ASME Conference Presenter Attendance Policy and Archival Proceedings

2017;():V002T00A001. doi:10.1115/MSEC2017-NS2.

This online compilation of papers from the ASME 2017 12th International Manufacturing Science and Engineering Conference (MSEC2017) 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presenter attendance policy, if a paper is not presented at the Conference by an author of the paper, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.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: Additive Manufacturing Process Improvements for Microstructure and Material Properties

2017;():V002T01A001. doi:10.1115/MSEC2017-2753.

In this study, a penitential additive manufacturing method - cold spray was used to deposit Ti6Al4V powders onto Ti6Al4V substrates with different surface roughness by using a high pressure cold spray system. The coating quality was good with limited porosity and without phase transition. Interface bonding behavior between coating and substrate was studied, which indicated that smoother substrate surface would increase the bonding strength. Bending test showed that all the coated samples started to delaminate before substrate failure and smoother surface samples could resist higher stress than the rougher surface samples.

Commentary by Dr. Valentin Fuster
2017;():V002T01A002. doi:10.1115/MSEC2017-2841.

Layers of Stellite-6 and Stellite-21 were deposited on tool steel substrates using co-axial laser cladding process with a goal to obtain hard, wear and corrosion resistant coatings. Clad-layers of the two types of Stellite alloys were investigated and compared in terms of microstructure, hardness and sliding wear resistance. Corrosion tests were also performed to study their corrosion behaviour. Micrographs indicated that both the Stellite grades form dendritic structure. However, there were certain differences in composition of dendritic and interdendritic regions of tungsten (W) containing Stellite-6 and molybdenum containing Stellite-21. Stellite-6 clad-layer was found to be slightly harder than Stellite-21 clad-layer near the top surface. Wear resistance of Stellite-21found to be marginally higher than that of Stellite-6 due to lower coefficient of friction. However, Stellite-21layer was found to be more corrosion resistant. Hence, for application involving mechanical loading and wear, both Stellite-6 and Stellite-21 could be a good choice as a clad-material on engineering components; but if the component is going to be subjected to mechanical loading and wear under corrosive environment Stellit-21 could be a better choice.

Commentary by Dr. Valentin Fuster
2017;():V002T01A003. doi:10.1115/MSEC2017-2843.

Fused-coating based metal additive manufacturing (FCAM) is a newly established direct metal forming process. This method is characterized by deposition metal materials in a crucible and under the driving pressure the molten metal is extruded out from a special designed nozzle. Hence, dense metal parts with different kind of materials can be built on the moving substrate layer by layer. It provides a method to fabricate metal components with lower costs, clean and cheap materials compared with other AM processes. To study the feasibility of this new AM methodology, an experimental system with a molten metal stream generator, a fused-coating nozzle, a process monitor unit, an inert atmosphere protection unit and a temperature measurement unit has been established. In order to determine the proper parameters in the building process, a metal fused-coating heat transfer model analysis and experimental study is performed by using Sn63-37Pb alloy in building three-dimensional components. The process parameters that may affect fabrication are molten and substrate temperature, layer thickness, the substrate-speed, the temperature of substrate, the distance between the nozzle and substrate and the pressure. Microscopy images were used to investigate the metallurgical bonding between layers. The influence of different parameters on the layer thickness and width was studied quantitatively. At last, the optimal parameter was used to fabricate complex metal parts to demonstrate the feasibility of this new technology compared with other AM methods.

Commentary by Dr. Valentin Fuster
2017;():V002T01A004. doi:10.1115/MSEC2017-2873.

A multi-scale modeling framework is developed in this work to simulate the transport phenomena and grain growth in Laser Engineered Net Shaping (LENS) process of austenitic stainless steel AISI 316. A three-dimensional (3D) model is included to simulate the transient molten pool geometry and heat/mass transfer on a macro-scale; and a 3D meso-scale model based on the Cellular Automata method is included to predict the grain growth during molten pool solidification. The predicted grain structure is found to be consistent with the experimental results and reveals that the grain structure is highly dependent on the molten pool geometry.

Commentary by Dr. Valentin Fuster
2017;():V002T01A005. doi:10.1115/MSEC2017-2974.

Powder capture efficiency is indicative of the amount of material that is added to the substrate during laser additive manufacturing processes, and thus, being able to predict capture efficiency provides capability of predictive modeling during such processes. The focus of the work presented in this paper is to create a numerical model to understand particle trajectories and velocities, which in turn allows for the prediction of capture efficiency. To validate the numerical model, particle tracking velocimetry experiments at two powder flow rates were conducted on free stream particle spray to track individual particles such that particle concentration and velocity fields could be obtained. Results from the free stream comparison showed good agreement to the trends observed in experimental data and were subsequently used in a direct laser deposition simulation to assess capture efficiency and temperature profile at steady-state. The simulation was validated against a single track deposition experiment and showed proper correlation of the free surface geometry, molten pool boundary, heat affected zone boundary and capture efficiency.

Commentary by Dr. Valentin Fuster
2017;():V002T01A006. doi:10.1115/MSEC2017-3024.

Laser polishing is a highly effective surface treatment process mainly used on metals and optical components, but it can also be used on plastic parts. It requires no manual labor, can be applied on parts of any size, and produces no hazardous or polluting substances on many plastic parts. Fused deposition modeling (FDM) is an additive manufacturing process in which parts are built by extruding thin layers of hot material through a nozzle. It has the advantage of producing complicated part geometries, and the possibility to change a design with no additional cost. This study investigates the use of laser polishing as an auxiliary post-process on Polylactic Acid (PLA) parts produced with FDM to improve the surface quality of final products. Although YAG lasers are commonly used in assisting metal machining processes, a CO2 laser was utilized in this study to post-process 3D-printed parts in order to reduce the staircase appearance. The main purpose of this study is to demonstrate that instead of reducing step size in 3D printing processes, it is possible to use bigger step sizes and laser treat the surface quickly afterwards to decrease the total process time while not compromising from surface quality. Laser speeds of 43–180 mm/s and laser powers of 0.75–3.75 W were tested on blocks of 3D-printed PLA with a parallelogram prism shape at 0.3 mm layer height. By varying laser speed and power, roughness reductions of up to 97% were achieved resulting in a uniform average surface roughness of 2.02 μm. This presents a fast, automatable, and inexpensive auxiliary post-process to FDM.

Commentary by Dr. Valentin Fuster

Additive Manufacturing: Additive Manufacturing Process Improvements for Part Functionality

2017;():V002T01A007. doi:10.1115/MSEC2017-2624.

This study describes a new analysis framework for additive manufacturing. The concept of processes mechanics and thermo-mechanical processing are introduced to provide a physics-based understanding of the materials behavior and the state of residual stresses. A semi-Analytical approach based on the well-known moving heat source is used to predict temperature. Subsequently, the thermal stresses are calculated analytically thanks to Green’s functions. In order to demonstrate the influence of the process parameters on the mechanical properties, the tensile behavior and fracture morphology experiments on 316L are investigated experimentally. The obtained results are analyzed in the context of the predicted temperature and thermal stresses.

Commentary by Dr. Valentin Fuster
2017;():V002T01A008. doi:10.1115/MSEC2017-2666.

This work reports the development of robust and efficient algorithms for optimum process planning of Additive Manufacturing (AM) processes needing support structures during fabrication. In particular, it addresses issues like part hollowing, support structure generation and optimum part orientation. Input to the system is a CAD model in STL format which is voxelized and hollowed using the 2D Hollowing strategy. A novel approach to design external as well as internal support structures for the hollowed model is developed considering the wall thickness and material properties.

Optimum orientation of the hollowed part model is computed using Genetic Algorithm (GA). The Fitness Function for optimization is the weighted average of process performance parameters like build time, part quality and material utilization. A new performance measure has been proposed to choose the weightages for performance parameters to obtain overall optimum performance.

The paper presents, in detail, the design and development of algorithms with results for typical case studies. The proposed methodology will significantly contribute to improving part quality, productivity and material utilization for AM processes.

Commentary by Dr. Valentin Fuster
2017;():V002T01A009. doi:10.1115/MSEC2017-2769.

One of the most popular additive manufacturing processes is laser based direct metal laser sintering process which enables us to make complex three dimensional parts directly from CAD models. Due to layer by layer formation, parts built in this process tend to be anisotropic in nature. Suitable heat treatment can reduce this anisotropic behaviour by changing the microstructure. Depending upon the applications, a wide range of mechanical properties can be achieved between 482–621° C temperature for precipitation-hardened stainless steels. In the present study effect of different heat treatment processes, namely solution annealing, ageing and overaging, on tensile strength, hardness and wear properties has been studied in detail. Suitable metallurgical and mechanical characterization techniques have been applied wherever required, to support the experimental observations. Results show H900 condition gives highest yield strength and lowest tensile strain at break whereas solution annealing gives lowest yield strength and as-built condition gives highest tensile strain at break. SEM images show that H900 and H1150 condition produces brittle and ductile morphology respectively which in turn gives highest and lowest hardness value respectively.XRD analysis shows presence of austenite phases which can increase hardness at the cost of ductility. Average wear loss for H900 condition is highest whereas it is lowest for solution annealed condition. Further optical and SEM images have been taken to understand the basic wear mechanism involved.

Commentary by Dr. Valentin Fuster
2017;():V002T01A010. doi:10.1115/MSEC2017-2796.

This paper proposes an integrated approach to determine optimal build orientation for Powder bed fusion by laser (PBF-L), by simultaneously optimizing mechanical properties, surface roughness, the amount of support structure and build time-cost. Experimental data analysis has been used to establish the objective functions for different mechanical properties and surface roughness. Geometry analysis of the part has been used to estimate the needed support structure and thus evaluate the build time and cost. Normalized weights are assigned to different objectives depending on their relative importance allowing solving the multi-objective optimization problem using a genetic optimization algorithm. A study case is presented to demonstrate the capabilities of the developed system. The major achievements of this work are the consideration of multiple objectives, the establishment of objective function considering different load direction and heat treatments. A user-friendly graphical user interface was developed allowing to control different optimization process factors and providing different visualization and evaluation tools.

Topics: Lasers , Optimization
Commentary by Dr. Valentin Fuster
2017;():V002T01A011. doi:10.1115/MSEC2017-2823.

Building 3D objects in sequential layers is a technique employed by rapid manufacturing processes and allows great design freedom in manufacturing. Scaling up such automated additive fabrication from building small industrial parts to constructing buildings has been challenging for researchers during the recent years. Compared to the traditional construction methods, numerous advantages are offered by a well-developed layer based automated construction process, including architectural design freedom, lower construction cost, superior construction speed, and higher degree of customization. Concrete has been recognized as most viable option as the material to be used with such a process. However, there are several main challenges that yet have to be solved. Obtaining a mixture with high shape stability in the fresh state is among these challenges. Ideally, non-stop printing of successive layers is desired in building a structure, so the total construction time is minimized.

