Fabrice Schmidt

Modelling of infrared heating of thermoplastic sheet used in thermoforming process

Thermoforming consists of warming a plastic sheet and forming it into a cavity or over a tool using vacuum, air pressure and mechanical means. The process begins by heating a thermoplastic sheet slightly above the glass transition temperature, for amorphous polymers, or slightly below the melting point, for semi-crystalline materials. As the final thickness distribution of the part is drastically controlled by the initial temperature distribution inside the sheet, it is very important to optimise the heating stage. In most of the thermoforming machine, this step is performed using an infrared oven constituted of long waves infrared emitters. The goal of this study is to determine the efficiency of short waves infrared emitters (halogen lamps) for the heating step. The infrared heating of thermoplastic sheets will be modelled following two steps: an experimental set-up developed in our laboratory permits to measure the influence of parameters such as heaters temperature, incidence of the radiation, heat transfer coefficient, etc. An 880 LW AGEMA infrared camera is used to evaluate the surface distribution of the transmitted heat flux by measuring the temperature distribution on the surface of the thermoplastic sheet. In addition, a numerical model using control volume method (software called PLASTIRAD) has been developed to simulate the heating stage. In particular, it takes into account the spectral properties of both heaters and plastic sheet as well as the heaters directivity. Comparisons between experimental data and numerical simulations allow validating the numerical model using different types of emitters and polystyrene (PS).

Viscoelastic simulation of PET stretch/blow molding process

In the stretch/blow molding process of poly(ethylene terephthalate) (PET) bottles, various parameters such as displacement of the stretch rod, inflation pressure, and polymer temperature distribution, have to be adjusted in order to improve the process. An axisymmetric numerical simulation code has been developed using a volumic approach. The numerical model is based on an updated-Lagrangian finite element method together with a penalty treatment of mass conservation. An automatic remeshing technique has been used. In addition, a decoupled technique has been developed in order to compute the viscoelastic constitutive equation. Successful stretch/blow molding simulations have been performed and compared to experiments.

Experimental study and numerical simulation of preform or sheet exposed to infrared radiative heating

Thermoplastic processing like the injection stretch blow moulding and thermoforming processes provide the heating stage with infrared oven. This is a critical stage of the process, as the final part thickness is strongly dependent on the preform or sheet temperature distribution prior to forming. Optimisation of the infrared oven is therefore necessary. Experiments have been conducted in order to characterise the heat source of the infrared emitter and the interaction between the heaters and a semi-transparent PET sheet. An 880 LW AGEMA infrared camera has been used to determine the surface distribution of the transmitted heat flux by measuring the temperature distribution on the surface of the thermoplastic sheet. In addition, numerical simulations of the temperature distribution using control-volume method have been carried out and compared with experimental data.

Quantitative infrared thermography applied to blow moulding process: measurement of a heat transfer coefficient

This paper deals with the heat conditioning stage of blow moulding process applied to P.E.T bottles forming. One of the most important stage of this process is the radiative heating stage which is performed with infrared ovens using powerful halogen lamps. To validate a 3D control volume thermal software, called Plastirad, developed in our laboratory, temperatures maps were needed on the plastic preforms as well as convective heat transfer coefficient inside the oven. This measurement has been performed with two different methods : IR thermography and hot wire anemometry. These two methods are investigated and the main results are compared to focus on the interest of IR thermography.

Mold Filling Simulation of Resin Transfer Molding Combining BEM and Level Set Method

Liquid Composite Molding (LCM) is a popular manufacturing process used in many industries. In Resin Transfer Molding (RTM), the liquid resin flows through the fibrous preform placed in a mold. Numerical simulation of the filling stage is a useful tool in mold design. In this paper the implemented method is based on coupling a Boundary Element Method (BEM) with a Level Set tracking. The present contribution is a two-dimensional approach, decoupled from kinetics, thermal analysis and reinforcement deformation occurring during the flow. Applications are presented and tested, including a flow close to industrial conditions.

