ASME Conference Presenter Attendance Policy and Archival Proceedings

2018;():V001T00A001. doi:10.1115/MSEC2018-NS1.

This online compilation of papers from the ASME 2018 13th International Manufacturing Science and Engineering Conference (MSEC2018) represents the archival version of the Conference Proceedings. According to ASME’s conference presenter attendance policy, if a paper is not presented at the Conference by an author of the paper, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.

Commentary by Dr. Valentin Fuster

Additive Manufacturing: Advances in 3D Printing of Tissue Scaffolds

2018;():V001T01A001. doi:10.1115/MSEC2018-6543.

Fabrication of biomimetic cell microenvironment closely resembling the native tissues is critical for regenerative medicine. It remains challenging to create a 3D fibrous microstructure of extracellular matrix on a clinical-relevant scale. In this paper we presented a novel divergence electrospinning strategy for 3D nanofiber structure fabrication. The electrospinning induced by a double-bevel collector was able to quickly generate a multi-layer scaffold, comprised of uniaxially aligned nanofibers, at centimeter scales in all dimensions. The results showed that the internal nanofiber distribution was largely determined by the inclination angle of the axisymmetric bevels of the collector. A larger inclination angle alleviated the polarization of the fiber distribution due to a lower electric force gradient between the spinneret and the bevel surfaces. This technique can be applied in engineering of musculoskeletal soft tissues in which fibrous cytoskeletal organization is critical.

Commentary by Dr. Valentin Fuster
2018;():V001T01A002. doi:10.1115/MSEC2018-6567.

3D additive manufacturing, namely 3D printing, has been increasingly needed in the fabrication of biological materials and devices. Compared to traditional fabrication, direct 3D digital transformation simplifies the manufacturing process and enhances capability in geometric fabrication. In this paper, we demonstrated a rapid and low-cost 3D printing approach for “lego” assembly of micro-structured parts as an electro-transfection device. Electro-transfection is an essential equipment for engineering and regulating cell biological functions. Nevertheless, existing platforms are mainly employed to monolayer cell suspensions in vitro, which showed more failures for translating into tissues and in vivo systems constituted by 3D cells. The knowledge regarding the three-dimensional electric transport and distribution in a tissue microenvironment is lacking. In order to bridge the gap, we assembled PDMS parts molded from 3D-printed molds as the 3D-cell culture chamber, which connects arrays of perfusion channels and electrodes. Such design allows spatial and temporal control of electric field uniformly across a large volume of 3D cells (105∼106 cells). Most importantly, multi-dimensional electric frequency scanning creates local oscillation, which can enhance mass transport and electroporation for improving transfection efficiency. The COMSOL electrostatic simulation was employed for proof of concept of 3D electric field distribution and transport in this “lego” assembled electro-transfection device, which builds the foundation for engineering 3D-cultured cells and tissues.

Commentary by Dr. Valentin Fuster

Additive Manufacturing: Advances in Additive Manufacturing Process Design and Part Performance

2018;():V001T01A003. doi:10.1115/MSEC2018-6389.

The popularity of additive manufacturing for producing porous bio-ceramics using vat photopolymerization in the recent years has gained a lot of impetus due to its high resolution and low surface roughness. In this study, a commercial vat polymerization printer (Nobel Superfine, XYZprinting) was used to create green bodies using a ceramic suspension consisting of 10 vol.% of alumina particles in a photopolymerizable resin. Four different sizes of cubical green bodies were printed out. They were subjected to thermal processing which included de-binding to get rid of the polymer and thereafter sintering for joining of the ceramic particles. The porosity percentage of the four different sizes were measured and compared. The lowest porosity was observed in the smallest cubes (5 mm). It was found to be 43.3%. There was an increase in the porosity of the sintered parts for the larger cubes (10, 15 and 20 mm). However, the difference in the porosity among these sizes was not significant and ranged from 61.5% to 65.2%. The compressive testing of the samples showed that the strength of the 5-mm cube was the maximum among all samples and the compressive strength decreased as the size of the samples increased. These ceramic materials of various densities are of great interest for biomedical applications.

Commentary by Dr. Valentin Fuster
2018;():V001T01A004. doi:10.1115/MSEC2018-6406.

Additive manufacturing (AM) processes allow for complex geometries to be developed in a cost- and time-efficient manner in small-scale productions. The unique functionality of AM offers an ideal collaboration between specific applications of human variability and thermal management. This research investigates the intersection of AM, human variability and thermal management in the development of a military helmet heat exchanger. A primary aim of this research was to establish the effectiveness of AM components in thermal applications based on material composition. Using additively manufactured heat pipe holders, the thermal properties of a passive evaporative cooler are tested for performance capability with various heat pipes over two environmental conditions.

This study conducted a proof-of-concept design for a passive helmet heat exchanger, incorporating AM components as both the heat pipe holders and the cushioning material targeting internal head temperatures of ≤ 35°C. Copper heat pipes from 3 manufactures with three lengths were analytically simulated and experimentally tested for their effectiveness in the helmet design. A total of 12 heat pipes were tested with 2 heat pipes per holder in a lateral configuration inside a thermal environmental chamber. Two 25-hour tests in an environmental chamber were conducted evaluating temperature (25°C, 45°C) and relative humidity (25%, 50%) for the six types of heat pipes and compared against the analytical models of the helmet heat exchangers.

Many of the heat pipes tested were good conduits for moving the heat from the head to the evaporative wicking material. All heat pipes had Coefficients of Performance under 3.5 when tested with the lateral system. Comparisons of the analytical and experimental models show the need for the design to incorporate a re-wetting reservoir. This work on a 2-dimensional system establishes the basis for design improvements and integration of the heat pipes and additively manufactured parts with a 3-dimensional helmet.

Commentary by Dr. Valentin Fuster
2018;():V001T01A005. doi:10.1115/MSEC2018-6418.

One of the versatile additive manufacturing processes is laser based Selective Laser Melting (SLM) which allows to build complex intricate shapes directly from its three dimensional digital images. Layer by layer deposition and depending upon build orientations, SLM parts tends to be anisotropic in nature. Also non-uniformity in thermal loading across the part leads to inhomogeneous microstructure which may have detrimental effect on various mechanical properties. Heat treatment of as-built SLM parts could be used as a post processing technique to reduce the anisotropy and produce homogenous microstructure to ensure reproducible mechanical properties. Application oriented mechanical properties can be obtained for precipitation hardened stainless steel by suitable heat treatment process. Present study is based on effect of heat treatments namely solution annealing, ageing and overaging on impact toughness of SLM 15-5 PH stainless steel. In order to support experimental observations, various metallurgical techniques have been applied. Effect of notch orientations causes anisotropy in impact toughness but this anisotropy is reduced with application of suitable heat treatment. In case of ageing, Transmission Electron Microscopy (TEM) analysis shows formation of fine spherical Cu precipitates which solution strengthens but makes the specimen brittle. As a result relatively lower impact toughness is obtained as compared to overaged condition where combined effect of coarsening of Cu precipitates and increased retained austenite makes the specimen ductile. Increased ageing temperature and soaking time does not have significant effect on impact toughness. However, solution annealing before ageing is recommended for homogenous precipitation throughout the specimen and statistically less scattered data. In all the cases SLM specimens have lower impact toughness to that of cold rolled 15-5 PH stainless steel. Present study could be used as a guideline to get application oriented mechanical properties mainly impact toughness.

Commentary by Dr. Valentin Fuster
2018;():V001T01A006. doi:10.1115/MSEC2018-6421.

Selective Laser Melting process enables production of geometrically complex parts directly from CAD model by melting metal powders layer by layer. For successful building of parts, some auxiliary structures namely support structures are also built to ensure proper heat conduction from actual parts to be built to the base plate. Support structures are needed if there are overhang surfaces in the design of the part. If the design of the part is very complex and features many overhang surfaces, then too many supports get generated. After building the part, these support structures need to be removed properly to get desired geometrical features and it may deteriorate the surface quality from where supports are removed. Sometimes removal of support structures becomes very difficult specially for parts having internal features. In this study, first effect of inclined angle, aspect ratio and different scanning strategies on the quality of overhang surfaces produced without any support structure under constant laser power and scan speed has been investigated. Scanning Electron Microscopy (SEM) images of overhang surfaces have been analyzed to investigate the presence of warping and uneven fused edges if any. It was found that with increase in inclined angles and aspect ratio, warping and presence of uneven fused edges increases. Rotational scanning strategy found to be better than linear alternate scanning strategy for reduced uneven fused edges formation and warping. Results show an overhang without any support structure can be built successfully with a single laser process parameters upto 25.343 degree which is less than theoretical critical angle of 26.565 degree. Further, it has been shown, using a novel strategy of building overhang with multiple laser process parameters, it is possible to build overhang even upto 24.132 degree.

Topics: Lasers , Melting
Commentary by Dr. Valentin Fuster
2018;():V001T01A007. doi:10.1115/MSEC2018-6429.

