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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Why It Is Difficult to Mold Parts within Tolerance in Pattern Based Injection Mold Tooling
Over the last few years, a tremendous amount of work has been done to develop alternatives to conventional machining methods of creating injection mold tooling. Because such alternative methods offer the potential to create injection mold tooling for prototype purposes faster or less expensively than conventional machined tooling, there has been a great deal of interest in alternative tooling. A number of older tooling creating methods have been revived and several new methods have been developed and reported on. Most involve creating a pattern against which the tool is formed, usually by casting a tooling material against the pattern or a copy of the pattern. In general the tooling created by these methods can be referred to as pattern-based tooling. In October, 1997, Dr. Paul Jacobs delivered a paper which defined the relationship between dimensional variation in a cast tool resulting from variations in shrink and the mean shrink level of the tooling material(1). This groundbreaking work provided fundamental information on tolerances in alternative tooling processes. In addition it clearly identified the role shrink in the tooling material plays in determining the ability of any particular tooling process to hold tolerances. Specifically, Jacobs showed that shrink is not uniform; it is in effect a random variable distributed normally around a mean. Furthermore, he showed that the standard deviation of that distribution is proportional to the mean shrink rate. With that information, it is possible to predict the range of dimensional errors in a tool, or tolerance, that result from variations in the shrink rate of the tooling material. As valuable as that work is, its use is limited because it only includes the effects of shrinkage in the tooling material. Other factors such as the accuracy of the pattern building process, any errors introduced in finishing the pattern and variations in shrinkage of the molded part will contribute additional error and make the toler
Opportunities for Solid Freeform Fabrication in Prototyping and Manufacturing
Solid Freeform Fabrication (SFF) of parts and components is an area of active development and tremendous potential. SFF is a layered manufacturing technique in which the required component/part is built from a CAD model. This model is mathematically sectioned into a number of layers and a material deposition or tool path is generated for each layer. A fabricator uses this tool path information to build the part, layer by layer. This family of manufacturing techniques offers several advantages over traditional routes, such as: no part specific tooling, fabrication of complex geometries to net shape, and greater design flexibility. There is also a significant potential for lowering cost of prototyping as well as small-scale manufacturing. Many of the SFF routes that are currently available are for fabrication of plastic, ceramic and metal parts. Some of these SFF techniques are, Stereolithography (SLA) Laminated Object Manufacturing (LOM) or Computer-Aided Manufacturing of Laminated Engineering Materials (CAM-LEM), 3D Printing (3DP)/Sander Prototyping (SP)/Droplet Deposition, and Selective Laser Sintering (SLS). Most of the SFF routes are similar in concept, i.e., model generation, followed by mathematical sectioning and layerwise building, and differ only in the method of layer fabrication. In order to manufacture ceramics and metals, the polymer based SFF methods have been adapted using powders as a second phase in a base polymer or fluid. Parts can then be made directly or indirectly. In the direct route, a green ceramic part is directly manufactured to shape. Alternately, in the indirect process, parts are made by infiltrating a ceramic or metal slurry into a polymer or metal mold made by SFF. Subsequent processing of these green parts (i.e., debinding/drying and sintering) is similar to that of traditionally manufactured components and results in a near net shape sintered part.
Time to Market & Rapid Tooling an OEM Prospective
Time to market is the item that is critical to survival in the international and domestic markets. Considering that almost all products today have some plastics compounds or are entirely produced in plastics, plastics engineering becomes a critical path technology. In the plastics industry there is one item that drives time to market and that is tooling. How a company approaches rapid tooling will directly affect time to market and can severely affect product release. The machine tool suppliers recognized these issues several years ago. Toolmakers now have machining centers that can reduce chip-cutting time by 40-50%. This shortens tool fabrication time dramatically. We should get our tool in 6-8 weeks instead of 14-16 weeks. However it doesn’t happen that way in real life. Tool fabrication accounts for less that 40% of the tool build time. Design and design modifications have a stronger impact on tooling deliveries. What will make the greatest impact in reducing product development time for OEMs is defining product requirements up front and concurrently deciding on the best approach in rapid tooling. This presentation will review how the injection molder and the OEM can utilize these assets and engineering personnel to achieve the best rapid tooling technology to meet design requirements. Rapid tooling will not satisfy the customer’s needs if it does not work!