In this paper, an experimental investigation of the shape stability of freshly printed concrete layers using a small-scale linear concrete printing setup with remote control capability is outlined. First, longer stoppage time between successive layers is examined to determine the effects on the deformations of fresh printing concrete. Then, heat application is proposed and studied as a measure to improve the shape stability of freshly printed concrete without adding any delay to the construction process. Furthermore, a one-story building is considered and the influence of each scenario on the total construction time is discussed.

Commentary by Dr. Valentin Fuster
2017;():V002T01A012. doi:10.1115/MSEC2017-2835.

Tensile and compression test specimens comprising lattice structures with simple cubic, crossing-rod and body-centered cubic (BCC) unit cells are produced via SLM additive manufacturing (AM) of AISI 316L stainless steel and CoCr powder. Equivalent stress-elongation curves are obtained, with equivalent strength, specific strength, stiffness modulus and specific stiffness calculated based on specimen density and sample cross-section. The obtained results highlight the fact that analogous structures can behave very differently depending on the chosen material. While large differences are obtained in strength and stiffness between the different unit cell types, specific strength and specific stiffness vary to a lesser extent. Two case studies are presented, including a porous structure suitable for bone implants in the field of biomedical engineering and an AISI 316L food packaging machine component. The results obtained in this study provide useful guidelines and equivalent properties for designers wishing to exploit the advantages of internal lattice structures in AM.

Commentary by Dr. Valentin Fuster
2017;():V002T01A013. doi:10.1115/MSEC2017-2918.

Inconel 718 (IN718) is a nickel based Ni-Cr-Fe super alloy. It has a unique set of properties such as good workability, corrosion resistance, high temperature strength, favorable weldability and excellent manufacturability. Due to its wide range of applications, IN718 is an alloy of great interest for many industries. Meanwhile, additive manufacturing assisted with laser has caught much interest from researchers and practitioners in the past three decades. In this study, IN718 alloy coupons are manufactured by selective laser melting (SLM) technique. The SLMed IN718 alloys are treated by ultrasonic nanocrystal surface modification (UNSM), and the residual stress distributions underneath the surfaces are measured. It is found that residual stress mostly tensile is induced while building the part by the SLM technique. The tensile stresses can be reduced to almost zero value by post heat treatment. Moreover, the heat treatment helps to homogenize the microstructure, and results in the increase in hardness. More importantly, it is observed that UNSM effectively induces compressive residual stresses in the as-built and heat-treated parts. The residual stresses of compressive nature in as built parts has depth of around 530 μm where as in heat treated parts has a depth of around 530μm.

Commentary by Dr. Valentin Fuster
2017;():V002T01A014. doi:10.1115/MSEC2017-2949.

In the present research, one of the additive manufacturing techniques, fused deposition modeling (FDM) fabricated parts are considered for investigation of their material behavior. The FDM process is a layer upon layer deposition of a material to build three dimensional parts and such parts behave as laminated composite structures. Each layer of the part acts as a unidirectional fiber reinforced lamina, which is treated as an orthotropic material. The mesostructure of a part fabricated via fused deposition modeling process is accounted for in the investigation of its mechanical behavior. The finite element (FE) procedure for characterization of a material constitutive law for the FDM processed parts is presented. In the analysis, the mesostructure of the part obtained via FDM process is replicated in the finite element models. Finite element models of tensile specimens are developed with mesostructure that would be obtained from FDM process, then uniaxial tensile test simulations are conducted. The elastic moduli of a lamina are calculated from the linear analysis and the strength parameters are obtained from the nonlinear finite element analysis. The present work provides a FE methodology to find elastic moduli and strength parameters of a FDM processed part by accounting its mesostructure in the analysis.

Topics: Modeling
Commentary by Dr. Valentin Fuster
2017;():V002T01A015. doi:10.1115/MSEC2017-2951.

Additive manufacturing has attracted the attention of industries such as aerospace and automotive as well as the medical technology sectors in recent years. Among all metal-based additive techniques, laser metal wire deposition offers some advantages like shorter processing time, more efficient material usage, and a larger buildup envelop. It has been found that robotized laser/wire additive manufacturing (RLWAM) is a demanding process. A plethora of process parameters must be controlled compared to other laser-based metal deposition processes. The influence of main process parameters such as laser power, stepover increment, wire feed speed, travel speed and z-increment was investigated in this study to find the optimal values. Droplet formation, wire dripping, irregular deposition in the first layer, and deviation of the wire tip were also found to be the main obstacles throughout the process and practical solutions were proposed to deal with these issues. In this study, an 8-axis robot (6-axis arm robot with a 2-axis positioner) and a 4 kW fiber laser along with a wire feeder were integrated to print the different geometrical shapes in 3D. In order to verify the geometrical accuracy of the as-built part, the buildup was scanned using a portable 3D laser scanner. The 3D representation, the Standard Tessellation Language (STL) format obtained from the buildup, was compared with the original CAD model. The results show that RLWAM can be successfully applied in printing even complicated geometries.

Commentary by Dr. Valentin Fuster
2017;():V002T01A016. doi:10.1115/MSEC2017-2978.

Traditional extrusion based additive manufacturing (AM) processes build parts by depositing material in planar layers. The development of processes that adopt a non-planar approach is becoming a subject of significant interest in AM research. It is expected that such processes will impart superior mechanical strength to anisotropic and thin-walled structures, and will especially be useful in exploiting continuous fiber reinforced composites in additive manufacturing. This paper presents an extrusion based non-planar additive manufacturing process. The process allows for the deposition of material along 3-dimensional paths, providing the capability to reorient deposition head, build objects on curved platforms, and create complete structures using one continuous strand. Two different parts are fabricated and tested in this paper. One is produced using the developed process, while the other is created using a commercial FDM 3D printer. The two specimens are then mechanically tested to examine their behavior in two different loading configurations, and to investigate the effect that the deposition method and orientation has on the failure mode.

Commentary by Dr. Valentin Fuster
2017;():V002T01A017. doi:10.1115/MSEC2017-3015.

Surface roughness is an inherent attribute of parts fabricated by Powder-Bed Electron Beam Additive Manufacturing (PB-EBAM) process. The wide application of PB-EBAM technology is affected by the part surface quality and therefore needs to be studied and optimized so as to establish PB-EBAM process among other manufacturing processes. Therefore, in this study, the build surface of fabricated parts built with different speed function (SF) is analyzed using white light interferometry. The results show that, in general the build surface roughness along the beam moving direction slightly increases with the scanning speed. On the other hand, the hatch spacing noticeably affects the surface roughness in the transverse direction. The experimentally acquired average surface roughness increased with increasing speed function from about 3 μm for SF20 case to 11 μm for SF65 case. In addition, a 3D VOF model has been attempted to predict the surface formation during the PB-EBAM process. Thus simulated SF36 case was able to predict different surface features and was in good agreement with experiment which shows that surface roughness analysis with numerical model may be a possible approach.

Commentary by Dr. Valentin Fuster
2017;():V002T01A018. doi:10.1115/MSEC2017-3018.

Overhang structures are commonly found in Powder-bed metal additive manufacturing (AM) such as electron beam additive manufacturing (EBAM) process. The EBAM is assumed to build overhang structure without support features since powder bed could provide support. However, heat dissipation difference by sintered powder and solid substrate for overhang feature actually causes severe part distortion and requires support structure. Current support generation methods usually used certain types of structure to cover the overhang space. They may overestimate the support volume or put a large amount of supports, which could not be necessary and increase the post process time. Thus, the object of this task is to enhance the performance and efficient usage of the EBAM technology through effective support structure designs. In this study, a combined heat support and support anchor design method has been proposed. Numerical model has been used to evaluate stress and deformation during the design process. The detailed design process has been presented for a typical overhang and the simulation results have indicated that overhang deformation can be greatly reduced using this new method.

Commentary by Dr. Valentin Fuster
2017;():V002T01A019. doi:10.1115/MSEC2017-3021.

Friction Stir Welding (FSW) offers significantly better performance on aluminum alloy joints compared to the conventional fusion arc welding techniques; however, plastic deformation, visco-plastic flow of metals, and complex non-uniform heating cycles during FSW processes, result in dissolution of alloying elements, intrinsic microstructural changes, and post-weld residual stress development. As a consequence, about 30% reduction in ultimate strength (UTS) and 60% reduction in yield strength (YS) were observed in defect-free, as-welded AA2219-T87 joints. PWHT is a common practice to refine grain-coarsened microstructures which removes or redistributes post-weld residual stresses; and improves mechanical properties of heat-treatable welded aluminum alloys by precipitation hardening. An extensive experimental program was undertaken on PWHT of FS-welded AA2219-T87 to obtain optimum PWHT conditions and improvement of the tensile properties. Artificial age-hardening (AH) helped in the precipitation of supersaturated alloying elements produced around weld nugget area during the welding process. As a result, an average 20% improvement in YS and 5% improvements in UTS was observed in age-hardened (AH-170°C-18h) specimens as compared to AW specimens. To achieve full benefit of PWHT, solution-treatment followed by age-hardening (STAH) was performed on FS-welded AA2219-T87 specimens. Solution-treatment (ST) helps in the grain refinement and formation of supersaturated precipitates in aluminum alloys. Age-hardening of ST specimens help in the precipitation of alloying elements around grain boundaries and strengthen the specimens. Optimum aging period is important to achieve better mechanical properties. For FS-welded AA2219-T87 peak aging time was 5 hours at 170°C. STAH-170°C -5h treated specimens showed about 78% JE based on UTS, 61% JE based on yield strength, and 36% JE based on tensile toughness values of base metal.

Topics: Friction , Heat
Commentary by Dr. Valentin Fuster
2017;():V002T01A020. doi:10.1115/MSEC2017-3048.

This paper investigates a new technology to create functionally graded material (FGM) by additive manufacturing (AM). In particular, this paper focuses on creating graphene-polymer composite FGM by laser-based sintering processes. Graphene-polymer composites have received high attention in AM due to their excellent electrical conductivity, thermal stability and mechanical strength. However, AM of the graphene-polymer composites has a huge challenge to overcome. The heterogeneous materials should be mixed properly, and it is not easy to achieve the desired composite characteristics solely by changing the mass ratio of graphene. This paper shows a newly developed laser-assisted AM system for the graphene-polymer composite FGM by laser-based sintering processes. The paper also describes two methods of material integration: mixing graphene and polyethylene powders before sintering, and depositing the different material powders separately and sintering them. This study identified that the two methods led to different mechanical and electrical properties of the created parts. Thus this paper demonstrates the possibility to create quite useful hybrid (mechanically and electrically) FGM composites.

