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In this investigation, the optimization of mechanical properties with thermal post-processing treatments was analyzed across a wide range of variants. A major aspect of additive manufacturing is the correlation between heat treatments and the effects on the mechanical properties and microstructure of the printed materials. Therefore, the present paper describes a comprehensive overview of post-process heat treatments for Laser Powder Bed Fusion fabricated AlSi10Mg alloy consisting of stress relief anneals at 190 C and 285 C for 2 h, hot isostatic pressing at 515 C for 3 h, hot isostatic pressing + T6 treatment for 6 h, and final aging of each of these conditions at 177 C for up to 1000 h. This has resulted in 40 experimental variants: 20 in the vertical and 20 in the horizontal tensile direction. After tensile testing, the resulting mechanical properties (ultimate tensile strength, yield strength, and elongation) and stress–strain curves are analyzed for comparison between all variants. Ultra-fine cellular, micro dendritic structures (0.6–1.2 μm) along with melt-band structures dominated the asbuilt and stress relief anneal conditions. In contrast, hot isostatic pressing and hot isostatic pressing + T6 conditions were dominated by ~10 μm, equiaxed, recrystallized grain structures and pseudo-eutectic silicon particles with varying sizes and size distributions. Microhardness and fractography results also corresponded to their specific heat treatment and microstructure. The comparison and correlation of the heat treatments are presented to help advance the selection of design strategies for high performance applications.

Laser-assisted gas nitriding of selective Ti-6Al-4 V surfaces has been achieved during laser powder bed fusion fabrication by exchanging the argon build gas environment with nitrogen. Systematic variation of processing parameters allowed microdendritic TiN surface coatings to be formed having thicknesses ranging from a few tens of microns to several hundred microns, with TiN dendrite microstructure volume fractions ranging from 0.6 to 0.75; and corresponding Vickers microindentation hardness values ranging from ∼ 7.5 GPa–9.5 GPa. Embedded TiN hard layers ranging from 50 μm to 150 μm thick were also fabricated in the laser-beam additively manufactured Ti-6Al-4 V alloy producing prototype, hybrid, planar composites having alternating, ductile Ti-6Al-4 V layers with a hardness of ∼ 4.5 GPa and a stiff, TiN layer with a hardness of ∼8.5 GPa. The results demonstrate prospects for fabricating novel, additively manufactured components having selective, hard, wear and corrosion resistant coatings along with periodic, planar or complex metal matrix composite regimes exhibiting superior toughness and related mechanical properties.

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.

This research explores the prospect of fabricating a face-centered cubic (fcc) Ni-base alloy cladding (Inconel 690) on an fcc Fe-base alloy (316 L stainless-steel) having improved mechanical properties and reduced sensitivity to corrosion through grain boundary and microstructure engineering concepts enabled by additive manufacturing (AM) utilizing electron-beam powder bed fusion (EPBF). The unique solidification and associated constitutional supercooling phenomena characteristic of EPBF promotes [100] textured and extended columnar grains having lower energy grain boundaries as opposed to random, high-angle grain boundaries, but no coherent {111} twin boundaries characteristic of conventional thermo-mechanically processed fcc metals and alloys, including Inconel 690 and 316 L stainless-steel. In addition to [100] textured grains, columnar grains were produced by EPBF fabrication of Inconel 690 claddings on 316 L stainless-steel substrates. Also, irregular 2–3 μm diameter, low energy subgrains were formed along with dislocation densities varying from 108 to 109 cm−2, and a homogeneous distribution of Cr23C6 precipitates. Precipitates were formed within the grains (with ∼3 μm interparticle spacing), but not in the subgrain or columnar grain boundaries. These inclusive, hierarchical microstructures produced a tensile yield strength of 0.527 GPa, elongation of 21%, and Vickers microindentation hardness of 2.33 GPa for the Inconel 690 cladding in contrast to a tensile yield strength of 0.327 GPa, elongation of 53%, and Vickers microindentation hardness of 1.78 GPa, respectively for the wrought 316 L stainless-steel substrate. Aging of both the Inconel 690 cladding and the 316 L stainless-steel substrate at 685 °C for 50 h precipitated Cr23C6 carbides in the Inconel 690 columnar grain boundaries, but not in the low-angle (and low energy) subgrain boundaries. In contrast, Cr23C6 carbides precipitated in the 316 L stainless-steel grain boundaries, but not in the low energy coherent {111} twin boundaries. Consequently, the Inconel 690 subgrain boundaries essentially serve as surrogates for coherent twin boundaries with regard to avoiding carbide precipitation and corrosion sensitization.

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.

