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Experimental examples of as-built microstructures and associated microindentation hardnesses (HV) for a wide range of metal additive manufacturing (AM) processes for Inconel 625 alloy are presented in this research paper. These processes included cold spray, laser powder bed fusion, wire arc additive manufacturing, electron beam directed energy deposition, laser hot wire, binder jetting, laser power directed energy deposition, electron beam melting, and laser wire directed energy deposition. Microstructures ranged from impact bonded, flattened 625 alloy grains containing microdendrites and dislocations, having a microindentation hardness of HV 590 for cold spray, to large, equiaxed grains for binder jet-printed components having a microindentation hardness of HV 180. Electron and laser beam melt-related processes, including wire and powder feeds, produced varying sizes of columnar grains with parallel and cellular arrays of microdendrites, having microindentation hardnesses ranging from HV 304 to HV 228. Delta phase precipitate needles were also produced in laser-powered directed energy deposition microstructures along with columns of gamma double-prime precipitates for electron beam melting. The results demonstrate a range of AM processes applications and strategies to produce as-built and surface-modified Inconel 625 alloy products and components. These results demonstrate differences in the microstructure from the various AM processes and considerations for use in end use applications.

An unmodified, non-spherical, hydride-dehydride (HDH) Ti-6Al-4V powder having a substantial economic advantage over spherical, atomized Ti-6Al-4V alloy powder was used to fabricate a range of test components and aerospace-related products utilizing laser beam powder-bed fusion processing. The as-built products, utilizing optimized processing parameters, had a Rockwell-C scale (HRC) hardness of 44.6. Following heat treatments which included annealing at 704 °C, HIP at ~926 °C (average), and HIP + anneal, the HRC hardnesses were observed to be 43.9, 40.7, and 40.4, respectively. The corresponding tensile yield stress, UTS, and elongation for these heat treatments averaged 1.19 GPa, 1.22 GPa, 8.7%, 1.03 GPa, 1.08 GPa, 16.7%, 1.04 GPa, 1.09 GPa, 16.1%, respectively. The HIP yield strength and elongation of 1.03 GPa and 16.7% are comparable to the best commercial, wrought Ti-6Al-4V products. The corresponding HIP component microstructures consisted of elongated small grains (~125 microns diameter) containing fine, alpha/beta lamellae.

Mass casualty incidents such as those that are being experienced during the novel coronavirus disease (COVID-19) pandemic can overwhelm local healthcare systems, where the number of casualties exceeds local resources and capabilities in a short period of time. The influx of patients with lung function deterioration as a result of COVID-19 has strained traditional ventilator supplies. To bridge the gap during ventilator shortages and to help clinicians triage patients, manual resuscitator devices can be used to deliver respirations to a patient requiring breathing support. Bag-valve mask (BVM) devices are ubiquitous in ambulances and healthcare environments, however require a medical professional to be present and constantly applying compression to provide the patient with respirations. We developed an automated manual resuscitator-based emergency ventilator-alternative (AMREV) that provides automated compressions of a BVM in a repetitive manner and is broadly compatible with commercially-available BVM devices approximately 5 inches (128 mm) in diameter. The AMREV device relieves the medical professional from providing manual breathing support and allows for hands-free operation of the BVM. The AMREV supports the following treatment parameters: 1) adjustable tidal volume (V T ), 2) positive end-expiratory pressure (PEEP) (intrinsic and/or external), 3) 1:1 inspiratory: expiratory ratio, and 4) a controllable respiratory rate between 10-30 breaths per minute. The relationship between the inherent resistance and compliance of the lung and the delivered breaths was assessed for the AMREV device. Adjustable V T of 110-700 ml was achieved within the range of simulated lung states. A linear increase in mean airway pressure (P aw ), from 10-40 cmH2O was observed, as the resistance and compliance on the lung model moved from normal to severe simulated disease states. The AMREV functioned continuously for seven days with less than 3.2% variation in delivered V T and P aw . Additionally, the AMREV device was compatible with seven commercially-available BVM setups and delivered consistent V T and P aw within 10% between models. This automated BVM-based emergency-use resuscitator can provide consistent positive pressure, volume-controlled ventilation over an extended duration when a traditional ventilator is not available. True ventilator shortages may lead to manual resuscitators devices such as the AMREV being the only option for some healthcare systems during the COVID-19 pandemic.

Fabrication of parts exhibiting multi-functionality has recently been complemented by hybrid polymer extrusion additive manufacturing in combination with wire embedding technology. While much mechanical characterization has been performed on parts produced with fused deposition modeling, limited characterization has been performed when combined electrical and thermal loads are applied to 3D printed multi-material parts. As such, this work describes the design, fabrication, and testing of 3D printed thermoplastic coupons containing embedded copper wires that carried current. An automated fabrication process was used employing a hybrid additive manufacturing machine that dispensed polycarbonate thermoplastic and embedded bare copper wires. Testing included AC and DC hipot testing as well as thermal testing on as-fabricated and heat treated coupons to determine the effect of porosity in the substrate. The heat-treated parts contained reduced amounts of porosity, as corroborated through scanning electron microscopy, which led to 50 % increased breakdown strength and 30 to 40 % increased heat dissipation capabilities. The results of this research are describing a set of design protocol that can be used as a guideline for 3D printed embedded electronics to predict the electrical and thermal behavior.

In this work, a 3D printed patch antenna is fabricated within a complex dielectric structure relevant to the construction of satellites – an isogrid panel. The antenna was fabricated via a multi-process, hybrid, additive manufacturing system that included polymer material extrusion enhanced with complementary manufacturing capabilities of foil placement and patterning, wire integration and component placement. The antenna design targeted the commercial frequency of Bluetooth communication at 2.4 GHz by introducing a rectangular conductor of precise width, height and thickness from ground plane for the specific resonance. The measured reflection and gain coefficients were reasonable, however, two challenges were identified with the fabrication related to (1) imperfections typical of material extrusion additive manufacturing processes including unintentional porosity and (2) the insecure mechanical bonding between the output connector and substrate. Porosity impacted the dielectric features (permittivity) of the substrate and consequently introduced error in final antenna resonance (2.13 GHz versus the target of 2.4 GHz). The bonding affected mechanical reliability and caused changes in input impedance which affected signal quality for some orientations depending on cable flexing. Several remediations were identified, all of which included reinforcing the connector during embedding with a bonding agent. In the end, the antenna was compared to a commercial dipole antenna and the signal-to-noise ratios were within 6%.

Build defects, such as nozzle clogging and thermal substrate deformation, are common in material extrusion additive manufacturing technologies, and are difficult to detect because of the high-temperature environment of fused deposition modeling (FDM) machines that do not accommodate internal sensors. To overcome this difficulty, this paper integrated an external sensor to monitor the supply current of the motor that fed filament into an extrusion head. This paper describes the investigation of the relationship between the deposition status and the reaction torque on the filament-feed motor. A dynamic model of the internal operation of the FDM extrusion head was developed and used to infer printing defects. The change in reaction force opposing extrusion was indirectly measured by monitoring the current delivered to the filament-feed motor, and consequently, the use of other sensors in the high-temperature chamber was avoided. An analysis of the supply current, in both time and frequency domains, enabled the detection of defects during material deposition.

The ability to access individual layers of a part as they are being printed has allowed additive manufacturing (AM) researchers to experiment with the in situ placement of components, thereby creating multi-process parts with additional functionality, such as customized printed electronics. As AM has evolved to become an established method for creating end-use parts, this interest in multi-process printing has increased. Although progress has been made in developing multi-process hardware, which can combine AM with other technologies, holistic design software, capable of readily integrating these processes, is developing at a slower rate. In this paper, an integrated software solution capable of supporting multi-process 3D printing from design through manufacture is described, featuring the integration of electronic components and circuits interconnected by copper wires. This solution features automated generation of the cavities that accommodate electronic components as well as toolpath generation for a multi-process 3D printer capable of automated wire embedding. As a case study of the developed technology, a hexagonal 3D printed body, which included a microcontroller, four LEDs, a USB connector, two resistors, and a Zener diode, all interconnected by embedded copper wires, was fabricated within a short cycle time: 5.75 h from design to fabricated part. Short cycle times allow multiple design iterations to be realized and printed within the same day.

