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Conference Proceedings

Practical Experiences with a System for In-Line Monitoring of Melting Spherulites in Semicrystalline Polypropylene Sheets
Edmund Haberstroh, Jürgen Wirtz, May 2004

In thermoforming, it is found difficult to process Polypropylene if the heating control is based on measured sheet temperatures. It is shown that monitoring the melting of spherulites provides a better method. Testing is carried out using a novel device transmitting a laser beam through the PP-sheet. The scattering of the beam at spherulites within the sheet is indirectly measured via remaining beam intensity behind the sheet. With translucent Polypropylene, the melting of spherulites can be observed during heating.

Twin Sheet Thermoforming of a Fuel Tank with a Converted Blow Mould
C. deGrandpré, N. Nardini, P. Girard, L. Savoni, R. DiRaddo, May 2004

Twin sheet thermoforming has increased in usage over the last ten years, in particular due to its inherent ability to produce hollow parts and consequently challenge blow moulding. Blow moulded automotive fuel tanks are the parts that are the most challenged by twin sheet thermoforming.This work considers the conversion of a fuel tank blow mould for use in twin sheet thermoforming. The added challenge for the project is that the mould needs to maintain a flexibility to return to blow moulding, upon demand. Furthermore, the work includes the use of finite element simulation to reduce the sheet heating times.

On-Line Hybrid Model Based Tuning of Simulation Provides Soft Sensors for the Estimation of Sheet Temperature Distributions in Thermoforming
P. Girard, V. Thomson, B. Hou, A. Yousefi, R. DiRaddo, May 2004

Some of the main problems to be solved when applying simulation to a process are the discrepancies between the predicted and measured parameters. This can be due to the fact that the actual operating conditions are different from the ones that were input into the simulation due to variations in material properties and errors in the assumptions for the simulation model. This work proposes a technique to tune the results of the simulation to the actual sensor outputs of the machine. The simulation can then be used as a generalized soft sensor for the process: Since the model of the simulation has been fitted to the actual process, the predictions of the simulation for non-readily accessible points will be that much closer to reality. A further advantage is that variations of the process are back-propagated to the input, so that faults that may appear in the system are presented as more easily interpretable variations of the input data.

The Science Based Optimization of Material Heating during Thermoforming Processes
Bunyong Rungroungdouyboon, John P. Coulter, May 2004

In this paper, the optimized radiative heating of opaque thermoplastic sheet during thermoforming processes has been studied by using a newly developed modeling and optimization approach. The net radiation method has been employed to develop a comprehensive numerical code that can compute the total radiative heat and associated temperature developments locally on the thermoplastic sheet. The resultant simulation model can accommodate full non-symmetric zone heating situations and multi-layered forming materials. A coupled optimization package was then developed to obtain optimized heater pattern solutions that will lead to desired material temperatures during thermoforming processes. This is done by specifying a desired thermoplastic sheet temperature distribution and iteratively solving for the heater setting needed to obtain the desired results

Modeling of the Behavior of Semi-Crystalline Polypropylene at Elevated Strain Rate and Temperature
K.Y. Tshai, E.M.A. Harkin-Jones, P.J. Martin, G.H. Menary, May 2004

A non-linear viscoelastic model comprised of two components, a rubber-like hyperelastic component and a viscoelastic time-dependent relaxation spectrum was used to model the behavior of semi-crystalline PP at rates and temperatures close to that found in the thermoforming process. Temperature dependence was introduced through time-temperature-superposition (TTS) using WLF. The hyperelastic constants were identified from equibiaxial tensile experimental tests while the time-dependent relaxation spectrum was characterized through a temperature-frequency sweep analysis from a strain controlled DMTA test. Results show that the developed model is capable of simulating the behavior of semicrystalline PP fairly well.

Polymer-Polymeric Friction at Temperatures and Rates Simulating the Thermoforming Process
Bernhard Hegemann, Peter Eyerer, Noel Tessier, Karel Kouba, Tom Bush, May 2004

Plug assist thermoforming is one of the most important process variants for the thermoforming industry. The purpose of the plug assist is to pre-stretch the heated polymer sheet prior to the application of pressure and/or vacuum during the final part formation. Parametric studies performed on simulation models of the thermoforming process have shown friction between the polymer and the plug assist to be critical in predicting material distribution in the thermoformed part.This report presents the results of investigating the friction behaviour of a polymer to plug assist material at thermoforming conditions. A new measurement technique to determine friction coefficients will be shown and explained in detail. This technique allows the characterization of the friction coefficient as a function of temperature and rate and shows the sensitivity respectively.

Multiple Criteria Optimization Studies in In-Mold Coated Sheet Molding Compound (SMC)
Mauricio Cabrera-Ríos, José M. Castro, May 2004

Sheet Molding Compound (SMC) is a widely utilized material to manufacture automotive exterior body panels. Cycle time, dimensional consistency, and surface finish are among the most important aspects to consider in the production of SMC due to their impact in profit and quality. These performance measures often exhibit conflicting behavior i.e. lowering the cycle time might imply decreasing the part surface quality and/or achieving a lower overall part dimensional consistency. One must exercise especial care in identifying the best compromises between these performance measures (PMs) along with the processing conditions that result in these best compromises. This paper describes an application in SMC processing where the multiple criteria optimization problem is addressed by means of a non-parametric approach known as Data Envelopment Analysis.

