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Conference Proceedings

Evaluating the Use of Aluminum Inserts on SL Puzzle Molds for Injection Molding of Complex Parts: A Case Study
Valter Estevão Beal, Aurélio da Costa Sabino Netto, Carlos Henrique Ahrens, May 2004

Stereolithography is a rapid prototyping technique that is also capable to producing rapid molds with high accuracy in a short time. The mold's life expectancy is strongly dependent on the part geometry. This factor could induce weak regions in the mold that are more susceptible to collapse, like sharp corners and thin features. An alternative that could be used is to conceive the mold as a puzzle where slides are manually placed inside a main slot and drawn during the ejection. This work describes a comparison between two puzzle molds that had been made with and without aluminum inserts.

Determining, Understanding & Controlling the Morphology of Injection Moulded Parts Produced in Stereolithography Moulds
R.A. Harris, P.M. Dickens, May 2004

The direct use of moulds produced by stereolithography (SL) provides a rapid tooling technique, which allows low volume production by plastic injection moulding. The process’ greatest advantage is that it provides parts that are the same as those that would be produced by the conventional hard tooling in a fraction of the time and cost. However, work by the author demonstrates that the parts possess different characteristics to those produced by conventional tooling methods. These revelations defy the greatest advantages of the SL injection moulding tooling process - the moulded parts do not replicate parts that would be produced by conventional hard tooling. This work investigates the mechanisms in SL tooling that induce these different part properties and describes different approaches to modifying the process which allow the moulded parts to demonstrate characteristics closer to those produced by conventional means. The work also indicates control methods that may be unique to SL tooling.

Mold Conceptual Design Based on Fuzzy Logic
Wang Yu, Ruan Xue-yu, May 2004

Mold conceptual design is the most important phase of mold design. The decisions made during this phase are of high level and have a direct influence on performance of the mold and development costs. The main task for mold conceptual design is the in-principle determination of each mold element type (design scheme). Because of its non-algorithmic nature, technologies and methodologies such as knowledge-based system (KBS), case-based reasoning (CBR) has been used to do the work. In this paper, a novel approach was proposed to map mold element design requirements onto the corresponding design scheme by using fuzzy logic. The proposed methodology follows three steps: (1) Design requirements for mold element is extracted and generalized. (2) Possible design schemes are presented. (3) The fuzzy mapping relationship between mold element design requirements and design scheme is established based on fuzzy composition and fuzzy relation transition matrices that are assigned by domain experts. A gate type selection example was presented to illustrate the feasibility of the proposed methodology.

Keeping It Straight: The Five Sided Box
Kurt Hayden, Paul Engelmann, Jay Shoemaker, Michael Monfore, May 2004

Every molder that has tried to maintain squareness in the corners of a plastic part has come to appreciate the unique cooling problems inherent to the five sided box. It has long been understood that corners where two sidewalls meet the top or bottom of a product provide substantially increased heat load to the core of the mold. This increased heat load yields differential cooling, thus corners tend to develop stress, causing the sidewall to warp in. This investigation studied the effect of various core materials to and their effect on the warpage of the sidewalls of a five-sided box. The relative cycle time required to achieve maximum squareness for a given core material was also investigated.

Approach for a Mechanical Design of Plastics Injection Molds by Means of FEA
Ernst Schmachtenberg, Marco Thornagel, May 2004

At the design phase the injection mold maker should endeavor to ensure a maximum reliability of the mold to avoid additional costs for subsequent modifications. It is astonishing that today the mechanical design of injection moulds is predominantly done in a conventional and crude way. Finite element analysis has the potential to improve that practice. Hence an approach has been developed to couple iteratively the structural analysis of the injection mold with the filling simulation of the plastics part. That approach for an automatically coupled simulation has resulted in the first prototype version and has shown good results. This paper seeks to present the theoretical and experimental data for review.