One of the most popular additive manufacturing processes among today’s manufacturing industries is Selective Laser Melting (SLM) in which very intricate shapes can be fabricated directly from its three dimensional digital design data by melting metal powders using laser. Layer by layer deposition of material about different build axes make SLM parts anisotropic in nature. Also, non-uniformity in thermal loading at top and bottom surfaces of a SLM part leads to inhomogeneous microstructure and may change electro-chemical properties across the part. Suitable heat treatment as a post processing technique can reduce this anisotropy and produce homogeneous microstructure leading to reproducible mechanical and electrochemical properties. Depending upon the application in actual industrial scenarios, SLM parts may be subjected to corrosive media and thus may affect service life of the part. In the present study, effect of different heat treatment namely solution annealing, ageing, overaging on corrosion properties of SLM 15-5 Precipitation-Hardened (PH) stainless steel have been studied. Various metallurgical characterizations have been carried out wherever required to support experimental observations. As-built specimens have approximately six times higher pitting potential which may be attributed to higher nitrogen content present in as-built specimens but corrode more over time than solution annealed (SA) specimens. Relatively bigger size pits and non-uniformity in their distributions can be attributed to residual stresses and inhomogeneous microstructure associated with as-built SLM specimens respectively. Specimen undergone standard ageing condition (H900) corrodes least over time among all the heat treatment conditions considered in the present study. However, in this case, a large number of shallow pits can be observed from the corroded surface. Overaged (H1150) specimens corrode more than H900 specimens but pitting starts late in case of H1150 specimens since pitting potential is almost ten times higher in the former case. Increased ageing temperature and soaking time (Mod H900 (SA)) increases formation of higher Cr23C6 precipitates than that of H900 condition and hence corrode more over time. Ageing without solution annealing (Mod H900 (AB)) leads to higher corrosion and larger pit size non-uniformly distributed over the corroded surface than that of Mod H900 (SA) condition which may be attributed to presence of residual stresses and non-uniform precipitation throughout the matrix. Present study will be useful for selecting suitable heat treatment yielding desired corrosion resistance for SLM stainless steel parts.

Commentary by Dr. Valentin Fuster
2018;():V001T01A008. doi:10.1115/MSEC2018-6437.

Additive manufacturing (AM) for metals has attracted attention from industry because of its great potential to enhance production efficiency and reduce production costs. Directed energy deposition (DED) is a metal AM process suitable to produce large-scale freeform metal products. DED entails irradiating the baseplate with a laser beam and launching the metal powder onto the molten spot to produce a metal part on the baseplate. Because the process enables powder from different materials to be used, DED is widely applicable to valuable production work such as for a dissimilar material joint, a graded material, or a part with a special structure.

With regard to parts with a special structure, directional solidification can prospectively be used in the power plant and aerospace industries because it can enhance the stiffness in a specific direction via only a simple process. However, conventional approaches for directional solidification require a special mold in order to realize a long-lasting thermal gradient in the part. On the other hand, from the viewpoint of thermal distribution in a produced part, DED is able to control the gradient by controlling the position of the molten pool, i.e., the position of the laser spot. Moreover, unlike casting, the thermal gradient can be precisely oriented in the expected direction, because the laser supplies heat energy on the regulated spot.

In this study, the applicability of DED to directional solidification in Inconel® 625 is theoretically and experimentally evaluated through metal structure observation and Vickers hardness measurements. Furthermore, the effect of two different cooling processes on directional solidification is also considered with the aim of improving the mechanical stiffness of a part produced by DED. The observations and experimental results show that both the cooling methods (baseplate cooling and intermittent treatment with coolant) are able to enhance the hardness while retaining the anisotropy.

Commentary by Dr. Valentin Fuster
2018;():V001T01A009. doi:10.1115/MSEC2018-6496.

This article presents manufacturing of exemplary knee prostheses using selective laser melting (SLM) technology. All phases of design and production are considered, from acquisition of the STL build file to optimization of process parameters, printing and post-build heat treatments. Geometric differences are acquired and compared with a 3D scanner.

Commentary by Dr. Valentin Fuster
2018;():V001T01A010. doi:10.1115/MSEC2018-6500.

Improved simulations are created to mimic the nature of compressive failure related to macro-structure and loading direction in fuse deposition modeling (FDM) additively manufactured nylon parts. Unlike prior work, the simulations incorporate internal fluid cavities to model the effects of entrapped gas within the internal geometric voids. Until now, such modeling technique has only been applied in simulations involving polymer foams. Experimental tests are also conducted to provide a baseline comparisons. The nylon FDM specimens studied vary in terms of infill pattern (hexagonal, triangular, and rectilinear) and infill density. Compressive loads are applied in orthogonal part directions to examine degree of anisotropic compressive strength at onset of permanent deformation. A comparative simulation study with and without the fluid cavity modeling reveals how the accuracy of the results improves when the effects of the entrapped gas is included. The aim of the work is to help establish an improved general method for creating simulations of sufficient fidelity to predict part macro-strengths for various 3D printed infill patterns and densities without the need for time-consuming experimental analyses for every variation in geometry.

Commentary by Dr. Valentin Fuster
2018;():V001T01A011. doi:10.1115/MSEC2018-6561.

The importance of the post-processing is increasing to remove the supporter afterward the additive manufacture process. The machining, known as the material removal process, achieve the high efficiency and rapid process as compared with the others techniques. This paper experimentally investigated the tool wear during the milling operations of the additive manufactured workpieces for the post-processing. The XRD analysis resulted that Inconel 718 powder used in the additive manufacturing has crystal structure FCC, which homologies the chemical compositions in wrought Inconel 718. The selective laser melting process had built the additive manufactured samples with two different orientations. Wrought Inconel 718 was the lowest hardness among the workpieces, whereas the severe tool wear was observed during the milling operation of wrought Inconel 718. The defects as the pores and cavities in the additive manufactured parts lead the low tool wears, even though the high hardness on the surfaces of the SLM Inconel 718. Further, the built orientation dominated the re-melted zone in the SLM parts, the contact between the tool and re-melted zone controlled the tool wears. Therefore, it should consider the built orientations to apply the machining as the post-processes.

Topics: Wear , Lasers , Alloys , Milling
Commentary by Dr. Valentin Fuster
2018;():V001T01A012. doi:10.1115/MSEC2018-6620.

Thin multifunctional structures need to be composed from many different materials. Currently, very few additive manufacturing processes are capable of working with multiple materials. Additive manufacturing processes that work with multiple different materials pose significant constraints on material options. This significantly limits the kind of multifunctional structures that can be produced using additive manufacturing. A robot assisted sheet lamination based additive manufacturing system is developed in this paper. The system utilizes a 6-DOF robotic manipulator to perform the manufacturing operations such as cutting, assembly, tape-layup, and bonding to build the part layer by layer. A flexible ornithopter wing have been built using the proposed system. We have characterized the system in terms of part performance as well as automation efficiency.

Commentary by Dr. Valentin Fuster
2018;():V001T01A013. doi:10.1115/MSEC2018-6643.

The particle-polymer composite can perform multiple functionalities according to particle property, local particle distribution, and alignment. This paper shows thermal management applications of in situ manipulations of particle dispersion patterns within a 3D printed polymeric composite architecture. A 3D printed particle-polymer composite with enhanced thermal conductive properties was developed. Composite structures containing 30-micron-sized aluminum particles embedded in the acrylate polymer were produced using a novel acoustic field assisted projection based Stereolithography process. Thermal properties of the pure polymer and prepared uniform composite with 2.75 wt% particle were characterized by using the transient hot bridge technique. To investigate the effect of material composition and particle distribution pattern on composite thermal behavior, heat sinks were designed and fabricated with the pure polymer, homogeneous composite with particles uniformly distributed in the polymer matrix, and composite with patterned particles for comparison. Infrared thermal imaging was performed on the 3D printed objects. The homogeneous composites displayed slight enhancement in thermal conductivity. A significant improvement of heat dissipation speed was observed for the patterned composite, due to a densely interconnected aluminum aggregate network. To further improve the thermal property of the patterned composite, varying layer thicknesses were tested. The developed patterned composites with superior performance compared to the inherent polymer material and homogeneous composites can be used for fabricating thermal management applications in electronic and fluidic devices.

Commentary by Dr. Valentin Fuster
2018;():V001T01A014. doi:10.1115/MSEC2018-6651.

Binder jetting additive manufacturing is a promising technology for fabricating ceramic parts with complex or customized geometries. However, this process is limited by the relatively low density of the fabricated parts even after sintering. This paper reports a study on effects of mixing powders with graded particle sizes on the powder bed packing density and consequently the sintered density. For the first time, a linear packing model, which can predict the packing density of mixed powders, has been used to guide the selection of particle sizes and fractions of constituent powders. A selection process was constructed to obtain the maximum mixed packing density. In the part of model validation, three types of alumina powders with average sizes of 2 μm, 10 μm, and 70 μm, respectively, were mixed in optimum volumetric fractions that could lead to the maximum packing density based on model predictions. Powder bed packing density was measured on binary mixtures, ternary mixture, and each constituent powders. Furthermore, disk-shaped samples were made, using binder jetting additive manufacturing, from each constituent and mixed powder. Results show that binary and ternary mixtures have higher powder bed packing densities and sintered densities than the corresponding constituent powders. The disks made from the ternary mixture achieved the highest sintered density of 65.5%.

Commentary by Dr. Valentin Fuster
2018;():V001T01A015. doi:10.1115/MSEC2018-6666.

Additive manufacturing enables the design of components with intricate geometries that can be manufactured with lead times much shorter when compared with conventional manufacturing. The ability to manufacture components out of high-performance metals through additive manufacturing technologies attracts industries that wish to develop more complex parts, but require components to maintain their structural integrity in demanding operating environments. Nickel-based superalloys are of particular interest due to their excellent mechanical, creep, wear, and oxidation properties at both ambient and elevated temperatures. However, relationship between process parameters and the resulting microstructure is still not well understood. The control of the microstructure, in particular the precipitation of secondary phases, is of critical importance to the performance of nickel-based superalloys. This paper reviews the additive manufacturing methods used to process nickel-based superalloys, the influence of the process parameters on microstructure and mechanical properties, the effectiveness of various heat treatment regimens, and the addition of particles in order to further improve mechanical properties.