The Development of Medium to Long Run Tooling with a View to Rapid Manufacturing
As emerging technologies develop and existing technologies mature, rapid manufacturing of plastic injection molds has become a reality. Molded plastic parts out of the desired material in days, not weeks was once a dream. With the advances in both mold manufacturing materials and rapid prototyping equipment this is now a reality. Using non-traditional manufacturing methods to produce traditional injection molds, product development cycles can be drastically reduced. With the recent development of materials for rapid prototyping machines, manufacturing molds is now possible using current technology. Using materials for short run tooling, tools can be manufactured in 3 to 7 days that are capable of producing 50 to 250 parts. Long run materials like stainless steel are capable of 100,000 plus shots and can be produced in 5 to 15 days. The technology used to produce these molds is selective laser sintering (SLS). A solid model is produced of the cavity and core and using a laser the mold is produced layer by layer. A heat treat furnace is required to harden the inserts and infiltrate to full density. Very detailed part geometry's are possible. Mold details can be incorporated into the solid model and manufactured into the inserts. Cooling lines both conformal and traditional, ejector pin holes, runner and gates, SPRUE and SPRUE pullers can all be incorporated. The inserts can be polished to a diamond finish, textured using traditional methods, welded, and machined using conventional machining equipment and techniques. These molds are capable of molding both thermoplastic and thermoset materials. Normal pressures and molding cycles are possible. Research and development underway promises to push the envelope of this technology even further. Advances in new materials, techniques and equipment will enhance or obsolete current technology. This technology has the potential to significantly impact the plastics industry.
Development of Structural Hierarchy in Injection Molded Dynamically Vulcanized PP/EPDM Blends
When injection molded, the polymers exhibit complex structural hierarchy from angstrom size levels up to optical. This is particularly true when the polymers have multiple phases such as in the case of polymer blends. It is as a result of a complex thermal -deformation history that this process imparts on the flowing fluid as it subjects it to severe thermal deformation gradients during the course of its formation. This dependence results in a three dimensionally varying structure and corresponding properties1,23. This complexity further increases with a composition as a variable in a multiphase blends systems as in the case of dynamically vulcanized PP/EPDM blends. In order to understand the details of the spatially varying structural hierarchy, one needs to investigate it using a variety of characterization tools that allows the observation of the localized structure at different size levels. For this purpose, we developed a unique microbeam WAXS instrument that allow us to probe the spatial variation crystalline regions for their order and orientation quantitatively. In this research, the effect of blend composition and processing conditions on the development of structural hierarchy in injection molded parts were studied through optical microscopy and matrixing microbeam X-ray diffraction technique and thermal analysis techniques.
Effect of Pulling Speed on the Sizes of the Liquid, Gel and Solid Zone during Thermoset Pultrusion
The temperature and the degree of cure distributions inside a thermoset composite profile during the pultrusion process are calculated numerically using the finite difference method. The degrees of cure at the beginning of the gel and the solid zones i.e ?GL and ?GS are determined using appropriate experimental techniques. These results enabled us to predict the location and the size of the liquid, gel and solid zones inside a pultrusion die. It is found that the pulling speed affects the size and the position of each zone considerably. The relationships between the sizes of these zones and the pull-force is discussed.
Banning Heavy Metal Pigments in Minnesota - The Next Iceberg?
For several years the Minnesota Legislature, guided by the MPCA (Minnesota Pollution Control Agency), has been evolving a law to significantly reduce heavy metal pigment use in the state. The finalized law takes CONEG (Coalition of Northeastern Governor's) guidelines to a higher level. CONEG was intended to reduce the amount of heavy metals in the consumer waste stream by limiting their use in disposable packaging materials. The Minnesota law applies CONEG limits of lead, cadmium, mercury and hexavalent chromium to all pigments, including plastic colorants. This paper will review the evolution of this law. What could this mean to the plastics industry if similar events occur in other states?
Numerical Investigation on Mixing in a Pin Mixing Section for Screw Extruders
Non-Newtonian, non-isothermal, 3D finite element simulation of mixing performance in a pin mixing section with different axial gap of pins has been carried out according to their realistic configurations. To learn and to compare the local mixing performance in a standard screw and a pin mixing section, the local mixing efficiency distribution proposed by J. M. Ottino was calculated. Also RTDs of these mixers were calculated to try to measure mixing. Then, the integration of above parameters, which was referred as integral mixing efficiency, gave a quantitative judgement of total mixing ability of the mixer. The calculated result showed a non-linear dependence of mixing ability of a pin mixing section on the axial gap of pins. Finally, the calculation result was compared with the experimental one obtained in our previous study.