Radiation thermometry methods used in powder bed fusion (PBF) additive manufacturing for in situ monitoring and control and quality assurance are increasing in importance. Arguably, the most significant challenge associated with radiation thermometry methods is the limited understanding of the emissivity, that is the emissive behavior of the entire region being measured. This work describes a new approach for measuring the emissive behaviors of PBF materials during processing using a multi-wavelength (MW) or Spectropyrometer operating in the spectral range from 1000 to 1650 nm. The approach was implemented in an electron beam (EB) PBF machine, using the electron beam as a heat source, allowing for (1) measuring spectral emissive behavior of the surface in a fixed small region (~2.65 mm) throughout a variety of dynamic processing conditions including heating, melting, and cooling; (2) controlling the scanning (heating) profile during processing while rejecting radiative interference in the measurements due to heating lasers (~1070 nm) commonly used in laser PBF; and (3) processing in an evacuated environment to assist with reduction of additional environmental effects that could impact the measurements. The experimental setup included a sight tube that prevented both metallization of the viewport and resultant signal decay, which enabled near-continuous measurements throughout processing. Measurements from the MW pyrometer were compared against those of a type K thermocouple that was placed in the vicinity of the measurement area. Prior to the powder bed preheating experiment, the MW pyrometer was calibrated against a NIST traceable blackbody source. The utility of the approach was demonstrated by acquiring measurements from the surface of a copper (d50~75 µm) powder bed that was progressively heated in a series of nine steps inside an Arcam A2 EB-PBF system through scanning with the electron beam. Following the preheat steps, seven consecutive melt steps were implemented enabling measurements of the emissive behavior for copper during its multiple solid-liquid-solid transitions. The unique capabilities of the MW pyrometer provided measured values of emissivity of copper that exhibited temporal, spectral (1080–1640 nm) and thermal dependence, verifying the non-graybody behavior for copper. Ongoing work will demonstrate the applicability of this technique across multiple powder metal alloy systems and PBF technologies.

The final functionality of parts produced by Additive Manufacturing (AM) can, in part, be improved by the inclusion of multi-material capabilities. The Multi3D Manufacturing System uses material extrusion printing (fused deposition modeling technology from Stratasys), solid conductor wire embedding, direct-write, component placement, and micromachining to enable the fabrication of multi-functional products. The material handling methodology, implemented by the Multi3D System, transports a workpiece between manufacturing stations via a six-axis robot, portable build platform, and a controlled temperature environment or chamber that travels to each manufacturing station. Also discussed in this work, is the investigation and improvement of registration parameters between the two material extrusion printers within this system. The registration was ultimately quantified to have minimal errors: 69 μm along the x-axis, 183 μm along the y-axis, and 215 μm along the z-axis. The fabrication of a multi-colored part demonstrated the automated transfer of the workpiece, which offers early promise for an automated solution for multi-material fabrication using commercially-available fused deposition modeling machines.

Polymer extrusion three dimensional (3D) printing, such as fused deposition modeling (FDM), has recently garnered attention due to its inherent process flexibility and rapid prototyping capability. Specifically, the addition of electrical components and interconnects into a 3D printing build sequence has received heavy interest for space applications. However, the addition of these components, along with the thermal load associated with space-based applications, may prove problematic for typical thermally insulating 3D printed polymer structures. The work presented here addresses thermally conductive polymer matrix composites (specifically, graphite, carbon fiber, and silver in an acrylonitrile butadiene styrene polymer matrix) to identify the effect of composite geometry and print direction on thermal anisotropic properties. The work also examines the effect of these composites on print quality, mechanical tensile properties, fracture plane analysis, micrograph imaging, and cube satellite thermal analysis. The thermal conductivity of 3D printed material systems in this work may enable the production of thermally stable 3D printed structures, supports, and devices. Key results of this work include anisotropic thermal conductivity for 3D printed structures related to print direction and filler morphology meaning that thermal conductivity can be controlled through a combination of print raster direction and material design. When the materials analyzed in this work are incorporated with other active cooling systems, space-based 3D printed applications can then be designed to incorporate increasing thermal loads, opening a new door to producing space-ready 3D printed structures.

The article presents an exploration of design and prototyping of oxy-fuel injectors with integrated temperature sensing capabilities using powder bed fusion additive manufacturing (AM) technologies. A primary focus of this work was to develop powder removal techniques to completely remove sintered powders from internal cavities, which facilitated the implementation of complex injector geometries as well as sensor placements within the parts. It was found that submerging the part in liquid nitrogen, in combination with exposure to ultrasonic vibration, provided effective powder removal. Mechanical testing of fabricated components and test coupons showed no significant change in the mechanical strength of the part due to the addition of liquid nitrogen which creates a thermal shock. Metallography and powder characterization through the use of SEM and EDS showed no change in metallurgical properties of the parts due to the use of liquid nitrogen and ultrasonic energy. The injectors were then test fired in both atmospheric and high-pressure conditions at different firing inputs (55–275 kW).

In-process process sensing and monitoring is being incorporated across additive manufacturing technologies due to the need for part qualification. Implementation of additively manufactured end-use parts has been hindered by the inherent process variability and anisotropy that adversely affect part performance. Process monitoring methods have the potential to ensure fabrication integrity is achieved and part isotropy is maintained across the entirety of a part. This manuscript compares two methods (pyrometer and infrared thermography) that have the potential to monitor layerwise surfaces of a powder bed fusion process. Measurement of surface temperatures during fabrication can be useful for parameter development of novel materials, prediction of resulting microstructural architectures, and ultimately as feedback used in a closed-loop control system to allow full spatial and temporal control of melting and microstructure. A multi-wavelength pyrometer was externally mounted atop an electron beam melting (EBM) additive manufacturing system to observe and record surface temperatures during the fabrication process. The multi-wavelength pyrometer used in this study was a non-contact device that was emissivity independent and capable of taking fixed spot sized measurements. An infrared camera was also installed atop an EBM system to monitor the fabrication surface and was used to measure temperature variations across the entire build area. Although the IR camera produces spatial measurements of an entire part, temperature data is emissivity dependent. Parts with variations in processing were fabricated and monitored using each instrument. Thermal variations between parts were identified with each instrument and related to microstructure. The advantages and disadvantages of each monitoring device were documented and are discussed in this manuscript.

Joining of dissimilar metals using high energy-density beams such as lasers and electron beams offer several advantages including precision, narrow fusion zones, and narrow heat affected zones (HAZ) that consequently result in reduced part distortion when compared to traditional joining processes. When high energy-density beams are combined with the design freedom offered by additive manufacturing (AM), or a layer-by-layer part fabrication process, it becomes possible to manufacture complex multi-material parts with improved joint characteristics resulting from controlled process parameters. Complex multi-material parts can be achieved that have tremendous impact on applications ranging from nuclear power plant components to repair applications. This research explores the feasibility of joining Inconel 718 with 316L Stainless Steel, and vice versa, by utilizing electron beam melting (EBM) additive manufacturing, a class of powder bed fusion technology. The use of this process can help avoid the use of filler materials, provides an evacuated processing environment resulting in limited contamination of oxides and nitrides, and can provide a high quality metallurgical joint while minimizing the thermal damage to surrounding material. Multi-material components were fabricated and the joint interfaces were characterized. Assessments of the interfaces revealed minimized thermal effects from the process and finer weld joints. Keywords: Additive manufacturing, Electron beam melting, Multi-material, Inconel 718, 316L

Izod impact test specimens were fabricated via a desktop grade material extrusion 3D printer process using ABS in four build orientations. The 3D printed impact test specimens were examined in order to compare the effect of stress concentrator fabrication on impact test data where two methods were used to fabricate the stress concentrating notch: (1) printing the stress concentrator; and (2) machining the stress concentrator where the dimensions of the notch matched those specified in the ASTM standard D256-10. In both test cases, sensitivity to build orientation was also observed. The sample sets with printed stress concentrators were found to be statistically similar to their counterparts with milled stress concentrators. The experiment was repeated again on a commercial grade material extrusion 3D printer using ABS, PC, PC-ABS, and Ultem 9085 and differences in impact test results were observed most notably when Ultem 9085 was tested. Scanning electron microscopy was utilized to perform fractograpy on impact test specimens to explore the effect of stress concentrator fabrication on the fracture surface morphology of the failed specimens. The work here demonstrates the need for materials testing standards that are specific to additive manufacturing technologies; as well as concluding that all-printed impact test specimens may offer the best representation of the impact characteristics of 3D printed structures.