Commentary by Dr. Valentin Fuster
2018;():V001T01A016. doi:10.1115/MSEC2018-6677.

Transparent, bubble-free glass structures can be printed using a filament-fed, laser-heated additive manufacturing process. In this process, a stationary CO2 laser beam is focused at the intersection of the filament and workpiece to locally heat the glass above its working temperature. Glass enters the molten region and is deposited on the workpiece as the workpiece is translated/rotated using a 4-axis stage. This paper studies creating free-form, free-standing objects which is facilitated by the glass rapidly achieving structural rigidity as it cools upon exiting the molten region. The effects of the process parameters and printing techniques are examined and optimized to print simple wall and truss structures.

Topics: Glass , Printing
Commentary by Dr. Valentin Fuster
2018;():V001T01A017. doi:10.1115/MSEC2018-6681.

Binder jet printing (BJP), one of the early metal 3D printing technologies, has distinct advantages over the other 3D printing processes that employ locally melting or welding to build 3D parts. Some of the advantages of BJP include printed parts free of residual stresses, build plate not being required, and less powder usage. However, the BJP technology has been adopted only in limited applications such as prototyping and sand molding because of its difficulty in achieving full-density parts. Based on our previous work on stainless steel (SS) 420, the same BJP protocol was used to attain full-density parts made of SS 316L. The effect of the particle size, mixture ratio, and sintering additives on the densities of printed and sintered parts is investigated for SS 316L powder. Three distinct sizes of SS 316L powders are mixed to improve the packing density. A systematic study of the binder burn-out procedure is conducted using thermogravimetric analysis, leading to a complete removal of binder phase without oxidizing SS 316L powder. The optimal sintering condition for some powder mixtures is determined to obtain the maximum density with the addition of small amounts of boron compounds as sintering additives. The quality of the fully-sintered SS 316L parts is evaluated using the various measurements including density, microstructure, hardness, and surface roughness. As we did with SS 420, the relative density of 99.6% is obtained for SS 316L without structural distortion. This is the first demonstration of such density for SS 316L using the BJP technology without any infiltration.

Commentary by Dr. Valentin Fuster
2018;():V001T01A018. doi:10.1115/MSEC2018-6688.

Additive manufacturing (AM) has applications in several fields ranging from aerospace and consumer goods to the medical industry. However, applications of AM in civil infrastructure design and construction are very limited. Based on information shared at the NSF workshop on Additive Manufacturing (3D Printing) for Civil Infrastructure Design and Construction in July 2017, this paper summarizes the current state of the field, gaps, and recommendations.

Commentary by Dr. Valentin Fuster
2018;():V001T01A019. doi:10.1115/MSEC2018-6701.

In this paper, the residual stress of 316L stainless steel obtained from selective laser melting process is measured, and the process factors that influence residual stress are analyzed. Two levels of laser power, two levels of scanning speed, and other auxiliary factors such as height of support structure are considered. For each combination of condition, the residual stress is measured at three in-depth positions, and the microstructure is also observed. The results show that the as-built 316L samples have fine microstructure with no clear grain boundaries, and the residual stresses at all measuring depths are tensile for all as-built SLM specimens. Meanwhile, it is found that the higher laser power and the lower scanning speed lead to the increase of tensile residual stress. Also, the tensile residual stress tends to increase with the depth into surface. In addition, the increase in position symmetry of specimen on the build platform appears to be able to reduce the magnitude of tensile residual stress. On the other hand, the effects of specimen location with respect to powder spreading and height of support are less conclusive.

Commentary by Dr. Valentin Fuster
2018;():V001T01A020. doi:10.1115/MSEC2018-6704.

A co-continuous piezocomposite architecture is presented to achieve mechanical flexibility and piezoelectricity simultaneously in piezoelectric materials. This architecture is comprised of an active ferroelectric ceramic phase and a passive flexible polymer phase, which are separated by a tailorable phase interface. Triply periodic minimal surfaces are used to define the phase interface, due to their excellent elastic properties and load transfer efficiency. A Suspension-Enclosing Projection-Stereolithography process is used to additively manufacture this material. Post processes including polymer infiltration, electroding and poling are introduced. Piezoelectric properties of the piezocomposites are numerically and experimentally studied. The results highlight the role of tailorable triply periodic phase interfaces in promoting mechanical flexibility and piezoelectricity of co-continuous piezocomposites.

Commentary by Dr. Valentin Fuster
2018;():V001T01A021. doi:10.1115/MSEC2018-6708.

The mask image projection based stereolithography (MIP-SL) is a low cost and high-resolution additive manufacturing (AM) process. However, the slow speed of part separation and resin refilling is the primary bottleneck that limits the fabrication speed of the MIP-SL process. In addition, the stair steeping effect due to the layer-based fabrication process limits the surface quality of built parts. To address the critical issues in the MIP-SL process related to resin refilling and layer-based fabrication, we present a mask video projection based stereolithography (MVP-SL) process with continuous resin flow and light exposure. The newly developed AM process enables the continuous fabrication of three-dimensional (3D) objects with ultra-high fabrication speed. In the paper. The system design to achieve mask video projection and the process settings to achieve ultrafast fabrication speed are presented. The relationship between process parameters and the surface quality of the fabricated parts is discussed. Test results illustrate the MVP-SL process with continuous resin flow can build three-dimensional objects within minutes and the surface quality of the fabricated objects can be significantly improved.

Commentary by Dr. Valentin Fuster
2018;():V001T01A022. doi:10.1115/MSEC2018-6709.

Dye-Sensitized Solar Cells (DSSC) are third generation solar cells used as an alternative to c-Si solar cells. DSSC are mostly flexible, easier to handle and are less susceptible to damage compared to c-Si solar cells. Additionally, DSSC is an excellent choice for indoor application as they perform better under diverse light condition. Most DSSCs are made of liquid medium sandwiched between two conductive polymer layers. However, DSSCs have significantly lower efficiencies compared to silicon solar cells. Also, use of liquid medium resulting in leaking of liquid, and occasional freezing during cold weather, and thermal expansion during hot weather conditions. DSSC can be manufactured in small quantities using relatively inexpensive solution-phase techniques such as roll-to-roll processing and screen printing technology. However, scaling-up the DSSC manufacturing from small-scale laboratory tests to sizeable industrial production requires better and efficient manufacturing processes. This research studies the feasibility of using additive manufacturing technique to fabricate electrodes of DSSC. The study aims to overcome the limitations of DSSCs including preventing leakage and providing more customized design. Experimental studies are performed to evaluate the effects of critical process parameters affecting the quality of electrodes for DSSC. Volume resistivity test is performed to evaluate the efficiency of the electrodes. In this study, the electrodes of DSSC are successfully fabricated using Fused Disposition Modeling (FDM) 3D printing technique. The results of this study would enable additive manufacturing technology towards rapid commercialization of DSSC technology.

Commentary by Dr. Valentin Fuster

Additive Manufacturing: Advances in Micro- and Nano-Additive Manufacturing

2018;():V001T01A023. doi:10.1115/MSEC2018-6302.

The emerging 3D printing technology has the potential to transform manufacturing customized optical elements, which currently heavily relies on the time-consuming and costly polishing and grinding processes. However, the inherent speed-accuracy trade-off seriously constraints the practical applications of 3D printing technology in optical realm. In addressing this issue, here, we report a new method featuring a significantly faster fabrication speed, at 24.54 mm3/h, without compromising the fabrication accuracy or surface finish required to 3D-print customized optical components. We demonstrated a high-speed 3D printing process with deep subwavelength (sub-10 nm) surface roughness by employing the projection micro-stereolithography process and the synergistic effects from the grayscale photopolymerization and the meniscus equilibrium post-curing methods. Fabricating a customized aspheric lens with 5 mm in height and 3 mm in diameter could be accomplished in less than four hours. The 3D-printed singlet aspheric lens demonstrated a maximal imaging resolution of 2.19 μm with low field distortion less than 0.13% across a 2-mm field of view. This work demonstrates the potential of 3D printing for rapid manufacturing of optical components.

Commentary by Dr. Valentin Fuster
2018;():V001T01A024. doi:10.1115/MSEC2018-6365.

Nanotwinned (nt) metals exhibit superior electrical and mechanical properties compared to their coarse-grained and nano-grained counterparts. They have a unique microstructure with grains that contain layered nanoscale twins divided by coherent twin boundaries (TBs). Since nanotwinned metals have low electrical resistivity and high resistance to electromigration, they are ideal materials for making nanowires, interconnections and switches. In this paper we show the possibility of making nanotwinned copper interconnections on a non-conductive substrate using a novel additive manufacturing technique called L-PED. Through this approach, microscale interconnections can be directly printed on the substrate in environmental conditions and without post processing.

Commentary by Dr. Valentin Fuster
2018;():V001T01A025. doi:10.1115/MSEC2018-6383.