Inconel 718 alloy fabricated by selective laser melting (SLM) (or laser powder-bed fusion (LPBF)) has been post-process heat-treated by stress-relief anneal at 1065 &deg, C, stress-relief anneal (1065 &deg, C) + solution treatment (at 720 &deg, C) + aging (at 620 &deg, C), hot isostatic pressing (HIP) (at 1120&ndash, 1200 &deg, stress-relief anneal + HIP, and stress-relief anneal + HIP + solution treatment + aging. Microstructure analysis utilizing optical metallography revealed primarily equiaxed grain structures (having average diameters ranging from ~30 to 49 microns) containing annealing twins, and a high concentration of carbide precipitates in all HIP-related treatments in the grain boundaries and intragrain regions. However, no precipitates nucleated on the {111} coherent annealing twin boundaries because of their very low interfacial free energy in contrast to regular grain boundaries. The mechanical properties for the as-fabricated Inconel 718 exhibited a yield stress of 0.64 GPa, UTS of 0.98 GPa, and elongation of 26%. Following stress-relief anneal at 1065 &deg, C, the yield stress dropped to 0.60 GPa, while the elongation increased to 43%. The associated grain structure was an irregular, somewhat elongated, recrystallized structure. This structure was preserved at a stress anneal at 1065 &deg, C + solution treatment + aging, but grain boundary and intragrain precipitation resulted in a doubling of the yield stress to 1.3 GPa and a reduced elongation of 12.6%. The results of HIP-related post-process heat treatments involving temperatures above 1060 &deg, C demonstrated that the yield stress and elongations could be varied from 1.07 to 1.17 GPa and 11.4% to 19%, respectively. Corresponding Rockwell C-scale hardness values also varied from 33 for the as-fabricated Inconel 718 to 53 for simple post-process HIP treatment at 1163 &deg, C.

During solidification of many so-called high-performance engineering alloys, such as 6000 and 7000 series aluminum alloys, which are also unweldable autogenously, volumetric solidification shrinkage and thermal contraction produces voids and cracks. During additive manufacturing processing, these defects can span the length of columnar grains, as well as intergranular regions. In this research, laser powder bed fusion (LPBF) of aluminum alloy (AA) 6061 used powder bed heating at 500 °C in combination with other experimentally determined processing parameters to produce crack-free components. In addition, melt-pool banding, which is a normal solidification feature in LPBF, was eliminated, illustrating solidification process modification as a consequence of powder bed heating. Corresponding microindentation hardness and tensile testing of the as-fabricated AA6061 components indicated an average Vickers hardness of HV 54, and tensile yield, ultimate strength, and elongation values of 60 MPa, 130 MPa, and 15%, respectively. These mechanical properties and those of heat treated parts showed values comparable to annealed and T6 heat treated wrought products, respectively. X-ray diffraction and optical microscopy revealed columnar grain growth in the build direction with the as-fabricated, powder-bed heated product microstructure characterized by [100] textured, elongated grains (∼ 25 μm wide by 400 μm in length), and both intragranular and intergranular, noncoherent Al-Si-O precipitates which did not contribute significantly to the mechanical properties. The results of this study are indicative that powder bed heating may be used to assist with successful fabrication of AA6061 and other alloy systems susceptible to additive manufacturing solidification cracking.

The ability to fabricate or join components of 316 L austenitic stainless steel using additive manufacturing (AM) processes such as laser and electron beam melting (EBM®) offers several advantages including enhanced part complexity, narrow or absent heat affected zones, increased part precision, avoidance of filler materials (such as traditional welds), and the ability to create metallurgically sound bonds. These attributes can contribute to improved mechanical properties of the fabricated components and component repair in nuclear, aerospace, and chemical industries. In the present work, we report that austenitic 316 L stainless steel additively manufactured by EBM exhibits a 76% increase in the yield strength and a corresponding increase of 29% in the ultimate tensile strength in contrast to the wrought substrate and commercial forged 316 L stainless steel. The EBM clad 316 L stainless steel elongation was 36%. The wrought substrate equiaxed grain size was ∼30 μm in contrast to elongated, columnar grains ∼0.1 mm wide and >1 mm in length for the EBM cladding. Transmission Electron Microscopy (TEM) analysis revealed that these columnar grains, which exhibited very straight, and presumably special grain boundaries having a very high (100) texture, contained a variety of sub-grain microstructures consisting of low-angle sub-grain boundaries containing dislocation tangles and stacking-fault arrays, and homogeneously distributed Cr23C6 carbide precipitates, with no preferential carbide precipitation on either the straight, special columnar grain boundaries, or the very low-angle sub-grain boundaries. This observation and the formation of hierarchical microstructures which produce high strength and possibly corrosion resistance as a consequence of the absence of grain boundary carbide precipitation, illustrate the prospects for AM as a novel concept for achieving grain boundary engineering to promote high-strength and corrosion resistant alloys for high-temperature, corrosive environments, including elevated temperature nuclear reactor applications.

