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RESEARCH ON RESIDUAL STRESSES OF INJECTION MOLDED PC PARTS
Haimei Li , Yiyan Peng , Lih-Sheng Turng , Xin Wang, May 2010
Residual stresses in injection molded parts may have negative effects on optical and mechanical properties. It is usually two types residual stresses in the injection molded parts - flow-induced and thermally-induced stresses. In this paper thermal residual stresses are investigated by comparing tensile properties of the injection molded PC parts before and after annealing. A dielectrostrictive sensor is developed to conduct the flow-induced stress analysis during filling stage. The physical meaning of obtained dielectrostriction signals is given based on the experimental and numerical results. First the pressure measured by the transducers was compared with the numerical simulated results. These two values agree well which indicates that the numerical prediction should also be reliable for shear stress analysis. Then the shear stress calculated based on the measured dielectrostriction signal was compared with its corresponding numerical result. And it has been found that the difference between these two values within 5% at the various processing condition.
RESEARCH ON RESIDUAL STRESSES OF INJECTION MOLDED PC PARTS
Haimei Li , Yiyan Peng , Lih-Sheng Turng , Xin Wang, May 2010
Residual stresses in injection molded parts may have negative effects on optical and mechanical properties. It is usually two types residual stresses in the injection molded parts - flow-induced and thermally-induced stresses. In this paper, thermal residual stresses are investigated by comparing tensile properties of the injection molded PC parts before and after annealing. A dielectrostrictive sensor is developed to conduct the flow-induced stress analysis during filling stage. The physical meaning of obtained dielectrostriction signals is given based on the experimental and numerical results. First the pressure measured by the transducers was compared with the numerical simulated results. These two values agree well, which indicates that the numerical prediction should also be reliable for shear stress analysis. Then the shear stress calculated based on the measured dielectrostriction signal was compared with its corresponding numerical result.And it has been found that the difference between these two values within 5% at the various processing condition.
STUDY OF PROCESSING PARAMETERS ON PART WARPAGE OF INMOLDPOLLER INJECTION MOLDING INJECTION MOLDING
H. C. Chen , S. C. Chen , P.M. Hsu , H. S. Peng , Y. C. Wang, May 2010
In-mold roller (IMR) injection molding is one of the commonly used In-Mold Decoration technology for ink transfer. The effect of processing parameters on part‘s warpage is very important for product quality. In this study the PET film with thickness of 0.05mm and 0.036mm is molded and computer simulation analysis is performed to compare the result with experiment. It was found that high melt temperature and thick film would result in heat stagnation between surface-frozen layer and film interface leading to a large part’s warpage. However a high mold temperature resulted in a low warpage. For IMR molding the mold temperature difference between core and cavity surface was about 6.71~12.94? and the warpage varied from 0.15mm to 0.91mm under specified conditions.
STUDY OF PROCESSING PARAMETERS ON PART WARPAGE OF IN-MOLDPOLLER INJECTION MOLDING
H. C. Chen , S. C. Chen , P.M. Hsu , H. S. Peng , Y. C. Wang, May 2010
In-mold roller (IMR) injection molding is one of the commonly used In-Mold Decoration technology for ink transfer. The effect of processing parameters on partƒ??s warpage is very important for product quality. In this study, the PET film with thickness of 0.05mm and 0.036mm is molded and computer simulation analysis is performed to compare the result with experiment. It was found that high melt temperature and thick film would result in heat stagnation between surface-frozen layer and film interface leading to a large partƒ??s warpage. However, a high mold temperature resulted in a low warpage. For IMR molding, the mold temperature difference between core and cavity surface was about 6.71~12.94ƒ?Ÿ and the warpage varied from 0.15mm to 0.91mm under specified conditions.
CORE MORPHOLOGY OF PBS ALLOYS AND PROPERTIES OF PP-BASED SANDWICH INJECTION MOLDINGS
Yuji Fujita , Naoya Aoki , Toshihiro Yoshida , Hironari Sano , Masaya Kotaki, May 2010
Polypropylene (PP)-based sandwich injection moldings with polybutylene succinate (PBS) alloys in core were studied. Different core morphologies of PBS/PP alloys were obtained by changing content and melt flow rate (MFR) of PBS and core-PP, and injection molding conditions. It was found that the core morphologies significantly affected skin/core interfacial adhesion and mechanical properties of the sandwich injection moldings. The spreading index considering dynamic viscosity and volume fraction of PBS and core-PP was proposed to discuss the mechanism of the core morphology development. Scratch and Izod impact tests according to ASTM standards were performed to investigate the effects of skin/core adhesion on scratch and impact characteristics.The sandwich injection moldings with poor skin/core adhesion caused the skin/core delamination upon the scratch and Izod impact tests.
