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IN THIS ISSUE

### Research Papers

J. Manuf. Sci. Eng. 2018;140(5):051001-051001-12. doi:10.1115/1.4038996.

In recent years, the industry's responsibility to join in sustainable manufacturing becomes huge, while innovating sustainability has been a new trend. Industrial enterprises are pursuing energy reduction to meet future needs for sustainable globalization and government legislations for green manufacturing. To run a manufacturing line in an energy-efficient manner, an energy-oriented maintenance methodology is developed. At the machine layer, the multi-attribute model (MAM) method is extended by modeling the energy attribute. Preventive maintenance (PM) intervals of each machine are dynamically scheduled according to the machine deterioration, maintenance effects, and environmental conditions. At the system layer, a novel energy saving window (ESW) policy is proposed to reduce energy for the whole line. Energy consumption interactivities, batch production characteristics, and system-layer maintenance opportunities are comprehensively considered. Real-time choice of PM adjustments is scheduled by comparing the energy savings of advanced PM and delayed PM. The results prove the energy reduction achieved by this MAM-ESW methodology. It effectively utilizes standby power, reduces energy consumption, avoids manufacturing breakdown, and decreases scheduling complexity. Furthermore, this energy-oriented maintenance framework can be applied not only in the automotive industry but also for a broader range of manufacturing domains such as the aerospace, semiconductor, and chemical industries.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2018;140(5):051002-051002-11. doi:10.1115/1.4039114.

In most trendsetting industries like the aerospace, automotive and medical industry functionally critical parts are of highest importance. Due to strict legal requirements regarding the securing of the functionality of high-risk parts, both production costs and quality costs contribute significantly to the manufacturing costs. Thus, both types of costs have to be taken into consideration during the stage of technology planning. Due to the high variety of potential interactions between individual component properties as well as between component properties and manufacturing processes, the analysis of the influence of the manufacturing history on an efficient design of inspection processes and inspection strategies is extremely complex. Furthermore, the effects of inspection strategies and quality costs on the planning of manufacturing process sequences cannot be modeled to date. As a consequence, manufacturing and inspection processes are designed separately and thus a high cost reduction potential remains untapped. In this paper, a new approach for an integrative technology and inspection planning is presented and applied to a case study in medical industry. At first, existing approaches with regard to technology and inspection planning are reviewed. After a definition of relevant terms, the case study is introduced. Following, an approach for an integrative technology and inspection planning is presented and applied to the case study. In the presented approach, the complex causalities between technology planning, manufacturing history, and inspection planning are considered to enable a cost-effective production process and inspection sequence design.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2018;140(5):051003-051003-11. doi:10.1115/1.4038894.

Laser engineering net shaping (LENS) is one of the representative processes of directed energy deposition (DED) in which a moving heat source having high-intensity melts and fuses metal powders together to print parts. The complex and nonuniform thermal gradients during the laser heating and cooling cycles in the LENS process directly affect the microstructural characteristics, and thereby the ultimate mechanical properties of fabricated parts. Therefore, prediction of microstructure evolution during the LENS process is of paramount importance. The objective of this study is to present a thermo-microstructural model for predicting microstructure evolution during the LENS process of Ti-6Al-4V. First, a detailed transient thermal finite element (FE) model is developed and validated for a sample LENS process. Then, a density type microstructural model which enables calculation of the α-phase fractions (i.e., Widmanstätten colony and basketweave α-phase fractions), β-phase fraction, and alpha lath widths during LENS process is developed and coupled to the thermal model. The microstructural algorithm is first verified by comparing the phase fraction results with the results presented in the literature for a given thermal history data. Second, the average lath width values calculated using the model are compared with the experimentally measured counterparts, where a reasonable agreement is achieved in both cases.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2018;140(5):051004-051004-15. doi:10.1115/1.4039116.