Material extrusion 3D printing (ME3DP), based on fused deposition modeling (FDM) technology is currently the most widely available 3D printing platform. As is the case with other 3D printing methods, parts fabricated from ME3DP will exhibit physical property anisotropy where build direction has an effect on the mechanical properties of a given part. The work presented in this paper analyzes the effect of physical property-altering additives to acrylonitrile butadiene styrene (ABS) on mechanical property anisotropy. A total of six ABS-based polymer matrix composites and four polymer blends were created and evaluated. Tensile test specimens were printed in two build orientations and the differences in ultimate tensile strength and % elongation at break were compared between the two test sample versions. Fracture surface analysis was performed via scanning electron microscopy (SEM) which gave insight to the failure modes and rheology of the novel material systems as compared to specimens fabricated from the same ABS base resin. Here it was found that a ternary blend of ABS combined with styrene ethylene butadiene styrene (SEBS) and ultra high molecular weight polyethylene (UHMWPE) lowered the mechanical property anisotropy in terms of relative UTS to a difference of 22 ± 2.07% as compared to 47 ± 7.23% for samples printed from ABS. The work here demonstrates the mitigation of a problem associated with 3D printing as a whole through novel materials development and analyzes the effects of adding a wide variety of materials on the physical properties of a thermoplastic base resin.

Purpose – The purpose of this paper is to demonstrate the strategy for increasing the applicability of material extrusion additive manufacturing (AM) technologies, based on fused deposition modeling (FDM), through the development of materials with targeted physical properties. Here, the authors demonstrate materials specifically developed for the manufacture of electromechanical and electromagnetic applications, the use of FDM-type processes in austere environments and the application of material extrusion AM. Design/methodology/approach – Using a twin screw polymeric extrusion process, novel polymer matrix composites and blends were created where the base material was a material commonly used in FDM-type processes, namely, acrylonitrile butadiene styrene (ABS) or polycarbonate (PC). Findings – The work presented here demonstrates that, through targeted materials development, the applicability of AM platforms based on FDM technology can be increased. Here, the authors demonstrate that that the physical properties of ABS and PC can be manipulated to be used in several applications such as electromagnetic and X-ray shielding. Other instances of the development of new materials for FDM led to mitigation of problems associated with the process such as surface finish and mechanical property anisotropy based on build orientation. Originality/value – This paper is an overview of a research effort dedicated to increasing the amount of material systems available to material extrusion AM. Here materials development is shown to not only increase the number of suitable applications for FDM-type processes, but to be a pathway toward solving inherent problems associated with FDM such as surface finish and build orientation-caused mechanical property anisotropy.

Material extrusion 3D printing (ME3DP) based on fused deposition modeling (FDM) technology is currently the most commonly used additive manufacturing method. However, ME3DP suffers from a limitation of compatible materials and typically relies upon amorphous thermoplastics, such as acrylonitrile butadiene styrene (ABS). The work presented here demonstrates the development and implementation of binary and ternary polymeric blends for ME3DP. Multiple blends of acrylonitrile butadiene styrene (ABS), styrene ethylene butadiene styrene (SEBS), and ultrahigh molecular weight polyethylene (UHMWPE) were created through a twin screw compounding process to produce novel polymer blends compatible with ME3DP platforms. Mechanical testing and fractography were used to characterize the different physical properties of these new blends. Though the new blends possessed different physical properties, compatibility with ME3DP platforms was maintained. Also, a decrease in surface roughness of a standard test piece was observed for some blends as compared with ABS.

Purpose – The purpose of this paper is to investigate a build process variation for fused deposition modeling (FDM) in which contours and rasters (also referred to as internal fill patterns) are built using different layer thicknesses and road widths. In particular, the paper examines the effect of the build process variation on surface roughness, production times and mechanical properties. Additionally, a unique FDM process was developed that enabled the deposition of discrete multiple materials at different layers and regions within layers. Design/methodology/approach – A multi-material, multi-technology FDM system was developed and constructed to enable the production of parts using either discrete multi-materials or the build process variation (variable layer thickness and road width). Two legacy FDM machines were modified and installed onto a single manufacturing system to allow the strategic, spatially controlled thermoplastic deposition with multiple extrusion nozzles of multiple materials during the same build. This automated process was enabled by the use of a build platform attached to a pneumatic slide that moved the platform between the two FDM systems, an overall control system, a central PC and a custom-made program (FDMotion) and graphic user interface. The term multi-technology FDM system used here implies the two FDM systems and the integration of these systems into a single manufacturing environment using the movable platform and associated hardware and software. Future work will integrate additional technologies within this system. Parts produced using the build process variation utilized internal roads with 1,524 μm road width and 508 μm layer height, while the contours used 254 μm road width and 127 μm layer height. Measurements were performed and compared to standard FDM parts that included surface roughness of planes at different inclinations, tensile testing and fabrication times. Findings – Results showed that when compared to the standard FDM process, the parts produced using the build process variation exhibited the same tensile properties as determined by a student's t-test (p-values > 0.05, μ1-μ2 = 0, n = 5). Surface roughness measurements revealed that the process variation resulted in surface roughness (Ra) improvements of 55, 43, 44 and 38 per cent for respective planes inclined at 10, 15, 30 and 45° from vertical. In addition, for a 50.8 × 50.8 mm square section (25.4 mm tall), the build process variation required a minimum of 2.8 hours to build, while the standard FDM process required 6.0 hours constituting a 53 per cent reduction in build time. Finally, several manufacturing demonstrations were performed including the fabrication of a discrete PC-ABS sandwich structure containing tetragonal truss core elements. Originality/value – This paper demonstrates a build strategy that varies contour and raster widths and layer thicknesses for FDM that can be used to improve surface roughness – a characteristic that has historically been in need of improvement – and reduce fabrication time while retaining mechanical properties.

