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### Research Papers

J. Manuf. Sci. Eng. 2017;139(8):081001-081001-13. doi:10.1115/1.4036289.

Fine finishing of cylindrical internal surfaces without affecting geometric form is a critical requirement in several mechanical and aerospace applications. Although various methodologies using flexible abrasive media are reported for the same, many of them demand complex tooling and fixtures to be developed in tune with the internal dimensions to feed the abrasive media. The present paper investigates the feasibility of using magneto-elastic abrasive balls with the aid of a mechanically deployable tool for microfinishing of geometrically symmetric tubular specimens. The deployable tool used for the present experimentation is designed like an umbrella mechanism, with magnetic pads to hold the elastic abrasive balls, expandable for bore diameter ranges from 45 to 75 mm. The magnetic type elastic abrasive balls proposed in the form of mesoscale balls of diameter 3.5 ± 0.25 mm are capable of finishing the bore surface without altering its roundness. Effects of elastomeric medium, mechanics of material removal and generation of finished profile during the proposed technique have been discussed in detail, through a comprehensive mathematical model. Effect of various process variables on surface roughness was investigated experimentally using response surface methodology and the theoretical predictions were validated at optimum operating condition. Sixty-two percent reduction in average roughness on brass tubes of initial roughness 0.168 μm, with significant improvement in all the associated two-dimensional roughness parameters and without any deviation on roundness, was clearly demonstrating the potential of proposed methodology.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2017;139(8):081002-081002-14. doi:10.1115/1.4036226.

Tissue regeneration with scaffolds has proven promising for the repair of damaged tissues or organs. Dispensing-based printing techniques for scaffold fabrication have drawn considerable attention due to their ability to create complex structures layer-by-layer. When employing such printing techniques, the flow rate of the biomaterial dispensed from the needle tip is critical for creating the intended scaffold structure. The flow rate can be affected by a number of variables including the material flow behavior, temperature, needle geometry, and dispensing pressure. As such, model equations can play a vital role in the prediction and control of the flow rate of the material dispensed, thus facilitating optimal scaffold fabrication. This paper presents the development of a model to represent the flow rate of medium viscosity alginate dispensed for the purpose of scaffold fabrication, by taking into account the shear and slip flow from a tapered needle. Because the fluid flow behavior affects the flow rate, model equations were also developed from regression of experimental data to represent the flow behavior of alginate. The predictions from both the flow behavior equation and flow rate model show close agreement with experimental results. For varying needle diameters and temperatures, the slip effect occurring at the needle wall has a significant effect on the flow rate of alginate during scaffold fabrication.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2017;139(8):081003-081003-17. doi:10.1115/1.4035897.

The volume variation of multiple chambers of a workpiece is one of the most important factors that can directly influence the performance of the final product. This paper presents a novel systematic approach for online minimizing the volume difference of multiple chambers of a workpiece based on high-definition metrology (HDM). First, the datum of high-density points is transformed by a random sample consensus (RANSAC) algorithm due to its good robustness in fitting. Second, a procedure containing reconstruction of interior curved surfaces of chambers, boundary extraction, and projection is developed to calculate the accurate volumes of the multiple chambers. Third, a model for obtaining an optimized machining parameter for depth of chambers is explored to minimize the volume difference of any two ones of all the chambers. The model is formulated as a multi-objective optimization (MOO) problem, and a new procedure of multi-objective particle swarm optimization (MOPSO) algorithm is developed to solve this problem. Finally, a milling depth is output as the optimal milling parameter for controlling the volume variation of multiple chambers. The results of a case study show that the proposed approach can minimize the volume difference of four combustion chambers of a cylinder head and it can be well applied online in volume variation control of multiple chambers in machining processes.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2017;139(8):081004-081004-15. doi:10.1115/1.4036348.

The direct electrostatic printing of highly viscous thermoplastic polymers onto movable collectors, a process known as melt electrospinning writing (MEW), has significant potential as an additive biomanufacturing (ABM) technology. MEW has the hitherto unrealized potential of fabricating three-dimensional (3D) porous interconnected fibrous mesh-patterned scaffolds in conjunction with cellular-relevant fiber diameters and interfiber distances without the use of cytotoxic organic solvents. However, this potential cannot be readily fulfilled owing to the large number and complex interplay of the multivariate independent parameters of the melt electrospinning process. To overcome this manufacturing challenge, dimensional analysis is employed to formulate a “Printability Number” (NPR), which correlates with the dimensionless numbers arising from the nondimensionalization of the governing conservation equations of the electrospinning process and the viscoelasticity of the polymer melt. This analysis suggests that the applied voltage potential (Vp), the volumetric flow rate (Q), and the translational stage speed (UT) are the most critical parameters toward efficient printability. Experimental investigations using a poly(ε-caprolactone) (PCL) melt reveal that any perturbations arising from an imbalance between the downstream pulling forces and the upstream resistive forces can be eliminated by systematically tuning Vp and Q for prescribed thermal conditions. This, in concert with appropriate tuning of the translational stage speed, enables steady-state equilibrium conditions to be achieved for the printing of microfibrous woven meshes with precise and reproducible geometries.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2017;139(8):081005-081005-11. doi:10.1115/1.4036522.

