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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Injection Molding of Micro-Structured Surfaces
Communication and information technology are branches of industry with a high potential for growth and innovation. Micro-structured light guiding elements made from plastics can e.g. help improving display technology referring to illumination. On the one hand the investigations considered different polymers (PMMA, PC, POM, COC) and on the other hand several test structures. The processing parameters were varied systematically. Especially a high mold surface temperature is a precondition for the accurate reproduction of microstructures, but leads to increased cycle times. Therefore, within the investigations the use of a dynamic heating system by induction was analyzed to heat the cavity surface efficiently. The aim is to improve the molding accuracy and to reduce the formation of orientations in the molded part. Furthermore, new demolding technologies are analyzed using different demolding principles.
Water Assisted Injection Molding for Thermoplastic Materials
This study investigated the water-assisted injection molding of thermoplastic materials. The first part of this report was to develop a water assisted injection-molding system, which included a water pump, a water injection pin, a water tank equipped with a temperature regulator, and a control circuit. Two types of water injection pins were designed and made to mold the parts. The second part of this report is to test the moldability of the developed system on various thermoplastic materials, including polystyrene, polyethylene, polypropylene, and acrylonitrile-butadiene-styrene. A comparison has been made between the parts molded by water assisted injection molding and gas assisted injection molding. The final goal of this research is to gain better understanding of the moldability of water assisted injection-molded parts, so that steps can be taken to optimize the process. This would provide significant advantages in improving parts quality.
In-Situ Observation of Birefringence during Vibration-Assisted Injection Molding
The phenomenon of birefringence has been widely used in the study of steady state and transient polymer flows as well as for stress analysis but has seldom been applied to the actual injection molding process. The current study utilizes a custom designed mold with built-in windows for observation of the polymer melt within the cavity. A polystyrene melt is viewed through crossed polarizers to reveal the birefringence pattern in the melt during the molding cycle. A high-speed CCD camera is used to record the birefringence patterns in real time throughout the cycle for subsequent analysis. The use of birefringence yields information regarding the molecular orientation of the polymer that can be compared under different processing conditions.
In-Mold Coating of Thermoplastic Substrates: Further Developments
In-mold coating (IMC) is carried out by injecting a liquid low viscosity thermoset material onto the surface of the thermoplastic substrate while it is still in the mold. A computer code based on the Control Volume based Finite Element Method (CV/FEM) has been developed to predict the fill pattern and pressure distribution during the coating flow assuming the coating to be a power law fluid. A packing module is being added to further improve the pressure prediction and achieve desired coating thickness, the preliminary results are presented. Regression based statistical analysis is used to demonstrate the significance of various control variables used in a 1-D IMC flow condition. Data envelopment analysis (DEA) is used to find the optimal compromises between multiple performance measures (PMs) to prescribe the settings of IMC process variables in the 2-D IMC flow case and the location of the injection point on a real part. Case studies are presented for this purpose.
Multi-Component Laminate Moulding (MLM): Process Evaluation
Multi-component Laminate Moulding (MLM) is a novel injection moulding process that can produce multi-layered injection mouldings from at least two thermoplastic compounds. The principle of the process and initial results were presented at the Antec Meeting in 2002. This paper will describe recent developments in the process and the results from moulding trials carried out on combinations of thermoplastics including several engineering thermoplastic compounds. The discussion will highlight the potential benefits of the technology. Reference will be made to the relationship between the mechanical properties and the level of compatibility between the separate components. An assessment of the potential cost saving from the use of the MLM process with engineering resins will also be presented.
Rapid Mold Surface Heating/Cooling Using Electromagnetic Induction Technology
In this study, electromagnetic induction heating is developed to achieve a rapid mold surface heating. Both a single turn of circular coil and a spiral coil were properly designed for induction heating experiments on a flat steel mold plate. Mold surface temperature distribution during induction heating process was measured using infrared thermal image system. Simulation tool was also developed by integration of both thermal and electromagnetic analysis modules of ANSYS. The capability and accuracy of simulations on the induction heating were verified via experiments. To evaluate the practical purpose of induction heating on the real injection molding, a mold plate, roughly about an inset size of cellular phone housing, designed with four cooling channel design and running 12? coolant were utilized for the demo experiment. After 3 seconds’ induction heating, mold surface temperature increases from 110? to 180?. It takes another 21 seconds for mold surface to cool down to 110?. The rapid heating and cooling of mold surface temperatures using induction technology was successfully illustrated via both experiments and simulations.
