Somjate Patcharaphun

Simulation and Experimental Investigations of Material Distribution in the Sandwich Injection Molding Process

In sandwich injection molding, two polymeric materials are sequentially injected into a mold to form a multilayer product with a skin and core structure. Different properties of these polymers and their distribution in the cavity greatly affect the applications of the moldings. In an ideal situation, the core material should be entirely encapsulated in the skin material. When the flow front of the core material overtakes that of the skin material, breakthrough occurs, resulting in a defective part. The focus of this study is to determine the effect of molding parameters on the skin/core material distribution. The commercial simulation package (Moldflow) has been extensively compared with experiments. Both simulated and measured results suggest that in order to obtain the optimum encapsulated skin/core structure in the sandwich injection molded parts, it is necessary to select a proper core volume fraction and suitable processing parameters. A good agreement between simulation and experimental results indicates that the Moldflow program can be used as a valuable tool for the prediction of melt-flow behavior during the sandwich injection process.

Investigation on Weldline Strength of Short-glass-fiber Reinforced Polycarbonate Manufactured through Push-Pull-processing Technique

Push-pull-processing (PPP) is a live in-mold manipulation method of co-injection molding used for enhancing the orientation of the polymer molecules and reinforcing fillers. This technique implements an alternating shear field induced by a coordinated action of two injection units to create multiple oriented layers across the thickness of molding during the packing phase. In this investigation, the PPP is employed to enhance the weldline strength of short-glass-fiber reinforced polycarbonate (SFRPC) with respect to the fiber orientation in the weldline areas. The effects of glass-fiber concentration and processing parameters including the number of push-pull strokes and the holding pressure differences between both of the injection units have been studied. In addition the degradation of the fiber length caused by the oscillation is also investigated.

Simulation of Three-dimensional Fiber Orientation in Weldline Areas During Push-pull-processing:

Push-pull-processing (PPP) is a live in-mold manipulation method of co-injection molding providing increased opportunities for controlling the melt flow during solidification. The mold has two gates connected to two synchronized injection units. During the packing phase, the melt moves through the mold several times. This modified filling process influences the orientation of fibers in a part significantly. In this work, a modified 3-D model for PPP has been developed and performed with the aid of a commercial software package (Moldflow) in order to predict the fiber orientation distribution within the weldline area of PPP parts. The predicted values of orientation tensor components (a11) are found to agree reasonably well with corresponding experimental measurements.

The Effect of Thickness on the Weld-Line Strength of Injection-Molded Thermoplastic Composites

Weld lines are a major concern to designers since they result in poor mechanical properties. Designers may overdesign parts when considering anticipated failure modes and safety factors by locating weld lines in non-critical areas without taking into account material factors. This study focus on the effect of part thickness on the weld-line strength of injection-molded short-fiber-reinforced thermoplastic composites. Comparisons were made with specimens without weld lines. The use of design data which takes into account fiber orientation and part thickness will enable designers to more accurately predict the performance of an injection-molded thermoplastic composites under applied load.

Flow Properties and Melt Distortion in Molten Rubber Compounds under Capillary Extrusion: Effects of Vulcanizing Systems and Fillers

This work aimed to make use of a rate-controlled capillary rheometer for investigating the effects of vulcanizing system using various fillers on the apparent viscosity and extrudate swelling of natural rubber (NR) compounds. The results suggested that the rubber compounds exhibited a pseudoplastic non-Newtonian behavior. At any given shear rates, the viscosities of rubber compound utilizing conventional (CV) and efficient vulcanizing (EV) systems were lower than that of non-sulfur (NS) system. This was due to the occurrence of premature crosslinking at the skin layer and subsequently led to the wall slip of rubber compound during the flow in capillary die. The irregular surface and the onset of smooth surface of rubber extrudate were evidently seen, especially for CV and EV systems. This could be associated with the amount of required energy to obtain the steady state flow in the die. The results also suggested that the swelling ratio of rubber extrudate ranged from 1.2 to 2.2 and the effect of filler type was more pronounced at high shear rates above 400 s−1. In the case of silica filler (SiO2) system, the severe irregularity of rubber extrudate was observed. The lower shear rate employed to obtain the smooth surface for rubber extrudate containing 30 phr of SiO2 was possibly caused by high amount of PEG acting as an external lubricant which promoted the uniform slippage during the flow in capillary die.

