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Molding Process (molding + process)
Kinds of Molding Process Selected AbstractsPowder Metallurgical Near-Net-Shape Fabrication of Porous NiTi Shape Memory Alloys for Use as Long-Term Implants by the Combination of the Metal Injection Molding Process with the Space-Holder Technique,ADVANCED ENGINEERING MATERIALS, Issue 12 2009Manuel Köhl Abstract A new method was developed for producing highly porous NiTi for use as an implant material. The combination of the space-holder technique with the metal injection molding process allows a net-shape fabrication of geometrically complex samples and the possibility of mass production for porous NiTi. Further, the porosity can be easily adjusted with respect to pore size, pore shape, and total porosity. The influence of the surface properties of powder metallurgical NiTi on the biocompatibility was first examined using human mesenchymal stem cells (hMSCs). It was found that pre-alloyed NiTi powders with an average particle size smaller than 45,,m led to the surface properties most suitable for the adhesion and proliferation of hMSCs. For the production of highly porous NiTi, different space-holder materials were investigated regarding low C- and O-impurity contents and the reproducibility of the process. NaCl was the most promising space-holder material compared to PMMA and saccharose and was used in subsequent studies. In these studies, the influence of the total porosity on the mechanical properties of NiTi is investigated in detail. As a result, bone-like mechanical properties were achieved by the choice of Ni-rich NiTi powder and a space-holder content of 50,vol% with a particle size fraction of 355,500,,m. Pseudoelasticity of up to 6% was achieved in compression tests at 37,°C as well as a bone-like loading stiffness of 6.5,GPa, a sufficient plateau stress ,25 of 261,MPa and a value for ,50 of 415,MPa. The first biological tests of the porous NiTi samples produced by this method showed promising results regarding proliferation and ingrowth of mesenchymal stem cells, also in the pores of the implant material. [source] A Soft Molding Process for Fabrication of Micromachine Parts from Stainless Steel Powder,ADVANCED ENGINEERING MATERIALS, Issue 3 2009Mohamed Imbaby This work introduces a valid approach to fabricate high quality micromachine parts from stainless steel powder using soft molding and powder metallurgy techniques. In soft molding, SU-8 and negative replicas micromolds are produced. A mixture of Duramax B-10007 and B-1000 is successfully used as a binder in the preparation of stainless steel slurry. Sintering in forming gas atmosphere is very effective of preventing the oxidation of the stainless. [source] Powder Metallurgical Near-Net-Shape Fabrication of Porous NiTi Shape Memory Alloys for Use as Long-Term Implants by the Combination of the Metal Injection Molding Process with the Space-Holder Technique,ADVANCED ENGINEERING MATERIALS, Issue 12 2009Manuel Köhl Abstract A new method was developed for producing highly porous NiTi for use as an implant material. The combination of the space-holder technique with the metal injection molding process allows a net-shape fabrication of geometrically complex samples and the possibility of mass production for porous NiTi. Further, the porosity can be easily adjusted with respect to pore size, pore shape, and total porosity. The influence of the surface properties of powder metallurgical NiTi on the biocompatibility was first examined using human mesenchymal stem cells (hMSCs). It was found that pre-alloyed NiTi powders with an average particle size smaller than 45,,m led to the surface properties most suitable for the adhesion and proliferation of hMSCs. For the production of highly porous NiTi, different space-holder materials were investigated regarding low C- and O-impurity contents and the reproducibility of the process. NaCl was the most promising space-holder material compared to PMMA and saccharose and was used in subsequent studies. In these studies, the influence of the total porosity on the mechanical properties of NiTi is investigated in detail. As a result, bone-like mechanical properties were achieved by the choice of Ni-rich NiTi powder and a space-holder content of 50,vol% with a particle size fraction of 355,500,,m. Pseudoelasticity of up to 6% was achieved in compression tests at 37,°C as well as a bone-like loading stiffness of 6.5,GPa, a sufficient plateau stress ,25 of 261,MPa and a value for ,50 of 415,MPa. The first biological tests of the porous NiTi samples produced by this method showed promising results regarding proliferation and ingrowth of mesenchymal stem cells, also in the pores of the implant material. [source] Synthesis and Structure,Property Relations of a Series of Photochromic Molecular Glasses for Controlled and Efficient Formation of Surface Relief NanostructuresADVANCED FUNCTIONAL MATERIALS, Issue 16 2009Roland Walker Abstract This paper reports on the synthesis and properties of a new series of photochromic molecular