In the present work, thermoset carbon fiber–reinforced polymer (CFRP) was spot joined to magnesium alloy AZ31B by a friction self-piercing riveting (F-SPR) process. Lap shear tensile and cross-tension testing were used to evaluate the mechanical joint performance. An average lap shear tensile load of 5.18 kN was achieved, while an average of 2.81 kN was found from cross-tension testing. All F-SPR samples showed pull-out of AZ31B after mechanical testing, indicating good mechanical interlocking between the steel rivet and AZ31B. Corrosion potential was measured for each material to establish the galvanic corrosion characteristics. As expected, AZ31B was found to be the most active, while thermoset CFRP was the most noble. The steel rivet fell between the AZ31B (active) and the thermoset CFRP (noble). Salt fog corrosion testing (ASTM B-117) was performed to evaluate the corrosion performance of the uncoated F-SPR joint. With up to 200 h of exposure, the post-corroded F-SPR joint integrity retained 81.2% of the pre-exposure F-SPR joint strength with AZ31B pull-out failure mode. From cross-sectional analysis of the F-SPR joint, extensive corrosion of AZ31B was observed at the joint and other exposure areas. However, steel rivet was not significantly corroded potentially due to sacrificial anode effect by which AZ31B corroded first in the galvanic couple.

Cold sprayed polymer substrates offer a promising platform for bridging electroless deposition methods and applications. This study’s contribution to the field is the combination of cold sprayed polymer substrate and the electroless-plating process. In simulation, finite element analysis of the as-sprayed polymer substrate using a viscoelastic model that considers large strain time-dependent behavior were conducted. A three-network constitutive model was applied to capture the non-linear and time-dependent response of large strain polymer deformation. In experiment, the process-structure-property relationship was examined from the as-sprayed specimen to the final coated electroless-plated samples. A controlled coating process of Cu powders was first cold sprayed on polyamide 6. The as-sprayed specimen was then electroless deposited. Mechanical testing was performed on as-sprayed specimens and adhesion testing was performed on electroless deposited specimens. Scanning electron microscopy (SEM) was employed to observe the surface and the cross-section of the as-sprayed and electroless deposited specimens. Lastly, the behavior of Cu coated specimens immersed in KOH solution was examined by cyclic voltammetry.

Cryogenic manufacturing processes have emerged as environmental-friendly, increase tool life and improve surface integrity of machined components by efficiently removing the heat from the cutting zone. Especially considered to be an efficient method to machine difficult-to-cut metals which are poor thermal conductivity, such as nickel, titanium alloys and polymer materials and so on. Many researchers have studied the effectiveness of cryogenic machining process, such as increasing tool life and improving surface integrity and so on. However, most articles on this topic were not considered the applications of actual industry. Cutting tool is one of the most important parts of industry applications. Most of cutting tools were not designed for cryogenic machining. In this work, the internally cooled turning tool was developed for cryogenic machining. The spray angle and diameter of the outlet were optimized by thermal field simulations. The results showed that 15° injection angle was more suitable to the machining process. Compare to 1mm outlet diameter, 3mm outlet diameter had better cooling effect. And the shape of outlet was optimized. A pressure simulation of the inner channel is carried out. The result shows that the pressure drop from inlet to outlets is only 66.696277Pa (about 6‰). Then, a spray test of the cutting tool was performed. The tests revealed that liquid nitrogen could be transmitted accurately and stably to the tool nose and the machining area. At last, a machining experiment proved that the turning tool could reduce the cutting temperature effectively when machining Ti-6Al-4V.

The growth of laser-induced nanocarbons, referred to here are LINC for short, directly on polymeric surfaces is a promising route toward surface engineering of commercial polymers. This paper aims to demonstrate how this new approach can enable achieving varied surface properties based on tuning the nanostructured morphology of the formed graphitic material on commercial polyimide (Kapton) films. We elucidate the effects of tuning laser processing parameters on the achieved nanoscale morphology and the resulting surface hydrophobicity or hydrophilicity. Our results show that by varying lasing power, rastering speed, laser spot size, and line-to-line gap sizes, a wide range of water contact angles are possible, i.e. from below 20° to above 110°. Combining water contact angle measurements from an optical tensiometer with LINC surface characterization using optical microscopy, electron microscopy, and Raman spectroscopy enables building the process-structure-property relationship. Our findings reveal that both the value of contact angle and the anisotropic wetting behavior of LINC on polyimide are dependent on their hierarchical surface nanostructure which ranges for isotropic nanoporous morphology to fibrous morphology. Results also show that increasing gap sizes lead to an increase in contact angles and thus an increase in the hydrophobicity of the surface. Hence, our work highlight the potential of this approach for manufacturing flexible devices with tailored surfaces.