IMPROVEMENT OF MECHANICAL PROPERTIES OF AN ALL RENEWABLE BASED WOOD-RESIN COMPOSITE
Rahul M. Rasal, Douglas E. Hirt, May 2010
Impregnation of linseed epoxy resin into softwood creates an all-renewable composite. This composite is intended to be a substitute for expensive hardwoods used in applications such as decking and flooring. Initial epoxy impregnation was conducted within a custom vacuum-pressure chamber with positive results. The impregnation process begins with an initial vacuum treatment to remove the air inside the wood, followed by the use of pressure to drive the resin into the wood under certain temperature conditions. This process was improved by optimizing vacuum-pressure levels and temperature, as well as the use of a high temperature curing agent. In this way, superior impregnation depths were obtained. The final result was a composite material with better mechanical properties than both the resin and the softwood themselves. Specifically, the impregnated samples showed Youngƒ??s modulus over three times higher than those of unimpregnated wood samples, in both tension and compression. Furthermore, the hardness of the wood increased significantly; depending on impregnation depth, hardness reached and surpassed 4500 lbf, the estimated value of Lignum Vitae, the hardest wood available. Secondary testing focused on automation of the initial process in order to facilitate optimized impregnation on an industrial scale. A custom multi-chambered impregnation machine was designed to perform a continuous impregnation.
THE OPTIMIZATION OF HIGH INORGANIC CONTENT HYBRID BARRIER MATERIALS
Jing Wang, Wenli Zhu, Chul B. Park, Jed Randall, May 2010
Much work has been done to model the behavior of platelet-filled hybrid barrier materials and produce high barrier polymer/nanoclay composites with low clay contents. Little has been done to test the applicability of these models over a wide range of clay contents and determine whether current systems are near ideal or could be further improved. In this work, cyclic olefin copolymers are combined with organically modified montmorillonite clay via a spray deposition technique to create transparent, highly aligned model hybrids containing up to 100% clay. The structure and properties of these sheets are then characterized via XRD, DMA and OPA.
IMPACT OF MOLECULAR BRANCHING ON MICROCELLULAR FOAMING OF POLYLACTIC ACID IN EXTRUSION
Jing Wang , Wenli Zhu , Chul B. Park , Jed Randall, May 2010
Microcellular foams of polylactic acids (PLA) with and without molecular branching were produced on a tandem extrusion system using carbon dioxide as the physical blowing agent. Cell density and expansion ratio were found to be strong functions of the molecular structure the blowing agent content and the processing temperature. Very low density foams were produced with the branched PLA at the optimal processing condition while the linear PLA exhibited severe cell opening beyond a reasonable expansion ratio. Very low crystallinity was detected in the foamed samples indicating that shearing and the presence of supercritical carbon dioxide in the extrusion system did not induce crystal growth.
IMPACT OF MOLECULAR BRANCHING ON MICROCELLULAR FOAMING OF POLYLACTIC ACID IN EXTRUSION
Jing Wang , Wenli Zhu , Chul B. Park , Jed Randall, May 2010
Microcellular foams of polylactic acids (PLA), with and without molecular branching, were produced on a tandem extrusion system using carbon dioxide as the physical blowing agent. Cell density and expansion ratio were found to be strong functions of the molecular structure, the blowing agent content, and the processing temperature. Very low density foams were produced with the branched PLA at the optimal processing condition, while the linear PLA exhibited severe cell opening beyond a reasonable expansion ratio. Very low crystallinity was detected in the foamed samples, indicating that shearing and the presence of supercritical carbon dioxide in the extrusion system did not induce crystal growth.
DEPTH SENSING NANO-INDENTATION TECHNIQUE TO ASSESS DEGRADATION OF WEATHERED POLYMER SURFACES
Lei-Ti Huang, Ping-Shun Hsu, Shia-Chung Che, May 2010
Measurement of surface appearance often fails to predict mechanical failure while bulk mechanical testing confirms failure only after prolonged exposure in weathering. In this study, we attempt to detect small changes in surface mechanical properties during initial stages on the weathered surface of polycarbonate-based materials using surface sensitive nano-indentation technique. Samples were also characterized using various techniques including transmission electron microscopy and infrared spectroscopy. Information on the degradation layer thickness may help in assessing mechanical failure of polymer during early stages. Studies show the superiority of Lexan* SLX resin over polycarbonate in weathering.