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.

An essentially fully acicular alpha-prime martensite within an equiaxed grain structure was produced in an Electron Beam Melting (EBM)-fabricated Ti-6Al-2Sn-4Zr-2Mo (Ti6242) alloy using two different Arcam EBM machines: An A2X system employing tungsten filament thermionic electron emission, and a Q20 system employing LaB6 thermionic electron emission. Post-process Hot Isostatic Pressing (HIP) treatment for 2 h at 850, 950, and 1050 &deg, C resulted in grain refinement and equiaxed grain growth along with alpha-prime martensite decomposition to form an intragranular mixture of acicular martensite and alpha at 850 &deg, C, and acicular alpha phase at 950 and 150 &deg, C, often exhibiting a Widmanst&auml, tten (basketweave) structure. The corresponding tensile yield stress and ultimate tensile strength (UTS) associated with the grain growth and acicular alpha evolution decreased from ~1 and ~1.1 GPa, respectively, for the as-fabricated Ti6242 alloy to ~0.8 and 0.9 GPa, respectively, for HIP at 1050 &deg, C. The optimum elongation of ~15&ndash, 16% occurred for HIP at 850 &deg, C, for both EBM systems. Because of the interactive role played by equiaxed grain growth and the intragrain, acicular alpha microstructures, the hardness varied only by ~7% between 41 and 38 HRC.

In the last decade, research has focused on 3D printing for not only creating conceptual models but functional end-use products as well. As patents for 3D printing expire, new low cost desktop systems are being adopted more widely. This trend is leading to products being fabricated locally and improving supply chain logistics. However, currently low cost 3D printing is limited in the number of materials used simultaneously in fabrication and consequently is confined to fabricating enclosures and conceptual models. For additively manufactured end-use products to be useful, supplementary features and functionalities will need to be incorporated in to the final structures in terms of electronic, electromechanical, electromagnetic, thermodynamic, and optical content. The University of Texas at El Paso has recently been reporting on embedding electronic components and electrical interconnect into 3D printed structures either by interrupting the process or by inserting the additional content after the structure has been built. However, only until recently and with an investment from the presidential initiative on Additive Manufacturing “America Makes” has there been a concentrated research focus on developing technology that produces multi-functionality. This presentation will describe a project in which copper wires were used to supply a short burst of energy at high voltages in order to activate electro-propulsion. Pulsed Plasma Thursters provided by Busek were demonstrated where one joule of energy was supplied at 2000 volts in order to ablate the thruster in a vacuum and provide precise micro-newton-levels of force - as required for attitude control in small and nano satellites.

After the US government declared 3D printing technology a next-generation manufacturing technology, there have been many practical studies conducted to expand 3D printing technology to manufacturing technologies, called AMERICA MAKES. In particular, the Keck Center, located at the University of Texas at El Paso, has studied techniques for easily combing the 3D stacking process with space mobility and expanded these techniques to simultaneous staking techniques for multiple materials. Additionally, it developed convergence manufacturing techniques, such as direct inking techniques, in order to produce a module structure that combines electronic circuits and components, such as CUBESET. However, in these studies, it is impossible to develop a unified system using traditional independent through simple sequencing connections. This is because there are many problems in the integration between the stacking modeling of 3D printers and post-machining, such as thermal deformations, the precision accuracy of 3D printers, and independently driven coordinate problems among process systems. Therefore, in this paper, the integration method is suggested, which combines these 3D printers and subsequent machining process systems through an Internet-based cloud. Additionally, the sequential integrated system of a 3D printer, an NC milling machine, machine vision, and direct inking are realized.

Recent efforts have concentrated on 3D printing for use not only in creating conceptual models but functional end-use products as well and the expiration of many of the additive manufacturing process patents of the 1980s has led to lower cost systems in general. The freedom of 3D printing along with the change in economics is leading to the democratization of manufacturing, where products will soon be fabricated locally and with requirements specified individually by the end user. However, currently 3D printing is limited to single material fabrication and consequently can only create mechanical structures. For additively manufactured end-use products to be relevant, additional features will need to be incorporated into the complex structures in terms of electronic, electromechanical, electromagnetic and thermal composition. Recent research has been reported of embedding electronic components and electrical interconnect into 3D printed structures either by interrupting the process or by inserting the additional content after the structure has been built. However, only until recently with an investment from the presidential initiative on manufacturing � America Makes � has there been a focused research effort on technology that produces multi-functionality with enhanced 3D printing, where additional manufacturing technologies are leveraged. This presentation will describe the development and status of the Multi3D Manufacturing System underway at the University of Texas at El Paso.