Gelation of Hydroxy Propyl Cellulose with Sodium Dodecyl Sulfate: Temperature, Frequency and HPC Concentration Effects
Christopher Todd Snively, Nandika Anne D’Souza, Zhibing Hu, Xihua Lu, May 2004

The gelation of hydroxypropyl cellulose (HPC) solutions with an anionic surfactant was investigated. First the influence of HPC concentration (1-8%) on viscosity of water was examined. This indicated a change from Newtonian to Non-Newtonian and the development of a biphasic system. A 2 and 8% solution mixed with an anionic surfactant, sodium dodecylsulfate (SDS), was then investigated. At concentrations below the critical micelle concentration of the SDS, a peak in viscosity-concentration was observed. The concentration corresponding to the peak was found to be frequency dependent. The introduction of the SDS into HPC eliminated the biphasic structure of HPC.

Microstructure Evolution during Flow Startup of a Thermotropic Liquid Crystalline Copolyester
Tianren Guo, Graham M. Harrison, Amod A. Ogale, May 2004

The microstructure evolution and corresponding transient rheological behavior of a thermotropic liquid crystalline polymer (TLCP), Vectran V400P, is reported. The structure was characterized by using a Linkam CSS- 450 shearing/hot-stage mounting on a polarized microscope. Rheological characterization in the transient mode revealed that the transient shear stress exhibited two overshoots. We believe that the domain and defect rearrangement leads to the first shear stress overshoot. The relative magnitude of the second shear stress overshoot increases with increasing shear rate and with decreasing temperature.

Small-Scale Studies of Flowing Polymer Melts within Recirculation Flowcells
T. Gough, R. Spares, M.T. Martyn, J. Bent, E. Heeley, P.D. Coates, May 2004

Two small scale (30g and 200g full charge) recirculation flow cells have been designed, manufactured and commissioned for the study of newly synthesised novel polymers. Full field stress and velocity measurements for a number of polymer melts through two abrupt contraction dies have been made utilising stress birefringence and particle tracking velocimetry techniques. These results have been compared with those through geometrically identical contractions mounted in flow cells on 38mm and 60mm extruders in order to quantify the effects of scale up. Complimentary small angle neutron scattering (SANS) and X-ray scattering (SAXS) studies on molecular configuration and shear induced crystallisation show the usefulness of these flow cells and brief results from these experiments will be presented.

Effect of Low Temperature Shift Factor Modeling on Predicted Part Quality
Bingfeng Fan, David Kazmer, May 2004

The effect of low temperature modeling of the time-temperature shift factor on the prediction of residual stress and warpage of injection-compression molded compact discs is studied for an optical grade polycarbonate. Predicted residual stress and warpage with WLF and Arrhenius shift factors truncated at different temperatures indicate that the truncation temperature has a significant effect on the predicted part qualities. A double domain approach is employed to fit the shift factor with WLF function above Tg and an asymptotic function below Tg, and the simulation results are compared with the experimental observations. The comparison shows that the double domain shift factor yields good model fit and part quality prediction of injection-compression molded compact discs.

Mechanical Hole Burning Spectroscopy: A Comparison of Two Scenarios
Xiang Fu Shi, Gregory B. McKenna, May 2004

A mechanical hole-burning (MSHB) scheme was constructed to compare the analogous observations to those from dielectric non-resonant spectral hole burning (NSHB) for glass-forming liquids near their glass transitions. We used the framework of the BKZ and Bernstein-Shokooh nonlinear viscoelastic constitutive equations to examine the modified responses in a way that does not invoke an explicit heterogeneous or homogeneous nature for the relaxation response. From the BKZ model only partial hole-burning features are observed in the modified shear modulus. The Bernstein- Shokooh model used to calculate the modified compliance shows no evidence at all of a hole-burning event. These results suggest that in addition to showing potential as a probe of dynamic heterogeneity, MSHB may also a prove to be a sensitive test for the validity of nonlinear constitutive laws.