While NASA explores the power of 3D printing in the development of the next generation space exploration vehicle, a CubeSat Trailblazer was launched in November 2013 that integrated 3D-printed structures with embedded electronics. Space provides a harsh environment necessary to demonstrate the durability of 3D-printed devices with radiation, extreme thermal cycling, and low pressure—all assaulting the structure at the atomic to macroscales. Consequently, devices that are operational in orbit can be relied upon in many terrestrial environments—including many defense and biomedical applications. The 3D-printed CubeSat module (a subsystem occupying approximately 10 % of the total volume offered by the 10 × 10 × 10-cm CubeSat enclosure) has a substrate that fits specifically into the available volume—exploiting 3D printing to provide volumetric efficiency. Based on the best fabrication technology at the time for 3D-printed electronics, stereolithography (SL), a vat photopolymerization technology, was used to fabricate the dielectric structure, while conductive inks were dispensed in channels to provide the electrical interconnect between components. In spite of the structure passing qualification—including temperature cycling, shock and vibration, and outgas testing—the photocurable materials used in SL do not provide the level of durability required for long-term functionality. Moreover, the conductive inks with low-temperature curing capabilities as required by the SL substrate material are widely known to provide suboptimal performance in terms of conductivity. To address these challenges in future 3D-printed electronics, a next generation machine is under development and being referred to as the multi3D system, which denotes the use of multiple technologies to produce 3D, multi-material, multifunctional devices. Based on an extrusion process necessary to replace photocurable polymers with thermoplastics, a material extrusion system based on fused deposition modeling (FDM) technology has been developed that integrates other technologies to compensate for FDM’s deficiencies in surface finish, minimum dimensional feature size, and porosity. Additionally, to minimize the use of conductive inks, a novel thermal embedding technology submerges copper wires into the thermoplastic dielectric structures during FDM process interruptions—providing high performance, robust interconnect, and ground planes—and serendipitously improving the mechanical properties of the structure. This paper compares and contrasts stereolithography used for 3D-printed electronics with the FDM-based system through experimental results and demonstrates an automated FDM-based process for producing features not achievable with FDM alone. In addition to the possibility of using direct write for electronic circuitry, the novel fabrication uses thermoplastics and copper wires that offer a substantial improvement in terms of performance and durability of 3D-printed electronics.

In new product development, time to market (TTM) is critical for the success and profitability of next generation products. When these products include sophisticated electronics encased in 3D packaging with complex geometries and intricate detail, TTM can be compromised - resulting in lost opportunity. The use of advanced 3D printing technology enhanced with component placement and electrical interconnect deposition can provide electronic prototypes that now can be rapidly fabricated in comparable time frames as traditional 2D bread-boarded prototypes; however, these 3D prototypes include the advantage of being embedded within more appropriate shapes in order to authentically prototype products earlier in the development cycle. The fabrication freedom offered by 3D printing techniques, such as stereolithography and fused deposition modeling have recently been explored in the context of 3D electronics integration - referred to as 3D structural electronics or 3D printed electronics. Enhanced 3D printing may eventually be employed to manufacture end-use parts and thus offer unit-level customization with local manufacturing; however, until the materials and dimensional accuracies improve (an eventuality), 3D printing technologies can be employed to reduce development times by providing advanced geometrically appropriate electronic prototypes. This paper describes the development process used to design a novelty six-sided gaming die. The die includes a microprocessor and accelerometer, which together detect motion and upon halting, identify the top surface through gravity and illuminate light-emitting diodes for a striking effect. By applying 3D printing of structural electronics to expedite prototyping, the development cycle was reduced from weeks to hours.

Atomized, pre-alloyed Ti–24Nb–4Zr–7.9Sn (wt%) powder was used to fabricate solid, prototype components by electron beam melting (EBM). Vickers microindentation hardness values were observed to average 2 GPa for the precursor powder and 2.5 GPa for the solid, EBM-fabricated products. The powder and solid product microstructures were examined by optical and electron microscopy. X-ray diffraction analyses showed that they had bcc β-phase microstructure. However, it was found by transmission electron microscopy that the EBM-fabricated product had plate morphology with space ∼100–200 nm. Although the corresponding selected area diffraction patterns can be indexed by β-phase plus α″-martensite with orthorhombic crystal structure, the dark-field analyses failed to observe the α″-martensite. Such phenomenon was also found in deformed gum metals and explained by stress-induced diffusion scattering due to phonon softening.

Rene 142, a commercial, columnar grained, gas turbine airfoil Ni-based superalloy, has been fabricated from a pre-alloyed, atomized powder by additive manufacturing using electron beam melting. Monolithic components having [0 0 1] oriented, columnar grain structures exhibited a creep-optimized 59% volume fraction of cuboidal, coherent, γ ′-phase precipitates averaging 275 nm on the side, and with γ / γ ′ channel widths ranging from 25 to 75 nm. Transmission electron microscopy, utilizing bright and dark field imaging of optimally oriented γ / γ ′ interfaces showed prominent misfit coherency strains as δ-fringe patterns. Corresponding hardness measurements also indicated the possibility of creep strength comparable with the commercial alloy. The notable feature of this study was the monolithic development of desirable superalloy properties without conventional, multi-step heat treatments.

This article presents columnar grain structures characteristic of niobium components fabricated by electron beam melting, using two different size and size distribution spherical powders produced by rapid solidification atomization. The precursor powder microstructures are characterized by equiaxed grains while the columnar grain structure in the electron beam melted (EBM)-fabricated products contain dislocation substructures ranging in density from ~109 to 1010/cm2 as observed by transmission electron microscopy. X-ray diffraction analysis illustrates the variations in orientations in both the processor powders and the fabricated components. Microindentation hardness values ranged from 0.8 GPa for the precursor powders and 1.1 and 0.92 GPa for the EBM-fabricated, solid components.

In this work, results are given for controlling waves arbitrarily inside a lattice with spatially variant self-collimation. To demonstrate the concept, an unguided beam was made to flow around a 90◦ bend without scattering due to the bend or the spatial variance. Control of the field was achieved by spatially varying the orientation of the unit cells throughout a self-collimating photonic crystal, but in a manner that almost completely eliminated deformations to the size and shape of the unit cells. The device was all-dielectric, monolithic, and made from an ordinary dielectric with low relative permittivity (er = 2.45). It was manufactured by fused deposition modeling, a form of 3D printing, and its performance confirmed experimentally at around 15 GHz.

For more than a decade, our group has been developing the methods and systems required to have spatial control over material placement and structure creation, leading to, for example, the realisation of complex three-dimensional (3D) devices that integrate electronics and thus intelligence within mechanical structures as well as 3D spatially complex bioactive, implantable, tissue engineered constructs. There are myriad issues associated with combining multiple materials to create functional products, ranging from the deposition and processing of different materials to the combined performance of the materials in the resulting product. Stereolithography (SL) has been the primary technology focus of this work because it offers high quality surface finish, dimensional accuracy, and a variety of material options that includes implantable materials. Moreover, SL builds in essentially ambient, minimally controlled environmental conditions that provide easy access to the build chamber and enable straightforward ...

Purpose – The purpose of this paper is to investigate the effects of aging, pre‐conditioning, and build orientation on the mechanical properties of test samples fabricated using stereolithography (SL) and a commercially available resin.Design/methodology/approach – American Society for Testing and Materials (ASTM) Standard D638 Type I specimens were manufactured in a Viper si2 SL system using WaterShed™ 11120 resin. The specimens were manufactured in two different build setups, designed to fit batches of 18 or 24 specimens with different build orientations. The specimens were randomly tested in tension, and a design of experiments (DOE) was used to determine the effect of aging (4, 30 or 120 days), pre‐conditioning (ambient, desiccant, or ASTM recommended conditioning), and build orientation (flat, on an edge, or vertical) on the ultimate tensile stress (UTS) and elastic modulus (E) of SL fabricated samples. Additionally, the fractured samples were imaged using scanning electron microscopy (SEM) to charac...