Polymeric materials are often used as structural binders for biomedical applications. The mechanical properties of the material strongly depend on the fabrication process. To this end, we illustrate a set of casting methods for the production of samples to be tested via destructive methods. The curing process of the artifact was controlled during fabrication, and the molds were also made of polymeric materials. The fabrication of molds is illustrated where particular emphasis is posed on the manufacturing and testing of silicone molds using off-the-shelf material. Cyanoacrylate (CA), Epoxy resin (EP) and Methacrylate ester monomers (MEMs) artifacts have been fabricated using said molds. Of the aforementioned resins, MEMs are a class of thermosetting biocompatible polymers in which fabrication is especially problematic because of the very narrow temperature window at which the monomers polymerize. This research analyzes the casting process of curable materials highlighting the setbacks of using plastic-based molds. Among the cast based manufacturing techniques, specific focus was given to the case where MEMs is made to polymerize in a silicone mold controlling the temperature of the environment. The thermal properties that the silicone-based molds require for the appropriate curing of the polymer are analyzed. It was found that due to the very high heat capacity of silicone, the regulation of the temperature within the mold is difficult often exciding the boiling point of the casted resin.

Origami-based fabrication strategies open the door for developing new manufacturing processes capable of producing complex three-dimensional (3D) geometries from two-dimensional (2D) sheets. Nevertheless, for these methods to translate into scalable manufacturing processes, rapid techniques for creating controlled folds are needed. In this work, we propose a new approach for controlled self-folding of shape memory polymer sheets based on direct laser rastering. We demonstrate that rapidly moving a CO 2 laser over pre-strained polystyrene sheets results in creating controlled folds along the laser path. Laser interaction with the polymer induces localized heating above the glass transition temperature with a temperature gradient across the thickness of the thin sheets. This gradient of temperature results in a gradient of shrinkage owing to the viscoelastic relaxation of the polymer, favoring folding towards the hotter side. We study the influence of laser power, rastering speed and number of passes on the fold angle. Moreover, we investigate process parameters that produce the highest quality folds with minimal undesired deformations. Our results show that we clean folds up to and exceeding 90°, which highlights the potential of our approach for creating lightweight 3D geometries with smooth surface finishes that are challenging to create using 3D printing methods. Hence, laser-induced self-folding of polymers is an inherently mass-customizable approach to manufacturing, especially when combined with cutting for integration of origami and kirigami.

Additive Manufacturing (AM) — one of several core digital technologies in “Industry 4.0” — is increasingly being deployed in industrial-scale contexts. The successful serial production of end-use polymer and metal components has demonstrated the possibility of AM as a primary production process in several applications. However, one of the principal challenges to greater adoption is a lack of organizational mastery over AM’s implementation in production contexts, and, more specifically, the absence of clear decision-making tools to facilitate exploration of implementation scenarios. To this end, this work proposes the use of a discrete-event simulation-based software modelling tool to investigate the influences of different facility-level planning decisions on techno-economic characteristics of serial production by AM. By changing key parameters, this tool enables users to observe variation in part cost, identify the contributions of individual system elements to part cost, and assess overall system throughput. The tool enables users to identify locally optimal solutions and make corresponding planning decisions, and to explore limiting cases of cost and lead time. In conclusion, we identify the limitations in the current modeling approach, and propose additional directions for future study.

Previous studies have shown that metallic coatings can be successfully cold sprayed onto several polymer substrates. The electrical performance of the cold-sprayed polymers, however, is not generally sufficient enough to utilize them as an electronic device. In this paper, an environment-friendly metallization technique has been proposed to fabricate conductive metal patterns onto polymer substrates combining cold spray deposition and electroless plating to address that challenge. Copper feedstock powder was cold sprayed onto the surface of the acrylonitrile-butadiene-styrene (ABS) parts. The as-cold sprayed powders then served as the activating agent for selective electroless copper plating (ECP) to modify the surface of the polymers to be electrically conductive. A series of characterizations are conducted to investigate the morphology, analyze the surface chemistry, and evaluate the electrical performance and adhesion performance of the fabricated coatings. After 6 hours of ECP, the sheet resistance and resistivity of copper patterns on the ABS parts were measured as 2.854 mΩ/sq and 6.699 × 10 −7 Ωm respectively. Moreover, simple electrical circuits were demonstrated for the metallized ABS parts through the described method. The results show that low-pressure cold spray (LPCS) and ECP processes could be combined to fabricate electrically conductive patterns on ABS polymer surfaces in an environmental-friendly way.