Development of a Kraft Paper Box Lined with Thermal-Insulating Materials by Utilizing Natural Wastes

This research studied the feasibility of using natural fibers extracted from natural wastes as a thermal-insulating material lined in a Kraft paper box packaging. The natural fibers were extracted from natural waste of rice straws using NaOH solutions. The extracted fibers were then formed as a porous thermal-insulating pad by a spray lay-up method using natural rubbers as binders. The thermal conductivities, specific heat capacities and temperature-rise time of the natural fiber insulation and other thermal-insulating materials including polystyrene foam, a polyethylene foam, and a glass fiber insulation were studied and compared. The glass fiber insulation showed the highest thermal conductivity, while the thermal conductivities of the other studied insulating materials were found to be similar. Moreover, the polymeric and natural-fiber insulations show better temperature-rise resistance than the glass fiber insulation. The temperature rises for different insulating materials were estimated using the analytical analysis of heat transfer. The calculated temperature-rise times were compared with the empirical results; both results are in the same order of magnitude. Consequently, a Kraft paper box lined with natural-fiber pads was constructed and compared with a Kraft paper box (without insulation lining) and a polystyrene box of equal sizes. The boxes were packed with an equal amount of ice and left under room temperature for 24 hours. The results show that, after 24 hours, the temperatures inside the natural-fiber lined box and the polystyrene box were contained below 15 °C, while the temperature inside the Kraft paper box increase to room temperature only after 16 hours. The observation shows that a natural fiber pad can potentially be used as an alternative insulating material in packaging industries, which can enhance environmental-friendly packaging products.

Production of Tensioner Pulley from Nylon-Glass Fiber Composites

This paper shows the feasibility of replacing the SPCC steel with glass fiber reinforced Nylon composites for the manufacturing of tensioner pulley. Three series of Nylon (Nylon 66, Nylon 46 and Nylon 46 with PTFE) reinforced with 30wt% of glass fiber were investigated. Finite Element Analysis (FEA) was carried out to simulate the stress distribution and to predict the maximum stress located on the pulley component. It was found that all Nylon composites had higher tensile modulus than SPCC steel, while the SPCC steel exhibited higher tensile strength. FEA demonstrated that the maximum stress on Nylon composite pulley was lower than the SPCC steel pulley, however these stresses were higher than yield stress of materials. The addition of supporting rib can reduce the stress concentration to lower the yield stress of materials. Finally the performance of Nylon composite pulley was considered. Pulley with plain-surface bearing was meet the criteria for endurance test, however, the interfacial adhesion between bearing and Nylon composite pulley can be improved by glued and gouged surface. According to the experimental results, glass fiber reinforced Nylon composites can be the representative materials of replacing SPCC steel for tensioner pulley.

Development of Hyperelastic Model for Natural Rubber Containing Weldlines

Several constitutive models of non-linear large elastic deformation based on strain-energy-density functions have been developed for hyperelastic materials. These models, coupled with the Finite Element Method (FEM), can effectively utilized by design engineers to analyze and design elastomeric products operating under the deformation states. However, due to the complexities of the mathematical formulation which can only obtained at the moderate strain and the assumption of material used for the analysis. Therefore it is formidable task for design engineer to make use of these constitutive relationships. In the present work, the strain-energy-density function of natural rubber part containing a weldline was constructed by using the Neural Network (NN) model. The analytical results were compared to those obtained by Neo-Hookean, Mooney-Rivlin, Ogden models. Good agreement between developed NN model and the existing experimental data was found, especially at very low strain and at very high strain.

Development of Hyperelastic Model for Weldlines Containing Natural Rubber Molded Part

Several constitutive models of non-linear large elastic deformation based on strain-energy-density functions have been developed for hyperelastic materials. These models, coupled with the Finite Element Method (FEM), can effectively utilized by design engineers to analyze and design elastomeric products operating under the deformation states. However, due to the complexities of the mathematical formulation which can only obtained at the moderate strain and the assumption of material used for the analysis. Therefore it is formidable task for design engineer to make use of these constitutive relationships. In the present work, the strain-energy-density function of weldline containing rubber part was constructed by using the Neural Network (NN) model. The analytical results were compared to those obtained by Neo-Hookean, Mooney-Rivlin, Ogden models. Good agreement between developed NN model and the existing experimental data was found, especially at very low strain and at very high strain.