glasses and their structure,property relations with respect to a controlled and efficient formation of surface relief nanostructures. The aim of the paper is to establish a correlation between molecular structure, optical susceptibility, and the achievable surface relief heights. The molecular glasses consist of a triphenylamine core and three azobenzene side groups attached via an ester linkage. Structural variations are performed with respect to the substitution at the azobenzene moiety in order to promote a formation of a stable amorphous phase and to tune absorption properties and molecular dynamics. Surface relief gratings (SRGs) and complex surface patterns can easily be inscribed via holographic techniques. The modulation heights are determined with an equation adapted from the theory for thin gratings, and the values are confirmed with AFM measurements. Temperature-dependent holographic measurements allow for monitoring of SRG build-up and decay and the stability at elevated temperatures, as well as determination of the glass transition temperature. SRG modulation heights of above 600,nm are achieved. These are the highest values reported for molecular glasses to date. The surface patterns of the molecular glasses are stable enough to be copied in a replica molding process. It is demonstrated that the replica can be used to transfer the surface pattern onto a common thermoplastic polymer. [source] A Lagrangian boundary element approach to transient three-dimensional free surface flow in thin cavitiesINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 4 2001Jie Zhang Abstract The lubrication theory is extended for transient free-surface flow of a viscous fluid inside a three-dimensional thin cavity. The problem is closely related to the filling stage during the injection molding process. The pressure, which in this case is governed by the Laplace's equation, is determined using the boundary element method. A fully Lagrangian approach is implemented for the tracking of the evolving free surface. The domain of computation is the projection of the physical domain onto the (x,,y) plane. This approach is valid for simple and complex cavities as illustrated for the cases of a flat plate and a curved plate. It is found that the flow behavior is strongly influenced by the shape of the initial fluid domain, the shape of the cavity, and inlet flow pressure. Copyright © 2001 John Wiley & Sons, Ltd. [source] Systematic optimization for the evaluation of the microinjection molding parameters of light guide plate with TOPSIS-based Taguchi methodADVANCES IN POLYMER TECHNOLOGY, Issue 1 2010Te-Li Su Abstract A back light module is a key product for providing sufficient light source for a liquid crystal display (LCD). The light guide plate (LGP), used to increase the light usage rate, is a key component in the back light module. This study researches the microinjection molding process parameters and the quality performance of the LGP. Its purpose was to develop a combining Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) with the Taguchi method. This is to optimize the multiquality performance of the LGP for the injection molding manufacturing process, in which both the LCD and the LGP spontaneously produce the best quality performance for V-cut depth and angle. First, an L18 orthogonal array was planned for the manufacturing parameters that affect the microinjection molding process. These included cooling time, mold temperature, melt temperature, injection speed, injection pressure, packing pressure, packing switching, and packing time. The TOPSIS was used to deal with the single-quality optimization disadvantage of the Taguchi method. Then, the TOPSIS response table was used to obtain the optimized manufacturing parameters combination for a multiresponse process optimization. From the analysis of variance, the significant factors for the quality performance of the LGP could be obtained. In other words, by controlling these factors, it was possible to efficiently control the quality performance of the LGP. Finally, with the five verified experiments, the optimized processing parameters came within a 95% confidence interval. © 2010 Wiley Periodicals, Inc. Adv Polym Techn 29:54,63, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20181 [source] Online control of the injection molding process based on process variablesADVANCES IN POLYMER TECHNOLOGY, Issue 2 2009Walter Michaeli Abstract The conventional control of the injection molding process is based on machine variables, which cannot sufficiently characterize the course of the process. Hence, a system that controls the injection molding process based on process variables has been developed at the Institute of Plastics Processing at RWTH Aachen University during the last years. It controls the quality determining process variable cavity pressure directly and realizes a desired course of cavity pressure in the injection and holding pressure phases. The cavity pressure course in the holding pressure phase is controlled online on the basis of pvT