Key Engineering Materials Vols. 611-612

Abstract: In recent decades, the weight of passenger vehicles has constantly increased. This leads to a rise in fuel consumption and higher CO₂ emissions. On this basis, vehicle weight reduction is a privileged research axis to meet regulatory requirements on emissions by 2020. The current study is focused on the development of thermoplastic polymer used in the automotive sector. In fact, thermoplastic polymers allow innovative design and offer the advantage of being recycled for sustainable development purposes. Some lighter fillers were incorporated in this polymer by melt processing for weight saving benefits. We were interested mainly in hollow microspheres which are lower density than conventional mineral fillers (such as: talc, calcium carbonate, glass fibers etc ...). This study explores the impact of pilot-scale melt-processing on six (6) hollow microspheres embedded in high impact polypropylene commonly used for car bumpers. We found that two commercially available microspheres (grades iM30K and K37) withstand melt-processing successfully and reduce the polymer density.

Abstract: This paper deals with the parameter identification for polyurethane foaming process simulation by using an inverse analysis coupled with a Finite Pointset Method. Simultaneous measurements of the foam height rise, the reaction temperature and the viscosity on a cylindrical cardboard test tube are obtained by using the foam measurement system (FOAMAT). The simulation of the foam expansion is obtained by solving unsteady Navier-Stokes equations coupled with the energy equation, the curing reaction (reaction of isocyanate with polyol) and the foaming reaction (reaction of isocyanate with water to emit the CO₂ gas) by using a mesh-free method. The inverse identification method consists in determining the parameters by comparing the computed quantities (height rise, reaction temperature and viscosity) computed by the finite pointset method to those measured experimentally.

Abstract: A novel pinch valve has been developed for micro fluidic applications. It has significant advantages regarding dead volume, pressure tolerance, replaceability, scalability and dosage frequency in comparison to competing valve principles and other pinch valves. The transfer of the valve from laboratory sample to an industrial usage required particularly a modification of the tubes. A new geometry has to be developed and sufficient tube material has to be identified. Different silicone rubbers were examined in the course of prototype manufacturing. Preliminary investigations were carried out to qualify the manual manufacturing of the silicones, according to the manufactures specification. Based on these results, the new developed tubes were manufactured and compared to its technical properties. The required parameters were achieved by using heat-cured silicone elastomer. Preliminary dosage tests of the final developed pinch valve had shown good results and satisfy industrial specification.

Abstract: Starting point of this paper is photopolymer printing plate used for flexographic printing. It is used for transfer of the printing ink onto the printing surface during the reproduction process. Photopolymer printing plate consists of several layers: polyester basis, photo sensitive polymer material and LAMS - Laser Ablation Mask. In the platemaking process the photosensitive material, which will form a printing plate, has to be several time exposed to different radiation in order to obtain a functional printability performance. LAMS layer has a role of masking in the exposure process. Upon pre-exposure, LAMS layer has to be removed by laser ablation only at the surfaces where photopolymer printing plate needs to be exposed. After ablation the exposures to UV lights follows and the plate will be finished with chemical removal of the unexposed parts of the polymer. Functionality of the finished printing plate has to be characterised and monitored in every procedure step because the formed image element on the printing plate has a major influence on the quality of the finished printed product. In this paper observing of the changes in the polymer material which is caused by exposure through LAMS layer will be performed. The aim is to measure the surface openings on the LAMS mask and to measure surface coverage (image elements) on the polymer material formed by exposure through the LAMS. Measuring will be made by image analysis software based on microscopic images of the control fields of differing halftone values. It is assumed that there will be a correlation between the LAMS openings and formed image elements on the printing plates. Preliminary results indicate that certain differences in image elements can be detected and are probably the consequence of the different amount of irradiated surface of the polymer material. Since the polymer material which forms the printing plate should be stable in the graphic reproduction process, results of the paper will explain the influence of UV exposures on polymerisation process and on the functional printability performance of the plates.

Abstract: Liquid-Driven Stretch Blow Molding is a new and innovative method to produce PET bottles [. In the well-established Stretch Blow Molding (SBM) process, preforms are biaxially deformed by pressurized air into a cavity. The resulting bottles are transferred to a separate machine, where the desired product is filled in. In contrast to that, Liquid-Driven Stretch Blow Molding is characterized by employing the liquid product to deform the material. The former separated blowing and filling steps are thus combined to a single forming stage leading to numerous advantages in energy consumption, cycle time and machine footprint. In this paper, a numerical simulation of the new process is presented. An additional challenge compared to SBM simulations is thereby the consideration of the interaction between liquid and preform. The load application cannot be solely represented by the pressure because the influx behavior as well as gravity and inertia forces influence the preform deformation. A smoothed particle hydrodynamics (SPH) approach is applied to the simulation to incorporate the additional effects. The process model is evaluated by prototype experiments. In addition, a feasibility study shows the applicability of a rotary forming system to the new process.