Commentary by Dr. Valentin Fuster
2017;():V002T01A021. doi:10.1115/MSEC2017-3061.

Additive manufacturing has led to increasing number of applications that require complex geometries and multiple materials. This paper presented a bi-material structure (BMS) composed of a cushion matrix held by a 3D printed frame structure for an improved impact resistance. The study mainly focused on understanding the effects of structural topology and matrix material. Two matrix materials, silicone elastomer and polyurethane (PU) foam, were selected to impregnate into two different PLA frame structures. Drop weight impact test was carried out to measure the impact force and energy absorption. The results showed that the overall impact resistance was dominated by the frame, while the matrix reinforcement required proper structural interlocking mechanism and material matching. In the particular specimens of this study, PU foam led to more energy absorption and force bearing capacity of the structure than the silicone elastomer.

Commentary by Dr. Valentin Fuster

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

2017;():V002T01A022. doi:10.1115/MSEC2017-2684.

As an emerging and effective nano-manufacturing technology, the directional freezing based 3D printing can form 3-Dimensional (3D) nano-structures with complex shapes and superior functionalities, and thus has received ever increasing publicity in the past years. One of the key challenges in this process is the proper heat management, since the heat induced melting and solidification process significantly affects the functional integrity and structural integrity of the 3D printed nano-structures. To address this challenge, this paper proposes a novel path planning modeling and optimization framework to intelligently control the internal and external heat transfer process and ultimately optimize both the macro- and micro-structure of the printed part. Specifically, a heuristic tool path planning model was formulated and optimized based on thermal analysis process. The simulation results demonstrate that the tool path planning highly affects the spatial and temporal temperature distribution of the being printed part and the optimized tool path planning can effectively improve the uniformity of the temperature distribution which will consequently enhance the performance of the fabricated nano-structures.

Commentary by Dr. Valentin Fuster
2017;():V002T01A023. doi:10.1115/MSEC2017-2731.

In this work, a novel liquid bridge based microstereolithography (LBMSL) was proposed and developed. The liquid bridge was first introduced into the MSL process by replacing the vat, allowing the entire fabrication process to occur within the liquid bridge. The liquid bridge was studied theoretically and experimentally in order to obtain the stable equilibrium shape and the relationship between the height and the volume of the liquid bridge. Using the LBMSL process, the fabrication layer thickness of 0.5 μm was reached. This could not be easily achieved in the vat-based MSL due to the oxygen inhibition to the photopolymer. Fabrication of a photopolymer with a viscosity of 3000 cP was tested and significant results were obtained. Compared with the vat-based MSL, the material consumption in LBMSL was reduced and the fabrication time was improved greatly, in particular, when using higher viscous materials.

Commentary by Dr. Valentin Fuster
2017;():V002T01A024. doi:10.1115/MSEC2017-2779.

Multi-scale and multi-material 3D printing is new frontier in additive manufacturing. It has shown great potential to implement the simultaneous and full control for fabricated object including external geometry, internal architecture, functional surface, material composition and ratio as well as gradient distribution, feature size ranging from nano, micro, to marco-scale, embedded components and electro-circuit, etc. Furthermore, it has the ability to construct the heterogeneous and hierarchical structured object with tailored properties and multiple functionalities which cannot be achieved through the existing technologies. That paves the way and may result in great breakthrough in various applications, e.g., functional tissue and organ, functionally graded material/structure, wearable devices, soft robot, functionally embedded electronics, metamaterial, multi-functionality product, etc. However, very few of the established additive manufacturing processes have now the capability to implement the multi-material and multi-scale 3D printing. This paper presented a single nozzle-based multi-scale and multi-material 3D printing process by integrating the electrohydrodynamic jet (E-jet) printing and the active mixing multimaterial nozzle. The proposed AM technology has the capability to create multifunctional heterogeneously structured objects with control of the macro-scale external geometry and micro-scale internal structures as well as functional surface features, particularly, the potential to dynamically mix, grade and vary the ratios of different materials. An active mixing nozzle, as a core functional component of the 3D printer, is systematically investigated by combining with the theoretical analysis, numerical simulation and experimental verification. The study aims at exploring a feasible solution to implement the multi-scale and multi-material 3D printing at low cost.

Commentary by Dr. Valentin Fuster
2017;():V002T01A025. doi:10.1115/MSEC2017-2788.

Stereolithography of three-dimensional, arbitrarily-shaped objects is achieved by successively curing photopolymer on multiple 2D planes and then stacking these 2D slices into 3D objects. Often as a bottleneck for speeding up the fabrication process, this layer-by-layer approach originates from the lack of axial control of photopolymerization. In this paper, we present a novel stereolithography technology with which two-photon polymerization can be dynamically controlled in the axial direction using Bessel beam generated from a spatial light modulator (SLM) and an axicon. First, we use unmodulated Bessel beam to fabricate micro-wires with an average diameter of 100 μm and a length exceeding 10 mm, resulting in an aspect ratio > 100:1. A study on the polymerization process shows that a fabrication speed of 2 mm/s can be achieved. Defect and deformation are observed, and the micro-wires consist of multiple narrow fibers which indicate the existence of the self-writing effect. A test case is presented to demonstrate fast 3D printing of a hollow tube within one second. Next, we modulate the Bessel beam with an SLM and demonstrate the simultaneous generation of multiple focal spots along the laser propagation direction. These spots can be dynamically controlled by loading an image sequence on the SLM. The theoretical foundation of this technology is outlined, and computer simulation is conducted to verify the experimental results. The presented technology extends current stereolithography into the third dimension, and has the potential to significantly increase 3D printing speed.

Commentary by Dr. Valentin Fuster
2017;():V002T01A026. doi:10.1115/MSEC2017-2811.

Sintering of nanoparticles to create films and patterns of functional materials is emerging as a key manufacturing process in applications like flexible electronics, solar cells and thin-film devices. Further, there is the emerging potential to use nanoparticle sintering to perform additive manufacturing as well. While the effect of nanoparticle size on sintering has been well studied, very little attention has been paid to the effect of nanoparticle shape on the evolution of sintering. This paper uses Molecular dynamics (MD) simulations to determine the influence of particle shape on shrinkage and neck growth for two common nanoparticle shape combinations, i.e., sphere-sphere and sphere-cylinder nanoparticles of different sizes. These sintering indicators are examined at two different temperature ramps. The results from this work show that depending on their relative sizes, degree of neck growth and shrinkage are both significantly affected by the nanoparticle shape. The possibility of using this phenomenon to control density and stresses during nanoparticle sintering are discussed.

Commentary by Dr. Valentin Fuster
2017;():V002T01A027. doi:10.1115/MSEC2017-2893.

Electrohydrodynamic processes were used for direct-writing of bead arrays with controllable bead sizes. Experiments were conducted to align layers of bead-on-string structures in an effort to create three-dimensional patterns. The results show that the jet focuses on previously deposited droplets allowing for the selective deposition of material over already deposited patterns. Jet attraction to already deposited solutions on the substrate is attributed to the charge transport at the liquid ink-metal collector interface and the dielectric properties of the water/poly(ethylene oxide) solution under an electric field. The deposition process consists of 3 steps: (1) deposition of a layer of bead-on-string structures, (2) addition of extra volume to the beads by subsequent passes of the jet, and (3) evaporation of the solvent resulting in an array of beads with varying sizes. Patterns with up to 20 passes were experimentally obtained. The beads’ height was seen to be independent of the number of passes. The process reported is a simple, fast, and low-cost method for deposition of bead arrays with varying diameters.

Commentary by Dr. Valentin Fuster
2017;():V002T01A028. doi:10.1115/MSEC2017-2900.

Lithium ion battery electrodes were manufactured using a new additive manufacturing process based on dry powders. By using dry powder based process, solvent and drying process used in conventional battery process can be removed which allows large-scale Li-ion battery production be more economically viable in markets such as automotive energy storage systems. Thermal activation time has been greatly reduced due to the time and resource demanding solvent evaporation process needed with slurry-cast electrode manufacturing being replaced by a hot rolling process. It has been found that thermal activation time to induce mechanical bonding of the thermoplastic polymer to the remaining active electrode particles is only a few seconds. By measuring the surface energies of various powders and numerical simulation of powder mixing, the powder mixing and binder distribution, which plays a vital role in determining the quality of additive manufactured battery electrodes, have been predicted and compared favorably with experiments.

Commentary by Dr. Valentin Fuster
2017;():V002T01A029. doi:10.1115/MSEC2017-2911.

Graphene possesses many outstanding properties, such as high strengths, light weight, making it an ideal reinforcement for metal matrix composite (MMCs). Meanwhile, fabricating MMCs through laser assisted additive manufacturing (LAAM) has attracted much attention in recent years due to the advantages of low waste, high precision, short production lead time, and high flexibility. In this study, graphene reinforced aluminum alloy AlSi10Mg is fabricated using selective laser melting. Composite powder is prepared using high-energy ball milling. Room temperature tensile tests are conducted to evaluate the tensile properties. Scanning electron microscopy (SEM) observations are conducted to investigate the microstructure and fracture surface of obtain composite. It is found that adding GNPs significantly increases porosity and therefore deteriorates material tensile performance. The relationship between porosity and material strength are numerically investigated. Taking into consideration the strength reduction caused by large porosity, the strengthening effect of GNPs turns out to be significant, which reaches 60.2 MPa.

Commentary by Dr. Valentin Fuster
2017;():V002T01A030. doi:10.1115/MSEC2017-2913.

Selective laser melting (SLM) is an additive manufacturing process that uses laser beam to melt metal powders and allow the melt to solidify in a layerwise way. SLM has drawn much attention from industry and academia in recent years. Improving the mechanical properties and performance of components fabricated by SLM has been a focused research area. Adding hard second phase particles into metal matrix has been proven an effective measure to strengthen metal material by SLM. In this research, we adopt nano sized TiC particles to reinforce pure iron matrix using the SLM process. The reinforced TiC/iron composite with 0.5 wt.% TiC is successfully fabricated. Tensile tests and fatigue tests are carried out to demonstrate the strengthening effect, and fatigue fracture surfaces are characterized by SEM to understand the fatigue failure mechanism. The obtained experimental data are compared with an existing composite fatigue life prediction model. The results indicate that nano TiC is effective in improving the tensile performance of pure iron, where the ultimate tensile strength (UTS) and yield strength (YS) increase by 17% and 6.3% respectively. TiC nano particles improve the fatigue life principally at lower cycle fatigue regime, while the beneficial effect at high cycle fatigue regime is not significant, mainly due to the large porosity introduced in SLM process. In addition, it is discovered that traditional Ding’s model does not accurately predict the fatigue life of nano TiC/iron composite, and thus more accurate fatigue modeling work is called for.

Commentary by Dr. Valentin Fuster
2017;():V002T01A031. doi:10.1115/MSEC2017-2960.