In the last decade, global competition has forced manufacturers to optimize logistics. The implementation of collapsible containers provides a new perspective for logistics cost savings, since using collapsible containers reduces the frequency of shipping freight. However, optimization of logistic cost is complicated due to the interactions in a system, such as market demand, inventory, production throughput, and uncertainty. Therefore, a systematic model and accurate estimation of the total cost and system performance are of great importance for decision making. In this paper, a mathematical model is developed to describe deterministic and stochastic scenarios for a closed-loop container dynamic flow system. The uncertainties in a factory and a supplier are considered in the model. The performance evaluation of the collapsible container system and total cost estimation are provided through model analysis. Furthermore, fuzzy control method is proposed to monitor the processing rate of the supplier and the factory and to adjust the rate of the supplier operation then further reduce the logistic cost. A case study with a matlab simulation is presented to illustrate the accuracy of the mathematical model and the effectiveness of the fuzzy controller.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2017;139(8):081006-081006-11. doi:10.1115/1.4036423.

This paper introduces a new method that uses slice geometry to compute the global visibility map (GVM). Global visibility mapping is a fundamentally important process that extracts geometric information about an object, which can be used to solve hard problems, for example, setup and process planning in computer numerical control (CNC) machining. In this work, we present a method for creating the GVM from slice data of polyhedron models, and then show how it can help determine around which axis of rotation a part can be machined. There have been various methods of calculating the GVM to date, tracing back to the well-known seminal methods that use Gaussian mapping. Compared to the considerable amount of work in this field, the proposed method has an advantage of starting from feature-free models like stereolithography (STL) files and has adjustable resolution. Moreover, since it is built upon slicing the model, the method is embarrassingly parallelizable in nature, thus suitable for high-performance computing. Using the GVM obtained by this method, we generate an axis of rotation map to facilitate the setup planning for four-axis CNC milling machines as one implementation example.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2017;139(8):081007-081007-9. doi:10.1115/1.4036529.

In this study, an AZ31 magnesium alloy plate was processed by constrained groove pressing (CGP) under three deformation cycles at temperatures from 503 to 448 K. The process resulted in a homogeneous fine grain microstructure with an average grain size of 1.8 μm. The as-processed microstructure contained a high fraction of low-angle grain boundaries (LAGB) of subgrains and dislocation boundaries that remained in the structure due to incomplete dynamic recovery and recrystallization. The material's yield strength was found to have increased from 175 to 242 MPa and with a significant weakening of its initial basal texture. The microstructure stability of the CGP-processed material was further investigated by isothermal annealing at temperature from 473 to 623 K and for different time. Abnormal grain growth was observed at 623 K, and this was associated with an increased in nonbasal grains at the expense of basal grains. The effect of annealing temperature and time on the grain growth kinetics was interpreted by using the grain growth equation, , and Arrhenius equation, $k=k0 exp (−(Q/RT))$. The activation energy (Q) was estimated to be 27.8 kJ/mol which was significantly lower than the activation energy for lattice self-diffusion (QL = 135 kJ/mol) and grain boundary diffusion (Qgb = 92 kJ/mol) in pure magnesium. The result shows that grain growth is rapid but average grain size still remained smaller than the as-received material, especially at the shorter annealing time.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2017;139(8):081008-081008-10. doi:10.1115/1.4036521.

This paper reports on numerical and experimental investigations involving examination of the effects of an interfacial gap in the range of 0–0.3 mm on keyhole and molten pool dynamics. A numerical model was developed to investigate the three-dimensional transient dynamics of the keyhole in lap welding processes with an interface gap. The model was able to reliably predict the weld profile. In addition, the modeling results provided detailed information regarding the interaction between the molten pool and the solid/liquid boundary that led to the extended weld width. Experimentally, AISI 304 stainless steel was joined in a lap welding configuration using an IPG YLR-1000 fiber laser. The tensile shear and T-peel testing of the lap joints showed that adding an adequate amount of interface gap improves weld strength.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2017;139(8):081009-081009-12. doi:10.1115/1.4036488.