PurposeThe purpose of this paper is to present a hybrid manufacturing system that integrates stereolithography (SL) and direct print (DP) technologies to fabricate three‐dimensional (3D) structures with embedded electronic circuits. A detailed process was developed that enables fabrication of monolithic 3D packages with electronics without removal from the hybrid SL/DP machine during the process. Successful devices are demonstrated consisting of simple 555 timer circuits designed and fabricated in 2D (single layer of routing) and 3D (multiple layers of routing and component placement).Design/methodology/approachA hybrid SL/DP system was designed and developed using a 3D Systems SL 250/50 machine and an nScrypt micro‐dispensing pump integrated within the SL machine through orthogonally‐aligned linear translation stages. A corresponding manufacturing process was also developed using this system to fabricate 2D and 3D monolithic structures with embedded electronic circuits. The process involved part design, process planning, integrated manufacturing (including multiple starts and stops of both SL and DP and multiple intermediate processes), and post‐processing. SL provided substrate/mechanical structure manufacturing while interconnections were achieved using DP of conductive inks. Simple functional demonstrations involving 2D and 3D circuit designs were accomplished.FindingsThe 3D micro‐dispensing DP system provided control over conductive trace deposition and combined with the manufacturing flexibility of the SL machine enabled the fabrication of monolithic 3D electronic structures. To fabricate a 3D electronic device within the hybrid SL/DP machine, a process was developed that required multiple starts and stops of the SL process, removal of uncured resin from the SL substrate, insertion of active and passive electronic components, and DP and laser curing of the conductive traces. Using this process, the hybrid SL/DP technology was capable of successfully fabricating, without removal from the machine during fabrication, functional 2D and 3D 555 timer circuits packaged within SL substrates.Research limitations/implicationsResults indicated that fabrication of 3D embedded electronic systems is possible using the hybrid SL/DP machine. A complete manufacturing process was developed to fabricate complex, monolithic 3D structures with electronics in a single set‐up, advancing the capabilities of additive manufacturing (AM) technologies. Although the process does not require removal of the structure from the machine during fabrication, many of the current sub‐processes are manual. As a result, further research and development on automation and optimization of many of the sub‐processes are required to enhance the overall manufacturing process.Practical implicationsA new methodology is presented for manufacturing non‐traditional electronic systems in arbitrary form, while achieving miniaturization and enabling rugged structure. Advanced applications are demonstrated using a semi‐automated approach to SL/DP integration. Opportunities exist to fully automate the hybrid SL/DP machine and optimize the manufacturing process for enhancing the commercial appeal for fabricating complex systems.Originality/valueThis work broadly demonstrates what can be achieved by integrating multiple AM technologies together for fabricating unique devices and more specifically demonstrates a hybrid SL/DP machine that can produce 3D monolithic structures with embedded electronics and printed interconnects.

Microstructure and variations in porosity in Ti-6Al-4V samples built with electron beam melting (EBM) over a range of melt scan speeds, ranging from 100 mm·s-1 to 1000 mm·s-1 were examined. Microstructure was characterized by refinement of α-phase and transformation to α′-martensite. Light optical microscopy, scanning electron microscopy, and transmission electron microscopy were used to observe these phenomena, while corresponding tensile testing and associated macro and microindentation hardness measurements were used to define the microstructural variations. Relative stiffness was observed to be linearly log-log related to relative density, corresponding to ideal porosity associated with open-cellular structures.

Selective laser melting (SLM) and electron beam melting (EBM) are relatively new rapid, additive manufacturing technologies which can allow for the fabrication of complex, multi-functional metal or alloy monoliths by CAD-directed, selective melting of precursor powder beds. By altering the beam parameters and scan strategies, new and unusual, even non-equilibrium microstructures can be produced; including controlled microstructural architectures which ideally extend the contemporary materials science and engineering paradigm relating structure-properties-processing-performance. In this study, comparative examples for SLM and EBM fabricated components from pre-alloyed, atomized precursor powders are presented. These include Cu, Ti-6Al-4V, alloy 625 (a Ni-base superalloy), a Co-base superalloy, and 17-4 PH stainless steel. These systems are characterized by optical metallography, scanning and transmission electron microscopy, and X-ray diffraction.

Methods and systems of stereolithography for building cost-efficient and time-saving multi-material, multi-functional and multi-colored prototypes, models and devices configured for intermediate washing and curing/drying is disclosed including: laser(s), liquid and/or platform level sensing system(s), controllable optical system(s), moveable platform(s), elevator platform(s), recoating system(s) and at least one polymer retaining receptacle. Multiple polymer retaining receptacles may be arranged in a moveable apparatus, wherein each receptacle is adapted to actively/passively maintain a uniform, desired level of polymer by including a recoating device and a material fill/remove system. The platform is movably accessible to the polymer retaining receptacle(s), elevator mechanism(s) and washing and curing/drying area(s) which may be housed in a shielded enclosure(s). The elevator mechanism is configured to vertically traverse and rotate the platform, thus providing angled building, washing and curing/drying capabilities. A horizontal traversing mechanism may be included to facilitate manufacturing between components of SL cabinet(s) and/or alternative manufacturing technologies.

Development of a flexible and mobile fused deposition modeling (FDM) system from an existing FDM system to enable deposition of material on virtually any surface without being confined to a build chamber is described. Flexibility of the system was demonstrated by depositing ABS on different surfaces, and simple pull tests were performed to determine bonding strength between the deposited materials. To develop the flexible FDM system, a Stratasys FDM 3000 machine was used and modified by reversing the z stage and attaching the x–y table controlling the FDM head to the bottom of the z stage. In this new configuration, the z stage transports the x–y table vertically, and the x–y table controls the x–y motion of the FDM dispensing head, which is exposed at the bottom of the machine. The mean of the absolute value of the difference between 49 part dimensions (based on 20 part features) measured on a modified Grimm test part (n = 5) was ∼0.44 mm for parts fabricated using the developed flexible FDM system, while a mean of ∼0.11 mm was measured using parts produced by the commercial system (n = 5). The dimensional accuracy of the flexible system was comparable but expectedly larger than the commercial system, due to the configuration of the flexible FDM system with the x–y table attached at the bottom of the z stage. There are many possible design improvements particularly focused on reducing deflections in the mechanical components that can be explored and implemented to improve the overall dimensional accuracy of the flexible system, but these investigations are left for future research. Instead, manufacturing flexibility of this new configuration was demonstrated by successfully building a cylinder on flat and 3D cupped surfaces, including building a horizontally oriented cylinder on a wall by orienting the FDM system in the horizontal position. Pull tests were performed and showed that bonding strength for the cylinders built on flat surfaces compared favorably to a glued part (3.06 ± 1.38 MPa for the specimens manufactured with the flexible FDM system compared with 2.00 ± 1.06 MPa for the glued specimens). Additional flexibility was demonstrated by printing directly on a complex curved surface, thus illustrating the possibilities for using AM (a traditional 2D layer-stacking processing technique) in conformal printing applications. It is concluded that this new machine can provide enormous flexibility in freeform manufacturing with applications in part repair, 3D conformal adhesive dispensing, and a number of applications where the removal of the size constraints imposed by the build chamber enables one to deposit new arbitrary features directly on existing parts.

PurposeThe purpose of this paper is to investigate the use of medical‐grade polymethylmethacrylate (PMMA) in fused deposition modeling (FDM) to fabricate porous customized freeform structures for several applications including craniofacial reconstruction and orthopaedic spacers. It also aims to examine the effects of different fabrication conditions on porosity and mechanical properties of PMMA samples.Design/methodology/approachThe building parameters and procedures to properly and consistently extrude PMMA filament in FDM for building 3D structures were determined. Two experiments were performed that examined the effects of different fabrication conditions, including tip wipe frequency, layer orientation, and air gap (AG) (or distance between filament edges) on the mechanical properties and porosity of the fabricated structures. The samples were characterized through optical micrographs, and measurements of weight and dimensions of the samples were used to calculate porosity. The yield strength, strain, and modulus of elasticity of the samples were determined through compressive testing.FindingsResults show that both the tip wipe frequency (one wipe every layer or one wipe every ten layers) and layer orientation (transverse or axial with respect to the applied compressive load) used to fabricate the scaffolds have effects on the mechanical properties and resulting porosity. The samples fabricate in the transverse orientation with the high tip wipe frequency have a larger compressive strength and modulus than the lower tip wipe frequency samples (compressive strength: 16±0.97 vs 13±0.71 MPa, modulus: 370±14 vs 313±29 MPa, for the high vs low tip wipe frequency, respectively). Also, the samples fabricated in the transverse orientation have a larger compressive strength and modulus than the ones fabricated in the axial orientation (compressive strength: 16±0.97 vs 13±0.83 MPa, modulus: 370±14 vs 281±22 MPa; for samples fabricated with one tip wipe per layer in the transverse and axial orientations, respectively). In general, the stiffness and yield strength decreased when the porosity increased (compressive strength: 12±0.71 to 7±0.95 MPa, Modulus: 248±10 to 165±16 MPa, for samples with a porosity ranging from 55 to 70 percent). As a demonstration, FDM is successfully used to fabricate patient‐specific, 3D PMMA implants with varying densities, including cranial defect repair and femur models.Originality/valueThis paper demonstrates that customized, 3D, biocompatible PMMA structures with varying porosities can be designed and directly fabricated using FDM. By enabling the use of PMMA in FDM, medical implants such as custom craniofacial implants can be directly fabricated from medical imaging data improving the current state of PMMA use in medicine.