One of the limitations of commercially available metal Additive Manufacturing (AM) processes is the minimum feature size most processes can achieve. A proposed solution to bridge this gap is microscale selective laser sintering (μ-SLS). The advent of this process creates a need for models which are able to predict the structural properties of sintered parts. While there are currently a number of good SLS models, the majority of these models predict sintering as a melting process, which is accurate for microparticles. However, when particles tend to the nanoscale, sintering becomes a diffusion process dominated by grain boundary and surface diffusion between particles. As such, this paper presents an approach to model sintering by tracking the diffusion between nanoparticles on a bed scale. Phase Field Modeling (PFM) is used in this study to track the evolution of particles undergoing sintering. Part properties such as relative density, porosity, and shrinkage are then calculated from the results of the PFM simulations. These results are compared to experimental data gotten from a Thermogravimetric Analysis done on dried copper nanoparticle inks, and the simulation constants are calibrated to match physical properties.

Commentary by Dr. Valentin Fuster
2018;():V001T01A026. doi:10.1115/MSEC2018-6451.

This paper presents an electric-field-driven (EFD) jet deposition 3D printing technique, which is based on the induced electric field and electrohydrodynamic (EHD) cone-jetting behavior. Unlike the traditional EHD-jet printing with two counter electrodes, the EFD jet 3D printing only requires a nozzle electrode to induce an electric field between the nozzle and the target substrate. Taking into account both printing accuracy and printing efficiency, two novel working modes which involve pulsed cone-jet mode and continuous cone-jet mode, are proposed for implementing multi-scale 3D printing. In this work, significant relationships between the printing results and process parameters (voltage, air pressure, pulse duration time, and stage velocity) were investigated to guide the reliable printing in both working modes. Furthermore, the experimental studies were carried out to demonstrate the capabilities and advantages of the proposed approach, which included the suitability of various substrate, the capacity of conformal printing, and the diversity of the compatible materials. Finally, four typical printing results were provided to demonstrate the feasibility and effectiveness of the proposed technology for micro-scale 2D patterning and macro/microstructures multi-scale fabrication. As a result, this research provides a novel micro-scale 3D printing technique with low cost, high resolution and good generalizability. The breakthrough technique paves a way for implementing highresolution 3D printing, especially for multi-scale and multimaterial additive manufacturing.

Commentary by Dr. Valentin Fuster
2018;():V001T01A027. doi:10.1115/MSEC2018-6552.

Direct printing of three-dimensional nanoscale metallic wires with controlled microstructure is useful for applications in the 3D integrated circuits, flexible electronics and nanoelectronics. In this paper, we demonstrate the localized pulsed electrodeposition process for direct printing of 3D free-standing nanotwinned Copper (nt-Cu) nanowires. Nt-Cu offers unique mechanical and electrical properties, which are advantageous in different applications. Focused ion beam (FIB) analysis confirmed the nanocrystalline nanotwinned (nc-nt) microstructure of the wires. Mechanical properties of the 3D printed nc-nt Cu were characterized using in situ SEM micro-compression experiments. The 3D printed nc-nt Cu exhibited a flow stress of over 960 MPa, which is outstanding for an additively manufactured material.

Commentary by Dr. Valentin Fuster
2018;():V001T01A028. doi:10.1115/MSEC2018-6562.

Metamaterials are architected artificial materials engineered to exhibit properties not typically found in natural materials. Increasing attention has recently been given to mechanical metamaterials with unprecedented mechanical properties including high stiffness, strength, or/and resilience even at extremely low density. These unusual mechanical performances emerge from the three-dimensional (3D) spatial arrangement of the micro-structural elements designed to effectively distribute mechanical loads. Recent advances in additive manufacturing in micro-/nano-scale have catalyzed the growing interest in this field.

This work presents a new lightweight microlattice with tunable and recoverable mechanical properties using a three-dimensionally architected shape memory polymer (SMP). SMP microlattices were fabricated utilizing our micro additive manufacturing technique called projection micro-stereolithography (PμSL), which uses a digital micro-mirror device (DMD™) as a dynamically reconfigurable photomask. We use a photo-crosslinkable and temperature-responsive SMP which can retain its large deformation until heated for spontaneous shape recovery. In addition, it exhibits remarkable elastic modulus changes during this transition. We demonstrate that mechanical responses of the micro 3D printed SMP microlattice can be reversibly tuned by temperature control. Mechanical testing result showed that stiffness of a SMP microlattice changed by two orders of magnitude by a moderate temperature shift by 60°C. Furthermore, the shape memory effect of the SMP allows for full restitution of the original shape of the microlattice upon heating even after substantial mechanical deformation. Mechanical metamaterials with lightweight, reversibly tunable properties, and shape recoverability can potentially lead to new smart structural systems that can effectively react and adapt to varying environments or unpredicted loads.

Commentary by Dr. Valentin Fuster
2018;():V001T01A029. doi:10.1115/MSEC2018-6609.

A novel and simple near-field electrospinning (NFES) method has been developed to fabricate wavy or helical nanofibrous arrays. By alternating the electrostatic signals applied on auxiliary-electrodes (AE), the structural parameters of deposited patterns can be actively controlled. Compared with the traditional electrospinning methods based on the bending and buckling effects or collector movement, the proposed method shows advantages in the controllability, accuracy, and minimal feature size. Forces operating on the electrospinning jet and the time-varying electric field distribution were analyzed to explain the kinematics of the jet. Nanoscale wavy and helical patterns with various structural parameters were fabricated. The effects of experimental process parameters on structural parameters of deposited patterns were analyzed to demonstrate the controllability of our method in fabricating wavy or helical nanofibrous structures. It is envisioned that this method will benefit the applications in the field of photovoltaic devices, sensors, transducers, resonators, and stretchable electronics.

Topics: Electrospinning
Commentary by Dr. Valentin Fuster
2018;():V001T01A030. doi:10.1115/MSEC2018-6664.

Powder bed metal additive manufacturing (AM) utilizes a high-energy heat source scanning at the surface of a powder layer in a pre-defined area to be melted and solidified to fabricate parts layer by layer. It is known that powder bed metal AM is primarily a thermal process and further, heat conduction is the dominant heat transfer mode in the process. Hence, understanding the powder bed thermal conductivity is crucial to process temperature predictions, because powder thermal conductivity could be substantially different from its solid counterpart. On the other hand, measuring the powder thermal conductivity is a challenging task. The objective of this study is to investigate the powder thermal conductivity using a method that combines a thermal diffusivity measurement technique and a numerical heat transfer model. In the experimental aspect, disk-shaped samples, with powder inside, made by a laser powder bed fusion (LPBF) system, are measured using a laser flash system to obtain the thermal diffusivity and the normalized temperature history during testing. In parallel, a finite element model is developed to simulate the transient heat transfer of the laser flash process. The numerical model was first validated using reference material testing. Then, the model is extended to incorporate powder enclosed in an LPBF sample with thermal properties to be determined using an inverse method to approximate the simulation results to the thermal data from the experiments. In order to include the powder particles’ contribution in the measurement, an improved model geometry, which improves the contact condition between powder particles and the sample solid shell, has been tested. A multi-point optimization inverse heat transfer method is used to calculate the powder thermal conductivity. From this study, the thermal conductivity of a nickel alloy 625 powder in powder bed conditions is estimated to be 1.01 W/m·K at 500 °C.

Commentary by Dr. Valentin Fuster
2018;():V001T01A031. doi:10.1115/MSEC2018-6700.

3D printing (additive manufacturing) has become a popular method to create three-dimensional objects due to its high efficiency and is easy to operate. 3D printing of continuous fiber reinforced polymers has been a challenge. The fused deposition modeling (FDM) processes for this purpose were proposed and made possible only several years ago. The 3D printed continuous fiber reinforced polymers are able to improve the mechanical properties by leaps and bounds. In this paper, we aim to investigate the possibility of further improve the mechanical properties of 3D printed continuous fiber reinforced polymers by adding nano fillers to the polymer matrix. In experiment, the Kevlar fiber is chosen to be the continuous fiber material, and nylon 6 (PA 6) is chosen to be the polymer matrix material. Carbon nanotubes (CNTs) and graphene nano platelets (GNPs) nanoparticles are first mixed with nylon 6 pellets to make nanocomposites. The nanocomposites are then extruded into filaments for 3D printing. During the 3D printing process, both Kevlar filament and nanocomposite filament are fed through the printing nozzle and deposited on the platform. Tensile specimens are made from pure PA 6 and four types of nanocomposites, namely, 0.1wt% CNT/PA 6, 1wt% CNT/PA 6, 0.1wt% GNP/PA 6, 1wt% GNP/PA 6. By incorporating four layers of Kevlar fiber, which leads to the weight percentage of about 9% for Kevlar fiber in materials, fiber composite tensile specimens are made from Kevlar/PA 6 composite and four fiber reinforced nanocomposites, namely, Kevlar/0.1%CNT/PA 6, Kevlar/1%CNT/PA 6, Kevlar/0.1%GNP/PA 6, and Kevlar/1%GNP/PA 6. The tensile tests reveal that CNTs filled PA 6 nanocomposites show less significant improvements in mechanical properties as compared to the GNP filled PA 6. With only 0.1wt% of GNP, the tensile modulus improves by 101%, and with 1wt% of GNP, the modulus improves by 153%. The results also indicate that although Kevlar fibers dominate the main mechanical properties of the printed composite materials, the existence of GNP nano fillers also provide noticeable contribution to the enhancement of tensile strengths and moduli, while the effect of CNTs is much less pronounced.

Commentary by Dr. Valentin Fuster

Additive Manufacturing: Design for Manufacturability for Additive Manufacturing

2018;():V001T01A032. doi:10.1115/MSEC2018-6412.