Commercially available fused deposition modeling (FDM) printers have yet to bridge the gap between printing soft, flexible materials and printing hard, rigid materials. This work presents a custom printer solution, based on open-source hardware and software, which allows a user to print both flexible and rigid polymer materials. The materials printed include NinjaFlex, SemiFlex, acrylonitrile-butadiene-styrene (ABS), Nylon, and Polycarbonate. In order to print rigid materials, a custom, high-temperature heated bed was designed to act as a print stage. Additionally, high temperature extruders were included in the design to accommodate the printing requirements of both flexible and rigid filaments. Across 25 equally spaced points on the print plate, the maximum temperature difference between any two points on the heated bed was found to be ∼9°C for a target temperature of 170°C. With a uniform temperature profile across the plate, functional prints were achieved in each material. The print quality varied, dependent on material; however, the standard deviation of layer thicknesses and size measurements of the parts were comparable to those produced on a Zortrax M200 printer. After calibration and further process development, the custom printer will be integrated into the NEXUS system — a multiscale additive manufacturing instrument with integrated 3D printing and robotic assembly (NSF Award #1828355).

The selective light absorption of pre-stretched thermoplastic polymeric films enables wireless photothermal shape morphing from two-dimensional Euclidean geometry of films to three-dimensional (3D) curvilinear architectures. For a facile origami-inspired programming of 3D folding, black inks are printed on glassy polymers that are used as hinges to generate light-absorption patterns. However, the deformation of unpatterned areas and/or stress convolution of patterned areas hinder the creation of accurate curvilinear structures. In addition, black inks remain in the film, prohibiting the construction of transparent 3D architectures. In this study, we demonstrate the facile preparation of transparent 3D curvilinear structures with the selection of the curvature sign and chirality via the selective light absorption of detachable tapes. The sequential removal of adhesive patterns allowed sequential folding and the control of strain responsivity in a single transparent architecture. The introduction of multiple heterogeneous non-responsive materials increased the complexity of strain engineering and functionality. External stimuli responsive kirigami-based bridge triggered the multi-material frame to build the Gaussian curvature. Conductive material casted on the film in a pattern retained the conductivity, despite local deformation. This type of tape patterning system, adopting various materials, can achieve multifunction including transparency and conductivity.

3D bioprinting has more and more applications in tissue engineering, in vitro drug testing, and regenerative medicine. The bioink consisting of the biocompatible polymer (as extracellular matrix) and the living cells is the starting material. Because the typical bioprinting process may take several hours, the suspended cells in the bioink sediment with time, which significantly affects the bioink stability as well as the following bioprinting quality and reliability. The cell sedimentation is determined by the integral effects of drag force and buoyancy and gravity. The gravitational force is related to the cells, and the drag force and buoyant force is related to the polymer concentration. This paper is the first paper to quantify the cell sedimentation process of the bioink within 0.5% and 1% (w/v) polymer concentrations respectively. The cell sedimentation phenomenon has been observed using the bioink within 0.5% and 1% (w/v) polymer concentrations. The cell sedimentation velocity has been estimated to be 1.18 μm/s with the polymer concentrations to be 0.5% (w/v) and 0.88 μm/s for the bioink with the polymer concentrations to be 1% (w/v). It is also found that the cell concentration increases significantly at the bottom of the bioink reservoir, resulting in cell aggregates due to cell-cell interaction.

In attempts to engineer human tissues in the lab, bio-mimicking the cellular arrangement of natural tissues is critical to achieve the required biological and mechanical form and function. Although biofabrication employing cellular bioinks continues to evolve as a promising solution over polymer scaffold based techniques in creating complex multi-cellular tissues, the ability of most current biofabrication processes to mimic the requisite cellular arrangement is limited. In this study, we propose a novel biofabrication approach that uses forces generated by bulk standing acoustic waves (BSAW) to non-deleteriously align cells within viscous bioinks. We computationally determine the acoustic pressure pattern generated by BSAW and experimentally map the effects of BSAW frequency (0.71, 1, 1.5, 2 MHz) on the linear arrangement of two types of human cells (adipose-derived stem cells and MG63) in alginate. Computational results indicate a non-linear relationship between frequency and acoustic pressure amplitude. Experimental results demonstrate that the spacing between adjacent strands of aligned cells is affected by frequency (p < 0.0001), and this effect is independent of the cell type. Lastly, we demonstrate a synergistic technique of gradual crosslinking in tandem with the BSAW-induced alignment to entrap cells within crosslinked hydrogels. This study represents an advancement in engineered tissue biofabrication aimed at bio-mimicry.