This paper is the study of a surgical instrument which directly performs MIS(Minimally Invasive surgery) on a patient, instead of a surgeon. The instrument used in robot assisted laparoscopy adopts a tendon driven mechanism so that it generates hand-like surgical motion through aperture of trocar. To create a high DOF of motion in restricted spaces, cable systems for end-effector have been organized by serial kinematic chains which can cause interference among joints sharing same axis. Also, to prevent the elongation of any cable, composited and pre-extended cables, which show nonlinear characteristics, are used in surgical instrument tendon system. As aforementioned difficulty and complexity, there are not many studies about measuring or estimating the operating force of instruments without sensors, which is needed for safety but still impossible in commercial systems. This paper derives governing a dynamic model of a coupled cable pulley structure while considering the material tensile characteristics of the cables. The derived model can estimate the operating force on end-effector as well as states of all inner pulleys without encoders. This paper proves the availability of proposed methodology with comparison of numerical analysis and the experimental test of 2 DOF serial kinematic chained cable pulley link apparatus.

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.

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.

The purpose of this paper is to evaluate the capability of five desktop additive manufacturing (AM) machines based on the ability to produce a standard component. This work also developed a model/method for evaluating and ranking AM technologies based on select criteria that can facilitate purchasing decisions. A standard part was designed and printed on each machine, and evaluated based on dimensional accuracy and surface finish. Additionally, the machines were compared based on build time for single and multiple parts as well as material consumption and unit cost. The research highlights the differences between AM units and suggests a method by which to ascertain the differences. With the rapid proliferation of desktop additive manufacturing units, a quantitative ranking system was developed to rate the units so a comparison can be made. Although the focus of the work was on desktop systems, the approach can be applied across all AM technologies.

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.

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 ...

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.

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.

Total knee replacement implants consisting of a Co-29Cr-6Mo alloy femoral component and a Ti-6Al-4V tibial component are the basis for the additive manufacturing of novel solid, mesh, and foam monoliths using electron beam melting (EBM). Ti-6Al-4V solid prototype microstructures were primarily α-phase acicular platelets while the mesh and foam structures were characterized by α(')-martensite with some residual α. The Co-29Cr-6Mo containing 0.22% C formed columnar (directional) Cr(23)C(6) carbides spaced ~2 μm in the build direction, while HIP-annealed Co-Cr alloy exhibited an intrinsic stacking fault microstructure. A log-log plot of relative stiffness versus relative density for Ti-6Al-4V and Co-29Cr-6Mo open-cellular mesh and foams resulted in a fitted line with a nearly ideal slope, n = 2.1. A stress shielding design graph constructed from these data permitted mesh and foam implant prototypes to be fabricated for compatible bone stiffness.

An organic polymer electrical interconnect is demonstrated. The ionomer mixture poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS; 1:2.5, w:w) was cast onto silk fibers from a 50:50 (v:v) ethylene glycol solution by a dip-coating process. Dynamic mechanical analysis (DMA) results show that Young’s modulus and mechanical strength are maintained during the coating process from acidic solution (pH ∼1). DMA dynamic temperature scans reveal two new thermal transitions once PEDOT:PSS is applied to the silk fiber, and they are assigned to the glass transition temperature (59 °C) and melting point (146 °C) of the ionomer pair. Electrical conductivities of 8.5 S/cm were achieved with four cycles of the dip-coating process, only 10x less than Ag-coated thread control samples. SEM imaging of the PEDOT:PSS-coated fibers show slight texturing to the fibers due to the coating, as well as significant charging in the uncoated samples when compared to PEDOT:PSS-coated samples. The conductive fibers fabricated by this process were successfully applied as electrical interconnects in flexible, fully functional 555 timer circuits stitched into fabric substrates.

