<p>Flow phenomena associated with the injection mold filling process have a significant impact on the microstructure development and hence on the final properties of molded articles. The present work is concerned with the mathematical modeling and numerical simulation of the mold filling process. The aim is to provide in-depth understanding of the flow phenomena involved and investigate their impact on the microstructure of the molded polymer article.</p> <p>The mold filling process takes place as a rolling-type advancement of the flow front over the mold walls. The flow field behind the advancing flow front is known as fountain flow, and it is the salient feature of mold filling. The fountain flow phenomenon is examined extensively with finite element techniques, both in the steady-state and in the time domain. The u-v-p-h-δ formulation described in the present work is a powerful numerical technique for the simulation of free surface flows, and determines simultaneously the flow field and the free surface shape. Steady-state and transient simulations with Newtonian and shear-shinning fluids in planar and axisymmetric geometries are presented. Various features of fountain flow are described with the aid of velocity vector, pressure, free surface shape, and streamline plots. The general problem of fountain and reverse fountain flow (immiscible liquid displacement) and the collision of two flow fronts to form a weldline are also investigated.</p> <p>The deformation history experienced by the fluid due to fountain flow is examined on the basis of the numerically computed flow field, by tracking material elements as they move through the flow domain. It is found that material elements from the centerline migrate towards the mold walls, extend in the flow direction and form characteristic V-shapes, fully in agreement with available visualization experiments.</p> <p>A viscoelastic constitutive equation (multi-mode Leonov model) is introduced in order to investigate the effect of fountain flow on the molecular orientation of injection molded parts, as reflected in available birefringence measurements. A finite element algorithm for the numerical simulation of viscoelastic free surface flows is described. Fountain flow simulations are performed for material properties and processing conditions corresponding to available experiments. Finite element solutions are obtained at high levels of fluid elasticity and they converge with mesh refinement, provided that a slip boundary condition is applied at the wall to alleviate the stress singularities. The finite element results are combined with a simple theory to predict frozen-in stress and birefringence distributions. Computational results are compared to, and agree favorably with, available experimental data. It is demonstrated quantitatively that fountain flow is responsible for the molecular orientation pattern of the surface layer of injection molded parts. A viscoel~stic constitl1tive eq~ation (multi-mode Leonov model) is introduced in , order to investig'ate the effect of fountain flow on the molecular orientation of injectio~ molded parts, a~ refl~cted in available birefringence measurements. A finite element algorithm for the numerical simulation of viscoelastic fre~ surface flows 'is described. Fountain flow simulations are performed for material properties and processing conditions corresponding to available' experiments. Finite element ~olutionsare obtained at high levels of fluid elasticity and they converge with mesh refinement, provided that a slip boundary ..... condition is applied at the wall to alleviate the stress singularities. The finite element results are combined with a simple theory to predict frozen-in stress and birefringence d!stributions. Computational results are compared to, and agree favorably with, available experimental data. It is demonstrated quantitatively that fountain flow is responsible for the molecular orientation pattern of the surface layer ofinjection molded parts.</p> / Doctor of Philosophy (PhD)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/6696 |
| Date | 04 1900 |
| Creators | Mavridis, Harilaos |
| Contributors | Hrymak, A.N., Vlachopoulos, J., Chemical Engineering |
| Source Sets | McMaster University |
| Detected Language | English |
| Type | thesis |
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