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No description available.

No description available.

In this work, two mathematical models for the simulation of the injection molding process were tested and their predictions were validated with experimental data. One of these models is based on the well-known "Hele-Shaw" approximation which, is commonly used by a considerable number of commercial packages. This method utilizes the fact that generally the flow is confined in a narrow gap in which out-of-plane flows may be ignored and, therefore, only a two-dimensional (2-D) solution of the flow field is necessary. One remarkable limitation of this approach is its impossibility of predicting the so-called "fountain flow". Furthermore, this model neglects the role of crystallization kinetics. On the other hand, the other model proposes a methodology that deals with fountain flow and crystallization. It is based on the so-called "2½-D" numerical simulation since it combines a 2-D flow analysis with a 3-D solution of the energy equation. First, a two-dimensional analysis in the gap-wise direction is performed in order to obtain fountain flow information. Then, in-plane two-dimensional flow solutions are coupled with three-dimensional energy results, which incorporate the heat generated by crystallization. Two different thermoplastics were investigated. Polyethylene was selected to characterize the crystalline behavior. Polystyrene was chosen as the amorphous material. In order to obtain insight of the overall injection molding cycle, pressure evolution in the cavity and in the nozzle was examined carefully. More accurate pressure results were computed when using the 2½-D model. This study thus puts in evidence the importance of including fountain flow and crystallization kinetics in the injection molding process.

Polymer melts exhibit some degree of viscoelasticity in most industrial forming operations, and elasticity is particularly important in flows involving an abrupt contraction or expansion in the flow direction. However, the incorporation of a viscoelastic constitutive equation into computer models for polymer processing poses many problems, and for this reason inelastic models have been used almost exclusively to represent rheological behavior for flow simulation in the plastics industry. / In order to explore the limits of viscoelastic flow simulations, we used two nonlinear viscoelastic models (Leonov and Phan-Thien/Tanner) to simulate axisymmetric and planar contraction flows and extrudate swell. Their predictions were compared with those obtained using a strictly viscous model (Carreau-Yasuda) and with experimental results. The models are implemented in a modified Elastic Viscous Split Stress (EVSS) mixed finite element formulation. The viscoelastic constitutive equations are calculated using the Lesaint-Raviart method, and the divergence-free Stokes problem is solved applying Uzawa's algorithm. The decoupled iterative scheme is used as a preconditioner for the Generalized Minimal Residual (GMRES) method. Numerical instability was observed starting at quite low elasticity levels. For the converging flows, the predicted flow patterns were in fair agreement with experimental results, but there was a large discrepancy in the entrance pressure drop. In the case of extrudate swell, the agreement with observation was poor, and convergence was impossible except at the lowest flow rate. / After exploring the limits of simulations using viscoelastic models, we conclude that there are serious barriers to progress in the simulation of viscoelastic flows of industrial importance. The ultimate source of the problem is the melt elasticity, and traditional numerical methods and rheological models do not provide a suitable basis for simulating practical flows. A new approach is required, and we propose that a rule-based expert system be used.

A major obstacle in the prediction of stress profiles in the viscoelastic flow of polymers is a mysterious breakdown of the numerical procedure, which occurs at relatively small values of the Deborah number. Numerous papers have been devoted to analyzing the reason for this failure, but the exact cause remains unclear. Amazingly, all constitutive equations attempted and all kinds of different numerical procedures employed have run into the very same problem. We have investigated several currently popular constitutive models in a viscometric flow field and have found serious limitations in shear flows which may be the source of numerical problems. There is often a lack of appreciation for the computational uses of fluid models in the process of formulating constitutive equations. In the future, the use of the corrotational time derivative, which appears to create this trouble, may be prohibited. Alternatively, it may be possible to avoid the limitation by adding a proper retardation time in constitutive models which use the corrotational time derivative. The well known upper convected Maxwell model does not exhibit limitation but it is believed that a different source of numerical instability may be inherently present. We have adopted the cylindrical axisymmetric 4:1 contraction channel (the die-entry region) to simulate this fluid using the mixed finite element method. The worrisome infinite elongational viscosity predicted by this model in steady extensional flow, indeed, is responsible for the singular behavior of the stress solution field. The most difficult region for convergence, as might be expected, is found to be just after the reentrant corner.

