Research Papers

J. Manuf. Sci. Eng. 2016;139(2):021001-021001-11. doi:10.1115/1.4034009.

In this study, cold metal transfer (CMT) plug welding of 1 mm thick Mg AZ31 to 1 mm thick hot-dipped galvanized mild steel (i.e., Q235) was studied. Welding tests were performed and the process variables optimized with Mg AZ61 wire and 100% argon shielding gas for a plug weld located in the center of the 25 mm overlap region. It was found that it is feasible to join 1 mm thick Mg AZ31 workpiece to 1 mm thick galvanized mild steel using CMT plug welding. The optimized process variables for CMT plug welding Mg AZ31-to-galvanized mild steel were a wire feed speed of 10.5 m/min, a predrilled hole with a diameter of 8 mm in Mg AZ31 workpiece and a welding time of 0.8 s. CMT plug welded Mg AZ31-to-galvanized mild steel joints were composed of the fusion zone between Mg AZ31 base metal and Mg weld metal, Mg weld metal (i.e., combined base metal, filler wire and Zn coating), and the brazing interface between magnesium weld metal and galvanized mild steel. The brazing interface mainly consisted of Al, Zn, Mg, Si intermetallic compounds and oxides (i.e., Fe3Al, Mg2Si, MgZn, and MgZn2), and magnesium solid solution. The static strength of CMT welded-brazed Mg AZ31-galvanized steel was determined primarily by the strength and area of the brazed interface and thickness of the intermetallic reaction layer.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2016;139(2):021002-021002-14. doi:10.1115/1.4034305.

Polymerization shrinkage and thermal cooling effect have been identified as two major factors that lead to the curl distortion in the stereolithography apparatus (SLA) process. In this paper, the photocuring temperature during the building process of mask image projection-based stereolithography (MIP-SL) and how it affects parts' curl distortion are investigated using a high-resolution infrared (IR) camera. Test cases of photocuring layers with different shapes, sizes, and layer thicknesses have been designed and tested. The experimental results reveal that the temperature increase of a cured layer is mainly related to the layer thickness, while the layer shapes and sizes have little effect. The photocuring temperatures of built layers using different exposure strategies including varying exposure time, grayscale levels, and mask image patterns have been studied. The curl distortions of a test case based on various exposure strategies have been measured and analyzed. It is shown that, by decreasing the photocuring temperature of built layers, the exposure strategies using grayscale levels and mask image patterns can effectively reduce the curl distortion with the expense of increased building time. In addition to curl distortion control, the photocuring temperature study also provides a basis for the curl distortion simulation in the MIP-SL process.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2016;139(2):021003-021003-10. doi:10.1115/1.4034282.

The mechanical ruling process using a diamond tool is an important method for fabrication of low-density diffraction gratings. In mechanical ruling, a deposited film of aluminum or gold is mechanically burnished by the diamond tool to form equally spaced and high-quality grooves. The goal of this work is to evaluate the effects of Al film properties and ruling tool loading conditions on the resultant groove formation. The microstructure of the Al film is first studied using scanning electron microscope (SEM) and X-ray diffraction (XRD). The mechanical properties of the Al film are measured by nano-indentation and scratch tests. Mechanical ruling experiments are then carried out on a 10.5 μm thick Al film under various ruling loads ranging from 20 to 105 g. The groove geometry is investigated, and the tool wear of the diamond tool is inspected after the mechanical ruling tests. Finally, a three-dimensional (3D) thermomechanical-coupled finite-element (FE) model is developed to predict the deformation and temperature fields for the micron-scale groove formation by incorporating the Al film properties and a strain-gradient plasticity for modeling the size effect. Multiruling pass simulations are performed to analyze the groove formation under different loading conditions. Through comparison of simulation results with experimental measurement, this model is demonstrated as a useful numerical tool for modeling the mechanical ruling process using a diamond tool.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2016;139(2):021004-021004-7. doi:10.1115/1.4034400.

Polymer electrolyte membrane (PEM) fuel cell efficiency must be improved in order to become cost competitive with fossil fuel-based technologies. Approaches to increasing cost efficiency include raising fuel cell operating temperature, reducing component cost, and properly controlling fuel cell humidification. We sought to fulfill all three requirements by developing a new low-cost, high-temperature humidification membrane material. Currently, Nafion dominates the membrane humidifier market due to its excellent water transport characteristics, but its high price (∼$1000/m2) and low maximum operating temperature (<90 °C) drive up fuel cell cost. We developed a competing polyethersulfone (PES)–zeolite mixed matrix membrane (MMM) with a porous microstructure. Solvent casting was used to form the initial PES–zeolite films, followed by solid-state foaming to alter the film morphology and create a porous structure. The effects of both zeolite weight loading and foaming duration on membrane permeability were investigated. Membrane measurement results show that both foaming and increased zeolite weight loading enhance membrane water permeability close to levels seen in Nafion. Meanwhile, the membranes satisfy the Department of Energy (DOE) crossover gas requirement for humidification membrane materials.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2016;139(2):021005-021005-10. doi:10.1115/1.4034280.