Wire and arc additive manufacturing (WAAM) technology has received increasing attention. In this paper, the thin-walled parts with the height of 230mm and cylindrical parts with the diameter of 100mm were fabricated by WAAM using H13 wire and Metal-Inert Gas Welding (MIG) method. Process parameters of current I = 140A, arc voltage U = 25V, velocity v = 4mm/s were applied to manufacture the thin-walled and cylindrical parts. During the WAAM process of the cylindrical parts, when the overlap length of a circle equal to the length of the puddle, the forming appearance of the part is reasonably good. By cooling the former layers with water, continuous processing of the parts was successfully realized. No obvious differences were detected when testing the hardness and the microstructure of the parts built by these two processes. The application of cooling may be a key technology for the continuous WAAM processing of the cylindrical specimens.

Commentary by Dr. Valentin Fuster
2018;():V001T01A033. doi:10.1115/MSEC2018-6450.

Cellular structures are broadly applicable to lightweight design and multifunctional applications. Especially, with unprecedented fabrication freedom provided by additive manufacturing (AM), design and optimization of nonuniform cellular structures have recently attracted great research interests. Topology optimization is one of the most powerful tools to obtain the optimized material distribution, and much research have been conducted to optimize cellular structures with the help of this optimization technique. In general, the optimized cellular structure is generated based on a predefined ground structure, and thickness of each strut is then decided based on the optimization result. However, many existing studies did not consider the constraints of AM processes, such as some generated struts may be too thin to be manufactured. Besides, only load support structure was considered in these studies. Other applications, such as heat dissipation or energy absorption, were rarely researched. In this paper, a novel cellular structure design method, which considered both functionality and manufacturability, is proposed. Different from other methods, wall thickness of the structure was set as a constant. To get the optimized material distribution, variable cell sizes were applied. Because of uniform wall thickness, the smaller the unit cell is, the higher its volume fraction will be. By mapping small unit cells to high density area and large cell to low density area, the final optimized cellular structure can be generated. In addition, because smaller unit cells have higher surface-to-volume ratio, this method can also be applied to solve heat transfer problem. Two examples, minimum compliance design of a cantilever beam and maximum heat dissipation efficiency design of a CPU heat sink, were conducted to validate the proposed method.

Commentary by Dr. Valentin Fuster
2018;():V001T01A034. doi:10.1115/MSEC2018-6578.

The work aims to study the performance of 3D-printed parts under In-Plane and Out-of-Plane shear stresses. The test articles are made from Acrylonitrile Butadiene Styrene (ABS) by the 3D printing process (Fused Deposition Modeling - FDM). The testing procedures have been performed according to the ASTM D3846–02 method for defining the In-Plane shear strength while the ASTM D5379 method has been used for determining the Out-of-Plane shear properties. The statistical distribution functions were determined for both test data. Failure analysis has been performed for determining the Probability Density Function, the Survival Function, and the Hazard Function. The probability of failure at a certain stress level has been determined. A comparison between parts manufactured using the 3D printer and the commercially manufacturing process has been performed using the nonparametric two-sample Kolmogorov-Smirnov normality test of the underlying distributions and also supported by Mann-Whitney test.

Commentary by Dr. Valentin Fuster

Additive Manufacturing: Quality Assurance in Additive Manufacturing Systems: Sensing, Analytics, and Control

2018;():V001T01A035. doi:10.1115/MSEC2018-6332.

Metal 3D printing is one of the fastest growing additive manufacturing (AM) technologies in recent years. Despite the improvements and capabilities, reliable metal printing is still not well understood. One of the barriers of industrialization of metal AM is process monitoring and quality assurance of the printed product. These barriers are especially much highlighted in aerospace and medical device manufacturing industries where the high reliability and quality is needed. Selective Laser Melting (SLM) is one of the main metal 3D printing methods where it is known that more than 50 parameters are affecting the quality of the print. However, the current SLM printing process barely utilize a fraction of the collected data during production. Up to this point, no study to the best of our knowledge examines the correlation of factors affecting the quality of the print. After reviewing the current state of the art of process monitoring for metal AM involving SLM, we propose a method to control the process of the print in each layer and prevent the defects using data-driven techniques. A numerical study using simulated numbers is provided to demonstrate how the proposed method can be implemented.

Commentary by Dr. Valentin Fuster
2018;():V001T01A036. doi:10.1115/MSEC2018-6440.

Selective laser melting (SLM) is a powder bed based additive manufacturing (AM) process to manufacture metallic parts. SLM is the complex thermal-physical-chemical process of the interaction between a laser source and metallic powders. The SLM printing method has been applied widely for fabricating the metallic parts. However, the high temperature in heating and fast cooling during SLM process result in the large residual stress which affects to the quality of the SLM printed parts such as distortion and cracks. This research proposes to develop a system for predicting the quality of the part from the manufacturing planning to remove the failures before carrying out the real printing process. For developing such system, a model for predicting the temperature distribution should be generated. From this model, an interrelationship between process parameters and temperature distribution should be derived out. Based on that, the deformation can be predicted by calculating residual stress along with the result of temperature distribution.

Commentary by Dr. Valentin Fuster
2018;():V001T01A037. doi:10.1115/MSEC2018-6470.

The goal of this work is to detect the onset of material cross-contamination in laser powder bed fusion (L-PBF) additive manufacturing (AM) process using data from in-situ sensors. Material cross-contamination refers to trace foreign materials that may be introduced in the powder feedstock used in the process due to reasons, such as poor cleaning of the AM machine after previous builds, or inadequate quality control during production and storage of the feedstock powder material. Material cross-contamination may lead to deleterious changes in the microstructure of the AM part and consequently affect its functional properties. Accordingly, the objective of this work is to develop and apply a spectral graph theoretic approach to detect the occurrence of material cross-contamination in real-time during the build using in-process sensor signatures, such as those acquired from a photodetector. To realize this objective Inconel alloy 625 test parts were made on a custom-built L-PBF apparatus integrated with multiple sensors, including a photodetector (300 nm to 1100 nm). During the process the powder bed was contaminated with two types of foreign materials, namely, tungsten and aluminum powders under varying degrees of severity. Offline X-ray Computed Tomography (XCT) and metallurgical analyses indicated that contaminant particles may cascade to over eight subsequent layers of the build, and enter up to three previously deposited layers. This research takes the first-step towards detecting cross-contamination in AM by tracking the process signatures from the photodetector sensor hatch-by-hatch invoking spectral graph transform coefficients. These coefficients are subsequently traced on a Hoteling T2 statistical control chart. Using this approach, instances of Type II statistical error in detecting the onset of material cross-contamination was 5% in the case of aluminum, in contrast, traditional stochastic time series modeling approaches, e.g., ARMA had corresponding error exceeding 15%.

Topics: Lasers , Contamination
Commentary by Dr. Valentin Fuster
2018;():V001T01A038. doi:10.1115/MSEC2018-6477.

The goal of this work is to understand the effect of process conditions on part porosity in laser powder bed fusion (LPBF) Additive Manufacturing (AM) process, and subsequently, detect the onset of process conditions that lead to porosity from in-process sensor data. In pursuit of this goal, the objectives of this work are two-fold:

(1) Quantify the count (number), size and location of pores as a function of three LPBF process parameters, namely, the hatch spacing (H), laser velocity (V), and laser power (P).

(2) Monitor and identify process conditions that are liable to cause porosity through analysis of in-process layer-by-layer optical images of the build invoking multifractal and spectral graph theoretic features.

This is important because porosity has a significant impact on the functional integrity of LPBF parts, such as fatigue life. Furthermore, linking process conditions to sensor signatures and defects is the first-step towards in-process quality assurance in LPBF. To achieve the first objective, titanium alloy (Ti-6Al-4V) test cylinders of 10 mm diameter × 25 mm height were built under differing H, V, and P settings on a commercial LPBF machine (EOS M280). The effect of these parameters on count, size and location of pores was quantified based on X-ray computed tomography (XCT) images. To achieve the second objective, layerwise optical images of the powder bed were acquired as the parts were being built. Spectral graph theoretic and multifractal features were extracted from the layer-by-layer images for each test part. Subsequently, these features were linked to the process parameters using machine learning approaches. Through these image-based features, process conditions under which the parts were built was identified with the statistical fidelity over 80% (F-score).

Topics: Lasers
Commentary by Dr. Valentin Fuster
2018;():V001T01A039. doi:10.1115/MSEC2018-6487.

Aerosol jet printing (AJP) is a complex process for additive electronics that is often unstable. To overcome this instability, real-time observation and control of the printing process using image based monitoring is demonstrated. This monitoring is validated against images taken after the print and shown highly correlated and useful for determination of printed linewidth. These images and the observed linewidth are used as input for closed-loop control of the printing process, with print speed changed in response to changes in observed linewidth. Linear regression is used to relate these quantities and forms the basis of a proportional control. A test using multiple print speeds and the observed linewidths is used to set the control gain. Electrical test structures were printed with controlled and uncontrolled printing, and it was found that the control influenced their linewidth and electrical properties, giving improved uniformity in both size and electrical performance.

Topics: Aerosols , Printing
Commentary by Dr. Valentin Fuster
2018;():V001T01A040. doi:10.1115/MSEC2018-6586.

