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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Welding of Recycled Thermoplastic Lumber for Structural Components
This paper reviews experimental work on welding of reinforced recycled thermoplastic lumber for the fabrication of structural components. Recently the use of thermoplastic lumber has become more accepted due to the materials longevity. However, because of extrusion difficulties, such as shrinkage holes and long cooling times, plastic lumber has not been widely used for structural components, such as pilings and supports. In order to solve some of these issues, it has been proposed to extrude standard, relatively small cross sectional components, such as 2x4 and 2x6, and join these components into larger structural components, such as 6x6 to 10x10 or engineering components such as I-beams. This work evaluated a wide range of welding processes, including; hot plate, vibration, IR and non-contact hot plate welding as well as adhesive bonding. Star design of experiments was conducted for each process and relevant parameters. Process optimization was preformed for each process in order to minimize cycle time and maximize weld strength. In addition, flexural tests of selected samples were performed. It was found that welding could produce joints as strong and as stiff as the base material.
Effect of Paint Over Spray for Vibration and Ultrasonic Welding Processes
Thermoplastic Olefin (TPO) has been commonly used for automotive interior parts. TPO material used for this study was a Polypropylene (PP) and Polyethylene (PE) copolymer for better impact resistance and it contained 20% of talc. Considering the facts that PP and PE are semi-crystalline thermoplastics with high molecular weights, and that it contains rubbery contents and talc, weldability of the material needed to be carefully evaluated. Especially for the ultrasonic welding process utilizing 40 - 60 microns of ultrasonic vibration amplitude for welding, these could affect the material weldability significantly.Additionally during manufacturing processes, the paint over-spray (undesired painting at the weld joint area) is sometimes unavoidable. Specific effects of the paint layers on the welding processes have been investigated. To investigate the effects effectively, the processes have been fully optimized by through Design of Experimentation (DOE).
Vibration Welding Polypropylene-Based Nanocomposites
Nanocomposite materials present interesting mechanical properties due to the high surface area to volume ratio of the dispersed reinforcement. The vibration weldability of these new composites has not yet been reported in the open literature. This research examines the effect of the vibration welding parameters of weld pressure and target meltdown on the strength of butt welds made from two polypropylene-based nanocomposites. The results of unreinforced polypropylene are shown for reference. The nanocomposites were made by melt compounding two levels of organoclay with polypropylene. All welded assemblies were assessed by tensile testing. The results show that 3-6% of organoclay causes a significant decrease in weld strength.
Microstructure of Polyamide-6 Vibration Welded Joints
The microstructure and morphology of the Heat Affected Zone (HAZ) of vibration welded joints of polyamide-6 were studied using Polarized light microscopy (PLM), Fourier Transform infrared (FTIR) microspectrometry and scanning electron microscopy (SEM). PLM images showed existence of two distinct HAZ layers: an inner layer (HAZ-I) with small spherulites and an outer deformed layer (HAZ-II) adjacent to the bulk zone. The thickness of the HAZ-I and HAZ-II layers and the size of spherulites in HAZ-I depended significantly on the welding pressure. The microstructure study suggests that HAZ-I originates from molten fluid film and HAZ-II mainly consists of deformed crystallites. Etched HAZ surfaces also showed clear distinction between the two HAZ layers. Birefringence measurements showed that HAZ-I is more highly oriented than HAZ-II. HAZs obtained under high pressure retain higher molecular orientation than those obtained under low pressure. FTIR results show that the ?-crystal phase content of HAZ-I is higher than that of HAZ-II and higher welding pressure induces more ?-crystal phase.
The Effect of Molding Condition on Interfacial Mechanical and Morphological Properties of Film Insert Injection Molded PP-Film/PP Matrix
The effects of barrel temperature and injection rate on the interfacial mechanical and morphological properties of film-insert injection-molded PP-film/PP matrix were investigated. In high barrel temperature and injection rate, film did not peel from the injected PP. In this situation, the surface of the film was found to have melted by the heat of injected PP, which resulted in higher crystallinity of PP film near the interface. On the other hand, in low barrel temperature and injection rate, the film peeled from the substrate. In this situation, crystallinity of the surface of the film was found to be low because the heat of the injected PP did not affect the film.