In transportation sector, there is an increasing need for joining dissimilar materials for lightweight structures; however, substantial barriers to the joining of dissimilar materials have led to an investigation and development of new joining techniques. Friction stir blind riveting (FSBR), a newly invented method, has shown great promise in joining complex structures with dissimilar materials. The process can be utilized more effectively if knowledge regarding the failure mechanisms of the FSBR joints becomes available. This research focuses on investigating the different mechanisms that lead to a failure in FSBR joints under lap-shear tensile tests. An in situ, nondestructive, acoustic emission (AE) testing method was applied during quasi-static tensile tests to monitor the initiation and evolution of damage in FSBR joints with different combinations of dissimilar materials (including aluminum, magnesium, and a carbon-fiber reinforced polymeric composite). In addition, a fractographic analysis was conducted to characterize the failure modes. Finally, based on the analysis, the distinct failure modes and damage accumulation processes for the joints were identified. An AE accumulative hit history curve was found to be efficient to discriminate the deformation characteristics, such as the deformation zone and failure mode, which cannot be observed through a traditional extensometer measurement method. In addition, the AE accumulative hit history curve can be applied to predict the failure extension or moment of FSBR joints through an identification of the changes in curve slope. Such slope changes usually occur around the middle of Zone II, which is defined in this study.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2016;139(2):021006-021006-11. doi:10.1115/1.4034336.

Extrusion die profile has a significant role on material flow characteristics, product microstructure, die life, and required load. Nowadays, economic requirements and effort to improve and homogenize metallurgical product properties have compelled the researchers to modify the conventional constant angle extrusion dies by employing streamlined die profiles. In the present research work, an optimum plane strain extrusion profile has been presented through implementation of upper bound analysis and Bezier curve in a simulated annealing (SA) algorithm to minimize the process force and its redundant work. The effect of material properties, friction conditions, reduction of area, and cross-sectional ratio on the optimum die profile is considered. The results of finite-element simulation proved that utilizing the optimum curved die instead of the constant angle die is superior regarding the decrease of the maximum required force, 10.5%, and the product inhomogeneity factor (IF), 50%. In addition, based on stress analysis of die/work piece interfaces, it is expected that the die life of optimal curved dies be longer than that of the optimum constant angle dies. Also, it has been demonstrated that the material work hardening characteristics does not have remarkable effect on the optimum curved die profile.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2016;139(2):021007-021007-11. doi:10.1115/1.4034437.

The residual stress profile in dissimilar metal sheets joined by a self-piercing rivet is simulated and compared to experimental measurements. Simulation of joining aluminum alloy 6111-T4 and steel HSLA340 sheets by self-piercing riveting (SPR) is performed using a two-dimensional axisymmetric model with an internal state variable (ISV) plasticity material model. Strain rate and temperature dependent deformation of the base materials is described by the ISV material model and calibrated with experimental data. Using the LS-DYNA simulation package, an element erosion technique is adopted in an explicit analysis of the separation of the upper sheet with maximum shear strain failure criterion. An explicit analysis with dynamic relaxation technique was then used for springback and cooling down analysis following the riveting simulation. The residual stress profile of SPR experimental joint with same configuration is characterized using neutron diffraction, and good agreement was found between the simulation and residual stress measurements.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2016;139(2):021008-021008-10. doi:10.1115/1.4033903.

In this paper, a rapid prototyping method for fabrication of highly conductive micropatterns on insulating substrates was developed and evaluated. Sub-20 μm microstructures were printed on flexible insulating substrates using alternating current (AC) modulated electrohydrodynamic jet (e-jet) printing. The presented technique resolved the challenge of current rapid prototyping methods in terms of limited resolution and conductivity for microelectronic components for flexible electronics. Significant variables of fabrication process, including voltage, plotting speeds, curing temperature, and multilayer effect, were investigated to achieve reliable printing of silver tracks. Sub-20 μm silver tracks were successfully fabricated with resistivity about three times than bulk silver on flexible substrates, which indicates the potential applications of electrohydrodynamic printing in flexible electronics and medical applications, such as lab-on-chip systems.

