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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Additive Manufacturing & 3D Printing
Comparative Study of Filled and Unfilled PLA Produced Via Injection Molding and 3D Printing
This study investigates the impact of two different processing methods, Injection molding (IM) and 3D printing (3Dp), on Neat/unfilled polylactic acid (NPLA) and the short carbon fibers (SCFs) filled polylactic acid (SPLA). Furthermore, the resulting processing conditions and its influence on mechanical properties, such as tensile, flexural, notched Charpy impact test, and heat deflection temperature (HDT) along with the process-induced effects, such as fiber length distribution and voids were studied. The process-induced voids were evident in all the computed tomography (CT) scans, 3Dp specimens have higher void volume fraction compared to no visible voids in IM specimens. Similarly, the mechanical test results such as tensile, flexural and notched Charpy impact test follow the trend for 3Dp SPLA and IM SPLA. On the contrary, 3Dp 0° and ±45° NPLA tensile test results are comparable to IM NPLA, whereas 3Dp 0° NPLA has the highest impact resistance compared to injection molded NPLA and SPLA as well as 3Dp SPLA specimens, indicating the annealing effect induced by the heated 3D printing bed along with increased void volume fraction. Furthermore, the HDT study indicates the maximum serviceable temperature of both NPLA and SPLA remained comparable regardless of the processing method. Moreover, the change in fiber length distribution for SPLA injection molded and extruded filament specimens were negligible.
3D Printed Hybrid Composite Structures - Design and Optimization of A Bike Saddle
As designers and engineers continue to push the boundaries of high performance and lightweight design, the use of complex geometries and composite materials is growing. However, traditional composite manufacturing often requires the use of additional tooling and molds which can significantly increase the cost. In this study, a carbon fiber reinforced composite bike saddle is designed and manufactured to demonstrate a newly developed hybrid composite manufacturing process. Using a 3D printed epoxy to print the final part geometry and co-cure pre-impregnated carbon fiber reinforcement, the bike saddle can be optimized, designed and manufactured in less than 24 hours.
Compressibility In Fused Filament Fabrication
Fused filament fabrication (FFF) is one of the most accessible and flexible additive manufacturing processes. However, it is plagued by consistency issues related to material deposition. The role of compressibility is explored with an instrumented nozzle to relate the observed printing pressure to variations in deposited road widths. Variations in road width are analyzed relative to those predicted using a double domain Tait equation (PVT model) for high impact polystyrene (HIPS). Compressibility was found a critical effect, varying the road widths by up to 50% when accelerating and decelerating. The effect of the speed of transient stress propagation was also investigated but found insignificant.
Design and Evaluation of Bicomponent Core-Sheath Die for 3D Printer Filament Feedstock Co-extrusion
Carbon based or inorganic fillers in 3D filament can enhance properties of 3D printed parts and are attracting considerable interest from academic and industry researchers, such as MarkForge, BASF, ColorFabb, and Graphene 3D Lab. Although 3D-tailored composites have been developed, very little work has been done on the production of advanced 3D filament feedstock for FDM. Work is needed on biomedical application filaments which require (i) high filler or nanoparticle loading, (ii) dimensional accuracy and (iii) superior surface finish. Current FDM filaments rarely exceed filler concentration of 10%, for example, in case of calcium phosphate without sacrificing quality. In this work, a melt-spinning die was designed with 2D FEM flow simulations to minimize interfacial flow instabilities. With the die, a co-axial 3D feedstock filament up to 20% filler concentration was spun. Tensile bars were successfully printed with 15% filler content and had similar tensile properties to neat PLA.
Determination of Physical Properties of Fused Filament Fabrication Parts as Influenced by the Nozzle
A design of experiments using different nozzle diameters with varying road heights and shear rates (based on print speed) was done using lab-made polylactic acid filament. Subsequent tensile testing and calculation was done to obtain the main responses of ultimate engineering stress and tensile modulus. Linear models were made to determine the significance between the different dependent and independent variables. The main results show that larger nozzles, shorter layer heights, and lower shear rates provide stronger, heavier and stiffer fused filament fabrication parts.