Development of an Environmentally Friendly Solventless Process for Electronic Prepregs
F. Permadi, Jose M. Castro, May 2004

The most common commercial processes for manufacturing pre-pregs for electronic boards use solvent-based resin systems. Solvents are environmentally unfriendly and contribute to voids in the pre-preg and laminate. The resin impregnation process is done in an open resin bath. This low-pressure impregnation is conducent to voids in the prepregs. Voids cause product variability, which is a major source of scrap in board shops. To eliminate the above mentioned drawbacks, a solventless process, based on the concept of injection pultrusion, is developed. The impregnation is done in a die under pressure to minimize voids.In previous work, chemo-rheological and kinetic measurements were used to identify a potential epoxy-based resin system. In addition, flow visualization using model fluids was used to establish the basic flow mechanism. Here, we use the previous results to develop a mathematical model for the B-staging process. Based on the mathematical model, three potential alternatives to produce prepreg are developed and analyzed. A prototype B-staging die is built and used to verify the mathematical model. The result shows that the model agrees well with the experimental data for low pulling speed and slightly under predicts the high pulling speed runs.

Investigation of Electron Beam Curing of Bismaleimide (BMI) and BMI/NVP Resins
Yuntao Li, Roger J. Morgan, Francisco Tschen, Jianjun Lu, H.- J. Sue, Vince Lopata, May 2004

Electron beam curing of a 4,4’-Bismaleimidodiphenyl-methane (BMPM) / BMI-1,3-tolyl / o,o’-diallylbisphenol A (DABPA) based BMI system, and the mixture of the above BMI resin with N-vinylpyrrolidone (NVP) is investigated to build the relationship of temperature rise, dosage and dosage rate and corresponding cure extents. The cure kinetics and effect of initiator on cure reactions are also carried out. Low intensity E-beam exposure cannot initiate BMI polymerization but high intensity E-beam exposure gives high reaction yield due to high temperature rise, which induced thermal curing. However, BMI/NVP systems can be initiated easily by low intensity E-beam exposure without thermal curing being induced. According to FT-IR measurements, 70% reaction conversion of BMI/NVP can be achieved by 200 kGy dosage exposure at 10 kGy per pass with the temperature rise no more than 50°C. The product having a Tg of 180°C can be obtained.

Numerical Simulation of the Curing Reaction during Pultrusion Processes with a Diffusion Controlled Model
Lina M. Lopez, Paul A. Wilichowski, Tim A. Osswald, May 2004

A numerical simulation of the pultrusion process was developed. The material properties were determined experimentally and fitt to a numerical diffusion controlled curing model. The DiBenedetto equation was used to calculate the instantaneous glass transition temperature during the curing process. The simulation determines the expected temperatures and degrees of cure throughout the part, in response to varied processing conditions. The primary application of the simulation is the pultrusion process and part design as well as testing the effect of new unsaturated polyester resins during processing.

Developing Time-Temperature-Transformation Diagrams for Unsaturated Polyesters Using DSC Data
Soenarto Hadiprajitno, Juan P. Hernandez, Tim A. Osswald, May 2004

A general concept of time-temperature-transformation (TTT) diagrams was numerically established to portray the effects of processing conditions during the curing of unsaturated polyester resins. The isothermal curing curves and the vitrification line were constructed based on a numerical procedure to model the curing of an unsaturated polyester resin. Isothermal and dynamic DSC modes were used to obtain the experimental data. A non-linear least squares Levenberg-Marquardt algorithm was used to fit the reaction rates with an autocatalytic kinetic model with diffusion effects. The DiBenedetto equation (1987) was utilized to correlate the degree of curing and glass transition temperature to model the diffusion-limited part of the reaction. The fitted model shows a good agreement between the experimental DSC scans and the predicted reaction rates. The numerical TTT diagram can be utilized during process design and optimization, since most of the curing behavior is represented in the diagram.

A New Class of Epoxy Thermosets
A. Bonnet, F. Court, L. Gervat, E. Girard-Reydet, M. Glotin, L. Leibler, C. Navarro, J.P. Pascault, May 2004

SBM, PolyStyrene-block-1,4-polyButadiene-block-polyMethylMethacrylate, is a new family of block copolymers offering an original way to modify polymer materials performances. Blended with a polymer compatible with one block, SBM disperses readily and imposes a structuration to the host matrix. This organization imparts unique combinations of properties, such as impact strength, high rigidity and transparency. This stands both for thermoplastics and thermosets. Here nanostructured thermosets are presented. These supramolecular architectures yield significant toughness improvements while preserving the optical transparency of the material.

