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The SPE Library contains thousands of papers, presentations, journal briefs and recorded webinars from the best minds in the Plastics Industry. Spanning almost two decades, this collection of published research and development work in polymer science and plastics technology is a wealth of knowledge and information for anyone involved in plastics.

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Conference Proceedings
Automatic Injection Velocity Initialization for Computer-Assisted Injection Molding Setup
David R Astbury, Alexander S. Bakharev, Russel Speight, May 2004
Modern systems for computer-assisted injection molding use data acquired from sensors and feedback from operators to setup the injection-molding process, to automate optimization of process parameters and to provide a statistical process control. A good initial starting point greatly streamlines injection molding setup and increases its robustness. Here we describe an algorithm for initial determination of injection velocity based on rheological calculations of the melt flow inside the mold cavity.
Measuring Clamping Force with Piezoelectric Strain Transducers
J. Wortberg, T. Kamps, May 2004
Strain gauges are one of the best measures of clamping force on the toggle clamp units. By means of FEA-calculations, it will be demonstrated that a problem with this kind of clamping force measurement lies with the superposition of strain and bending in the tie bars. In addition, FEA-results will show that only parts of the toggle are elongated, and therefore measuring at these parts will lead to higher precision. In the following paper, measurements of clamping forces with the new Kistler piezoelectric strain transducers will be presented and compared to measurements of a strain gauge.
Geometric Variation of Micro-Features in Injection Molding Experiment
Sung K. Lee, Charles L. Thomas, May 2004
Micro features were produced on inserts for a macroscopic polymer injection mold. The inserts were produced using traditional machining and micro machining techniques. The inserts were installed and subsequent moldings were examined to measure the accuracy of replication of the micro features. The molding conditions were varied to identify the processing window available for accurate production of the micro features.
Numerical Simulation and Experimental Validation of the Filling Stage in the Co-Injection Molding Process
Florin Ilinca, Abdessalem Derdouri, Jean-François Hétu, Djebar Ait Messaoud, Bernard Sanchagrin, May 2004
In this work, a three-dimensional finite element flow analysis code is used to solve sequential co-injection molding problems. Non-Newtonian, non-isothermal flow solutions are obtained by solving the momentum, mass and energy equations. Two additional transport equations are solved for tracking polymer/air and skin/core polymers interfaces. Solutions are shown for a rectangular plate filled with polypropylene. The numerical solutions are compared with experimental results.
Flow Prediction in the Presence of Inserts for the Injection Over-Molding Process
Shishir Ray, Franco S. Costa, May 2004
Injection over-molding involves injection of molten polymer into complex cavities over solid inserts to form fabricated parts. This process is non-isothermal and the flow is strongly affected by the presence of the insert, and its thermal and mechanical properties. This paper compares the three dimensional flow simulation results of metal and polymer inserts and reviews their effects on filling pattern with experimental data. Furthermore, a two shot over-molding simulation is also presented.
A Genetic Optimization of Shrinkage by Runner Balancing
Kevin Alam, M.R. Kamal, May 2004
A new approach to runner balancing is proposed which identifies and deals with limitations associated with the traditional approach to runner balancing. The runner diameters are varied by a multi-objective genetic algorithm, which simultaneously optimizes the product shrinkage and cost. The results suggest that balanced runner systems, which exhibit large differences in cavity pressure, have lower product costs than systems characterized by similar fill times and cavity pressures. The optimization of the secondary runner lengths also reduced costs significantly.
Theoretical and Experimental Comparison of the Four Major Types of Mesh Currently Used in CAE Injection Molding Simulation Software
Matthew J. Jaworski, Zhongshuang Yuan, May 2004
Currently, CAE injection molding simulation software uses four major types of mesh for analysis. These four mesh types are beam (1D), mid-plane (2.5D), Dual Domain™ (modified 2.5D) and three dimensional (3D). Each mesh type is useful for simulating different types of plastic part geometries but also has its own limitations and assumptions. This paper will discuss the advantages and disadvantages of each mesh type through theoretical and experimental data.
Microcellular Injection Molding
Lih-Sheng Turng, May 2004
The paper reviews the processing advantages and challenges of microcellular injection molding and summarizes the recent research results obtained at the University of Wisconsin-Madison. The study emphasizes on how the process conditions and micro-/nano-scaled fillers affect the microstructure and mechanical properties of microcellular injection molded components. In addition, initial results of a novel co-injection molding process that combines the aesthetic and processing advantages of injection molding with the property attributes and benefits of microcellular plastics (MCPs) are presented.