Analysis of Residual Stress in Hot Plate Welded Polycarbonate
The analysis of thermally induced residual stresses has gained a lot of importance because residual stresses are known to affect the strength, fatigue life and chemical resistance of a welded component. In this paper, the effects of annealing on residual stresses in hot-plate welded polycarbonate (LEXAN) samples were studied. The GE solvent stress analysis test provided a quantitative means for determining the stress levels in the samples. Temperature distribution along the length of the welded samples was measured as a function of time using thermocouples. A simple model for predicting the residual stresses in hot plate welded PC samples was developed. Our results showed that the residual stress in non-annealed samples were in the range of 10.5-12 MPa.
Interfacial Properties of Film-Insert Injection Molded Polyethylene-Film/Polyethylene Matrix
This study involves the investigation of interfacial adhesion strength between a polyethylene (PE) film and a PE substrate fused together by means of film-insert injection molding technique. 180° peel tests were done and the barrel temperature was found to have a significant influence on the adhesion strength, whereby if the melt temperature is sufficiently high, adhesion strength is comparable to, if not stronger than, the film. Several models were used to pinpoint the region of the load-displacement curve that could denote the true peel strength.
Experimental Study and Modeling of Bond Formation between ABS Filaments in the FDM Process
The application of Fused Deposition Modeling (FDM), a plastic based rapid prototyping technique, has been limited due to poor bonding between the filaments forming the parts. This study focuses on understanding the bonding mechanism and its dependence on processing parameters. The bond quality was experimentally assessed based on the growth of the neck formed between adjacent filaments and their failure under flexural loading. We present two thermally driven models which describe the formation of bonds due to sintering and molecular diffusion. Experimental results suggest that the diffusion model is more appropriate for this application.
HDPE Effects on the Heat-Sealing Properties of LLDPE
Heat sealing properties of Linear Low Density Polyethylene (LLDPE) blend with varying proportions of High Density Polyethylene (HDPE) was investigated. Heat sealing properties of LLDPE namely, heat seal strength and hot tack strength are evaluated as a function of HDPE content in the binary blends. To elucidate their relevance, the thermal behaviour obtained by Differential Scanning Calorimetry (DSC) is correlated to these heat sealing properties. Keeping the process variables of seal pressure and dwell time constant, experimental results indicate that HDPE induced pronounced changes on the heat sealing ability of LLDPE.
Experiments in Hot Plate Welding of Polypropylene Nanocomposite
Clay-based nanocomposites have recently attracted attention in many industries due to their high specific strength, modulus and low permeability. A typical nanocomposite plastic has only about 3 to 6 percent by weight nanoclay, where after being purified and surface-treated they are mixed with pure resins to produce polymeric nanocomposites. As the usage of these nanocomposites increases in industry, knowledge of its weldability becomes important. The hot plate weldability of three specific Polypropylene nanocomposites with 0wt%, 3wt% and 6wt% nanoclay was investigated. A three factors (heating temperature, welding time and welding pressure), two level design of experiments (DOE) was used to screen welding parameters and obtain near optimum welding conditions. The maximum joint strength was found to be 94%, 79% and 62% of the bulk strength for 0wt%, 3wt% and 6wt% nanoclay samples, respectively. While increasing nanoclay levels in the composite improved the bulk material strength, it reduced the weld strength significantly.
Ultrasonic Treatment of Advanced Thermoset Composites
This paper reviews experimental work on ultrasonic treatment of advanced thermoset composites. It has been proposed that treating these composites with high power ultrasonics (~10-50 W) may cause a decrease in void content without adverse effects, such as premature partial curing or a degradation of mechanical properties. Samples of advanced composites were treated with ultrasonic energy at various travel speeds, amplitudes, force, orientations of the horn to the surface and number of pregregs plies treated at once. Significant heating was observed but there was no evidence that the treatment had any adverse effects. It was seen that the treatment reduced the overall thickness of the samples, implying that the void content was decreased. In addition, there was evidence that ultrasonic treatment slightly increased the stiffness and short beam shear strength of the samples.
