Célio Bruno Pinto Fernandes

Modeling of Plasticating Injection Molding – Experimental Assessment

Abstract A computational model for the description of polymer flow during the plasticating phase of the injection molding process is proposed. The polymer behavior is determined during the dynamic and static phases of the process. The model takes into account the backwards movement of the screw, the presence of a non-return valve and the conduction of heat during the idle times. Results for the dynamic and static phases of the plasticization are presented. The model is also used to study the influence of some important operative process parameters, such as, screw speed, backpressure, barrel temperatures and injection chamber length. The assessment of the computational results is made experimentally by comparing the average temperature calculated with measurements made in front of the screw nozzle using both, an IR camera and an IR thermometer. The differences between the computational and the IR camera measurements are below 5%.

Using Multi-objective Evolutionary Algorithms for Optimization of the Cooling System in Polymer Injection Molding

Abstract The cooling process in polymer injection molding is of great importance as it has a direct impact on both productivity and product quality. In this paper a Multi-objective Optimization Genetic Algorithm, denoted as Reduced Pareto Set Genetic Algorithm with Elitism (RPSGAe), was applied to optimize both the position and the layout of the cooling channels in the injection molding process. The optimization model proposed in this paper is an integration of genetic algorithms and Computer-Aided Engineering, CAE, technology applied to polymer process simulations. The main goal is to implement an automatic optimization scheme capable of defining the best position and layout of the cooling channels and/or setting the processing conditions of injection moldings. In this work the methodology is applied to an L-shape molding with the aim of minimizing the part warpage quantified by two different conflicting measures. The results produced have physical meaning and correspond to a successful process optimization.

Design Guidelines to Balance the Flow Distribution in Complex Profile Extrusion Dies

Abstract In this work a novel methodology to balance the flow distribution in complex extrusion dies is proposed. For this purpose, the profile cross section geometry is divided into simpler geometries (L and T shaped profiles), which are balanced with a surrogate model obtained by a detailed numerical study. The numerical simulations are performed considering the non-isothermal flow of Bird-Carreau inelastic fluids, and the numerical computations are performed with a solver implemented in OpenFOAM computational library. The proposed methodology is assessed with some case studies.

Multi-Objective Optimization of Gate Location and Processing Conditions in Injection Molding Using MOEAs: Experimental Assessment

The definition of the gate location in injection molding is one of the most important factors in achieving dimensionally accuracy of the parts. This paper presents an optimization methodology for addressing this problem based on a Multi-objective Evolutionary Algorithm (MOEA). The algorithm adopted here is named Reduced Pareto Set Genetic Algorithm (RPSGA) and was used to create a balanced filling pattern using weld line characterization. The optimization approach proposed in this paper is an integration of evolutionary algorithms with Computer-Aided Engineering (CAE) software (Autodesk Moldflow Plastics software). The performance of the proposed optimization methodology was illustrated with an example consisting in the injection of a rectangular part with a non-symmetrical hole. The numerical results were experimentally assessed. Physical meaning was obtained which guaranteed a successful process optimization.

Guidelines for balancing the flow in extrusion dies: the influence of the material rheology

Abstract In this work we present improved design guidelines to support the die designer activity, when searching for the flow channel geometry that allows the achievement of a balanced flow distribution, in complex profile extrusion dies. The proposed methodology relies on surrogate models, obtained through a detailed and extensive numerical study, carried out with the open source computational library OpenFOAM®, in which an appropriate numerical solver for the problems under study was implemented. The main contribution of this work is to further enlarge the applicability of the simplified design methodology (Rajkumar A, Ferrás LL, Fernandes C, Carneiro OS, Becker M, Nóbrega JM. Int. Polym. Proc. 2017, 32, 58–71.) previously proposed by this group for similar purposes, by considering the effect of processing parameters and material rheology. The sensitivity analyses performed showed that, among the studied parameters, the power-law exponent was the only one that affected the system behavior. Thus, the previous proposed surrogate models were modified to include the effect of this parameter. Verification studies performed for three geometries and different rheological and process parameters evidenced the effectiveness of the proposed simplified design methodology.