To understand the different aspects of the laser cladding (LC) process, process models can be of aid. Presently, the correct parameter settings for different manufacturing processes, such as machining and casting, are based on simulation tools that can evaluate the influence of the process parameters for different conditions. However, there are no comprehensive, focused simulation process planning tools available for the LC process. In the past, most of the research has focused on the experimentally based optimization strategies for a process configuration, typically for a single track bead in steady-state conditions. However, an understanding of realistic transient conditions needs to be explored for effective process planning simulation tools and build strategies to be developed. A set of cladding experiments have been performed for single and multiple bead scenarios, and the effects of the transient conditions on the bead geometry for these scenarios have been investigated. It is found that the lead-in and lead-out conditions differ, corner geometry influences the bead height, and when changing the input power levels, the geometry values oscillate differently than the input pulses. Changes in the bead geometry are inherent when depositing material; consequently, real-time adjustments for the process setting are essential. The dynamic, time varying heating and solidification, for multiple layer scenarios, leads to challenging process planning and real-time control strategies.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2017;139(8):081010-081010-9. doi:10.1115/1.4035420.

Additive manufacturing (AM) is increasingly of interest for commercial and military applications due to its potential to create novel geometries with increased performance. For additive manufacturing to find commercial application, it must be cost competitive against traditional processes such as forging. Forecasting the production costs of future products prior to large-scale investment is challenging due to the limits of traditional cost accounting's ability to handle both the systemic process implications of new technologies and the cognitive biases in humans' additive and systemic estimates. Leveraging a method uniquely suited to these challenges, we quantify the production and use economics of an additively manufactured versus a traditionally forged GE engine bracket of equivalent performance for commercial aviation. Our results show that, despite the simplicity of the engine bracket, when taking into account the part redesign for AM and the associated lifetime fuel savings of the additively designed bracket, the additively manufactured part and design is cheaper than the forged one for a wide range of scenarios, including at higher volumes of 2000–12,000 brackets per year. Opportunities to further reduce costs include accessing lower material prices without compromising quality, producing vertical builds with equivalent performance to horizontal builds, and increasing process control so as to enable reduced testing. Given the conservative nature of our assumptions as well as our choice of part, these results suggest that there may be broader economic viability for additively manufactured parts, especially when systemic factors and use costs are incorporated.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2017;139(8):081011-081011-10. doi:10.1115/1.4036424.

During the past few years, metal-based additive manufacturing technologies have evolved and may enable the direct fabrication of heterogeneous objects with full spatial material variations. A heterogeneous object has potentially many advantages, and in many cases can realize the appearance and/or functionality that homogeneous objects cannot achieve. In this work, we employ a preprocess computing combined with a multi-objective optimization algorithm based on the modeling of the direct metal deposition (DMD) of dissimilar materials to optimize the fabrication process. The optimization methodology is applied to the deposition of Inconel 718 and Ti–6Al–4V powders with prescribed powder feed rates. Eight design variables are accounted in the example, including the injection angles, injection velocities, and injection nozzle diameters for the two materials, as well as the laser power and scanning speed. The multi-objective optimization considers that the laser energy consumption and the powder waste during the fabrication process should be minimized. The optimization software modeFRONTIER® is used to drive the computation procedure with a matlab code. The results show the design and objective spaces of the Pareto optimal solutions and enable the users to select preferred setting configurations from the set of optimal solutions. A feasible design is selected which corresponds to a relatively low material cost, with laser power 370 W, scanning speed 55 mm/s, injection angles 15 deg, injection velocities 45 m/s for Inconel 718, 30 m/s for Ti–6Al–4V, and nozzle widths 0.5 mm under the given condition.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2017;139(8):081012-081012-7. doi:10.1115/1.4036125.