behavior of the processed plastic material. Thus, an optimal course of the process in the pvT diagram can be guaranteed and the quality constancy of the molded parts can be clearly increased. Using the pvT-based process control, the effect of varying mold and melt temperatures on the molded part weight can be decreased by about 90% compared with the conventional process control. © 2009 Wiley Periodicals, Inc. Adv Polym Techn 28:65,76, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20153 [source] Cavity pressure control during cooling in plastic injection moldingADVANCES IN POLYMER TECHNOLOGY, Issue 3 2006B. Pramujati Abstract Cavity pressure control during filling, packing, and cooling phases is imperative for maintaining product quality in injection molding process. This paper presents the design and implementation of a strategy to control cavity pressure profile during the cooling phase. In order to do this, a controlled variable parameter was defined to be the time constant , of the pressure profile. This parameter can be used effectively to control the shape of the cavity pressure over the cooling cycle. The coolant flow rate through the mold was used as the manipulated variable. A predictive control system was designed and implemented successfully to allow monitoring and control of , at several setpoints ,sp resulting in good and effective cavity pressure control. © 2006 Wiley Periodicals, Inc. Adv Polym Techn 25:170,181, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20068 [source] Control of rotational molding using adaptive fuzzy systemsADVANCES IN POLYMER TECHNOLOGY, Issue 4 2005D. I. Abu-Al-Nadi Abstract Rotational molding is a method for manufacturing hollow plastic parts. In the work reported here, adaptive fuzzy logic techniques have been used to relate the machine oven temperature to other manipulated parameters of the process. The objective is to design a reliable control system for the rotational molding process. An adaptive fuzzy network was developed to correlate changes in oven temperature to changes in the opening of the control valve on the fuel system. The network parameters were optimized using real-valued genetic algorithms. This network gave good results when its performance was compared with experimental data from a commercial rotational molding machine. The network was successfully utilized to design a control system, which works well in regard to set point tracking and load rejection. © 2005 Wiley Periodicals, Inc. Adv Polym Techn 24: 266,277, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20047 [source] A review of current developments in process and quality control for injection moldingADVANCES IN POLYMER TECHNOLOGY, Issue 3 2005Zhongbao Chen Abstract Injection molding is one of the most versatile and important manufacturing processes capable of mass-producing complicated plastic parts in net shape with excellent dimensional tolerance. Injection molding process and quality control has been an active research area for many years, as part quality and yield requirements become more stringent. This paper reviews the state-of-the-art research and development in injection molding control. It organizes prior studies into four categories, namely, process setup, machine control, process control, and quality control, and presents the distinction and connection of these different levels of control. This paper further reviews and compares the typical variables, models, and control methods that have been proposed and employed for those control tasks. Strictly speaking, real online quality control without human intervention has yet to be realized, primarily due to the lack of transducers for online, real time quality response measurement, and a robust model that correlates the control variables with quantitative quality measurements. Based on the research progress to date, this paper suggests that the different levels of control tasks have to be integrated into a multilevel quality control system, and that the quality sensor and the process and quality model are the two most important areas for further advancement in injection molding control. © 2005 Wiley Periodicals, Inc. Adv Polym Techn 24: 165,182, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20046 [source] Simulation of injection-compression molding process, Part 3: Effect of process conditions on part birefringenceADVANCES IN POLYMER TECHNOLOGY, Issue 3 2002Shia-Chung Chen Abstract Simulations of the injection-compression molding (ICM) process based on a Leonov viscoelastic fluid model has been employed to study the effects of processing conditions on the birefringence development and distribution in injection-compression molded parts. A numerical algorithm combined with a modified control-volume/finite-element method is developed to predict the melt front advancement and the distributions of pressure, temperature, and flow velocity dynamically during the injection melt-filling, compression melt-filling, and postfilling stages of the entire process. Part birefringence was then calculated from residual