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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Solution of Inverse Thermoforming Problems Using Finite Element Simulation
Finite element simulation of thermoforming can provide highly accurate predictions of final part thickness. The majority of these simulations have been for isothermal situations. Similar calculations can also be performed for non-isothermal processing conditions, provided suitable temperature dependent material properties are available for the polymer of interest. For these simulations, it is assumed that the initial sheet temperature is known and does not change significantly during forming. In this paper sample results are presented for the so-called inverse thermoforming problem, where an initial temperature distribution is sought that will result in a specific final thickness distribution. Thus, a finite element simulation is combined with an iterative algorithm to obtain inverse solutions for a simple axisymmetric thermoformed part. In this example, the required initial temperature distributions that result in a uniform final thickness, are determined for a deeply drawn part. It is shown that the calculated results are quite sensitive to perturbations in the specified initial temperature profile and thus the practical application of optimal temperature distributions may require high precision thermal sensors and controls.
Analysis of Adhesive Properties of Different Engineering Thermoplastics to Elastomers by a Two-Shot Injection Molding Process
The objective of this research was to study the adhesion between a core (hard) material and skin (soft) material mainly used for the interior applications in automotive industry, using the two-shot injection molding process. Two different groups of materials were tested for the adhesive bond strength. In the first group, filled polypropylene (PP) and two thermoplastic polyolefins (TPO) were tested with two thermoplastic elastomers (TPE). In the second group, polycarbonate (PC), acrylonitrile butadiene styrene (ABS), and PC+ABS alloy were tested with thermoplastic polyurethane (TPU). Since many current applications involve the use of an elastomeric material as a skin material for a hard material, this research will provide some guideline for materials to be used, part design, process parameters, adhesive joint design, and post conditioning.
Kinetic Welding of Plastic Parts
Typical consumer products cannot be produced as a single part. Most items require the manufacturing of multiple parts followed by an assembly procedure. Assembly methods vary depending on the nature of the parts and their end uses. Typical assembly methods utilize bosses with nuts and bolts, snap fits, ultrasonic or spin welding and press fits. This report addresses tests undertaken on a variety of plastics, to determine the viability of the patented kinetic weld process invented at Bell Labs, the research and development arm of Lucent Technologies. In order to develop design guidelines for kinetic welding it is necessary to test a wide range of materials with different pin and boss combinations. The first series of tests were performed with welds of three different materials at three different assembly pressures and two geometric configurations. It was found that materials with relatively higher impact strengths tend to perform better than less resilient ones. It was also found that numerical design guidelines were important in optimizing the dimensions of the pin, boss and weld so as to have equalized stress throughout the part.
Ultrasonic Heating and Hardening of Hot Melt Adhesive
The application of hot melt adhesives is based on heating the adhesive from solid state to liquid state for wetting, and cooling back to its solid state to develop cohesive and adhesive strength. Conventional hot melt adhesive application methods use a separate heat source to melt the adhesive and apply it onto one of the substrates. Frequently, the adhesive cools while the second substrate is brought into contact with it resulting in inadequate wetting. With ultrasonic vibration, viscoelastic internal heating of the adhesive is used to melt it and to aid in wetting of the pre-placed hot melt adhesive film on the surfaces of both substrates. In this work, a conventional 40 kHz ultrasonic welder was used to heat a coated hot melt adhesive film in a laminate. The effects of the processing parameters of heating time, vibration amplitude, heating pressure, and hold pressure on bond performance were studied. It was found that the holding pressure plays an important role in sealing and bonding performance. Through the use of ultrasonic vibration it was possible to produce high quality seals in very short cycle times of less than 7 seconds.