Abstract: The breadmaking process can be defined by the succession of operations with operating conditions as input variables and dough properties as output ones, any output variable at step i being an input at step i+1. In this paper, we strive to show how the main properties of bread, density, porosity and alveolar structure (crumb), can be predicted from basic knowledge models (BKMs). So we have defined the variables of breadmaking, proposed BKMs for the two first operations, mixing and proofing, and underlined the needs to define them for shaping and baking, after a short review of existing models. The specific energy delivered during mixing is determined by a simple balance equation in order to predict gluten structuration and dough viscosity, the main output of mixing operation. Then an analysis of dough proofing at different structural scales, by rheology and imaging, allows to assess its alveolar structure, and to fit the kinetics of porosity and stability by phenomenological models. Finally we show how these BKMs could be integrated in order to help the design of baked products with target properties.

Abstract: Micro injection moulding is a key technology for mass-production of micro structured surfaces, such as optical and microfluidic devices. The manufacturing of a microstructured master mould with traditional technologies poses challenges about durability, accuracy and high - volume production. This paper introduces a new approach to realize micro mould inserts in a fast and economical way. Suitable engineered materials as alternative inserts to the metallic one are proposed exploiting the following new strategy: a thermosetting epoxy resin from renewable sources was synthesized and used to realize the mould insert via casting. The initial low viscosity of the liquid epoxy resin precursors allows the achievement of a high fidelity replica of different micro structures and provides an inexpensive and convenient route for rapidly duplicate master mould. A staggered harringbone (SHM) micro-mixer geometry was replicated and the epoxy based resin insert withstood 900 moulding cycles showing good features replication and durability.

Abstract: Reducing vehicle weight to decrease energy consumption and engine emissions is one of the major objectives of the automotive industry today. This goal is mainly achieved by developing new manufacturing technologies for structural lightweight components, such as the hybrid injection molding/composite forming process, which involves preforming a thermoplastic composite laminate and overmolding it to add ribs, attachment points and other features. High part lightness, short cycle times and high degree of automation have recently made this technology an effective solution for the manufacturing of automotive interiors, including door side-impact beams and front ends. In this paper a model of the adhesion bonding mechanism between the overmolded reinforced thermoplastic and the formed composite sheet is proposed, and its dependence on the main process parameters is investigated. The model has been developed conducting experimental tests and eventually validated by means of a significant case study.

Abstract: Polyethylene terephthalate (PET) is a polyester widely used as packaging material in drink-bottling application. PET is rather sensitive to heat and oxidation and during processing it may undergo degradation reaction with generation of acetaldehyde. In this work the generation of acetaldehyde in a hot runner system has been measured. A special test apparatus was developed to separate the contributions due to the action of the extruder screw from those due to the melt residence at high temperature. Results showed that the acetaldehyde content non-linearly increases with temperature and residence time. A model has been proposed to provide for the generation of acetaldehyde as a function of temperature and residence time regardless of the geometry and other specific conditions of the process.

Abstract: The main objective of the presented work is to describe the crystallization kinetics of semi-crystalline thermoplastics with a multiscale model implemented into the COMSOL software and the in-house developed code SphäroSim. The filling and cooling simulations, implemented by using the computational fluid dynamics (CFD) and heat transfer (HT) modules of COMSOL, require the simultaneous solution of non-Newtonian multi-phase flow (polymer/air) and thermal fields in non-isothermal condition and transient regime. The simulation results are collected, converted into the OpenSource file format VTK (Visualization Toolkit) and transferred to the SphäroSim code after a matching operation with the COMSOL mesh. The SphäroSim code uses COMSOL results as input data to compute crystallization kinetics, using the COMSOL data as boundary conditions in the microstructure simulation. This allows the time resolved calculation of the crystallization process and a prediction of the final microstructure in the part which can be used in further simulations such as a structural analysis. The analytical parameters needed to connect crystallization kinetics with molecular material properties and applying the analytical scheme to the numerical simulation during filling and cooling in an injection moulding process are identified.