Linear motion commands of multi-axis computer numerical control (CNC) machine tools need to be smoothed at the transition corners, because the velocity discontinuities at corners can result in fluctuations on machine tool motions and lead to poor surface quality. However, no research has been reported on local corner smoothing algorithm for four-axis CNC machine tools with two rotary axes by considering their special kinematic characteristics. To this end, this paper proposes an analytical $C3$ continuous local corner smoothing algorithm for four-axis CNC machines with two rotary axes. After coordinates transformation, the tool tip positions and tool orientations are smoothed by locally inserting specially designed three-dimensional (3D) quintic B-splines and one-dimensional (1D) quintic B-splines into the corners between linear motion segments, respectively. The smoothing algorithm guarantees $C3$ continuity of the tool tip position and $C3$ continuous synchronization of the tool orientation related to the tool tip position, through analytically evaluating control points of the inserted microsplines. The maximum error tolerances of the tool tip position and tool orientation are mathematically constrained. Experiments on an in-house developed four-axis machine verify the efficacy of the proposed algorithm, where maximal errors caused by the local corner smoothing algorithm are constrained, the synchronization of the tool orientation and the tool tip position are achieved, and the proposed $C3$ continuous corner smoothing algorithm has lower jerk and jounce but higher tracking and contour accuracy than $C2$ continuous algorithm.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2018;140(5):051005-051005-9. doi:10.1115/1.4038888.

A governing equation for web tension in a span considering thermal and viscoelastic effects is developed in this paper. The governing equation includes thermal strain induced by web temperature change and assumes viscoelastic material behavior. A closed-form expression for temperature distribution in the moving web is derived, which is utilized to obtain thermal strain. A model for web tension in a multispan roll-to-roll system can be developed using this governing equation. To evaluate the governing equation, measured data from an industrial web process line are compared with data from model simulations. Since the viscoelastic behavior of web materials is affected by the web temperature change, elevated temperature creep, and stress-relaxation experiments are conducted to determine the temperature-dependent viscoelastic parameters of the utilized viscoelastic model. Comparisons of the measured data with model simulation data are presented and discussed. An analysis of the web tension disturbance propagation behavior is also provided to compare transport behavior of elastic and viscoelastic materials.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2018;140(5):051006-051006-12. doi:10.1115/1.4039196.

The single explicit analysis using time-dependent damping (SEATD) technique for laser shock peening (LSP) simulation employs variable damping to relax the excited model between laser shots, thus distinguishing it from conventional optimum constant damping methods. Dynamic relaxation (DR) is the well-established conventional technique that mathematically identifies the optimum constant damping coefficient and incremental time-step that guarantees stability and convergence while damping all mode shapes uniformly when bringing a model to quasi-static equilibrium. Examined in this research is a new systematic procedure to strive for a more effective, time-dependent variable damping profile for general LSP configurations and boundary conditions, based on excited modal parameters of a given laser-shocked system. The effects of increasing the number of mode shapes and selecting modes by contributed effective masses are studied, and a procedure to identify the most efficient variable damping profile is designed. Two different simulation cases are studied. It is found that the computational time is reduced by up to 25% (62.5 min) for just five laser shots using the presented variable damping method versus conventional optimum constant damping. Since LSP typically involved hundreds of shots, the accumulated savings in computation time during prediction of desired process parameters is significant.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2018;140(5):051007-051007-13. doi:10.1115/1.4038891.

Machining is among the most versatile material removal processes in the manufacturing industry. To better optimize the machining process, the knowledge of shear strains and shear strain rates within the primary shear zone (PSZ) during chip formation has been of great interest. The objective of this study is to study the strain and strain rate progression within the PSZ both in the chip flow direction and along the thickness direction during machining equal channel angular extrusion (ECAE) processed titanium (Ti). ECAE-processed ultrafine-grained Ti has been machined at cutting speeds of 0.1 and 0.5 m/s, and the shear strain and the shear strain rate have been determined using high speed imaging and digital image correlation (DIC). It is found that the chip morphology is saw-tooth at 0.1 m/s while continuous at 0.5 m/s. The cumulative shear strain and the incremental shear strain rate of the saw-tooth chip morphology can reach approximately 3.9 and 2.4 × 103 s−1, respectively, and those of the continuous chip morphology may be approximately 1.3 and 5.0 × 103 s−1, respectively. There is a distinct peak shift in the shear strain rate distribution during saw-tooth chip formation while there is a stable peak position of the strain rate distribution during continuous chip formation. The PSZ thickness during saw-tooth chip formation is more localized and smaller than that during continuous chip formation (28 versus 35 μm).