Laser Transmission Welding of Semi-Crystalline Thermoplastics-Part I: Optical Characterization of Nylon-Based Plastics
Optimization of welding for thermoplastic parts strongly depends on the material properties, part design, as well as the welding operating technology conditions. Laser transmission welding requires preferential deposition of energy and subsequent melting of the material in the interfacial zone. This is optimized when the laser beam is transmitted through the transparent part and absorbed by the adjoining part to be welded. Energy deposition can be controlled to some extent by adjusting laser parameters (power, choice of beam focussing optics, sweep rate etc.) The thermoplastic material properties may have the greater influence and need to be characterized for optimum material selection. Commercial nylon type materials cover a large array of compositions, which may affect the welding process. To guide selection of nylon based plastics for a range of applications we have measured the influence of specific factors such as fiber-glass, mineral filler, impact modifier content, additives, and color versions on the Near InfraRed (NIR) transmission properties. In a following paper (Part II)a1 we have related these findings to the mechanical performance of shear and butt joints produced under various laser welding technology conditions (laser beam power, welding speed, laser beam/spot diameter, clamp pressure, plastic color, etc.). Comprehensive results of this evaluation will assist designers and technologists in thermoplastics selection for laser welding applications. The purpose of this report is to increase the understanding of the plastics engineering community regarding the usefulness and possible applicability of laser transmission welding (LTW) technology for nylon made components.
Comparative Study of Contact and Non-Contact Hot Plate Welding of HDPE
Hot plate welding is one of the most popular plastics joining methods and it is employed in most industries. Traditionally, the hot plate is coated with a non-stick" surface usually polytetrafluoroethylene (PTFE) which is usable to temperatures not exceeding 260°C. To avoid sticking to the hot plate and to accommodate higher hot plate temperatures non-contact hot plate is used. This paper is concerned with determining the optimum process parameters for non-contact hot plate welding of high-density polyethylene. For a given welding pressure the melt layer thickness weld displacement and their ratios were used as control or reduced parameters. During heating the melt layer thickness of the high-density polyethylene samples was measured. An empirical relationship between melt layer thickness and hot plate temperature and heating time was developed and used to predict the melt layer thickness in future experiments. The effects of the reduced welding parameters on joint quality are presented and compared with contact hot plate welding. For both processes the maximum attainable joint strength is 100% of the bulk material strength with the optimum melt layer thickness of 3.5 mm (1.75 mm for each part). The energy at break was more dependent on the ratio of weld displacement to melt layer thickness. For non-contact hot plate the optimum weld displacement melt layer thickness ratio was 0.75 compared to a ratio of 0.4 for contact hot plate welding.
Non Destructive Evaluation of Plastic Parts Using 3D Computed Tomography
During the production of plastic parts the presence of voids, inclusions, fiber reinforcement and fillers can play a critical role in the structural integrity of the product. Although in recent years tremendous improvements have been made in the field of analysis and design software to predict such factors, their physical detection is more difficult to accomplish. Certainly, when considering quality assurance and quality control, the ability to accurately and efficiently determine internal structure in a non-destructive manner is beneficial. This paper presents a novel method of using Computed Tomography (CT) to detect and visualize internal structure in polymer articles.
Biodegradable Polymer Blends for Medical Applications
Biodegradable polymers are used in medical applications, among many reasons, because of their history of biocompatibility. In this report an attempt has been made to establish the structure created by reactive processing of poly (caprolactone) and Easter 14766 with dicumyl peroxide (DCP). Results showed that PCL quantitatively formed tetra-functional branches while the Easter 14766 formed a combination of tri and tetra-functional branch points. The Easter 14766 was also shown to be more reactive than the PCL, with half as much DCP being required to achieve equivalent amounts of branching. Both Easter 14766 and PCL displayed typical branching behavior with increase in melt elasticity and zero shear viscosity. Easter 14766 showed a little improvement in mechanical properties. However, studies showed PCL to be insensitive to branching.
Practical Risk Analysis as a Tool for Minimizing Plastic Product Failures
Risk analysis techniques have become increasingly popular in the industrial sector, especially with the increasing number of mandated quality programs worldwide. Methods such as Failure Modes and Effects Analysis (FMEA), Fault Tree Analysis (FTA) and others are gaining wide recognition for their utility in product design. This paper discusses the practical use of risk analysis in plastic product systems as an up-front tool for design and product evaluation. Simplified techniques are presented which minimize the cumbersome nature of the risk analysis process and allow for more effective and efficient design and testing programs.