Three-dimensional (3D) printing of microscale structures with high resolution (sub-micron) and low cost is still a challenging work for the existing 3D printing techniques. Here we report a direct writing process via near-field melt electrospinning to achieve microscale printing of single filament wall structures. The process allows continuous direct writing due to the linear and stable jet trajectory in the electric near-field. The layer-by-later stacking of fibers, or self-assembly effect, is attributed to the attraction force from the molten deposited fibers and accumulated negative charges. We demonstrated successful printing of various 3D thin wall structures (freestanding single walls, double walls, annular walls, star-shaped structures, and curved wall structures) with a minimal wall thickness less than 5 μm. By optimizing the process parameters of near-field melt electrospinning (electric field strength, collector moving speed, and needle-to-collector distance), ultrafine poly (ε-caprolactone) (PCL) fibers have been stably generated and precisely stacked and fused into 3D thin-wall structures with an aspect ratio of more than 60. It is envisioned that the near-field melt electrospinning can be transformed into a viable high-resolution and low-cost microscale 3D printing technology.

Commentary by Dr. Valentin Fuster
2017;():V002T01A032. doi:10.1115/MSEC2017-2975.

Copper (Cu) has already replaced aluminum as the primary material for interconnect fabrication due to its superior electrical and thermal conductivity. Low resistivity of Cu decreases the RC delay which in turn increases the integrated circuit (IC) speed. Copper nanoparticle (NP) inks can also serve as a promising replacement of silver NP inks in 2D printing applications on solid and flexible substrates. This paper presents a simplified model to estimate optimum laser sintering parameters of Cu NPs. The model is validated by the experimental sintering results using nanosecond and femtosecond pulsed lasers. The predicted sintering thresholds agree well with sintering experiments.

Commentary by Dr. Valentin Fuster
2017;():V002T01A033. doi:10.1115/MSEC2017-3031.

Current Stereolithography (SL) can fabricate three-dimensional (3D) objects in a single scale level, e.g. printing macro-scale or micro-scale objects. However, it is difficult for the SL printers to fabricate a 3D macro-scale object with micro-scale features. In the paper a novel SL-based multi-scale fabrication method is presented to address such a problem. The developed SL process can fabricate multi-scale features by dynamically changing the shape and size of a laser beam. Different shaped beams are realized by switching apertures with different micro-patterns. The laser beam without using any micro-patterns is used to fabricate the macro-scale features, while the shaped laser beams with smaller sizes are used to fabricate micro-patterned features. Accordingly, the tool path planning method for the multi-scale fabrication process are developed so that macro-scale and micro-scale features can be built by using different layer thicknesses, laser exposure time, and scanning paths. Compared with the conventional SL process based on a fixed laser beam size, our process can fabricate multi-scale features in a 3D object. It also has fast fabrication speed and good surface quality.

Commentary by Dr. Valentin Fuster
2017;():V002T01A034. doi:10.1115/MSEC2017-3032.

In electrospray printing, a plume of highly charged droplets is created from a conductive ink. Printing occurs by positioning a target substrate in the path of the emitted material. Here, the ink used is a colloidal dispersion consisting of nanoparticles suspended in a volatile solvent. The selection of a volatile solvent allows for rapid evaporation of the droplets in-flight to produce dry nanoparticles. An excess electric charge is imparted on the emitted particles during electrospray. The interaction of this charge with the global electric field and with other charged particles/droplets governs the particles trajectory and determines the microstructure of the printed deposit. In this study, we characterized the structure of nanoparticle deposits printed using electrospray for short spray times. Electrospray printing is capable of exerting much finer control over microstructure compared to other printing techniques. This has significant implications for the manufacturing of thin-films.

Topics: Sprays
Commentary by Dr. Valentin Fuster
2017;():V002T01A035. doi:10.1115/MSEC2017-3074.

To date, various multi-material and multi-functional Additive Manufacturing technologies have been developed for the production of multi-functional smart structures. Those technologies are capable of controlling the local distributions of materials, hence achieving gradient or heterogeneous properties and functions. Such multi-material and multi-functional manufacturing capability opens up new applications in many fields. However, it is still largely unknown that how to design the localized material distribution to achieve the desired product properties and functionalities. To address this challenge, the correlation between the micro-scale material distribution and the macroscopic composite performance needs to be established. In our previous work, a novel Magnetic-field-assisted Stereolithography (M-PSL) process has been developed, for fabricating magnetic particle-polymer composites. Hence, in this work, we focus on the study of magnetic-field-responsive particle-polymer composite design, with the aim of developing some guidelines for predicting the magnetic-field-responsive properties of the composite fabricated by M-PSL process. Micro-scale particle distribution parameters, including particle loading fraction, particle magnetization, and distribution patterns, are investigated. Their influences on the properties of particle-polymer liquid suspensions, and the properties of the 3D printed composites, are characterized. By utilizing the magnetic anisotropy properties of the printed composites, different motions of the printed parts could be triggered at different relative positions under the applied magnetic field. Physical models are established, to predict the particle-polymer liquid suspension properties and the trigger conditions of fabricated parts. Experiments are performed to verify the physical models. The predicted results agree well with the experimental measurements, indicating the effectiveness of predicting the macroscopic composite performance using micro-scale distribution data, and the feasibility of using the physical models for guiding the multi-material and multi-functional composite design.

Commentary by Dr. Valentin Fuster
2017;():V002T01A036. doi:10.1115/MSEC2017-3075.

Surface plasmon polaritons are associated with the light-nanoparticle interaction and results in high enhancement in the gap between the particles. Indeed, this is affected by particle size, spacing, interlayer distance and light source properties. Polarization effect on three-dimensional (3D) and out of plane nanoparticle packings are presented herein to understand the out of plane configuration effect by using 532 nm plane wave light. This analysis gives insight on the particle interactions between the adjacent layers for multilayer nanoparticle packings. It has been seen that the electric field enhancement is up to 400 folds for TM (Transverse magnetic) or X-polarized light and 26 folds for TE (Transverse electric) or Y-polarized light. Thermo-optical properties change nonlinearly between 0 and 10 nm gap spacing due to the strong and non-local near-field interaction between the particles for the TM polarized light; however, this is linear for TE polarized light. This will give insight on the micro/nano heat transport for the interlayer particles for 100 nm diameter of Cu nanoparticle packings under 532 nm light under different polarization for 3-D interconnect (IC) manufacturing.

Commentary by Dr. Valentin Fuster

Additive Manufacturing: Environmental Sustainability of Additive Manufacturing Processes

2017;():V002T01A037. doi:10.1115/MSEC2017-2871.

Complexity has been one of the focal points of attention in the supply chain management domain, as it deteriorates the performance of the supply chain and makes controlling it problematic. The complexity of supply chains has been significantly increased over the past couple of decades. Meanwhile, Additive Manufacturing (AM) not only revolutionizes the way that the products are made, but also brings a paradigm shift to the whole production system. The influence of AM extends to product design and supply chain as well. The unique capabilities of AM suggest that this manufacturing method can significantly affect the supply chain complexity. More product complexity and demand heterogeneity, faster production cycles, higher levels of automation and shorter supply paths are among the features of additive manufacturing that can directly influence the supply chain complexity. Comparison of additive manufacturing supply chain complexity to its traditional counterpart requires a profound comprehension of the transformative effects of AM on the supply chain. This paper first extracts the possible effects of AM on the supply chain and then tries to connect these effects to the drivers of complexity under three main categories of 1) market, 2) manufacturing technology, and 3) supply, planning and infrastructure. Possible impacts of additive manufacturing adoption on the supply chain complexity have been studied using information theoretic measures. An Agent-based Simulation (ABS) model has been developed to study and compare two different supply chain configurations. The findings of this study suggest that the adoption of AM can decrease the supply chain complexity, particularly when product customization is considered.

Commentary by Dr. Valentin Fuster
2017;():V002T01A038. doi:10.1115/MSEC2017-2957.

Additive manufacturing (AM), owning to the unique layer-by-layer manufacturing method and its associated advantages, has been implemented in a great number of industries. To further expand the AM applications, the current low throughput of AM system needs to be improved. Consequently, the batch production method, where multiple parts are fabricated in one batch, has gained increasing research interest. In the current state of literature, most research efforts assess the batch production approach based on its manufacturing cost saving potential. Nevertheless, environmental sustainability, serving as a critical part in AM development, is less explored. Environmental sustainability of AM batch production needs to be thoroughly investigated and assessed, due to the potential environmental impacts and human health risks that AM batch production activities might cause. This research aims to advance the state-of-the-art on environmental sustainability evaluation for AM batch production, by experimentally comparing three main environmental sustainability aspects (i.e., energy consumption, emission, and material waste) for batch production processes with different batch sizes. Based on the experimental results, the feasibility of batch production method for AM is discussed. The outcomes of this research will help evaluate the AM batch production method from an environmental sustainability standpoint, and facilitate the development of AM batch production.

Commentary by Dr. Valentin Fuster
2017;():V002T01A039. doi:10.1115/MSEC2017-2983.

The additive manufacturing (AM) technology provides a unique opportunity to realize as-built assemblies, i.e., assemblies which can be fabricated as a whole in one build cycle. Some of the introduced challenges, however, are the design issues of these assembly structures and understanding the dimensional performance of the AM process to ensure proper mobility. While process improvement techniques have been proposed for dealing with individual additive components, it is also necessary to study the dimensional behavior of as-built assemblies compared to individual additive components. This paper studies and compares the dimensional performance of as-built assemblies with ordinary assemblies in which the components are fabricated individually and then assembled together. A design of experiment approach is applied to study the effect of assembly type and orientation on the final clearances. The results suggest that in addition to orientation factor, the type of assembly can also play an important role in the final clearance values. In addition, a different dimensional behavior exists in the as-built assembly structures compared to ordinary assemblies, i.e., clearances in as-built assembly tend to be smaller and also more uniform along the clearance profile.

Commentary by Dr. Valentin Fuster
2017;():V002T01A040. doi:10.1115/MSEC2017-3007.

Throughout the past decade the popularity of additive manufacture (AM) has grown tremendously. Although AM has been deemed as an environmentally friendly alternative to traditional processes, there have already been several studies done showing that AM processes can affect human health and the environment by emitting particles of a dynamic size range into its surrounding during a print. The objective of this paper is to look deeper into the issue of particle emissions from one of the most popular AM processes i.e. fused deposition modeling (FDM). Particle emissions from a Makeblock 3-D printer enclosed in a chamber and placed in a Class 1 cleanroom are measured using a high temporal resolution electrical low pressure impactor (ELPI) which takes close-to-real-time measurements of particles in the range of 6–200nm. A honeycomb cube with side length 1.25” and the NIST standard testing part are printed using acrylonitrile butadiene styrene (ABS) filament. Results show that particle emissions are closely related to the filament residence time in the extruder while less related to extruding speed. The initial spike of particle concentration right after printing starts is likely due to the long time needed to heat the extruder and the bed to the desired temperature. It is suggested that part geometry/features and build path could significantly affect particle emissions. TEM images suggest that particles may be formed through vapor condensation and coagulation of small particles.