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2018;140(5):051008-051008-11. doi:10.1115/1.4038728.

In order to further improve the processing performance of rotary ultrasonic machining (RUM), a novel longitudinal–torsional-coupled (LTC) vibration was applied to the RUM. An experimental study on quartz glass was performed to access the feasibility of the LTC-RUM of a brittle material. The LTC-RUM was executed through the addition of helical flutes on the tool of conventional longitudinal RUM (Con-RUM). The experimental results demonstrated that the LTC-RUM could reduce the cutting force by 55% and the edge chipping size at the hole exit by 45% on an average, compared to the Con-RUM. Moreover, the LTC-RUM could also improve the quality of the hole wall through the reduction of surface roughness, in particular, when the spindle speed was relatively low. The mechanism of superior processing performance of LTC-RUM involved the corresponding specific moving trajectory of diamond abrasives, along with higher lengths of lateral cracks produced during the abrasives indentation on the workpiece material. The higher edge chipping size at the hole entrance of LTC-RUM indicated a higher length of lateral cracks in LTC-RUM, due to the increase in the maximum cutting speed. Furthermore, the effect of spindle speed on the cutting force and surface roughness variations verified the important role of the moving trajectory of the diamond abrasive in the superior processing performance mechanism of LTC-RUM.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2018;140(5):051009-051009-11. doi:10.1115/1.4039113.

In this study, weldability of ultrasonic welding of 4-mm-thick fiber carbon/nylon 66 composite in lap configuration was investigated. Ultrasonic welding tests were performed, and the weld appearance, microstructure, and fractography of the welded joints were examined using optical and scanning electron microscope. The transient temperatures near the faying surfaces and horn-workpiece interfaces were recorded to understand the weld growth mechanism. It was found that it is feasible to join 4-mm-thick lapped carbon fiber reinforced nylon 66 composite with ultrasonic welding. Under the ultrasonic vibration, the weld initiated and grew at the faying surfaces, while the weld indentation developed at the horn-workpiece interface. The pores observed in the regions between the heat-affected-zone (HAZ) and the fusion zone (FZ), and the severe weld indentation on the surface of upper workpieces decreased the loading capacity of the ultrasonic welded (UW) joints and caused the welded carbon/nylon 66 composite fractured prematurely. The strengths of the ultrasonic welds were determined by the balance of positive effect of the weld area and negative effects of the weld indentation and porosity near the FZ. To ensure the joint strength, it is necessary to apply the proper weld schedules (i.e., welding time and horn pressure) in ultrasonic welding of 4-mm-thick carbon fiber reinforced nylon 66 composite, which were developed based on the joint strength criterion.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2018;140(5):051010-051010-12. doi:10.1115/1.4038295.

A coordinated experimental and computational analysis was undertaken to investigate the temperature field, heat generation, and stress distribution within a spark plasma sintering (SPS) tooling-specimen system during single- and multipellet fabrication of uranium dioxide (UO2) fuel pellets. Different SPS tool assembly configurations consisting of spacers, punches, pellets, and a die with single or multiple cavities were analyzed using ANSYS finite element (FE) software with coupled electro-thermo-mechanical modeling approach. For single-pellet manufacture, the importance of the die dimensions in relation to punch length and their influence on temperature distribution in the pellet were analyzed. The analysis was then extended to propose methods for reducing the overall power consumption of the SPS fabrication process by optimizing the dimensions and configurations of tooling for simultaneous sintering of multiple pellets in each processing cycle. For double-pellet manufacture, the effect of the center punch length (that separates the two pellets) on the temperature distribution in the pellets was investigated. Finally, for the multiple pellet fabrication, the optimum spacing between the pellets as well as the distance between the die cavities and the outer surface of the die wall were determined. A good agreement between the experimental data on the die surface temperature and FE model results was obtained. The current analysis may be utilized for further optimization of advanced tooling concepts to control temperature distribution and obtain uniform microstructure in fuel pellets in large-scale manufacturing using SPS process.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2018;140(5):051011-051011-16. doi:10.1115/1.4039381.