Injection Family Molds Productivity Using CAD/CAE Tools
The main purpose of this study was to evaluate the efficiency of a injection family mold for produce security caps for pharmaceutical bottles using the computer aided design (CAD) and the computer aided engineer (CAE) tools. Such caps are made of two pieces: an internal and an external. A conventional four cavity mold with removable cores, as well as, an eight cavity family mold, both with an x" type distribution was evaluated. A manufacturing cost analysis for both molds was done finding the eight cavity mold as the cheapest one to be used for manufacturing such caps. The feasibility of these molds depends on the production cycle time the labor work shifts and the price of the injection mold."
Tool Development for Semiautomatic Design of Moulds
This paper presents the work developed for last years in TIIP, Associate Unit to CSIC, in order to make easier and faster, the task of designing a thermoplastic injection mould. During a mold design, there is a great amount of repetitive tasks that makes the designer loose a lot of time.The work presented consists of a semiautomatic software that covers the complete generation of the mould, according to standard components. It also allows the most suitable orientation of the part into the mould, according to specified criteria, and the generation of its parting surface, and cavities.The software has a very easy and intuitive running, and it follows the methodology of mould design developed in TIIP.
The Integration of Informational Functions in the Chain from Idea to Manufacturing of Molds for Injection Molding
Tooling has lived through substantial changes. The toolmaker has been, first of all, the designer and maker in one and the same person. Then, in the second part of the 20th century the division took place in the form of the increased specialization. Three function specialists: the mold designer, function makers of mold elements, and the assembling operators, toolmakers exist. The introduction of computers caused new redistribution of tasks. The mold designer activities (CAD) are followed by the mold manufacturing-planning phase (CAP), which includes also the software development for NC-equipment (CAM). The function element makers started to disappear they are materials machining-operators. A new reintegration, of part and mold designer functions will be discussed.
Thermoforming Prototype Mold Evaluation using a CAE Software
The main objective of this project consisted on the development of a measure container prototype and its mold, using Computer-Aided Design (CAD) / Computer Aided Engineer (CAE) / Computer Aided Manufacture (CAM) tools, through a 3D program and a simulation software of the thermoforming process, to determine the geometry corrections in the part design. The part prototype was carried out by using the material deposition rapid prototyping (RP) technique and the mold prototype was carried out for the machine technique. To evaluate both prototypes, the results obtained in a thermoforming machine and in a simulation software were compared.
Processing Strategies for Rotational Molding of Integral Skin Polyethylene Foams
This paper focuses on the study of the single-shot rotational foam molding technology for producing integral skin polyethylene foams. In this context, parametric studies over the mold rotational speed and in-mold temperature transition have been conducted. In conjunction with the utilization of the particle size difference between foamable and non-foamable resins, it has been found that increased mold rotational speeds can significantly improve the crucial separation of the time of formation of the skin layer from that of the foam layer. The proposed processing strategies secure the formation of a distinct layer of solid skin surrounding the high quality foamed polyethylene core.
Experimental Study on the Mixing and Segregation of Granular Particles in Rotational Molding
The nature of powder flow and its effect on particle deposition in rotationally molded parts is studied in this work. Experiments were carried out to see the effects of various parameters such as powder characteristics and operating conditions on the deposition pattern. Models for cohesive forces were developed and their effects on particle movements were estimated. Results indicate that the polymeric powders are cohesive enough to prevent size segregation at room temperature. When heating, the particles become sticky and a relatively new phenomenon of cohesive segregation is seen.
Single Site Polyethylene Resins with Enhanced Processability for Rotational Molding Applications
The performance of a new generation of single site polyethylene resins is compared to that of conventional Ziegler-Natta (Z/N) resins. Results from rotational molding trials showed that under comparable molding conditions, the mechanical properties of parts produced from single-site resins superior to those of Z/N resins. Moreover, the densification of the single site resins is complete at significantly shorter residence time in the oven versus Z/N resins. The processing window is wider and shifted to lower temperatures for the single site resins compared to the Z/N resins. The enhanced densification arises from faster dissolution of bubbles formed during the heating cycle.
The Effect of Surface Tension on the Sintering of Polyethylene Copolymers and Blends in Rotational Molding
Polymer sintering is a formation of a homogenous melt through the coalescence of powder particles during the heating cycle of rotational molding. Although the importance of surface tension in rotational molding has been recognized as one of the most important controlling parameters, there is only limited information on the role of surface tension in rotational molding.The objective of this work was to develop an experimental technique for characterizing the surface tension of materials used in rotational molding. The effect of surface tension on sintering was investigated. This paper summarizes the results of the effect of surface tension on the rotomoldability of selected polyethylene copolymers and blends.