Microstructures and a microstructural, columnar architecture as well as mechanical behavior of as-fabricated and processed INCONEL alloy 625 components produced by additive manufacturing using electron beam melting (EBM) of prealloyed precursor powder are examined in this study. As-fabricated and hot-isostatically pressed (“hipped”) [at 1393 K (1120 °C)] cylinders examined by optical metallography (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive (X-ray) spectrometry (EDS), and X-ray diffraction (XRD) exhibited an initial EBM-developed γ″ (bct) Ni3Nb precipitate platelet columnar architecture within columnar [200] textured γ (fcc) Ni-Cr grains aligned in the cylinder axis, parallel to the EBM build direction. Upon annealing at 1393 K (1120 °C) (hot-isostatic press (HIP)), these precipitate columns dissolve and the columnar, γ, grains recrystallized forming generally equiaxed grains (with coherent {111} annealing twins), containing NbCr2 laves precipitates. Microindentation hardnesses decreased from ~2.7 to ~2.2 GPa following hot-isostatic pressing (“hipping”), and the corresponding engineering (0.2 pct) offset yield stress decreased from 0.41 to 0.33 GPa, while the UTS increased from 0.75 to 0.77 GPa. However, the corresponding elongation increased from 44 to 69 pct for the hipped components.

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.

Intermetallic, γ-TiAl, equiaxed, small-grain (∼2 μm) structures with lamellar γ/α2-Ti3Al colonies with average spacing of 0.6 μm have been fabricated by additive manufacturing using electron beam melting (EBM) of precursor, atomized powder. The residual microindentation (Vickers) hardness (HV) averaged 4.1 GPa, corresponding to a nominal yield strength of ∼1.4 GPa (∼HV/3), and a specific yield strength of 0.37 GPa cm3 g−1 (for a density of 3.76 g cm−3), in contrast to 0.27 GPa cm3 g−1 for EBM-fabricated Ti–6Al–4V components. These results demonstrate the potential to fabricate near net shape and complex titanium aluminide products directly using EBM technology in important aerospace and automotive applications.

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.

To achieve high gain and electronic beam steering, phased array systems are commonly used. The phased array technique plays an important role in sensing and communication systems. Practical phased array system usually consists of many components including RF power feeding networks, antennas, and active parts such as phase shifters and amplifiers. Single-layer implementation of phased arrays usually leads to large system size and limited applicability as the functionality becomes more complex. Multilayer structure is useful to make the system compact. In addition, it increases the flexibility to add more functions by increasing the total structure thickness without increasing the footprint size. However, it is more challenging to design and fabricate multilayer phased array. The vertical transitions between layers require careful design to have low loss and conventional fabrication technique may not be cost effective. Additive manufacturing (AM), which enables 3D objects of arbitrary shape to be printed automatically layer by layer, is a potentially promising technique to manufacture multilayer phased array that has reduced size and cost but still possesses good electromagnetic performance.

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.

To build multimaterial objects using additive manufacturing (AM), modifications to the majority of current conventional AM processes are required. Typically, deposition can only occur on flat surfaces and motion requires three degrees of freedom (DOFs) in a Cartesian coordinate system. In this work, metal wire and mesh were successfully embedded using ultrasonic energy on curved thermoplastic structures fabricated via the material extrusion AM technology named fused deposition modeling (FDM). The direct wire embedding process was executed by installing an ultrasonic horn on a three-axis prismatic machine and fixing an FDM-built curved part on a rotary stage. Since the part was nonplanar, a need existed to accurately place metal wire along the curved surface with positions defined by Cartesian and angular coordinates. Two additional DOFs were generated by moving both the build platform and tool head, and trajectory planning allowed for synchronized motion between the two motion systems.

A multi-step dip-spin coating procedure by which synthetic vessels of virtually the entire cardiovascular system can be constructed from medical imaging data was developed to consistently and accurately fabricate silicone membranes with prescribed compliance for in vitro hemodynamic experimentation and medical device development. Experimental results showed that the three factors tested (silicone mixture viscosity, mold diameter, and number of dips in solution) each had a statistically significant effect on the resulting wall thickness of the fabricated silicone membranes. A setup was designed and constructed to test the compliance of the silicone membranes, and a prediction model showed that the most important factors for compliance were the mean pressure used to pressurize the membranes, the membrane wall thickness, and the difference in membrane diameter between the two test pressures. The manufacturing process was repeatable with a process standard deviation of 0.002753 cm for an average wall thickness of 0.063576 cm (4.33%).

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.

Additive manufacturing (AM), often called 3D printing, has received much attention recently with impressive demonstrations ranging from musical instruments, to vehicles, to housing components or even entire buildings. Although it has been argued that 3D printing could be the future of manufacturing, the potential and applicability of these methods for creating functional electronics at RF / microwave frequency remain largely unexplored.