Topics: Silver , Drops , Printing
Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2016;139(2):021009-021009-8. doi:10.1115/1.4034474.

This paper focuses on series systems' dynamic opportunistic maintenance scheduling. Based on the machine-level predictive maintenance (PdM) method, a novel TOC–VLLTW methodology combined theory of constraints (TOC) policy and variable lead-lag time window (VLLTW) policy is proposed. The TOC policy provides machines' priorities according to their PdM durations to decrease system downtime when scheduling opportunistic maintenance. The VLLTW policy provides variable lead-lag time windows against different machines, allowing for more flexible and economic system opportunistic maintenance schedules. This proposed methodology is demonstrated through the case study based on the collected reliability information from a quayside container system. The results can effectively prove the effectiveness of the TOC–VLLTW methodology.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2016;139(2):021010-021010-10. doi:10.1115/1.4034276.

The capabilities of specialized elastomeric tooling (SET), a low-cost and low-energy autoclave alternative for consolidating and curing thermoset and thermoplastic composite parts made of “prepreg” material, are expanded to allow vacuum infusion of dry fiber preforms through a simple demonstration project. In this case, SET was designed to allow vacuum infusion of a flat five-ply, woven carbon fiber preform with epoxy resin, consolidate under uniform pressure in a press, and thermally cure while still under load. As expected, parts made using this process were thinner, showed slight increases in stiffness and strength, and had less surface voids as consolidation pressure was increased. Curing temperature/time has no significant effect on part quality. This expanded SET process was further characterized through a full-factorial set of experiments with replicates and quality metrics measured, such as stiffness, strength, surface roughness, and composite volume fractions. Future work will include the design and fabrication of tooling for a realistic part shape.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2016;139(2):021011-021011-11. doi:10.1115/1.4034399.

This paper presents a geometric error compensation method for large five-axis machine tools. Compared to smaller machine tools, the longer axis travels and bigger structures of a large machine tool make them more susceptible to complicated, position-dependent geometric errors. The compensation method presented in this paper uses tool tip measurements recorded throughout the axis space to construct an explicit model of a machine tool's geometric errors from which a corresponding set of compensation tables are constructed. The measurements are taken using a laser tracker, permitting rapid error data gathering at most locations in the axis space. Two position-dependent geometric error models are considered in this paper. The first model utilizes a six degree-of-freedom kinematic error description at each axis. The second model is motivated by the structure of table compensation solutions and describes geometric errors as small perturbations to the axis commands. The parameters of both models are identified from the measurement data using a maximum likelihood estimator. Compensation tables are generated by projecting the error model onto the compensation space created by the compensation tables available in the machine tool controller. The first model provides a more intuitive accounting of simple geometric errors than the second; however, it also increases the complexity of projecting the errors onto compensation tables. Experimental results on a commercial five-axis machine tool are presented and analyzed. Despite significant differences in the machine tool error descriptions, both methods produce similar results, within the repeatability of the machine tool. Reasons for this result are discussed. Analysis of the models and compensation tables reveals significant complicated, and unexpected kinematic behavior in the experimental machine tool. A particular strength of the proposed methodology is the simultaneous generation of a complete set of compensation tables that accurately captures complicated kinematic errors independent of whether they arise from expected and unexpected sources.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2016;139(2):021012-021012-9. doi:10.1115/1.4034036.

Incremental forming of thermoplastic surfaces has recently received significant interest due to the potential for simultaneous reduction in thermal energy consumption and in part-shape specific tooling. This paper examines the mechanical properties and the chain orientation of the formed material in single point incremental forming (SPIF) of amorphous polyvinyl chloride (PVC) and semicrystalline polyamide sheets. Tensile and stress relaxation properties of the formed polymers are compared to those of the unformed polymer. The effect of incremental depth and tool rotation speed on the above properties, and on the temperature rise of the sheet during SPIF, is quantified. Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) are used to compare the chain orientation and crystallinity of the formed and the unformed polymers. It is observed that the formed material has greater toughness and ductility, but lower yield stress and reduced Young's modulus, as compared to the unformed material. We also observe deformation-induced chain reorientation in the formed polymer, with minimal change in the degree of crystallinity. The link between the SPIF process parameters, temperature rise of the polymer during SPIF, change in chain orientation, and change in mechanical properties of the polymer is discussed.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2016;139(2):021013-021013-12. doi:10.1115/1.4034304.