Subsurface damage (SSD) and grinding damage-induced stress (GDIS) are a focus of attention in the study of grinding mechanisms. Our previous study proposed a load identification method and analyzed the GDIS in a silicon wafer ground (Zhou et al., 2016, “A Load Identification Method for the GDIS Distribution in Silicon Wafers,” Int. J. Mach. Tools Manuf., 107, pp. 1–7.). In this paper, a more concise method for GDIS analysis is proposed. The new method is based on the curvature analysis of the chip deformation, and a deterministic solution of residual stress can be derived out. Relying on the new method, this study investigates the GDIS distribution feature in the silicon wafer ground by a #600 diamond wheel (average grit size 24 μm). The analysis results show that the two principal stresses in the damage layer are closer to each other than that ground by the #3000 diamond wheel (average grit size 4 μm), which indicates that the GDIS distribution feature in a ground silicon wafer is related to the depth of damage layer. Moreover, the GDIS distribution presents a correlation with crystalline orientation. To clarify these results, SSD is observed by transmission electron microscopy (TEM). It is found that the type of defects under the surface is more diversified and irregular than that observed in the silicon surface ground by the #3000 diamond wheel. Additionally, it is found that most cracks initiate and propagate along the slip plane due to the high shear stress and high dislocation density instead of the tensile stress which is recognized as the dominant factor of crack generation in a brittle materials grinding process.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2017;139(8):081013-081013-10. doi:10.1115/1.4036489.

A stamp forming die whose flexible blank holder (BH) was designed using finite element (FE) analysis was built. The tooling also included active draw beads, local wrinkling sensors, and local force transducers. Wrinkling was controlled using a proportional–integral–derivative (PID) feedback loop and blank holder force (BHF). Local forces in the tooling were also controlled using blank holder forces in a PID feedback loop. A third closed-loop control system that could be used to control local punch forces (LPF) near draw beads featured an advanced PID controller with a Smith Predictor and Kalman Filter. A Bang–bang controller was also incorporated into that control system in order to prevent control saturation. Fuzzy logic was used to transition from one controller to the other. Once closed-loop control was implemented, tests were performed in order to evaluate the strains in the pans for various forming conditions. These results were compared to open-loop tests and it was found that the strains' paths for closed-loop control tests resulted in convergence and were further from the forming limit than strains from open-loop control tests. Furthermore, it was seen that the strains in critical regions had more uniform strain fields once closed-loop control of local punch forces was implemented. Hence, it was concluded that controlling local punch forces resulted in the indirect control of strains in critical regions.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2017;139(8):081014-081014-8. doi:10.1115/1.4036559.

Vibration assisted nano impact-machining by loose abrasives (VANILA) is a novel nanomachining process to perform target-specific nano abrasive machining of hard and brittle materials. In this study, molecular dynamic (MD) simulations are performed to understand the nanoscale material removal mechanisms involved in the VANILA process. The simulation results revealed that the material removal for the given impact conditions happens primarily in ductile mode through three distinct mechanisms, which are nanocutting, nanoplowing, and nanocracking. It was found that domination by any of these mechanisms over the other mechanisms during the material removal process depends on the impact conditions, such as angle of impact and the initial kinetic energy of the abrasive grain. The transition zone from nanocutting to nanoplowing is observed at angle of impact of near 60 deg, while the transition from the nanocutting and nanoplowing mechanisms to nanocracking mechanism is observed for initial abrasive kinetic energies of about 600–700 eV. In addition, occasional lip formation and material pile-up are observed in the impact zone along with amorphous phase transformation. A material removal mechanism map is constructed to illustrate the effects of the impacts conditions on the material removal mechanism. Confirmatory experimentation on silicon and borosilicate glass substrates showed that all the three nanoscale mechanisms are possible, and the nanoplowing is the most common mechanism. It was also found that the material removal rate (MRR) values are found to be highest when the material is removed through nanocracking mechanism and is found to be lowest when the material removal happens through nanocutting mechanism.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2017;139(8):081015-081015-10. doi:10.1115/1.4036530.

The combination of a susceptible material, tensile stress, and corrosive environment results in stress corrosion cracking (SCC). Laser shock peening (LSP) has previously been shown to prevent the occurrence of SCC on stainless steel. Compressive residual stresses from LSP are often attributed to the improvement, but this simple explanation does not explain the electrochemical nature of SCC by capturing the effects of microstructural changes from LSP processing and its interaction with the hydrogen atoms on the microscale. As the hydrogen concentration of the material increases, a phase transformation from austenite to martensite occurs. This transformation is a precursor to SCC failure, and its prevention would thus help explain the mitigation capabilities of LSP. In this paper, the role of LSP-induced dislocations counteracting the driving force of the martensitic transformation is explored. Stainless steel samples are LSP processed with a range of incident laser intensities and overlapping. Cathodic charging is then applied to accelerate the rate of hydrogen absorption. Using XRD, martensitic peaks are found after 24 h in samples that have not been LSP treated. But martensite formation does not occur after 24 h in LSP-treated samples. Transmission electron microscopy (TEM) analysis is also used for providing a description of how LSP provides mitigation against hydrogen enhanced localized plasticity (HELP), by causing tangling and prevention of dislocation movement. The formation of dislocation cells is attributed with further mitigation benefits. A finite element model predicting the dislocation density and cell formation is also developed to aid in the description.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2017;139(8):081016-081016-9. doi:10.1115/1.4036225.