Commentary by Dr. Valentin Fuster

Additive Manufacturing: Quality Assurance in Additive Manufacturing Systems: Integrated Sensing and Control

2017;():V002T01A041. doi:10.1115/MSEC2017-2657.

The current study focuses on the process monitoring of thermal history and its significance in laser cladding technology. Thermal history of the molten pool during laser cladding was monitored using an IR-pyrometer and the molten pool life time, solidification shelf duration and cooling rates were calculated. Effect of these on three different cases was studied in brief: (a) Elemental segregation in nickel based super alloy, (b) Wettability between metal matrix and WC particles and (c) Decomposition of TiC particles in metal matrix. It was found that with slow cooling rate, formation of Laves phases in Inconel 718 became dominant which is detrimental to the mechanical properties. Also, slow cooling resulted in the decomposition of TiC particles resulting in poor wear properties of the coating. In contrast to the above two cases where slow cooling was found to be detrimental for mechanical properties of the coating, it increased wettability as well as bonding through diffusion between the WC particles and the metal matrix. Also the effect of presence of TiC and WC in metal matrix on molten pool thermal history was studied. The microstructures, elemental segregations and fractured surfaces were characterized using SEM and EDS analyses.

Commentary by Dr. Valentin Fuster
2017;():V002T01A042. doi:10.1115/MSEC2017-2794.

This work proposes a novel approach for geometric integrity assessment of additive manufactured (AM, 3D printed) components, exemplified by acrylonitrile butadiene styrene (ABS) polymer parts made using fused filament fabrication (FFF) process. The following two research questions are addressed in this paper: (1) what is the effect of FFF process parameters, specifically, infill percentage (If) and extrusion temperature (Te) on geometric integrity of ABS parts?; and (2) what approach is required to differentiate AM parts with respect to their geometric integrity based on sparse sampling from a large (∼ 2 million data points) laser-scanned point cloud dataset? To answer the first question, ABS parts are produced by varying two FFF parameters, namely, infill percentage (If) and extrusion temperature (Te) through design of experiments. The part geometric integrity is assessed with respect to key geometric dimensioning and tolerancing (GD&T) features, such as flatness, circularity, cylindricity, root mean square deviation, and in-tolerance percentage. These GD&T parameters are obtained by laser scanning of the FFF parts. Concurrently, coordinate measurements of the part geometry in the form of 3D point cloud data is also acquired. Through response surface statistical analysis of this experimental data it was found that discrimination of geometric integrity between FFF parts based on GD&T parameters and process inputs alone was unsatisfactory (regression R2 < 50%). This directly motivates the second question. Accordingly, a data-driven analytical approach is proposed to classify the geometric integrity of FFF parts using minimal number (< 2% of total) of laser-scanned 3D point cloud data. The approach uses spectral graph theoretic Laplacian eigenvalues extracted from the 3D point cloud data in conjunction with a modeling framework called sparse representation to classify FFF part quality contingent on the geometric integrity. The practical outcome of this work is a method that can quickly classify the part geometric integrity with minimal point cloud data and high classification fidelity (F-score > 95%), which bypasses tedious coordinate measurement.

Commentary by Dr. Valentin Fuster
2017;():V002T01A043. doi:10.1115/MSEC2017-2892.

Despite recent advances in improving mechanical properties of parts fabricated by Additive Manufacturing (AM) systems, optimizing geometry accuracy of AM parts is still a major challenge for pushing this cutting-edge technology into the mainstream. This work proposes a novel approach for improving geometry accuracy of AM parts in a systematic and efficient manner. Initial experimental data show that different part geometric features are not necessary positively correlated. Hence, it may not be possible to optimize them simultaneously. The proposed methodology formulates the geometry accuracy optimization problem as a multi-objective optimization problem. The developed method targeted minimizing deviations within part’s major Geometric Dimensioning and Tolerancing (GD&T) features (i.e., Flatness, Circularity, Cylindricity, Concentricity and Thickness). First, principal component analysis (PCA) is applied to extract key components within multi-geometric features of parts. Then, experiments are sequentially designed in an accelerated and integrated framework to achieve sets of process parameters resulting in acceptable level of deviations within principal components of multi-geometric features of parts. The efficiency of proposed method is validated using simulation studies coupled with a real world case study for geometry accuracy optimization of parts fabricated by fused filament fabrication (FFF) system. The results show that optimal designs are achieved by fewer numbers of experiments compared with existing methods.

Commentary by Dr. Valentin Fuster
2017;():V002T01A044. doi:10.1115/MSEC2017-2909.

The microstructure and mechanical properties of Laser Based Additive Manufacturing (LBAM) are often inconsistent and unreliable for many industrial applications. One of the key technical challenges is the lack of understanding of the underlying process-structure-property relationship. The objective of the present research is to use the melt pool thermal profile to predict porosity within the LBAM process. Herein, we propose a novel porosity prediction method based on morphological features and the temperature distribution of the top surface of the melt pool as the LBAM part is being built. Self-organizing maps (SOM) are then used to further analyze the 2D melt pool dataset to identify similar and dissimilar melt pools. The performance of the proposed method of porosity prediction uses X-Ray tomography characterization, which identified porosity within the Ti-6Al-4V thin wall specimen. The experimentally identified porosity locations were compared to the porosity locations predicted based on the melt pool analysis. Results show that the proposed method is able to predict the location of porosity almost 85% of the time when the appropriate SOM model is selected. The significance of such a methodology is that this may lead the way towards in situ monitoring and on-the-fly modification of melt pool thermal profile to minimize or eliminate pores within LBAM parts.

Commentary by Dr. Valentin Fuster
2017;():V002T01A045. doi:10.1115/MSEC2017-2942.

This work presents high speed thermographic measurements of the melt pool length during single track laser scans on nickel alloy 625 substrates. Scans are made using a commercial laser powder bed fusion machine while measurements of the radiation from the surface are made using a high speed (1800 frames per second) infrared camera. The melt pool length measurement is based on the detection of the liquidus-solidus transition that is evident in the temperature profile. Seven different combinations of programmed laser power (49 W to 195 W) and scan speed (200 mm/s to 800 mm/s) are investigated and numerous replications using a variety of scan lengths (4 mm to 12 mm) are performed. Results show that the melt pool length reaches steady state within 2 mm of the start of each scan. Melt pool length increases with laser power, but its relationship with scan speed is less obvious because there is no significant difference between cases performed at the highest laser power of 195 W. Although keyholing appears to affect the anticipated trends in melt pool length, further research is required.

Topics: Lasers
Commentary by Dr. Valentin Fuster
2017;():V002T01A046. doi:10.1115/MSEC2017-2947.

The goal of this work is online quality monitoring of flexible electronic devices made using Aerosol jet printing (AJP) additive manufacturing (AM) process. In pursuit of this goal, the objective is to recover and quantify the 3D topology of AJP-printed electronic traces (lines) through in situ images. The intent is to use the estimated 3D topology for online prediction of the device electrical performance characteristics. To realize this objective different shape-from-shading (SfS) techniques are tested to recover the 3D topology of lines from high resolution in situ 2D images. These images are obtained from a CCD camera installed on our experimental Optomec AJ300 AJP setup. White light interferometry is used offline to verify the online experimental trends. Three types of SfS algorithms are tested, namely, minimization method, Pentland’s method, and Shah’s method. Tests with synthetic images and experimental data indicate that Shah’s method is more suitable. The correlation between online and offline estimates of line thickness was ∼80%.

Commentary by Dr. Valentin Fuster
2017;():V002T01A047. doi:10.1115/MSEC2017-2991.

Quality assurance of Additive Manufacturing (AM) products has become an important issue as the AM technology is extending its application throughout the industry. However, with no definite measure to quantify the error of the product and monitor the manufacturing process, many attempts are made to propose an effective monitoring system for the quality assurance of AM products. In this research, a novel approach for quantifying the error in real-time is presented through a closed-loop vision-based tracking method. As conventional AM processes are open-loop processes, we focus on the implementation of real-time error quantification of the products through the utilization of a closed-loop process. Three test models are designed for the experiment, and the tracking data from the camera will be compared with the G-code of the product to evaluate the geometrical errors. The results obtained from the camera analysis will then be validated through comparison of the results obtained from a 3D scanner.

Commentary by Dr. Valentin Fuster
2017;():V002T01A048. doi:10.1115/MSEC2017-3016.

Selective laser melting (SLM) based on added-material manufacturing method is one of the Additive Manufacturing (AM) technologies that can build full density metallic components. In this study, a thermal imager with about 670 nm wavelength was employed to collect build surface process temperature information during SLM fabrication using Monel K500 powder. The major findings are as follows. (1) At nominal process conditions of 600 mm/s beam speed and 180 W beam power, the melt pool has a length of about 0.6 mm and a width of about 0.36 mm. (2) The obtained melt pool length/width ratio is about 1.5 for different build height. With the increase of build height, no clear trend was observed for melt pool length/width ratio and melt pool length value. (3) It is difficult to obtain true temperature in this study but it is possible to estimate melt pool dimension with the identified radiant liquidus temperature.

Commentary by Dr. Valentin Fuster

Materials: Advances in Composites Manufacturing Processes

2017;():V002T03A001. doi:10.1115/MSEC2017-2659.

Composite materials are important engineering materials due to their outstanding mechanical properties. Composite materials offer superior properties to conventional alloys for various applications as they have high stiffness, strength and wear resistance. The high cost and difficulty of processing these composites restricted their application and led to the development of reinforced composites. In the last two decades, wear studies on Particulate Metal Matrix Composites (PMMCs) reinforced with various reinforcements ranging from very soft materials like graphite, talc etc., to high hardened ceramic particulates like SiCp, Al2O3 etc., have been reported to be superior to their respective unreinforced alloys. Therefore, present work focused on the study of machinability of Al based binary composites reinforced with 8.5% SiC and Al based Hybrid composite reinforced with 8.5% SiC, 2% and 4% Graphite powder (Solid lubricant) have been studied by considering the effect of process parameters such as speed, feed, depth of cut and composition of material. Binary and hybrid composite materials have been casted by stir casting methodology. Experiments have been conducted using Design of Experiments approach to reduce the number of experiments and time. The cutting force and surface roughness in turning of both the binary and hybrid materials have been measured using cutting force dynamometer (4 component kistler dynamometer) and the roughness has been measured using surface roughness tester (Marsurf M400) simultaneously. The multi objective optimization has been carried out using Grey relational based Taguchi method. It was observed that feed was the most influencing factor compared to others factors and also results shown that the performance characteristics cutting force and the surface roughness are greatly enhanced by using Grey relational Analysis.