As part of a four-week fluid mechanics laboratory, Mechanical Engineering students were challenged to design and manufacture the least restrictive flow nozzle for a standard test condition within several design constraints. The Nozzle Design Challenge (NDC) combined analysis, design, manufacturing, and experimentation. The positive student responses to the NDC were overwhelming. Formal evaluation of the NDC included the measured nozzle flow rates and the amount of time spent in the laboratory. The highest flow rate nozzle allowed substantially more flow than the nozzle with a 1-inch diameter hole used for demonstration. Every group spent more time in the laboratory than was scheduled, which may indicate high levels of motivation for the project. The examination scores covering the principles learned in this laboratory were compared to the previous semester's students who did not perform the innovation-based design and fabrication project. After blocking out the effects of GPA, the results indicate that the students who undertook the design experience performed significantly better on the examination.

The microstructures and residual hardnesses for solid components of 2-phase TiAl (Ti-48Al-2Nb-2Cr in a / o ) and Inconel 625 (Ni-19Cr-9Mo-4Nb in w / o ) fabricated by electron beam melting (EBM) were compared with a 10:1 blend of TiAl: alloy 625 pre-alloyed powders producing a complex alloy having the composition 48Ti-24Al-9Ni-8Nb-4.5Cr-4Ni (in w / o ). The blended alloy hardness (HV) reached 7.5 GPa in contrast to 1.4 GPa for the Alloy 625 and 4.0 for the 2-phase TiAl alloy. Reticulated mesh samples and stochastic foam samples prepared from the blended alloy by EBM exhibited a relative stiffness versus relative density plotted on a log-log basis consistent with other reference alloys fitted to a straight line with a slope n = 2 for ideal open cellular materials.

This project enabled the integration of ultrasonic consolidation, direct write dispensing, and material deposition technologies into a manufacturing workcell capable of fabricating advanced, integrated Naval-relevant structures. The workcell was shown to be capable of spatial composition control and complex internal geometries - including embedded electronics, thermal management, reinforcement fibers and other features - along with the resolution, scalability, repeatability, dimensional accuracy and surface finish of milling, all within an integrated Direct Digital Manufacturing (DDM) workcell. A one-year extension led to the development of a computational modeling infrastructure for ultrasonic consolidation that has revolutionized the prediction of the effects of process parameter variations on bonding, microstructure and mechanical properties of parts made using ultrasonic consolidation.

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.

This paper presents some examples of knee and hip implant components containing porous structures and fabricated in monolithic forms utilizing electron beam melting (EBM). In addition, utilizing stiffness or relative stiffness versus relative density design plots for open-cellular structures (mesh and foam components) of Ti-6Al-4V and Co-29Cr-6Mo alloy fabricated by EBM, it is demonstrated that stiffness-compatible implants can be fabricated for optimal stress shielding for bone regimes as well as bone cell ingrowth. Implications for the fabrication of patient-specific, monolithic, multifunctional orthopaedic implants using EBM are described along with microstructures and mechanical properties characteristic of both Ti-6Al-4V and Co-29Cr-6Mo alloy prototypes, including both solid and open-cellular prototypes manufactured by additive manufacturing (AM) using EBM.

Microstereolithography (microSL) technology can fabricate complex, three-dimensional (3D) microstructures, although microSL has difficulty producing macrostructures with micro-scale features. There are potentially many applications where 3D micro-features can benefit the overall function of the macrostructure. One such application involves a medical device called a coaxial phacoemulsifier where the tip of the phacoemulsifier is inserted into the eye through a relatively small incision and used to break the lens apart while removing the lens pieces and associated fluid from the eye through a small tube. In order to maintain the eye at a constant pressure, the phacoemulsifier also includes an irrigation solution that is injected into the eye during the procedure through a coaxial sleeve. It has been reported, however, that the impinging flow from the irrigation solution on the corneal endothelial cells in the inner eye can damage these cells during the procedure. As a result, a method for reducing the impinging flow velocities and the resulting shear stresses on the endothelial cells during this procedure was explored, including the design and development of a complex, 3D micro-vane within the sleeve. The micro-vane introduces swirl into the irrigation solution, producing a flow with rapidly dissipating flow velocities. Fabrication of the sleeve and fitting could not be accomplished using microSL alone, and thus, a two-part design was accomplished where a sleeve with the micro-vane was fabricated with microSL and a threaded fitting used to attach the sleeve to the phacoemulsifier was fabricated using an Objet Eden 333 rapid prototyping machine. The new combined device was tested within a water container using particle image velocimetry, and the results showed successful swirling flow with an ejection of the irrigation fluid through the micro-vane in three different radial directions corresponding to the three micro-vanes. As expected, the sleeve produced a swirling flow with rapidly dissipating streamwise flow velocities where the maximum measured streamwise flow velocities using the micro-vane were lower than those without the micro-vane by 2 mm from the tip where they remained at approximately 70% of those produced by the conventional sleeve as the flow continued to develop. It is believed that this new device will reduce damage to endothelial cells during cataract surgery and significantly improve patient outcomes from this procedure. This unique application demonstrates the utility of combining microSL with a macro rapid prototyping technology for fabricating a real macro-scale device with functional, 3D micro-scale features that would be difficult and costly to fabricate using alternative manufacturing methods.