THE GENERATION OF THE PTFE POROUS STRUCTURE INDUCED BY UNIAXIAL STRETCHING PROCESS WITH ASYMMETRIC HEATING OPERATION
Lei-Ti Huang , Ping-Shun Hsu , Shia-Chung Che, May 2010
Polytetrafluoroethylene (PTFE) is a remarkable membrane material. Due to its high melting point, PTFE cannot be processed using the conventional melting processing methods. In addition, porous materials have been used in many industrial technologies and life surroundings. Plastic expansion technology has created a new class of filter material, called expanded PTFE (ePTFE). The material comprises a highly fibrillated and porous microstructure that contributes to its excellent filter capability. In this paper, different stretching ratio, asymmetry heating temperature, and different heating time was used to modify the ePTFE membrane pore size. It was found that a longer heating times and lower stretching times, the porosity of PTFE membrane was increased from 30 to 70% and the mean pore size was decreased from 0.22 to 0.08 ?¬m.
WARPAGE MANAGEMENT USING THREE DIMENSIONAL THICKNESS CONTROL METHOD IN INJECTION MOLDING
Yuing Chang , Shih Tsun Huang , Sung-Wei Huang , Shia-Chung Chen , Chao-Tsai Huang , Meng- Chih Chen , Venny Yang, May 2010
Warpage is one of the most crucial problems in injection molding quality control. Since many factors will cause shrinkage and warpage it is very difficult to distinguish which factor always dominates warpage. In this study we have developed Three Dimensional Thickness Control Method (3DTCM) to manage the warpage of the injected parts. Using this method we will specify the geometry of parts with non-uniform three dimensional structures. After integrated with special gate design material selection various operation conditions warpage of injected parts can be managed significantly. Also to verify our results both numerical and experimental investigation will be performed in this study.
WARPAGE MANAGEMENT USING THREE DIMENSIONAL THICKNESS CONTROL METHOD IN INJECTION MOLDING
Yuing Chang , Shih Tsun Huang , Sung-Wei Huang , Shia-Chung Chen , Chao-Tsai Huang , Meng- Chih Chen , Venny Yang, May 2010
Warpage is one of the most crucial problems in injection molding quality control. Since many factors will cause shrinkage and warpage, it is very difficult to distinguish which factor always dominates warpage. In this study, we have developed Three Dimensional Thickness Control Method (3DTCM) to manage the warpage of the injected parts. Using this method, we will specify the geometry of parts with non-uniform three dimensional structures. After integrated with special gate design, material selection, various operation conditions, warpage of injected parts can be managed significantly. Also, to verify our results, both numerical and experimental investigation will be performed in this study.
CYCLE TIME OPTIMIZATION AND PART QUALITY IMPROVEMENT USING NOVEL COOLING CHANNELS IN PLASTIC INJECTION MOULDING
Abul B.M. Saifullah , S. H. Masood , Igor Sbarski, May 2010
Cooling channel design in injection moulding is very important as it greatly affects the cycle time as well as the shrinkage and warpage of the plastic part. Traditionally, cooling channels have been machined into mould components with gun-barrel drilling, with that only straight channels were possible to manufacture. An advanced method of cooling system that 'conforms' to the shape of the part in the mould can be made possible with free form fabrication technique such as DMD (direct metal deposition). This paper presents an investigation on the optimization of mould design of conformal cooling channels of different cross sections for plastic injection moulding. Comparative study has been done with the conventional straight cooling channels. ANSYS thermal simulation software has been used to get comparative temperature profile on the mould and Moldflow simulation software has been used to compare shrinkage, warpage and temperature profile of the part itself during moulding process . Comparative results are presented based on temperature distribution and cooling time for the mould and warpage deflection, volumetric shrinkage and temperature profile of the part. The results provide a uniform temperature distribution with reduced shrinkage and warpage and reduction in cycle time for the plastic part.
DYNAMIC MOLD SURFACE TEMPERATURE CONTROL FOR MOLDING HIGH GLOSS, PAINTING FREE PART SURFACE ACHIEVING CYCLE TIME AND COST REDUCTION
Shia-Chung Chen , Jen-An Chang , Jin-Chuan Cin, May 2010
The study shows the molding of a high gloss surface notebook computer (NB) display support without painting using dynamic mold temperature control. The required mass production rate is 300,000 pieces per month. Both water heating/cooling and induction heating/water cooling were employed to investigate the cycle time, mold and machine requirements. The former requires 60s cycle time whereas the later needs only 36s to achieve a weld line free surface. The associated cost reduction in energy consumption is US $23,700 per month, injection machine operation is US $52,800 per month, mold making cost is US $75,000 and painting cost saving is US $190,500. Annual savings could reach US $3,237,900.