The Effect of Process Aids on the Rheological Properties of Rigid PVC Melt
Nafaa Mekhilef, May 2004

This work presents an overview on the role of process aids on the rheological properties of rigid PVC. A new rheological approach is introduced to allow a better assessment of the role of these additives. This system comprises a combination of a Couette-type cell and a capillary rheometer. The former allows a good control of the thermo-mechanical history of the compound prior to injection into the capillary barrel where a viscosity measurement is performed. The results showed that rigid PVC undergoes a fusion and gelation processes during the early stages of processing. In this step, the particles are agglomerated under the influence of heat and mostly shear. There seems to be an optimal morphological state where the best mechanical properties are obtained. Additional work showed that the addition of high molecular weight impact modifiers which also act as “binders” in the matrix promote the fusion and gelation of PVC. The results are supported by impact testing and microscopy.

Practical Application of a Portable Rheometer
Andreas Limper, Gordon Fattmann, May 2004

A portable rheometer has been developed for characterizing plastic melts for different measurement purposes. The rheometer is intended particularly for use with rigid PVC processing, but can be used for other materials too. Measurements showing the accuracy of the instrument and its reproducibility are discussed. Comparisons are made between measurements on a conventional laboratory capillary rheometer and ones on the rheometer developed, using polypropylene. The practical application of the rheometer is also shown. This is used in combination with a twin-screw extrusion line to evaluate the rheological data of different pressure pipe and profile PVC formulations in order to develop new die geometries.

Microrheology and Melt Index Calculations of Polymer Melts
John D. Clay, Rachel M. Thurston, May 2004

There is a demand for the development of techniques for viscosity measurements of very small polymer samples. Traditional rheological equipment and standard tools are limited in their capabilities to measure milligram samples of polymers. This paper outlines methods and tools used to measure the melt viscosity of polymer samples as small as 5 mg. Special, small diameter parallel plates are used to quantify the shear rheology of these samples. The data is fit to several GNF models, and the melt index is calculated from these parameters. Results from this technique are compared to results from actual melt index measurements.

Rheological Changes in CO2 Impregnated Polystyrene Reinforced with Nanoclays
Maxwell J. Wingert, Xiangmin Han, Changchun Zeng, Hongbo Li, L. James Lee, David L. Tomasko, Kurt W. Koelling, May 2004

The addition of small quantities of plate-like nanoclay can substantially increase the polymer melt viscosity, while adding dissolved gases such as CO2 can reduce the viscosity of a polymer melt. The combined effect of nanoclay and CO2 on polymer melt rheology was investigated for an extrusion process. The shear viscosities of polystyrene/CO2/nanoclay melts were measured using an extrusion slit die rheometer with a backpressure regulator. Our results show, without the presence of CO2, that the viscosity of the nanocomposite increases with nanoclay loading. However, when the nanocomposite melt is swelled by CO2, the nanoclay acts to reduce viscosity compared to the pure polystyrene/CO2 system. A possible explanation is that a significant amount of CO2 is adsorbed on the surface of the nanoclay to lubricate the flow due to the existence of surface modifier and a unique nanoclay particle layering structure.

A Novel Device for Characterizing Polymer Flows in Uniaxial Extension
Martin L. Sentmanat, May 2004

A novel extensional rheometer has been developed for use in characterizing the flow behavior of polymers in uniaxial extension. The device has been designed as a fixture for use on a commercial rotational rheometer and incorporates dual wind-up drums that allow for a truly uniform extensional deformation during flow measurement. The miniature unit can be accommodated within the oven chamber of almost any rotational rheometer such that the extensional flow properties of filled and unfilled polymers can be measured over a very wide range of extensional rates, deformations, and temperatures. Validation results with this robust instrument are in excellent agreement with published data in the literature. These and other results indicate the potentially invaluable impact that this novel device could have as a polymer characterization tool.