There has been continuing effort in developing analytical, numerical, and empirical models of laser-based additive manufacturing (AM) processes in the literature. However, advanced physics-based models that can be directly used for feedback control design, i.e., control-oriented models, are severely lacking. In this paper, we develop a physics-based multivariable model for directed energy deposition. One important difference between our model from the existing work lies in a novel parameterization of the material transfer rate in the deposition as a function of the process operating parameters. Such parameterization allows an improved characterization of the steady-state melt-pool geometry compared to the existing lumped-parameter models. Predictions of melt-pool geometry and temperature from our model are validated using experimental data obtained from deposition of Ti-6AL-4V and deposition of Inconel® 718 on a laser engineering net shaping (LENS) AM process and finite-element analysis. Then based on this multivariable model, we design a nonlinear multi-input multi-output (MIMO) control, specifically a feedback linearization (FL) control, to track both melt-pool height and temperature reference trajectories using laser power and laser scan speed.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2016;139(2):021014-021014-11. doi:10.1115/1.4034278.

The manufacture of natural fiber and core preforms for biocomposite sandwich structures that bound together with fungal mycelium-based polymer is investigated. The complete manufacturing process involves: (1) cutting individual textile plies; (2) impregnating multi-ply layups with natural glue conducive to mycelium growth; (3) simultaneously forming, sterilizing and setting impregnated skins; (4) filling formed skins with mycelium-laden agri-waste; (5) allowing mycelium to colonize and bind together core substrate and skins into a unitized preform; (6) high temperature drying that also inactivates fungus; and (7) infusing skins with bioresin using resin transfer molding. Aspects of steps 3–6 related to the preform shells and sandwich structure are the main focus of this paper. Three-point bending tests are performed on dry, natural glue-bonded, four-ply specimens in a full-factorial experimental design, and test results are analyzed by analysis of variance (ANOVA) to assess process parameter effects and sensitivities along with environmental condition effects. New specimens are then made using the optimized process and tested for beam bending in creep within an environmental chamber that mimics the actual mycelium growth environment for three days. Two- and six-ply specimens loaded to provide identical maximum tensile stress in flexure are tested, and useful conclusions are drawn based on all creep test results. Finally, preforms in the shape of a viable commercial product are filled with mycelium-inoculated substrate, grown and dried, and part quality is evaluated based on the amount of skin ingrowth and deviation between the measured and desired shapes.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2016;139(2):021015-021015-21. doi:10.1115/1.4034591.

The objectives of this paper in the context of aerosol jet printing (AJP)—an additive manufacturing (AM) process—are to: (1) realize in situ online monitoring of print quality in terms of line/electronic trace morphology; and (2) explain the causal aerodynamic interactions that govern line morphology based on a two-dimensional computational fluid dynamics (2D-CFD) model. To realize these objectives, an Optomec AJ-300 aerosol jet printer was instrumented with a charge coupled device (CCD) camera mounted coaxial to the nozzle (perpendicular to the platen). Experiments were conducted by varying two process parameters, namely, sheath gas flow rate (ShGFR) and carrier gas flow rate (CGFR). The morphology of the deposited lines was captured from the online CCD images. Subsequently, using a novel digital image processing method proposed in this study, six line morphology attributes were quantified. The quantified line morphology attributes are: (1) line width, (2) line density, (3) line edge quality/smoothness, (4) overspray (OS), (5) line discontinuity, and (6) internal connectivity. The experimentally observed line morphology trends as a function of ShGFR and CGFR were verified with computational fluid dynamics (CFD) simulations. The image-based line morphology quantifiers proposed in this work can be used for online detection of incipient process drifts, while the CFD model is valuable to ascertain the appropriate corrective action to bring the process back in control in case of a drift.

Commentary by Dr. Valentin Fuster

Technical Brief

J. Manuf. Sci. Eng. 2016;139(2):024501-024501-6. doi:10.1115/1.4034139.

In this paper, the method, system setup, and procedure of a new additive manufacturing (AM) technology for manufacturing three-dimensional (3D) metal parts are introduced. Instead of using metal powders as in most commercial AM technologies, the new method uses metal foils as feed stock. The procedure consists of two alternating processes: foil-welding by a high-power continuous-wave (CW) laser and foil-cutting by a Q-switched ultraviolet (UV) laser. The foil-welding process involves two subprocesses: laser spot welding and laser raster-scan welding. The reason for using two lasers is to achieve simultaneously the high-speed and high-precision manufacturing. The results on laser foil-welding and foil-cutting show that complete and strong welding bonds can be achieved with determined parameters, and that clean and no-burr/distortion cut of foil can be obtained. Several 3D AISI 1010 steel parts fabricated by the proposed AM technology are presented, and the microhardness and tensile strength of the as-fabricated parts are both significantly greater than those of the original foil.

Commentary by Dr. Valentin Fuster

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