Avoiding the GIGO Syndrome - Combining the Real and Virtual Worlds in Analysis of Polymer Product Failures
In recent years, the advance of high speed processors in personal computers has placed the capability of sophisticated analytical methods on nearly every desktop. In the plastics industry, codes are readily available to model, among other things, stresses, thermal characteristics and flow. Without proper input, however, such analyses are subjected to the Garbage In, Garbage Out (GIGO) syndrome and can produce misleading results. This paper discusses an approach to analytical modeling that includes experimentation for model input and constitutive model development, as well as the use of experimentation for verification of numerical modeling results.
Ternary Composites: An Innovative Form to Improve Final Properties of Polypropylene
The incorporation of glass fibers in a thermoplastic matrix improves its tensile properties but decreases the impact strength. The addition of a third component such as an elastomer generates a new material with improved impact resistance but poor mechanical properties. In this work, a rubber phase was added to a glass short fiber reinforced polypropylenes to obtain a material with balanced tensile and impact properties. Two different types of rubber was used and analyzed. Some composites with different concentration rubber/FV/PP was prepared and molded by injection. Its mechanical an impact behavior was studied and the processing window was analyzed.
Municipal Plastic Waste: Alternatives for Recycling with Profit
The recovery and recycling with profit of municipal plastic waste (MPW) is still an unsolved problem. Only in the developed countries a small portion of their MPW is used with profit. The major part of the plastic residue is disposed of landfilling. This work analyses the existing methodologies for recycling and assesses their potential application to MPW. Also, a comparative study of incineration, in terms of energy saving and contamination risks, is performed. The energy required for recycling and the energy obtained for controlled incineration is calculated, and the maximum energy opportunity is obtained. On the other hand, the energy needed to recycle either commingled or separated plastic residues was compared, taking into account the final properties obtained and the compatibilization step.
Poly(vinyl alcohol)/Sodium Montmorillonite Nanocomposites
Poly(vinyl alcohol) / Sodium Montmorillonite hybrids of various compositions formed from water solution have been characterized utilizing X-ray diffraction (XRD) and Differential Scanning Calorimetry (DSC). Compositions with polymer concentration lower than 60 wt% formed intercalated hybrids predominantly, whereas higher concentrations of poly(vinyl alcohol) resulted in exfoliation of the clay layers in the polymer matrix. Furthermore, montmorillonite acted as a nucleating agent resulting in polymer crystallizing at higher temperatures for the hybrids compared to bulk polymer. It has also been observed that the presence of clay seems to induce a change in the polymer structure that is normally obtained through the annealing of poly(vinyl alcohol).
Determination of Solvent Independent Interaction Parameters for the HDPE/LDPE Blend by an Improved Inverse Gas Chromatographic Approach
The technique of inverse gas chromatography has been used to investigate the thermodynamics of blend of high-density polyethylene (HDPE) and low-density polyethylene (LDPE) at three different concentrations and four elevated temperatures. The measured polymer-polymer Flory-Huggins interaction parameters, c23, suggest that the well-known probe dependence problem cannot be solved by simply satisfying the zero Dc criterion. The problem is mainly attributed to the use of different reference volumes in the calculations of c12, c13, and c1(23) for different solvents. By selecting a common reference volume, probe independent c23 values were obtained.
A Miscibility Study of LDPE/LLDPE Blends at Elevated Temperatures Using IGC
The technique of inverse gas chromatography (IGC) has been used to study the miscibility of low-density polyethylene (LDPE) with six linear low-density polyethylene (LLDPE) with different solid state density, molecular weight averages, and molecular weight distribution. In particular, the Hildebrand solubility parameters of the pure polymers were measured and used to calculate the corresponding interaction parameters ?LDPE-LLDPE at four elevated temperatures. Our results suggest that the two types of polyethylene are thermodynamically miscible in the chosen temperature range. And the miscibility behavior of LDPE/LLDPE blends seems to be insensitive to the properties of LLDPE.