Numerical methods have become a powerful tool to quantify hemodynamic forces in the cardiovascular system. Studying these forces enables us to understand cardiovascular disease mechanisms, as well as better evaluate and design cardiovascular medical devices. However, much work remains to validate numerical methods against experimental data. Vignon-Clementel and colleagues have shown that the boundary conditions (BCs) prescribed at the outlets of numerical domains dramatically influence the flow and pressure computational results [1]. While many in-vitro studies have implemented simple BCs to allow for acceptable validations of numerical methods, none has implemented BCs that provide physiologically realistic flows and pressures.Copyright © 2010 by ASME

PurposeTo operate a multiple material stereolithography (MMSL) system, a material build schedule is required. The purpose of this paper is to describe a scheduling and process‐planning software system developed for MMSL and designed to minimize the number of material changeovers by using low‐viscosity resins that do not require sweeping.Design/methodology/approachThis paper employs the concept of using low‐viscosity resins that do not require sweeping to minimize the number of material changeovers required in MMSL fabrication. A scheduling and process‐planning software system specific to MMSL is introduced that implements four simple rules. Two rules are used to select the material to be built in the current layer, and two rules are used to determine at which layer a material changeover is required. The schedule for the material to be built depends on the material properties stored in a user‐defined materials library. The developed algorithm produces sliced loop data for each material using the predetermined layer thickness from an input CAD model, and the four rules are applied at each layer. The algorithm then determines the build order for each material, the material‐specific number of layers to be built, and whether or not sweeping is required. Output data from the program are the scheduling and process‐planning report and the partitioned computer‐aided design models to be built before changing a material according to the process planning. Two examples of the algorithm applied to multiple material parts are provided.FindingsThe MMSL scheduling and process‐planning software system is developed using Microsoft Visual C++7.0. For verification, a simple demonstration is conducted on a two material part where the process plan could be easily determined through intuition. A more complex multiple material part is also tested that consisted of four subparts. Several cases of resin assignment are tested showing that the ultimate scheduling and process planning vary significantly depending on the material combinations and specifications. These examples demonstrate that the strategy, method, and software developed in this paper can be successfully applied to prepare for MMSL fabrication.Research limitations/implicationsAlthough the software system is demonstrated on two multiple material parts, more extensive work will be performed in the future on fabricating multiple material parts using the MMSL machine. It is expected that additional rules will be developed as additional limitations of MMSL are identified. It is also anticipated that particular emphasis will be placed on building without sweeping as well as development of advanced non‐contact recoating processes.Originality/valueAs designs incorporating multiple materials increase in the future and additive manufacturing (AM) technologies advance in both building out of multiple materials and fabricating production parts, the scheduling and process‐planning concepts presented here can be applied to virtually any AM technology.

Next generation electronics will be painted onto plastic substrates providing both functionality and physical flexibility. The corresponding manufacturing process will lead to significantly reduced cost; however the performance of the resulting circuits will not match many existing high-performance electronic circuits fabricated with traditional technology today. High performance is not always necessary, but when required, Printed Electronics may still be a viable solution. The future of Printed Electronics is bright and will eventually include sophisticated function, but until that time, a Printed Hybrid option will simultaneously provide the cost savings of printing and the high performance of silicon and printed circuit boards. An interim contribution is to use state-of-the-art silicon devices and print the supporting conductive patterns and passives on substrates for flexible systems integration. This paper describes and demonstrates a hybrid circuit technology, which can manufacture circuits more easily adapted to complex shapes and diverse sizes. Additionally, a number of printed components and devices are reviewed and a demonstration of two circuits is provided: an RF antenna and the supporting substrate design of a Field Programmable Gate Array.