An Open-Source Framework for the Computer Aided Design of Complex Profile Extrusion Dies

Abstract This work presents a new design procedure for improving the flow distribution in complex profile extrusion dies. The proposed approach is based on open source software and aims to motivate both academics and industrials to consider numerical methodologies in their future developments. A new solver was implemented in OpenFOAM computational library in order to model the steady non-isothermal flow of inelastic fluids. The developed code was verified with the Method of Manufactured Solutions. The capability of the proposed design procedure was experimentally assessed with an industrial case study, and the results obtained suggest that the computational based design aid is an excellent alternative to the usual experimental trial-and-error procedure used in industry.

On the use of high viscosity polymers in the fused filament fabrication process

Purpose This work aims to provide additional insights regarding the practicability of using conventional materials in the fused filament fabrication (FFF) process. Design/methodology/approach Two different acrylonitryle butadiene styrene (ABS) grades are studied and compared, aiming to check to what extent the regular ABS developed for conventional polymer processing, with a different rheology than the one provided for the FFF process, can also be used in this process (FFF). Findings The rheological results show that a general-purpose ABS (ABS-GP) melt is much more viscous and elastic than ABS-FFF. It is clear that using ABS-GP as feedstock material in the FFF process results in poor coalescence and adhesion between the extruded filaments, which has a detrimental effect on the mechanical properties of the printed specimens. Despite its lower performance, ABS-GP can be a good choice if the objective is to produce an aesthetical prototype. If the objective is to produce a functional prototype or a final part, its mechanical performance requirements will dictate the choice. Originality/value This work provides insightful information regarding the use of high viscosity materials on the 3D printing process.

Development and experimental assessment of a numerical modelling code to aid the design of profile extrusion cooling tools

On the extrusion of thermoplastic profiles, upon the forming stage that takes place in the extrusion die, the profile must be cooled in a metallic calibrator. This stage must be done at a high rate, to assure increased productivity, but avoiding the development of high temperature gradients, in order to minimize the level of induced thermal residual stresses. In this work, we present a new coupled numerical solver, developed in the framework of the OpenFOAM® computational library, that computes the temperature distribution in both domains simultaneously (metallic calibrator and plastic profile), whose implementation aimed the minimization of the computational time. The new solver was experimentally assessed with an industrial case study.

Computer aided die design: A new open-source methodology

In this work we present a detailed description of how to use open source based computer codes to aid the design of complex profile extrusion dies, aiming to improve its flow distribution. The work encompasses the description of the overall open-source die design methodology, the implementation of the energy conservation equation in an existing OpenFOAM® solver, which will be then capable of simulating the steady non-isothermal flow of an incompressible generalized Newtonian fluid, and two case studies to illustrate the capabilities and practical usefulness of the developed methodology. The results obtained with these case studies, used to solve real industrial problems, demonstrate that the computational design aid is an excellent alternative, from economical and technical points of view, to the experimental trial-and-error procedure commonly used in industry.

Weld Lines in Extrusion: Understanding the Role of the Flow Conditions

This work presents a numerical and experimental study on the flow behavior of a polymer melt around the spider leg of a prototype extrusion die, designed to study the relationship between the thermo-mechanical conditions in which the weld lines are formed and their impact. The numerical simulations will enable to study the influence of the spider leg location on the flow type developed and on the corresponding stress, velocity and pressure fields. Extrusion runs were also performed in the same conditions and the resulting extrudates were mechanically characterized. These two sources of information (numerical and experimental) are complementary and will, therefore, help to better understand the aforementioned relationship. For the numerical simulations we consider that the flow is isothermal and that the polymer melt (a polystyrene) can be modeled adequately by the multimode Giesekus model.