The goal of this work is in situ monitoring of the functional properties of aerosol jet-printed electronic devices. In pursuit of this goal, the objective is to develop a multiple-input, single-output (MISO) machine learning model to estimate the device functional properties in a near real-time fashion as a function of process parameters as well as 2D/3D features of line morphology. The aim is to use the MISO model for in situ estimation and thus, monitoring of line/device resistance in aerosol jet printing (AJP) process. To realize this objective, silver nanoparticle structures are printed by varying three process parameters: (i) sheath gas flow rate (ShGFR), (ii) exhaust gas flow rate (EGFR), and (iii) print speed (PS). Subsequently, line morphology is captured in situ using a high-resolution charge-coupled device (CCD) camera, mounted coaxial to the nozzle. Besides, utilizing 2D/3D quantifiers (introduced in the authors’ previous publications), the line morphology is further quantified, and the extracted features (e.g., line width, overspray, cross-sectional area, etc.) are fed as inputs to a novel sparse representation-based classification (SRC) model. The four-point probe method is used for measurement of resistance, and definition of a priori classification labels. The outcome of this research paves the way for future control of device functional properties in AJP process.

Topics: Aerosols
Commentary by Dr. Valentin Fuster
2018;():V001T01A041. doi:10.1115/MSEC2018-6587.

Compared with other metals, titanium has a wide range of applications in laser induced forward transfer (LIFT) due to its unique properties of low thermal conductivity and high melting point. In general, the titanium film is used as a sacrificial layer or transferred material in LIFT with different laser fluence. In this study, four different topography types are classified under the laser irradiation of ultraviolet nanosecond pulses. For Ti films with different thicknesses, probability distribution of these types is provided to demonstrate how topographies evolve with the increasing laser fluence. Through the research, the understanding of the physical mechanism of titanium film would be deepened.

Commentary by Dr. Valentin Fuster
2018;():V001T01A042. doi:10.1115/MSEC2018-6623.

The present work delineates a novel and scalable approach to characterization of defects in additively manufactured components. The approach is based on digital image correlation and involves characterization of surface speeds during rigid body rotation of the workpiece, followed by normalization with respect to rotation speed. Towards this, two different imaging sources were tested, viz. smartphone camera and sophisticated high-resolution/high-speed camera. The proposed approach successfully delineated horizontal and vertical notch defects in a simple FDM fabricated component. Accuracy of this approach was tested with concomitant laser based scanning. Some limitations of this approach were discussed.

Commentary by Dr. Valentin Fuster
2018;():V001T01A043. doi:10.1115/MSEC2018-6644.

Selective Laser Melting (SLM) has been a major subject of study in the field of powder bed additive manufacturing (AM) process. It is desired to know the melt pool size and the associated thermal gradient during the powder melting process. However, there are challenges associated with accurately measuring the melt pool size as a whole by experiment alone. Therefore, the combination of experimental and numerical study may help analyze the melt pool shape in a better way. In this study, a 3D powder scale model using volume of fluid (VOF) approach has been developed using ANSYS FLUENT. A temperature dependent material property is defined and then volumetric heat source is applied to melt the powder particles. The single track results obtained from the simulation are compared with the experiment and the results show that single track width predicted by the simulation is in good agreement with the experimental counterpart. The predicted track width is within 10% error.

Commentary by Dr. Valentin Fuster

Bio and Sustainable Manufacturing: Advances in Analysis, Design, and Manufacturing of Biomedical Devices

2018;():V001T05A001. doi:10.1115/MSEC2018-6340.

The paper presents a methodology to optimize drill bits to realize safe drilling of bone materials for many surgeries like orthopedics and neurosurgery. First, a mechanistic model is introduced to relate drilling forces to main drill bit geometry parameters. Then a genetic algorithm is developed to optimize drill bit geometry parameters by minimization of drilling forces based on the mechanistic model. Finally prototypes of drill bits with optimized geometry parameters are produced and drilling experiments are conducted to verify the advantages of these new drill bits. The results show that by comparison with normal drill bit, the average drilling forces are reduced to more than 50% by drill bits with optimized geometry parameters under a wide range of drilling conditions.

Commentary by Dr. Valentin Fuster
2018;():V001T05A002. doi:10.1115/MSEC2018-6358.

Endoscopic biopsy forceps are the key to minimally invasive procedures to an endoscopic surgeon. These surgeons have to maneuver forceps with cutting performance through the body while maintaining minimal damage to the narrow channels during insertion. The amount of precision the user needs to successfully perform endoscopic surgery is high enough to create a preference amongst surgeons.

Physicians are often not involved in the purchasing decision on the instruments, but they usually can provide their preference of instrument mainly based on the subjective perception of how an instrument feels or works in their hands. To base discussions between surgeons and purchasing departments on quantitative data of forceps use performance, this study aims to provide a performance testing method for different instruments such as different brands, designs, reusable or single-use, or instruments in different wear stages. Ultimately, this will allow to determine which instrument performs with the maximum efficiency at the lowest cost.

First, findings in the literature on forceps failure, wear and testing are described. Then, the forceps design and handling during a biopsy are investigated. A preliminary test set-up is introduced for a repeatable biopsy test for endoscopic forceps. Different tissue types and samples can be used in the test stand to define an ideal acceleration profile for the forceps during biopsy and the cut can be analyzed by microscopy afterwards. A sensor on the operator’s wrist measures acceleration and jerk while pulling at the forceps, which will give new insight into the performance of different forceps types and forceps in different wear states, independent from forceps’ brand, design or wear states.

Commentary by Dr. Valentin Fuster
2018;():V001T05A003. doi:10.1115/MSEC2018-6366.

Flexible tactile sensors have been utilized for epidermal pressure sensing, motion detecting, and healthcare monitoring in robotic and biomedical applications. This paper develops a novel piezoresistive flexible tactile sensor based on porous graphene sponges. The structural design, working principle, and fabrication method of the tactile sensor are presented. The developed tactile sensor has 3 × 3 sensing units and has a spatial resolution of 3.5 mm. Then, experimental setup and characterization of this tactile sensor are conducted. Results indicated that the developed flexible tactile sensor has good linearity and features two sensitivities of 2.08 V/N and 0.68 V/N. The high sensitivity can be used for tiny force detection. Human body wearing experiments demonstrated that this sensor can be used for distributed force sensing when the hand stretches and clenches. Thus the developed tactile sensor may have great potential in the applications of intelligent robotics and healthcare monitoring.

Commentary by Dr. Valentin Fuster
2018;():V001T05A004. doi:10.1115/MSEC2018-6485.

Projection-based printing has been proven to be an effective way to fabricate user defined complex structures in biomedical applications. Large-scale printing of this process remains a challenge due to the lack of light source with large irradiation area and long transmitting distances. This paper presents a novel method by using multi-step exposure for large-scale parts printing in projection-based printing system. The multi-step exposure method takes the advantage of using a serial of digital masks for exposure incrementally, thus can compensate the printing differences induced by unevenly distributed ultraviolet (UV) intensity. The system setup and printing characterization of the projection-based printing system are studied. The distribution of the UV light power density is measured and the relationship between the printed height and printing parameters are investigated. Then, a multi-step exposure method is proposed and followed by experimental validation. Results showed that the developed printing system with five-step exposure can be used for a relatively large-scale parts printing, and a relatively flat profile can be achieved. Thus, this method provides the potential ability to print large-scale objects for biomedical applications.

Topics: Printing
Commentary by Dr. Valentin Fuster
2018;():V001T05A005. doi:10.1115/MSEC2018-6575.

Needle insertion physical experiments are used as the ground truth for model validation and parameter estimation by measuring the needle defection and tissue deformation during the needle-tissue interactions. Hence parameter uncertainties can contribute experiment errors. To improve the repeatability and accuracy of such experiments, one-at-a-time (OAT) sensitivity analysis is used to study the impacts of the factors, such as stirring temperature, frozen time, thawing time during the process of making hydrogels as well as repeated path insertion and different puncture plane in the planer needle insertion experiments. The results show that the puncture plane has the greatest effect on the repeatability of needle insertion physic experiments, followed by repeated path insertion, while other factors have the least effect. The results serve to guide future experiment design for greater repeatability and accuracy.

Commentary by Dr. Valentin Fuster
2018;():V001T05A006. doi:10.1115/MSEC2018-6614.

Tubular structures of hydrogel are used in a variety of applications such as 3D cell culturing for delivery of nutrient supplies. The wall thickness of the tube determines the speed of diffusion or delivery rate. In this study, we aimed to fabricate tubular structures with varying of wall thicknesses using a thermal-crosslinking hydrogel, gellan gum, with the coaxial needle approach. The wall thickness is controlled by changing the flow rate ratio between the inner (phosphate-buffered saline) and outer needles (gellan gum). A simulation model was developed to estimate the proper extrusion speed to allow the gellan gum to be extruded around its glass transition temperature. While keeping the extrusion rate of gellan gum fixed, different PBS extrusion rates were tested to investigate the printability to form continuous tubular structures, range of printable wall thickness, and possibility to form tubes with closed ends to encapsulate fluid or drug inside the tube. The ranges of printable wall thickness with two pairs of coaxial needle were identified. It was found that at about 200% of the baseline PBS extrusion speed, a maximum of 20% difference in wall thickness can be achieved, while a close end can still be formed.

Commentary by Dr. Valentin Fuster
2018;():V001T05A007. doi:10.1115/MSEC2018-6632.