Challenges remain in tissue engineering to control the spatial, mechanical, temporal and biochemical architectures of scaffolds. Unique capabilities of stereolithography (SL) for fabricating multi-material spatially controlled bioactive scaffolds were explored in this work. To accomplish multi-material builds, a mini-vat setup was designed allowing for self-aligning X-Y registration during fabrication. The mini-vat setup allowed the part to be easily removed and rinsed, and different photocrosslinkable solutions to be easily removed and added to the vat. Two photocrosslinkable hydrogel biopolymers, poly(ethylene glycol) dimethacrylate (PEG-dma, MW 1000) and poly(ethylene glycol) diacrylate (PEG-da, MW 3400), were used as the primary scaffold materials. Multi-material scaffolds were fabricated by including controlled concentrations of fluorescently labeled dextran, fluorescently labeled bioactive PEG or bioactive PEG in different regions of the scaffold. The presence of the fluorescent component in specific regions of the scaffold was analyzed with fluorescent microscopy, while human dermal fibroblast cells were seeded on top of the fabricated scaffolds with selective bioactivity and phase contrast microscopy images were used to show specific localization of cells in the regions patterned with bioactive PEG. Multi-material spatial control was successfully demonstrated in features down to 500 microm. In addition, the equilibrium swelling behavior of the two biopolymers after SL fabrication was determined and used to design constructs with the specified dimensions at the swollen state. The use of multi-material SL and the relative ease of conjugating different bioactive ligands or growth factors to PEG allows for the fabrication of tailored three-dimensional constructs with specified spatially controlled bioactivity.

We have previously described the development of a microstereolithography (µSL) system using a Digital Micromirror Device (DMD) for dynamic pattern generation and an ultraviolet (UV) lamp filtered at 365 nm for crosslinking a photoreactive polymer solution. The µSL system was designed with x–y resolution of approximately 2 µm and a vertical (z) resolution of approximately 1 µm (with practical build limitations on vertical resolution of approximately 30 µm due to limitations on controlling UV penetration in z). The developed µSL system is capable of producing real three-dimensional (3D) microstructures, which can be employed in applications such as microfluidics, tissue engineering, and various functional microsystems. Many benefits will potentially be derived from producing multiple material microstructures in µSL, and one particular application area of interest is in producing multi-material microscaffolds for tissue engineering. In the present work, a method for multi-material µSL fabrication was developed using a syringe pump system to add a material to a small, removable vat designed specifically for the multi-material µSL system. Multi-material fabrication was accomplished using a material changeover process that included manually removing the vat, draining the current material, rinsing the vat, returning the vat to the system, and finally dispensing a prescribed volume in the vat using the syringe pump. Layer thicknesses of approximately 30 µm were achieved using this process. To demonstrate this system, several multi-material microstructures were produced to highlight the capability of this promising technology for fabricating 3D functional, multi-material microstructures with spatial control over placement of both material and structure.

Microstereolithography (μSL) technology can fabricate three-dimensional (3D) tissue engineered scaffolds with controlled biochemical and mechanical micro-architectures. A μSL system for tissue engineering was developed using a Digital Micromirror Device (DMD™) for dynamic pattern generation and an ultraviolet (UV) lamp filtered at 365 nm for crosslinking the photoreactive polymer solution. The μSL system was designed with x – y resolution of ∼2 μm and a vertical ( z ) resolution of ∼1 μm. To demonstrate the use of μSL in tissue engineering, poly(propylene fumarate) (PPF) was synthesized with a molecular weight of ∼1200 Da. The viscosity of the PPF was reduced to ∼150 cP (at 50 °C) by mixing with diethyl fumarate (DEF) in the ratio of 7:3 (w/w). Finally, ∼2% (w/w) of bis(2,4,6-trimethylbenzoyl) phenylphosphine oxide (BAPO) was added to the solution to serve as a photoinitiator. Cure depth experiments were performed to determine the curing characteristics of the synthesized PPF, and the resulting system and prepolymer were used to construct a 3D porous scaffold with interconnected pores of ∼100 μm. Scanning electron microscopy (SEM), and micro-computed tomography (μCT) images of the micro-architecture illustrate that the developed μSL system is a promising technology for producing biodegradable and biocompatible 3D micro-scaffolds with fully interconnected pores.

Recently, a multiple-material stereolithography (MMSL) system was introduced, which included the novel feature of stacking different photocurable resins to produce a multiple-material part. This process is capable of fabricating intricately detailed parts with smooth surface finish and internal structures of various colors. However, the MMSL system requires a washing process when switching materials, and this additional step increases the fabrication time and also introduces deformations in the build structure as registration errors accumulate. Consequently, reducing the number of material changeovers in this process is a priority, and the minimum number of changeovers is imposed in part by the sweep interference between layers of different materials. Fortunately, the use of low-viscosity resins permits possible fabrication without sweeping. As a result, multiple layers of one material can be continuously built without changing resins, and subsequently, a different low-viscosity material can be added without resulting in sweep obstruction with the original layers. In this paper, a stacking simulation, which determines the maximum number of layers possible to be continuously built between material changeovers, is described. This paper presents a novel interference-detection algorithm, which identifies interference by inspecting the overlap between loop segments. In addition, the algorithm successfully manages the triangulation errors that occur at a curved surface when two materials are adjacent within a layer. Finally, several practical examples are shown to verify the algorithm and provide compelling evidence that the proposed algorithm is effective and applicable in MMSL.

A statistical design of experiments (DOE) approach was used to determine if specific build orientation parameters impacted mechanical strength of stereolithography (SL) fabricated parts. A single platform (25.4 × 25.4-cm cross-section) on the 3D Systems Viper si2 SL machine was designed to hold 18 ASTM D-638 type I samples manufactured in different orientations. The DOE tested three factors: axis, layout, and position. Samples were fabricated parallel with the x-axis or y-axis, or 45° to both axes (called axes 1, 2, and 3, respectively). For each axis, samples were fabricated either flat or on an edge relative to the x–y plane (called layouts 1 and 2, respectively). Three samples were manufactured for each layout and axis combination, and the samples were labeled as positions 1, 2, or 3 depending on the distance from the center of the platform with position 1 being the closest to the center. The results from the statistical analyses showed that axis and position had no significant effect on ultimate tensile stress (UTS) or modulus of elasticity in tension (E). However, layout (or whether a sample was built flat or on an edge) was shown to have a statistically significant effect on UTS and E (at a 95% level of confidence). The differences between average UTS and E for each of the samples built flat and on an edge were ~3.53% (43.2 versus 44.8 MPa) and ~4.59% (763.9 versus 800.7 MPa), respectively. Because of the relatively small differences in means for UTS and E, the statistical differences between layout most likely would not have been identified without performing the multifactor analysis of variance. Furthermore, layout was the only factor that tested different orientations of build layers (or layer-to-layer interfaces) with respect to the sample part, and thus, it appears that the orientation of the build layer (layer-to-layer interfaces) with respect to the fabricated part has a significant effect on the resulting mechanical properties. This study represents one of many to follow that is using statistical analyses to identify and classify important fabrication parameters on mechanical properties for layer-manufactured parts. Although SL is the focus of this work, the techniques developed and presented here can be applied to any layered manufacturing technology producing any ASTM-type specimen with any particular material.