Epoxy + Montmorillonite Nanocomposite: Effects of Water, Ultrasound, and Stoichiometry on Aggregates
Peter Butzloff, Nandika Anne D'Souza, May 2004

The effect of controlled water addition to the development of random aggregates of alkonium ion substituted montmorillonite clay in epoxy was studied based on changes to the hardener mix ratio, clay composition, and ultrasonic treatment before cure. The effects on the glass transition temperature and microhardness were determined. The introduction of water before ultrasonic mixing altered the apparent size of the treated clay aggregates observed in these mixtures after cure. The clay aggregates also appeared to change the location and the distribution of water-induced microcracks in the cured nanocomposites. This information was used to develop a technique to remove aggregates without causing microcracks.

Development of a New Solution to Vary the Thickness of the Parison over its Circumference While It Is Extracted
Heinz G. Gross, May 2004

Complex blow molded parts afford not only a variation of the thickness of the parison in axial direction but also in circumference direction to end up in the desired optimal thickness distribution in the final part. Integrating a partial multi-walled Flex Ring into a blow molding die allows to alter the local flow channel geometry. While deforming the Flex Ring its geometry alters gradually, so no dead spots are created. As additionally the deformation of the Flex Ring keeps within its linear elastic range the deformation can be repeated for every cycle. The principle of the technology will be explained and potential solutions of the new technology will be discussed.

Preform Optimization Using Non-Linear Finite Element Simulations
Jerry Dees, May 2004

Non-linear finite element simulations of the blow molding and thermoforming processes have been used to provide accurate predictions of the material thinning. However, this powerful simulation tool has provided limited assistance to the design and optimization of the wall thickness distribution of preforms used in injection blow molding. Trial-and-error methods are often used in design. This paper presents a technique that converts finite element analysis of the injection blow molding process into a design/optimization tool. A systematic optimization technique for preform design that uses an iterative series of non-linear finite element simulations will be described. The series of simulations converges on a preform wall thickness distribution that will result in a specified thickness distribution in the blow molded product. This design technique is especially effective for non-circular or irregular shaped products.

The Influence of Blowing Time and Blowing Pressure on Bottle's Labeling
Sylvain Jeannin, May 2004

Extrusion Blow Molding process is one of the only ways to produce hollow parts. This process is particularly difficult to control due to the parison swelling in the air without mould, contrary to the Injection Blow Molding in which all the different steps of the process take place in mould.There are four stages in this process. First of all the plasticising, followed to the extrusion through the die head. The next stage consists of the parison’s forming, then the transfer in the mould. The third stage is the blowing of the hollow part and finally there is the deflashing so that to obtain the final product.The purpose of this study is to show the importance of the cooling on the final quality of the product. The study has particularly been concentrated on two parameters of the forming of the hollow part. These two parameters are the blowing time and the blowing pressure. We have studied the different shapes obtained with the adjustment of these parameters and we tried to find a correlation between shape and quality of the labeling.

How to Reduce the Costs of the Rheological Simulation in Blow Molding Industry?
Jean-Emmanuel Noreux, Sylvain Jeannin, May 2004

The aim of our study is to show that we can readily obtain a first estimate of the behavior of a tube in blow molding only using free software. From a numerical model of biaxial stretching and blowing of a parison with specific boundary conditions and thanks to a mathematical package freely available on internet : « Octave », we have studied some rheological laws of plastic materials in order to find the evolution of the radius and of the height of the tube during the blowing process. Finally, to prove that our method can be right, we check our analytical results against a complete Finite Elements simulation performed with « Polyflow ».

Stretch Blow Molding of PET Bottle: Simulation of Blowing Process and Prediction of Bottle Propeties
Hern-Jin Park, Jong Ryang Kim, In Seon Yoon, May 2004

This paper presents a technique for describing more accurately mechanical behaviors of a PET stretch blow molded bottle by using distributions of modulus and thickness over the bottle surface. The values of modulus and thickness at each point of surface of the bottle were predicted from deformation histories of the material during the blowing process, which were obtained in numerical simulation of the blowing process. It also needed experimental measurements and estimation of mechanical properties of a stretched material up to stretch conditions in the blowing process in order to find out dependency of the properties on stretch conditions.

Nozzle Melt Density Sensor Application for a Hot Runner
Frederick John Buja, May 2004

When a hot runner mold manifold transfers a melt “shot size” into the mold cavity, the hot runner system reduces the shot size, but it also adds a second heat history to the melt.Since temperature has a dynamic impact on the molding process, a melt sensor was developed to measure Volumetric-Pressure-Temperature change and, consequently, confirm the consistency of the thermal state.This sensor was installed into a machine nozzle, and the injected melt fill-and-pack “density” was profiled for consecutive cycles. The sensor application for a hot runner mold and resulting profiles are presented.

Rapid Tooling - It’s Not Rocket Science
Barbara Arnold-Feret, May 2004

Rapid tooling (RT) pushed tool making into new areas. In the 1990s, rapid tooling using SLA, SLS, lasers, and other rapid prototyping (RP) technologies were the new wave. The promise of the processes threatened traditional machining methods, and mold-making shops pondered investment in exotic furnaces, raw materials and dedicated RP technicians.Looking at 2003, trends have changed. Rapid tooling is a reality, but the tooling is made using tied and true methods combined with better communication, verification of design and better machining. Rapid tooling changed the market. Now the question is what is the next step for RP and RT.







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