Development of An Agile, Battlefield Additive Manufacturing Plant For Recycled Pet
The objective of the overall project is to conduct applied research that will lead to the development of an innovative agile manufacturing plant for onsite fabrication of recycled thermoplastic products at the US military’s forward operating bases (FOBs). The proposed manufacturing plant needs to be contained in 20-foot ISO containers for both shipment and operation. A study by the US Department of Defense (DoD) of base camp waste confirmed that the single largest source of waste plastics is Polyethylene Terephthalate (PET) from water and other beverage bottles. The on-going project to convert waste or reclaimed PET (rPET) to useful products is currently being conducted by Emc2 and the US Army Corps of Engineers and is being supported by the DoD’s Strategic Environmental Research and Development Program (SERDP) as a three year effort starting in June 2018.
Electro-Spun PVP (POLYVINYLPYRROLIDONE) Nanofibers: An Experimental Investigation
Electrospinning is a well-established and straightforward method of manufacturing nanofibers from different materials like polymers, ceramics, and metals. In the current study, Polyvinylpyrrolidone (PVP) nanofibers were produced using the electrospinning process. The process control parameters viz. polymer concentration, voltage, collecting drum rotational speed, flow rate and collecting distance were studied to obtain the minimum fiber diameter for sound absorption applications. The effects of these electrospinning parameters on morphology and diameter of fibers were investigated. The minimum fiber diameter was found to be regulated by two main parameters, i.e. polymer concentration and voltage applied that both had significant effects on fiber morphology. On the other hand, flow rate, rpm, and collecting distance had the least significant effects compared to the other two. This work offers a promising attempt in the open literature to carefully study the effect of electrospinning control parameters in PVP nanofiber fabrication.
Enhancement of Binding Matrix Stiffness In Composite Filament Co-Extrusion Additive Manufacturing
The Flexural modulus and strength are an intrinsic aspect of parts produced via dual matrix composite filament co-extrusion (CFC) based additive manufacturing. In this research work, the main objective is to optimize thermoplastic’s (TP) flexural properties by reinforcing it with particulate fillers for CFC printed parts. Accordingly, an effort has been made in this respect and neat Polyamide-6 (PA6) and its composite (PA6.CF) was chosen as a binding matrix for CFC flexural specimens. The PA6 binding matrix is reinforced with particulate carbon fibers (PCF). To improve the compatibility between the PCF and matrix, stearyl titanate coupling agent (1.5 wt. %) was utilized. Constraints such as defects and porosity are of critical attributes and play a vital role in defining the mechanical performance of the 3D printed parts. Herein, the printed specimens were subjected to a non-destructive testing method: micro-computed thermography (µ-CT). PA6 and reinforced PA6 specimen revealed similar porosity and defect volume. Furthermore, the three-point bending test results of 3D printed CFC composite with PA6.CF as a binding matrix showed approx. 46% increase in flexural stiffness and 27% increase in flexural strength when compared to CFC specimens printed with neat PA6 as a binding matrix. In addition, the cryo-fractured fractography of carbon composite filament, an epoxy-based thermo-cured continuous carbon fiber, revealed even distribution of carbon fibers with no visible voids.
Investigation of Glass Bubbles iM16K Polyamide 12 Composites for Selective Laser Sintering
Selective Laser Sintering is an additive manufacturing technique that has been increasingly exploited in small-batch production to supplement traditional polymer processing techniques. Integrating specialized additives with PA12 SLS powder allows for the production of parts with tailored properties. 3MTM Glass Bubbles iM16K offers the possibility to reduce SLS powder cost, reduce part weight, and improve mechanical performance. Both intrinsic and extrinsic properties and their effects on SLS processing have been investigated. Tensile testing revealed the average Young’s modulus could be improved by 30% at 5 wgt% loadings, while maintaining ultimate tensile strength.