Comparison of Control Algorithms for Ultrasonic Welding of Plastics
This paper reviews experimental work that compares the various control algorithms for ultrasonic welding of plastic. The three algorithms/modes that were compared were time, energy and collapse. Amorphous and crystalline materials were studied using both energy director and shear joints. Welds were made with all materials and joint designs and tested for strength and final part dimensions. The standard deviation of the resulting strengths and final dimensions of the parts were compared for all the modes. It was found that the collapse mode produced the most consistent weld strengths and final dimensions. In addition, compared to each other the time and energy modes produced comparable consistency (strength and final dimensions) for the materials and samples studied.
Laser Transmission Welding of Thermoplastics - Modelling of Flows and Temperature Profiles
Laser transmission welding of thermoplastics becomes more and more important in industrial series production due to an array of its advantageous properties. In the practice the interest in this technology increases continuously. At the same time, the demand for ongoing investigations and research – especially regarding the laser welding process and its understanding – is being noticed.In this report a simplified mathematic-physical model of laser transmission welding based on the finite-element-method (FEM) will be presented. For the primary calculations the material PA6 was chosen. The developed model comprises the whole laser welding process including the heating and the cooling phase. First of all, the boundary conditions as well as the relevant process parameters like the intensity of the laser beam, the joining pressure and the welding time will be specified and then the simulation will be started. As a result, flow and temperature profiles will be calculated. Due to an array of available boundary conditions it is possible to continuously improve the model while comparing the simulated data with the data got by experiments.
Numerical Simulation of Laser/IR Assisted Micro-Embossing
The use of hot embossing for fabrication of polymeric microfluidic devices is gaining a great deal of attention in recent years because it is a relatively simple and low-cost process. Conventional microembossing is a relatively slow process that requires both the mold and the polymer substrate to be heated during embossing and cooled before de-embossing. In order to shorten the cycle time, a laser/IR-assisted microembossing (LIME) process was evaluated in this study. Since laser/IR heats the substrate rapidly and locally, the heating and cooling time can be substantially reduced. Experimental results have shown that both shorter cycle time and good replication accuracy can be achieved. In order to better understand this process, a commercially available FEM code DEFORM® was used for process simulation. Because the temperature distribution inside the polymer substrate is affected by the penetration of radiation energy flux from laser/IR heating, the relationship between penetration energy flux and temperature distribution was implemented into the FEM code. Rheological properties of selected amorphous and crystalline polymers were characterized and incorporated into the FEM code. Two different modes of IR embossing were simulated, in which either a transparent mold or transparent substrate was used. The flow patterns observed in the experiments agreed reasonably well with the DEFORM-3D simulation and a quantitative comparison between experimental and simulation results was made using DEFORM-2D.
Laser Transmission Welding of Unreinforced Nylon 6
Laser transmission welding is a relatively new joining process in which laser energy is used to melt polymer at the interface between laser-transparent and laser-absorbing components. This study examined the effect of diode laser speed, power, beam area and weld pressure on the meltdown, microstructure and weld strength of T-joints made from unreinforced nylon 6. The results show that meltdown increases strongly with line energy and is also affected by beam area and weld pressure. For the range of parameters selected, the strength was observed to depend largely on the ability to make welds free of local stress concentrations and degraded material. This can be achieved by obtaining a relatively uniform power flux distribution along the weld-line cross-section.