Effect of Isotacticity on the Simultaneous Equibiaxial Stretching of Isotactic Polypropylene Films
L. Capt, M.R. Kamal, S. Rettenberger, H. Münstedt, May 2004

A laboratory film stretcher that closely simulates the stretching conditions encountered on the industrial biaxial tenter-frame stretching process was utilized to investigate the simultaneous biaxial stretching of isotactic polypropylene films in the partly molten sate. The effects of chain tacticity of the polypropylene resins on the biaxial deformation behavior and the resulting mechanical properties were studied. Correlations were found and explained between the deformation behavior, end-film properties and the morphological characteristics of the partly molten state.

Selectivity of Extensional Viscosity Measurement under Different Conditions – Melt Elongation Versus Converging Flow
A. Göttfert, J. Sunder, May 2004

Elongational viscosity becomes more and more important due to increasing processing velocities in industrial processing. For film blowing, blow moulding and spinning process it is inevitable to consider elongational properties. The most important requirements for industrial application areFast testing with easy useHigh selectivityElongation rates similar to processingOnline measurement.Several methods of measurement have been analyzed and some are introduced on the market but not under all aspects mentioned above.First an online elongational viscosity measurement on the basis of the so called “Rheotens” is presented in this work. This method of melt elongation is then compared with converging flow method (entrance pressure loss), were different calculations of elongational viscosity are used. Different lots of polyolefine types are selected for elongational viscosity measurement. The selectivity of both methods to material differences are compared discussing measurement uncertainty.

Low-Coherence Interferometry Applied to Uniaxial Elongational Rheometry
R. Gendron, P. Sammut, M. Dufour, B. Gauthier, May 2004

The relevance of transient uniaxial elongational viscosity determination of polymers to industrial processes such as film blowing and foam extrusion is now being well recognized. Elongational rheometry is also beginning to be well documented, but it remains a delicate measurement technique, with reliability of the equipment and reproducibility of the data still being of prime concern.Recent developments in experimental evaluation coupled with state-of-the art optical techniques extend a step further the capabilities of generating reliable response in elongation, especially for large Hencky strains where dimensions of the sample being stretched is subjected to uncertainty. This paper will review the current approaches used and present a new way of monitoring in real time the true elongational response of polymeric materials, which exhibits enhancement of both the accuracy and the rapidness of the data acquisition.

An Evaluation of Elongational Viscosity of Polyethylenes Obtained from a Semi-Hyperbolic Die
D.G. Baird, J. Huang, May 2004

A semi-hyperbolic (SHPB) die attached to capillary rheometer has been proposed as a method to obtain extensional viscosity data for polymer melts at high extension rates and strains. There has been very little confirmation that data obtained from this type of device is a true measure of the extensional viscosity, ?e. Values of ?e+(transient extensional viscosity) were obtained on a Münstedt device for several polyethylenes (PE) at extension rates which overlapped with those obtained from a semi-hyperbolic die. For a highly branched PE the values obtained on a SHPB die were qualitatively in agreement with those from the extensional rheometer. However, for a linear and a sparsely branched PE the values were an order of magnitude higher than those obtained from the Münstedt device. A new analysis was carried out relating the pressure drop to the extensional viscosity which included a correction term for the variation of pressure along the die wall.

Investigation of the Predictive Capability of Advanced Differential Constitutive Equations for Polymer Melts under Different Flow Conditions
M. Zatloukal, J. Vl?ek, P. Sáha, May 2004

The predictive capabilities of three models (modified White-Metzner model, eXtended Pom-Pom model and newly proposed modification of the Leonov model) are tested for steady shear and uniaxial extensional flows of LDPE, mLLDPE and PVB melts. The input low-shear-rate viscosity data was measured on ARES Rheometrics parallel plate rheometer, whereas RH7-2 capillary rheometer was used for the determination of shear viscosity (capillary), first normal stress coefficient (slit die) and uniaxial elongational viscosity (Cogswell method). A newly proposed ‘effective entry length correction‘ has been applied to deal with all extensional viscosity data.

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