Commentary by Dr. Valentin Fuster
2017;():V002T03A002. doi:10.1115/MSEC2017-2694.

Aramid honeycomb composite structures have revolutionized the aerospace industry by providing high strength, light weight, energy absorbing structures for many applications. To finder wider utilization, the costs of producing honeycomb structures must be reduced and one important area of focus is to reduce tool wear and increase tool life. This study began with the hypothesis that the high rate of tool wear was due to excessive tool rubbing because of the lower stiffness of this material when compared to solid materials. Tool wear measurements were taken over the life of a tool and high speed video was utilized to study the machining process. The results of the tool wear test showed a standard tool wear timeline. The video analyses showed the tool experiencing rubbing far beyond expectations due to the collapse of honeycomb cells induced by twisting far in advance of the arrival of the tool.

Commentary by Dr. Valentin Fuster
2017;():V002T03A003. doi:10.1115/MSEC2017-2737.

C-C composite is a kind of typical difficult-to-machine materials due to its high hardness, high strength, and obvious anisotropy features. But, water-based or oil-based coolant cannot be used during its machining process. As a result, the machining defects, including burrs, orifice ripping, and interlayer delamination, are always unavoidable. In this article, taking the liquid nitrogen as coolant, C-C composite cryogenic drilling is researched experimentally. Taking the way of LN2 external spray cooling, a series of cryogenic drilling experiments were designed. Comparing with dry drilling, the thrust force was reduced, the machining defects were significantly inhibited, and a better roundness of holes was achieved in cryogenic drilling. It indicates that cryogenic condition has a positive effect on improving the C-C composite drilling quality.

Commentary by Dr. Valentin Fuster
2017;():V002T03A004. doi:10.1115/MSEC2017-2887.

In this paper we describe an experimental method for investigating the autoclave co-cure of honeycomb core composite sandwich structures. The design and capabilities of a custom-built, lab-scale “in-situ co-cure fixture” are presented, including procedures and representative results for three types of experiments. The first type of experiment involves measuring changes in gas pressure on either side of a prepreg laminate to determine the prepreg air permeability. The second type involves co-curing composite samples using regulated, constant pressures, to study material behaviors in controlled conditions. For the final type, “realistic” co-cure, samples are processed in conditions mimicking autoclave cure, where the gas pressure in the honeycomb core evolves naturally due to the competing effects of air evacuation and moisture desorption from the core cell walls. The in-situ co-cure fixture contains temperature and pressure sensors, and derives its name from a glass window that enables direct in-situ visual observation of the skin/core bond-line during processing, shedding light on physical phenomena that are not observable in a traditional manufacturing setting. The experiments presented here are a first step within a larger research effort, whose long-term goal is to develop a physics-based process model for autoclave co-cure.

Commentary by Dr. Valentin Fuster
2017;():V002T03A005. doi:10.1115/MSEC2017-2895.

This paper demonstrates the use of boundary control on embedded resistive heaters with the purpose of precision temperature control for curing high strength adhesives when joining composite adherends. This is particularly useful in the presence of heatsinks, where a uniform heating technique will lead to temperature variations in the bondline. The major contribution of this work is to reduce such temperature variations by using boundary control on the embedded heater. This technique is demonstrated experimentally for bonding a single-lap joint, and the temperature variation in the bond area was reduced from 20.3% to 2.7%.

Commentary by Dr. Valentin Fuster
2017;():V002T03A006. doi:10.1115/MSEC2017-2981.

A low concentrated polystyrene (PS) additive to epoxy is used since it is able to reduce the curing reaction rate but not at the cost of increasing viscosity and decreasing glass transition temperature of the curing epoxy. The modified epoxy is co-cured with a compatible thermoplastic interleaf during the vacuum assisted resin transfer molding (VARTM) to toughen the interlaminar of the composites. Using viscometry, the solubilities of thermoplastics polycarbonate (PC), polyetherimide (PEI), and polysulfone (PSU) are determined to predict their compatibility with epoxy. The diffusion and precipitation process between the most compatible polymer PSU and epoxy formed semiinterpenetration networks (semi-IPN). To optimize bonding adhesion, these diffusion and precipitation regions were studied via optical microscopy under curing temperatures from 25 C to 120 C and PS additive concentrations to epoxy of 0% to 5%. Uniaxial tensile tests were performed to quantify the effects of diffusion and precipitation regions on composite delamination resistance and toughness. Crack paths were observed to characterize crack propagation and arrest mechanism. Fracture surfaces were examined by scanning electron microscopy (SEM) to characterize the toughening mechanism of the thermoplastic interleaf reinforcements. The chemically etched interface between diffusion and precipitation region showed semi-IPN morphology at different curing temperatures. Results revealed deeper diffusion and precipitation regions increases energy required to break semi-IPN for crack propagation resulting in crack arrests and improved toughness.

Commentary by Dr. Valentin Fuster
2017;():V002T03A007. doi:10.1115/MSEC2017-2982.

Various methods of toughening the bonding between the interleaf and laminate glass fiber reinforced polymer (GFRP) has been developed due to the increasing applications in industries. A polystyrene (PS) additive modified epoxy is used to improve the diffusion and precipitation region between polysulfone (PSU) interleaf and epoxy due to its influence on the curing kinetics without changing glass transition temperature and viscosity of the curing epoxy. The temperature dependent diffusivities of epoxy, amine hardener, and PSU are determined by using Attenuated Total Reflection-Fourier Transfer Infrared Spectroscopy (ATR-FTIR) through monitoring the changing absorbance of their characteristic peaks. Effects of PS additive on diffusivity in the epoxy system is investigated by comparing the diffusivity between non-modified and PS modified epoxy. The consumption rate of the epoxide group in the curing epoxy reveals the curing reaction rate, and the influence of PS additive on the curing kinetics is also studied by determining the degree of curing with time. A diffusivity model coupled with curing kinetics is applied to simulate the diffusion and precipitation process between PSU and curing epoxy. The effect of geometry factor is considered to simulate the diffusion and precipitation process with and without the existence of fibers. The simulation results show the diffusion and precipitation depths which matches those observed in the experiments.

Commentary by Dr. Valentin Fuster
2017;():V002T03A008. doi:10.1115/MSEC2017-3052.

Magnesium (Mg) and its alloys are among the lightest metallic structural materials, making them very attractive for use in the aerospace and automotive industries. Recently, Mg has been used in metal matrix composites (MMCs), demonstrating significant improvements in mechanical performance. However, the machinability of Mg-based MMCs is still largely elusive. In this study, Mg-based MMCs are machined using a wide range of cutting speeds in order to elucidate both the chip morphology and chip formation mechanism. Cutting speed is found to have the most significant influence on both the chip morphology and chip formation mechanism, with the propensity of discontinuous, particle-type chip formation increasing as the cutting speed increases. Saw-tooth chips are found to be the primary chip morphology at low cutting speeds (lower than 0.5 m/s), while discontinuous, particle-type chips prevail at high cutting speeds (higher than 1.0 m/s). Using in situ high speed imaging, the formation of the saw-tooth chip morphology is found to be due to crack initiation at the free surface. However, as the cutting speed (and strain rate) increases, the formation of the discontinuous, particle-type chip morphology is found to be due to crack initiation at the tool tip. In addition, the influences of tool rake angle, particle size, and particle volume fracture are investigated and found to have little effect on the chip morphology and chip formation mechanism.

Commentary by Dr. Valentin Fuster

Materials: Advances in Materials and Manufacturing Processes for Energy Technologies

2017;():V002T03A009. doi:10.1115/MSEC2017-2603.

This paper illustrates the effects of the laser and mechanical forming on the hardness and microstructural distribution in commercially pure grade 2 Titanium alloy plates. The two processes were used to bend commercially pure grade 2 Titanium alloy plates to a similar radius also investigate if the laser forming process could replace the mechanical forming process in the future. The results from both processes are discussed in relation to the mechanical properties of the material. Observations from hardness testing indicate that the laser forming process results in increased hardness in all the samples evaluated, and on the other hand, the mechanical forming process did not influence hardness on the samples evaluated. There was no change in microstructure as a result of the mechanical forming process while the laser forming process had a major influence on the overall microstructure in samples evaluated. The size of the grains became larger with increases in thermal gradient and heat flux, causing changes to the overall mechanical properties of the material. The thermal heat generated has a profound influence on the grain structure and the hardness of Titanium. It is evident that the higher the thermal energy the higher is the hardness, but this only applies up to a power of 2.5kW. Afterwards, there is a reduction in hardness and an increase in grain size. The cooling rate of the plates has been proved to play a significant role in the resulting microstructure of Titanium alloys. The scanning speed plays a role in maintaining the surface temperatures of laser formed Titanium plates resulting in changes to both hardness and the microstructure. An increase in heat results in grain growth affecting the hardness of Titanium.

Commentary by Dr. Valentin Fuster
2017;():V002T03A010. doi:10.1115/MSEC2017-2604.

This paper discusses the investigation of residual stresses developed as a result of mechanical and laser forming processes in commercially pure grade 2 Titanium alloy plates as well as the concept of total fatigue stress. The intention of the study was to bend the plates using the respective processes to a final radius of 120mm using both processes. The hole drilling method was used to measure residual strains in all the plates. High stress gradients were witnessed in the current research and possible cases analyzed and investigated. The effects of processing speeds and powers used also played a significant role in the residual stress distribution in all the formed plates. A change in laser power resulted in changes to residual stress distribution in the plates evaluated. This study also dwells into how the loads that are not normally incorporated in fatigue testing influence fatigue life of commercially pure grade 2 Titanium alloy plates. Also, the parent material was used to benchmark the performance of the two forming processes in terms of stresses developed. Residual stresses developed from the two forming processes and those obtained from the parent material were used. The residual stress values were then added to the mean stress and the alternating stress from the fatigue machine to develop the concept of total fatigue stress. This exercise indicated the effect of these stresses on the fatigue life of the parent material, laser and mechanically formed plate samples. A strong link between these stresses was obtained and formulae explaining the relationship formulated. A comparison between theory and practical application shown by test results is found to be satisfactory in explaining concerns that may arise. The laser forming process is more influential in the development of residual stress, compared to the mechanical forming process. With each parameter change in laser forming there is a change in residual stress arrangement. Under the influence of laser forming the stress is more tensile in nature making the laser formed plate specimens more susceptible to early fatigue failure. The laser and mechanical forming processes involve bending of the plate samples and most of these samples experienced a two-dimensional defect which is a dislocation. The dislocation is the defect responsible for the phenomenon of slip by which most metals deform plastically. Also the high temperatures experienced in laser forming were one of the major driving factors in bending.