stresses following the thermal-mechanical history of the entire molding process. Simulations of a disk part under different process conditions including compression speed, switch time from injection to compression, compression stroke, packing pressure, and postfilling time were performed to understand their effects on birefringence variation. The simulated results were also compared with those required by conventional injection molding (CIM). It has been found that an ICM part shows a significant reduction of part birefringence near the gate area as compared with CIM parts. However, ICM parts exhibit higher birefringence values near the rim of the disk. The minimum birefringence occurs around the location where injection is switched over to compression. Although longer postfilling time and higher packing pressure result in higher birefringence values, their effects are not very significant. On the other hand, higher compression speed, larger compression stroke, and shorter switch time exhibit greater effects on the increase of part birefringence. Flow-induced residual stress is the major origin of birefringence formation in the present case. The simulated birefringence for both ICM and CIM parts show good coincidence with those obtained from measurements by using a digital photoelasticity technique. © 2002 Wiley Periodicals, Inc. Adv Polym Techn 21: 177,187, 2002; Published online in Wiley Interscience (www.interscience.wiley.com). DOI 10.1002/adv.10024 [source] Influence of processing conditions and part design on the gas-assisted injection molding processADVANCES IN POLYMER TECHNOLOGY, Issue 4 2001Nan-Shing Ong Gas-assisted injection molding has been developed to solve the problems that the conventional injection molding process is not able to. It is believed that the new process is able to produce final parts with higher quality at a more effective cost. Warpage and sink marks are reduced and there is material-savings to be reaped. This research aims to investigate some of the processing parameters that come with this new process. They include shot size, gas delay time, gas pressure, and melt temperature. The influence of part design is also looked into. Five designs were used in the research and compared. The responses evaluated include gas bubble length, residual wall thickness, bending strength, warpage, and fingering. © 2001 John Wiley & Sons, Inc. Adv Polym Techn 20: 270,280, 2001 [source] Preparation and HPLC applications of rigid macroporous organic polymer monolithsJOURNAL OF SEPARATION SCIENCE, JSS, Issue 10-11 2004Frantisek Svec Abstract Rigid porous polymer monoliths are a new class of materials that emerged in the early 1990s. These monolithic materials are typically prepared using a simple molding process carried out within the confines of a closed mold. For example, polymerization of a mixture comprising monomers, free-radical initiator, and porogenic solvent affords macroporous materials with large through-pores that enable applications in a rapid flow-through mode. The versatility of the preparation technique is demonstrated by its use with hydrophobic, hydrophilic, ionizable, and zwitterionic monomers. Several system variables can be used to control the porous properties of the monolith over a broad range and to mediate the hydrodynamic properties of the monolithic devices. A variety of methods such as direct copolymerization of functional monomers, chemical modification of reactive groups, and grafting of pore surface with selected polymer chains is available for the control of surface chemistry. Since all the mobile phase must flow through the monolith, the convection considerably accelerates mass transport within the molded material, and the monolithic devices perform well, even at very high flow rates. The applications of polymeric monolithic materials are demonstrated mostly on the separations in the HPLC mode, although CEC, gas chromatography, enzyme immobilization, molecular recognition, advanced detection systems, and microfluidic devices are also mentioned. [source] Laser Welding of Plastics , a Neat ThingLASER TECHNIK JOURNAL, Issue 5 2010The story of a popular laser application Industry has been dealing with the joining of plastics for over half a century. The wish for an economically viable method of joining components was there already when the injection molding process was developed. With the advent of industrial laser technology, laser welding developed into a practical solution for many plastics joining problems. [source] Effect of Processing Parameters on the Mechanical Properties of Injection Molded Thermoplastic Polyolefin (TPO) Cellular FoamsMACROMOLECULAR MATERIALS & ENGINEERING, Issue 7 2008Steven Wong Abstract In this study, the effects of processing parameters on the mechanical properties of injection molded thermoplastic polyolefin (TPO) foams are investigated. Closed cell TPO foams were prepared by injection molding process. The microstructure of these foamed samples was controlled by carefully altering the processing parameters on the injection molding