Modern wireless communication industries need high performance antennas having better connectivity, ultra-wide bandwidth, lightweight and miniaturized. The current design and manufacturing process for antennas have several limitations. This study aims to address some of the limitations of designing and fabricating modern radio frequency wireless antennas. The study proposes a combination of fractal-based monopole antenna design followed by fabrication using additive manufacturing and selective electrochemical deposition process. Multiple designs of monopole antennas are compared, and the performance testing showed that the three-dimensional fractal-based antenna design showed the highest performance. The results of this study would be extremely crucial for overcoming challenges of modern antenna technologies.

The claim in additive manufacturing (AM) changes from simply producing prototypes as show objects to the fabrication of final parts and products in small volume batches. Thereby the focus is on freedom of material, dimensional accuracy and mechanical component properties. A novel extrusion-based AM technology has been developed focusing on these issues. The working principle is to form spheres from a thermoplastic polymer melt and build parts by single droplets. The material preprocessing is similar to the injection molding technology and enables a wide range of different thermoplastic polymers as build materials. With the droplet-based working principle high mechanical component properties and dimensional accuracy can be reached compared to similar processes. Further improvements to the process need a detailed knowledge of the physical effects during the build process. The temperature distribution during the manufacturing process determines at which temperature material is fused and how solidification takes place and shrinkage can occur or is suppressed. Thus, it has a significant influence on the mechanical properties and warpage effects of produced parts. In this work a thermal model is presented that describes the heat transfer during the build process. The necessary input data are the material properties and a print job description including the part geometry and building strategy. The basic idea is to simulate each single droplet deposition by applying a dynamic Finite Element Method. All relevant heat transfer effects are analyzed and represented in the model. The model was validated with measurements using a thermal imaging camera. Several measurements were performed during the build process and compared to the simulation results. A high accuracy could be reached with an average model error of about 4° Celsius and a maximal error of 10° Celsius.

Flow Drill Screws are self-piercing, self-tapping screws used for single sided joining of light metals, such as aluminum. This technology has been adopted by many automotive OEMs for use in metals. Thread forming profiles exist for material stackups that are made of entirely metals and entirely polymers/composites. This research evaluated the effectiveness of these thread profiles in dissimilar metal-on-composite stackups. Thread profiles designed for use in polymers/composites and aluminum were compared with a traditional machine screw thread profile for flow drill joining of 1mm and 2mm thick 6061-T6 aluminum to 3mm thick thermoset carbon fiber reinforced polymer. The three thread profiles were manufactured as M5x25mm flow drill screws in their commercially available configurations and materials. Two parameter sets from the FDS equipment manufacturer were evaluated, the first designed for use with the polymer thread forming profile, the second designed for use with the aluminum thread forming profile. The thread profiles were evaluated based on outputs of process time, peak torque, and lap shear strength. The polymer thread profile had shorter process times than the other 2 profiles but caused more damage to itself and its mating material. All 3 thread profiles exhibited greater shear strength when aluminum was used as the lower sheet material.

Joining soft polymers and metals is receiving increasing attention in both industry and academia to enable the manufacturing of innovative products. One motivation arises from the production of next-generation heat exchanges, the structure of which is primarily composed of polymers and metals. Waste heat coming from low temperature exhaust gas stream is significant in industries in the U.S. However, traditional heat exchangers that are available to recover heat in the presence of small temperature difference are large and costly, restricting the wide application of such heat exchangers. To address this challenge, a hybrid materials design is proposed to achieve a balance between thermal conductivity and mechanical strength. High quality requirement induced by the changing operating conditions necessitates a strong bonding between polymers and copper. In this research, the possibility of using ultrasonic welding, which is conventionally employed to join dissimilar or similar metal layers, is explored. Preliminary results from welding experiments and tensile shear tests reveal that two bonding modes exist in the welding of PET and copper. Furthermore, analysis of power signals collected during welding shows that one can potentially monitor and optimize welding processes using monitoring signals. It is concluded from this study that ultrasonic welding has excellent potential in joining soft polymers and metals. Future work is also discussed on the process improvement and mechanism investigation.