A Six Sigma" Approach to Process Optimization for the Rotational Molding Industry"
There is a consensus in the rotational molding and related industries that crosslinkable polyethylene (XLPE) is the choice material for gasoline-type reservoirs. Field failure of XLPE-based reservoirs is not common, and to resolve one such situation involving hydraulic fluid tanks, students of Pittsburg State University's plastics engineering technology program are utilizing the concepts of six sigma (DMAIC), define, measure, analyze, improve and control. In collaboration with the reservoir producing and user companies, the problem situation was defined; film products from the hydraulic fluid-XLPE tank interface clog up the fuel filter system and subsequently result in damaged pumps. Preliminary DSC (differential scanning calorimetry) measurements indicate similar thermal transition profiles for both film and tank materials, suggesting that the film is a plasticization rather than reaction product. Additional analysis of DSC, torque rheometry, rotational molding and solvent test data yield insightful information and the optimum processing parameters for improving and controlling XLPE hydraulic reservoir production.
Acetal Copolymer - A Potential Fuel Permeation Barrier for Rotationally Molded Fuel Tanks
Acetal copolymers can be rotationally molded into a wide variety of shapes and sizes, using conventional grinding and rotational molding equipment. Celcon® M15HP acetal copolymer is one such grade that was recently developed by Ticona to offer substantially improved physical, mechanical and thermal properties over general purpose grades of acetal copolymer. In particular, it exhibits higher tensile strength, flexural modulus, impact resistance, heat deflection, fatigue endurance, abrasion resistance and surface hardness.Because of its extremely low permeability to gasoline and alcohol, along with its excellent long-term chemical resistance and dimensional stability, acetal copolymer is currently being evaluated as a potential fuel permeation barrier to meet proposed CARB and EPA evaporative emissions regulations for small offroad engine and marine fuel tanks, which are found in numerous products manufactured by the Lawn & Garden, Outdoor Power Equipment, Recreation Vehicle and Marine industries. This paper will present some basic guidelines for the rotational molding of acetal copolymer, along with some techniques for data generation and analysis using six-sigma methodology, which have enabled us to optimize the rotational molding process around this material.
Two-Dimensional Slip-Flow Model of Rotational Molding
A new slip-flow model is developed to simplify and to overcome the current numerical difficulties of two-dimensional rotomolding model in predicting the internal air temperature inside the mold during the rotomolding process. The lumped-parameter system and coincident node technique have been incorporated with the Galerkin finite element method to address these rotomolding problems. This proposed methodology allows macroscopic multi-layered deposition" of heating polymer powder onto the mold surface in order to account for the complex thermal interactions between the internal air and its surroundings (mold and polymer). A semi-implicit method is applied to deal with the overall internal air temperature inside the mold. The predicted results agree with the available experimental data for rotomolded parts of cross sectional thicknesses up to 12 mm."
Computer Simulation of the Effect of Coefficient of Friction in Plug Assist Thermoforming
In plug assist thermoforming, surface friction strongly affects the final part thickness distribution. This work investigates the effect of plug material, plug temperature, and sheet temperature on coefficient of friction between the plug and sheet. Three different plug materials (epoxy syntactic, engineering thermoplastic nonsyntactic and engineering thermoplastic syntactic) with a range of friction coefficients were investigated for thermoforming polypropylene sheet. The coefficient of friction was assessed using simulation software (T-SIM®). Coefficient of friction values were varied in the simulation software until the thickness distribution predicted by simulation was similar to that obtained experimentally.
Development of a Measurement Technique for Tailored Material Characterization and Validation of Thermoforming Simulation
For thermoforming simulation a measurement technique was developed to enable material characterization. A holistic approach was chosen to measure material parameters and the coefficient of friction. An improved “reverse-engineering” algorithm generates the material data.This paper explains the measurement devices and emphasizes the importance of the coefficient of friction. While static and dynamic friction occur in the thermoforming process, for simulation a “mixed” coefficient is used. As an example PET and ABS are investigated.
Optimization of Acrylic Capped ABS Coextruded Systems for Sheet Applications
There is a need for high quality, high gloss, scratch resistant, weatherable Acrylonitrile-Butadiene-Styrene (ABS) sheet for exterior applications. This sheet can be obtained by co-extruding a thin capstock layer of a weather resistant and weather protective acrylic resin over an ABS substrate. This paper discusses the key parameters for the design of this sheet. It is intended to be an aid for sheet converters and those specifying weatherable coextruded sheet. The Dow Chemical Company and Atofina Chemicals, Inc. have combined their materials expertise to manufacture and test the sheet structures presented in this paper.
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