Shear-Induced Crystallization in Injection Moldings of Ziegler-Natta and Metallocene Based Isotactic Polypropylenes
A comparative analysis of the shear-induced crystallization of metallocene and Ziegler-Natta based isotactic polypropylenes (i-PP's) was carried out. Numerous injection molding runs were performed and the effect of the shear-induced crystallization on the moldings was elucidated. The simulation of the injection molding process was performed using our unified crystallization model proposed earlier. The gapwise distributions of birefringence, crystallinity, spherulite size and thickness of the shear-induced crystallization layer in moldings were measured along with the mechanical properties of the moldings. The effects of processing conditions on these properties were determined. The measured values of crystallinity, spherulite size and thickness of the shear-induced crystallization layer were compared with the results obtained from the simulation of the injection molding process.
Electromagnetic Shielding and Protection against ESD by Using Stainless Steel Fibres
Non-conductive plastics are transparent for electromagnetic radiation. This can prevent the use of plastics in housings for electronic devices. A solution to this problem is to apply a conductive coating, or to make the plastic itself conductive by adding conductive fillers. We have proven that stainless steel fibres are an excellent means to make plastic conductive for EMI (Electro Magnetic Interference) shielding purposes. Electrically insulating polymers can cause electrostatic charging/discharging (ESD) problems in some applications. Integration of stainless steel fibres in the polymer can overcome these problems by preventing charge build-up and/or by providing a safe path for discharge currents. Stainless steel fibres can be mixed in thermoplastics (injection moulding), epoxy and poly-urethane (conductive floors), paint, elastomer, rubber, ...
Computer Aided Engineering Simulation versus Actual Performance of an Automotive Structural Component
Computer Aided Engineering (CAE) tools are able to provide powerful solutions to complex product design issues. A certain level of confidence in these solutions is assumed. However, the solutions provided are a function of several parameters: • Solver algorithm • Boundary conditions • Material properties • Fabrication process • Mesh size and type. How confident can we be in solutions from software that is performing an approximation of a real world condition based on all these variables? This paper will examine the effects of mesh size and solver method on the analysis accuracy when compared to the physical testing. To increase our confidence in these solutions, we wanted to understand the relationship between the key parameters and physical testing results. We compared various Finite Element meshing methodologies and analysis codes (structural and moldfilling) to lab tests of a Ford Ranger Pickup truck tailgate handle. Lab tests consisted of a tensile machine pulling directly on the back face of the ranger handle, which was injection molded in Nylon 6 polymer with 15% glass and 25% mineral fillings. Since material properties change with water absorption for nylon resins, all tests were conducted on dry as molded samples. Displacements and load values were documented for each test. The solutions provided from the analysis codes (while modifying element type and mesh size) were compared to the physical test results. Additional analytical lab testing was completed on the molded samples to confirm part composition, physical properties and glass orientation. Conclusions and recommendations were based on how closely the solutions matched the physical tests.
Increased Speed to Market Using CAE Simulation for Injection Molded Plastics Parts
The ability to cut time and cost from a molding program is a significant advantage for injection molders operating in an increasingly competitive marketplace. Warpage and other defects that show up in molded plastics parts, as well as inefficiencies in production are unacceptable. Innovation, productivity, and dedication to quality are crucial for suppliers of injection molded parts. CAE simulation software offers a competitive advantage to those who wish to eliminate inefficiencies in their operations - advantages such as shortened time to market, efficiency improvements in the use of raw materials, reduced cycle times, and optimized production efficiency and product quality.
Chemo-Rheology and Structure Development of a Solventless System for Manufacturing Electronic Pre-Pregs
Current processes used to manufacture electronic pre-pregs and laminates use solvent based systems. Solvents are environmentally unfriendly and add no value to the final product. We are developing a new solventless process, based on the concept of continuous Resin Transfer Molding or Injection Pultrusion. The first step in designing the process is to select a suitable chemical system. The viscosity of the system should be such that it allows proper impregnation at a temperature at which not much reaction takes place. To predict the required pulling force, the friction at the wall as the material solidifies needs to be truly understood. A potential resin system has been identified and its chemo-rheology and structure formation will be discussed.
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