Commentary by Dr. Valentin Fuster
2017;():V002T03A011. doi:10.1115/MSEC2017-2735.

Energy efficiency state identification of milling process plays an important role in energy saving efforts for manufacturing systems. However, it is very difficult to track energy efficiency state in machining processes based on traditional signal processing strategies due to the fact that energy state is usually coupled with a lot of factors like machine tool states, tool conditions, and cutting conditions. An identification method of information reasoning and Hidden Markov model (HMM) for energy efficiency state is proposed in this paper. Utilizing cutting conditions, empirical models of the energy efficiency, experimental data and signal features, an expert system is established for initial probability optimization and the state is further identified by HMM. The experiments show that energy efficiency state can be identified with this method.

Commentary by Dr. Valentin Fuster
2017;():V002T03A012. doi:10.1115/MSEC2017-2834.

The objective of this study was to develop a strategy for miniaturizing heat exchangers used for the thermal management of sorbent beds within adsorption refrigeration systems. The thermal mass of the microchannel heat exchanger designed and fabricated in this study is compared with that of commercially available tube-and-fin heat exchangers. Efforts are made to quantify the overall effects of miniaturization on system coefficient of performance and specific cooling power. A thermal model for predicting the cycle time for desorption is developed and experiments are used to quantify the effect of the intensified heat exchanger on overall system performance.

Commentary by Dr. Valentin Fuster
2017;():V002T03A013. doi:10.1115/MSEC2017-2882.

It is essential to understand basic deformation mechanism(s) of conventional alloys in order to develop improved or novel alloys for their applications in much more challenging conditions. Zircaloy-4 is extensively used in pressurized water reactor for nuclear fuel cladding application. It operates at very high temperature in the presence of mechanical loads, corrosive atmosphere, and neutron irradiation environment. Present work explores the fundamental plastic deformation mechanism(s) of Zircaloy-4 in the temperature range 20 to 600 °C by subjecting tensile samples to uniaxial tensile loads under quasi-static deformation conditions. Based on the results of uniaxial tensile testing as a function of temperature, repeated stress-relaxation experiments were carried out to determine the activation volume of the alloy at 20 and 500 °C. The results from uniaxial tensile and stress-relaxation testing were used to gain insight into potential deformation mechanism(s) in Zircaloy-4.

Topics: Deformation
Commentary by Dr. Valentin Fuster
2017;():V002T03A014. doi:10.1115/MSEC2017-2894.

The U.S. is sustainably producing of over 1 billion dry tons of biomass annually. This amount of biomass is sufficient to produce bioenergy that can replace about 30 percent of the nation’s current annual consumption of conventional fossil fuels. This then gives us the opportunity to turn waste into bioenergy that can assist in meeting the U.S. Renewable Fuel Standard (RFS). Besides being converted into bioethanol through the biochemical platform, biomass can also be utilized solid fuels to generate bioenergy through the thermochemical platform. Co-firing power plants use torrefied biomass pellets combined with coal for electricity generation. A two-step process, torrefaction followed by pelleting, is the prevailing technique that the industry is currently using to produce torrefied biomass pellets. Torrefaction converts biomass into biochar with high heating value, and pelleting densifies torrefied biochar into pellets with high durability and density. For the same purpose, we developed the ultrasonic pelleting and synchronized torrefaction of cellulosic biomass process, which is a single-step process to generate high quality solid fuel pellets with high heating value together with good durability and density. This study reports the first experimental investigation to demonstrate the feasibility of the novel process. Key process parameters have been identified, and their effects on the feasibility of generating quality torrefied biomass pellets are reported. Pellets are evaluated from the aspects of feasibility, durability, heating value, and thermal stability.

Commentary by Dr. Valentin Fuster
2017;():V002T03A015. doi:10.1115/MSEC2017-3008.

This paper addresses experimental investigations of turning Super Duplex Stainless Steel (DSS) with uncoated and Physical Vapor Deposition PVD coated carbide inserts under dry cutting condition. The parametric influence of cutting speed, feed and depth of cut on the surface finish and machinability aspects such as cutting force and tool wear are studied and conclusions are drawn. The turning parameters considered are cutting speed of 60–360 m/min, feed of 0.05–0.35 mm/rev and depth of cut of 0.5–2 mm. Tool wear was analysed by using an optical microscope and scanning electron microscope. The study includes identification of tool wear mechanism occurring on the flank face. The characterization of the coating was made by Calo test for measurement of coating thickness and nanoindentation for hardness. Comparison of performance of PVD coatings TiAlSiN (3.3μm), AlTiN (3 μm) and AlTiN (7 μm) have been made in terms of tool life. The coatings were produced on P-grade tungsten carbide inserts by using High Power Impulse Magnetron Sputtering (HiPIMS) technology. The findings of the study also provide the economic solution in case of dry turning of super DSS.

Commentary by Dr. Valentin Fuster

Materials: Advances in Processing of Polymers and Polymer-Based Composites

2017;():V002T03A016. doi:10.1115/MSEC2017-2760.

In this study, the structure-property relationships in thermoplastic polyurethane (TPU) filled with multi-walled carbon nanotubes (MWCNTs) were investigated. Firstly, the contribution of MWCNTs to the melt shear viscosity and the pressure-volume-temperature (pVT) behavior was investigated. Secondly, injection-molded samples and 2 mm diameter filaments of TPU/MWCNT composites were fabricated and their mechanical and electrical properties analyzed. It was found that the melt processability of TPU/MWCNT composites is not affected by the addition of a small amount (1–5 wt.%) of MWCNTs, all composites displaying shear-thinning at high shear rates. The mechanical and electrical properties of the TPU/MWCNT composites were substantially enhanced with the addition of MWCNTs. However, the conductivity values of composites processed by injection molding were two and three orders of magnitude lower than those of composites processed by extrusion, highlighting the role of melt shear viscosity on the dispersion and agglomeration of nanotubes.

Commentary by Dr. Valentin Fuster
2017;():V002T03A017. doi:10.1115/MSEC2017-2763.

In this paper, millimeter-scale straight parallel micro-channels were fabricated in PMMA (Polymethyl-methacrylate) using the tip-based micro-fabrication method. The dimensional characteristics (channel width, channel depth and pile-up height) of micro-channels were evaluated and the effects of normal load and speed on the micro-channel geometry and friction were examined. A logarithmic relationship between the normal load and micro-channel depth was identified. The experimental results indicate that the selection of the normal load is critical to achieve a desired micro-channel geometry using a single pass scratching. To machine a micro-channel with a finite depth in PMMA, the normal load must be higher than 4.5 N. Within the range of the tested normal loads, about 70% of the channel height was elastically recovered after a single pass, and pile-ups as high as 50–60% of the depth were observed along the micro-channel sides.

Commentary by Dr. Valentin Fuster
2017;():V002T03A018. doi:10.1115/MSEC2017-2775.

Cosmic ray (CR) shielding is the main issue for future long missions far for the protection of the Earth’s magnetic field. Many experiments have been performed in Space to evaluate the effect of the Space environment on the material stability (mainly MISSE experiments from NASA). However those experiments were not able to evaluate CR shielding performances of materials, and results are mainly present in the form of erosion yield due to atomic oxygen erosion. In this study, a conceptual design is shown for further experiments on the International Space Station by focusing on the effect of cosmic rays on material aging. Shields will be made by using polyolefin sheets coupled or not with metallic foils. Polymeric sheets will be filled or coated with magnetic nano-particles to provide a small magnetic activity.

Commentary by Dr. Valentin Fuster
2017;():V002T03A019. doi:10.1115/MSEC2017-2776.

Shape memory polymers (SMP) and composites (SMPC) may be used for many applications in Space, from self-deployable structures (such as solar sails, panels, shields, booms and antennas), to grabbing systems for Space debris removal, up to new-concept actuators for telescope mirror tuning. Experiments on the International Space Station are necessary for testing prototypes in relevant environment, above all for the absence of gravity which affects deployment of slender structures but also to evaluate the aging effects of the Space environment. In fact, several aging mechanisms are possible, from polymer cracking to cross-linking and erosion, and different behaviors are expected as well, from consolidating the temporary shape to composite degradation. Evaluating the possibility of shape recovery because of sun exposure is another interesting point. In this study, a possible experiment on the ISS is shown with the aim of evaluating the aging effect of Space on material performances. The sample structure is described as well as the testing strategy.

Commentary by Dr. Valentin Fuster
2017;():V002T03A020. doi:10.1115/MSEC2017-2792.

This paper is concerned with defining a new Weight Function Based model (WFB), which describes the hyper-elastic materials stress-strain behavior. Numerous hyper-elastic theoretical material models have been proposed over the past 60 years capturing the stress-strain behavior of large deformation incompressible isotropic materials. The newly proposed method has been verified against the historic Treloar’s test data for uni-axial, bi-axial and pure shear loadings of Treloar’s vulcanized rubber material, showing a promising level of confidence compared to the Ogden and the Yeoh methods. A non-linear least square optimization Matlab tool was used to determine the WFB, Yeoh and Ogden models material parameters. A comparison between the results of the three models was performed showing that the newly proposed model is more accurate for uni-axial tension as it has an error value which is less than the Ogden and Yeoh models by 1.0 to 39%. Also, the parameters calculation by more than 95%, for the bi-axial and pure shear loading cases compared to the Ogden model. Natural rubber test specimens have been tensioned using a tensile testing machine and the WFB model was applied to fit the test data results showing a very good curve fitting with an average error of 0.44%.WFB model has reduced processing time for the model.

Topics: Natural rubber
Commentary by Dr. Valentin Fuster
2017;():V002T03A021. doi:10.1115/MSEC2017-2809.

In recent years, tissue engineering has been utilized as an alternative approach for the organ transplantation. The success rate of tissue regeneration is influenced by the type of biomaterials, cell sources, growth factors and scaffold fabrication techniques used. The poly(ethylene glycol) diacrylate (PEGDA) is one of commonly used biomaterials because of its biocompatibility, ease of use, and porous microstructure. The mechanical properties of PEGDA have been studied to some extent by several research groups. However, the stability of the mechanical properties with time has not been investigated.

In this research, we studied how the mechanical properties of different concentrations of PEGDA change with the post-fabrication ageing time. Cylindrical PEGDA samples were prepared 20%, 40%, 60%, 80%, and 100% concentrations and cured under the UV light. After the solidification process, weight of each sample was monitored in every 0, 2, 4, 6, and 24 hours post-fabrication ageing time until the mechanical testing. Compressive elastic modulus and strength were calculated and statistically analyzed. Our results indicated that the water content of each PEGDA group constantly decreased by time, however, this loss significantly affected the elastic modulus and strength only after 6 hours in some PEGDA concentration.