Precise and firm fixation of the cranium is critical during craniotomy and delicate brain neurosurgery making head immobilization devices (HIDs) a staple instrument in brain neurosurgical operations today. However, despite their popularity, there is no standard procedure for their use and many complications arise from using HIDs in pediatric neurosurgery. In this paper, we identify biomechanical causes of complications and quantify risks in pin-type HIDs including clamping force selection, positioning and age effects. Based on our root cause analysis, we develop a framework to address the biomechanical factors that influence complications and understand the biomechanics of the clamping process. We develop an age-dependent finite element model (FEM) of a single pin on a cranial bone disc with the representative properties and skull thickness depending on age. This model can be utilized to reduce risk of complications by design as well as to provide recommendations for current practices.

Commentary by Dr. Valentin Fuster
2018;():V001T05A008. doi:10.1115/MSEC2018-6637.

Electrosurgical tissue joining is an effective way to create hemostasis, especially in surgical procedures performed in the minimally-invasive manner. The quality of tissue joints and potential thermal damage to the surroundings are the two main concerns when using electrosurgical tissue joining tools. A more robust method for quality control is still needed. In this study, we developed an experimental setup to join tissues and performed tensile tests to evaluate the quality of the tissue joint, while also monitoring the process parameters including voltage, current, impedance, temperature and thermal dose. Three joining times (4, 6, and 8 seconds) and three compression levels (80%, 90%, and 95%) were used to join porcine arterial tissues. It was found that 95% compression can form a strong joint with a shorter joining time and less energy, but the joint strength decreases when the joining time is extended to 8 seconds. A lower compression level can still form a quality joint but requires longer joining time and energy which could lead to more thermal damages. A new index, specific strength (mmHg/J), which is defined as the ratio between tensile strength and the consumed energy, is proposed. Specific strength offers a new way to estimate the required joining time to achieve sufficient joining strength while minimizing the energy consumption to reduce thermal damages.

Commentary by Dr. Valentin Fuster
2018;():V001T05A009. doi:10.1115/MSEC2018-6642.

This paper presents an experimental measurement of the thermal conductivity of bovine cortical bone by an improved parallel plate method to increase the accuracy of the measurement. An experimental apparatus was designed to measure the thermal conductivity of the cortical bone using a reference material with a known thermal conductivity by the heat transfer through the samples. To improve the measurement accuracy, a reference material was selected as quartz, which is of the same order of magnitude of the thermal conductivity of bovine cortical bone reported in the existing literature. Additionally, the temperatures at the heat source and heat sink were set to ±5°C from the ambient temperature to reduce the inevitable heat loss in the measurement. The temperature offset was determined numerically. The current experimental measurement was validated by an in-house finite-difference numerical program. The heat loss in the measurement was predicted from the numerical program. The thermal conductivity of the bovine cortical bone was then determined to be 0.55 ± 0.02 W/mK with compensating heat loss.

Commentary by Dr. Valentin Fuster
2018;():V001T05A010. doi:10.1115/MSEC2018-6686.

Rotational atherectomy (RA) utilizes a high-speed diamond grinding wheel to remove the calcified atherosclerotic plaque off the vessel wall via a catheter inside an artery for blood flow restoration and treatment of cardiovascular diseases. RA in angulated lesions is challenging due to the geometric constrains on the wheel motion, potentially leading to vessel dissection and perforation. To understand the grinding wheel motion and force during RA in curved arteries, experiments were conducted based on 3D printed anatomically accurate coronary artery phantoms with plaster coating as the plaque surrogate, a high-speed camera, and a multi-axis force transducer. Results showed that the grinding wheel did not orbit inside right coronary artery phantom which led to a highly biased ground region aligned with several contact points between the guidewire and the arterial wall. The grinding wheel orbital motion facilitated an even treatment of several segments in left anterior descending coronary artery phantom. The grinding force, ranging from 0.05 to 0.20 N, increased with the wheel rotational speed when the wheel orbited and was insensitive to the wheel speed without wheel orbital motion. This study explained the clinically observed guidewire bias from the engineering perspective and further revealed the RA mechanism of action in angulated artery, which may assist to improve the device design and the operating technique.

Commentary by Dr. Valentin Fuster
2018;():V001T05A011. doi:10.1115/MSEC2018-6702.

Bipolar tissue welding is often performed with a set of laparoscopic forceps in a minimal invasive surgery to achieve less bleeding and shorter recovery time. However, problems such as tissue sticking, thermal damage, and joint failure need to be solved before the process can be reliably used in more surgical procedures. In this study, experiments were conducted to examine the effect of process parameters and dynamic impedance for prediction of the size of denatured tissue zone during welding. A weld lobe that defines suitable process conditions was constructed. It is found that tissue denaturation starts from the center of the heated region. Dynamic impedance is strongly affected by the compression level and heating power. The size of denatured tissue zone can be predicted with the heating energy; however, the prediction is strongly dependent on the compression level.

Commentary by Dr. Valentin Fuster
2018;():V001T05A012. doi:10.1115/MSEC2018-6719.

This study investigates the extrusion-based additive manufacturing (AM) of silicone 3D contour nonwoven fabrics by liquid rope coiling. Customized contour fabrics are ideal for wearable devices for individualized fit and comfort in contact. The AM using silicone liquid rope coiling can fabricate the porous and 3D contour nonwoven fabrics with enhanced breathability and comfortability. The key challenge in the proposed fabrication is the inability to generate consistent coiling pattern because the nozzle orientation deviates from the surface normal vector. A five-axis machine for silicone extrusion AM of nonwoven fabrics was developed to continuously align the nozzle orientation continuously with the surface normal vector. Three cases of silicone printing by coiling were investigated: 1) 3-axis printing, 2) 4-axis printing with nozzle axis normal to the tangent of the toolpath, and 3) 5-axis printing with nozzle axis parallel to the base surface normal. The coiling pattern and geometrical accuracy of the contour fabrics are studied. Results show that the 5-axis AM can generate the consistent coiling pattern and the desired contour geometry to fabricate the silicone 3D contour nonwoven fabrics.

Commentary by Dr. Valentin Fuster

Bio and Sustainable Manufacturing: Advancing Biomedicine Through Innovative Manufacturing and Materials

2018;():V001T05A013. doi:10.1115/MSEC2018-6313.

A porous polymer-based three-dimensional (3D) cell culture device has been developed as an in vitro tissue model system for the cytotoxicity of anticancer drug test. The device had two chambers connected in tandem, each loaded with a 3D scaffold made of highly biocompatible poly (lactic acid) (PLA). Hepatoma cells (HepG2) and glioblastoma multiforme (GBM) cancer cells were cultured in the two separate porous scaffolds. A peristaltic pump was adopted to realize a perfusion cell culture. In this study, we focus on cell viability inside the 3D porous scaffolds under flow-induced shear stress effects. A flow simulation was conducted to predict the shear stress based on a realistic representation of the porous structure. The simulation results were correlated to the cell variability measurements at different flow rates. It is shown that the modeling approach presented in this paper can be useful for shear stress predication inside porous scaffolds and the computational fluid dynamics model can be an effective way to optimize the operation parameters of perfused 3D cell culture devices.

Commentary by Dr. Valentin Fuster
2018;():V001T05A014. doi:10.1115/MSEC2018-6345.

In this paper, we for the first-time synthesized vertically aligned polyaniline (PANI) nanowire arrays on flat-end AFM tips via template-free solution methods. 4-Aminothiophenol was used for tailoring the nucleation size, chain propagation and orientation of the PANI nanowires. The microscopy characterization indicated that diameter was centered at a mean of 33.7 nm with a standard deviation of 6.5 nm, and length was centered at a mean of 50.3 nm with a standard deviation of 7.6 nm. PANI nanowire arrays are non-toxic, low-cost, and tunable, and thus PANI nanowire-grown tips could perfectly simulate different nanosurfaces. Via the force spectroscopy, we demonstrate the feasibility in quantifying the nanostructure-cell interactions at the single cell level in real time with high reliability and accuracy. This work will enable a new tool in precisely quantifying the interactions of single living cells and nanosurface, and thus opens a new door to understand how single living cells sense and respond to the specific nanostructures.

Commentary by Dr. Valentin Fuster
2018;():V001T05A015. doi:10.1115/MSEC2018-6582.

Hydroxyl ion treatment of different hydroxyapatite-calcium hydrogen phosphate composite in-situ coatings synthesized through pulsed electro-deposition with varying amount of hydroxyapatite phase and degree of crystallinity were carried out with the help of highly basic solution in order to achieve a more chemically stable and corrosion resistance performance under contact with body fluid. The coatings exhibit altogether completely different behaviour in terms of bond formation, surface topography generation, phase transformation and corrosion behaviour. Detailed characterizations of formed top surface layer were carried out with the help of XRD, SEM and FTIR in order to correlate the results with their base surface characteristics. Transformation of <020> and <121> surface parallel planes of calcium hydrogen phosphate in to <002> and <112> planes of hydroxyapatite took place in all the coatings along with formation of nano-crystalline structure. Calcium-rich porous hydroxyapatite scaffold formation takes place in low current density coating which in general exhibits low stability in terms of chemical bonding strength vis-à-vis corrosion protection performance. 10 mA/cm2 coating, which come with optimum presence of hydroxyapatite phase and crystallinity post electro-deposition, showed significant improvement in terms of increasing hydroxyl and phosphate bond polarization strength of hydroxyapatite phase and the same lead to improvement in the overall corrosion resistance performance of the coating by two times. Despite of formation of highest amount of hydroxyapatite phase during hydroxyl ion treatment in 20 mA/cm2 coatings, the corrosion protection performance results are negative on account of dilution of mostly low bonding amorphous phases with high internal residual stress.

