Luisa Silva

Structure Development in Injection Molding: A 3D Simulation with a Differential Formulation of the Kinetic Equations

Abstract The purpose of the present work is to introduce a crystallization law into Rem3D, a 3D code written in C++ and dedicated to the injection molding of polymers. We kept the basic hypotheses of Avramis model and cast the kinetic equations into a differential system that is solved numerically. The variation of the density of potential nuclei with temperature is taken into account. Furthermore, the distribution of mean spherulite sizes can be deduced from the calculations. The second part of the paper is an experimental study of crystallization in well-controlled conditions (2D, isothermal or constant cooling-rate). It establishes a procedure for the determination of the nucleation and growth parameters used in the theoretical model, and gives a first validation of this model. Finally, the crystallization equations are introduced into Rem3D, in order to assess the feasibility of our new approach. Some typical results concerning the evolution of the transformed volume fraction in injection-molded parts are presented.

Implicit Boundary and Adaptive Anisotropic Meshing

Implicit boundary means that the boundaries and/or interfaces between domains are not anymore defined by an explicit boundary mesh but rather by an implicit function. It is the case with embedded boundary methods or immersed boundary methods. Here we consider a filtered level set methods and meshing is then performed using an anisotropic mesh adaptation framework applied to the level sel interpolation. The interpolation error estimate is driving the adaptive process giving rise to a new way of boundary recovery. The accuracy of the recovery process depends then on the user given parameter, an arbitrary thickness of the interface. The thickness is normally related to the mesh size, but it is shown that adaptive meshing enables to reverse this condition: fixing the thickness parameter and accounting for the adaptation process to fulfill the mesh size condition. Several examples are given to demonstrate the potential of this approach.

Injection Molding of Fibre Reinforced Thermoplastics: Integration of Fibre Orientation and Mechanical Properties Computations

Abstract Injection molding is widely used to process short fibre reinforced thermoplastics. The quality and especially the mechanical properties of the resulting part are linked to the mold conception (for example the gate(s) and the venting port(s) locations) and to the processing parameters which will govern fibre orientation distribution. Fibre orientation modelling is based on the well known Folgar and Tucker equation. The models differ one from another by the interaction parameter, the closure approximation and by the coupling with the rheology of the reinforced melt. Quantitative comparison with experiments is very tedious and generally limited to simple part geometries (plaque or disk). As a consequence, in complex geometries, fibre orientation distribution is experimentally checked using several techniques and the resulting anisotropic thermo-mechanical properties are computed using various homogenization theories. In this paper, we propose a first integrated approach of the injection molding of fibre reinforced thermoplastics starting from rheology of the material, orientation equation, interaction parameter and closure approximation. The resulting local fibre orientation distribution is then used in two ways in order to predict the mechanical properties of the part: first, using classical analytical homogenization theories, but based on the computed orientation tensor and not on an experimental one, and then, using numerical homogenization which consists in generating a Representative Elementary Volume (REV), determining its unidirectional mechanical properties and finally, in computing directly the anisotropic properties of the part.

Three-Dimensional Injection Molding Simulation

The widespread application of polymers in almost every area of industry results in an increasing need for injection molding processes that must satisfy the specifications concerning high quality parts. Injection molds are usually complex parts with high dimensional requirements. Furthermore, to guarantee the quality of the final parts, a precise characterization and monitoring of the injection molding process is required. In fact, polymer processing is complex: polymer melts exhibit high viscosity with temperature dependence, nonlinear viscoelastic behavior, low thermal diffusivity, crystallization and solidification kinetics, among others. To manufacture products with specifications in terms of dimensional stability and mechanical behavior, knowledge is required in how the processing variables, the rheology of the material, the geometry of the mold will influence the final properties of the product. The influence of these parameters on the final properties is far from obvious. It often results in a large amount of trials and errors when new products are developed. Numerical tools can speed up product innovation, reduce the associated costs, and help us to understand the material behavior along the entire process. The complex 3D injected parts and the complexity of material behavior in injection molding represent the main issues considered in this chapter, for process simulation purposes.

Massively parallel mesh adaptation and linear system solution for multiphase flows

ABSTRACT In this paper, a work performed to allow massively parallel finite element flow computations is presented. It includes the development and optimisation of two particular features of a finite element multiphase computational fluid dynamics software, which are mesh generation and linear system solution, using anisotropic adaptation and multigrid preconditioning. Parallel performances on supercomputers are shown, where the largest generated mesh (on 65 536 Intel Xeon or 261 144 Power PC cores) had 33.4 billions of nodes, leading to a 100 billion of unknowns linear system solution. Final applications concern, between others, image-based flow simulations.

Numerical Implementation of a Rheology Model for Fiber-Reinforced Composite and Viscous Layer Approach for Friction Study

A transverse isotropic viscous model accounting for the anisotropy exhibited in fiber-reinforced composite is integrated in the numerical platform of the software Rem3D®. Simulations under various mechanical loading are tested for volume fiber concentrations of 3.5% and 14.7%. Equivalent stresses and equivalent strain rate deformations given by the software were compared to the ones predicted by the model, finding very good agreements. As a second point developed on this paper, we comment on the slip condition between Die/Punch tool with the composite under compression. We noticed that the variation of the viscosity value on a small layer between the Die/Punch tooland the composite affects the nature of the contact. A viscous friction is then formulated as a technique to set slip/no-slip contact condition. We found that the slip condition is recovered at lower values of the viscosity in the interface Die/Punch with the reinforced composite, whereas the no slip condition stated for higher viscosity values.

Massively parallel anisotropic mesh adaptation

Mesh adaptation has proven to be very efficient for simulating transient multiphase computational fluid dynamics applications. In this work, we present a new parallel anisotropic mesh adaptation technique relying on an edge based error estimator. It provides a high level of accuracy while substantially reducing the computational effort. This technique enables a good capture of physical phenomena, boundary layers, interfaces, free surfaces and even multiphase turbulent flows, and has a great potential to simulate a large variety of applications. Current investigations explore the performance of the new algorithm on massively parallel resources. In this paper, we show that the developed adaptive meshing works very well in a parallel environment involving topological mesh modifications and dynamic repartitioning of parallel slots. It is also shown that the proposed methodology provides an additional gain in terms of computational cost due the production of a non-uniform mesh size distribution. Runs performed on national and European supercomputers will show the scalability and pertinence of our developments.

Multiphase and multiscale approaches for modelling the injection of textured moulds

Micro-injection moulding is frequently used for the mass production of devices in micro-medical technologies, micro-optics and micro-mechanics. This work focuses mainly on offering numerical tools to model the injection of micro-textured moulds. Such tools can predict the different filling scenarios of the micro-details and consequently offer optimal operating conditions (mould and melt temperatures, melt flow, stresses, etc.) to analyse the final part quality. To do so, a full Eulerian approach is used to model the injection of textured moulds at both the macroscopic and microscopic scales as usual industrial software cannot handle the filling of micro details. Since heat transfers with the mould are very relevant due to high cooling rates, the coupling between micro-and macro-simulations is primordial to insure a complete and accurate representation of textured mould injection.