Additive manufacturing (AM), partly due to its compatibility with computer-aided design (CAD) and fabrication of intricate shapes, is an emerging production process. Postprocessing, such as machining, is particularly necessary for metal AM due to the lack of surface quality for as-built parts being a problem when using as a production process. In this paper, a predictive model for cutting forces has been developed by using artificial neural networks (ANNs). The effect of tool path and cutting condition, including cutting speed, feed rate, machining allowance, and scallop height, on the generated force during machining of spherical components such as prosthetic acetabular shell was investigated. Also, different annealing processes like stress relieving, mill annealing and β annealing have been carried out on the samples to better understand the effect of brittleness, strength, and hardness on machining. The results of this study showed that ANN can accurately apply to model cutting force when using ball nose cutters. Scallop height has the highest impact on cutting forces followed by spindle speed, finishing allowance, heat treatment/annealing temperature, tool path, and feed rate. The results illustrate that using linear tool path and increasing annealing temperature can result in lower cutting force. Higher cutting force was observed with greater scallop height and feed rate while for higher finishing allowance, cutting forces decreased. For spindle speed, the trend of cutting force was increasing up to a critical point and then decreasing due to thermal softening.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2018;140(5):051012-051012-7. doi:10.1115/1.4037571.

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 (PBF) 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 (49–195 W) and scan speed (200–800 mm/s) are investigated, and numerous replications using a variety of scan lengths (4–12 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.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2018;140(5):051013-051013-6. doi:10.1115/1.4038140.

The objective of this work is to fabricate instrumented cutting tools with embedded thermocouples to accurately measure the tool–chip interface temperature in interrupted and continuous turning. Thin-film thermocouples were sputtered directly onto the flat rake face of a commercially available tungsten carbide cutting insert using micromachined stencils and the measurement junction was coated with a protective layer to obtain temperature data 1.3 μm below the tool–chip interface. Oblique interrupted cutting tests on AISI 12L14 steel were performed to observe the influence of varying cutting speeds and cooling intervals on tool–chip interface temperature. An additional cutting experiment was conducted to monitor the interface temperature change between interrupted and continuous cuts.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2018;140(5):051014-051014-10. doi:10.1115/1.4037572.

Bioprinted tissue constructs can be produced by microextrusion-based materials processing or coprinting of cells and hydrogel materials. In this paper, a gelatin–alginate hydrogel material formulation is implemented as the bio-ink toward a three-dimensional (3D) cell-laden tissue construct. However, of fundamental importance during the printing process is the interplay between the various parameters that yield the final cell distribution and cell density at different dimensional scales. To investigate these effects, this study advances a multidimensional analytical framework to determine both the spatial variations and temporal evolution of cell distribution and cell density within a bioprinted cell-laden construct. In the one-dimensional (1D) analysis, the cell distribution and single printed fiber shape in the circular cross-sectional view are observed to be dependent on the process temperature and material concentration parameters, along with the initial bio-ink cell densities. This is illustrated by reliable fabrication verified by image line profile analyses of structural fiber prints. Round fiber prints with width 809.5 ± 52.3 μm maintain dispersive cells with a degree of dispersion (Dd) at 96.8 ± 6.27% that can be achieved at high relative material viscosities under low temperature conditions (21 °C) or high material concentrations (10% w/v gelatin). On the other hand, flat fiber prints with width 1102.2 ± 63.66 μm coalesce cells toward the fiber midline with Dd = 76.3 ± 4.58% that can be fabricated at low relative material viscosities under high temperature (24 °C) or low material concentrations (7.5% w/v gelatin). A gradual decrement of Dd (from 80.34% to 52.05%) is observed to be a function of increased initial bio-ink cell densities (1.15 × 106–16.0 × 106 cells/ml). In the two-dimensional (2D) analysis, a printed grid structure yields differential cell distribution, whereby differences in localized cell densities are observed between the strut and cross regions within the printed structure. At low relative viscosities, cells aggregate at the cross regions where two overlapping filaments fuse together, yielding a cell density ratio of 2.06 ± 0.44 between the cross region and the strut region. However, at high relative viscosities, the cell density ratio decreases to 0.96 ± 0.03. In the 3D analysis, the cell density attributed to the different layers is studied as a function of printing time elapsed from the initial bio-ink formulation. Due to identifiable cell sedimentation, the dynamics of cell distribution within the original bio-ink cartridge or material reservoir yield initial quantitative increases in the cell density for the first several printed layers, followed by quantitative decreases in the subsequent printed layers. Finally, during incubation, the evolution of cell density and the emergence of material degradation effects are studied in a time course study. Variable initial cell densities (0.6 × 106 cells/mL, 1.0 × 106 cells/mL, and acellular control group) printed and cross-linked into cell-laden constructs for a 48 h time course study exhibit a time-dependent increase in cell density owing to proliferation within the constructs that are presumed to affect the rate of bio-ink material degradation.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2018;140(5):051015-051015-10. doi:10.1115/1.4039074.