Commentary by Dr. Valentin Fuster
2018;():V001T05A016. doi:10.1115/MSEC2018-6611.

Post-surgery infection is one of the major causes of orthopedic implantation failure. Silver has been widely used as a broad-spectrum antimicrobial component in medical instrument. This paper presents a pioneering study on laser engineered net shaping (LENS) of titanium-silver (Ti-Ag) alloy for implant-related infection control. Ti-Ag alloy coupons were 3D printed through LENS process and characterized by 3D microscopy. The biofilm resistance and biocompatibility of the alloy samples were investigated. Results showed that the alloy significantly reduced the bacterial attachment for both Gram-positive and Gram-negative strains, and has no cytotoxicity to human fibroblast cells. This study demonstrated a great potential of laser 3D printed Ti-Ag alloy for orthopedic implant.

Commentary by Dr. Valentin Fuster
2018;():V001T05A017. doi:10.1115/MSEC2018-6675.

Microextrusion-based bioprinting within a support bath material is an emerging additive manufacturing technique for fabricating complex three-dimensional (3D) tissue constructs. However, there exists fundamental knowledge gaps in understanding the spatiotemporal mapping of cells within the bioprinted constructs and their shape fidelity when embedded in a support bath material. To address these questions, this paper advances quantitative analyses to systematically determine the spatial distribution for cell-laden filament-based tissue constructs as a function of the bio-ink properties. Also, optimal bio-ink formulations are investigated to fabricate complex 3D structures with superior shape integrity. Specifically, for a 1D filament printed in a support bath, cells suspended in low viscosity liquid hydrogel precursors are found to exhibit a characteristic non-uniform distribution as measured by a degree of separation (Ds) metric. In a 2D square wave pattern print, cells are observed to flow and aggregate downstream at certain positions along the in-plane print direction. In a 3D analysis, owing to the high cell density and gravity effects, a non-uniform cell distribution within a printed cylindrical structure is observed in the build direction. From the structural standpoint, the addition of CaCl2 to the support bath activates the hydrogel cross-linking process during printing, resulting in 3D prints with enhanced structural outcomes. This multidimensional print analysis provides evidence that, under the emerging bioprinting support bath paradigm, the printable parameter space can be extended to low viscosity liquid hydrogel precursor materials that can be systematically characterized and optimized for key process performance outcomes in cell distribution and shape fidelity.

Commentary by Dr. Valentin Fuster

Bio and Sustainable Manufacturing: Cloud-Based Smart Manufacturing

2018;():V001T05A018. doi:10.1115/MSEC2018-6435.

Nowadays, smart manufacturing has attracted more and more interesting and attentions of researchers. As an important prerequisite for smart manufacturing, the cyber-physical integration of manufacturing is becoming more and more important. Cyber-physical systems (CPS) and digital twin (DT) are the preferred means to achieve the interoperability and integration between the physical and cyber worlds. From the perspective of hierarchy, CPS and DT can be divided into unit level, system level, and SoS (system of system) level. To meet the different requirements of each level, the following three complementary technologies, i.e., edge computing, fog computing and cloud computing, are instrumental to accelerate the development of various CPS and DT. In this article, the perspectives of unit-level, system-level, and SoS-level of CPS and DT supported by edge computing, fog computing and cloud computing are discussed.

Commentary by Dr. Valentin Fuster
2018;():V001T05A019. doi:10.1115/MSEC2018-6531.

Most researches on process planning optimized machining process routings and cutting parameters independently and ignored their comprehensive effects on carbon reduction. In order to further reduce carbon emissions in manufacturing processes, an optimization model of cutting parameters and machining process routings is proposed to minimize total carbon emissions and total processing time of all processes. Carbon emissions include those caused by energy consumptions of machines in cutting state, material consumption of cutting tools and cutting fluid in all processes. As the optimization of cutting parameters is a continuous optimization problem, but the optimization of machining process routings including machining methods, process sequences, machine allocating and cutter selecting are discrete optimization problems, the whole optimization of process planning is divided into two parts. One is continuous optimization of cutting parameters. Another is discrete optimization of machining process routings. A hybrid optimization strategy of bird swarm algorithm (BSA) and NSGA-II algorithm is proposed to optimize the proposed model. Cutting parameters are optimized using BSA aiming at minimizing carbon emissions and machining time of each process. Machining process routings are optimized using NSGA-II under each optimized group of cutting parameters from the Pareto set. Four kinds of mutation operators in NSGA-II are designed for the discrete optimization of machining process routings. A workpiece with six machining features to be machined in a workshop with two CNC lathes, two CNC milling machines and two drilling machines is taken as a case study. The validity of the proposed model and hybrid strategy is verified by computational and analytical results. Several conclusions are yielded.

Commentary by Dr. Valentin Fuster
2018;():V001T05A020. doi:10.1115/MSEC2018-6538.

Industrial Cloud Robotics (ICR), with the characteristics of resource sharing, lower cost and convenient access, etc., can realize the knowledge interaction and coordination among cloud Robotics (CR) through the knowledge sharing mechanism. However, the current researches mainly focus on the knowledge sharing of service-oriented robots and the knowledge updating of a single robot. The interaction and collaboration among robots in a cloud environment still have challenges, such as the improper updating of knowledge, the inconvenience of online data processing and the inflexibility of sharing mechanism. In addition, the industrial robot (IR) also lacks a well-developed knowledge management framework in order to facilitate the knowledge evolution of industrial robots. In this paper, a knowledge evolution mechanism of ICR based on the approach of knowledge acquisition - interactive sharing - iterative updating is established, and a novel architecture of ICR knowledge sharing is also developed. Moreover, the semantic knowledge in the robot system can encapsulate knowledge of manufacturing tasks, robot model and scheme decision into the cloud manufacturing process. As new manufacturing tasks arrived, the robot platform downloads task-oriented knowledge models from the cloud service platform, and then selects the optimal service composition and updates the cloud knowledge by simulation iterations. Finally, the feasibility and effectiveness of the proposed architecture and approaches are demonstrated through the case studies.

Topics: Robotics
Commentary by Dr. Valentin Fuster
2018;():V001T05A021. doi:10.1115/MSEC2018-6613.

The advancement of various product development technologies is contributing to a total integrated manufacturing process. And model-based design (MBD) is a key enabler for such a total integration. The current MBD approach still does not support retaining of information needed at different stages of a product lifecycle. Collaboration among different Computer Aided Design (CAD) systems still becomes an issue due to the different proprietary data format. This research provides a consolidated approach to complete product definition based on STEP AP242 neutral data format using general notes data structure. To validate and demonstrate the solution, the approach is instantiated in P21 design file and implemented in cloud manufacturing as a case study.

Topics: Manufacturing
Commentary by Dr. Valentin Fuster

Bio and Sustainable Manufacturing: Sustainability and the Industrial Internet: How Data Can Lead to Improved Sustainability

2018;():V001T05A022. doi:10.1115/MSEC2018-6331.

Targeting the improvement of environmental analysis of manufacturing systems, ASTM 3012-16 provides guidelines for formally characterizing manufacturing processes. However, the difficulty that has arisen in the early use of the standard illustrates the need for intuitive tools for helping modeling experts to conform to the specified information model. In response, we present the Unit Manufacturing Process (UMP) Builder, a browser-based tool integrating symbolic mathematical and guided textual inputs, helping to consistently record and exchange manufacturing process models for environmental sustainability. The tool provides an initial layer of governance and verification with respect to the conformance to ASTM 3012-16. In this paper, we (1) detail the requirements with developing such a tool, (2) propose an improved schema to represent UMP models accommodating data-driven techniques, and (3) demonstrate the tool using a contributed model from an open challenge for modeling manufacturing processes.

Commentary by Dr. Valentin Fuster
2018;():V001T05A023. doi:10.1115/MSEC2018-6547.

Condition-based maintenance (CBM) is important to improve production system performance because it is capable to effectively prevent costly equipment failures. However, CBM usually has to stop machines for maintenance during operation and this may severely impede the normal production. This paper establishes a real-time CBM decision making method to minimize the negative impact of CBM stoppage events in a multistage manufacturing system. The method utilizes an event-based analysis method to estimate the permanent production loss resulted from a CBM event. An online control algorithm is introduced to effectively explore the optimal CBM control options. Simulation case studies are performed to validate the event-based CBM decision making method.

Commentary by Dr. Valentin Fuster
2018;():V001T05A024. doi:10.1115/MSEC2018-6707.

Over the past decade, several efforts have characterized manufacturing processes from a sustainability perspective. In addition, frameworks, methodologies, and standards development for characterizing and linking unit manufacturing process (UMP) models to construct manufacturing system models for supporting sustainability assessment have been pursued. In this paper these research efforts are first briefly reviewed, and then, ASTM standards derived from this work are described and built upon. The contribution of this research is to demonstrate how more formalization of these prior efforts will facilitate systematic reuse of developed models by encapsulating different aspects of complex processes into reusable building blocks. The research proposes a methodology to define template UMP information models, which can further be abstracted and customized to represent an application-specific, upgraded manufacturing process. The methodology developed is based on the ASTM standards of characterizing manufacturing process for sustainability characterization. The approach is demonstrated for analyzing manual and computer numerically controlled (CNC) machining processes.

Commentary by Dr. Valentin Fuster

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