PurposeThe paper's aim is to explore a method using light absorption for improving manufacturing of complex, three‐dimensional (3D) micro‐parts with a previously developed dynamic mask projection microstereolithography (MSL) system. A common issue with stereolithography systems and especially important in MSL is uncontrolled penetration of the ultraviolet light source into the photocrosslinkable resin when fabricating down‐facing surfaces. To accurately fabricate complex 3D parts with down‐facing surfaces, a chemical light absorber, Tinuvin 327™ was mixed in different concentrations into an acrylate‐based photocurable resin, and the solutions were tested for cure depths and successful micro‐part fabrication.Design/methodology/approachTinuvin 327 was selected as the light absorber based on its high absorption characteristics (∼0.4) at 365 nm (the filtered light wavelength used in the MSL system). Four concentrations of Tinuvin 327 in resin were used (0.00, 0.05, 0.10, and 0.15 percent (w/w)), and cure depth experiments were performed. To investigate the effects of different concentrations of Tinuvin 327 on complex 3D microstructure fabrication, several microstructures with overhanging features such as a fan and spring were fabricated.FindingsResults showed that higher concentrations of Tinuvin 327 reduced penetration depths and thus cure depths. For the resin with 0.15 percent (w/w) of the Tinuvin 327, a cure depth of ∼30 μm was achieved as compared to ∼200 μm without the light absorber. The four resin solutions were used to fabricate complex 3D microstructures, and different concentrations of Tinuvin 327 at a given irradiance and exposure energy were required for successful fabrication depending on the geometry of the micro‐part (concentrations of 0.05 and 0.1 percent (w/w) provided the most accurate builds for the fan and spring, respectively).Research limitations/implicationsAlthough two different concentrations of light absorber in solution were required to demonstrate successful fabrication for two different micro‐part geometries (a fan and spring), the experiments were performed using a single irradiance and exposure energy. A single solution with the light absorber could have possibly been used to fabricate these micro‐parts by varying irradiance and/or exposure energy, although the effects of varying these parameters on geometric accuracy, mechanical strength, overall manufacturing time, and other variables were not explored.Originality/valueThis work systematically investigated 3D microstructure fabrication using different concentrations of a light absorber in solution, and demonstrated that different light absorption characteristics were required for different down‐facing micro‐features.

An advantage of electron beam melting (EBM) additive manufacturing technology is the ability to process high-melting temperature, refractory, and/or reactive materials. This research focused on the processing of high-purity niobium precursor powder using EBM technology primarily for the freeform design and fabrication of next-generation superconducting radiofrequency (SRF) cavities. SRF accelerating cavities have been used in particle accelerators for over 35 years and are used in today’s leading applications in high-energy and nuclear physics. Procedures were developed and employed in this research to successfully fabricate high-density niobium parts (>99 % relative density) with a thermal conductivity of ~50 W/m-K that were evaluated mechanically (140 ± 14 MPa yield strength and 225 ± 11 MPa ultimate tensile strength) and compared to wrought reactor-grade niobium (135 ± 17 MPa yield strength and 205 ± 17 MPa ultimate tensile strength). Re-engineered SRF cavities were successfully fabricated whose complex design was intended to overcome nonuniform Lorentz forces during operation. The fabrication of niobium using EBM suggests that similar procedures from this research can be applied to successfully fabricate other refractory materials such as niobium alloys as well as highly conductive materials such as copper.

Direct Metal Laser Sintering (DMLS) and Electron Beam Melting (EBM) 3D printing technologies were utilized to create lightweight, optical grade mirrors out of AlSi10Mg aluminum and Ti6Al4V titanium alloys at the University of Arizona in Tucson. The mirror prototypes were polished to meet the λ/20 RMS and λ/4 P-V surface figure requirements. The intent of this project was to design topologically optimized mirrors that had a high specific stiffness and low surface displacement. Two models were designed using Altair Inspire software, and the mirrors had to endure the polishing process with the necessary stiffness to eliminate print-through. Mitigating porosity of the 3D printed mirror blanks was a challenge in the face of reconciling new printing technologies with traditional optical polishing methods. The prototypes underwent Hot Isostatic Press (HIP) and heat treatment to improve density, eliminate porosity, and relieve internal stresses. Metal 3D printing allows for nearly unlimited topological constraints on design and virtually eliminates the need for a machine shop when creating an optical quality mirror. This research can lead to an increase in mirror mounting support complexity in the manufacturing of lightweight mirrors and improve overall process efficiency. The project aspired to have many future applications of light weighted 3D printed mirrors, such as spaceflight. This paper covers the design/fab/polish/test of 3D printed mirrors, thermal/structural finite element analysis, and results.

Ohmic curing was utilized as a method to improve the conductivity of three-dimensional (3D) interconnects printed from silver-loaded conductive inks and pastes. The goal was to increase conductivity of the conductive path without inducing damage to the substrate. The 3D via/interconnect structure was routed within 3D polymeric substrates and had external and internal sections. The 3D structures were created by the additive manufacturing (AM) process of stereolithography (SL) and were designed to replicate manufacturing situations which are common in the fabrication of 3D structural electronics that involve a combination of AM and direct write (DW) processing steps. The photocurable resins the 3D substrates were made of possessed glass transition temperatures of 75 °C and 42 °C meaning that a nonthermal method to increase the conductivity of the printed traces was needed as the conductive inks tested in this study required oven cure temperatures greater than 100 °C to perform properly. Ohmic curing was shown to decrease the measured resistance of the via/interconnect structure without harming the substrate. Substrate damage was observed on thermally cured samples and was characterized by discoloration and scaling of the substrate. Resistance measurements of the via/interconnect structures revealed samples cured by the ohmic curing process performed equal or better than samples subjected to thermal curing. The work presented here demonstrates a method to overcome the thermal cure temperature limitations of polymeric substrates imposed on the processing parameters of conductive inks during the fabrication of 3D structural electronics and presents an example of overcoming a manufacturing process problem associated with this emerging technology. An ink selection process involving characterization of the compatibility of inks with the substrate material and the use of different inks for the via and interconnect sections was also discussed.

Fused deposition modeling (FDM) technology, one of the most commonly used by 3D printers, builds parts layer-by-layer by heating and extruding thermoplastic filament. However, building failures such as nozzle clogging, substrate deformation, etc. often occur when using FDM systems. All of these failures are unpredictable and undetectable, resulting in lost time and money. The present research studies a methodology to detect the material deposition status to solve this crux of FDM 3D printing by sensing the inner pressure change of the liquefied material. The paper hypothesized that the change in deposition status of the FDM system affects the current supplied to the feeding motor in the extrusion head due to a chain reaction. This was corroborated by experiments which investigated how supplied current reacts when an unexpected substance invades the deposition area during a build.

Exploiting nanostructured materials’ characteristics and properties in stereolithography (SL) may open new markets for unique rapidly manufactured functional devices. Controlled amounts of multi-walled carbon nanotubes (MWCNTs) were successfully dispersed in SL epoxy-based resins and complex three-dimensional (3D) parts were successfully fabricated by means of a modified SL setup. The effect of the nanosized filler was evaluated by means of mechanical testing. Small concentrations of MWCNTs resulted in significant effects on the physical properties of the polymerized resin. A MWCNT concentration of 0.05% (w/v) increased the ultimate tensile stress and fracture stress an average of 17% and 37%, respectively. Increasing the MWCNT concentration to 0.5% (w/v) enhanced the integrity of the nanocomposite samples over much wider operating temperatures. Sample parts were characterized by scanning and transmission electron microscopy to measure the impact of this particular nanomaterial on the morphology of the nanocomposite samples and results showed affinity between the constituents and identified buckled nanotubes that illustrated strong interfacial bonding. These improved physical properties may provide opportunities for using nanocomposite SL resins in end-use applications. Varying types and concentrations of nanomaterials can be used to tailor existing SL resins for particular applications.