This paper studies a friction stir spot welding (FSSW) process that has been successfully applied to join aluminum alloy 6061-T6 to transformation-induced plasticity steel (TRIP) 780/800 steel. Cross sections of weld specimens show the formation of a hook with a swirling structure. A higher magnified scanning electron microscope (SEM) view of the swirling structure with energy dispersive X-ray spectroscopy (EDS) analysis reveals that it is composed of alternating thin layers of steel and Al–Fe intermetallic compounds (IMCs). To check the effect of different process parameters on the weld strength, the effects of tool plunge speed and dwell time were studied through the design of experiments (DOE) and analysis of variance (ANOVA) method. It shows that dwell time is a more dominant parameter in affecting the weld strength than plunge speed. Furthermore, investigation of failure using a lap shear tests reveals that cross nugget failure is the only failure mode. It also shows that cracks are initiated in the swirling structure at the tensile side of the weld nugget. After failure, a cleavage feature can be observed on the fractured surface.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2017;139(8):081017-081017-11. doi:10.1115/1.4036642.

Nanoparticle clustering phenomenon is a critical quality issue in metal-matrix nanocomposites (MMNCs) manufacturing. Accurate estimation of the 3D cluster size distribution based on the 2D cross section images is essential for quality assessment, quality control, and process optimization. The existing studies often draw conclusions with observable samples, which are inherently biased because large clusters are more likely to be intersected by scanning electron microscope (SEM) images compared with small ones. This paper takes into account this sampling bias and proposes two statistical approaches, namely, the maximum likelihood estimation (MLE) and the method of moments (MM), to estimate the distribution parameters accurately. Numerical studies and real case study demonstrate the effectiveness and accuracy of the proposed approaches.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2017;139(8):081018-081018-12. doi:10.1115/1.4036713.

This paper presents a comprehensive experimental study in exploring the influence of key printing parameters on mechanical properties and failure mechanisms of acrylonitrile butadiene styrene (ABS) material. Three parameters with three levels—layer thickness (0.09 mm, 0.19 mm, and 0.39 mm), printing plane (XY, YZ, and ZX), and printing orientation (horizontal, diagonal, and vertical)—are considered, which form an L27 experimental design. Following L27, tensile and compressive specimens are fabricated and tested. Young's modulus, yield strength, failure strength, and strain of specimens are measured, evaluated, and compared with their injection-molded counterparts. Experimental results indicate that tensile specimens with a layer thickness of 0.09 mm and printing plane orientation of YZ-H reveal the highest stiffness and failure strength. While injection-molded specimen shows the highest yield strength, ductility of printed specimens is 1.45 times larger than that of injection-molded part. YZ along with XY specimens shows a neat and clean standard fracture failure at 45 deg, where the layers reorient themselves followed by stretching before fracture failure, thus providing sufficient ductility as opposed to ZX specimens, which fail along the direction perpendicular to the loading. Compressive XY-H and XY-D specimens have the highest stiffness and yield strength, and failure mechanisms involve initial compression followed by squeezing of layers leading to compactness followed by breakage due to tearing off or fracture of layers. The findings imply that anisotropy of fused deposition modeling (FDM) parts cannot be avoided and hence the appropriate parameters must be chosen, which satisfy the intended properties of the material subject to specific loading scenario.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2017;139(8):081019-081019-6. doi:10.1115/1.4036640.

The binder jetting additive manufacturing (AM) process provides an economical and scalable means of fabricating complex parts from a wide variety of materials. While it is often used to fabricate metal parts, it is typically challenging to fabricate full density parts without large degree of sintering shrinkage. This can be attributed to the inherently low green density and the constraint on powder particle size imposed by challenges in recoating fine powders. To address this issue, the authors explored the use of bimodal powder mixtures in the context of binder jetting of copper. A variety of bimodal powder mixtures of various particle diameters and mixing ratios were printed and sintered to study the impact of bimodal mixtures on the parts' density and shrinkage. It was discovered that, compared to parts printed with monosized fine powders, the use of bimodal powder mixtures improves the powder's packing density (8.2%) and flowability (10.5%), and increases the sintered density (4.0%) while also reducing the sintering shrinkage (6.4%).

Commentary by Dr. Valentin Fuster

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