machine. The foam morphologies were characterized in terms of skin thickness, surface roughness, and relative foam density. Tensile properties and impact resistance of various injection molded TPO samples were correlated with various foam morphologies. The findings show that the mechanical properties are significantly affected by foam morphologies. The experimental results obtained from this study can be used to predict the microstructure and mechanical properties of cellular injection molded TPO foams prepared with different processing parameters. [source] An Approach to Calculating Wear on Annular Non-Return ValvesMACROMOLECULAR MATERIALS & ENGINEERING, Issue 11 2002Helmut Potente Abstract The serviceability of non-return valves has a major influence on the productivity of the injection molding process. During a meeting of experts held at our Institute, it was seen that closing behavior and wear are the key problems encountered in practice. The conducted investigations to tackle these questions have shown that both an improved closing behavior and a lower level of wear can be achieved by reducing the inside radius of the locking ring. Pressure profile over the length of a non-return valve (n,=,0.4; ,=,25,000 mm3/s). [source] Improved Design of Shearing Sections with New Calculation Models Based on 3D Finite-Element SimulationsMACROMOLECULAR MATERIALS & ENGINEERING, Issue 11 2002Helmut Potente Abstract New models for the Maddock and spiral shearing sections have been developed, employing three-dimensional finite element analysis (3D FEA). These models describe the pressure-throughput and power consumption behavior of the shearing sections for both the extrusion and the injection molding process and have been implemented in the REX 6.0 and PSI 4.0 simulation software. As a consequence it is now possible to describe the process behavior of these shearing sections within just a few seconds with the accuracy of FEA calculations. Actual Maddock shearing section (left) and actual spiral shearing section (right). [source] Modeling and analysis of thickness gradient and variations in vacuum-assisted resin transfer molding processPOLYMER COMPOSITES, Issue 5 2008Jing Li As vacuum-assisted resin transfer molding (VARTM) is being increasingly used in aerospace applications, the thickness gradient and variation issues are gaining more attention. Typically, thickness gradient and variations result from the infusion pressure gradient during the process and material variations. Pressure gradient is the driving force for resin flow and the main source of thickness variation. After infusion, an amount of pressure gradient is frozen into the preform, which primarily contributes to the thickness variation. This study investigates the mechanism of the thickness variation dynamic change during the infusion and relaxing/curing processes. A numerical model was developed to track the thickness change of the bagging film free surface. A time-dependent permeability model as a function of compaction pressure was incorporated into an existing resin transfer molding (RTM) code for obtaining the initial conditions for relaxing/curing process. Control volume (CV) and volume of fluid (VOF) methods were combined to solve the free surface problem. Experiments were conducted to verify the simulation results. The proposed model was illustrated with a relatively complex part. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers [source] Flow modeling and simulation for vacuum assisted resin transfer molding process with the equivalent permeability methodPOLYMER COMPOSITES, Issue 2 2004Renliang Chen Vacuum assisted resin transfer molding (VARTM) offers numerous advantages over traditional resin transfer molding, such as lower tooling costs, shorter mold filling time and better scalability for large structures. In the VARTM process, complete filling of the mold with adequate wet-out of the fibrous preform has a critical impact on the process efficiency and product quality. Simulation is a powerful tool for understanding the resin flow in the VARTM process. However, conventional three-dimensional Control Volume/Finite Element Method (CV/FEM) based simulation models often require extensive computations, and their application to process modeling of large part fabrication is limited. This paper introduces a new approach to model the flow in the VARTM process based on the concept of equivalent permeability to significantly reduce computation time for VARTM flow simulation of large parts. The equivalent permeability model of high permeable medium (HPM) proposed in the study can significantly increase convergence efficiency of simulation by properly adjusting the aspect ratio of HPM elements. The equivalent permeability model of flow channel can simplify the computational model of the CV/FEM simulation for VARTM processes. This new modeling technique was validated by the results from conventional 3D computational methods and experiments. The model was further validated with a case study of an automobile hood component fabrication. The flow simulation results of the equivalent permeability models were in agreement with those from experiments. The results indicate that the computational time required by this new approach was greatly reduced compared to that by the conventional 3D CV/FEM simulation model, while maintaining the accuracy, of filling time and flow pattern. This approach makes the flow simulation of large VARTM parts with 3D CV/FEM method computationally feasible and may help broaden the application base of the process simulation. Polym. Compos. 