Topics: Manufacturing
Commentary by Dr. Valentin Fuster
2017;():V002T03A022. doi:10.1115/MSEC2017-2973.

Carbon fiber composites have received growing attention because of their high performance. One economic method to manufacturing the composite parts is the sequence of forming followed by the compression molding process. In this sequence, the preforming procedure forms the prepreg, which is the composite with the uncured resin, to the product geometry while the molding process cures the resin. Slip between different prepreg layers is observed in the preforming step and this paper reports a method to characterize the properties of the interaction between different prepreg layers, which is critical to predictive modeling and design optimization. An experimental setup was established to evaluate the interactions at various industrial production conditions. The experimental results were analyzed for an in-depth understanding about how the temperature, the relative sliding speed, and the fiber orientation affect the tangential interaction between two prepreg layers. The interaction factors measured from these experiments will be implemented in the computational preforming program.

Commentary by Dr. Valentin Fuster
2017;():V002T03A023. doi:10.1115/MSEC2017-3039.

When manufacturing polymer and rubber products, the parts are frequently exposed to cryogenic temperatures after molding or forming in order to improve the ability to remove excess material and flash. However, there has been very little investigation into the effect that cryogenic temperatures may have on polymers. As such, the goal of the research described herein is to examine the effect of this type of treatment on the properties of one such polymer, Nylon 6/6. More specifically, the temperature of the environment surrounding Nylon 6/6 is decreased at two different rates into the cryogenic temperature range, allowed to soak, and then returned to ambient. Whereupon the material properties of the treated Nylon are compared to baseline. This testing demonstrates that the exposure to the cold environment resulted in a decrease in the yield and ultimate tensile strength of the Nylon while leaving the area reduction and strain after necking roughly unchanged. Examination of the surface condition of the treated specimens did not bring to light corresponding cracking from the treatments, thereby indicated that the resultant change in mechanical behavior is likely caused by structural changes within the Nylon. Additional testing of the Nylon, with respect to frequency response, further demonstrated that exposure to cryogenic temperatures resulted in decreases in the Nylon’s natural response at the structure’s dominate mode. These initial findings indicate that the conventional technique of lowering a part’s temperature to enhance the ability to remove flash does, in fact, result in measurable changes in the mechanical behavior of the Nylon product.

Topics: Nylon fabrics
Commentary by Dr. Valentin Fuster

Materials: Surface and Sub-Surface Functionalization

2017;():V002T03A024. doi:10.1115/MSEC2017-2687.

Higher temperature assisted processing of silicon, such as in heat-assisted diamond turning, is often being considered to improve surface integrity. At higher temperatures and under mechanical loading and unloading, caused by the moving tool, silicon deforms plastically often in association with occurrence of phase transformations. This paper investigates such phase transformations in rotational scratching of single crystal (100) p-type silicon with a conical diamond tool under various furnace-controlled temperatures ranging from room temperature to 500 °C and at scratching speeds comparable to that used in the diamond turning process (1 m/s). Phase transformation study, using Raman spectroscopy, at various crystal orientations, show differences in phases formed at various temperatures when compared to that reported in indentation. The tendency to form phases is compared between scratched and diamond turned surfaces at room temperature, and also with that reported at low scratching speeds in the literature. Analysis of depths of the scratched groove indicates that that at temperatures beyond a certain threshold, plastic deformation and significant elastic recovery may be causing shallow grooves. This study is expected to help tune heat-assisted diamond turning conditions to improve surface formation.

Commentary by Dr. Valentin Fuster
2017;():V002T03A025. doi:10.1115/MSEC2017-2710.

This work is focused on the experimental investigations for wear properties of rapid tooling with nano scale fillers for grinding applications. The rapid tooling has been prepared by using composite material feed stock filament (consisting of Nylon6 as a binder, reinforced with biocompatible nano scaled Al2O3 particles on fused deposition modeling (FDM) for the development of grinding wheel having customized wear resistant properties. A comparative study has been conducted under dry sliding conditions in order to understand the tribological characteristics of FDM prints of composite material and commercially used acrylonitrile butadiene styrene (ABS) material. This study also highlights the various wear mechanisms (such as adhesive, fatigue and abrasive) encountered with newly prepared composite material while grinding. The FDM printed parts of proposed composite material feedstock filament are more suitable for grinding applications especially in clinical dentistry.

Commentary by Dr. Valentin Fuster
2017;():V002T03A026. doi:10.1115/MSEC2017-2746.

In order to increase the hot workability and provide proper hot forming parameters for nitrogen controlled Z2CN19-10 austenitic stainless steel, the static recrystallization behavior was investigated by double-pass hot compression tests in the temperature range of 950–1100°C, initial grain size of 72μm–152μm, and the strain rates of 0.01, 0.1, 1, and 5 s−1. The tests were conducted with inter-pass times varying between 1 and 100 s after achieving a pass strain of 0.05, 0.1, 0.15 and 0.2 in the first pass on a Gleeble-1500 thermo-mechanical simulator. The static recrystallization fraction has been predicted by the 2 % offset stress method and verified by metallographic observations. The metallographic results indicate the crystallized grains generate at the cross of the prior austenite grain boundary and grow up. Also the kinetics of static recrystallization behavior for Z2CN19-10 steel are proposed. Experimental results show that the volume fraction of static recrystallization increases with the increase of deformation temperature, strain rates, pass strain and interval time, while it decreases with the increase of initial grain size. According to the present experimental results, the activation energy (Q) and Avrami exponent (n) was determined as 199.02kJ/mol and 0.69. The established equations can give a reasonable estimate of the static recrystallization behavior for Z2CN19-10 steel.

Commentary by Dr. Valentin Fuster
2017;():V002T03A027. doi:10.1115/MSEC2017-2847.

The effects of Ultrasonic Nanocrystal Surface Modification (UNSM) on the gas nitriding of Ti6Al4V alloy has been investigated. The gas nitriding was performed at 700 and 800 °C. The microstructure after UNSM and gas nitriding was characterized using X-ray diffraction and scanning electron microscopy. Microstructural investigations revealed the formation of an approximately 10 μm thick severe plastic deformation (SPD) layer after UNSM treatment. After nitriding at 700 °C and 800 °C, a compound layer consisting of an approximately 0.2 μm and 1.9 μm thick nitride layer was observed in UNSM-treated Ti6Al4V alloy, which exhibits a nearly two-fold increase in nitride layer thickness as compared with the un-treated sample. This suggests that the nitrogen adsorption and the reaction capability are enhanced in the UNSM-treated Ti6Al4V alloy. This enhancement can be attributed to the high density dislocations and grain boundaries introduced by UNSM that serve as efficient diffusivity channels for interstitial gaseous atoms.

Commentary by Dr. Valentin Fuster
2017;():V002T03A028. doi:10.1115/MSEC2017-2980.

This paper proposes the use of a hybrid magnetic tool, consisting of magnetic particles bonded with water-soluble glue, to improve both surface roughness and form accuracy of brittle materials such as ceramics. As the binder gradually dissolves into the lubricant, the bonded hybrid magnetic tool transforms to a particle brush in a magnetic field, increasing the deformability of the tool and its ability to conform to the target surface. This paper describes the effects of the tool transformation — from a bonded tool to a particle brush — on the characteristics of finished yttrium aluminum garnet (YAG) laser ceramics. The bonded tool removes material to flatten and smooth the target surface at the start of the process, gradually transitions to a particle brush (starting at the tool periphery), and finally smooths the surface as a flexible particle brush. The tool deformability and transition speed are adjustable by the binder content.

Commentary by Dr. Valentin Fuster
2017;():V002T03A029. doi:10.1115/MSEC2017-3080.

The fast corrosion rate of magnesium (Mg) alloys is the main problem associated with the use of such biocompatible alloys for bone fixation applications. The corrosion resistance of Mg alloys can be improved by different post-fabrication processes such as heat treatment and coating. We have heat-treated a biocompatible Mg-1.2Zn-0.5Ca (wt.%) alloy at optimized heat treatment parameters to achieve the highest mechanical strength and corrosion resistance. Afterwards, the heat-treated alloy was coated with a ceramic layer using micro arc oxidation (MAO) process to further enhance the corrosion resistance.

The microstructure of the prepared samples was investigated using optical microscopy and scanning electron microscopy (SEM). The corrosion characteristics were determined by conducting in vitro electrochemical and immersion corrosion tests.

The results showed that the heat treatment process successfully improved the mechanical and corrosion properties of the Mg-1.2Zn-0.5Mn (wt.%) alloy. Both the in vitro electrochemical and immersion corrosion tests showed that the MAO-coated samples have a significantly higher corrosion resistance which results in a significantly lower corrosion rate. This study indicated that the biocompatible coating produced by MAO process may be suitable for providing heat-treated Mg-Zn-Ca-based alloys with protection from corrosion towards synthesizing bone fixation materials in clinical application.

Commentary by Dr. Valentin Fuster

Materials: Tribology of Material Removal/Deformation Processes and Machinery

2017;():V002T03A030. doi:10.1115/MSEC2017-2915.

Severe plastic burnishing was investigated as a promising surface severe plastic deformation technique for generating gradient microstructure surfaces. The deformed state of oxygen free high conductivity copper workpieces during the surface deformation process was determined with high-speed imaging, this complemented by microstructure characterization using orientation image microscopy based on electron backscatter diffraction. Varying deformation levels in terms of both magnitude and gradient on the processed surface were achieved through control of the incident tool angle. Refined microstructures, including laminate grains elongated in the velocity direction and equiaxed sub-micron grains were observed in the subsurface and were found to be controlled by the combined effects of strain and strain rate in the surface deformation process. Additionally, crystallographic texture evolutions were characterized, showing typical shear textures predominately along the <110> partial fiber. The rotation of texture from original ideal orientation positions was related directly to the deformation history produced by sliding process. Based on these observations, a controllable framework for producing the processed surface with expected mechanical and microstructural responses is suggested.

Commentary by Dr. Valentin Fuster
2017;():V002T03A031. doi:10.1115/MSEC2017-3060.

In minimum quantity lubrication (MQL) machining, mist flow plays a critical role in both lubrication and cooling. This paper aims to characterize the mist flow structure of different coolant channel designs for through-tool MQL drilling. Two different channel geometries (circular and triangular cross-section) and two sizes of each channel were selected for both experimental and computational analyses. The flow structure was captured by a high-speed camera and explained using computational fluid dynamics (CFD). The results showed that, for all the channel geometries, higher oil concentration was found close to the drill center. Specifically, in the triangular channel, the flow tends to accumulate at three corners. This study also measured the airspeed, which increased with the hydraulic diameter of the channel. These results have demonstrated the effects of channel geometry and the feasibility of using CFD in mist flow analysis.

Commentary by Dr. Valentin Fuster

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