Chromatography-Infrared Spectroscopy Characterization of Polymers
Polymer systems demonstrate simultaneous multivariate distribution of properties (molecular weight, composition, chain configuration). These molecular properties directly effect the physical properties of the polymer system. The polymer engineer typically adjusts these molecular properties in an attempt to optimize the end-use properties of a polymer. The characterization of the distributed molecular properties and their relationship to end-use physical properties is thus a key to the tailoring and optimization of a polymer product. Polymer analysis methods can be divided into three categories: methods that measure fundamental molecular properties, methods that fractionate a polymer, and physical test methods. Table 1. illustrates some of the principal techniques in each category. Molecular composition and configuration frequently varies across the molecular weight distribution of a polymer. As a result, a spectrum of an whole polymer sample provides at best a limited characterization of the polymer. This paper describes a technique whereby infrared spectroscopy is combined with one of the fractionation methods to obtain a more insightful characterization of a complex polymer system.
Thermal Stabilization of Polymers Containing Residual Catalysts
Residual polymerization catalysts are known to promote degradation reactions in many polymeric materials. Such reactions were studied in poly(methyl methacrylate) (PMMA) doped with a typical catalyst at temperatures slightly above Tg using thermogravimetric analysis. Several novel approaches to minimizing the adverse effects of residual catalyst on thermal stability were investigated. Extraction of residual catalyst using liquid CO2 and a fluorinated chelating agent was shown to significantly improve the stability of PMMA film. Encapsulation of the residual catalyst using strongly a binding chelating agent, an azo-derivative of a crown ether, is also shown to enhance thermal stability.
Interfacial Tension Measurement of Polymers with the Pendant Drop Method: A Comprehensive Experimental Review
The pendant drop apparatus is the most reliable and accurate method of measuring the interfacial tension of polymer melts. However, the lack of a defined experimental method is a possible contributor to conflicting data in the literature. This paper reviews all practical aspects of pendant drop experiments with polymers including material preparation, syringe diameter selection, drop stability, necking and capillary effects, equilibration time and interfacial tension measurement error, repeatability and dependence on drop size. Original experimental data with polyethylene and polystyrene resins is discussed and compared to literature results.
Fabrication and Characterization of Electro-Optic Polymeric E-Field Sensors
The guiding of light beams along dielectric layers, first realized experimentally in the early sixties has stimulated the growth of a new class of passive and active components using light guided by films deposited on wafer-like substrates. These optical components provide the advantage of greater bandwidth and immunity from electromagnetic radiation hence making them become sufficiently effective to herald the beginning of a sophisticated technology called integrated optics. Current integrated optics technology is based upon inorganic crystalline LiNbO3. The concept of integrating an electro-optic polymer into a reverse poled Mach-Zehnder modulator to be used as an electrode-less E-field sensor is discussed here.
Structural Investigation of Plasma-Polymerized Pyrrole Films
Fourier-transform infrared spectrometry (FT-IR) and X-ray photoelectron spectroscopy (XPS) have been carried out to characterize plasma-polymerized pyrrole (PPy) films deposited under two deposition conditions, viz. high plasma excitation power/low monomer pressure (i.e. HW/LP) and low plasma excitation power/high monomer pressure (i.e. LW/HP) in RF and DC glow discharges. LW/HP PPy films deposited with a pulsed DC discharge were also investigated. Substantial differences were found between the structures of the films deposited under different conditions. The LW/HP films appeared to contain less unsaturation and conjugation than the HW/LP films. A comparison is made of the FT-IR spectrum of pyrrole monomer with those of PPy films and electrochemically polymerized pyrrole, which consists of disubstituted pyrrole rings. Evidence is presented that in low power RF conditions, the pyrrole ring structure can be maintained. The plasma polymerization processes of pyrrole under different deposition conditions are proposed.
Study of the Curing of Polymerizable Reaction Mixtures, PMR-15
The curing of PMR-15 was investigated using Fourier transform infrared spectroscopy (FT-IR) as a function of time (3 ? t ? 150 mins) and temperature (65 ? T ? 300°C). Imidization was measured by the changes in the imide carbonyl absorption at 1778 cm-1. The imide carbonyl absorption increased with temperature and time. Very little Imidization, <5%, occurred at 65°C irrespective of time. However, between 95 and 300°C, the extent of imidization was completed in 2.5 h at 300°C. FTIR also showed that thermal imidization and anhydride formation occurred simultaneously at high curing temperatures and longer curing times. Anhydride formation peaked at 0.5 h of curing at 135°C. Kinetic analysis for imidization was performed at low conversions. An Avrami-type kinetic analysis for imidization was also performed.