Thermal history and residual stresses in dissimilar friction stir welding (FSW) of AA2024 and AZ31 were studied under different tool offsets using a coupled Eulerian–Lagrangian (CEL) finite element model and a mechanical model. Welding experiments and residual stresses' measurements were conducted to validate the models. Comparisons between the experimental and numerical results indicated good agreement. The maximum temperature in the welded zone was predicted to be slightly lower than 400 °C, regardless of offset, and that its location shifted with tool offset from the advancing side (AS) to the retreating side (RS). Longitudinal residual stresses changed from tensile under the tool shoulder to compressive beyond this region and it appeared to be the dominant stress component. The transverse stresses were tensile and of lower magnitude. Both the longitudinal and transverse residual stresses have their maximum values within the weld zone near the end of the weld length. For both peak temperatures and residual stresses, higher values were obtained at the AS with no tool offset and 1 mm offset to the AS, and at the RS with 1 mm offset to the RS. Lower residual stresses and better weld quality were obtained with tool offset to the aluminum side.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2018;140(5):051016-051016-13. doi:10.1115/1.4038729.

Accurate information about the evolution of the temperature field is a theoretical prerequisite for investigating grinding burn and optimizing the process parameters of grinding process. This paper proposed a new statistical model of equivalent grinding heat source with consideration of the random distribution of grains. Based on the definition of the Riemann integral, the summation limit of the discrete point heat sources was transformed into the integral of a continuous function. A finite element method (FEM) simulation was conducted to predict the grinding temperature field with the embedded net heat flux equation. The grinding temperature was measured with a specially designed in situ infrared system and was formulated by time–space processing. The reliability and correctness of the statistical heat source model were validated by both experimental temperature–time curves and the maximum grinding temperature, with a relative error of less than $20%$. Finally, through the FEM-based inversed calculation, an empirical equation was proposed to describe the heat transfer coefficient (HTC) changes in the grinding contact zone for both conventional grinding and creep feed grinding.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2018;140(5):051017-051017-16. doi:10.1115/1.4039198.

Additive manufacturing (AM) provides tremendous advantage over conventional manufacturing processes in terms of creative freedom, and topology optimization (TO) can be deemed as a potential design approach to exploit this creative freedom. To integrate these technologies and to create topology optimized designs that can be easily manufactured using AM, manufacturing constraints need to be introduced within the TO process. In this research, two different approaches are proposed to integrate the constraints within the algorithm of density-based TO. Two AM constraints are developed to demonstrate these two approaches. These constraints address the minimization of number of thin features as well as minimization of volume of support structures in the optimized parts, which have been previously identified as potential concerns associated with AM processes such as powder bed fusion AM. Both the manufacturing constraints are validated with two case studies each, along with experimental validation. Another case study is presented, which shows the combined effect of the two constraints on the topology optimized part. Two metrics of manufacturability are also presented, which have been used to compare the design outputs of conventional and constrained TO.

Commentary by Dr. Valentin Fuster

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