25:146,164, 2004. © 2004 Society of Plastics Engineers. [source] Modeling and simulation approaches in the resin transfer molding process: A reviewPOLYMER COMPOSITES, Issue 4 2003A. Shojaei A review of current approaches in modeling and simulation of the resin transfer molding (RTM) process is presented. The processing technology of RTM is discussed and some available experimental techniques to monitor the process cycle are presented. A master model is proposed for the entire process cycle consisting of mold filling and curing stages. This master model contains the fundamental and constitutive sub-models for both stages. The key elements of the master model discussed in this study are: flow, heat and mass balance equations for fundamental sub-models, permeability, cure kinetics, resin viscosity and void formation for constitutive sub-models. At the end, numerical methods widely used to simulate the filling process are presented and published simulation results of mold filling and process cycle are reviewed. [source] Flow front measurements and model validation in the vacuum assisted resin transfer molding processPOLYMER COMPOSITES, Issue 4 2001R. Mathuw Through-thickness measurements were recorded to experimentally investigate the through thickness flow and to validate a closed form solution of the resin flow during the vacuum assisted resin transfer molding process (VARFM). During the VART'M process, a highly permeable distribution medium is incorporated into the preform as a surface layer and resin is inftised Into the mold, under vacuum. During Infusion, the resin flaws preferentially across the surface and simultaneously through the thickness of the preform, giving rise to a three dimensional-flow front. The time to fill the mold and the shape of the flow front, which plays a key role in dry spot formation, are critical for the optimal manufacture of large composite parts. An analytical model predicts the flow times and flow front shapes as a function of the properties of the preform, distribution media and resin. It was found that the flow front profile reaches a parabolic steady state shape and the length of the region saturated by resin is proportional to the square root of the time elapsed. Experimental measurements of the flow front in the process were carried out using embedded sensors to detect the flow of resin through the thickness of the preform layer and the progression of flow along the length of the part. The time to fill the part, the length of flow front and its shapes show good agreement between experiments and the analytical model. The experimental study demonstrates the need for control and optimization of resin injection during the manufacture of large parts by VARTM. [source] Analysis of the vacuum infusion molding processPOLYMER COMPOSITES, Issue 1 2000A. Hammami The vacuum infusion molding process is becoming increasingly popular for the production of large composite parts. A comprehensive model of the process has not been proposed yet, making its optimization difficult. The flexible nature of the vacuum bag coupled to the varying pressure inside the mold cavity results in a variation of the cavity thickness during the impregnation. A complete simulation model must incorporate this phenomenon. In this paper, a complete analysis of the vacuum infusion molding process is presented. The analysis is not restricted to the theoretical aspects but also reviews the effect of the main processing parameters. The parameters investigated in this paper are thought to be those of most interest for the process, i.e. the compaction of the reinforcement, the permeability, the infusion strategy and the presence of flow enhancement layers. Following the characterization experiments, a 1-D model for the vacuum infusion molding process is presented. This model is derived assuming that an elastic equlibrium holds in the mold cavity during mold filling. Even though good agreement was found between simulation results and experiments, it is concluded that additional work is needed on the numerical model to integrate interesting findings from the experimental part. [source] Theoretical and visual study of bubble dynamics in foam injection moldingPOLYMER ENGINEERING & SCIENCE, Issue 3 2010Mehdi Mahmoodi This article presents an experimental observation and a theoretical prediction of bubble dynamics in foam injection molding process with a main focus on the cell collapse phenomenon under pressure. Using a visualizing setup, cell growth behavior under a nonisothermal condition was monitored. In conjunction with the growth behavior, dynamics of cell collapse under different pressures and the effect of growing time on collapse behavior and final cell size were studied. Theoretical simulation of bubble behavior included power law model, which predicted bubble dynamics during foaming process. The results show that collapse phenomenon strongly depends on both exerted holding pressure and growth time. The presented model can also give a reasonable prediction of growth and collapse of cells and could give insight to control of cell size in injection foaming process. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers [source] A comprehensive experimental study and numerical modeling of parison formation in extrusion blow molding,POLYMER ENGINEERING & SCIENCE, Issue 1 2007Azizeh-Mitra Yousefi Parison dimensions in extrusion blow molding are affected by two phenomena, swell due to stress relaxation and sag drawdown due to gravity. It is well established that the parison swell and sag are strongly dependent on the die geometry and the operating conditions. The availability of a modeling technique ensures a more accurate prediction of the entire blow molding process, as the proper prediction of the parison formation is the input for the remaining process phases. This study considers both the simulated and the experimental effects of the die geometry, the operating conditions, and the resin properties on the parison dimensions using high density polyethylene. Parison programming with a moving mandrel and the flow rate evolution in intermittent extrusion are also considered. The parison dimensions are measured experimentally by using the pinch-off mold technique on two industrial scale machines. The finite element software BlowParison® developed at IMI is used to predict the parison formation, taking into account the swell, sag, and nonisothermal effects. The comparison between the predicted parison/part dimensions and the corresponding experimental data demonstrates the efficiency of numerical tools in the prediction of the final part thickness and weight distributions. POLYM. ENG. SCI., 47:1,13, 2007. © 2006 Society of Plastics Engineers [source] Modeling of rotational molding process: Multi-layer slip-flow model, phase-change, and warpagePOLYMER ENGINEERING & SCIENCE, Issue 7 2006K.K. Lim A new multilayer slip-flow model has been developed to simplify and to overcome current numerical difficulties of two-dimensional model in predicting the internal air temperature inside a mold during a rotational molding process. The proposed methodology considers a macroscopic "layer-by-layer" deposition of a heating polymer bed onto the inner mold surface. A semi-implicit approach is introduced and applied to compute the complex thermal interactions between the internal air and its surroundings. In the model, the lumped-parameter system and the coincident node technique are incorporated with the Galerkin finite element model to address the internal air and the deposition of molten polymer beds, respectively. The simple phase-change algorithm has been proposed to improve the computational cost, numerical nonlinearity, and predicted results. The thermal aspects of the inherent warpage are explored to study its correlation to the weak apparent crystallization-induced plateau in the temperature profile of the internal air, as in practice. The overall predicted results are in favor with the available experimental data for rotomolded parts of cross-sectional thicknesses up to 12 mm. POLYM. ENG. SCI. 46:960,969, 2006. © 2006 Society of Plastics Engineers [source] Effects of process parameters on the micro molding processPOLYMER ENGINEERING & SCIENCE, Issue 9 2003J. Zhao The trend towards miniaturization has brought about strong demand for increasingly smaller precision-molded plastic components. In order to control metering accuracy and homogeneity of the very small quantities of melt in the micro molding process, new micro molding machines that use an injection system comprising a screw extruder and a plunger injection unit have been developed. By use of such injection systems, standard plastic granules can be handled by the screw extruder and melt accuracy can be achieved by the electrically driven injection plunger. The objective of this work is to investigate the effects of the process parameters on the micro molding process and part quality. A series of micro gears were molded using a polyoxymethylene resin in a set of statistically designed experiments. Micro component inspection, characterization, and data analysis work was carried out to study the molded gears. It was found that metering size and holding pressure time are the process parameters that have the most significant effects on part quality, and that the process is also significantly affected by the interaction of these two parameters. There is an optimum metering size range in which the hold pressure can act together with the metering size to properly fill micro mold cavities. [source] Computer simulation of stress-induced