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Injection molded Short Glass Fiber Reinforced Thermoplastics (SFRTP) are widely used in industry because of advantages in material properties, availability, economics and ease of processing. The thermo-mechanical history experienced by the material during processing produces significantly anisotropic microstructural and consequently mechanical properties, varying not only spatially, but directionally. / This work attempts to examine quantitatively various aspects of microstructure and the effect of processing conditions in SFRTP. The matrix phase properties, such as crystallinity, morphology and molecular orientation distribution, as well as the fiber phase microstructure such as concentration, length and orientation distributions have been analyzed quantitatively, and explained. Experimental techniques, including optical and electron microscopy, differential scanning calorimetry, Fourier transform infrared spectroscopy, thermo-gravimetric analysis, etc. have been used. The results indicate complex changes in microstructure from skin to core in the injection molded samples. Both matrix and fiber phase microstructures are affected by the basic thermal and flow processes that occur during the injection molding process. A first order model has been developed to predict fiber orientation distributions, which agree well with the experimental results.

Injection moulding is one of the most important manufacturing processes in the plastic industry. The temperature distribution of the polymer, while it is inside the mould cavity, influences the properties of the product. The measurement and control of these temperature profiles can enhance the economy of the process and the part quality. / A method to measure melt temperature inside the mould cavity was developed. It consists of an insert, located in the movable plate, that can place thermocouples at different positions. The depth of the thermocouple tip is adjusted manually. These sensors offer an attractive way to perform the measurements because of their easy calibration procedure. The temperature measurements were influenced by the thermocouple tip geometry. / Data were collected at different locations and depths of the mould cavity and the temperature profiles were analyzed. The temperature distribution depended on the wall temperature and the temperature of the polymer as it enters the cavity. The effect of different flow rates was also studied and it demonstrated to affect the temperature profiles. / A control algorithm was developed to control the average of the peak temperatures at three locations in the cavity. The manipulated variable was the coolant temperature and the process disturbance was the front barrel temperature. The transfer functions of the controlled variable with respect to the manipulated and disturbance variables were identified and modeled. / Finally two controllers were designed, tuned, simulated and implemented on the machine. The first is a static feedforward - feedback controller, and the second is a dynamic feedforward - feedback controller. The feedback loop was designed using an internal model control (IMC) algorithm. The static feedforward - feedback controller was found to have a better performance.

The injection molding process, due to its versatility, cost effectiveness, and ability to produce precise complex articles is widely used in plastics processing. Mold cavity pressure is a good indicator of the processes taking place in the cavity and plays an important role in determining the quality of the molded articles. The dynamic modeling and control of cavity pressure, based on a physically-based approach, is studied in this research project. The work deals with the filling and packing phases. / A lumped physically-based model was developed in order to study the behavior of the system. The model is derived from conservation laws and incorporates a physical understanding of the process. The whole system was divided into subsystems including the hydraulic system, ram-screw, barrel, and polymer delivery system. It was found necessary to account for polymer melt elasticity as well as non-Newtonian behavior of the polymer melt flow. Consideration of the growing solid skin in the polymer delivery system was found to be necessary. / The dynamics of the cavity pressure during the filling phase were investigated and found to be non-linear and time-varying in relation to the hydraulic servo-valve opening which is the manipulated variable. The dynamic behavior of the cavity pressure is approximated by piece-wise linearization of the non-linear governing equations to derive a transfer function using the physically-based model which is of fifth order. Adaptive PI, PID, and IMC controllers were designed and tested for the control of the cavity pressure. Various tuning techniques, along with changes in set-point, were used to determine conservative settings for the PI and PID controllers. / A similar approach was used to study the dynamics of the cavity pressure during the packing phase. A sixth order transfer function, with piece-wise linearization, was derived to approximate the non-linear and time-varying behavior of the cavity pressure during packing. The adaptive PI, PID, and IMC controllers were successfully applied into the packing phase. The transition of the filling-to-packing was selected to be detected by the derivative of the cavity pressure and adaptive controllers were successfully used for this phase. / Two commonly used injection molding grade thermoplastics, polyethylene and polystyrene, were used in experimental part of this work for model validation and controller testing.