this paper. The model elucidates the effect of intercalated and agglomerated clays, where the elastic modulus of the nanocomposite foams is affected by the addition of clays to the polymer matrix. A viscoelastic model was adapted for the tensile behavior of the material. The detrimental effect by clay agglomeration was considered on the determination of the elastic modulus. For the verification of the constitutive model, PMMA/clay nanocomposite foams were manufactured by batch process method and their uniaxial tensile test results were compared with theoretical results. The proposed constitutive equation showed agreement with the tensile test results.
Layered silicate PMR-15 polyimide nanocomposites are being developed for high-performance aerospace applications. The goal is to achieve full exfoliation under quiescent conditions using a novel approach, whereby intra- and extra-gallery modulus and viscosity are engineered to result in a net force pushing clay layers apart during cure. The current study explores treatment of clay with reactive surfactants which are thermally stable and participate in crosslinking with PMR resin, providing higher thermo-oxidative stability than possible with current technologies.
Injection Molded Polycarbonate Parts are extensively employed in optical, optoelectronic and electronic applications. But the molded residual stress can deteriorate the optical properties of the final product. Compared with PMMA, residual stress has more effects on PC injection-molded parts. In this research, the distributions of residual stress of the transparent molded polycarbonate parts have been inspected firstly under polarized light to understand effects of flow-induced and thermal-induced stresses and their interaction. Then based on optical experiment results of photoelasticity, the value of residual stresses was calculated. Flow-induced stress and thermal-induced residual stress of different molding conditions was investigated by numerical methods. A series of multicolored band or fringed pattern and simulation results showed the effect of non-uniform temperature distribution and fill pattern were the causes of residual stresses of thin PC parts.
A new test methodology based on materials science and mechanics tools for evaluating scratch resistance of polymers has recently been developed and approved as a new ASTM standard. This new test method allows for simple, unambiguous quantitative evaluation and ranking of scratch resistance of polymeric materials. A low-cost scratch tester that can perform a constant load scratch test, an accelerated rate test, and a progressive load scratch test was built in our laboratory for the present study. Finite element methods (FEM) simulation has also been carried out to correlate between material parameters and the surface damage observed during scratch. An overview of the state of the art understanding of scratch behavior of polymers and coatings will be presented. Approaches for designing scratch resistant polymers and coatings will also be discussed.
Radiant heating systems comprised of tubing installed beneath floors is widely used in the United States and Europe. Some radiant heating tubes are composites of multiple rubber compounds and textile reinforcement. In this paper, we present a detailed forensic examination of failed nitrile rubber radiant heating hose, based on techniques including field investigation, ion chromatography, high performance liquid chromatography, fractography, and gas permeability testing. Enduse testing of the nitrile tubing performed in the laboratory is described and correlated to field performance.
A polymer film lamination shows an unexpected delamination failure. The lamination is produced by adhesive laminating a previously printed metallized polyester film to a LLDPE sealant. In use the lamination is found to fail by delamination between the polyester film and the metal layer. Chemical surface analysis of the failure surface by X-ray photon spectroscopy (XPS) indicates a degraded polyester surface creating a weak boundary layer at the polyester/metal interface which is the cause of the delamination. Possible causes for the degraded polyester surface are discussed.
Molecular orientation in weldline region in injection molded polycarbonate was investigated by laser-Raman spectroscopy. The observation was focused, in particular, on the area surrounding a V-notch on the surface of weldline. In the case of opposite flow weldline occurring in moldings produced with a two-gated dog bone cavity, the molecules just on the V-notch were slightly oriented along the notch, whereas those of the area within 1 mm from the V-notch were highly oriented parallel to the notch. Similar characteristics were found in an adjacent flow weldline occurring just behind an obstructive pin in a plaque mold. However, the degree of orientation varied along the weldline or flow direction. The degree of orientation was low near the obstacle and increased along the flow direction, resulting in high orientation in spite of complete disappearance of the V-notch at the area ca. 10 mm apart from the obstacle. In addition, further orientation was found in the position slightly apart from the disappeared V-notch. This suggested that the interface of the adjacent flow weldline behaved as a mold wall to generate shear flow during filling process.
A micro porous film with HDPE/MMT nanocomposite has been developed. The HDPE/MMT nanocomposites were prepared by melt blending with twin screw extruder with two step process. The master batches were manufactured by melt compounding with maleic anhydride grafted HDPE (HDPE-g-MAH) and MMT. The HPDE/MMT master batches were subsequently mixed with HDPE. Non-porous nanocomposite blown films were obtained by a single screw extruder attached film blowing and take-off unit. The micro porous film prepared by uniaxial stretching of non porous films. X-ray and TEM images showed the partially exfoliated nanocomposites which have the 5:1 – 20:1 ratios of HPDE-g-MAH and MMT. The thermal and mechanical properties of nanocomposites were enhanced by increasing the contents of MMT and in the presence of compatibilizer. The influences of annealing and stretching conditions were evaluated on micro porous film.
Flow induced stresses, caused by viscoelastic flow of the polymer during the filling and post-filling stage, determines the anisotropy of mechanical, thermal and optical properties and influences the long term dimensional stability. A numerical method for solving viscoelastic fluid flow problem is presented in this study. The governing equations are in terms of generalized Hele-Shaw flow for incompressible, non-Newtonian, non-isothermal fluid and Maxwell model. The conventional Galerkin method is employed to discrete the constitutive equations expressed by pressure gradient, while the implicit scheme combined with up-wind method is used to discrete the energy equation. The typical example proves the viscoelastic constitutive relation is significantly better than the viscous.
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