Thermal Modeling in Composite Transmission Laser Welding Process: Light Scattering and Absorption Phenomena Coupling

In previous studies [1, , we have presented a detailed formulation of a macroscopic analytical model of the optical propagation of laser beams in the case of unidirectional thermoplastic composites materials. This analytical model presented a first step which concerns the estimation of the laser beam intensity at the welding interface. It describes the laser light path in scattering transparent composites (first component) by introducing light scattering ratio and scattering standard deviation. The absorption was assumed to be negligible in regard to the scattering effect. In this current paper, in order to describe completely the laser welding process in composite materials, we introduce the absorption phenomenon in the model, in the absorbing material (second component), in order to determine the radiative heat source generated at the welding interface. Finally, we will be able to perform a three dimensional temperature field calculation using a commercial FEM software. In laser welding process, the temperature distribution inside the irradiated materials is essential in order to optimize the process. Experimental measurements will be performed in order to valid the analytical model.

Measurement Of Thermal Contact Resistance Between The Mold And The Polymer For The Stretch‐blow Molding Process

In the stretch‐blow molding process, the heat transfer between the polymer and the mold is of prime interest. Although the time of contact is very short (typically around 0.5 s), the heat transfer affects the mechanical properties of the bottle, and the quality of final parts. In order to model heat transfers at the interface, a classical approach — generally adopted in numerical softwares — is to impose the heat flux density boundary condition thanks to a parameter called Thermal Contact Resistance (TCR). This paper focuses on describing the experimental method developed in order to measure evolution of this thermal parameter (TCR) versus time, as well as results obtained on the CROMeP blowing machine. In this study, a mold has been instrumented with two different sensors. The first probe allows to estimate the heat flux density and temperature at the mold surface temperature, using a linear inverse heat condution problem (Function Specification Method). The second device is used to measure the surface t...

Simulation of the Two Stages Stretch-Blow Molding Process: Infrared Heating and Blowing Modeling

In the Stretch‐Blow Molding (SBM) process, the temperature distribution of the reheated perform affects drastically the blowing kinematic, the bottle thickness distribution, as well as the orientation induced by stretching. Consequently, mechanical and optical properties of the final bottle are closely related to heating conditions. In order to predict the 3D temperature distribution of a rotating preform, numerical software using control‐volume method has been developed. Since PET behaves like a semi‐transparent medium, the radiative flux absorption was computed using Beer Lambert law. In a second step, 2D axi‐symmetric simulations of the SBM have been developed using the finite element package ABAQUS®. Temperature profiles through the preform wall thickness and along its length were computed and applied as initial condition. Air pressure inside the preform was not considered as an input variable, but was automatically computed using a thermodynamic model. The heat transfer coefficient applied between the mold and the polymer was also measured. Finally, the G’sell law was used for modeling PET behavior. For both heating and blowing stage simulations, a good agreement has been observed with experimental measurements. This work is part of the European project “APT_PACK” (Advanced knowledge of Polymer deformation for Tomorrow’s PACKaging).

Optimization of the Incident IR Heat Flux upon a 3D Geometry Composite Part (Carbon/Epoxy)

The main purpose of this study is to cure a 3D geometry composite part (carbon fiber reinforced epoxy matrix) using an infrared oven. The work consists of two parts. In the first part, a FE thermal model was developed, for the prediction of the infrared incident heat flux on the top surface of the composite during the curing process. This model was validated using a reference solution based on ray tracing algorithms developed in Matlab®. Through the FE thermal model, an optimization study on the percentage power of each infrared heater is performed in order to optimize the incident IR heat flux uniformity on the composite. This optimization is performed using the Matlab® optimization algorithms based on Sequential Quadratic Programming and dynamically linked with the FE software COMSOL Multiphysics®. In a second part, the optimized parameters set is used in a model developed for the thermo-kinetic simulations of the composite IR curing process and the predictions of the degree of cure and temperature distribution in the composite part during the curing process.

Experimental Determination and Modeling of Thermal Conductivity Tensor of Carbon/Epoxy Composite

In this study, the effective thermal conductivity tensor of carbon/epoxy laminates was investigated experimentally in the three states of a typical LCM-process: dry-reinforcement, raw and cured composite. Samples were made of twill-weave carbon fabric impregnated with epoxy resin. The transverse thermal conductivity was determined using a classical estimation algorithm, whereas a special testing apparatus was designed to estimate in-plane conductivity for different temperatures and different states of the composite. Experimental results were then compared to modified Charles & Wilson and Maxwell models. The comparison showed clearly that these models can be used to accurately and efficiently predict the effective thermal conductivities of woven-reinforced composites.