Reliability Evaluation of Conductive Tracks Integrated Into Additively Manufactured Components
The use of 3D printing technologies enhanced with component placement and electrical interconnect deposition can provide structural electronic systems with higher fabrication freedom. Thermosetting resins that are used as adhesives in electronic packaging processes have the potential to fulfill new requirements coming from this application. Their use as building and conductive materials in additive manufacturing can lead to advantages, especially when selecting the same chemical basis. In this work, an extrusion-based additive manufacturing process was used to process the adhesives. A basic concept is introduced how the integration of electrical components and conductive tracks can be realized with this process-material combination and experimental work on two-dimensional tracks is presented. The developed process and the material selection for 2D-tracks was evaluated electrically as well as mechanically and was supported by highly accelerated life tests to ensure reliable performance. Different aspects of the integration were covered with three experiments that provide an understanding of properties of conductive adhesives printed as a tracks as well as their contacting behavior on SMD components. First design rules are derived from these experiments that can serve as a first step for developing processes for three-dimensional tracks and the procedure of contacting a component within the printing process.
Simulation of a Saxton-Mixer in High-Performance Extruders Using the Immersed Boundary Method
The Immersed Boundary Surface Method(IBS)is a novel and very promising implementation of the Immersed Boundary Method (IBM) for modeling complex, moving processes. In order to validate IBS for the first time in plastics processing, this paper deals with the numerical simulation of a Saxton-mixer in foam-extend (release of OpenFOAM)as a complex application geometry.The Saxton-mixer  is well suited for validation because it canstillbe solved using traditional simulationmethods, but is alreadycomplex enough to test andvalidate IBS within a real-worldprocessing environment. For this purpose, body-fitted andIBS simulations are performedin the same wayand their results compared. In addition, the mixing zone is also investigated experimentally in order to evaluate the model qualityof the simulations.The results of both simulation methods are consistent and differ only slightly. Thus, the implementation of IBS is valid. Furthermore, a comparison of the simulation model with experimentsreveals asignificant influence of the rheological flow model. The results of thenon-Newtonian IBS modelare already approaching the experiments well and are therefore promising results for further applicationsof IBSin plastics processing.
The Influence of Laser Power Variation on SLS-printed PA6 Parts and their Long-term Properties
In the field of Additive Manufacturing (AM), Selective Laser Sintering (SLS) is well-known as anAM technique to produce partswith comparatively high load capacity. The usage of Polyamide 6 (PA6) materials allowshigher continuous operating temperatures than Polyamide 12 (PA12) materials, which aretypicallyused forSLS. For this work,PA6 SLS specimens were printed with a high temperature SLS industry printer. The samples were aged thermo-oxidatively at different temperatures, tested mechanically and investigated with different analytical methods. The SLS processing of PA6 materials has not beenstudied sufficiently yet. The aim of this study was to deliver first contributions:the laser power energy wasvaried to identify the influence on the mechanical properties of the printed specimens andtheirlong-term properties. In addition, the material structure of the specimens wasinvestigated and the viscosity number (VN) was determined.
Understanding the Limitations of 3D Printed Polymers Through A Staged Screening Protocol
Direct printing of polymers has continued to advance with new printing technologies and engineering grade materials allowing actual additive manufacturing versus 3D printing of prototypes. Key developments include the adaptation of digital light processing (DLP) printers as well as improvements to and novel powder-based printing systems. These technologies offer the ability to bring new printed materials to the market. However, simply because a material can be printed does not mean that it will function well. With the number of printing and material advances, the need to understand possible failure modes and incorporate that knowledge into screening testing is critical. This work provides basic consideration and screening methodology to ensure that these possible material failure modes are accounted for.
Expanding the Impact of Polymeric-based 3D Printing Technologies
Over the past two decades, additive manufacturing (AM) technology has become fully ingrained into pop culture, with Do it Yourself (DIY) applications for the home, schools and other locations in addition to industrial applications for the aerospace, automotive, and biomedical industries. While AM can be used to fabricate objects from metals, polymers, and ceramics, polymeric materials are currently the most common. ASTM Standard F2792-12a describes techniques that can convert polymeric materials into useful products: 1) sheet lamination; 2) material extrusion; 3) vat photopolymerization; 4) powder bed fusion (with polymers); 5) binder jetting; and 6) material jetting. The automotive industry was an early adopter of 3D printing of polymeric materials, for example in the early 1990s a Japanese manufacturers used a commercialized vat photopolymerization process (widely known as stereolithography (SL)) to manufacture prototype door panels. More recently, an extrusion-based AM system was used on the International Space Station (ISS) .
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