crystallization in injection molded thermoplasticsPOLYMER ENGINEERING & SCIENCE, Issue 11 2001Jianxin Guo Injection molding of semicrystalline plastics was simulated with the proposed stress-induced crystallization model. A pseudo-concentration method was used to track the melt front advancement. Stress relaxation was considered using the WFL model. Simulations were carried out under different processing conditions to investigate the effect of processing parameters on the crystallinity of the final part. The simulation results reproduced most of the experimental results in the literature. Comparison is made between the slow-crystallizing polymer (PET) and fast-crystallizing polymer (PP) to demonstrate the effect of stress on the crystallization kinetics during the injection molding process for materials with different crystallization properties. The results show that for fast-crystallizing plastics, stress has little effect on the final crystallinity in the injection molded parts. [source] Modeling of structural reaction injection molding process.POLYMER ENGINEERING & SCIENCE, Issue 5 2001A mathematical model of the infusion process in producing reinforced articles is proposed. The model is based on the analysis of flow of a Newtonian liquid inside a rectangular multilayer channel. According to the model, a liquid enters the central (feeding) layer, moves through this layer, and simultaneously impregnates peripheral layers. So, the flow is two-dimensional. Flow inside the porous layers is treated in terms of the Darcy equation with different permeability coefficients in two directions. Principal solutions for the flow front development and pressure evolution were obtained and analyzed. Then the initial model, developed for a Newtonian liquid, is generalized for the so-called "rheokinetic" liquid, which changes its rheological properties in time as a result of temperature variation and/or any possible chemical process, in particular, the reaction of curing of a binder. It was proven that in this case the solution is automodel. This means that the solutions obtained for a Newtonian liquid in the dimensionless form are valid for an arbitrary rheokinetic liquid. [source] A simulation of the non-isothermal resin transfer molding processPOLYMER ENGINEERING & SCIENCE, Issue 12 2000Vincenza Antonucci A simulation of the non-isothermal resin transfer molding manufacturing process accounting for both the filling and the consolidation stage has been developed. The flow of an exothermally reactive resin through a porous medium has been analyzed with reference to the Darcy law, allowing for the chemorheological properties of the reacting resin. Thermal profile calculations have been extended to a three phase domain, namely the mold, the dry preform and the filled preform. The mold has been included in order to evaluate the thermal inertial effects. The energy balance equation includes the reaction term together with the conductive and convective terms, and particular attention has been devoted to setting the thermal boundary condition at the flow front surface. The moving boundary condition has been derived by a jump equation. The simulation performance has been tested by comparing the predicted temperature profiles with experimental data from literature. Further numerical analysis assessed the relevance of using the jump equation at the flow front position for both filling time and thermal profile determination. [source] Overall numerical simulation of extrusion blow molding processPOLYMER ENGINEERING & SCIENCE, Issue 8 2000Shin-Ichiro Tanifuji This paper focuses on the overall numerical simulation of the parison formation and inflation process of extrusion blow molding. The competing effects due to swell and drawdown in the parison formation process were analyzed by a Lagrangian Eulerian (LE) finite element method (FEM) using an automatic remeshing technique. The parison extruded through an annular die was modeled as an axisymmetric unsteady nonisothermal flow with free surfaces and its viscoelastic properties were described by a K-BKZ integral constitutive equation. An unsteady die-swell simulation was performed to predict the time course of the extrudate parison shape under the influence of gravity and the parison controller. In addition, an unsteady large deformation analysis of the parison inflation process was also carried out using a three-dimensional membrane FEM for viscoelastic material. The inflation sequence for the parison molded into a complex-shaped mold cavity was analyzed. The numerical results were verified using experimental data from each of the sub-processes. The greatest advantage of the overall simulation is that the variation in the parison dimension caused by the swell and drawdown effect can be incorporated into the inflation analysis, and consequently, the accuracy of the numerical prediction can be enhanced. The overall simulation technique provides a rational means to assist the mold design and the determination of the optimal process conditions. [source] | ||||||||||||||||||||||||||||