Purpose – The present research investigates tailoring the physical properties of stereolithography (SL) epoxy‐based resins by dispersing controlled small amounts of multi‐walled carbon nanotubes (MWCNTs) directly in SL resins prior to layered manufacturing.Design/methodology/approach – A modified 3D Systems 250/50 SL multi‐material machine was used where the machine was equipped with a solid‐state (355 nm) laser, unique ∼ 500 ml vat, overfill drain vat design that continuously flowed resin into the vat via a peristaltic pump, and 8.89 by 8.89 cm2 platform. The vat did not include a recoating system. Pumping the composite resin assisted in maintaining the MWCNTs dispersed over long periods of time (with MWCNT settling times on the order of one week). The research approach required developing a method for dispersing the MWCNTs in SL resin, determining new SL build parameters for the modified resin and SL machine, and building and testing tensile specimens.Findings – Mechanical mixing and ultrasonic dispersi...

Stereolithography (SL) was used to fabricate complex 3-D poly(ethylene glycol) (PEG) hydrogels. Photopolymerization experiments were performed to characterize the solutions for use in SL, where the crosslinked depth (or hydrogel thickness) was measured at different laser energies and photoinitiator (PI) concentrations for two concentrations of PEG-dimethacrylate in solution (20% and 30% (w/v)). Hydrogel thickness was a strong function of PEG concentration, PI type and concentration, and energy dosage, and these results were utilized to successfully fabricate complex hydrogel structures using SL, including structures with internal channels of various orientations and multi-material structures. Additionally, human dermal fibroblasts were encapsulated in bioactive PEG photocrosslinked in SL. Cell viability was at least 87% at 2 and 24 h following fabrication. The results presented here indicate that the use of SL and photocrosslinkable biomaterials, such as photocrosslinkable PEG, appears feasible for fabricating complex bioactive scaffolds with living cells for a variety of important tissue engineering applications.

PurposeThis paper presents a novel mesoscale RF (mRF) relay that integrates advanced high resolution stereolithography (SL) and micro wire electro discharge machining (μEDM) technologies. Methods and infrastructure for reliable batch assembly of electromechanical actuators and structural parts less than 5 mm3 in volume are described. Switches made using these techniques are expected to have greater power handling capability relative to current micro RF relay products.Design/methodology/approachThe conjecture is that the integration of SL and similar rapid additive manufacturing with other mesofabrication technologies can yield innovative miniature products with novel capabilities. A series of mRF prototypes consisting of a contact mechanism and actuator with return spring were fabricated assembled, inspected, and characterized for electromechanical performance. Characterization results led to specific conclusions regarding capabilities of the mRF product, and the integrated manufacturing technique.FindingsThe microassembly apparatus and epoxy‐based fastening system led to durable prototypes within 4 h (excluding a 16‐24 h cure cycle). Relay stroke ranged from 560 to 1,650 μm indicating a relative assembly accuracy of 90 percent. Prototypes demonstrated insertion loss of 1.3 dB at 100 MHz and isolation of better than 30 dB through 300 MHz.Research limitations/implicationsResults indicated that fully functional and robust mesoscale relays are possible using integrated manufacturing with SL. However, prototypes exhibited high contact resistance and lacked assembly precision in the context of contact mechanism stroke. Opportunities exist to reduce contact resistance and switching time.Practical implicationsThe research provides a practical new product application for integrated mesoscale rapid manufacturing.Originality/valueThis work represents one of the first examples of a mesoscale relay rapidly manufactured with a combination of μEDM and SL components.

PurposeIn an effort to directly manufacture devices with embedded complex and three‐dimensional (3D) micro‐channels on the order of microns to millimeters, issues associated with micro‐fabrication using current commercially available line‐scan stereolithography (SL) technology were investigated.Design/methodology/approachPractical issues associated with the successful fabrication of embedded micro‐channels were divided into software part preparation, part manufacture, and post‐cleaning with emphasis on channel geometry, size, and orientation for successful micro‐fabrication. Accurate representation of intended geometries was investigated during conversion from CAD to STL and STL to machine build file, and fabricated vertical and horizontal micro‐channels were inspected. Additional build issues investigated included accurate spatial registration of the build platform, building without base support, and Z‐stage position accuracy during the build.FindingsFor successful fabrication of micro‐channels using current technology, it is imperative to inspect the conversion process from CAD to STL and STL to machine build file. Inaccuracies in micro‐channel representation can arise at different stages of part preparation, although newer software versions appear to improve representation of micro‐geometries. Square channel cross‐sections are most easily sliced and vertical channels are most easily stacked together for layered manufacturing. While building, a means should be developed for building without base and internal supports, providing feedback on Z‐stage position, and having the capability for cleaning the micro‐channels.Research limitations/implicationsThis research demonstrates that commercial SL technology is capable of accurately fabricating embedded vertical square cross‐section micro‐channels on the order of 100 μm (with reasonable advancements to smaller scales on the order of 10 μm achievable). Additional practical limitations exist on other channel geometries and orientations. The research used a single resin and additional material resins should be explored for improved micro‐fabrication characteristics.Practical implicationsPractical issues associated with micro‐fabrication of embedded channels with appropriate solutions using available SL technology were provided. It is expected that these solutions will enable unique applications of micro‐channel fabrication for micro‐fluidic and other devices.Originality/valueThis work represents an original investigation of the capabilities of current line‐scan SL technology for fabricating embedded micro‐channels, and the solutions provide the means for applying this technology in micro‐fabrication.

Today, the use of material extrusion processes, like fused deposition modeling (FDM), in aerospace, biomedical science, and other industries, is gaining popularity because of the access to production-grade thermoplastic polymer materials. This paper focuses on how modifying process parameters such as build orientation, raster angle (RA), contour width (CW), raster width (RW), and raster-to-raster air gap (RRAG) can improve ultimate tensile strength (UTS), Young's modulus, and tensile strain. This was assessed using three methods: default, Insight revision, and visual feedback. On average, parameter modification through the visual feedback method improved UTS in all orientations, 16% in XYZ, 7% in XZY, and 22% in ZXY.

The layer-by-layer building of monolithic, 3D metal components from selectively melted powder layers using laser or electron beams is a novel form of 3D printing or additive manufacturing. Microstructures created in these 3D products can involve novel, directional solidification structures which can include crystallographically oriented grains containing columnar arrays of precipitates characteristic of a microstructural architecture. These microstructural architectures are advantageously rendered in 3D image constructions involving light optical microscopy and scanning and transmission electron microscopy observations. Microstructural evolution can also be effectively examined through 3D image sequences which, along with x-ray diffraction (XRD) analysis in the x-y and x-z planes, can effectively characterize related crystallographic/texture variances. This paper compares 3D microstructural architectures in Co-base and Ni-base superalloys, columnar martensitic grain structures in 17–4 PH alloy, and columnar copper oxides and dislocation arrays in copper.

In recent years, additive manufacturing (AM) or rapid prototyping (RP) technologies, initially developed to create prototypes prior to production for the automotive, aerospace, and other industries, have found applications in tissue engineering (TE) and their use is growing rapidly. RP technologies are increasingly demonstrating the potential for fabricating biocompatible 3D structures with precise control of the micro- and macro-scale characteristics. Several comprehensive reviews on the use of RP technologies, also known as solid freeform fabrication, Additive Manufacturing, direct digital manufacturing, and other names, have been published recently [1–4].