A DIMENSIONAL ANALYSIS OF VISCOUS HEATING IN RUNNER SYSTEMS USING THE RADIAL FUNCTIONS METHOD
William M. Aquite, Iván D. López, Tim A. Osswald, May 2010
Polymer flow through circular tubes is a common occurrence in injection molding runner systems. Viscous dissipation affects the temperature distribution of the melt as it enters the cavity. The Radial Functions Method was used to model the flow and heat transfer inside runner systems in dimensionless form. Temperature increases are obtained from simple expressions as a function of the dimensionless Brinkman and Graetz numbers. This eliminates the necessity of simulation or experimental test of such flows when predicting temperature increments as a function of processing conditions.
EVALUATION OF THE CRACK INITIATION CHARACTERISTICS OF PIPE GRADE POLYETHYLENE UNDER FATIGUE LOADS
Jing Wang, John W. S. Lee, Jae D. Yoon, Chul B. Park, May 2010
Recently, a circular notched specimen (CNS) is selected for studying the crack initiation characteristics of pipe grade polyethylene as a part of understanding quasibrittle failure. In this study, four types of pipe grade polyethylene were chosen and tested under variable fatigue loading conditions using CNS with various notch depths. The fatigue characteristics of four polyethylenes were evaluated, and the fracture surface of CNS after failure is analyzed by optical microscope and scanning electron microscope (SEM) to evaluate the fracture mechanism of pipe grade polyethylenes. In addition, the technical issues with CNS during tests were also investigated by finite element analysis.
CHALLENGE TO THE FOAMING OF A THIN-WALL INJECTION MOLDED PART- INFLUENCE OF INJECTION SPEED AND GATE GEOMETRY
Jing Wang , John W. S. Lee , Jae D. Yoon , Chul B. Park, May 2010
Foaming of a thin-wall part during injection molding is challenging. Cell nucleation and growth are significantly constrained by rapid cooling from the mold by limited cavity space and by high mold cavity pressure generated by the viscous polymer melt. In this paper we study the influence of injection speed and gate geometry on the cell size uniformity and void fraction control of a foamed thinwall part. Real-time mold cavity pressures were recorded using pressure transducers and a computer system. It was found that high injection speed and proper gate design can minimize cooling from the mold maximize shear thinning at the gate and thus making possible uniform foaming throughout the part volume.
POLYMER-GRAPHITE AND POLYMER-CARBON NANOTUBE NANOCOMPOSITES:PROCESSING VIA SOLID-STATE SHEAR PULVERIZATION
Jun’ichi Mausda , Katsuyuki Wakabayashi , Philip J. Brunner , John M. Torkelson, May 2010
A continuous, industrially scalable process method called solid-state shear pulverization is shown to be effective in producing well-dispersed polypropylene/ carbon nanotube and polypropylene/ as-received graphite nanocomposites that cannot be obtained by conventional melt processing alone. Major improvements in Young's modulus (> 100% increase) and yield strength (65% increase) are obtained in the nanocomposites made by SSSP, with the maximum increases being observed in samples containing the highest concentrations of nanofiller that are well-dispersed. In contrast, electrical conductivity is correlated to dispersion of carbon-based nanofiller in a different manner, with conductivity increasing with increasing nanofiller content even when an increase in nanofiller content results in less effective dispersion or exfoliation.
POLYLACTIDE COMPOSITES FILLED WITH MICROCRYSTALLINE CELLULOSE, NANOCRYSTALLINE CELLULOSE AND CELLULOSE NANOFIBERS
Karen Stoeffler , Minh-Tan Ton-That , Johanne Denault , John Luong , Crystal Wu , Mohini Sain, May 2010
Polylactide (PLA) nanocomposites based on microcrystalline cellulose (MCC), nanocrystalline cellulose (NCC) and cellulose nanofibers (CNF) were prepared in the molten state by microextrusion. The dispersion was investigated by optical and electron microscopy. The mechanical properties of the nanocomposites were analyzed by dynamic mechanical analysis (DMA). The thermal properties were analyzed by differential scanning calorimetry (DSC). The effect of the addition of a proper coupling agent on dispersion and mechanical properties was analyzed.


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