Penetration Welding of Thermoplastics Using a Quartz-Halogen Lamp with a Transparent Heat Sink
It is not easy to achieve the desired standard of welding, without causing surface thermal damage, in infrared welding of overlapped plastics when placing an infrared absorbing part in the irradiated side. The irradiated surface layer is heated up due to the intense absorption of infrared radiation and easily suffers from thermal damage such as shrinkage, burns, perforations, or other undesirable degradations. Our previous work which was an innovative solution for this problem employed a transparent heat sink in contact with the irradiated surface of the plastics during CO2 laser irradiation.This paper deals with the extended research concerning the penetration welding technique for overlapped thermoplastics by using infrared radiation heating with a transparent heat sink. In our previous study, a fixed wavelength of 10.6 ?m of a CO2 laser light was used. In this study, a quartz-halogen lamp with a transparent heat sink had been employed in order to examine the feasibility of deep penetration welding for various types of plastics without using dyes and pigments. Most plastics themselves have several weaker infrared absorption bands in the wavelength range emitted from the lamp than those emitted from a CO2 laser light. The results of welding experiments show that both visually transparent thermoplastics (polymethyl methacrylate and polycarbonate) and translucent thermoplastics (low density polyethylene) of several millimeters in thickness can be welded without causing thermal damage.
Study of Controllability of Melt Depth in Infrared Laser Penetration Welding of Thermoplastics
Extended research has been carried out concerning our proposed penetration welding technique for overlapped thermoplastics using infrared lasers with transparent heat sinks.Numerical simulations for a heat transfer model in welding process were conducted to test the effect of various kinds of welding conditions on the melt depth of plastics. The temperature profile variations in plastics to be welded during heating process were obtained by manipulating different parameters, such as the heat sink, the plastic material, the thickness of the plastic, the absorption coefficient, the incident radiation power density and the irradiation time.The results show that the melt depth and the starting time of melting greatly depend upon the radiation absorption and thermal diffusion in the plastics. For example, as the absorption coefficient of plastics increases, the starting position of melting in the plastics approaches the irradiated surface. It is therefore worthwhile for overlap welding to know the depth at which the maximum temperature appears inside of the plastics during radiation heating. This is dependent on the heat conductivity of heat sinks, the thickness of the plastic, the absorption coefficient, the radiation power density and the irradiation time.
Fiber Laser Welding of Elastomer to TPO
Thermoplastic Polyolefin (TPO) has been used in automotive applications extensively. Polyolefin elastomer is one of the major modifiers in the TPO to improve the impact performance. The weld strength between the TPO and elastomer modifier could be used to indicate the adhesion between these two materials during compounding. Therefore, through transmission laser welding of these two materials was performed to evaluate the interfacial adhesion. Three different grades of elastomer modifiers and one TPO were studied. Three-factor two-level full factorial design of experiments was used to evaluate the effect of welding parameters on weld strength. The results indicated that the weld strength was proportional to the laser power and inverse proportional to the welding speed. In addition, the weld strength was proportional to the strength of the elastomer.
Infrared Micro-Embossing of Thermoplastics
This paper reviews experimental work on through-transmission infrared micro-embossing of thermoplastics for replication of micro-fluidic devices. Two separate modes were evaluated. In one mode, a transparent mold/die was used in where IR radiation was passed through a die and directed onto an opaque thermoplastic substrate. The substrate would heat and soften and then the die was pressed against the substrate, allowing the features of the mold/die to be transferred to the substrate. In contrast, the other mode that was evaluated involved passing IR radiation through a transparent substrate onto an absorbing die that would heat as it was pressed against the substrate. The parameters that were evaluated included: power density, heating time, preheating, holding time, and pressure. Optical microscopy evaluation of the samples allowed correlation of these parameters to image transfer quality, including depth of features (Over 100 ?m) and sharpness.
Comparison of Weld Morphology of Polycarbonate and Polypropylene for Hot Plate, Vibration and Ultrasonic Welding
Plastic welding processes result in a wide range of heating and cooling rates of the welds and the heat affected zone. This results in a range of morphology and residual stress levels. The weld morphologies of polycarbonate and polypropylene were studied for hot-plate, vibration and ultrasonic welding. A microtome was used to cut 25-30 micron thick slices across the polypropylene welds for microscopic examination. For Polycarbonate, a diamond saw was used to cut 1-1.5 mm thick slices across the weld for microscopic examination. For both materials, polarized light microscopy was used. It was observed that rapid heating and cooling welding methods (Ultrasonic and Vibration) produced the narrowest weld lines and heat affected zones with a high degree of molecular orientation and low levels of crystallinity. Hot plate welding produced the widest heat affected zones with the lowest amount of molecular orientation.
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