Numerical Analysis of Microcellular Injection Molding
Sejin Han, R. Zheng, P. Kennedy, J. Xu, L. Kishbaugh, May 2004
This study presents a simulation model for the microcellular injection molding process in which supercritical fluid such as carbon dioxide or nitrogen is mixed with molten polymer and injected into the mold. Our model simulates the development of cells in the melt during injection molding. The effects of cell growth on material properties and flow have been investigated. Some simulation results such as melt pressure and final cell size distribution are compared with experimental results.
Structure Development and Mechanical Properties of Overmolded Parts
D.B. Tchalamov, A.M. Cunha, May 2004
Overmolding is a non-conventional injection molding method in which two or more polymers are introduced sequentially with a time lag into a special mold. In this study experimental design was employed for investigating retractable insert overmolding of two PP/HDPE combinations. Optical microscopy was used for evaluating structure development. Mechanical properties were examined through flexural and impact tests. The role of the interface of the two materials on the overall mechanical behavior was analyzed.
Effect of Overdrying Hygroscopic Resins and a Technological Solution for its Prevention
Suhas Kulkarni, David Hart, May 2004
Hygroscopic resins are dried before processing. Most polymers are blended with low molecular weight additives as heat stabilizers, processing aids and/or other specialty additives. If the resin is dried for an extended period of time, these additives tend to break down causing deterioration properties. Moisture can play an important role in the melt rheology. Experiments were done to study this effect with the help of thermal analysis and evaluation of physical properties. A technological solution to prevent overdrying is presented.
Effects of Design Solutions and Moulding Operating Conditions in Warpage
P.G. Martinho, C.C. Neves, A.M. Brito, May 2004
Injection molded parts with plane surfaces and complex flow are subjected to distortion depending on the mould geometry and general processing conditions. In this study, the effects of several mould and part design solutions were evaluated as well as the operating conditions of the injection molding machine. To examine warpage, the geometry of the plastic parts was defined and a modular mould was designed integrating pressure and temperature sensors. Experimental results, namely pressure, temperature and warpage values, were compared with those obtained from C-MOLD simulations.
Thermoformability of ABS Grades
L. Pecora, A. Bardetti, D. Laroche, May 2004
Relationships between the rheological properties of different material grades with their processability are often difficult to make. In this work, a parameterization technique of the rheological properties is proposed to quantify the variations from grade to grade, within the same family. The impact of the identified parameters on the thermoformability of different ABS grades was investigated with the use of finite element simulation of the thermoforming process.
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.
Production of Segmented Mold to Control the Distribution of Materials in the Thermoforming Process
Majid Tabrizi, May 2004
Control of temperature distribution throughout a segmented mold to reduce a part’s residual stress and improve material distribution has been studied. A segmented mold has been produced using a rapid mold making technique with in-cast cooling lines for a non-uniform cooling of the different segments of the mold.Polystyrene and polyvinyl chloride has been used to produce a number of parts for evaluation. The result showed a noticeable improvement in reduction of the internal residual stress with minimal effect on material distribution.
Influencing Wall-Thickness of Small Diameter Parisons
Walter Michaeli, Jens Grünewald, May 2004
Many complex blow-molded parts demand wall-thickness influencing systems to achieve a regular wall-thickness distribution in the part. For small parison diameters the standard systems can not be employed because of the high stiffness of the used deformable metal rings. A new die concept with turnable elliptical rings and an elliptical mandrel allows to change the flow channel height over the circumference and the parison swell behavior at the die outlet can be influenced.
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.
Minimum Requirement for a Reliable Hot Runner Controller
Thomas P. Linehan, May 2004
There are many types of hot runner control designs. Some provide only basic features. There is a growing trend towards integrated or “GUI” (Graphic User Interface) styles of systems. However, despite the high-end features that many of these newer systems provide, they often have problems accurately measuring and therefore controlling temperature.This paper will discuss differences in system designs and how to detect the presence of potential problems.
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.
Significant Factors on the Dimensional Accuracy of Fused Deposition Modeling
Robert C. Pennington, Nicole L. Hoekstra, Jeffrey L. Newcomer, May 2004
This project investigated the dimensional accuracy of parts produced using the rapid prototyping method of Fused Deposition Modeling. Parts with six different features were created on a Stratasys FDM2000 out of ABS and then measured with a Coordinate Measurement Machine and digital micrometers. An analysis of 12 different measurements on parts produced using FDM identified that part size, location in the work envelope, and envelope temperature had a significant effect on the dimensional accuracy of FDM.


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