A procedure for manufacturing cardiovascular system models using patient-specific data, rapid prototyping, and a multistep dip-spin coating process is presented here. Improvements to a previously developed process permitted the fabrication of flexible complex vascular replicas. The primary improvement included the development of a two-axis rotation mechanism that enabled a pseudorandom rotation of the coated mold in space, providing uniform coats. Other improvements included the use of a low viscosity (1500–2000cP) silicone solution that allowed for complete coverage of the mold, and developing a procedure for fixing defects. The dip-spin coating procedure was shown to be effective for the manufacture of compliant cardiovascular membranes, such as an arterial bypass graft with an internal flow passage and an abdominal aorta with nonuniform radial geometry, tapered diameters, bifurcations, and small branches. Results from a design of experiments comparing two dipping setups demonstrated that horizontally dipping the model produced coatings with more uniform thicknesses along the length of the model when compared to vertical dipping. For a 250-mm-long model, the difference in thickness between the top and bottom of the membrane was 0.42±0.069mm and 0.09±0.077mm for vertical and horizontal dippings, respectively. Mold diameter also affected the thickness of the membrane, with membrane thickness increasing as mold diameter decreased. Thickness data comparing locations at approximately the same height of the mold but with different diameters showed thicknesses of 2.54±0.198mm and 1.95±0.140mm for 7.85mm and 15.20mm diameters, respectively. Moreover, the differences in thickness between these locations were 0.60±0.128mm and 0.58±0.231mm for vertical and horizontal dippings, respectively; thus, membrane thickness variations occurred with mold diameter irrespective of the dipping setup. Depending on the prescribed tolerance for membrane thickness, the vertical dipping setup may be recommended for use because (1) it was easier to use since only the mold was immersed in the coating solution and no special protection of the dipping mechanism was required and (2) it produced fewer defects in the coatings since the solution always dripped from downfacing surfaces of the mold. Using this dip-spin coating procedure, patient-specific cardiovascular membranes can be manufactured and used in the development of medical devices, research requiring accurate anatomical models, and education and training.

The use of modern microstreolithography (MSL) technology gives optics developers the freedom to integrate mounting and positioning structures directly into an optical mask structure. We have created Hadamard spectrometer masks with increments of 150 μm and less using the Sony SCS-6000 microstereolithography apparatus (MSLA). Due to laser over cure and other parameters, adjustments were made iteration by iteration until appropriate mask tolerances were met. A mounting structure was integrated with the mask for testing and application. At the computer aided design (CAD) model level, the mounting geometry can be adjusted to fit any specific mounting apparatus. By using the MSLA, features as small as 75 μm and larger than 300 mm can be created in the same build. Additionally, the conceptual design of an entire positioning system constructed using layer additive MSLA microfabrication is underway. This positioning system may be built as an integrated assembly, encapsulating necessary components. Optical characterization results are presented.

Research in rapid prototyping of high-density circuitry (RPHDC) involves integrating direct write (DW) conductive ink dispensing technology with stereolithography (SL) to manufacture smart structural members with integrated three-dimensional electronics. A significant challenge in this effort is realizing practical three-dimensional interconnect for discrete electronic packages encapsulated within a SL matrix. This paper presents research into SL-encapsulated DW three-dimensional interconnect. Results suggest that robust three-dimensional electronics are possible within an integrated DWSL structure. A power supply circuit is demonstrated that converts a 28 VDC input to a 5 VDC output with electromagnetic interference filtering capability. Additional work is necessary to improve resistance of DW interconnect, and planarity of device planes. Strategies for improving resistance of DW ink through localized laser curing and thermal curing are discussed in addition to the encapsulation performance of advanced SL resins. Future work in this area may impact the widely accepted MCM-L and MCM-C multichip module technologies.

Designing complex internal cooling passages is extremely difficult without detailed information about the flow behavior due to the presence of separated flow zones and strong secondary flows. This paper describes a new approach to designing internal flow passages called Rapid Iterative Design Using Experimentation (RIDUE). RIDUE utilizes rapid prototyping (RP) manufacturing to quickly build an accurate model of a complex internal flow passage and magnetic resonance velocimetry (MRV) to measure the full three dimensional velocity field. Because both techniques offer very fast turnaround, it is feasible to conduct iterative design with a cycle time of 1–2 days. RIDUE is demonstrated using a generic turbine blade internal cooling passage with four serpentine channels. Two channels have rectangular cross-section and two are square. In each channel, two of the four walls have ribs (also called turbulators) angled at 45 degrees to the main flow direction. Two models based on the generic geometry are studied, each with different turbulator cross-sections, one square and one rounded. Both models were built using a stereo lithography apparatus. MRV provided three-component velocity vectors for flow at a Reynolds number of 10,000 based on the hydraulic diameter of the first passage. Sample vector fields are presented to illustrate the detail with which the flow can be investigated. Although little difference is seen in the flows between the two models, it is demonstrated that through its use of RP processes and the MRV measurement technique, RIDUE is a viable technique for modern internal passage design.Copyright © 2003 by ASME