Determination of the Mechanism of Formation of Polypyrrole on Reactive Metals by Infrared Spectroscopy
The formation of polypyrrole coatings on steel was performed by an electrochemical process in aqueous oxalate solutions. The pH of the reaction medium and applied current density were varied from 1.2 to 8.4 and 0.56 to 5.63 mA/cm2, respectively. The mechanism of formation of polypyrrole coatings on steel, in acdic medium (pH < 6) was found to differ from that in basic medium (pH = 8.4). In acidic reaction medium, formation of polypyrrole on steel occurred in three stages: (i) dissolution of steel, (ii) passivation of steel and (iii) formation of polypyrrole. No passivation period was observed in the basic medium. The mechanism of passivation of steel and the composition of the coatings was investigated by reflection-absorption infrared spectroscopy. Our results show that increasing the current density decreased the passivation period. In acidic medium (pH =_6.0), minimal passivation time was observed to occur at a pH 2.4. IR analysis shows that passivation of steel was due to the formation and precipitation of FeC2O4.2H2O passive films on steel .
Influence of Adhesion Promoters on Properties Short Glass Fiber/Polypropylene Composites
Acrylic acid grafted polypropylene (PP-g-AA) and two maleic anhydride grafted PP (PP-g-MA) of different viscosities and grafting levels are used, together with pyrolyzed fibers and ?-aminopropyl-triethoxysilane sized fibers. Mechanical characterization on injection-molded parts and fragmentation test on single fiber composite (SFC) are performed in order to correlate adhesion and performances. A higher level of grafting appears to be an important factor for best adhesion enhancement. The crystalline morphology was characterized in previous work and was found to play a key role on the resulting properties, in spite of good interfacial interactions. Highly grafted PP-g-MA is the best adhesion promoter characterized in this work.
Orientation Effects on the Weldability of Polypropylene Strapping Tape
Polypropylene strapping tape is commonly sealed by welding using high temperature tools. Despite the widespread use of the technique no work has been done to study the influence of the welding process parameters on the properties of the joint. In this work polypropylene strapping tape, produced with different draw ratios and types of surface embossing, was welded with a standard semi-automatic strapping machine. The effect of the process parameters (temperature, sealing pressure and surface profile of the sealing tool) and the tape properties (draw ratio and embossing pattern) on the microstructure and the joint strength was studied. An optimal temperature range could be identified. The draw ratio of the tape influences the weld efficiency.
Characterization of PP/PPgAA Blends by Contact Angle
Polypropylene (PP) was functionalized with Acrylic Acid (AA) by means of a radical-initiated melt grafting reaction. The content of AA grafted onto PP was determined by using acid-basic titration. Blends of PP with 0 to 100% wt of Polypropylene grafted with Acrylic Acid (PP-gAA) were prepared by melt mixing. The effect of the modified polymer content on the surface of cast films was characterized through contact angle and ink adhesion measurements as well as attenuated total reflection infrared spectroscopy (FTIR-ATR). The contact angles of water on cast film surfaces of PP/PPgAA blends decreases with increasing modified polymer content. A notorious improvement on ink adhesion on the surface was observed when increasing the content of modified polymer. From FTIR-ATR spectra of the blends, the carbonyl index on the films surface was calculated. It was found that the higher the carbonyl index, the lower the contact angle value for the polypropylene blends.
A Process Comparison of Orbital and Linear Vibration Welding of Thermoplastics
This paper reviews a study comparing the physical differences between orbital and linear vibration welding of thermoplastics. For the same welding conditions, it was found that orbital welding dissipated 56% more power than linear vibration welding in Phase I (solid-to-solid friction) of the process. Similarly, in phase III (steady state) orbital welding dissipated 100% more power than linear vibration welding. The duration of phase I and phase III was 36% and 50% shorter for orbital welding than for linear vibration welding. A theoretical comparison for phases I and III were consistent with the experimental results. Comparison of micrographs of welded sections shows that orbital welding produces thinner weld lines than linear vibration welding.
Development of Underfilling Encapsulant Based on Ternary Systems of Benzoxazine, Epoxy, and Phenolic Resins
We have developed a new polymeric system based on the ternary mixture of benzoxazine resin, epoxy resin, and phenolic resin. Low melt viscosity resin renders void free specimens with minimal processing steps. The material properties show a wide range of desirable reliability and processability which are highly dependent on the composition of the monomers in the mixture. A glass transition temperature as high as 170°C and considerable thermal stability up to 370°C can be obtained from these systems. The materials exhibit promising characteristics suitable for application as underfilling encapsulation and other highly fiilled systems. the curing aid of polybenzoxazine. The mixture of these three resins to form the ternary systems is believed to provide a great variety of resin properties suitable for wide applications, particularly in the microelectronic application and the highly filled systems.
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