Semi-crystalline polymers offer great mechanical properties and are ubiquitously found in everyday life. Despite of this, they are not yet widespread among additive manufacturing processes, due to their high tendency to warp. This leads to unstable build processes and dimensionally inaccurate parts, which greatly reduces their usability. This paper describes the findings of an experimental study designed to identify relevant parameters that affect the warpage and investigate the influence of the manufacturing method on the mechanical properties of semi-crystalline PA6. The first experiment investigates the effect of water absorption over time, measuring weight and curling of 64 specimens over three weeks. The second part of this study focuses on the changes in geometry caused by the warpage by evaluating a basic model for simple part geometries. At last, a tension test was conducted and the results were compared to injection molded parts of the same material. The results indicate, that while the absorption of water plays an important role in the warpage of hydrophilic polymers like PA6, other environmental factors also have a significant influence. The model evaluation showed, that the warpage geometry of the tested parts can be approximated with only three parameters for very simple parts, if there are no irregularities in the manufacturing process. The tensile tests revealed, that the additively manufactured specimens reach up to 85.9% of the strength of the injection molded reference parts, most likely due to imperfect filling and reduced density. Overall, this study provides an insight into the challenges of additively manufacturing semi-crystalline polymers and the potential of PA6 as a tougher alternative to the common materials.

Single point incremental forming (SPIF) is more accurate and economical than the conventional forming process for customized products. Majority of the work in SPIF has been carried out on metals. However, polymers are also required to shape. Polycarbonate has wide application in safety glass, bottles, automotive and aircraft industry due to its transparent as well as attractive processing and mechanical properties as compared to other polymeric plastics. In present work, the Polycarbonate (PC) sheet of thickness 1.8 mm is deformed to make a square cup at different angles. Tensile testing is done to analyze the effect of wall angle on the deformed cup. This work illustrates the effect of the SPIF process on material strength in a different directions (vertical and horizontal) of the final deformed product. Tool forces are evaluated using ABAQUS ® simulation for SPIF. Numerical simulation approach is used to calculate the fracture energy, which utilizes the force-displacement curve of the specimen and is verified.

The purpose of this paper is to characterize the kinetics and direction of self-folding of pre-strained polystyrene (PSPS) and non-pre-strained styrene (NPS), which results from local shrinkage using a resistively heated ribbon in contact with the polymer sheet. A temperature gradient across the thickness of this shape memory polymer (SMP) sheet induces folding along the line of contact with the heating ribbon. Varying the electric current changes the degree of folding and extent of local material flow. This method can be used to create practical 3D structures. Sheets of PSPS and NPS were cut to 10 × 20 mm samples and their folding angles were plotted with respect to time, as obtained from in situ videography. In addition, the use of polyimide tape (Kapton) was investigated for controlling the direction of self-folding. Results show that folding happens on the opposite side of the sample with respect to the tape, regardless of which side the heating ribbon is on, or whether gravity is opposing the folding direction. Given the tunability of fold times and extent of local material flow, heat-assisted folding is a promising approach for manufacturing complex 3D lightweight structures by origami engineering.

The synergistic effect of combining different modification methods was investigated in this study to improve the interlaminar toughness and delamination resistance of fiber reinforced polymers (FRP). Epoxy-compatible polysulfone (PSU) was end-capped with epoxide group through functionalization, and the fiber surface was chemically grafted with amino functional group to form a micron-size rough surface. Consequently, the long chain of PSU entangles into crosslinked thermoset epoxy network, additionally, epoxide group on PSU further improves the bonding through chemical connection to the epoxy network and amino group on fiber surface. The combined modification methods can generate both strong physical and chemical bonding. The feasibility of using this method in vacuum assisted resin transfer molding was determined by rheometer. The impact of formed chemical bonds on the crosslinking density was examined through glass transition temperatures. The chemical modifications were characterized by Raman Spectroscopy to determine the chemical structures. Synergistic effect of the modification was established by Mode I and Mode II fracture tests which quantify the improvement on composites delamination resistance and toughness. The mechanism of synergy was explained based on the fracture mode and interaction between the modification methods. Finally, Numerical simulation was used to compare samples with and without modifications. The experiment results showed that synergy is achieved at low concentration of modified PSU because the formed chemical bonds compensate the effect of low crosslinking density and interact with the modified fiber.